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EPA/625/R-00/008
February 2002
Onsite Wastewater Treatment
Systems Manual
Office of Water
Office of Research and Development
U.S. Environmental Protection Agency
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Errata Sheet
Onsite Wastewater Treatment
Systems Manual
EPA/625/R-00/008
June 2003
Page
Number
xi
3-29
4-33
TFS-8
TFS-23
TFS-57
TFS-65
Errata
The following names were omitted from the list of contributors:
William C. Boyle, Ph.D.,PE, and Damann L. Anderson, Ayres
Associates.
In Table 3-19, in the row entitled "Phosphorus," and the columns
entitled "Sand Filter Effluent" and "Foam or textile filter effluent" both
superscripts "4" should be "3" to correspond with footnote #3 below
the table. These numbers are not exponents.
The last paragraph on this page should be removed from the box and
moved to page 4-32, as the last paragraph of section 4.4.7. The
following should be added after the first sentence of that paragraph:
"However, siphons distribute wastewater to treatment media on
demand rather than via timed dosing approach, resulting in more
frequent dosing cycles during heavy use periods and fewer cycles
during off-peak times."
Figure 2 should be disregarded. Peat is more generally used as
media in a filter and is discussed in Section 4.7.
Arrows above and below Figure 1 should be disregarded.
The headings for Table 2 should be:
BOD (mg/L) TSS (mg/L)
TKN (mg/L) TN (mg/L) Fecal Coliform
(CFU/100ml)
The second formula under Step 6 of Recirculating tank sizing should
be: Freeboard volume = (Qinf + Qdose - Qeff ) x T
Under conditions of peak flows (Qinf >Qdose) there is no recycle flow so
Qeff=Qinf. Therefore the freeboard volume necessary is (Qinf-Qdose)x
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Notice
This document has been reviewed in accordance with U.S. Environmental Protection Agency
policy and approved for publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
USEPA Onsite Wastewater Treatment Systems Manual
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Foreword
The U.S. Environmental Protection Agency is pleased to publish the "Onsite Wastewater Treatment
Systems Manual". This manual provides up-to-date information on onsite wastewater treatment
system (OWTS) siting, design, installation, maintenance, and replacement. It reflects significant
advances that the expert community has identified to help OWTSs become more cost-effective and
environmentally protective, particularly in small suburban and rural areas.
In addition to providing a wealth of technical information on a variety of traditional and new
system designs, the manual promotes a performance-based approach to selecting and designing
OWTSs. This approach will enable States and local communities to design onsite wastewater
programs that fit local environmental conditions and communities' capabilities. Further details on
the proper management of OWTSs to prevent system failures that could threaten ground and surface
water quality will be provided in EPA's forthcoming "Guidelines for Management of Onsite/
Decentralized Wastewater Systems". EPA anticipates that the performance-based approach to
selecting and managing appropriate OWTSs at both the watershed and site levels will evolve as
States and communities develop programs based on resources that need protection and
improvement.
Robert H. Wayland III, Director
Office of Wetlands, Oceans and Watersheds
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
USEPA Onsite Wastewater Treatment Systems Manual
in
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USEPA Onsite Wastewater Treatment Systems Manual
IV
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Table of Contents
Notice ii
Foreword iii
List of Figures vii
List of Tables ix
Acknowledgments xi
Introduction xiii
Chapter 1. Background and use of onsite wastewater treatment systems 1-1
1.1 Introduction 1-1
1.2 History of onsite wastewater treatment systems 1-2
1.3 Regulation of onsite wastewater treatment systems 1-3
1.4 Onsite wastewater treatment system use, distribution, and failure rate 1-4
1.5 Problems with existing onsite wastewater management programs 1-5
1.6 Performance-based management of onsite wastewater treatment systems 1-10
1.7 Coordinating onsite system management with watershed protection efforts 1-11
1.8 USEPA initiatives to improve onsite system treatment and management 1-12
1.9 Other initiatives to assist and improve onsite management efforts 1-15
Chapter!. Management of onsite wastewater treatment systems 2-1
2.1 Introduction 2-1
2.2 Elements of a successful program 2-3
2.3 Types of management entities 2-6
2.4 Management program components 2-13
2.5 Financial assistance for management programs and system installation 2-41
Chapter 3. Establishing treatment system performance requirements 3-1
3.1 Introduction 3-1
3.2 Estimating wastewater characteristics 3-1
3.3 Estimating wastewater flow 3-2
3.4 Wastewater quality 3-8
3.5 Minimizing wastewater flows and pollutants 3-10
3.6 Integrating wastewater characterization and other design information 3-20
3.7 Transport and fate of wastewater pollutants in the receiving environment 3-20
3.8 Establishing performance requirements 3-40
3.9 Monitoring system operation and performance 3-53
Chapter 4. Treatment processes and systems 4-1
4.1 Introduction 4-1
4.2 Conventional systems and treatment options 4-2
4.3 Subsurface wastewater infiltration 4-2
4.4 Design considerations 4-6
4.5 Construction management and contingency options 4-34
4.6 Septic tanks 4-37
4.7 Sand/media filters 4-48
4.8 Aerobic treatment units 4-52
USEPA Onsite Wastewater Treatment Systems Manual
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Table of Contents, Cont'd.
Onsite wastewater treatment systems technology fact sheets
1 Continuous-Flow, Suspended-Growth Aerobic Systems (CFSGAS) TFS-1
2 Fixed-film processes TFS-7
3 Sequencing batch reactor systems TFS-13
4 Effluent disinfection processes TFS-17
5 Vegetated submerged beds and other high-specific-surface anaerobic reactors TFS-23
6 Evapotranspiration and evapotranspiration/infiltration TFS-31
7 Stabilization ponds, FWS constructed wetlands, and other aquatic systems TFS-37
8 Enhanced nutrient removal—phosphorus TFS-41
9 Enhanced nutrient removal—nitrogen TFS-45
10 Intermittent sand/media filters TFS-53
11 Recirculating sand/media filters TFS-61
12 Land treatment systems TFS-71
13 Renovation/restoration of subsurface wastewater infiltration systems (SWIS) TFS-77
Onsite wastewater treatment systems special issues fact sheets
1 Septic tank additives SIFS-1
2 High-organic-strength wastewaters (including garbage grinders) SIFS-3
3 Water softeners SIFS-7
4 Holding tanks and hauling systems SIFS-9
Chapters. Treatment system selection 5-1
5.1 Factors for selecting appropriate system design and size 5-1
5.2 Design conditions and system selection 5-1
5.3 Matching design conditions to system performance 5-1
5.4 Design boundaries and boundary loadings 5-3
5.5 Evaluating the receiving environment 5-9
5.6 Mapping the site 5-24
5.7 Developing the initial system design 5-24
5.8 Rehabilitating and upgrading existing systems 5-32
USEPA Onsite Wastewater Treatment Systems Manual
VI
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Figures
Figure 1-1. Conventional onsite wastewater treatment system 1-1
Figure 1-2. Typical single-compartment septic tank 1-3
Figure 1-3. Onsite treatment system distribution in the United States 1-5
Figure 1-4. Fate of water discharged to onsite wastewater treatment systems 1-7
Figure 1-5. The watershed approach planning and management cycle 1-13
Figure 1-6. Large-capacity septic tanks and other subsurface discharges 1-14
Figure 2-1. Onsite wastewater management overlay zones example 2-18
Figure 2-2. Process for developing onsite wastewater management 2-20
Figure 3-1. Distribution of mean household daily per capita indoor water use 3-5
Figure 3-2. Indoor water use percentage, including leakage, for 1,188 data logged homes 3-6
Figure 3-3. Daily indoor water use pattern for single-family residence 3-7
Figure 3-4. Peak wastewater flows for single-family home 3-8
Figure 3-5. Average hourly distribution of total unfiltered BOD5 3-10
Figure 3-6. Typical graywater reuse approach 3-19
Figure 3-7. Strategy for estimating wastewater flow and composition 3-21
Figure 3-8. Plume movement through the soil to the saturated zone 3-22
Figure 3-9. An example of effluent plume movement 3-25
Figure 3-10. Soil treatment zones 3-26
Figure 3-11. Zinc sorptionby clay as a function of pH 3-38
Figure 3-12. Example of compliance boundaries for onsite wastewater treatment systems 3-40
Figure 3-13. Input and output components of the MANAGE assessment method 3-44
Figure 3-14. Probability of environmental impact decision tree 3-50
Figure 4-1. Conventional subsurface wastewater infiltration system 4-2
Figure 4-2. Lateral view of conventional SWIS-based system 4-5
Figure 4-3. Subsurface infiltration system design versus depth to a limiting condition 4-7
Figure 4-4. Raising the infiltration surface with a typical mound system 4-9
Figure 4-5. Schematic of curtain drain construction 4-9
Figure 4-6. Capacity chart for subsurface drains 4-11
Figure 4-7. Pathway of subsoil reaeration 4-16
Figure 4-8. Distribution box with adjustable weir outlets 4-19
Figure 4-9. Serial relief line distribution network and installation detail 4-19
Figure 4-10. Drop box distribution network 4-21
USEPA Onsite Wastewater Treatment Systems Manual vii
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Figures, Cont'd.
Figure 4-11. Various gravelless systems 4-21
Figure 4-12. Placement of leaching chambers in typical application 4-22
Figure 4-13. Typical pressurized distribution system layout 4-23
Figure 4-14. Pressure manifold detail 4-24
Figure 4-15. Horizontal design for pressure distribution 4-25
Figure 4-16. Rigid pipe pressure distribution networks with flushing cleanouts 4-26
Figure 4-17. Pressure manifold and flexible drip lines prior to trench filling 4-28
Figure 4-18. Emitter discharge rates versus in-line pressure 4-29
Figure 4-19. Dripline layout on a site with trees 4-31
Figure 4-20. Pumping tank (generic) 4-32
Figure 4-21. Profile of a single-compartment septic tank with outlet screen 4-38
Figure 4-22. Two-compartment tank with effluent screen and surface risers 4-40
Figure 4-23. Examples of septic tank effluent screens/filters 4-41
Figure 4-24. Tongue and groove joint and sealer 4-43
Figure 4-25. Underdrain system detail for sand filters 4-48
Figure 4-26. Schematics of the two most common types of sand media filters 4-50
Figure 5-1. Preliminary design steps and considerations 5-2
Figure 5-2. Performance (design) boundaries associated with onsite treatment systems 5-4
Figure 5-3. Subsurface wastewater infiltration system design/performance boundaries 5-5
Figure 5-4. Effluent mounding effect above the saturated zone 5-8
Figure 5-5. General considerations for locating a SWIS on a sloping site 5-13
Figure 5-6. Landscape position features (see table 5-6 for siting potential) 5-14
Figure 5-7. Conventional system layout with SWIS replacement area 5-15
Figure 5-8. Site evaluation/site plan checklist 5-16
Figure 5-9. Soil textural triangle 5-19
Figure 5-10. Types of soil structure 5-20
Figure 5-11. Potential evaporation versus mean annual precipitation 5-24
Figure 5-12. Development of the onsite wastewater system design concept 5-25
Figure 5-13. Onsite wastewater failure diagnosis and correction procedure 5-33
USEPA Onsite Wastewater Treatment Systems Manual
VIII
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Tables
Table 1-1. Typical pollutants of concern from onsite wastewater treatment systems 1-2
Table 1-2. Census of housing tables: sewage disposal, 1990 1-6
Table 1-3. Estimated onsite treatment system failure rates in surveyed states 1-7
Table 2-1. Organizational approaches for managing onsite systems 2-7
Table 2-2. Survey of state certification and licensing programs 2-33
Table 2-3. Components of an onsite system regulatory program 2-36
Table 2-4. Compliance assurance approaches 2-38
Table 2-5. Example of functional responsibilities matrix 2-42
Table 2-6. Funding options 2-43
Table 2-7. Advantages and disadvantages of various funding sources 2-47
Table 3-1. Summary of average daily residential wastewater flows 3-3
Table 3-2. Comparison of daily per capita indoor water use for 12 study sites 3-4
Table 3-3. Residential water use by fixture or appliance 3-5
Table 3-4. Typical wastewater flow rates from commercial sources 3-7
Table 3-5. Typical wastewater flow rates from institutional sources 3-8
Table 3-6. Typical wastewater flow rates from recreational facilities 3-9
Table 3-7. Constituent mass loadings and concentrations 3-11
Table 3-8. Residential wastewater pollutant contributions by source 3-11
Table 3-9. Wastewater flow reduction methods 3-13
Table 3-10. Flow rates and flush volumes before and after U.S. Energy Policy Act 3-14
Table 3-11. Wastewater flow reduction: water-carriage toilets and systems 3-14
Table 3-12. Wastewater flow reduction: non-water-carriage toilets 3-15
Table 3-13. Wastewater flow reduction: showering devices and systems 3-15
Table 3-14. Wastewater flow reduction: miscellaneous devices and systems 3-16
Table 3-15. Reduction in pollutant loading achieved by eliminating garbage disposals 3-18
Table 3-16. Typical wastewater pollutants of concern 3-23
Table 3-17. Examples of soil infiltration system performance 3-23
Table 3-18. Case study: septic tank effluent and soil water quality 3-28
Table 3-19. Wastewater constituents of concern and representative concentrations 3-29
Table 3 -20. Waterborne pathogens found in human waste and associated diseases 3-32
Table 3-21. Typical pathogen survival times at 20 to 30 °C 3-33
Table 3-22. MCLs for selected organic chemicals in drinking water 3-35
Table 3-23. Case study: concentration of metals in septic tank effluent 3-36
Table 3-24. MCLs for selected inorganic chemicals in drinking water 3-37
Table 3-25. Treatment performance requirements for New Shoreham, Rhode Island 3-45
USEPA Onsite Wastewater Treatment Systems Manual
IX
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Tables, Cont'd.
Table 3-26. Resource listing, value ranking, and wastewater management schematic 3-46
Table 3-27. Proposed onsite system performance standards in various control zones 3-48
Table 3-28. Treatment performance standards in various control zones 3-48
Table 3-29. Nitrogen loading values used in the Buttermilk Bay assessment 3-52
Table 3-30. Typical laboratory costs for water quality analysis 3-61
Table 4-1. Commonly used treatment processes and optional treatment methods 4-3
Table 4-2. Characteristics of typical SWIS applications 4-5
Table 4-3. Suggested hydraulic and organic loading rates for sizing infiltration surfaces 4-12
Table 4-4. Geometry, orientation, and configuration considerations for SWISs 4-16
Table 4-5. Distribution methods and applications 4-18
Table 4-6. Dosing methods and devices 4-23
Table 4-7. Pressure manifold sizing 4-25
Table 4-8. Contingency options for SWIS malfunctions 4-34
Table 4-9. Operation, maintenance, and monitoring activities 4-36
Table 4-10. Characteristics of domestic septic tank effluent 4-38
Table 4-11. Average septic tank effluent concentrations for selected parameters 4-39
Table 4-12. Average septic tank effluent concentrations from various commercial establishments 4-39
Table 4-13. Septic tank capacities for one- and two-family dwellings 4-40
Table 4-14. Watertightness testing procedure/criteria for precast concrete tanks 4-43
Table 4-15. Chemical and physical characteristics of domestic septage 4-46
Table 4-16. Single pass and recirculating filter performance 4-53
Table 5-1. Types of mass loadings to subsurface wastewater infiltration systems 5-6
Table 5-2. Potential impacts of mass loadings on soil design boundaries 5-7
Table 5-3. Types of mass loadings for point discharges to surface waters 5-9
Table 5-4. Types of mass loadings for evapotranspiration systems 5-9
Table 5-5. Site characterization and assessment activities for SWIS applications 5-11
Table 5-6. SWIS siting potential vs. landscape position features 5-14
Table 5-7. Practices to characterize subsurface conditions through test pit inspection 5-18
Table 5-8. Example of atotal cost summary worksheet to compare alternatives 5- 31
Table 5-9. Common onsite wastewater treatment system failures 5-32
Table 5-10. General OWTS inspection and failure detection process 5-35
Table 5-11. Response of corrective actions on SWIS boundary mass loadings 5-35
USEPA Onsite Wastewater Treatment Systems Manual
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Acknowledgments
This update of the 1980 Design Manual: Onsite Wastewater Treatment and Disposal Systems (see
http://www.epa.gov/ORD/NRMRL/Pubs/625180012/625180012.htm) was developed to provide supplemental and new
information for wastewater treatment professionals in both the public and private sectors. This manual
is not intended to replace the previous manual, but rather to further explore and discuss recent
developments in treatment technologies, system design, and long-term system management.
The information in the chapters that follow is provided in response to several calls for a more focused
approach to onsite wastewater treatment and onsite system management. Congress has expressed interest
in the status of site-level approaches for treating wastewater, and the Executive Branch has issued
directives for moving forward with improving both the application of treatment technologies and
management of the systems installed.
The U.S. Environmental Protection Agency (USEPA) responded to this interest by convening a team
of subject matter experts from public agencies, private organizations, professional associations, and
the academic community. Two representatives from the USEPA Office of Water and a representative
from the Office of Research and Development coordinated the project team for this document. Close
coordination with the USEPA Office of Wastewater Management and other partners at the federal,
state, and local levels helped to ensure that the information in this manual supports and complements
other efforts to improve onsite wastewater management across the nation.
The principal authors of the document are Richard Otis of Ayres Associates; Jim Kreissl, Rod Frederick,
and Robert Goo of USEPA; Peter Casey of the National Small Flows Clearinghouse; and Barry
Terming of Tetra Tech, Inc. Other persons who made significant contributions to the manual include
Robert Siegrist of the Colorado School of Mines; Mike Hoover of North Carolina State University;
Jean Caudill of the Ohio Department of Health; Bob Minicucci of the New Hampshire Department of
Environmental Services; Tom Groves of the New England Interstate Water Pollution Control Com-
mission; Tom Yeager of Kennedy/Jenks Consultants; Robert Rubin of North Carolina State Univer-
sity; Pio Lombardo of Lombardo Associates; Dov Weitman and Joyce Hudson of USEPA; Lisa Brown,
Seldon Hall, Richard Benson, and Tom Long of the Washington Department of Health; David Pask
and Tricia Angoli of the National Small Flows Clearinghouse; James Davenport of the National
Association of Counties; Jim Watson of the Tennessee Valley Authority; John Austin of the U.S.
Agency for International Development; Pat Fleming of the U.S. Bureau of Land Management; James
Jacobsen of the Maine Department of Human Services; Richard Barror of the Indian Health Service;
GlendonDeal of the U.S. Department of Agriculture; Lisa Knerr, Jonathan Simpson, and Kay Rutledge
of Tetra Tech; Kenneth Pankow of Pankow Engineering; Linda Stein of Eastern Research Group;
Robert Adler, Charles Pycha, Calvin Terada, and Jonathon Williams of USEPA Region 10; Richard
Carr of the World Health Organization; Ralph Benson of the Clermont County, Ohio, General Health
District; Rich Piluk of the Anne Arundel, Maryland, county government; Jerry Nonogawa of the
Hawaii Department of Health; Tony Smithson of the Lake County, Illinois, Health Department;
Conrad G. Keyes, Jr., and Cecil Lue-Hing of the EWRI of ASCE; Robert E. Lee of the National Onsite
Wastewater Recycling Association; Anish Jantrania, private consultant; Larry Stephens of Stephens
Consultants; Bruce Douglass and Bill Heigis of Stone Engineering; Alan Hassett of Oak Hill Co.;
StevenBraband of Biosolutions, Inc.; MattByers of Zoeller Co.; Carl Thompson, Infiltrator Systems,
Inc.; Alex Mauck of EZ Drain; Bob Mayer of American Manufacturing; Rodney Ruskin of Geoflow;
Fred Harned of Netafim; Don Canada of the American Decentralized Wastewater Association, and
Michael Price, Norweco, Inc.
Graphics in the manual were provided by John Mori of the National Small Flows Clearinghouse,
Ayres Associates, and other sources. Regina Scheibner, Emily Faalasli, Krista Carlson, Monica Morrison,
Liz Hiett, and Kathryn Phillips of Tetra Tech handled layout and production; Martha Martin of Tetra
Tech edited the manual. The cover was produced by the National Small Flows Clearinghouse.
USEPA Onsite Wastewater Treatment Systems Manual xi
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Review Team Members for the
Onsite Wastewater Treatment Systems Manual
Robert Goo, USEPA, Office of Wetlands (OW), Oceans
and Watersheds
Rod Frederick, USEPA, OW, Oceans and Watersheds
Eric Slaughter, USEPA, OW, Oceans and Watersheds
Jim Kreissl, USEPA, Office of Research and
Development (ORD)
Don Brown, USEPA, ORD
Robert Bastian, USEPA, Office of Wastewater
Management (OWM)
Charlie Vanderlyn, USEPA, OWM
Steve Hogye, USEPA, OWM
Joyce Hudson, USEPA, OWM
Joel Salter, USEPA, Office of Science and Technology
Philip Berger, USEPA, Office of Ground Water and
Drinking Water (OGWD W)
Howard Beard, USEPA, OGWDW
Robert Adler, USEPA Region 1
Charles Pycha, USEPA Region 5
Ernesto Perez, USEPA Region 6
Calvin Terada, USEPA Region 10
Danny Averett, U.S. Army Corps of Engineers
Ed Smith, US ACE Research Laboratory
Rick Scholz, USAGE Research Laboratory
John Austin, U.S. Agency for International Development
Patrick Fleming, National Park Service
RickBarror, U.S. Public Health Service
Gary Morgan, USDA Rural Development Administration
Andree Duvarney, USDA Natural Resources
Conservation Service
Phil Mummert, Tennessee Valley Authority
Raymond Reid, Pan American Health Organization
Homero Silva, Organization Mundial de la Salud, Costa
Rica
Dennis Warner, World Health Organization
Tom Groves, New England Interstate Water Pollution
Control Commission
Paul Chase, DuPage County (Illinois) Health
Department
Douglas Ebelherr, Illinois Department of Public Health
Randy Clarkson, Missouri Department of Natural
Resources
Anish Janrania, Virginia Department of Health
Steve Steinbeck, North Carolina Department of Health
and Natural Resources
Ron Frey, Arizona Department of Environmental Quality
Mark Soltman, Washington State Department of Health
Alex Campbell, Ontario Ministry of Environment and
Approvals
Jerry Tyler, University of Wisconsin
Mike Hoover, North Carolina State University
Ruth Alfasso, Massachusetts Department of
Environmental Protection
Jerry Nunogawa, Hawaii Department of Health
Robert Siegrist, Colorado School of Mines
Rick Piluk, Anne Arundel County (Maryland) Health
Department
Gary Eckler, Erie County (Ohio) Sanitary Engineering
Department
Janet Rickabaugh, Clermont County (Ohio) Health
District
Jay Harrell, Mohave County (Arizona) Environmental
Health Division
Dan Smith, Coconino County (Arizona) Environmental
Health Services
Tom Yeager, Kennedy/Jenks Consultants
Richard Otis, Ayres Associates
Robert Mayer, American Manufacturing Co.
Hamilton Brown, National Association of Towns and
Townships
Larry Markham, National Environmental Health
Association
Robert Rubin, Water Environment Federation
Thomas McLane, American Society of Civil Engineers
Dan MacRitchie, American Society of Civil Engineers
Don Canada, American Decentralized Wastewater
Association
Naomi Friedman, National Association of Counties
Peter Casey, National Small Flows Clearinghouse
Tricia Angoli, national Small Flows Clearinghouse
Thomas Bruursema, National Sanitation Foundation
USEPA Onsite Wastewater Treatment Systems Manual
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Introduction
Background and Purpose
The U.S. Environmental Protection Agency (USEPA)
first issued detailed guidance on the design, construc-
tion, and operation of onsite wastewater treatment
systems (OWTSs) in 1980. Design Manual: Onsite
Wastewater Treatment and Disposal Systems (USEPA,
1980) was the most comprehensive summary of onsite
wastewater management since the U.S. Public Health
Service had published a guidance on septic tank
practice in 1967 (USPHS, 1967). The 1980 manual
focused on both treatment and "disposal" of wastewa-
ter in general accordance with the approach and
terminology in use at the time. The 1980 design
manual stressed the importance of site-specific soil,
landscape, ground water, and effluent characterization
and included soil percolation tests as one of several
site evaluation tools to be used in system design and
placement. The manual's discussion of water conser-
vation to reduce hydraulic flows, pollutant reduction
to minimize contaminant loading, and management
programs to oversee the full range of treatment
activities was especially important to the developing
field of onsite wastewater treatment in the United
States and other countries.
Technologies explored in the 1980 manual include
the conventional system (a septic tank with a subsur-
face wastewater infiltration system), alternating leach
fields, uniform distribution systems, intermittent sand
filters, aerobic units, disinfection technologies, and
evapotranspiration systems. The original manual also
contains guidance on dosing chambers, flow diver-
sion methods for alternating beds, nutrient removal,
and disposal of residuals. Although much of that
information is still useful, advances in regional
planning, improvements in ground water and surface
water protection, and new technologies and manage-
ment concepts necessitate further guidance for public
health districts, water quality agencies, planning
boards, and other audiences. In addition, the growing
national emphasis on management programs that
establish performance requirements rather than
prescriptive codes for the design, siting, installation,
operation, and maintenance of onsite systems under-
scores the importance of revising the manual to
address these emerging issues in public health and
water resource protection.
USEPA is committed to elevating the standards for
onsite wastewater management practice and removing
barriers that preclude widespread acceptance of onsite
treatment technologies. The purpose of this update of
the 1980 manual is to provide more comprehensive
information on management approaches, update
information on treatment technologies, and describe
the benefits of performance-based approaches to
system design. The management approaches sug-
gested in this manual involve coordinating onsite
system planning and management activities with land
use planning and watershed protection efforts to
ensure that the impacts of onsite wastewater systems
are considered and controlled at the appropriate scale.
The management approaches described in this manual
support and are consistent with USEPA's draft Guide-
lines for Management of Onsite/Decentralized
Wastewater Systems (USEPA, 2000). The incorpora-
tion of performance standards for management
programs and for system design and operation can
help ensure that no onsite system alternative presents
an unacceptable risk to public health or water
resources.
This manual contains overview information on
treatment technologies, installation practices, and
past performance. It does not, however, provide
detailed design information and is not intended as a
substitute for region- and site-specific program
criteria and standards that address conditions,
technologies, and practices appropriate to each
individual management jurisdiction. The information
in the following chapters provides an operational
framework for developing and improving OWTS
program structure, criteria, alternative designs, and
performance requirements. The chapters describe the
importance of planning to ensure that system densi-
ties are appropriate for prevailing hydrologic and
geologic conditions, performance requirements to
guide system design, wastewater characterization to
accurately predict waste strength and flows, site
evaluations that identify appropriate design and
performance boundaries, technology selection to
USEPA Onsite Wastewater Treatment Systems Manual
XIII
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ensure that performance requirements are met, and
management activities that govern installation,
operation, maintenance, and remediation of failed
systems.
This manual is intended to serve as a technical
guidance for those involved in the design, construc-
tion, operation, maintenance, and regulation of onsite
systems. It is also intended to provide information to
policy makers and regulators at the state, tribal, and
local levels who are charged with responsibility for
developing, administering, and enforcing wastewater
treatment and management program codes. The
activities and functions described herein might also
be useful to other public health and natural resource
protection programs. For example, properly planned,
designed, installed, operated, and maintained onsite
systems protect wellhead recharge areas, drinking
water sources, watershed, estuaries, coastal zones,
aquatic habitat, and wetlands.
Finally, this manual is intended to emphasize the need
to improve cooperation and coordination among the
various health, planning, zoning, development,
utility, and resource protection programs operated by
public and private organizations. A watershed
approach to protecting public health and environmen-
tal resources requires an integrated operational
framework that encourages independent partners to
function cooperatively while each retains the ability
to satisfy internal programmatic and management
objectives. Integrating onsite wastewater management
processes with other activities conducted by public
and private entities can improve both the effective-
ness and the efficiency of efforts to minimize the risk
onsite systems might present to health and ecological
resources.
Overview
Onsite wastewater treatment systems collect, treat, and
release about 4 billion gallons of treated effluent per
day from an estimated 26 million homes, businesses,
and recreational facilities nationwide (U.S. Census
Bureau, 1997). These systems, defined in this manual
as those serving fewer than 20 people, include
treatment units for both individual buildings and
small clusters of buildings connected to a common
treatment system. Recognition of the impacts of
onsite systems on ground water and surface water
quality (e.g., nitrate and bacteria contamination,
nutrient inputs to surface waters) has increased
interest in optimizing the systems' performance.
Public health and environmental protection officials
now acknowledge that onsite systems are not just
temporary installations that will be replaced eventu-
ally by centralized sewage treatment services, but
permanent approaches to treating wastewater for
release and reuse in the environment. Onsite systems
are recognized as potentially viable, low-cost, long-
term, decentralized approaches to wastewater treatment
if they are planned, designed, installed, operated, and
maintained properly (USEPA, 1997). NOTE: In
addition to existing state and local oversight, decen-
tralized wastewater treatment systems that serve more
than 20 people might become subject to regulation
under the USEPA's Underground Injection Control
Program, although EPA has proposed not to include
them (64FR22971:5/7/01).
Although some onsite wastewater management
programs have functioned successfully in the past,
problems persist. Most current onsite regulatory
programs focus on permitting and installation.
Few programs address onsite system operation and
maintenance, resulting in failures that lead to un-
necessary costs and risks to public health and water
resources. Moreover, the lack of coordination among
agencies that oversee land use planning, zoning,
development, water resource protection, public health
initiatives, and onsite systems causes problems that
could be prevented through a more cooperative
approach. Effective management of onsite systems
requires rigorous planning, design, installation,
operation, maintenance, monitoring, and controls.
Public health and water resource impacts
State and tribal agencies report that onsite septic
systems currently constitute the third most common
source of ground water contamination and that these
systems have failed because of inappropriate siting or
design or inadequate long-term maintenance (USEPA,
1996a). In the 1996 Clean Water Needs Survey
(USEPA, 1996b), states and tribes also identified more
than 500 communities as having failed septic systems
that have caused public health problems. The dis-
charge of partially treated sewage from malfunction-
ing onsite systems was identified as a principal or
contributing source of degradation in 32 percent of
all harvest-limited shellfish growing areas. Onsite
wastewater treatment systems have also contributed to
an overabundance of nutrients in ponds, lakes, and
coastal estuaries, leading to the excessive growth of
algae and other nuisance aquatic plants (USEPA,
1996b). In addition, onsite systems contribute to
contamination of drinking water sources. USEPA
estimates that 168,000 viral illnesses and 34,000
bacterial illnesses occur each year as a result of con-
USEPA Onsite Wastewater Treatment Systems Manual
XIV
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sumption of drinking water from systems that rely on
improperly treated ground water. Malfunctioning
septic systems have been identified as one potential
source of ground water contamination (USEPA, 2000).
Improving treatment through performance
requirements
Most onsite wastewater treatment systems are of the
conventional type, consisting of a septic tank and a
subsurface wastewater infiltration system (SWIS). Site
limitations and more stringent performance require-
ments have led to significant improvements in the
design of wastewater treatment systems and how they
are managed. Over the past 20 years the OWTS
industry has developed many new treatment technolo-
gies that can achieve high performance levels on sites
with size, soil, ground water, and landscape limita-
tions that might preclude installing conventional
systems. New technologies and improvements to
existing technologies are based on defining the
performance requirements of the system, characteriz-
ing wastewater flow and pollutant loads, evaluating
site conditions, defining performance and design
boundaries, and selecting a system design that
addresses these factors.
Performance requirements can be expressed as
numeric criteria (e.g., pollutant concentration or mass
loading limits) or narrative criteria (e.g., no odors or
visible sheen) and are based on the assimilative
capacity of regional ground water or surface waters,
water quality objectives, and public health goals.
Wastewater flow and pollutant content help define
system design and size and can be estimated by
comparing the size and type of facility with measured
effluent outputs from similar, existing facilities. Site
evaluations integrate detailed analyses of regional
hydrology, geology, and water resources with site-
specific characterization of soils, slopes, structures,
property lines, and other site features to further define
system design requirements and determine the
physical placement of system components.
Most of the alternative treatment technologies
applied today treat wastes after they exit the septic
tank; the tank retains settleable solids, grease, and oils
and provides an environment for partial digestion of
settled organic wastes. Post-tank treatment can
include aerobic (with oxygen) or anaerobic (with no
or low oxygen) biological treatment in suspended or
fixed-film reactors, physical/chemical treatment, soil
infiltration, fixed-media filtration, and/or disinfec-
tion. The application and sizing of treatment units
based on these technologies are defined by perfor-
mance requirements, wastewater characteristics, and
site conditions.
Toward a more comprehensive approach
The principles of the 1980 onsite system design
manual have withstood the test of time, but much has
changed over the past 20 years. This manual incorpo-
rates much of the earlier guide but includes new
information on treatment technologies, site evalua-
tion, design boundary characterization, and especially
management program functions. The manual is
organized by functional topics and is intended to be a
comprehensive reference. Users can proceed directly
to relevant sections or review background or other
information (see Contents).
Although this manual focuses on individual and
small, clustered onsite systems, state and tribal
governments and other management entities can use
the information in it to construct a framework for
managing new and existing large-capacity decentral-
ized systems (those serving more than 20 people),
subject to regulation under state or local Underground
Injection Control (UIC) programs. The UIC program
was established by the Safe Drinking Water Act to
protect underground sources of drinking water from
contamination caused by the underground injection
of wastes. In most parts of the nation, the UIC pro-
gram, which also deals with motor vehicle waste
disposal wells, large-capacity cesspools, and storm
water drainage wells, is managed by state or tribal
water or waste agencies with authority delegated by
USEPA.
The Class V UIC program and the Source Water
Protection Program established by the 1996 amend-
ments to the federal Safe Drinking Water Act are
bringing federal and state drinking water agencies
into the field of onsite wastewater treatment and
management. Both programs will likely require more
interagency involvement and cooperation to charac-
terize wastewater impacts on ground water resources
and to develop approaches to deal with real or
potential problems. States currently have permit-by-
rule provisions for large-capacity septic systems.
Overview of the revised manual
The first two chapters of this manual present over-
view and management information of special interest
to program administrators. Chapters 3, 4, and 5
contain technical information on wastewater charac-
terization, site evaluation and selection, and treat-
ment technologies and how to use them in develop-
USEPA Onsite Wastewater Treatment Systems Manual
xv
-------
ing a system design. Those three chapters are intended
primarily for engineers, soil scientists, permit writers,
environmental health specialists, site evaluators, and field
staff. Summaries of all the chapters appear below. The level
of detail provided in this manual is adequate for preliminary
system design and development of a management program.
References are provided for additional research and
information on how to incorporate local characteristics into
an optimal onsite management program.
Overview of the Onsite Wastewater Treatment Systems Manual
Chapter 1, Background and use of
onsite wastewater treatment systems
Chapter 2, Management and
regulation of onsite wastewater
treatment systems
Chapter 3, Establishing treatment
system performance requirements
Chapter 4, Treatment processes and
systems
Chapter 5, Treatment system
selection
Glossary
Resources
Review of the history and current use of onsite treatment
systems, introduction of management concepts, and brief
discussion of alternative technologies.
Discussion of methods to plan, institutionalize, and manage
OWTS programs, including both prescriptive and
performance-based approaches. If prescriptive-based
management programs are used, parts of this chapter will not
apply because the basic functions of prescriptive-based
management are more simplified.
Discussion of methods for estimating wastewater flow and
composition, identifying pollutants of concern and their
transport and fate in the environment, establishing
performance requirements, and estimating watershed-scale
impacts.
Identification of conventional and alternative OWTS
technologies, pollutant removal effectiveness, design
parameters, operation and maintenance requirements, costs,
and special issues.
Discussion of strategies for establishing site-specific
performance requirements and performance boundaries
based on wastewater flow and composition and site
characteristics, selection of treatment alternatives, and
analysis of system failure and repair or replacement
alternatives.
Definitions of terms used in the manual.
Selected reference documents and Internet resources.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
Chapter 1:
Background and use of onsite wastewater treatment systems
1.1 Introduction
1.2 History of onsite wastewater treatment systems
1.3 Regulation of onsite wastewater treatment systems
1.4 Onsite wastewater treatment system use, distribution, and failure rate
1.5 Problems with existing onsite wastewater management programs
1.6 Performance-based management of onsite wastewater treatment systems
1.7 Coordinating onsite system management with watershed protection efforts
1.8 USEPA initiatives to improve onsite system treatment and management
1.9 Other initiatives to assist and improve onsite management efforts
1.1 Introduction
Onsite wastewater treatment systems (OWTSs)
have evolved from the pit privies used widely
throughout history to installations capable of
producing a disinfected effluent that is fit for
human consumption. Although achieving such a
level of effluent quality is seldom necessary, the
ability of onsite systems to remove settleable solids.
floatable grease and scum, nutrients, and pathogens
from wastewater discharges defines their importance
in protecting human health and environmental
resources. In the modern era, the typical onsite
system has consisted primarily of a septic tank and
a soil absorption field, also known as a subsurface
wastewater infiltration system, or SWIS (figure
1-1). In this manual, such systems are referred to as
conventional systems. Septic tanks remove most
settleable and floatable material and function as an
anaerobic bioreactor that promotes partial digestion
of retained organic matter. Septic tank effluent,
which contains significant concentrations of
pathogens and nutrients, has traditionally been
discharged to soil, sand, or other media absorption
fields (SWISs) for further treatment through
biological processes, adsorption, filtration, and
infiltration into underlying soils. Conventional
systems work well if they are installed in areas with
appropriate soils and hydraulic capacities; designed to
treat the incoming waste load to meet public health,
ground water, and surface water performance
standards; installed properly; and maintained to
ensure long-term performance.
These criteria, however, are often not met. Only
about one-third of the land area in the United States
has soils suited for conventional subsurface soil
absorption fields. System densities in some areas
exceed the capacity of even suitable soils to
assimilate wastewater flows and retain and trans-
form their contaminants. In addition, many systems
are located too close to ground water or surface
waters and others, particularly in rural areas with
newly installed public water lines, are not designed
to handle increasing wastewater flows. Conven-
tional onsite system installations might not be
adequate for minimizing nitrate contamination of
ground water, removing phosphorus compounds,
and attenuating pathogenic organisms (e.g.,
bacteria, viruses). Nitrates that leach into ground
Figure 1-1. Conventional onsite wastewater treatment system
Source: NSFC, 2000.
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
water used as a drinking water source can cause
methemoglobinemia, or blue baby syndrome, and
other health problems for pregnant women.
Nitrates and phosphorus discharged into surface
waters directly or through subsurface flows can
spur algal growth and lead to eutrophication and
low dissolved oxygen in lakes, rivers, and coastal
areas. In addition, pathogens reaching ground water
or surface waters can cause human disease through
direct consumption, recreational contact, or inges-
tion of contaminated shellfish. Sewage might also
affect public health as it backs up into residences or
commercial establishments because of OWTS
failure.
Nationally, states and tribes have reported in their
1998 Clean Water Act section 303(d) reports that
designated uses (e.g., drinking water, aquatic
habitat) are not being met for 5,281 waterbodies
because of pathogens and that 4,773 waterbodies
are impaired by nutrients. Onsite systems are one of
many known contributors of pathogens and nutrients
to surface and ground waters. Onsite wastewater
systems have also contributed to an overabundance
of nutrients in ponds, lakes, and coastal estuaries,
leading to overgrowth of algae and other nuisance
aquatic plants.
Threats to public health and water resources
(table 1-1) underscore the importance of instituting
management programs with the authority and
resources to oversee the full range of onsite system
activities—planning, siting, design, installation,
operation, monitoring, and maintenance. EPA has
issued draft Guidelines for Management of Onsite/
Decentralized Wastewater Systems (USEPA, 2000)
to improve overall management of OWTSs. These
guidelines are discussed in more detail in chapter 2.
1.2 History of onsite wastewater
treatment systems
King Minos installed the first known water closet
with a flushing device in the Knossos Palace in
Crete in 1700 BC. In the intervening 3,700 years,
societies and the governments that serve them have
sought to improve both the removal of human
wastes from indoor areas and the treatment of that
waste to reduce threats to public health and eco-
logical resources. The Greeks, Romans, British, and
French achieved considerable progress in waste
removal during the period from 800 BC to AD
1850, but removal often meant discharge to surface
waters; severe contamination of lakes, rivers,
streams, and coastal areas; and frequent outbreaks
of diseases like cholera and typhoid fever.
By the late 1800s, the Massachusetts State Board of
Health and other state health agencies had docu-
mented links between disease and poorly treated
sewage and recommended treatment of wastewater
through intermittent sand filtration and land
application of the resulting sludge. The past
century has witnessed an explosion in sewage
treatment technology and widespread adoption of
centralized wastewater collection and treatment
services in the United States and throughout the
world. Although broad uses of these systems have
vastly improved public health and water quality in
urban areas, homes and businesses without central-
ized collection and treatment systems often con-
Table 1-1. Typical pollutants of concern in effluent from onsite wastewater treatment systems
Pollutant
Public health or water resource impacts
Pathogens Parasites, bacteria, and viruses can cause communicable diseases through direct or indirect body contact or ingestion of
contaminated water or shellfish. Pathogens can be transported for significant distances in ground water or surface waters.
Nitrogen Nitrogen is an aquatic plant nutrient that can contribute to eutrophication and dissolved oxygen loss in surface waters,
especially in nitrogen-limited lakes, estuaries, and coastal embayments. Algae and aquatic weeds can contribute
trihalomethane (THM) precursors to the water column that might generate carcinogenic THMs in chlorinated drinking
water. Excessive nitrate-nitrogen in drinking water can cause methemoglobinemia in infants and pregnancy
complications.
Phosphorus Phosphorus is an aquatic plant nutrient that can contribute to eutrophication of phosphorus-limited inland surface waters.
High algal and aquatic plant production during eutrophication is often accompanied by increases in populations of
decomposer bacteria and reduced dissolved oxygen levels for fish and other organisms.
1-2
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
tinue to depend on technologies developed more
than 100 years ago. Septic tanks for primary
treatment of wastewater appeared in the late 1800s.
and discharge of tank effluent into gravel-lined
subsurface drains became common practice during
the middle of the 20th century (Kreissl, 2000).
Scientists, engineers, and manufacturers in the
wastewater treatment industry have developed a wide
range of alternative technologies designed to address
increasing hydraulic loads and water contamination
by nutrients and pathogens. These technologies can
achieve significant pollutant removal rates. With
proper management oversight, alternative systems
(e.g., recirculating sand filters, peat-based systems,
package aeration units) can be installed in areas
where soils, bedrock, fluctuating ground water levels,
or lot sizes limit the use of conventional systems.
Alternative technologies typically are applied to the
treatment train beyond the septic tank (figure 1-2).
The tank is designed to equalize hydraulic flows;
retain oils, grease, and settled solids; and provide
some minimal anaerobic digestion of settleable
organic matter. Alternative treatment technologies
often provide environments (e.g., sand, peat, artificial
media) that promote additional biological treatment
and remove pollutants through filtration, absorption,
and adsorption. All of the alternative treatment
technologies in current use require more intensive
management and monitoring than conventional
OWTSs because of mechanical components, addi-
tional residuals generated, and process sensitivities
(e.g., to wastewater strength or hydraulic loading).
Replacing gravity-flow subsurface soil infiltration
beds with better-performing alternative distribution
technologies can require float-switched pumps and/
or valves. As noted in chapter 4, specialized
excavation or structures might be required to house
some treatment system components, including the
disinfection devices (e.g., chlorinators, ultraviolet
lamps) used by some systems. In addition, it is
often both efficient and effective to collect and
treat septic tank effluent from clusters of individual
sources through a community or cluster system
driven by gravity, pressure, or vacuum. These
devices also require specialized design, operation,
and maintenance and enhanced management
oversight.
1.3 Regulation of onsite
wastewater treatment systems
Public health departments were charged with
enforcing the first onsite wastewater "disposal"
laws, which were mostly based on soil percolation
tests, local practices, and past experience. Early
codes did not consider the complex interrelation-
ships among soil conditions, wastewater character-
istics, biological mechanisms, and climate and
Figure 1-2. Typical single-compartment septic tank with at-grade inspection ports and effluent screen
Inspection ports
From house
To additional treatment
and/or dispersal
Effluent
screen
Source: NSFC, 2000.
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
prescribed standard designs sometimes copied from
jurisdictions in vastly different geoclimatic re-
gions. In addition, these laws often depended on
minimally trained personnel to oversee design,
permitting, and installation and mostly untrained,
uninformed homeowners to operate and maintain
the systems. During the 1950s states began to adopt
laws upgrading onsite system design and installa-
tion practices to ensure proper functioning and
eliminate the threats posed by waterborne patho-
gens (Kreissl, 1982). Despite these improvements,
many regulations have not considered cumulative
ground water and surface water impacts, especially
in areas with high system densities and significant
wastewater discharges.
Kreissl (1982) and Plews (1977) examined changes
in state onsite wastewater treatment regulations
prompted by the publication of the first U.S. Public
Health Service Manual of Septic-Tank Practice in
1959. Plews found significant code revisions under
way by the late 1970s, mostly because of local
experience, new research information, and the need
to accommodate housing in areas not suited for
conventional soil infiltration systems. Kreissl found
that states were gradually increasing required
septic tank and drainfield sizes but also noted that
32 states were still specifying use of the percola-
tion test in system sizing in 1980, despite its proven
shortcomings. Other differences noted among state
codes included separation distances between the
infiltration trench bottom and seasonal ground
water tables, minimum trench widths, horizontal
setbacks to potable water supplies, and maximum
allowable land slopes (Kreissl, 1982).
Although state lawmakers have continued to revise
onsite system codes, most revisions have failed to
address the fundamental issue of system perfor-
mance in the context of risk management for both a
site and the region in which it is located. Prescribed
system designs require that site conditions fit
system capabilities rather than the reverse and are
sometimes incorrectly based on the assumption that
centralized wastewater collection and treatment
services will be available in the future. Codes that
emphasize prescriptive standards based on empiri-
cal relationships and hydraulic performance do not
necessarily protect ground water and surface water
resources from public health threats. Devising a
new regime for protecting public health and the
environment in a cost-effective manner will require
increased focus on system performance, pollutant
transport and fate and resulting environmental
impacts, and integration of the planning, design,
siting, installation, maintenance, and management
functions to achieve public health and environmen-
tal objectives.
1.4 Onsite wastewater treatment
system use, distribution, and
failure rate
According to the U.S. Census Bureau (1999),
approximately 23 percent of the estimated 115
million occupied homes in the United States are
served by onsite systems, a proportion that has
changed little since 1970. As shown in figure 1-3
and table 1-2, the distribution and density of homes
with OWTSs vary widely by state, with a high of
about 55 percent in Vermont and a low of around 10
percent in California (U.S. Census Bureau, 1990).
New England states have the highest proportion of
homes served by onsite systems: New Hampshire
and Maine both report that about half of all homes
are served by individual wastewater treatment
systems. More than a third of the homes in the
southeastern states depend on these systems,
including approximately 48 percent in North
Carolina and about 40 percent in both Kentucky
and South Carolina. More than 60 million people
depend on decentralized systems, including the
residents of about one-third of new homes and
more than half of all mobile homes nationwide
(U.S. Census Bureau, 1999). Some communities
rely completely on OWTSs.
A number of systems relying on outdated and
underperforming technologies (e.g., cesspools,
drywells) still exist, and many of them are listed
among failed systems. Moreover, about half of the
occupied homes with onsite treatment systems are
more than 30 years old (U.S. Census Bureau, 1997),
and a significant number report system problems. A
survey conducted by the U.S. Census Bureau
(1997) estimated that 403,000 homes experienced
septic system breakdowns within a
3-month period during 1997; 31,000 reported four
or more breakdowns at the same home. Studies
reviewed by USEPA cite failure rates ranging from
10 to 20 percent (USEPA, 2000). System failure
surveys typically do not include systems that might
be contaminating surface or ground water, a
situation that often is detectable only through site-
1-4
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
Percentage of state
residents using onsite
wastewater systems
10-25% D
26-40% Q
>40% •
.©nsitestreatrriepft system distribution in the United States
level monitoring. Figure 1-4 demonstrates ways
that effluent water from a septic system can reach
ground water or surface waters.
Comprehensive data to measure the true extent of
septic system failure are not currently collected by
any single organization. Although estimates of
system failure rates have been collected from 28
states (table 1-3), no state had directly measured its
own failure rate and definitions of failure vary
(Nelson et al., 1999). Most available data are the
result of incidents that directly affect public health
or are obtained from homeowners' applications for
permits to replace or repair failing systems. The 20
percent failure rate from the Massachusetts time-of-
transfer inspection program is based on an inspec-
tion of each septic system prior to home sale, which
is a comprehensive data collection effort. However,
the Massachusetts program only identifies failures
according to code and does not track ground water
contamination that may result from onsite system
failures.
In addition to failures due to age and hydraulic
overloading, OWTSs can fail because of design,
installation, and maintenance problems. Hydrauli-
cally functioning systems can create health and
ecological risks when multiple treatment units are
installed at densities that exceed the capacity of
local soils to assimilate pollutant loads. System
owners are not likely to repair or replace aging or
otherwise failing systems unless sewage backup,
septage pooling on lawns, or targeted monitoring
that identifies health risks occurs. Because ground
and surface water contamination by onsite systems
has rarely been confirmed through targeted moni-
toring, total failure rates and onsite system impacts
over time are likely to be significantly higher than
historical statistics indicate. For example, the
Chesapeake Bay Program found that 55 to 85 percent
of the nitrogen entering an onsite system can be
discharged into ground water (USEPA, 1993). A
1991 study concluded that conventional systems
accounted for 74 percent of the nitrogen entering
Buttermilk Bay in Massachusetts (USEPA, 1993).
1.5 Problems with existing onsite
wastewater management
programs
Under a typical conventional system management
approach, untrained and often uninformed system
owners assume responsibility for operating and
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
Table 1-2. Census of housing tables: sewage disposal, 1990
United States
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
District of Columbia
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Public sewer
Number
76,455,211
910,782
144,905
1,348,836
601,188
10,022,843
1,283,186
935,541
212,793
276,481
4,499,793
1,638,979
312,812
264,618
3,885,689
1,525,810
869,056
847,767
849,491
1,246,678
266,344
1,533,799
1,803,176
2,724,408
1,356,520
585,185
1,617,996
218,372
534,692
456,107
250,060
2,703,489
452,934
5,716,917
1,403,033
204,328
3,392,785
1,028,594
835,545
3,670,338
293,901
825,754
207,996
1,213,934
5,690,550
528,864
115,201
1,740,787
1,387,396
427,930
1,440,024
151,004
Percent
74.8
54.5
62.3
81.3
60.1
89.6
86.9
70.8
73.4
99.3
73.8
62.1
80.2
64.0
86.2
67.9
76.0
81.2
56.4
72.6
45.4
81.1
72.9
70.8
73.4
57.9
73.6
60.5
80.9
87.9
49.6
87.9
71.7
79.1
49.8
73.9
77.6
73.1
70.0
74.3
70.9
58.0
71.1
59.9
81.2
88.4
42.5
69.7
68.3
54.8
70.0
74.2
Septic tank or cesspool
Number
24,670,877
728,690
59,886
282,897
382,467
1,092,174
183,817
378,382
74,541
575
1,559,113
970,686
72,940
142,879
598,125
703,032
264,889
187,398
600,182
442,758
301,373
342,523
659,120
1,090,481
467,936
387,406
532,844
135,371
117,460
60,508
246,692
357,890
161,068
1,460,873
1,365,632
66,479
940,943
367,197
349,122
1,210,054
118,410
578,129
78,435
781,616
1,266,713
65,403
149,125
707,409
630,646
318,697
580,836
49,055
Percent
24.1
43.6
25.7
17.0
38.2
9.8
12.4
28.6
25.7
0.2
25.6
36.8
18.7
34.6
13.3
31.3
23.2
17.9
39.8
25.8
51.3
18.1
26.7
28.3
25.3
38.3
24.2
37.5
17.8
11.7
49.0
11.6
25.5
20.2
48.5
24.1
21.5
26.1
29.3
24.5
28.6
40.6
26.8
38.6
18.1
10.9
55.0
28.3
31.0
40.8
28.3
24.1
Other means
Number
1,137,590
30,907
27,817
27,697
17,012
67,865
10,346
6,927
2,585
1,433
41,356
28,753
4,058
5,830
22,461
17,204
9,724
8,947
57,172
26,805
19,328
15,595
10,415
33,037
23,989
37,832
48,289
7,412
8,469
2,243
7,152
13,931
18,056
49,101
49,528
5,533
38,217
10,708
8,900
57,748
2,261
20,272
6,005
30,517
51,736
4,121
6,888
48,138
14,336
34,668
34,914
3,352
Percent
1.1
1.9
12.0
1.7
1.7
0.6
0.7
0.5
0.9
0.5
0.7
1.1
1.0
1.4
0.5
0.8
0.9
0.9
3.8
1.6
3.3
0.8
0.4
0.9
1.3
3.7
2.2
2.1
1.3
0.4
1.4
0.5
2.9
0.7
1.8
2.0
0.9
0.8
0.7
1.2
0.5
1.4
2.1
1.5
0.7
0.7
2.5
1.9
0.7
4.4
1.7
1.6
Source: U.S. Census Bureau, 1990.
1-6
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
Figure 1-4. Fate of water discharged to onsite wastewater treatment systems.
Evapotranspiration
House
Septic
tank
/E
Dispersal
system
rr r 7'Trf
Percolation I
Seep
No restrictive horizon
4.
1
1
4.
1
1
Grou
/ .Rgsjrtctiy^ rjofizpti ,
id water mound/
perched water table
Bedr
ockor
impermeable
soil layer
Runoff to
lakes and
streams
To wells, springs, —>
and base flow
Source: Adapted from Venhuizen, 1995.
Ground water
Table 1-3. Estimated onsite treatment system failure rates in surveyed states
State
Alabama
Arizona
California
Florida
Georgia
Hawaii
Idaho
Kansas
Louisiana
Maryland
Massachusetts
Minnesota
Missouri
Nebraska
New Hampshire
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Rhode Island
South Carolina
Texas
Utah
Washington
West Virginia
Wyoming
Estimated system failure
rate (percentage)
20
0.5
1-4
1-2
1.7
15-35
20
10-15
50
1
25
50-70
30-50
40
<5
20
4
15-20
28
25-30
5-10
25
6-7
10-15
0.5
33
60
0.4
Failure definition
Not given
Surfacing, backup, surface or ground water contamination
Surfacing, backup, surface or ground water contamination
Surfacing, backup, surface or ground water contamination
Public hazard
Improper construction, overflow
Backup, surface or ground water contamination
Surfacing, nuisance conditions (for installations after 1980)
Not given
Surfacing, surface or ground water contamination
Public health
Cesspool, surfacing, inadequate soil layer, leaking
Backup, surface or ground water contamination
Nonconforming system, water quality
Surfacing, backup
Surfacing
Backup, surface or ground water contamination
Not given
Backup, surfacing
Backup, surfacing
Backup, surfacing, discharge off property
Not given
Backup, surface or ground water contamination
Surfacing, surface or ground water contamination
Surfacing, backup, exceed discharge standards
Public health hazard
Backup, surface or ground water contamination
Backup, surfacing, ground water contamination
* Failure rates are estimated and vary with the definition of failure.
Source: Nelson etal., 1999.
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
maintaining their relatively simple, gravity-based
systems. Performance results under this approach
can vary significantly, with operation and mainte-
nance functions driven mostly by complaints or
failures. In fact, many conventional system failures
have been linked to operation and maintenance
failures. Typical causes of failure include unpumped
and sludge-filled tanks, which result in clogged
absorption fields, and hydraulic overloading caused
by increased occupancy and greater water use
following the installation of new water lines to replace
wells and cisterns. Full-time or high use of vacation
homes served by systems installed under outdated
practices or designed for part-time occupancy can
cause water quality problems in lakes, coastal bays,
and estuaries. Landscape modification, alteration of
the infiltration field surface, or the use of outdated
technologies like drywells and cesspools can also
cause contamination problems.
Newer or "alternative" onsite treatment technolo-
gies are more complex than conventional systems
and incorporate pumps, recirculation piping,
aeration, and other features (e.g., greater generation
of residuals) that require ongoing or periodic
monitoring and maintenance. However, the current
management programs of most jurisdictions do not
typically oversee routine operation and mainte-
nance activities or detect and respond to changes in
wastewater loads that can overwhelm a system. In
addition, in many cases onsite system planning and
siting functions are not linked to larger ground
water and watershed protection programs. The
challenge for onsite treatment regulators in the new
millennium will be to improve traditional health-
based programs for ground water and surface water
protection while embracing a vigorous role in
protecting and restoring the nation's watersheds.
The challenge is significant. Shortcomings in many
management programs have resulted in poor system
performance, public health threats, degradation of
surface and ground waters, property value declines,
and negative public perceptions of onsite treatment
as an effective wastewater management option.
(See examples in section 1.1.) USEPA (1987) has
identified a number of critical problems associated
with programs that lack a comprehensive manage-
ment program:
• Failure to adequately consider site-specific
environmental conditions.
• Codes that thwart adaptation to difficult local
site conditions and are unable to accommodate
effective innovative and alternative technologies.
• Ineffective or nonexistent public education and
training programs.
• Failure to include conservation and potential
reuse of water.
• Ineffective controls on operation and mainte-
nance of systems, including residuals (septage,
sludge).
• Failure to consider the special characteristics
and requirements of commercial, industrial, and
large residential systems.
• Weak compliance and enforcement programs.
• These problems can be grouped into three
primary areas: (1) insufficient funding and
public involvement; (2) inappropriate system
design and selection processes; and (3) poor
inspection, monitoring, and program evaluation
components. Management programs that do not
address these problems can directly and indi-
rectly contribute to significant human health
risks and environmental degradation.
1.5.1 Public involvement and
education
Public involvement and education are critical to
successful onsite wastewater management. Engag-
ing the public in wastewater treatment issues helps
build support for funding, regulatory initiatives,
and other elements of a comprehensive program.
Educational activities directed at increasing
general awareness and knowledge of onsite man-
agement efforts can improve the probability that
simple, routine operation and maintenance tasks
(e.g., inspecting for pooled effluent, pumping the
tank) are carried out by system owners. Specialized
training is required for system managers respon-
sible for operating and maintaining systems with
more complex components. Even conventional,
gravity-based systems require routine pumping,
monitoring, and periodic inspection of sludge and
scum buildup in septic tanks. Failing systems can
cause public health risks and environmental
damage and are expensive to repair. System owners
should be made aware of the need for periodically
removing tank sludge, maintaining system compo-
1-8
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
nents, and operating systems within their design
limitations to help maximize treatment effective-
ness and extend the life of the systems.
Information regarding regular inspections, pump-
ing, ground water threats from chemicals, hydrau-
lic overloading from roof runoff or other clear
water sources, pollutant loads from garbage disposal
units, drain field protection, and warning signs of
failing systems can be easily communicated. Flyers,
brochures, posters, news media articles, and other
materials have proven effective in raising aware-
ness and increasing public knowledge of onsite
wastewater management issues (see Resources
section). Meetings with stakeholders and elected
officials and face-to-face training programs for
homeowners can produce better results when
actions to strengthen programs are required
(USEPA, 1994). Public involvement and education
programs are often overlooked because they require
resources, careful planning, and management and
can be labor-intensive. However, these efforts can
pay rich dividends in building support for the
management agency and improving system perfor-
mance. Public education and periodic public input
are also needed to obtain support for developing
and funding a wastewater utility or other compre-
hensive management program (see chapter 2).
1.5.2 Financial support
Funding is essential for successful management of
onsite systems. Adequate staff is required to
implement the components of the program and
objectively enforce the regulations. Without money
to pay for planning, inspection, and enforcement
staff, these activities will not normally be properly
implemented. Financial programs might be needed
to provide loans or cost-share grants to retrofit or
replace failing systems. Statewide public financing
programs for onsite systems like the PENNVEST
initiative in Pennsylvania provide a powerful
incentive for upgrading inadequate or failed
systems (Pennsylvania Infrastructure Investment
Authority, 1997). Regional cost-share programs
like the Triplett Creek Project in Kentucky, which
provided funding for new septic tanks and drain
field repairs, are also effective approaches for
addressing failed systems (USEPA, 1997). Chap-
ter 2 and the Resources section provide more
information on funding options for onsite systems
and management programs.
Managing onsite systems is particularly challenging
in small, unincorporated communities without paid
staff. Programs staffed by trained volunteers and
regional "circuit riders" can help deliver technical
expertise at a low cost in these situations. Develop-
ing a program uniquely tailored to each community
requires partnerships, ingenuity, commitment, and
perseverance.
1.5.3 Support from elected officials
In most cases the absence of a viable oversight
program that addresses the full range of planning,
design, siting, permitting, installation, operation,
maintenance, and monitoring activities is the main
reason for inadequate onsite wastewater system
management. This absence can be attributed to a
number of factors, particularly a political climate in
which the value of effective onsite wastewater
management is dismissed as hindering economic
development or being too restrictive on rural
housing development. In addition, low population
densities, low incomes, underdeveloped manage-
ment entities, a history of neglect, or other unique
factors can impede the development of comprehen-
sive management programs. Focusing on the public
health and water resource impacts associated with
onsite systems provides an important perspective
for public policy discussions on these issues.
Sometimes state and local laws prevent siting or
design options that could provide treatment and
recycling of wastewater from onsite systems. For
example, some state land use laws prohibit using
lands designated as resource lands to aid in the
development of urban uses. Small communities or
rural developments located near state resource
lands are unable to use those lands to address
onsite problems related to space restrictions, soil
limitations, or other factors (Fogarty, 2000).
The most arbitrary siting requirement, however, is
the minimum lot size restriction incorporated into
/Vote:This manual is not intended to be used to
determine appropriate or inappropriate uses of land. The
information the manual presents is intended to be used to
select appropriate technologies and management
strategies that minimize risks to human health and water
resources in areas that are not connected to centralized
wastewater collection and treatment systems.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
many state and local codes. Lot size limits prohibit
onsite treatment system installations on noncon-
forming lots without regard to the performance
capabilities of the proposed system. Lot size
restrictions also serve as an inappropriate but de
facto approach to land use planning in many
localities because they are often seen as establishing
the allowable number of housing units in a devel-
opment without regard to other factors that might
increase or decrease that number.
When developing a program or regulation, the
common tendency is to draw on experience from
other areas and modify existing management plans
or codes to meet local needs. However, programs
that are successful in one area of the country might
be inappropriate in other areas because of differ-
ences in economic conditions, environmental
factors, and public agency structures and objectives.
Transplanting programs or program components
without considering local conditions can result in
incompatibilities and a general lack of effective-
ness. Although drawing on the experience of others
can save time and money, local planners and health
officials need to make sure that the programs and
regulations are appropriately tailored to local
conditions.
Successful programs have site evaluation, inspec-
tion, and monitoring processes to ensure that
regulations are followed. Programs that have poor
inspection and monitoring components usually
experience low compliance rates, frequent com-
plaints, and unacceptable performance results. For
example, some states do not have minimum stan-
dards applicable to the various types of onsite
systems being installed or do not require licensing
of installers (Suhrer, 2000). Standards and enforce-
ment practices vary widely among the states, and
until recently there has been little training for local
officials, designers, or installers.
USEPA has identified more effective management
of onsite systems as a key challenge for efforts to
improve system performance (USEPA, 1997). In its
Response to Congress on Use of Decentralized
Wastewater Treatment Systems, USEPA noted that
"adequately managed decentralized wastewater
treatment systems can be a cost-effective and long-
term option for meeting public health and water
quality goals, particularly for small towns and rural
areas."
In addition, the Agency found that properly
managed onsite systems protect public health and
water quality, lower capital and maintenance costs
for low-density communities, are appropriate for
varying site conditions, and are suitable for eco-
logically sensitive areas (USEPA, 1997). However,
USEPA identified several barriers to the increased
use of onsite systems, including the lack of adequate
management programs. Although most communities
have some form of management program in place,
there is a critical lack of consistency. Many manage-
ment programs are inadequate, underdeveloped, or
too narrow in focus, and they might hinder wide-
spread public acceptance of onsite systems as
viable treatment options or fail to protect health
and water resources.
1.6 Performance-based
management of onsite
wastewater treatment systems
Performance-based management approaches have
been proposed as a substitute for prescriptive
requirements for system design, siting, and opera-
tion. In theory, such approaches appear to be both
irresistibly simple and inherently logical. In
practice, however, it is often difficult to certify the
performance of various treatment technologies
under the wide range of climates, site conditions,
hydraulic loads, and pollutant outputs they are
subjected to and to predict the transport and fate of
those pollutants in the environment. Despite these
difficulties, research and demonstration projects
conducted by USEPA, the National Small Flows
Clearinghouse, the National Capacity Development
Project, private consultants and engineering firms,
academic institutions, professional associations, and
public agencies have collectively assembled a body
of knowledge that can provide a framework for
developing performance-based programs. Perfor-
mance ranges for many alternative systems operating
under a given set of climatic, hydrological, site, and
wastewater load conditions have been established.
The site evaluation process is becoming more
refined and comprehensive (see chapter 5) and has
moved from simple percolation tests to a more
comprehensive analysis of soils, restrictive horizons,
seasonal water tables, and other factors. New
technologies that incorporate lightweight media,
recirculation of effluent, or disinfection processes
have been developed based on performance.
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
A performance-based management program makes
use of recent developments to select and size
system technologies appropriate for the estimated
flow and strength of the wastewater at the site
where treatment is to occur. For sites with appropri-
ate soils, ground water characteristics, slopes, and
other features, systems with subsurface wastewater
infiltration systems (SWISs) might be the best
option. Sites with inadequate soils, high seasonal
water tables, or other restrictions require alterna-
tive approaches that can achieve performance
objectives despite restrictive site features. Select-
ing proven system designs that are sized to treat the
expected wastewater load is the key to this ap-
proach. Installing unproven technologies on
provisional sites is risky even if performance
monitoring is to be conducted because monitoring
is often expensive and sometimes inconclusive.
1.6.1 Prescriptive management programs
Onsite system management has traditionally been
based on prescriptive requirements for system
design, siting, and installation. Installation of a
system that "complies" with codes is a primary
goal. Most jurisdictions specify the type of system
that must be installed and the types and depth of
soils that must be present. They also require
mandatory setbacks from seasonally high water
tables, property lines, wells, surface waters, and
other landscape features. Some of these require-
ments (e.g., minimum setback distances from
streams and reservoirs) are arbitrary and vary
widely among the states (Curry, 1998). The pre-
scriptive approach has worked well in some
localities but has severely restricted development
options in many areas. For example, many regions
do not have appropriate soils, ground water tables,
slopes, or other attributes necessary for installation
of conventional onsite systems, hi Florida, 74 percent
of the soils have severe or very severe limitations
for conventional system designs, based on USDA
Natural Resources Conservation Service criteria
(Florida HRS, 1993).
1.6.2 Hybrid management programs
Some jurisdictions are experimenting with perfor-
mance-based approaches while retaining prescrip-
tive requirements for technologies that have proven
effective under a known range of site conditions.
These prescriptive/performance-based or "hybrid"
programs represent a practical approach to onsite
system management by prescribing specific sets of
technologies or proprietary systems for sites where
they have proven to be effective and appropriate.
Regulatory entities review and evaluate alternative
systems to see if they are appropriate for the site
and the wastewater to be treated. Performance-
based approaches depend heavily on data from
research, wastewater characterization processes,
site evaluations, installation practices, and ex-
pected operation and maintenance activities, and
careful monitoring of system performance is
strongly recommended. Programs that allow or
encourage a performance-based approach must
have a strong management program to ensure that
preinstallation research and design and
postinstallation operation, maintenance, and
monitoring activities are conducted appropriately.
Representatives from government and industry are
supporting further development of management
programs that can adequately oversee the full range
of OWTS activities, especially operation and
maintenance. The National Onsite Wastewater
Recycling Association (NOWRA) was founded in
1992 to promote policies that improve the market
for onsite wastewater treatment and reuse products.
NOWRA has developed a model framework for
onsite system management that is based on perfor-
mance rather than prescriptive regulations. The
framework endorses the adoption and use of
alternative technologies that achieve public health
and environmental protection objectives through
innovative technologies and comprehensive
program management. (NOWRA, 1999)
1.7 Coordinating onsite system
management with watershed
protection efforts
During the past decade, public and private entities
involved in protecting and restoring water resources
have increasingly embraced a watershed approach
to assessment, planning, and management. Under
this approach, all the land uses and other activities
and attributes of each drainage basin or ground
water recharge zone are considered when conduct-
ing monitoring, assessment, problem targeting, and
remediation activities (see figure 1-5). A watershed
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
approach incorporates a geographic focus, scientific
principles, and stakeholder partnerships.
Because onsite systems can have significant impacts
on water resources, onsite/decentralized wastewater
management agencies are becoming more involved
in the watershed protection programs that have
developed in their regions. Coordinating onsite
wastewater management activities with programs
and projects conducted under a watershed approach
greatly enhances overall land use planning and
development processes. A cooperative, coordinated
approach to protecting health and water resources
can achieve results that are greater than the sum of
the individual efforts of each partnering entity.
Onsite wastewater management agencies are
important components of watershed partnerships,
and their involvement in these efforts provides
mutual benefits, operating efficiencies, and public
education opportunities that can be difficult for
agencies to achieve individually.
1.8 USEPA initiatives to improve
onsite system treatment and
management
In 1996 Congress requested USEPA to report on the
potential benefits of onsite/decentralized wastewater
treatment and management systems, the potential
costs or savings associated with such systems, and
the ability and plans of the Agency to implement
additional alternative wastewater system measures
within the current regulatory and statutory regime.
A year later USEPA reported that properly managed
onsite/decentralized systems offer several advan-
tages over centralized wastewater treatment facili-
ties (USEPA, 1997; see http://www.epa.gov/owm/
decent/response/index.htm). The construction and
maintenance costs of onsite/decentralized systems
can be significantly lower, especially in low-density
residential areas, making them an attractive alterna-
tive for small towns, suburban developments,
remote school and institutional facilities, and rural
regions. Onsite/decentralized wastewater treatment
systems also avoid potentially large transfers of
water from one watershed to another via central-
ized collection and treatment (USEPA, 1997).
USEPA reported that both centralized and onsite/
decentralized systems need to be considered when
upgrading failing systems. The report concluded
that onsite/decentralized systems can protect public
health and the environment and can lower capital
and maintenance costs in low-density communities.
They are also appropriate for a variety of site
conditions and can be suitable for ecologically
sensitive areas (USEPA, 1997). However, the
Agency also cited several barriers to implementing
more effective onsite wastewater management
programs, including the following:
• Lack of knowledge and public misperceptions
that centralized sewage treatment plants
perform better, protect property values, and are
more acceptable than decentralized treatment
systems.
• Legislative and regulatory constraints and
prescriptive requirements that discourage local
jurisdictions from developing or implementing
effective management and oversight functions.
Model framework for onsite wastewater management
• Performance requirements that protect human health and the environment.
• System management to maintain performance within the established performance requirements.
• Compliance monitoring and enforcement to ensure system performance is achieved and maintained.
• Technical guidelines for site evaluation, design, construction, and operation and acceptable prescriptive designs
for specific site conditions and use.
• Education/training for all practitioners, planners, and owners.
• Certification/licensing for all practitioners to maintain standards of competence and conduct.
• Program reviews to identify knowledge gaps, implementation shortcomings, and necessary corrective actions.
Source: NOWRA, 1999.
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
• Splitting of regulatory authority, which limits
the evaluation of alternatives, and a lack of
management programs that consolidate plan-
ning, siting, design, installation, and mainte-
nance activities under a single entity with the
resources and authority to ensure that perfor-
mance requirements are met and performance
is maintained.
• Liability laws that discourage innovation, as
well as cost-based engineering fees that
discourage investment in designing innovative,
effective, low-cost systems.
• Grant guidelines, loan priorities, and other
financial or institutional barriers that prevent
rural communities from accessing funds,
considering alternative wastewater treatment
approaches, or creating management entities
that span the jurisdictions of multiple agencies.
USEPA is committed to elevating the standards of
onsite wastewater management practice and remov-
ing barriers that preclude widespread acceptance of
onsite treatment technologies. In addition, the Agency
is responding to calls to reduce other barriers to
onsite treatment by improving access to federal
funding programs, providing performance informa-
tion on alternative onsite wastewater treatment
technologies through the Environmental Technology
Verification program (see http://www.epa.gov/etv/)
and other programs, partnering with other agencies
to reduce funding barriers, and providing guidance
through cooperation with other public agencies and
private organizations. USEPA supports a number of
efforts to improve onsite treatment technology
design, application, and funding nationwide. For
example, the National Onsite Demonstration Project
(NODP), funded by USEPA and managed by the
National Small Flows Clearinghouse at West
Virginia University, was established in 1993 to
encourage the use of alternative, decentralized
wastewater treatment technologies to protect public
health and the environment in small and rural
communities (see http://www.nesc.wvu.edu).
In addition, USEPA is studying ground water
impacts caused by large-capacity septic systems,
which might be regulated under the Class V Under-
ground Injection Control (UIC) program. Large-
capacity septic systems serve multiple dwellings,
business establishments, and other facilities and are
used to dispose of sanitary and other wastes through
Figure 1-5. The watershed approach planning and management cycle
Build public
support
Create an
inventory
of the
watershed
Implement
and
evaluate
Define the
problems
Create an
action plan
Set goals
and develop
solutions
Source: Ohio EPA, 1997.
subsurface application (figure 1-6). Domestic and
most commercial systems serving fewer than 20
persons are not included in the UIC program (see
http://www.epa.gov/safewater/uic/classv.html for
exceptions and limitations), but some commercial
facilities serving fewer than 20 people may be
regulated. States and tribes with delegated authority
are studying possible guidance and other programs
that reduce water resource impacts from these
systems. USEPA estimates that there are more than
350,000 large-capacity septic systems nationwide.
USEPA also oversees the management and reuse or
disposal of septic tank residuals and septage
through the Part 503 Rule of the federal Clean
Water Act. The Part 503 Rule (see http://
www.epa.gov/ owm/bio/503pe/) established
requirements for the final use or disposal of sewage
sludge when it is applied to land to condition the
soil or fertilize crops or other vegetation, deposited
at a surface disposal site for final disposal, or fired
in a biosolids incinerator. The rule also specifies
other requirements for sludge that is placed in a
municipal solid waste landfill under Title 40 of the
Code of Federal Regulations (CFR), Part 258. The
Part 503 Rule is designed to protect public health
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
Figure 1-6. Large-capacity septic tanks and other subsurface
discharges subject to regulation under the Underground Injection
Control Program and other programs
Septic Tank
Septic Tank
Drainfield
and the environment from any reasonably antici-
pated adverse effects of certain pollutants and
contaminants that might be present in sewage
sludge, and it is consistent with USEPA's policy of
promoting the beneficial uses of biosolids.
USEPA has also issued guidance for protecting
wellhead recharge areas and assessing threats to
drinking water sources under the 1996 amendments
to the Safe Drinking Water Act (see http://
www.epa.gov/safewater/protect.html and http://
www.epa.gov/safewater/whpnp.html). State source
water assessment programs differ because they are
tailored to each state's water resources and drinking
water priorities. However, each assessment must
include four major elements:
• Delineating (or mapping) the source water
assessment area
• Conducting an inventory of potential sources
of contamination in the delineated area
• Determining the susceptibility of the water
supply to those contamination sources
• Releasing the results of the determinations to
the public
Local communities can use the information col-
lected in the assessments to develop plans to
protect wellhead recharge areas and surface waters
used as drinking water sources. These plans can
include local or regional actions to reduce risks
associated with potential contaminant sources,
prohibit certain high-risk contaminants or activities
in the source water protection area, or specify other
management measures to reduce the likelihood of
source water contamination. Improving the perfor-
mance and management of onsite treatment systems
can be an important component of wellhead and
source water protection plans in areas where nitrate
contamination, nutrient inputs, or microbial
Integrating public and private entities with watershed management
In 1991 the Keuka Lake Association established a watershed project to address nutrient, pathogen, and other
pollutant loadings to the upstate New York lake, which provides drinking water for more than 20,000 people and
borders eight municipalities and two counties. The project sought to assess watershed conditions, educate the
public on the need for action, and foster interjurisdictional cooperation to address identified problems. The
project team established the Keuka Watershed Improvement Cooperative as an oversight committee composed
of elected officials from the municipalities and counties. The group developed an 8-page intermunicipal
agreement under the state home rule provisions (which allow municipalities to do anything collectively that they
may do individually) to formalize the cooperative and recommend new laws and policies for onsite systems and
other pollutant sources.
Voters in each municipality approved the agreement by landslide margins after an extensive public outreach
program. The cooperative developed regulations governing onsite system permitting, design standards,
inspection, and enforcement. The regulations carry the force of law in each town or village court and stipulate
that failures must be cited and upgrades required. Inspections are required every 5 years for systems within
200 feet of the lake, and alternative systems must be inspected annually. The cooperative coordinates its
activities with state and county health agencies and maintains a geographic information system (CIS) database
to track environmental variables and the performance of new technologies. The program is financed by onsite
system permit fees, some grant funds, and appropriations from each municipality's annual budget.
Source: Shephard, 1996.
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
contaminants are identified as potential risks to
drinking water sources.
1.9 Other initiatives to assist and
improve onsite management
efforts
Financing the installation and management of
onsite systems can present a significant barrier for
homeowners and small communities. USEPA and
other agencies have developed loan, cost-share, and
other programs to help homeowners pay for new
systems, repairs, or upgrades (see chapter 2). Some
of the major initiatives are the Clean Water State Re-
volving Fund (CWSRF), the Hardship Grant Program,
the Nonpoint Source Pollution Program, USDA Rural
Development programs, and the Community
Development Block Grant (CDBG) program.
The CWSRF is a low-interest or no-interest loan
program that has traditionally financed centralized,
publicly owned treatment works across the nation
(see http://www.epa.gov/owm/finan.htm). The
program guidance, issued in 1997, emphasizes that
the fund can be used as a source of support for the
installation, repair, or upgrading of OWTSs in
small-town, rural, and suburban areas. The CWSRF
programs are administered by states and the
territory of Puerto Rico and operate like banks.
Federal and state contributions are used to capital-
ize the fund, which makes low- or no-interest loans
for important water quality projects. Funds are then
repaid to the CWSRFs over terms as long as 20
years. Repaid funds are recycled to support other
water quality projects. Projects that might be
eligible for CWSRF funding include new system
installations and replacement or modification of
existing systems. Also covered are costs associated
with establishing a management entity to oversee
onsite systems in a region, including capital outlays
(e.g., for pumper trucks or storage buildings).
Approved management entities include city and
county governments, special districts, public or
private utilities, and private for-profit or nonprofit
corporations.
The Hardship Grant Program of the CWSRF was
developed in 1997 to provide additional resources
for improving onsite treatment in low-income
regions experiencing persistent problems with
onsite treatment because of financial barriers. The
new guidance and the grant program responded to
priorities outlined in the Safe Drinking Water Act
Amendments of 1996 and the Clean Water Action
Plan, which was issued in 1998.
The Nonpoint Source Pollution Program provides
funding and technical support to address a wide
range of polluted runoff problems, including
contamination from onsite systems. Authorized
under section 319 of the federal Clean Water Act
and financed by federal, state, and local contribu-
tions, the program provides cost-share funding for
individual and community systems and supports
broader watershed assessment, planning, and
management activities. Demonstration projects
funded in the past have included direct cost-share
for onsite system repairs and upgrades, assessment
of watershed-scale onsite wastewater contributions
to polluted runoff, regional remediation strategy
development, and a wide range of other projects
dealing with onsite wastewater issues. (See http://
www.epa.gov/OWOW/NPS for more information.)
The USEPA Office of Wastewater Management
supports several programs and initiatives related to
onsite treatment systems, including development of
guidelines for managing onsite and cluster systems
(see http://www.epa.gov/own/bio.htm). The
disposition of biosolids and septage pumped from
septic tanks is also subject to regulation by state
and local governments (see chapter 4).
The U.S. Department of Agriculture provides grant
and loan funding for onsite system installations
through USDA Rural Development programs. The
Rural Housing Service program (see http://
www.rurdev.usda.gov/rhs/Individual/
ind_splash.htm) provides direct loans, loan
guarantees, and grants to low or moderate-income
individuals to finance improvements needed to
make their homes safe and sanitary. The Rural
Utilities Service (http:www.usda.gov/rus/water/
programs.htm) provides loans or grants to public
agencies, tribes, and nonprofit corporations seeking
to develop water and waste disposal services or
decrease their cost.
The U.S. Department of Housing and Urban
Development (HUD) operates the Community
Development Block Grant Program, which pro-
vides annual grants to 48 states and Puerto Rico.
The states and Puerto Rico use the funds to award
grants for community development to small cities
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
and counties. CDBG grants can be used for numer-
ous activities, including rehabilitation of residen-
tial and nonresidential structures, construction of
public facilities, and improvements to water and
sewer facilities, including onsite systems. USEPA is
working with HUD to improve system owners'
access to CDBG funds by raising program aware-
ness, reducing paperwork burdens, and increasing
promotional activities in eligible areas. (More
information is available at http://www.hud.gov/
cpd/cdbg.html.)
The Centers for Disease Control and Prevention
(CDC) of the U.S. Public Health Service (see http://
www.cdc.gov) conduct research and publish studies
on waterborne infectious disease outbreaks and
illness linked to nitrate contamination of ground
water, both of which have been linked to OWTSs,
among other causes. Disease outbreaks associated
with contaminated, untreated ground water and
recreational contact with water contaminated by
pathogenic organisms are routinely reported to the
CDC through state and tribal infectious disease
surveillance programs.
Individual Tribal Governments and the Indian
Health Service (1HS) handle Indian wastewater
management programs. The IHS Sanitation Facili-
ties Construction Program, within the Division of
Facilities and Environmental Engineering of the
Office of Public Health, is supported by engineers,
sanitarians, technicians, clerical staff, and skilled
construction workers. Projects are coordinated
through the headquarters office in Rockville,
Maryland, and implemented through 12 area offices
across the nation. The program works cooperatively
with tribes and tribal organizations, USEPA, HUD,
the USDA's Rural Utilities Service, and other
agencies to fund sanitation and other services
throughout Indian Country (see http://
www.ihs.gov/nonmedicalprograms/dfee/reports/
rptl998.pdf).
References
Curry, D. 1998. National Inventory of Key Activities
Supporting the Implementation of
Decentralized Wastewater Treatment. Fact
Sheet No. 3-2. Research conducted by the U.S.
Environmental Protection Agency, Office of
Wastewater Management. Available from Terra
Tech, Inc., Fairfax, VA.
Florida Department of Health and Rehabilitative
Services (Florida DHRS). 1993. Onsite Sewage
Disposal System Research in Florida: An
Evaluation of Current OSDS Practices in
Florida. Report prepared for the Florida
Department of Health and Rehabilitative
Services, Environmental Health Program, by
Ayres Associates, Tallahassee, FL.
Fogarty, S. 2000. Land Use and Zoning Laws. Small
Flows Quarterly 1(1): 13.
Hoover, M.T., A.R. Rubin, and F. Humenik. 1998.
Choices for Communities: Wastewater
Management Options for Rural Areas. AG-585.
North Carolina State University, College of
Agriculture and Life Sciences, Raleigh, NC.
Kreissl, J.F. 1982. Evaluation of State Codes and
Their Implications. In Proceedings of the
Fourth Northwest On-Site Wastewater Disposal
Short Course, September, University of
Washington, Seattle, WA.
Kreissl, J.F. 2000. Onsite Wastewater Management
at the Start of the New Millenium. Small Flows
Quarterly 1(1): 10-11.
National Onsite Wastewater Recycling Associations
(NOWRA). 1999. Model Framework for
Unsewered Wastewater Infrastructure. National
Onsite Wastewater Recycling Association. July
1999. . Accessed March 29, 2000.
Nelson, V.I., S.P Dix, and F. Shepard. 1999.
Advanced On-Site Wastewater Treatment and
Management Scoping Study: Assessment of
Short-Term Opportunities and Long-Run
Potential. Prepared for the Electric Power
Research Institute, the National Rural Electric
Cooperative Association, and the Water
Environment Research Federation.
Ohio Environmental Protection Agency (Ohio EPA).
1997. A Guide to Developing Local Watershed
Action Plans in Ohio. Ohio Environmental
Protection Agency, Division of Surface Water,
Columbus, OH.
Otis, J. 2000. Performance management. Small
Flows Quarterly 1(1): 12.
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Chapter 1: Background and Use ofOnsite WastewaterTreatment Systems
Parsons Engineering Science. 2000. Septic System
Failure Summary. Prepared for U.S. Environ-
mental Protection Agency, Office of Water,
under Contract 68-C6-0001. June 13, 2000.
Pennsylvania Infrastructure Investment Authority
(PENNVEST). 1997. A Water, Sewer, and
Stormwater Utility's Guide to Financial and
Technical Assistance Programs. Pennsylvania
Infrastructure Investment Authority,
Harrisburg, PA.
Plews, G.D. 1977. The Adequacy and Uniformity of
Regulations for Onsite Wastewater Disposal—
A State Viewpoint. In Proceedings of the
National Conference on Less Costly Treatment
Systems for Small Communities. U.S. Environ-
mental Protection Agency, Cincinnati, OH.
Shephard, F.C. 1996, April. Managing Wastewater:
Prospects in Massachusetts for a Decentralized
Approach. Prepared for the ad hoc Task Force
for Decentralized Wastewater Management.
Marine Studies Consortium and Waquoit Bay
National Estuarine Research Reserve.
Suhrer, T. 2000. NODPII at Work in the Green
Mountain State. Small Flows Quarterly 1(1): 12.
Published by the National Small Flows
Clearinghouse, Morgantown, WV.
Tchobanoglous, G. 2000. Decentralized Wastewater
Management: Challenges and Opportunities for
the Twenty-First Century. In Proceedings of the
Southwest On-Site Wastewater Management
Conference and Exhibit, sponsored by the
Arizona County Directors of Environmental
Health Services Association and the Arizona
Environmental Health Association, Laughlin,
Nevada, February 2000.
U.S. Census Bureau. 1990. Historical Census of
Housing Tables: Sewage Disposal. .
U.S. Census Bureau. 1999. 1997 National Data
Chart for Total Occupied Housing Units.
.
U.S. Environmental Protection Agency (USEPA).
1980b. Planning Wastewater Management
Facilities for Small Communities. EPA-600/8-
80-030. U.S. Environmental Protection Agency,
Office of Research and Development, Waste-
water Research Division, Municipal
Environmental Research Laboratory,
Cincinnati, OH.
U.S. Environmental Protection Agency
(USEPA). 1980a. Design Manual: Onsite
Wastewater Treatment and Disposal Systems.
EPA 625/1-80/012. U.S. Environmental
Protection Agency, Washington, DC.
U.S. Environmental Protection Agency (USEPA).
1987. It's Your Choice: A Guidebook for Local
Officials on Small Community Wastewater
Management Options. USEPA Office of
Municipal Pollution Control (WH-595).
U.S. Environmental Protection Agency (USEPA).
1993. Guidance Specifying Management
Measures for Sources of Nonpoint Pollution in
Coastal Waters. EPA840-B-92-002. U.S.
Environmental Protection Agency, Office of
Water, Washington, DC.
U.S. Environmental Protection Agency (USEPA).
1994. Environmental Planning for Small
Communities: A Guide for Local Decision-
Makers. EPA/625/R-94/009, U.S.
Environmental Protection Agency, Office of
Research and Development, Office of Regional
Operations and State/Local Relations,
Washington, DC.
U.S. Environmental Protection Agency (USEPA).
1996a. National Water Quality Inventory
Report to Congress. [305b Report.] EPA 841-R-
97-008. U.S. Environmental Protection Agency,
Washington, DC.
U.S. Environmental Protection Agency (USEPA).
1996b. Clean Water Needs Survey Report to
Congress, .
U.S. Environmental Protection Agency (USEPA).
1997. Response to Congress on Use of
Decentralized Wastewater Treatment Systems.
EPA 832-R-97-001b. U.S. Environmental
Protection Agency, Washington, DC.
U.S. Environmental Protection Agency (USEPA).
1998. Guidelines for Ecological Risk
Assessment. EPA 630-R-95-002F. U.S.
Environmental Protection Agency, Office of
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Chapter 1: Background and Use of Onsite Wastewater Treatment Systems
Research and Development, Risk Assessment
Forum, Washington, DC.
U.S. Environmental Protection Agency (USEPA).
2000. Draft EPA Guidelines for Management
ofOnsite/Decentralized Wastewater Systems.
U.S. Environmental Protection Agency, Office
of Wastewater Management, Washington, DC.
Federal Register, October 6, 2000, 65(195):
59840-59841.
U.S. Public Health Service (USPHS). 1967.
(Updated from 1959 version.) Manual of
Septic Tank Practice. U.S. Public Health
Service Publication No. 526. U.S. Department
of Health, Education and Welfare.
Venhuizen, D. 1995. An Analysis of the Potential
Impacts on Ground Water Quality ofOn-Site
Watershed Management Using Alternative
Management Practices. .
Water Environment Research Foundation (WEF).
1998. Watershed-Scale Ecological Risk
Assessment—Watersheds. Final report, Project
93-IRM-4(A). Water Environment Research
Foundation, Alexandria, VA.
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Chapter 2:
Management of Onsite Wastewater Treatment Systems
2.1 Introduction
2.2 Elements of a successful program
2.3 Types of management entities
2.4 Management program components
2.5 Financial assistance for management programs and system installation
2.1 Introduction
Effective management is the key to ensuring that
the requisite level of environmental and public
health protection for any given community is
achieved. It is the single most important factor in
any comprehensive wastewater management
program. Without effective management, even the
most costly and advanced technologies will not be
able to meet the goals of the community. Numerous
technologies are currently available to meet a broad
range of wastewater treatment needs. Without
proper management, however, these treatment
technologies will fail to perform as designed and
efforts to protect public health and the environment
will be compromised.
In recognition of the need for a comprehensive
management framework that communities can use in
developing and improving OWTS management
programs, USEPA is publishing Guidelines for
Management of Decentralized Wastewater Systems
(see http://www.epa.gov/owm/decent/index.htm). At
the time of the publication of this manual, the final
guidelines and accompanying guidance manual are
almost complete. USEPA envisions that tribes, states,
local governments, and community groups will use the
management guidelines as a reference to strengthen
their existing onsite/decentralized programs. The
guidelines include a set of recommended program
elements and activities and model programs that OWTS
program managers can refer to in evaluating their
management programs.
The literature on OWTSs is replete with case
studies showing that adequate management is
critical to ensuring that OWTSs are sited, designed,
installed, and operated properly. As USEPA
pointed out in its Response to Congress on Use of
Decentralized Wastewater Treatment Systems
(1997), "Few communities have developed organi-
zational structures for managing decentralized
wastewater systems, although such programs are
required for centralized wastewater facilities and
for other services (e.g., electric, telephone, water,
etc)."
Good planning and management are inseparable.
The capacity of the community to manage any
given technology should be factored into the
decision-making process leading to the planning
and selection of a system or set of systems appro-
priate for the community. As Kreissl and Otis noted
in New Markets for Your Municipal Wastewater
Services: Looking Beyond the Boundaries (1999),
appropriate technologies should be selected based
on whether they are affordable, operable, and
reliable. The selection of individual unit processes
and systems should, at a minimum, be based on
those three factors. Although managing OWTSs is
obviously far more complicated than assessing
whether the systems are affordable, operable and
reliable, an initial screening using these criteria is a
critical element of good planning.
Historically, the selection and siting of OWTSs has
been an inconsistent process. Conventional septic
tank and leach field systems were installed based on
economic factors, the availability of adequate land
area, and simple health-based measures aimed only
at preventing direct public contact with untreated
wastewater. Little analysis was devoted to under-
standing the dynamics of OWTSs and the potential
impacts on ground water and surface waters. Only
recently has there been an understanding of the
issues and potential problems associated with
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Chapter 2: Management of Onsite Wastewater Treatment Systems
failing to manage OWTSs in a comprehensive,
holistic manner.
Many case studies and reports from across the
country provide documentation that a significant
number of OWTSs lack adequate management
oversight, which results in inadequate pollutant
treatment (USEPA, 2000). The lack of system
inventories in many communities makes the task of
system management even more challenging.
As a result of the perception that onsite/decentral-
ized systems are inferior, old-fashioned, less
technologically advanced, and not as safe as
centralized wastewater treatment systems from both
an environmental and public health perspective,
many communities have pursued the construction
of centralized systems (collection systems and
sewage treatment plants). Centralized wastewater
collection and treatment systems, however, are not
the most cost-effective or environmentally sound
option for all situations (e.g., sewage treatment
plants can discharge high point source loadings of
pollutants into receiving waters). They are costly to
build and operate and are often infeasible or cost-
prohibitive, especially in areas with low popula-
tions and dispersed households. Many communities
lack both the revenue to fund these facilities and
the expertise to manage the treatment operations. In
addition, centralized treatment systems can contrib-
ute to unpredicted growth and development that
might threaten water quality.
As development patterns change and increased
development occurs in rural areas and on the urban
fringe, many communities are evaluating whether
they should invest in centralized sewage treatment
plants or continue to rely on OWTSs. The avail-
ability of innovative and alternative onsite tech-
nologies and accompanying management strategies
now provides small communities with a practical,
cost-effective alternative to centralized treatment
plants. For example, analysis included in USEPA's
Response to Congress on Use of Decentralized
Wastewater Treatment Systems (1997) shows that
the costs of purchasing and managing an OWTS or
a set of individual systems can be significantly (22
to 80 percent) less than the cost of purchasing and
managing a centralized system.
Regardless of whether a community selects more
advanced decentralized systems, centralized sys-
tems, or some combination of the two, a compre-
hensive management program is essential. As
USEPA noted in Wastewater Treatment/Disposal for
Small Communities (1992), effective management
strategies depend on carefully evaluating all
feasible technical and management alternatives and
selecting appropriate solutions based on the needs
of the community, the treatment objectives, the
economic capacity, and the political and legislative
climate.
The management tasks listed have become increas-
ingly complex, especially given the need to develop
a management strategy based on changing priorities
primarily driven by new development activities.
Rapid urbanization and suburbanization, the
presence of other sources that might discharge
nutrients and pathogens, water reuse issues, increas-
ingly stringent environmental regulations, and
recognition of the need to manage on a watershed
basis increase the difficulty of this task. Multiple
objectives (e.g., attainment of water quality criteria,
protection of ground water, efficient and affordable
wastewater treatment) now must be achieved to
reach the overarching goal of maintaining eco-
nomically and ecologically sound communities.
Investment by small communities in collection and
treatment systems increases taxes and costs to
consumers—costs that might be reduced substan-
tially by using decentralized wastewater treatment
systems. From a water resource perspective achiev-
ing these goals means that public health, contact
recreation activities, fisheries, shellfisheries,
drinking water resources, and wildlife need to be
protected or restored. From a practical standpoint,
achieving these goals requires that the management
entity develop and implement a program that is
consistent with the goal of simultaneously meeting
and achieving the requirements of the Safe Drink-
ing Water Act, the Clean Water Act, the Endan-
gered Species Act, and other applicable federal,
state, tribal, and local requirements.
Changing regulatory contexts point to scenarios in
which system selection, design, and replacement
will be determined by performance requirements
tied to water quality standards or maximum
contamination limits for ground water. Cumulative
effects analyses and antidegradation policies might
be used to determine the level of technology and
management needed to meet the communities'
resource management goals. Comprehensive
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Chapter 2: Management of Onsite Wastewater Treatment Systems
coordinated management programs are needed to
meet this challenge. These programs require
interdisciplinary consultations among onsite system
management entities, water quality
agencies, land use planners, engineers, wildlife
biologists, public health specialists, and others to
ensure that these goals and objectives are efficiently
achieved with a minimum of friction or program
overlap.
Fortunately, there are solutions. Technologies that
can provide higher levels of pollutant reduction
than were practical in the past appear to be
emerging. Better monitoring and assessment
methods are now available to determine the
effectiveness of specific technologies. Remote
sensing is possible to help monitor and understand
system operation, and more sophisticated inspec-
tion tools are available to complement visual
septic tank/SWIS inspections.
2.2 Elements of a successful
program
The success or failure of an onsite wastewater
management program depends significantly on
public acceptance and local political support;
adequate funding; capable and trained technical and
field staff; and clear and concise legal authority,
regulations, and enforcement mechanisms (Ciotoli
and Wiswall, 1982). Management programs should
include the following critical elements:
• Clear and specific program goals
• Public education and outreach
• Technical guidelines for site evaluation, design,
construction, and operation/maintenance
• Regular system inspections, maintenance, and
monitoring
• Licensing or certification of all service providers
• Adequate legal authority, effective enforcement
mechanisms, and compliance incentives
• Funding mechanisms
• Adequate record management
• Periodic program evaluations and revisions
Although all of these elements should be present in a
successful management program, the responsibility
for administering the various elements might fall on
a number of agencies or entities. Regardless of the
size or complexity of the program, its components
must be publicly accepted, politically feasible,
fiscally viable, measurable, and enforceable.
Many of the program elements discussed in this
chapter are described in more detail in the other
chapters of this manual. The elements described in
detail in this chapter are those essential to the
selection and adoption of a management program.
2.2.1 Clear and specific program goals
Developing and meeting program goals is critical
to program success. Management programs typi-
cally focus on two goals—protection of public
health and protection of the environment. Each
onsite system must be sited, designed, and managed
to achieve these goals.
Public health protection goals usually focus on
preventing or severely limiting the discharge of
pathogens, nutrients, and toxic chemicals to ground
water. Surface water bodies, including rivers, lakes,
streams, estuaries, and wetlands, can also be
adversely affected by OWTSs. Program goals
should be established to protect both surface and
ground water resources.
Public participation opportunities during
program planning and implementation
Agreement on basic need for program
Participation on committees, e.g., finance, technical,
educational
Selection of a consultant or expert (request for
proposal, selection committee, etc.)
Choosing the most appropriate options from the
options identified by a consultant or expert
Obtaining financing for the preferred option
Identifying and solving legal questions and issues
Providing inputforthe enforcement/compliance plan
Implementation and construction
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2.2.2 Public education and outreach
Public education
Public participation in and support for planning,
design, construction, and operation and mainte-
nance requirements are essential to the acceptance
and success of an onsite wastewater management
program. Public meetings involving state and local
officials, property owners, and other interested
parties are an effective way to garner support for
the program. Public meetings should include
discussions about existing OWTS problems and
cover issues like program goals, costs, financing,
inspection, and maintenance. Such meetings
provide a forum for identifying community
concerns and priorities so that they can be consid-
ered in the planning process. Public input is also
important in determining management and compli-
ance program structure, defining the boundaries of
the program, and evaluating options, their relative
requirements and impacts, and costs.
Public outreach
Educating homeowners about the proper operation
and maintenance of their treatment systems is an
essential program activity. In most cases, system
owners or homeowners are responsible for some
portion of system operation and maintenance or
for ensuring that proper operation and mainte-
nance occurs through some contractual agreement.
The system owner also helps to monitor system
performance. Increased public support and
program effectiveness can be promoted by educat-
ing the public about the importance of OWTS
management in protecting public health, surface
waters, ground water resources, and property
values.
Onsite system owners are often uninformed about
how their systems function and the potential for
ground water and surface water contamination
from poorly functioning systems. Surveys show
that many people have their septic tanks pumped
only after the system backs up into their homes or
yards. Responsible property owners who are
educated in proper wastewater disposal and mainte-
nance practices and understand the consequences of
system failure are more likely to make an effort to
ensure their systems are in compliance with opera-
tion and maintenance requirements. Educational
materials for homeowners and training courses for
designers, site evaluators, installers, inspectors, and
operation/maintenance personnel can help reduce
the impacts from onsite systems by reducing the
number of failing systems, which potentially
reduces or eliminates future costs for the system
owner and the management program.
2.2.3 Technical guidelines for site
evaluation, design, and
construction
The regulatory authority (RA) should set technical
guidelines and criteria to ensure effective and
functioning onsite wastewater systems. Guidelines
for site evaluation, system design, construction,
operation/maintenance, and inspection are neces-
sary to maintain performance consistency. Site
evaluation guidelines should be used to determine
the site's capability to accept the expected wastewa-
ter volume and quality. Guidelines and standards on
system design ensure the system compatibility with
the wastewater characteristics to be treated and its
structural integrity over the life of the system.
Construction standards should require that systems
conform to the approved plan and use appropriate
construction methods, materials, and equipment.
2.2.4 Regular system operation,
maintenance, and monitoring
An OWTS should be operated and maintained to
ensure that the system performs as designed for its
service life. Both individual systems and sets of
systems within a delineated management area
should be monitored to ensure proper performance
and the achievement of public health and environ-
mental goals. A combination of visual, physical,
bacteriological, chemical, and remote monitoring
approaches can be used to assess system perfor-
mance. Specific requirements for reporting to the
appropriate regulatory agency should also be
defined in a management program. The right to
enter private property to access and inspect compo-
nents of the onsite system is also an essential
element of an effective management program.
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2.2.5 Licensing or certification of
service providers
Service providers include system designers, site
evaluators, installers, operation/maintenance
personnel, inspectors, and septage pumpers/haulers.
A qualifications program that includes certification
or licensing procedures for service providers should
be incorporated into a management program.
Licensing can be based on examinations that assess
basic knowledge, skills, and experience necessary
to perform services. Other components include
requirements for continuing education, defined
service protocols, and disciplinary guidelines or
other mechanisms to ensure compliance and
consistency. Many states already have, or are
planning, certification programs for some service
providers. These and other existing licensing
arrangements should be incorporated when they
complement the objectives of the management
program.
2.2.6 Adequate legal authority, effective
enforcement mechanisms, and
compliance incentives
Onsite wastewater management programs need a
combination of legal authorities, enforcement
mechanisms, and incentives to ensure compliance
and achievement of program goals. To ensure
program effectiveness, some program mechanisms
should be enforceable. Although the types of
mechanisms management entities use will vary by
program, the following mechanisms should be
enforceable: construction and operating permits,
requirements for performance bonds to ensure
proper construction or system operation and
maintenance, and licensing/certification require-
ments to ensure that service providers have the
necessary skills to perform work on treatment
systems. Management entities should also have the
authority to carry out repairs or replace systems
and, ultimately, to levy civil penalties. Enforce-
ment programs, however, should not be based
solely on fines if they are to be effective. Informa-
tion stressing public health protection, the mon-
etary benefits of a clean environment, and the
continued functioning of existing systems (avoid-
ance of system replacement costs) can provide
additional incentives for compliance. Finally, it
should be recognized that the population served by
the management program must participate in and
support the program to ensure sustainability.
2.2.7 Funding mechanisms
Funding is critical to the functioning of an effec-
tive OWTS management program. Management
entities should ensure that there is adequate funding
available to support program personnel, education
and outreach activities, monitoring and evaluation,
and incentives that promote system upgrades and
replacement. Funding might also be needed for
new technology demonstrations and other program
enhancements.
2.2.8 Adequate record management
Keeping financial, physical, and operational
records is an essential part of a management
program. Accurate records of system location and
type, operation and maintenance data, revenue
generated, and compliance information are neces-
sary to enhance the financial, operational, and
regulatory health of the management program.
Electronic databases, spreadsheets, and geographic
information systems can help to ensure program
effectiveness and appropriate targeting of program
resources. At a minimum, program managers
should maintain records of system permits, design,
size, location, age, site soil conditions, complaints,
inspection results, system repairs, and maintenance
schedules. This information should be integrated
with land use planning at a watershed or wellhead
protection zone scale.
2.2.9 Periodic program evaluations and
revisions
Management programs for onsite systems are
dynamic. Changing community goals, resources,
environmental and public health concerns, develop-
ment patterns, and treatment system technologies
require that program managers—with public
involvement—regularly evaluate program effec-
tiveness and efficiency. Program managers might
need to alter management strategies because of
suburban sprawl and the close proximity of central-
ized collection systems. Resource and staff limita-
tions might also necessitate the use of service
providers or designated management entities to
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Twelve problems that can affect OWTS management programs
1. Failure to adequately consider site-specific environmental conditions (site evaluations)
2. Codes that thwart system selection or adaptation to difficult local site conditions and that do not
allow the use of effective innovative or alternative technologies
3. Ineffective or nonexistent public education and training programs
4. Failure to include water conservation and reuse
5. Ineffective controls on operation and maintenance of systems
6. Lack of control over residuals management
7. Lack of OWTS program monitoring and evaluation, including OWTS inspection and monitoring
8. Failure to consider the special characteristics and requirements of commercial, industrial, and
large residential systems
9. Weak compliance and enforcement programs
10. Lack of adequate funding
11. Lack of adequate legal authority
12. Lack of adequately trained and experienced personnel
Source: Adapted from USEPA, 1986.
ensure that systems in a jurisdiction are adequately
managed.
2.3 Types of management entities
Developing, implementing, and sustaining a
management program requires knowledge of the
political, cultural, and economic context of the
community, the current institutional structure, and
available technologies. Also required are clearly
defined environmental and public health goals and
adequate funding. A management program should
be based on the administrative, regulatory, and
operational capacity of the management entity and
the goals of the community. In many localities,
partnerships with other entities in the management
area (watershed, county, region, state, or tribal
lands) are necessary to increase the capacity of the
management program and ensure that treatment
systems do not adversely affect human health or
water resources. The main types of management
entities are federal, state, and tribal agencies; local
government agencies; special-purpose districts and
public utilities; and privately owned and operated
management entities. Descriptions of the various
types of management entities are provided in the
following subsections.
2.3.1 Federal, state, tribal, and local
agencies
Federal, state, tribal, and local governments have
varying degrees of authority and involvement in the
development and implementation of onsite waste-
water management programs. In the United States,
tribal, state, and local governments are the main
entities responsible for the promulgation and enforce-
ment of OWTS-related laws and regulations. Many of
these entities provide financial and technical assis-
tance. Tribal, state, and local authority determines the
degree of control these entities have in managing
onsite systems. General approaches and responsibili-
ties are shown in table 2-1.
At the federal level, USEPA is responsible for
protecting water quality through the implementa-
tion of the Clean Water Act (CWA), the Safe
Drinking Water Act (SDWA), and the Coastal Zone
Act Reauthorization Amendments (CZARA). Under
these statutes, USEPA administers a number of
programs that affect onsite system management.
The programs include the Water Quality Standards
Program, the Total Maximum Daily Load Pro-
gram, the Nonpoint Source Management Program,
the National Pollutant Discharge Elimination
System (NPDES) Program, the Underground
Injection Control (UIC) Program, and the Source
Water Protection Program. Under the CWA and the
2-6
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
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L/SER4 0/7srte l/l/astewater Treatment Systems Manual
2-7
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Chapter 2: Management of Onsite Wastewater Treatment Systems
SDWA, USEPA has the authority to directly
regulate specific categories of onsite systems under
the UIC and NPDES programs. The CZARA
section 6217 Coastal Nonpoint Source Program
requires the National Oceanic and Atmospheric
Administration (NOAA) and USEPA to review and
approve upgraded state coastal nonpoint source
programs to meet management measures for new
and existing OWTSs. These measures address
siting, designing, installing, maintaining, and
protecting water quality. See chapter 1 for addi-
tional information and Internet web sites.
State and tribes might manage onsite systems
through various agencies. Typically, a state or tribal
public health office is responsible for managing
onsite treatment systems. Regulation is sometimes
centralized in one state or tribal government office
and administered from a regional or local state
office. In most states, onsite system management
responsibilities are delegated to the county or
municipal level. Where such delegation occurs, the
state might exercise varying degrees of local
program oversight.
Leadership and delegation of authority at the state
level are important in setting technical, manage-
ment, and performance requirements for local
programs. In states where local governments are
responsible for managing onsite systems, state
authority often allows flexibility for local programs
to set program requirements that are appropriate
for local conditions and management structures as
long as the local program provides equal or greater
protection than that of state codes. Statewide
consistency can be promoted by establishing
• Administrative, managerial, and technological
requirements
• Performance requirements for natural resource
and public health protection
• Requirements for monitoring and laboratory
testing
• Education and training for service providers
• Technical, financial, and administrative support
• Periodic program reviews and evaluations
• Enforcement of applicable regulations
Many states set minimum system design and siting
requirements for onsite systems and are actively
involved in determining appropriate technologies.
Other states delegate some or all of this authority to
local governments. Some states retain the responsi-
bility for the administrative or technical portions of
the onsite management program; in these states, the
local governments' primary role is to implement
the state requirements.
2.3.2 Local government agencies
In many states, local governments have the respon-
sibility for onsite wastewater program manage-
ment. These local management programs are
administered by a variety of municipal, county, or
district-level agencies. The size, purpose, and
authority of county, township, city, or village
government units vary according to each state's
statutes and laws. Depending on the size of the
jurisdiction and the available resources, an onsite
wastewater management program can be adminis-
tered by a well-trained, fully staffed environmental
or public health agency or by a board composed of
local leaders. In some states, some or most of the
responsibility for onsite system management is
delegated by the legislature to local governments.
In states with "home rule" provisions, local units of
government have the authority to manage onsite
systems without specific delegation by the state
legislature. Some local home rule governments also
have the power to enter into multiple agency or
jurisdictional agreements to jointly accomplish any
home rule function without any special authority
from the state (Shephard, 1996).
County governments can be responsible for a
variety of activities regarding the management of
onsite systems. A county can assume responsibility
for specific activities, such as OWTS regulation,
within its jurisdiction, or it can supplement and
support existing state, city, town, or village waste-
water management programs with technical,
financial, or administrative assistance. Counties can
provide these services through their normal opera-
tional mechanisms (e.g., a county department or
agency), or they can establish a special district to
provide designated services to a defined service
area. County agency responsibilities might include
• Adoption of state minimal requirements or
development of more stringent requirements
• Planning, zoning, and general oversight of
proposed development
• Review of system designs, plans, and installa-
tion practices
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• Permitting of systems and construction over-
sight
• Inspection, monitoring, and enforcement
• Reports to public and elected officials
Township, city, or village governments can be
responsible for planning, permitting, and operat-
ing onsite wastewater facilities and enforcing
applicable regulations. The precise roles and
responsibilities of local governments depend on
the preferences, capabilities, and circumstances
of each jurisdiction. Because of the variability in
state enabling legislation and organizational
structures, the administrative capacity, jurisdic-
tion, and authority of local entities to manage
onsite wastewater systems vary considerably.
2.3.3 Special-purpose districts and
public utilities
The formation of special-purpose districts and
public utilities is usually enabled by state law to
provide public services that local governments do
not or cannot provide. A special-purpose district
or public utility is a quasigovernmental entity
established to provide specific services or to
conduct activities specified by the enabling
legislation. Special districts (e.g., sanitation
districts) provide single or multiple services, such
as managing planning and development activities,
conducting economic development programs,
improving local conditions, and operating drinking
water and wastewater treatment facilities. The
territory serviced by this entity is variable and can
include a single community, a portion of a commu-
nity, a group of communities, parts of several
communities, an entire county, or a regional area.
State enabling legislation usually outlines the
authority, structure, and operational scope of the
district, including service area, function, organiza-
tional structure, financial authority, and perfor-
mance criteria.
Special-purpose districts and public utilities are
usually given sufficient financial authority to apply
for or access funds, impose service charges, collect
fees, impose special assessments on property, and
issue revenue or special assessment bonds. Some
special-purpose districts have the same financing
authority as municipalities, including the authority
to levy taxes and incur general obligation debt.
These districts are usually legal entities that might
enter into contracts, sue, or be sued. There might
be situations where eminent domain authority is
needed to effectively plan and implement onsite
programs. Special-purpose districts and public
Sanitation district management of onsite systems: New Mexico
Onsite systems in the community of Pena Blanca, New Mexico, are managed by the Pena Blanca Water and
Sanitation District, which is organized understate statutes that require a petition signed by 25 percent of the
registered voters and a public referendum before a district may be formed. Once formed, water and sanitation
districts in New Mexico are considered subdivisions of the state and have the powerto levy and collect ad
i/a/oremtaxes and the right to issue general obligation and revenue bonds.
Residents and public agency officials in Pena Blanca sought to improve the management of systems in the
community after a 1985 study found that 86 percent of existing systems required upgrades, repair, or
replacement. The water and sanitation district was designated as the lead agency for managing OWTSs
because it already provided domestic water service to the community and had an established administrative
structure. The sanitation district relies on the New Mexico Environment Department to issue permits and monitor
installation, while the district provides biannual pumping services through an outside contractor for a monthly fee
of $10.64 for a 1,000-gallon tank. The district also supervises implementation of the community's onsite system
ordinance, which prohibits untreated and unauthorized discharges, lists substances that might not be discharged
into onsite systems (e.g., pesticides, heavy metals), and provides for sampling and testing. Penalties for
noncompliance are set at $300 per violation and not more than 90 days imprisonment. Liens might be placed on
property for nonpayment of pumping fees.
The program has been in operation since 1991 and serves nearly 200 homes and businesses. Septage pooling
on ground surfaces, a problem identified in the 1985 study, has been eliminated.
Source: Rose, 1999.
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Chapter 2: Management of Onsite Wastewater Treatment Systems
utilities will most likely have to work closely with
state or local authorities when program planning or
implementation requires the use of this authority.
Special districts and public utilities can be an effective
option for managing onsite systems. The special
district and public utility models have been adopted
successfully in many states. A good example is the
creation of water districts and sanitation districts,
which are authorized to manage and extend potable
water lines and extend sewerage service in areas
near centralized treatment plants. The development
of onsite system management functions under the
authority of existing sanitation districts provides
support for planning, installation, operation,
maintenance, inspection, enforcement, and financ-
ing of these programs. Traditional onsite manage-
ment entities (e.g., health departments) can partner
with sanitation or other special districts to build a
well-integrated program. For example, a health
department could retain its authority to approve
system designs and issue permits while the sanita-
tion district could assist with regional planning and
conduct inspection, maintenance, and remediation/
repair activities.
In some areas, special districts or public utilities
have been created to handle a full range of manage-
ment activities, from regional planning and system
permitting to inspection and enforcement. In 1971
the City of Georgetown, California, developed and
implemented a comprehensive, community-wide
onsite management program in the Lake Auburn
Trails subdivision (Shephard, 1996). The district
does not own the onsite systems in the subdivision
but is empowered by the state and county govern-
ments to set performance requirements, review and
approve system designs, issue permits, oversee
construction, access treatment system sites to
conduct monitoring, and provide routine mainte-
nance. The initial permit fees were approximately
$550. Annual fees in 1995 were approximately
$170 per dwelling and $80 for undeveloped lots
(Shephard, 1996).
Onsite management districts or public utilities,
whether wholly or partially responsible for system
oversight, can help ensure that treatment systems
are appropriate for the site and properly planned,
designed, installed, and maintained. Typical goals
for the management district or utility might include
• Providing appropriate wastewater collection/
treatment service for every residence or business
• Integrating wastewater management with land
use and development policies
• Managing the wastewater treatment program at
a reasonable and equitable cost to users
Management districts and public utilities generally
are authorized to generate funds from a variety of
sources for routine operation and maintenance,
inspections, upgrades, and monitoring and for
future development. Sources of funds can include
initial and renewable permit fees, monthly service
charges, property assessments, and special fees.
Onsite wastewater management districts that are
operated by or closely allied with drinking water
supply districts can coordinate collection of system
service charges with monthly drinking water bills
in a manner similar to that used by centralized
wastewater treatment plants. Although some home-
owners might initially resist fees and other charges
that are necessary to pay for wastewater manage-
ment services, outreach information on the effi-
ciencies, cost savings, and other benefits of coop-
erative management (e.g., financial support for
system repair, upgrade, or replacement and no-cost
pumping and maintenance) can help to build
support for comprehensive programs. Such support
is especially needed if a voter referendum is
required to create the management entity. When
creating a new district, public outreach and stake-
holder involvement should address the following
topics:
• Proposed boundaries of the management district
• Public health and natural resource protection
issues
• Problems encountered under the current man-
agement system
• Performance requirements for treatment systems
• Onsite technologies appropriate for specific site
conditions
• Operation and maintenance requirements for
specific system types
• Septage treatment and sewage treatment plant
capacity to accept septage
• Cost estimates for management program compo-
nents
• Program cost and centralized system manage-
ment cost comparisons
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Chapter 2: Management of Onsite Wastewater Treatment Systems
• Potential program partners and inventory of
available resources
• Proposed funding source(s)
• Compliance and enforcement strategies
• Legal, regulatory, administrative, and manage-
rial actions to create, develop, or establish the
management entity
Another type of special district is the public
authority. A public authority is a corporate body
chartered by the state legislature with powers to
own, finance, construct, and operate revenue-
producing public facilities. A public authority can
be used in a variety of ways to construct, finance,
and operate public facilities, including OWTSs.
It should be noted that some state codes restrict or
disallow a managed group of special districts from
managing onsite systems. In other cases, clear legal
authority for program staff to enter private prop-
erty to perform inspections and correct problems
has not been provided. These limitations can be
addressed through special legislation authorizing
the creation of entities with explicit onsite manage-
ment responsibilities. Laws and regulations can also
be changed to provide special districts the authority
to manage onsite systems and to conduct inspec-
tion, maintenance, and remediation activities.
2.3.4 Privately owned and operated
management entities
Private sector management entities are another
option for ensuring OWTS are properly managed.
These entities are often responsible for system
design, installation, operation, and maintenance. In
some cases, these private firms also serve as the
sole management entity; for example, a firm might
manage an onsite system program for a residential
subdivision as a part of a public-private partner-
ship. Several options exist for public/private
partnerships in the management of onsite systems.
OWTS management programs can contract with
private firms to perform clearly defined tasks for
which established protocols exist, such as site
evaluation, installation, monitoring/inspection, or
maintenance. An example of such an arrangement
would be to contract with a licensed/certified
provider, such as a trained septage pumper/hauler
who could be responsible for system inspection,
maintenance, and record keeping. Another example
would be the case where treatment systems in
residential subdivisions are serviced by a private
entity and operated under a contract with the
subdivision or neighborhood association.
Private for-profit corporations or utilities that
manage onsite systems are often regulated by the
state public utility commission to ensure continu-
Development company creates a service district in Colorado
The Crystal Lakes Development Company has been building a residential community 40 miles northwest of Fort
Collins, Colorado, since 1969. In 1972 the company sponsored the creation of the Crystal Lakes Water and
Sewer Association to provide drinking water and sewage treatment services. Membership in the association is
required of all lot owners, who must also obtain a permit for onsite systems from the Larimer County Health
Department. The association enforces county health covenants, aids property owners in the development of
onsite water and wastewater treatment systems, monitors surface and ground water, and has developed
guidelines for inspecting onsite water and wastewater systems. System inspections are conducted at the time
of property transfer.
The association conducts preliminary site evaluations for proposed onsite systems, including inspection of a
backhoe pit excavated by association staff with equipment owned by the association. The county health
department has also authorized the association to design proposed systems. The association currently
manages systems for more than 100 permanent dwellings and 600 seasonal residences. Management services
are provided for all onsite systems in the development, including 300 holding tanks, 7 community vault toilets,
recreational vehicle dump stations, and a cluster system that serves 25 homes on small lots and the
development's lodge, restaurant, and office buildings. The association is financed by annual property owner
dues of $90 to $180 and a $25 property transfer fee, which covers inspections.
Source: Mancl, 1999.
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Responsibilities of a Comprehensive Onsite Wastewater Management Program
Power to propose legislation and establish and enforce program rules and regulations
Land use planning involvement, review and approval of system designs, permit issuance
Construction and installation oversight
Routine inspection and maintenance of all systems
Management and regulation of septage handling and disposal
Local water quality monitoring
Administrative functions (e.g., bookkeeping, billing)
Grant writing, fund raising, staffing, outreach
Authority to set rates, collect fees, levy taxes, acquire debt, issue bonds, make purchases
Authority to obtain easements for access to property, enforce regulations, require repairs
Education, training, certification, and licensing programs for staff and contractors
Record keeping and database maintenance
Source: NSFC, 1996.
ous, acceptable service at reasonable rates. Service
agreements are usually required to ensure private
organizations will be financially secure, provide
adequate service, and be accountable to their
customers. These entities can play a key role in
relieving the administrative and financial burden on
local government by providing system management
services. It is likely that in the future private firms
will build, own, and operate treatment systems and
be subject only to responsible administrative
oversight of the management entity.
2.3.5 Regulatory authorities and
responsible management entities
Most regulatory authorities (e.g., public health
departments and water quality authorities) lack
adequate funding, staff, and technical expertise to
develop and implement comprehensive onsite
system management programs. Because of this lack
of resources and trained personnel, program
managers across the country are considering or
implementing alternative management structures
that delegate responsibility for specified manage-
ment program elements to other entities. Hoover
and Beardsley (2000) recommend that management
entities develop alliances with public and private
organizations to establish environmental quality
goals, evaluate treatment system performance
information, and promote activities that ensure
onsite system management programs meet perfor-
mance requirements.
English and Yeager (2001) have proposed the
formation of responsible management entities
(RMEs) to ensure the performance of onsite and
other decentralized (cluster) wastewater treatment
systems. RMEs are defined as legal entities that
have the technical, managerial, and financial
capacity to ensure viable, long-term, cost-effective
centralized management, operation, and mainte-
nance of all systems within the RME's jurisdiction.
Viability is defined as the capacity of the RME to
protect public health and the environment effi-
ciently and effectively through programs that focus
on system performance rather than adherence to
prescriptive guidelines (English and Yeager, 2001).
RMEs can operate as fully developed management
programs under existing oversight programs (e.g.,
health departments, sanitation districts) in states
with performance-based regulations, and they are
usually defined as comprehensive management
entities that have the managerial, technical, and
financial capacity to ensure that proposed treatment
system applications will indeed achieve clearly
defined performance requirements. System technol-
ogy performance information can be ranked along
a continuum that gives greater weight to confirma-
tory studies, peer-reviewed assessments, and third
party analysis of field applications. Under this
approach, unsupported performance assertions by
vendors and results from limited field studies
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receive less emphasis in management entity evalua-
tions of proposed treatment technologies (Hoover
and Beardsley, 2001).
Management responsibilities can be assigned to an
entity designated by the state or local government
to manage some or all of the various elements of
onsite wastewater programs. The assignment of
management responsibilities to a comprehensive
RME or to some less-comprehensive management
entity (ME) appears to be a practical solution to the
dilemma of obtaining adequate funding and
staffing to ensure that critical management activi-
ties occur. The use of an RME, however, makes
developing and implementing an onsite manage-
ment program more complex. Increased coordina-
tion and planning are necessary to establish an
effective management program. All of the manage-
ment program activities described below can be
performed by an RME; some may be executed by a
management entity with a smaller scope of capa-
bilities. In jurisdictions where management pro-
gram responsibilities are delegated to an RME, the
regulatory authority (RA; e.g., local health depart-
ment) must oversee the RME to ensure that the
program achieves the comprehensive public health
and environmental goals of the community. De-
pending on state and local codes, a formal agree-
ment or some other arrangement between the RME
and the RA might be required for RME execution
of some program elements, such as issuing permits.
The accompanying text insert, adapted from the
National Small Flows Clearinghouse (1996),
contains an example of activities that a comprehen-
sive RME typically must incorporate into its
management program. It should be noted that the
involvement of an ME to perform some manage-
ment program tasks or an RME to perform the full
range of management tasks should be tailored to
each local situation. Given the evolving nature of
onsite wastewater management programs, activities
in some cases might be performed by an RME,
such as an onsite system utility or private service
provider. In other cases, these responsibilities might
be divided among several state or local government
agencies, such as the local public health depart-
ment, the regional planning office, and the state
water quality agency. Changes in management
strategies (movement toward performance-based
approaches, institution of model management
structures) have resulted in the addition of other
responsibilities, which are discussed later in this
section.
When a less-comprehensive ME conducts a speci-
fied set of these activities, the RA usually retains
the responsibility for managing some or all of the
following activities:
• Defining management responsibilities for the
RA and the ME
• Overseeing the ME
• Issuing permits
• Inspecting onsite systems
• Responding to complaints
• Enforcement and compliance actions
• Monitoring receiving water quality (surface and
ground water)
• Regulation of septage handling and disposal
• Licensing and certification programs
• Keeping records and managing databases for
regulatory purposes
• Coordinating local and regional planning efforts
The RA, however, will often delegate to the ME
the responsibility for implementing some of the
activities listed above. The activities delegated to
the ME will be determined by the capacity of the
ME to manage specific activities, the specific
public health and environmental problems to be
addressed by the ME, and the RA's legal authority
to delegate some of those activities. For example, if
the ME is an entity empowered to own and operate
treatment systems in the service area, the ME
typically would be responsible for all aspects of
managing individual systems, including setting
fees, designing and installing systems, conducting
inspections, and monitoring those systems to ensure
that the RA's performance goals are met. Otis,
McCarthy, and Crosby (2001) have presented a
framework appropriate for performance manage-
ment that illustrates the concepts discussed above.
2.4 Management program
components
Developing and implementing an effective onsite
wastewater management program requires that a
systematic approach be used to determine necessary
program elements. Changes and additions to the
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Chapter 2: Management of Onsite Wastewater Treatment Systems
management program should be based on evalua-
tions of the program to determine whether the
program has adequate legal authorities, funding,
and management capacity to administer both
existing and new OWTSs and respond to changing
environmental and public health priorities and
advances in OWTS technologies.
The management program elements described in
the following sections are common to the most
comprehensive onsite management programs (e.g.,
RMEs). USEPA recognizes that states and local
governments are at different stages along the
continuum of developing and implementing
comprehensive management programs that address
their communities' fiscal, institutional, environ-
mental, and public health goals.
2.4.1 Authority for regulating and
managing onsite treatment
systems
Onsite wastewater program managers should
identify all legal responsibilities of the RA that
might affect the implementation of an effective
program. Legal responsibilities can be found in
state and local statutes, regulations, local codes,
land use laws, and planning requirements. Other
legal mechanisms such as subdivision covenants,
private contracts, and homeowner association rules
might also affect the administration of the pro-
gram. In many jurisdictions, legal authorities that
do not specifically refer to onsite programs and
authorities, such as public nuisance laws, state
water quality standards, and public health laws,
might be useful in implementing the program. A
typical example would be a situation where the
public health agency charged with protecting
human health and preventing public nuisances
interprets this mandate as sufficient authorization to
require replacement or retrofit of onsite system that
have surface seepage or discharges.
The extent and interpretation of authority assigned
to the RA will determine the scope of its duties, the
funding required for operation, and the personnel
necessary to perform its functions. In many juris-
dictions, the authority to perform some of these
activities might be distributed among multiple RAs.
Typical Authorities of a Regulatory Authority
Develop and implement policy and regulations
Provide management continuity
Enforce regulations and program requirements through fines or incentives
Conduct site and regional-scale evaluations
Require certification or licensing of service providers
Oversee system design review and approval
Issue installation and operating permits
Oversee system construction
Access property for inspection and monitoring
Inspect and monitor systems and the receiving environment
Finance the program through a dedicated funding source
Charge fees for management program services (e.g., permitting, inspections)
Provide financial or cost-share assistance
Issue and/or receive grants
Develop or disseminate educational materials
Provide training for service providers and staff
Conduct public education and involvement programs
Hire, train, and retain qualified employees
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Where this is the case, the organizations involved
should have the combined authority to perform all
necessary activities and should coordinate their
activities to avoid program gaps, redundancy, and
inefficiency. In some cases, the RA might delegate
some of these responsibilities to an ME. When a
comprehensive set of responsibilities are delegated
to an RME, the RA should retain oversight and
enforcement authority to ensure compliance with
legal, performance, and other requirements.
Each state or local government has unique organi-
zational approaches for managing onsite wastewater
systems based on needs, perceptions, and circum-
stances. It is vitally important that the authorizing
legislation, regulations, or codes allow the RAs and
MEs to develop an institutional structure capable of
fulfilling mandates through adoption of appropriate
technical and regulatory programs. A thorough
evaluation of authorized powers and capabilities at
various levels and scales is necessary to determine
the scope of program authority, the scale at which
RAs and MEs can operate, and the processes they
must follow to enact and implement the manage-
ment program. Involving stakeholders who repre-
sent public health entities, environmental groups,
economic development agencies, political entities,
and others in this process can ensure that the lines
and scope of authority for an onsite management
program are well understood and locally supported.
In some cases, new state policies or regulations
must be implemented to allow for recognition of
onsite MEs.
2.4.2 Onsite wastewater management
program goals
Developing and implementing an effective manage-
ment program requires first establishing program
goals. Program goals should be selected based on
public health, environmental, and institutional
factors and public concerns. Funding availability,
institutional capability, and the need to protect
consumers and their interests typically affect the
selection of program goals and objectives. One or
more entities responsible for public health and
environmental protection, such as public health and
water quality agencies, can determine the goals.
The development of short- and long-term compre-
hensive goals will most likely require coordination
among these entities. Community development and
planning agencies as well as residents should also
play a role in helping to determine appropriate
goals.
Traditionally, the main goals of most onsite
management programs have been to reduce risks to
public health (e.g., prevent direct public contact
with sewage and avoid pathogenic contamination of
ground water and surface waters); abate public
nuisances (e.g., odors from pit privies and cess-
pools); and provide cost-effective wastewater
treatment systems and management programs.
More recently, there has been an increased focus on
preventing OWTS-related surface and ground
water quality degradation and impacts on aquatic
habitat. Program goals have been expanded to
address nutrients, toxic substances, and a broader
set of public health issues regarding pathogens.
Onsite wastewater-related nutrient enrichment
leading to algae blooms and eutrophication or low
dissolved oxygen levels in surface waters is of
concern, especially in waters that lack adequate
assimilative capacity, such as lakes and coastal
embayments or estuaries. The discharge of toxic
substances into treatment systems and eventually
into ground water has also become a more promi-
nent concern, especially in situations where onsite/
decentralized treatment systems are used by com-
mercial or institutional entities like gasoline service
stations and nursing homes. The potential impacts
from pathogens discharged from OWTS on shell-
fisheries and contact recreation activities have also
moved some OWTS program managers to adopt
goals to protect these resources.
Historically, in many jurisdictions the public health
agency has had the primary role in setting program
goals. Without documented health problems
implicating onsite systems as the source of
problem(s), some public health agencies have had
little incentive to strengthen onsite management
programs beyond the goals of ensuring there was
no direct public contact with sewage or no obvious
drinking water-related impacts, such as bacterial or
chemical illnesses like methemoglobinemia ("blue
baby syndrome"). The availability of more ad-
vanced assessment and monitoring methodologies
and technologies and a better understanding of
surface water and ground water interactions,
however, has led to an increased focus on protect-
ing water quality and aquatic habitat. As a result, in
many states and localities, water quality agencies
have become more involved in setting onsite
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program goals and managing onsite wastewater
programs. Some water quality agencies (e.g.,
departments of natural resources), however, lack
direct authority or responsibility to regulate onsite
systems. This lack of authority points to the need
for increased coordination and mutual goal setting
among health agencies that have such authority.
Regardless of which agency has the legal authority
to manage onsite systems, there is the recognition
that both public health and water quality goals need
to be incorporated into the management program's
mission. Achievement of these goals requires a
comprehensive watershed-based approach to ensure
that all of the program's goals are met. Partnerships
with multiple agencies and other entities are often
required to integrate planning, public health
protection, and watershed protection in a meaning-
ful way. Because of the breadth of the issues
affecting onsite system management, many pro-
grams depend on cooperative relationships with
planning authorities, environmental protection and
public health agencies, universities, system manu-
facturers, and service providers to help determine
appropriate management goals and objectives.
2.4.3 Public health and resource
protection goals
OWTS programs should integrate the following
types of goals: public health protection, abatement
of nuisances, ground and surface water resource
protection, and aquatic ecosystem protection.
Setting appropriate program goals helps onsite
program managers determine desired performance
goals for treatment systems and influence siting,
design, and management criteria and requirements.
Examples of more detailed goals follow.
Public health protection goals:
• Reduce health risk due to sewage backup in
homes.
• Prevent ground water and well water contami-
nation due to pathogens, nitrates, and toxic
substances.
• Prevent surface water pollution due to patho-
gens, nutrients, and toxic substances.
• Protect shellfish habitat and harvest areas from
pathogenic contamination and excessive nutri-
ents
• Prevent sewage discharges to the ground surface
to avoid direct public contact.
• Minimize risk from reuse of inadequately
treated effluent for drinking water, irrigation, or
other uses.
• Minimize risk from inadequate management of
septic tank residuals.
• Minimize risk due to public access to system
components.
Public nuisance abatement goals:
• Eliminate odors caused by inadequate plumbing
and treatment processes.
• Eliminate odors or other nuisances related to
transportation, reuse, or disposal of OWTS
residuals (septage).
Environmental protection goals:
• Prevent and reduce adverse impacts on water
resources due to pollutants discharged to onsite
systems, e.g., toxic substances.
• Prevent and reduce nutrient overenrichment of
surface waters.
• Protect sensitive aquatic habitat and biota
2.4.4 Comprehensive planning
Comprehensive planning for onsite systems has
three important components: (1) establishing and
implementing the management entity, (2) establish-
ing internal planning processes for the management
entity, and (3) coordination and involvement in the
broader land-use planning process. Comprehensive
The Department of Environmental Resources and
Health Department in Maryland's Prince George's
County worked together to develop geographic
information system (CIS) tools to quantify and
mitigate nonpoint source nutrient loadings to the
lower Patuxent River, which empties into the
Chesapeake Bay. The agencies developed a
database of information on existing onsite systems,
including system age, type, and location, with
additional data layers for depth to ground water
and soils. The resulting CIS framework allows users
to quantify nitrogen loadings and visualize likely
impacts under a range of management scenarios.
Information from CIS outputs is provided to
decision makers for use in planning development
and devising county management strategies.
Source: County Environmental Quarterly, 1997.
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planning provides a mechanism to ensure that the
program has the necessary information to function
effectively.
It is necessary to ensure that onsite management
issues are integrated into decisions regarding future
growth and development. An effective onsite waste-
water management program should be represented
in the ongoing land use planning process to ensure
achievement of the goals of the program and to
assist planners in avoiding the shortcomings of past
planning efforts, which generally allowed the
limitations of conventional onsite technologies to
drive some land use planning decisions. Such
considerations are especially important in situations
where centralized wastewater treatment systems are
being considered as an alternative or adjunct to
onsite or cluster systems. Comprehensive planning
and land use zoning are typically interrelated and
integrated: the comprehensive planning process
results in the development of overarching policies
and guidance, and the land use zoning process
provides the detailed regulatory framework to
implement the comprehensive plan. Honachefsky
(2000) provides a good overview of comprehensive
planning processes from an ecological perspective.
In general, the comprehensive plan can be used to
set the broad environmental protection goals of the
community, and the zoning ordinance(s) can be
used to
• Specify performance requirements for indi-
vidual or clustered systems installed in
unsewered areas, preferably by watershed and/or
subwatershed.
• Limit or prevent development on sensitive
natural resource lands or in critical areas.
• Encourage development in urban growth areas
serviced by sewer systems, if adequate capacity
exists.
• Factor considerations such as system density,
hydraulic and pollutant loadings, proximity to
water bodies, soil and hydrogeological condi-
tions, and water quality/quantity into planning
and zoning decisions.
• Restore impaired resources.
Integrating comprehensive planning and zoning
programs with onsite wastewater program manage-
ment also can provide a stronger foundation for
determining and requiring the appropriate level of
treatment needed for both the individual site and
the surrounding watershed or subwatershed. The
integrated approach thus allows the program
manager to manage both existing and new onsite
systems from a cumulative loadings perspective or
performance-based approach that is oriented toward
the protection of identified resources. Local health
departments (regulatory authorities) charged with
administering programs based on prescriptive codes
typically have not had the flexibility or the re-
Comprehensive planning program elements
Define management program boundaries.
Select management entity(ies).
Establish human health and environmental protection goals.
Form a planning team composed of management staff and local stakeholders.
Identify internal and external planning resources and partners.
Collect information on regional soils, topography, rainfall, and water quality and quantity.
Identify sensitive ecological areas, recreational areas, and water supply protection areas.
Characterize and map past, current, and future development where OWTSs are necessary.
Coordinate with local sewage authorities to identify current and future service areas and determine treatment
plant capacity to accept septage.
Identify documented problem areas and areas likely to be at risk in the future.
Prioritize and target problem areas for action or future action.
Develop performance requirements and strategies to deal with existing and possible problems.
Implement strategy; monitor progress and modify strategy if necessary.
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sources to deviate from zoning designations and as
a result often have had to approve permits for
developments where onsite system-related impacts
were anticipated. Coordinating onsite wastewater
management with planning and zoning activities
can ensure that parcels designated for development
are permitted based on a specified level of onsite
system performance that considers site characteris-
tics and watershed-level pollutant loading analyses.
To streamline this analytical process, some manage-
ment programs designate overlay zones in which
specific technologies or management strategies are
required to protect sensitive environmental re-
sources. These overlay zones may be based on soil
type, topography, geology, hydrology, or other site
characteristics (figure 2-1). Within these overlay
zones, the RA may have the authority to specify
maximum system densities, system design require-
ments, performance requirements, and operation/
maintenance requirements. Although the use of
overlay zones may streamline administrative
efforts, establishing such programs involves the use
of assumptions and generalizations until a sufficient
number of site-specific evaluations are available to
ensure proper siting and system selection.
Internally, changes in program goals, demograph-
ics, and technological advances require information
and coordination to ensure that the short- and long-
term goals of the program can continue to be met.
Many variables affect the internal planning process,
including factors such as the locations and types of
treatment systems within the jurisdictional area, the
present or future organizational and institutional
structure of the management entity, and the funding
available for program development and implemen-
tation.
The box "Performance-based program elements"
(page 2-21) provides guidance for planning pro-
cesses undertaken by an onsite/decentralized
wastewater management entity. At a minimum, the
onsite management entity should identify and
delineate the planning region, develop program
goals, and coordinate with the relevant public
health, resource protection, economic development,
and land-use planning agencies.
Figure 2-2 shows a process that might be useful in
developing and implementing a performance-based
program whose objectives are to protect specific
resources or achieve stated public health objectives.
2.4.5 Performance requirements
Many state and local governments are currently
adopting or considering the use of performance
requirements to achieve their management goals.
The management entity can use performance
requirements to establish specific and measurable
standards for the performance of onsite systems
that are necessary to achieve the required level of
environmental or public health protection for an
identified management area and resource. All onsite
wastewater management programs are based to
varying degrees on this concept. Traditional
programs have elected to use prescriptive siting,
design, and setback requirements to dictate where
and when conventional septic tank/SWIS systems
are appropriate. The prescriptive standards were
based on the presumption that systems sited and
designed to these standards would protect public
health. In most cases, this assumption provided an
adequate level of protection, but the prescriptions
often were based on standards adopted by others
and not based on scientific evaluations of the site
conditions of the community using them. As a
result, many programs based on prescriptive
requirements do not adequately protect the
resource. (See chapter 5 for more detailed informa-
tion about performance-based approaches.) The
NOWRA Model Frameworkfor Unsewered Waste-
water Infrastructure, discussed in chapter 1, also
provides a model for the development of perfor-
mance-based programs (Walsh et al., 2001; see
http: //www. nowra. org).
Performance requirements provide the onsite
system regulatory agency with an objective basis to
oversee siting, system selection and design, installa-
tion, maintenance, and monitoring of OWTS in
order to protect an identified resource or achieve a
stated public health goal. In jurisdictions where
performance requirements are used, the regulatory
agency should not conduct site evaluations and
specify system designs because of potential conflict
of interest issues regarding enforcement and
compliance; that is, the agency would be evaluating
the performance of systems it designed and sited.
The role of the regulatory agency in such a situa-
tion should be to establish performance require-
ments and provide oversight of management,
operation, maintenance, and other activities con-
ducted by private contractors or other entities.
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Figure 2-2. Process for developing onsite wastewater management
Establish/revise management structure and program
Identify legal authority and responsibilities of regulatory authority,
management entity and other responsible entities
Provide for long-term funding of the management program
Develop public education, outreach, and involvement programs
Assess watershed (ground water and surface waters)
Determine water resources at risk
Assess potential for OWTS impacts
Establish performance requirements
Inventory onsite and centralized wastewater treatment systems
Identify existing and planned OWTS installations
Assess current and future loadings to ground/surface waters
Characterize potential to exceed water quality criteria
New onsite systems: initial considerations
Perform preliminary evaluation of available sites,
performance requirements
Analyze nearby systems, discharge options, reuse potential
Evaluate site (soils, hydrology, dimensions, geology, slopes)
Identify treatment options meeting performance requirements
New onsite systems: design procedures
Estimate wastewater flow and composition
Evaluate potential receiver sites
Delineate design boundaries
Establish/revise performance requirements
Determine design boundary loadings
Identify feasible treatment train alternatives
Evaluate alternative treatment trains
Develop conceptual design
Develop final design
Obtain final desiqn approval and construction permit
Inspection and monitoring
to meet performance
requirements
Assess and repair or replace failing onsite systems
Evaluate causes of failure (design, site conditions, maintenance)
Consider changes in plumbing fixtures, waste generation patterns
Evaluate cost-effectiveness of repair vs. replacement
Replacement follows sequence described for new systems
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Where appropriate, prescriptive guidelines for
siting, design, and operation that are accepted by
the management entity as meeting specific perfor-
mance requirements for routine system applications
can be appended to local codes or retained to avoid
cost escalation and loss of qualified service provid-
ers (Otis et al., 2001). Designating performance
requirements for areas of a management district
with similar environmental sensitivities and site
conditions can provide property owners with
valuable information on performance expectations
and their rationale (Otis et al., 2001). Performance
standards can be determined based on the need to
protect a site-specific resource, such as residential
drinking wells, or they can be based on larger-scale
analyses intended to manage cumulative OWTS
pollutant loadings (e.g., to protect a lake or
estuary from nutrient enrichment).
Implementation of performance-based programs
might result in increased management expenditures
due to the need for staff to conduct site or areawide
(e.g., watersheds, subwatersheds, or other geo-
graphic areas) evaluations, inspect, and monitor
system performance as necessary. Service provider
training, the evaluation and approval of new or
alternative system designs, public outreach efforts
to establish public support for this approach, and
new certification/licensing or permit programs will
also increase program costs. These increases can
usually be recovered through permit/license fees.
Also, system owners will be responsible for
operation and maintenance costs. The following
box contains a recommended list of elements for a
performance-based program.
2.4.6 Performance requirements and
the watershed approach
USEPA encourages the use of performance require-
ments on a watershed, subwatershed, or source
water protection zone basis. These are useful
natural units on which to develop and implement
performance-based management strategies. In
situations where jurisdictional boundaries cross
watershed, subwatershed, or source water recharge
boundaries, interagency coordination might be
needed. Setting performance requirements for
individual watersheds, subwatersheds, or source
water areas allows the program manager to deter-
mine and allocate cumulative hydraulic and pollut-
ant loads to ensure that the goals of the community
can be met. To do so, an analysis to determine
whether the cumulative pollutant or hydraulic
loadings can be assimilated by the receiving
environment without degrading the quality of the
resource or use is necessary. There is some uncer-
tainty in this process, and program managers
should factor in a margin of safety to account for
errors in load and treatment effectiveness estimates.
(Refer to chapter 3 for more information on
estimating treatment effectiveness.)
Onsite systems are typically only one of many
potential sources of pollutants that can negatively
affect ground or surface waters. In most cases other
Performance-based program elements
Obtain or define legal authority to enact management regulations.
Identify management area.
Identify program goals.
Identify specific resource areas that need an additional level of protection, e.g., drinking water
aquifers, areas with existing water quality problems, and areas likely to be at risk in the future.
Establish performance goals and performance requirements for the management area and specific
watersheds, subwatersheds, or source water protection areas.
Define performance boundaries and monitoring protocols.
Determine and set specific requirements for onsite systems based on protecting specific
management areas and achieving of a specified level of treatment (e.g., within a particular
subbasin, there will be no discharge that contains more than 1.0 mg/L of total phosphorus).
Develop or acquire information on alternative technologies, including effectiveness information and
operation and maintenance requirements (see chapter 4).
Develop a review process to evaluate system design and system components (see chapter 5).
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Establishing performance requirements at a watershed scale
Establishing performance requirements involves a sequential set of activities at both the landscape level and
the site level. The following steps describe the general process of establishing performance requirements for
onsite systems:
• Identify receiving waters (ground water, surface waters) for OWTS effluent.
• Define existing and planned uses for receiving waters (e.g., drinking water, recreation, habitat).
• Identify water quality standards associated with designated uses (check with state water agency).
• Determine types of OWTS-generated pollutants (e.g., nutrients, pathogens) that might affect use.
• Identify documented problem areas and areas likely to be at risk in the future.
• Determine whether OWTS pollutants pose risks to receiving waters.
• If there is a potential risk,
- Estimate existing and projected OWTS contributions to total pollutant loadings.
- Determine whether OWTS pollutant loadings will cause or contribute to violations of water quality or
drinking water standards.
- Establish maximum output level (mass or concentration in the receiving water body) for specified
OWTS effluent pollutants based on the cumulative load analysis of all sources of pollutant(s) of
concern.
- Define performance boundaries for measurement of OWTS effluent and pollutant concentrations to
achieve watershed- and site-level pollutant loading goals.
sources of OWTS-generated pollutants (primarily
nutrients and pathogens), such as agricultural
activities or wildlife, are also present in the water-
shed or subwatershed. To properly calculate the
cumulative acceptable OWTS-generated pollutant
loadings for a given watershed or subwatershed, all
other significant sources of the pollutants that
might be discharged by onsite systems should be
identified. This process requires coordination
between the onsite program manager and the
agencies responsible for assessing and monitoring
both surface waters and ground water. Once all
significant sources have been identified, the relative
contributions of the pollutants of concern from
these sources should be determined and pollutant
loading allocations made based on factors the
community selects. State water quality standards
and drinking source water protection requirements
are usually the basis for this process. Once loading
allocations have been made for all of the significant
contributing sources, including onsite systems, the
OWTS program manager needs to develop or
revise the onsite program to ensure that the overall
watershed-level goals of the program are met.
Cumulative loadings from onsite systems must be
within the parameters set under the loading alloca-
tions, and public health must be protected at the
site level; that is, the individual OWTS must meet
the performance requirements at the treatment
performance boundary or the point of compliance.
It should be noted that the performance-based
approach is a useful program tool both to prevent
degradation of a water resource and to restore a
degraded resource. Additional information on
antidegradation is available in USEPA's Water
Quality Standards Handbook. (See http://
www.epa.gov/waterscience/library/wqstandards/
handbook.pdf. For general information on the
USEPA Water Quality Standards Program, see
http://www.epa.gov/OST/standards/.) The Clean
Water Act Section 303(d) program (Total Maxi-
mum Daily Load [TMDL] program) has published
numerous documents and technical tools regarding
the development and implementation of pollutant
load allocations. This information can be found at
http://www.epa.gov/owow/tmdl/. (NOTE: The
identification of other pollutant sources and the
analyses of loadings and modeling related to
TMDL are beyond the scope of this document.)
The text above contains a list of steps that the OWTS
program manager should consider in developing
performance requirements at a watershed scale.
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The use of a watershed-based approach also affords
the water quality and onsite program managers
some flexibility in determining how to most cost-
effectively meet the goals of the community. Given
the presence of both onsite systems and other
sources of pollutants of concern, evaluations can be
made to determine the most cost-effective means of
achieving pollutant load reductions. For example,
farmer or homeowner nutrient management
education might result in significant loading
reductions of nitrogen that could offset the need to
require expensive, more technically advanced
onsite systems designed for nitrogen removal.
Watershed-level evaluations, especially in cases
where new and refined monitoring methods are
employed, might also negate the need for system
upgrade or replacement in some watersheds. For
example, new genetic tracing methods can provide
the water quality program manager with a reliable
tool to differentiate between human sources of
fecal coliform and animal contributions, both
domestic and wild (see chapter 3). The use of these
new methods can be expensive, but they might
provide onsite program managers with a means of
eliminating onsite systems as a significant contrib-
uting source of pathogens.
Onsite program managers have legitimate concerns
regarding the adoption of a performance-based
approach. The inherent difficulty of determining
cumulative loadings and their impacts on a watershed,
the technical difficulties of monitoring the impacts
of OWTS effluent, the evaluation of new technolo-
gies and the potential costs, staffing and expertise
needed to implement a performance-based program
can make this option more costly and difficult to
implement. (NOTE: In general, the RA should not
have the responsibility for monitoring systems
Performance requirements in Texas
In 1996 Texas eliminated percolation test requirements
for onsite systems and instituted new performance
requirements for alternative systems (e.g., drip
systems, intermittent sand filters, leaching chambers).
Site evaluations in Texas are now based on soil and site
analyses, and service providers must be certified.These
actions were taken after onsite system installations
nearly tripled between 1990 and 1997.
Source: Texas Natural Resource Conservation
Commission, 1997.
Arizona's performance-based technical standards
In 2001 Arizona adopted a rule containing technical standards for
onsite systems with design flows less than 24,000 gallons per day
(Arizona Administrative Code, Title 18, Chapters 5,9,11, and 14). Key
provisions of the rule include site investigation requirements,
identification of site limitations, design adjustments for better-than-
primary treatment to overcome site limitations, and design criteria and
nominal performance values for more than 20 treatment or effluent
dispersal technologies. Applications for proposed systems are required
to contain wastewater characterization information, technology
selections that address site limitations, soil treatment calculations, and
effluent dispersal area information. Technology-specific general ground
water discharge permits required under the new rule specify design
performance values for TSS, BOD, total coliforms, and TN. Products
with satisfactory third-party performance verification data might receive
additional credits for continuing performance improvement. The
Arizona rule contains important elements of performance-based and
hybrid approaches through adoption of performance values and
specific use criteria for certain systems.
Source: Swanson, 2001.
other than conducting random quality assurance
inspections. Likewise, the RA should not have the
primary responsibility of evaluating new or alterna-
tive technologies. Technologies should be evaluated
by an independent entity certified or licensed to
conduct such evaluations, such as an RME.)
Prescriptive regulatory codes that specify technolo-
gies for installation under a defined set of site
conditions have worked reasonably well in the past
in many localities. The use of this approach, in
which baseline design requirements and treatment
effectiveness are estimated based on the use of the
specified technology at similar sites, will continue
to be a key component of most management
programs because it is practical, efficient, and easy
to implement. Programs based purely on prescriptive
requirements, however, might not consistently
provide the level of treatment needed to protect
community water resources and public health.
Many programs using prescriptive requirements are
based on empirical relationships that do not neces-
sarily result in appropriate levels of treatment. Site-
specific factors can also result in inadequate
treatment of OWTS effluent where a prescriptive
approach is used. Political pressure to approve
specific types of systems for use on sites where
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Florida's performance-based permit program
Florida adopted provisions for permitting residential performance-based treatment systems in September 2000.
The permit regulations, which can be substituted for provisions governing the installation of onsite systems under
existing prescriptive requirements, apply to a variety of alternative and innovative methods, materials, processes,
and techniques fortreating onsite wastewaters statewide. Discharges underthe performance-based permit
program must meet treatment performance criteria for secondary, advanced secondary, and advanced wastewater
treatment, depending on system location and the proximity of protected water resources. Performance
requirements for each category of treatment are as follows:
Secondary treatment: annual arithmetic mean for BOD and TSS < 20 mg/L, annual arithmetic mean for fecal
coliform bacteria < 200 cfu/100 ml.
Advanced secondary treatment: annual arithmetic mean for BOD and TSS < 10 mg/L, annual arithmetic mean
for total nitrogen < 20 mg/L, annual arithmetic mean for total phosphorus < 10 mg/L, annual arithmetic mean for
fecal coliform bacteria < 200 cfu/100 mL.
Advanced wastewater treatment: annual arithmetic mean for BOD and TSS < 5 mg/L, annual arithmetic mean
for total nitrogen
< 3 mg/L, annual arithmetic mean for total phosphorus < 1 mg/L, fecal coliform bacteria count for any one
sample < 25 cfu/100 mL.
Operation and maintenance manuals, annual operating permits, signed maintenance contracts, and biannual
inspections are required forall performance-based systems installed underthe new regulation.The operating
permits allow for property entry, observation, inspection, and monitoring of treatment systems by state health
department personnel.
Source: Florida Administrative Code, 2000.
prescriptive criteria are not met is another factor
that leads to the installation of inadequate systems.
2.4.7 Implementing performance
requirements through a hybrid
management approach
RAs often adopt a "hybrid" approach that includes
both prescriptive and performance elements. To set
appropriate performance requirements, cumulative
load analyses should be conducted to determine the
assimilative capacity of the receiving environ-
ment^). This process can be costly, time-consum-
ing, and controversial when water resource charac-
terization data are incomplete, absent, or contested.
Because of these concerns, jurisdictions might elect
to use prescriptive standards in areas where it has
been determined that onsite systems are not a
significant contributing source of pollutants or in
areas where onsite systems are not likely to cause
water quality problems. Prescriptive designs might
also be appropriate and practical for sites where
previous experience with specified OWTS designs
has resulted in the demonstration of adequate
performance (Ayres Associates, 1993).
In those areas where problems due to pollutants
typically found in OWTS discharges have been
identified and in areas where there is a significant
threat of degradation due to OWTS discharges
(e.g., source water protection areas, recreational
swimming areas, and estuaries), performance
requirements might be appropriate. The use of a
performance-based approach allows jurisdictions to
prioritize their resources and efforts to target
collections of systems within an area or subwater-
shed or individual sites within a jurisdictional area.
2.4.8 Developing and implementing
performance requirements
OWTS performance requirements should be
developed using risk-based analyses on a watershed
or site level. They should be clear and quantifiable
to allow credible verification of system perfor-
mance through compliance monitoring. Perfor-
mance requirements should at a minimum include
stipulations that no plumbing backups or ground
surface seepage may occur and that a specified
level of ground/surface water quality must be
maintained at some performance boundary, such as
the terminus of the treatment train, ground water
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surface, property line, or point of use
(e.g., water supply well, recreational surface water,
aquatic habitat area; see chapter 5).
If prescriptive designs are allowed under a perfor-
mance-based program, these systems should be
proven capable of meeting the same performance
requirements as a system specifically designed for
that site. Under this approach, the management
entity should determine through experience (monitor-
ing and evaluation of the prescribed systems on
sites with similar site characteristics) that the
system will perform adequately to meet stated
performance requirements given sufficiently
frequent operating inspections and maintenance.
Performance monitoring might be difficult and
costly. Although plumbing backups and ground
surface seepage can be easily and inexpensively
observed through visual monitoring, monitoring
the receiving environment (surface receiving waters
and ground water) might be expensive and compli-
cated. Monitoring of ground water is confounded
by the difficulty of locating and sampling subsur-
face effluent plumes. Extended travel times,
geologic factors, the presence of other sources of
ground water recharge and pollutants, and the
dispersal of OWTS pollutants in the subsurface all
complicate ground water monitoring.
To avoid extensive sampling of ground water and
surface waters, especially where there are other
contributing sources of pollutants common to
OWTS discharges, performance requirements can
be set for the treated effluent at a designated
performance boundary before release into the
receiving environment (refer to chapters 3 and 5).
Adjustments for the additional treatment, disper-
sion, and dilution that will occur between the
performance boundary and the resource to be
protected should be factored into the performance
requirements. For example, pretreated wastewater
is typically discharged to unsaturated soil, through
which it percolates before it reaches ground water.
The performance requirement should take into
account the treatment due to physical (filtration),
biological, and chemical processes in the soil, as
well as the dispersion and dilution that will occur
in the unsaturated soil and ground water prior to
the point where the standard is applied.
As a practical matter, performance verification of
onsite systems can be relaxed for identified types of
systems that the RA knows will perform as antici-
pated. Service or maintenance contracts or other
legal mechanisms might be prerequisites to waiving
or reducing monitoring requirements or inspec-
tions. The frequency and type of monitoring will
depend on the management program, the technolo-
gies employed, and watershed- and site-specific
factors. Monitoring and evaluation might occur at
or near the site and include receiving environment
or water quality monitoring and monitoring to
ascertain hydraulic performance and influent flows.
In addition, the OWTS management program needs
to be evaluated to ascertain whether routine mainte-
nance is occurring and whether individual systems
and types of systems are operating properly.
Chapter 4 contains descriptions of most of the
onsite wastewater treatment processes currently in
use. OWTS program managers developing and
implementing performance-based programs will
often need to conduct their own site-specific
evaluations of these treatment options. The text box
that follows documents one approach used to
cooperatively evaluate innovative or alternative
wastewater treatment technologies. Many tribal,
state, and local programs lack the capability to
continually evaluate new and innovative technology
alternatives and thus depend on regional evalua-
tions and field performance monitoring to provide
a basis on which to develop their programs.
2.4.9 Public education, outreach, and
involvement
Public education and outreach are critical aspects of
an onsite management program to ensure public
support for program development, implementation,
and funding. In addition, a working understanding
of the importance of system operation and mainte-
nance is necessary to help ensure an effective
program. In general the public will want to know
the following:
• How much will it cost the community and the
individual?
• Will the changes mean more development in my
neighborhood? If so, how much?
• Will the changes prevent development?
• Will the changes protect our resources (drinking
waters, shellfisheries, beaches)?
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
A cooperative approach for approving innovative/alternative designs in New England
The New England Interstate Water Pollution Control Commission is a forum for consultation and cooperative action
among six New England state environmental agencies. NEIWPCC has adopted an interstate process for reviewing
proposed wastewater treatment technologies. A technical review committee composed of representatives from New
England state onsite wastewater programs and other experts evaluates innovative or alternative technologies or
system components that replace part of a conventional system, modify conventional operation or performance, or
provide a higher level of treatment than conventional onsite systems.
Three sets of evaluation criteria have been developed to assess proposed replacement, modification, or advanced
treatment units. Review teams from NEIWPCC assess the information provided and make determinations that are
referred to the full committee. The criteria are tailored for each category but in general include:
Treatment system or treatment unit size, function, and applicability or placement in the treatment train.
Structural integrity, composition, durability, strength, and corresponding independent test results.
Life expectancy and costs including comparisons with conventional systems/units.
Availability and cost of parts, service, and technical assistance.
Test data on prior installations or uses, test conditions, failure analysis, and tester identity.
Source: New England Interstate Water Pollution Control Commission, 2000.
• How do the proposed management alternatives
relate to the above questions?
A public outreach and education program should
focus on three components—program audience,
information about the program, and public out-
reach media. An effective public outreach program
makes information as accessible as possible to the
public by presenting the information in a nontech-
nical format. The public and other interested
parties should be identified, contacted, and con-
sulted early in the process of making major deci-
sions or proposing significant program changes.
Targeting the audience of the public outreach and
education program is important for both maximiz-
ing public participation and ensuring public
confidence in the management program. For onsite
wastewater system management programs, the
audiences of a public outreach and education
program can vary and might include:
• Homeowners
• Manufacturers
• Installers
• System operators and maintenance contractors
• Commercial or industrial property owner
• Public agency planners
• Inspectors
• Site evaluators
• Public
• Students
• Citizen groups and homeowner neighborhood
associations
• Civic groups such as the local Chamber of
Commerce
• Environmental groups
Onsite management entities should also promote
and support the formation of citizen advisory
groups composed of community members to build
or enhance public involvement in the management
program. These groups can play a crucial role in
representing community interests and promoting
support for the program.
Typical public outreach and education program
information includes:
• Promoting water conservation
• Preventing household and commercial/industrial
hazardous waste discharges
• Benefits of the onsite management program
Public outreach and education programs use a
variety of media options available for information
dissemination, including:
• Local newspapers
• Radio and TV
• Speeches and presentations
• Exhibits and demonstrations
• Conferences and workshops
• Public meetings
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Site evaluation program elements
Establish administrative processes for perm it/site
evaluation applications.
Establish processes and policies for evaluating site
conditions (e.g., soils, slopes, water resources).
Develop and implement criteria and protocols for
wastewater characterization.
Determine level of skill and training required for site
evaluators.
Establish licensing/certification programs for site
evaluators.
Offer training opportunities as necessary.
• School programs
• Local and community newsletters
• Reports
• Direct mailings, e.g., flyers with utility bills
2.4.10 Site evaluation
Evaluating a proposed site in terms of its environ-
mental conditions (climate, geology, slopes, soils/
landscape position, ground water and surface water
aspects), physical features (property lines, wells,
hydrologic boundaries structures), and wastewater
characteristics (anticipated flow, pollutant content,
waste strength) provides the information needed to
size, select, and site the appropriate wastewater
treatment system. In most cases (i.e., under current
state codes and lower-level management entity
structures) RAs issue permits—legal authorizations
to install and operate a particular system at a
specific site—based on the information collected
and analyses performed during the site evaluation.
(NOTE: Detailed wastewater characterization
procedures are discussed in chapter 3; site evalua-
tion processes are presented in section 5.5.)
2.4.11 System design criteria and
approval process
Performance requirements for onsite systems can
be grouped into two general categories—numeric
requirements and narrative criteria. Numeric
requirements set measurable concentration or mass
loading limits for specific pollutants (e.g., nitrogen
or pathogen concentrations). Narrative require-
ments describe acceptable qualitative aspects of the
wastewater (e.g., sewage surface pooling, odor). A
numerical performance requirement might be that
all septic systems in environmentally sensitive areas
must discharge no more than 5 pounds of nitrogen
per year, or that concentrations of nitrogen in the
effluent may be no greater than 10 mg/L. Some of
the parameters for which performance requirements
are commonly set for OWTSs include:
• Fecal coliform bacteria (an indicator of patho-
gens)
• Biochemical oxygen demand (BOD)
• Nitrogen (total of all forms, i.e., organic,
ammonia, nitrite, nitrate)
• Phosphorus (for surface waters)
• Nuisance parameters (e.g., odor, color)
Under a performance-based approach, performance
requirements, site conditions, and wastewater
characterization information drive the selection of
treatment technologies at each site. For known
technologies with extensive testing and field data,
the management agency might attempt to institute
performance requirements prescriptively by
designating system type, size, construction prac-
tices, materials to be used, acceptable site condi-
tions, and siting requirements. For example, the
Arizona Department of Environmental Quality has
adopted a rule that establishes definitions, permit
requirements, restrictions, and performance criteria
for a wide range of conventional and alternative
treatment systems. (Swanson, 2001). Alaska
requires a 2-foot-thick sand liner when the receiv-
ing soil percolates at a rate faster than 1 minute per
inch (Alaska Administrative Code, 1999). At a
minimum, prescriptive system design criteria
Performance requirements and system design in
Massachusetts
Massachusetts onsite regulations identify certain wellhead protection
areas, public water supply recharge zones, and coastal embayments
as nitrogen-sensitive areas and require OWTSs in those areas to meet
nitrogen loading limitations. For example, recirculating sand filters or
equivalent technologies must limit total nitrogen concentrations in
effluent to no more than 25 mg/L and remove at least 40 percent of
the influent nitrogen load. All systems in nitrogen-sensitive areas must
discharge no more than 440 gallons of design flow per acre per day
unless system effluent meets a nitrate standard of 10 mg/L or other
nitrogen removal technologies or attenuation strategies are used.
Source: Massachusetts Environmental Code, Title V.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
should consider the following. (See chapter 5 for
details.)
• Wastewater characterization and expected
effluent volumes.
• Site conditions (e.g., soils, geology, ground
water, surface waters, topography, structures,
property lines).
• System capacity, based on estimated peak and
average daily flows.
• Location of tanks and appurtenances.
• Tank dimensions and construction materials.
• Alternative tank effluent treatment units and
configuration.
• Required absorption field dimensions and
materials.
• Requirements for alternative soil absorption
field areas.
• Sizing and other acceptable features of system
piping.
• Separation distances from other site features.
• Operation and maintenance requirements (access
risers, safety considerations, inspection points).
• Accommodations required for monitoring.
2.4.12 Construction and installation
oversight authority
A comprehensive construction management pro-
gram will ensure that system design and specifica-
tions are followed during the construction process.
If a system is not constructed and installed prop-
erly, it is unlikely to function as intended. For
Simplified incorporation of system design requirements
into a regulatory program: the Idaho approach
Idaho bypasses cumbersome legislative processes when making
adjustments to its onsite system design guidelines by referencing a
technical manual in the regulation that is not part of the state
regulation. Under this approach, new research findings, new
technologies, or other information needed to improve system design
and performance can be incorporated into the technical guidance
without invoking the regulatory rulemaking process. The regulations
contain information on legal authority, responsibilities, permit
processes, septic tanks, and conventional systems. The reference
guidance manual outlines types of alternative systems that can be
installed, technical and design considerations, soil considerations, and
operation and maintenance requirements.
Source: Adapted from NSFC, 1995b.
Construction oversight program elements
Establish preconstruction review procedure for site
evaluation and system design.
Determine training and qualifications of system
designers and installers.
Establish designer and installer licensing and
certification programs.
Define and codify construction oversight
requirements.
Develop certification process for overseeing and
approving system installation.
Arrange training opportunities for service providers
as necessary
example, if the natural soil structure is not pre-
served during the installation process (if equipment
compacts infiltration field soils), the percolation
potential of the infiltration field can be signifi-
cantly reduced. Most early failures of conventional
onsite systems' soil absorption fields have been
attributed to hydraulic overloading (USEPA,
1980). Effective onsite system management
programs ensure proper system construction and
installation through construction permitting,
inspection, and certification programs.
Construction should conform to the approved plan
and use appropriate methods, materials, and
equipment. Mechanisms to verify compliance with
performance requirements should be established to
ensure that practices meet expectations. Typical
existing regulatory mechanisms that ensure proper
installation include reviews of site evaluation
procedures and findings and inspections of systems
during and after installation, i.e., before cover-up
and final grading. A more effective review and
inspection process should include
• Predesign meeting with designer, owner, and
contractor
• Preconstruction meeting with designer, owner,
and contractor
• Field verification and staking of each system
component
• Inspections during and after construction
• Issuance of a permit to operate system as
designed and built
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Construction oversight inspections should be con-
ducted at several stages during the system installa-
tion process to ensure compliance with regulatory
requirements. During the construction process,
inspections before and after backfilling should verify
compliance with approved construction documents
and procedures. An approved (i.e., licensed or
certified) construction oversight inspector, prefer-
ably the designer of the system, should oversee
installation and certify that it has been conducted
and recorded properly. The construction process for
soil-based systems must be flexible to accommo-
date weather events because construction during
wet weather can compact soils in the infiltration
field or otherwise alter soil structure.
2.4.13 Operation and maintenance
requirements
A recurring weakness of many existing OWTS
management programs has been the failure to
ensure proper operation and maintenance of
installed systems. Few existing oversight agencies
conduct inspections to verify basic system perfor-
mance, and many depend on uninformed, untrained
system owners to monitor tank residuals buildup,
schedule pumping, ensure that flow distribution is
occurring properly, check pumps and float
switches, inspect filtration media for clogging, and
perform other monitoring and maintenance tasks.
Complaints to the regulatory authority or severe
and obvious system failures often provide the only
formal notification of problems under present
codes. Inspection and other programs that monitor
system performance (e.g., Critical Point Monitor-
ing; see chapter 3) can help reduce the risk of
premature system failure, decrease long-term
investment costs, and lower the risk of ground
water or surface water contamination (Eliasson et
al., 2001; Washington Department of Health,
1994).
Various options are available to implement opera-
tion and maintenance oversight programs. These
range from purely voluntary (e.g., trained
homeowners responsible for their system operation
and maintenance activities) to more sophisticated
operating permit programs and ultimately to
programs administered by designated RMEs that
conduct all management/maintenance tasks. In
general, voluntary maintenance is possible only
where systems are nonmechanical and gravity-
based and located in areas with very low population
densities. The level of management should increase
if the system is more complex or the resource(s) to
be protected require a higher level of performance.
Alarms (onsite and remote) should be considered to
alert homeowners and service providers that system
malfunction might be occurring. In addition to
simple float alarms, several manufacturers have
developed custom-built control systems that can
program and schedule treatment process events,
remotely monitor system operation, and notify
technicians by pager or the Internet of possible
problems. New wireless and computer protocols,
cellular phones, and personal digital assistants are
being developed to allow system managers to
remotely monitor and assess operation of many
systems simultaneously (Nawathe, 2000), further
enhancing the centralized management of OWTSs
in outlying locations. Using such tools can save
considerable travel and inspection time and focus
Operation, maintenance, and residuals management program elements
Establish guidelines or permit program for operation and maintenance of systems.
Develop reporting system for operation and maintenance activities.
Circulate operation and maintenance information and reminders to system owners.
Develop operation and maintenance inspection and compliance verification program.
Establish licensing/certification programs for service providers.
Arrange for training opportunities as necessary.
Establish procedures for follow-up notices or action when appropriate.
Establish reporting and reminder system for monitoring system effluent.
Establish residuals (septage) management requirements, manifest system, and disposal/use
reporting.
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Onsite system disclosure requirements in Minnesota
Minnesota law requires that before signing an agreement to sell ortransfer real property, a seller must disclose to
a buyer in writing the status and location of all septic systems on the property, including existing or abandoned
systems. If there is no onsite treatment system on the property, the seller can satisfy the disclosure requirement
by making such a declaration at the time of property transfer. The disclosure must indicate whether the system is
in use and whether it is, to the seller's knowledge, in compliance with applicable laws and rules. A map indicating
the location of the system on the property must also be included. A seller who fails to disclose the existence or
known status of a septic system at the time of sale and who knew or had reason to know the existence or known
status of a system might be liable to the buyer for costs relating to bringing the system into compliance, as well
as reasonable attorney's fees incurred in collecting the costs from the seller. An action for collection of these
sums must be brought within 2 years of the closing date.
Source: Minnesota Statutes, 2000.
field personnel on systems that require attention or
regular maintenance. Telemetry panels at the
treatment site operating through existing or dedi-
cated phone lines can be programmed to log and
report information such as high/low water alarm
warnings, pump run and interval times, water level
readings in tanks/ponds, amperage drawn by system
pumps, and other conditions. Operators at a
centralized monitoring site can adjust pump run
cycles, pump operation times, alarm settings, and
high-level pump override cycles (Stephens, 2000).
Some management entities have instituted com-
prehensive programs that feature renewable/
revocable operating permits, mandatory inspec-
tions or disclosure (notification/inspection) upon
property transfer (e.g., Minnesota, Wisconsin,
Massachusetts), and/or periodic monitoring by
licensed inspectors. Renewable operating permits
might require system owners to have a contract with a
certified inspection/maintenance contractor or
otherwise demonstrate that periodic inspection and
maintenance procedures have been performed for
permit renewal (Wisconsin Department of Commerce,
2001). Minnesota, Wisconsin, Massachusetts, and
some counties (e.g., Cayuga and other counties in
New York, Washtenaw County in Michigan) require
that sellers of property disclose or verify system
performance (e.g., disclosure statement, inspection
by the local oversight entity or other approved
inspector) prior to property transfer. Financial
incentives usually aid compliance and can vary from
small fines for poor system maintenance to preventing
the sale of a house if the OWTS is not functioning
properly. Inspection fees might be one way to
cover or defray these program costs. Lending
institutions nationwide have influenced the adoption
of a more aggressive approach toward requiring
system inspections before home or property loans
are approved. In some areas, inspections at the time
of property transfer are common despite the
absence of regulatory requirements. This practice is
incorporated into the loan and asset protection
policies of local banks and lending firms.
RAs, however, should recognize that reliance on
lending institutions to ensure that proper inspec-
tions occur can result in gaps. Property transfers
without lending institution involvement might
occur without inspections. In addition, in cases
where inspections are conducted by private
individuals reporting to the lending agents, the
inspectors might not have the same degree of
accountability that would occur in jurisdictions that
have mandatory requirements for state or local
licensing or certification of inspectors. RAs should
require periodic inspections of systems based on
system design life, system complexity, and
changes in ownership.
Wisconsin's new Private Onsite Wastewater Treat-
ment System rule (see http://www.commerce.
state.wi.us/SB/SB-POWTSProgram.html)
requires management plans for all onsite treatment
systems. The plans must include information and
procedures for maintaining the systems in accor-
dance with the standards of the code as designed
and approved. Any new or existing system that is
not maintained in accordance with the approved
management plan is considered a human health
hazard and subject to enforcement actions. The
maintenance requirements are specified in the code.
All septic tanks are to be pumped when the com-
bined sludge and scum volume equals one-third of
the tank volume. Existing systems have the added
requirement of visual inspections every 3 years for
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Requiring pump-outs to ensure proper
maintenance
Periodic pumping of septic tanks is now required by law
in some jurisdictions and is becoming established
practice for many public and private management
entities. In 1991 Fairfax County, Virginia, amended its
onsite systems management code to require pumping
at least every 5 years. The action, which was based on
provisions of the Chesapeake Bay Preservation Act,
was accompanied by public outreach notices and news
articles. System owners must provide the county health
department with a written notification within 10 days of
pumpout. A receipt from the pumpout contractor, who
must be licensed to handle septic tank residuals, must
accompany the notification.
Source: Fairfax County Health Department, 1995.
wastewater ponding on the ground surface. Only
persons certified by the department may perform
the inspections or maintenance. Systems requiring
maintenance more than once annually require
signed maintenance contracts and a notice of
maintenance requirements on the property deed.
The system owner or designated agent of the owner
must report to the department each inspection or
maintenance action specified in the management
plan at its completion (Wisconsin Department of
Commerce, 2001).
2.4.14 Residuals management
requirements
The primary objective of residuals management is
to establish procedures and rules for handling and
disposing of accumulated wastewater treatment
system residuals to protect public health and the
environment. These residuals can include septage
removed from septic tanks and other by-products
of the treatment process (e.g., aerobic-unit-generated
sludge). When planning a program a thorough
knowledge of legal and regulatory requirements
regarding handling and disposal is important. In
general, state and local septage management
programs that incorporate land application or burial
of septage must comply with Title 40 of the U.S.
Code of Federal Regulations (CFR), Parts 503 and
257. Detailed guidance for identifying, selecting,
developing, and operating reuse or disposal sites
for septage can be found in the USEPA Process
Design Manual: Land Application of Sewage
Sludge and Domestic Septage (USEPA, 1995c),
which is posted on the Internet at http://
www.epa.gov/ORDAA/ebPubs/sludge.pdf. Addi-
tional information is provided in Domestic Septage
Regulatory Guidance (USEPA, 1993b), posted at
http://www.epa.gov/oia/tips/scws.htm. Another
document useful to practitioners and small commu-
nities is the Guide to Septage Treatment and
Disposal (USEPA, 1994).
States and municipalities typically establish other
public health and environmental protection regula-
tions for residuals handling, transport, treatment, and
reuse/disposal. In addition to regulations, practical
Installer and designer permitting in New Hampshire
Onsite system designers and installers in New Hampshire have been required to obtain state-issued permits since
1979. The New Hampshire's Department of Environmental Services Subsurface Systems Bureau issues the
permits, which must be renewed annually. Permits are issued after successful completion of written examinations.
The designer's test consists of three written sections and a field test for soil analysis and interpretation. The
installers must pass only one written examination.
The tests are broad and comprehensive, and they assess the candidate's knowledge of New Hampshire's codified
system design, regulatory setbacks, methods of construction, types of effluent disposal systems, and new
technology. Completing the three tests designers must take requires about 5 hours. The passing grade is
80 percent. The field test measures competency in soil science through an analysis of a backhoe pit,
determination of hydric soils, and recognition of other wetland conditions. The 2-hour written exam for installers
measures understanding of topography, regulatory setbacks, seasonal high watertable determination, and
acceptable methods of system construction.
Sources: Bass, 2000; New Hampshire Department of Environmental Services, 1991.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
RA/ME activities for training, certifying, and
licensing service providers
• Identify tasks that require in-house or contractor
certified/licensed professionals.
• Develop certification and/or licensing program based
on performance requirements.
• Establish process for certification/licensing
applications and renewals if necessary.
• Develop database of service providers, service
provider qualifications and contact information.
• Establish education, training, and experience
requirements for service providers.
• Develop or identify continuing training opportunities
for service providers.
• Circulate information on available training to service
providers.
• Update service provider database to reflect verified
training participation/performance.
limitations such as land availability, site conditions,
buffer zone requirements, hauling distances, fuel
costs, and labor costs play a major role in evaluating
septage reuse/disposal options. These options
generally fall into three basic categories—land
application, treatment at a wastewater treatment
plant, and treatment at a special septage treatment
plant (see chapter 4). The initial steps in the
residuals reuse/disposal decision-making process are
characterizing the quality of the septage and determining
potential adverse impacts associated with various reuse/
disposal scenarios, hi general, program officials strive to
minimize exposure of humans, animals, ground water,
and ecological resources to the potentially toxic or
hazardous chemicals and pathogenic organisms
found in septage. Other key areas of residuals
management programs include tracking or manifest
systems that identify septage sources, pumpers,
transport equipment, final destinations, and treat-
ment methods, as well as procedures for controlling
human exposure to residuals, including vector
control, wet weather runoff management, and
limits on access to disposal sites. (Refer to chap-
ter 4 for more details.)
2.4.15 Certification and licensing of
service providers and program
staff
Certification and licensing of service providers such
as septage haulers, designers, installers, and mainte-
nance personnel can help ensure management pro-
gram effectiveness and compliance and reduce the
administrative burden on the RA. Certification and
licensing of service providers is an effective means of
ensuring that a high degree of professionalism and
experience is necessary to perform specified activities.
Maine instituted a licensing program for site evalua-
tors in 1974 and saw system failure rates drop to
insignificant levels (Kreissl, 1982). The text box that
follows provides a list of activities that management
entities should consider in setting up certification and
licensing programs or requirements.
RAs should establish minimum criteria for licens-
ing/certification of all service providers to ensure
protection of health and water resources. Maine
requires that site evaluators be licensed (certified)
and that designers of systems treating more than
Statewide training institute for onsite professionals in North Carolina
North Carolina State University and other partners in the state developed the Subsurface Wastewater
System OperatorTraining School (see http://www.soil.ncsu.edu/swetc/subsurface/
subsurface.htm) in response to state rules requiring operators of some systems (e.g., large systems
and those using low-pressure pipe, drip irrigation, pressure-dosed sand filter, or peat biofilter
technologies) to be certified. The school includes classroom sessions on wastewater characteristics,
laws, regulations, permit requirements, and the theory and concepts underlying subsurface treatment
and dispersal systems. Training units also coverthe essential elements of operating small and large
mechanical systems, with field work in alternative system operation at NCSU's field laboratory.
Participants receive a training manual before they arrive for the 3-day training course. Certification of
those successfully completing the educational program is handled by the Water Pollution Control
System Operators Certification Commission, an independent entity that tests and certifies system
operators throughout North Carolina.
Source: NCSU, 2001
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Chapter 2: Management of Onsite Wastewater Treatment Systems
2,000 gallons per day or systems with unusual
wastewater characteristics be registered professional
engineers. Prerequisites for applying for a site
evaluator permit and taking the certification
examination are either a degree in engineering,
soils, geology, or a similar field plus 1 year of
experience or a high school diploma or equivalent
and 4 years of experience (Maine Department of
Human Services, 1996). State certification and
licensing programs are summarized in table 2-2.
Table 2-2. Survey of state certification and licensing programs
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Contractors
Y
Y
Y
N
N
N
NA
Y
Y
Y
N
N
Y
N
N
NA
Y
NA
N
N
Y
N
NA
NA
Y
N
N
NA
N
N
Y
N
N
Y
N
Y
Y
N
Y
Y
N
N
N
N
N
N
N
N
N
N
Installers
Y
Y
Y
Y
N
N
Y
Y
Y
Y
N
Y
Y
N
N
NA
Y
Y
Y
Y
Y
N
Y
Y
N
N
N
NA
Y
N
Y
N
N
Y
N
Y
Y
N
Y
Y
Y
Y
Y
N
N
N
N
Y
Y
N
Inspectors
Y
NA
NA
N
N
N
Y
N
Y
Y
N
Y
NA
N
N
NA
Y
NA
Y
Y
Y
N
Y
Y
N
N
N
NA
N
N
N
N
Y
Y
N
N
Y
Y
Y
NA
N
N
Y
N
N
N
Y
N
Y
N
Pumpers
Y
NA
Y
Y
N
N
Y
Y
Y
Y
N
Y
Y
N
Y
NA
Y
NA
N
N
Y
N
Y
Y
Y
N
N
NA
N
N
N
Y
Y
N
N
Y
Y
N
N
Y
N
Y
Y
N
N
N
N
Y
Y
N
Designers
N
NA
NA
Y
N
N
NA
Y
N
N
N
N
NA
N
N
NA
N
NA
Y
N
Y
N
Y
NA
N
N
N
NA
Y
N
N
N
N
N
N
Y
Y
N
Y
NA
N
N
N
N
Y
N
Y
N
Y
Y
Engineers
Y
Y
Y
N
N
Y
Y
Y
N
N
Y
N
NA
N
N
Y
N
NA
Y
N
Y
N
NA
NA
Y
N
N
NA
Y
N
N
N
N
N
N
N
Y
Y
Y
NA
N
Y
N
N
N
Y
N
N
Y
Y
Geologists
Y
NA
Y
N
N
N
NA
Y
N
N
N
N
NA
N
N
Y
N
NA
Y
N
N
N
NA
NA
N
N
N
NA
N
N
N
N
N
N
N
N
Y
Y
N
NA
N
Y
N
N
N
Y
N
N
Y
Y
Operators
Y
NA
NA
N
N
Y
NA
Y
N
N
Y
N
NA
N
N
Y
N
NA
N
N
Y
N
Y
NA
N
N
N
NA
Y
N
N
N
Y
N
N
Y
Y
N
Y
NA
N
Y
Y
N
Y
Y
N
N
N
N
Source: Noah, 2000.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
2.4.16 Education and training programs
for service providers and
program staff
Onsite system RAs, RMEs, and service provider
staff should have the requisite level of training and
experience to effectively assume necessary program
responsibilities and perform necessary activities.
Professional programs are typically the mechanism
for ensuring the qualifications of these personnel.
They usually include licensing or certification
elements, which are based on required coursework
or training; an assessment of knowledge, skills, and
professional judgment; past experience; and
demonstrated competency. Most licensing programs
require continuing education through recommended
or required workshops at specified intervals. For
example, the Minnesota program noted previously
requires 3 additional days of training every 3 years.
Certification programs for inspectors, installers,
and septage haulers provide assurance that systems
are installed and maintained properly. States are
beginning to require such certification for all
service providers to ensure that activities the
providers conduct comply with program require-
ments. Violation of program requirements or poor
performance can lead to revocation of certification
and prohibitions on installing or servicing onsite
systems. This approach, which links professional
performance with economic incentives, is highly
effective in maintaining compliance with onsite
program requirements. Programs that simply
register service providers or fail to take disciplinary
action against poor performers cannot provide the
same level of pressure to comply with professional
and technical codes of behavior.
Some certification and licensing programs for those
implementing regulations and performing site
evaluations require higher educational achievement.
For example, Kentucky requires a 4-year college
degree with 24 hours of science coursework,
completion of a week-long soils characterization
class, and another week of in-service training for
all permit writers and site evaluators (Kentucky
Revised Statutes, 2001). Regular training sessions
are also important in keeping site evaluators,
permit writers, designers, and other service person-
nel effective. For example, the Minnesota Coopera-
tive Extension Service administers 3-day work-
shops on basic and advanced inspection and mainte-
nance practices, which are now required for
certification in 35 counties and most cities in the
state (Shephard, 1996). Comprehensive training
programs have been developed in other states,
including West Virginia and Rhode Island.
Sixteen states have training centers. For more
information on training programs for onsite
wastewater professionals, including a calendar of
planned training events and links to training
providers nationwide, visit the web site of the
National Environmental Training Center for Small
Communities at West Virginia University at http://
www.estd.wvu.edu/netc/
NSF onsite wastewater inspector accreditation program
NSF International has developed an accreditation program designed to verify the proficiency of persons
performing inspections of existing OWTSs.The accreditation program includes written and field tests and provides
credit for continuing education activities. Inspectors who pass the tests and receive accreditation are listed on the
NSF International web site and in the NSF Listing Book, which is circulated among industry, government, and
other groups.
The accreditation process includes four components. A written examination, conducted at designated locations
around the country, covers a broad range of topics related to system inspections, including equipment, evaluation
procedures, troubleshooting, and the NSF International Certification Policies. The field examination includes an
evaluation of an existing OWTS. An ethics statement, required as part of the accreditation, includes a pledge by
the applicant to maintain a high level of honesty and integrity in the performance of evaluation activities. Finally,
the continuing education component requires requalification every 5 years through retesting or earning
requalification credits by means of training or other activities.
To pass the written examination, applicants must answer correctly at least 75 of the 100 multiple-choice questions
and score at least 70 percent on the field evaluation. A 30-day wait is required for retesting if the applicant fails
either the written or field examination.
Source: Noah, 2000.
2-34
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Inspection and monitoring program elements
Develop/maintain inventory of all systems in management area (e.g., location, age, owner, type, size).
Establish schedule, parameters, and procedures for system inspections.
Determine knowledge level required of inspectors and monitoring program staff.
Ensure training opportunities for all staff and service providers.
Establish licensing/certification program for inspectors.
Develop inspection program (e.g., owner inspection, staff inspection, contractor inspection).
Establish right-of-entry provisions to gain access for inspection or monitoring.
Circulate inspection program details and schedules to system owners.
Establish reporting system and database for inspection and monitoring program.
Identify existing ground water and surface water monitoring in area and determine supplemental monitoring
required.
Providing legal access for inspections in
Colorado
Colorado regulations state that "the health officer or his/
her designated agent is authorized to enter upon
private property at reasonable times and upon
reasonable notice... to conduct required tests, take
samples, monitor compliance, and make inspections."
Source: NSFC, 1995a.
NETCSC_curricula.html. For links to state onsite
regulatory agencies, codes, and other information,
visit http://www.estd.wvu.edu/nsfc/
NSFC_links.html.
2.4.17 Inspection and monitoring
programs to verify and assess
system performance
Routine inspections should be performed to ascer-
tain system effectiveness. The type and frequency
of inspections should be determined by the size of
the area, site conditions, resource sensitivity, the
complexity and number of systems, and the re-
sources of the RA or RME. The RA should ensure
that correct procedures are followed.
Scheduling inspections during seasonal rises in
ground water levels can allow monitoring of
performance during "worst case" conditions. A site
inspection program can be implemented as a system
owner training program, an owner/operator con-
tract program with certified operators, or a routine
program performed by an RME. A combination of
visual, physical, bacteriological, chemical, and
remote monitoring and modeling can be used to
assess system performance. Specific requirements
for reporting to the appropriate regulatory agency
should be clearly defined for the management
program. Components of an effective inspection,
monitoring, operation, and maintenance program
include
• Specified intervals for required inspections
(e.g., every 3 months, every 2 years, at time of
property transfer or change of use).
• Legal authority to access system components for
inspections, monitoring, and maintenance.
• Monitoring of overall operation and perfor-
mance, including remote sensing and failure
reporting for highly mechanical and complex
systems.
• Monitoring of receiving environments at
compliance boundaries to meet performance
requirements.
• Review of system use or flow records, (e.g.,
water meter readings).
• Required type and frequency of maintenance for
each technology.
• Identification, location, and analysis of system
failures.
• Correction schedules for failed systems through
retrofits or upgrades.
• Record keeping on systems inspected, results,
and recommendations.
Inspection programs are often incorporated into
comprehensive management programs as part of a
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
seamless approach that includes planning site
evaluation, design, installation, operation, mainte-
nance, and monitoring. For example, the Town of
Paradise, California, established an onsite wastewa-
ter management program in Butte County in 1992
after voters rejected a sewage plant proposal for a
commercial area (NSFC, 1996). The program
manages 16,000 systems through a system of
installation permits, inspections, and operating
permits with terms up to 7 years. Operating permit
fees are less than $15 per year and are included in
monthly water bills. Regular inspections, tank
pumping, and other maintenance activities are
conducted by trained, licensed service providers,
who report their activities to program administra-
tors. Paradise is one of the largest unsewered
incorporated towns in the nation.
Outreach programs to lending institutions on the
benefits of requiring system inspections at the time
of property transfer can be an effective approach
for identifying and correcting potential problems
and avoiding compliance and enforcement actions.
Many lending institutions across the nation require
system inspections as part of the disclosure require-
ments for approving home or property loans. For
example, Washington State has disclosure provi-
sions for realtors at the point of sale, and many
lending institutions have incorporated onsite system
performance disclosure statements into their loan
approval processes (Soltman, 2000)
Regulatory component
Description/function
Legal authority
Administration
Definitions
Location/separation
guidelines
Site evaluation
System selection and
design criteria
Construction and
permitting
Performance
requirements
Operation and
maintenance
Enforcement
Licensing and certification
Septage disposal
State and local laws, regulations, ordinances, and the like that assign authority to enact
specific onsite wastewater system management regulations and operate management
program.
Processes, procedures, and operational practices for system planning, design approval,
permitting, inspection, reporting, enforcement, and other functions. Includes licensing,
certification, or registration of service providers, training requirements, and so forth.
Definitions of the terms used in the regulations.
Guidelines for siting system components at specified minimum distances from wells,
residences, property lines, surface waters, and ground water (e.g., perched water tables,
seasonal high water table).
Analyses and evaluations of soil classification, depth, and structure. Assessment of
hydrogeology, slopes, vegetation, and other features for each site proposed for system
installation.
Criteria for proposed systems based on site conditions, wastewater characterization,
anticipated flow, public health and resource protection goals, and treatment technologies.
Mandatory approval processes for constructing a designated system at a particular site. Based
on site evaluation and system design and selection criteria (see above).
Numeric or narrative requirements for system effluent discharges. Based on health and
resource protection goals.
Requirements for proper operation (e.g., no solvent discharges to onsite system) and
maintenance (e.g., tank pumped every 3 years) of system components.
Incentives (e.g., operating permit renewed) and disincentives (e.g., fines, water service
suspended) to ensure compliance with onsite system regulations.
Training, licensing, and certification programs for system designers and service providers,
especially those operating and servicing alternative or mechanized systems
Requirements for licensing/registration of pumpers and haulers, storage and handling of
septage, disposal or reuse of septage.
SPYree:J\daDted from Ciotoli and WiswalL 1982: USEPA, 2000.
Tabfe 2-3. Components of an onsite system regufatory program
2-36
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Chapter 2: Management of Onsite Wastewater Treatment Systems
2.4.18 Compliance, enforcement, and
corrective action programs
Requiring corrective action when onsite systems
fail or proper system maintenance does not occur
helps to ensure that performance goals and require-
ments will be met. Compliance and enforcement
measures are more acceptable to system owners and
the public when the RA is clear and consistent
regarding its mission, regulatory requirements, and
how the mission relates to public health and water
resource protection. An onsite wastewater compli-
ance and enforcement program should be based on
reasonable and scientifically defensible regulations,
promote fairness, and provide a credible deterrent
to those who might be inclined to skirt its provi-
sions. Regulations should be developed with
community involvement and provided in summary
or detailed form to all stakeholders and the public
at large through education and outreach efforts.
Service provider training programs are most
effective if they are based on educating contractors
and staff on technical and ecological approaches for
complying with regulations and avoiding known
and predictable enforcement actions. Table 2-3
describes the components of a regulatory program
for onsite/decentralized systems.
Various types of legal instruments are available to
formulate or enact onsite system regulations.
Regulatory programs can be enacted as ordinances,
management constituency agreements, or local or
state codes, or simply as guidelines. Often, local
health boards or other units of government can
modify state code requirements to better address
local conditions. Local ordinances that promote
performance-based approaches can reference
Corrective action program elements
Establish process for reporting and responding to
problems (e.g., complaint reporting, inspections).
Define conditions that constitute a violation of
program requirements.
Establish inspection procedures for reported
problems and corrective action schedule.
Develop a clear system for issuing violation notices,
compliance schedules, contingencies, fines, or other
actions to address uncorrected violations.
technical design manuals for more detailed criteria
on system design and operation. Approaches for
enforcing requirements and regulations of a
management program can include
• Response to complaints
• Performance inspections
• Review of required documentation and reporting
• Issuance of violation notices
• Consent orders and court orders
• Formal and informal hearings
• Civil and criminal actions or injunctions
• Condemnation of systems and/or property
• Correcting system failures
• Restriction of real estate transactions (e.g.,
placement of liens)
• Issuance of fines and penalties
Some of these approaches can become expensive or
generate negative publicity and provide little in
terms of positive outcomes if public support is not
present. Involvement of stakeholders in the devel-
opment of the overall management program helps
ensure that enforcement provisions are appropriate
for the management area and effectively protect
human health and water resources. Stakeholder
involvement generally stresses restoration of
performance compliance rather than more formal
punitive approaches.
Information on regional onsite system perfor-
mance, environmental conditions, management
approaches by other agencies, and trends analyses
might be needed if regulatory controls are in-
creased. Most states establish regulatory programs
and leave enforcement of these codes up to the
local agencies. Table 2-4 contains examples of
enforcement options for onsite management
programs.
A regulatory program focused on achieving
performance requirements rather than complying
with prescriptive requirements places greater
responsibilities on the oversight/permitting agency,
service providers (site evaluator, designer, contrac-
tor, and operator), and system owners. The man-
agement entity should establish credible perfor-
mance standards and develop the competency to
review and approve proposed system designs that a
manufacturer or engineer claims will meet estab-
lished standards. Continuous surveillance of the
performance of newer systems should occur
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Collection
method
Description
Advantages
Disadvantages
Liens on property
Recording
violations on
property deed
Presale inspections
Termination of
public services
Fines
Local governing entity (with
taxing powers) might add the
costs of performing a service or
past unpaid bills as a tax on the
property.
Copies of violations can,
through administrative or
legislature requirement, be
attached to the property title
(via registrar of deed).
Inspections of onsite
wastewater systems are
conducted prior to transfer of
property or when property use
changes significantly
A customer's water, electric, or
gas service might be
terminated (as applicable).
Monetary penalties for each
day of violation, or as a
surcharge on unpaid bills.
Has serious enforcement
ramifications and is
enforceable.
Relatively simple procedure.
Effectively limits the transfer of
property ownership.
Notice of violation might be
given to potential buyer at the
time of system inspection;
seller might be liable for repairs
Effective procedure, especially
if management entity is
responsible for water supply.
Fines can be levied through
local judicial system as a result
of enforcement of violations.
Local government might be
reluctant to apply this approach
unless the amount owed is
substantial.
Can be applied to enforce
sanitary code violations; might
be ineffective in collecting
unpaid bills.
Can be difficult to implement
because of additional
resources needed. Inspection
fees can help cover costs.
Termination of public services
poses potential health risks.
Cannot terminate water service
if property owner has well.
Effectiveness will depend on
the authority vested in the
entity issuing the fine.
Source: Ciotoli and Wiswall, 1982.
Table 2-4. Conolp*iaii^ba£sufarteiedppt-6ac|tie6l ion and compliance
program. The service providers should be involved
in such programs to ensure that they develop the
knowledge and skills to successfully design, site,
build, and/or operate the treatment system within
established performance standards. Finally, the
management entity should develop a replicable
process to ensure that more new treatment tech-
nologies can be properly evaluated and appropri-
ately managed.
2.4.19 Data collection, record keeping,
and reporting
Onsite wastewater management entities require a
variety of data and other information to function
effectively. This information can be grouped in the
following categories:
Environmental assessment information', climate,
geology, topography, soils, slopes, ground water
and surface water characterization data (includ-
ing direction of flow), land use/land cover
information, physical infrastructure (roads,
water lines, sewer lines, commercial develop-
ment, etc.).
Planning information', existing and proposed
development, proposed water or sewer line
extensions, zoning classifications, population
trends data, economic information, information
regarding other agencies or entities involved in
onsite wastewater issues.
Existing systems information', record of site
evaluations conducted and inventory of all
existing onsite systems, cluster systems, package
plants, and wastewater treatment plants, includ-
ing location, number of homes/facilities served
and size (e.g., 50-seat restaurant, 3-bedroom
2-38
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Record keeping and reporting program
elements
Establish a database structure and reporting systems,
at a minimum, for
• Environmental assessments
• Planning and stakeholder involvement functions
• Existing systems
• Staff, service providers, financial, and other
administrative functions
• Inspection and monitoring program, including
corrective actions required
• Septage and residuals management, including
approved haulers, disposal sites, and manifest
system records
home), system owner and contact information,
location and system type, design and site
drawings (including locations of property lines,
wells, water resources), system components
(e.g., concrete or plastic tank, infiltration lines
or leaching chambers), design hydraulic capac-
ity, performance expectations or effluent
requirements (if any), installation date, mainte-
nance records (e.g., last pumpout, repair,
complaints, problems and actions taken, names
of all service providers), and septage disposal
records. Many states and localities lack accurate
system inventories. USEPA (2000) recommends
the establishment and continued maintenance of
accurate inventories of all OWTSs within a
management entity's jurisdiction as a basic
requirement of all management programs.
• Administrative information', personnel files
(name, education/training, work history, skills/
expertise, salary rate, job review summaries),
financial data (revenue, expenses, debts and debt
service, income sources, cost per unit of service
estimates), service provider/vendor data (name,
contact information, certifications, licenses, job
performance summaries, disciplinary actions,
work sites, cost record), management program
initiatives and participating entities, program
development plans and milestones, septage
management information, and available resources.
Data collection and management are essential to
program planning, development, and implementa-
tion. The components of a management informa-
tion system include database development, data
collection, data entry, data retrieval and integration,
data analysis, and reporting. A variety of software
is commercially available for managing system
inventory data and other information. Electronic
databases can increase the ease of collecting,
storing, retrieving, using, and integrating data after
the initial implementation and learning curve have
been overcome. For example, if system locations
Use of onsite system tracking software in the Buzzards Bay watershed
The Buzzards Bay Project is a planning and technical assistance initiative sponsored by the state
environmental agency's Coastal Zone Management Program. The Buzzards Bay Project was the first National
Estuary Program in the country to develop a watershed Comprehensive Conservation and Management Plan,
which the Governor and USEPA approved in 1991. The primary focus of the Buzzards Bay management plan is
to provide financial and technical assistance to Buzzards Bay municipalities to address nonpoint source
pollution and facilitate implementation of Buzzards Bay Management Plan recommendations. The Buzzards Bay
Project National Estuary Program provided computers and a software package to municipal boards of health in
the watershed to enable better tracking of septic system permits, inspection results, and maintenance
information. The software, along with the user's manual and other information, can be downloaded from the
Internet to provide easy access for jurisdictions interested in its application and use (see http://
www.buzzardsbay.org/septrfct.htm). This approach is designed to help towns and cities reduce the time they
spend filing, retrieving, and maintaining information through a system that can provide—at the click of a
mouse—relevant data on any lot in the municipality. The software program can also help towns respond to
information requests more effectively, process permit applications more quickly, and manage new inspection
and maintenance reporting requirements more efficiently.
Source: Buzzards Bay Project National Estuary Program, 1999.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
are described in terms of specific latitude and
longitude coordinates, a data layer for existing
onsite systems can be created and overlaid on
geographic information system (GIS) topographic
maps. Adding information on onsite wastewater
hydraulic output, estimated mass pollutant loads,
and transport times expected for specified
hydrogeomorphic conditions can help managers
understand how water resources become contami-
nated and help target remediation and prioritization
actions. Models can also be constructed to predict
impacts from proposed development and assist in
setting performance requirements for onsite
systems in development areas.
System inventories are essential elements for
management programs, and most jurisdictions
maintain databases of new systems through their
permitting programs. Older systems (those installed
before 1970), however, are often not included in
the system inventories. Some onsite management
programs or other entities conduct inventories of
older systems when such systems are included in a
special study area. For example, Cass County and
Crow Wing County in Minnesota have developed
projects to inventory and inspect systems at more
than 2,000 properties near lakes in the north-central
part of the state (Sumption, personal communica-
tion, 2000). The project inventoried systems that
were less than 5 years old but did not inspect them
unless complaint or other reports indicated possible
problems. Costs for inventorying and inspecting
234 systems in one lake watershed totaled $9,000, or
nearly $40 per site (Sumption, personal communica-
tion, 2000). Mancl and Patterson (2001) cite a cost
of $30 per site inspection at Lake Panorama, Iowa.
Some data necessary for onsite system management
might be held and administered by other agencies.
For example, environmental or planning agencies
often collect, store, and analyze land and water
resource characterization data. Developing data
sharing policies with other entities through coop-
erative agreements can help all organizations
involved with health and environmental issues
improve efficiency and overall program perfor-
mance. The management agency should ensure that
data on existing systems are available to health and
water resource authorities so their activities and
analyses reflect this important aspect of public
health and environmental protection.
2.4.20 Program evaluation criteria and
procedures
Evaluating the effectiveness of onsite management
program elements such as planning, funding,
enforcement, and service provider certification can
provide valuable information for improving
programs. A regular and structured evaluation of
any program can provide critical information for
program managers, the public, regulators, and
decision makers. Regular program evaluations
should be performed to analyze program methods
and procedures, identify problems, evaluate the
potential for improvement through new technolo-
gies or program enhancements, and ensure funding
is available to sustain programs and adjust program
goals. The program evaluation process should
include
• A tracking system for measuring success
and for evaluating and adapting program
components
• Processes for comparing program achievements
to goals and objectives
• Approaches for adapting goals and objectives if
internal or external conditions change
• Processes for initiating administrative or legal
actions to improve program functioning
• An annual report on the status, trends, and
achievements of the management program
• Venues for ongoing information exchange
among program stakeholders
A variety of techniques and processes can be used
to perform program evaluations to assess adminis-
trative and management elements. The method
chosen for each program depends on local circum-
stances, the type and number of stakeholders in-
volved, and the level of support generated by
management agencies to conduct a careful, unbiased,
detailed review of the program's success in protecting
health and water resources. Regardless of the
method selected, the program evaluation should be
performed at regular intervals by experienced staff,
and program stakeholders should be involved.
A number of state, local, and private organizations
have implemented performance-based management
programs for a wide range of activities, from state
budgeting processes to industrial production
operations. The purpose of these programs is
2-40
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Performance-based budgeting in Texas
Since 1993 state agencies in Texas have been required
to develop a long-term strategic plan that includes a
mission statement, goals for the agency, performance
measures, an identification of persons served by the
agency, an analysis of the resources needed for the
agency to meet its goals, and an analysis of expected
changes in services due to changes in the law. Agency
budget line items are tied to performance measures
and are available for review through the Internet.
Information on the budgeting process in Texas is
available from the Texas Legislative Budget Board at
http://www.lbb.state.tx.us.
Source: Texas Senate Research Center, 2000.
twofold: linking required resources with manage-
ment objectives and ensuring continuous improve-
ment. Onsite management programs could also ask
partnering entities to use their experience to help
develop and implement in-house evaluation processes.
2.5 Financial assistance for
management programs and
system installation
Most management programs do not construct or
own the systems they regulate. Homeowners or
other private individuals usually pay a permit fee to
the agency to cover site evaluation and permitting
costs and then finance the installation, operation,
maintenance, and repair of their systems them-
selves. During recent years, however, onsite
management officials and system owners have
become increasingly supportive of centralized operation,
maintenance, and repair services, hi addition, some
management programs are starting to provide
assistance for installation, repair, or replacement in the
form of cost-share funding, grants, and low-interest
loans. Some communities have elected to make a
transition from individual systems to a clustered
approach to capitalize on the financial and other
benefits associated with the joint use of lagoons,
drain fields, and other system components linked by
gravity, vacuum, or low-pressure piping. Developers of
cluster systems, which feature individual septic tanks
and collective post-tank treatment units, have been
particularly creative and aggressive in obtaining
financing for system installation.
Funding for site evaluation, permitting, and
enforcement programs is generally obtained from
permit fees, property assessments (e.g., health district
taxes), and allocations from state legislatures for
environmental health programs. However, many
jurisdictions have discovered that these funding
sources do not adequately support the full range of
planning, design review, construction oversight,
inspection and monitoring, and remediation functions
that constitute well-developed onsite management
programs. Urbanized areas have supplemented
funding for their management programs with fees
paid by developers, monthly wastewater treatment
service fees (sometimes based on metered water
use), property assessment increases, professional
licensing fees, fines and penalties, and local general
fund appropriations. This section includes an
overview of funding options for onsite system
management programs.
2.5.1 Financing options
Two types of funding are usually necessary for
installation and management of onsite wastewater
systems. First, initial funding is required to pay for
any planning and construction costs, which include
legal, administrative, land acquisition, and engi-
neering costs. Once the construction is complete,
additional funding is needed to finance the ongoing
operation and maintenance, as well as to pay for
the debt service incurred from borrowing the initial
funds. Table 2-6 lists potential funding sources and
the purposes for which the funds are typically used.
As indicated in the table, each funding source has
advantages and disadvantages. Decision makers
must choose the funding sources that best suit their
community.
Primary sources of funds include
• Savings (capital reserve)
• Grants (state, federal)
• Loans (state, federal, local)
• Bond issues (state, local)
• Property assessments
Publicly financed support for centralized wastewa-
ter treatment services has been available for
decades from federal, state, and local sources.
Since 1990 support for public funding of onsite
treatment systems has been growing. The following
section summarizes the most prominent sources of
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Form.
agenc
Define
compo
Table 2
Review
prog re
used, c
Identif
resour
propos
Comm
are co
Suggested approach for conducting a formal program evaluation
3 program evaluation team composed of management program staff, service providers, public health
/ representatives, environmental protection organizations, elected officials, and interested citizens.
the goals, objectives, and operational elements of the various onsite management program
nents.This can be done simply by using a checklist to identify which program components currently exist.
>-5 provides an excellent matrix for evaluating the management program.
N the program components checklist and feedback collected from staff and stakeholders to determine
ss toward goals and objectives, current status, trends, cost per unit of service, administrative processes
and cooperative arrangements with other entities.
y program components or elements in need of improvement, define actions or amount and type of
ces required to address deficient program areas, identify sources of support or assistance, discuss
ed program changes with the affected stakeholders, and implement recommended improvement actions.
unicate suggested improvements to program managers to ensure that the findings of the evaluation
isidered in program structure and function.
Fable 2-5. Example of Functional Responsibilities Matrix
Planning/Administration
Plan preparation
Plan review coordination
Research and development
Office and staff management
Site Evaluation
Guidelines and criteria
Evaluation certification
Site sustainability analysis
System Design
Standards and criteria
Designer certification
System design
* Design review
Permit Issuance
Installation
* Construction supervision
Installer certification
* Record-keeping
Permit issuance
Operation and Maintenance
* Procedures and regulations
Operator/inspector certification
* Routine inspections
* Emergency inspections
* System repair/replacement
* Repair supervision
Performance certification
System ownership
Residuals Disposal
Disposal regulations
* Hauler certification
Record-keeping
Equipment inspections
Facility inspections
Facility operations
Financing
* Secure funding
* Set changes
* Collect charges
Monitoring
* Reporting system
Sampling
Public Education
Develop methods
* Disseminate information
* Respond to complaints
State health
departments
X
X
X
X
X
X
X
X
X
County health
departments
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Towns
X
X
Homeowners
X
X
Private
firms
X
X
X
Comments
Not done
Not done
Not done
Not done
Not done
Not done
Not applicable
Not applicable
Not applicable
Not applicable
Management functions that require local agency input.
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Table 2-6. Funding options
Fund type
Initial funds
Management
program
funds
(continual)
Source of funds
Municipality receives
state grants, state
revolving funds, state
bonds
Municipality uses
savings (capital
reserve)
Municipality obtains
federal grants or
loans
Municipality obtains
loans from local bank
Cost sharing with
major users
Property
assessments (might
require property
owner to obtain low-
interest loans)
User fees (property
owner)
Taxes
(property owner)
Fees for specific
services, punitive fees
(property owner)
Capital reserve fund
Developer-paid fees
(connection fees,
impact fees)
How funds are used
Construction
and repair
X
X
X
X
X
X
X
X
Inspections
X
X
X
X
X
X
X
X
X
X
Permitting
X
X
X
X
X
X
X
X
X
X
Planning
X
X
X
X
X
X
X
X
Capital
reserve
X
X
X
Principal
and
interest
X
X
X
Operation
and
maintenance
X
X
X
X
a Principal and interest payment (debt service) on various loans used for initial financing.
Sources: Ciotoli and Wiswall, 1982, 1986; Shephard, 1996.
grant, loan, and loan guarantee funding and outline
other potential funding sources.
2.5.2 Primary funding sources
The following agencies and programs are among the
most dependable and popular sources of funds for
onsite system management and installation programs.
Clean Water State Revolving Fund
The Clean Water State Revolving Fund, or CWSRF
(see http://www.epa.gov/owm/finan.htm), is a
low- or no-interest loan program that has tradition-
ally financed centralized sewage treatment plants
across the nation. Program guidance issued in 1997
emphasized that the fund could be used as a source
of support for the installation, repair, or upgrading
of onsite systems in small towns, rural areas, and
suburban areas. The states and the territory of
Puerto Rico administer CWSRF programs, which
operate like banks. Federal and state contributions
are used to capitalize the fund programs, which
make low- or no-interest loans for water quality
projects. Funds are then repaid to the CWSRF over
terms as long as 20 years. Repaid funds are re-
cycled to fund other water quality projects. Projects
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Financial assistance program elements
Determine program components or system aspects
that require additional financial assistance.
Identify financial resources available for system
design, installation, operation, maintenance, and
repair.
Research funding options (e.g., permit or user fees,
property taxes, impact fees, fines, grants/loans).
Work with stakeholder group to execute or establish
selected funding option(s).
that might be eligible for CWSRF funding include
new system installations and replacement or
modification of existing systems. Costs associated
with establishing a management entity to oversee
onsite systems in a region, including capital outlays
(e.g., for trucks on storage buildings), may also be
eligible. Approved management entities include
city and county governments, special districts,
public or private utilities, and private for-profit or
nonprofit corporations.
U.S. Department of Agriculture Rural
Development programs
U.S. Department of Agriculture Rural Develop-
ment programs provide loans and grants to low and
moderate-income persons. State Rural Develop-
ment offices administer the programs; for state
office locations, see http://www.rurdev.usda.gov/
recd_map.html. A brief summary of USDA Rural
Development programs is provided below.
Rural Housing Service
The Rural Housing Service Single-Family Housing
Program (http://www.rurdev.usda.gov/rhs/Indi-
vidual/ind_splash.htm) provides homeownership
opportunities to low- and moderate-income rural
Americans through several loan, grant, and loan
guarantee programs. The program also makes
funding available to individuals to finance vital
improvements necessary to make their homes safe
and sanitary. The Direct Loan Program (section
502) provides individuals or families direct finan-
cial assistance in the form of a home loan at an
affordable interest rate. Most loans are to families
with incomes below 80 percent of the median
income level in the communities where they live.
Applicants might obtain 100 percent financing to
build, repair, renovate, or relocate a home, or to
purchase and prepare sites, including providing
water and sewage facilities. Families must be
without adequate housing but be able to afford the
mortgage payments, including taxes and insurance.
These payments are typically within 22 to 26
percent of an applicant's income. In addition,
applicants must be unable to obtain credit else-
where yet have reasonable credit histories. Elderly
and disabled persons applying for the program may
have incomes up to 80 percent of the area median
income.
Home Repair Loan and Grant Program
For very low-income families that own homes in
need of repair, the Home Repair Loan and Grant
Program offers loans and grants for renovation.
Money might be provided, for example, to repair a
leaking roof; to replace a wood stove with central
heating; or to replace a pump and an outhouse with
running water, a bathroom, and a waste disposal
system. Homeowners 62 years and older are
eligible for home improvement grants. Other low-
income families and individuals receive loans at a
1 percent interest rate directly from the Rural
Housing Service. Loans of up to $20,000 and
grants of up to $7,500 are available. Loans are for
up to 20 years at 1 percent interest.
Rural Utilities Service
The Rural Utilities Service (http://www.usda.gov/
rus/water/programs.htm) provides assistance for
public or not-for-profit utilities, including waste-
water management districts. Water and waste
disposal loans provide assistance to develop water
and waste disposal systems in rural areas and towns
with a population of 10,000 or less. The funds are
available to public entities such as municipalities,
counties, special-purpose districts, Indian tribes,
and corporations not operated for profit. The
program also guarantees water and waste disposal
loans made by banks and other eligible lenders.
Water and Waste Disposal Grants can be accessed to
reduce water and waste disposal costs to a reason-
able level for rural users. Grants might be made for
up to 75 percent of eligible project costs in some
cases.
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Chapter 2: Management of Onsite Wastewater Treatment Systems
Rural Business-Cooperative Service
The Rural Business-Cooperative Service (http://
www.rurdev.usda.gov/rbs/busp/b&i_gar.htm)
provides assistance for businesses that provide
services for system operation and management.
Business and Industry Guaranteed Loans can be
made to help create jobs and stimulate rural
economies by providing financial backing for rural
businesses. This program provides guarantees up to
90 percent of a loan made by a commercial lender.
Loan proceeds might be used for working capital,
machinery and equipment, buildings and real
estate, and certain types of debt refinancing.
Assistance under the Guaranteed Loan Program is
available to virtually any legally organized entity,
including a cooperative, corporation, partnership,
trust or other profit or nonprofit entity, Indian tribe
or federally recognized tribal group, municipality,
county, or other political subdivision of a state.
Community Development Block Grants
The U.S. Department of Housing and Urban
Development (HUD) operates the Community
Development Block Grant (CDBG) program, which
provides annual grants to 48 states and Puerto Rico.
The states and Puerto Rico use the funds to award
grants for community development to smaller cities
and counties. CDBG grants may be used for
numerous activities, including rehabilitating
residential and nonresidential structures, construct-
ing public facilities, and improving water and
sewer facilities, including onsite systems. USEPA
is working with HUD to improve access to CDBG
funds for treatment system owners by raising
program awareness, reducing paperwork burdens,
and increasing promotional activities in eligible
areas. More information is available at http://
www.hud.gov/cpd/cdbg.html.
Nonpoint Source Pollution Program
Clean Water Act section 319 (nonpoint source
pollution control) funds can support a wide range
of polluted runoff abatement, including onsite
wastewater projects. Authorized under section 319
of the federal Clean Water Act and financed by
federal, state, and local contributions, these projects
provide cost-share funding for individual and
community systems and support broader watershed
assessment, planning, and management activities.
Projects funded in the past have included direct
cost-share for onsite system repairs and upgrades,
assessment of watershed-scale onsite system
contributions to polluted runoff, regional
remediation strategy development, and a wide
range of other programs dealing with onsite
wastewater issues. For example, a project con-
ducted by the Gateway District Health Department
in east-central Kentucky enlisted environmental
science students from Morehead State University to
collect and analyze stream samples for fecal
coliform "hot spots." Information collected by the
students was used to target areas with failing
systems for cost-share assistance or other
remediation approaches (USEPA, 1997b). The
Rhode Island Department of Environmental
Management developed a user-friendly system
inspection handbook with section 319 funds to
improve system monitoring practices and then
developed cost-share and loan programs to help
system owners pay for needed repairs (USEPA,
1997). For more information, see http://
www.epa.gov/OWOW/NPS/.
2.5.3 Other funding sources
Other sources of funding include state finance
programs, capital reserve or savings funds, bonds,
PENNVEST: Financing onsite wastewater systems in the Keystone State
The Pennsylvania Infrastructure Investment Authority (PENNVEST) provides low-cost financing for systems on
individual lots or within entire communities. Teaming with the Pennsylvania Housing Finance Agency and the
state's Department of Environmental Protection, PENNVEST created a low-interest onsite system loan program
for low- to moderate-income (150 percent of the statewide median household income) homeowners. The $65
application fee is refundable if the project is approved. The program can save system owners $3,000 to $6,000
in interest payments on a 15-year loan of $10,000. As of 1999 PENNVEST had approved 230 loans totaling $3.5
million. Funds forthe program come from state revenue bonds, special statewide referenda, the state general
fund, and the State Revolving Fund.
Source: PADEP, 1998.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
certificates of participation, notes, and property
assessments. Nearly 20 states offer some form of
financial assistance for installation of OWTSs,
through direct grants, loans, or special project cost-
share funding. Capital reserve or savings funds are
often used to pay for expenses that might not be
eligible for grants or loans, such as excess capacity
for future growth. Capital reserve funds can also be
used to assist low- and moderate-income house-
holds with property assessment or connection fees.
Bonds usually finance long-term capital projects
such as the construction of OWTSs. States, munici-
palities, towns, townships, counties, and special
districts issue bonds. The two most common types
of bonds are general obligation bonds, which are
backed by the faith and credit of the issuing
government, and revenue bonds, which are sup-
ported by the revenues raised from the beneficiaries
of a service or facility. General obligation bonds
are rarely issued for wastewater treatment facilities
because communities are often limited in the
amount of debt they might incur. These bonds are
generally issued only for construction of schools,
libraries, municipal buildings, and police or fire
stations.
Revenue bonds are usually not subject to debt
limits and are secured by repayment through user
fees. Issuing revenue bonds for onsite projects
allows a community to preserve the general obliga-
tion borrowing capacity for projects that do not
generate significant revenues. A third and less
commonly used bond is the special assessment
bond, which is payable only from the collection of
special property assessments. Some states adminis-
ter state bond banks, which act as intermediaries
between municipalities and the national bond
market to help small towns that otherwise would
have to pay high interest rates to attract investors or
would be unable to issue bonds. State bond banks,
backed by the fiscal security of the state, can issue
one large, low-interest bond that funds projects in a
number of small communities
Communities issue Certificates of Participation
(COPs) to lenders to spread out costs and risks of
loans to specific projects. If authorized under state
law, COPs can be issued when bonds would exceed
debt limitations. Notes, which are written promises
to repay a debt at an established interest rate, are
similar to COPs and other loan programs. Notes are
used mostly as a short-term mechanism to finance
construction costs while grant or loan applications
are processed. Grant anticipation notes are secured
by a community's expectation that it will receive a
grant. Bond anticipation notes are secured by the
community's ability to sell bonds.
Finally, property assessments might be used to
recover capital costs for wastewater facilities that
benefit property owners within a defined area. For
example, property owners in a specific neighbor-
Funding systems and management in
Massachusetts
The Commonwealth of Massachusetts has developed
three programs that help finance onsite systems and
management programs. The loan program provides
loans at below-market rates. A tax credit program
provides a tax credit of up to $4,500 over 3 years to
defray the cost of system repairs for a primary
residence. Finally, the Comprehensive Community
Septic Management Program provides funding for long-
term community, regional, or watershed-based
solutions to system failures in sensitive environmental
areas. Low-interest management program loans of up
to $100,000 are available.
Source: Massachusetts DEP, 2000.
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USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 2: Management of Onsite Wastewater Treatment Systems
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2-47
-------
Chapter 2: Management of Onsite Wastewater Treatment Systems
hood could be assessed for the cost of installing
sewers or a cluster treatment system. Depending on
the amount of the assessment, property owners
might pay it all at once or pay in installments at a
set interest rate. Similar assessments are often
charged to developers of new residential or com-
mercial facilities if the developers are not required
to install wastewater treatment systems approved by
the local regulatory agency. Funding for ongoing
management of onsite systems in newly developed
areas should be considered when these assessments
are calculated.
Although funds from grants, special projects, and
other one-time sources can help initiate special
projects or develop new functions, support for
onsite management over the long term should come
from sources that can provide continuous funding
(table 2-7). Monthly service fees, property assess-
ments, regular general fund allocations, and permit/
licensing fees can be difficult to initiate but provide
the most assurance that management program
activities can be supported over the long term.
Securing public acceptance of these financing
mechanisms requires stakeholder involvement in
their development, outreach programs that provide
a clear picture of current problems and expected
benefits, and an appropriate matching of commu-
nity resources with management program need.
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of Wastewater Management, Washington, DC.
Federal Register, October 6, 2000.
Walsh, J., R.J. Otis, and T.L. Loudon. 2001.
NOWRA Model Framework for Unsewered
Wastewater Infrastructure. In Onsite
Wastewater Treatment: Proceedings of the
Ninth National Symposium on Individual and
Small Community Sewage Systems. American
Society of Agricultural Engineers, St. Joseph,
MI.
Washington Department of Health. 1994. On-site
sewage system regulations. Chapter 246-272,
Washington Administrative Code, adopted
March 9, 1994, effective January 1, 1995.
Washington Department of Health, Olympia,
WA. .
Wisconsin Department of Commerce. 2001. Private
Onsite Wastewater Treatment Systems Program.
WI DOC. POWTS Code, Comm 83, State
Plumbing Code. Wisconsin Department of
Commerce, Safety and Buildings Division,
Madison, WI.
.
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Chapter 3: Establishing Treatment System Performance Requirements
Chapter 3:
Establishing treatment system performance requirements
3.1 Introduction
3.2 Estimating wastewater characteristics
3.3 Estimating wastewater flow
3.4 Wastewater quality
3.5 Minimizing wastewater flows and pollutants
3.6 Integrating wastewater characterization and other design information
3.7 Transport and fate of wastewater pollutants in the receiving environment
3.8 Establishing performance requirements
3.1 Introduction
This chapter outlines essential steps for characteriz-
ing wastewater flow and composition and provides
a framework for establishing and measuring
performance requirements. Chapter 4 provides
information on conventional and alternative
systems, including technology types, pollutant
removal effectiveness, basic design parameters,
operation and maintenance, and estimated costs.
Chapter 5 describes treatment system design and
selection processes, failure analysis, and corrective
measures.
This chapter also describes methods for establishing
and ensuring compliance with wastewater treatment
performance requirements that protect human
health, surface waters, and ground water resources.
The chapter describes the characteristics of typical
domestic and commercial wastewaters and discusses
approaches for estimating wastewater quantity and
quality for residential dwellings and commercial
establishments. Pollutants of concern in wastewa-
ters are identified, and the fate and transport of
these pollutants in the receiving environment are
discussed. Technical approaches for establishing
performance requirements for onsite systems, based
on risk and environmental sensitivity assessments,
are then presented. Finally, the chapter discusses
performance monitoring to ensure sustained
protection of public health and water resources.
3.2 Estimating wastewater
characteristics
Accurate characterization of raw wastewater,
including daily volumes, rates of flow, and associated
pollutant load, is critical for effective treatment
system design. Determinating treatment system
performance requirements, selecting appropriate
treatment processes, designing the treatment
system, and operating the system depends on an
accurate assessment of the wastewater to be treated.
There are basically two types of onsite system
wastewaters—residential and nonresidential.
Single-family households, condominiums, apart-
ment houses, multifamily households, cottages, and
resort residences all fall under the category of
residential dwellings. Discharges from these
dwellings consist of a number of individual waste
streams generated by water-using activities from a
variety of plumbing fixtures and appliances.
Wastewater flow and quality are influenced by the
type of plumbing fixtures and appliances, their
extent and frequency of use, and other factors such
as the characteristics of the residing family, geo-
graphic location, and water supply (Anderson and
Siegrist, 1989; Crites and Tchobanoglous, 1998;
Siegrist, 1983).
A wide variety of institutional (e.g., schools),
commercial (e.g., restaurants), and industrial
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Chapter 3: Establishing Treatment System Performance Requirements
establishments and facilities fall into the
nonresidential wastewater category. Wastewater-
generating activities in some nonresidential estab-
lishments are similar to those of residential dwellings.
Often, however, the wastewater from nonresidential
establishments is quite different from that from of
residential dwellings and should be characterized
carefully before Onsite Wastewater Treatment
System (OWTS) design. The characteristics of
wastewater generated in some types of nonresidential
establishments might prohibit the use of conven-
tional systems without changing wastewater loadings
through advanced pretreatment or accommodating
elevated organic loads by increasing the size of the
subsurface wastewater infiltration system (SWIS).
Permitting agencies should note that some commer-
cial and large-capacity septic systems (systems
serving 20 or more people, systems serving com-
mercial facilities such as automotive repair shops)
might be regulated under USEPA's Class V Under-
ground Injection Control Program (see http://
www.epa.gov/safewater/uic/classv.html).
In addition, a large number of seemingly similar
nonresidential establishments are affected by subtle
and often intangible influences that can cause
significant variation in wastewater characteristics.
For example, popularity, price, cuisine, and
location can produce substantial variations in waste-
water flow and quality among different restaurants
(University of Wisconsin, 1978). Nonresidential
wastewater characterization criteria that are easily
applied and accurately predict flows and pollutant
loadings are available for only a few types of
establishments and are difficult to develop on a
national basis with any degree of confidence. There-
fore, for existing facilities the wastewater to be
treated should be characterized by metering and
sampling the current wastewater stream. For many
existing developments and for almost any new
development, however, characteristics of nonresi-
dential wastewaters should be estimated based on
available data. Characterization data from similar
facilities already in use can provide this information.
3.3 Estimating wastewater flow
The required hydraulic capacity for an OWTS is
determined initially from the estimated wastewater
flow. Reliable data on existing and projected flows
should be used if onsite systems are to be designed
properly and cost-effectively. In situations where
onsite wastewater flow data are limited or unavail-
able, estimates should be developed from water
consumption records or other information. When
using water meter readings or other water use
records, outdoor water use should be subtracted to
develop wastewater flow estimates. Estimates of
outdoor water use can be derived from discussions
with residents on car washing, irrigation, and other
outdoor uses during the metered period under
review, and studies conducted by local water
utilities, which will likely take into account climatic
and other factors that affect local outdoor use.
Accurate wastewater characterization data and
appropriate factors of safety to minimize the
possibility of system failure are required elements
of a successful design. System design varies
considerably and is based largely on the type of
establishment under consideration. For example,
daily flows and pollutant contributions are usually
expressed on a per person basis for residential
dwellings. Applying these data to characterize
residential wastewater therefore requires that a
second parameter, the number of persons living in
the residence, be considered. Residential occupancy
is typically 1.0 to 1.5 persons per bedroom; recent
census data indicate that the average household size
is 2.7 people (U.S. Census Bureau, 1998). Local
census data can be used to improve the accuracy of
design assumptions. The current onsite code
practice is to assume that maximum occupancy is
2 persons per bedroom, which provides an estimate
that might be too conservative if additional factors
of safety are incorporated into the design.
For nonresidential establishments, wastewater flows
are expressed in a variety of ways. Although per
person units may also be used for nonresidential
wastewaters, a unit that reflects a physical charac-
teristic of the establishment (e.g., per seat, per meat
served, per car stall, or per square foot) is often
used. The characteristic that best fits the wastewater
characterization data should be employed (Univer-
sity of Wisconsin, 1978).
When considering wastewater flow it is important
to address sources of water uncontaminated by
wastewater that could be introduced into the
treatment system. Uncontaminated water sources
(e.g., storm water from rain gutters, discharges
from basement sump pumps) should be identified
and eliminated from the OWTS. Leaking joints,
3-2
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Chapter 3: Establishing Treatment System Performance Requirements
cracked treatment tanks, and system damage caused
by tree roots also can be significant sources of clear
water that can adversely affect treatment perfor-
mance. These flows might cause periodic hydraulic
overloads to the system, reducing treatment effec-
tiveness and potentially causing hydraulic failure.
3.3.1 Residential wastewater flows
Average daily flow
The average daily wastewater flow from typical
residential dwellings can be estimated from indoor
water use in the home. Several studies have evalu-
ated residential indoor water use in detail (Ander-
son and Siegrist, 1989; Anderson et al., 1993;
Brown and Caldwell, 1984; Mayer et al., 1999). A
summary of recent studies is provided in table 3-1.
These studies were conducted primarily on homes
in suburban areas with public water supplies.
Previous studies of rural homes on private wells
generally indicated slightly lower indoor water use
values. However, over the past three decades there
has been a significant increase in the number of
suburban housing units with onsite systems, and it
has recently been estimated that the majority of
OWTSs in the United States are located in subur-
ban metropolitan areas (Knowles, 1999). Based on
the data in table 3-1, estimated average daily
wastewater flows of approximately 50 to 70 gallons
per person per day (189 to 265 liters per person per
day) would be typical for residential dwellings
built before 1994.
In 1994 the U.S. Energy Policy Act (EPACT)
standards went into effect to improve water use
efficiency nationwide. EPACT established national
flow rates for showerheads, faucets, urinals, and
water closets. In 2004 and again in 2007 energy use
standards for clothes washers will go into effect,
and they are expected to further reduce water use
by those appliances. Homes built after 1994 or
retrofitted with EPACT-efficient fixtures would
have typical average daily wastewater flows in the
40 to 60 gallons/person/day range. Energy- and
water-efficient clothes washers may reduce the per
capita flow rate by up to 5 gallons/person/day
(Mayer et al., 2000).
Of particular interest are the results of the Residen-
tial End Uses of Water Study (REUWS), which
was funded by the American Water Works Associa-
tion Research Foundation (AWWARF) and 12
water supply utilities (Mayer et al., 1999). This
study involved the largest number of residential
water users ever characterized and provided an
evaluation of annual water use at 1,188 homes in
12 metropolitan areas in North America. In addi-
tion, detailed indoor water use characteristics of
approximately 100 homes in each of the 12 study
areas were evaluated by continuous data loggers
and computer software that identified fixture-
specific end uses of water. Table 3-2 provides the
Table 3-1. Summary of average daily residential wastewater flows3
Study
Brown & Caldwell (1984)
Anderson & Siegrist (1989)
Anderson etal. (1993)
Mayer etal. (1999)
Weighted Average
Number of
residences
210
90
25
1188
153
Study duration
(months)
3
3
1°
Study average
(gal/pers/day)"
66.2(250.6)"
70.8 (268.0)
50.7(191.9)
69.3 (262.3)
68.6 (259.7)
Study range
(gal/pers/day)
57.3-73.0
(216.9-276.3)"
65.9-76.6
(249.4-289.9)
26.1-85.2
(98.9-322.5)
57.1-83.5
(216.1-316.1)
" Based on indoor water use monitoring and not wastewater flow monitoring.
b Liters/person/day in parentheses.
0 Based on 2 weeks of continuous flow monitoring in each of two seasons at each home.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-2. Comparison of daily per capita indoor water use for 12 study sites
Study Site
Seattle, WA
San Diego, CA
Boulder, CO
Lompoc, CA
Tampa, FL
Walnut Valley Water District, CA
Denver, CO
Las Virgenes Metropolitan Water
District, CA
Waterloo & Cambridge, ON
Phoenix, AZ
Tempe & Scottsdale, AZ
Eugene, OR
12 study sites
Sample size
(number of
houses)
99
100
100
100
99
99
99
100
95
100
99
98
1188
Mean daily per
capita indoor use
(gal/pers/day)1
57.1
58.3
64.7
65.8
65.8
67.8
69.3
69.6
70.6
77.6
81.4
83.5
69.3 (316.5)"
Median daily per
capita indoor use
(gal/pers/day)'
54.0
54.1
60.3
56.1
59.0
63.3
64.9
61.0
59.5
66.9
63.4
63.8
60.5 (289.0)b
Standard deviation of
per capita indoor use
(gal/pers/day)'
28.6
23.4
25.8
33.4
33.5
30.8
35.0
38.6
44.6
44.8
67.6
68.9
39.6(149.9)"
"Multiply gallons/person/day by 3.875 to obtain liters/person/day.
" Liters/person/day in parentheses.
Source: Mayer etal., 1999.
average daily per capita indoor water use by study
site for the 1,188 homes. The standard deviation
data provided in this table illustrate the significant
variation of average daily flow among residences. The
median daily per capita flow ranged from 54 to 67
gallons/person/day (204 to 253 liters/person/day) and
probably provides a better estimate of average daily
flow for most homes given the distribution of mean
per capita flows in figure 3-1 (Mayer et al., 2000).
This range might be reduced further in homes with
EPACT-efficient fixtures and appliances.
Individual activity flows
Average daily flow is the average total flow generated
on a daily basis from individual wastewater-
generating activities in a building. These activities
typically include toilet flushing, showering and
bathing, clothes washing and dishwashing, use of
faucets, and other miscellaneous uses. The average
flow characteristics of several major residential water-
using activities are presented in table 3-3. These data
were derived from some 1 million measured indoor
water use events in 1,188 homes in 12 suburban
areas as part of the REUWS (Mayer et al., 1999).
Figure 3-2 illustrates these same data graphically.
One of the more important wastewater-generating
flows identified in this study was water leakage
from plumbing fixtures. The average per capita
leakage measured in the REUWS was 9.5 gallons/
person/day (35.0 liters/person/day). However, this
value was the result of high leakage rates at a
relatively small percentage of homes. For example,
the average daily leakage per household was 21.9
gallons (82.9 liters) with a standard deviation of
54.1 gallons (204.8 liters), while the median
leakage rate was only 4.2 gallons/house/day (15.9
liters/house/day). Nearly 67 percent of the homes
in the study had average leakage rates of less than
10 gallons/day (37.8 liters/day), but 5.5 percent of
the study homes had leakage rates that averaged
more than 100 gallons (378.5 liters) per day. Faulty
toilet flapper valves and leaking faucets were the
primary sources of leaks in these high-leakage-rate
homes. Ten percent of the homes monitored
accounted for 58 percent of the leakage measured.
This result agrees with a previous end use study
where average leakage rates of 4 to 8 gallons/
person/day (15.1 to 30.3 liters/person/day) were
measured (Brown and Caldwell, 1984). These data
point out the importance of leak detection and
repair during maintenance or repair of onsite
3-4
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-3. Residential water use by fixture or appliance^"
Fixture/use
Toilet
Shower
Bath
Clothes washer
Dishwasher
Faucets
Leaks
Other Domestic
Total
Gal/use:
Average
range
3.5
2.9-3.9
17.2"
14.9-18.6
See shower
40.5
10.0
9.3-10.6
1.4"
NA
NA
NA
Uses/person/day:
Average
range
5.05
4.5-5.6
0.75"
0.6-0.9
See shower
0.37
0.30-0.42
0.10
0.06-0.13
8.1'
6.7-9.4
NA
NA
NA
Gal/person/day:
Average
range0
18.5
15.7-22.9
11.6
8.3-15.1
1.2
0.5-1.9
15.0
12.0-17.1
1.0
0.6-1.4
10.9
8.7-12.3
9.5
3.4-17.6
1.6
0.0-6.0
69.3
57.1-83.5
% Total:
Average
range
26.7
22.6-30.6
16.8
11.8-20.2
1.7
0.9-2.7
21.7
17.8-28.0
1.4
0.9-2.2
15.7
12.4-18.5
13.7
5.3-21.6
2.3
0.0-8.5
100
' Results from AWWARF REUWS at 1,188 homes in 12 metropolitan areas. Homes surveyed were serve by public water supplies, which operate at higher pressures
than private water sources. Leakage rates might be lower for homes on private water supplies.
" Results are averages over range. Range is the lowest to highest average for 12 metropolitan areas.
° Gal/person/day might not equal gal/use multiplied by uses/person/day because of differences in the number of data points used to calculate means.
' Includes shower and bath.
' Gallons per minute.
' Minutes of use per person per day.
Source: Mayer etal., 1999.
Figure 3-1. Distribution of mean household daily per capita indoor water use for 1,188 data-logged homes
18% •
14%-
g.12%.
10% •
I
fl II ^ n n , .
I
Source: Mayer etal., 1999.
Mean Indoor Gallons Per Capita Per Day
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Chapter 3: Establishing Treatment System Performance Requirements
Figure 3-2. Indoor water use percentage, including leakage, for 1,188 data logged homes3
Leaks
13.7%
9.5 gpcd
Other domestic
2.3%
1.6 gpcd
Toilet
26.7%
18.5 gpcd
Faucets
15.7%
10.9 gpcd
Dishwasher
1.4%
1.0 gpcd
Total gpcd = 69.3
Shower
16.8%
11.6 gpcd
Clothes washer
21.7%
15.0 gpcd
a gpcd = gallons per capita (person) per day
Source: Mayer etal. 1999.
systems. Leakage rates like those measured in the
REUWS could significantly increase the hydraulic
load to an onsite wastewater system and might
reduce performance.
Maximum daily and peak flows
Maximum and minimum flows and instantaneous
peak flow variations are necessary factors in
properly sizing and designing system components.
For example, most of the hydraulic load from a
home occurs over several relatively short periods of
time (Bennett and Lindstedt, 1975; Mayer et al..
1999; University of Wisconsin, 1978). The system
should be capable of accepting and treating normal
peak events without compromising performance.
For further discussion of flow variations, see
section 3.3.3.
3.3.2 Nonresidential wastewater flows
For nonresidential establishments typical daily
flows from a variety of commercial, institutional,
and recreational establishments are shown in tables
3-4 to 3-6 (Crites and Tchobanoglous, 1998;
Tchobanoglous and Burton, 1991). The typical
values presented are not necessarily an average of
the range of values but rather are weighted values
based on the type of establishment and expected
use. Actual monitoring of specific wastewater flow
and characteristics for nonresidential establishments
is strongly recommended. Alternatively, a similar
establishment located in the area might provide
good information. If this approach is not feasible,
state and local regulatory agencies should be
consulted for approved design flow guidelines for
nonresidential establishments. Most design flows
provided by regulatory agencies are very conserva-
tive estimates based on peak rather than average
daily flows. These agencies might accept only their
established flow values and therefore should be
contacted before design work begins.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-4.Typical wastewater flow rates from commercial sources
a,b
Facility
Airport
Apartment house
Automobile service station0
Bar
Boarding house
Department store
Hotel
Industrial building (sanitary waste only)
Laundry (self-service)
Office
Public lavatory
Restaurant (with toilet)
Conventional
Short order
Bar/cocktail lounge
Shopping center
Theater
Unit
Passenger
Person
Vehicle served
Employee
Customer
Employee
Person
Toilet room
Employee
Guest
Employee
Employee
Machine
Wash
Employee
User
Meal
Customer
Customer
Customer
Employee
Parking space
Seat
Flow, gallons/unit/day
Range Typical
2-4
40-80
8-15
9-15
1-5
10-16
25-60
400-600
8-15
40-60
8-13
7-16
450-650
45-55
7-16
3-6
2-4
8-10
3-8
2-4
7-13
1-3
2-4
3
50
12
13
3
13
40
500
10
50
10
13
550
50
13
5
3
g
6
3
10
2
3
Flow, liters/unil/day
Range Typical
8-15
150-300
30-57
34-57
4-19
38-61
95-230
1,500-2,300
30-57
150-230
30-49
26-61
1,700-2,500
170-210
26-61
11-23
8-15
30-38
11-30
8-15
26-49
4-11
8-15
11
190
45
49
11
49
150
1,900
38
190
38
49
2,100
190
49
19
11
34
23
11
38
8
11
"Some systems serving more than 20 people might be regulated under USEPA's Class V Underground Injection Control (UIC) Program. See
http://www.epa.gov/safewater/uic.html for more information.
" These data incorporate the effect of fixtures complying with the U.S. Energy Policy Act (EPACT) of 1994.
° Disposal of automotive wastes via subsurface wastewater infiltration systems is banned by Class V UIC regulations to protect ground water. See
http://www.epa.gov/safewater/uic.html for more information.
Source: Crites and Tchobanoglous, 1998.
3.3.3 Variability of wastewater flow
Variability of wastewater flow is usually character-
ized by daily and hourly minimum and maximum
flows and instantaneous peak flows that occur
during the day. The intermittent occurrence of
individual wastewater-generating activities can
create large variations in wastewater flows from
residential or nonresidential establishments. This
variability can affect gravity-fed onsite systems by
potentially causing hydraulic overloads of the
system during peak flow conditions. Figure 3-3
illustrates the routine fluctuations in wastewater
flows for a typical residential dwelling.
Wastewater flow can vary significantly from day to
day. Minimum hourly flows of zero are typical for
Figure 3-3. Daily indoor water use pattern for single-family residence
I5
10
Q.
O
^
-1
T-TOILET
L-LAUNDRY
B- BATH/SHOWER
D-DISH WASH
W-WATER SOFTENER
0-OTHER
9 N 3
TIME OF DAY
Source: University of Wisconsin, 1978.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-5.Typical wastewater flow rates from institutional sources3
Facility
Assembly hall
Hospital, medical
Hospital, mental
Prison
Rest home
School, day-only:
With cafeteria, gym, showers
With cafeteria only
Without cafeteria, gym, or showers
School, boarding
Unit
Seat
Bed
Employee
Bed
Employee
Inmate
Employee
Resident
Employee
Student
Student
Student
Student
Flow, gallons/unit/day
Range Typical
2-4
125-240
5-15
75-140
5-15
80-150
5-15
50-120
5-15
15-30
10-20
5-17
50-100
3
165
10
100
10
120
10
90
10
25
15
11
75
Flow, liters/unit/day
Range Typical
8-15
470-910
19-57
280-530
19-57
300-570
19-57
190-450
19-57
57-110
38-76
19-64
190-380
11
630
38
380
38
450
38
340
38
95
57
42
280
'Systems serving more than 20 people might be regulated under USEPA's Class V UIC Program. See http://www.epa.gov/safewater/uic.html for more information.
Source: Crites and Tchobanoglous, 1998.
residential dwellings. Maximum hourly flows as
high as 100 gallons (380 L/hr) (Jones, 1976;
Watson et al., 1967) are not unusual given the
variability of typical fixture and appliance usage
characteristics and residential water use demands.
Hourly flows exceeding this rate can occur in cases
of plumbing fixture failure and appliance misuse
(e.g., broken pipe or fixture, faucets left running).
Wastewater flows from nonresidential establish-
ments are also subject to wide fluctuations over
time and are dependent on the characteristics of
water-using fixtures and appliances and the busi-
Figure 3-4. Peak wastewater flows for single-family home
15
10
CL
<
O
T-TOILET
L- LAUNDRY
B-BATH/SHOWER
D -DISH WASH
W-WATER SOFTENER
0-OTHER
MN
9 N 3
TIME OF DAY
Source: University of Wisconsin, 1978.
ness characteristics of the establishment (e.g., hours
of operation, fluctuations in customer traffic).
The peak flow rate from a residential dwelling is
a function of the fixtures and appliances present
and their position in the plumbing system con-
figuration. The peak discharge rate from a given
fixture or appliance is typically around 5 gallons/
minute (19 liters/minute), with the exception of
the tank-type toilet and possibly hot tubs and
bathtubs. The use of several fixtures or appliances
simultaneously can increase the total flow rate
above the rate for isolated fixtures or appliances.
However, attenuation occurring in the residential
drainage system tends to decrease peak flow rates
observed in the sewer pipe leaving the residence.
Although field data are limited, peak discharge
rates from a single-family dwelling of 5 to 10
gallons/minute (19 to 38 liters/minute) can be
expected. Figure 3-4 illustrates the variability in
peak flow from a single home.
3.4 Wastewater quality
The qualitative characteristics of wastewaters
generated by residential dwellings and nonresiden-
tial establishments can be distinguished by their
physical, chemical, and biological composition.
Because individual water-using events occur
intermittently and contribute varying quantities of
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-6. Typical wastewater flow rates from recreational facilities3
Facility
Apartment, resort
Bowling alley
Cabin, resort
Cafeteria
Camps:
Pioneer type
Children's, with central toilet/bath
Day, with meals
Day, without meals
Luxury, private bath
Trailer camp
Campground-developed
Cocktail lounge
Coffee Shop
Country club
Dining hall
Dormitory/bunkhouse
Fairground
Hotel, resort
Picnic park, flush toilets
Store, resort
Swimming pool
Theater
Visitor center
Unit
Person
Alley
Person
Customer
Employee
Person
Person
Person
Person
Person
Trailer
Person
Seat
Customer
Employee
Guests onsite
Employee
Meal served
Person
Visitor
Person
Visitor
Customer
Employee
Customer
Employee
Seat
Visitor
Flow, gallons/unit/day
Range Typical
50-70
150-250
8-50
1-3
8-12
15-30
35-50
10-20
10-15
75-100
75-150
20-40
12-25
4-8
8-12
60-130
10-15
4-10
20-50
1-2
40-60
5-10
1-4
8-12
5-12
8-12
2-4
4-8
60
200
40
2
10
25
45
15
13
90
125
30
20
6
10
100
13
7
40
2
50
8
3
10
10
10
3
5
Flow, liters/unit/day
Range Typical
190-260
570-950
30-190
4-11
3(M5
57-110
130-190
38-76
38-57
280-380
280-570
76-150
45-95
15-30
30-45
230-490
38-57
15-38
76-190
4-8
150-230
19-38
4-15
3(M5
19-45
3(M5
8-15
15-30
230
760
150
8
38
95
170
57
49
340
470
110
76
23
38
380
49
26
150
8
190
30
11
38
38
38
11
19
"Some systems serving more than 20 people might be regulated under USEPA's Class V UIC Program.
Source: Crites and Tchobanoglous, 1998.
pollutants, the strength of residential wastewater
fluctuates throughout the day (University of
Wisconsin, 1978). For nonresidential establishments,
wastewater quality can vary significantly among
different types of establishments because of differ-
ences in waste-generating sources present, water
usage rates, and other factors. There is currently a
dearth of useful data on nonresidential wastewater
organic strength, which can create a large degree of
uncertainty in design if facility-specific data are not
available. Some older data (Goldstein and Moberg,
1973; Vogulis, 1978) and some new information
exists, but modern organic strengths need to be
verified before design given the importance of this
aspect of capacity determination.
Wastewater flow and the type of waste generated
affect wastewater quality. For typical residential
sources peak flows and peak pollutant loading rates
do not occur at the same time (Tchobanoglous and
Burton, 1991). Though the fluctuation in wastewa-
ter quality (see figure 3-5) is similar to the water
use patterns illustrated in figure 3-3, the fluctua-
tions in wastewater quality for an individual home
are likely to be considerably greater than the
multiple-home averages shown in figure 3-5.
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Chapter 3: Establishing Treatment System Performance Requirements
Figure 3-5. Average hourly distribution of total unfiltered BOD5
4000
3000
Q 2000
LU
cc
1000
T TOILET
L LAUNDRY
B BATH or SHOWER
KS KITCHEN SINK
DW DISHWASHER
MN
Source: University of Wisconsin, 1978.
OWTSs should be designed to accept and process
hydraulic flows from a residence (or establishment)
while providing the necessary pollutant removal
efficiency to achieve performance goals. The
concentrations of typical pollutants in raw residen-
tial wastewaters and average daily mass loadings
are summarized in table 3-7. Residential water-using
activities contribute varying amounts of pollutants to
the total wastewater flow. Table 3-8 contains a
summary of the average mass loading of several
key pollutants from the sources identified in table 3-7.
If the waste-generating sources present at a particu-
lar nonresidential establishment are similar to those
of a typical residential dwelling, an approximation
of the pollutant mass loadings and concentrations in
the wastewater can be derived using the residential
wastewater quality data for those categories pre-
sented in tables 3-7 and 3-8. However, the results
of previous studies have demonstrated that in many
cases nonresidential wastewater is considerably
different from residential wastewater. Restaurant
wastewater, for example, contains substantially
higher levels of organic matter, solids, and grease
compared to typical residential wastewater (Siegrist
et al., 1984; University of Wisconsin, 1978).
Restaurant wastewater BOD5 concentrations
reported in the literature range from values similar
to those for domestic waste to well over 1,000
milligrams/liter, or 3.5 to 6.5 times higher than
residential BODy Total suspended solids and grease
concentrations in restaurant wastewaters were
reported to be 2 to 5 times higher than the concen-
trations in domestic wastewaters (Kulesza, 1975;
NOON 3
TIME OF DAY
Shaw, 1970). For shopping centers, the average
characteristics determined by one study found
BOD5 average concentrations of 270 milligrams/
liter, with suspended solids concentrations of 337
milligrams/liter and grease concentrations of 67
milligrams/liter (Hayashida, 1975).
More recent characterizations of nonresidential
establishments have sampled septic tank effluent,
rather than the raw wastewater, to more accurately
identify and quantify the mass pollutant loads
delivered to the components of the final treatment
train (Ayres Associates, 1991; Siegrist et al., 1984).
Because of the variability of the data, for establish-
ments where the waste-generating sources are
significantly different from those in a residential
dwelling or where more refined characterization
data might be appropriate, a detailed review of the
pertinent literature, as well as wastewater sampling
at the particular establishment or a similar estab-
lishment, should be conducted.
3.5 Minimizing wastewater flows
and pollutants
Minimizing wastewater flows and pollutants
involves techniques and devices to (1) reduce water
use and resulting wastewater flows and (2) decrease
the quantity of pollutants discharged to the waste
stream. Minimizing wastewater volumes and
pollutant concentrations can improve the efficiency
of onsite treatment and lessen the risk of hydraulic
or treatment failure (USEPA, 1995). These meth-
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-7. Constituent mass loadings and concentrations in typical residential wastewater3
Constituent
Total solids (TS)
Volatile solids
Total suspended solids (TSS)
Volatile suspended solids
5-day biochemical oxygen demand (BOD5)
Chemical oxygen demand (COD)
Total nitrogen (TN)
Ammonia (NH4)
Nitrites and nitrates (N02-N; NCyN)
Total phosphorus (TP)C
Fats, oils, and grease
Volatile organic compounds (VOC)
Surfactants
Total coliforms (TC)d
Fecal coliforms (FC)d
Mass loading
(grams/person/day)
115-200
65-85
35-75
25-60
35-65
115-150
6-17
1-3
<1
1-2
12-18
0.02-0.07
2-4
-
-
Concentration"
(mg/L)
500-880
280-375
155-330
110-265
155-286
500-660
26-75
4-13
<1
6-12
70-105
0.1-0.3
9-18
108-1010
106-10"
" For typical residential dwellings equipped with standard water-using fixtures and appliances.
" Milligrams per liter; assumed water use of 60 gallons/person/day (227 liters/person/day).
° The detergent industry has lowered the TP concentrations since early literature studies; therefore, Sedlak (1991) was used for TP data.
" Concentrations presented in Most Probable Number of organisms per 100 milllllters.
Source: Adapted from Bauer et al., 1979; Bennett and Linstedt, 1975; Laak, 1975,1986; Sedlak, 1991; Tchobanoglous and Burton, 1991.
Table 3-8. Residential wastewater pollutant contributions by source
a,b
Parameter
BOD5
Total suspended
solids
Total nitrogen
Total phosphorus"
mean
range
% of total
mean
range
% of total
mean
range
% of total
mean
range
% of total
Garbage disposal
(gpcd)c
18.0
10.9-30.9
(28%)
26.5
15.8^3.6
(37%)
0.6
0.2-0.9
(5%)
0.1
—
(4%)
Toilet
(gpcd)c
16.7
6.9-23.6
(26%)
27.0
12.5^36.5
(38%)
8.7
4.1-16.8
(78%)
1.6
—
(59%)
Bathing, sinks,
appliances
(gpcd)c
28.5
24.5-38.8
(45%)
17.2
10.8-22.6
(24%)
1.9
1.1-2.0
(17%)
1.0
—
(37%)
Approximate total
(gpcd)c
63.2
(100%)
70.7
(100%)
11.2
(100%)
2.7
—
(100%)
" Adapted from USEPA, 1992.
1 Means and ranges for BOD, TSS, and TN are results reported in Bennett and Linstedt, 1975; Laak, 1975;Ligman et al
" Grams per capita (person) per day.
" The use of low-phosphate detergents In recent years has lowered the TP concentrations since early literature studies;
I., 1974; Olsson et al., 1968; and Siegrist et al., 1976.
therefore, Sedlak (1991) was used for TP data.
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Chapter 3: Establishing Treatment System Performance Requirements
ods have been developed around two main strate-
gies—wastewater flow reduction and pollutant
mass reduction. Although this section emphasizes
residential flows, many of the concepts are appli-
cable to nonresidential establishments. (For more
information on both residential and nonresidential
water use reduction, see http://www.epa.gov/OW/
you/intro.html.)
3.5.1 Minimizing residential wastewater
volumes
The most commonly reported failure of residential
OWTS infiltration systems is hydraulic overload-
ing. Hydraulic overloads can be caused by waste-
water flow or pollutant loads that exceed system
design capacity. When more water is processed than
an OWTS is designed to handle, detention time
within the treatment train is reduced, which can
decrease pollutant removal in the tank and overload
the infiltration field. Reducing water use in a
residence can decrease hydraulic loading to the
treatment system and generally improve system
performance. If failure is caused by elevated
pollutant loads, however, other options should be
considered (see chapter 5).
Indoor residential water use and resulting wastewa-
ter flows are attributed mainly to toilet flushing,
bathing, and clothes washing (figure 3-2). Toilet
use usually accounts for 25 to 30 percent of indoor
water use in residences; toilets, showers, and
faucets in combination can represent more than 70
percent of all indoor use. Residential wastewater
flow reduction can therefore be achieved most
dramatically by addressing these primary indoor
uses and by minimizing wastewater flows from
extraneous sources. Table 3-9 presents many of the
methods that have been applied to achieve waste-
water flow reduction.
Eliminating extraneous flows
Excessive water use can be reduced or eliminated
by several methods, including modifying water use
habits and maintaining the plumbing system
appropriately. Examples of methods to reduce
water use include
• Using toilets to dispose of sanitary waste only
(not kitty litter, diapers, ash tray contents, and
other materials.)
• Reducing time in the shower
• Turning off faucets while brushing teeth or
shaving
• Operating dishwashers only when they are full
• Adjusting water levels in clothes washers to
match loads; using machine only when full
• Making sure that all faucets are completely
turned off when not in use
• Maintaining plumbing system to eliminate leaks
These practices generally involve changes in water
use behavior and do not require modifying of
plumbing or fixtures. Homeowner education
programs can be an effective approach for modify-
ing water use behavior (USEPA, 1995). Waste-
water flow reduction resulting from eliminating
wasteful water use habits will vary greatly depend-
ing on past water use habits. In many residences,
significant water use results from leaking plumbing
fixtures. The easiest ways to reduce wastewater
flows from indoor water use are to properly
maintain plumbing fixtures and repair leaks when
they occur. Leaks that appear to be insignificant,
such as leaking toilets or dripping faucets, can
generate large volumes of wastewater. For
example, a 1/32-inch (0.8 millimeters) opening at
40 pounds per square inch (207 mm of mercury) of
pressure can waste from 3,000 to 6,000 gallons
(11, 550 to 22,700 liters) of water per month. Even
apparently very slow leaks, such as a slowly
dripping faucet, can generate 15 to 20 gallons
(57 to 76 liters) of wastewater per day.
Reducing wastewater flow
Installing indoor plumbing fixtures that reduce
water use and replacing existing plumbing fixtures
or appliances with units that use less water are
successful practices that reduce wastewater flows
(USEPA, 1995). Recent interest in water conserva-
tion has been driven in some areas by the absence
of adequate source water supplies and in other areas
by a desire to minimize the need for expensive
wastewater treatment. In 1992 Congress passed the
U.S. Energy Policy Act (EPACT) to establish
national standards governing the flow capacity of
showerheads, faucets, urinals, and water closets for
the purpose of national energy and water conserva-
tion (table 3-10). Several states have also imple-
mented specific water conservation practices
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-9. Wastewater flow reduction methods
Non-water-carriage toilets
- Biological (compost) toilets
- Incinerator toilets
Elimination of extraneous flows
• Improved water-use habits
• Improved plumbing and appliance maintenance and monitoring
• Elimination of excessive water supply pressure
Reduction of existing wastewater flows
• Toilets
Water-carriage toilets
- Toilet-tank inserts
-Ultra-low flush (ULF) toilets
(1.6 gal or 6 L per flush or less)
Wash-down flush
Pressurized tank
• Bathing devices, fixtures, and appliances
- Shower flow controls
- Reduced-flow showerheads
- On/off showerhead valves
- Mixing valves
- Air-assisted, low-flow shower system
• Clothes-washing devices, fixtures, and appliances
- High-efficiency washer
- Adjustable cycle settings
- Washwater recycling feature
• Miscellaneous
- Faucet inserts
- Faucet aerators
- Reduced-flow faucet fixtures
- Mixing valves
- Hot water pipe insulation
- Pressure-reducing valves
- Hot water recirculation
Wastewater recycle/reuse systems
• Sink/bath/laundry wastewater recycling for toilet flushing
• Recycling toilets
• Combined wastewater recycling for toilet flushing
• Combined wastewater recycling for outdoor irrigation
Sources: Adapted from USEPA, 1992,1995.
(USEPA, 1995; for case studies and other informa-
tion, see http://www.epa.gov/OW/you/intro.html.
Several toilet designs that use reduced volumes of
water for proper operation have been developed.
Conventional toilets manufactured before 1994
typically use 3.5 gallons (13.2 liters) of water per
flush. Reduced-flow toilets manufactured after
1994 use 1.6 gallons (6.1 liters) or less per flush.
Though studies have shown an increased number of
flushes with reduced-flow toilets, potential savings
of up to 10 gallons/person/day (37.8 liters/person/
day) can be achieved (Aher et al., 1991; Anderson
et al., 1993; Mayer et al., 1999, 2000). Table 3-11
contains information on water carriage toilets and
systems; table 3-12 contains information on non-
water-carriage toilets. The reader is cautioned that
not all fixtures perform well in every application
and that certain alternatives might not be acceptable
to the public.
The volume of water used for bathing varies
considerably based on individual habits. Averages
indicate that showering with common showerheads
using 3.0 to 5.0 gallons/minute (0.19 to 0.32 liters/
second) amounts to a water use of 10 to 12.5
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-10. Comparison of flow rates and flush volumes before and after U.S. Energy Policy Act
Fixture
Fixtures installed prior to 1994 in
gallons/minute (liters/second)
EPACT requirements
(effective January, 1994)
Potential reduction in
water used (%)
Kitchen faucet
Lavatory faucets
Showerheads
Toilet (tank type)
Toilet (valve type)
Urinal
3.0gpm(0.19L/s)
3.0gpm(0.19L/s)
3.5 gpm (0.22 Us)
3.5 gal (1 3.2 L)
3.5 gal (1 3.2 L)
3.0 gal (11. 4 L)
2.5 gpm (0.1 6 L/s)
2.5 gpm (0.1 6 L/s)
2.5 gpm (0.1 6 L/s)
1.6gal(6.1L)
1.6gala(6.1L)
1.0gal(3.8L)
16
16
28
54
54
50
Source: Konen, 1995.
Table 3-11. Wastewater flow reduction: water-carriage toilets and systems'•
Generic type
Toilets with tank
inserts
Description
Displacement devices placed into
storage tank of conventional toilet
to reduce volume but not height of
stored water.
Application considerations
Device must be compatible
with existing toilet and not
interfere with flush
mechanism
Operation &
maintenance
Frequent post-
installation inspections
to ensure proper
positioning
Water use
per event
gal(L)
3.3-3.8
(12.5-14.4)
Total flow
reduction in gpcd
(Lpcd);%ofuseb
1.8-3.5
(6.8-13.2)
4%-8%
Varieties: Plastic bottles, flexible
panels, drums, or plastic bags
Installation by owner
Reliability low; failure can
result in large flow increase
Water-saving toilets
Washdown flush
toilets
Pressurized-tank
toilets
Variation of conventional flush toilet
fixture; similar in appearance and
operation. Redesigned flushing rim
and priming jet to initiate siphon
flush in smaller trapway with less
water.
Flushing uses only water, but
substantially less due to washdown
flush
Varieties: Few
Note: Water usage may increase
due to multiple flushings
Specially designed toilet tank to
pressurize air contained in toilet
tank. Upon flushing, compressed air
propels water into bowl at increased
velocity
Varieties: Few
Interchangeable with
conventional fixture
Rough-in for unit may be
nonstandard
Drain-line slope and lateral-
run restrictions
Plumber installation
advisable
Compatible with most
conventional toilet units
Increased noise level
Water supply pressure of
35-120 psi (180-620 cm Hg)
required
Essentially the same
as for a conventional
unit
Similar to conventional
toilet
Cleaning possible
Periodic maintenance
of compressed air
source
1.0-1.6
(3.8-13.2)
0.8-1.6
(3.0-6.1)
(but more
frequent
flushings
possible)
2.0-2.5
(7.6-9.5)
5.3-13
(12.1-49.2)
6%-20%
9.4-12.2
(35.6-46.2)
21%-27%
6.3-8.0
(23.8-30.3)
14%-18%
* Adapted from USEPA, 1992. Compared to conventional toilet usage (4.3 gallons/flush [16.3 liters/flush], 3.5 uses per person per day,
and a total daily flow of 45 gallons/person/day [170 liters/person/day]).
" gpcd = gallons per capita (person) per day; Lpcd = liters per capita (person) per day.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-12.Wastewater flow reduction: non-water-carriage toilets:
Generic type Description
Application considerations
Operation and maintenance
Biological toilets
Large units with a separated
decomposition chamber. Accept
toilet wastes and other organic
matter, and over a long time
period partially stabilize excreta
through biological activity and
evaporation.
Installation requires 6- to 12-in (150-mm to 300-
mm)-diameter roof vent, space beneath floor for
decomposition chamber, ventilation system,
and heating
Handles toilet waste and some kitchen waste
Restricted usage capacity cannot be exceeded
Difficult to retrofit and expensive
Periodic addition of organic matter
Removal of product material at 6-
to 24-month intervals should be
performed by management
authority due to risk of exposure to
pathogens in wastes
Heat loss through vent
Incinerator toilets Small self-contained units that
volatilize the organic components
of human waste and evaporate
the liquids.
Installation requires 4-in-diameter roof vent
Handles only toilet waste
Power or fuel required
Increased noise level
Residuals disposal
Limited usage rate (frequency)
9 Adapted from USEPA, 1992. None of these devices uses any water; therefore, the amount of flow and pollutant reduction equal to those of conventional toilet use (see table 3-3).
Significant quantities of pollutants (including N, BOD5, SS, P, and pathogens) are therefore removed from the wastewater stream (table 3-8).
Weekly removal of ash
Semiannual cleaning and
adjustment of burning assembly or
heating elements
Fuel units could pose safety
concerns
Table 3-13. Wastewater flow reduction: showering devices and systems'•
Generic type
Description
Application considerations
Water use rate
Shower flow-control Reduce flow rate by reducing diameter of Compatible with most existing showerheads.
inserts and restrictors supply line ahead of showerhead User habits may negate potential savings by
extended shower duration
Reduced-flow
showerheads
On/off showerhead
valve
Mixing valves
Air-assisted, low-flow
shower system
Fixtures similar to conventional, except
restrict flow rate
Varieties: Many manufacturers, but units
similar
Small valve device placed in supply line
ahead of showerhead allows shower flow
to be turned on and off without
readjustment of volume or temperature
Specifically designed valves maintain
constant temperature of total flow. Faucets
may be operated (on and off) without
temperature adjustment
Specifically designed system uses
compressed air to atomize water flow and
provide shower sensation
Compatible with most conventional plumbing
Installed by user
Compatible with most conventional plumbing
and fixtures
Usually installed by plumber
Compatible with most conventional plumbing
and fixtures
Usually installed by plumber
May be difficult and expensive to retrofit
Requires shower location less than 50 ft (15.3
m) away from water heater
Requires compressed air and power source
Requires maintenance of air compressor
1.5-3.0 gal/min
(0.09-0.19 L/s)
1.5-2.5 gal/min
(0.09-0.19 L/s)
Unchanged, but
total duration and
use are reduced
Unchanged, but
daily duration and
use are reduced
0.5 gal/min
(0.3 L/s)
Note: gal/min = gallons per minute; L/s = liters per second.
'Adapted from USEPA, 1992.
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Chapter 3: Establishing Treatment System Performance Requirements
gallons/person/day (37.9 to 47.3 liters/person/day).
Table 3-13 provides an overview of showering
devices available to reduce wastewater flows
associated with shower use. A low-flow
showerhead can reduce water flow through the
shower by 2 or 3 gallons/minute (0.13 to 0.19
liters/second), but if the user stays in the shower
twice as long because the new showerhead does not
provide enough pressure or flow to satisfy shower-
ing preferences, projected savings can be negated.
Indoor water use can also be reduced by installing
flow reduction devices or faucet aerators at sinks
and basins. More efficient faucets can reduce water
use from 3 to 5 gallons/minute (0.19 to 0.32 liters/
second) to 2 gallons/minute (0.13 liters/second),
and aerators can reduce water use at faucets by as
much as 60 percent while still maintaining a strong
flow. Table 3-14 provides a summary of waste-
water flow reduction devices that can be applied to
water use at faucets.
Reducing water pressure
Reducing water pressure is another method for
reducing wastewater flows. The flow rate at faucets
and showers is directly related to the water pressure
in the water supply line. The maximum water flow
from a fixture operating on a fixed setting can be
reduced by reducing water pressure. For example, a
reduction in pressure from 80 pounds per square
inch (psi) (414 cm Hg) to 40 psi (207 cm Hg) can
reduce the flow rate through a fully opened faucet
by about 40 percent. Reduced pressure has little
effect on the volume of water used by fixtures that
operate on a fixed volume of water, such as toilets
and washing machines, but it can reduce waste-
water flows from sources controlled by the user
(e.g., faucets, showerheads).
3.5.2 Reducing mass pollutant loads in
wastewater
Pollutant mass loading modifications reduce the
amount of pollutants requiring removal or treat-
ment in the OWTS. Methods that may be applied
for reducing pollutant mass loads include modify-
ing product selection, improving user habits, and
eliminating or modifying certain fixtures. House-
hold products containing toxic compounds, com-
monly referred to as "household hazardous waste,"
should be disposed of properly to minimize threats
to human health and the environment. For more
information on disposal options and related issues,
visit the USEPA Office of Solid Waste's Household
Hazardous Waste web site at http://www.epa.gov/
epaoswer/non-hw/muncpl/hhw.htm.
Table 3-14. Wastewater flow reduction: miscellaneous devices and systems
Generic type
Description
Application considerations
Faucet insert
Faucet aerator
Reduced-flow faucet
Mixing valves
Hot-water system
insulation
Device that inserts into faucet valve or supply line and
restricts flow rate with a fixed or pressure-compensating
orifice
Devices attached to faucet outlet that entrain air into water
flow
Similar to conventional unit, but restricts flow rate with a fixed
or pressure-compensating orifice
Specifically designed valve units that allow flow and
temperature to be set with a single control
Hot-water heater and piping are wrapped with insulation to
reduce heat loss and water use (faucet delivers hot water
quicker)
Compatible with most plumbing
Installation simple
Compatible with most plumbing
Installation simple
Periodic cleaning of aerator screens
Compatible with most plumbing
Installation identical to conventional faucet
Compatible with most plumbing
Installation identical to conventional valve units
May be difficult to wrap entire hot-water piping
system after house is built.
"Adaoted from USEPA. 1992.
Source: Adapted from USEPA, 1992.
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Chapter 3: Establishing Treatment System Performance Requirements
Selecting cleaning agents and household
chemicals
Toilet flushing, bathing, laundering, washing
dishes, operating garbage disposals, and general
cleaning are all activities that can include the use of
chemicals that are present in products like disinfec-
tants and soaps. Some of these products contribute
significant quantities of pollutants to wastewater
flows. For example, bathing, clothes washing, and
dish washing contribute large amounts of sodium to
wastewater. Before manufacturers reformulated
detergents, these activities accounted for more than
70 percent of the phosphorus in residential flows.
Efforts to protect water quality in the Chesapeake
Bay, Great Lakes, and major rivers across the
nation led to the first statewide bans on phosphorus
in detergents in the 1970s, and other states issued
phosphorus bans throughout the 1980s. The new
low-phosphorus detergents have reduced phospho-
rus loadings to wastewater by 40 to 50 percent
since the 1970s.
The impacts associated with the daily use of
household products can be reduced by providing
public education regarding the environmental
impacts of common household products. Through
careful selection of cleaning agents and chemicals,
pollution impacts on public health and the environ-
ment associated with their use can be reduced.
Improving onsite system performance by
improving user habits
The University of Minnesota Extension Service's Septic
System Owner's Guide recommends the following
practices to improve onsite system performance:
• Do not use "every flush" toilet bowl cleaners.
• Reduce the use of drain cleaners by minimizing the
amount of hair, grease, and food particles that go
down the drain.
• Reduce the use of cleaners by doing more
scrubbing with less cleanser.
• Use the minimum amount of soap, detergent, and
bleach necessary to do the job.
• Use minimal amounts of mild cleaners and only as
needed.
• Do not drain chlorine-treated water from swimming
pools and hot tubs into septic systems.
• Dispose of all solvents, paints, antifreeze, and
chemicals through local recycling and hazardous
waste collection programs.
• Do not flush unwanted prescription or over-the-
counter medications down the toilet.
Adapted from University of Minnesota, 1998.
Improving user habits
Everyday household activities generate numerous
pollutants. Almost every commonly used domestic
product—cleaners, cosmetics, deodorizers, disin-
fectants, pesticides, laundry products, photographic
products, paints, preservatives, soaps, and medi-
cines—contains pollutants that can contaminate
ground water and surface waters and upset biologi-
cal treatment processes in OWTSs (Terrene Insti-
tute, 1995). Some household hazardous waste
(HHW) can be eliminated from the wastewater
stream by taking hazardous products to HHW
recycling/reuse centers, dropping them off at HHW
collection sites, or disposing of them in a solid
waste form (i.e., pouring liquid products like paint,
cleaners, or polishes on newspapers, allowing them
to dry in a well-ventilated area, and enclosing them
in several plastic bags for landfilling) rather than
dumping them down the sink or flushing them
down the toilet. Improper disposal of HHW can
best be reduced by implementing public education
and HHW collection programs. A collection
program is usually a 1-day event at a specific site.
Permanent programs include retail store drop-off
programs, curbside collection, and mobile facilities.
Establishing HHW collection programs can signifi-
cantly reduce the amount of hazardous chemicals in
the wastewater stream, thereby reducing impacts on
the treatment system and on ground water and
surface waters.
Stopping the practice of flushing household wastes
(e.g., facial tissue, cigarette butts, vegetable
peelings, oil, grease, other cooking wastes) down
the toilet can also reduce mass pollutant loads and
decrease plumbing and OWTS failure risks.
Homeowner education is necessary to bring about
these changes in behavior. Specific homeowner
information is available from the National Small
Flows Clearinghouse at http://www.estd.wvu.edu/
nsfc/NSFC_septic_news.html.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-15. Reduction in pollutant loading achieved by eliminating
garbage disposals
Parameter
Total suspended solids
Biochemical oxygen
demand
Total nitrogen
Total phosphorus
Fats, oils, and grease
Reduction in pollutant loading (%)
25^0
20-28
3.6
1.7
60-70
Source: University of Wisconsin, 1978.
Eliminating use of garbage disposals
Eliminating the use of garbage disposals can
significantly reduce the amount of grease, suspended
solids, and BOD in wastewater (table 3-15). Reducing
the amount of vegetable and other food-related
material entering wastewater from garbage dispos-
als can also result in a slight reduction in nitrogen
and phosphorus loads. Eliminating garbage disposal
use also reduces the rate of sludge and scum
accumulation in the septic tank, thus reducing the
frequency of required pumping. OWTSs, however,
can accommodate garbage disposals by using larger
tanks, SWISs, or alternative system designs. (For
more information, see Special Issue Fact Sheets 2
and 3 in the Chapter 4 Fact Sheets section.)
Using graywater separation approaches
Another method for reducing pollutant mass
loading to a single SWIS is segregating toilet
waste flows (blackwater) from sink, shower,
washing machine, and other waste flows
(graywater). Some types of toilet systems provide
separate handling of human excreta (such as the
non-water-carriage units in table 3-14). Signifi-
cant quantities of suspended solids, BOD, nitro-
gen, and pathogenic organisms are eliminated
from wastewater flows by segregating body wastes
from the OWTS wastewater stream through the
use of composting or incinerator toilets. This
approach is more cost-effective for new homes,
homes with adequate crawl spaces, or mobile or
modular homes. Retrofitting existing homes,
especially those with concrete floors, can be
expensive. (For more information on graywater
reuse, see Special Issue Fact Sheet 4 in the
Chapter 4 Fact Sheets section and http://
www.epa.gov/OW/you/chap3.html.)
Graywaters contain appreciable quantities of
organic matter, suspended solids, phosphorus,
grease, and bacteria (USEPA, 1980a). Because of
the presence of significant concentrations of
bacteria and possibly pathogens in graywaters from
bathing, hand washing, and clothes washing, caution
should be exercised to ensure that segregated
graywater treatment and discharge processes occur
below the ground surface to prevent human contact.
In addition, siting of graywater infiltration fields
should not compromise the hydraulic capacity of
treatment soils in the vicinity of the blackwater
infiltration field.
3.5.3 Wastewater reuse and recycling
systems
Many arid and semiarid regions in the United
States have been faced with water shortages,
creating the need for more efficient water use
practices. Depletion of ground water and surface
water resources due to increased development,
irrigation, and overall water use is also becoming a
growing concern in areas where past supplies have
been plentiful (e.g., south Florida, central Geor-
gia). Residential development in previously rural
areas has placed additional strains on water supplies
and wastewater treatment facilities. Decentralized
wastewater management programs that include
onsite wastewater reuse/recycling systems are a
viable option for addressing water supply shortages
and wastewater discharge restrictions. In munici-
palities where water shortages are a recurring
problem, such as communities in California and
Arizona, centrally treated reclaimed wastewater has
been used for decades as an alternative water
supply for agricultural irrigation, ground water
recharge, and recreational waters.
Wastewater reuse is the collection and treatment of
wastewater for other uses (e.g., irrigation, orna-
mental ponds, and cooling systems). Wastewater
recycling is the collection and treatment of
wastewater and its reuse in the same water-use
scheme, such as toilet and urinal flushing
(Tchobanoglous and Burton, 1991). Wastewater
reuse/recycling systems can be used in individual
homes, clustered communities, and larger institu-
tional facilities such as office parks and recre-
ational facilities. The Grand Canyon National
Park has reused treated wastewater for toilet
flushing, landscape irrigation, cooling water, and
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Chapter 3: Establishing Treatment System Performance Requirements
boiler feedstock since 1926, and other reuse
systems are gaining acceptance (Tchobanoglous
and Burton, 1991). Office buildings, schools, and
recreational facilities using wastewater reuse/
recycling systems have reported a 90 percent
reduction in water use and up to a 95 percent
reduction in wastewater discharges (Burks and
Minnis, 1994).
Wastewater reuse/recycling systems reduce potable
water use by reusing or recycling water that has
already been used at the site for nonpotable pur-
poses, thereby minimizing wastewater discharges.
The intended use of wastewater dictates the degree
of treatment necessary before reuse. Common
concerns associated with wastewater reuse/recycling
systems include piping cross-connections, which
could contaminate potable water supplies with
wastewater, difficulties in modifying and integrat-
ing potable and nonpotable plumbing, public and
public agency acceptance, and required mainte-
nance of the treatment processes.
A number of different onsite wastewater reuse/
recycling systems and applications are available.
Some systems, called combined systems, treat and
reuse or recycle both blackwater and graywater
(NAPHCC, 1992. Other systems treat and reuse or
recycle only graywater. Figure 3-6 depicts a typical
graywater reuse approach. Separating graywater
and blackwater is a common practice to reduce
pollutant loadings to wastewater treatment systems
(Tchobanoglous and Burton, 1991).
3.5.4 Factors of safety in
characterization estimates
Conservative predictions or factors of safety are
typically used to account for potential variability
in wastewater characteristics at a particular
dwelling or establishment. These predictions
attempt to ensure adequate treatment by the onsite
system without requiring actual analysis of the
variability in flow or wastewater quality. How-
ever, actual measurement of wastewater flow and
quality from a residential dwelling or nonresiden-
tial establishment always provides the most
accurate estimate for sizing and designing an
OWTS. Metering daily water use and analyzing a
set of grab samples to confirm wastewater
strength estimates are often substituted for direct
Figure 3-6. Typical graywater reuse approach
Composting Toilei
measurement of concentrations because of cost
considerations.
Minimum septic tank size requirements or mini-
mum design flows for a residential dwelling may
be specified by onsite codes (NSFC, 1995). Such
stipulations should incorporate methods for the
conservative prediction of wastewater flow. It is
important that realistic values and safety factors
be used to determine wastewater characteristics in
order to design the most cost-effective onsite
system that meets performance requirements.
Factors of safety can be applied indirectly by the
choice of design criteria for wastewater characteris-
tics and occupancy patterns or directly through an
overall factor. Most onsite code requirements for
system design of residential dwellings call for
estimating the flow on a per person or per bedroom
basis. Codes typically specify design flows of 100 to
150 gallons/bedroom/day (378 to 568 liters/bedroom/
day), or 75 to 100 gallons/person/day (284 to 378
liters/person/day), with occupancy rates of between
1.5 and 2 persons/bedroom (NSFC, 1995).
For example, if an average daily flow of 75 gal-
lons/person/day (284 liters/person/day) and an
occupancy rate of 2 persons per bedroom were the
selected design units, the flow prediction for a
three-bedroom home would include a factor of
safety of approximately 2 when compared to
typical conditions (i.e., 70 gallons/person/day and
1 person/bedroom). In lieu of using conservative
design flows, a direct factor of safety (e.g., 2)
may be applied to estimate the design flow from a
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Chapter 3: Establishing Treatment System Performance Requirements
residence or nonresidential establishment. Multi-
plying the typical flow estimated (140 gallons/
day) by a safety factor of 2 yields a design flow
of 280 gallons/day (1,058 liters/day). Factors of
safety used for individual systems will usually be
higher than those used for larger systems of 10
homes or more.
Great care should be exercised in predicting
wastewater characteristics so as not to accumulate
multiple factors of safety that would yield unrea-
sonably high design flows and result in unduly high
capital costs. Conversely, underestimating flows
should be avoided because the error will quickly
become apparent if the system overloads and
requires costly modification.
3.6 Integrating wastewater
characterization and other
design information
Predicting wastewater characteristics for typical
residential and nonresidential establishments can be a
difficult task. Following a logical step-by-step
procedure can help simplify the characterization
process and yield more accurate wastewater charac-
teristic estimates. Figure 3-7 is a flow chart that
illustrates a procedure for predicting wastewater
characteristics. This strategy takes the reader through
the characterization process as it has been described
in this chapter. The reader is cautioned that this
flowchart is provided to illustrate one simple
strategy for predicting wastewater characteristics.
Additional factors to consider, such as discrepancies
between literature values for wastewater flow and
quality and/or the need to perform field studies,
should be addressed based on local conditions and
regulatory requirements.
In designing wastewater treatment systems, it is
recommended that designers consider the most
significant or limiting parameters, including those
that may be characterized as outliers, when
considering hydraulic and mass pollutant treat-
ment requirements and system components. For
example, systems that will treat wastewaters with
typical mass pollutant loads but hydraulic loads
that exceed typical values should be designed to
handle the extra hydraulic input. Systems de-
signed for facilities with typical hydraulic loads
but atypical mass pollutant loads (e.g., restaurants,
grocery stores, or other facilities with high-
strength wastes) should incorporate pretreatment
units that address the additional pollutant load-
ings, such as grease traps.
3.7 Transport and fate of
wastewater pollutants in the
receiving environment
Nitrate, phosphorus, pathogens, and other contami-
nants are present in significant concentrations in
most wastewaters treated by onsite systems. Al-
though most can be removed to acceptable levels
under optimal system operational and performance
conditions, some may remain in the effluent exiting
the system. After treatment and percolation of the
wastewater through the infiltrative surface biomat
and passage through the first few inches of soil, the
wastewater plume begins to migrate downward
until nearly saturated conditions exist. The worst
case scenario occurs when the plume is mixing with
an elevated water table. At that point, the wastewa-
ter plume will move in response to the prevailing
hydraulic gradient, which might be lateral, vertical,
or even a short distance upslope if ground water
mounding occurs (figure 3-8). Moisture potential,
soil conductivity, and other soil and geological
characteristics determine the direction of flow.
Further treatment occurs as the plume passes
through the soil. The degree of this additional
treatment depends on a host of factors (e.g.,
residence time, soil mineralogy, particle sizes).
Permit writers should consider not only the
performance of each individual onsite system but
also the density of area systems and overall
hydraulic loading, the proximity of water re-
sources, and the collective performance of onsite
systems in the watershed. Failure to address these
issues can lead ultimately to contamination of
lakes, rivers, streams, wetlands, coastal areas, or
ground water. This section examines key wastewa-
ter pollutants, their impact on human health and
water resources, how they move in the environ-
ment, and how local ecological conditions affect
wastewater treatment.
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Chapter 3: Establishing Treatment System Performance Requirements
Figure 3-7. Strategy for estimating wastewater flow and composition
Determine primary function of facility
and classify accordingly (e.g., single-family residence,
restaurant, assembly hall, camp, etc.)
Residential facilities
Nonresidential facilities
Determine physical characteristics:
- Waste-generating fixtures/appliances
- System design units (number of
bedrooms, etc.)
- Unusual conditions (seasonal use,
group home, etc.)
Determine physical characteristics:
- Waste-generating fixtures/appliances
- System design units (number of
seats, etc.)
- Operational patterns (hours of
operation, seasonal use, etc.)
Estimate total
& daily flows
- Table 3-1
- Table 3-2
- Table 3-3
- Similar
facilities
Determine
wastewater
composition
- Table 3-7
- Table 3-8
- Similar
facilities
I
Estimate total
& daily flows
- Table 3-4
- Table 3-5
- Table 3-6
- Similar
facilities
I
Determine
wastewater
composition
- Table 3-7
- Table 3-8
- Similar
facilities
Integrate data from tables, existing facilities, and/or other
research to develop initial wastewater flow
and composition profile
Incorporate wastewater flow and/or mass pollutant reduction
factors (tables 3-9, 3-10, 3-11, 3-12, 3-13, 3-14)
Incorporate factors of safety, based on best professional
judgement of anticipated daily/peak flows, wastewater
composition, facility usage, possible future use, water supply
changes (e.g., cistern to public water), and other factors
Calculate final estimates of wastewater flow and composition
and incorporate performance requirements to define system
size, technology type, and treatment unit components
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Chapter 3: Establishing Treatment System Performance Requirements
3.7.1 Wastewater pollutants of concern
Environmental protection and public health agen-
cies are becoming increasingly concerned about
ground water and surface water contamination
from wastewater pollutants. Toxic compounds,
excessive nutrients, and pathogenic agents are
among the potential impacts on the environment
from onsite wastewater systems. Domestic waste-
water contains several pollutants that could cause
significant human health or environmental risks if
not treated effectively before being released to the
receiving environment.
A conventional OWTS (septic tank and SWIS) is
capable of nearly complete removal of suspended
solids, biodegradable organic compounds, and fecal
coliforms if properly designed, sited, installed,
operated, and maintained (USEPA, 1980a, 1997).
These wastewater constituents can become pollut-
ants in ground water or surface waters if treatment
is incomplete. Research and monitoring studies
have demonstrated removals of these typically
found constituents to acceptable levels. More
recently, however, other pollutants present in
wastewater are raising concerns, including nutrients
(e.g., nitrogen and phosphorus), pathogenic
parasites (e.g., Cryptosporidumparvum, Giardia
lamblid), bacteria and viruses, toxic organic
compounds, and metals. Their potential impacts on
ground water and surface water resources are
summarized in table 3-16. Recently, concerns have
been raised over the movement and fate of a
variety of endocrine disrupters, usually from use of
Pharmaceuticals by residents. No data have been
developed to confirm a risk at this time.
3.7.2 Fate and transport of pollutants
in the environment
When properly designed, sited, constructed, and
maintained, conventional onsite wastewater treat-
ment technologies effectively reduce or eliminate
most human health or environmental threats posed
by pollutants in wastewater (table 3-17). Most
traditional systems rely primarily on physical,
biological, and chemical processes in the septic
tank and in the biomat and unsaturated soil zone
below the SWIS (commonly referred to as a leach
field or drain field) to sequester or attenuate
pollutants of concern. Where point discharges to
surface waters are permitted, pollutants of concern
should be removed or treated to acceptable, permit-
specific levels (levels permitted under the National
Pollutant Discharge Elimination System of the
Clean Water Act) before discharge.
Figure 3-8. Plume movement through the soil to the saturated zone.
Well
Source: Adapted from NSFC, 2000.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-16. Typical wastewater pollutants of concern
Pollutant
Reason for concern
Total suspended solids
(TSS) and turbidity (NTU)
Biodegradable organics
(BOD)
Pathogens
Nitrogen
In surface waters, suspended solids can result in the development of sludge deposits that smother benthic
macroinvertebrates and fish eggs and can contribute to benthic enrichment, toxicity, and sediment oxygen
demand. Excessive turbidity (colloidal solids that interfere with light penetration) can block sunlight, harm
aquatic life (e.g., by blocking sunlight needed by plants), and lower the ability of aquatic plants to increase
dissolved oxygen in the water column. In drinking water, turbidity is aesthetically displeasing and interferes
with disinfection.
Biological stabilization of organics in the water column can deplete dissolved oxygen in surface waters,
creating anoxic conditions harmful to aquatic life. Oxygen-reducing conditions can also result in taste and
odor problems in drinking water.
Parasites, bacteria, and viruses can cause communicable diseases through direct/indirect body contact or
ingestion of contaminated water or shellfish. A particular threat occurs when partially treated sewage pools
on ground surfaces or migrates to recreational waters. Transport distances of some pathogens (e.g., viruses
and bacteria) in ground water or surface waters can be significant.
Nitrogen is an aquatic plant nutrient that can contribute to eutrophication and dissolved oxygen loss in
surface waters, especially in lakes, estuaries, and coastal embayments. Algae and aquatic weeds can
contribute trihalomethane (THM) precursors to the water column that may generate carcinogenic THMs in
chlorinated drinking water. Excessive nitrate-nitrogen in drinking water can cause methemoglobinemia in
infants and pregnancy complications for women. Livestock can also suffer health impacts from drinking
water high in nitrogen.
Phosphorus is an aquatic plant nutrient that can contribute to eutrophication of inland and coastal surface
waters and reduction of dissolved oxygen.
Toxic organic compounds present in household chemicals and cleaning agents can interfere with certain
biological processes in alternative OWTSs. They can be persistent in ground water and contaminate
downgradient sources of drinking water. They can also cause damage to surface water ecosystems and
human health through ingestion of contaminated aquatic organisms (e.g., fish, shellfish).
Heavy metals like lead and mercury in drinking water can cause human health problems. In the aquatic
ecosystem, they can also be toxic to aquatic life and accumulate in fish and shellfish that might be
consumed by humans.
Chloride and sulfide can cause taste and odor problems in drinking water. Boron, sodium, chlorides, sulfate,
and other solutes may limit treated wastewater reuse options (e.g., irrigation). Sodium and to a lesser extent
potassium can be deleterious to soil structure and SWIS performance.
Source: Adapted in part from Tchobanoglous and Burton, 1991.
Phosphorus
Toxic organics
Heavy metals
Dissolved inorganics
Table3-17. Examples of soil infiltration system performance
Parameter
BOD5
Total nitrogen
Total phosphorus
Fecal coliforms
Applied concentration
in milligrams per liter
130-150
45-55
8-12
NA"
Percent removal
90-98
1(MO
85-95
99-99.99
References
Siegristetal., 1986
U.Wisconsin,1978
Reneau1977
Sikoraetal., 1976
Sikoraetal., 1976
Gerba, 1975
" Fecal coliforms are typically measured in other units, e.g., colony-forming units per 100 milliliters.
Source: Adapted from USEPA, 1992.
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Chapter 3: Establishing Treatment System Performance Requirements
Onsite systems can fail to meet human health and
water quality objectives when fate and transport of
potential pollutants are not properly addressed.
Failing or failed systems threaten human health if
pollutants migrate into ground waters used as
drinking water and nearby surface waters used for
recreation. Such failures can be due to improper
siting, inappropriate choice of technology, faulty
design, poor installation practices, poor operation, or
inadequate maintenance. For example, in high-
density subdivisions conventional septic tank/SWIS
systems might be an inappropriate choice of technol-
ogy because leaching of nitrate-nitrogen could result
in nitrate concentrations in local aquifers that exceed
the drinking water standard. In soils with excessive
permeability or shallow water tables, inadequate
treatment in the unsaturated soil zone might allow
pathogenic bacteria and viruses to enter the ground
water if no mitigating measures are taken. Poorly
drained soils can restrict reoxygenation of the subsoil
and result in clogging of the infiltrative surface.
A number of factors influence the shape and
movement of contaminant plumes from OWTSs.
Climate, soils, slopes, landscape position, geology,
regional hydrology, and hydraulic load determine
whether the plume will disperse broadly and deeply
or, more commonly, migrate in a long and rela-
tively narrow plume along the upper surface of a
confining layer or on the surface of the ground
water. Analyses of these factors are key elements in
understanding the contamination potential of
individual or clustered OWTSs in a watershed or
ground water recharge area.
Receiving environments and contaminant
plume transport
Most onsite systems ultimately discharge treated
water to ground water. Water beneath the land
surface occurs in two primary zones, the aerated or
vadose zone and the saturated (groundwater) zone.
Interstices in the aerated (upper) vadose zone are
unsaturated, filled partially with water and partially
with air. Water in this unsaturated zone is referred to
as vadose water. In the saturated zone, all interstices
are filled with water under hydrostatic pressure.
Water in this zone is commonly referred to as
ground water. Where no overlying impermeable
barrier exists, the upper surface of the ground water
is called the water table. Saturation extends slightly
above the water table due to capillary attraction but
water in this "capillary fringe" zone is held at less
than atmospheric pressure.
Onsite wastewater treatment system performance
should be measured by the ability of the system to
discharge a treated effluent capable of meeting
public health and water quality objectives estab-
lished for the receiving water resource. Discharges
from existing onsite systems are predominantly to
ground water but they might involve direct (point
source) or indirect (nonpoint source) surface water
discharges in some cases. Ground water discharges
usually occur through soil infiltration. Point source
discharges are often discouraged by regulatory
agencies because of the difficulty in regulating
many small direct, permitted discharges and the
potential for direct or indirect human contact with
wastewater. Nonpoint source surface water dis-
charges usually occur as base flow from ground
water into watershed surface waters. In some cases
regional ground water quality and drinking water
wells might be at a lesser risk from OWTS dis-
charges than nearby surface waters because of the
depth of some aquifers and regional geology.
The movement of subsurface aqueous contaminant
plumes is highly dependent on soil type, soil
layering, underlying geology, topography, and
rainfall. Some onsite system setback/separation
codes are based on plume movement models or
measured relationships that have not been sup-
ported by recent field data. In regions with moder-
ate to heavy rainfall, effluent plumes descend
relatively intact as the water table is recharged
from above. The shape of the plume depends on
the soil and geological factors noted above, the
uniformity of effluent distribution in the SWIS, the
orientation of the SWIS with respect to ground
water flow and direction, and the preferential flow
that occurs in the vadose and saturated zones (Otis,
2000).
In general, however, plumes tend to be long,
narrow, and definable, exhibiting little dispersion
(figure 3-9). Some studies have found SWIS
plumes with nitrate levels exceeding drinking water
standards (10 mg/L) extending more than 328 feet
(100 meters) beyond the SWIS (Robertson, 1995).
Mean effluent plume dispersion values used in a
Florida study to assess subdivision SWIS nitrate
loadings over 5 years were 60 feet, 15 feet, and 1.2
feet for longitudinal, lateral, and vertical disper-
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Chapter 3: Establishing Treatment System Performance Requirements
Plume
Septic
Tank
that examined SWIS plume movement in a shal-
low, unconfined sand aquifer found that after 12
years the plume had sharp lateral and vertical
boundaries, a length of 426 feet (130 meters), and
a uniform width of about 32.8 feet (10 meters)
(Robertson, 1991). At another site examined in that
study, a SWIS constructed in a similar carbonate-
depleted sand aquifer generated a plume with
discrete boundaries that began discharging into a
river 65.6 feet (20 meters) away after 1.5 years of
system operation.
Given the tendency of OWTS effluent plumes to
remain relatively intact over long distances (more
than 100 meters), dilution models commonly used
in the past to calculate nitrate attenuation in the
vadose zone are probably unrealistic (Robertson,
1995). State codes that specify 100-foot separation
distances between conventional SWIS treatment
units and downgradient wells or surface waters
should not be expected to always protect these
resources from dissolved, highly mobile contami-
nants such as nitrate (Robertson, 1991). Moreover,
published data indicate that viruses that reach
groundwater can travel at least 220 feet (67 meters)
vertically and 1,338 feet (408 meters) laterally in
some porous soils and still remain infective (Gerba,
1995). One study noted that fecal coliform bacteria
moved 2 feet (0.6 meter) downward and 50 feet
(15 meters) longitudinally 1 hour after being
injected into a shallow trench in saturated soil on a
14 percent slope in western Oregon (Cogger,
1995). Contaminant plume movement on the
surface of the saturated zone can be rapid, espe-
cially under sloping conditions, but it typically
slows upon penetration into ground water in the
saturated zone. Travel times and distances under
unsaturated conditions in more level terrain are
likely much less.
Ground water discharge
A conventional OWTS (septic tank and SWIS)
discharges to ground water and usually relies on the
unsaturated or vadose zone for final polishing of
the wastewater before it enters the saturated zone.
The septic tank provides primary treatment of the
wastewater, removing most of the settleable solids,
greases, oils, and other floatable matter and anaero-
bic liquifaction of the retained organic solids. The
biomat that forms at the infiltrative surface and
within the first few centimeters of unsaturated soil
below the infiltrative field provides physical,
chemical, and biological treatment of the SWIS
effluent as it migrates toward the ground water.
Because of the excellent treatment the SWIS pro-
vides, it is a critical component of onsite systems
that discharge to ground water. Fluid transport from
the infiltrative surface typically occurs through three
zones, as shown in figure 3-10 (Ayres Associates,
1993a). In addition to the three zones, the figure
shows a saturated zone perched above a restrictive
horizon, a site feature that often occurs.
Pretreated wastewater enters the SWIS at the
surface of the infiltration zone. A biomat forms in
this zone, which is usually only a few centimeters
thick. Most of the physical, chemical, and biologi-
cal treatment of the pretreated effluent occurs in
this zone and in the vadose zone. Particulate matter
in the effluent accumulates on the infiltration surface
and within the pores of the soil matrix, providing a
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Figure 3-10. Soil treatment zones
VADOSE' ZONE (UNSATURATED)
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Chapter 3: Establishing Treatment System Performance Requirements
Act. The NPDES permitting process, which is
administered by all but a few states, defines
discharge performance requirements in the form of
numerical criteria for specific pollutants and
narrative criteria for parameters like color and
odor. The treated effluent should meet water
quality criteria before it is discharged. Criteria-
based standards may include limits for BOD5, TSS,
fecal coliforms, ammonia, nutrients, metals, and
other pollutants, including chlorine, which is often
used to disinfect treated effluent prior to discharge.
The limits specified vary based on the designated
use of the water resource (e.g., swimming, aquatic
habitat, recreation, potable water supply), state
water classification schemes (Class I, II, III, etc.),
water quality criteria associated with designated
uses, or the sensitivity of aquatic ecosystems—
especially lakes and coastal areas—to eutrophica-
tion. Surface water discharges are often discour-
aged for individual onsite treatment systems,
however, because of the difficulty in achieving
regulatory oversight and surveillance of many
small, privately operated discharges.
Atmospheric discharge
Discharges to the atmosphere also may occur
through evaporation and transpiration by plants.
Evapotranspiration can release significant volumes
of water into the atmosphere, but except for areas
where annual evaporation exceeds precipitation
(e.g., the American Southwest), evapotranspiration
cannot be solely relied on for year-round discharge.
However, evapotranspiration during the growing
season can significantly reduce the hydraulic
loading to soil infiltration systems.
Contaminant attenuation
Performance standards for ground water discharge
systems are usually applied to the treated effluent/
ground water mixture at some specified point away
from the treatment system (see chapter 5). This
approach is significantly different from the effluent
limitation approach used with surface water
discharges because of the inclusion of the soil
column as part of the treatment system. However,
monitoring ground water quality as a performance
measure is not as easily accomplished. The fate and
transport of wastewater pollutants through soil
should be accounted for in the design of the overall
treatment system.
Contaminant attenuation (removal or inactivation
through treatment processes) begins in the septic
tank and continues through the distribution piping
of the SWIS or other treatment unit components,
the infiltrative surface biomat, the soils of the
vadose zone, and the saturated zone. Raw wastewa-
ter composition was discussed in section 3.4 and
summarized in table 3-7. Jantrania (1994) found
that chemical, physical, and biological processes in
the anaerobic environment of the septic tank produce
effluents with TSS concentrations of 40 to 350 mg/
L, oil and grease levels of 50 to 150 mg/L, and total
coliform counts of 106 to 108 per 100 milliliters.
Although biofilms develop on exposed surfaces as
the effluent passes through piping to and within the
SWIS, no significant level of treatment is provided
by these growths. The next treatment site is the
infiltrative zone, which contains the biomat. Filtra-
tion, microstraining, and aerobic biological decom-
position processes in the biomat and infiltration zone
remove more than 90 percent of the BOD and
suspended solids and 99 percent of the bacteria
(University of Wisconsin, 1978).
As the treated effluent passes through the biomat
and into the vadose and saturated zones, other
treatment processes (e.g., filtration, adsorption,
precipitation, chemical reactions) occur. The
following section discusses broadly the transport
and fate of some of the primary pollutants of
concern under the range of conditions found in
North America. Table 3-18 summarizes a case
study that characterized the septic tank effluent and
soil water quality in the first 4 feet of a soil
treatment system consisting of fine sand. Results
for other soil types might be significantly different.
Note that mean nitrate concentrations still exceed
the 10 mg/L drinking water standard even after the
wastewater has percolated through 4 feet of fine
sand under unsaturated conditions.
Biochemical oxygen demand and total
suspended solids
Biodegradable organic material creates biochemical
oxygen demand (BOD), which can cause low
dissolved oxygen concentrations in surface water,
create taste and odor problems in well water, and
cause leaching of metals from soil and rock into
ground water and surface waters. Total suspended
solids (TSS) in system effluent can clog the infiltra-
tive surface or soil interstices, while colloidal solids
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-18. Case study: septic tank effluent and soil water qualitya
Parameter
(units)
BOD
(mg/L)
TOG
(mg/L)
TKN
(mg/L)
N03-N
(mg/L)
TP
(mg/L)
IDS
(mg/L)
Cl
(mg/L)
F. Coli
(log # per
100mL)
F. strep.
(log # per
100mL)
Statistics
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Mean
Range
# samples
Septic tank effluent
quality
93.5
46-156
11
47.4
31-68
11
44.2
19-53
11
0.04
0.01-0.16
11
8.6
7.2-17.0
11
497
354-610
11
70
37-110
11
4.57
3.6-5.4
11
3.60
1.9-5.3
11
Soil water
quality" at
0.6 meter
<1
<1
6
7.8
3.7-17.0
34
0.77
0.40-1.40
35
21.6
1.7-39.0
35
0.40
0.01-3.8
35
448
184-620
34
41
9-65
34
nd°
<1
24
nd
<1
23
Soil water
Quality" at
1.2 meters
<1
<1
6
8.0
3.1-25.0
33
0.77
0.25-2.10
33
13.0
2.0-29.0
32
0.18
0.02-1.80
33
355
200-592
32
29
9^9
31
nd
<1
21
nd
<1
20
" The soil matrix consisted of a fine sand; the wastewater loading rate was 3.1 cm per day over 9 months. TOC = total organic carbon; TKN = total Kjeldahl nitrogen;
TDS = total dissolved solids; Cl = chlorides;
F. coll = fecal conforms; F. strep = fecal streptococci.
b Soil water quality measured in pan lysimeters at unsaturated soil depths of 2 feet (0.6 meter) and 4 feet (1.2 meters).
"nd = none detected.
Source: Adapted from Anderson et al., 1994.
cause cloudiness in surface waters. TSS in direct
discharges to surface waters can result in the devel-
opment of sludge layers that can harm aquatic
organisms (e.g., benthic macro invertebrates).
Systems that fail to remove BOD and TSS and are
located near surface waters or drinking water wells
may present additional problems in the form of
pathogens, toxic pollutants, and other pollutants.
Under proper site and operating conditions, how-
ever, OWTSs can achieve significant removal rates
(i.e., greater than 95 percent) for biodegradable
organic compounds and suspended solids. The risk
of ground water contamination by BOD and TSS
(and other pollutants associated with suspended
solids) below a properly sited, designed, con-
structed, and maintained SWIS is slight (Anderson
et al., 1994; University of Wisconsin, 1978). Most
settleable and floatable solids are removed in the
septic tank during pretreatment. Most particulate
BOD remaining is effectively removed at the
infiltrative surface and biomat. Colloidal and
dissolved BOD that might pass through the biomat
are removed through aerobic biological processes
in the vadose zone, especially when uniform dosing
and reoxygenation occur. If excessive concentra-
tions of BOD and TSS migrate beyond the tank
because of poor maintenance, the infiltrative
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Chapter 3: Establishing Treatment System Performance Requirements
surface can clog and surface seepage of wastewater
or plumbing fixture backup can occur.
Nitrogen
Nitrogen in raw wastewater is primarily in the
form of organic matter and ammonia. After the
septic tank, it is primarily (more than 85 percent)
ammonia. After discharge of the effluent to the
infiltrative surface, aerobic bacteria in the biomat
and upper vadose zone convert the ammonia in the
effluent almost entirely to nitrite and then to nitrate.
Nitrogen in its nitrate form is a significant ground
water pollutant. It has been detected in urban and
rural ground water nationwide, sometimes at levels
exceeding the USEPA drinking water standard of 10
mg/L (USGS, 1999). High concentrations of nitrate
(greater than 10 mg/L) can cause methemoglobin-
emia or "blue baby syndrome," a disease in infants
that reduces the blood's ability to carry oxygen, and
problems during pregnancy. Nitrogen is also an
important plant nutrient that can cause excessive
algal growth in nitrogen-limited inland (fresh)
waters and coastal waters, which are often limited in
available nitrogen. High algal productivity can block
sunlight, create nuisance or harmful algal blooms,
and significantly alter aquatic ecosystems. As algae
die, they are decomposed by bacteria, which can
deplete available dissolved oxygen in surface waters
and degrade habitat conditions.
Nitrogen contamination of ground water below
infiltration fields has been documented by many
investigators (Anderson et al., 1994; Andreoli et
al., 1979; Ayres Associates, 1989, 1993b, c; Bouma
et al., 1972; Carlile et al., 1981; Cogger and
Table 3-19. Wastewater constituents of concern and representative concentrations in the effluent of various treatment units
Constituents of
concern
Oxygen demand
Participate solids
Nitrogen
Phosphorus
Bacteria (e.g.,
Clostridium
perfringens,
Salmonella,
Shigella)
Virus (e.g.,
hepatitis, polio,
echo, coxsackie,
coliphage)
Organic
chemicals (e.g.,
solvents, petro-
chemicals,
pesticides)
Heavy metals
(e.g., Pb, Cu, Ag,
Hg)
Example direct
or indirect
measures
(Units)
BOD5(mg/L)
TSS (mg/L)
Total N (mg
N/L)
Total P (mg
P/L)
Fecal coliform
(organisms per
100mL)
Specific virus
(pfu/mL)
Specific
organics or
totals (ug/L)
Individual
metals (ug/L)
Tank-based treatment unit effluent concentrations
Domestic STE1
140-200
50-100
40-100
5-15
106-10"
0-1 0s
(episodically
present at high
levels)
0 to trace levels
(?)
0 to trace levels
Domestic STE
with N-removal
recycle2
80-120
50-80
10-30
5-15
106-10"
0-1 0s (episodically
present at high
levels)
0 to trace levels
(?)
0 to trace levels
Aerobic unit
effluent
5-50
5-100
25-60
4-10
103-104
0-1 05
(episodically
present at high
levels)
0 to trace levels
(?)
0 to trace levels
Sand filter
effluent
2-15
5-20
10-50
<1-104
10'-103
0-1 05
(episodically
present at high
levels)
0 to trace levels
(?)
0 to trace levels
SWIS percolate
into ground water
Foam or textile at 3 to 5 ft depth
filter effluent (% removal)
5-15
5-10
30-60
5-1 54
101-103
0-1 05
(episodically
present at high
levels)
0 to trace levels
(?)
0 to trace levels
>90%
>90%
10-20%
0-100%
>99.99%
>99.9%
>99%
>99%
1 Septic tank effluent (STE) concentrations given are for domestic wastewater. However, restaurant STE is markedly higher particularly in BODS, COD, and suspended solids while
concentrations in graywater STE are noticeably lower in total nitrogen.
2 N-removal accomplished by recycling STE through a packed bed for nitrification with discharge into the influent end of the septic tank for denitrification.
3 P-removal by adsorption/precipitation is highly dependent on media capacity, P loading, and system operation.
Source: Siegrist, 2001 (after Siegrist et al., 2000)
Source: Siegrist, 2001 (after Siegrist et al., 2000).
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Carlile, 1984; Ellis and Childs, 1973; Erickson and
Bastian, 1980; Gibbs, 1977a, b; Peavy and
Brawner, 1979; Peavy and Groves, 1978; Polta,
1969; Preul, 1966; Reneau, 1977, 1979; Robertson
et al, 1989, 1990; Shaw and Turyk, 1994; Starr
and Sawhney, 1980; Tinker, 1991; Uebler, 1984;
Viraraghavan and Warnock, 1976a, b, c; Walker et
al., 1973a, b; Wolterink et al., 1979). Nitrate-
nitrogen concentrations in ground water were
usually found to exceed the drinking water standard
of 10 mg/L near the infiltration field. Conventional
soil-based systems can remove some nitrogen from
septic tank effluent (table 3-19), but high-density
installation of OWTSs can cause contamination of
ground or surface water resources. When nitrate
reaches the ground water, it moves freely with little
retardation. Denitrification has been found to be
significant in the saturated zone only in rare
instances where carbon or sulfur deposits are
present. Reduction of nitrate concentrations in
ground water occurs primarily through dispersion
or recharge of ground water supplies by precipita-
tion (Shaw and Turyk, 1994).
Nitrogen can undergo several transformations in
and below a SWIS, including adsorption, volatil-
ization, mineralization, nitrification, and denitrifi-
cation. Nitrification, the conversion of ammonium
nitrogen to nitrite and then nitrate by bacteria
under aerobic conditions, is the predominant
transformation that occurs immediately below the
infiltration zone. The negatively charged nitrate ion
is very soluble and moves readily with the percolat-
ing soil water.
Biological denitrification, which converts nitrate to
gaseous forms of nitrogen, can remove nitrate from
percolating wastewater. Denitrification occurs
under anaerobic conditions where available electron
donors such as carbon or sulfur are present. Deni-
trifying bacteria use nitrate as a substitute for
oxygen when accepting electrons. It has been
generally thought that anaerobic conditions with
organic matter seldom occur below soil infiltration
fields. Therefore, it is has been assumed that all the
nitrogen applied to infiltration fields ultimately
leaches to ground water (Brown et al., 1978;
Walker et al., 1973a, b). However, several studies
indicate that denitrification can be significant.
Jenssen and Siegrist (1990) found in their review
of several laboratory and field studies that approxi-
mately 20 percent of nitrogen is lost from waste-
water percolating through soil. Factors found to
favor denitrification are fine-grained soils (silts and
clays) and layered soils (alternating fine-grained
and coarser-grained soils with distinct boundaries
between the texturally different layers), particularly
if the fine-grained soil layers contain organic
material. Jenssen and Siegrist concluded that
nitrogen removal below the infiltration field can be
enhanced by placing the system high in the soil
profile, where organic matter in the soil is more
likely to be present, and by dosing septic tank
effluent onto the infiltrative surface to create
alternating wetting and drying cycles. Denitrifica-
tion can also occur if ground water enters surface
water bodies through organic-rich bottom sedi-
ments. Nitrogen concentrations in ground water
were shown to decrease to less than 0.5 mg/L after
passage through sediments in one Canadian study
(Robertson et al., 1989, 1990).
It is difficult to predict removal rates for wastewa-
ter-borne nitrate or other nitrogen compounds in
the soil matrix. In general, however, nitrate con-
centrations in SWIS effluent can and often do
exceed the 10 mg/L drinking water standard. Shaw
and Turyk (1994) found nitrate concentrations
ranging from 21 to 108 mg/L (average of 31 to 34
mg/L) in SWIS effluent plumes analyzed as part of
a study of 14 pressure-dosed drain fields in sandy
soils of Wisconsin. The limited ability of conven-
tional SWISs to achieve enhanced nitrate reduc-
tions and the difficulty in predicting soil nitrogen
removal rates means that systems sited in drinking
water aquifers or near sensitive aquatic areas should
incorporate additional nitrogen removal technolo-
gies prior to final soil discharge.
Phosphorus
Phosphorus is also a key plant nutrient, and like
nitrogen it contributes to eutrophication and
dissolved oxygen depletion in surface waters,
especially fresh waters such as rivers, lakes, and
ponds. Monitoring below subsurface infiltration
systems has shown that the amount of phosphorus
leached to ground water depends on several factors:
the characteristics of the soil, the thickness of the
unsaturated zone through which the wastewater
percolates, the applied loading rate, and the age of
the system (Bouma et al., 1972; Brandes, 1972;
Carlile et al., 1981, Childs et al., 1974; Cogger and
Carlile, 1984; Dudley and Stephenson, 1973; Ellis
and Childs, 1973; Erickson and Bastian, 1980;
Gilliom and Patmont, 1983; Harkin et al., 1979;
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Chapter 3: Establishing Treatment System Performance Requirements
Jones and Lee, 1979; Whelan and Barrow, 1984).
The amount of phosphorus in ground water varies
from background concentrations to concentrations
equal to that of septic tank effluent. However,
removals have been found to continue within
ground water aquifers (Carlile et al., 1981; Childs
et al., 1974; Cogger and Carlile, 1984; Ellis and
Childs, 1973; Gilliom and Patmont, 1983; Rea and
Upchurch, 1980; Reneau, 1979; Reneau and Pettry,
1976; Robertson et al., 1990).
Retardation of phosphorus contamination of surface
waters from SWISs is enhanced in fine-textured
soils without continuous macropores that would
allow rapid percolation. Increased distance of the
system from surface waters is also an important
factor in limiting phosphorus discharges because of
greater and more prolonged contact with soil
surfaces. The risk of phosphorus contamination,
therefore, is greatest in karst regions and coarse-
textured soils without significant iron, calcium, or
aluminum concentrations located near surface waters.
The fate and transport of phosphorus in soils are
controlled by sorption and precipitation reactions
(Sikora and Corey, 1976). At low concentrations
(less than 5 mg/L), the phosphate ion is chemi-
sorbed onto the surfaces of iron and aluminum
minerals in strongly acid to neutral systems and on
calcium minerals in neutral to alkaline systems. As
phosphorus concentrations increase, phosphate
precipitates form. Some of the more important
precipitate compounds formed are strengite,
FeP042H20; variscite, A1P042H20; dicalcium
phosphate, CaHP04 2H20; octacalcium phosphate,
Ca4H(P04)3 3H20; and hydroxyapatite, Ca10
(P04)6(OH2). In acidic soils, phosphate sorption
probably involves the aluminum and iron com-
pounds; in calcareous or alkaline soils, calcium
compounds predominate.
Estimates of the capacity of the soil to retain
phosphorus are often based on sorption isotherms
such as the Langmuir model (Ellis and Erickson,
1969; Sawney, 1977; Sawney and Hill, 1975;
Sikora and Corey, 1976; Tofflemire and Chen,
1977). This method significantly underestimates
the total retention capacity of the soil (Anderson et
al., 1994; Sawney and Hill, 1975; Sikora and
Corey, 1976; Tofflemire and Chen, 1977). This is
because the test measures the chemi-sorption
capacity but does not take into account the slower
precipitation reactions that regenerate the chemi-
sorption sites. These slower reactions have been
shown to increase the capacity of the soil to retain
phosphorus by 1.5 to 3 times the measured capacity
calculated by the isotherm test (Sikora and Corey,
1976; Tofflemire and Chen, 1977). In some cases
the total capacity has been shown to be as much as
six times greater (Tofflemire and Chen, 1977).
These reactions can take place in unsaturated or
saturated soils (Ellis and Childs, 1973; Jones and
Lee, 1977a, b; Reneau and Pettry, 1976; Robertson
et al., 1990; Sikora and Corey, 1976).
The capacity of the soil to retain phosphorus is
finite, however. With continued loading, phospho-
rus movement deeper into the soil profile can be
expected. The ultimate retention capacity of the
soil depends on several factors, including its
mineralogy, particle size distribution, oxidation-
reduction potential, and pH. Fine-textured soils
theoretically provide more sorption sites for
phosphorus. As noted above, iron, aluminum, and
calcium minerals in the soil allow phosphorus
precipitation reactions to occur, a process that can
lead to additional phosphorus retention. Sikora and
Corey (1976) estimated that phosphorus penetration
into the soil below a SWIS would be 52 centime-
ters per year in Wisconsin sands and 10 centimeters
per year in Wisconsin silt loams.
Nevertheless, knowing the retention capacity of the
soil is not enough to predict the travel of phospho-
rus from subsurface infiltration systems. Equally
important is an estimate of the total volume of soil
that the wastewater will contact as it percolates to
and through the ground water. Fine-textured,
unstructured soils (e.g., clays, silty clays) can be
expected to disperse the water and cause contact
with a greater volume of soil than coarse, granular
soils (e.g., sands) or highly structured fine-textured
soils (e.g., clayey silts) having large continuous
pores. Also, the rate of water movement and the
degree to which the water's elevation fluctuates are
important factors.
There are no simple methods for predicting phos-
phorus removal rates at the site level. However,
several landscape-scale tools that provide at least
some estimation of expected phosphorus loads from
clusters of onsite systems are available. The
MANAGE assessment method, which is profiled in
section 3.9.1, is designed to estimate existing and
projected future (build-out) nutrient loads and to
identify "hot spots" based on land use and cover
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Chapter 3: Establishing Treatment System Performance Requirements
(see http://www.epa.gov/owow/watershed/
Proceed/joubert.html; http://www.edc.uri.edu/
cewq/manage.html). Such estimates provide at
least some guidance in siting onsite systems and
considering acceptable levels of both numbers and
densities in sensitive areas.
Pathogenic microorganisms
Pathogenic microorganisms found in domestic
wastewater include a number of different bacteria,
viruses, protozoa, and parasites that cause a wide
range of gastrointestinal, neurological, respiratory,
renal, and other diseases. Infection can occur
through ingestion (drinking contaminated water;
incidental ingestion while bathing, skiing, or
fishing), respiration, or contact (table 3-20). The
occurrence and concentration of pathogenic micro-
organisms in raw wastewater depend on the sources
contributing to the wastewater, the existence of
infected persons in the population, and environ-
mental factors that influence pathogen survival
rates. Such environmental factors include the
following: initial numbers and types of organisms,
temperature (microorganisms survive longer at
lower temperatures), humidity (survival is longest
at high humidity), amount of sunlight (solar
radiation is detrimental to survival), and additional
soil attenuation factors, as discussed below. Typical
ranges of survival times are presented in table 3-21.
Among pathogenic agents, only bacteria have any
potential to reproduce and multiply between hosts
(Oliver, 2000). If temperatures are between 50 and
80 degrees Fahrenheit (10 to 25 degrees Celsius)
Table 3-20. Waterborne pathogens found in human waste and associated diseases
Type
Organism
Disease
Effects
Bacteria Escherichia coli
enteropathogenic)
Legionella pneumophila
Leptospira
Salmonella typhi
Salmonella
Shigella
Vibrio cholerae
Yersinia enterolitica
Protozoans Balantidium coli
Cryptosporidium
Entamoeba histolytica
Giardia lambia
Naegleria fowleti
Viruses Adenovirus
(31 types)
Enterovirus
(67 types, e.g., polio-, echo-,
and Coxsackie viruses)
Hepatitis A
Norwalk agent
Reovirus
Rotavirus
Gastroenteritis
Legionellosis
Leptospirosis
Typhoid fever
Salmonellosis
Shigellosis
Cholera
Yersinosis
Balantidiasis
Crypotosporidiosis
Ameobiasis
(amoebic dysentery)
Giardiasis
Amebic
Meningoencephalitis
Conjunctivitis
Gastroenteritis
Infectious hepatitis
Gastroenteritis
Gastroenteritis
Gastroenteritis
Vomiting, diarrhea, death in susceptible populations
Acute respiratory illness
Jaundice, fever (Well's disease)
High fever, diarrhea, ulceration of the small intestine
Diarrhea, dehydration
Bacillary dysentery
Extremely heavy diarrhea, dehydration
Diarrhea
Diarrhea, dysentery
Diarrhea
Prolonged diarrhea with bleeding, abscesses of the liver
and small intestine
Mild to severe diarrhea, nausea, indigestion
Fatal disease; inflammation of the brain
Eye, other infections
Heart anomalies, meningitis
Jaundice, fever
Vomiting, diarrhea
Vomiting, diarrhea
Vomiting, diarrhea
Source: USEPA, 1999.
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Table 3-21.Typical pathogen survival times at 20 to 30 °C
Pathogen
Viruses'
Enteroviruses"
Bacteria
Fecal coliforms'
Salmonella spp.a
Shigella spp.a
Protozoa
Entamoeba histolytica cysts
Helminths
Ascaris lumbricoides eggs
Typical survival times in days
In fresh water & sewage In unsaturated soils
< 120 but usually < 50
< 60 but usually < 30
< 60 but usually < 30
< 30 but usually < 10
< 30 but usually < 15
Many months
"In seawater, viral survival is less and bacterial survival is very much less than in fresh water.
"Includes polio-, echo-, and Coxsackie viruses.
Source: Adapted from Feacham et al., 1983, cited in UNDP-World Bank, 1992.
< 100 but usually < 20
< 70 but usually < 20
< 70 but usually < 20
< 20 but usually < 10
Many months
and nutrients are available, bacterial numbers may
increase 10- to 100-fold. However, such multiplica-
tion is usually limited by competition from other,
better-adapted organisms (Oliver, 2000).
Enteric bacteria are those associated with human
and animal wastes. Once the bacteria enter a soil,
they are subjected to life process stresses not
encountered in the host. In most nontropical
regions of the United States, temperatures are
typically much lower; the quantity and availability
of nutrients and energy sources are likely to be
appreciably lower; and pH, moisture, and oxygen
conditions are not as likely to be conducive to
long-term survival. Survival times of enteric
bacteria in the soil are generally reduced by higher
temperatures, lower nutrient and organic matter
content, acidic conditions (pH values of 3 to 5),
lower moisture conditions, and the presence of
indigenous soil microflora (Gerba et al., 1975).
Potentially pathogenic bacteria are eliminated faster
at high temperatures, pH values of about 7, low
oxygen content, and high dissolved organic sub-
stance content (Pekdeger, 1984). The rate of
bacterial die-off approximately doubles with each
10-degree increase of temperature between 5 and
30 °C (Tchobanoglous and Burton, 1991). Ob-
served survival rates for various potential patho-
genic bacteria have been found to be extremely
variable. Survival times of longer than 6 months
can occur at greater depths in unsaturated soils
where oligotrophic (low-nutrient) conditions exist
(Pekdeger, 1984).
The main methods of bacterial retention in unsatur-
ated soil are filtration, sedimentation, and adsorp-
tion (Bicki et al., 1984; Cantor and Knox, 1985;
Gerba et al., 1975). Filtration accounts for the most
retention. The sizes of bacteria range from 0.2 to 5
microns (um) (Pekdeger, 1984; Tchobanoglous and
Burton, 1991); thus, physical removal through
filtration occurs when soil micropores and surface
water film interstices are smaller than this. Filtra-
tion of bacteria is enhanced by slow permeability
rates, which can be caused by fine soil textures,
unsaturated conditions, uniform wastewater distri-
bution to soils, and periodic treatment system
resting. Adsorption of bacteria onto clay and
organic colloids occurs within a soil solution that
has high ionic strength and neutral to slightly acid
pH values (Canter and Knox, 1985).
Normal operation of septic tank/subsurface infiltra-
tion systems results in retention and die-off of
most, if not all, observed pathogenic bacterial
indicators within 2 to 3 feet (60 to 90 centimeters)
of the infiltrative surface (Anderson et al., 1994;
Ayres Associates, 1993a, c; Bouma et al., 1972;
McGauhey and Krone, 1967). With a mature
biomat at the infiltrative surface of coarser soils,
most bacteria are removed within the first 1 foot
(30 centimeters) vertically or horizontally from the
trench-soil interface (University of Wisconsin,
1978). Hydraulic loading rates of less than 2
inches/day (5 centimeters/day) have also been
found to promote better removal of bacteria in
septic tank effluent (Ziebell et al., 1975). Biomat
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Chapter 3: Establishing Treatment System Performance Requirements
formation and lower hydraulic loading rates
promote unsaturated flow, which is one key to soil-
based removal of bacteria from wastewater. The
retention behavior of actual pathogens in unsatur-
ated soil might be different from that of the
indicators (e.g., fecal coliforms) that have been
measured in most studies.
Failure to properly site, design, install, and/or
operate and maintain subsurface infiltration systems
can result in the introduction of potentially patho-
genic bacteria into ground water or surface waters.
Literature reviews prepared by Hagedorn (1982)
and Bicki et al. (1984) identify a number of
references that provide evidence that infiltrative
surfaces improperly constructed below the ground
water surface or too near fractured bedrock corre-
late with such contamination. Karst geology and
seasonally high water tables that rise into the
infiltrative field can also move bacteria into ground
water zones. Once in ground water, bacteria from
septic tank effluent have been observed to survive
for considerable lengths of time (7 hours to 63
days), and they can travel up to and beyond 100
feet (30 meters) (Gerba et al., 1975).
Viruses are not a normal part of the fecal flora.
They occur in infected persons, and they appear in
septic tank effluent intermittently, in varying
numbers, reflecting the combined infection and
carrier status of OWTS users (Berg, 1973). It is
estimated that less than 1 to 2 percent of the stools
excreted in the United States contain enteric viruses
(University of Wisconsin, 1978). Therefore, such
viruses are difficult to monitor and little is known
about their frequency of occurrence and rate of
survival in traditional septic tank systems. Once an
infection (clinical or subclinical) has occurred,
however, it is estimated that feces may contain 106
to 1010 viral particles per gram (Kowal, 1982).
Consequently, when enteric viruses are present in
septic tank effluent, they might be present in
significant numbers (Anderson et al., 1991; Hain
and O'Brien, 1979; Harkin et al., 1979; Vaughn
and Landry, 1977; Yeager and O'Brien, 1977).
Some reduction (less than 1 log) of virus concen-
trations in wastewater occurs in the septic tank.
Higgins et al. (2000) reported a 74 percent decrease in
MS2 coliphage densities, findings that concurs with
those of other studies (Payment et al., 1986; Roa,
1981). Viruses can be both retained and inactivated in
soil; however, they can also be retained but not
inactivated. If not inactivated, viruses can accumu-
late in soil and subsequently be released due to
changing conditions, such as prolonged peak
OWTS flows or heavy rains. The result could be
contamination of ground water. Soil factors that
decrease survival include warm temperatures, low
moisture content, and high organic content. Soil
factors that increase retention include small particle
size, high moisture content, low organic content,
and low pH. Sobsey (1983) presents a thorough
review of these factors. Virus removal below the
vadose zone might be negligible in some geologic
settings. (Cliver, 2000).
Most studies of the fate and transport of viruses in
soils have been columnar studies using a specific
serotype, typically poliovirus 1, or bacteriophages
(Bitton et al., 1979; Burge and Enkiri, 1978;
Drewry, 1969, 1973; Drewry and Eliassen, 1968;
Duboise et al., 1976; Goldsmith et al., 1973; Green
and Cliver, 1975; Hori et al., 1971; Lance et al.,
1976; Lance et al., 1982; Lance and Gerba, 1980;
Lefler and Kott, 1973, 1974; Nestor and Costin,
1971; Robeck et al., 1962; Schaub and Sorber, 1977;
Sobsey et al., 1980; Young and Burbank, 1973;
University of Wisconsin, 1978). The generalized
results of these studies indicate that adsorption is the
principal mechanism of virus retention in soil.
Increasing the ionic strength of the wastewater
enhances adsorption. Once viruses have been retained,
inactivation rates range from 30 to 40 percent per day.
Various investigations have monitored the transport
of viruses through unsaturated soil below the
infiltration surface has been monitored by (Ander-
son et al., 1991; Hain and O'Brien, 1979; Jansons
et al., 1989; Schaub and Sorber, 1977; Vaughn and
Landry, 1980; Vaughn et al., 1981; Vaughn et al.,
1982, 1983; Wellings et al., 1975). The majority of
these studies focused on indigenous viruses in the
wastewater and results were mixed. Some serotypes
were found to move more freely than others. In
most cases viruses were found to penetrate more
than 10 feet (3 meters) through unsaturated soils.
Viruses are less affected by filtration than bacteria
(Bechdol et al., 1994) and are more resistant than
bacteria to inactivation by disinfection (USEPA,
1990). Viruses have been known to persist in soil
for up to 125 days and travel in ground water for
distances of up to 1,339 feet (408 meters). How-
ever, monitoring of eight conventional individual
home septic tank systems in Florida indicated that
2 feet (60 centimeters) of fine sand effectively
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Chapter 3: Establishing Treatment System Performance Requirements
removed viruses (Anderson et al., 1991; Ayres
Associates, 1993c). Higgins (2000) reported 99
percent removal of virus particles within the first 1
foot (30.5 centimeters) of soil.
Recent laboratory and field studies of existing
onsite systems using conservative tracers (e.g.,
bromide ions) and microbial surrogate measures
(e.g., viruses, bacteria) found that episodic break-
throughs of virus and bacteria can occur in the
SWIS, particularly during early operation (Van
Cuyk et al., 2001). Significant (e.g., 3-log) removal
of viruses and near complete removal of fecal
bacteria can be reasonably achieved in 60 to 90
centimeters of sandy media (Van Cuyk et al., 2001).
Inactivation of pathogens through other physical,
chemical, or biological mechanisms varies consid-
erably. Protozoan cysts or oocysts are generally killed
when they freeze, but viruses are not. Ultraviolet
light, extremes of pH, and strong oxidizing agents
(e.g., hypochlorite, chlorine dioxide, ozone) are also
effective in killing or inactivating most pathogens
(Cliver, 2000). Korich (1990) found that in demand-
free water, ozone was slightly more effective than
chlorine dioxide against Cryptosporidium parvum
oocysts, and both were much more effective than
chlorine or monochloramine. C. parvum oocysts were
found to be 30 times more resistant to ozone and
14 times more resistant to chlorine dioxide than are
Giardia lamblia cysts (Korich et al., 1990).
Toxic organic compounds
A number of toxic organic compounds that can
cause neurological, developmental, or other
problems in humans and interfere with biological
processes in the environment can be found in septic
tank effluent. Table 3-22 provides information on
potential health effects from selected organic
chemicals, along with USEPA maximum contain-
ment levels for these pollutants in drinking water.
The toxic organics that have been found to be the
most prevalent in wastewater are 1,4-dichloroben-
zene, methylbenzene (toluene), dimethylbenzenes
(xylenes), 1,1-dichloroethane, 1,1,1-
trichloroethane, and dimethylketone (acetone).
These compounds are usually found in household
products like solvents and cleaners.
No known studies have been conducted to deter-
mine toxic organic treatment efficiency in single-
family home septic tanks. A study of toxic organics
in domestic wastewater and effluent from a com-
munity septic tank found that removal of low-
molecular-weight alkylated benzenes (e.g., toluene,
Table 3-22. Maximum contaminant levels (MCLs) for selected organic chemicals in drinking water
Contaminant
Benzene
Chlordane
Chlorobenzene
2,4-D
o-Dichlorobenzene
1 ,2-Dichloroethane
Dichloromethane
Dioxin
Ethylbenzene
Hexachlorobenzene
Lindane
Toluene
Trichloroethylene
Vinyl chloride
Xylenes (total)
MCL(mg/L)
0.005
0.002
0.1
0.07
0.6
0.005
0.005
0.00000003
0.7
0.001
0.0002
1.0
0.005
0.002
10
Potential health effects
Anemia; decrease in blood platelets; increased risk of cancer
Liver or nervous system problems; increased risk of cancer
Liver or kidney problems
Liver, kidney, or adrenal gland problems
Liver, kidney, or circulatory system problems
Increased risk of cancer
Liver problems, increased risk of cancer
Reproductive difficulties; increased risk of cancer
Liver or kidney problems
Liver or kidney problems; reproductive difficulties; increased risk of cancer
Liver or kidney problems
Nervous system, kidney, or liver problems
Liver problems; increased risk of cancer
Increased risk of cancer
Nervous system damage
Source: USEPA, 2000a.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 3: Establishing Treatment System Performance Requirements
xylene) was noticeable, whereas virtually no
removal was noted for higher-molecular-weight
compounds (DeWalle et al., 1985). Removal
efficiency was observed to be directly related to
tank detention time, which is directly related to
settling efficiency.
The behavior of toxic organic compounds in unsatur-
ated soil is not well documented. The avenues of
mobility available to toxic organics include those
which can transport organics in both gaseous and
liquid phases. In the gaseous phase toxic organics
diffuse outward in any direction within unobstructed
soil voids; in the liquid phase they follow the move-
ment of the soil solution. Because of their nonpolar
nature, certain toxic organics are not electrochemi-
cally retained in unsaturated soil. Toxic organics can
be transformed into less innocuous forms in the soil
by indigenous or introduced microorganisms. The
biodegradability of many organic compounds in the
soil depends on oxygen availability. Halogenated
straight-chain compounds, such as many chlori-
nated solvents, are usually biodegraded under
anaerobic conditions when carbon dioxide replaces
oxygen (Wilhelm, 1998). Aromatic organic com-
pounds like benzene and toluene, however, are
biodegraded primarily under aerobic conditions. As
for physical removal, organic contaminants are
adsorbed by solid organic matter. Accumulated
organic solids in the tank and in the soil profile,
therefore, might be important retainers of organic
contaminants. In addition, because many of the
organic contaminants found in domestic wastewater
are relatively volatile, unsaturated conditions in
drain fields likely facilitate the release of these
compounds through gaseous diffusion and volatil-
ization (Wilhelm, 1998).
Rates of movement for the gaseous and liquid
phases depend on soil and toxic organic compound
type. Soils having fine textures, abrupt interfaces
of distinctly different textural layers, a lack of
fissures and other continuous macropores, and low
moisture content retard toxic organic movement
(Hillel, 1989). If gaseous exchange between soil
and atmosphere is sufficient, however, appreciable
losses of low-molecular-weight alkylated benzenes
such as toluene and dimethylbenzene (xylene) can
be expected because of their relatively high vapor
pressure (Bauman, 1989). Toxic organics that are
relatively miscible in water (e.g., methyl tertiary
butyl ether, tetrachloroethane, benzene, xylene) can
be expected to move with soil water. Nonmiscible
toxic organics that remain in liquid or solid phases
(chlorinated solvents, gasoline, oils) can become
tightly bound to soil particles (Preslo et al., 1989).
Biodegradation appears to be an efficient removal
mechanism for many volatile organic compounds.
Nearly complete or complete removal of toxic
organics below infiltration systems was found in
several studies (Ayres Associates, 1993 a, c;
Robertson, 1991; Sauer and Tyler, 1991).
Some investigations have documented toxic organic
contamination of surficial aquifers by domestic
wastewater discharged from community infiltration
fields (Tomson et al., 1984). Of the volatile
organic compounds detected in ground water
samples collected in the vicinity of subsurface
infiltration systems, Kolega (1989) found trichlo-
romethane, toluene, and 1,1,1-trichloroethane most
frequently and in some of the highest concentra-
tions. Xylenes, dichloroethane, and dichloro-
methane were also detected.
Table 3-23. Case study: concentration of metals in septic tank effluent3
Metal constituent
Mean concentration (ug/L)
Range (uxj/L)
Arsenic
Barium
Cadmium
Chromium
Lead
Mercury
Nickel
Selenium
37(5)b
890 (5)
83(7)
320 (7)
2700(1)
2(2)
4000(1)
15(6)
6-59
400-1310
30-330
60-1400
1-3
3-39
" Samples collected from the outlet of nine septic tanks.
b Number In parentheses indicates number of septic tanks In which metals were detected.
Source: Florida MRS, 1993, after Watkins, 1991.
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Once toxic organics reach an aquifer, their move-
ment generally follows the direction of ground
water movement. The behavior of each within an
aquifer, however, can be different. Some stay near the
surface of the aquifer and experience much lateral
movement. Others, such as aliphatic chlorinated
hydrocarbons, experience greater vertical movement
because of their heavier molecular weight (Dagan and
Bresler, 1984). Based on this observation, 1,4-
dichlorobenzene, toluene, and xylenes in septic tank
effluent would be expected to experience more lateral
than vertical movement in an aquifer; 1,1-dichloro-
ethane, 1,1,1-trichloroethane, dichloromethane, and
trichloromethane would be expected to show more
vertical movement. Movement of toxic organic
compounds is also affected by their degree of solubil-
ity in water. Acetone, dichloromethane, trichloro-
methane, and 1,1-dichloroethane are quite soluble in
water and are expected to be very highly mobile;
1,1,1-trichloroethane, toluene, and 1,2-dimethyl-
benzene (o-xylene) are expected to be moderately
mobile; and 1,3-dimethylbenzene (m-xylene), 1,4-
dimethylbenzene (p-xylene), and 1,4-dichlorobenzene
are expected to have low mobility (Fetter, 1988).
System design considerations for removing toxic
organic compounds include increasing tank reten-
tion time (especially for halogenated, straight-chain
compounds like organic solvents), ensuring greater
vadose zone depths below the SWIS, and placing
the infiltration system high in the soil profile,
where higher concentrations of organic matter and
oxygen can aid the volatilization and treatment of
aromatic compounds. It should be noted that
significantly high levels of toxic organic compounds
can cause die-off of tank and biomat microorgan-
isms, which could reduce treatment performance.
Onsite systems that discharge high amounts of toxic
organic compounds might be subject to USEPA's
Class V Underground Injection Control Program
(see http://www.epa.gov/safewater.uic.html).
Metals
Metals like lead, mercury, cadmium, copper, and
chromium can cause physical and mental develop-
mental delays, kidney disease, gastrointestinal
illnesses, and neurological problems. Some informa-
tion is available regarding metals in septic tank
effluent (DeWalle et. al. 1985). Metals can be
present in raw household wastewater because many
commonly used household products contain metals.
Aging interior plumbing systems can contribute
lead, cadmium, and copper (Canter and Knox,
1985). Other sources of metals include vegetable
matter and human excreta. Several metals have been
found in domestic septage, confirming their presence
in wastewater. They primarily include cadmium,
copper, lead, and zinc (Bennett et al., 1977; Feige et
al., 1975; Segall et al., 1979). OWTSs serving
nonresidential facilities (e.g., rural health care
facilities, small industrial facilities) can also experi-
ence metal loadings. Several USEPA priority
pollutant metals have been found in domestic septic
tank effluent (Whelan and Titmanis, 1982). The
most prominent metals were nickel, lead, copper,
Table 3-24. Maximum contaminant levels (MCLs) for selected inorganic chemicals in drinking water
Contaminant
Arsenic
Cadmium
Chromium
Copper
Lead
Inorganic mercury
Nitrate-nitrogen
Nitrite-nitrogen
Selenium
MCL (mg/L)
0.051
0.005
0.1
1.3 (action level)
0.01 5 (action level)
0.002
10.0
1.0
0.05
Potential health effects
Increase in blood cholesterol; decrease in blood glucose
Kidney damage
Possible allergic dermatitis after long exposures
Gastrointestinal distress with short-term exposure; liver or kidney damage possible with
long-term exposure
Physical and mental developmental delays in children; kidney problems, high blood
pressure for adults
Kidney damage
Methemoglobinemia (blue baby syndrome)
Methemoglobinemia (blue baby syndrome)
Hair or fingernail loss; numbness in fingers or toes; circulatory problems
1 The MCL for arsenic is currently under review by USEPA.
Source: USEPA, 2000a.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 3: Establishing Treatment System Performance Requirements
zinc, barium, and chromium. A comparison of
mean concentrations of metals in septic tank
effluent as found in one study (table 3-23) with the
USEPA maximum contaminant levels for drinking
water noted in table 3-24 reveals a potential for
contamination that might exceed drinking water
standards in some cases.
The fate of metals in soil is dependent on complex
physical, chemical, and biochemical reactions and
interactions. The primary processes controlling the
fixation/mobility potential of metals in subsurface
infiltration systems are adsorption on soil particles
and interaction with organic molecules. Because the
amount of naturally occurring organic matter in the
soil below the infiltrative surface is typically low,
the cation exchange capacity of the soil and soil
solution pH control the mobility of metals below
the infiltrative surface. Acidic conditions can
reduce the sorption of metals in soils, leading to
increased risk of ground water contamination
(Evanko, 1997; Lim et al., 2001). (See figure 3-11.)
It is likely that movement of metals through the
unsaturated zone, if it occurs at all, is accomplished
by movement of organic ligand complexes formed at
or near the infiltrative surface (Canter and Knox,
1985; Matthess, 1984).
Information regarding the transport and fate of
metals in ground water can be found in hazardous
waste and soil remediation literature (see http://
www.gwrtac.org/html/Tech_eval.html#METALS).
One study attempted to link septic tank systems to
Figure 3-11. Zinc sorption by clay as a function of pH at various
loading concentrations (in 0.05 M NaCI medium)
100
80
•B 60
Q_
20
Zn Loading
(mol/kg soil)
-•- 200
-H- 100
-•- 60
-e- 40
-A- 20
-*- 10
-e- s
-•- 3
2 3
Source: Lim etal., 2001.
5
PH
6
8
metal contamination of rural potable water supplies,
but only a weak correlation was found (Sandhu et
al., 1977). Removal of sources of metals from the
wastewater stream by altering user habits and
implementing alternative disposal practices is
recommended. In addition, the literature suggests
that improving treatment processes by increasing
septic tank detention times, ensuring greater
unsaturated soil depths, and improving dose and
rest cycles may decrease risks associated with metal
loadings from onsite systems (Chang, 1985;
Evanko, 1997; Lim et al., 2001).
Surfactants
Surfactants are commonly used in laundry detergents
and other soaps to decrease the surface tension of
water and increase wetting and emulsification.
Surfactants are the largest class of anthropogenic
organic compounds present in raw domestic waste-
water (Dental et al., 1993). Surfactants that survive
treatment processes in the septic tank and subse-
quent treatment train can enter the soil and mobi-
lize otherwise insoluble organic pollutants. Surfac-
tants have been shown to decrease adsorption — and
even actively desorb — the pollutant trichlorobenzene
from soils (Dental, 1993). Surfactants can also change
soil structure and alter wastewater infiltration rates.
Surfactant molecules contain both strongly hydro-
phobic and strongly hydrophilic properties and thus
tend to concentrate at interfaces of the aqueous
system including air, oily material, and particles.
Surfactants can be found in most domestic septic tank
effluents. Since 1970 the most common anionic
surfactant used in household laundry detergent is
linear alkylbenzenesulfonate, or LAS. Whelan and
Titmanis (1982) found a range of LAS concentra-
tions from 1.2 to 6.5 mg/L in septic tank effluent.
Dental (1993) cited studies finding concentra-
tions of LAS in raw wastewater ranging from
3 mg/L to 21 mg/L.
Because surfactants in wastewater are associated
with particulate matter and oils and tend to concen-
trate in sludges in wastewater treatment plants
(Dental, 1993), increasing detention times in the
tank might aid in their removal. The behavior of
surfactants in unsaturated soil is dependent on
surfactant type. It is expected that minimal retention
of anionic and nonionic surfactants occurs in unsatur-
ated soils having low organic matter content. How-
ever, the degree of mobility is subject to soil
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Chapter 3: Establishing Treatment System Performance Requirements
solution chemistry, organic matter content of the
soil, and rate of degradation by soil microorganisms.
Soils with high organic matter should favor
retention of surfactants because of the lipophilic
component of surfactants. Surfactants are readily
biodegraded under aerobic conditions and are more
stable under anaerobic conditions. Substantial attenua-
tion of LAS in unsaturated soil beneath a subsurface
infiltration system has been demonstrated (Anderson
et al., 1994; Robertson et al., 1989; Shimp et al.,
1991). Cationic surfactants strongly sorb to cation
exchange sites of soil particles and organic matter
(McAvoy et al., 1991). Thus, fine-textured soils and
soils having high organic matter content will gener-
ally favor retention of these surfactants.
Some investigations have identified the occurrence
of methylene blue active substance (MBAS) in
ground water (Perlmutter and Koch, 1971; Thurman
et al., 1986). The type of anionic surfactant was not
specifically identified. However, it was surmised
that the higher concentrations noted at the time of
the study were probably due to use of alkyl-
benzenesulfonate (ABS), which is degraded by
microorganisms at a much slower rate than LAS.
There has also been research demonstrating that all
types of surfactants might be degraded by microor-
ganisms in saturated sediments (Federle and
Pastwa, 1988). No investigations have been found
that identify cationic or nonionic surfactants in
ground water that originated from subsurface
wastewater infiltration systems. However, because
of concerns over the use of alkylphenol
polyethoxylates, studies of fate and transport of this
class of endocrine disrupters are in progress.
Summary
Subsurface wastewater infiltration systems are
designed to provide wastewater treatment and
dispersal through soil purification processes and
ground water recharge. Satisfactory performance is
dependent on the treatment efficiency of the
pretreatment system, the method of wastewater
distribution and loading to the soil infiltrative
surface, and the properties of the vadose and
saturated zones underlying the infiltrative surface.
The soil should have adequate pore characteristics,
size distribution, and continuity to accept the daily
volume of wastewater and provide sufficient soil-
water contact and retention time for treatment before
the effluent percolates into the ground water.
Ground water monitoring below properly sited,
designed, constructed, and operated subsurface
infiltration systems has shown carbonaceous
biochemical oxygen demand (CBOD), suspended
solids (TSS), fecal indicators, metals, and surfactants
can be effectively removed by the first 2 to 5 feet
of soil under unsaturated, aerobic conditions.
Phosphorus and metals can be removed through
adsorption, ion exchange, and precipitation reac-
tions, but the capacity of soil to retain these ions is
finite and varies with soil mineralogy, organic
content, pH, reduction-oxidation potential, and
cation exchange capacity. Nitrogen removal rates
vary significantly, but most conventional SWISs do
not achieve drinking water standards (i.e., 10 mg/L)
for nitrate concentrations in effluent plumes.
Evidence is growing that some types of viruses are
able to leach with wastewater from subsurface
infiltration systems to ground water. Longer
retention times associated with virus removal are
achieved with fine-texture soil, low hydraulic
loadings, uniform dosing and resting, aerobic sub-
soils, and high temperatures. Toxic organics appear
to be removed in subsoils, but further study of the
fate and transport of these compounds is needed.
Subsurface wastewater infiltration systems do
affect ground water quality and therefore have the
potential to affect surface water quality (in areas
with gaining streams, large macropore soils, or
karst terrain or in coastal regions). Studies have
shown that after the treated percolate enters ground
water it can remain as a distinct plume for as much
as several hundred feet. Concentrations of nitrate,
dissolved solids, and other soluble contaminants
can remain above ambient ground water concentra-
tions within the plume. Attenuation of solute
concentrations is dependent on the quantity of
natural recharge and travel distance from the
source, among other factors. Organic bottom
sediments of surface waters appear to provide some
retention or removal of wastewater contaminants if
the ground water seeps through those sediments to
enter the surface water. These bottom sediments
might be effective in removing trace organic
compounds, endotoxins, nitrate, and pathogenic
agents through biochemical activity, but few data
regarding the effectiveness and significance of
removal by bottom sediments are available.
Public health and environmental risks from prop-
erly sited, designed, constructed, and operated
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 3: Establishing Treatment System Performance Requirements
septic tank systems appear to be low. However.
soils with excessive permeability (coarse-texture
soil or soil with large and continuous pores), low
organic matter, low pH, low cation exchange
capacities, low oxygen-reduction potential, high
moisture content, and low temperatures can in-
crease health and environmental risks under certain
circumstances.
3.8 Establishing performance
requirements
As noted in chapter 2, the OWTS regulatory
authority and/or management entity establishes
performance requirements to ensure future compli-
ance with the public health and environmental
objectives of the community. Performance require-
ments are based on broad goals such as eliminating
health threats from contact with effluent or direct/
indirect ingestion of effluent contaminants. They are
intended to meet standards for water quality and
public health protection and can be both quantita-
tive (total mass load or concentration) or qualita-
tive (e.g., no odors or color in discharges to surface
waters). Compliance with performance requirements
is measured at a specified performance boundary (see
chapter 5), which can be a physical boundary or a
property boundary. Figure 3-12 illustrates perfor-
mance and compliance boundaries and potential
monitoring sites in a cutaway view of a SWIS.
Figure 3-12. Example of compliance boundaries for onsite
wastewater treatment systems
Compliance
Boundary
_ • '. -.' • ' -V .; l.-;:;. .• . :.•';. .-•;;/•.' ;:-ife ^^
:^!#i^l^^^^
t• ,--.'.•»£;• :o• • .:•!?•"Ai.-Sf-•*•• ,s•:*vr:-.r-:- *
Design boundaries are where conditions abruptly
change. A design boundary can be at the intersection
of unit processes or between saturated and unsaturated
soil conditions (e.g., the delineation between the
infiltrative, vadose, and ground water zones) or at
another designated location, such as a drinking water
well, nearby surface water, or property boundary.
Performance requirements for onsite treatment
systems should be established based on water
quality standards for the receiving resource and the
assimilative capacity of the environment between
the point of the wastewater release to the receiving
environment and the performance boundary
designated by the management entity or regulatory
authority. Typically, the assimilative capacity of the
receiving environment is considered part of the
treatment system to limit costs in reaching the desired
performance requirement or water quality goals (see
figure 3-12). The performance boundary is usually a
specified distance from the point of release, such as a
property boundary, or a point of use, such as a
drinking water well or surface water with desig-
nated uses specified by the state water agency.
Achievement of water quality objectives requires
that treatment system performance consider the
assimilative capacity of the receiving environment.
If the assimilative capacity of the receiving envi-
ronment is overlooked because of increases in
pollutant loadings, the treatment performance of
onsite systems before discharge to the soil should
increase. OWTSs serving high-density clusters of
homes or located near sensitive receiving waters
might be the subject of more stringent requirements
than those serving lower-density housing farther
from sensitive water resources.
Performance requirements for onsite systems
should be based on risk assessments that consider
the hazards of each potential pollutant in the
wastewater to be treated, its transport and fate,
potential exposure opportunities, and projected
effects on humans and environmental resources. A
variety of governmental agencies have already
established water quality standards for a wide range
of surface water uses. These include standards for
protecting waters used for recreation, aquatic life
support, shellfish propagation and habitat, and
drinking water. In general, these standards are
based on risk assessment processes and procedures
that consider the designated uses of receiving
waters, the hazard and toxicity of the pollutants,
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Nitrogen contributions from onsite systems
The San Lorenzo River basin in California is served primarily by onsite wastewatertreatment systems. Since
1985 the Santa Cruz County Environmental Health Service has been working with local stakeholders to develop a
program for inspecting all onsite systems, assessing pollutant loads from those systems, and correcting identified
problems. Studies conducted through this initiative included calculations of nutrient inputs to the river from onsite
systems. According to the analyses performed by the county and its contractors, 55 to 60 percent of the nitrate
load in the San Lorenzo River during the summer months came from onsite system effluent. Assumptions
incorporated into the calculations included an average septic tank effluent total nitrogen concentration of 50 mg/L,
per capita wastewater generation of 70 gallons per day, and an average house occupancy of 2.8 persons. Nitrogen
removal was estimated at 15 percent for SWISs in sandy soils and 25 percent for SWISs in other soils.
Source: Ricker et al., 1994.
Performance requirements of Wisconsin's ground water quality rule
Wisconsin was one of the first states to promulgate ground water standards. Promulgated in 1985, Wisconsin's
ground water quality rule establishes both public health and public welfare ground water quality standards for
substances detected in or having a reasonable probability of entering the ground water resources of the state.
Preventive action and enforcement limits are established for each parameter included in the rule. The preventive
action limits (PALs) inform the Department of Natural Resources (DNR) of potential threats to ground water quality.
When a PAL is exceeded, the Department is required to take action to control the contamination so that the
enforcement limit is not reached. For example, nitrate-nitrogen is regulated through a public health standard. The
PAL for nitrate is 2 mg/L (nitrogen), and its enforcement limit is 10 mg/L (nitrogen). If the PAL is exceeded, the
DNR requires a specific control response based on an assessment of the cause and significance of the elevated
concentration. Various responses may be required, including no action, increased monitoring, revision of
operational procedures at the facility, remedial action, closure, or other appropriate actions that will prevent further
ground water contamination.
Source: State of Wisconsin Administrative Code, Chapter NR 140.
the potential for human and ecosystem exposure,
and the estimated impacts of exposure. Although
federally mandated ground water quality standards
(maximum contaminant levels; see tables in section
3.8) are currently applicable only to drinking water
supply sources, some states have adopted similar
local ground water quality standards (see sidebar).
Local needs or goals need to be considered when
performance requirements are established. Water-
shed- or site-specific conditions might warrant
lower pollutant discharge concentrations or mass
pollutant limits than those required by existing
water quality standards. However, existing water
quality standards provide a good starting point for
selecting appropriate OWTS performance require-
ments. The mass of pollutants that should be
removed by onsite treatment systems can be
determined by estimating the mass of cumulative
OWTS pollutants discharged to the receiving
waters and calculating the assimilative capacity of
the receiving waters. Mass pollutant loads are
usually apportioned among the onsite systems and
other loading sources (e.g., urban yards and
landscaped areas, row crop lands, animal feeding
operations) in a ground water aquifer or watershed.
3.8.1 Assessing resource vulnerability
and receiving water capacity
Historically, conventional onsite systems have been
designed primarily to protect human health. Land
use planning has affected system oversight require-
ments, but environmental protection has been a
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Chapter 3: Establishing Treatment System Performance Requirements
Massachusetts' requirements for nitrogen-sensitive areas
Nitrogen-sensitive areas are defined in state rules as occurring within Interim Wellhead Protection Areas, 1-year
recharge areas of public water supplies, nitrogen-sensitive embayments, and other areas that are designated as
nitrogen-sensitive based on scientific evaluations of the affected water body (310 Code of Massachusetts
Regulations 15.000,1996). Any new construction using onsite wastewatertreatment in these designated areas
must abide by prescriptive standards that limit design flows to a maximum of 440 gallons per day of aggregated
flows per acre. Exceptions are permitted for treatment systems with enhanced nitrogen removal capability. With
enhanced removal, the maximum design flow may be increased. If the system is an approved alternative system
or a treatment unit with a ground water discharge permit that produces an effluent with no more than 10 mg/L of
nitrate, the design flow restrictions do not apply.
Source: Title V, Massachusetts Environmental Code.
tertiary objective, at best, for most regulatory
programs. Human health protection is assumed (but
not always ensured) by infiltrating septic tank
effluent at sufficiently low rates into moderately
permeable, unsaturated soils downgradient and at
specified distances from water supply wells. Site
evaluations are performed to assess the suitability
of proposed locations for the installation of conven-
tional systems. Criteria typically used are estimated
soil permeability (through soil analysis or percola-
tion tests), unsaturated soil depth above the season-
ally high water table, and horizontal setback
distances from wells, property lines, and dwellings
(see chapter 5).
OWTS codes have not normally considered in-
creased pollutant loads to a ground water resource
(aquifer) due to higher housing densities, potential
contamination of water supplies by nitrates, or the
environmental impacts of nutrients and pathogens
on nearby surface waters. Preserving and protecting
water quality require more comprehensive evalua-
tions of development sites proposed to be served by
onsite systems. A broader range of water contami-
nants and their potential mobility in the environ-
ment should be considered at scales that consider
both spatial (site vs. region) and temporal (existing
vs. planned development) issues (see tables 3-20 to
3-24). Some watershed analyses are driven by
TMDLs (Total Maximum Daily Loads established
under section 303 of the Clean Water Act) for
interconnected surface waters, while others are
driven by sole source aquifer or drinking water
standards.
Site suitability assessments
Some states have incorporated stricter site suitabil-
ity and performance requirements into their OWTS
permit programs. Generally, the stricter require-
ments were established in response to concerns over
nitrate contamination of water supplies or nutrient
inputs to surface waters. For example, in Massa-
chusetts the Department of Environmental Protec-
tion has designated "nitrogen-sensitive areas" in
which new nitrogen discharges must be limited.
Designation of these areas is based on ecological
sensitivity and relative risk of threats to drinking
water wells.
Multivariate rating approaches: DRASTIC
Other approaches are used that typically involve
regional assessments that inventory surface and
ground water resources and rate them according to
their sensitivity to wastewater impacts. The ratings
are based on various criteria that define vulnerabil-
ity. One such method is DRASTIC (see sidebar).
DRASTIC is a standardized system developed by
USEPA to rate broad-scale ground water vulner-
ability using hydrogeologic settings (Aller et al.,
1987). The acronym identifies the hydrogeologic
factors considered: depth to ground water, (net)
recharge, aquifer media, soil media, topography
(slope), impact of the vadose zone media, and
(hydraulic) conductivity of the aquifer. This
method is well suited to geographic information
system (GIS) applications but requires substantial
amounts of information regarding the natural
resources of a region to produce meaningful
results. Landscape scale methods and models are
excellent planning tools but might have limited
utility at the site scale. These approaches should be
3-42
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Chapter 3: Establishing Treatment System Performance Requirements
Using GIS tools to characterize potential water quality threats in Colorado
Summit County, Colorado, developed a GIS to identify impacts that OWTS-generated nitrates might have on
water quality in the upper Blue River watershed. The GIS was developed in response to concerns that increasing
residential development in the basin might increase nutrient loadings into the Dillon Reservoir. Database
components entered into the GIS included geologic maps, soil survey maps, topographic features, land parcel
maps, domestic well sampling data, onsite system permitting data, well logs, and assessors'data. The database
can be updated with new water quality data, system maintenance records, property records, and onsite system
construction permit and repair information. The database is linked to the DRASTIC ground water vulnerability
rating. The approach is being used to identify areas that have a potential for excessive contamination by nitrate-
nitrogen from OWTSs. These assessments could support onsite system placement and removal decisions and
help prioritize water quality improvement projects.
Source: Stark et al., 1999.
supported and complemented by other information
collected during the site evaluation (see chapter 5).
GIS overlay analysis: MANAGE
A simpler GIS-based method was developed by the
University of Rhode Island Cooperative Extension
Service (see http://www.edc.uri.edu/cewq/
manage.html). The Method for Assessment,
Nutrient-loading, and Geographic Evaluation
(MANAGE) uses a combination of map analyses
that incorporates landscape features, computer-
generated GIS and other maps, and a spreadsheet to
estimate relative pollution risks of proposed land
uses (Joubert et al., 1999; Kellogg et al., 1997).
MANAGE is a screening-level tool designed for
areawide assessment of entire aquifers, wellhead
protection areas, or small watersheds (figure 3-13).
Local knowledge and input are needed to identify
critical resource areas, refine the map data, and
select management options for analysis. Commu-
nity decision makers participate actively in the
assessment process (see sidebar).
The spreadsheet from the MANAGE application
extracts spatial and attribute data from the national
Soil Survey Geographic (SSURGO) database
(USDA, 1995; see http://www.ftw.nrcs.usda.gov/
ssur_data.html) and Anderson Level III Land
Cover data (Anderson, 1976) through the Rhode
Island GIS system. The soils are combined into
hydrologic groups representing the capability of the
soils to accept water infiltration, the depth to the
water table, and the presence of hydraulically
restrictive horizons. Estimates of nutrient loadings
are made using published data and simplifying
assumptions. The spreadsheet estimates relative
pollutant availability, surface water runoff pollutant
concentrations, and pollutant migration to ground
water zones without attempting to model fate and
transport mechanisms, which are highly uncertain.
From these data the spreadsheet calculates a
hydrologic budget, estimates nutrient loading, and
summarizes indicators of watershed health to create
a comprehensive risk assessment for wastewater
management planning. (For mapping products
available from the U.S. Geological Survey, see
http://www.nmd.usgs.gov/.)
MANAGE generates three types of assessment
results that can be displayed in both map and chart
form: (1) pollution "hot spot" mapping of potential
high-risk areas, (2) watershed indicators based on
land use characteristics (e.g., percent of impervious
area and forest cover), and (3) nutrient loading in
the watershed based on estimates from current
research of sources, and generally assumed fates of
nitrogen and phosphorus (Joubert et al., 1999).
It is important to note that before rules, ordinances,
or overlay zones based on models are enacted or
established, the models should be calibrated and
verified with local monitoring information col-
lected over a year or more. Only models that
accurately and consistently approximate actual
event-response relationships should serve as the
basis for management action. Also, the affected
population must accept the model as the basis for
both compliance and possible penalties.
Value analysis and vulnerability assessment
Hoover et al. (1998) has proposed a more subjec-
tive vulnerability assessment method that empha-
sizes public input. This approach considers risk
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Chapter 3: Establishing Treatment System Performance Requirements
assessment methods and management control
strategies for both ground waters and surface
waters. It uses three components of risk assessment
and management, including consideration of
• Value of ground and surface water as a public
water supply or resource
• Vulnerability of the water supply or resource
• Control measures for addressing hazards
The first part of the onsite risk assessment and
management approach involves a listing of all the
ground water and surface water resources in a
region or community (table 3-26). Through
community meetings consensus is developed on the
relative perceived value of each identified resource
and the potential perceived consequences of
contamination. For example, a community might
determine that shellfish waters that are open to
public harvesting are less important than public
drinking water supply areas but more important
than secondary recreational waters that might be
used for body contact sports. This ranking is used
to create a table that shows the relative importance
of each resource (table 3-26 and case study).
The second part of this risk assessment process is
development of a vulnerability assessment matrix.
One potential measure of pollution vulnerability is
the ability of pollutants to move vertically from the
point of release to the water table or bedrock.
Figure 3-13. Input and output components of the MANAGE assessment method
Rhode Island Geographic
Information System
(RIGIS) Input:
Land Use - 22 Categories
Soils - 4 Groups
Sewer Lines
Streams and Ponds
Watershed/Groundwater
boundary
Other GIS Layers:
• Roads
• Town Boundaries
. Villages
. DEM Natural Heritage
Areas
• EPA Resource Protection
Project
• Industrial Zoning
• Digital Ortho-Photo Quads
• USGS Topographic Quads
. 1990 US Census Block
Data
Supporting Data:
. Watershed Studies
• Monitoring Data
Applying MANAGE
Step by Step
Update land use or re-run
with future land use map
• Display Maps
Hot-Spot Analysis
• Nutrient Loading
Watershed Indicate
Re-run spreadsheet with
alternative best
management practices or
minor land use changes
Final Products:
•Maps
•Reports
•Presentations
•Factsheets
University of Rhode Island Cooperative Extension
MANAGE Watershed Assessment Method, 11/1998
Source: Kellogg etal., 1997.
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Chapter 3: Establishing Treatment System Performance Requirements
Application of the MANAGE tool to establish performance requirements
The town of New Shoreham, Rhode Island, is a popular vacation resort on a 6,400-acre island 10 miles off the southern coast of the state.
The permanent population is approximately 800, but during the summer the population swells to as many as 10,000 overnight visitors and
another 3,000 daily tourists. Proper wastewater management is a serious concern on the island. A publicly owned treatment works serves
the town's harbor/commercial/business district, but 85 percent of the permanent residents and 54 percent of the summer population are
served by OWTSs, many of which ultimately discharge to the island's sole source aquifer. Protection of this critical water resource is vital to
the island's residents and tourism-based economy.
The University of Rhode Island (URI) Cooperative Extension Service's MANAGE risk analysis model was used to identify potential sources
of ground water contamination (Kellogg et al., 1997). The model was also used to analyze potential ground water impacts at build-out
assuming current zoning. This projection was used to compare the relative change in pollution risk under future development scenarios
including the use of alternative technologies that provide better removal of nitrogen and pathogens. Onsite treatment systems were
estimated to contribute approximately 72 percent of the nitrogen entering ground water recharge areas. The model indicated that nitrogen
removal treatment technologies could effectively maintain nitrogen inputs at close to existing levels even with continued growth. It also
showed that nitrogen removal technologies were not necessary throughout the island but would be most beneficial in "hot spots" where the
risk of system failure and pollutant delivery to sensitive areas was the greatest.
The town adopted a wastewater management ordinance that mandated regular inspections of onsite systems by a town inspector (Town of
New Shoreham, 1996,1998). It also established septic tank pumping schedules and other maintenance requirements based on inspection
results. Inspection schedules have the highest priority in public drinking water supply reservoirs, community wellhead protection zones, and
"hot spots" such as wetland buffers. Because the town expected to uncover failed and substandard systems, zoning standards were
developed for conventional and alternative OWTS technologies to ensure that new and reconstructed systems would be appropriate for
difficult sites and critical resource areas (Town of New Shoreham, 1998). A type of site vulnerability matrix was developed in cooperation
with URI Cooperative Extension using key site characteristics—depth to seasonally high water table, presence of restrictive layers, and
excessively permeable soils (Loomis et al., 1999). The matrix was used to create a vulnerability rating that is used to establish the level of
treatment needed to protect water quality in that watershed or critical resource area.
Three treatment levels were established: T1, primary treatment with watertight septic tanks and effluent screens; T2N, nitrogen removal
required to meet < 19 mg/L; and T2C, fecal coliform removal < 1,000 MPN/100 ml (table 3-25). The town provides a list of specific state-
approved treatment technologies considered capable of meeting these standards. By the year 2005, cesspools and failing systems must be
upgraded to specified standards. In addition, all septic tanks must be retrofitted with tank access risers and effluent screens.
Source: Loomis et al., 1999.
Table 3-25. Treatment performance requirements for New Shoreham, Rhode Island
Treatment
level zone
Tested &
certified water-
tight septic tank
Water-tight
access risers
to grade
Effluent filter
& tipping
D-box
Effluent BOD
&TSS
(mg/L)
TN removal
percent
TN effluent
{mg/L)
Fecal conforms
(CPUs per
100 ml)
T1
T2NC :
T2C°
'a s ^ NSb
s v =d <30e
= ^d <10
NS
>50
NS
NS
<19
NS
NS
NS
<1000
"Required by town ordinance.
"NS = not specified by town ordinance.
'Shallow pressure-dosed drain fields may be required when soil suitability rating is poor, when site vulnerability rating is high to extreme,
or when the proposed system is in a wetland buffer, or where other constraints exist.
"Required if feasible.
"All concentrations and reductions are determined and measured at the outlet of the treatment unit prior to discharge to a drain field.
Source: Adapted from Loomis, 2000.
USEPA Onsite Wastewater Treatment Systems Manual
3-45
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Chapter 3: Establishing Treatment System Performance Requirements
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Chapter 3: Establishing Treatment System Performance Requirements
Resource value ranking and wastewater management
A northern U.S. unsewered coastal community was concerned about the impacts onsite treatment systems might
have on its ground water resources (Hoover et al., 1998). Public water in the community is derived exclusively
from ground water. The extended recharge zone for the community well fields is also a water supply source in the
community. Other resources in the community include regionally important sand and gravel glacial outwash
aquifers, public beaches, shellfish habitat in shallow surface waters, nutrient-sensitive surface waters, low-yield
glacial till aquifers, and other surface waters used as secondary recreational waters.
Through public meetings, the community identified and ranked the various water resources according to their
perceived value. After ranking, the vulnerability of each resource to pollution from onsite treatment systems was
estimated. The vulnerability ratings were based on the thickness of the unsaturated zone in the soil, the rate of
water movement through the soil, and the capability of the soil to attenuate pollutants (table 3-25). For each
rating, a control zone designation was assigned (R5, R4, R3, R2, orR1).The criteria used forthe vulnerability
ratings were documented in the community's wastewater management plan. Control measures were established
for each control zone. In this instance, specific wastewater treatment trains were prescribed for use in each
control zone based on the depth of the unsaturated soil zone (tables 3-26 and 3-27). The treatment standards are
TS1 = primary treatment, TS2 = secondary treatment, TS3 = tertiary treatment, TS4 = nutrient reduction, and TS5
= tertiary treatment with disinfection.
Important criteria considered include the thickness
of the unsaturated soil layer and the properties of
the soil. The vulnerability assessment matrix
(table 3-26) identifies areas of low, moderate, high,
or extreme vulnerability depending on soil conditions.
For example, vulnerability might be "extreme" for
coarse or sandy soils with less than 2 feet of
vertical separation between the ground surface and
the water table or bedrock. Vulnerability might be
"low" for clay-loam soils with a vertical separation
of greater than 6 feet and low permeability. Each
resource specified in the first part of the risk
assessment process can be associated with each
vulnerability category. A more detailed discussion
of ground water vulnerability assessment is provided
in Groundwater Vulnerability Assessment Predicting
Relative Contamination Potential under Conditions
of Uncertainty (National Research Council, 1993).
The third and final part of the risk assessment
process is developing a management matrix that
specifies a control measure for each vulnerability
category relative to each resource (tables 3-27,
3-28). Several categories of management control
measures (e.g., stricter performance requirements
for OWTSs) might be referenced depending on the
value and vulnerability of the resource. Generally,
each management control measure would define
• Management entity requirements for each
control measure
• System performance and resource impact
monitoring requirements for each vulnerable
category
• Types of acceptable control measures based on
the vulnerability and value of the resource
• Siting flexibility allowed for each control
measure
• Performance monitoring requirements for each
control measure and vulnerability category
Probability of impact approach
Otis (1999) has proposed a simplified "probability
of environmental impact" approach. This method
was developed for use when resource data are
insufficient and mapping data are unavailable for
a more rigorous assessment. The approach is
presented in the form of a decision tree that
considers mass loadings to the receiving environ-
ment (ground water or surface water), population
density, and the fate and transport of potential
pollutants to a point of use (see following case
study and figure 3-14). The decision tree (figure
3-14) estimates the relative probability of water
resource impacts from wastewater discharges
generated by sources in the watershed. Depending
on the existing or expected use of the water
resource, discharge standards for the treatment
systems can be established. The system designer
can use these discharge standards to assemble an
appropriate treatment train.
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Chapter 3: Establishing Treatment System Performance Requirements
Table 3-27. Proposed onsite system treatment performance standards in various control zones
Standard
TS1 - primary treatment
TS1u-unfiltered
TS1f- filtered
TS2 - secondary treatment
TSS - tertiary treatment
TS4 - nutrient reduction
TS4n - nitrogen reduction
TS4p - phosphorus reduction
TS4np - N & P reduction
TSS - bodily contact disinfection
TS6 - wastewater reuse
TS7- near drinking water
BOD
(mg/L)
300
200
30
10
10
10
10
10
5
5
TSS
(mg/L)
300
80
30
10
10
10
10
10
5
5
P04-P
(mg/L)
15
15
15
15
15
2
2
15
15
1
NH4-N
(mg/L)
80
80
10
10
5
10
5
10
5
5
N03-N
(mg/L)
NA
NA
NA
NA
NA
NA
NA
NA
NA
10
Total N
(% removed)'
NA
NA
NA
NA
50%
25%
50%
25%
50%
75%
Fecal conforms
(CFU/1000mL)
10,000,000
10,000,000
50,000
10,000
10,000
10,000
10,000
200
14
<1b
NA = not available.
' Minimum percentage reduction of total nitrogen (as nitrate -nitrogen plus ammonium nitrogen) concentration in the raw, untreated wastewater.
" Total colifonm colony densities < 50 per 100 ml of effluent.
Source: Hoover etal., 1998.
Table 3-28.Treatment performance standards in various control zones
Vertical
separation
distance
(feet)
>4
3 to 4
2 to 3
1 to 3
<1
Control zone (with management entity)
R1
R2a
R2b
R3
R4
R5
Treatment performance standard
TS1
TS1
TS1
TS2
TSS
TS1
TS1
TS2
TSS
TS4
TS1 OR
TS4
TS1 OR
TS4
TS2OR
TS4
TSS OR
TS4
TS4
TS1
TS2
TSS
TS4
TSS
TS2
TS2
TSS
TS4
TSS
TS4
TSS
NA
NA
NA
»t
c S
co JO
II
Increasing Resource Value
Assessment and modeling through
quantitative analysis
Numeric performance requirements for onsite
wastewater treatment systems can be derived by
quantifying the total pollutant assimilative capacity
of the receiving waters, estimating mass pollutant
loads from non-OWTS sources, and distributing
the remaining assimilative capacity among onsite
systems discharging to the receiving waters.
Consideration of future growth, land use and
management practices, and a margin of safety
should be included in the calculations to ensure that
estimation errors favor protection of human health
and the environment.
Assimilative capacity is a volume-based (parts of
pollutant per volume of water) measurement of the
ability of water to decrease pollutant impacts
through dilution. Threshold effects levels are
usually established by state, federal, or tribal water
quality standards, which assign maximum concen-
trations of various pollutants linked to designated
uses of the receiving waters (e.g., aquatic habitat,
drinking water source, recreational waters). Be-
cause wastewater pollutants of concern (e.g.,
nitrogen compounds, pathogens, phosphorus) can
come from a variety of non-OWTS sources,
characterization of all pollutant sources and poten-
tial pathways to receiving waters provides impor-
tant information to managers seeking to control or
reduce elevated levels of contaminants in those
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Chapter 3: Establishing Treatment System Performance Requirements
Establishing performance requirements by assessing the probability of impact
The "probability of impact" method estimates the probability that treated water discharged from an onsite system
will reach an existing or future point of use in an identified water resource. By considering the relative probability
of impact based on existing water quality standards (e.g., drinking water, shellfish water, recreational water),
acceptable treatment performance standards can be established. The pollutants and their concentrations or mass
limits to be stipulated in the performance requirements will vary with the relative probability of impact estimated,
the potential use of the water resource, and the fate and transport characteristics of the pollutant.
As an example, the assessment indicates that a ground water supply well that provides water for drinking without
treatment might be adversely affected by an onsite system discharge. Soils are assumed to be of acceptable
texture and structure, with a soil depth of 3 feet. Nitrate-nitrogen and fecal conforms are two wastewater pollutants
that should be addressed by the performance requirements forthe treatment system (i.e., constructed
components plus soil). With a relative probability of impact estimated to be "high," the regulatory authority
considers it reasonable to require the treatment system to achieve drinking water standards for nitrate and fecal
conforms before discharge to the saturated zone. The drinking water standards for nitrate and fecal conforms in
drinking water are 10 mg/L for nitrate and zero for fecal conforms. Considering the fate of nitrogen in the soil, it
can be expected that any of the nitrogen discharged by the pretreatment system will be converted to nitrate in the
unsaturated zone of the soil except for 2 to 3 mg/L of refractory organic nitrogen. Because nitrate is very soluble
and conditions for biological denitrification in the soil cannot be relied on, the performance standard forthe onsite
system is 12 mg/L of total nitrogen (10 mg/L of nitrite + 2 mg/L of refractory organic nitrogen) prior to soil
discharge. In the case of fecal conforms, the natural soil is very effective in removing fecal indicators where
greater than 2 feet of unsaturated natural soil is present. Therefore, no fecal conform standard is placed on the
pretreatment (i.e., constructed) system discharge because the standard will be met aftersoil treatment and before
final discharge to the saturated zone.
If the probability of impact is estimated to be "moderate" or "low," only the nitrogen treatment standard would
change. If the probability of impact is "moderate" because travel time to the point of use is long, dispersion and
dilution of the nitrate in the ground water is expected to reduce the concentration in the discharge substantially.
Therefore, the treatment standard for total nitrogen can be safely raised, perhaps to 20 to 30 mg/L of nitrogen. If
the probability of impact is "low," no treatment standard for nitrogen is necessary.
If the probability of impact is "high" but the point of ground water use at risk is an agricultural irrigation well, no
specific pollutants in residential wastewater are of concern. Therefore, the treatment required need be no more
than that provided by a septic tank.
Source: Otis, 1999.
waters. For example, the mass balance equation
used to predict nitrate-nitrogen (or other soluble
pollutant) concentrations in ground water and
surface waters is
As the examples above indicate, there are a wide
range of approaches for assessing water resource
vulnerability and susceptibility to impacts from
Nitrate-nitrogen (mg/L) =
Annual nitrogen loading from
all sources in
Ib/yrx 454,000 mg/lb
Annual water recharge volume
from all
sources in liters
onsite wastewater treatment systems. Other meth-
odologies include risk matrices similar to those
summarized above and complex contaminant
transport models, including Qual2E, SWMM, and
BASINS, the EPA-developed methodology for
integrating point and nonpoint source pollution
assessments (see http://www.epa.gov/ow/compen-
dium/toc.htm for more information on BASINS
and other water quality modeling programs).
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Chapter 3: Establishing Treatment System Performance Requirements
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Chapter 3: Establishing Treatment System Performance Requirements
Environmental sensitivity assessment key (for figure 3-14).
Wastewater management zone
Includes the entire service area of the district.
B
Receiving environment
Receiving water to which the wastewater is discharged.
Fate of ground water discharge
The treated discharge to ground water may enter the regional flow or become base flow to surface water.
Ground water flow direction can be roughly estimated from ground surface topography if other sources of
information are not available. In some instances both regional flow and base flow routes should be assessed to
determine the controlling point of use.
Planning area density (population equivalents per acre)
The risk of higher contaminate concentrations in the ground water from ground water-discharging treatment
facilities will increase with increasing numbers of people served. Where building lots are served by individual
infiltration systems, the population served divided by the total area composed by contiguous existing and
planned lots would determine population equivalents per acre (p.e./acre). For a large cluster system, the
p.e./acre would be determined by the population served divided by the area of the infiltration surface of the
cluster system.
Well construction
Wells developed in an unconfined aquifer with direct hydraulic connections to the wastewater discharge have a
higher probability of impact from the wastewater discharge than wells developed in a confined aquifer. Wells
that are considered within the zone of influence from the wastewater discharge should be identified and their
construction determined from well logs.
Travel time to base flow discharge, Tb,
Treated wastewater discharges in ground water can affect surface waters through base flow. The potential
impacts of base flows are inversely proportional to the travel time in the ground water, Tb), because of the
dispersion and dilution (except in karst areas) that will occur. Where aquifer characteristics necessary to
estimate travel times are unknown, distance can be substituted as a measure. If travel time, Tbf, is greater than
time to a ground water point of use, Ta, the ground water should be assumed to be the receiving environment.
Stream flow
Stream flow will provide dilution of the wastewater discharges. The mixing and dilution provided are directly
proportional to the stream flow. Stream flow could be based on the 7-day, 10-year low-flow condition (7Q10) as a
worst case. "High" and "low" stream flow values would be defined by the ratio of the 7Q10 to the daily wastewater
discharge. For example, ratios greater than 100:1 might be
"high," whereas those less than 100:1 might be "low." Stream flow based on the watershed area might also be
used (cfs/acre).
H
Travel time to aquifer or surface water point of use, T. or Ts
The potential impacts of wastewater discharges on points of use (wells, coastal embayments, recreational
areas, etc.) are inversely proportional to the travel time. Except for karst areas, distance could be used as a
substitute for travel time if aquifer or stream characteristics necessary to estimate travel times are unknown.
Relative probability of impact
The relative probability of impact is a qualitative estimate of expected impact from a wastewater discharge on a
point of use. The risk posed by the impact will vary with the intended use of the water resource and the nature
of contaminants of concern.
Source: Otis, 1999.
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Estimating nitrogen loadings and impacts for Buttermilk Bay, Massachusetts
In Buttermilk Bay, a 530-acre shallow coastal bay at the northern end of Buzzards Bay in Massachusetts, elevated nitrogen levels
associated with onsite systems and land use in the watershed have contributed to nuisance algal growth and declines in eelgrass beds in
some areas. An investigation in the early 1990s supported by the New England Interstate Water Pollution Control Commission and
USEPA established a critical (maximum allowable) nitrogen loading rate of 115,600 pounds per year by identifying an appropriate
ecological effects threshold (the nitrogen concentration associated with significant ecological impacts, or 0.24 mg/L in nitrogen-sensitive
Buttermilk Bay) and considering both the size and recharge rate of the bay:
Critical Loading Rate (pounds per year) =
Threshold nitrogen concentration x volume x number of annual water body recharges =
240 milligrams of N per cubic meter x 2,996,000 cubic meters x 73 annual recharges =
52,489,920,000 milligrams of N / 454,000 milligrams in one pound =
115,617 pounds per year = critical loading rate for nitrogen
After establishing the critical nitrogen loading rate, the watershed assessment team sought to quantify annual nitrogen loads discharged
to the bay under existing conditions. Loading values for various sources of nitrogen in the watershed were estimated and are presented
in table 3-29. For the purposes of estimating nitrogen contributions from onsite systems, it was assumed that the total nitrogen
concentration in onsite treated effluent was 40 mg/L and the per capita flow was 55 gallons per day. [It should be noted that nitrogen
concentrations in onsite system treated effluent commonly range between 25 and 45 mg/L for soil-based systems, though some
researcher have found higher effluent concentrations. In general, SWIS nitrogen removal rates range between 10 and 20 percent (Van
Cuyk et al., 2001) for soil-based systems. Mechanized systems designed for nitrogen removal can achieve final effluent N concentrations
as low as 10-25 mg/L.]
Using the research-based assumptions and estimates summarized in the table, the assessment team estimated that total current
nitrogen loadings totaled about 91,053 Ib/yr. Onsite wastewater treatment systems represented a significant source (74 percent) of the
overall nitrogen input, followed by lawn fertilizers (15 percent) and cranberry bogs (7 percent).
The final part of the Buttermilk Bay analysis involved projecting the impact of residential build-out on nitrogen loads to the bay. With a
critical (maximum allowable) nitrogen loading rate of 115,617 Ib/yr and an existing loading rate of 91,053 Ib/yr, planners had only a
24,564 Ib/yr cushion with which to work. Full residential build-out projections generated nitrogen loading rates that ranged from 96,800 Ib/
yr to 157,500 Ib/yr. Regional planners used this information to consider approaches for limiting nitrogen loadings to a level that could be
safely assimilated by the bay. Among a variety of options that could be considered under this scenario are increasing performance
requirements for onsite systems, decreasing system densities, limiting the total number of new residences with onsite systems in the bay
watershed, and reducing nitrogen inputs from other sources (e.g., lawn fertilizers, cranberry bogs).
Table 3-29. Nitrogen loading values used in the Buttermilk Bay assessment
Nitrogen source
Nitrogen concentration Loading rate
Flow/recharge
Total loading
Onsite wastewater
systems
Fertilizers-lawns
Fertilizers-cranberry bogs
Pavement runoff
Roof runoff
Atmospheric deposition
Total
40 mg/L
NA
NA
2.0 mg/L
0.75 mg/L
0.3 mg DIN/L
6.72 Ib N/person/yr
0.9lbN/1000ft2/yr
15.8lbN/1000ft2/yr
0.42 lbN/1000 ftVyr
0.15lbN/1000ft2/yr
3.03 Ib N/acre
55 gal/person/day
(165 gal/dwelling)
18in./yr
NA
40 in./year
40 in./year
NA
66,940 Ib
13,721 Ib
6,378 Ib
1,723lb
686 Ib
1,606lb
91,053lb
NA = not available.
Source: Horsley Witten Hegemann, 1991, after Nelson etal., 1988.
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3.8.2 Establishing narrative or
numerical performance
requirements
Performance requirements should reflect acceptable
environmental impacts and public health risks based
on assessment methods such as those described in
the preceding section. They should specify observ-
able or measurable requirements in narrative or
numerical form. Conventional onsite treatment
systems (septic tanks with SWISs) have used
narrative requirements such as prohibitions on
wastewater backup in plumbing fixtures or effluent
pooling on the ground surface. These requirements
are measurable through observation but address
only some specific public health issues. An example
of a narrative performance requirement that
addresses potential environmental impacts is the
Town of Shoreham's requirement for specifically
approved treatment trains for environmentally
sensitive areas (see sidebar and table 3-26 in
preceding section). Compliance is determined by
whether the required treatment processes are in
place; water quality monitoring is not involved.
The regulating agencies assume that the water
quality objectives are achieved if these narrative
performance requirements are met. Although there
is merit in this approach, some additional steps
(e.g., operation and maintenance monitoring,
targeted water quality monitoring) would be
included in a more comprehensive program.
Numerical performance requirements specify the
critical parameters of concern (e.g., nitrate,
phosphorus, fecal coliforms), the maximum
allowable concentration or mass pollutant/flow
discharge permitted per day, and the point at which
the requirements apply. Examples of numerical
performance requirements include Massachusetts'
requirement for limited volume discharges (mea-
sured in gallons per day) in designated nitrogen-
sensitive areas or a water quality standard for
nitrogen of 25 mg/L, to be met at the property
boundary. Unlike the narrative requirements,
numerical performance requirements provide more
assurance that the public health and water quality
goals are being met.
3.9 Monitoring system operation
and performance
Performance monitoring of onsite treatment
systems serves several purposes. Its primary
purpose is to ensure that treatment systems are
operated and maintained in compliance with the
performance requirements. It also provides perfor-
mance data useful in making corrective action
decisions and evaluating areawide environmental
impacts for land use and wastewater planning.
Historically, performance monitoring of onsite
treatment systems has not been required. Regula-
tory agencies typically limit their regulatory
Onsite system inspection/maintenance guidance for Rhode Island
The Rhode Island Department of Environmental Management published in 2000 the Septic System Checkup, an
inclusive guide to inspecting and maintaining septic systems. The handbook, available to the public, is written for
both lay people and professionals in the field. The guide is an easy-to-understand, detailed protocol for inspection
and maintenance and includes newly developed state standards for septic system inspection and maintenance. It
describes two types of inspections: a maintenance inspection to determine the need for pumping and minor
repairs, and a functional inspection for use during property transfers. The handbook also includes detailed
instructions for locating septic system components, diagnosing in-home plumbing problems, flow testing and dye
tracing, and scheduling inspections. Several Rhode Island communities, including New Shoreham, North
Kingstown and Glocester, currently use Septic System Checkup as their inspection standard. The University of
Rhode Island offers a training course for professionals interested in becoming certified in the inspection
procedures.
The handbook is available free on-line at http://www.state.ri.us/dem/regs/water/isdsbook.pdf. Individual spiral-
bound copies can be purchased for $10 with inspection report forms or$7forthe manual without forms from
OEM's Office of Technical and Customer Assistance at 401.222.6822.
Source: Rhode Island Department of Environmental Management.
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control primarily to system siting, design, and
construction and certification of site evaluators,
designers, and other service providers. System
performance is largely ignored by the regulatory
authority or management entity or addressed
through sometimes weak owner education and
voluntary compliance programs until a hydraulic
failure is reported or observed (see chapters 2 and 5).
OWTS oversight agencies typically exert regula-
tory control by conducting the site evaluation and
reviewing the proposed design for compliance with
administrative code prescriptions for proven
systems. If the site characteristics and selected
system design meet the prescriptions in the code, a
construction permit is issued for installation by a
certified contractor. The regulatory authority or
management entity usually performs a pre-coverup
inspection before final approval is given to use the
system. At that point the regulatory authority
typically relinquishes any further oversight of the
system until a hydraulic failure is observed or
reported. The owner may be given educational
materials and instructions describing the system and
what maintenance should be performed, but routine
operation and maintenance is left up to the owner.
Tank pumping or other routine maintenance tasks
are seldom required or even tracked by the regula-
tory authority or management entity for informa-
tion purposes. Regular inspections of systems are
usually not mandated.
This regulatory approach might be adequate for the
degree of risk to human health and the environment
posed by isolated and occasional hydraulic failures.
Where onsite treatment is used in moderate-to-
high-density suburban and seasonal developments,
however, it has not proven to be adequate, particu-
larly where treatment failures can be expected to
significantly affect ground water and surface water
quality. Onsite system failure rates across the nation
range as high as 10 percent or more in some areas
(see Section 1.3). In cases where high system
densities or system age indicates the likelihood of
ground or surface water contamination, incorpora-
tion of mandated performance monitoring into
OWTS management programs is strongly recom-
mended. In 2000 USEPA issued suggested guide-
lines for onsite system management programs.
Draft Guidelines for Management of Onsite/
Decentralized Wastewater Systems (USEPA, 2000b)
provides an excellent framework for developing a
comprehensive management program that considers
the full range of issues involved in OWTS plan-
ning, siting, design, installation, operation, mainte-
nance, monitoring, and remediation (see chapter 2).
Local OWTS regulatory and management agencies
in many areas are embracing more rigorous opera-
tion, maintenance, and inspection programs to deal
with problems caused by aging systems serving
developments built before 1970, poor maintenance
due to homeowner indifference or ignorance, and
regional hydraulic or pollutant overloads related to
high-density OWTS installations. Operation and
maintenance management programs adopted by
these agencies consist mostly of an integrated
performance assurance system that inventories new
and existing systems, establishes monitoring or
inspection approaches, requires action when
systems fail to operate properly, and tracks all
activities to ensure accountability among regulatory
program staff and system owners. (See chapter 2
and Draft Guidelines for Management of Onsite/
Decentralized Wastewater Systems at http://
www.epa.gov/owm/decent/index.htm for more
information and examples.)
3.9.1 Operating permits
Periodic review of system performance is necessary to
ensure that systems remain in compliance with
established performance requirements after they are
installed. Thus, regulatory agencies need to maintain
rigorous, perpetual oversight of systems to ensure
periodic tank pumping, maintenance of system
components, and prompt response to problems that
may present threats to human health or water re-
sources. Some jurisdictions are fulfilling this responsi-
bility by issuing renewable/revocable operating
permits. The permit stipulates conditions that the
system must meet before the permit can be renewed
(see sidebar). The duration of such permits might
vary. For example, shorter-term permits might be
issued for complex treatment systems that require
more operator attention or to technologies that are less
proven (or with which the regulatory authority has
less comfort). The owner is responsible for docu-
menting and certifying that permit conditions have
been met. If permit conditions have not been met, a
temporary permit containing a compliance schedule
for taking appropriate actions may be issued. Failure
to meet the compliance schedule can result in fines or
penalties.
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Onsite system operating permits in St. Louis County, Minnesota
St. Louis County, located in the northeastern region of Minnesota, extends from the southwestern tip of Lake
Superior north to the Canadian border. The physical characteristics of the region are poorly suited for application
of traditional onsite treatment systems. Many of the soils are very slowly permeable lacustrine clays, shallow to
bedrock, and often near saturation. The existing state minimum code restricts onsite systems to sites featuring
permeable soils with sufficient unsaturated depths to maintain a 3-foot separation distance to the saturated zone.
To allow the use of onsite treatment, the county has adopted performance requirements that may be followed in
lieu of the prescriptive requirements where less than 3 feet of unsaturated, permeable soils are present. In such
cases the county requires that the owner continuously demonstrate and certify that the system is meeting the
performance requirements. This is achieved through the issuance of renewable operating permits for higher-
performance alternative treatment systems. The operating permit is based on evaluation of system performance
ratherthan design prescription and includes the following:
• System description
• Environmental description
• Site evaluation documentation
• Performance requirements
• System design, construction plan, specifications, and construction drawings
• Maintenance requirements
• Monitoring requirements (frequency, protocol, and reporting)
• Contingency plan to be implemented if the system fails to perform to requirements
• Enforcement and penalty provisions
The permit is issued for a limited term, typically 5 years. Renewal requires that the owner document that the
permit requirements have been met. If the documentation is not provided, a temporary permit is issued with a
compliance schedule. If the compliance schedule is not met, the county has the option of reissuing the temporary
permit and/or assessing penalties. The permit program is self-supporting through permit fees.
3.9.2 Monitoring programs
Monitoring individual or regional onsite system
performance may include performance inspections
(see Chapter 2 and Draft Management Guidelines
for Onsite/Decentralized Wastewater Systems),
water quality sampling at performance boundaries,
drinking water well monitoring, and assessment of
problem pollutant concentrations (pathogens,
nitrate, phosphorus) in nearby surface waters. In
general, monitoring of system performance seeks to
ascertain if onsite systems are meeting performance
requirements, i.e., protecting public health and
water quality. Assessing the sensitivity of water
resources to potential pollutant loadings from
onsite systems helps in developing performance
requirements and the monitoring methods and
sampling locations that might be used.
Monitoring system performance through water
quality sampling is difficult for conventional onsite
systems because the infiltration field and underly-
ing soil are part of the treatment system. The
percolate that enters the ground water from the
infiltration system does not readily mix and
disperse in the ground water. It can remain as a
distinct, narrow plume for extended distances from
the system (Robertson et al., 1991). Locating this
plume for water quality sampling is extremely
difficult, and the cost involved probably does not
warrant this type of monitoring except for large
systems that serve many households or commercial
systems constructed over or near sensitive ground
water and surface water resources (see chapter 5).
Monitoring of onsite treatment systems is enhanced
considerably by the inclusion of inspection and
sampling ports at performance boundaries (e.g.,
between treatment unit components) and the final
discharge point. Other methods of monitoring such
as simple inspections of treatment system operation
or documentation of required system maintenance
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Monitoring requirements in Washington
The Department of Health of the state of Washington has adopted a number of monitoring requirements that
OWTS owners must meet (Washington Department of Health, 1994). Because such requirements place additional
oversight responsibilities on management agencies, additional resources are needed to ensure compliance.
Among the requirements are the following:
The system owner is responsible for properly operating and maintaining the system and must
• Determine the level of solids and scum in the septic tank once every 3 years.
• Employ an approved pumping service provider to remove the septage from the tank when the level of solids
and scum indicates that removal is necessary.
• Protect the system area and the reserve area from cover by structures or impervious material, surface
drainage, soil compaction (for example, by vehicular traffic or livestock), and damage by soil removal and
grade alteration.
• Keep the flow of sewage to the system at or below the approved design both in quantity and waste strength.
• Operate and maintain alternative systems as directed by the local health officer.
• Direct drains, such as footing or roof drains away from the area where the system is located.
Local health officers in Washington also perform monitoring duties, including the following;
Providing operation and maintenance information to the system owner upon approval of any installation, repair,
or alteration of a system.
Developing and implementing plans to monitor all system performance within areas of special concern1;
initiating periodic monitoring of each system by no later than January 1, 2000, to ensure that each system
owner properly maintains and operates the system in accordance with applicable operation and maintenance
requirements; disseminating relevant operation and maintenance information to system owners through
effective means routinely and upon request; and assisting in distributing educational materials to system
owners.
Finally, local health officers may require the owner of the system to perform specified monitoring, operation, or
maintenance tasks, including the following:
Using one or more of the following management methods or another method consistent with the following
management methods for proper operation and maintenance: obtain and comply with the conditions of a
renewable or operational permit; employ a public entity eligible under Washington state statutes to directly or
indirectly manage the onsite system; or employ a private management entity, guaranteed by a public entity
eligible under Washington state statutes or sufficient financial resources, to manage the onsite system.
Evaluating any effects the onsite system might have on ground water or surface water.
Dedicating easements for inspections, maintenance, and potential future expansion of the onsite system.
1 "Areas of special concern" are areas where the health officer or department determines additional requirements
might be necessary to reduce system failures or minimize potential impacts upon public health. Examples include
shellfish habitat, sole source aquifers, public water supply protection areas, watersheds of recreational waters,
wetlands used in food production, and areas that are frequently flooded.
Source: Washington Department of Health, 1994.
might be sufficient and more cost-effective than
water quality sampling at a performance boundary.
The Critical Point Monitoring (CPM) approach
being developed in Washington State provides a
systematic approach to choosing critical locations
to monitor specific water quality parameters
(Eliasson et al., 2001). The program is most
suitable for responsible management entities
operating comprehensive management programs.
CPM provides an appropriate framework for
monitoring treatment train components, though it
should be recognized that evaluations of overall
system effectiveness—and compliance with
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State of Massachusetts' onsite treatment system inspection program
Massachusetts in 1996 mandated inspections of OWTSs to identify and address problems posed by failing
systems (310CMR 15.300,1996). The intent of the program is to ensure the proper operation and maintenance of
all systems. A significant part of the program is the annual production of educational materials for distribution to
the public describing the importance of proper maintenance and operation of onsite systems and the impact
systems can have on public health and the environment.
Inspections are required at the time of property transfer, a change in use of the building, or an increase in discharges to the system.
Systems with design flows equal to or greater than 10,000 gpd require annual inspections. Inspections are to be performed only by persons
approved by the state. The inspection criteria are established by code and must include
• A general description of system components, their physical layout, and horizontal setback distances from
property lines, buildings, wells, and surface waters.
• Description of the type of wastewater processed by the system (domestic, commercial, or industrial).
• System design flow and daily water use, if metered.
• Description of the septic tank, including age, size, internal and external condition, water level, etc.
• Description of distribution box, dosing siphon, or distribution pump, including evidence of solids carryover,
clear water infiltration, and equal flow division, and evidence of backup, if any.
• Description of the infiltration system, including signs of hydraulic failure, condition of surface vegetation,
level of ponding above the infiltration surface, other sources of hydraulic loading, depth to seasonally high
water table, etc.
A system is deemed to be failing to protect public health, safety, and the environment if the septic tank is made
of steel, if the OWTS is found to be backing up, if it is discharging directly or indirectly onto the surface of the
ground, if the infiltration system elevation is below the high ground water level elevation, or if the system
components encroach on established horizontal setback distances.
The owner must make the appropriate upgrades to the system within 2 years of discovery. The owner's failure to
have the system inspected as required orto make the necessary repairs constitutes a violation of the code.
Source: Title V, Massachusetts Environmental Code.
performance requirements—should be based on
monitoring at the performance boundaries (see
chapter 5).
Elements of a monitoring program
Any monitoring program should be developed
carefully to ensure that its components consider
public health and water quality objectives, regula-
tory authority / management entity administrative
and operational capacity, and the local political,
social, and economic climate. Critical elements for
a monitoring program include
• Clear definition of the parameters to be moni-
tored and measurable standards against which
the monitoring results will be compared.
• Strict protocols that identify when, where, and
how monitoring will be done, how results will
be analyzed, the format in which the results will
be presented, and how data will be stored.
• Quality assurance and quality control measures
that should be followed to ensure credible data.
System inspections
Mandatory inspections are an effective method for
identifying system failures or systems in need of
corrective actions. Inspections may be required at
regular intervals, at times of property transfer or
changes in use of the property, or as a condition to
obtain a building permit for remodeling or expan-
sion. Twenty-three states now require some form of
inspection for existing OWTSs (NSFC, 1999). The
OWTS regulatory authority or management entity
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Effluent quality requirements in Minnesota
St. Louis County, Minnesota, has established effluent standards for onsite systems installed on sites that do not
have soils meeting the state's minimum requirements. Many of the soils in the county do not meet the minimum
3-foot unsaturated soil depth required by the state code. To allow for development the county has adopted a
performance code that establishes effluent requirements for systems installed where the minimums cannot be
met. Where the natural soil has an unsaturated depth of less than 3 feet but more than 1 foot, the effluent
discharged to the soil must have no more than 10,000 fecal coliform colonies per 100 ml. On sites with 1 foot of
unsaturated soil or less, the effluent must have no more than 200 fecal coliform colonies per 100 ml. These
effluent limits are monitored prior to final discharge at the infiltrative surface but recognize treatment provided by
the soil. If hydraulic failure occurs, the county considers the potential risk within acceptable limits. The
expectation is that any discharges to the surface will meet at least the primary contact water quality requirements
of 200 fecal coliform colonies per 100 ml. Other requirements, such as nutrient limitations, may be established
for systems installed in environmentally sensitive areas.
Documenting wastewater migration to streams in Northern Virginia
The Northern Virginia Planning District Commission uses commercially available ultraviolet light bulbs and cotton
swatches to screen for possible migration of residential wastewater into area streams. The methodology is based
on the presence of optical brighteners in laundry detergents, which are invisible to the naked eye but glow under
"black" lights. The brighteners are very stable in the environment and are added to most laundry soaps. They are
readily absorbed onto cotton balls or cloth swatches, which can be left in the field for up to two weeks. Users
must ensure that the absorbent medium is free from optical brighteners prior to use.
Although the methodology is acceptable for screening-level analysis, it does not detect wastewater inputs from
buildings that do not have laundry facilities and does not verify the presence of other potential contaminants (e.g.;
bacteria, nitrogen compounds). Despite these shortcomings, the approach is inexpensive, effective, and a good
tool for screening and public education.
Source: Northern Virginia Regional Commission, 1999.
should collect information on new systems (system
owner, contact information, system type, location,
design life and capacity, recommended service
schedule) at the time of permitting and installation.
Inventories of existing systems can be developed by
consulting wastewater treatment plant service area
maps, identifying areas not served by publicly
owned treatment works (POTWs), and working
with public and private utilities (drinking water,
electricity, and solid waste service providers) to
develop a database of residents and contact infor-
mation. Telephone, door-to-door, or mail surveys
can be used to gather information on system type,
tank capacity, installation date, last date of service
(e.g., pumping, repair), problem incidents, and
other relevant information.
Minnesota, Massachusetts, Wisconsin, and a
number of counties and other jurisdictions require
disclosure of system condition or assurances that
they are functioning properly at the time of prop-
erty transfer (see sidebar). Assurances are often in
the form of inspection certificates issued by county
health departments, which have regulatory jurisdic-
tion over OWTSs. Clermont County, Ohio, devel-
oped an OWTS owner database by cross-referenc-
ing water line and sewer service customers. Contact
information from the database was used for a mass
mailing of information on system operation and
maintenance and the county's new inspection
program to 70 percent of the target audience. Other
approaches used in the Clermont County outreach
program included advisory groups, homeowner
education meetings, news media releases and
interview programs, meetings with real estate
agents, presentations at farm bureau meetings,
displays at public events, and targeted publications
(Caudill, 1998).
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Biochemical application of a bacterial source tracking methodology
Researchers from Virginia Tech analyzed antibiotic resistance in fecal streptococci to determine the sources of
bacteria found in streams in rural Virginia. The team first developed a database of antibiotic resistance patterns for
7,058 fecal streptococcus isolates from known human, livestock, and wildlife sources in Montgomery County,
Virginia. Correct fecal streptococcus source identification averaged 87 percent for the entire database and ranged
from 84 percent for deer isolates to 93 percent for human isolates. Afield test of the database yielded an overall
bacteria source accuracy rate of 88 percent, with an accuracy rate of at least 95 percent for differentiation
between human and animal sources.
The approach was applied to a watershed improvement project on Page Brook in Clarke County, Virginia, to
determine the impacts of a cattle exclusion fencing and alternative stock watering project. Pre-project bacterial
analyses showed heavy bacteria contamination from cattle sources (more than 78 percent), with smaller
proportions from waterfowl, deer, and unidentified sources (about 7 percent each). Afterthe fencing and alternative
stock watering stations were installed, fecal coliform levels from all sources declined by an average of 94 percent,
from 15,900/100 ml to 960/100 ml. Analysis of bacteria conducted afterthe project also found that cattle-linked
isolates decreased to less than 45 percent of the total.
Source: Hagedorn et al., 1999.
The Town of Shoreham, Rhode Island, adopted a
similar inspection program by ordinance in 1996
(Loomis et al., 1999). The ordinance mandates
regular inspection of all systems by a town inspec-
tor. Septage pumping schedules and other mainte-
nance requirements are based on the results of the
inspection. Factors considered in the inspections
include site characteristics, system technology and
design, system use, and condition. The ordinance
allows the town to prioritize inspection schedules in
critical resource areas such as public wellheads and
high-risk areas determined to be prone to onsite
system failure. It also authorizes the town to assess
fees, levy fines, and track the inspections.
Prescribed maintenance
Where specific unit processes or treatment trains
have satisfactorily demonstrated reliable perfor-
mance through a credible testing program, some
programs assume that identical processes or treat-
ment trains will perform similarly if installed under
similar site-specific conditions. The system would
need to be managed according to requirements of
the designer/manufacturer as outlined in the
operation and maintenance manual to maximize the
potential for assured performance. Therefore, some
states monitor system maintenance as an alternative
to water quality-based performance monitoring.
The method of monitoring varies. In several states
the owner must contract with the equipment
manufacturer or certified operator to provide
operation and maintenance services. If the owner
severs the contract, the contractor is obligated to
notify the state regulatory authority or other
management entity. Failure to maintain a contract
with an operator is a violation of the law. Other
states require that the owner provide certified
documentation that required maintenance has been
performed in accordance with the system manage-
ment plan. Requiring the owner to provide periodic
documentation helps to reinforce the notion that the
owner is responsible for the performance of the
system. Chapter 2 provides additional information
on prescriptive and other approaches to monitoring,
operation, and maintenance.
Water quality sampling and bacterial
source tracking
OWTS effluent quality sampling is a rigorous and
expensive method of onsite system compliance
monitoring. Such programs require that certain
water quality criteria be met at designated locations
after each treatment unit (see chapter 5). Sampling
pretreated effluent before discharge to the soil
requires an assumption of the degree of treatment
that will occur in the soil. Therefore, the perfor-
mance requirements used to determine compliance
should be adjusted to credit soil treatment. Unfor-
tunately, some incomplete or inaccurate data equate
travel time in all types of soil to pollutant removals
under various conditions. Even when better data
are available, it is often difficult to match condi-
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tions at the site from which the data were derived
to the soils, geology, water resources, slopes,
topography, climate, and other conditions present at
the site under consideration. Effluent monitoring
should be undertaken only when the potential risk
to human health and the environment from system
failure is great enough to warrant the cost of
sampling and analysis or when assessment informa-
tion is needed to establish performance require-
ments or identify technologies capable of protect-
ing valued water resources.
Ground water sampling is the most direct method
of compliance monitoring. However, because of the
difficulty of locating monitoring wells in the
effluent plume it has historically been used only for
compliance monitoring of large infiltration sys-
tems. If performance standards are to be used in the
future, ground water monitoring will become more
commonplace despite its cost because it is the only
true determinant of compliance with risk assess-
ment criteria and values. Installing small-diameter
drop tubes at various depths at strategic
downgradient locations can provide a cost-effective
approach for continuous sampling.
Monitoring of the unsaturated zone has been
conducted as an alternative to ground water moni-
toring. This method avoids the problem of locating
narrow contaminant plumes downgradient of the
infiltration system, but allowances should be made
in parameter limits to account for dispersion and
treatment that could occur in the saturated zone. To
obtain samples, suction lysimeters are used. Porous
cups are installed in the soil at the desired sample
depth, and a vacuum is applied to extract the
sample. This type of sampling works reasonably
well for some dissolved inorganic chemical species
but is not suitable for fecal indicators (Parizek and
Lane, 1970; Peters and Healy, 1988). Use of this
method should be based on a careful evaluation of
whether the method is appropriate for the param-
eters to be monitored because it is extremely
expensive and proper implementation requires
highly skilled personnel.
Water quality sampling of lakes, rivers, streams,
wetlands, and coastal embayments in areas served
by OWTSs can provide information on potential
resource impacts caused by onsite systems. Concen-
trations of nitrogen, phosphorus, total and fecal
coliforms, and fecal streptococci are often mea-
sured to determine possible impacts from system
effluent. Unless comprehensive source sampling
that characterizes OWTS pollutant contributions is
in place, however, it is usually difficult to attribute
elevated measurements of these parameters directly
to individual or clustered OWTSs. Despite this
difficulty, high pollutant concentrations often
generate public interest and provide the impetus
necessary for remedial actions (e.g., tank pumping;
voluntary water use reduction; comprehensive
system inspections; system repairs, upgrades,
replacements) that might be of significant benefit.
Tracer dye tests of individual systems, infrared
photography, and thermal imaging are used in
many jurisdictions to confirm direct movement of
treated or partially treated wastewater into surface
waters. Infrared and thermal photography can show
areas of elevated temperature and increased chloro-
phyll concentrations from wastewater discharges.
Areas with warmer water during cold months or
high chlorophyll during warm months give cause
for further investigation (Rouge River National Wet
Weather Demonstration Project, 1998). The
Arkansas Health Department has experimented with
helicopter-mounted infrared imaging equipment to
detect illicit discharges and failed systems around
Lake Conway with some success (Eddy, 2000),
though these and other monitoring approaches
(e.g., using tracers such as surfactants, laundry
whiteners, and caffeine) are not typical and are still
undergoing technical review.
Recently, some success has been demonstrated by
advanced bacterial source tracking (BST) method-
ologies, which identify bacteria sources (humans,
cattle, dogs, cats, wildlife) through molecular or
biochemical analysis. Molecular (genotype) assess-
ments match bacteria collected at selected sampling
points with bacteria from known mammalian
sources using ribotype profiles, intergenetic DNA
sequencing, ribosomal DNA genetic marker profile
analyses, and other approaches (Bernhard and
Field, 2000; Dombek et al, 2000; Parveen et al.,
1999). Biochemical (phenotype) assessments of
bacteria sources conduct similar comparisons
through analysis of antibiotic resistance in known
and unknown sources of fecal streptococci
(Hagedorn et al., 1999), coliphage serological
differentiation, nutritional pattern analysis, and
other methods. In general, molecular methods seem
to offer the most precise identification of specific
3-60
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Chapter 3: Establishing Treatment System Performance Requirements
types of sources (animal species), but are costly,
time-consuming, and not yet suitable for large-
scale use. The precision of most biochemical
approaches appears to be somewhat less than
molecular methods, but analyte costs are lower,
processing times are shorter, and large numbers of
samples can be assayed in shorter time periods
(Virginia Tech, 2001). It has been suggested that
biochemical methods be used to screen large
numbers of bacterial isolates for likely sources
followed by an analysis of a subset of the isolates
through molecular approaches to validate the
findings. (For more information, see http://
www.bsi.vt.edu/bioL4684/BST/BST.html).
Finally, some OWTS management agencies use
fecal coliform/fecal streptococci (FC/FS) ratios as a
screening tool to detect the migration of poorly
treated effluent to inland surface waters. Under this
approach, which is effective only if samples are
taken near the source of contamination, the number
of fecal coliforms in a sample volume is divided by
the number of fecal streptococci in an equal sample
volume. If the quotient is below 0.7, the bacteria
sources are most likely animals. Quotients above
4.0 indicate a greater likelihood of human sources
of bacteria, while values between 0.7 and 4.0
indicate a mix of human and animal sources.
Several factors should be considered when using
the FC/FS screening approach:
• Bacterial concentrations can be highly variable
if the pH is outside the 4.0 to 9.0 range
• Faster die-off rates of fecal coliforms will alter
the ratio as time and distance from contaminant
sources increase
• Pollution from several sources can alter the ratio
and confuse the findings
• Ratios are of limited value in assessing bays,
estuaries, marine waters, and irrigation return
waters
Sampling and analysis costs vary widely across the
nation and are influenced by factors such as the
number of samples to be collected and assessed,
local business competition, and sample collection,
handling, and transport details. Because of variabil-
ity in price and the capacity of local agencies to
handle sample collection, transport, and analysis,
several cost estimates should be solicited. Some
example analytical costs are provided in table 3-30.
Table 3-30. Typical laboratory costs for water quality
analysis
Parameter
BOD6
N02
N03
Fecal coliform
TKN
Total phosphorus
TSS
Cost range per
sample
(in dollars)
15-50
10-25
10-25
15-50
4-50
5-35
8-25
Typical cost per
sample
(in dollars)
35
20
20
30
35
25
15
Source: Tetra Tech, 2000.
Because of the cost and difficulty of monitoring,
underfunded management agencies have often
opted to focus their limited resources on ensuring
that existing systems are properly operated and
maintained and new systems are appropriately
planned, designed, installed, operated, and main-
tained. They have relied on limited water quality
monitoring of regional ground water and surface
waters to provide an indication of regional onsite
system performance. Additional site-specific
monitoring is recommended, however, where
drinking water or valued surface water resources
are threatened.
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Chapter 4: Treatment Processes and Systems
Chapter 4
Treatment processes and systems
4.1 Introduction
4.2 Conventional systems and treatment options
4.3 Subsurface wastewater infiltration
4.4 Design considerations
4.5 Construction management and contingency options
4.6 Septic tanks
4.7 Sand/media filters
4.8 Aerobic Treatment Units
4.1 Introduction
This chapter contains information on individual
onsite/decentralized treatment technologies or unit
processes. Information on typical application,
design, construction, operation, maintenance, cost,
and pollutant removal effectiveness is provided for
most classes of treatment units and their related
processes. This information is intended to be used
in the preliminary selection of a system of treat-
ment unit processes that can be assembled to
achieve predetermined pollutant discharge concen-
trations or other specific performance require-
ments. Complete design specifications for unit
processes and complete systems are not included in
the manual because of the number of processes and
process combinations and the wide variability in
their application and operation under various site
conditions. Designers and others who require more
detailed technical information are referred to such
sources.
Chapter 4 is presented in two main sections. The
first section contains information about conven-
tional (soil-based or subsurface wastewater infiltra-
tion) systems, referred to as SWISs in this docu-
ment. Both gravity-driven and mechanized SWISs
are covered in this section of chapter 4. The second
section contains a general introduction to sand
filters (including other media), and a series of fact
sheets on treatment technologies, alternative
systems (e.g., fixed-film and suspended growth
systems, evapotranspiration systems, and other
applications), and special issues pertaining to the
design, operation, and maintenance of onsite
wastewater treatment systems (OWTSs). This
approach was used because the conventional system
is the most economical and practical system type
that can meet performance requirements in many
applications.
The first section is further organized to provide
information about the major components of a
conventional system. Given the emphasis in this
manual on the design boundary (performance-
based) approach to system design, this section was
structured to lead the reader through a discussion of
system components by working backwards from
the point of discharge to the receiving environment
to the point of discharge from the home or other
facility served by the onsite system. Under this
approach, soil infiltration issues are discussed first,
the distribution piping to the infiltration system
including graveless sytems is addressed next, and
matters related to the most common preliminary
treatment device, the septic tank, are covered last.
The fact sheets in the second section of this chapter
describe treatment technologies and discuss special
issues that might affect system design, perfor-
mance, operation, and maintenance. These treat-
ment technologies are often preceded by a septic
tank and can include a subsurface wastewater
infiltration system. Some treatment technologies
may be substituted for part or all of the conven-
tional system, though nearly all alternative ap-
proaches include a septic tank for each facility
being served. Fact sheets are provided for the more
widely used and successful treatment technologies,
such as sand filters and aerobic treatment units.
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Chapter 4: Treatment Processes and Systems
The component descriptions provided in this
chapter are intended to assist the reader in screen-
ing components and technologies for specific
applications. Chapter 5 presents a strategy and
procedures that can be used to screen and select
appropriate treatment trains and their components
for specific receiver sites. The reader should review
chapter 5 before selecting system components.
4.2 Conventional systems and
treatment options
The three primary components of a conventional
system (figure 4-1) are the soil, the subsurface
wastewater infiltration system (SWIS; also called a
leach field or infiltration trench), and the septic
tank. The SWIS is the interface between the
engineered system components and the receiving
ground water environment. It is important to note
that the performance of conventional systems relies
primarily on treatment of the wastewater effluent
in the soil horizon(s) below the dispersal and
infiltration components of the SWIS. Information
on SWIS siting, hydraulic and mass loadings,
design and geometry, distribution methods, and
construction considerations is included in this
chapter. The other major component of a conven-
tional system, the septic tank, is characterized by
describing its many functions in an OWTS.
Treatment options include physical, chemical, and
biological processes. Use of these options is
determined by site-specific needs. Table 4-1 lists
common onsite treatment processes and methods
that may be used alone or in combination to
assemble a treatment train capable of meeting
established performance requirements. Special
issues that might need to be addressed in OWTS
design include treatment of high-strength wastes
(e.g., biochemical oxygen demand and grease from
schools and restaurants), mitigation of impacts
from home water softeners and garbage disposals,
management of holding tanks, and additives (see
related fact sheets).
4.3 Subsurface wastewater
infiltration
Subsurface wastewater infiltration systems (SWISs)
are the most commonly used systems for the
treatment and dispersal of onsite wastewater.
Infiltrative surfaces are located in permeable,
unsaturated natural soil or imported fill material so
wastewater can infiltrate and percolate through the
underlying soil to the ground water. As the waste-
water infiltrates and percolates through the soil, it
is treated through a variety of physical, chemical,
and biochemical processes and reactions.
Many different designs and configurations are used,
but all incorporate soil infiltrative surfaces that are
located in buried excavations (figure 4-1). The
primary infiltrative surface is the bottom of the
excavation, but the sidewalls also may be used for
infiltration. Perforated pipe is installed to distribute
the wastewater over the infiltration surface. A porous
Figure 4-1. Conventional subsurface wastewater infiltration system
Absorption Field (Trench)
OOP OOP O I'
C ooooo ooo >:
W~~' " "~
Unexcavated
Gravel or Crushed Rock
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Chapter 4: Treatment Processes and Systems
Table 4-1. Commonly used treatment processes and optional treatment methods
Treatment objective
Suspended solids
removal
Soluble carbonaceous
BOD and ammonium
removal
Nitrogen transformation
Phosphorus removal
Pathogen removal
(bacteria, viruses,
parasites)
Grease removal
Treatment process
Sedimentation
Filtration
Aerobic, suspended-growth
reactors
Fixed-film aerobic
bioreactor
Lagoons
Biological
Nitrification (N)
Denitrification (D)
Ion exchange
Physical/Chemical
Biological
Filtration/Predation/lnactivation
Disinfection
Flotation
Adsorption
Aerobic biological treatment
(incidental removal will occur;
overloading is possible)
Treatment methods
Septic tank
Free water surface constructed wetland
Vegetated submerged bed
Septic tank effluent screens
Packed-bed media filters (incl. dosed systems)
Granular (sand, gravel, glass, bottom ash)
Peat, textile
Mechanical disk filters
Soil infiltration
Extended aeration
Fixed-film activated sludge
Sequencing batch reactors (SBRs)
Soil infiltration
Packed-bed media filters (incl. dosed systems)
Granular (sand, gravel, glass)
Peat, textile, foam
Trickling filter
Fixed-film activated sludge
Rotating biological contactors
Facultative and aerobic lagoons
Free water surface constructed wetlands
Activated sludge (N)
Sequencing batch reactors (N)
Fixed film bio-reactor (N)
Recirculating media filter (N, D)
Fixed-film activated sludge (N)
Anaerobic upflow filter (N)
Anaerobic submerged media reactor (D)
Submerged vegetated bed (D)
Free-water surface constructed wetland (N, D)
Cation exchange (ammonium removal)
Anion exchange (nitrate removal)
Infiltration by soil and other media
Chemical flocculation and settling
Iron-rich packed-bed media filter
Sequencing batch reactors
Soil infiltration
Packed-bed media filters
Granular (sand, gravel, glass bottom ash)
Peat, textile
Hypochlorite feed
Ultraviolet light
Grease trap
Septic tank
Mechanical skimmer
Aerobic biological systems
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Chapter 4: Treatment Processes and Systems
medium, typically gravel or crushed rock, is placed
in the excavation below and around the distribution
piping to support the pipe and spread the localized
flow from the distribution pipes across the excavation
cavity. Other gravelless or "aggregate-free" system
components may be substituted. The porous
medium maintains the structure of the excavation,
exposes the applied wastewater to more infiltrative
surface, and provides storage space for the waste-
water within its void fractions (interstitial spaces,
typically 30 to 40 percent of the volume) during peak
flows with gravity systems. A permeable geotextile
fabric or other suitable material is laid over the porous
medium before the excavation is backfilled to prevent
the introduction of backfill material into the porous
medium. Natural soil is typically used for backfilling,
and the surface of the backfill is usually slightly
mounded and seeded with grass.
Subsurface wastewater infiltration systems provide
both dispersal and treatment of the applied waste-
water. Wastewater is transported from the infiltration
system through three zones (see chapter 3). Two of
these zones, the infiltration zone and vadose zone, act
as fixed-film bioreactors. The infiltration zone, which
is only a few centimeters thick, is the most biologi-
cally active zone and is often referred to as the
"biomat." Carbonaceous material in the wastewater is
quickly degraded in this zone, and nitrification occurs
immediately below this zone if sufficient oxygen is
present. Free or combined forms of oxygen in the soil
must satisfy the oxygen demand generated by the
microorganisms degrading the materials. If sufficient
oxygen is not present, the metabolic processes of the
microorganisms can be reduced or halted and both
treatment and infiltration of the wastewater will be
adversely affected (Otis, 1985). The vadose (unsatur-
ated) zone provides a significant pathway for oxygen
diffusion to reaerate the infiltration zone (Otis, 1997,
Siegrist et al., 1986). Also, it is the zone where most
sorption reactions occur because the negative moisture
potential in the unsaturated zone causes percolating
water to flow into the finer pores of the soil, resulting
in greater contact with the soil surfaces. Finally, much
of the phosphorus and pathogen removal occurs in
this zone (Robertson and Harman, 1999; Robertson et
al., 1998; Rose et al., 1999; Yates and Yates, 1988).
4.3.1 SWIS designs
There are several different designs for SWISs.
They include trenches, beds, seepage pits, at-grade
systems, and mounds. SWIS applications differ in
their geometry and location in the soil profile.
Trenches have a large length-to-width ratio, while
beds have a wide, rectangular or square geometry.
Seepage pits are deep, circular excavations that rely
almost completely on sidewall infiltration. Seepage
pits are no longer permitted in many jurisdictions
because their depth and relatively small horizontal
profile create a greater point-source pollutant
loading potential to ground water than other
geometries. Because of these shortcomings, seepage
pits are not recommended in this manual.
Infiltration surfaces may be created in natural soil
or imported fill material. Most traditional systems
are constructed below ground surface in natural
soil. In some instances, a restrictive horizon above
a more permeable horizon may be removed and the
excavation filled with suitable porous material in
which to construct the infiltration surface (Hinson
et al., 1994). Infiltration surfaces may be con-
structed at the ground surface ("at-grades") or
elevated in imported fill material above the natural
soil surface ("mounds"). An important difference
between infiltration surfaces constructed in natural
soil and those constructed in fill material is that a
secondary infiltrative surface (which must be
considered in design) is created at the fill/natural
soil interface. Despite the differences between the
types of SWISs, the mechanisms of treatment and
dispersal are similar.
4.3.2 Typical applications
Subsurface wastewater infiltration systems are
passive, effective, and inexpensive treatment
systems because the assimilative capacity of many
soils can transform and recycle most pollutants
found in domestic and commercial wastewaters.
SWISs are the treatment method of choice in rural,
unsewered areas. Where point discharges to surface
waters are not permitted, SWISs offer an alterna-
tive if ground water is not closely interconnected
with surface water. Soil characteristics, lot size, and
the proximity of sensitive water resources affect the
use of SWISs. Table 4-2 presents characteristics for
typical SWIS applications and suggests applications
to avoid. Local codes should be consulted for
special requirements, restrictions, and other
relevant information.
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Table 4-2. Characteristics of typical SWIS applications
Characteristic
Typical application
Applications to avoid*
Type of wastewater
Daily flow
Minimum pretreatment
Lot orientation
Domestic and commercial
(residential, mobile home parks,
campgrounds, schools, restaurants, etc.)
< 20 population equivalents unless a
management entity exists
Septic tank, Imhoff tank
Loading along contour(s) must not exceed
the allowable contour loading rate
Facilities with non-sanitary and/or Industrial wastewaters.
Check local codes for other possible restrictions
> 20 population equivalents without a management program.
Check local codes for specific or special conditions (e.g.,
USEPA or state Underground Injection Control Program Class
V rule)
Discharge of raw wastewater to SWIS
Any site where hydraulic loads from the system will exceed
allowable contour loading rates
Landscape position
Topography
Soil texture
Soil structure
Drainage
Ridge lines, hilltops, shoulder/side slopes
Planar, mildly undulating slopes of
< 20% grade
Sands to clay loams
Granular, blocky
Moderately drained or well drained sites
Depressions, foot slopes, concave slopes, floodplains
Complex slopes of > 30%
Very fine sands, heavy clays, expandable clays
Platy, prismatic, or massive soils
Extremely well, somewhat poor, or very poorly drained sites
Depth to ground water or > 5 feet
bedrock
< 2 feet. Check local codes for specific requirements.
aAvoid when possible.
Source: Adapted from WEF, 1990.
4.3.3 Typical performance
Results from numerous studies have shown that
SWISs achieve high removal rates for most waste-
water pollutants of concern (see chapter 3) with the
notable exception of nitrogen. Biochemical oxygen
demand, suspended solids, fecal indicators, and
surfactants are effectively removed within 2 to 5
feet of unsaturated, aerobic soil (figure 4-2).
Phosphorus and metals are removed through
adsorption, ion exchange, and precipitation reac-
tions. However, the retention capacity of the soil is
finite and varies with soil mineralogy, organic
content, pH, redox potential, and cation exchange
capacity. The fate of viruses and toxic organic
compounds has not been well documented (Tomson
et al., 1984). Field and laboratory studies suggest
that the soil is quite effective in removing viruses,
but some types of viruses apparently are able to
leach from SWISs to the ground water. Fine-
textured soils, low hydraulic loadings, aerobic
subsoils, and high temperatures favor destruction of
viruses and toxic organics. The most significant
documented threats to ground water quality from
SWISs are nitrates. Wastewater nitrogen is nearly
completely nitrified below properly operating
SWISs. Because nitrate is highly soluble and
environments favoring denitrification in subsoil are
limited, little removal occurs (see chapter 3).
Chlorides also leach readily to ground water
because they, too, are highly soluble and are
nonreactive in soil.
Figure 4-2. Lateral view of conventional SWIS-based system
Trench
Soil Layers
JL. Purification *
I
Ground Water
Source: Bouma, 1975.
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Dispersion of SWIS percolate in the ground water
is often minimal because most ground water flow is
laminar. The percolate can remain for several
hundred feet as a distinct plume in which the solute
concentrations remain above ambient ground water
concentrations (Robertson et al., 1989, Shaw and
Turyk, 1994). The plume descends in the ground
water as the ground water is recharged from the
surface, but the amount of dispersion of the plume
can be variable. Thus, drinking water wells some
distance from a SWIS can be threatened if they are
directly in the path of a percolate plume.
4.4 Design considerations
Onsite wastewater treatment system designs vary
according to the site and wastewater characteristics
encountered. However, all designs should strive to
incorporate the following features to achieve
satisfactory long-term performance:
• Shallow placement of the infiltration surface
(< 2 feet below final grade)
• Organic loading comparable to that of septic
tank effluent at its recommended hydraulic
loading rate
• Trench orientation parallel to surface contours
• Narrow trenches (< 3 feet wide)
• Timed dosing with peak flow storage
• Uniform application of wastewater over the
infiltration surface
• Multiple cells to provide periodic resting,
standby capacity, and space for future repairs or
replacement
Based on the site characteristics, compromises to
ideal system designs are necessary. However, the
designer should attempt to include as many of the
above features as possible to ensure optimal long-
term performance and minimal impact on public
health and environmental quality.
4.4.1 Placement of the infiltration
surface
Placement of a SWIS infiltration surface may be
below, at, or above the existing ground surface (in
an in-ground trench, at grade, or elevated in a
mound system). Actual placement relative to the
original soil profile at the site is determined by
desired separation from a limiting condition
(figure 4-3). Treatment by removal of additional
pollutants during movement through soils and the
potential for excessive ground water mounding will
control the minimum separation distance from a
limiting condition. The depth below final grade is
affected by subsoil reaeration potential. Maximum
delivery of oxygen to the infiltration zone is most
likely when soil components are shallow and
narrow and have separated infiltration areas.
(Erickson and Tyler, 2001).
4.4.2 Separation distance from a
limiting condition
Placement of the infiltration surface in the soil
profile is determined by both treatment and hy-
draulic performance requirements. Adequate
separation between the infiltration surface and any
saturated zone or hydraulically restrictive horizon
within the soil profile (secondary design boundary
as defined in section 5.3.1) must be maintained to
achieve acceptable pollutant removals, sustain
aerobic conditions in the subsoil, and provide an
adequate hydraulic gradient across the infiltration
zone. Treatment needs (performance requirements)
establish the minimum separation distance, but the
potential for ground water mounding or the
availability of more permeable soil may make it
advantageous to increase the separation distance by
raising the infiltration surface in the soil profile.
Most current onsite wastewater system codes
require minimum separation distances of at least 18
inches from the seasonally high water table or
saturated zone irrespective of soil characteristics.
Generally, 2- to 4-foot separation distances have
proven to be adequate in removing most fecal
coliforms in septic tank effluent (Ayres Associates,
1993). However, studies have shown that the
applied effluent quality, hydraulic loading rates,
and wastewater distribution methods can affect the
unsaturated soil depth necessary to achieve accept-
able wastewater pollutant removals. A few studies
have shown that separation distances of 12 to 18
inches are sufficient to achieve good fecal coliform
removal if the wastewater receives additional
pretreatment prior to soil application (Converse and
Tyler, 1998a, 1998b; Duncan et al., 1994). How-
ever, when effluents with lower organic and
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Chapter 4: Treatment Processes and Systems
Figure 4-3. Suggested subsurface infiltration system design versus depth (below the original ground surface) to a
limiting condition
©
LESS THAN 12" GREATER THAN 12" BUT LESS THAN
TO LIMITING THE MINIMUM ACCEPTABLE SEPARATION
CONDITION DISTANCE TO LIMITING CONDITION
GREATER THAN THE MINIMUM
ACCEPTABLE SEPARATION DISTANCE
BUT INSUFFICIENT COVER DEPTH
GREATER THAN THE MINIMUM
ACCEPTABLE SEPARATION DISTANCE
»ITH SUFFICIENT COVER DEPTH
(2!
(3)
11) A MOUND MAY BE ACCEPTABLE WHEN THE
LIMITING CONDITION IS A SHALLOW SEASONALLY
SATURATED ZONE. WHEN THE LIMITING CONDITION IS
BEDROCK OR WATER TABLE, THE SITE SHOULD BE AVOIDED.
12" MINIMUM TO 24" SUITABLE FILL BELOW INFILTRATION
SURFACE IN MOUND.
SUGGESTED PRETREATMENT SHOULD BE SUFFICIENT TO ACHIEVE AN EFFLUENT
QUALITY THAT CAN MEET THE ESTABLISHED WATER QUALITY GOALS AFTER
PERCOLATING THROUGH THE UNSATURATED ZONE.
(4) PROVIDE LOAMY FILL IN SUFFICIENT DEPTH OVER IN-GROUND SYSTEM TO PROVIDE
PROTECTION AGAINST FREEZING.
15) ON SLOPING SITES WHERE A SHALLOW PERCHED SATURATED ZONE EXISTS, CURTAIN DRAINS MAY
BE EFFECTIVE IN LOWERING THE SURFACE OF THE SATURATED ZONE TO INCREASE THE SEPARATION DISTANCE.
ACCEPTABLE
PERM3BLE SOIL
MBOMUM ACCEPTABLE
COVER DEPTH
UNDUf ACCEPTABLE
SEPARATION DISTANCE
NOTE: MOUNDS OR AT-GRADES MAY BE APPROPRIATE UNDER CONDITIONS
TAKE ADVANTAGE OF MORE PERMEABLE SURFACE SOIL HORIZONS.
AND
TO
Source: Otis, 2001.
oxygen-demanding content are applied to the
infiltration surface at greater hydraulic loading
rates than those typically used for septic tank
effluents (during extended periods of peak flow).
treatment efficiency can be lost (Converse and
Tyler, 1998b, Siegrist et al., 2000).
Reducing the hydraulic loading rate or providing
uniform distribution of the septic tank effluent has
been shown to reduce the needed separation
distance (Bomblat et al., 1994; Converse and Tyler,
1998a; Otis, 1985; Siegrist et al., 2000; Simon and
Reneau, 1987). Reducing both the daily and
instantaneous hydraulic loading rates and providing
uniform distribution over the infiltration surface
can help maintain lower soil moisture levels.
Lower soil moisture results in longer wastewater
retention times in the soil and causes the wastewa-
ter to flow though the smaller soil pores in the
unsaturated zone, both of which enhance treatment
and can reduce the necessary separation distance.
Based only on hydraulics, certain soils require
different vertical separation distances from ground
water to avoid hydrologic interference with the
infiltration rate. From a treatment standpoint,
required separation distances are affected by dosing
pattern, loading rate, temperature, and soil charac-
teristics. Uniform, frequent dosing (more than 12
times/day) in coarser soils maximizes the effective-
ness of biological, chemical, and physical treatment
mechanisms. To offset inadequate vertical separa-
tion, a system designer can raise the infiltration
surface in an at-grade system or incorporate a
mound in the design. If the restrictive horizon is a
high water table and the soil is porous, the water
table can be lowered through the use of drainage
tile or a curtain drain if the site has sufficient relief
to promote surface discharge from the tile piping.
For flat terrain with porous soils, a commercial
system has been developed and is being field tested.
It lowers the water table with air pressure, thereby
avoiding any aesthetic concerns associated with a
raised mound on the site. Another option used
where the terrain is flat and wet is pumped drain-
age surrounding the OWTS (or throughout the
subdivision) to lower the seasonal high water table
and enhance aerobic conditions beneath the
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Chapter 4: Treatment Processes and Systems
drainfield. These systems must be properly oper-
ated by certified operators and managed by a public
management entity since maintenance of off-lot
portions of the drainage network will influence
performance of the SWIS.
The hydraulic capacity of the site or the hydraulic
conductivity of the soil may increase the minimum
acceptable separation distance determined by
treatment needs. The soil below the infiltration
surface must be capable of accepting and transmit-
ting the wastewater to maintain the desired unsatur-
ated separation distance at the design hydraulic
loading rate to the SWIS. The separation distance
necessary for satisfactory hydraulic performance is
a function of the permeability of the underlying
soil, the depth to the limiting condition, the
thickness of the saturated zone, the percentage of
rocks in the soil, and the hydraulic gradient.
Ground water mounding analyses may be necessary
to assess the potential for the saturated zone to rise
and encroach upon the minimum acceptable
separation distance (see section 5.4). Raising the
infiltration surface can increase the hydraulic
capacity of the site by accommodating more
mounding. If the underlying soil is more slowly
permeable than soil horizons higher in the profile,
it might be advantageous to raise the infiltration
surface into the more permeable horizon where
higher hydraulic loading rates are possible (Hoover
et al., 1991; Weymann et al., 1998). A shallow
infiltration system covered with fill or an at-grade
system can be used if the natural soil has a shallow
permeable soil horizon (Converse et al., 1990;
Penninger, and Hoover, 1998). If more permeable
horizons do not exist, a mound system constructed
of suitable sand fill (figure 4-4) can provide more
permeable material in which to place the infiltra-
tion surface.
4.4.3 Depth of the infiltration surface
The depth of the infiltration surface is an important
consideration in maintaining adequate subsoil
aeration and frost protection in cold climates. The
maximum depth should be limited to no more than
3 to 4 feet below final grade to adequately reaerate
the soil and satisfy the daily oxygen demand of the
applied wastewater. The infiltrative surface depth
should be less in slowly permeable soils or soils
with higher ambient moisture. Placement below
this depth to take advantage of more permeable
soils should be resisted because reaeration of the
soil below the infiltration surface will be limited.
In cold climates, a minimum depth of 1 to 2 feet
may be necessary to protect against freezing.
Porous fill material can be used to provide the
necessary cover even with an elevated (at-grade or
mound) system if it is necessary to place the
infiltration surface higher.
4.4.4 Subsurface drainage
Soils with shallow saturated zones sometimes can
be drained to allow the infiltration surface to be
placed in the natural soil. Curtain drains, vertical
drains, underdrains, and mechanically assisted
commercial systems can be used to drain shallow
water tables or perched saturated zones. Of the
three, curtain drains are most often used in onsite
wastewater systems to any great extent. They can
be used effectively to remove water that is perched
over a slowly permeable horizon on a sloping site.
However, poorly drained soils often indicate other
soil and site limitations that improved drainage
alone will not overcome, so the use of drainage
enhancements must be carefully considered. Any
sloping site that is subject to frequent inundation
during prolonged rainfall should be considered a
candidate for upslope curtain drains to maintain
unsaturated conditions in the vadose zone.
Curtain drains are installed upslope of the SWIS to
intercept the permanent and perched ground water
flowing through the site over a restrictive horizon.
Perforated pipe is laid in the bottom of upslope
trenches excavated into the restrictive horizon. A
durable, porous medium is placed around the
piping and up to a level above the estimated
seasonally high saturated zone. The porous medium
intercepts the ground water and conveys it to the
drainage pipe (figure 4-5). To provide an outfall
for the drain, one or both ends of the pipe are
extended downslope to a point where it intercepts
the ground surface. When drainage enhancements
are used, the outlet and boundary conditions must
be carefully evaluated to protect local water
quality.
The drain should avoid capture of the SWIS
percolate plume and ground water infiltrating from
below the SWIS or near the end of the drain. A
separation distance between the SWIS and the drain
that is sufficient to prevent percolate from the
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Chapter 4: Treatment Processes and Systems
Figure 4-4. Raising the infiltration surface with atypical mound system.
OBSERVATION TUBE
DISTRIBUTION
LATERAL
SAND
FILL
- -';/>."-"••"-- ^ •"••'••]'•: f :'/\• y-7-'' •" % SLOPE
BASAL AREA-' / \ --AGGREGATE
PLOWED LAYER
FROM
HOUSE
HIGH WATER
ALARM SWITCH
SEPTIC TANK
• PUMP SWITCH
DOSING CHAMBER
Source: ASAE, Converse and Tyler, 1998b.
SWIS from entering the drain should be main-
tained. The vertical distance between the bottom of
the SWIS and the drain and soil permeability
characteristics should determine this distance. As
the vertical distance increases and the permeability
decreases, the necessary separation distance in-
creases. A 10-foot separation is used for most
applications. Also, if both ends of the drain cannot
be extended to the ground surface, the upslope end
should be extended some distance along the surface
contour beyond the end of the SWIS. If not done,
ground water that seeps around the end of the drain
can render the drain ineffective. Similar cautions
should be observed when designing and locating
outlet locations for commercial systems on flat
sites.
The design of a curtain drain is based on the
permeability of the soil in the saturated zone, the
size of the area upslope of the SWIS that contrib-
utes water to the saturated zone, the gradient of the
drainage pipe, and a suitable outlet configuration.
Curtain
Drain
Fill
Material —
Perched
Water
Table \
,M
••*&
4^**
Gravel Filled
Above High
Water Table
Absorption
Trenches
Impermeable Layer
Jigjtfg^E&hrfBffl*'0 of curtain drain construction
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Chapter 4: Treatment Processes and Systems
If the saturated hydraulic conductivity is low and
the drainable porosity (the percentage of pore space
drained when the soil is at field capacity) is small,
even effectively designed curtain drains might have
limited effect on soil wetness conditions. Penninger
et al. (1998) illustrated this at a site with a silty
clay loam soil at field capacity that became com-
pletely re-saturated with as little as 1-inch of
precipitation. Figure 4-6 provides a useful design
chart that considers most of these parameters. For
further design guidance, refer to the U.S. Depart-
ment of Agriculture's Drainage of Agricultural
Land (USDA, 1973).
4.4.5 Sizing of the infiltration surface
The minimum acceptable infiltration surface area is
a function of the maximum anticipated daily
wastewater volume to be applied and the maximum
instantaneous and daily mass loading limitations of
the infiltration surface (see chapter 5). Both the
bottom and sidewall area of the SWIS excavation
can be infiltration surfaces; however, if the sidewall
is to be an active infiltration surface, the bottom
surface must pond. If continuous ponding of the
infiltration surface persists, the infiltration zone
will become anaerobic, resulting in loss of hydrau-
lic capacity. Loss of the bottom surface for infiltra-
tion will cause the ponding depth to increase over
time as the sidewall also clogs (Bouma, 1975; Keys
et al., 1998; Otis, 1977). If allowed to continue,
hydraulic failure of the system is probable. There-
fore, including sidewall area as an active infiltra-
tion surface in design should be avoided. If
sidewall areas are included, provisions should be
made in the design to enable removal of the ponded
system from service periodically to allow the
system to drain and the biomat to oxidize naturally.
Design flow
An accurate estimation of the design flow is critical
to infiltration surface sizing. For existing buildings
where significant changes in use are not expected,
water service metering will provide good estimates
for design. It is best to obtain several weeks of
metered daily flows to estimate daily average and
peak flows. For new construction, water use
metering is not possible and thus waste flow
projections must be made based on similar estab-
lishments. Tables of "typical" water use or waste-
water flows for different water use fixtures, usage
patterns, and building uses are available (see
section 3.3.1). Incorporated into these guidelines
are varying factors of safety. As a result, the use of
these guides typically provides conservatively high
estimates of maximum peak flows that may occur
only occasionally. It is critical that the designer
recognizes the conservativeness of these guides and
how they can be appropriately adjusted because of
their impacts on the design and, ultimately, perfor-
mance of the system.
Curtain drain design
Curtain drain design (see preceding figures) is dependent on the size of the contributing drainage area, the
amount of water that must be removed, the soil's hydraulic properties, and the available slope of the site.
The contributing drainage area is estimated by outlining the capture zone on a topographic map of the site.
Drainage boundaries are determined by extending flow lines perpendicularto the topographic contours upslope
from the drain to natural divides (e.g., ridge tops) or natural or man-made "no-flow" boundaries (e.g., rock
outcrops, major roads). The amount of waterthat must be removed is an estimate of the volume of precipitation
that would be absorbed by the soil after a rainfall event. This is called the drainage coefficient, which is expressed
as the depth of water to be removed over a specified period of time, typically 24 hours. Soil structure, texture,
bulk density, slope, and vegetated coverall affect the volume of waterto be drained.
The slope of the drain can be determined afterthe upslope depth of the drain invert and the outfall invert are
established. These can be estimated from the topographic map of the site. The contributing drainage area, water
volume to be removed, and slope of the drain are estimated. Figure 4-6 can be used to determine the drain
diameter. For example, the diameter of a curtain drain that will drain an area upslope of 50 acres with a drainage
coefficient of % inch on a slope of 5 percent would be 8 inches (see figure). At 0.5 percent, the necessary drain
diameterwould be 12 inches.
4-10
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
Figure 4-6. Capacity chart for subsurface drains
DRAINAGE CHART FOR
CORRUGATED PLASTIC DRAINAGE TUBING
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GRADE IN FEET PER 100 FEET
ACRES
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•5000
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DRAINAGE
COEFFICIENT
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Source: USDA, 1973.
Space between lines is the range of drain
capacity for the size shown between lines
V= velocity in feet per second
n=0.015
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
Infiltration surface loading limitations
Infiltration surface hydraulic loading design rates
are a function of soil morphology, wastewater
strength, and SWIS design configuration. Hydrau-
lic loadings are traditionally used to size infiltration
surfaces for domestic septic tank effluent. In the
past, soil percolation tests determined acceptable
hydraulic loading rates. Codes provided tables that
correlated percolation test results to the necessary
infiltration surface areas for different classes of
soils. Most states have supplemented this approach
with soil morphologic descriptions. Morphologic
features of the soil, particularly structure, texture,
and consistence, are better predictors of the soil's
hydraulic capacity than percolation tests (Brown et
al., 1994; Gross et al, 1998; Kleiss and Hoover,
1986; Simon and Reneau, 1987; Tyler et al., 1991;
Tyler and Converse, 1994). Although soil texture
analysis supplemented the percolation test in most
states by the mid-1990s, soil structure has only
recently been included in infiltrative surface sizing
tables (table 4-3). Consistence, a measure of how
well soils form shapes and stick to other objects, is
an important consideration for many slowly
permeable soil horizons. Expansive clay soils that
become extremely firm when moist and very sticky
or plastic when wet (exhibiting firm or extremely
firm consistence) are not well suited for SWISs.
Not all soil conditions are represented in table 4-3,
which is a generic guide to the effects of soil
properties on the performance of SWISs. Also
Table 4-3. Suggested hydraulic and organic loading rates for sizing infiltration surfaces
Texture
Coarse sand, sand, loamy
coarse sand, loamy sand
Fine sand, very fine sand,
loamy fine sand, loamy very
fine sand
Coarse sandy loam, sandy
loam
Fine sandy loam, very fine
sandy loam
Loam
Silt loam
Sandy clay loam, clay loam,
silty clay loam
Sandy clay, clay, silty clay
Structure
Shape
Single grain
Single grain
Massive
Platy
Prismatic, blocky,
granular
Massive
Platy
Prismatic, blocky,
granular
Massive
Platy
Prismatic, blocky,
granular
Massive
Platy
Prismatic, blocky,
granular
Massive
Platy
Prismatic, blocky,
granular
Massive
Platy
Prismatic, blocky,
granular
Grade
Structureless
Structureless
Structureless
Weak
Moderate, strong
Weak
Moderate, strong
Structureless
Weak, mod., strong
Weak
Moderate, strong
Structureless
Weak, mod., strong
Weak
Moderate, strong
Structureless
Weak, mod., strong
Weak
Moderate, strong
Structureless
Weak, mod., strong
Weak
Moderate, strong
Structureless
Weak, mod., strong
Weak
Moderate, strong
Hydraulic loading
(gal/tf-day)
BOD=150
0.8
0.4
0.2
0.2
0.4
0.6
0.2
0.2
0.4
0.2
0.4
0.6
0.4
0.6
0.2
0.4
0.2
BOD=30
1.6
1.0
0.6
0.5
0.7
1.0
0.5
0.6
0.8
0.5
0.6
0.8
0.2
0.6
0.8
0.3
0.6
0.3
Organic loading
(Ib BODflOOOtf-day)
BOD=150
1.00
0.50
0.25
0.25
0.50
0.75
0.25
0.25
0.50
0.25
0.50
0.75
0.00
0.50
0.75
0.25
0.50
0.25
BOD=30
0.40
0.25
0.15
0.13
0.18
0.25
0.13
0.15
0.20
0.13
0.15
0.20
0.05
0.15
0.20
0.08
0.15
0.08
Source: Adapted from Tyler, 2000.
4-12
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Chapter 4: Treatment Processes and Systems
available are many other state and local guides that
include loadings for soils specific to local geomor-
phology. North Carolina, for example, uses the
long-term acceptance rate (LTAR) for soil load-
ings, which is the volume of wastewater that can be
applied to a square foot of soil each day over an
indefinite period of time such that the effluent
from the onsite system is absorbed and properly
treated (North Carolina DEHNR, 1996). In the
North Carolina rules, LTAR and loading rate values
are the same.
Increasingly, organic loading is being used to size
infiltration surfaces. Based on current understand-
ing of the mechanisms of SWIS operation, organic
loadings and the reaeration potential of the subsoil
to meet the applied oxygen demand are critical
considerations in successful SWIS design. Anaero-
bic conditions are created when the applied oxygen
demand exceeds what the soil is able to supply by
diffusion through the vadose zone (Otis, 1985,
1997; Siegrist et al, 1986). The facultative and
anaerobic microorganisms that are able to thrive in
this environment are less efficient in degrading the
waste materials. The accumulating waste materials
and the metabolic by-products cause soil clogging
and loss of infiltrative capacity.
Further, higher forms of soil fauna that would help
break up the biomat (e.g., worms, insects, non-
wetland plants) and would be attracted to the
carbon and nutrient-rich infiltration zone are
repelled by the anoxic or anaerobic environment. If
wastewater application continues without ample
time to satisfy the oxygen demand, hydraulic
failure due to soil clogging occurs. Numerous
studies have shown that wastewaters with low BOD
concentrations (e.g., < 50 mg/L) can be applied to
soils at rates 2 to 16 times the typical hydraulic
loading rate for domestic septic tank effluent (Jones
and Taylor, 1965; Laak, 1970, 1986; Louden et al.,
1998; Otis, 1985; Siegrist and Boyle, 1987; Tyler
and Converse, 1994).
The comparatively higher hydraulic loadings that
highly treated wastewater (highly treated in terms
of TSS, ammonium-nitrogen, and BOD) may
permit should be considered carefully because the
resulting rapid flow through the soil may allow
deep penetration of pathogens (Converse and Tyler,
1998a, 1998b; Siegrist et al., 2000; Siegrist and
Van Cuyk, 2001b; Tyler and Converse, 1994). The
trench length perpendicular to ground water
movement (footprint) should remain the same to
minimize system impacts on the aquifer.
Unfortunately, well-tested organic loading rates for
various classes of soils and SWIS design configura-
tions have not been developed. Most organic
loading rates have been derived directly from the
hydraulic loadings typically used in SWIS design
by assuming a BOD5 concentration (see box and
table 4-3). The derived organic loading rates also
incorporate the implicit factor of safety found in
the hydraulic loading rates. Organic loadings do
appear to have less impact on slowly permeable
soils because the resistance of the biomat that forms
at the infiltrative surface presents less resistance to
infiltration of the wastewater than the soil itself
(Bouma, 1975). For a further discussion of SWIS
performance under various environmental condi-
tions, see Siegrist and Van Cuyk, 200Ib.
Constituent mass loadings
Constituent mass loadings may be a concern with
respect to water quality. For example, to use the
soil's capacity to adsorb and retain phosphorus
when systems are located near sensitive surface
waters, a phosphorus loading rate based on the soil
adsorption capacity might be selected as the
controlling rate of wastewater application to the
infiltration surface to maximize phosphorus
removal. Placement of the effluent distribution
piping high in the soil profile can promote greater
phosphorus removal because the permeability of
medium- and fine-textured soils tends to decrease
with depth and because the translocation of alumi-
num and iron—which react with phosphorus to
form insoluble compounds retained in the soil
matrix—occurs in some sandy soils, with the
maximum accumulation usually above 45 cm
(Mokma et al., 2001). Many lakes are surrounded
by sandy soils with a low phosphorus adsorption
capacity. If effluent distribution systems are
installed below 45 cm in these sandy soils, less
phosphorus will be removed from the percolating
effluent. In the case of a soluble constituent of
concern such as nitrate-nitrogen, a designer might
decide to reduce the mass of nitrate per unit of
application area. This would have the effect of
increasing the size of the SWIS footprint, thereby
reducing the potential concentration of nitrate in
the ground water immediately surrounding the
SWIS (Otis, 2001).
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Chapter 4: Treatment Processes and Systems
Factors of safety in infiltration surface sizing
Sizing of onsite wastewater systems for single-family homes is typically based on the estimated peak daily flow
and the "long term acceptance rate" of the soil for septic tank effluent. In most states, the design flow is based on
the number of bedrooms in the house. A daily flow of 150 gallons is commonly assumed for each bedroom. This
daily flow per bedroom assumes two people per bedroom that generate 75 gpd each. Bedrooms, ratherthan
current occupancy, are used for the basis of SWIS design because the number of occupants in the house can
change.
Using this typical estimating procedure, a three-bedroom home would have a design flow of 150 gpd/bedroom x 3
bedrooms or 450 gpd. However, the actual daily average flow could be much less. Based on the 1990 census, the
average home is occupied by 2.8 persons. Each person in the United States generates 45 to 70 gpd of domestic
wastewater. Assuming these averages, the average daily flow would be 125 to 195 gpd or 28 to 44 percent of the
design flow, respectively. Therefore, the design flow includes an implicit factor of safety of 2.3 to 3.6. Of course,
this factor of safety varies inversely with the home occupancy and water use.
Unfortunately, the factors of safety implicitly built into the flow estimates are seldom recognized. This is
particularly true in the case of the design hydraulic loading rates, which were derived from existing SWISs. In
most codes, the hydraulic loading rates for sand are about 1.0 to 1.25 gpd/ft2. Because these hydraulic loading
rates assume daily flows of 150 gpd per bedroom, they are overestimated by a factor of 2.3 to 3.6. Fortunately,
these two assumptions largely cancel each other out in residential applications, but the suggested hydraulic
loading rates often are used to size commercial systems and systems for schools and similar facilities, where the
ratios between design flows and actual daily flows are closer to 1.0.This situation, combined with a lack of useful
information on allowable organic loading rates, has resulted in failures, particularly for larger systems where
actual flow approximates design.
4.4.6 Geometry, orientation, and
configuration of the infiltration
surface
The geometry, orientation, and configuration of the
infiltration surface are critical design factors that
affect the performance of SWISs. They are impor-
tant for promoting subsoil aeration, maintaining an
acceptable separation distance from a saturated
zone or restrictive horizon, and facilitating con-
struction. Table 4-4 lists the design considerations
discussed in this section.
Geometry
The width and length of the infiltration surface are
important design considerations to improve perfor-
mance and limit impacts on the receiving environ-
ment. Trenches, beds, and seepage pits (or dry
wells) are traditionally used geometries. Seepage
pits can be effective for wastewater dispersal, but
they provide little treatment because they extend
deep into the soil profile, where oxygen transfer
and treatment are limited and the separation
distance to ground water is reduced. They are not
recommended for onsite wastewater treatment and
are not included as an option in this manual.
Width
Infiltration surface clogging and the resulting loss
of infiltrative capacity are less where the infiltra-
tion surface is narrow. This appears to occur
because reaeration of the soil below a narrow
infiltration surface is more rapid. The dominant
pathway for oxygen transport to the subsoil appears
to be diffusion through the soil surrounding the
infiltration surface (figure 4-7). The unsaturated
zone below a wide surface quickly becomes
anaerobic because the rates of oxygen diffusion are
too low to meet the oxygen demands of biota and
organics on the infiltration surface. (Otis, 1985;
Siegrist et al., 1986). Therefore, trenches perform
better than beds. Typical trench widths range from
1 to 4 feet. Narrower trenches are preferred, but
soil conditions and construction techniques might
limit how narrow a trench can be constructed. On
sloping sites, narrow trenches are a necessity
because in keeping the infiltration surface level, the
uphill side of the trench bottom might be excavated
into a less suitable soil horizon. Wider trench
infiltration surfaces have been successful in at-
grade systems and mounds probably because the
engineered fill material and elevation above the
natural grade promote better reaeration of the fill.
4-14
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
Comparing hydraulic and organic mass loadings for a restaurant wastewater
Infiltration surface sizing traditionally has been based on the daily hydraulic load determined through experience
to be acceptable for the soil characteristics. This approach to sizing fails to account for changes in applied
wastewater strength. Since soil clogging has been shown to be dependent on applied wastewater strength, it
might be more appropriate to size infiltration surfaces based on organic mass loadings.
To illustrate the impact of the different sizing methods, sizing computations for a restaurant are compared. A
septic tank is used for pretreatment prior to application to the SWIS. The SWIS is to be constructed in a sandy
loam with a moderate, subangularblocky structure. The suggested hydraulic loading rate for domestic septic tank
effluent on this soil is 0.6 gpd/ft2 (table 4-3). The restaurant septic tank effluent has the following characteristics:
BOD5 800 mg/L
TSS 200 mg/L
Average daily flow 600 gpd
Infiltration area based on hydraulic loading:
Area = 600 gpd/0.6 gpd/ft2 = 1,000 ft2
Infiltration area based on organic loading:
At the design infiltration rate of 0.6 gpd/ft2 recommended for domestic septic tank effluent, the equivalent organic
loading is (assuming a septic tank BOD5 effluent concentration of 150 mg/L)
Organic Loading = 150 mg/L x 0.6 gpd/ft2 x (8.34 Ib/mg/L x 1Q-6 gal)
= 7.5x10-4lbBOD5/ft2-d
Assuming 7.5 x 10~4 Ib BOD5/ft2-d as the design organic loading rate,
Area = (800 mg-BODG/L x 600 gpd x 8.34 Ibs/mg/L x 10^ gal)
(7.5x10-4lbBOD5/ft2-d)
4.0 Ib BODJd = 5337 ft2 (a 540% increase)
(7.5x10-4lbBOD5/ft2-d)
Impact of a 40% water use reduction on infiltration area sizing
Based on hydraulic loading,
Area = (1 - 0.4) x600 gpd = 600ft2
0.6 gpd/ft2
Based on organic loading (note the concentration of BOD5 increases with water conservation but the mass of
BOD5discharged does not change),
Area = (800 ma-BOD./L x 600 gpd) x (8.34 Ib/ma/L x 10^ aaD
[(1 - 0.4) x 600 gpd] x (7.5 x 10'4 Ib BOD5/ft2-d)
4.0 Ib BOD./d = 5337 ft2 (an 890% increase)
(7.5x10-4lbBOD5/ft2-d)
However, infiltration bed surface widths of greater
than 10 feet are not recommended because oxygen
transfer and clogging problems can occur (Con-
verse and Tyler, 2000; Converse et al., 1990).
Length
The trench length is important where downslope
linear loadings are critical, ground water quality
impacts are a concern, or the potential for ground
water mounding exists. In many jurisdictions,
trench lengths have been limited to 100 feet. This
restriction appeared in early codes written for
gravity distribution systems and exists as an artifact
with little or no practical basis when pressure
distribution is used. Trench lengths longer than 100
feet might be necessary to minimize ground water
impacts and to permit proper wastewater drainage
from the site. Long trenches can be used to reduce
the linear loadings on a site by spreading the
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
Table 4-4. Geometry, orientation, and configuration considerations for SWISs
Design type
Design considerations
Trench
Geometry
Width
Preferably less than 3 ft. Design width is affected by distribution method, constructability, and available area.
Length
Restricted by available length parallel to site contour, distribution method, and distribution network design.
Sidewall height Sidewalls are not considered an active infiltration surface. Minimum height is that needed to encase the
distribution piping or to meet peak flow storage requirements.
Orientation/ Should be constructed parallel to site contours and/or water table or restrictive layer contours. Should not exceed
configuration the site's maximum linear hydraulic loading rate per unit of length. Spacing of multiple, parallel trenches is also
limited by the construction method and slow dispersion from the trenches.
Bed
Geometry
Width
Should be as narrow as possible. Beds wider than 10 to 15 feet should be avoided.
Length
Restricted by available length parallel to site contour, distribution method, and distribution network design.
Sidewall height Sidewalls are not considered an active infiltration surface. Minimum height is that needed to encase the
distribution piping or to meet peak flow storage requirements.
Orientation/ Should be constructed parallel to site contours and/or water table or restrictive layer contours. The loading over
configuration the total projected width should not exceed the estimated downslope maximum linear hydraulic loading.
Seepage pit
Not recommended because of limited treatment capability.
Figure 4-7. Pathway of subsoil reaeration
VADOSE1 ZONE (UNSATURATED)
GROUNDWATER TABLE
Source: Ayres Associates, 2000
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USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
wastewater loading parallel to and farther along the
surface contour. With current distribution/dosing
technology, materials, and construction methods,
trench lengths need be limited only by what is
practical or feasible on a given site. Also, use of
standard trench lengths, e.g., X feet of trench/BR,
is discouraged because it restricts the design options
to optimize performance for a given site condition.
Height
The height of the sidewall is determined primarily
by the type of porous medium used in the system,
the depth of the medium needed to encase the
distribution piping, and/or storage requirements for
peak flows. Because the sidewall is not included as
an active infiltration surface in sizing the infiltra-
tion area, the height of the sidewall can be mini-
mized to keep the infiltration surface high in the
soil profile. A height of 6 inches is usually suffi-
cient for most porous aggregate applications. Use
of a gravelless system requires a separate analysis
to determine the height based on whether it is an
aggregate-free (empty chamber) design or one that
substitutes a lightweight aggregate for washed
gravel or crushed stone.
Orientation
Orientation of the infiltration surface(s) becomes
an important consideration on sloping sites, sites
with shallow soils over a restrictive horizon or
saturated zone, and small or irregularly shaped lots.
The long axes of trenches should be aligned
parallel to the ground surface contours to reduce
linear contour hydraulic loadings and ground water
mounding potential. In some cases, ground water
or restrictive horizon contours may differ from
surface contours because of surface grading or the
soil's morphological history. Where this occurs,
consideration should be given to aligning the
trenches with the contours of the limiting condition
rather than those of the surface. Extending the
trenches perpendicular to the ground water gradient
reduces the mass loadings per unit area by creating
a "line" source rather than a "point" source along
the contour. However, the designer must recognize
that the depth of the trenches and the soil horizon
in which the infiltration surface is placed will vary
across the system. Any adverse impacts this might
have on system performance should be mitigated
through design adjustments.
Configuration
The spacing of multiple trenches constructed
parallel to one another is determined by the soil
characteristics and the method of construction. The
sidewall-to-sidewall spacing must be sufficient to
enable construction without damage to the adjacent
trenches. Only in very tight soils will normally
used spacings be inadequate because of high soil
wetness and capillary fringe effects, which can
limit oxygen transfer. It is important to note that
the sum of the hydraulic loadings to one or more
trenches or beds per each unit of contour length
(when projected downslope) must not exceed the
estimated maximum contour loading for the site.
Also, the finer (tighter) the soil, the greater the
trench spacing should be to provide sufficient
oxygen transfer. Quantitative data are lacking, but
Camp (1985) reported a lateral impact of more
than 2.0 meters in a clay soil.
Given the advantages of lightweight gravelless
systems in terms of potentially reduced damage to
the site's hydraulic capacity, parallel trenches may
physically be placed closer together, but the
downslope hydraulic capacity of the site and the
natural oxygen diffusion capacity of the soil cannot
be exceeded.
4.4.7 Wastewater distribution onto the
infiltration surface
The method and pattern of wastewater distribution
in a subsurface infiltration system are important
design elements. Uniform distribution aids in
maintaining unsaturated flow below the infiltration
surface, which results in wastewater retention times
in the soil that are sufficiently long to effect
treatment and promote subsoil reaeration. Uniform
distribution design also results in more complete
utilization of the infiltration surface.
Gravity flow and dosing are the two most com-
monly used distribution methods. For each method,
various network designs are used (table 4-5).
Gravity flow is the most commonly used method
because it is simple and inexpensive. This method
discharges effluent from the septic tank or other
pretreatment tank directly to the infiltration surface
as incoming wastewater displaces it from the
tank(s). It is characterized by the term "trickle
flow" because the effluent is slowly discharged
over much of the day. Typically, tank discharges
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
are too low to flow throughout the distribution
network. Thus, distribution is unequal and local-
ized overloading of the infiltration surface occurs
with concomitant poor treatment and soil clogging
(Bouma, 1975; McGauhey and Winneberger, 1964;
Otis, 1985; Robeck et al., 1964).
Dosing, on the other hand, accumulates the waste-
water effluent in a dose tank from which the water
is periodically discharged under pressure in "doses"
to the infiltration system by a pump or siphon. The
pretreated wastewater is allowed to accumulate in
the dose tank and is discharged when a predeter-
mined water level, water volume, or elapsed time is
reached. The dose volumes and discharge rates are
usually such that much of the distribution network
is filled, resulting in more uniform distribution
over the infiltration surface. Dosing outperforms
gravity-flow systems because distribution is more
uniform. In addition, the periods between doses
provide opportunities for the subsoil to drain and
reaerate before the next dose (Bouma et al., 1974;
Hargett et al., 1982; Otis et al., 1977). However,
which method is most appropriate depends on the
specific application.
Gravity flow
Gravity flow can be used where there is a sufficient
elevation difference between the outlet of the
pretreatment tank and the SWIS to allow flow to
and through the SWIS by gravity. Gravity flow
systems are simple and inexpensive to construct but
are the least efficient method of distribution.
Distribution is very uneven over the infiltration
surface, resulting in localized overloading (Con-
verse, 1974; McGauhey and Winneberger, 1964;
Otis et al., 1978; University of Wisconsin, 1978).
Until a biomat forms on the infiltration surface to
slow the rate of infiltration, the wastewater resi-
dence time in the soil might be too short to effect
good treatment. As the biomat continues to form on
the overloaded areas, the soil surface becomes
clogged, forcing wastewater effluent to flow
through the porous medium of the trench until it
reaches an unclogged infiltration surface. This
phenomenon, known as "progressive clogging,"
occurs until the entire infiltration surface is ponded
and the sidewalls become the more active infiltra-
tion surfaces. Without extended periods of little or
no flow to allow the surface to dry, hydraulic
failure becomes imminent. Although inefficient,
these systems can work well for seasonal homes
with intermittent use or for households with low
occupancies. Seasonal use of SWISs allows the
infiltration surface to dry and the biomat to oxi-
dize, which rejuvenates the infiltration capacity.
Low occupancies result in mass loadings of waste-
water constituents that are lower and less likely to
exceed the soil's capacity to completely treat the
effluent.
Perforated pipe
Four-inch-diameter perforated plastic pipe is the
most commonly used distribution piping for
Table 4-5. Distribution methods and applications.
Method
Typical applications
Gravity flow
4-inch perforated pipe
Distribution box
Serial relief line
Drop box
Single or looped trenches at the same elevation; beds.
Multiple independent trenches on flat or sloping sites.
Multiple serially connected trenches on a sloping site.
Multiple independent trenches on a sloping site.
Dosed distribution
4-inch perforated pipe (with or
without a distribution box)
Pressure manifold
Rigid pipe pressure network
Dripline pressure network
Single (or multiple) trenches, looped trenches at the same elevation, an d beds.
Multiple independent trenches on sloping sites.
Multiple independent trenches at the same elevation
(a preferred method for larger SWISs)
Multiple independent trenches on flat or sloping sites
(a preferred method for larger SWISs)
4-18
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Chapter 4: Treatment Processes and Systems
gravity flow systems. The piping is generally
smooth-walled rigid polyvinyl chloride (PVC), or
flexible corrugated polyethylene (PE) or acryloni-
trile-butadiene-styrene (ABS). One or two rows of
holes or slots spaced 12 inches apart are cut into the
pipe wall. Typically, the piping is laid level in
gravel (figure 4-1) with the holes or slots at the
bottom (ASTM, undated). One distribution line is
used per trench. In bed systems, multiple lines are
installed 3 to 6 feet apart.
Distribution box
Distribution boxes are used to divide the wastewa-
ter effluent flow among multiple distribution lines.
They are shallow, flat bottomed, watertight struc-
tures with a single inlet and individual outlets
provided at the same elevation for each distribution
line. An above-grade cover allows access to the
inside of the box. The "d-box" must be laid level
on a sound, frost-proof footing to divide the flow
evenly among the outlets. Uneven settlement or
frost heaving results in unequal flow to the lateral
lines because the outlet hole elevations cease to be
level. If this occurs, adjustments must be made to
reestablish equal division of flow. Several devices
can be used. Adjustable weirs that can level the
outlet inverts and maintain the same length of weir
per outlet are one option. Other options include
designs that allow for leveling of the entire box
(figure 4-8). The box can also be used to take
individual trenches out of service by blocking the
outlet to the distribution lateral or raising the outlet
weir above the weir elevations for the other outlets.
Because of the inevitable movement of d-boxes,
their use has been discouraged for many years
(USPHS, 1957). However, under a managed care
system with regular adjustment, the d-box is
acceptable.
Serial relief line
Serial relief lines distribute wastewater to a series
of trenches constructed on a sloping site. Rather
than dividing the flow equally among all trenches
as with a distribution box, the uppermost trench is
loaded until completely flooded before the next
(lower) trench receives effluent. Similarly, that
trench is loaded until flooded before discharge
occurs to the next trench, and so on. This method
of loading is accomplished by installing "relief
lines" between successive trenches (figure 4-9).
Figure 4-8. Distribution box with adjustable weir outlets
Source: Ayres Associates.
Figure 4-9. Serial relief line distribution network and installation
detail
rFlow From Pretreatment Unit
Distribution Pipe \ r-+-A
Absorption
Trenches
Follow Contours
>urs
•*- Relief
Line
i Ends Capped
L*A Distributi
.1- Relief Trench to
Line
listribution Pipe— n
•i- Relief
Line
Source: USEPA, 1980.
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Chapter 4: Treatment Processes and Systems
The relief lines are simple overflow lines that
connect one trench to the adjacent lower trench.
They are solid-wall pipes that connect the crown of
the upper trench distribution pipe with the distribu-
tion pipe in the lower trench. Successive relief lines
are separated by 5 to 10 feet to avoid short-
circuiting. This method of distribution makes full
hydraulic use of all bottom and sidewall infiltration
surfaces, creates the maximum hydrostatic head
over the infiltration surfaces to force the water into
the surrounding soil, and eliminates the problem of
dividing flows evenly among independent trenches.
However, because continuous ponding of the
infiltration surfaces is necessary for the system to
function, the trenches suffer hydraulic failure more
rapidly and progressively because the infiltration
surfaces cannot regenerate their infiltrative capacity.
Drop box
Drop box distribution systems function similarly to
relief line systems except that drop boxes are used
in place of the relief lines. Drop boxes are installed
for each trench. They are connected in manifolds to
trenches above and below (figure 4-10). The outlet
invert can be placed near the top of each trench to
force the trench to fill completely before it dis-
charges to the next trench if a serial distribution
mode of operation is desired. Solid-wall pipe is
used between the boxes.
The advantage of this method over serial relief
lines is that individual trenches can be taken out of
service by attaching 90 degree ells to the outlets
that rise above the invert of the manifold connec-
tion to the next trench drop box. It is easier to add
additional trenches to a drop box system than to a
serial relief line network. Also, the drop box
system may be operated as an alternating trench
system by using the 90 degree ells on unused lines.
With this and the serial distribution system, the
designer must carefully evaluate the downslope
capacity of the site to ensure that it will not be
overloaded when the entire system or specific
trench combinations are functioning.
Gravelless wastewater dispersal systems
Gravelless systems have been widely used. They
take many forms, including open-bottomed cham-
bers, fabric-wrapped pipe, and synthetic materials
such as expanded polystyrene foam chips (fig-
ure 4-11). Some gravelless drain field systems use
large-diameter corrugated plastic tubing covered
with permeable nylon filter fabric not surrounded
by gravel or rock. The area of fabric in contact
with the soil provides the surface for the septic tank
effluent to infiltrate the soil. The pipe is a mini-
mum of 10 to 12 inches (25.4 to 30.5 centimeters)
in diameter covered with spun bonded nylon filter
fabric to distribute water around the pipe. The pipe
is placed in a 12- to 24-inch (30.5- to 61-centime-
ter)-wide trench. These systems can be installed in
areas with steep slopes with small equipment and in
hand-dug trenches where conventional gravel
systems would not be possible.
Reduced sizing of the infiltration surface is often
promoted as another advantage of the gravelless
system. This is based primarily on the premise that
gravelless systems do not "mask" the infiltration
surface as gravel does where the gravel is in direct
contact with the soil. Proponents of this theory
claim that an infiltration surface area reduction of
50 percent is warranted. However, these reductions
are not based on scientific evidence though they
have been codified in some jurisdictions (Amerson
et al, 1991; Anderson et al., 1985; Carlile and
Osborne, 1982; Effert and Cashell, 1987). Al-
though gravel masking might occur in porous
medium applications, reducing the infiltration
surface area for gravelless systems increases the
BOD mass loading to the available infiltration
surface. Many soils might not be able to support
the higher organic loading and, as a result, more
severe soil clogging and greater penetration of
pollutants into the vadose zone and ground water
can occur (University of Wisconsin, 1978), negat-
ing the benefits of the gravelless surface.
A similar approach must be taken with any con-
taminant in the pretreatment system effluent that
must be removed before it reaches ground water or
nearby surface waters. A 50 percent reduction in
infiltrative surface area will likely result in less
removal of BOD, pathogens, and other contami-
nants in the vadose zone and increase the presence
and concentrations of contaminants in effluent
plumes. The relatively confined travel path of a
plume provides fewer adsorption sites for removal
of adsorbable contaminants (e.g., metals, phospho-
rus, toxic organics). Because any potential reduc-
tions in infiltrative surface area must be analyzed in
a similar comprehensive fashion, the use of
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Chapter 4: Treatment Processes and Systems
Figure 4-10. Drop box distribution network
Inlet From
Pretreatment
Outlet to
Trench
urop box ^otrv\ ^
-^O3
TT Outlet to
l-p Trench
Plan
"~*fiH^ T\ r*- ^f110*^ Voj*"
-i , LTP-^ £3
- : o< ^C3 i
i ^
Outlets to •
Trench
Profile End Vic
A uistnoution \\\ ' \\\
t_ ..rOtJi
i i| ^ jQ f ;L-J-
Pretreatment^^^ \Lff //
Unit Water-Tight^
Pipes
Overflow
to Next
Drop Box
I --Inlet
1—1+. Outlet to
r — "^' Trench
JW
\)\
/|J_Drop
L^- / , ' / Dnv
t™-^'^ BOX
p^sri
i ' Extra Trenches
Can be
Added 11
Necessary
Covers Should be Exposed at
Surface if Insulated in
Cold Climates
Source: USEPA, 1980
Figure 4-11. Various gravelless systems
Polystyrene
Wrapped Pipe
Geotextile
Wrapped Pipe
Chamber
Source: National Small Flows Clearinghouse.
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Chapter 4: Treatment Processes and Systems
gravelless medium should be treated similarly to
potential reductions from increased pretreatment
and better distribution and dosing concepts.
Despite the cautions stated above, the overall
inherent value of lightweight gravelless systems
should not be ignored, especially in areas where
gravel is expensive and at sites that have soils that
are susceptible to smearing or other structural
damage during construction due to the impacts of
heavy machinery on the site. In all applications
where gravel is used (see SWIS Media in the
following section), it must be properly graded and
washed. Improperly washed gravel can contribute
fines and other material that can plug voids in the
infiltrative surface and reduce hydraulic capability.
Gravel that is embedded into clay or fine soils
during placement can have the same effect.
Leaching chambers
A leaching chamber is a wastewater treatment
system that consists of trenches or beds and one or
more distribution pipes or open-bottomed plastic
chambers. Leaching chambers have two key
functions: to disperse the effluent from septic tanks
and to distribute this effluent throughout the
trenches. A typical leaching chamber consists of
several high-density polyethylene injection-molded
arch-shaped chamber segments. A typical chamber
has an average inside width of 15 to 40 inches (38
to 102 centimeters) and an overall length of 6 to 8
feet (1.8 to 2.4 meters). The chamber segments are
usually 1-foot high, with wide slotted sidewalls.
Depending on the drain field size requirements, one
or more chambers are typically connected to form
an underground drain field network.
Typical leaching chambers (figure 4-12) are
gravelless systems that have drain field chambers
with no bottoms and plastic chamber sidewalls,
available in a variety of shapes and sizes. Use of
these systems sometimes decreases overall drain
field costs and may reduce the number of trees that
must be removed from the drain field lot.
About 750,000 chamber systems have been installed
over the past 15 years. Currently, a high percentage
of new construction applications use lightweight
plastic leaching chambers for new wastewater
treatment systems in states like Colorado, Idaho,
North Carolina, Georgia, Florida, and Oregon. The
gravel aggregate traditionally used in drain fields
can have large quantities of mineral fines that also
clog or block soil pores. Use of leaching chambers
avoids this problem. Recent research sponsored by
manufacturers shows promising results to support
reduction in sizing of drain fields through the use
of leaching chambers without increased hydraulic
and pollutant penetration failures (Colorado School
of Mines, 2001; Siegrist and Vancuyk, 2001a, 2001b).
These studies should be continued to eventually yield
rational guidelines for proper sizing of these systems
based on the type of pretreatment effluent to be
received (septic tank effluent, effluent from filters
or aerobic treatment units, etc.), as well as different
soil types and hydrogeological conditions. Many
states offer drain field sizing reduction allowances
when leaching chambers are used instead of
conventional gravel drain fields.
Because leaching chamber systems can be installed
without heavy equipment, they are easy to install
Figure 4-12. Placement of leaching chambers in typical application
Source: Hoover etal., 1996.
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Chapter 4: Treatment Processes and Systems
and repair. These high-capacity, open-bottom drain
field systems can provide greater storage than
conventional gravel systems and can be used in
areas appropriate for gravel aggregate drain fields.
Leaching systems can operate independently and
require little day-to-day maintenance. Their
maintenance requirements are comparable to those
of aggregate trench systems.
The lightweight chamber segments available on the
market stack together compactly for efficient
transport. Some chambers interlock with ribs
without fasteners, cutting installation time by
more than 50 percent reused and conventional
gravel/pipe systems. Such systems can be reused
and relocated if the site owner decides to build
on another drain field site. A key disadvantage of
leaching chambers compared to gravel drain
fields is that they can be more expensive if a
low-cost source of gravel is readily available.
Porous media should be placed along the chamber
sidewall area to a minimum compacted height of
8 inches above the trench bottom. Additional backfill
is placed to a minimum compacted height of 6 to 12
inches above the chamber, depending on the chamber
strength. Individual chamber trench bottoms should
be leveled in all directions and follow the contour of
the ground surface elevation without any dams or
other water stops. The manufacturer's installation
instructions should be followed, and systems should
be installed by an authorized contractor.
Figure 4-13.Typical pressurized distribution system layout
Pressurized Distribution Network
Pump Chamber
From Septic Tank
Source: National Small Flows Clearinghouse
Dosed flow distribution
Dosed-flow distribution systems are a significant
improvement over gravity-flow distribution systems.
The design of dosed-flow systems (figure 4-13)
includes both the distribution network and the
dosing equipment (see table 4-6). Dosing achieves
better distribution of the wastewater effluent over
the infiltration surface than gravity flow systems and
provides intervals between doses when no wastewater
is applied. As a result, dosed-flow systems reduce the
rate of soil clogging, more effectively maintain
unsaturated conditions in the subsoil (to effect good
treatment through extended residence times and
increased reaeration potential), and provide a means
to manage wastewater effluent applications to the
infiltration system (Hargett et al., 1982). They can be
used in any application and should be the method of
choice. Unfortunately, they are commonly perceived
to be less desirable because they add a mechanical
Table 4-6. Dosing methods and devices.
Dosing method Typical application
On-Demand Dosing occurs when a sufficient volume of wastewater has accumulated in the dose tank to activate the
pump switch or siphon. Dosing continues until the preselected low water level is reached. Typically, there
is no control on the daily volume of wastewater dosed.
Timed Dosing is performed by pumps on a timed cycle, typically at equal intervals and for preset dose volumes
so that the daily volume of wastewater dosed does not exceed the system's design flow. Controls can be
set so that only full doses occur. Peak flows are stored in the dose tank for dosing during low flow
periods. Excessive flows are retained in the tank, and, if they persist, a high water alarm alerts the owner
of the need for remedial action. This approach prevents unwanted and detrimental discharges to the
SWIS.
Dosing device
Pump Pressure distribution networks are set at elevations that are typically higher than the dose tank. Multiple
infiltration areas can be dosed from the same tank using multiple, alternating pumps or automatic valves.
Siphon On-demand dosing of gravity or pressure distribution networks is used where the elevation between the
siphon invert and the distribution pipe orifices is sufficient for the siphon to operate. Siphons cannot be
used for timed dosing. Two siphons in the same dose tank can be used to alternate automatically
between two infiltration areas.
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Chapter 4: Treatment Processes and Systems
component to an otherwise "passive" system and
add cost because of the dosing equipment. The
improved performance of dosed-flow systems over
gravity flow systems should outweigh these perceived
disadvantages, especially when a management
entity is in place. It must be noted, however, that if
dosed infiltration systems are allowed to pond, the
advantages of dosing are lost because the bottom
infiltration surface is continuously inundated and
no longer allowed to rest and reaerate. Therefore,
there is no value in using dosed-flow distribution in
SWISs designed to operate ponded, such as systems
that include sidewall area as an active infiltration
surface or those using serial relief lines.
Perforated pipe
Four-inch perforated pipe networks (with or
without d-boxes or pressure manifolds) that receive
dosed-flow applications are designed no differently
than gravity-flow systems. Many of the advantages
of dosing are lost in such networks, however,
because the distribution is only slightly better than
that of gravity-flow systems (Converse, 1974).
Pressure manifold
A pressure manifold consists of a large-diameter
pipe tapped with small outlet pipes that discharge
to gravity laterals (figure 4-14). A pump pressur-
izes the manifold, which has a selected diameter to
ensure that pressure inside the manifold is the same
at each outlet. This method of flow division is
more accurate and consistent than a distribution
box, but it has the same shortcoming since flow
after the manifold is by gravity along each distribu-
Figure4-14. Pressure manifold detail
tion lateral. Its most common application is to
divide flow among multiple trenches constructed at
different elevations on a sloping site.
Table 4-7 can be used to size a pressure manifold
for different applications (see sidebar). This table was
developed by Berkowitz (1985) to size the manifold
diameter based on the spacing between pressure lateral
taps, the lateral tap diameter, and the number of
lateral taps. The hydraulic computations made to
develop the table set a maximum flow differential
between laterals of 5 percent. The dosing rate is
determined by calculating the flow in a single lateral
tap assuming 1 to 4 feet of head at the manifold
outlets and multiplying the result by the number of
lateral taps. The Hazen-Williams equation for pipe
flow can be used to make this calculation.
Pressure distribution is typically constructed of
Schedule 40 PVC pipe (figure 4-15). The lateral
taps are joined by tees. They also can be attached
by tapping (threading) the manifold pipe, but the
manifold pipe must be Schedule 80 to provide a
thicker pipe wall for successful tapping. Valves on
each pressure tap are recommended to enable each
line to be taken out of service as needed by closing
the appropriate valve. This allows an opportunity
to manage, rest, or repair individual lines. To
prevent freezing, the manifold can be drained back
to the dose tank after each dose. If this is done, the
volume of water that will drain from the manifold
and forcemain must be added to the dose volume to
achieve the desired dose.
Rigid pipe pressure network
Rigid pipe pressure distribution networks are used
to provide relatively uniform distribution of
Inlet pipe
Distribution laterals
Enlargers to increase pipe
to size of trench pipe
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Table 4-7. Pressure manifold sizing
Tap spacing
(feet)
0.5
Manifold size
(inches)
2
3
4
6
8
3.0
2
3
4
6
6.0
2
3
4
6
Single-sided manifold
Lateral tap diameter (inches)
0.50
0.75
1.00
1.25 1.50 2.00
Maximum number of lateral taps
4
9
2
5
16 9
>40 21
8
14
38
2
12
21 | 18
38
5
9
14
27
30
4
7
11
20
3
5
12
22
3
6
26
6
9
17
2
3
7
12
2
3
8
2
4
14
2
5
9
2
5
2
7
3
5
3
3
Double-sided manifold
Lateral tap diameter (inches)
0.50 1 0.75
1.00
1.25
1.50 2.00
Maximum number of lateral taps
2
4
7
18
2
6
16
>20
4
7
10
19
2
4
10
17
2
5
19
3
9
15
2
6
10
3
7
2
3
13
3
6
3
4
2
4
2
3
2
Source: Adapted from Berkowitz, 1985.
Figure 4-15. Horizontal design for pressure distribution
Source: Washington Department of Health, 1998.
wastewater effluent over the entire infiltration
surface simultaneously during each dose. They are
well suited for all dosed systems. Because they
deliver the same volume of wastewater effluent per
linear length of lateral, they can be used to dose
multiple trenches of unequal length. Although rigid
pipe pressure networks can be designed to deliver
equal volumes to trenches at different elevations
(Mote, 1984; Mote et al., 1981; Otis, 1982), these
situations should be avoided. Uniform distribution
is achieved only when the network is fully pressur-
ized. During filling and draining of the network,
the distribution lateral at the lowest elevation
receives more water. This disparity increases with
increasing dosing frequency. As an alternative on
sloping sites, the SWIS could be divided into
multiple cells, with the laterals in each cell at the
same elevation. If this is not possible, other
distribution designs should be considered.
The networks consist of solid PVC pipe manifolds
that supply water to a series of smaller perforated
PVC laterals (figure 4-16). The laterals are de-
signed to discharge nearly equal volumes of
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Chapter 4: Treatment Processes and Systems
Pressure manifold design
A SWIS consisting of 12 trenches of equal length is to be constructed on a slope. To divide the septic tank
effluent equally among the 12 trenches, a pressure manifold is to be used. The lateral taps are to be spaced 6
inches apart on one side of the manifold.
Table 4-7 can be used to size the manifold. Looking down the series of columns under the Single-sided manifold,
up to sixteen 1/2-inch taps could be made to a 4-inch manifold. Therefore, a 4-inch manifold would be acceptable. If
%- or 1-inch taps were used, a 6-inch manifold would be necessary.
Using the orifice equation, the flow from each lateral tap can be estimated by assuming an operating pressure in
the manifold:
Q = Ca(2gh)2
where Q is the lateral discharge rate, C is a dimensionless coefficient that varies with the characteristics of the
orifice (0.6 for a sharp-edged orifice), a is the area of the orifice, g is the acceleration due to gravity, and h is the
operating pressure within the manifold. In English units using a 0.6 orifice coefficient, this equation becomes
Q = 11.79cP/7/2
where Q is the discharge rate in gallons per minute, d is the orifice diameter in inches, and h is the operating
pressure in feet of water.
Assuming 1/2-inch taps with a operating pressure of 3 feet of water, the discharge rate from each outlet is
Q = 11.79(1/2)231/2 = 5.1 gpm
Thus, the pump must be capable of delivering 12x5.1 gpm or approximately 60 gpm against an operating
pressure of 3 feet of water plus the static lift and friction losses incurred in the forcemain to the pressure
manifold.
wastewater from each orifice in the network when
fully pressurized. This is accomplished by main-
taining a uniform pressure throughout the network
during dosing. The manifolds and laterals are sized
relative to the selected orifice size and spacing to
achieve uniform pressure. A manual flushing
mechanism should be included to enable periodic
flushing of slimes and other solids that accumulate
in the laterals.
Figure 4-16. Rigid pipe pressure distribution networks with flushing
cleanouts
Small Diameter
Pressure Distribution
Septic Tank
Pumping (Dosing)
Chamber
Cleanout
Effluent
Pump
Design of dosed flow systems
A simplified method of network design has been
developed (Otis, 1982). Lateral and manifold
sizing is determined using a series of graphs and
tables after the designer has selected the desired
orifice size and spacing and the distal pressure in
the network (typically 1 to 2 feet of head). These
graphs and tables were derived by calculating the
change in flow and pressure at each orifice between
the distal and proximal ends of the network. The
method is meant to result in discharge rates from
the first and last orifices that differ by no more
than 10 percent in any lateral and 15 percent across
the entire network. However, subsequent testing of
field installations indicated that the design model
overestimates the maximum lateral length by as
much as 25 percent (Converse and Otis, 1982).
Therefore, if the graphs and tables are used, the
maximum lateral length for any given orifice size
and spacing should not exceed 80 percent of the
maximum design length suggested by the lateral
sizing graphs. In lieu of using the graphs and
tables, a spreadsheet could be written using the
equations presented and adjusting the orifice
discharge coefficient.
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Design procedure for rigid pipe pressure distribution network
The simplified design procedure for rigid pipe pressure networks as presented by Otis (1982) includes the
following steps:
1. Lay out the proposed network.
2. Select the desired orifice size and spacing. Maximize the density of orifices over the infiltration surface,
keeping in mind that the dosing rate increases as the orifice size increases and the orifice spacing
decreases.
3. Determine the appropriate lateral pipe diameter compatible with the selected orifice size and spacing using a
spreadsheet or sizing charts from Otis (1982).
4. Calculate the lateral discharge rate using the orifice discharge equation (0.48 discharge coefficient or 80
percent of 0.6).
5. Determine the appropriate manifold size based on the number, spacing, and discharge rate of the laterals
using a spreadsheet or sizing table from Otis (1982).
6. Determine the dose volume required. Use either the minimum dose volume equal to 5 times the network
volume or the expected daily flow divided by the desired dosing frequency, whichever is larger.
7. Calculate the minimum dosing rate (the lateral discharge times the number of laterals).
8. Select the pump based on the required dosing rate and the total dynamic head (sum of the static lift, friction
losses in the forcemain to the network, and the network losses, which are equal to 1.3 times the network
operating pressure).
To achieve uniform distribution, the density of
orifices over the infiltration surface should be as
high as possible. However, the greater the number
of orifices used, the larger the pump must be to
provide the necessary dosing rate. To reduce the
dosing rate, the orifice size can be reduced, but the
smaller the orifice diameter, the greater the risk of
orifice clogging. Orifice diameters as small as 1/8
inch have been used successfully with septic tank
effluent when an effluent screen is used at the
septic tank outlet. Orifice spacings typically are 1.5
to 4 feet, but the greater the spacing, the less
uniform the distribution because each orifice
represents a point load. It is up to the designer to
achieve the optimum balance between orifice
density and pump size.
The dose volume is determined by the desired
frequency of dosing and the size of the network.
Often, the size of the network will control design.
During filling and draining of the network at the
start and end of each dose, the distribution is less
uniform. The first holes in the network discharge
more during initial pressurization of the network,
and the holes at the lowest elevation discharge
more as the network drains after each dose. To
minimize the relative difference in discharge
volumes, the dose volume should be greater than
five times the volume of the distribution network
(Otis, 1982). A pump or siphon can be used to
pressurize the network.
Driplinepressure network
Drip distribution, which was derived from drip
irrigation technology, was recently introduced as a
method of wastewater distribution. It is a method
of pressure distribution capable of delivering small,
precise volumes of wastewater effluent to the
infiltration surface. It is the most efficient of the
distribution methods and is well suited for all types
of SWIS applications. A dripline pressure network
consists of several components:
• Dose tank
• Pump
• Prefilter
• Supply manifold
• Pressure regulator (when turbulent, flow
emitters are used)
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Chapter 4: Treatment Processes and Systems
• Dripline
• Emitters
• Vacuum release valve
• Return manifold
• Flush valve
• Controller
The pump draws wastewater effluent from the dose
tank, preferably on a timed cycle, to dose the
distribution system. Before entering the network,
the effluent must be prefiltered through mechanical
or granular medium filters. The former are used
primarily for large SWIS systems. The backflush
water generated from a self-cleaning filter should
be returned to the headworks of the treatment
system. The effluent enters the supply manifold
that feeds each dripline (figure 4-17). If turbulent
flow emitters are used, the filtered wastewater must
first pass through a pressure regulator to control the
Figure 4-17. Pressure manifold and flexible drip lines
prior to trench filling
1
Source: Ayres Associates.
maximum pressure in the dripline. Usually, the
dripline is installed in shallow, narrow trenches 1 to 2
feet apart and only as wide as necessary to insert
the dripline using a trenching machine or vibratory
plow. The trench is backfilled without any porous
medium so that the emitter orifices are in direct
contact with the soil. The distal ends of each
dripline are connected to a return manifold. The
return manifold is used to regularly flush the
dripline. To flush, a valve on the manifold is
opened and the effluent is flushed through the
driplines and returned to the treatment system
headworks.
Because of the unique construction of drip distribu-
tion systems, they cause less site disruption during
installation, are adaptable to irregularly shaped lots
or other difficult site constraints, and use more of
the soil mantle for treatment because of the shallow
depth of placement. Also, because the installed cost
per linear foot of dripline is usually less than the
cost of conventional trench construction, dripline
can be added to decrease mass loadings to the
infiltration surface at lower costs than other
distribution methods. Because of the equipment
required, however, drip distribution tends to be
more costly to construct and requires regular
operation and maintenance by knowledgeable
individuals. Therefore, it should be considered for
use only where operation and maintenance support
is ensured.
The dripline is normally a /4-inch-diameter flexible
polyethylene tube with emitters attached to the
inside wall spaced 1 to 2 feet apart along its length.
Because the emitter passageways are small, friction
losses are large and the rate of discharge is low
(typically from 0.5 to nearly 2 gallons per hour).
Two types of emitters are used. One is a "turbulent-
flow" emitter, which has a very long labyrinth.
Flow through the labyrinth reduces the discharge
pressure nearly to atmospheric rates. With increas-
ing in-line pressure, more wastewater can be forced
through the labyrinth. Thus, the discharges from
turbulent flow emitters are greater at higher
pressures (figure 4-18). To more accurately control
the rate of discharge, a pressure regulator is
installed in the supply manifold upstream of the
dripline. Inlet pressures from a minimum of 10 psi
to a maximum of 45 psi are recommended. The
second emitter type is the pressure-compensating
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Chapter 4: Treatment Processes and Systems
emitter. This emitter discharges at nearly a constant
rate over a wide range of in-line pressures (fig-
ure 4-18).
Head losses through driplines are high because of
the small diameter of the tubing and its in-line
emitters, and therefore dripline lengths must be
limited. Manufacturers limit lengths at various
emitter spacings. With turbulent flow emitters, the
discharge from each successive emitter diminishes
in response to pressure loss created by friction or
by elevation changes along the length of the
dripline. With pressure-compensating emitters, the
in-line pressure should not drop below 7 to 10 psi
at the final emitter. The designer is urged to work
with manufacturers to ensure that the system meets
their requirements.
Pressure-compensating emitters are somewhat more
expensive but offer some important advantages
over turbulent-flow emitters for use in onsite
wastewater systems. Pressure-compensating
dripline is better suited for sloping sites or sites
with rolling topography where the dripline cannot
be laid on contour. Turbulent-flow emitters dis-
charge more liquid at lower elevations than the
same emitters at higher elevations. The designer
should limit the difference in discharge rates
between emitters to no more than 10 percent. Also,
because the discharge rates are equal when under
pressure, monitoring flow rates during dosing of a
pressure-compensating dripline network can
provide an effective way to determine whether
leaks or obstructions are present in the network or
emitters. Early detection is important so that simple
and effective corrective actions can be taken.
Usually, injection of a mild bleach solution into the
dripline is effective in restoring emitter perfor-
mance if clogging is due to biofilms. If this action
proves to be unsuccessful, other corrective actions
are more difficult and costly. An additional advan-
tage of pressure-compensating emitters is that
pressure regulators are not required. Finally, when
operating in their normal pressure range, pressure-
compensating emitters are not affected by soil
water pressure in structured soils, which can cause
turbulent-flow emitters to suffer reduced dosing
volumes.
Figure4-18. Turbulent-flowand pressure-compensating emitter
discharge rates versus in-line pressure
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Controlling clogging in drip systems
With small orifices, emitters are susceptible to
clogging. Particulate materials in the wastewater,
soil particulates drawn into an emitter when the
dripline drains following a dose, and biological
slimes that grow within the dripline pose potential
clogging problems. Also, the moisture and nutrients
discharged from the emitters may invite root
intrusion through the emitter. Solutions to these
problems lie in both the design of the dripline and
the design of the distribution network. Emitter
hydrodynamic design and biocide impregnation of
the dripline and emitters help to minimize some of
these problems. Careful network design is also
necessary to provide adequate safeguards. Monitor-
ing allows the operator to identify other problems
such as destruction from burrowing animals.
To control emitter clogging, appropriate engineer-
ing controls must be provided. These include
prefiltration of the wastewater, regular dripline
flushing, and vacuum release valves on the net-
work. Prefiltration of the effluent through granular
or mechanical filters is necessary. These filters
should be capable of removing all particulates that
could plug the emitter orifices. Dripline manufactur-
ers recommend that self-cleaning filters be designed
to remove particles larger than 100 to 115 microns.
Despite this disparate experience, pretreatment with
filters is recommended in light of the potential cost
of replacing plugged emitters. Regular cleaning of
the filters is necessary to maintain satisfactory
performance. The backflush water should be
returned to the head of the treatment works.
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Chapter 4: Treatment Processes and Systems
The dripline must be flushed on a regular schedule
to keep it scoured of solids. Flushing is accom-
plished by opening the flush valve on the return
manifold and increasing the pumping rate to
achieve scouring velocity. Each supplier recom-
mends a velocity and procedure for this process.
The flushing rate and volume must include water
losses (discharge) through the emitters during the
flushing event. Both continuous flushing and timed
flushing are used. However, flushing can add a
significant hydraulic load to the treatment system
and must be considered in the design. If intermit-
tent flushing is practiced, flushing should be
performed at least monthly.
Aspiration of soil particles is another potential
emitter clogging hazard. Draining of the network
following a dosing cycle can create a vacuum in the
network. The vacuum can cause soil particles to be
aspirated into the emitter orifices. To prevent this
from occurring, vacuum relief valves are used. It is
best to install these at the high points of both the
supply and return manifolds.
Placement and layout of drip systems
When drip distribution was introduced, the ap-
proach to sizing SWISs using this distribution
method was substantially different from that for
SWISs using other distribution methods. Manufac-
turer-recommended hydraulic loading rates were
expressed in terms of gallons per day per square
foot of drip distribution footprint area. Typically,
the recommended rates were based on 2-foot
emitter and dripline spacing. Therefore, each
emitter would serve 4 square feet of footprint area.
Because the dripline is commonly plowed into the
soil without surrounding it with porous medium,
the soil around the dripline becomes the actual
infiltration surface. The amount of infiltration
surface provided is approximately 2/3 to 1 square
foot per 5 linear feet of dripline. As a result, the
wastewater loading rate is considerably greater than
the hydraulic loadings recommended for traditional
SWISs. Experience has shown however, that the
hydraulic loading on this surface can be as much as
seven times higher than that of traditional SWIS
designs (Ayres Associates, 1994). This is probably
due to the very narrow geometry, higher levels of
pretreatment, shallow placement, and intermittent
loadings of the trenches, all of which help to
enhance reaeration of the infiltration surface.
The designer must be aware of the differences
between the recommended hydraulic loadings for
drip distribution and those customarily used for
traditional SWISs. The recommended drip distribu-
tion loadings are a function of the soil, dripline
spacing, and applied effluent quality. It is necessary
to express the hydraulic loading in terms of the
footprint area because the individual dripline trenches
are not isolated infiltration surfaces. If the emitter
and/or dripline spacing is reduced, the wetting
fronts emanating from each emitter could overlap
and significantly reduce hydraulic performance. There-
fore, reducing the emitter and/or dripline spacing should
not reduce the overall required system footprint.
Reducing the spacing might be beneficial for irrigat-
ing small areas of turf grass, but the maximum daily
emitter discharge must be reduced proportionately by
adding more dripline to maintain the same footprint
size. Using higher hydraulic loading rates must be
carefully considered in light of secondary boundary
loadings, which could result in excessive ground
water mounding (see chapter 5). Further, the instanta-
neous hydraulic loading during a dose must be
controlled because storage is not provided in the
dripline trench. If the dose volume is too high, the
wastewater can erupt at the ground surface.
Layout of the drip distribution network must be
considered carefully. Two important consequences
of the network layout are the impacts on dose
pump sizing necessary to achieve adequate flushing
flows and the extent of localized overloading due
to internal dripline drainage. Flushing flow rates
are a function of the number of manifold/dripline
connections: More connections create a need for
greater flushing flows, which require a larger
pump. To minimize the flushing flow rate, the
length of each dripline should be made as long as
possible in accordance with the manufacturer's
recommendations. To fit the landscape, the dripline
can be looped between the supply and return
manifolds (figure 4-19). Consideration should also
be given to dividing the network into more than
one cell to reduce the number of connections in an
individual network. A computer program has been
developed to evaluate and optimize the hydraulic
design for adequate flushing flows of dripline
networks that use pressure-compensating emitters
(Berkowitz and Harman, 1994).
Internal drainage that occurs following each dose
or when the soils around the dripline are saturated
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Figure 4-19. Dripline layout on a site with trees
Central
Unit
(CU)
Supply to
Air/Vacuum
Release Valve
Source: Adapted from American Manufacturing, 2001.
can cause significant hydraulic overloading to
lower portions of the SWIS. Following a dose
cycle, the dripline drains through the emitters. On
sloping sites, the upper driplines drain to the lower
driplines, where hydraulic overloading can occur.
Any free water around the dripline can enter
through an emitter and drain to the lowest eleva-
tion. Each of these events needs to be avoided as
much as possible through design. The designer can
minimize internal drainage problems by isolating
the driplines from each other in a cell, by aligning
the supply and return manifolds with the site's
contours. A further safeguard is to limit the number
of doses per day while keeping the instantaneous
hydraulic loadings to a minimum so the dripline
trench is not flooded following a dose. This trade-
off is best addressed by determining the maximum
hydraulic loading and adjusting the number of
doses to fit this dosing volume.
Freezing of dripline networks has occurred in
severe winter climates. Limited experience indicates
that shallow burial depths together with a lack of
uncompacted snow cover or other insulating
materials might lead to freezing. In severe winter
climates, the burial depth of dripline should be
increased appropriately and a good turf grass
established over the network. Mulching the area the
winter after construction or every winter should be
considered. Also, it is good practice to install the
vacuum release valves below grade and insulate the
air space around them. Although experience with
drip distribution in cold climates is limited, these
safeguards should provide adequate protection.
Dosing methods
Two methods of dosing have been used (table 4-6).
With on-demand dosing, the wastewater effluent
rises to a preset level in the dose tank and the pump
or siphon is activated by a float switch or other
mechanism to initiate discharge (figure 4-20).
During peak-flow periods, dosing is frequent with
little time between doses for the infiltration system
to drain and the subsoil to reaerate. During low-
flow periods, dosing intervals are long, which can
be beneficial in controlling biomat development
but is inefficient in using the hydraulic capacity of
the system.
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Chapter 4: Treatment Processes and Systems
Figure 4-20. Pumping tank (generic)
PUMP CONTROL BOX
AIR VENT
FROM-!
SEPTIC TANK
Source: Purdue University, 1990
Timed dosing overcomes some of the shortcomings
of on-demand dosing. Timers are used to turn the
pump on and off at specified intervals so that only
a predetermined volume of wastewater is discharged
with each dose. Timed dosing has two distinct
advantages over on-demand dosing. First, the doses
can be spaced evenly over the entire 24-hour day to
optimize the use of the soil's treatment capacity.
Second, the infiltration system receives no more
than its design flow each day. Clear water infiltra-
tion, leaking plumbing fixtures, or excessive water
use are detected before the excess flow is discharged
to the infiltration system because the dose tank will
eventually fill to its high water alarm level. At that
point, the owner has the option of calling a septage
pumper to empty the tanks or activating the pump to
dose the system until the problem is diagnosed and
corrected. Unlike on-demand dosing, timed dosing
requires that the dose tank be sized to store peak
flows until they can be pumped (see sidebar).
Dosing frequency and volume are two important
design considerations. Frequent, small doses are
preferred over large doses one or two times per
day. However, doses should not be so frequent that
distribution is poor. This is particularly true with
either of the pressure distribution networks. With
pressure networks, uniform distribution does not
occur until the entire network is pressurized. To
ensure pressurization and to minimize unequal
discharges from the orifices during filling and
draining, a dose volume equal to five times the
network volume is a good rule of thumb. Thus,
doses can be smaller and more frequent with dripline
networks than with rigid pipe networks because the
volume of drip distribution networks is smaller.
4.4.8 SWIS media
A porous medium is placed below and around SWIS
distribution piping to expand the infiltration surface
area of the excavation exposed to the applied waste-
water. This approach is similar in most SWIS designs,
except when drip distribution or aggregate-free
designs are used. In addition, the medium also
supports the excavation sidewalls, provides storage of
peak wastewater flows, minimizes erosion of the
infiltration surface by dissipating the energy of the
influent flow, and provides some protection for the
piping from freezing and root penetration.
Traditionally, washed gravel or crushed rock,
typically ranging from 3/4 to 21A inches in diam-
eter, has been used as the porous medium. The
rock should be durable, resistant to slaking and
dissolution, and free of fine particles. A hardness
of at least 3 on the Moh's scale of hardness is
suggested. Rock that can scratch a copper penny
without leaving any residual meets this criterion.
It is important that the medium be washed to
remove fine particles. Fines from insufficiently
washed rock have been shown to result in signifi-
cant reductions in infiltration rates (Amerson et
al., 1991). In all applications where gravel is
used, it must be properly graded and washed.
Improperly washed gravel can contribute fines and
other material that can plug voids in the infiltra-
tive surface and reduce hydraulic capability.
Gravel that is embedded into clay or fine soils
during placement can have the same effect.
In addition to natural aggregates, gravelless systems
have been widely used as alternative SWIS medium
(see preceding section). These systems take many
forms, including open-bottomed chambers, fabric-
wrapped pipe, and synthetic materials such as
expanded polystyrene foam chips, as described in
the preceding section. Systems that provide an open
chamber are sometimes referred to as "aggregate-
free" systems, to distinguish them from others that
substitute lightweight medium for gravel or stone.
These systems provide a suitable substitute in
locales where gravel is not available or affordable.
Some systems (polyethylene chambers and light-
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Dose tank sizing for timed dosing
Timed dosing to a SWIS is to be used in an onsite system serving a restaurant in a summer resort area. Timed
dosing will equalize the flows, enhancing treatment in the soil and reducing the required size of the SWIS.
The restaurant serves meals from 11 a.m. to 12 midnight Tuesday through Saturday and from
9 a.m. to 2 p.m. Sundays. The largest number of meals is served during the summer weekends. The restaurant is
closed on Mondays. The metered water use is as follows:
Average weekly water use (summer) 17,500 gal
Peak weekend water use (4 p.m. Friday to 2 p.m. Sunday) 9,500 gal
The dose tank will be sized to equalize flows over a 7-day period. The dosing frequency is to be six times daily or
one dose every 4 hours. Therefore, the dose volume will be
Dose volume = 17,500 gal/wk, (7 d/wk x 6 doses/day) = 417 gal/dose
The necessary volume of the dose tank to store the peak flows and equalize the flow to the SWIS over the 7-day
week can be determined graphically.
I
O
4,000 -
V=12,50MOOO = 4,500 gals
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
Time
Source: Ayres Associates.
The accumulated water use over the week and the daily dosing rate (6 doses/day x 417 gal/dose = 2,500 gpd) is
plotted on the graph. Lines parallel to the dosing rate are drawn tangent to points 1 and 2 representing the
maximum deviations of the water use line above and below the dosing rate line. The volume represented by the
difference between the two parallel lines is the tank volume needed to achieve flow equalization. A 4,500-gallon
tankwould be required.
Both siphons and pumps can be used for dosing distribution networks. Only drip distribution networks cannot be
dosed by siphons because of the higher required operating pressures and the need to control instantaneous
hydraulic loadings (dose volume). Siphons can be used where power is not available and elevation is adequate to
install the siphon sufficiently above the distribution network to overcome friction losses in the forcemain and
network. Care must be taken in their selection and installation to ensure proper performance. Also, owners must
be aware that siphon systems require routine monitoring and occasional maintenance. "Dribbling" can occur when
the siphon bell becomes saturated, suspending dosing and allowing the wastewater effluent to trickle out under
the bell. Dribbling can occur because of leaks in the bell or a siphon out of adjustment. Today, pumps are favored
over siphons because of the greater flexibility in site selection and dosing regime.
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weight aggregate systems) can also offer substantial
advantages in terms of reduced site disruption over
the traditional gravel because their light weight
makes them easy to handle without the use of
heavy equipment. These advantages reduce labor
costs, limit damage to the property by machinery,
and allow construction on difficult sites where
conventional medium could not reasonably be used.
4.5 Construction management and
contingency options
Onsite wastewater systems can and do fail to
perform at times. To avoid threats to public health
and the environment during periods when a system
malfunctions hydraulically, contingency plans
should be made to permit continued use of the
system until appropriate remedial actions can be
taken. Contingency options should be considered
during design so that the appropriate measures are
designed into the original system. Table 4-8 lists
common contingency options.
4.5.1 Construction considerations
Construction practices are critical to the perfor-
mance of SWISs. Satisfactory SWIS performance
depends on maintaining soil porosity. Construc-
tion activities can significantly reduce the porosity
and cause SWISs to hydraulically fail soon after
being brought into service. Good construction
practices should carefully consider site protection
before and during construction, site preparation,
and construction equipment selection and use.
Good construction practices for at-grade and
mound systems can be found elsewhere (Converse
and Tyler, 2000; Converse et al, 1990). Many of
them, however, are similar to those described in
the following subsections.
Site protection
Construction of the onsite wastewater system is
often only one of many construction activities that
occur on a property. If not protected against
intrusion, the site designated for the onsite system
can be damaged by other, unrelated construction
Table 4-8. Contingency options for SWIS malfunctions
Contingency
option
Description
Comments
Reserve area Unencumbered area of suitable soils
set aside for a future replacement
system.
Multiple cells Two or more infiltration cells with a
total hydraulic capacity of 100% to
200% of the required area that are
alternated into service.
Water conservation Water-conserving actions taken to
reduce the hydraulic load to the
system, which may alleviate the
problem.
Pump and haul Conversion of the septic tank to a
holding tank that must be
periodically pumped. The raw waste
must be hauled to a suitable
treatment and/or disposal site.
Does not provide immediate relief from performance problems
because the replacement system must be constructed.
The replacement system should be constructed such that use
can be alternated with use of the original system.
Provide immediate relief from performance problems by
providing stand-by capacity. Rotating cells in and out of
service on an annual or other regular schedule helps to
maintain system capacity. Alternating valves are commercially
available to implement this option. The risk from performance
problems is reduced because the malfunction of a single cell
involves a smaller proportion of the daily flow.
A temporary solution that may necessitate a significant
lifestyle change by the residents, which creates a disincentive
for continued implementation. The organic loading will remain
the same unless specific water uses or waste inputs are
eliminated from the building or the wastewaters are removed
from the site.
Holding tanks are a temporary or permanent solution that can
be effective but costly, creating a disincentive for long -term
use.
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activities. Therefore, the site should be staked and
roped off before any construction activities begin
to make others aware of the site and to keep traffic
and materials stockpiles off the site.
The designer should anticipate what activities will
be necessary during construction and designate
acceptable areas for them to occur. Site access
points and areas for traffic lanes, material stockpil-
ing, and equipment parking should be designated
on the drawings for the contractor.
Site preparation
Site preparation activities include clearing and
surface preparation for filling. Before these activi-
ties are begun, the soil moisture should be deter-
mined. In nongranular soils, compaction will occur
if the soil is near its plastic limit. This can be tested
by removing a sample of soil and rolling it between
the palms of the hands. If the soil fails to form a
"rope" the soil is sufficiently dry to proceed.
However, constant care should be taken to avoid
soil disturbance as much as possible.
Clearing
Clearing should be limited to mowing and raking
because the surface should be only minimally
disturbed. If trees must be removed, they should be
cut at the base of the trunk and removed without
heavy machinery. If it is necessary to remove the
stumps, they should be ground out. Grubbing of
the site (mechanically raking away roots) should be
avoided. If the site is to be filled, the surface
should be moldboard- or chisel-plowed parallel to
the contour (usually to a depth of 7 to 10 inches)
when the soil is sufficiently dry to ensure maxi-
mum vertical permeability. The organic layer
should not be removed. Scarifying the surface with
the teeth of a backhoe bucket is not sufficient.
Excavation
Excavation activities can cause significant reduc-
tions in soil porosity and permeability (Tyler et al.,
1985). Compaction and smearing of the soil
infiltrative surface occur from equipment traffic
and vibration, scraping actions of the equipment, and
placement of the SWIS medium on the infiltration
surface. Lightweight backhoes are most commonly
used. Front-end loaders and blades should not be used
because of their scraping action. All efforts should
be made to avoid any disturbance to the exposed
infiltration surface. Equipment should be kept off
the infiltration field. Before the SWIS medium is
installed, any smeared areas should be scarified and
the surface gently raked. If gravel or crushed rock
is to be used for SWIS medium, the rock should be
placed in the trench by using the backhoe bucket
rather than dumping it directly from the truck. If
damage occurs, it might be possible to restore the
area, but only by removing the compacted layer. It
might be necessary to remove as much as 4 inches
of soil to regain the natural soil porosity and
permeability (Tyler et al., 1985). Consequences of
the removal of this amount of soil over the entire
infiltration surface can be significant. It will reduce
the separation distance to the restrictive horizon
and could place the infiltration surface in an
unacceptable soil horizon.
To avoid potential soil damage during construction,
the soil below the proposed infiltration surface
elevation must be below its plastic limit. This
should be tested before excavation begins. Also,
excavation should be scheduled only when the
infiltration surface can be covered the same day to
avoid loss of permeability from wind-blown silt or
raindrop impact. Another solution is to use light-
weight gravelless systems, which reduce the
damage and speed the construction process.
Before leaving the site, the area around the site
should be graded to divert surface runoff from the
SWIS area. The backfill over the infiltration
surface should be mounded slightly to account for
settling and eliminate depressions over the system
that can pond water. Finally, the area should be
seeded and mulched.
4.5.2 Operation, maintenance, and
monitoring
Subsurface wastewater infiltration systems require
little operator intervention. Table 4-9 lists typical
operation, maintenance, and monitoring activities
that should be performed. However, more complex
pretreatment, larger and more variable flows, and
higher-risk installations increase the need for
maintenance and monitoring. More information is
provided in the USEPA draft Guidelines for Onsite/
Decentralized Wastewater Systems (2000) and in the
chapter 4 fact sheets.
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Table 4-9. Operation, maintenance, and monitoring activities
Task
Description
Frequency
Water meter reading
Dosing tank controls
Pump calibration
Infiltration cell rotation
Infiltration surface
ponding
Inspect surface and
perimeter of SWIS
Tank solids levels and
integrity assessment
Recommended for large, commercial systems
Check function of pump, switches, and timers for pressure-dosed
systems
Check pumping rate and adjust dose timers as appropriate for
pressure-dosed systems
Direct wastewater to standby cells to rest
operating cells
Record wastewater ponding depths over the infiltration surface and
switch to standby cell when ponding persists for more than a month
Walk over SWIS area to observe surface ponding or other signs of
stress or damage
Check for sludge and scum accumulation, condition of baffles and
inlet and outlet appurtenances, and potential leaks
Daily
Monthly
Annually
Annually
(optimally in the spring)
Monthly
Monthly
Varies with tank size and
management program
4.5.3 Considerations for large and
commercial systems
Designs for systems treating larger flows follow the
same guidelines used for residential systems, but they
must address characteristics of the wastewater to be
treated, site characteristics, infiltration surface sizing,
and contingency planning more comprehensively.
Wastewater characteristics
Wastewaters from cluster systems serving multiple
homes or commercial establishments can differ
substantially in flow pattern and waste strength from
wastewaters generated by single family residences.
The ratio of peak to average daily flow from residen-
tial clusters is typically much lower than what is
typical from single residences. This is because the
moderating effect associated with combining multiple
water use patterns reduces the daily variation in flow.
Commercial systems, on the other hand, can vary
significantly in wastewater strength. Typically,
restaurants have high concentrations of grease and
BOD, laundromats have high sodium and suspended
solids concentrations, and toilet facilities at parks
and rest areas have higher concentrations of BOD,
TSS, and nitrogen. These differences in daily flow
patterns and waste strengths must be dealt with in
the design of SWISs. Therefore, it is important to
characterize the wastewater fully before initiating
design (see chapter 3).
Site characteristics
The proposed site for a SWIS that will treat waste-
water from a cluster of homes or a commercial
establishment must be evaluated more rigorously
than a single-residence site because of the larger
volume of water that is to be applied and the
greater need to determine hydraulic gradients and
direction. SWIS discharges can be from 10 to more
than 100 times the amount of water that the soil
infiltration surface typically receives from precipi-
tation. For example, assume that an area receives an
average of 40 inches of rainfall per year. Of that, less
than 25 percent (about 10 inches annually) infiltrates
and even less percolates to the water table. A waste-
water infiltration system is designed to infiltrate
0.4 to 1.6 inches per day, or 146 to 584 inches per
year. Assuming actual system flows are 30 percent
of design flows, this is reduced to 44 to 175 inches
per year even under this conservative approach.
The soils associated with small systems can usually
accommodate these additional flows. However,
systems that treat larger flows load wastewaters to
the soil over a greater area and might exceed the
site's capacity to accept the wastewater. Restrictive
horizons that may inhibit deep percolation need to
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be identified before design. Ground water mounding
analysis should be performed to determine whether
the hydraulic loading to the saturated zone (second-
ary design boundary), rather than the loading to the
infiltration surface, controls system sizing (see Chap-
ter 5). If the secondary boundary controls design, the
size of the infiltration surface, its geometry, and even
how wastewater is applied will be affected.
Infiltration surface sizing
Selection of the design flow is a very important
consideration in infiltration surface sizing. State
codified design flows for residential systems
typically are 2 to 5 times greater than the average
daily flow actually generated in the home. This
occurs because the design flow is usually based on
the number of bedrooms rather than the number of
occupants. As a result, the actual daily flow is often
a small fraction of the design flow.
This is not the case when the per capita flows for
the population served or metered flows are used as
the design flow. In such instances, the ratio of
design flow to actual daily flow can approach
unity. This is because the same factors of safety are
typically not used to determine the design flow. In
itself, this is not a problem. The problem arises
when the metered or averaged hydraulic loading
rates are used to size the infiltration surface. These
rates can be more than two times what the soil
below the undersized system is actually able to
accept. As a result, SWISs would be significantly
undersized. This problem is exacerbated where the
waste strength is high.
To avoid the problem of undersizing the infiltration
surface, designs must compensate in some way.
Factors of safety of up to 2 or more could be
applied to accurate flow estimates, but the more
common practice is to design multiple cells that
provide 150 to 200 percent of the total estimated
infiltration surface needed. Multiple cells are a
good approach because the cells can be rotated into
service on a regular schedule that allows the cells
taken out of service to rest and rejuvenate their
hydraulic capacity. Further, the system provides
standby capacity that can be used when malfunc-
tions occur, and distribution networks are smaller
to permit smaller and more frequent dosing,
thereby maximizing oxygen transfer and the
hydraulic capacity of the site. For high-strength
wastewaters, advanced pretreatment can be speci-
fied or the infiltration surface loadings can be
adjusted (see Special Issue Fact Sheet 4).
Contingency planning
Malfunctions of systems that treat larger flows can
create significant public health and environmental
hazards. Therefore, adequate contingency planning
is more critical for these systems than for residen-
tial systems. Standby infiltration cells, timed
dosing, and flow monitoring are key design
elements that should be included. Also, professional
management should be required.
4.6 Septic tanks
The septic tank is the most commonly used waste-
water pretreatment unit for onsite wastewater systems.
Tanks may be used alone or in combination with
other processes to treat raw wastewater before it is
discharged to a subsurface infiltration system. The
tank provides primary treatment by creating quiescent
conditions inside a covered, watertight rectangular,
oval, or cylindrical vessel, which is typically buried.
In addition to primary treatment, the septic tank stores
and partially digests settled and floating organic solids
in sludge and scum layers. This can reduce the sludge
and scum volumes by as much as 40 percent, and it
conditions the wastewater by hydrolyzing organic
molecules for subsequent treatment in the soil or by
other unit processes (Baumann et al, 1978). Gases
generated from digestion of the organics are vented
back through the building sewer and out of the house
plumbing stack vent. Inlet structures are designed to
limit short circuiting of incoming wastewater across
the tank to the outlet, while outlet structures (e.g., a
sanitary "tee" fitting) retain the sludge and scum
layers in the tank and draw effluent only from the
clarified zone between the sludge and scum layers.
The outlet should be fitted with an effluent screen
(commonly called a septic tank filter) to retain larger
solids that might be carried in the effluent to the
SWIS, where it could contribute to clogging and
eventual system failure. Inspection ports and manways
are provided in the tank cover to allow access for
periodically removing the tank contents, including the
accumulated scum and sludge (figure 4-21). A
diagram of a two-compartment tank is shown later
in this section.
Septic tanks are used as the first or only pretreat-
ment step in nearly all onsite systems regardless of
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Chapter 4: Treatment Processes and Systems
Figure 4-21. Profile of a single-compartment septic
tank with outlet screen
daily wastewater flow rate or strength. Other
mechanical pretreatment units may be substituted for
septic tanks, but even when these are used septic
tanks often precede them. The tanks passively
provide suspended solids removal, solids storage
and digestion, and some peak flow attenuation.
4.6.1 Treatment
A septic tank removes many of the settleable solids,
oils, greases, and floating debris in the raw waste-
water, achieving 60 to 80 percent removal
(Baumann et al., 1978; Boyer and Rock, 1992;
University of Wisconsin, 1978). The solids removed
are stored in sludge and scum layers, where they
undergo liquefaction. During liquefaction, the first
step in the digestion process, acid-forming bacteria
Table 4-10. Characteristics of domestic septic tank effluent
partially digest the solids by hydrolyzing the
proteins and converting them to volatile fatty acids,
most of which are dissolved in the water phase. The
volatile fatty acids still exert much of the biochemical
oxygen demand that was originally in the organic
suspended solids. Because these acids are in the
dissolved form, they are able to pass from the tank in
the effluent stream, reducing the BOD removal
efficiency of septic tanks compared to primary sedi-
mentation. Typical septic tank BOD removal efficien-
cies are 30 to 50 percent (Boyer and Rock, 1992;
University of Wisconsin, 1978; see table 4-10). Com-
plete digestion, in which the volatile fatty acids are
converted to methane, could reduce the amount of BOD
released by the tank, but it usually does not occur to a
significant extent because wastewater temperatures in
septic tanks are typically well below the optimum
temperature for methane-producing bacteria.
Gases that form from the microbial action in the
tank rise in the wastewater column. The rising gas
bubbles disturb the quiescent wastewater column,
which can reduce the settling efficiency of the tank.
They also dislodge colloidal particles in the sludge
blanket so they can escape in the water column. At
the same time, however, they can carry active anaero-
bic and facultative microorganisms that might help
to treat colloidal and dissolved solids present in the
wastewater column (Baumann and Babbit, 1953).
Septic tank effluent varies naturally in quality
depending on the characteristics of the wastewater
and condition of the tank. Documented effluent
quality from single-family homes, small communi-
ties and cluster systems, and various commercial
septic tanks is presented in tables 4-10 through 4-12.
Parameter
No. tanks sampled
Location
(No. samples)
BOD5 (mg/L)
COD (mg/L)
TSS (mg/L)
TKN (mgN/L)
TP(rngP/l)
Oil/Grease (mg/L)
Fecal conforms (log#/L)
University of Wis.
(1978)
7
Wisconsin
(150)
138
327
49
45
13
—
4.6
Harkin.etal.
(1979)
33
Wisconsin
(140-215)
132
445
87
82
21.8
—
6.5
Ronayne, et al.
(1982)
8
Oregon
(56)
217
—
146
57.1
—
—
6.4
Ayres Associates
(1993)
8
Florida
(36)
141
—
161
39
11
36
5.1-8.2
Ayres Associates
(1996)
1
Florida
(3)
179
—
59
66
17
37
7.0
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Table 4-11. Average septic tank effluent concentrations for selected parameters from small community and cluster systems
Parameter
BOD5 (mg/L)
COD (mg/L)
TSS (mg/L)
TN (mgN/L)
TP (mgP/L)
Oil/Grease (mg/L)
Fecal coliforms (log#/L)
PH
Flow (gpcd)
Westboro,wr
168
338
85
63.4
8.1
-
7.3
6.9-7.4
36
Bend, ORb
157
276
36
41
-
65
-
6.4-7.2
40-60
Glide, ORC
118
228
52
50
-
16
-
6.4-7.2
48
Manila, CAd
189
284
75
--
--
22
--
6.5-7.8
40-57
College Sta.,TX8
-
266
-
29.5
8.2
-
6.0
7.4
-
' Small-diameter gravity sewer serving a small community collecting septic tank effluent from 90 connections (Otis, 1978).
b Pressure sewer collecting septic tank effluent from eleven homes (Bowne, 1982).
0 Pressure sewer collecting septic tank effluent from a small community (Bowne, 1982).
" Pressure sewer serving a small community collecting septic tank effluent from 330 connections (Bowne, 1982).
' Effluent from one septic tank accepting wastewater from nine homes (Brown et al., 1977).
Table 4-12. Average septic tank effluent concentrations of selected parameters from various commercial establishments3
Wastewater
Type
Restaurant A
Restaurant B
Restaurant C
Restaurant D
Restaurant E
Restaurant F
Motel
Country Club A
Country Club B
Country Club C
Bar/Grill
BOD5
(mg/L)
582
245
880
377
693
261
171
197
333
101
179
COD
(mg/L)
1196
622
1667
772
1321
586
381
416
620
227
449
TSS
(mg/L)
187
65
372
247
125
66
66
56
121
44
79
TKN
(mgN/L)
82
64
71
30
78
73
34
36
63
36
61
TP
(mgP/L)
24
14
23
15
28
19
20
13
17
10
7
Oil/Grease
(mg/L)
101
40
144
101
65
47
45
24
46
33
49
Temp
(°C)
8-22
8-22
13-23
16-21
4-26
7-25
20-28
6-20
13-26
10-23
8-22
pH
5.6-6.4
6.6-7.0
5.8-6.3
5.7-6.8
5.5-6.9
5.8-7.0
6.5-7.1
6.5-6.8
6.2-6.8
6.2-7.4
6.0-7.0
' Averages based on 2 to 9 grab samples depending on the parameter taken between March and September 1983.
Source: Siegrist et al., 1985.
4.6.2 Design considerations
The primary purpose of a septic tank is to provide
suspended solids and oil/grease removal through
sedimentation and flotation. The important factor
to achieving good sedimentation is maintaining
quiescent conditions. This is accomplished by
providing a long wastewater residence time in the
septic tank. Tank volume, geometry, and compart-
mentalization affect the residence time.
Volume
Septic tanks must have sufficient volume to provide
an adequate hydraulic residence time for sedimenta-
tion. Hydraulic residence times of 6 to 24 hours have
been recommended (Baumann and Babbitt, 1953:
Kinnicutt et al., 1910). However, actual hydraulic
residence times can vary significantly from tank to
tank because of differences in geometry, depth, and
inlet and outlet configurations (Baumann and Babbitt,
1953). Sludge and scum also affect the residence
time, reducing it as the solids accumulate.
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Table 4-13. Septic tank capacities for one- and two-
family dwellings (ICC, 1995).
Number of
bedrooms
1
2
3
4
5
6
7
8
Septic tank volume
(gallons)
750"
750"
1,000
1,200
1,425
1,650
1,875
2,100
" Many states have established
1,000 gallons or more as the minimum size.
Most state and national plumbing codes specify the
tank volume to be used based on the building size
or estimated peak daily flow of wastewater. Table
4-13 presents the tank volumes recommended in
the International Private Sewage Disposal Code
specified for one- and two-family residences (ICC.
1995). The volumes specified are typical of most
local codes, but in many jurisdictions the minimum
tank volume has been increased to 1,000 gallons or
more. For buildings other than one- or two-family
residential homes, the rule of thumb often used for
sizing tanks is to use two to three times the esti-
mated design flow. This conservative rule of thumb
is based on maintaining a 24-hour minimum
hydraulic retention time when the tank is ready for
pumping, for example, when the tank is one-half to
two-thirds full of sludge and scum.
Geometry
Tank geometry affects the hydraulic residence time
in the tank. The length-to-width ratio and liquid
depth are important considerations. Elongated tanks
with length-to-width ratios of 3:1 and greater have
been shown to reduce short-circuiting of the raw
wastewater across the tank and improve suspended
solids removal (Ludwig, 1950). Prefabricated tanks
generally are available in rectangular, oval, and
cylindrical (horizontal or vertical) shapes. Vertical
cylindrical tanks can be the least effective because
of the shorter distance between the inlets and
outlets. Baffles are recommended.
Among tanks of equal liquid volumes, the tank
with shallower liquid depths better reduces peak
outflow rates and velocities, so solids are less likely
to remain in suspension and be carried out of the
tank in the effluent. This is because the shallow
tank has a larger surface area. Inflows to the tank
cause less of a liquid rise because of the larger
surface area. The rate of flow exiting the tank
(over a weir or through a pipe invert) is propor-
Figure 4-22.Two-compartment tank with effluent screen and surface risers
Source: Washington Department of Health, 1998.
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tional to the height of the water surface over the
invert (Baumann et al., 1978; Jones, 1975). Also,
the depth of excavation necessary is reduced with
shallow tanks, which helps to avoid saturated
horizons and lessens the potential for ground water
infiltration or tank flotation. A typically specified
minimum liquid depth below the outlet invert is 36
inches. Shallower depths can disturb the sludge
blanket and, therefore, require more frequent
pumping.
Compartmentalization
Compartmentalized tanks (figure 4-23) or tanks
placed in series provide better suspended solids
removal than single-compartment tanks alone,
although results from different studies vary
(Baumann and Babbitt, 1953; Boyer and Rock,
1992; Weibel et al., 1949, 1954; University of
Wisconsin, 1978). If two compartments are used,
better suspended solids removal rates are achieved
if the first compartment is equal to one-half to two-
thirds the total tank volume (Weibel et al., 1949,
1954). An air vent between compartments must be
provided to allow both compartments to vent. The
primary advantage of these configurations is when
gas generated from organic solids digestion in the
first compartment is separated from subsequent
compartments.
Inlets and outlets
The inlet and outlet of a septic tank are designed to
enhance tank performance. Their respective invert
elevations should provide at least a 2- to 3-inch
drop across the tank to ensure that the building
sewer does not become flooded and obstructed
during high wastewater flows (figure 4-24). A clear
space of at least 9 inches should be provided above
the liquid depth (outlet invert) to allow for scum
storage and ventilation. Both the inlet and outlet
are commonly baffled. Plastic sanitary tees are the
most commonly used baffles. Curtain baffles
(concrete baffles cast to the tank wall and fiberglass
or plastic baffles bolted to the tank wall) have also
been used. The use of gasket materials that achieve
a watertight joint with the tank wall makes plastic
sanitary tees easy to adjust, repair, or equip with
effluent screens or filters. The use of a removable,
cleanable effluent screen connected to the outlet is
strongly recommended.
Figure 4-23. Examples of septic tank effluent screens/filters
• discharge
ports
slots
Source: Adapted from various manufacturers' drawings.
The inlet baffle is designed to prevent short-
circuiting of the flow to the outlet by dissipating
the energy of the influent flow and deflecting it
downward into the tank. The rising leg of the tee
should extend at least 6 inches above the liquid
level to prevent the scum layer from plugging the
inlet. It should be open at the top to allow venting
of the tank through the building sewer and out the
plumbing stack vent. The descending leg should
extend well into the clear space between the sludge
and scum layers, but not more than about 30 to 40
percent of the liquid depth. The volume of the
descending leg should not be larger than 2 to 3
gallons so that it is completely flushed to expel
floating materials that could cake the inlet. For this
reason, curtain baffles should be avoided.
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The outlet baffle is designed to draw effluent from
the clear zone between the sludge and scum layers.
The rising leg of the tee should extend 6 inches
above the liquid level to prevent the scum layer
from escaping the tank. The descending leg should
extend to 30 or 40 percent of the liquid depth.
Effluent screens (commonly called septic tank
filters), which can be fitted to septic tank outlets,
are commercially available. Screens prevent solids
that either are buoyant or are resuspended from the
scum or sludge layers from passing out of the tank
(figures 4-22 and 4-23). Mesh, slotted screens, and
stacked plates with openings from 1/32 to 1/8 inch
are available. Usually, the screens can be fitted into
the existing outlet tee or retrofitted directly into the
outlet. An access port directly above the outlet is
required so the screen can be removed for inspec-
tion and cleaning.
Quality-assured, reliable test results have not shown
conclusively that effluent screens result in effluents
with significantly lower suspended solids and BOD
concentrations. However, they provide an excellent,
low-cost safeguard against neutral-buoyancy solids
and high suspended solids in the tank effluent
resulting from solids digestion or other upsets.
Also, as the effluent screens clog over time, slower
draining and flushing of home fixtures may alert
homeowners of the need for maintenance before
complete blockage occurs.
Tank access
Access to the septic tank is necessary for pumping
septage, observing the inlet and outlet baffles, and
servicing the effluent screen. Both manways and
inspection ports are used. Manways are large
openings, 18 to 24 inches in diameter or square. At
least one that can provide access to the entire tank
for septage removal is needed. If the system is
compartmentalized, each compartment requires a
manway. They are located over the inlet, the outlet,
or the center of the tank. Typically, in the past
manway covers were required to be buried under
state and local codes. However, they should be
above grade and fitted with an airtight, lockable
cover so they can be accessed quickly and easily.
Inspection ports are 8 inches or larger in diameter
and located over both the inlet and the outlet unless
a manway is used. They should be extended above
grade and securely capped.
(CAUTION: The screen should not be removed for
inspection or cleaning without first plugging the
outlet or pumping the tank to lower the liquid level
below the outlet invert. Solids retained on the screen
can slough off as the screen is removed. These
solids will pass through the outlet and into the
SWIS unless precautions are taken. This caution
should be made clear in homeowner instructions
and on notices posted at the access port.)
Septic tank designs for large wastewater flows do
not differ from designs for small systems. How-
ever, it is suggested that multiple compartments or
tanks in series be used and that effluent screens be
attached to the tank outlet. Access ports and
manways should be brought to grade and provided
with locking covers for all large systems.
Construction materials
Septic tanks smaller than 6,000 gallons are typi-
cally premanufactured; larger tanks are constructed
in place. The materials used in premanufactured
tanks include concrete, fiberglass, polyethylene,
and coated steel. Precast concrete tanks are by far
the most common, but fiberglass and plastic tanks
are gaining popularity. The lighter weight fiber-
glass and plastic tanks can be shipped longer
distances and set in place without cranes. Concrete
tanks, on the other hand, are less susceptible to
collapse and flotation. Coated steel tanks are no
longer widely used because they corrode easily.
Tanks constructed in place are typically made of
concrete.
Tanks constructed of fiberglass-reinforced polyester
(FRP) usually have a wall thickness of about 1/4
inch (6 millimeters). Most are gel- or resin-coated
to provide a smooth finish and prevent glass fibers
from becoming exposed, which can cause wicking.
Polyethylene tanks are more flexible than FRP
tanks and can deform to a shape of structural
weakness if not properly designed. Concrete tank
walls are usually about 4 inches thick and rein-
forced with no. 5 rods on 8-inch (20-centimeter)
centers. Sulfuric acid and hydrogen sulfide, both of
which are present in varying concentrations in
septic tank effluent, can corrode exposed rods and
the concrete itself over time. Some plastics (e.g.,
polyvinyl chloride, polyethylene, but not nylon)
are virtually unaffected by acids and hydrogen
sulfide (USEPA, 1991).
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Quality construction is critical to proper perfor-
mance. Tanks must be properly designed, rein-
forced, and constructed of the proper mix of
materials so they can meet anticipated loads
without cracking or collapsing. All joints must be
watertight and flexible to accommodate soil
conditions. For concrete tank manufacturing, a
"best practices manual" can be purchased from the
National Pre-Cast Concrete Association (NPCA,
1998). Also, a Standard Specification for Precast
Concrete Septic Tanks (C 1227) has been published
by the American Society for Testing and Materials
(ASTM, 1998).
Watertightness
Watertightness of the septic tank is critical to the
performance of the entire onsite wastewater system.
Leaks, whether exfiltrating or infiltrating, are
serious. Infiltration of clear water to the tank from
the building storm sewer or ground water adds to
the hydraulic load of the system and can upset
subsequent treatment processes. Exfiltration can
threaten ground water quality with partially treated
wastewater and can lower the liquid level below the
outlet baffle so it and subsequent processes can
become fouled with scum. Also, leaks can cause the
tank to collapse.
Tank joints should be designed for Watertightness.
Two-piece tanks and tanks with separate covers
should be designed with tongue and groove or lap
joints (figure 4-24). Manway covers should have
similar joints. High-quality, preformed joint sealers
should be used to achieve a watertight seal. They
should be workable over a wide temperature range
and should adhere to clean, dry surfaces; they must
not shrink, harden, or oxidize. Seals should meet
the minimum compression and other requirements
prescribed by the seal manufacturer. Pipe and
Figure 4-24. Tongue and groove joint and sealer
Source: Ayres Associates
inspection port joints should have cast-in rubber
boots or compression seals.
Septic tanks should be tested for Watertightness
using hydrostatic or vacuum tests, and manway
risers and inspection ports should be included in the
test. The professional association representing the
materials industry of the type of tank construction
(e.g., the National Pre-cast Concrete Association)
should be contacted to establish the appropriate
testing criteria and procedures. Test criteria for
precast concrete are presented in table 4-14.
4.6.3 Construction considerations
Important construction considerations include tank
location, bedding and backfilling, Watertightness,
and flotation prevention, especially with non-
concrete tanks. Roof drains, surface water runoff,
and other clear water sources must not be routed to
the septic tank. Attention to these considerations
Table 4-14. Watertightness testing procedure/criteria for precast concrete tanks
Standard
NPCA (1998)
Hydrostatic test
Vacuum test
C 1227,
ASTM (1993)
Preparation
Seal tank, fill with water, and
let stand for 24 hours. Refill
Pass/fail criterion
Approved if water level is
held for 1 hour
Preparation
Seal tank and apply a
vacuum of 2 in. Hg.
Pass/fail criterion
Approved if 90% of vacuum
is held for 2 minutes.
tank.
Seal tank, fill with water, and
let stand for 8 to 10 hours.
Refill tank and let stand for
another 8 to 10 hours.
Approved if no further
measurable water level drop
occurs
Seal tank and apply a
vacuum of 4 in. Hg. Hold
vacuum for 5 minutes. Bring
vacuum back to 4 in. Hg.
Approved if vacuum can be
held for 5 minutes without a
loss of vacuum.
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will help to ensure that the tank performs as
intended.
Location
The tank should be located where it can be accessed
easily for septage removal and sited away from
drainage swales or depressions where water can
collect. Local codes must be consulted regarding
minimum horizontal setback distances from
buildings, property boundaries, wells, water lines,
and the like.
Bedding and backfilling
The tank should rest on a uniform bearing surface.
It is good practice to provide a level, granular base
for the tank. The underlying soils must be capable
of bearing the weight of the tank and its contents.
Soils with a high organic content or containing
large boulders or massive rock edges are not
suitable.
After setting the tank, leveling, and joining the
building sewer and effluent line, the tank can be
backfilled. The backfill material should be free-
flowing and free of stones larger than 3 inches in
diameter, debris, ice, or snow. It should be added in
lifts and each lift compacted. In fine-textured soils
such as silts, silt loams, clay loams, and clay,
imported granular material should be used. This is
a must where freeze and thaw cycles are common
because the soil movement during such cycles can
work tank joints open. This is a significant concern
when using plastic and fiberglass tanks.
The specific bedding and backfilling requirements
vary with the shape and material of the tank. The
manufacturer should be consulted for acceptable
materials and procedures.
Watertightness
All joints must be sealed properly, including tank
joints (sections and covers if not a monolithic
tank), inlets, outlets, manways, and risers (ASTM,
1993; NPCA, 1998). The joints should be clean
and dry before applying the joint sealer. Only high-
quality joint sealers should be used (see previous
section). Backfilling should not proceed until the
sealant setup period is completed. After all joints
have been made and have cured, a watertightness
test should be performed (see table 4-14 for precast
concrete tanks). Risers should be tested.
Flotation prevention
If the tank is set where the soil can be saturated,
tank flotation may occur, particularly when the
tank is empty (e.g., recently pumped dose tanks or
septic tank after septage removal). Tank manufac-
turers should be consulted for appropriate
antiflotation devices.
4.6.4 Operation and maintenance
The septic tank is a passive treatment unit that
typically requires little operator intervention.
Regular inspections, septage pumping, and periodic
cleaning of the effluent filter or screen are the only
operation and maintenance requirements. Commer-
cially available microbiological and enzyme
additives are promoted to reduce sludge and scum
accumulations in septic tanks. They are not neces-
sary for the septic tank to function properly when
treating domestic wastewaters. Results from studies
to evaluate their effectiveness have failed to prove
their cost-effectiveness for residential application.
For most products, concentrations of suspended
solids and BOD in the septic tank effluent increase
upon their use, posing a threat to SWIS perfor-
mance. No additive made up of organic solvents or
strong alkali chemicals should be used because they
pose a potential threat to soil structure and ground
water.
Inspections
Inspections are performed to observe sludge and
scum accumulations, structural soundness, water-
tightness, and condition of the inlet and outlet
baffles and screens. (Warning: In performing
inspections or other maintenance, the tank should
not be entered. The septic tank is a confined space
and entering can be extremely hazardous because of
toxic gases and/or insufficient oxygen.)
Sludge and scum accumulations
As wastewater passes through and is partially
treated in the septic tank over the years, the layers
of floatable material (scum) and settleable material
(sludge) increase in thickness and gradually reduce
the amount of space available for clarified waste-
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water. If the sludge layer rises to the bottom of the
effluent T-pipe, solids can be drawn through the
effluent port and transported into the infiltration
field, increasing the risk of clogging. Likewise, if
the bottom of the thickening scum layer moves
lower than the bottom of the effluent T-pipe, oils
and other scum material can be drawn into the
piping that discharges to the infiltration field.
Various devices are commercially available to
measure sludge and scum depths. The scum layer
should not extend above the top or below the
bottom of either the inlet or outlet tees. The top of
the sludge layer should be at least 1 foot below the
bottom of either tee or baffle. Usually, the sludge
depth is greatest below the inlet baffle. The scum
layer bottom must not be less than 3 inches above
the bottom of the outlet tee or baffle. If any of
these conditions are present, there is a risk that
wastewater solids will plug the tank inlet or be
carried out in the tank effluent and begin to clog
the SWIS.
Structural soundness andwatertightness
Structural soundness and watertightness are best
observed after the septage has been pumped from
the tank. The interior tank surfaces should be
inspected for deterioration, such as pitting,
spalling, delamination, and so forth and for cracks
and holes. The presence of roots, for example,
indicates tank cracks or open joints. These observa-
tions should be made with a mirror and bright
light. Watertightness can be checked by observing
the liquid level (before pumping), observing all
joints for seeping water or roots, and listening for
running or dripping water. Before pumping, the
liquid level of the tank should be at the outlet
invert level. If the liquid level is below the outlet
invert, exfiltration is occurring. If it is above, the
outlet is obstructed or the SWIS is flooded. A
constant trickle from the inlet is an indication that
plumbing fixtures in the building are leaking and
need to be inspected.
Baffles and sere ens
The baffles should be observed to confirm that they
are in the proper position, secured well to the
piping or tank wall, clear of debris, and not
cracked or broken. If an effluent screen is fitted to
the outlet baffle, it should be removed, cleaned,
inspected for irregularities, and replaced. Note that
effluent screens should not be removed until the
tank has been pumped or the outlet is first plugged.
Septic tank pumping
Tanks should be pumped when sludge and scum
accumulations exceed 30 percent of the tank
volume or are encroaching on the inlet and outlet
baffle entrances. Periodic pumping of septic tanks
is recommended to ensure proper system perfor-
mance and reduce the risk of hydraulic failure. If
systems are not inspected, septic tanks should be
pumped every 3 to 5 years depending on the size of
the tank, the number of building occupants, and
household appliances and habits (see Special Issues
Fact Sheets). Commercial systems should be
inspected and/or pumped more frequently, typically
annually. There is a system available that provides
continuous monitoring and data storage of changes
in the sludge depth, scum or grease layer thickness,
liquid level, and temperature in the tank. Long-
term verification studies of this system are under
way. Accumulated sludge and scum material stored
in the tank should be removed by a certified,
licensed, or trained service provider and reused or
disposed of in accordance with applicable federal,
state, and local codes. (Also see section 4.5.5.)
4.6.5 Septage
Septage is an odoriferous slurry (solids content of
only 3 to 10 percent) of organic and inorganic
material that typically contains high levels of grit,
hair, nutrients, pathogenic microorganisms, oil, and
grease (table 4-15). Septage is defined as the entire
contents of the septic tank—the scum, the sludge,
and the partially clarified liquid that lies between
them—and also includes pumpings from aerobic
treatment unit tanks, holding tanks, biological
("composting") toilets, chemical or vault toilets,
and other systems that receive domestic wastewa-
ters. Septage is controlled under the federal regula-
tions at 40 CFR Part 503. Publications and other
information on compliance with these regulations
can be found at http://www.epa.gov/oia/tips/
scws.htm.
Septage also may harbor potentially toxic levels of
metals and organic and inorganic chemicals. The
exact composition of septage from a particular
treatment system is highly dependent upon the type
of facility and the activities and habits of its users.
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Table 4-15. Chemical and physical characteristics of domestic
septage
Parameter -
Total solids
Total volatile solids
Total suspended solids
Volatile suspended solids
Biochemical oxygen demand
Chemical oxygen demand
Total Kjeldahl nitrogen
Ammonia nitrogen
Total phosphorus
Alkalinity
Grease
PH
Concentration (mg/L)
Average
34,106
23,100
12,862
9,027
6,480
31,900
588
97
210
970
5,600
—
Range
1,132-130,475
353-71,402
310-93,378
95-51,500
440-78,600
1,500-703,000
66-1,060
3-116
20-760
522-4,190
208-23,368
1.5-12.6
Source: USEPA, 1994.
For example, oil and grease levels in septage from
food service or processing facilities might be many
times higher than oil and grease concentrations in
septage from residences (see Special Issues Fact
Sheets). Campgrounds that have separate graywater
treatment systems for showers will likely have
much higher levels of solids in the septage from the
blackwater (i.e., toilet waste) treatment system.
Septage from portable toilets might have been
treated with disinfectants, deodorizers, or other
chemicals.
Septage management programs
The primary objective of a septage management
program is to establish procedures and rules for
handling and disposing of septage in an affordable
manner that protects public health and ecological
resources. When planning a program it is important
to have a thorough knowledge of legal and regula-
tory requirements regarding handling and disposal.
USEPA (1994) has issued regulations and guidance
that contain the type of information required for
developing, implementing, and maintaining a
septage management program. Detailed guidance
for identifying, selecting, developing, and operat-
ing reuse or disposal sites for septage is provided in
Process Design Manual: Surface Disposal of
Sewage Sludge and Domestic Septage (USEPA,
1995b), which is on the Internet at http://
www.epa.gov/ORD/WebPubs/sludge.pdf. Addi-
tional information can be found in Domestic
Septage Regulatory Guidance (USEPA, 1993), at
http://www.epa.gov/oia/tips/scws.htm.
States and municipalities typically establish public
health and environmental protection regulations for
septage management (pumping, handling, trans-
port, treatment, and reuse/disposal). Key compo-
nents of septage management programs include
tracking or manifest systems that identify accept-
able septage sources, pumpers, transport equip-
ment, final destination, and treatment, as well as
procedures for controlling human exposure to
septage, including vector control, wet weather
runoff, and access to disposal sites.
Septage treatment/disposal: land
application
The ultimate fate of septage generally falls into
three basic categories—land application, treatment
at a wastewater treatment plant, or treatment at a
special septage treatment plant. Land application is
the most commonly used method for disposing of
septage in the United States. Simple and cost-
effective, land application approaches use minimal
energy and recycle organic material and nutrients
back to the land. Topography, soils, drainage
patterns, and agricultural crops determine which
type of land disposal practice works best for a
given situation. Some common alternatives are
surface application, subsurface incorporation, and
burial. Disposal of portable toilet wastes mixed
with disinfectants, deodorizers, or other chemicals
at land application sites is not recommended. If
possible, these wastes should be delivered to the
collection system of a wastewater treatment plant to
avoid potential chemical contamination risks at
septage land application sites. Treatment plant
operators should be consulted so they can deter-
mine when and where the septage should be added
to the collection system.
When disposing of septage by land application,
appropriate buffers and setbacks should be pro-
vided between application areas and water re-
sources (e.g., streams, lakes, sinkholes). Other
considerations include vegetation type and density,
slopes, soils, sensitivity of water resources, climate,
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and application rates. Agricultural products from
the site must not be directly consumed by humans.
Land application practices include the following:
Spreading by hauler truck or farm equipment
In the simplest method, the truck that pumps the
septage takes it to a field and spreads it on the soil.
Alternatively, the hauler truck can transfer its
septage load into a wagon spreader or other special-
ized spreading equipment or into a holding facility
at the site for spreading later.
Spray irrigation
Spray irrigation is an alternative that eliminates the
problem of soil compaction by tires. Pretreated
septage is pumped at 80 to 100 psi through nozzles
and sprayed directly onto the land. This method
allows for septage disposal on fields with rough
terrain.
Ridge and furrow irrigation
Pretreated septage can be transferred directly into
furrows or row crops. The land should be relatively
level.
Subsurface incorporation of septage
This alternative to surface application involves
placing untreated septage just below the surface.
This approach reduces odors and health risks while
still fertilizing and conditioning the soil. The
method can be applied only on relatively flat land
(less than 8 percent slope) in areas where the
seasonally high water table is at least 20 inches.
Because soil compaction is a concern, no vehicles
should be allowed to drive on the field for 1 to 2
weeks after application. Subsurface application
practices include the following:
• Plow and furrow irrigation: In this simple
method, a plow creates a narrow furrow 6 to 8
inches (15 to 20 centimeters) deep. Liquid
septage is discharged from a tank into the
furrow, and a second plow covers the furrow.
• Subsurface injection: A tillage tool is used to
create a narrow cavity 4 to 6 inches (10 to 15
centimeters) deep. Liquid septage is injected
into the cavity, and the hole is covered.
Codisposal of septage in sanitary landfills
Because of the pollution risks associated with
runoff and effluent leaching into ground water,
landfill disposal of septage is not usually a viable
option. However, some jurisdictions may allow
disposal of septage/soil mixtures or permit other
special disposal options for dewatered septage
(sludge with at least 20 percent solids). Septage or
sludge deposited in a landfill should be covered
immediately with at least 6 inches of soil to control
odors and vector access (USEPA, 1995b). (Note:
Codisposal of sewage sludge or domestic septage at
a municipal landfill is considered surface disposal
and is regulated under 40 CFR Part 258.)
Septage treatment/disposal: treatment
plants
Disposal of septage at a wastewater treatment plant
is often a convenient and cost-effective option.
Addition of septage requires special care and
handling because by nature septage is more concen-
trated than the influent wastewater stream at the
treatment plant. Therefore, there must be adequate
capacity at the plant to handle and perhaps tempo-
rarily store delivered septage until it can be fed into
the treatment process units. Sites that typically
serve as the input point for septage to be treated at
a wastewater treatment plant include the following:
Upstream sewer manhole
This alternative is viable for larger sewer systems
and treatment plants. Septage is added to the
normal influent wastewater flow at a receiving
station fitted with an access manhole.
Treatment plant headworks
The septage is added at the treatment plant up-
stream of the inlet screens and grit chambers. The
primary concern associated with this option is the
impact of the introduced wastes on treatment unit
processes in the plant. A thorough analysis should
be conducted to ensure that plant processes can
accept and treat the wastes while maintaining
appropriate effluent pollutant concentrations and
meeting other treatment requirements. In any
event, the treatment plant operator should be
consulted before disposal.
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Sludge-handling process
To reduce loading to the liquid stream, the septage
can be sent directly to the sludge-handling process.
Like the headworks option, the impact on the
sludge treatment processes must be carefully
analyzed to ensure that the final product meets
treatment and other requirements.
Treatment at a special septage treatment plant
This method of septage disposal is usually em-
ployed in areas where land disposal or treatment at
a wastewater treatment plant is not a feasible
option. There are few of these facilities, which
vary from simple lagoons to sophisticated plants
that mechanically and/or chemically treat septage.
Treatment processes used include lime stabilization,
chlorine oxidation, aerobic and anaerobic digestion,
composting, and dewatering using pressure or
vacuum filtration or centrifugation. This is the
most expensive option for septage management and
should be considered only as a last resort.
Public outreach and involvement
Developing septage treatment units or land applica-
tion sites requires an effective public outreach
program. Opposition to locating these facilities in
the service area is sometimes based about incom-
plete or inaccurate information, fear of the un-
known, and a lack of knowledge on potential
impacts. Without an effective community-based
program of involvement, even the most reasonable
plan can be difficult to implement. Traditional
guidance on obtaining public input in the develop-
ment of disposal or reuse facilities can be found in
Process Design Manual: Surface Disposal of
Sewage Sludge and Domestic Septage (USEPA,
1995b), which is on the Internet at http://
www.epa.gov/ORD/WebPubs/sludge.pdf.
Figure 4-25. Underdrain system detail for sand filters
Filter Sand
2"
1/2" to 3/4" rock
4" slotted PVC
Underdrain
Additional information can be found in Domestic
Septage Regulatory Guidance (USEPA, 1993),
posted at http://www.epa.gov/oia/tips/scws.htm.
General guidance on developing and implementing
a public outreach strategy is available in Getting In
Step: A Guide to Effective Outreach in Your
Watershed, published by the Council of State
Governments (see chapter 2) and available at http:/
/www.epa.gov/owow/watershed/outreach/
documents/.
4.7 Sand/media filters
Sand (or other media) filters are used to provide
advanced treatment of settled wastewater or septic
tank effluent. They consist of a lined (lined with
impervious PVC liner on sand bedding) excavation
or watertight structure filled with uniformly sized
washed sand (the medium) that is normally placed
over an underdrain system (figure 4-25). These
contained media filters are also known as packed
bed filters. The wastewater is dosed onto the
surface of the sand through a distribution network
and is allowed to percolate through the sand to the
underdrain system. The underdrain collects the
filtrate for further processing, recycling, or dis-
charging to a SWIS. Some "bottomless" designs
directly infiltrate the filtered effluent into the soil
below.
4.7.1 Treatment mechanisms and filter
design
Sand filters are essentially aerobic, fixed-film
bioreactors used to treat septic tank effluent. Other
very important treatment mechanisms that occur in
sand filters include physical processes such as
straining and sedimentation, which remove sus-
pended solids within the pores of the media, and
chemical adsorption of dissolved pollutants (e.g.,
phosphorus) to media surfaces. The latter phenom-
enon tends to be finite because adsorption sites
become saturated with the adsorbed compound, and
it is specific to the medium chosen. Bioslimes from
the growth of microorganisms develop as attached
films on the sand particle surfaces. The microorgan-
isms in the slimes absorb soluble and colloidal waste
materials in the wastewater as it percolates around
the sand surfaces. The absorbed materials are
incorporated into new cell mass or degraded under
aerobic conditions to carbon dioxide and water.
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Most of the biochemical treatment occurs within
approximately 6 inches (15 centimeters) of the
filter surface. As the wastewater percolates through
this active layer, carbonaceous BOD and ammo-
nium-nitrogen are removed. Most of the suspended
solids are strained out at the filter surface. The
BOD is nearly completely removed if the wastewa-
ter retention time in the sand media is sufficiently
long for the microorganisms to absorb and react
with waste constituents. With depleting carbon-
aceous BOD in the percolating wastewater, nitrify-
ing microorganisms are able to thrive deeper in this
active surface layer, where nitrification will readily
occur.
To achieve acceptable treatment, the wastewater
retention time in the filter must be sufficiently long
and reaeration of the media must occur to meet the
oxygen demand of the applied wastewater. The
pore size distribution and continuity of the filter
medium, the dose volume, and the dosing fre-
quency are key design and operating considerations
for achieving these conditions. As the effective size
and uniformity of the media increases, the
reaeration rate increases, but the retention time
decreases. Treatment performance might decline if
the retention time is too short. If so, it may be
necessary to recirculate the wastewater through the
filter several times to achieve the desired retention
time and concomitant treatment performance.
Multiple small dose volumes that do not create a
saturated wetting front on the medium can be used
to extend residence times. If saturated conditions
are avoided, moisture tensions within the medium
will remain high, which will redistribute the
applied wastewater throughout the medium,
enhancing its contact with the bioslimes on the
medium. The interval between doses provides time
for reaeration of the medium to replenish the
oxygen depleted during the previous dose.
Filter surface clogging can occur with finer media
in response to excessive organic loadings. Biomass
increases can partially fill the pores in the surface
layer of the sand. If the organic loadings are too
great, the biomass will increase to a point where
the surface layer becomes clogged and is unable to
accept further wastewater applications. However, if
the applied food supply is less than that required by
resident microorganisms, the microorganisms are
forced into endogenous respiration; that is, they
begin to draw on their stored metabolites or
surrounding dead cells for food. If the microorgan-
isms are maintained in this growth phase, net
increases of biomass do not occur and clogging can
be minimized.
Chemical adsorption can occur throughout the
medium bed, but adsorption sites in the medium
are usually limited. The capacity of the medium to
retain ions depends on the target constituent, the
pH, and the mineralogy of the medium. Phospho-
rus is one element of concern in wastewater that
can be removed in this manner, but the number of
available adsorption sites is limited by the charac-
teristics of the medium. Higher aluminum, iron, or
calcium concentrations can be used to increase the
effectiveness of the medium in removing phospho-
rus. Typical packed bed sand filters are not effi-
cient units for chemical adsorption over an ex-
tended period of time. However, use of special
media can lengthen the service (phosphorus re-
moval) life of such filters beyond the normal, finite
period of effective removal.
Filter designs
Sand filters are simple in design and relatively
passive to operate because the fixed-film process is
very stable and few mechanical components are
used. Two types of filter designs are common,
"single-pass" and "recirculating" (figure 4-26).
They are similar in treatment mechanisms and
performance, but they operate differently. Single-
pass filters, historically called "intermittent" filters,
discharge treated septic tank effluent after one pass
through the filter medium (see Fact Sheet 10).
Recirculating filters collect and recirculate the
filtrate through the filter medium several times
before discharging it (see Fact Sheet 11). Each has
advantages for different applications.
Single-pass filters
The basic components of single-pass filters (see
Fact Sheet 10) include a dose tank, pump and
controls (or siphon), distribution network, and the
filter bed with an underdrain system (figure 4-25).
The wastewater is intermittently dosed from the
dose tank onto the filter through the distribution
network. From there, it percolates through the sand
medium to the underdrain and is discharged. On-
demand dosing has often been used, but timed
dosing is becoming common.
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Chapter 4: Treatment Processes and Systems
Figure 4-26. Schematics of the two most common types of sand media filters
Intermittent (single-pass) sand filter
Septic Tank
gravity ^
Ine *"
S^
(pu,
V.
Dot
dun
>v
^
s
ifeig
P^
Sand
Recirculating sand filter
Septic Tank
Diaki
To create the wastewater retention times necessary
for achieving desired treatment results, single-pass
filters must use finer media than that typically used
in recirculating filters. Finely sized media results in
longer residence times and greater contact between
the wastewater and the media surfaces and their
attached bioslimes. BOD removals of greater than
90 percent and nearly complete ammonia removal
are typical (Darby et al., 1996; Emerick et al., 1997;
University of Wisconsin, 1978). Single-pass filters
typically achieve greater fecal coliform removals
than recirculating filters because of the finer media
and the lower hydraulic loading. Daily hydraulic
loadings are typically limited to 1 to 2 gpd/ft2, de-
pending on sand size, organic loading, and espe-
cially the number of doses per day (Darby et al.,
1996).
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Recirculating filters
The basic components of recirculating filters (see
Fact Sheet 11) are a recirculation/dosing tank,
pump and controls, a distribution network, a filter
bed with an underdrain system, and a return line
fitted with a flow-splitting device to return a
portion of the filtrate to the recirculation/dosing
tank (figure 4-26). The wastewater is dosed to the
filter surface on a timed cycle 1 to 3 times per
hour. The returned filtrate mixes with fresh septic
tank effluent before being returned to the filter.
Media types
Many types of media are used in packed bed filters.
Washed, graded sand is the most common medium.
Other granular media used include gravel, anthra-
cite, crushed glass, expanded shale, and bottom ash
from coal-fired power plants. Bottom ash has been
studied successfully by Swanson and Dix (1987).
Crushed glass has been studied (Darby et al., 1996;
and Emerick et al., 1997), and it was found to
perform similarly to sand of similar size and
uniformity. Expanded shale appears to have been
successful in some field trials in Maryland, but the
data are currently incomplete in relation to long-
term durability of the medium.
Foam chips, peat, and nonwoven coarse-fiber
synthetic textile materials have also been used.
These are generally restricted to proprietary units.
Probably the most studied of these is the peat filter,
which has become fairly common in recent years.
Depending on the type of peat used, the early perfor-
mance of these systems will produce an effluent with
a low pH and a yellowish color. This is accompa-
nied by some excellent removal of organics and
microbes, but would generally not be acceptable as
a surface discharge (because of low pH and visible
color). However, as a pretreatment for a SWIS,
low pH and color are not a problem. Peat must
meet the same hydraulic requirements as sand (see
Fact Sheets 10 and 11). The primary advantage of
the proprietary materials, the expanded shale, and to
some degree the peat is their light weight, which
makes them easy to transport and use at any site.
Some short-term studies of nonwoven fabric filters
have shown promise (Roy and Dube, 1994).
System manufacturers should be contacted for
application and design using these materials.
4.7.2 Applications
Sand media filters may be used for a broad range
of applications, including single-family residences,
large commercial establishments, and small com-
munities. They are frequently used to pretreat
wastewater prior to subsurface infiltration on sites
where the soil has insufficient unsaturated depth
above ground water or bedrock to achieve adequate
treatment. They are also used to meet water quality
requirements before direct discharge to a surface
water. They are used primarily to treat domestic
wastewater, but they have been used successfully in
treatment trains to treat wastewaters high in organic
materials such as those from restaurants and
supermarkets. Single pass filters are most fre-
quently used for smaller applications and sites
where nitrogen removal is not required. Recirculat-
ing filters are used for both large and small flows
Performance of sand and other filters
Twelve innovative treatment technologies were installed to replace failed septic systems in the Narragansett Bay
watershed, which is both pathogen-and nitrogen-sensitive. The technologies installed consisted of an at-grade
recirculating sand filter, single pass sand filters, Maryland-style recirculating sand filters, foam biofilters, and a
recirculating textile filter. The treatment performance of these systems was monitored over an 18-month period. In
the field study, TSS and BOD5 concentrations were typically less than 5 mg/L for all sand filter effluent and less
than 20 mg/L for both the foam biofilter and textile filter effluents. Single pass sand filters achieved substantial
fecal coliform reductions, reaching mean discharge levels ranging from 200 to 520 colonies per 100 ml for all 31
observations. The at-grade recirculating sand filter achieved the highest total nitrogen reductions of any
technology investigated and consistently met the Rhode Island state nitrogen removal standard (aTN reduction of
50 percent or more and a TN concentration of 19 mg/L or less) throughout the study.
Source: Loomis etal., 2001.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
and are frequently used where nitrogen removal is
necessary. Nitrogen removal of up to 70 to 80
percent can be achieved if an anoxic reactor is used
ahead of the recirculation tank, where the nitrified
return filtrate can be mixed with the carbon-rich
septic tank effluent (Anderson et al., 1998; Boyle
et al., 1994; Piluk and Peters, 1994).
4.7.3 Performance
The treatment performance of single-pass and
recirculating filters is presented in table 4-16. The
medium used was sand or gravel as noted. Recircu-
lating sand filters generally match or outperform
single-pass filters in removal of BOD, TSS, and
nitrogen. Typical effluent concentrations for
domestic wastewater treatment are less than 10 mg/
L for both BOD and TSS, and nitrogen removal is
approximately 50 percent. Single-pass sand filters
can also typically produce an effluent of less than
10 mg/L for both BOD and TSS. Effluent is nearly
completely nitrified, but some variability can be
expected in nitrogen removal capability. Pell and
Nyberg (1989) found typical nitrogen removals of
18 to 33 percent with their intermittent sand filter.
Fecal coliform removal is somewhat better in
single pass filters. Removals range from 2 to 4 logs
in both types of filters. Intermittent sand filter fecal
coliform removal is a function of hydraulic load-
ing; removals decrease as the loading rate increases
above 1 gpm/ft2 (Emerick et al., 1997).
Effluent suspended solids from sand filters are
typically low. The medium retains the solids. Most
of the organic solids are ultimately digested. Gravel
filters, on the other hand, do not retain solids as
well.
excessive solids buildup due to the lack of periodic
sludge pumping and removal. In such cases, the
solids storage capacity of the final settling compart-
ment might be exceeded, which results in the
discharge of solids into the effluent. ATU perfor-
mance and effluent quality can also be negatively
affected by the excessive use of toxic household
chemicals. ATUs must be properly operated and
maintained to ensure acceptable performance.
4.8 Aerobic treatment units
Aerobic treatment units (ATUs) refer to a broad
category of pre-engineered wastewater treatment
devices for residential and commercial use. ATUs
are designed to oxidize both organic material and
ammonium-nitrogen (to nitrate nitrogen), decrease
suspended solids concentrations and reduce patho-
gen concentrations.
A properly designed treatment train that incorpo-
rates an ATU and a disinfection process can provide
a level of treatment that is equivalent to that level
provided by a conventional municipal biological
treatment facility. The AUT, however, must be
properly designed, installed, operated and main-
tained.
Although most ATUs are suspended growth de-
vices, some units are designed to include both
suspended growth mechanisms combined with
fixed-growth elements. A third category of ATU is
designed to provide treatment entirely through the
use of fixed-growth elements such as trickling
filters or rotating biological contactors (refer to
sheets 1 through 3). Typical ATU's are designed
using the principles developed for municipal-scale
wastewater treatment and scaled down for residen-
tial or commercial use.
Most ATUs are designed with compressors or
aerators to oxygenate and mix the wastewater.
Partial pathogen reduction is achieved. Additional
disinfection can be achieved through chlorination,
UV treatment, ozonation or soil filtration. In-
creased nutrient removal (denitrification) can be
achieved by modifying the treatment process to
provide an anaerobic/anoxic step or by adding
treatment processes to the treatment train.
4.8.1 Treatment mechanisms
ATUs may be designed as continuous or batch flow
systems (refer to fact sheets 1 through 3). The
simplest continuous flow units are designed with no
flow equalization and depend upon aeration tank
volume and/or baffles to reduce the impact of
hydraulic surges. Some units are designed with
flow-dampening devices, including air lift or float-
controlled mechanical pumps to transfer the
wastewater from the aeration tank to a clarifier.
Other units are designed with multiple-chambered
tanks to attenuate flow. The batch (fill and draw)
flow system design eliminates the problem of
hydraulic variation. Batch systems are designed to
collect and treat wastewater over a period of time.
4-52
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 4: Treatment Processes and Systems
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Sand media: not reported. Design hydraulic
loading=1 gpd/ft2. Daily flows not reported.
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USEPA Onsite Wastewater Treatment Systems Manual
4-53
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Chapter 4: Treatment Processes and Systems
Pumps are used to discharge the settled effluent at
the end of the cycle (usually one day). Fixed film
treatment plants typically are operated as continu-
ous flow systems.
Oxygen is transferred by diffused air, sparged
turbine, or surface entrainment devices. When
diffused air systems are used, blowers or compres-
sors are used to force the air through diffusers near
the bottom of the tank. The sparged turbine is
typically designed with a diffused air source and an
external mixer, e.g., a submerged flat-bladed
turbine. The sparged turbine is more complex than
the simple diffused air system. A variety of surface
entrainment devices aerate and mix the wastewater.
Air is entrained and circulated in the mixed liquor
through violent agitation from mixing or pumping.
The separation of process-generated solids by
clarification or filtration is a critical design factor
for successful ATU performance. Most ATUs are
designed to rely on the process of simple gravity
separation to remove most of the solids. Some
systems include effluent filters within the clarifier
to further screen and retain solids in the treatment
plant. Gas deflection barriers and scum baffles are
a part of some designs and are a simple way to
keep floating solids away from the weir area.
Properly managed uplow clarifiers can improve
separation.
4.8.2 Design Considerations
ATU's are typically rated by hydraulic capacity and
organic and solids loadings. ATU daily treatment
volumes may range from 400 gpd to a maximum
of 1,500 gpd. ATUs typically can be used to treat
residential wastewaters with influent concentrations
which have 100 mg/L to 300 mg/L total organic
compounds and 100 mg/L to 350 mg/L total
suspended solids. Design flows are generally set by
local sanitary codes for residential and commercial
dwellings using methods described in Section 3.3.
ATU's should be equipped with audio and visual
alarms to warn of compressor/aerator failure and
high water. These alarms alert the owner and/or
service provider of service issues that require
immediate attention.
ATU's should be constructed of noncorrosive
materials, including reinforced plastics and
fiberglass, coated steel, and reinforced concrete.
Buried ATU's must be designed to provide easy
access to mechanical parts, electrical control
systems, and appurtenances requiring maintenance
such as weirs, air lift pump lines, etc. ATU's
installed above ground should be properly housed
to protect against severe climatic conditions.
Installation should be in accordance with manufac-
turers' specifications.
Appurtenances should be constructed of corrosion-
free materials including polyethylene plastics. Air
diffusers are usually constructed of PVC or ceramic
stone. Mechanical components must be either
waterproofed and/or protected from the elements.
Because blowers, pumps, and other prime movers
can be subject to harsh environments and continu-
ous operation, they should be designed for heavy
duty use. Proper housing can reduce blower noise.
4.8.3 Applications
ATUs are typically integrated in a treatment train to
provide additional treatment before the effluent is
discharged to a SWIS. ATU-treatment trains can
also be designed to discharge to land and surface
waters; ATU discharge is suitable for drip irrigation
if high quality effluent is consistently maintained
through proper management. Although some
jurisdictions allow reductions in vertical separation
distances and/or higher soil infiltration rates when
ATUs are used, consideration must be given to the
potential impacts of higher hydraulic and pollutant
loadings. Increased flow through the soil may
allow deeper penetration of pathogens and
decreased treatment efficiency of other pollutants
(see sections 4.4.2 and 4.4.5).
4.8.4 Performance
Managed ATU effluent quality is typically
characterized as 25 mg/L or less CBOD5 and 30
mg/L or less TSS. Fecal coliform counts are
typically 3-4 log # / 100 ml (Table 3-19) when the
ATUs are operated at or below their design flows
and the influent is typical domestic sewage.
Effluent nutrient levels are dependent on influent
concentrations, climate, and operating conditions.
Other wastewater characteristics may influence
performance. Cleaning agents, bleach, caustic
4-54
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Chapter 4: Treatment Processes and Systems
agents, floating matter, and other detritus can plug
or damage equipment. Temperature will affect
process efficiency, i.e., treatment efficiency
generally will improve as the temperature
increases.
Owners should be required by local sanitary codes
or management program requirements to maintain
ongoing service agreements for the life of the
system. ATU's should be inspected every three
months to help ensure proper operation and
treatment effectiveness. Many ATU manufacturers
offer a two-year warranty with an optional service
agreement after the warranty expires. Inspections
generally include visual checks of hoses, wires,
leads and contacts, testing of alarms, examination
of the mixed liquor, cleaning of filters, removal of
detritus, and inspection of the effluent. ATU's
should be pumped when the mixed-liquor (aerator)
solids are above 6,000 mg/L or the final settler is
more than 1/3 full of settled solids.
4.8.5 Risk management
ATU's should be designed to protect the treatment
capability of the soil dispersal system and also to
sound alarms or send signals to the management
entity (owners and/or service providers) when
inspection or maintenance is needed. All biological
systems are sensitive to temperature, power
interruptions, influent variability, and shock
loadings of toxic chemicals. Successful operation
of ATUs depends on adherence to manufacturers'
design and installation requirements and good
management that employs meaningful measure-
ments of system performance at sufficiently
frequent intervals to ascertain changes in system
function. Consistent performance depends on a
stable power supply, an intact system as designed,
and routine maintenance to ensure that components
and appurtenances are in good order. ATU's, like
all other onsite wastewater treatment technologies,
will fail if they are not designed, installed, or
operated properly. Vigilance on the part of owners
and service providers is essential to ensure ATUs
are operated and maintained to function as
designed.
4.8.6 Costs
Installed ATU costs range from $2500 to $9000
installed. Pumping may be necessary at any time
due to process upsets, or every eight to twelve
months, depending on influent quality, temperature
and type of process. Pumping could cost from
$100-to-$300, depending on local requirements.
Aerators/compressors last about three to five years
and cost from $300 to $500 to replace.
Many communities require service contracts.
These contracts typically range in cost between
$100 and $400 per year, depending on the options
and features the owners choose. The high end
includes pumping costs. Power requirements are
generally quoted at around $200/year.
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 1
Continuous-Flow, Suspended-
Growth Aerobic Systems (CFSGAS)
Description
The activated sludge process is an aerobic suspended-growth process that maintains a relatively high population of micro-
organisms (biomass) by recycling settled biomass back to the treatment process. The biomass converts soluble and colloi-
dal biodegradable organic matter and some inorganic compounds into cell mass and metabolic end products. The biomass
is separated from the wastewater through settling in a clarifier for recycling or wasting to sludge handling processes.
Preliminary treatment to remove settleable solids and floatable materials is usually provided by a septic tank or other
primary treatment device. Most onsite designs are capable of providing significant ammonia oxidation and effective
removal of organic matter.
The basic system consists of a number of interrelated components (as shown in figure 1):
Figure 1. A basic CFSGAS configuration
Influent
Air
V
\
\
Aeration
tank
b
^
Sludge
recycling
V
\
)
\
Clarifier
Effluent
• An aeration tank or basin.
• An oxygen source and equipment to disperse atmo-
spheric or pressurized air or oxygen into the aeration
tank at a rate sufficient to always maintain positive
dissolved oxygen.
• A means to appropriately mix the aeration basin and
ensure suspension of the biomass (usually accom-
plished by the aeration system).
• A clarifier to separate the biomass from the treated
effluent and collect settled biomass for recycling to the
aeration basin.
Several modifications of this basic process are commercially available. These include different aeration devices; different
means of sludge collection and recycling to the aerator; the use of coarse membrane filters in lieu of, or in addition to, the
clarifier; and process enhancement through the addition of an inert media area on which biofilms can grow. The addition
of surfaces where biota can become attached and grow increases the capacity of the system (increased organic loading
possible). This last modification is the most significant enhancement and is described below.
The combined fixed-film/suspended growth process is sometimes referred to as a class of treatment processes called
coupled contact aeration, enhanced, or high biomass systems. To enhance performance and increase the capacity of the
aeration tank, an inert support medium is added to the aeration tank. This allows a fixed film of biomass to attach and
grow on the medium to augment the suspended microbial population, providing more biomass to feed on wastewater
constituents (figure 2). Synthetic trickling filter media, loops of fiber bundles, and a variety of different plastic surface
configurations can be suspended in the aeration tank. Advantages include increased active microbial mass per unit volume,
enhanced potential for nitrification, reduced suspended solids loading to the clarifier, improved solids separation character-
istics, reduced sludge production, and resilience under variable influent conditions.
TFS-1
-------
Figure 2. An enhanced CFSGASor"high biomass"system
Typical application
These systems are usually preceded by a septic
tank and followed by a subsurface wastewater
infiltration system (SWIS). Despite some claims
of reduced SWIS sizing when compared to the
conventional septic tank pretreatment, the
designer is cautioned to consider ground water
protection. These systems should be applied only
where onsite system management services are
available. For surface water discharge, the system
must be followed by disinfection at a minimum
to consistently meet discharge standards. How-
ever, some subsurface (non-human-contact) reuse may be implemented without further treatment. High biomass systems
can be a low-cost means of upgrading existing overloaded CFSGAS units that currently do not meet BOD or nitrification
goals. They can also compete directly with conventional designs because they have greater stability in handling highly
variable loadings.
Influent
i
;
Air
Aeration
tank
\
\
Treatment
media ••••••:•
\
\
\
\
Suspended
solids
separation
_*
Effluent
Sludge recycling
Design assumptions
The extended aeration type of CFSGAS is the most commonly used design. At present there is no generic information on
design parameters for fixed film activated sludge systems. Package plants are delivered based on design flow rates. A
conservative design approach for extended aeration systems is presented in table 1. The inert medium should support
additional biomass and add to the total system microbial mass. Because the increase in microbial population is difficult to
measure, any "credits" for this addition would have to be based on empirical observation. Claims for significantly de-
creased sludge production, increased oxygen transfer efficiency, and improved settleability of the sludge have not been
universally proved. However, a number of successful installations for onsite and small municipal systems have been in
operation throughout the world for more than 10 years (Mason, 1977; Rogella et al., 1988; Rusten et al., 1987).
Table 1-1. Design parameters for CFSGAS extended aeration package plants
Parameter
Pretreatment (if needed)
Mixed Liquor Suspended Solids (mg/L)a
F/M Load (Ib BOD/d/MLVSS) b
Hydraulic Retention Time (h)
Solids Retention Time (days)
Mixing Power Inpuf
Clarifier Overflow Rate (gpd/ft2)
Clarifier Solids Loading (Ib/d/ft2)
Dissolved Oxygen (mg/L)
Residuals Generated
Sludge Removal
Extended Aeration
Septic tank or equivalent
2,000-6,000
0.05-0.15
24-120
20-40
0.2-3.0 hp/1, 000 ft3
200-400 avg., 800 peak
30 avg., 50 peak
>2.0
0.6-0.9 Ib TSS/lb BOD removed
3-6 months as needed
aTSS in aeration tank.
"Organic loading (pounds of BOD per day) to aeration tank volatile fraction of MLSS.
"Power input per cubic foot of tank volume.
TFS-2
-------
Figure 3. Components of a typical aerobic treatment unit
I Mixing Return | / I Slud3e Retum I
Onsite package treatment units (see figure 3) should be constructed of noncorrosive materials, such as coated concrete,
plastic, fiberglass, or coated steel. Units may be stand-alone or manufactured to drop into a compartmented septic tank.
Some units are installed aboveground on a concrete slab with proper housing to protect against severe climatic conditions.
Units may also be buried underground as long as easy access is provided to all mechanical parts, electrical control systems,
and water surfaces. All electrical components should follow NEC code and be waterproof and/or housed from the ele-
ments. If airlift pumps are used, large-diameter units should be provided to avoid clogging. Blowers, pumps, and other
mechanical devices should be designed for continuous use because they will be abused by climatic conditions and the
corrosive atmosphere within the treatment environment. Easy access to all moving parts should be provided for routine
maintenance. An effective alarm system should be employed. Typical land area requirements for package plants are
modest.
For engineered package plants, final clarifier designs should be conservative for high MLSS and poor settleability of
biomass. Because of the potential for bulking sludge, secondary clarifiers should be equipped with surface skimming
devices to remove greases and floating solids, as well as efficient screens.
Performance
Well-operated CFSGAS extended aeration units that are well operated can achieve BOD concentrations ranging from 10 to
50 mg/L and TSS concentrations ranging from 15 to 60 mg/L. Some studies (Brewer et al., 1978; Hutzler et al., 1978)
have indicated poorer performance owing to surge flows, variable loading, and inadequate maintenance. Nitrification can
also be significant in these aeration units during warmer periods. Some nitrogen removal can be achieved by denitrifica-
tion, which can remove 30 to 40 percent of the total nitrogen (TN) under optimum conditions. Average total nitrogen
effluent concentrations in residential extended aeration units range from 17 to 40 mg/L. Fecal coliform and virus removal
has been reported in the range of 1 to 2 logs.
High biomass systems have produced BOD and TSS effluents of 5 to 40 mg/L. Although they are less dependent on
temperature than the extended aeration CFSGAS, temperature does have an impact on their seasonal capability to nitrify
the influent ammonium-nitrogen to nitrate-nitrogen. All CFSGAS systems do an excellent job of removing toxic organics
and heavy metals. Most CFSGAS systems do not remove more than a small percentage of phosphorus (10 to 20 percent)
and nitrogen (15 to 25 percent).
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Management requirements
CFSGAS systems must be managed and maintained by trained personnel rather than homeowners to perform acceptably.
Power requirements vary from 2.5 to 10 kWh/day. They should be inspected at least every 2 to 3 months. During these
inspections, excess solids pumping should be based on the mixed liquor measurements. It is estimated that an effective
program will require between 12 and 28 person-hours annually, in addition to analytical testing of the effluent, where
required. Management contracts should be in place for the life of the system. Common operational problems with ex-
tended aeration systems are provided in table 2. Residuals generated will vary from 0.6 to 0.9 Ib TSS per Ib BOD re-
moved, over and above the normal septic tank sludge produced.
Table 1-2. Common operational problems of extended aeration package plants
Observation
Excessive local turbulence
In aeration tank
White, thick, billowy foam on aeration
tank
Thick, scummy, dark tan foam on
aeration tank
Dark brown/black foam and mixed
liquor In aeration tank
Billowing sludge washout in clarlfier
Clumps of rising sludge In clarlfier
Fine dispersed floe, turbid effluent
Poor TSS and/or BOD removal
Poor nitrification
Cause
Diffuser plugging
Pipe breakage
Excessive aeration
Insufficient MLSS
High MLSS
Anaerobic conditions
Aerator failure
Hydraulic or solids overload
Bulking sludge
Denitrification
Septic conditions in clarifier
Turbulence in aeration tank
Sludge age too high
Excess flow and strength variations
Low temperatures
Excessive biocide use
Remedy
Remove and clean
Replace as required
Throttle blower
Avoid wasting solids
Waste solids
Check aeration system,
aeration tank DO
Waste sludge; check flow to unit
See EPA, 1977
Increase sludge return rate to
decrease sludge retention time in
clarifier
Increase return rate
Reduce power input
Waste sludge
Install flow smoothing system
Insulate, upgrade to high biomass, etc.
Reduce biocide loading
Risk management issues
CFSGAS systems require effluent disinfection at a minimum to meet surface discharge or any surface reuse water quality
requirements. They are quite sensitive to temperature, interruption of electric supply, influent variability, or shock load-
ings of toxic chemicals. The septic tank helps protect these units from the latter problems. Aesthetically, noise from the
blowers is the major irritant, while odors can be significant during power outages or organic overloading periods. High
biomass units are more resistant to the above impacts. The systems are not well suited to seasonal use because of long
start-up times.
Costs
The installed costs of package plants are highly variable but are usually less than $10,000. Operation and maintenance (O/
M) costs are primarily dependent on local power and labor costs, varying from $400 to $600 per year in most cases.
References
Ayres Associates. 1998. Florida Keys Onsite Wastewater Nutrient Reduction Systems Demonstration Project. Contract no.
LP 988. Florida Department of Health Onsite Sewage Program, Tallahassee, FL.
Brewer, W.S., J. Lucas, and G. Prascak. 1978. An evaluation of the performance of household aerobic sewage treatment
units. Journal of Environmental Health 41(2):82-84.
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Converse, J.C., and M.M. Converse. 1998. Pump Chamber Effluent Quality Following Aerobic Units and Sand Filters
Serving Residences. In Proceedings of the Eighth National Symposium on Individual and Small Community Sewage
Systems. American Society of Agricultural Engineers, Orlando, FL.
Englehardt, J.D., and R.C. Ward. 1986. Operation and maintenance requirements for small flow treatment systems.
Journal of the Water Pollution Control Federation 58(10).
Hutzler, N.L., L. Waldorf, and J. Fancy. 1978. Performance of Aerobic Treatment Units. In Proceedings of the Second
National Home Sewage Treatment Symposium. American Society of Agricultural Engineers, Chicago, IL.
Kellam, J.G., et al. 1993. Evaluation of Performance of Five Aerated Package Treatment Systems. Bull. 178. Virginia
Water Resources Research Center, Blacksburg, VA.
Mason, D.G. 1977. A Unique Biological Treatment System for Small Plants. Paper presented at the 50th Water Pollution
Control Federation Conference, Philadelphia, PA.
Midwest Plan Service. 1982. On-site Domestic Sewage Disposal Handbook. Midwest Plan Service, University of
Minnesota, St. Paul, MN.
Otis, R.J., and WC Boyle. 1976. Performance of single household treatment units. Journal of Environmental Engineering
Division, ASCE, 102, EE1, 175.
Otis R.J., et al. 1975. The Performance of Household Wastewater Treatment Units under Field Conditions. In Proceedings
of the Third National Home Sewage Disposal Symposium. American Society of Agricultural Engineers, Chicago, IL.
Rogella, F, J. Sibony, G. Boisseau, and M. Benhomme. 1988. Fixed Biomass to Upgrade Activated Sludge. Paper
presented at 61st Annual Water Pollution Control Federation Conference, Philadelphia, PA.
Rusten, B., M.J. Tetreault, and J.F. Kreissl. 1987. Assessment of Phased Isolation Ditch Technologies for Nitrogen
Control. In Proceedings of the Seventh European Sewage and Refuse Symposium, pp. 279-291, Munich, Germany.
Tchobanoglous, G., and F. Burton. 1991. Wastewater Engineering. 3rd ed. McGraw-Hill, Inc., New York.
U.S. Environmental Protection Agency (USEPA). 1978. Management of Small Waste Flows. Small Scale Waste
Management Project. EPA 600/2-78-173. National Technical Information Service PB 286 474.
U.S. Environmental Protection Agency (USEPA). 1980. Design Manual: Onsite Wastewater Treatment and Disposal
Systems. EPA 625/1-80-012. U.S. Environmental Protection Agency, Office of Water Programs, Washington, DC.
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 2
Fixed-Film Processes
Description
Fixed-film systems (FFS) are biological treatment processes that employ a medium such as rock, plastic, wood, or other
natural or synthetic solid material that will support biomass on its surface and within its porous structure. At least two
types of fixed-film systems may be considered —those in which the medium is held in place and is stationary relative to
fluid flow (trickling filter) and those in which the medium is in motion relative to the wastewater (e.g., rotating biological
disk). A third classification includes dual-process systems that encompass both fixed and suspended biomass together or
in series. This approach is covered in Fact Sheet No. 1 on continuous-flow suspended-growth aerobic systems
(CFSGAS).
Trickling filter systems are typically constructed as beds of media through which wastewater flows. Oxygen is normally
provided by natural or forced ventilation. Flow distributors or sprayers distribute the wastewater evenly onto the surface
of the medium. As the wastewater moves by gravity through the medium, soluble and colloidal organic matter is metabo-
lized by the biofilm that forms on the medium. Excess biomass sloughs from the medium and is carried with the treated
wastewater to the clarifier, where the solids settle and separate from the treated effluent. At this point the treated wastewa-
ter may be discharged or recycled back to the filter medium for further treatment (figure 1).
Figure 1.Trickling filter treatment system
Optional recirculation of effluent
Influent
t '
1
.4— .
\
\
\
Septic
tank
n~-
i
t .
\
\
\
Fixed-film
reactor
\
\
\
Clarifier
^
£
1 Effluent
Optional sludge return
A fixed-film biological treatment process that employs rotating disks that move within the wastewater is referred to as a
rotating biological contactor (RBC). Developed in the late 1960s, the RBC employs a plastic medium configured as disks
and mounted on a horizontal shaft. The shafts are rotated slowly (1 to 2 rpm) by mechanical or compressed air drive. For
a typical aerobic RBC, approximately 40 percent of the medium is immersed in the wastewater. Anoxic or anaerobic RBCs
(far less common) are fully immersed in the wastewater. Wastewater flows through the medium by simple displacement
and gravity. Biomass continuously sloughs from the disks, and some suspended biomass develops within the wastewater
channels through which the disks rotate, making the addition of a secondary clarifier necessary. The rotation of the disks
exposes the attached biomass to atmospheric air and wastewater. Oxygen is supplied by natural surface transfer to the
biomass. Some oxygenation of the wastewater is also created by turbulence at the disk-water interface. The use of
TFS-7
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exposed and submerged stages in multiple tanks to create aerobic and anoxic conditions may be employed where nitrogen
removal is required.
Commercially available modifications primarily address the media employed, the configuration of the tankage, and the
mechanical supporting systems (e.g., supplemental aeration, programmable cycling, etc.). Some FFS sludges are wasted
directly by pumping of the clarifier, whereas others convey all excess solids back to the pretreatment stage (septic tank)
for subsequent removal. Lightweight synthetic media have greater surface area and are easier to install. Numerous varia-
tions ranging from extruded foam to high-specific-surface PVC and other plastic shapes are available commercially.
Typical applications
Fixed-film systems (FFS) are an alternative to CFSGAS for reducing biochemical oxygen demand (BOD) and total
suspended solids (TSS) from septic tank effluent to meet a higher effluent standard (figure 2). Like CFSGAS, they can
meet secondary effluent standards (30 mg/L of BOD and TSS), but they would need a minimum of effluent disinfection to
be acceptable for surface water discharges. They might meet onsite water reuse requirements as long as the effluent is
distributed below the ground surface. Some data support the potential for soil absorption field infiltrative surface reduction
following FFS, but caution is urged regarding ground water quality protection from use of such reductions. FFS can also
be used as part of a nutrient reduction treatment train (see Facts Sheet No. 8 and No. 9 on nutrient removal). FFS provide
an aerobic oxidation step in those sequences.
Figure 2. Fixed-film system using peat moss as a treatment medium
Dwelling Served
SINGLE HOUSE INSTALLATION
AUDIO & VISUAL ALARM
SEPTIC TANK
PEAT MEDIA ACTS LIKE A
CONDENSED DRAINFIELD
BIOLOGICAL PURIFICATION
OCCURS IN THE MEDIA
4 POLYETHYLENE MODULES
CONTAINING BIOFIBROUS PEAT
RAMP UP WITH SOIL TO
UNDER EDGE OF COVER
\
Pump/Sump
PERFORATIONS IN BASE
FOR PERCOLATION
TREATED EFFLUENT CAN PERCOLATE
TO SOIL OR DISCHARGE TO DRAIN
Source: Bord Na Mona, 1999.
Design assumptions
Design guidelines for fixed-film systems are given in table 1. FFS package units should be constructed of noncorrosive
materials. Some are installed aboveground on a concrete slab with proper housing to anticipate local climatic conditions.
The units may also be buried underground as long as access is provided to all mechanical parts, control systems,
underdrains, distribution system, and water surfaces. All electric components must meet NEC code and should be water-
proofed and housed from the elements. If natural ventilation is required for aeration, proper design and construction must
be considered to ensure adequate oxygen transfer. Pumps, drives (for rotating units), and other mechanical devices should
be designed for continuous heavy-duty use and climatic conditions. Access and drainage capability should be provided to
underdrains and distribution systems because they may become clogged over time. Alarms that alert homeowners or
management entities should be provided to warn of system malfunctions.
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Table 1. Design parameters for fixed-film systems
Parameter
Pretreatment
Surface hydraulic loading
Organic loading a
Clarifier overflow rate
Average flow
Peak flow
Clarifier TSS loading rate
Average flow
Peak flow
Recirculation
Sludge generated"
Trickling filter
Septic tank (primary Clarifier)
10-25 gal/d-ft2
5-20 Ib BOD/d-ft2
(3-1 0 Ib BOD/d-ft2to nitrify)
600-800 gal/d-ft2
1 ,000-1 ,200 gal/d-ft2
0.8-1 .2 IbTSS/d-ft2
2.0 Ib TSS /d-ft2
Optional
0.6-1 .1 Ib TSS /Ib BOD removed
RBC
Septic tank (primary Clarifier)
N/A
2.5lbSBOD/d-1000ft2
(e^lbBOD/d-IOOOft2)
600-800 gal/d-ft2
1 ,000-1 ,200 gal/d-ft2
0.8-1 .2 Ib TSS /d-ft2
2.0 IbTSS/d-ft2
Optional
0.6-1 .1 Ib TSS /Ib BOD removed
a Loading rates for RBC are expressed per 1,000 ft2 of total disk surface.
b Sludge generated is in addition to solids removed in septic tank.
Onsite RBC package units should also be constructed of noncorrosive materials. Disk shafts and bearings and drives should
be designed for heavy-duty use since they will be abused by the corrosive atmosphere generated by treatment processes
and climatic conditions. Access should be provided to bearings, drives, and disks for maintenance. RBC units should be
covered and insulated against cold weather and sunlight. Proper ventilation of the unit is necessary to ensure adequate
oxygen transfer.
Performance
Typical trickling filters and rotating medium systems currently available should be capable of producing effluent BOD and
TSS concentrations of 5 to 40 mg/L. System reliability is somewhat better than suspended growth package plants because
of the more effective capture and control of suspended solids. Nitrification is achievable at low loading rates in warm
climates. Factors affecting performance include influent wastewater characteristics, hydraulic and organic loading, me-
dium type, maintenance of optimal dissolved oxygen levels, and recirculation rates. The process is characteristically
vulnerable to climatic conditions because of the cooling effect of the wastewater as it passes through the medium. Proper
insulation, reduced effluent recirculation, and improved distribution techniques can lessen the impact of cold temperatures.
Limited denitrification has been noted in nitrifying filters when oxygenation is poor and within dead zones (anaerobic
portions) of the filter. Fecal coliform reductions are 1 to 2 logs. Nitrogen removal varies from 0 to 35 percent, while
phosphorus removal of 10 to 15 percent might be expected.
Combined fixed-growth/suspended-growth package units are commercially available and are generally valuable in treating
high-strength wastewaters. These "high-biomass" units can be organically loaded at much higher rates than either fixed-
film or flow-through suspended growth systems. They are covered in the fact sheet on CFSGAS.
Management needs
With proper management, RBC package plants are reliable and should pose no unacceptable risks to the homeowner or the
environment. If not properly managed, however, the process can result in either premature failure of subsurface systems
or environmental damage through the production of poor-quality effluent that may pose public health risks. Odors and
filter flies may also create an environmental nuisance. Although there are benefits to RBCs, they do not come without
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some cost. The mechanical complexity of some proprietary systems causes them to require more management attention.
Additional management is needed when disinfection and surface discharge are used.
The manufacturer normally fixes the pumping and recirculation rates for fixed-film systems, and the rates require minimal
adjustments once performance objectives are attained. Sludge wasting from the clarifier to the septic tank is normally
fixed by timer setting and requires occasional adjustment to avoid biomass buildup. Where mechanical or diffused aeration
is employed, complexity and required frequency of inspection increase. The most frequent need is to remove solids from
the distribution system. Other maintenance requirements are listed in table 2.
Fixed-film units are also operation and maintenance intensive. Startup of the unit does not require seeding with bacterial
cultures and may require 6 to 12 weeks for effective performance depending on the season. This makes them unsuitable
for seasonal application. Most operating parameters in package systems cannot be controlled by the operator. The process
is less labor-intensive than extended aeration (CFSGAS) systems, but it also requires semiskilled management personnel.
Based on limited data on these systems, it is estimated that 4 to 12 person-hours per year plus analytical services should be
sufficient. If disinfection is required, see Technology Fact Sheet 4. Power requirements depend on the package system
selected but may range from 1 to 8 kW-h/day. Sludge production is 0.6 to 1.0 Ib TSS/lb BOD removed over and above
normal septic tank sludge (septage) production. Long power outages can be particularly damaging to RBC units, and any
FFS will become odiferous under these conditions.
Inspections are recommended three to four times per year, with septage pumping (solid wasting) as needed based on
inspection results. Routine maintenance requirements for onsite fixed-film systems are provided in table 2; certain tasks
may not be required based on system design. For example, servicing of the final clarifier may be less critical if solids
Table 2. Suggested maintenance for onsite fixed-film package plants
System component
Medium tank
RBC unit
Aeration system
Clarifier
Controls
Analytical
Septic tank/sludge wasting
Suggested maintenance
Check medium for debris accumulation, ponding, and excessive biomass accumulation;
check distribution system and clean as required; check underdrain system and clean as
required.
Lubricate motors and bearings; replace seals as required; check integrity of disk/shaft
connections; observe biomass accumulations in each stage and adjust shaft speed and
direction as needed; maintain air-drive units if provided.
Natural ventilation — Check to ensure adequate ventilation through underdrains and
medium.
Mechanical/diffused air — See Extended Aeration fact sheet.
See CFSGAS fact sheet.
Check out functions of all controls and alarms; check electrical control box.
Collect effluent samples for analyses of BOD, TSS, pH (N and P if required).
Check for accumulated solids, and pump as required.
separated in the clarifier are returned to the primary settling chamber (septic tank). Field experience on operation and
maintenance for these units has not been as well documented as for CFSGAS.
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Risk management
Fixed-film systems also require a minimum of effluent disinfection to meet surface water discharge requirements. They
are more susceptible to extreme cold than CFSGAS but less sensitive to shock loading and influent variability. A prolonged
interruption of electric supply will result in odors. Filter flies may also be a nuisance with these systems if vents are not
properly screened.
Costs
Observed costs are highly variable depending on climate, location, onsite aesthetic requirements, and many other factors.
The cost of power should be in the range of $100 per year for RBC units and $35 per year for trickling filters. Capital
(installed) costs of $9,000 to $14,000 are typical. A management contract (estimated at about $100 to $200 per year) is
recommended.
References
Hutzler, N.L., L. Waldorf, and J. Fancy. 1978. Performance of Aerobic Treatment Units. In Proceedings of the Second
National Home Sewage Treatment Symposium. American Society of Agricultural Engineers, Chicago, IL.
Otis, R.J., and W. C. Boyle. 1976. Performance of single household treatment units. Journal of Environmental
Engineering Division, American Society of Civil Engineers, 102, EE1, 175.
Otis, R.J., et al. 1975. The Performance of Household Wastewater Treatment Units under Field Conditions. In
Proceedings of the Third National Home Sewage Disposal Symposium, American Society of Agricultural Engineers,
Chicago, IL, p. 191.
Tchobanoglous, G., and F. Burton. 1991. Wastewater Engineering. 3rd ed. McGraw-Hill, Inc., New York.
Water Environment Federation. 1998. Design of Municipal Wastewater Treatment Plants. Manual of Practice no. 8. 4th ed.
Water Environment Federation, Alexandria, VA.
Water Pollution Control Federation (WCPF). 1988. O&MofTricklingFilters, RBCs, and Related Processes. Manual of
Practice OM-10. Water Pollution Control Federation, Alexandria, VA.
U.S. Environmental Protection Agency (USEPA). 1984. Design Information on Rotating Biological Contactors. EPA-600/
2-84-106. U.S. Environmental Protection Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1984. Review of Current RBC Performance and Design Procedures.
EPA-600/2-85-033. U.S. Environmental Protection Agency, Cincinnati, OH.
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TFS-12
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 3
Sequencing Batch Reactor Systems
Description
The sequencing batch reactor (SBR) process is a sequential suspended growth (activated sludge) process in which all major
steps occur in the same tank in sequential order (figure 1). There are two major classifications of SBRs: the intermittent
flow (IF) or "true batch reactor," which employs all the steps in figure 1, and the continuous flow (CF) system, which does
not follow these steps. Both have been used successfully at a variety of U.S. and worldwide installations. SBRs can be
designed and operated to enhance removal of nitrogen, phosphorus, and ammonia, in addition to removing TSS and BOD.
The intermittent flow SBR accepts influent only at specified intervals and, in general, follows the five-step sequence.
There are usually two IF units in parallel. Because this system is closed to influent flow during the treatment cycle, two
units may be operated in parallel, with one unit open for intake while the other runs through the remainder of the cycles.
In the continuous inflow SBR, influent flows continuously during all phases of the treatment cycle. To reduce short-
circuiting, a partition is normally added to the tank to separate the turbulent aeration zone from the quiescent area.
Figure 1. Sequencing batch reactor (SBR) design principle
Aeration/mixing
Decant
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The SBR system is typically found in packaged configurations for onsite and small community or cluster applications. The
major components of the package include the batch tank, aerator, mixer, decanter device, process control system (including
timers), pumps, piping, and appurtenances. Aeration may be provided by diffused air or mechanical devices. SBRs are
often sized to provide mixing as well and are operated by the process control timers. Mechanical aerators have the added
value of potential operation as mixers or aerators. The decanter is a critical element in the process. Several decanter
configurations are available, including fixed and floating units. At least one commercial package employs a thermal
processing step for the excess sludge produced and wasted during the "idle" step. The key to the SBR process is the control
system, which consists of a combination of level sensors, timers, and microprocessors. Programmable logic controllers can
be configured to suit the owner's needs. This provides a precise and versatile means of control.
Typical applications
SBR package plants have found application as onsite systems in some states and counties where they are allowed by code.
They are normally used to achieve a higher degree of treatment than a continuous-flow, suspended-growth aerobic system
(CFSGAS) unit by eliminating impacts caused by influent flow fluctuations. For discharge to surface waters, they must
meet effluent permit limits on BOD, TSS, and possibly ammonia. Additional disinfection is required to meet effluent fecal
coliform requirements. For subsurface discharge, they can be used in situations where infiltrative surface organic loadings
must be reduced. There are data showing that a higher quality effluent may reduce soil absorption field area requirements.
The process may be used to achieve nitrification as well as nitrogen and phosphorus removal prior to surface and subsur-
face discharge. (See Fact Sheets 8 and 9.)
Design assumptions
Typical IF system design information is provided in table 1. With CF-type SBRs, a typical cycle time is 3 to 4 hours, with
50 percent of that cycle devoted to aeration (step 2), 25 percent to settling (step 3), and 25 percent to decant (step 4). With
both types, downstream or subsequent unit processes (e.g., disinfection) must be designed for greater capacity (because the
effluent flow is several times the influent flow during the decant period) or an equalization tank must be used to permit a
consistent flow to those processes.
Table 1. Design parameters for IF-type SBR treatment systems
Parameter
Pretreatment
Mixed liquor suspended solids (mg/L)
F/M load (Ib BOD/d/MLVSS)
Hydraulic retention time (h)
Total cycle times (h) '
Solids retention time (days)
Decanter overflow rate3 (gpm/ft2)
Sludge wasting
SBR systems
Septic tank or equivalent
2,000-6,500
0.04-0.20
9-30
4-12
20-40
<100
As needed to maintain performance
a Cycle times should be tuned to effluent quality requirements, wastewater flow, and other site constraints.
Onsite package units should be constructed of noncorrosive materials, such as coated concrete, plastic, fiberglass, or coated
steel. Some units are installed aboveground on a concrete slab with proper housing to protect against local climatic
concerns. The units can also be buried underground as long as easy access is provided to all mechanical parts, electrical
control systems, and water surfaces. All electric components should meet NEC code and should be waterproofed and/or
sheltered from the elements. If airlift pumps are used, large-diameter pipes should be provided to avoid clogging. Blow-
ers, pumps, and other mechanical devices should be designed for continuous heavy-duty use. Easy access to all moving
TFS-14
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parts must be provided for routine maintenance. An effective alarm system should be installed to alert homeowners or
management entities of malfunctions. The area requirements for SBR package plants are similar to those in Fact Sheets 1 and 2.
Performance
With appropriate design and operation, SBR plants have been reported to produce high quality BOD and TSS effluents.
Typical ranges of CBOD5 (carbonaceous 5-day BOD) are from 5 to 15 mg/L. TSS ranges from 10 to 30 mg/L in well-
operated systems. FC removal of 1 to 2 logs can be expected. Normally, nitrification can be attained most of the time
unless cold temperatures persist. The SBR systems produce a more reliable effluent quality than CFSGAS or FFS owing
to the random nature of the wastewater generated from an individual home. The CF/SBR is also capable of meeting
secondary effluent standards (30 mg/L of CBOD and TSS), but more subject to upset by randomly generated wastewaters
than the IF/SBR (Ayers Associates, 1998) if short-circuiting cannot be minimized.
Management needs
Long-term management (including operation and maintenance) of SBRs through homeowner service contracts or local
management programs is an important component of the operation and maintenance program. Homeowners do not
typically possess the skills needed or the desire to learn to perform proper operation and maintenance. In addition, home-
owner neglect, ignorance, or interference (e.g., disabling alarm systems) has contributed to operational malfunctions. No
wasting of biomass should be practiced until a satisfactory concentration has developed. Intensive surveillance by qualified
personnel is desirable during the first months of startup.
Most operating parameters in SBR package systems can be controlled by the operator. Time clock controls may be used to
regulate cycle times for each cycle, adjusted for and depending on observed performance. Alarm systems that warn of
aerator system failure and/or pump failure are essential.
Inspections are recommended three to four times per year; septage pumping (solids wasting) is dependent upon inspection
results. Routine maintenance requirements for onsite SBRs are given below. Operation and maintenance requires semi-
skilled personnel. Based on field experience, 5 to 12 person-hours per year, plus analytical services, are required. The
process produces 0.6 to 0.9 Ib TSS/lb BOD removed and requires between 3.0 and 10 kWh/day for operation. Operating
Table 2. Suggested maintenance for sequencing batch reactor package plants
System component
Reaction tank
Aeration system-diffused air
Aeration system-mechanical
Septic tank (primary clarifier)
Controls
Sludge wasting
Analytical
Suggested maintenance tasks
Check for foaming and uneven air distribution; check for floating scum; check
decanter operation and adjust as required; adjust cycle time sequences as
required to achieve effluent target concentrations; check settled sludge
volume and adjust waste pumping to maintain target MLVSS levels.
Check air filters, seals, oil level, and backpressure; perform manufacturer's
required maintenance.
Check for vibrations and overheating; check oil level, and seals; perform
manufacturer's required maintenance.
Check for accumulated solids and order pumping if required.
Check functions of all controls and alarms; check electrical control box.
Pump waste solids as required to maintain target MLVSS range (typically
2,500 to 4,000 mg/L).
Measure aeration tank grab sample for MLVSS, pH, and settleability; collect
final effluent decant composite sample and analyze for water quality
parameters as required (BOD, TSS, pH, N, P, etc.).
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personnel prefer these systems to CFSGAS for their simplicity of 0/M tasks. The key operational components are the
programmer and the decanter, and these must be maintained in proper working order. The primary 0/M tasks are provided
in table 2.
Risk management issues
With proper management, a package SBR system is reliable and should pose no unacceptable risks to the homeowner or
the environment. If neglected, however, the process can result in environmental damage through production of poor-
quality effluent that may pose public health risks and can result in the premature failure of subsurface systems. Odor and
noise may also create some level of nuisance. SBRs are less susceptible to flow and quality loading changes than other
aerobic biological systems, but they are still not suitable for seasonal applications. They are similarly susceptible to
extreme cold and should be buried and/or insulated in areas subjected to these extremes. Local authorities can provide
guidance on climatic effects on equipment and how to prevent them. The controller should be located in a heated environ-
ment. Long power outages can result in odors and effluent degradation, as is the case with other aerobic biological
systems.
Costs
For residential applications, typical system equipment costs are $7,000 to $9,000. Installation costs vary depending on site
conditions; installation costs between $1,500 and $3,000 are typical for uncomplicated sites with good access. It should be
noted that additional system components (e.g., subsurface infiltration system) will result in additional costs.
Annual operation and maintenance costs include electricity use (<$300/year), sludge removal (>$100/year), and equipment
servicing. (Some companies are providing annual service contracts for these units for $250 to $400.) Actual costs will vary
depending on the location of the unit and local conditions.
References
Arora, M.L., et al. 1985. Technology evaluation of sequencing batch reactors. Journal of the Water Pollution Control
Federation 57:867.
Ayres Associates. 1998. Florida Keys Onsite Wastewater Nutrient Reduction Systems Demonstration Project. HRS Contract
No. LP988. Florida Department of Health, Gainesville, FL.
Buhr, H.O., et al. 1984. Making full use of step feed capability. Journal of the Water Pollution Control Federation 56:325.
Deeny, K.J., and J.A. Heidman. 1991. Implementation of Sequencing Batch Reactor Technology in the United States.
Paper presented at the 64th Annual Meeting of the Water Pollution Control Federation, Toronto, Canada.
Eikum, A.S., and T. Bennett. 1992. New Norwegian Technology for Treatment of Small Flows. In Proceedings of Seventh
Northwest Onsite Wastewater Treatment Short Course, ed. R.W Seabloom. University of Washington, Seattle.
U.S. Environmental Protection Agency (USEPA). 1986. Summary Report, Sequencing Batch Reactors. EPA 625/8-86-
001. Technology Transfer, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1987. Analysis of a Full-Scale SBR Operation at Grundy Center, Iowa.
EPA 600/J-87-065. U.S. Environmental Protection Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1993. Process Design Manual for Nitrogen Removal. EPA 625/R-93-
010. U.S. Environmental Protection Agency, Cincinnati, OH.
Water Environment Federation. 1998. Design of Municipal Wastewater Treatment Plants. Manual of Practice No. 8. Water
Environment Federation, Alexandria, VA.
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 4
Effluent Disinfection Processes
Description
The process of disinfection destroys pathogenic and other microorganisms in wastewater. A number of important water-
borne pathogens are found in the United States, including some bacteria species, protozoan cysts, and viruses. All pre-
treatment processes used in onsite wastewater management remove some pathogens, but data are scant on the magnitude
of this destruction. The two methods described in this section, chlorination and ultraviolet irradiation, are the most com-
monly used (figure 1). Currently, the effectiveness of disinfection is measured by the use of indicator bacteria, usually
fecal coliform. These organisms are excreted by all warm-blooded animals, are present in wastewater in high numbers,
tend to survive in the natural environment as long as or longer than many pathogenic bacteria, and are easy to detect and
quantify.
A number of methods can be used to disinfect wastewater. These include chemical agents, physical agents, and irradia-
tion. For onsite applications, only a few of these methods have proven to be practical (i.e., simple, safe, reliable, and cost-
effective). Although ozone and iodine can be and have been used for disinfection, they are less likely to be employed
because of economic and engineering difficulties.
Figure 1. Generic disinfection diagram
i irom
pretreatment
\ \
\
Disinfection
mixing
^- v wui co awio 01
\
Contact
time
surface water
Chlorine
Chlorine is a powerful oxidizing agent and has been used as an effective disinfectant in water and wastewater treatment
for a century. Chlorine may be added to water as a gas (C12) or as a liquid or solid in the form of sodium or calcium
hypochlorite, respectively. Because the gas can present a significant safety hazard and is highly corrosive, it is not recom-
mended for onsite applications. Currently, the solid form (calcium hypochlorite) is most favored for onsite applications.
When added to water, calcium hypochlorite forms hypochlorous acid (HOC1) and calcium hydroxide (hydrated lime,
Ca(OH)2). The resulting pH increase promotes the formation of the anion, OC1", which is a free form of chlorine. Because
of its reactive nature, free chlorine will react with a number of reduced compounds in wastewater, including sulfide,
ferrous iron, organic matter, and ammonia. These nonspecific side reactions result in the formation of combined chlorine
(chloramines), chloro-organics, and chloride, the last two of which are not effective as disinfectants. Chloramines are
weaker than free chlorine but are more stable. The difference between the chlorine residual in the wastewater after some
TFS-17
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time interval (free and combined chlorine) and the initial dose of chlorine is referred to as chlorine demand. The 15-
minute chlorine demand of septic tank effluent may range from 30 to 45 mg/L as Cl; for biological treatment effluents.
such as systems in Technology Fact Sheets 1, 2, and 3, it may range from 10 to 25 mg/L; and for sand filtered effluent, it
may be 1 to 5 mg/L (Technology Fact Sheets 10 and 11).
Figure 2. Example of a stack-feed chlorinator
Water inlet
Feed tubes
Water outlet
Ca(OCI)2 tablets
Calcium hypochlorite is typically dosed to wastewater in an onsite treatment system using a simple tablet feeder device
(figure 2). Wastewater passes through the feeder and then flows to a contact tank for the appropriate reaction. The
product of the contact time and disinfectant residual concentration (Ct) is often used as a parameter for design of the
system. The contact basin should be baffled to ensure that short-circuiting does not occur. Chlorine and combined
chlorine residuals are highly toxic to living organisms in the receiving water. Because overdosing (ecological risk) and
underdosing (human health risk) are quite common with the use of tablets, long swales/ditches are recommended prior to
direct discharge to sensitive waters.
Use of simple liquid sodium hypochlorite (bleach) feeders is more reliable but requires more frequent site visits by opera-
tors. These systems employ aspirator or suction feeders that can be part of the pressurization of the wastewater, causing
both the pump and the feeder to require inspection and calibration. These operational needs should be met by centralized
management or contracted professional management.
Ultraviolet irradiation
The germicidal properties of ultraviolet (UV) irradiation have been recognized for many years. UV is germicidal in the
wavelength range of 250 to 270 nm. The radiation penetrates the cell wall of the organism and is absorbed by cellular
materials, which either prevents replication or causes the death of the cell. Because the only UV radiation effective in
destroying the organism is that which reaches it, the water must be relatively free of turbidity. Because the distance over
which UV light is effective is very limited, the most effective disinfection occurs when a thin film of the water to be
treated is exposed to the radiation. The quantity of UV irradiation required for a given application is measured as the
radiation intensity in micro Watt-seconds per square centimeter (mW-s/cm2). For each application, wastewater transmit-
tance, organisms present, bulb and sleeve condition, and a variety of other factors will have an impact on the mW-s/cm2
required to attain a specific effluent microorganism count per 100 mL. The most useful variable that can be readily
controlled and monitored is Total Suspended Solids. TSS has a direct impact on UV disinfection, which is related to the
level of pretreatment provided.
TFS-18
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Many commercial UV disinfection systems (figure 3) are
available in the marketplace. Each has its own approach to how
the wastewater contacts UV irradiation, such as the type of
bulb (medium or low pressure; medium, low, or high inten-
sity), the type of contact chamber configuration (horizontal or
vertical), or the sleeve material separating the bulb from the
liquid (quartz or teflon). All can be effective, and the choice
will usually be driven by economics.
Typical applications
Disinfection is generally required in three onsite-system
circumstances. The first is after any process that is to be
surface discharged. The second is before a SWIS where there
is inadequate soil (depth to ground water or structure too
porous) to meet ground water quality standards. The third is
prior to some other immediate reuse (onsite recycling) of
effluent that stipulates some specific pathogen requirement
(e.g., toilet flushing or vegetation watering).
Figure 3. Wastewater flow in a quartz UV unit
Flow out
Flow in
One typical UV lamp
housed in a quartz sleeve
Design assumptions
Chlorination units must ensure that sufficient chlorine release occurs (depending on pretreatment) from the tablet chlorina-
tor. These units have a history of erratic dosage, so frequent attention is required. Performance is dependent on pretreat-
ment, which the designer must consider. At the point of chlorine addition, mixing is highly desirable and a contact chamber
is necessary to ensure maximum disinfection. Working with chlorinator suppliers, designers should try to ensure consis-
tent dosage capability, maximize mixing usually by chamber or head loss, and provide some type of pipe of sufficient
length to attain effective contact time before release. Tablets are usually suspended in open tubes that are housed in a
plastic assembly designed to increase flow depth (and tablet exposure) in proportion to effluent flow. Without specific
external mixing capability, the contact pipe (large-diameter Schedule 40 PVC) is the primary means of accomplishing
disinfection. Contact time in these pipes (often with added baffles) is on the order of 4 to 10 hours, while dosage levels are
in excess of those stated in table 1 for different pretreatment qualities and pH values. The commercial chlorination unit is
generally located in a concrete vault with access hatch to the surface. The contact pipe usually runs from the vault toward
the next step in the process or discharge location. Surface discharges to open swales or ditches will also allow for dechlo-
rination prior to release to a sensitive receiving water.
Table 1. Chlorine disinfection dose (in mg/L) design guidelines for onsite applications
Calcium
hypochlorite
pH6
pH7
pH8
Septic tank
effluent
35-50
40-55
50-65
Biological treatment
effluent
15-30
20-35
30-45
Sand filter
effluent
2-10
10-20
20-35
Note: Contact time = 1 hour at average flow and temperature 20 °C. Increase contact time to 2 hours at 10 °C and 8 hours at 5
°C for comparable efficiency. Dose = mg/L as Cl. Doses assume typical chlorine demand and are conservative estimates based
on fecal coliform data.
TFS-19
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Table 2.Typical ultraviolet (UV) system design parameters
Design parameter
UV dosage
Contact time
UV intensity
Wastewater UV transmittance
Wastewater velocity
Typical design value
20-140mW-s/cm2
6-40 seconds
3-12mW-s/cm2
50-70%
2-1 5 inches per second
The effectiveness of UV disinfection is dependent
upon UV power (table 2), contact time, liquid film
thickness, wastewater absorbance, wastewater
turbidity, system configuration, and temperature.
Empirical relationships are used to relate UV power
(intensity at the organism boundary) and contact
time. Table 2 gives a general indication of the dose
requirements for selected pathogens. Since effective
disinfection is dependent on wastewater quality as
measured by turbidity, it is important that pretreat-
ment provide a high degree of suspended and colloi-
dal solids removal.
Commercially available UV units that permit internal contact times of 30 seconds at peak design flows for the onsite
system can be located in insulated outdoor structures or in heated spaces of the structure served, both of which must
protect the unit from dust, excessive heat, freezing, and vandals. Ideally, the unit should also provide the necessary UV
intensity (e.g., 35,000 to 70,000 mW-s/cm2) for achieving fecal coliform concentrations of about 200 CFU/100 mL. The
actual dosage that reaches the microbes will be reduced by the transmittance of the wastewater (e.g., continuous-flow
suspended-growth aerobic systems [CFSGAS] or fixed-film systems [FFS] transmittance of 60 to 65 percent). Practically,
septic tank effluents cannot be effectively disinfected by UV, whereas biological treatment effluents can meet a standard of
200 cfu/100 mL with UV. High-quality reuse standards will require more effective pretreatment to be met by UV disinfec-
tion. No additional contact time is required. Continuous UV bulb operation is recommended for maximum bulb service
life. Frequent on/off sequences in response to flow variability will shorten bulb life. Other typical design parameters are
presented in table 2.
Performance
There are few field studies of tablet chlorinators, but those that exist for post-sand-filter applications show fecal coliform
reductions of 2 to 3 logs/100 mL. Another field study of tablet chlorinators following biological treatment units exceeded a
standard of 200 FC/100 mL
93 percent of the time. No chlorine residual was present in 68 percent of the samples. Newer units managed by the
biological unit manufacturer fared only slightly better. Problems were related to TSS accumulation in the chlorinator, tablet
caking, failure of the tablet to drop into the sleeve, and failure to maintain the tablet supply. Sodium hypochlorite liquid feed
systems can provide consistent disinfection of sand filter effluents (and biological system effluents) if the systems are
managed by a utility.
Data for UV disinfection for onsite systems are also inadequate to perform a proper analysis. However, typical units
treating sand filter effluents have provided more than 3 logs of FC removal and more than 4 logs of poliovirus removal.
Since this level of pretreatment results in a very low final FC concentration (<100 CFU/100 mL), removals depend more
on the influent concentration than inherent removal capability. This is consistent with several large-scale water reuse
studies that show that filtered effluent can reach
Table S.Typical (UV) transmittance values for water essentially FC-free levels (<1 CFU/100 mL) with UV
dosage of about 100 mW-s/cm2, while higher (but
attainable) effluent FC levels require less dosage to
filtered effluent (about 48 mW-s/cm2) than is required
by aerobic unit effluent (about 60 mW-s/cm2). This
can be attributed to TSS, turbidity, and transmittance
(table 3). Average quartz tube transmittance is about
75 to 80 percent.
Wastewater treatment level
Primary
Secondary
Tertiary
Percent transmittance
45-67
60-74
67-82
Source: USEPA, 1986.
TFS-20
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Management needs
Chlorine addition by tablet feeders is likely to be the most practical method for chlorine addition for onsite applications.
Tablet feeders are constructed of durable, corrosion-free plastics and are designed for in-line installation. Tablet chlorina-
tors come as a unit similar to figure 2. If liquid bleach chlorinators are used, they would be similarly constructed. That
unit is placed inside a vault that exits to the contact basin. The contact basin may be plastic, fiberglass, or a length of
concrete pipe placed vertically and outfitted with a concrete base. Baffles should be provided to prevent short-circuiting of
the flow. The contact basin should be covered to protect against the elements, but it should be readily accessible for
maintenance and inspection.
The disinfection system should be designed to minimize operation and maintenance requirements, yet ensure reliable
treatment. For chlorination systems, routine operation and maintenance would include servicing the tablet or solution
feeder equipment, adding tablets or premixed solution, adjusting flow rates, cleaning the contact tank, and collecting and
analyzing effluent samples for chlorine residuals. Caking of tablet feeders may occur and will require appropriate mainte-
nance. Bleach feeders must be periodically refilled and checked for performance. Semiskilled technical support should be
sufficient, and estimates of time are about 6 to 10 hours per year. There are no power requirements for gravity-fed
systems. Chemical requirements are estimated to be about 5 to 15 pounds of available chlorine per year for a family of
four. During the four or more inspections required per year, the contact basin may need cleaning if no filter is located
ahead of the unit. Energy requirements for a gravity-fed system are nil. If positively fed by aspirator/suction with pump-
ing, the disinfection unit and alarms for pump malfunctions will use energy and require inspection. Essentially unskilled
(but trained) labor may be employed. Safety issues are minimal and include wearing of proper gloves and clothing during
inspection and tablet/feeder work.
Commercially available package UV units are available for onsite applications. Most are self-contained and provide low-
pressure mercury arc lamps encased by quartz glass tubes. The unit should be installed downstream of the final treatment
process and protected from the elements. UV units must be located near a power source and should be readily accessible
for maintenance and inspection. Appropriate controls for the unit must be corrosion-resistant and enclosed in accordance
with electrical codes.
Routine operation and maintenance for UV systems involves semiskilled technician support. Tasks include cleaning and
replacing the UV lamps and sleeves, checking and maintaining mechanical equipment and controls, and monitoring the UV
intensity. Monitoring would require routine indicator organism analysis. Lamp replacement (usually annually) will depend
upon the equipment selected, but lamp life may range from 7,500 to 13,000 hours. Based on limited operational experience,
it is estimated that 10 to 12 hours per year would be required for routine operation and maintenance. Power requirements
may be approximately 1 to 1.5 kWh/d. Quartz sleeves will require alcohol or other mildly acidic solution at each (usually
four per year) inspection.
Whenever disinfection is required, careful attention to system operation and maintenance is necessary. Long-term manage-
ment, through homeowner-service contracts or local management programs, is an important component of the operation
and maintenance program. Homeowners do not possess the skills needed to perform proper servicing of these units, and
homeowner neglect, ignorance, or interference may contribute to malfunctions.
Risk management issues
With proper management, the disinfection processes cited above are reliable and should pose little risk to the homeowner.
As mentioned above, a potentially toxic chlorine residual may have an important environmental impact if it persists at high
concentrations in surface waters. By-products of chlorine reactions with wastewater constituents may also be toxic to
aquatic species. If dechlorination is required prior to surface discharge, reactors containing sulfur dioxide, sodium bisul-
fate, sodium metabisulfate, or activated carbon can be employed. If the disinfection processes described above are improp-
erly managed, the processes may not deliver the level of pathogen destruction that is anticipated and may result in some
risk to downstream users of the receiving waters. The systems described are compact and require modest attention.
Chlorination does not inherently require energy input; UV irradiation and dosage pumps do consume some energy
TFS-21
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(>lkWh/day). Both processes will require skilled technical support for the monitoring of indicator organisms in the
process effluents.
Chlorination systems respond to flow variability if the tablets are feeding correctly. UV does not do so and is designed for
the highest flow scenario, thus overdosing at lower flows since there is no danger in doing so. Toxic loads are unlikely to
affect either system, but TSS can affect both. Inspections must include all pretreatment steps. UV is more sensitive to
extreme temperatures than chlorination, and must be housed appropriate to the climate. In extremely cold climates, the UV
system can be housed inside the home with minimal danger to the inhabitants. Power outages will terminate UV disinfec-
tion and pressurized pumps for both systems, while causing few problems for gravity-fed chlorination units. There should
be no odor problems during these outages.
Costs
Installed costs of a complete tablet chlorination unit are about $400 to $500 for the commercial chlorinator unit and
associated materials and $800 to $1,200 for installation and housing. Operation and maintenance would consist of tablets
($30 to $50 per year), labor ($75 to $100 per year), and miscellaneous repairs and replacements ($15 to $25 per year), in
addition to any analytical support required.
Installed costs of UV units and associated facilities are $1,000 to $2,000. 0/M costs include power ($35 to $40 per year),
semiskilled labor ($50 to $100 per year), and lamp replacement ($70 to $80 per year), plus any analytical support.
References
Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1981. Evaluation ofOnsite Wastewater Treatment and Disposal Options.
EPA 600/S2-81-178. NTIS No. PB-82-101-635. National Technical Information Service, Cincinnati, OH.
Crites, R., and G. Tchobanoglous. 1998. Small and Decentralized Wastewater Management Systems. WCB/McGraw-Hill,
San Francisco, CA.
Hanzon, B.D., and R. Vigilia. 1999. Just the facts. Water Environment and 7ec/wo7og7 November 1999, 34-42.
Scheible, O.K. 1987. Development of a rationally based design protocol for the ultraviolet light disinfection process.
Journal of the Water Pollution Control Federation 59:25.
University of Wisconsin. 1978. Management of Small Waste Flows. EPA 600/2-78-173. Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1980. Design Manual: Onsite Wastewater Treatment and Disposal
Systems. EPA 625/1-80-0012. U.S. Environmental Protection Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1986. Municipal Wastewater Disinfection Design Manual. EPA 625/1-
86-021. U.S. Environmental Protection Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1992. Ultraviolet Disinfection Technology Assessment. EPA-832/R-92-
004. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Water Environment Federation. 1998. Design of Municipal Wastewater Treatment Plants, 3d ed. Alexandria, VA.
White, G.C. 1992. The Handbook of Chlorination and Alternative Disinfectants. 3d ed. Van Nostrand Reinhold, New
York.
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 5
Vegetated Submerged Beds and
Other High-Specific-Surface
Anaerobic Reactors
Description
A high-specific-surface anaerobic reactor (figure 1) is any tank or cavity filled with solid media through which wastewater
flows with a high hydraulic retention time (HRT). In onsite treatment the two primary types are vegetated submerged beds
(VSBs) and anaerobic upflow filters (AUFs). The first is characterized by horizontal flow and prolific growth of macro-
phytes on the surface. The second comes in a variety of forms from upflow sludge blanket systems and fixed media
anaerobic filters to partially fluidized beds of fine media. Both have long HRTs, produce anaerobic effluents, generally
treat either high-strength or minimally pretreated wastewater, and usually require some form of posttreatment to meet
surface discharge or water reuse requirements.
The primary removal mechanisms in all of these systems are physical, that is, floculation, sedimentation, and adsorption.
Anaerobic biological reactions are extremely slow and do not have a significant impact on soluble BOD until HRTs
become quite long. Some toxic organic compounds may be reduced through these mechanisms and chemical precipitation
(e.g., sulfides) at shorter HRTs.
Figure 1. Generic high-specific surface anaerobic reactor
Top
Influent
\
Effluent
VSBs, as shown in figure 2, usually follow a septic tank and remove most of the suspended and larger colloidal particles,
BOD, organic forms of nitrogen, and other particles. Although they are frequently identified as subsurface constructed
wetlands, they do not fit the strict definition of a constructed wetland.
Three types of AUFs can be used as pretreatment devices for high-strength wastewater and some onsite pretreatment
applications in the United States. They are in shown in figures 3, 4, and 5. Figure 3, with a rock medium, is the most
typical U.S. application.
TFS-23
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Figure 2. Elements of a vegetated submerged bed (VSB) system
Pretreated
(settled)
influent
Inlet zone
Top slope
Treatment zone
(media)
Liner
Outlet zone
V
Effluent
Variable-level
outlet
CATTAILS
SLOTTED PIPE
FOR
WASTEWATER
DISTRIBUTION
Source: Toms Creek Project, VA.
TFS-24
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Figure 3. Schematic of the upflow anaerobic filter process
Biogas
Treatment
media
Flow
distributor
Drain
Figure 4. Schematic of the upflow anaerobic sludge blanket process
Biogas
Gas/solids
separator
Influent
Sludge
blanket
Sludge
bed
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Figure 5. Schematic of the anaerobic fluidized bed process
Fluidized
media
Flow
Distributor
Blogas
Effluent
Recycle
Influent
Typical applications
AUFs are widely used in hot climates where domestic wastewaters are several times higher in strength than U.S. wastewa-
ters. These systems can reduce high BOD and TSS to levels that can be readily treated by typical aerobic processes such
as suspended and fixed growth aerobic units or recirculating/intermittent media filters. International literature contains
numerous references to the three types of AUFs and their valuable contributions to water pollution abatement. Anaerobic
rock upflow filters (figure 6) are also used to lower septic tank effluent BOD and TSS concentrations prior to discharge to
the subsurface wastewater infiltration system (SWIS).
Figure 6. Anaerobic upflow filter
Manhole Access Door
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VSBs are extremely popular in the United States because of their aesthetic features and their ability to meet basic (second-
ary) effluent standards when treating septic tank effluent. Until recently they were purported to be capable of nitrification
and nutrient removal at economically competitive HRTs. Since they are largely anaerobic, this would be biochemically
impossible. However, they are fully capable of meeting secondary BOD and TSS standards. They are also sometimes used
before a SWIS and can meet the same effluent TSS and BOD standards as aerobic units (Technology Fact Sheets 1, 2, and
3). VSBs can be considered as pretreatment units regarding SWIS design requirements. They do not, however, remove
more than 2 logs of fecal coliform and would likely require disinfection for direct surface discharge. They also require
some form of aeration to meet effluent standards for dissolved oxygen (DO). These VSBs will capture rainfall and
snowmelt, effluent standards for requiring adjustment to designs of SWIS following these units.
Both VSBs and AUFs are being used in rural areas in combination with aerobic processes to remove significant amounts of
nitrogen through denitrification. These processes are included in the nutrient removal fact sheets.
Design assumptions
VSB design guidance for small communities is provided in table 1. In the first few months of operation, excellent phos-
phorus removal will occur until the rock medium becomes saturated with phosphorus and breakthrough occurs. (Note:
USEPA guidance on design of VSBs can be found in Manual: Constructed Wetlands Treatment of Municipal Wastewater,
posted at http://www.epa.gov/ordntrnt/ord/nrmrl/pubs/2001/wetlands/625r99010.pdf)
Except for the anaerobic upflow rock filter, AUFs are rarely employed for U.S. onsite applications. Since the primary
purpose of these systems is to improve the BOD and TSS of septic tank effluent, they are essentially physical processes.
Therefore, they must be designed to maximize their flocculation and sedimentation functions. Limited field studies
Table 1. Summary ofVSB design guidance
Pretreatment "
Surface area
BOD
TSS
TKN
TP
Depth
Media (typical)
Water (typical)
Length
Width
Bottom slope
Top slope
Hydraulic conductivity
First 30% of length
Last 70% of length
Media
Inlet zone (1st 2m [6.5 ft])
Treatment zone
Outlet zone (last 1 m [3.3 ft])
Planting media (top 1 0 cm [4 in])
Miscellaneous
Objective
Based on desired effluent quality and areal loading rates as follows:
6 g/m2-d (53.5 Ib/ac-d) to attain 30 mg/L effluent
1.6 g/m2-d (14.3 Ib/ac-d) to attain 20 mg/L effluent
20 g/m2-d (178 Ib/ac-d) to attain 30 mg/L effluent
Use another treatment process in conjunction with VSB
VSBs not recommended for phosphorus removal
0.5-0.6 m (20-24 in)
0.4-0.5 m (16-20 in)
Minimum of 15 m (49 ft.)
As calculated
0-1%
Level or nearly level
1% of clean K
10% of clean K
All media should be washed clean of fines and debris; more uniform
rounded media will generally have more void spaces; media should
be resistant to crushing or breakage.
40-80 mm (1 .5-3.0 in)
20-30 mm (3/4-1 in) use clean K = 100,000, if actual K not known
40-80 mm (1 .5-3.0 in)
5-20 mm (1/4-3/4 in)
Use adjustable outlet control device with capability to flood and drain
system and sizing of VSB and SWIS (if used) must include a water
balance analysis
" Use after primary sedimentation (e.g., septic tank, Imhoff tank, primary clarifier); not recommended
for use after ponds because of problems with algae.
TFS-27
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indicate that successful removal of particulate BOD and TSS could be obtained with an average HRT between 16 and 24
hours, rounded media size of 1 to 2 inches or greater, and a means of periodically draining excess accumulated solids from
the bottom of the unit. At higher temperatures, some partial digestion of accumulated organic solids occurs. This liquefac-
tion may by accompanied by gas production. The amount and makeup of that gas depend on pH, wastewater constituents
(e.g., protein, lipids, carbohydrates), sulfate, alkalinity, and other constituents.
Performance
VSB systems can treat septic tank effluent to a BOD of 20 to 30 mg/L, depending on the organic loading rate chosen. The
VSB effluent TSS is almost always less than 30 mg/L. Some removal of all constituents (e.g., heavy metals, organic
nitrogen and organic phosphorus, pesticides, and other toxic organics) can also be expected. Over and above these
removals, there will be some small percentage of dissolved organic removal owing to anaerobic biological activity.
Rock AUFs after septic tanks have not been widely studied, but they appear to remove TSS by as much as 55 percent from
septic tank effluent, while removing a similar percent of the BOD. Actual removals will depend on the specific fractions
of particulate, colloidal, and soluble matter in the septic tank effluent. Little soluble or fine particulate removal is likely.
Both systems will remove pathogens, with VSBs capable of removing from 1 to 3 logs (design average = 2 logs), while
AUF removal is estimated to be closer to 1 log because of shorter HRTs.
Management needs
All of these anaerobic systems are passive in nature and require minimal 0/M activity. AUF units may be constructed
aboveground, but they usually are below the ground surface to provide insulation and protect against severe climatic
conditions. The solid medium can be a coarse gravel or one of many commercially available synthetic media that will not
easily clog with biomass. Access to inlet and outlet systems should be provided for purposes of cleaning and servicing. An
easily accessible means to drain the unit and an effective alarm system should be provided.
VSB units are generally aesthetically pleasing additions to the landscape if sufficient area is available for their application. It
is estimated that fewer than 4 hours per year will be required for 0/M tasks, which will involve inspecting the system and
making any adjustments required. Therefore, until more information becomes available, a site visit schedule of three to
four times a year is suggested.
Residuals generate in VSB systems at a slow rate. Although the system inlet where most solids accumulate can be exca-
vated or piped for high-pressure removal, it is more likely that a replacement system would be built after the service life of
the original system ends.
AUF units will require periodic flushing of accumulated solids and inspection of inlet and outlet systems. If solids are
allowed to accumulate, the filter may clog or release high solids "events" to the SWIS. This will clog the infiltrative
surface or the distribution system. Therefore, a site visit schedule of three to four times per year is suggested until more
information becomes available. This would entail from 6 to 8 hours per year of labor. Disposal and transport of excess
solids will require similar management to septage.
Risk management issues
VSB systems can usually handle the flow variations likely to occur from residential sources, as well as toxic shock loads
and power outages. Reed and colleagues (1995) proposed some models to support the view that insulation provided by
dead vegetation (litter) on the surface should aid these systems during typical winters in northern climates. The potential
for odor is low for properly sized systems.
AUF systems should also accommodate typical flow variations, toxic shocks, and power outages. They should be insulated
from cold weather. AUFs are inherently odor and corrosion generators, so corrosion-resistant materials should be employed.
Odor (hydrogen sulfide) production may require the use of an odor-control system (e.g., soil filters) to deodorize off-gases.
TFS-28
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Costs
VSB systems for onsite application will cost about $20 per square foot (USEPA, 1999). Almost half of that cost is for the
media, while excavation, liner, plants, control structures, and piping make up the rest. Operation and maintenance costs
would run less than $100 per year if these services are professionally provided.
AUF systems are likely to cost about $1,000 to $1,500 per house, primarily related to the cost of the tank and related
containment features. 0/M costs would run around $200 per year, including solids transport as required.
References
Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1979. Evaluation of Onsite Wastewater Treatment and Disposal Options.
EPA 600/s2-81-178. U.S. Environmental Protection Agency, Cincinnati, OH.
Cowlter, J.B., S. Soneda, and M.B. Ettinger. 1957. Anaerobic contact process for sewage disposal. Sewage and Industrial
Wastes Journal29(4):468-477.
Crites, R., and G. Tchobanoglous. 1998. Small and Decentralized Wastewater Management Systems. WCB McGraw-Hill,
San Francisco, CA.
DeRenzo, D.J. 1977. Energy from Bioconversion of Waste Materials. Noyes Data Corporation, Park Ridge, NJ.
Hamilton, J. 1975. Treatment of Septic Tank Effluent with an Anaerobic Filter. Master's of Science in Civil Engineering
thesis, University of Washington, Seattle.
Hamilton, J. 1976. Proceedings of Northwest Onsite Wastewater Disposal Short Course. University of Washington, Seattle.
Jewell, WJ. 1987. Anaerobic sewage treatment. Journal of Environmental Science and Technology 2l(l):\4- 21.
Kennedy, J.C. 1979. Performance of Anaerobic Filters and Septic Tanks Applied to the Treatment of Residential
Wastewater. Master's thesis, University of Washington, Seattle.
Lombardo & Associates, Inc. 1983. Design Report. Anaerobic Up/low Filters. Newton, MA.
Netter, R., E. Stubner, PA. Wildner, and I. Sekoulov. 1993. Treatment of septic tank effluent in a subsurface biofilter.
Water Science Technology28(10): 117'-124.
Reed, S.C., R.W Crites, and E.J. Middlebrooks. 1995. Natural Systems for Waste Management and Treatment. McGraw
Hill, Inc, New York.
Switzenbaum, M.S. 1985. Proceedings of SeminarA/Vorkshop-anaerobic Treatment of Sewage. Report No. Env.E. 88-85-5.
University of Massachusetts, Amherst, MA.
Thaulow, H. 1974. Use of Anaerobic Filters for Onsite Treatment of Household Wastewater. Master's thesis, University of
Washington, Seattle.
U.S. Environmental Protection Agency (USEPA). 1992. Wastewater Treatment/Disposal for Small Communities. EPA 6257
R-92-005. U.S. Environmental Protection Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1993a. Nitrogen Control Manual. EPA 625/R-93/0010. U.S.
Environmental Protection Agency, Office of Research and Development, Washington, DC.
U.S. Environmental Protection Agency (USEPA). 1993b. Subsurface Flow Constructed Wetlands for Wastewater
Treatment: A Technology Assessment. EPA 832-R-93-008. U.S. Environmental Protection Agency, Office of Water,
Washington, DC.
U.S. Environmental Protection Agency (USEPA). 1999. Manual: Constructed Wetlands Treatment of Municipal
Wastewater. EPA 625/R-99/010. U.S. Environmental Protection Agency, Cincinnati, OH.
TFS-29
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TFS-30
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 6
Evapotranspiration and
Evapotranspiration/lnfiltration
Description
Onsite evapotranspiration wastewater treatment systems are designed to disperse effluent exclusively by evapotranspira-
tion. Evapotranspiration (ET) is defined as the combined effect of water removal from a medium by direct evaporation
and by plant transpiration. The evapotranspiration/infiltration (ETI) process is a subsurface system designed to dispose of
effluent by both evapotranspiration and infiltration into the soil. Both of these systems are preceded by primary pretreat-
ment units (e.g., septic tank) to remove settleable and floatable solids. The influent to the ET or ETI units enters through
a series of distribution pipes to a porous bed. In ET systems, a liner is placed below the bed to prevent water loss via
infiltration unless the soil is impermeable. The surface of the sand bed is planted with water-tolerant plants. Effluent is
drawn up through fine media by capillary wicking and evaporated or transpired into the atmosphere. In ETI systems,
effluent is allowed to percolate into the underlying soil.
Modifications to ET and ETI systems include mechanical evaporating devices and a broad array of different designs and
means of distribution, storage of excess influent, wicking, and containment or infiltration prevention. Some newer studies
are using drip irrigation with distribution to forested areas with purported success.
Typical applications
ET and ETI systems are best suited for arid (evaporation exceeds precipitation) climates. If ETI is selected, soil percola-
tion is also an important consideration. Both systems are often selected when site characteristics dictate that conventional
methods of effluent disposal are not appropriate (e.g., unprotected sole source aquifer, high water table or bedrock, tight
soils, etc.).
Although these systems normally follow septic tanks, additional pretreatment may be employed to minimize clogging of
the ET/ETI system piping and media. They are sometimes used as alternative systems during periods when normal
disposal methods are inoperable, for example, spray or other surface irrigation. Also, these systems have been widely used
for seasonal homes in areas where year-round application of ET/ETI is not practical and conventional methods are not
feasible. Year-round ET systems (see figure 1) require large surface areas and are most feasible in the areas shown on
figure 2. ETI systems can be employed to reduce the infiltrative burden on the site during the growing season. Such
applications can also result in some reduction in nutrients, which are transferred to the overlying vegetation (USEPA,
1999).
TFS-31
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Figure 1. Cross section of a generic evapotranspi ration bed (adapted from NSFC)
Surface soil
sloped to crown
Natural grade sloped to
drain away from system
\
Impervious liner
(optional)
Water storage
gravel fill
(optional)
Distribution
lines
Figure 2. Relative suitability for evapotranspi ration systems
D Least suitable
D Partially suitable
• Most suitable
Typical
observation
well
Ends of liner buried
in native soil
TFS-32
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Design assumptions
The design evapotranspiration rate is site specific. Some areas are arid (precipitation < evaporation) but lack the solar
radiation or wind velocities necessary to efficiently evaporate wastewater throughout the year. Therefore, simple use of
well-known evaporation estimates like Pentman, Blaney-Criddle, and Jensen-Haise will not likely be satisfactory. In fact,
historically, the definition of workable ET rates for an area has been a trial and error process, which is further complicated
by the system design and the plants used. The primary variables that have an impact on the potential ET rate are climate,
cover soil, and vegetation. The most important system variables, which control the movement of wastewater to the
surface, are media and the depth to saturated (stored) water. Most published designs are suspect because they store the
wastewater so deep that the wicking properties of the fill and the area (voids) through which water must rise restrict
delivery of water to the surface where it is evaporated.
Present ET system designs normally employ 20-mil polyethylene liners where the soil is too permeable and ground water
contamination is likely. Most employ distribution systems placed in 12 inches of gravel (0.75 to 2.5 inches) at the bottom
of the bed. Spacing of the distribution pipes is 4 to 12 feet, with lower values preferred for better distribution. Wicking is
accomplished by a 2- to 2.5-foot layer of sand (0.1 millimeter) and a loamy soil-sand mix to raise the water to the surface
or a thin layer of soil at the surface. Most have employed the formula:
A = nQ/ET - P
where:
A = surface area required to evaporate the wastewater
n = coefficient, which varies from 1 to 1.6
Q = annual flow volume
ET = annual evapotranspiration rate
P = annual precipitation rate
Each of these factors is open to some degree of interpretation. Because these systems are large and expensive, there has
been a tendency to minimize their design size and cost, resulting in significant failure rates. Typical ET estimates range
from 0.01 to 2.0 centimeters per day. The contribution of plants has remained a matter of controversy. ET bed sizing has
varied from 3,000 to 10,000 square feet and higher. A water balance based on at least 10 years of data is calculated to
provide sufficient storage for nonsurfacing operations or to estimate nonatmospheric volumes to be infiltrated.
The modern use of shallow trenches for SWIS is strongly related to the maximization of ET, and such systems could be
classified as ETI systems. Further, the use of shallow serial distribution where topographic relief is available is a classic
application of the ETI concept, that is, shallow trenches close to the surface, full of wastewater, with only a short wicking
distance to the evaporative surface. Such a system fulfills all the described features of an ideal ETI system. Similarly, drip
irrigation uses the shallowest of all SWIS burial requirements and, by nature, maximizes ET potential.
Performance
There have been few studies of ET and ETI systems. Most ET system studies have been less than impressive. In most
cases the fault has been related to poor design assumptions, for example, over-estimating the ET potential of shrubs and
trees planted on the surface and of the overall potential of ET itself. Poor system design has been somewhat offset by
leaking liners that give the appearance that the system is performing adequately. Inadequate wicking has been overcome by
raising water levels. However, better ET assessment and more rational designs will improve performance at increased
costs.
ETI systems have generally worked well, but no scientific studies have been performed to verify this observation. ETI
systems do fail when the ET contribution is overestimated, but many times the placement of the wastewater higher in the
soil profile offsets that error by increasing the infiltrative capacity of the site.
TFS-33
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Management needs
ET systems are very sensitive to variations in construction techniques. Poor construction can defeat their utility through
poor liner installation, poor placement and choice of wicking media, compaction, and inadequate surface drainage mitiga-
tion.
Operation and maintenance requirements are minimal, often consisting of simply mowing the grass on the surface.
Replanting cover crops to improve cold season performance has been suggested but offers little return. Shrubs or small
trees planted on the ET system generally improve active (warm) season ET and hinder ET in the dormant (cold) season.
Therefore, the 0/M needs of the system should be limited to two to three short visits to observe and record the water
height in the observation well. These tasks require about 1 to 2 hours per year of unskilled labor. No energy is required.
ET system salt buildup, if not diluted by precipitation, may require some media replacement after 5 to 10 years of opera-
tion depending on water supply characteristics. There are no known safety issues with these systems as long as they are
fenced or otherwise isolated from children's play areas.
ETI systems are very similar to SWIS systems, and their management requirements are similar to those of ET systems.
Because ETI systems infiltrate wastewater, they have ground water and surface water contamination concerns like those of
other SWIS designs, and they may require monitoring of effluent impacts depending on the uses of ground water and
performance standards to protect them.
Risk management issues
Because ET systems are large, there may be some visual aesthetic problems. Odors are usually not a problem, but they can
be on occasion. Flow peaks during low ET periods could result in overflows, thus leading to the usual restriction for year-
round ET use in areas where ET does not exceed precipitation by more than 2 inches per month. These systems do not
function when their surface freezes. They are typically unaffected by power outages since they are generally fed by
gravity. Toxics also have no impact unless they are phytotoxic and would then kill the surface vegetation.
Costs
Because of their large size and specific media (and often liner) requirements, ET systems are generally expensive, rein-
forcing their use as a "last resort" alternative. Installed costs of $10,000 to $15,000 and higher are possible depending on
climate and location. 0/M costs are relatively low, on the order of $20 to $30 per year, but they could increase if the
system fills and requires pumping. ETI systems have capital and 0/M costs similar to a SWIS.
References
Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1979. Evaluation of Existing and Potential Technologies for Onsite
Wastewater Treatment and Disposal. EPA 600/S2-81-178. U.S. Environmental Protection Agency, Cincinnati, OH.
Beck, A.F. 1979. Evapotranspiration bed design. Journal of Environmental Engineering Division-American Society of Civil
Engineers 105(2): 411-415.
Frank, WL. 1996. Engineering parameters in the design of evapotranspiration beds. Water and Engineering Management
November, 31-37.
Ingham, A.T. 1987. Guidelines for Evapotranspiration Systems. State Water Resources Control Board, State of California.
Sacramento, CA.
Lomax, K.M., et al. 1978. Guidelines for Evapotranspiration Systems. State Water Resources Control Board, State of
California. Sacramento, CA.
National Small Flows Clearinghouse (NSFC). 1998. Evapotranspiration Systems Fact Sheet. Cooperative Agreement
CX825652, U.S. Environmental Protection Agency, Washington, DC.
TFS-34
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National Small Flows Clearinghouse (NSFC). 2000. Evapotranspiration systems. Pipeline 11(1).
Peters, E.G. 1988. An Evaluation of Enhanced ET Onsite Sewage Treatment and Disposal Systems. Master's thesis,
University of Maryland, College Park.
Salvato, J.A. 1982. Rational design of evapotranspiration bed. Journal of Electrical Engineering-American Society of Civil
Engineers 109(3): 646-660.
U.S. Environmental Protection Agency (USEPA). 1999. Manual: Constructed Wetlands Treatment of Municipal
Wastewaters. EPA/625/R-99/010. U.S. Environmental Protection Agency, Cincinnati, OH.
Victoria (AUS)-Environmental Protection Agency. 1980. The Use of Transpiration Beds for Domestic Wastewater
Disposal. EPA Report No. 104. Melbourne, Australia.
Wheeter, D.W. 1979. The Use of Evapotranspiration as a Means of Wastewater Disposal. Research Report No. 73.
Tennessee Water Resources Research Center, University of Tennessee, Knoxville.
TFS-35
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TFS-36
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 7
Stabilization Ponds, FWS
Constructed Wetlands, and Other
Aquatic Systems
Description
Aquatic systems are large basins filled with wastewater undergoing some combination of physical, chemical, and/or
biological treatment processes that render the wastewater more acceptable for discharge to the environment (figure 1).
They are not widely used because they tend to be large in area, require some form of fencing to minimize human health
risk, often require supplemental treatment
before discharge or reuse, and are approved in Figure 1. Generic aquatic lagoon system
only a few states.
Influent
Aquatic
system (s)
Effluent
Stabilization ponds (lagoons) have many
forms, but the facultative lagoon is the most
widely used. Aerated lagoons are often pre-
ferred because of their smaller size require-
ments. Anaerobic lagoons and maturation
ponds are not used in the United States for
onsite application by design. In some areas,
lagoons must be lined according to codes,
which further limits their application. Facultative lagoons are large in size, perform best when segmented into at least
three cells, obtain necessary oxygen for treatment by surface reaeration from the atmosphere, combine sedimentation of
particulates with biological degradation, and produce large quantities of algae, which limits the utility of their effluent
Figure 2. Generic facultative lagoon wlthout further treatment. A typical
facultative lagoon is shown in figure 2.
Aerated lagoons use mechanical
equipment to enhance and intensify the
biodegradation rate. They do not
produce the intense algal load on
downstream processes and have smaller
areal requirements than facultative
systems.
Free water surface (FWS) constructed
wetlands have also been used, though rarely, for similar reasons. These systems perform best when divided into a mini-
mum of three zones, the first and last being fully vegetated with macrophytes (cattails or bulrushes) and the middle having
an open water surface, which performs like a facultative lagoon. In the first zone, the influent is suspended and colloidal
solids are flocculated and settled under anaerobic or anoxic conditions. The second zone reaerates the anaerobic wastewater
From
pretreatment
V
\
\
Cell
1
V
>
\
\
Cell
2
V
>
\
\
Cell
3
Outlet
TFS-37
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to provide oxygen for aerobic biodegradation and possible nitrification before the final-zone flocculation and sedimenta-
tion (and denitrification) steps. An FWS constructed wetland is shown in figure 3.
Figure 3. Elements of a free water surface (FWS) constructed wetland
Pretreated
(lagoon)
influent
Inlet
settling
zone
\
Floating and
emergent
plants
/
Submerged
growth
plants
Floating and
emergent
plants i
Zone 1
Fully vegetated
DO(-)
H < 0.75 m
Zone 2
Open water surface
D0( + )
H>1.2m
Zone 3
Fully vegetated
DO(-)
H < 0.75 m
Oulet
zone
Effluent
Variable level
outlet
Typical applications
Facultative lagoon systems, like evaporative (ET) systems, are not widely used for onsite wastewater treatment. They are
large in size, are expensive to build, perform only a portion of the treatment necessary to permit surface discharge or reuse
(table 1), and produce large concentrations of algae, which negates their use as direct pretreatment before soil infiltration.
They have been used in a few states as an alternative system when a subsurface wastewater infiltration system (SWIS) is
not feasible, usually to discharge without further treatment to surface waters, which is generally unacceptable under
normal circumstances. In some states intermittent discharge lagoons are required. Storage volume is for all cold weather
months (4 to 6 months), making the size of these systems too large for most applications.
Aerated lagoons require far less land and could theoretically be used in place of aerobic biological treatment, but they
cannot be buried and insulated in northern climates like those units. They could be used in southern climates as pretreat-
ment for SWISs and would otherwise have similar features to the fact sheets that describe those systems.
FWS constructed wetlands reliably produce an advanced secondary effluent and can be employed for significant nitrogen
removal. They require large land areas, similar to facultative lagoons. Their effluent quality is excellent for SWIS applica-
tion, but they require disinfection for surface discharge and many reuse options. They have a highly desirable appearance,
which often makes them the preferred alternative for owners with sufficient land areas.
Table 1.Typical design guidance
Parameter
HRT (days)
Power (hp/106gal)
Depth (ft)
Minimum no. of cells
BOD loading
(Ib/acre-day)
TSS loading
(Ib/acre-day)
Facultative
lagoon
30-180
0
3-5
3
20-60
N/A
Aerated
lagoon
3 (max)
30
10
2
200-600
N/A
FWS constructed
wetland
6 (min)
0
2-5
3
40-53
27^5
TFS-38
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All of these aquatic systems should be placed after the septic tank and before the disinfection or SWIS steps in the treat-
ment train.
Performance
Facultative lagoons are capable of 75 to 95 percent BOD removal, but TSS removal varies widely because of algal
growth. During nonalgal periods, up to 90 percent TSS removal is possible, but during warm seasons TSS removal can be
negligible. In summer months 80 percent of the ammonia-nitrogen is nitrified, total nitrogen removal can reach 60
percent, and total phosphorus removal can approach 50 percent. Very long detention times in hot climates can reduce fecal
coliforms to levels that can often meet surface water discharge standards, but typical U.S. retention times reduce fecal
coliforms by 2 to 3 logs/100 mL.
Aerated ponds have removal capabilities similar to facultative lagoons, except that TSS removal is more consistent with
aerobic biological systems (20 to 60 mg/L). Nitrification of ammonia-nitrogen can be nearly complete in warm seasons,
while cold weather will halt that process. Some minimal phosphorus and nitrogen removal (10 to 20 percent) can be
anticipated. Fecal coliform removal of 1 to 2 logs/100 mL is likely.
FWS systems can produce effluent BOD and TSS of 20 to 30 mg/L and can reduce nitrogen significantly. TP reduction is
generally minor and similar to that of lagoons. Fecal coliform removals of about 2 to 3 logs (99 to 99.9 percent) can be
expected.
Management needs
Aquatic systems are normally excavated in natural soil and constructed with earthen dikes. They may or may not be lined,
depending on soil type. Sufficient freeboard (up to 2 feet) must be provided to prevent topping during high winds. In
some cases the lagoon may act as a percolation pond, allowing effluent to infiltrate into the underlying soil. When used,
mechanical aeration devices must be installed and fixed in place. Aerators may be mounted on piers or floats. Appropriate
controls and electrical connections must be provided. Inlets should be located as far away from outlets as possible, and
both should be accessible for normal maintenance. Piping and pumps, as required, should be of corrosion-resistant materi-
als, and pumps should be readily accessible. Fencing will normally be required to restrict access by the public.
The operation and maintenance of aquatic systems is typically minimal. Some attention must be paid to flow monitoring
and adjustments, as required. Inlet and outlet structures, berms, and surface blockages should be inspected and maintained.
The use of mechanical aeration will require operation and maintenance tasks but less than those for extended aeration
systems. Sludge management is relatively simple, since sludge builds up very slowly over a period of 10 to 15 years.
Pretreatment of lagoon influent by septic tanks will greatly reduce sludge accumulations in the lagoon. Requiring septic
tanks for individual homes or facilities served by lagoon cluster systems is recommended. Monitoring of effluent quality
for parameters of interest should be provided.
Only aerobic ponds require energy and semiskilled operators. Energy costs are in the range of $150 to $250 per year, and
labor costs would be $200 to $250 per year. Sludge production would be similar to aerobic units. Facultative lagoons and
FWS systems require nonskilled 0/M personnel to visit the facility two to three times per year. Sludge removal will be
required every 10 to 15 years at most. A fence around the facility usually satisfies safety needs.
Risk management issues
Aquatic systems, particularly facultative lagoons and FWS constructed wetlands, are large, passive systems that are
minimally affected by flow variations, extreme cold, and power outages. The risk of drowning can be mitigated only with
restricted access, such as that provided by fencing and signage. Aerated lagoons are negatively affected by toxic loads,
extreme cold, and power outages. Both lagoon types can be overloaded, resulting in odors, and the aerated type may
become odorous during power outages. Poorly maintained facultative lagoons and FWS systems can become sources of
TFS-39
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vector problems such as mosquito infestations. FWS systems can be negatively affected by extended toxic discharges, but
their aesthetic image is extremely positive.
Costs
Capital costs for a facultative lagoon for an individual home would be in the range of $2,500 to $7,500, whereas an
aerated lagoon should cost somewhat more. An FWS system would cost $2,000 to $4,000.
Operation and maintenance costs for the facultative lagoon and FWS systems should be less than $100 per year, whereas
0/M costs for the aerated lagoon (including power) would be $350 to $500 per year.
References
Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1979. Evaluation ofOnsite Wastewater Treatment and Disposal Options.
EPA 600/S2-81-178. U.S. Environmental Protection Agency, Cincinnati, OH.
National Small Flows Clearinghouse. 1996. Summary of Onsite System in the United States, 1993. National Small Flows
Clearinghouse Publication, Morgantown, WV.
Reed, S.C., R.W Crites, and E.J. Middlebrooks. 1995. Natural Systems for Waste Management and Treatment McGraw-
Hill, New York, NY.
U.S. Environmental Protection Agency (USEPA). 1983. Design Manual: Municipal Wastewater Stabilization Ponds. EPA
625/1-83/015. Center for Environmental Research Information, U.S. Environmental Protection Agency, Cincinnati,
OH.
U.S. Environmental Protection Agency (USEPA). 1992. Manual: Wastewater Treatment Disposal for Small Communities.
EPA 625/R-92/005. U.S. Environmental Protection Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1999. Manual: Constructed Wetlands Treatment of Municipal
Wastewaters. EPA 625/R-99/010. U.S. Environmental Protection Agency, Cincinnati, OH.
Water Environment Federation. 1990. Natural Systems for Wastewater Treatment: Manual of Practice FD-16. Water
Environment Federation, Alexandria, VA.
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 8
Enhanced Nutrient Removal—
Phosphorus
Description
There are a large number of processes that can reduce nitrogen and a few that can reduce phosphorus. Most of these
phosphorus removal processes are additions to other pretreatment processes that enhance the overall removal of phosphorus
(figure 1). The degree of nutrient removal, the cost, and the 0/M difficulty of these combinations quickly reduce the
number of systems that are likely to be implemented for onsite nutrient removal. The removal of phosphorus is of concern
where effluents may enter surface waters via direct
surface discharge or subsurface flow through F'9ure 1 • Phosphorus removal
fractured bedrock, and in soils where little phos-
phorus exchange would take place (see chapter 3).
Phosphorus is a key element in the eutrophication
of natural or impounded freshwater bodies and
some estuarine waters.
Pin
\
\
Phosphorus
removal
system
\
Few phosphorus removal processes are well
developed for onsite wastewater systems applica-
tion. Those that have been successfully applied
generally fall into the categories of chemical, physical, and biological systems. The controlled addition of chemicals such
as aluminum, iron, and calcium compounds with subsequent flocculation and sedimentation has had only limited success
because of inadequate operation and maintenance of mechanical equipment problems and excessive sludge production.
Physical and chemical processes such as ion exchange and precipitation of phosphates have been tried, but with limited
success. Most notable successes have come with special filter materials that are naturally high in their concentration of the
above chemicals, but their service lives are finite. Studies of high-iron sands and high-aluminum muds indicate that 50 to
95 percent of the phosphorus can be removed. However, the life of these systems has yet to be determined, after which the
filter media will have to be removed and replaced. Use of supplemental iron powder mixed with natural sands is also being
researched. All calcareous sands and other sands with high concentrations of these three elements will exhibit high phos-
phorus removal rates for some finite periods. Typical calcium-containing U.S. sands will essentially exhaust their capacity
in 3 to 6 months, after which they will remove only particulate-based organic phosphorus or about 10 to 20 percent of the
phosphorus contained in the wastewater.
One other practical way to minimize phosphorus discharges to the environment is the use of low-phosphate or phosphate-
free detergents, which can reduce the wastewater P concentration from 7 to 8 mg/L to 5 to 6 mg/L. In terms of P move-
ment from the SWIS to nearby waters, such a change could add 30 to 40 percent to the site's service life in attenuating or
containing P from movement away from the SWIS. Of all the options, this may be the simplest, but concerns over public
acceptance of these detergents as cleaning agents persist.
The only other known P-removal approach is the use of biological treatment systems. All aerobic treatment systems
described in other fact sheets have the natural ability to remove 10 to 20 percent of the influent phosphorus, which is
connected to the organic form in the biological reactors and wasted with excess sludge. Certain processes such as the
TFS-41
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sequencing batch reactor (SBR) can improve on this removal by proper sequencing of aeration periods. Other aerobic
biological units can similarly upgrade their phosphorus removal performance by the addition of anaerobic steps up to an
effluent limit of 1 to 2 mg P/L, but the data to support the onsite applications of these upgrade technologies are lacking.
Typical application
Phosphorus is rarely designed to be removed in onsite pretreatment because most soils have the innate ability to adsorb
the nutrient for many years before it begins to migrate to nearby ground or surface waters. However, as onsite system sites
age, there is the potential for serious environmental degradation, as witnessed by the thousands of inland lakes where older,
onsite development is increasingly being cited as the primary reason for lake eutrophication.
Therefore, the most likely P-reduction systems that will be applied are iron-rich intermittent sand filter (ISF) media,
sequencing batch reactors (SBR), and phosphate-free detergents. Other systems will surely be developed, especially
upgraded aerobic treatment systems, but these three systems are most representative of current phosphorus reduction
programs.
Design assumptions
For special filter media, the design assumptions would be the same as those for an intermittent sand filter (ISF) with
adjustment to the hydraulic and phosphorus areal rates because they might differ from conventional systems. Hydraulic
loadings for one successful study are essentially 3 cm/day, and the TP loading is 0.16g/m2/day. The major unknown is the
life of the special P-adsorption media. Most high-calcium sands become saturated in a few months, but one specific case
has reported 2.5 years. Generally, these sands are not cost-effective. High-iron sands and crushed bricks are being studied
and show longer durations of P-removal effectiveness, but definitive service lives are as yet unknown. The use of "red
mud" and iron oxide powder mixed with sands and placed below the infiltrative surface in the SWIS has been successful,
but the life of such media and the difficulty of replacement make these concepts less attractive unless the former is in the
range of 20 years. Red mud (a bauxite mining by-product) must constitute at least 30 percent of the total volume of the
filter bed. In a SWIS, the material must be mixed with the natural soil to a depth of 1 foot (0.3 m) below the infiltrative
surface to attain high P-removal efficiency. Specific depths of mixed soils and loading rates have not been clearly delineated.
SBRs are capable of phosphorus removals greater than the typical CFSGAS, which can range from 20 to 40 percent. This
is best accomplished by the "true" SBR (IF), but also by continuous feed (CF) SBRs if designed to do so. The IF type
must not aerate during the fill stage in order to remove greater amounts of TP. The CF type must have a no-aeration
section immediately following the recycle point to accomplish similar goals. Such designs are capable of reaching effluent
TP in the range of 1.0 mg/L. The only onsite CF test available did not employ this sequence and removed only about 30
percent of the TP. Sludge wasting requirements are severe and limit the performance of this alternative.
Because carbon-to-phosphorus ratios in septic tank effluent are generally favorable (typically, 150 mg/L BOD to 7mg/L
TP), the anoxic/anaerobic first stages (combined with appropriate organic loading rates and HRTs, as noted in the SBR
fact sheet) can result in significant TP removal. Typically, this mode of SBR operation should also remove most of the
nitrogen. All the phosphorus removal options require noncorrosive materials of construction, appropriate alarms and
sensing systems, and regular management by semiskilled staff.
Performance
The systems described above, in concert with low- or non-phosphate detergent use, are capable of removing phosphorus to
an effluent value of 1 to 2 mg/L with proper maintenance. Subsequent travel through the soil's vadose zone would further
enhance TP concentrations to very low ambient values. Direct discharge (after disinfection) would meet most surface
discharge requirements.
Phosphorus removal should be provided in sensitive surface water areas if direct surface discharging systems are used, or
if SWISs are located in noncalcareous, low-iron or low-aluminum soils in close proximity to or directly influencing
sensitive surface waters.
TFS-42
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Management needs
The use of low- or non-phosphate detergents would generally be a regional responsibility. Management of a high-iron or a
high-aluminum filter would be similar to that required for ISFs. Flows and dosing rates should be checked on each 0/M
visit, along with annual recalibration of dosing pumps and monitoring of TP in the effluent. At least two visits per year
are suggested to manage these systems (or 8 hours per year).
The SBR option is exactly the same as in the SBR fact sheet or three to four visits per year by semiskilled personnel (6 to
12 hours), with electrical usage of 3 to 10 kWh/day The SBR will produce an additional 0.6 to 1.0 Ib TSS/lb BOD
removed, over and above the solids captured in the septic tank.
Risk management issues
The two treatment systems described above are relatively unaffected by wide flow variations. The SBR can be seriously
impaired by the toxic shocks but not the enhanced ISF. Both should be safe from extremely cold climates if properly
insulated, but the SBR will suffer reduced biochemical efficiency in such extremes. Power outages will affect the SBR,
producing odors and poor efficiency for some time after power restoration. The enhanced filter will also be interrupted
because of dosing pump failure, but it should not experience odors or subsequent impairment.
Costs
Enhanced TP-removal filters will have cost characteristics similar to conventional ISFs except in the initial and subsequent
replacement of the enhanced media. Such a system may have an initial media cost increment of at least 1.2 and possibly
2.0 or larger, and an annual additional 0/M cost related to more frequent media replacement. For example, a 5-year life
would mean that a substantial replacement charge would be incurred every 5 years, equating to several hundred dollars per
year in 0/M cost over and above the normal 0/M cost of $250 to $400 per year. The capital cost would vary between
$5,000 and $11,000.
The SBR would exhibit similar capital ($9,000 to $12,000 per year) and 0/M ($650 to $800 per year) costs as provided in
Technology Fact Sheet 3.
References
Ayres Associates. 1997. Florida Keys Onsite Wastewater Nutrient Reduction Systems (OWNRS) Demo Project Control
Testing Facility: 2nd Quarter Status Report. Report to Florida Department of Health under Contact No. LPQ988 and
U.S. Environmental Protection Agency under Contract No. X994394-93-0. Ayres Associates, Madison, WI.
Brandes, M. 1977. Effective phosporus removal by adding alum to septic tank. Journal of Water Pollution Control
Federation 49:2285-2296.
Ho, G.E., K. Mathew, and R.A. Gibbs. 1992. Nitrogen and phosphorus removal from sewage effluent in amended soil
columns. Water Resources 26(3):295-300.
Irvine, R.L., L.H. Ketchum, Jr., M.L. Arora, and E.F. Barth. 1985. An organic loading study of full-scale SBRs. Journal
of Water Pollution Control Federation 57(8):847-853.
National Small Flows Clearinghouse. 1999. Benzie County, Michigan, NODPI project completed. Small Flows 13(4): 10-
11.
U.S. Environmental Protection Agency (USEPA). 1987. Phosphorus Removal Design Manual. EPA 625/1-87/001. U.S.
Environmental Protection Agency, Water Engineering Research Laboratory, Cincinnati, OH.
TFS-43
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TFS-44
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 9
Enhanced Nutrient Removal—
Nitrogen
Description
Nitrogen is a pollutant of concern for a number of reasons. Nitrogen in the ammonia form is toxic to certain aquatic
organisms. In the environment, ammonia is oxidized rapidly to nitrate, creating an oxygen demand and low dissolved
oxygen in surface waters. Organic and inorganic forms of nitrogen may cause eutrophication (i.e., high productivity of
algae) problems in nitrogen-limited freshwater lakes and in estuarine and coastal waters. Finally, high concentrations of
nitrate can harm young children when ingested.
Ammonia oxidation (nitrification) occurs in some of the processes described in previous fact sheets, and is dependent upon
oxygen availability, organic biochemical oxygen demand (BOD), and hydraulic loading rates. Nitrogen removal by means
of volatilization, sedimentation, and denitrification may also occur in some of the systems and system components. The
amount of nitrogen removed (figure 1) is dependent upon process design and operation. Processes that remove 25 to 50
percent of the total nitrogen include aerobic biological systems and media filters, especially recirculating filters (Technol-
ogy Fact Sheet 11). Enhanced nitrogen removal systems can be categorized by their mode of removal. Wastewater separa-
tion systems, which remove toilet wastes and garbage grinding, are capable of 80 to 90 percent nitrogen removal. Physi-
cal-chemical systems such as ion exchange, volatilization, and membrane processes, are capable of similar removal rates.
Ion exchange resins remove NH4-N or N03- N. Membrane processes employ a variety of membranes and pressures that all
have a significant reject flow rate. Volatilization is generally significant only in facultative lagoon systems where ammonia
volatilization can be significant. The vast majority of practical nitrogen-removal systems employ nitrification and denitri-
fication biological reactions. Most notable of these are recirculating sand filters (RSFs) with enhanced anoxic modifica-
tions, sequencing batch reactors (SBR), and an array
of aerobic nitrification processes combined with an Figure 1. Nitrogen removal systems
anoxic/anaerobic process to perform denitrification.
Some of the combinations are proprietary. Any
fixed-film or suspended-growth aerobic reactor can
perform the aerobic nitrification when properly
loaded and oxygenated. A variety of upflow (AUF),
downflow, and horizontal-flow anaerobic reactors
can perform denitrification if oxygen is absent, a
degradable carbon source (heterotrophic) is pro-
vided, and other conditions (e.g., temperature, pH,
etc.) are acceptable.
The most commonly applied and effective nitrogen-removal systems are biological toilets or segregated plumbing options
and/or nitrification-denitrification process combinations. A more complete list is described below, along with accompany-
ing schematic diagrams.
Nin
\
Nitrogen
removal
system
TFS-45
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Source separation systems
Source separation relies on isolating toilet wastes or blackwater from wastewater. This requires separate interior collection
systems. Two source separation systems were identified: blackwater holding tank with low-volume-discharge toilets and
graywater septic tank system, and non-water-carriage toilets and graywater septic tank system (figure 2). These types of
toilets are discussed in chapter 3.
Blackwater holding tank with low-volume-discharge toilets and graywater septic tank system
Blackwater discharged directly to a holding tank requires periodic removal for offsite treatment. Graywater wastes can be
discharged to a conventional septic tank or subsurface infiltration system.
Figure 2. Source separation systems: A. blackwater holding tank with low-volume discharge toilets and graywater septic
tank system; B. non-water-carriage toilet and graywater septic tank system
A.
Offsite
treatment
B.
Human
excreta
+
\
\
\
Non-water
carriage
toilet
Offsite
treatment
Non-water-carriage toilets and graywater septic tank system
Excreta is discharged to non-water-carriage toilets to promote bulk reduction and decomposition. Biological and incinera-
tion toilets are the most common methods of accomplishing this. Non-water-carriage toilets that use these processes are
commercially available. The remaining graywater wastes can be discharged to a conventional septic tank subsurface
infiltration system.
Physical/chemical treatment systems
Two types of physical/chemical treatment systems, ion exchange and reverse osmosis, appear to have some promise for
single home use, although neither is in use at present (figure 9-3).
TFS-46
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Figure 3. Physical/chemical systems: A. cation (NH +) exchange; B. anion (NO,-) exchange; C. reverse osmosis
regeneration discharge
Ion exchange
Two types of systems may be employed: cationic or anionic exchange systems. In the cationic system, the ammonium in
septic tank effluent is removed. Clinoptilolite, a naturally occurring zeolite that has excellent selectivity for ammonium
over most other cations in wastewater, can be used as an exchange medium. In the anionic system, septic tank effluent
must be nitrified prior to passage through the exchange unit. Strong-base anion resins can be employed as an exchange
medium for nitrate. Both systems require resin regeneration offsite.
Reverse osmosis
This system requires pretreatment to remove much of the organic and inorganic suspended solids in wastewater. Pretreated
wastewater stored under pressure is fed to a chamber containing a semipermeable membrane that allows separation of ions
and molecules before disposal. Large volumes of waste brine are generated and must be periodically removed for offsite
treatment.
Biological treatment systems
A number of onsite treatment systems use biological denitrification for removal of nitrogen from wastewater. These
systems have received the most scrutiny with respect to development and performance monitoring. However, more
development and performance monitoring will be necessary to refine the performance consistency and improve under-
standing of operation processes and mechanisms (see figure 4).
TFS-47
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Figure 4. Biological systems: A. an aerobic/anaerobic trickling filter package plant; B. sequencing batch reactor (SBR)
design principle; C. ISF with AUF; D. source separation, treatment, recombination; E. recirculating sand filter with septic
tank option; F. recirculating sand filter with anaerobic filter and carbon source
A.
-
/ A
->
k
N
Septic
tank
>
\
\
Aerobic
unit
i
•>•
r
Subsurface
infiltration
B.
Idle
Recycle
Fill
Decant
React
Aeration/mixing
Draw
f:':-:.';.:':x ';,-•"•: ';,-•"•: v"-
1
Settle
C.
Wastewater
Discharge
D.
TFS-48
-------
Figure 4. (continued)
E.
Wastewater
Opntjr
tank
\
L .
->
i
>
k
\
Recircu-
lation
tank
+>
\
Sand
filter
i
— +
\\
\\
\
Subsurface
infiltration
Surface
discharge
(optional)
Aerobic/anaerobic trickling filter package plant
These commercial systems use synthetic media trickling filters that receive wastewater from overlying sprayheads for
aerobic treatment and nitrification. Filtrate returns to the anaerobic zone to mix with either septic tank contents or incom-
ing septic tank effluent and undergoes denitrification. A portion of the filtered effluent (equal to the influent flow) is
discharged for disposal or further treatment.
Sequencing batch reactor (SBR)
If sufficient hydraulic retention time (HRT) is provided to permit nitrification during the "react" phase of the SBR cycle
and if the fill stage is anoxic for a sufficient HRT, the system can remove significant amounts of nitrogen and phosphorus.
The SBR design is essentially the same as is described in the SBR fact sheet, while operationally the conditions noted
above must be maintained.
Intermittent sand filters with anaerobic filters
Nitrification is provided in the ISF, while denitrification is provided in either the preceding septic tank with recirculation
or a separate anaerobic filter. A vegetated submerged bed (VSB) ("subsurface flow wetland") may be substituted for the
anaerobic filter.
Source separation, treatment, and recombination
One commercial system employs this sequence where blackwater (toilet wastewater), after settling in a separate tank, is
aerobically treated with an ISF to nitrify the majority of the nitrogen before it is recombined with settled greywater in an
anaerobic upflow filter (AUF) for denitrification.
TFS-49
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Recircutating sand filters combined with anaerobic/anoxic filters
RSF systems normally remove 40 to 50 percent of influent nitrogen. To enhance this capability, they can be combined
with a greater supply of carbon, time, and mixing than is normally available from the conventional recirculation tank. The
anaerobic/anoxic options include recycling to the septic tank, better mixing, and longer HRT in a separate UF or VSB, or
adding supplemental carbon (e.g., methanol, ethanol) to enhance the potential of the denitrification step.
Typical applications
Nitrogen removal is increasingly being required when onsite systems are on or near coastal waters or over sensitive,
unconfmed aquifers used for drinking water. Nitrogen removal systems generally are located last in the treatment train
prior to SWIS disposal and may be followed by disinfection when the system must discharge to surface waters. Usually,
the minimum total nitrogen standard that can be regularly met is about 10 mg/L. Aerobic biological systems should not be
employed at seasonal facilities.
Design assumptions
A myriad of potential systems exist for enhanced nitrogen removal, and all of the major unit processes of such systems are
described elsewhere. Also, since waste stream modification is covered in chapter 3, only the most promising, developed
options are discussed in this fact sheet. Of the options discussed, granular media filters or aerobic biological systems
(usually combined with an anaerobic upflow filter or the original septic tank process) are discussed in more detail.
Some salient design considerations that are not covered in other fact sheets or text include the following:
• Autotrophic denitrification in packed-bed sulfur reactors (variation on AUF) has been successfully demonstrated, but
the need for additional alkalinity and the production of a high sulfate effluent have thus far limited the process.
• Denitrification improves with increased HRT in the recirculation tank, better mixing, and a pH between 7 and 8.
• Use of greywater as the degradable carbon source for denitrification limits the degree of denitrification attainable
owing to reduced nitrogen content and low carbon-to-nitrogen ratio. The latter should exceed 5:1 for good denitrifica-
tion.
• Use of synthetic anionic exchange resins appears impractical at this time. Cationic exchange of NH4-N with
clinoptilolite is feasible but very expensive because of the regeneration management costs. Both may be subject to
fouling and clogging problems.
• Membranes present a major problem given the volume of the reject stream, which must be collected and frequently
trucked to a site that will accept it for disposal.
• The use of beds of carbon-rich materials below SWIS leach lines could be a promising concept if the hydraulic
matching problems are solved and the bed service life can be extended for 10 years or more.
• Accessibility, size of the holding tank, and availability of residual management facilities are significant design consid-
erations in blackwater separation systems.
• Recycling to the septic tank may affect solids and grease removal in the tank and cause poor mixing of the nitrified
stream with the septic tank contents. This could raise the oxidation-reduction potential (ORP) of the mixture above the
normal range for an anoxic zone that accomplishes denitrification. Recycling to the second compartment of a
multicompartment tank is suggested at a ratio of less than 2.5 to 1 with a contact time of greater than 2 days.
• An AUF used for enhanced denitrification should be loaded with between 0.06 and 0.3 Ib COD/ft3 per day and have
an HRT of at least 24 hours (preferably 36 or more hours). It can be filled with large (> 2 inches) rocks or synthetic
media. A vegetated submerged bed (VSB) can be substituted for an AUF and may contribute some labile carbon to aid
the process.
TFS-50
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SBR design for nitrogen and phosphorus removal is essentially similar, but the amount of labile carbon required is
greater (6 to 8 mg/LCOD/ mg/L of TKN to be denitrified).
Modern microprocessor controls make very complex process combinations possible to remove nitrogen, but overall
simplicity is still desirable and requires less 0/M sophistication.
To attain full (>85 percent) nitrification, fixed-film systems cannot be loaded above 3 to 6 g BOD/m3 per day or 6 to
12 g BOD/m3 per day for rock and plastic media, respectively.
Performance
Some expected sustainable perfor-
mance ranges for the most likely
combinations of nitrogen removal
processes are given in table 1. Some
of the nitrogen-removal systems
could be combined with source
separation and product substitution
(low-phosphate detergents) for a
maximum reduction in nitrogen
where extreme measures might be
required. However, the removals
would not be additive owing to the
changes in wastewater characteris-
tics.
Management needs
Table 1. Typical N-removal ranges for managed systems
Process
RSF
RSF (with recycle to ST or AUF)
ST-FFS (with recycle to ST or AUF)"
SBR"
SS and removal
(SS-TT R)a
ISF-AUF
Percent TN removal
40-50
70-80
65-75
50-80
60-80
40-60
55-75
Commercially available systems.
Note: RSF = recirculating sand filters; AUF = anaerobic upflow filter; ST = septic tank; FFS = fixed-film system;
SBR = sequencing batch reactor; SS = source separation; TT = treatment applied to both systems; R =
recombined; ISF = intermittent sand filter.
Management needs for most unit processes are covered in other fact sheets. Source separation is feasible only for new
homes, as it would be prohibitively expensive for existing homes. AUF systems are different from the fact sheet in that
they must have HRTs greater than 2 days to enable anaerobic biological denitrification to be effective. This will add to Of
M tasks by requiring regular flushing of excess biological growth. Some separation and removal would require regular
inspection and maintenance of non-water-carriage toilets and periodic removal and proper disposal of excess solids from
these units and from holding tanks.
Risk management issues
Of the most likely systems shown in the table, few are extremely susceptible to upset by hydraulic loading variations.
However, soluble toxic shocks could affect any AUF, SBR, or fixed-film nitrification system. Extreme cold will also have
an impact on these systems. However, the ISF, RSF, and AUF systems have been the most resilient unit processes (exclud-
ing source separation) when properly housed and insulated. Power outages will affect all of the treatment systems. Reli-
ability would be greatest for those that incorporate filters and less for the SBR and fixed-film systems.
Costs
The capital and total costs of most of the nitrogen removal systems are very site specific, but non-water-carriage toilet
source separation (assuming new homes) is the least expensive (low-water-use fixtures and holding tanks would add about
$4,000 to $6,000). The biological combinations would be more expensive, and the physical/chemical systems would likely
be the most expensive. Multiple units will generally increase costs, while the use of gravity transfer between processes will
reduce them.
The additional 0/M associated with an AUF involves flushing and disposal of excess flushed solids. If methanol is em-
ployed to enhance denitrification, additional 0/M is required for the feeding system.
TFS-51
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References
Ayres Associates. 1991. Onsite Nitrogen Removal Systems: Phase I. Report to Wisconsin DILHR, Madison, WI.
Ayres Associates. \991.FloridaKeys Wastewater Nutrient Reduction Systems Demo Project: 2nd Quarter Report. Report
to Florida Department of Health and U.S. Environmental Protection Agency. Florida Department of Health,
Tallahassee, FL.
Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1979. Evaluation of Existing and Potential Technologies for Onsite
Wastewater Treatment and Disposal. EPA 600/S2/81/178. Cincinnati, OH.
Boyle, W.C., R.J. Otis, R.A. Apfel, R.W. Whitmeyer, J.C. Converse, B. Burkes, M.J. Bruch, Jr., and M. Anders. 1994.
Nitrogen Removal from Domestic Wastewater in Unsewered Areas. In Proceedings of the Seventh On-Site Wastewater
Treatment Conference. American Society of Agricultural Engineering, St. Joseph, MI.
Katers, J.F., and A.E. Zanoni. 1998. Nitrogen removal. Journal of Water Environment and Technology 10(3):32-36.
Lamb, B., A.J. Gold, G. Loomis, and C. McKiel. 1987. Evaluation of Nitrogen Removal Systems for Onsite Sewage
Disposal. In Proceedings of Fifth On-Site Wastewater Treatment Conference. American Society of Agricultural
Engineering, St. Joseph, MI.
U.S. Environmental Protection Agency (USEPA). 1993. Nitrogen Control Manual. EPA 625/R-93/010. U.S.
Environmental Protection Agency, Office of Research and Development, Cincinnati, OH.
Venhuizen, D. LCRA onsite demonstration project for nitrogen removal and water reclamation. Unpublished but available
from D. Venhuizen, P.E., 21 Cotton Gin Road, Uhland, TX 78640.
Whitmyer, R.W, R.A. Apfel, R.J. Otis, and R.L. Meyer. 1991. Overview of Individual Onsite Nitrogen Removal Systems.
In Proceedings of Sixth On-Site Wastewater Treatment Conference. American Society of Agricultural Engineering, St.
Joseph, MI.
Winkler, E.S., and PL.M.Veneman. 1991. A Denitrification System for Septic Tank Effluent Using Sphagnum Peat Moss.
In Proceedings of Sixth On-Site Wastewater Treatment Conference, American Society of Agricultural Engineering,
St. Joseph, MI.
TFS-52
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 10
Intermittent Sand/Media Filters
Description
The term intermittent sand filter (ISF) is used to describe a variety of packed-bed filters of sand or other granular materi-
als available on the market. Sand filters provide advanced secondary treatment of settled wastewater or septic tank efflu-
ent. They consist of a lined (e.g., impervious PVC liner on sand bedding) excavation or structure filled with uniform
washed sand that is placed over an underdrain system (see figure 1). The wastewater is dosed onto the surface of the sand
through a distribution network and allowed to percolate through the sand to the underdrain system. The underdrain system
collects the filter effluent for further processing or discharge.
Figure 1. Generic, open intermittent sand filter
Insulated Cover
(If required)
Dosing/distribution
network
24-36 inch
' media
Washed
gravel
30 mil liner or
rigid containment
Underdrain
Sand filters are aerobic, fixed-film bioreactors. Other treatment mechanisms that occur in sand filters include physical
processes, such as straining and sedimentation, that remove suspended solids within the pores of the media. Also, chemical
adsorption of pollutants onto media surfaces plays a finite role in the removal of some chemical constituents (e.g., phos-
phorus). Bioslimes from the growth of microorganisms develop as films on the sand particle surfaces. The microorganisms
in the slimes absorb soluble and colloidal waste materials in the wastewater as it percolates over the sand surfaces. The
adsorbed materials are incorporated into a new cell mass or degraded under aerobic conditions to carbon dioxide and
water.
Most biochemical treatment occurs within approximately 6 inches of the filter surface. As the wastewater percolates
through this layer, suspended solids and carbonaceous biochemical oxygen demand (BOD) are removed. Most suspended
TFS-53
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solids are strained out at the filter surface. The BOD is nearly completely removed if the wastewater retention time in the
sand media is sufficiently long for the microorganisms to absorb wastewater constituents. With depleting carbonaceous
BOD in the percolating wastewater, nitrifying microorganisms are able to thrive deeper in the surface layer where nitrifi-
cation will readily occur.
Chemical adsorption can occur throughout the media bed. Adsorption sites in the media are usually limited, however. The
capacity of the media to retain ions depends on the target constituent, the pH, and the mineralogy of the media. Phospho-
rous is one element of concern in wastewater that can be removed in this manner, but the number of available adsorption
sites is limited by the characteristics of the media.
The basic components of intermittent sand filters include a dosing tank, pump and controls (or siphon), distribution
network, and the filter bed with an underdrain system (see figure 1). The wastewater is intermittently dosed from the
dosing tank onto the filter through the distribution network. From there, it percolates through the sand media to the
underdrain and is discharged. On-demand dosing is usually used, but timed dosing is becoming common.
There are a large number of variations in ISF designs. For example, there are different means of distribution, underdrain
designs, housing schemes and, most notably, media choices. Many types of media are used in single-pass filters. Washed,
graded sand is the most common. Other granular media used include gravel, crushed glass, and bottom ash from coal-fired
power plants. Foam chips (polystyrene), peat, and coarse-fiber synthetic textile materials have also been used. These media
are generally restricted to proprietary units. System manufacturers should be contacted for application and design using
these materials.
There are also related single-pass designs, which are not covered in this fact sheet. These include lateral flow designs and
upflow-wicking concepts, both of which use physical removal concepts closer to the concepts described in the fact sheet on
anaerobic upflow filters and vegetated submerged beds. These processes are not discussed herein but may exhibit some
pollutant removal mechanisms that are described here. Simple gravity-fed, buried sand filters are not discussed because
their performance history is unsatisfactory.
Applications
Sand filters can be used for a broad range of applications, including single-family residences, large commercial establish-
ments, and small communities. Sand filters are frequently used to pretreat septic tank effluent prior to subsurface infiltra-
tion onsite where the soil has insufficient unsaturated depth above ground water or bedrock to achieve adequate treatment.
They are also used to meet water quality requirements (with the possible exception of fecal coliform removal) before
direct discharge to a surface water. Sand filters are used primarily to treat domestic wastewater, but they have been used
successfully in treatment trains to treat wastewaters high in organic materials such as those from restaurants and supermar-
kets. Single-pass ISF filters are most frequently used for smaller applications and sites where nitrogen removal is not
required. However, they can be combined with anaerobic processes to reduce nitrogen significantly. Many studies have
shown that ISF-treated onsite wastewaters can reduce clogging of the infiltrative surface by many times when compared
with septic-tank effluents. However, be careful to evaluate the overall loading of pollutants and pathogens to the underly-
ing aquifer and nearby surface waters before considering significant SWIS sizing reductions.
Design
ISF filter design starts with the selected media. The media characteristics determine the necessary filter area, dose vol-
umes, and dosing frequency. Availability of media for a specific application should be determined before completing the
detailed design. Typical specifications, mass loadings, and media depths are presented in table 1. The sand or gravel
selected should be durable with rounded grains. Only washed material should be used. Fine particles passing the U.S. No.
200 sieve (less than 0.074 mm) should be limited to less than 3 percent by weight. Other granular media that have been
used are bottom ash, expanded clay, expanded shale, and crushed glass. These media should remove BOD and TSS similar
to sand and gravel for similar effective sizes, uniformity, and grain shape. Newer commercial media such as textile
materials have had limited testing, but based on early testing should be expected to perform as well as the above types.
TFS-54
-------
Traditionally, sand filters have
been designed based on hydraulic
loadings. However, since these
filters are primarily aerobic
biological treatment units, it is
more appropriate that they be
designed based on organic load-
ings. Unfortunately, insufficient
data exist to establish well-defined
organic loading rates. Experience
presently suggests that BOD5
loadings on sand media should not
exceed about 5 lb/1,000 ft3 per day
(0.024 kg/m2 per day) where the
effective size is near 1.0 mm and
the dosing rate is at least 12 times
per day.
Higher hydraulic and organic
loadings have been described in
several studies, but the long-term
viability of the systems loaded at
those higher organic loads has not
yet been fully verified. The values
in the table are thus considered
conservative and may be subject to
increases as more quality-assured
data become available.
Table 1. Specifications, mass loadings, and depth for single-pass intermittent sand filters
Design parameter
Material
Specifications
Effective size
Sand
Gravel
Uniformity coefficient
Percent fines (passing 200 sieve or
< 0.074 mm)
Depth
Mass loadings
Hydraulic loading a
Sand
Gravel
Organic loading b
Sand
Gravel
Underdrains
Slope
Size
Dosing
Frequency
Dosing tank
Volume
Typical design value
Durable, washed sand/gravel
with rounded grains
0.25-1 .00 mm
N/A
<4
<3
2 to 3 ft
1-2 gpd/ft2
N/A
5lbBOD./1,OOOft2-d
N/A
0-0.1%
3-4 in. dia.
12-24 times per day
0.5-1 .5 times
design daily flow
1 gpd/ft2 = 4 cm/day = 0.04 m3/m2 per day
11b BOD/1000 ft2 per day = 0.00455 kg/m2 per day
Dosing volume and frequency
have been shown to be the critical design variables. Small dose volumes are preferred because the flow through the porous
media will occur under unsaturated conditions with higher moisture tensions. Better wastewater media contact and longer
residence times occur under these conditions. Smaller dose volumes are achieved by increasing the number of doses per
day. It has been suggested that each dose should be <0.5 cm (based on media surface perpendicular to infiltration direc-
tion) to fully nitrify the effluent in an ISF. This would limit maximum daily hydraulic loading to 12 cm/d, or 3 gpd/ft2, if
the maximum frequency of daily dosing is accepted as 24 (or hourly) as supported by the literature. Media characteristics
can limit the number of doses possible. Reaeration of the media must occur between doses. As the effective size of the
media decreases, the time for drainage and reaeration of the media increases.
Distribution network characteristics will also limit the number of doses possible. The primary characteristics are the
volume, pressure, orifice sizes, and spacing. To achieve uniform distribution over the filter surface, minimum dose
volumes are necessary and can vary with the distribution method selected. Therefore, if the dose volume dictated by the
distribution network design is too high, the network should be redesigned. Since the dose volume is a critical operating
parameter, the method of distribution and design of the distribution system should be considered carefully.
Distribution methods used include rigid pipe pressure networks with orifices or spray nozzles, drip distribution, and
surface flooding, which is no longer recommended for small ISFs (see chapter 4). Rigid pipe pressure networks are the
most commonly used method. Both orifices and spray nozzles are used. The use of spray nozzles is usually limited to
recirculating filters because nozzle fouling from suspended solids is less likely than with undiluted septic tank effluent.
Since the minimum dose volume required to achieve uniform distribution is five times the rigid pipe volume, the filter can
be divided into multiple cells that are loaded individually so the distribution networks can be smaller to reduce the dose
volume needed for uniform distribution. Optimum designs minimize the dose each time the system is dosed. Drip distribu-
tion is being used increasingly because the minimum dose volumes are much less than the volumes of rigid pipe networks.
TFS-55
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Figure 2. ISF constructed in a mound with direct subsurface infiltration
OBSERVATION TUBE
DISTRIBUTION
SAND
FILL
r-y/-;--v-^'*•-:•.-•.]••••: f-vV^V' %SLOPE -'£
BASAL AREA-' / \ "~ AGGREGATE
FROM
HOUSE
HIGH WATER
ALARM SWITCH
SEPTIC TANK
• PUMP SWITCH
DOSING CHAMBER
Source: Converse and Tyler, 1998.
The underdrain system is placed on the floor of the tank or lined excavation. Ends of the underdrains should be brought to
the surface of the filter and fitted with cleanouts that can be used to clean the biofilms underdrain, if necessary. The
underdrain outlet is cut in the basin wall such that the drain invert is at the floor elevation and the filter can be completely
drained. The underdrain outlet invert elevation must be sufficiently above the recirculation tank inlet to accommodate a
minimum of 0.1 percent slope on the return line and any elevation losses through the flow splitting device. The underdrain
(usually 1.25- to 2.0-inch PVC, class 200 [minimum]) is covered with washed, durable gravel to provide a porous
medium through which the filtrate can flow to the underdrain system. The gravel should be sized to prevent the filter
medium from mixing into the gravel, or a layer of 1/4- to 3/8-inch-diameter washed pea gravel should be placed over the
washed underdrain gravel before the filter medium is added.
The filter basin can be a lined excavation or fabricated tank. For single-home systems, prefabricated concrete tanks are
commonly used. Many single-home filters and most large filters are constructed within lined excavations. Typical liner
materials are polyvinyl chloride and polypropylene. A liner thickness of 30 mil can withstand reasonable construction
activities yet be relatively easy to work with. A sand layer should be placed below the liner to protect it from being
punctured if the floor and walls of the excavation are stony. The walls of the excavation should be brought above the final
grade to prevent entry of surface water.
Filters can be covered or buried. It is often necessary to provide a cover for the filter surface because the surface of a fine
medium (e.g., sand) exposed to sunlight can be fouled with algae. Also, there may be concerns about odors, cold weather
impacts, precipitation, leaf and debris accumulation, and snowmelt. In addition, the cover must provide ample fresh air
venting. Reaeration of the filter medium primarily occurs from the filter surface. The lower 20 percent of the medium's
depth maintains a high moisture content. At the bottom, the medium is near or at saturation, which is a barrier to air flow
and venting from the underdrain system. The gravel surrounding the distribution piping must be vented to the surface to
provide a fresh air flow. ISF filters open to the surface are built with roofs or removable covers or are merely shaded.
Roofs provide cold weather protection and shed precipitation, debris, and snowmelt that would otherwise enter the system.
Performance
Treatment field performance of single-pass intermittent sand filters is presented in table 2. Typical effluent concentrations
for these single-family wastewater treatment systems are less than 5 mg/L and less than 10 mg/L for BOD and TSS,
respectively. Effluent is nearly completely nitrified but some variability can be expected in nitrogen removal capability.
Controlled studies generally find typical nitrogen removals of 18 to 33 percent with an ISF. Fecal coliform removal ranges
TFS-56
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from 2 to 4 logs (99 to 99.99 percent). ISF fecal coliform removal is a function of hydraulic loading, with reduced
removals as the loading rate increases above 1 gpm/ft2 (Emerick et al., 1997). Effluent suspended solids from sand filters
are typically low. The media retains the solids. Most organic solids are digested by the media over time.
Table 2. Single-pass intermittent sand filter performance
Reference
Cagle and
Johnson, 1994"
(California)
Effertetal., 1985"
(Ohio)
Ronayne et al.,
1982°
(Oregon)
Sievers, 1998"
(California)
BOD(mg/L)
Influ. Efflu.
(% Removal)
160 2
(98.75%)
127 4
(96.85%)
217 3
(98.62%)
297 3
(98.99%)
BOD(mg/L)
Influ. Efflu.
(% Removal)
73 16
(78.08%)
53 17
(67.92%)
146 10
(93.15%)
44 3
(93.18%)
BOD(mg/L)
Influ. Efflu.
(% Removal)
61.8 5.9
(90.45%)
_
57.1 1.7
(97.02%)
37 0.5
(98.65%)
BOD(mg/L)
Influ. Efflu.
(% Removal)
61 .8 37.4
(39.48%)
41 .5 37.5
(9.64%)
57.5 30.3
(47.30%)
37.1 27.5
(25.88%)
BOD(mg/L)
Influ. Efflu.
(% Removal)
1.14E+05 1.11E+02
(99.90%)
2.19E+05 1.60E+03
(99.27%)
2.60E+05 4.07E+02
(99.84%)
4.56E+05 7.30E+01
(99.98%)
a Sand media: es = 0.25-0.65 mm; uc = 3-4. Design hydraulic loadings = 1.2 gpd/ft2 based on 150 gpd/bedroom. Actual flows not measured.
b Sand media: es = 0.4 mm; uc = 2.5. Average loadings = 0.4 gpd/ft2/ 0.42 Ib BOD/1,000 ft2. Doses per day = 3.3.
c Sand media: es = 0.14-0.30 mm; uc = 1.5-4.0. Average loadings = 0.33 gpd/ft2 / 0.6-1.27 Ib BOD/1000 ft2 per day.
d Sand media: not reported; uc = 3-4. Design hydraulic loadings = 1. gpd/ft2. Daily flows not reported.
Management needs
Construction of ISF units usually involves excavation, forming/framing, liner placement with supporting sand layers, and
plumbing. ISF units should never be placed in surface depressions without thoroughly sealing against prolonged inunda-
tion and drainage configurations that prevent stormwater entry. In all cases, units must be watertight with sealed entries
and exits for piping. Filter fabric should not be used at any location through which the filtrate would flow. Media deliv-
ered to the site should be tested against design-sizing specifications. Excess (3 percent or greater) fines are one of the
greatest concerns of the construction inspector.
The operation and maintenance requirements of packed bed filters are few and simple. As with all treatment systems, flow
monitoring should be conducted to identify excessive flows and check dose volumes and dosing rates. If the flows are
excessive, the source of the flows should be identified and corrective measures taken. Reduced dose volumes or dosing
rates suggest that the distribution network is plugged or the pump is not performing properly. The distribution network
should be flushed annually (or more often, as necessary) using the manual flushing device. Also, the dosing pump should
be recalibrated at least annually.
The filter surface should not pond if the filter is designed properly and the wastewater characteristics do not change
significantly. If standby cells are not available for regular resting and the surface is not covered with pea gravel, the
surface can be raked to break up any material clogging the filter surface. Reducing the dose volume and increasing the
dosing frequency may help to increase the reaeration potential and reduce clogging of the media. If the ponding problem
persists, however, removal of the top layer or complete replacement of the media may be necessary. Before replacing the
media, monitor wastewater flows and concentrations to determine if they are the cause of the problem. Problem sources
should be identified and addressed before repairs are effected. Premature clogging is often traceable to excess TSS and
BOD loading or to fines in the media. Where the problem develops naturally over time and standby cells are available,
resting may be used to supplement the raking and/or surface skimming steps.
Free-access ISFs should be checked regularly (at least every 3 to 4 months), to prevent surface problems. Periodic raking
and resting is recommended to maintain percolation and prevent ponding. Scraping off the top layer (e.g., 1 inch) of sand
helps to prevent clogging. Intervals between scraping vary from a minimum of 3 months up to greater than 1 year.
Removed surface layers need not be replaced until the total filter depth falls below 18 inches. If new filter material is not
TFS-57
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readily available, it may be cost-effective to clean and reuse the old filter material. Resting is considered the best rehabilita-
tion approach due to possible clogging contributions from raking/scraping.
ISFs have low energy requirements compared with other systems offering comparable effluent quality. Free-access ISFs
using pumped dosing would require approximately 0.3 to 0.4 kWh/day.
Risk management issues
ISF filters are simple in design and relatively passive to operate because the fixed-film process is very stable and few
mechanical components are used. High flow variations after equalization in a septic tank are not a problem because the
residual peaks and valleys are absorbed in the pressurization tank or in the last compartment of the preceding septic tank.
Although ISFs have biological properties, the impact of toxic loading shocks are not well documented.
Free-access ISFs are often installed with removable covers to regulate temperatures in cold climates and to reduce odors.
Space of 12 to 24 inches (30 to 61 cm) should be allotted between the sand surface and the installed cover (EPA, 1980).
Odors from free-access filters treating septic tank effluent may warrant installation away from dwellings, especially if
spray nozzles are used in distribution.
Power outages will impact ISF systems if these systems are uniformly dosed with pumps. During the power outage, all
wastewater generated will accumulate in that dosing facility and septic tank, increasing the potential for odors.
Costs
Filter media is the most expensive component in ISF construction. Typically, filter media can be installed for $10 to $15
per square foot, depending primarily on the type of media and the contractor's experience with ISF construction. Opera-
tion/maintenance costs include electricity for pumping/dosing, and 3 to 6 hours of semiskilled management visits per year
cost about $150 to $200. The electricity is about $10 to $20 of that total.
References
Anderson, D.L., R.L. Siegrist, and R.J. Otis. 1985. Technology Assessment of Intermittent Sand Filters. U.S.
Environmental Protection Agency, Office of Research and Development and Office of Water, Washington, DC.
Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1979. Evaluations of Existing and Potential Technologies for Onsite
Wastewater Treatment and Disposal. EPA/600/S2-81-178. U.S. Environmental Protection Agency, Office of Research
and Development, Cincinnati, OH.
Boiler, M, A. Schwager, J. Eugster, and V. Mottier. 1993. Dynamic Behavior of Intermittent Buried Filters. In Small
Wastewater Treatment Plants, ed., H. Odegaard, TAPIR, Trondheim, Norway.
Cagle, W.A., and L.A. Johnson. 1994. On-site intermittent sand filter systems: a regulatory/scientific approach to their
study in Placer County, California. In Proceedings of the Seventh Onsite Wastewater Treatment Symposium, American
Society of Agricultural Engineers, St. Joseph, MI.
Darby, J., G. Tchobanoglous, M. Asri Nor, and D. Maciolek. 1996. Small Flows Journal 2(31): 3-15.
Effert, D., J. Morand, and M. Cashell. 1985. Field performance of three onsite effluent polishing units. In Proceedings of
Fourth Onsite Wastewater Treatment Symposium, American Society of Agricultural Engineers, St. Joseph, MI.
Emerick, R.W, R.M. Test, G. Tchobanoglkous, and J. Darby. 1997. Small Flows Journal 3(1): 12-22.
National Small Flows Clearinghouse. 1998. Intermittent Sand Filters. NSFC Fact Sheet for U.S. Environmenetal
Protection Agency, Office of Water, Washington, DC.
Orenco Systems, Inc. 1993. Cost Estimating for STEP Systems and Sand Filters. Orenco Systems, Inc., Roseburg, OR.
TFS-58
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Rhode Island Department of Environmental Management (DEM). 2000. Sand Filter Guidance Document. Department of
Environmental Management, Providence, RI.
Ronayne, M.R, R.C. Paeth, and S.A. Wilson. 1982. Oregon On-site Experimental Systems Program. Final report to U.S.
Environmental Protection Agency, Office of Research and Development, Cincinnati, OH.
Sievers, D.M. 1998. Pressurized intermittent sand filter with shallow disposal field for a single residue in Boone County,
MO. In Proceedings of the Eighth On-site Wastewater Treatment Symposium. American Society of Agricultural
Engineers, St. Joseph, MI.
TFS-59
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TFS-60
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 11
Recirculating Sand/Media Filters
Description
Recirculating filters using sand, gravel, or other media provide advanced secondary treatment of settled wastewater or
septic tank effluent. They consist of a lined (e.g., impervious PVC liner on sand bedding) excavation or structure filled
with uniform washed sand that is placed over an underdrain system (see figure 1). The wastewater is dosed onto the
surface of the sand through a distribution network and allowed to percolate through the sand to the underdrain system.
The underdrain system collects and recycles the filter effluent to the recirculation tank for further processing or discharge.
Figure 1.Typical recirculating sand filter system
Inflow
Distribution lines
Outflow
Concrete or
liner enclosure
Underdrain
Pump
Recirculation/dosing tank
Recirculating sand filters (RSFs) are aerobic, fixed-film bioreactors. Other treatment mechanisms that occur in sand filters
include physical processes, such as straining and sedimentation, that remove suspended solids within the pores of the
media. Also, chemical sorption of pollutants onto media surfaces plays a finite role in the removal of some chemical (e.g.,
phosphorus) constituents. Bioslimes from the growth of microorganisms develop as films on the sand particle surfaces.
The microorganisms in the slimes absorb soluble and colloidal waste materials in the wastewater as it percolates over the
sand surfaces. The absorbed materials are incorporated into a new cell mass or degraded under aerobic conditions to
carbon dioxide and water.
Most biochemical treatment occurs within approximately 6 inches of the filter surface. As the wastewater percolates
through this layer, suspended solids and carbonaceous biochemical oxygen demand (BOD) are removed. Most suspended
solids are strained out at the filter surface. The BOD is nearly completely removed if the wastewater retention time in the
sand media is sufficiently long for the microorganisms to absorb waste constituents. With depleting carbonaceous BOD in
TFS-61
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the percolating wastewater, nitrifying microorganisms are able to thrive deeper in the surface layer, where nitrification will
readily occur.
Chemical adsorption can occur throughout the media bed. Adsorption sites in the media are usually limited, however. The
capacity of the media to retain ions depends on the target constituent, the pH, and the mineralogy of the media. Phospho-
rus is one element of concern that can be removed from wastewater in this manner, but the number of available adsorption
sites is limited by the characteristics of the media.
The basic components of recirculating filters include a recirculation/dosing tank, pump and controls, distribution network,
filter bed with an underdrain system, and a return line. The return line or the underdrain must split the flow to recycle a
portion of the filtrate to the recirculation/dosing tank. A small volume of wastewater and filtrate is dosed to the filter
surface on a timed cycle 1 to 3 times per hour. Recirculation ratios are typically between 3:1 and 5:1. In the recirculation
tank, the returned aerobic filtrate mixes with the anaerobic septic tank effluent before being reapplied to the filter.
Recirculating filters must use a coarser media than single-pass filters because recirculation requires higher hydraulic
loadings. Both coarse sand and fine gravel are used as filter media. Because of the high hydraulic conductivities of the
coarse media, filtrate recirculation is used to provide the wastewater residence times in the media necessary to meet the
treatment requirements. Based on forward flow, daily hydraulic loadings are typically about 3 gpd/ft2 (2 to 5 gpd/ft2) when
the filter media is coarse sand. Therefore, the corresponding combined daily filter hydraulic loading, including the recircu-
lated flow, may be 6 to 25 gpd/ft2. Where gravel is used as the media, the daily hydraulic loadings are increased to as much
as 10 to 15 gpd/ft2 with a combined daily loading of 30 to 75 gpd/ft2. BOD and TSS removals are generally the same as
those achieved by single-pass filters. Nearly complete ammonia removal by nitrification is also achieved. In addition, the
mixing of the return filtrate anaerobic septic tank effluent removes approximately 50 percent of the total nitrogen. How-
ever, because of the greater hydraulic loadings and coarser media, fecal coliform removal is somewhat less than in single-
pass filters.
Recirculating filters offer advantages over single-pass filters. Greater control of performance is possible because recircula-
tion ratios can be changed to optimize treatment. The filter can be smaller because of the higher hydraulic loading. Recir-
culation also reduces odors because the influent wastewater (septic tank effluent) is diluted with return filtrate that is low
in BOD and high in dissolved oxygen.
Many types of media are used in packed-bed filters. Washed, graded sand was the most common, but pea gravel has
generally replaced it in recent times. Other granular media used include crushed glass, garnet, anthracite, plastic, expanded
clay, expanded shale, open-cell foam, extruded polystyrene, and bottom ash from coal-fired power plants. Coarse-fiber
synthetic textile materials are also used. These materials are generally restricted to proprietary units. Contact the system
manufacturers for application and design using these materials.
Other modifications to the basic RSF design include the type of distribution system, the location and design of the recircu-
lation tank, the means of flow splitting the filtrate between discharge and return flows, and enhancements to improve
nitrogen removal. The last is addressed in Technology Fact Sheet 9 on nitrogen removal.
Applications
Recirculating sand filters can be used for a broad range of applications, including single-family residences, large commer-
cial establishments, and small communities. They are frequently used to pretreat wastewater prior to subsurface infiltration
on sites where soil has insufficient unsaturated depth above ground water or bedrock to achieve adequate treatment. They
are also used to meet water quality requirements before direct discharge to a surface water. RSFs are primarily used to
treat domestic wastewater, but they have also been used successfully in treatment trains to treat wastewaters high in
organic materials such as those from restaurants and supermarkets. Single-pass filters are most frequently used for smaller
applications and at sites where nitrogen removal is not required. Recirculating filters are used for both large and small
flows and are frequently used where nitrogen removal is necessary. RSFs frequently replace aerobic package plants in
many parts of the country because of their high reliability and lower 0/M requirements.
TFS-62
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Design
Packed-bed filter design starts with the selected media. The media characteristics determine the necessary filter area, dose
volumes, and dosing frequency. Availability of media for a specific application should be determined before completing the
detailed design. Typical specifications, mass loadings, and depths for sand and gravel media are presented in chapter 4.
The sand or gravel selected should be durable with rounded grains. Only washed material should be used. Fine particles
passing the U.S. No. 200 sieve (<0.074 mm) should be limited to less than 3 percent by weight. Other granular media are
bottom ash, expanded clay, expanded shale, and crushed glass. These media should perform similarly to sand and gravel
for similar effective sizes, uniformity, and grain shape. Newer commercial media such as textile materials have had limited
testing, but should be expected to perform as well as the above types.
Traditionally, media filters have
been designed based on hydraulic
loadings. However, since they are
primarily aerobic biological
treatment units, it is more appropri-
ate that they be designed based on
organic loadings. Unfortunately,
insufficient data exist to establish
well-defined organic loading rates.
Experience suggests that BOD5
loadings on sand media should not
exceed about 5 lb/1000 ft2 per day
(0.024 kg/m2 per day) where the
effective size is approximately 1.0
mm and the dosing rate is at least
12 times per day. Higher loadings
have been measured in short-term
studies, but designers are cautioned
about exceeding this loading rate
until quality-assured data confirm
these higher levels. The BOD5
loading should decrease with
decreasing effective size of the
sand. Because of the larger pore
size and greater permeability, gravel
filters can be loaded more heavily.
BOD5 loadings of 20 lb/1000 ft2 per
day (0.10 kg/m2 per day) have been
consistently successful, but again
higher loadings have been mea-
sured. Some often-quoted design
specifications for RSFs are given in
table 1.
Table 1 .Typical design specifications for individual home recirculating sand filters
Design parameter
Median
Specifications
Effective size
Sand
Gravel
Uniformity coefficient
Percent fines (passing 200 sieve or
< 0.074 mm)
Depth
Mass loadings
Hydraulic loading 1
Sand
Gravel
Organic loading 2
Sand
Gravel
Underdrains
Type
Slope
Transition bedding
Size
Dosing
Frequency
Per Dose
Recirculation tank
Volume
Recirculation rate
Typical design value
Durable, washed sand/gravel
with rounded grains
1.0-5.0 mm
3.0 - 20.0 mm
<2.5
<3
24 in. (18 to 36 in.)
3 -5 gpd/ft2
10-15gpd/ft2
<5lbBOD5/1000ft2-d
<_15lbBOD,/1000ft2-d
Slotted or perforated pipe
0-0.1%
0.6 - 1 .0 cm washed pea gravel
0.6 - 4.0 cm washed gravel or
crushed stone
48 times/day (every 30 min.) or more
1 to 2 gal ./orifice
1 .5 times design daily flow
3 to 5 times daily flow
1 gpd/ft2 = 4 cm/day = 0.04 m3 / m2 per day (forward flow only).
1 Ib BOD/1,000 ft2 per day = 0.00455 kg/m2 per day.
The RSF dose volume depends on the recirculation ratio, dosing frequency, and distribution network:
Dose Volume = Design Flow (gpd) x (Recirculation Ratio + 1) + Number of Doses/Day
Small dose volumes are preferred because the flow through the porous media will occur under unsaturated conditions with
higher moisture tensions. Better wastewater media contact and longer residence times occur under these conditions.
Smaller dose volumes are achieved by increasing the number of doses per day.
TFS-63
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The recirculation ratio increases the hydraulic loading without increasing the organic loading. For example, a 4:1 recircu-
lation ratio results in a hydraulic loading of five times the design flow (1 part forward flow to 4 parts recycled flow). The
increased hydraulic loading reduces the residence time in the filter so that recirculation is necessary to achieve the desired
treatment. Typical recirculation ratios range from 3:1 to 5:1. As the permeability of the media increases, the recirculation
ratio may need to increase to achieve the same level of treatment.
Media characteristics can limit the number of doses possible. Media reaeration must occur between doses. As the effective
size of the media decreases, the time for drainage and reaeration of the media increases. For single pass filters, typical
dosing frequencies are once per hour (24 times/day) or less. Recirculating sand filters dose 2 to 3 times per hour (48 to 72
times/day).
Distribution network requirements will also limit the number of doses possible. To achieve uniform distribution over the
filter surface, minimum dose volumes are necessary and can vary with the distribution method selected. Therefore, if the
dose volume dictated by the distribution network design is too high, the network should be redesigned. Since the dose
volume is a critical operating parameter, the method of distribution and the distribution system design should be consid-
ered carefully.
Distribution methods used include rigid pipe pressure networks with orifices or spray nozzles, and drip emitters. Rigid
pipe pressure networks are the most commonly used method. Orifices with orifice shields, facing upward, minimize hole
blockage by stones. Since the minimum dose volume required to achieve uniform distribution is five times the pipe
volume, large multihome filters are usually divided into multiple cells. Drip emitter distribution is being used increasingly
because the minimum dose volumes are much less than the rigid pipe network volumes.
Recirculation tanks are a component of most recirculation filter systems. These tanks consist of a tank, recirculation pump
and controls, and a return filter water flow splitting device. The flow splitting device may or may not be an integral part
of the recirculation tank. Recirculation tanks store return filtrate, mix the filtrate with the septic tank effluent, and store
peak influent flows. The tanks are designed to either remain full or be pumped down during periods of low wastewater
flows. Since doses to the recirculating filter are of a constant volume and occur at timed intervals, the water level in the
tank will rise and fall in response to septic tank effluent flow, return filtrate flow, and filter dosing.
In tanks designed to remain full, all filtrate is returned to the recirculation tank to refill the tank after each dosing event.
When the tank reaches its normal full level, the remaining return filtrate is discharged out of the system as effluent. This
design is best suited where treatment performance must be maintained continuously. For single-family home systems, the
recirculation tank is typically sized to be equal to 1.5 times the design peak daily flow.
When the filtrate flow is continuously split between the return (to the recirculation tank) and the discharge, the liquid
volume in the recirculation tank will vary depending on wastewater flows. During low flow periods the tank can be
pumped down to the point that the low-water pump off switch is activated. This method leaves less return filtrate available
to mix with the influent flow. While simple, this method of flow splitting can impair treatment performance because
minimum recirculation ratios cannot be maintained. This is less of a disadvantage, however, for large, more continuous
flows typical in small communities or large cluster systems.
The recirculation pump and controls are designed to dose a constant volume of mixed filtrate and septic tank effluent flow
onto the filter on a timed cycle. The pump must be sized to provide the necessary dosing rate at the operating discharge
head required by the distribution system. Pump operation is controlled by timers that can be set for pump time on and
pump time off. A redundant pump-off float switch is installed in the recirculation tank below the minimum dose volume
level. A high water alarm is also installed to provide notice of high water caused by pump failure, loss of pump calibra-
tion, or excessive influent flows.
TFS-64
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Recirculation tank sizing
In many types of commercial systems, daily flow variations can be extreme. In such systems, the recycle ratios necessary
to achieve the desired treatment may not be maintained unless the recirculation tank is sized properly. During prolonged
periods of high influent flows, the recirculation ratio can be reduced to the point that treatment performance is not maintained
unless the recirculation tank is sized to provide a sufficient reservoir of recycled filtrate to mix with the influent during the
high-flow periods.
To size the tank appropriately for the application, assess the water balance for the recirculation tank using the following
procedure:
1 . Select the dosing frequency based on the wastewater strength and selected media characteristics.
2. Calculate the dose volume based on the average daily flow:
Vdose = [(recycle ratio + 1) x Qave dai|y] •+• (doses/day)
Where V and Q are the flow volume and flow rate, respectively.
3. Adjust the dose volume if the calculated volume is less than the required minimum dose volume for the distribution
network.
4. Estimate the volumes and duration of influent peakflows that are expected to occur from the establishment.
5. Calculate the necessary recirculation tank"working" volume by performing a water balance around the recirculation tank
for the peakflow period with the greatest average flow rate during that peak period.
Inputs = Qinfx T + Qrecydex T = Qmf x T + (Qdose - QJ x T = V,nf + Vecyc|e
Outputs = Vdose x (T •*• dose cycle time)
Where T is the peakflow period duration.
If the inputs are greater than the outputs, then Qeff = Qdose and the peaks are stored in the available freeboard space of the
recirculation tank. If the inputs are less than the outputs, then Qeff = Qinf
To provide the necessary recycle ratio, sufficient filtrate must be available to mix with the influent septic tank effluent. The
filtrate is provided by the return filtrate flow and the filtrate already in the recirculation tank.
Recycle ratio x Qinf x T < Qrec cle x T + minimum tank working volume
Where minimum tank working volume = Recycle ratio x (Qinf - Qrecyde) x T
6. Calculate the necessary freeboard volume for storage of peakflows when the influent volume is greaterthan the dosing
volume during the peakflow period.
Freeboard volume = Qinf x T + Qrecyde x T - Qdose x T
7. Calculate the minimum total recirculation volume.
Total tank volume = minimum tank working volume + freeboard volume
(Adapted from Ayres Associates, 1998.)
TFS-65
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Several flow splitting devices maybe used. The most common are Figure 2. Flowsplitter operated by a float ball valve
ball float valves and proportional splitters. The ball float valve is used
where the recirculation tank is designed to remain full. The valve is
connected to the return filtrate line inside the recirculation tank (see
figure 2). The return line runs through the tank. The ball float valve is
open when the water level is below the normally full level. When the
tank fills from either the return filtrate or the influent flow, the ball
float rises to close the valve, and the remaining filtrate is discharged
from the system. The proportional splitters continuously divide the
flow between return filtrate and the filtrate effluent (see figure 3).
Another type of splitter consists of a sump in which two pipes are
stubbed into the bottom with their ends capped. In the crowns of each
capped line, a series of equal-sized, pluggable holes are drilled. The
return filtrate floods the sump, and the flow is split in proportion to
the relative number of holes left open in each perforated capped pipe.
Another type of splitter divides flow inside the filter. The filter floor is raised so that it slopes in opposite directions. The
raised point is located so that the ratio of the floor areas on either side is in proportion to the desired recirculation ratio.
Each side has its own underdrain. One side drains back to the recirculation tank, the other side drains to discharge. This
method has the disadvantage that adjustments to the recirculation ratio cannot easily be made.
Most RSFs are constructed aboveground and with an open filter surface; however, in cold climates, they can be placed in
Figure 3. Splitter basin
From
filter
Tees with
removable
caps
To
recirculation
tank
Adjustable
ports
(Side view)
the ground to prevent freezing.
Placing a cover over an RSF is
recommended to reduce odors and
to provide insulation in cold
climates, although no freezing
was observed in an open RSF in
Canada using coarse gravel media.
Covers must provide ample fresh
air venting, because reaeration of
the filter media occurs primarily
from the filter surface.
The filter basin can be a lined
excavation or fabricated tank. For
single-home systems, prefabri-
cated concrete tanks are com-
monly used. Many single-home filters and most large filters are constructed within lined excavations. Typical liner
materials are polyvinyl chloride and polypropylene. A liner thickness of 30 mil can withstand reasonable construction
activities yet be relatively easy to work with. A sand layer should be placed below the liner to protect it from puncturing if
the floor and walls of the excavation are stony. The excavation walls should be brought above the final grade to prevent
entry of surface water. It is often necessary to cover the filter surface to reduce the effects of algae fouling, odors, cold
weather impacts, precipitation, and snow melt. The cover must provide ample fresh air venting, however. Reaeration of
the filter media primarily occurs from the filter surface.
The underdrain system is placed on the floor of the tank or lined excavation (figure 4). Ends of the underdrains should be
brought to the surface of the filter and fitted with cleanouts that can be used to clean the underdrains of biofilms if
necessary. The underdrain outlet is cut in the basin wall such that the drain invert is at the floor elevation and the filter can
be completely drained. The underdrain outlet invert elevation must be sufficiently above the recirculation tank inlet to
accommodate a minimum of 0.1 percent slope on the return line and any elevation losses through the flow splitting device.
The underdrain is covered with washed, durable gravel to provide a porous medium through which the filtrate can flow to
TFS-66
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the underdrain system. The gravel should
be sized to prevent the filter media from
mixing into the gravel, or a layer of 1/4-
to 3/8-inch-diameter gravel should be
placed over the underdrain gravel before
the filter media is added.
Performance
RSF systems are extremely effective and
reliable in removing BOD, TSS, and
contaminants that associate with the
Figure4.Typical underdrain detail.
2"
6"
Filter Sand
1/2" to 3/4" rock
4" slotted PVC
Underdrain
particulate fraction of the incoming septic tank effluent. Some typical performance data are provided in table 2.
Normally, BOD and TSS effluent concentrations are less than 10 mg/L when RSF systems are treating residential waste-
water. Nitrification tends to be complete, except in severely cold conditions. Natural denitrification in the recirculating
tank results in 40 to 60 percent removal of total nitrogen (TN). Fecal coliform removal is normally 2 to 3 logs (99 to 99.9
percent). Phosphorus removal drops off from high percentages to about 20 to 30 percent after the exchange capacity of the
media becomes exhausted. Some media and media mixes have very high iron and/or aluminum content that extends the
initial period of high phosphorus removal. (See Enhanced Nutrient Removal—Phosphorus, Technology Fact Sheet 8.)
Table 2. Recirculating filter performance
Reference
Louden et al., 1985"
(Michigan)
Piluk and Peters, 1994"
(Maryland)
Ronayne, et al., 1982°
(Oregon)
Roy and Dube, 1994"
(Quebec)
Ayres Assoc., 1998°
(Wisconsin)
Owen and Bobb, 1994 '
(Wisconsin)
BOD
(mg/L)
Influ. Efflu.
(% Removal)
150 6
(96.00%)
235 5
(97.87%)
217 3
(98.62%)
101 6
(94.06%)
601 10
(98.34%)
80 8
(90.00%)
TSS
(mg/L)
Influ. Efflu.
(% Removal)
42 6
(85.71%)
75 8
(89.33%)
146 4
(97.26%)
77 3
(96.10%)
46 9
(98.35%)
36 6
(83.33%)
TKN
(mg-N/L)
Influ. Efflu.
(% Removal)
55 2.3
(95.82%)
Not reported
57.1 1.1
(98.07%)
37.7 7.9
(79.05%)
65.9 3
(95.45%)
(> 95%)
TN
(mg-N/L)
Influ. Efflu.
(% Removal)
55 26
(52.73%)
57 20
(64.91%)
57.5 31.5
(45.22%)
37.7 20.1
(46.68%)
65.9 16
(75.72%)
Not reported
Fecal Coliform
(#/100mL)
Influ. Efflu.
(% Removal)
3.40E+03 1.40E+01
(99.59%)
1.80E+06 9.20E+03
(99.49%)
2.60E+05 8.50E+03
(96.73%)
4.80E+05 1.30E+04
(97.29%)
> 2500 6.20E+01
(> 98%)
Not reported
aSingle-family home filters. Sand media: es = 0.3 mm; uc = 4.0. Average loadings = 0.9 gpd/ft2 (forward flow) / 1.13 Ib BOD/1,000 ft2 -day. Recirculation ratio
= 3:1. Dosed 4-6 times per hour. Open surface.
bSingle-family home filters. Sand media: es = 1 mm; uc = <2.5. Design hydraulic loadings = 3.54 gpd//ft2 (forward flow). Actual flow not measured.
Recirculation ratio = 3:1. Doses per day = 24.
cSingle-family home filters. Sand media: es = 1.2 mm; uc = 2.0. Maximum hydraulic loading (forward flow)= 3.1 gpd/ft2. Recirculation ratio = 3:1-4:1. Doses
per day = 48.
dSingle-family home filters. Gravel media: es = 4.0 mm; uc = <2/5. Design hydraulic loading (forward flow)= 23.4 gpd/ft2. Recirculation ratio = 5:1. Doses per
day = 48. Open surface, winter operation.
"Restaurant (grease and oil inf./eff. = 119/<1 mg/L, respectively). Gravel media: pea gravel (3/8 in. dia.) Design hydraulic loading (forward flow) = 15 gpd/ft2.
Recirculation ratio = 3:1- 5:1. Doses per day = 72. Open surface, seasonal operation.
'Small community treating average 15,000 gpd of septic tank effluent. Sand media: es = 1.5 mm; uc = 4.5. Design hydraulic loading (forward flow) = 2.74
gpd/ft2. Recirculation ratio = 1:1-4:1. Open surface, winter operation.
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Management needs
As with all treatment systems, the RSF should be constructed carefully according to design specifications using corrosion-
resistant materials. Every truckload of media delivered to the site should be tested for compliance with the specifications.
All tanks and lined basins, including the entry and exit plumbing locations, must be watertight.
Inspection and operation/maintenance (0/M) needs are primarily related to inspection and calibration of the recirculation
pump and controls. For sand media units, frequent removal of vegetation and scraping of the surface are required. Regular
maintenance tasks include periodic checks on the pressure head at the end of the distribution system, draining of the
accumulated solids from lines, and occasional brushing of the lines (at least once per year), with bottle brushes attached to
a plumber's snake.
The recirculation tank should be checked for sludge accumulation on each visit and pumped as necessary (usually one to
three times per year).
Risk management issues
RSFs are extremely reliable treatment devices and are quite resistant to flow variations. Toxic shocks are detrimental to
RSF treatment performance because of the resistance of biofilms to upset and the extended period of contact between
biofilms and wastewater.
Gravel RSFs (or RGFs) are likely viable throughout the United States when proper precautions (e.g., covering, insulation)
are taken. These systems perform best in warmer climates, but they increase opportunities for odor problems. In general,
gravel RSF systems are far less prone to odor production than ISFs. Increased recycle ratios should help minimize such
problems. However, power outages will stop the process from treating the wastewater, and prolonged outages would be
likely to generate some odors.
Costs
Construction costs for recirculating sand filters are driven by treatment media costs, the recirculating tank and pump/
control system costs, and containment costs. Total costs are therefore site specific, but tend to vary from $8,000 to
$11,000. Low-cost alternative media can reduce this figure significantly.
Power costs for pumping at 3 to 4 kWh/day are in the range of $90 to $120 per year, and management costs for monthly
visits/inspections by semiskilled personnel typically cost $150 to $200 annually.
References
Anderson, D.L., R.L. Siegrist, and R.J. Otis. 1985. Technology Assessment of Intermittent Sand Filters. U.S.
Environmental Protection Agency, Office of Research and Development, and Office of Water, Publication,
Washington, DC.
Ayres Associates. 1997. Florida Keys Wastewater Nutrient Reduction Systems Demo Project: Second Quarter Report.
Florida Department of Health, Tallahassee, FL.
Ayres Associates. 1998. Unpublished data from Wisconsin.
Bruen, M.G., and R.J. Piluk. 1994. Performance and Costs of Onsite Recirculating Sand Filters. In Proceedings of the
Seventh On-site Wastewater Treatment Symposium. American Society of Agricultural Engineers, St. Joseph, MI.
Kerri, K.D., and J. Brady. 1997. Small Wastewater System Operation and Maintenance: Vol. 1. California State
University, Sacramento, CA.
TFS-68
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Louden, T.L., D.B. Thompson, L. Fay, and L.E. Reese. 1985. Cold-Climate Performance of Recirculating Sand Filters.
In Proceedings of the Fourth On-site Wastewater Treatment Symposium. American Society of Agricultural Engineers,
St. Joseph, MI.
National Small Flows Clearinghouse. 1998. Recirculating Sand Filters. U.S. Environmental Protection Agency, Office of
Water, Washington, DC.
Orenco Systems, Inc. 1993. Cost Estimating for STEP Systems and Sand Filters. Orenco Systems, Inc., Roseburg, OR.
Owen, J.E., and K.L. Bobb. 1994. Winter Operation and Performance of a Recirculating Sand Filter. In Proceedings of the
WEFTEC 67th Annual Conference. Water Environment Federation, Alexandria, VA.
Piluk, R.J., and E.G. Peters. 1994. Small Recirculating Sand Filters for Individuals Homes. In Proceedings of the Seventh
On-site Wastewater Treatment Symposium. American Society of Agricultural Engineers, Joseph, MI.
Rhode Island Department of Environmental Management. 2000. Sand Filter Guidance Document. Rhode Island
Department of Environmental Management, Providence, RI.
Roy, C., and J.P Dube. 1994. A Recirculating Gravel Filter for Cold Climates. In Proceedings of the Seventh On-site
Wastewater Systems Symposium. American Society of Agricultural Engineers, St. Joseph, MI.
TFS-69
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TFS-70
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 12
Land Treatment Systems
Description
Land (surface) treatment systems (figures 1 and 2) are permitted in some states, but are not widely used because of their
large land area requirements exacerbated by code-required setbacks. For example, a spray irrigation system requires about
four times the area of an individual home lagoon. When these systems are used, large buffer areas and fencing may be
required to ensure minimal human exposure. Also, given the nature of these systems, all requirements include disinfection
and significant pretreatment before application. In wet and cold areas, an additional basin for storage or a larger dosing
Figure 1. Conceptual schematic of spray irrigation system
Applied
wastewater
Evapotranspiration
Percolation
Figure 2. Conceptual schematic of rapid infiltration system
Applied
wastewater
Evapotranspiration
Percolation
Hydraulic
Pathway
TFS-71
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Figure 3.Typical residential spray irrigation systems
7
T
8
9
10
1. House sewer; 2. Septic tank (two required); 3. Aerobic unit; 4. Dosing tank; 5. Sand filter; 6. CI2 disinfection (or UV); 7. Tank and pump (plus storage); 8. Piping
system; 9. Sprinklers; 10. Application site
Source: Adapted from Mclntyre et al., 1994.
tank is necessary to eliminate possible runoff from the application area. The most used variation of these systems is the
spray irrigation system (figure 3).
Spray irrigation systems distribute wastewater evenly on a vegetated plot for final treatment and discharge. Spray irriga-
tion can be useful in areas where conventional onsite wastewater systems are unsuitable due to low soil permeability,
shallow water depth table or impermeable layer, or complex site topography. Spray irrigation is not often used for residen-
tial onsite systems because of its large areal demands, the need to discontinue spraying during extended periods of cold
weather, and the high potential for human contact with the wastewater during spraying. Spray irrigation systems are
among the most land-intensive disposal systems. Drifting aerosols from spray heads can be a nuisance and must be moni-
tored for impact on nearby land use and potential human contact. Buffer zones for residential systems must often be as
large as, or even larger than, the spray field itself to minimize problems.
In a spray irrigation system, pretreatment of the wastewater is normally provided by a septic tank (primary clarifier) and
aerobic unit, as well as a sand (media) filter and disinfection unit. Some states do not require the aerobic unit if the filter is
used. The pretreated wastewater in spray irrigation systems is applied at low rates to grassy or wooded areas. Vegetation
and soil microorganisms metabolize most nutrients and organic compounds in the wastewater during percolation through
the first several inches of soil. The cleaned water is then absorbed by deep-rooted vegetation, or it passes through the soil
to the ground water.
Rapid infiltration (RI) is a soil-based treatment method in which pretreated (clarified) wastewater is applied intermittently
to a shallow earthen basin with exposed soil surfaces. It is only used where permeable soils, which generally can accept a
conventional OWTS, are available. Because loading rates are high, most wastewater infiltrates the subsoil with minimal
losses to evaporation. Treatment occurs within the soil before the wastewater reaches the ground water. The RI alternative
is rarely used for onsite wastewater management. It is more widely used as a small-community wastewater treatment
system in the United States and around the world.
The third and last type of land surface treatment is the overland flow (OF) process. In this system, pretreated wastewater is
spread along a contour at the top of a gently sloping site that has minimum permeability. The wastewater then flows down
the slope and is treated by microorganisms attached to vegetation as it travels by sheet flow over very impermeable soils
until it is collected at the bottom of the slope for discharge. This system (figure 4) requires land areas similar to the spray
TFS-72
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Figure 4. Overland flow system schematic
Wastewater
application by
surface spray or
sprinkler methods
Slope 2-8% Water to|erant
Sheet flow 9rasses
Collection
Terrace
back slope
Overland flow
Limited percolation terrace
Terrace
front slope
irrigation system. However, surface water discharge requirements (e.g., disinfection) from the OF system must still be
met. Overland flow, like rapid infiltration, is rarely used for onsite wastewater management.
Typical applications
Spray irrigation (SI) is normally considered at site locations that do not permit a conventional SWIS because of relative
impermeability and shallow depths caused by restrictive conditions (e.g., ground water or impermeable bedrock or
fragipan). SI is normally the final step in the treatment sequence as the effluent is reintroduced to the environment. Most
states require advanced treatment and disinfection prior to SI treatment.
Design assumptions
After pretreatment, which at a minimum should be a typical ISF effluent followed by disinfection, the treated wastewater
is conveyed to a holding tank with a pump and controls that deliver it to the sprinkler system. The sprinklers spread the
wastewater over a predetermined area at specific times. In wet climates or frozen soil conditions, an additional holding
(storage) basin or larger dosing tank is required to prevent irrigation during periods when the wastewater would not be
accepted by the soil for treatment and intended environmental incorporation. Regulations for buffer requirements from
Texas, Virginia, and Pennsylvania are incorporated into table 1. Typically, the features listed below and their peripheral
buffer zones are fenced to prevent exposure.
Application rates vary. Texas determines design rates based on evaporation, Virginia bases rates on soil texture, and
Pennsylvania uses a combination of soil depth and slope. From a performance code approach, the application rate should
be based on protecting the receiving surface/ground waters. It should be based on wastewater characteristics, critical
constituent required concentrations (at a monitoring location
where a specific quality standard must be met), and the
characteristics of the site (i.e., features that will mitigate
wastewater contaminants in order to meet the constituent
concentration at the point of use).
In practical terms, all three states require the same pretreat-
ment sequence, which yields SI influent of approximately 5,5,
25, and 4 mg/L of CBOD, TSS, TN, and TP, respectively, in
addition to a fecal coliform (FC) level of about 10 cfu/100 mL
(if the disinfection step is working properly). Passage through
1 foot of unsaturated soil should for a few years remove most
CBOD, TSS, TP, and FC; therefore, nitrogen will be the
Table 1. Buffer requirements to various features
Feature
Property lines
Roads, driveways
Dwellings
Streams and lakes
Wells and water supplies
Recreation areas
Buffer distance (ft)
10-100
25
0-100
25-100
100
100
Source: North Carolina DEHNR, 1996.
TFS-73
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constituent of most concern. During the growing season, removal should be feasible by crop uptake and, to a lesser degree,
ammonia volatilization.
Therefore, the hydraulic and nitrogen loading rates for a specific site are the primary design parameter. Also, these systems
are rarely considered for permeable soils. The design approach described below is for this set of circumstances.
Spray irrigation systems are designed to treat wastewater and evenly distribute the effluent on a vegetated lot for final
treatment. The application rate is determined by two major factors: hydraulic loading and nutrient loading (usually nitrogen
is the limiting factor). The application rate is designed to meet the capacity of the soil to accept the effluent hydraulically
and subsequently allow it to drain through the soil. The application rate can be varied according to the permeability of the
soil. In Pennsylvania and Virginia, this method results in application rates of 0.6 to 2.5 cm/week. Lower rates can greatly
improve nitrogen removal. The treated wastewater is spread over the required application area through a sprinkler or drip
irrigation system.
Sprinklers are generally low-angle (7 to 13 degrees), large-drop-size nozzles designed to minimize aerosols. Application
areas must be vegetated (with crops not intended for human consumption) and have slopes that preclude runoff to
streams. The type of vegetation determines the nitrogen loading capacity of the site, but the hydraulic capacity depends on
climate and soil characteristics. Additional nitrogen losses may occur through denitrification (only about 25 percent due to
the low BOD:N ratio) and ammonia volatilization (about 10 percent if soil pH is high; less to none if it is acidic).
Spray irrigation of wastewater effluent must be timed to coincide with plant uptake and nutrient use. Temperature factors
in some areas of the country may preclude the use of spray irrigation during certain times of the year. The wastewater
may need to be stored in holding tanks during the coldest period of the year, because plant growth is limited and the
nitrogen in effluent discharged during this time will be mineralized and unavailable for plant uptake.
Some SI systems irrigate only one or two days per week so that the soil can drain and aerate between applications. Others
spray twice during the night or in the early morning to minimize inconvenience to the homeowner and to minimize the
potential for human contact.
The width of the required buffer zone depends on the slope of the site, the average wind direction and velocity, the type of
vegetation, and the types of nearby land uses. For wastewater produced by a single-family home, the minimum recom-
mended SI plot area, including buffer zones, is commonly about 2 acres (0.81 hectares) in Pennsylvania and Virginia.
Performance
Studies that sample both the soil below the spray field and its runoff show that spray irrigation systems work as well as
other methods of managing wastewater. Spray irrigation systems are designed for no degradation; therefore, hydraulic and
nutrient loading rates are based on the type of vegetation used and the hydraulic properties of the soils. If the vegetation
cannot assimilate the amount of nitrogen applied, for example, then nitrogen removal to reduce the nitrogen content of the
effluent prior to spray irrigation may be required. The overall efficiency of a spray irrigation system in removing pollutants
will be a function of the pollutant removal efficiencies of the entire treatment process and plant uptake.
There have been few documented cases of health problems due to the spray irrigation, but use of proper buffer zones is
crucial. One benefit of spray irrigation is savings on potable water because the wastewater is used for irrigation.
Management needs
Construction factors include site preparation and installation of runoff controls, irrigation piping, return systems, and
storage facilities. Since sustained wastewater infiltration is an important component of successful system operation, it is
critical that construction activity be limited on the application site. Where stormwater runoff can be significant, measures
must be taken to prevent excessive erosion, including terracing of steep slopes, contour plowing, no-till farming, establish-
ment of grass border strips, and installation of sediment control basins. Earthworking operations should be conducted in
TFS-74
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such a way as to minimize soil compaction. Soil moisture should generally be low during these operations. High-flotation
tires are recommended for all construction vehicles.
The soil profile must also be managed to maintain infiltration rates by avoiding soil compaction and maintaining soil
chemical balance. Compaction and surface sealing (caused by harvesting equipment and development of fine layers from
multiple wastewater applications) can reduce soil infiltration and increase runoff.
Local regulatory agencies may require ground water monitoring to evaluate system performance. Soil fertility and chemical
balance should be evaluated periodically to determine if soil amendments are necessary. Trace elements may also be
analyzed to monitor possibly toxic accumulations.
Residuals produced by slow-rate land application systems are limited to harvested crops and crop residues that are not for
human consumption. Agricultural crop applications require the most intensive management, while forest application
requires the least management. Management tasks may include soil tillage, planting and harvesting of crops, nutrient
control, pH adjustment, and sodium and salinity control. No special equipment, other than the appropriate agricultural
equipment, is required. Typical pump, controls, and basin requirements prevail for the dosing system.
Virginia's 0/M requirements for onsite spray irrigation systems (not including pretreatment unit processes) include the
following:
• Monthly. Walk over spray area and examine for
- Ponding of effluent
- Bad odors
- Damage to spray heads
- Surfacing liquids
- Vegetation problems
- Surface soil collapse
• Quarterly. Conducted by a qualified, semi-skilled operator
- Proper spray sequence
- Proper pump function
- Proper liquid levels
• Biannually
- Erosion
- Storage unit capacity
• Annually. Effluent sampling by a certified laboratory
- Test water supplied to spray irrigation area for pH, total Kjeldahl nitrogen, fecal coliform bacteria, chlorine, TSS,
and BOD
- Reports of analyses are to be submitted by the laboratory to the local/district health department within 10 days of
the completion of the analyses.
A management contract with an approved operator or operations firm is also required.
TFS-75
-------
Risk management issues
No crops grown on the SI application area should be consumed by humans. Buffer zones should minimize aerosol expo-
sure. Spray irrigation systems with sufficient storage capacity are essentially unaffected by major flow variations. A water
balance should be conducted to determine the need under the climate conditions, soils, and application rates and patterns of
each rate. Similarly, toxic shock loadings should be largely dissipated in the preceding pretreatment steps, but phytotoxic
compounds may still be a concern at the application site. Spray irrigation cannot function during saturated or frozen
conditions, and the pretreated influent must be stored until proper vegetative uptake (usually nitrogen) conditions return.
Power outages will affect the upstream pretreatment processes rather than the SI system, even though the system must
have power to function.
However, by the time the wastewater effluent is discharged by the sprinklers, the water should be sufficiently treated so as
not to pose health risks. There have been no documented cases of health problems due to the spray irrigation of properly
treated wastewater. However, drifting aerosols from the spray heads should be monitored for impact on nearby land uses.
A benefit of spray irrigation is the use of effluent, instead of potable tap water, to water the landscape.
Costs
Construction costs of SI systems are very high if the generally required pretreatment is included, especially if both an
aerobic unit and a sand filter treating septic tank effluent are included. Such a system could easily cost $20,000 or more.
0/M costs for the SI system alone primarily include labor (15 to 20 hours per year), power (for pumps and other pretreat-
ment needs) and materials (e.g., chlorine, if chosen). 0/M costs are estimated at more than $500 per year, given the entire
treatment train suggested by figure 3. If the aerobic treatment unit is not required ahead of the sand filter, and a UV
disinfection unit is used, this cost may reduce to $300 to $400 annually.
References
Crites, R., and G. Tchobanoglous. 1996. Small and Decentralized Wastewater Management Systems. WCB/McGraw-Hill,
San Francisco, CA.
Emery, H.C. 1999. Onsite Spray Irrigation: A Tale of Three Cities. Pumper.
Mclntyre, C., C. D'Amico, and J.H. Willenbrock. 1994. Residential Wastewater Treatment and Disposal: On-Site Spray
Irrigation Systems. In Proceedings of the Seventh Onsite Wastewater Treatment Symposium. American Society of
Agricultural Engineers, St. Joseph, MI.
Monnett, G.T., R.B. Reneau, Jr., and C. Hagedorn. 1991. Evaluation of Onsite Spray Irrigation for Disposal on Marginal
Soils. In Proceedings of the 6th Onsite Wastewater Treatment Symposium. American Society of Agricultural Engineers,
St. Joseph, MI.
North Carolina, DEHNR. 1996. On-site Wastewater Management Guidance Manual. Division of Environmental Health.
Raleigh, NC.
Rubin, A.R. 1992. Slow-Rate Spray Irrigation and Drip Disposal Systems for Treatment and Renovation of Domestic
Wastewater from Individual Homes. In Proceedings of the Seventh Northwest Onsite Wastewater Treatment Short
Course. University of Washington, Seattle.
Shuval, H.I., A. Adin, B. Fattal, E. Raisitz, and P. Yekutiel. 1986. Wastewater Irrigation in Developing Countries. World
Bank technical paper no. 51. World Bank, Washington, DC.
U.S. Environmental Protection Agency (USEPA). 1992. Manual: Wastewater Treatment/Disposal for Small Communities.
EPA/625/R-92/005. U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1981. Process Design Manual for Land Treatment of Municipal
Wastewater. EPA 625/1-81-013. U.S. Environmental Protection Agency, Office of Research and Development,
Cincinnati, OH.
TFS-76
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Onsite Wastewater Treatment Systems
Technology Fact Sheet 13
Renovation/Restoration of
Subsurface Wastewater Infiltration
Systems (SWIS)
Although an analysis to diagnose problems in OWTSs is provided in chapter 5, this Fact Sheet is included to provide a
special reference to identify alternatives likely to be recommended to renovate and restore SWIS and observed results.
Functions of the subsurface wastewater infiltration system (SWIS)
The subsurface wastewater infiltration system (SWIS) receives the effluent pretreated in the septic tank and purifies it
through biological, physical, and chemical reactions as it passes through the unsaturated soil to the ground water. An
important component of the infiltration system is the biomat, a layer of organic and inorganic material and bacteria that
forms at the interface between the trench and the surrounding soil. The biomat enhances treatment efficiency because it
usually slows down the movement of the effluent, provides the flora and fauna necessary to biologically decompose
wastes, and enhances the physical and chemical removal of very small particles of matter in the wastewater. Permeable
soil textures and structures are required to support these processes.
SWISs are occasionally unable to accept the total daily wastewater load they receive, leading to ponding and eventual
hydraulic failure. This is typically caused by the accumulation of biomass and suspended solids in or near the biomat,
which reduces the soil's porosity and hydraulic conductivity. If the system fails hydraulic ally, the first step is usually to
pump the septic tank and clean and replace the effluent screen (also known as a filter).
Restoring the hydraulic function of the infiltration system involves eliminating or reducing the flow restrictions. Various
methods and products have been developed for restoring the infiltration capacity of SWISs. These include resting, addi-
tives, hydrogen peroxide, and soil fracturing.
A variety of additives are also marketed to improve the performance of septic tanks or eliminate the need for pumping.
These septic tank additives are discussed in Special Issue Fact Sheet 1.
SWIS restoration alternatives
Periodic resting
Periodic resting is a passive method for restoring the hydraulic capacity of the SWIS. Infiltration surfaces are "rested" by
removing them from service for an extended period of time, typically 6 to 12 months. To remove a portion of the SWIS
from service requires that the SWIS be constructed with multiple cells that have a total hydraulic capacity of 100 to 200
percent of the design flow, or enough suitable reserve SWIS area. Resting may also be used in seasonal facilities that
discharge no wastewater for extended periods of the year. The portion of the SWIS taken offline receives no wastewater
during the resting period, which allows the infiltration surface to drain and dry out. The resulting aerobic biochemical
oxidation of the biomat mass can restore the porosity of the biomat, helping to unclog the system.
TFS-77
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Several studies have shown resting to be an effective method to rejuvenate the hydraulic capacity of soil infiltration
surfaces (Sharpe et al., 1984). Extended periods of resting at regular intervals is effective in preventing excessive soil
clogging and restoring clogged infiltration surfaces. Seventy to eighty percent of the original infiltration capacity of the soil
can be recovered by resting. The rate of restoration is proportional to grain size; that is, sand restores more quickly than
silt and clay.
Some studies have explored the potential for adding earthworms when a malfunctioning SWIS is pumped. Generally, this
approach has not been successful. If the system is basically sound in design, loaded within design limits, and located in
well-drained soils, some improvement in hydraulic function may occur when worms are used, especially if some water
conservation measures are implemented. However, no quantitative data exist to support the concept that worms aid SWIS
restoration.
Additives
In addition to the additives described in Special Issue Fact Sheet 1, there are commercially available compounds that are
apparently benign to the treatment processes in the septic tank and have potential benefit to the SWIS by exchanging with
potentially harmful ions (e.g., sodium), that could destroy existing fine soil structure. Such additives could be useful in
places having high-sodium drinking water or in areas with hard water supplies where ion exchange softeners are used and
the regenerant is not discharged to the SWIS, leaving those soils with an excess of sodium ions. In general, however, the
benefits of SWIS additives are not well documented. Chemical additives that contain strong acids or bases or toxic
chemicals are generally discouraged or banned because of the possible adverse effects these chemical can have on system
components, the soil structure, or ground water quality. Biological additives, on the other hand, may have some small
benefits, but there is little published documentation to support this view. Microbial and enzyme preparations appear to
enhance liquefaction of biodegradable solids in septic tanks. However, the effects of their use on the soil infiltration surface
have not been documented. Studies have shown that biological additives are not directly harmful to traditional onsite
systems, but significant beneficial impacts have not been documented with domestic wastewaters (Clark, 1999).
Hydrogen peroxide
Hydrogen peroxide (H202) is a chemical treatment that was once promoted for its ability to treat a clogged SWIS. H202, a
strong oxidant, was pumped directly into the absorption trench to restore the hydraulic capacity of the infiltration zone by
oxidizing the biomat and breaking down the crust surrounding it. While early research on the use of hydrogen peroxide to
unclog SWIS in sandy, unstructured soils appeared positive, subsequent testing did not. Controlled field studies found
decreasing infiltration rates for clogged systems treated with H202 These reports suggest that hydrogen peroxide mobilizes
fine soil particles during initial treatment in some soils. As the chemical reactions subside, however, these fine particles are
deposited on top of the infiltrative surface, which can result in further clogging. Hydrogen peroxide can produce tempo-
rary benefits at a substantial cost, and is not recommended for regular long-term use in unclogging failed drainfields.
Hydrogen peroxide is a strong oxidant that has been shown to be very effective in eliminating biomats in SWIS, but it can
also reduce soil porosity and hydraulic conductivity. The process has been shown to oxidize or "boil" the soil, which
creates a layer of fine particles that are released when the soil peds are destroyed on the infiltrative surface. This dramati-
cally reduces the hydraulic capacity of SWIS.
Pneumatic soil fracturing
Pneumatic soil fracturing is a mechanical treatment used to increase soil porosity by fracturing and lifting the soil sur-
rounding the infiltration surface. A steel probe, inserted below the infiltration surface, is used to inject high-pressure air
into the soil. The air fractures and lifts the ground. As the soil expands, polystyrene beads are discharged into the soil
fractures, thereby holding them open to increase the porosity of the soil after the particles settle. However, any hydraulic
improvements are accompanied by a potential for contamination of underlying aquifers. Insufficient data are available to
recommend use of this concept in any area where sensitive ground water supplies lie in close proximity to the infiltrative
surface.
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Introduced in the early 1990s, pneumatic soil fracturing is a relatively new treatment method. Thus, available performance
data on the method are limited and incomplete. Appropriate applications and expected performance are unknown.
Application
These renovation methods can be applied for either preventive maintenance or rehabilitation after a hydraulic failure has
occurred. Resting and the application of additives are primarily preventive maintenance methods. Standby infiltration cells
to allow resting can be constructed with the original system or additional land can be held for replacement if failure of the
original infiltration system fails. It should be noted that the ability to alternate cells regularly during normal operation is
more effective as a preventive maintenance technique than a method to relieve a failed system. The use of additives and
hydrogen peroxide is generally not recommended.
Users must be aware that when any of these methods are used to correct hydraulic failures, only the symptoms of failure
is treated. The causes of the failure will usually persist. Therefore, the causes of failure should be identified and appropri-
ate corrective action taken to prevent recurrences. Excessive daily flows, inadequate or improperly maintained pretreat-
ment processes (e.g., failure to pump septic tank), and changes in wastewater characteristics because of new ownership
or changes in use are common causes of hydraulic failure. If these failures are not eliminated or accommodated through
appropriate system modifications, the effectiveness of the treatments will be short-lived.
Responsibilities of the homeowner
The key responsibilities of the homeowner in ensuring the best operation of an existing or new septic tank/SWIS system
include the following:
• Using household cleansers in moderation. Excessive use of household cleansers, disinfectants, and other common
products can kill bacteria residing in the septic tank and the soil adsorption field. Used in moderate amounts and
according to label directions, however, cleaners and disinfectants can be flushed into the wastewater system with no
significant impacts. The wastewater stream dilutes the product, and organic material adsorbs it. Slug loading (exces-
sive, instantaneous loadings) of household cleaners can be lethal to septic system bacteria, but normal follow-up usage
usually reestablishes the tank's bacterial population within a few hours.
• Avoiding disposal of toxic and hazardous materials in the wastewater stream. Many common household products have
toxic properties and should never be poured down the drain. The list includes drugs and antibiotics, solvents, paints,
varnishes, photography chemicals, weed killers, and insecticides. All of these products have the potential to wipe out
septic system bacteria and percolate into ground water supplies.
• Curbing the use of drain cleaners and openers. Products aimed at unclogging indoor wastewater pipes contain strong
acids or alkalis as the active ingredient. Used according to the label directions, they can be effective in removing clogs
of organic matter in indoor drainpipes. Most product labels warn, however, that the product is caustic or corrosive to
pipes and can be hazardous to the user if applied improperly. A controlled study concluded that as little as 1.3 ounces
of a name brand drain cleaner could destroy the bacteria population in a 1,000-gallon septic tank. This amount is
within the general range of normal usage for some people. Bacteria populations in the tank will recover in a few days if
the system inputs return to normal levels.
• Disposing of solids appropriately. Items such as cigarette butts, condoms, sanitary napkins, paper towels, and kitty
litter should never be flushed or washed down the toilet or sink. Septic tanks are not designed as a disposal receptacle
for these wastes. They can clog drainpipes and cause excessive and rapid sludge buildup in the tank.
• Keeping fats, oils, and grease out of kitchen drains. Fats, oils, and grease are natural by-products of cooking meats
and other foods. Grease washed down the drain can stick, accumulate, and in some cases block wastewater drain
pipes and the inlet and outlet structures in septic tanks. Food wastes should be scraped from plates and utensils and
discarded as solid waste.
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• Avoiding the use of a garbage disposal unless the treatment system is designed for one. Homes with garbage disposals
generally have 20 to 28 percent higher biochemical oxygen demand (BOD) and 25 to 40 percent higher suspended
solid loadings to septic tanks than homes without disposals. These significant contributions of organic matter require
special consideration when sizing and installing a septic tank or soil absorption system.
• Conserving water. To function at peak efficiency, the septic tank needs to provide a quiescent environment and
adequate detention time (i.e., more than 24 hours) for the solids and floatable matter to separate from the wastewater.
Limiting water flows and timely repair of leaking fixtures help maintain these conditions and prevent overloading of the
soil adsorption field.
References
Andress, S., and C. Jordan. 1998. Onsite Sewage Systems. Virginia Polytechnic Institute and State University, Civil
Engineering Department, Blacksburg, VA.
Angoli, T. 2000. Hydrogen peroxide not recommended to unclog failed drainfields. Small Flows Quarterly 1(2):42044.
Clark, G.H. 1999. The Effect of Bacterial Additives on Septic Tank Performance. Master's thesis, North Carolina State
University Department of Soil Science, Raleigh, NC.
Dow, D., and G. Loomis. 1999. Septic Tank Additives. University of Rhode Island Cooperative Extension Service, Onsite
Wastewater Training Center, Kingston, RI.
Gross, M.A. 1987. Assessment of the Effects of Household Chemicals upon Individual Septic Tank Performances.
University of Arkansas, Arkansas Water Resources Research Center, Fayetteville, AR.
Hairston, J.E., G. Speakman, and L. Stribling. 1995. Protecting Water Quality: Understanding Your Septic System and
Water Quality. Alabama Cooperative Extension Publication wq-125.al June 1995. Developed with support from
Auburn University. Auburn University, Auburn, AL.
Hargett, D.L., E.J. Tyler, J.C. Converse, and R.A. Apfel. 1984. Effects of Hydrogen Peroxide as a Chemical Treatment for
Clogged Wastewater Absorption Systems. In Proceedings of the Fourth National Symposium on Individual and Small
Community Sewage Treatment, American Society of Agricultural Engineers, St. Joseph, MI.
Hargett, D.L., E.J. Tyler, and R.L. Siegrist. 1982. Soil Infiltration Capacity as Affected by Septic Tank Effluent Application
Strategies. In Onsite Sewage Treatment, Proceedings of the Third National Symposium on Individual and Small
Community Sewage Treatment. American Society of Agricultural Engineers, St. Joseph, MI.
Jantrania, A., WA. Sack, and V. Earp. 1994. Evaluations of Additives for Improving Septic Tank Operation Under Stress
Condition. In Proceedings of the International Symposium on Individual and Small Community Sewer Systems.
American Society of Agricultural Engineers, St. Joseph, MI.
Olson, K., D. Gustafson, B. Liukkonnen, and V. Cook. 1977. Septic System Owner's Guide. University of Minnesota
Extension Services Publication PC-6583-GO. University of Minnesota, College of Agricultural, Food and
Environmental Sciences, St. Paul, MN.
Rupp, G. 1996. Questions and Answers about Septic System Additives. Montana State University Extension Service.
Bozeman, MT.
Scow, K.M. 1994. The Efficacy and Environmental Impact of Biological Additives to Septic Systems. University of
California, Berkeley, CA.
Sharpe, WE., C.A. Cole, and D.D. Fritton. 1984. Restoration of failing onsite wastewater systems using water
conservation. Journal of the Water Pollution Control Federation 56(7):855-866.
Simons, A.P, and FR. Magdoff. 1979. Disposal of septic tank effluent in mound and sand filter trench systems on a clay
soil. Journal of Environmental Quality 8:469-473.
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Thomas, R.E., et al. 1996. Soil chemical changes and infiltration rate reduction under sewage spreading. In Proceedings of
the Annual Meeting of the Soil Science Society of America, pp. 641-646. Madison, WI.
U.S. Environmental Protection Agency. 1998. A Project to Renovate Failing Gravity Septic Systems with Earthworms.
Section 319 project report. EPA 40-08/98/07/01. U.S. Environmental Protection Agency, Washington, DC.
Virginia Polytechnic Institute and State University. 1996. Septic System Maintenance. Produced by the Water Quality
Program Committee. VTU pub. no. 440-400. Virginia Polytechnic Institute and State University, Blacksburg, VA.
TFS-81
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Onsite Wastewater Treatment Systems
Special Issues Fact Sheet 1
Septic Tank Additives
Description
Because of the presence of significant numbers and types of bacteria, enzymes, yeasts, and other fungi and microorganisms
in typical residential and commercial wastewaters, the use of septic system additives containing these or any other ingredi-
ents is not recommended. The benefits of consumer products sold as septic system cleaners, degraders, decomposers,
deodorizers, organic digesters, or enhancers are not significant or have not been demonstrated conclusively, depending on
the product. Some of these products can actually interfere with treatment processes, affect biological decomposition of
wastes, contribute to system clogging, and contaminate ground water. The septic tank/soil absorption field system is the
most commonly used onsite wastewater treatment system in the United States. It is relatively low in cost, has no moving
parts, and requires little maintenance.
Septic tanks have a number of important functions, including:
• Remove oils, grease and settleable solids. The septic tank is designed to provide quiescent conditions over a sufficient
time period to allow settleable solids to sink to the bottom of the tank and floatable solids, oils, and grease to rise to the
surface. The result is a middle layer of partially clarified effluent that exits the tank to the soil absorption field.
• Store settleable and floatable material. Tanks are generously sized according to projected wastewater flow and
composition to accumulate sludge and scum at the bottom and top of the tank, respectively. Tanks require pumping at
infrequent intervals (e.g., 1 to 7 years), depending on sludge and scum accumulation rates.
• Digest/decompose organic matter. In an anaerobic environment, facultative and anaerobic bacteria can reduce retained
organic molecules to soluble compounds and gases, including H2, C02, NH3, H2S, and CH4. This digestion can signifi-
cantly reduce sludge volume in warm climates.
Types of additives and effects on treatment processes
There are three general types of commonly marketed septic system additives:
• Inorganic compounds, usually strong acids or alkalis, are promoted for their ability to open clogged drains. Product
ingredients (e.g., sulfuric acid, lye) are similar to those used in popular commercial drain cleaners. These products can
adversely affect biological decomposition processes in the treatment system and cause structural damage to pipes,
septic tanks, and other treatment system components. Hydrogen peroxide, once promoted as an infiltration field
reconditioner, has been found to actually degrade soil structure and compromise long-term viability of soil treatment
potential. Its use to unclog failed infiltration fields is no longer recommended.
• Organic solvents, often chlorinated hydrocarbons (e.g., methylene chloride, trichloroethylene) commonly used as
degreasers and marketed for their ability to break down oils and grease. Organic solvents represent significant risks to
ground water and wastewater treatment processes. These products can destroy resident populations of decomposer
and other helpful microorganisms in the treatment system. Use of products containing organic solvents in onsite
treatment systems is banned in many states. Introduction of organic solvents into onsite systems located in states that
ban the use of these products may trigger liability issues if ground water becomes contaminated.
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• Biological additives, like bacteria and extracellular enzymes mixed with surfactants or nutrient solutions, which
mirror but do not appear to significantly enhance normal biological decomposition processes in the septic tank. Some
biological additives have been found to degrade or dissipate septic tank scum and sludge. However, whether this
relatively minor benefit is derived without compromising long-term viability of the soil infiltration system has not
been demonstrated conclusively. Some studies suggest that material degraded by additives in the tank contributes to
increased loadings of BOD, TSS, and other contaminants in the otherwise clarified septic tank effluent.
Other products containing formaldehyde, paraformaldehyde, quaternary ammonia, and zinc sulfate are advertised to
control septic odors by killing bacteria. This objective, however, runs counter to the purpose and function of septic tanks
(promoting anaerobic bacterial growth). If odor is a problem, the source should be investigated because sewage may be
surfacing, a line might have ruptured, or another system problem might be present.
Another variety of consumer products is marketed for their ability to remove phosphorus from wastewater. These prod-
ucts are targeted at watershed residents who are experiencing eutrophication problems in nearby lakes and streams.
Phosphorus is an essential nutrient for aquatic plant growth and limiting its input to inland surface waters can help curtail
nuisance algae blooms. Aluminum (as alum, sodium aluminate, aluminum chloride, and activated alumna), ferric iron (as
ferric chloride and ferric sulfate), ferrous iron (as ferrous sulfate and ferrous chloride), and calcium (as lime) have been
proven to be effective in stripping phosphorus from effluent and settling it to the bottom of the tank. An important side
effect of this form of treatment, however, can be the destruction of the microbial population in the septic tank due to loss
of buffering capacity and a subsequent drop in pH. Treatment processes can be severely compromised under this sce-
nario.
Finally, baking soda and other flocculants are marketed as products that lower the concentration of suspended solids in
septic tank effluent. Theoretically, flocculation and settling of suspended solids would result in cleaner effluent discharges
to the subsurface wastewater infiltration system. However, research has not conclusively demonstrated significant success
in this regard.
References
Andress, S.; Jordan, C. 1998. Onsite Sewage Systems. Virginia Polytechnic Institute and State University, Civil
Engineering Department, Blacksburg, VA.
Angoli, T. 2000. Hydrogen peroxide not recommended to unclog failed drainfields. Small Flows Quarterly Vol. 1 No. 2, p.
42-44.
Clark, G.H. 1999. The Effect of Bacterial Additives on Septic Tank Performance. Master's thesis, North Carolina State
University, Department of Soil Science, Raleigh, NC.
Dow, D., and G. Loomis. 1999. Septic Tank Additives. University of Rhode Island Cooperative Extension Service Onsite
Wastewater Training Center, Kingston, RI.
Hairston, J.E., G. Speakman, and L. Stribling. 1995. Protecting Water Quality: Understanding Your Septic System and
Water Quality. Alabama Cooperative Extension Publication wq-125.al, June 1995. Developed with support from
Auburn University, Auburn, AL.
Olson, K., D. Gustafson; B. Liukkonen; and V Cook. 1977. Septic System Owner's Guide. University of Minnesota
Extension Services Publication PC-6583-GO. University of Minnesota, College of Agricultural, Food, and
Environmental Sciences, St.Paul, MN.
Rupp, G. 1996. Questions and Answers About Septic System Additives. Montana State University Extension Service,
Bozeman, MT.
Virginia Polytechnic Institute and State University (Virginia Tech). 1996. Septic System Maintenance. VTU publication
no. 440-400, October 1996. Water Quality Program Committee, Virginia Polytechnic Institute and State University,
Blacksburg, VA.
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Onsite Wastewater Treatment Systems
Special Issues Fact Sheet 2
High-Organic-Strength Wastewaters
(Including Garbage Grinders)
Description
Because many onsite treatment alternatives are sensitive to organic loading rate, high-strength wastewaters may require
additional treatment steps to ultimately meet environmental discharge or reuse goals. Among the individual home options
that increase the organic strength of the wastewater (see chapter 3) are water conservation and use of garbage grinders
(disposals). Commercial wastewater may also be high in organic concentration and, thus, organic loading. The database on
such wastewaters is extremely limited for use in design of OWTSs.
The major concern caused by high organic loadings in the pretreated wastewater is higher organic loadings (e.g., BOD) to
the infiltrative surface of the SWIS, which could result in clogging. A certain degree of clogging at the interface of
infiltration trenches and the surrounding soil is expected and helps the soil absorption field function properly. The clogging
layer, or biomat, which forms at this interface, is composed of organic material, trapped colloidal matter, bacteria, and
microorganisms and their by-products. The biomat may slow the infiltrative capacity of the SWIS, but it increases effluent
treatment time under unsaturated aerobic conditions (in the vadose zone below the trenches).
Physical clogging occurs when solid material such as grit, organic material, and grease is carried in the effluent beyond the
septic tank to the soil adsorption field and deposited on the biomat. Biological clogging generally occurs with excessive
organic loading to the biomat, which results in excess microbial growth that restricts the passage of effluent into the soil.
Slimes, sugars, ferrous sulfide, and the precipitation of metals such as iron and manganese are additional clogging by-
products. Chemical clogging can occur in clayey soils when high concentrations of sodium ions exchange with calcium
and magnesium ions in the clay. The soil loses its structure and becomes tighter and more impervious.
Garbage disposals
Garbage disposals, which have become a standard appliance in many residential kitchens in the United States, contribute
excessive organic loadings to the infiltrative field and other system components. Usually installed under the kitchen sink,
disposals are basically motorized grinders designed to shred food scraps, vegetable peelings and cuttings, bones, and other
food wastes to allow them to flow through drain pipes and into the wastewater treatment system. Disposing of food waste
in this manner eliminates the nuisance of an odor of food wastes decaying in a trashcan by moving this waste to the
wastewater stream. Many states accommodate these appliances by prescribing additional septic tank volume, service
requirements, or other stipulations (e.g., septic tank effluent filter, multiple tanks, larger infiltration field) that address
higher BOD and TSS loadings.
Table 1 contains reported information that illustrates that in-sink garbage disposal units increase septic tank loadings of
BOD by 20 to 65 percent, suspended solids by 40 to 90 percent, and fats, oils, and grease by 70 to 150 percent. For any
septic system, the installation of a disposal causes a more rapid buildup of the scum and sludge layers in the septic tank
and an increased risk of clogging in the soil adsorption field due to higher concentrations of suspended solids in the
effluent. Also, it means that septic tank volumes should be increased or tanks should be pumped more frequently.
SIFS-3
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Table 1. Increase in pollutant loading caused by addition of garbage disposal
Parameter Increase in
Karameier pollutant loading (%)
Suspended solids
Biochemical oxygen demand
Total nitrogen
Total phosphorus
Fats, oils, and grease
40-90
20-65
3-10
2-3
70-150
Sources: Hazeltine, 1951; Rawn, 1951; Univ. of Wisconsin, 1978; USEPA, 1992.
Eliminating the use of garbage disposals will significantly reduce the amount of grease, suspended solids, and BOD in
wastewater (see table 1). Elimination of garbage disposal use reduces the rate of sludge and scum accumulation in the
septic tank, thus reducing the frequency of required pumping. All of these can improve wastewater system performance.
For system owners who choose to use garbage grinders, manufacturers recommend grinding wastes with a moderate
flow of cold water. No research data representing claims of enhanced performance of garbage grinders equipped with
septic system additive injectors are available. Additives are not required nor recommended for onsite system operation, and
some might actually interfere with treatment, damage the drainfield, or contaminate ground water below the drainfield.
(See Special Issues Fact Sheet 1.)
The most common unsewered commercial sources that exhibit high organic strength are restaurants, although a variety of
commercial sources produce such wastewaters. These include other facilities with food service capability and dairy
product/processing plants. The preprocessing required to remove the source of excessive organic strength is a function of
(1) the fractionation of the organic content (settleable, supra-colloidal, colloidal, or soluble); (2) the site characteristics;
and (3) the final steps in OWTS processing and the environmental introduction method.
Typical Applications
Additional pretreatment is typically required before discharge to a SWIS or surface water. There are some proprietary
aerobic units that are designed to accept high organic loads, and greatly increase the potential for odors and, where
concrete structures are employed, corrosion. Therefore, odor protection becomes a major issue for the designer in these
situations. These units are usually a combination of suspended growth/fixed growth or enhanced Continuous-Flow,
Suspended Growth Aerobic Systems (CFSGAS; see Technology Fact Sheet 1). Alternatively, anaerobic upflow filters
(UAFs) and other anaerobic proprietary and nonproprietary systems can also "thin" excess organics to permit normal
loading to these final processing steps.
The Safe Drinking Water Act (SDWA) underground injection systems (UIC) Title V Rule, which is discussed in chapter 1,
is designed to eliminate some of these problem wastewater sources of potential ground water contamination (e.g., auto
repair facilities) from further consideration for SWIS disposal.
Design
For domestic systems the additional organic and oil/grease concentrations resulting from use of a garbage grinder usually
does not in itself cause the wastewater to require additional processing as described above, but the designer should at least
calculate any potential design changes that might be required by the increased strength. For example, for a sandy soil, the
SIFS-4
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bottom area hydraulic loading rate could be crosschecked against the limiting organic loading rate limits cited in table 4-2.
Most state codes require a septic tank size increase to account for the additional volume of sludge and scum accumulating
in a septic tank but offer no advice as to any increasing field size.
For restaurants, facilities with food preparation, and other producers of high-organic wastewaters, the designer must
evaluate alternative pretreatment schemes that can reduce the excess organics (and sometimes other constituents) to levels
that allow subsequent processes to function normally and achieve surface water effluent discharge or reuse standards, if
applicable.
An analysis of organic waste sources and waste characteristics (particulate/soluble fractions) is required to determine the
best pretreatment approach. On the latter issue, if the majority was coming from a highly concentrated, low-volume source
in the facility, a holding tank/hauling solution may be most cost-effective choice. The fraction that contains the majority
of the excess contaminants might be readily removable by a specific process (e.g., soluble and biodegradable (aerobic unit)
versus supracolloidal and removable by flocculation/sedimentation (vegetated submerged bed or anaerobic upflow filter).
Performance
The performance of these pretreatment devices is discussed in other fact sheets. Influent concentrations which still exceed
normal loading rates can be accommodated by increasing the size or other key basis of computing loading rate or by
investigating and implementating pollution prevention measures to reduce the source concentration of the constituent of
concern (e.g., BOD).
The reliability of anaerobic processes is highly temperature-dependent, thus requiring heating in northern climates. How-
ever short-term anaerobic upflow filters and vegetated submerged beds are less sensitive because of their primary reliance
on physical processes. Aerobic treatment processes are also temperature-sensitive, but less so than anaerobic processes.
There is little documented, quality-assured information on the performance of small alternative systems that treat high-
organic strength wastewater. However, well-managed aerobic units, upflow filters, and vegetated submerged beds are
known to perform reliably.
Management needs
Management needs are the same as those noted in the unit process fact sheets.
Risk management issues
Depending on the sequence of processes chosen, the impacts of flow variation, toxic shocks, extreme temperatures, and
power outages may cause significant variations from expected treatment performance. However, high-strength wastewa-
ters greatly increase the potential for odors and, where concrete structures are employed, corrosion. Therefore, protection
from odor becomes a major issue for the designer in these situations.
Costs
Costs of treatment trains for high-organic-strength wastewaters can be estimated from the costs of the unit process
components.
References
Andress, S., and C. Jordan. 1998. Onsite Sewage Systems. Virginia Polytechnic Institute and State University, Department
of Civil Engineering, Blacksburg, VA.
Hazeltine, T.R. 1951. Addition of garbage to sewage. Water & Sewage Works, pp. 151-154. Annual compilation, 1951.
S1FS-5
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Jensen, P.D., and R.L. Siegrist. 1991. Integrated Loading Rate Determination for Wastewater Infiltration System Sizing.
In Proceedings of Sixth Onsite Wastewater Treatment Symposium. American Society of Agricultural Engineers, St.
Joseph, MI.
Mancl, K.M. 1998. Septic Tank Maintenance. Ohio State University Extension publication AEX-740-98. Ohio State
University, Food, Agricultural and Biological Engineering, Columbus, OH
Rawn, A.M. 1951. Some effects of home garbage grinding upon domestic sewage. American City, March, pp. 110-111.
Siegrist, R.L. 1987. Hydraulic Loading Rates for Soil Absorption Systems Based on Wastewater Quality. In Proceedings
of the Fifth Onsite Wastewater Treatment Symposium. American Society of Agricultural Engineers, St. Joseph, MI.
Siegrist, R.L., D.L. Anderson, and J.C. Convene. 1984. Commercial Wastewater Onsite Treatment Symposium. American
Society of Agricultural Engineers, St. Joseph, MI.
Stuth, W.L. 1992. Treating Commercial High-Strength Waste. In Proceedings of Seventh Northwest On-Site Wastewater
Treatment Short Course. University of Washington, Seattle, WA.
Tyler, E.J., and J.C. Converse. 1994. Soil Acceptance of Onsite Wastewater as Affected by Soil Morphology and
Wastewater Quality. In Proceedings of Seventh Onsite Wastewater Treatment Symposium. American Society of
Agricultural Engineers, St. Joseph, MI.
University of Wisconsin. 1978. Management of Small Waste Flows. USEPA 600/2-78-73. September, 1978. U.S.
Environmental Protection Agency, Office of Research and Development, Cincinnati, OH.
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Onsite Wastewater Treatment Systems
Special Issues Fact Sheet 3
Water Softeners
Description
Home water softeners, which periodically generate a backwash that is high in sodium, magnesium, and calcium concentra-
tions, can affect wastewater treatment processes and the composition and structure of the infiltration field biomat and the
underlying soil. However, attempts to predict whether impacts will occur and to estimate their severity are difficult and
often inconclusive.
Water softeners remove "hardness" (dissolved calcium and magnesium) through ion exchange processes. Incoming hard
water passes through a tank of containing high-capacity ion exchange resin beads supersaturated with sodium. The
calcium and magnesium ions in the water attach to the resin beads, replacing the sodium, which is released into the water.
The softened water is then distributed for use throughout the house.
Over time, the ion exchange resin beads become saturated with calcium and magnesium ions. When this occurs, the tank
must be recharged by flushing with a salt brine solution. Sodium ions reclaim their position on the resin beads, and the
calcium and magnesium ions are released into the backwash water. The backwash water then exits the tank and is dis-
charged to the wastewater treatment system. The number of times the tank is recharged and the amount of wastewater
generated depends on a number of factors, including the hardness of the water, the amount of water used, the size of the
water softener, and the capacity of the resins to remove calcium and magnesium.
The wastewater generated during the recharge phase of the water softening process mixes with other household wastewa-
ters, enters the septic tank, and eventually moves to the soil adsorption field. Studies conducted by soil scientists at the
University of Wisconsin and the National Sanitation Foundation conclude that the wastewater effluent generated from
properly operating and maintained water softeners will not harm onsite systems that are designed, operated, and maintained
appropriately. Specifically, the studies conclude the following:
• High concentrations of calcium and manganese in the softener backwash water have no deleterious effect on the
biological functions occurring in the septic tank and may, in some cases, be helpful.
• The additional volume of wastewater generated (typically about 50 gallons per recharge cycle) is added slowly to the
wastewater stream and does not cause any hydraulic overload problems.
• Soil structure in the soil absorption field is positively affected by the calcium and mangnesium ions in water softener
effluent (Corey et al., 1977).
Regarding the last conclusion, some people have the misconception that the salt brine that enters the ion exchange tank
also exits the tank as wastewater. In fact, the influent with its high concentration of sodium ions is very different than the
effluent, which has a high concentration of calcium and magnesium ions. Consequently, the potential for chemical clog-
ging of clayey soil by sodium ions is reduced. The calcium and magnesium input may even help improve soil percolation.
Risk management issues
The human health impacts of ingesting softened water are increasingly discussed in addition to the traditional benefits of
reduced use of surfactants and plumbing repair requirements. The choice of the homeowner to soften or not to soften will
SIFS-7
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factor into all arguments. Also, the preceding descriptions are predicated on whole-house-supply softening. Today point-
of-use devices designed for use with specific features in the house make the traditional advantages and disadvantages less
clear.
References
Andress, S., and C. Jordan. 1998. Onsite Sewage Systems. Virginia Polytechnic Institute and State University, Civil
Engineering Department, Blacksburg, VA.
Corey, R.B., E.S. Tyler, and M.U. Olotu. 1997. Effects of Water Softner Use on the Permeability of Septic Tank Seepage
Fields. In Proceedings of Second National Home Sewage Treatment Symposium. Pub. no. 5-77. American Society of
Agricultural Engineers, St. Joseph, MI.
Mancl, K.M. 1998. Septic Tank Maintenance. Ohio State University Extension publication AEX-740-98. Ohio State
University, Food, Agricultural and Biological Engineering. Columbus, OH.
University of Wisconsin. 1978. Management of Small Waste Flows. EPA-600/2-78-173. U.S. Environmental Protection
Agency, Cincinnati, OH.
U.S. Environmental Protection Agency (USEPA). 1992. Manual: Wastewater Treatment/Disposal for Small Communities.
EPA 625/R-92/005. U.S. Environmental Protection Agency, Cincinnati, OH.
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Onsite Wastewater Treatment Systems
Special Issues Fact Sheet 4
Holding Tanks and Hauling Systems
Description
A holding tank or vault receives wastewater from a home or commercial establishment and stores it until it is pumped out
and hauled to a receiving/processing facility. Although similar to septic tanks, vaults have no outlet piping and must be
watertight. The volume can range from 1,000 gallons to 4,000 gallons or more. The vault should be equipped with an
audible and visible high-water alarm, which alters the resident to the need for pumping.
Different sizes of vaults and tank trucks can be used; water conservation can reduce costs considerably by reducing the
frequency of pumping. A vault can be equipped with a standpipe and a quick disconnect to which the pumping truck can
be directly connected for efficient (minimal spillage) emptying of the vault.
Holding tanks can be used for the entire wastewater flow in cases where conventional and typical alternative systems are
not feasible. They are often used this way for seasonal homes in sensitive environmental settings. Holding tanks can also
be used to collect only a part of the wastewater flow. Usually, they are used to collect the greywater when non-water-
carriage toilets are employed in sensitive areas. This option permits a significant reduction (usually one-third or more) in
the number of tank pumpings as compared to the whole wastewater collection option. Another holding tank option is to
collect only the blackwater fraction of the wastewater while the graywater is treated in an OWTS. This option is most
popular in estuarine areas where significant nitrogen removal is required because the blackwater may contain from 70 to
90 percent of the total nitrogen load. In this case the reduction in pumping frequency from the whole wastewater option
would be about two-thirds.
Over and above these combinations a program to reduce water use can be overlaid. The critical contribution of such a
program (see chapter 3) is to reduce the daily volume of wastewater (blackwater, graywater, or combined) produced and
the required frequency of holding tank pumping. Some onsite wastewater recycling can be added to this program in arid
regions where gravity feed and belowground watering of nonconsumable vegetation can be accomplished. However, such a
program must meet all local public health requirements.
Applications
Pump and haul collection is best used when soil absorption fields do not work (for example, where bedrock or ground
water levels are near the ground surface) and there is no sewer system. Typical applications are second homes, where
annual occupancy may be only a few days to a few months; where a nuisance or public health hazard must be abated;
where an isolated building has no running water; in temporary structures or gathering places; or where nutrients must be
excluded from ground water to protect environmentally sensitive areas. Pump and haul collection may also simply be the
least expensive alternative in some places.
Pump and haul systems are viable only under a wastewater authority that guarantees service. Pump and haul collection can
became prohibitively expensive when homes are occupied all the time or where the distance from the treatment plant to
the home is more than a few miles.
SIFS-9
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Management needs
Holding tanks should be used only where a proper management program is in place. Construction requirement are essen-
tially the same as for a septic tank in that the onsite testing for tank leakage is vital to a successful design and the alarm
system must be dredged for proper functioning before acceptance.
In addition to timely pumping, operation and maintenance requirements should include checking the alarm function,
cleaning the activation floats, and comparing volume used vs. volume accumulated in the tank. The skill requirements at
the site are minimal and can be estimated as approximately 1 hour per pumping. There are normally no energy require-
ments; the residuals are the tank contents, and confined-space entry safety requirements must be followed if tank entry is
required.
Risk management issues
Holding tanks are not subject to upset by flow variation, toxic loads or power outages. They should be insulated and
possibly heat-treated in extremely cold climates. If properly vented through the building sewer, they should not exhibit
odor problems, but use in hot climates may require an increase in pumping frequency or a regular addition of lime for
mitigation. There is a release of objectionable odors during tank pumping, which can cause some discomfort to residents.
Costs
More recent cost estimates for holding tank-hauling wastewater disposal indicate that tank installation is about $1 per
gallon of capacity (up to 5,000 gallons) while the alarm system is about $400.
Tank pumping is generally in range of 10 to 30 cents per gallon, to which labor, travel and equipment amortization may
be added (or these costs may be included in a flat fee). Travel costs will dominate if the round-trip distance to the holding
tank, to the disposal site, and back to home base exceeds 50 miles. The permit costs to discharge at an appointed sit
(treatment plant, land spreading site, or independent treatment facility) is also escalated, multiple pumping from a year-
round house can become extremely expensive.
References
Anderson, C.D. 1986 Trucked Collection Systems Experience in the Northwest Territories. In Proceedings of Appropriate
Wastewater Management Technologies for Rural Areas Under Adverse Conditions. Technical University of Nova
Scotia, Halifax, NS.
Burrows, R., and N. Bouwes. The Cost of Holding Tanks for Domestic Wastewater. Small Scale Waste Management
Report. University of Wisconsin, Madison, WI.
Dix, S.P. Case Study Number 4: Crystal Lakes, Colorado. National Small Wastewater Flows Clearinghouse, West Virginia
University, Morgantown, WV.
Mahoney, W.D., ed.-in-chief. 1989. Means Site Work Cost Data. R.S. Means Co., Kingston, MA.
Mahoney, W.D., ed.-in-chief. 1990. Means Site Work Cost Data. R.S. Means Co., Kingston, MA.
Manci, K. No date. Wastewater Treatment Alternatives... Holding Tanks. The Pennsylvania State University, College of
Agriculture, Cooperative Extension Service, University Park, PA.
Mooers, J.D., and D.H. Waller. 1996. Onsite Wastewater Research Program: Phase III. TUNS/Centre for Water Research
Study, Halifax, NS.
National Association of Waste Transporters (NAWT). 1998. Introduction to Proper Onsite Sewage Treatment. National
Association of Waste Transporters, Scandia, MN.
SIFS-10
-------
U.S. Environmental Protection Agency (USEPA). 1984. Final Generic Environmental Impact Statement: Wastewater
Management in Rural Lake Areas. U.S. Environmental Protection Agency, Region 5, Chicago, IL.
Waller D.H., and A.R. Townshend. 1987. Appropriate Wastewater Management Technologies for Rural Areas Under
Adverse Conditions. Special Publication, Technical University of Nova Scotia, Halifax, NS.
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Chapter 5: Treatment System Selection
Chapter 5:
Treatment System Selection
5.1 Introduction
5.2 Design conditions and system selection
5.3 Matching design conditions to system performance
5.4 Design boundaries and boundary loadings
5.5 Evaluating the receiving environment
5.6 Mapping the site
5.7 Developing the initial system design
5.8 Rehabilitating and upgrading existing systems
5.1 Introduction
Selecting the appropriate system type, size, and
location at the site depends on the wastewater flow
and composition information discussed in chap-
ter 3, site- and landscape-level assessments out-
lined in chapter 3 and in this chapter, performance
requirements as noted in chapter 3, and the array of
available technology options reviewed in chapter 4.
Key to selecting, sizing, and siting the system are
identifying the desired level of performance and
ensuring that the effluent quality at the perfor-
mance boundaries meets the expected performance
requirements.
5.2 Design conditions and system
selection
An appropriate onsite wastewater treatment system
concept for a given receiver site—proposed
location of the system, regional geologic and
hydrologic features, and downgradient soils used
for treatment—depends on the prevailing design
conditions. Designers must consider and evaluate
the design conditions carefully before selecting a
system concept. Design conditions include the
characteristics of the wastewater to be treated,
regulatory requirements, and the characteristics of
the receiver site (figure 5-1). With sufficient
knowledge of these factors, the designer can
develop an effective preliminary design concept.
This chapter focuses on general guidance for
evaluation of the receiver site, identification of the
site's design boundaries and requirements, and
selection of suitable designs to meet the perfor-
mance requirements. This chapter also provides
guidance for evaluating and rehabilitating systems
that are not meeting their performance requirements.
5.3 Matching design conditions to
system performance
Design conditions include wastewater characteristics;
system owner preferences for siting, operation and
maintenance, and cost; regulatory requirements
prescribed by the permitting agency's rules; and the
receiver site's capability to treat or otherwise
assimilate the waste discharge. Each of these must
be evaluated in light of the others before an appro-
priate system design concept can be developed.
5.3.1 Wastewater source considerations
Wastewater source considerations include projec-
tions of wastewater flow, wastewater composition,
and owner requirements. Chapter 3 provides
guidance for estimating flow and waste strength
characteristics. The owner's needs, capabilities, and
expectations might be explicit or implied. The first
consideration is the owner's use of the property
(present and projected), which informs analyses of
the character and volume of the wastewater gener-
ated. The footprint and location of existing or
planned buildings, paved areas, swimming pools,
and other structures or uses will limit the area
available for the onsite system. Second, the owner's
concern for the system's visual impact or odor
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Chapter 5: Treatment System Selection
Figure 5-1. Preliminary design steps and considerations.
WASTEWATER
SOURCE
SOURCE CHARACTERIZATION
Current and Future Use
Wastewater Flow Projections
• Daily min, average, max flow
• Temporal variations
Wastewater Pollutants
• Type
• Concentration
Owner Requirements
• Location and aesthetics
• O&M requirements
• Total and annual costs
REGULATORY
REQUIREMENTS
Treatment Requirements
• Effluent limits
• Unit processes required
Design Requirements
• Siting requirements
• Production/material approval
• Design parameters
• Submission requirements
Permit Requirements
• Construction
• Operation and monitoring
RECEIVER SITE EVALUATION
Ground Water Discharge
• Topography
• Soils
• Geology
• Ground water
Surface Water Discharge
• Stream flow
• Outfall locations
Atmospheric Discharge
• Monthly net evaporation and annual
water balance
PRELIMINARY DESIGN
Receiving Environment Selection
Design Boundary Loadings
• Mass loadings
• Concentration limits
Treatment Train Screening
• Unit processes
• Process sequence
Treatment Train Selection
Concept Design
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Chapter 5: Treatment System Selection
potential might restrict the range of alternatives
available to the designer. Third, the owner's ability
and willingness to perform operation and mainte-
nance tasks could limit the range of treatment
alternatives. Finally, costs are a critical concern for
the owner. Capital (construction) costs and recur-
ring (operation and maintenance) costs should be
estimated, and total costs over time should be
calculated if cost comparisons between alternative
systems are necessary. The owner should have both
the ability and willingness to pay construction and
operation and maintenance costs if the system is to
perform satisfactorily.
5.3.2 Regulatory requirements
Designs must comply with the rules and regulations
of the permitting entity. Onsite wastewater systems
are regulated by a variety of agencies in the United
States. At the state level, rules may be enacted as
public health codes, nuisance codes, environmental
protection codes, or building codes. In most (but
not all) states, the regulatory authority for onsite
single-family residential or small cluster systems is
delegated to counties or other local jurisdictions.
The state might enact a uniform code requirement
that all local jurisdictions must enforce equally, or
the state might have a minimum code that local
jurisdictions may adopt directly or revise to be
stricter. In a few states, general guidance rather
than prescriptive requirements is provided to local
jurisdictions. In such cases, the local jurisdictions
may enact more or less strict regulations or choose
not to adopt any specific onsite system ordinance.
Traditionally, state and local rules have been
prescriptive codes that require specific system
designs for a set of specific site criteria. Such rules
typically require that treated wastewater discharged
to the soil be maintained below the surface of the
ground, though a few states and local jurisdictions
do allow discharges to surface waters under their
National Pollutant Discharge Elimination System
(NPDES) permitting programs, as authorized by the
federal Clean Water Act. If applications are pro-
posed outside the prescriptive rules, the agency
usually requires special approvals or variances
before a permit can be issued. Circumstances that
require special action (approvals, variances) and
administrative processes for approving those
actions are usually specified in state or local codes.
5.3.3 Receiver site suitability
The physical characteristics of the site (the location
of the proposed system, regional geologic and
hydrologic features, and the soils to be used in the
treatment process) determine the performance
requirements and treatment needs. A careful and
thorough site evaluation is necessary to assess the
capacity of the site to treat and assimilate effluent
discharges. Treatment requirements for a proposed
system are based on the performance boundary
requirements established by rule and the natural
design boundaries identified through the site
evaluation.
5.4 Design boundaries and
boundary loadings
Wastewater system design must focus on the
critical design boundaries: between system compo-
nents, system/soil interfaces, soil layer and prop-
erty boundaries, or other places where design
conditions abruptly change (see figures 5-2 and
5-3). System failures occur at design boundaries
because they are sensitive to hydraulic and mass
pollutant loadings. Exceeding the mass loading
limit of a sensitive design boundary usually results
in system failure. Therefore, all critical design
boundaries must be identified and the mass load-
ings to each carefully considered to properly select
the upstream performance and design requirements
needed to prevent system failure (Otis, 1999).
The approach discussed in this chapter is based on
characterizing the assimilative capacity of the
receiving environment (ground water, surface
water) and establishing onsite system performance
requirements that protect human health and eco-
logical resources. Desired system performance, as
measured at the final discharge point (after treat-
ment in the soil matrix or other treatment train
components), provides a starting point for consid-
ering performance requirements for each preceding
system component at each design boundary (e.g.,
septic tank-SWIS interface, biomat at the infiltra-
tive surface, surface of the saturated zone).
Through this approach, system designers can
determine treatment or performance requirements
for each component of the treatment train by
assessing whether each proposed component can
meet performance requirements (acceptable mass
loading limits) at each subsequent design boundary.
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Chapter 5: Treatment System Selection
Source: Ayres Associates, 2000.
Figure 5-2. Performance (design) boundaries associated with
onsite treatment systems. ,
Determining the critical design boundaries 01 the
physical environment is the primary objective of
the site evaluation (see section 5.5). Design bound-
aries are physical planes or points, or they may be
defined by rule. More than one design boundary
can be expected in every system, but not all of the
identified boundaries are likely to control design.
The most obvious design boundaries are those to
which performance requirements are applied
(figure 5-2). These are defined boundaries that
might or might not coincide with a physical
boundary. For a ground water discharge, the design
boundary might be the water table surface, the
property line, or a drinking water well. For surface
water discharges the performance boundary is
typically designated at the outfall to the receiving
waters, where permit limits on effluent contami-
nants are applied. Physical boundaries are particu-
larly significant for conventional wastewater
treatment systems that discharge to ground water or
to the atmosphere. Soil infiltrative surfaces,
hydraulically restrictive soil horizons, or zones of
saturation are often the critical design boundaries
for ground water discharging systems.
The site evaluation must be sufficiently thorough to
identify all potential design boundaries that might
affect system design. Usually, the critical design
boundaries are obvious for surface water discharg-
ing and evaporation systems. Design boundaries for
subsurface wastewater infiltration systems, how-
ever, are more difficult to identify because they
occur in the soil profile and there might be more
than one critical design boundary.
5.4.1 Subsurface infiltration system
design boundaries and loadings
Subsurface wastewater infiltration systems (SWISs)
have traditionally been used to treat and discharge
effluent from residences, commercial buildings,
and other facilities not connected to centralized
sewage treatment plants. These systems accept and
treat wastewater discharged from one or more
septic tanks in below-grade perforated piping,
which is usually installed in moderately shallow
trenches 1.5 to 3.0 feet deep on a bed of crushed
rock 0.5 to 1.5 inches in diameter. Leaching
chambers, leach beds, and other SWIS technologies
have also been approved for use in some states.
Both the trench bottoms and sidewalls provide
infiltrative surfaces for development of the biomat
(see chapter 3) and percolation of treated wastewa-
ter to the surrounding soil matrix.
The soil functions as a biological, physical, and
chemical treatment medium for the wastewater, as
well as a porous medium to disperse the wastewater in
the receiving environment as it percolates to the
ground water. Therefore, the site evaluation must
determine the capacity of the soil to hydraulically
accept and treat the expected daily mass loadings of
wastewater. Site and soil characteristics must provide
adequate drainage of the saturated zone to maintain
the necessary unsaturated depth below the infiltrative
surface, allow oxygenation of aerobic biota in the
biomat and reaeration of the subsoil, and prevent
effluent surfacing at downgradient locations.
Traditional site evaluation and design procedures
consider only the infiltrative surface of the SWIS as a
design boundary (figure 5-3). Hydraulic loading
rates to this boundary are usually estimated from
percolation tests and/or soil profile analyses. The
recommended daily hydraulic loading rates typically
assume septic tank effluent is to be applied to the soil
(through the SWIS biomat, across the trench bottom/
sidewall soil interface, and into the surrounding soil).
The estimated daily wastewater volume is divided by
the applicable hydraulic loading rate to calculate the
needed infiltration surface area. This method of
design has endured since Henry Ryon first proposed
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Chapter 5: Treatment System Selection
Figure 5-3. Subsurface wastewater infiltration system design/performance boundaries.
Natural
Geotextile
Distribution pipe
\X\\\\\\
Design boundary
Infiltration zone and biomat
• Vadose zone (unsaturated)
"Perched" saturated zone
Design boundary*
Restrictive horizon*
Capillary
Design boundary
Groundwater surface
Saturated
* If present
Source: Adapted from Ayres Associates, 1993.
the percolation test and its empirical relationship to
infiltration system size nearly 100 years ago
(Fredrick, 1948). Although this method of design
has been reasonably successful, hydraulic and
treatment failures still occur because focusing on
the infiltrative surface overlooks other important
design boundaries. Identifying those critical
boundaries and assessing their impacts on SWIS
design will substantially reduce the number and
frequency of failures.
Usually there is more than one critical design
boundary for a SWIS. Zones where free water or
saturated soil conditions are expected to occur
above or below unsaturated zones identify perfor-
mance boundary layers (Otis, 2001). In SWISs,
these include
• The infiltrative surfaces where the wastewater
first contacts the soil.
• Secondary infiltration surfaces that cause
percolating wastewater to perch above an
unsaturated zone created by changes in soil
texture, structure, consistency, or bulk density.
• The ground water table surface, which the
percolating wastewater must enter without
excessive ground water mounding or degrada-
tion of ground water quality.
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Chapter 5: Treatment System Selection
The infiltrative surface is a critical design and
performance boundary in all SWISs since free
water enters the soil and changes to water under
tension (at pressures less than atmospheric) in the
unsaturated zone. Many wastewater quality trans-
formations occur at this boundary. For example,
biochemical activity usually causes a hydraulically
restrictive biomat to form at the infiltrative surface.
Failure to consider the infiltrative surface in system
design and to accommodate the changes that occur
there can lead to hydraulic or treatment failure.
Other surfaces that are often critical design bound-
aries include those associated with hydraulically
restrictive zones below the infiltrative surface that
can cause water to perch. If hydraulic loadings are
too great for these boundaries, surface seepage
might occur at downslope locations as effluent
slides along the perched boundary. Also, the
saturated zone could mound to encroach on the
unsaturated zone to the extent that sufficient
reaeration of the soil does not occur, which can
result in severe soil clogging. If hydraulic problems
do not occur, these conditions offer some treatment
advantages. For example, denitrification is aided
when saturation results in anaerobic conditions in
interstices in the normally unsaturated zones.
Perched or otherwise layered boundaries require
careful characterization, analysis, and assessment of
system operation to determine how they will affect
the movement of effluent plumes from the SWIS.
The water table surface is where treatment is usually
expected to be complete, that is, where pollutant
loadings, with proper mixing and dispersion, should
not create concentrations in excess of water quality
standards. System designers should seek to ensure
that hydraulic loadings from the system(s) to the
ground water will not exceed the aquifer's capacity
to drain water from the site. If a SWIS is to perform
properly, the mass loadings to the critical design
boundaries must be carefully considered and incorpo-
rated into the design of the system. The types of
mass loadings that should be considered in SWIS
design are presented in table 5-1.
The various design boundaries are affected differ-
ently by different types of mass loadings (table 5-2).
Table 5-1. Types of mass loadings to subsurface wastewater infiltration systems.
Mass loading type Units
Typical loading rates
Hydraulic
• Daily
• Instantaneous
Volume per day per unit area of
boundary surface
Volume per dose per unit area of
boundary surface
Septic tank effluent:
0.15-1 .Ogpd/ft2 (0.6-4.0 cm/d)
Secondary effluent:
0.15-> 2.0 gpd/ft2(0.6->8.0 cm/d)
1/24-1/8 of the average daily
wastewater volume
Contour (Linear)
Constituent
• Organic
Volume per day per unit length of
boundary surface contour (which can be a
critical design parameter in areas with high
water tables)
Mass of BOD per day per unit area of
boundary surface
Depends on soil KMta, maximum allowable thickness of
saturated zone, and slope of the boundary
surface (see section 5.3)
0.2-5.0 Ib BOD/1000 ft2
(1.0-29.4 kg BOD/1000m2)
Other pollutants Mass of specific wastewater pollutant of
concern per unit area of boundary surface
(e.g., number of fecal conforms, mass of
nitrate nitrogen, etc.)
Variable with the constituent, its fate and transport,
and the considered risk it imposes
"K^is the saturated conductivity of the soil.
Source: Otis, 2001.
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Chapter 5: Treatment System Selection
Table 5-2. Potential impacts of mass loadings on soil design boundaries
Boundary loading
Infiltrative boundary
Secondary boundaries
Water table boundary
Hydraulic
• Daily
• Instantaneous
• Linear
Constituent
• Solids
• Organic
• Other
(hydraulic capacity)
•
(hydraulic capacity)
N/A
(unit gradient below boundary)
(surface clogging)
•
(surface clogging)
N/A
(usually no impact on
infiltration)
(saturated zone encroachment)
N/A
(attenuated through soil)
(saturated zone encroachment)
N/A
(attenuated through soil)
(saturated zone encroachment) (saturated zone encroachment)
N/A
(removed through soil)
N/A
(removed through soil)
N/A
(no treatment requirements)
N/A
(removed through soil)
N/A
(removed through soil)
•
(treatment requirements)
Notes: • denotes that mass loading has potential impact.
N/A denotes that mass loading typically has no impact and does not apply.
Text in parentheses describes reason for impact or lack of impact of mass loading.
Loading impacts apply to both gravity-based and mechanical systems. See chapter 4 for hydraulic and organic loading rates
relative to soil texture and structure.
Source: Otis, 1999.
The infiltrative surface is the primary design
boundary. At this boundary, the partially treated
wastewater must pass through the biomat, enter the
soil pores, and percolate into unsaturated soil. The
wastewater cannot be applied at rates faster than
the soil can accept it, nor can the soil be overloaded
with solids or organic matter to the point where
soil pores become clogged with solids or an overly
thick development of the biomass. Because solids
are usually removed through settling processes in
the septic tank, the critical design loadings at this
boundary are the daily and instantaneous hydraulic
loading rates and the organic loading rate. System
design requires that daily hydraulic and instanta-
neous/peak loadings be estimated carefully so that
the total hydraulic load can be applied as uniformly
as feasible over the entire day to maximize the
infiltration capacity of the soil. Uniform dosing
and resting maximizes the reaeration potential of
the soil and meets the oxygen demand of the
applied wastewater loading more efficiently. The
organic loading rate is an important consideration
if the available area for the SWIS is small. In
moderately permeable or more permeable soils,
lower organic loading rates can increase infiltration
rates into the soil and may allow reductions in the
size of the infiltrative surface. Organic loadings to
slowly permeable, fine-textured soils are of lesser
concern because percolation rates through the
biomat created by the organic loading are usually
greater than the infiltration rate into the soil.
Preventing effluent backup (hydraulic failure) by
increasing the size of the SWIS and implementing
water conservation measures are important consid-
erations in these situations.
Secondary design boundaries are usually hydrauli-
cally restrictive horizons that inhibit vertical
percolation through the soil (figure 5-2). Water can
perch above these boundaries, and the perching can
affect performance in two significant ways. If the
perched water encroaches into the unsaturated zone,
treatment capacity of the soil is reduced and
reaeration of the soil below the infiltrative surface
might be impeded. Depending on the degree of
impedance, anoxic or anaerobic conditions can
develop, resulting in excessive clogging of the
infiltrative surface. Also, water will move laterally
on top of the boundary, and partially treated
wastewater might seep from the exposed bound-
aries of the restrictive soil strata downslope and out
onto the ground surface. Therefore, the contour
(linear) loading along the boundary surface contour
must be low enough to prevent water from mounding
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Chapter 5: Treatment System Selection
above the boundary to the point that inadequately
treated wastewater seeps to the surface and creates
a nuisance and possible risk to human health.
Organic loadings at these secondary boundaries are
seldom an issue because most organic matter is
typically removed as the wastewater passes through
the infiltrative surface boundary layer.
Hydraulic and wastewater constituent loadings are
the critical design loadings at the water table
boundary. Low aquifer transmissivity creates
ground water mounding (figure 5-4), which can
encroach on the infiltrative surface if the daily
hydraulic loading is too high. Mounding can affect
treatment and percolation adversely by inhibiting
soil reaeration and reducing moisture potential. A
further potential consequence is undesirable surface
seepage that can occur downslope. Constituent
loadings must be considered where protection of
potable water supply wells is a concern. Typical
wastewater constituents of human health concern
include pathogenic microbes and nitrates (see
chapter 3). Water resource pollutants of concern
include nitrogen in coastal areas, phosphorus near
inland waters, and toxic organics and certain metals
in all areas. If the wastewater constituent loadings
are too high at the water table boundary, pretreat-
ment before application to the infiltrative surface
might be necessary.
5.4.2 Surface water discharging
system design boundaries and
loadings
Surface water discharging systems typically consist
of a treatment plant (aeration/activated sludge/sand
filter "package" system with disinfection) discharg-
ing to an outfall (pipe discharge) to a surface water.
The important design boundaries for these systems
are the inlet to the treatment plant and the outfall to
the surface water. The discharge permit and the
performance history of the treatment process
typically establish the limits of mass loading that
can be handled at both the inlet to and the outlet
from the treatment process. The loadings are often
expressed in terms of daily maximum flow and
pollutant concentrations (table 5-3). The effluent
limits and wastewater characteristics establish the
extent of treatment (performance requirements)
needed before final discharge.
5.4.3 Atmospheric discharging system
design boundaries and loadings
Evapotranspiration systems are the most commonly
used atmospheric discharging systems. They can
take several forms, but the primary design bound-
Figure 5-4. Effluent mounding effect above the saturated zone
Source: Adapted from NSFC diagram.
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Chapter 5: Treatment System Selection
ary is the evaporative surface. Water (effluent)
flowing through the treatment system and site
hydrology must be considered in the design. Water
balance calculations in the system control design
(table 5-4). These loadings are determined by the
ambient climatic conditions expected. Procedures
for estimating these loadings are provided in
chapter 4 (Evapotranspiration Fact Sheet).
receiver sites and select the proper treatment train,
size, and physical placement at the site. This
section does not provide basic information on soil
science but rather suggests methods and procedures
that are standardized or otherwise proven for the
practice of site evaluation. It also identifies specific
steps or information that is crucial in the decision-
making process for the site evaluator.
5.5 Evaluating the receiving
environment
Evaluation of the wastewater receiver site is a
critical step in system selection and design. The
objective of the evaluation is to determine the
capacity of the site to accept, disperse, and safely
and effectively assimilate the wastewater discharge.
The evaluation should
• Determine feasible receiving environments
(ground water, surface water, or atmosphere)
• Identify suitable receiver sites
• Identify significant design boundaries associ-
ated with the receiver sites
• Estimate design boundary mass loading limitations
Considering the importance of site evaluation with
respect to system design, it is imperative that site
evaluators have appropriate training to assess
5.5.1 Role and qualifications of the site
evaluator
The role of the site evaluator is to identify, interpret,
and document site conditions for use in subsurface
wastewater treatment system selection, design, and
installation. The information collected should be
presented in a manner that is scientifically accurate
and spatially correct. Documentation should use
standardized nomenclature to provide geophysical
information so that the information can be used by
other site evaluators, designers, regulators, and
contractors.
The site evaluator needs considerable knowledge
and a variety of skills. A substantial knowledge of
soils, soil morphology, and geology is essential
because most onsite systems use the soil as the final
treatment and dispersal medium. Many states no
longer accept the percolation test as the primary
Table 5-3.Types of mass loadings for point discharges to surface waters
Mass loading type
Hydraulic
• Daily
Units
Volume per day through outfall
Typical loading rates
Determined by local regulatory agency based on
water resource classification and mixing zone.
Constituent
• Designated pollutant Concentration of pollutant in mg/L through outfall Determined by local regulatory agency based on
water resource classification and mixing zone.
Source: Otis, 1999.
Table 5-4. Types of mass loadings for evapotranspiration systems
Mass loading type
Units
Hydraulic
• Daily
• Annual
Typical loading rates
Volume per day per unit area of boundary surface Dependent on net evaporation, evapotranspiration potential,
solar energy, wind, exposure, mean temperature, and other
factors.
Volume per day per unit area of boundary surface Based on monthly water budget.
Source: Otis, 1999.
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Chapter 5: Treatment System Selection
North Carolina guidelines for OWTS site evaluations
The Division of Environmental Health of the North Carolina Department of Environment, Health, and Natural
Resources uses a 10-point guide for conducting site evaluations. The ten guidelines can be grouped into the
following components:
Collecting information before the site visit
Assessing the site and soil at the location
Recording site evaluation data for system design
Relaying the information to the system designer and the applicant.
1. Know the rules and know how to collect the needed information. Applicable codes for sewage treatment and
dispersal systems are usually established by the local agency.
2. Determine the wastewater flow rate and characteristics. Information on wastewater quantity and quality is used
to determine the initial size and type of the onsite system to be installed at a particular site.
3. Review preliminary site information. Existing published information will help the evaluator understand the types
of soils and their properties and distribution on the landscape.
4. Understand the septic system design options. Site evaluators must understand how onsite systems function in
order to assess trade-offs in design options.
5. View the onsite system as part of the soil system and the hydrologic cycle. Typically, onsite systems serving
single-family homes do not add enough water to the site to substantially change the site's hydrology, except in
areas of high densities of onsite systems.
6. Predict wastewater flow through the soil and the underlying materials. The soil morphological evaluation and
landscape evaluation are important in predicting flow paths and rates of wastewater movement through the soil
and underlying materials.
7. Determine if additional information is needed from the site. Site and soil conditions and the type of onsite
system being considered determine whether additional evaluation is required. Some additional evaluations that
may be required are ground water mounding analysis, drainage analysis, hydrogeologic testing, contour
(linear) loading rate evaluation, and hydraulic conductivity measurements.
8. Assess the treatment potential of the site. The treatment potential of the site depends on the degree of soil
aeration and the rate of flow of the wastewater through the soil.
9. Evaluate the site's environmental and public health sensitivity. Installing onsite systems in close proximity to
community wells, near shellfish waters, in sole-source aquifer areas, or other sensitive areas may raise
concerns regarding environmental and public health issues.
10. Provide the system designer with soil/site descriptions and your recommendations. Based on the information
gathered about the facility and the actual site and soil evaluation, the evaluator can suggest loading rates,
highlight site and design considerations, and point out special concerns in designing the onsite system.
Source: North Carolina DEHNR, 1996.
suitability criterion. A significant number of
permitting agencies now require a detailed soil
profile description and evaluation performed by
professional soil scientists or certified site evaluators.
In addition to a thorough knowledge of soil
science, the site evaluator should have a basic
understanding of chemistry, wastewater treatment,
and water movement in the soil environment, as
well as knowledge of onsite system operation and
construction. The evaluator should also have basic
skills in surveying to create site contour maps and
site plans that include temporary benchmarks,
horizontal and vertical locations of site features,
and investigation, sample, or test locations. A
general knowledge of hydrology, biology, and
botany is helpful. Finally, good oral and written
communication skills are necessary to convey site
information to others who will make important
decisions regarding the best use of the site.
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5.5.2 Phases of a site evaluation
Site evaluations typically proceed in three phases: a
preliminary review of documented site information, a
reconnaissance of potential sites, and a detailed
evaluation of the most promising site or sites. The
scale and detail of the evaluation depend on the
quantity and strength of the wastewater to be treated,
the nature of local soils and the hydrogeologic setting,
the sensitivity of the local environment, and the
availability of suitable sites. Using a phased approach
(table 5-5) helps to focus the site evaluation effort on
only the most promising sites for subsurface systems.
5.5.3 Preliminary review
The preliminary review is performed before any
fieldwork. It is based on information available
from the owner or local agencies or on general
resource information. The objectives of the pre-
liminary review are to identify potential receiver
sites, determine the most feasible receiving environ-
ments, identify potential design boundaries, and
develop a relative suitability ranking. Preliminary
screening of sites is an important aspect of the site
evaluator's role. More than one receiving environ-
ment might be feasible and available for use.
Focusing the effort on the most promising receiving
environments and receiver sites allows the evalua-
tor to reasonably and methodically eliminate the
least suitable sites early in the site evaluation
process. For example, basic knowledge of the local
climate might eliminate evaporation or evapotranspi-
ration as a potential receiving environment immedi-
ately. Also, the applicable local codes often prohibit
point discharges to surface waters from small systems.
Knowledge of local conditions and regulations is
essential during the screening process. Resource
materials and information to be reviewed may
include, but are not limited to, the following:
• Property information. This information should
include owner contact information, site legal
description or address, plat map or boundary
survey, description of existing site improve-
ments (e.g., existing onsite wastewater systems,
underground tanks, utility lines), previous and
proposed uses, surrounding land use and
zoning, and other available and relevant data.
• Detailed soil survey. Detailed soil surveys are
published by the U.S. Department of
Agriculture's Natural Resources Conservation
Table 5-5. Site characterization and assessment activities for
SWIS applications
Preliminary activities
Preliminary review
Scheduling
Field activities
Identification of unsuitable
areas
Subsurface investigations
Identification of
recommended SWIS site
Information from research
/ Site survey map
/ Soil survey, USGS topographic map
/ Aerial photos, wetland maps
/ Source water protection areas
/ Natural resource inventories
/ Applicable regulations/setbacks
/ Hydraulic loading rates
/ Criteria for alternative OWTS
/ Size of house/facility
/ Loading rates, discharge types
/ Planned location of water well
/ Planned construction schedule
/ Date and time for meeting
Information from field study
/ Water supply separation distances
/ Regulatory buffer zones/setbacks
/ Limiting physiographic features
/ Ground water depth from pit/auger
/ Soil profile from backhoe pit
/ Presence of high water table
/ Percolation tests
/ Integration of all collected data
/ Identification of preferred areas
/ Assessment of gravity-based flow
/ Final selection of SWIS site
Source: Adapted from ASTM, 1996a.
Service (NRCS), formerly the Soil Conserva-
tion Service (SCS). Detailed soil surveys
provide soil profile descriptions, identify soil
limitations, estimate saturated soil conductivities
and permeability values, describe typical
landscape position and soil formation factors,
and provide various other soil-related informa-
tion. Soil surveys are typically based on deduc-
tive projections of soil units based on topo-
graphical or landscape position and should be
regarded as general in nature. Because the
accuracy of soil survey maps decreases as
assessments move from the landscape scale to
the site scale, soil survey data should be supple-
mented with detailed soil sampling at the site
(table 5-5). Individual surveys are performed on
a county basis and are available for most
counties in the continental United States,
Alaska, Hawaii, and the U.S. territories. They
are available from county extension offices or
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the local NRCS office. Information on available
detailed soil surveys and mapping status can be
obtained from the National Soil Survey Center
through its web site at http://
www.statlab.iastate.edu/soils/nssc/. The NRCS
publication Fieldbookfor Describing and
Sampling Soils is an excellent manual for use in
site evaluation. It is available at http://
www.statlab.iastate.edu/soils/nssc/field_gd/
field_gd.pdf.
Quadrangle maps. Quadrangle maps provide
general topographic information about a site
and surrounding landscape. These maps are
developed and maintained by the U.S. Geological
Survey (USGS) and provide nationwide coverage
typically at a scale of 1 inch = 2000 feet, with
either a 10- or 20-foot contour interval. At this
scale, the maps provide information related to
land use, public improvements (e.g., roadways),
USGS benchmarks, landscape position and slope,
vegetated areas, wetlands, surface drainage
patterns, and watersheds. More information
about USGS mapping resources can be found at
http://mapping.usgs.gov/mac/findmaps.html.
Quadrangle maps also are available through
proprietary software packages.
Wetland maps. Specialized maps that identify
existing, farmed, and former wetlands are
available in many states from natural resource
or environmental agencies. These maps identify
wetland and fringe areas to be avoided for
wastewater infiltration areas. On-line and
published wetland maps for many parts of the
United States are available from the U.S. Fish
and Wildlife Service's National Wetlands
Inventory Center at http://www.nwi.fws.gov/.
Aerial photographs. If available, aerial photo-
graphs can provide information regarding past
and existing land use, drainage and vegetation
patterns, surface water resources, and approxi-
mate location of property boundaries. They are
especially useful for remote sites or those with
limited or difficult access. Aerial photographs
may be available from a variety of sources, such
as county or regional planning, property
valuation, and agricultural agencies.
Geology and basin maps. Geology and basin maps
are especially useful for providing general inform-
ation regarding bedrock formations and depths,
ground water aquifers and depths, flow direc-
tion and velocities, ambient water quality,
surface water quality, stream flow, and seasonal
fluctuations. If available, these maps can be
obtained from USGS at http://
www.nationalatlas.gov/
or Terra Server at http://
www.terraserver.microsoft.com.
Water resource and health agency information.
Permit and other files, state/regional water
agency staff, and local health department
sanitarians or inspectors can provide valuable
information regarding local onsite system
designs, applications, and performance. Regula-
tory agencies are beginning to establish Total
Maximum Daily Loads (TMDLs) for critical
wastewater constituents within regional drain-
age basins under federal and state clean water
laws. TMDLs establish pollutant "budgets" to
ensure that receiving waters can safely assimi-
late loads of incoming contaminants, including
those associated with an onsite system (e.g.,
bacteria, nutrients). If the site lies in the re-
charge area of a water resource listed as im-
paired (not meeting its designated use) because
of bacteria or nutrient contamination, site
evaluators need to be aware of all applicable
loading limits to ground water or surface water
in the vicinity of the site under review.
Local installer/maintenance firms. Helpful
information often can be obtained from inter-
views with system installation and maintenance
service providers. Their experience with other
sites in the vicinity, existing technology perfor-
mance, and general knowledge of soils and
other factors can inform both the site evaluation
and the selection of appropriate treatment
system components.
Climate. Temperature, precipitation, and pan
evaporation data can be obtained from the
National Oceanic and Atmospheric Administra-
tion (NOAA) at http://www.nic.noaa.gov. This
information is necessary if evapotranspiration
systems are being considered. The evaluator
must realize, however, that the data from the
nearest weather station might not accurately
represent the climate at the site being evaluated.
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Chapter 5: Treatment System Selection
5.5.4 Reconnaissance survey
The objectives of the reconnaissance survey are to
obtain preliminary site data that can be used to
determine the appropriate receiving environment.
screen potential receiver sites, and further focus the
detailed survey to follow. A reconnaissance survey
typically includes visual surveys of each potential
site, preliminary soils investigation using hand
borings, and potential system layouts. Information
gathered from the preliminary review, soil sampling
tools, and other materials should be on hand during
the reconnaissance survey.
The site reconnaissance begins with a site walkover
to observe and identify existing conditions, select
areas to perform soil borings, or view potential
routes for piping or outfall structures. The site
evaluator should have an estimate of the total area
needed for the receiver site based on the projected
design flow and anticipated soil characteristics. It is
advisable to complete the site walkover with the
owner and local regulatory staff if possible,
particularly with larger projects. Selection of an
area for soil investigation is based on the owner's
requirements (desired location, vegetation preserva-
tion, and general site aesthetics), regulatory
requirements (setbacks, slope, and prior land use),
and the site evaluator's knowledge and experience
(landscape position, local soil formation factors,
and geologic conditions). Visual inspections are
used to note general features that might affect site
suitability or system layout and design. General
features that should be noted include the following:
• Landscape position. Landscape position and
landform determine surface and subsurface
drainage patterns that can affect treatment and
infiltration system location. Landscape features
that retain or concentrate subsurface flows, such
as swales, depressions, or floodplains, should be
avoided. Preferred landscape positions are
convex slopes, flat areas with deep, permeable
soils, and other sites that promote wastewater
infiltration and dispersion through unsaturated
soils (figures 5-5 and 5-6).
• Topography. Long, planar slopes or plateaus
provide greater flexibility in design than ridges,
knolls, or other mounded or steeply sloping
sites. This is an important consideration in
gravity-flow treatment systems, collection
Figure 5-5. General considerations for locating a SWIS on a
sloping site
GOOD LOCATION
AVOID AREAS WHERE SURFACE FLOWS CONVERGE
Source: Purdue University, 1990.
piping for cluster systems, treatment unit sites,
and potential routes for point discharge outfalls.
• Vegetation. Existing vegetation type and size
provide information regarding soil depth and
internal soil drainage, which are important
considerations in the subsurface wastewater
infiltration system layout.
• Natural and cultural features. Surface waters,
wetlands, areas of potential flooding, rock
outcrops, wells, roads, buildings, buried utilities,
underground storage tanks, property lines, and
other features should be noted because they will
affect the suitability of the receiver site.
A good approach to selecting locations for soil
investigations is to focus on landscape position. The
underlying bedrock often controls landscapes,
which are modified by a variety of natural forces.
The site evaluator should investigate landscape
positions during the reconnaissance phase to
identify potential receiver sites (figures 5-5, 5-6
and 5-7; table 5-6). Ridgelines are narrow areas
that typically have limited soil depth but often a
good potential for surface/subsurface drainage.
Shoulderslopes and backslopes are convex slopes
where erosion is common. These areas often have
good drainage, but the soil mantle is typically thin
and exposed bedrock outcrops are common.
Sideslopes are often steep and erosion is active.
Footslopes and depressions are concave areas of
soil accumulation; however, depressions usually
have poor drainage. The deeper, better-drained
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Figure 5-6. Landscape position features
(see table 5-6 for siting potential)
Slope Shape - Slope shape is described in two directions: up and
down slope (perpendicular to the contour), and across slope (along the
horizontal contour); e.g., linear, convex, orLV.
(S&W, 1996)
surface flow
pathway
Hlllslope - Profile Position (Hillslope Position in PDP) - Two-
dimensional descriptions of parts of line segments (slope position)
along a transect that runs up and down the slope; e.g., backslope or
BS. This is best applied to transects or points, not areas.
Position
summit
shoulder
backslope
footslope
toeslooe
Code
SU
SH
BS
FS
TS
Su
Sh
[PJS.1B96;
Source: NRCS, 1998
Table 5-6. SWIS siting potential vs. landscape position features
soils are found on ridgelines, lower sideslopes, and
footslopes. Bottomlands might have deeper soils
but might also have poor subsurface drainage.
The visual survey might eliminate candidate
receiver sites from further consideration. Prelimi-
nary soil borings should be examined on the
remaining potential sites unless subsurface waste-
water infiltration as a treatment or dispersal option
has been ruled out for other reasons. Shallow
borings, typically to a depth of at least 5 feet (1.7
meters), should be made with a soil probe or hand
auger to observe the texture, structure, horizon
thickness, moisture content, color, bulk density, and
spatial variability of the soil. Excavated test pits are
not typically required during this phase because of
the expense and damage to noncommitted sites.
Enough borings must be made to adequately
characterize site conditions and identify design
boundaries. To account for grade variations,
separation distances, piping routes, management
considerations, and contingencies, an area sufficient
to provide approximately 200 percent of the
estimated treatment area needed should be investi-
gated. A boring density of one hole per half-acre
may be adequate to accomplish the objectives of
this phase. On sites where no reasonable number of
soil borings is adequate to characterize the continu-
ity of the soils, consideration should be given to
abandoning the site as a potential receiver site.
Onsite treatment with a point discharge (permitted
under the National Pollutant Discharge Elimination
System) requires evaluation of the potential
receiving water and an outfall location. The
feasibility of a point discharge is determined by
federal and state rules and local codes, if enacted
by the local jurisdiction. Where the impacts and
Landscape
position
LC
VC
CC
LV
VV
CV
LL
VL
CL
SWIS siting
potential
Poor
Fair
1 Clll
Best
Comments
Converging flows could
overload SWIS hydraulically
Might not be able to add
additional trench length later
Parallel flow across SWIS
provides best siting potential
by the regulating agency, effluent concentration
limits will be stipulated and an NPDES permit will
be required.
The final step of the reconnaissance survey is to
make a preliminary layout of the proposed system
on each remaining candidate site based on assessed
site characteristics and projected wastewater flows.
This step is necessary to determine whether the site
has sufficient area and to identify where detailed
soils investigations should be concentrated. In
practice, this step becomes integrated into the field
reconnaissance process so the conceptual design
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Chapter 5: Treatment System Selection
unfolds progressively as it is adapted to the grow-
ing body of site and soil information.
5.5.5 Detailed evaluation
The objective of the detailed evaluation is to
evaluate and document site conditions and charac-
teristics in sufficient detail to allow interpretation
and use by others in designing, siting, and install-
ing the system. Because detailed investigations can
be costly, they should not be performed unless the
preliminary and reconnaissance evaluations
indicate a high probability that the site is suitable.
Detailed site evaluations should attempt to identify
critical site characteristics and design boundaries
that affect site suitability and system design. At a
minimum, the detailed investigation should include
soil profile descriptions and topographic mapping.
(See figure 5-8, Site Evaluation/Site Plan Check-
list.) Several backhoe pits, deep soil borings, soil
permeability measurements, ground water charac-
terizations, and pilot infiltration testing processes
may be necessary for large subsurface infiltration
systems. For evapotranspiration systems, field
measurements of pan evaporation rates or other
parameters, as appropriate, might be necessary.
This information should be presented with an
accurate site plan.
The detailed evaluation should address surface
features such as topography, drainage, vegetation,
site improvements, property boundaries, and other
significant features identified during the reconnais-
sance survey. Subsurface features to be addressed
include soil characteristics, depth to bedrock and
ground water, subsurface drainage, presence of
rock in the subsoil, and identification of hydraulic
and treatment boundaries. Information must be
conveyed using standardized nomenclature for soil
descriptions and hydrological conditions. Testing
procedures must follow accepted protocol and
standards. Forms or formats and evaluation pro-
cesses specified by regulatory or management
agencies must also be used (for a state example see
http://www.deh.enr.state.nc.us/oww/LOSWW/
soil_fbrm.pdf).
5.5.6 Describing the soil profile
Descriptions and documentation of soil profiles
provide invaluable information for designing onsite
systems that use soil as the final wastewater
Figure 5-7. Conventional system layout with SWIS replacement
area
Septic Tank
Drainfield
\
treatment and dispersal medium. Detailed soil
characterizations are provided through observation,
description, and documentation of exposed soil
profiles within backhoe-excavated test pits.
Profiles can be described using a hand auger or
drill probe for any single-home SWISs site in
known soil and hydrogeology. However, backhoe-
excavated test pits should be used wherever large
SWISs or difficult single-home sites are proposed
because of the quality of information gained. The
grinding action or compression forces from soil
borings taken with a hand auger or drill probe limit
the information obtained for some soil characteris-
tics, especially structure, consistency, and soil
horizon relationships. Depending on project size, it
might be necessary to supplement soil evaluation
test pits with deep borings to provide more detail
regarding soil substratum, ground water, and
bedrock conditions. Table 5-7 summarizes the
processes and procedures discussed below.
It might not be possible to identify all design
boundaries, such as the permanent water table
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Chapter 5: Treatment System Selection
Figure 5-8. Site evaluation/site plan checklist
Owner/Client Information
Name
Contact nos.
Address
Projected design flow.
GPD
Existing use_
Intended use
Legal description.
Directions to site
Surface Features
Benchmark description
Property boundaries
Existing/proposed structures
Existing/proposed wastewater systems
Soil investigation points
Contour elevations
Proposed system component locations
North arrow
Comments
.Assigned elevation
Surface water features
ft
.Existing/proposed water supply wells
.Utility locations
.Location of area of suitable soils
.Slope aspect & percent
.Other significant features
Scale
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Chapter 5: Treatment System Selection
Figure 5-8. Site evaluation/site plan checklist (cont.)
Subsurface Features
.Detailed soil descriptions (horizon depth, texture, color, structure, redoximorphic
Comments
features, consistence, moisture, roots, and boundaries) (Use USDA nomenclature)
_Depth and thickness of strong textural contrasts
_Depth to seasonal saturation Depth to perched water table
_Soil testing results Soil samples collected
_Parent material Soil formation factors
_Deep completed Depth
_Depth to bedrock Type of bedrock
_Depth to permanent water table Sample
_Ground water flow direction Ground water gradient
Site Evaluator
Date
Site Evaluation Type:
Desktop.
.Preliminary.
Detailed
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Table 5-7. Practices to characterize subsurface conditions through test pit inspection
Description of activity
Process steps
Information to be collected
Select backhoe pit site
Excavate pit
Enter test pit
Expose natural soil structure
Describe soil horizons
Determine soil changes
Interpret results
Issue site report
Pick site near but not in proposed drain field;
orient pit so sunlight illuminates vertical face of pit
Excavate to depth required by agency regulations
Take safety precautions; beware of cave-ins;
select area of pit wall to examine
Use soil knife, blade, screwdriver or other tool to
pick at area 0.5 m wide along full height of pit wall
Note master soil horizon layers; describe features
of each horizon
Look for lateral changes in soil profile; use auger
and/or compare to profile of second pit
Identify limiting depths
Log all data onto required survey forms in
required format
Location of soil absorption field
Required ground water or seasonally high water
table separation distance, soil profile depth
Safe depths for unbraced pit walls
Soil structural type (e.g., prismatic, columnar,
angular blocky, subangular blocky, platy, granular)
/ List soil horizon features:
/" Depth of horizon, thickness
/ Moisture content
/ Color (hue, value, chroma)
y Volumetric percentage of rock
S Size, shape, type of rock
/ Texture of < 2 mm fraction of horizon
S Presence/absence of mottles
t/ Soil structure by grade
S Level of cementation
S Presence/absence of carbonates
-------
NRCS soil classification systems have many similari-
ties; both describe and categorize soils according to
silt, clay, and sand composition and relative plasticity.
However, the NRCS guide cited above is a field guide
and is based on soil characterization procedures that
can be conducted through tactile and visual tech-
niques in the field (e.g., the feel of a soil sample,
visual identification of the presence and color of
concretions and mottles) with minimal equipment.
The ASTM approach requires laboratory analysis of
soil particle size (with a series of sieves), plasticity,
and organic content (ASTM , 2000) and is more
commonly used in the engineering profession. Both
approaches meet the technical requirements for
conducting the site evaluation process described in
this section.
Based on the proposed design flow, an area equal to
approximately 200 percent of the estimated re-
quired treatment area should be investigated. Test
pits should be spaced in a manner that provides a
reasonable degree of confidence that conditions are
similar between pits. For small cluster systems,
three to five test pits may be sufficient if located
around the periphery and in the center of the
proposed infiltration area. Large projects require
more test pits. Test pit spacing can be adjusted
based on landscape position and observed condi-
tions. Hand auger borings or soil probes may be
used to confirm conditions between or at peripheral
test pit locations. Soil profiles should be observed
and documented under similar conditions of light
and moisture content. Features that should be noted
include the following:
• Soil depth. Test pits should be excavated to a
safe depth to describe soil conditions, typically
4 feet below the proposed infiltrative surface. A
vertical wall exposed to the sunlight is best for
examination. The wall should be picked with a
shovel or knife to provide an undisturbed
profile for evaluation and description. Horizon
thickness should be measured and the soil
properties described for each horizon.
Restrictive horizons that may be significant
secondary design boundaries must be noted. The
depths of each horizon should be measured to
develop a relationship with conditions in other test
pits. Soil below the floor of the backhoe pit can be
investigated by using hand augers in the excavated
pit bottom or by using deep boring equipment.
Chapter 5: Treatment System Selection
Key soil properties that describe a soil profile
are horizons, texture, structure, color, and
redoximorphic features (soft masses, nodules, or
concretions of iron or manganese oxides often
linked to saturated conditions). Other properties
include moisture content, porosity, rupture
resistance (resistance to applied stress), penetra-
tion resistance, roots, clay mineralogy, bound-
aries, and coatings. Attention to the listed key
soil properties will provide the most value in
determining water movement in soil.
Horizons. A soil horizon is a layer of soil that
exhibits similar properties and is generally
denoted based on texture and color. Soil horizons
result from natural soil-forming processes and
human practices. Horizons are designated as
master horizons and layers with subordinate
distinctions. All key soil properties and associ-
ated properties that are relevant to water
movement and wastewater treatment should be
described. Particular attention should be given
to horizons with strong textural contrast, stratified
materials, and redoximorphic indicators that
suggest a restriction to vertical water movement.
Certain soil conditions that create a design
boundary can occur within a soil horizon or
layer. These include horizons with low perme-
Figure 5-9. Soil textural triangle
100% day
100%
sand
%
100%
silt
percent sand
Source: USDA, 1951.
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Chapter 5: Treatment System Selection
ability that perch water, indurated or massive
horizons, or substrata of dense glacial till.
Texture. Soil texture is defined as the percentage
by weight of separates (sand, silt, and clay) that
make up the physical composition of a given
sample. It is one indicator of a soil's ability to
transmit water. The textural triangle (figure 5-9)
is used to identify soil textures based on percent-
age of separates (Schoeneberger et al., 1998).
The texture of soil profiles is typically identified
in the field through hand texturing. The
evaluator's skill and experience play an impor-
tant role in the accuracy of field texturing.
Several field guides, typically in the form of
flow charts, are available to assist the evaluator
in learning this skill and to assist with identify-
ing the texture of soils that occur at or near
texture boundaries. (ASTM, 1997)
Structure. Structure is more important than
texture for determining water movement in soils.
Soil structure is the aggregation of soil particles
into larger units called peds. The more common
types of structure are granular, angular blocky,
subangular blocky, and platy (figure 5-10).
Structureless soils include single-grain soils
(e.g., sand) and massive soils (e.g., hardpan).
The grade, size, shape, and orientation of soil
peds influence water movement in the soil
profile. This is especially true in fine-textured
Figure 5-10. Types of soil structure
Single-grain
Source: USDA, 1951.
soils. Smaller peds create more inter-pedal
fractures, which provide more flow paths for
percolating water. Grade, which defines the
distinctness of peds, is important for establish-
ing a soil loading rate for wastewater dispersal.
A soil with a "strong" grade of structure has
clearly defined fractures or voids between the
peds for the transmittance of water. The inter-
pedal fractures and voids in a soil with a "weak"
grade are less distinct and offer more resistance
to water flow. Soils with a strong grade can
accept higher hydraulic loadings than soils with
a weak grade. Platy and massive soils restrict
the vertical movement of water.
Color. Color is an obvious property of soil that
is easily discernible. It is an excellent indicator
of the soil's aeration status and moisture regime.
Soil colors are described using the Munsell
color system, which divides colors into three
elements—hue, value, and chroma (Munsell,
1994). Hue relates to the quality of color, value
indicates the degree of lightness or darkness,
and chroma is the purity of the spectral color.
Munsell soil color books are commercially
available and are universally accepted as the
standard for identifying soil color. The dominant
or matrix color is determined for each horizon,
and secondary colors are determined for
redoximorphic features, ped coatings, mineral
concretions, and other distinctive soil features.
Dark colors generally indicate higher organic
content, high-chroma colors usually suggest
highly oxygenated soils or high iron content,
and low-chroma soils imply reduced conditions
often associated with saturation. The site
evaluator must be aware that colors can be
modified by temperature, mineralogy, vegetation,
ped coatings, and position in the soil profile.
Redoximorphic features. Redoximorphic
features are used to identify aquic moisture
regimes in soils. An aquic moisture regime
occurs when the soil is saturated with water
during long periods, an indicator of possible
restrictive horizons, seasonal high water tables,
or perched water tables. The presence of
redoximorphic features suggests that the
surrounding soil is periodically or continuously
saturated. This condition is important to identify
because saturated soils prevent reaeration of the
vadose zone below infiltration systems and
reduce the hydraulic gradients necessary for
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adequate drainage. Saturated conditions can lead
to surfacing of wastewater or failure due to
significant decreases in soil percolation rates.
Redoximorphic features include iron nodules
and mottles that form in seasonally saturated
soils by the reduction, translocation, and
oxidation of iron and manganese oxides
(Vespaskas, 1996). Redoximorphic features
have replaced mottles and low-chroma colors in
the USDA NRCS soil taxonomy because mottles
include carbonate accumulations and organic
stains that are not related to saturation and
reduction. It is important to note that
redoximorphic features are largely the result of
biochemical activity and therefore do not occur
in soils with low amounts of organic carbon,
high pH (more than 7 standard pH units), low
soil temperatures, or low amounts of iron, or
where the ground water is aerated. Vespraskas
(1996) provides an excellent guide to the
identification of redoximorphic features and
their interpretation. As noted, the NRCS online
guide to redoximorphic and other soil properties
at http://www.statlab.iastate.edu/soils/nssc/
field_gd/field_gd.pdf addresses key identifica-
tion and characterization procedures for
redoximorphic and other soil features.
Soil consistence. Soil consistence in the general
sense refers to attributes of soil as expressed in
degree of cohesion and adhesion, or in resis-
tance to deformation or rupture. Consistence
includes the resistance of soil material to
rupture; the resistance to penetration; the
plasticity, toughness, or stickiness of puddled
soil material; and the manner in which the soil
material behaves when subjected to compres-
sion. Consistence is highly dependent on the
soil-water state. The general classifications of
soil consistence are loose, friable, firm, and
extremely firm. Soils classified as firm and
extremely firm tend to block subsurface waste-
water flows. These soils can become cemented
when dry and can exhibit considerable plasticity
when wet. Soils that exhibit extremely firm
consistence are not recommended for conven-
tional infiltration systems.
Restrictive horizons. Soil properties like pen-
etration resistance, rooting depth, and clay
mineralogy are important indicators of soil
porosity and hydraulic conductivity. Penetration
resistance is often correlated with the soil's bulk
density. The greater the penetration resistance,
the more compacted and less permeable the soil
is likely to be. Rooting depth is another measure
of bulk density and also soil wetness. Clay
mineralogies such as montmorillonite, which
expand when wetted, reduce soil permeability
and hydraulic conductivity significantly. A
discussion of these properties and their descrip-
tion can also be found in the USDA Soil Survey
Manual (USDA, 1993) and the USDA NRCS
Field Book for Describing and Sampling Soils
(Schoeneberger et al., 1998).
• Other soil properties. Other soil properties that
affect nutrient removal are organic content and
phosphorus adsorption potential. Organic
content can provide a carbon source (from
decaying organic matter in the uppermost soil
horizons) that will aid denitrification of nitrified
effluent (nitrate) in anoxic regions of the SWIS.
Phosphorus can be effectively removed from
wastewater effluent by soil through adsorption
and precipitation reactions (see chapter 3). Soil
mineralogy and pH affect the soil's capacity to
retain phosphorus. Adsorption isotherm tests
provide a conservative measure of the potential
phosphorus retention capacity.
• Characterization of unconsolidated material.
Geologists define unconsolidated material as the
material occurring between the earth's surface
and the underlying bedrock. Soil forms in this
parent material from the actions of wind, water,
or alluvial or glacial deposition. Soil scientists
refer to the soil portion of unconsolidated
material as the solum and the parent material as
the substratum. Typically, site evaluators expose
the solum and the upper portion of the substra-
tum. Knowledge of the type of parent material
and noted restrictions or boundary conditions is
important to the designer, particularly for large
wastewater infiltration systems. Often, if the
substratum is deep, normal test pit depth will be
insufficient and deep borings may be necessary.
5.5.7 Estimating infiltration rate and
hydraulic conductivity
Knowledge of the soil's capacity to accept and
transmit water is critical for design. The infiltration
rate is the rate at which water is accepted by the
soil. Hydraulic conductivity is the rate at which
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water is transmitted through the soil. As wastewater
is applied to the soil, the infiltration rate typically
declines well below the saturated hydraulic con-
ductivity of the soil. This occurs because the
biodegradable materials and nutrients in the
wastewater stimulate microbiological activity that
produces new biomass (see chapter 3). The biomass
produced and the suspended solids in the wastewa-
ter create a biomat that can fill many of the soil
pores and close their entrances to water flow. The
flow resistance created by the biomat can reduce
the infiltration rate to several orders of magnitude
less than the soil's saturated hydraulic conductiv-
ity. The magnitude of the resistance created by the
biomat is a function of the BOD and suspended
solids in the applied wastewater and the initial
hydraulic conductivity of the soil.
Estimating the design infiltration rate is difficult.
Historically, the percolation test has been used to
estimate the infiltration rate. The percolation test
was developed to provide an estimate of the soil's
saturated hydraulic conductivity. Based on experi-
ence with operating subsurface infiltration systems,
an empirical factor was applied to the percolation
test result to provide a design infiltration rate. This
method of estimating the design infiltration rate has
many flaws, and many programs that regulate onsite
systems have abandoned it in favor of detailed soil
profile descriptions. Soil texture and structure have
been found to correlate better with the infiltration
rate of domestic septic tank effluent (Converse and
Tyler, 1994). For other applied effluent qualities
such as secondary effluent, the correlation with
texture and structure is less well known.
Information on the hydraulic conductivity of the
soil below the infiltrative surface is necessary for
ground water mounding analysis and estimation of
the maximum hydraulic loading rate for the infiltra-
tion area. There are both field and laboratory
methods for estimating saturated hydraulic conduc-
tivity. Field tests include flooding basin, single- or
double-ring infiltrometer, and air entry permea-
meter. These and other field test procedures are
described elsewhere (ASTM, 1997; Black, 1965;
USEPA, 1981; 1984). Laboratory methods are less
accurate because they are performed on small soil
samples that are disturbed from their natural state
when they are taken. Of the laboratory tests, the
concentric ring permeameter (Hill and King, 1982)
and the cube method (Bouma and Dekker, 1981) are
the most useful techniques. The American Society
for Testing and Materials posts permeameter
information on its Internet site at http://
www.astm.org (see ASTM Store, ASTM Standards).
5.5.8 Characterizing the ground water
table
Where ground water is present within 5 feet below
small infiltration systems and 10 to 15 feet below
large systems, the hydraulic response of the water
table to prolonged loading should be evaluated.
The ground water can be adversely affected by
treated wastewater and under certain conditions can
influence system performance. This information is
valuable for understanding potential system
impacts on ground water and how the system
design can mitigate these impacts.
The depth, seasonal fluctuation, direction of flow,
transmissivity, and, where possible, thickness of the
water table should be estimated. With shallow, thin
water tables, depth, thickness, and seasonal fluctua-
tions can be determined through soil test pit
examination. However, deeper water tables require
the use of deep borings and possible installation of
piezometers or monitoring wells. At least three
piezometers, installed in a triangular pattern, are
necessary to determine ground water gradient and
direction of flow, which might be different from
surface water flow direction. Estimating the
saturated hydraulic conductivity of the aquifer
materials is necessary to determine ground water
travel velocity. Slug tests or pumping tests can be
performed in one or more existing or new wells
screened in the shallow water table to estimate the
hydraulic conductivity of the aquifer (Bouwer,
1978; Bouwer and Rice, 1976; Cherry and Freeze,
1979). In some cases, it may be possible to estimate
the saturated hydraulic conductivity from a particle
size analysis of aquifer materials collected from the
test pit, if the material is accessible (Bouwer, 1978;
Cherry and Freeze, 1979). Pumping tests may also
be used to determine the effective porosity or
specific yield of the saturated zone.
Ground water mounding beneath an infiltration
system can reduce both treatment and the hydraulic
efficiency of the system. Ground water mounding
occurs when the rate of water percolating vertically
into the saturated zone exceeds the rate of ground
water drainage from the site (figure 5-4). Mounding
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is more likely to occur where the receiver site is
relatively flat, the hydraulic conductivity of the
saturated zone is low, or the saturated zone is thin.
With continuous application, the water mounds
beneath the infiltrative surface and reduces the
vertical depth of the vadose zone. Reaeration of the
soil, treatment efficiency, and the infiltration
system's hydraulic capacity are all reduced when
significant mounding occurs. A mounding analysis
should be completed to determine site limits and
acceptable design boundary loadings (linear
hydraulic loading) for sites where the water table is
shallow or the soil mantle is thin, or for any large
infiltration system.
Both analytical and numerical ground water
mounding models are available. Because of the
large number of data points necessary for numeri-
cal modeling, analytical models are the most
commonly used. Analytical models have been
developed for various hydrogeologic conditions
(Brock, 1976; Finnemore and Hantzshe, 1983;
Hantush, 1967; Kahn et al., 1976). Also, commer-
cial computer software is available to estimate
mounding potential. The assumptions used in each
model must be compared to the specific site
conditions found to select the most appropriate
model. For examples of model selection and model
computations, see EPA's process design manual
(USEPA, 1981,1984). AUSEPA Office of Ground
Water and Drinking Water annotated bibliography
of ground water and well field characterization
modeling studies can be found on the Internet at
http://www.epa.gov/ogwdwOOO/swp/wellhead/
dewell.html#analytical. USGS has available a
number of software packages, which are posted at
http://water.usgs.gov/software/
ground_water.html. For links to software suppliers
or general information, visit the National Ground
Water Association web site at http://
www.ngwa.org/.
5.5.9 Assessments for point source and
evapotranspiration discharges
Sites proposed for point discharges to surface
waters require a permit from the National Pollutant
Discharge Elimination System (see http://
www.epa.gov/owm/npdes.htm) and a suitable
location for an outfall to a receiving water body.
Considerations for locating an outfall structure
include NPDES regulatory requirements, outfall
structure siting, routing from the treatment facility,
construction logistics and expense, and aesthetics.
Regulatory requirements generally address accept-
able entry points to receiving waters and hydraulic
and pollutant loadings. The state regulatory agency
typically sets effluent limits based on the water
resource classification, stream flow, and assimila-
tive capacity of the receiving water. Assimilative
capacities take into account the entire drainage
basin or watershed of nearby receiving waters to
ensure that pollutant levels do not exceed water
quality criteria. (See table 3-21 for applicable
Drinking Water Standards; USEPA Drinking Water
Standards are posted at http://www.epa.gov/
ogwdwOOO/creg.html.) In the case of state-listed
impaired streams (those listed under section 303(d)
of the Clean Water Act), discharges must consider
pollutant loads established or proposed under the
Total Maximum Daily Load provisions of the Clean
Water Act. Piping from the treatment facility needs
to consider gravity or forcemain, route, existing
utilities, and other obstacles to be avoided.
Evapotranspiration (ET) systems treat and dis-
charge wastewater by evaporation from the soil or
water surface or by plant transpiration. These
systems are climate-sensitive and require large land
areas. ET systems function best in arid climates
where there is large annual net evaporation and
active vegetative growth year-round. In the United
States this generally means only the southwestern
states, where humidity is low, rainfall is minimal,
and temperatures are warm enough to permit active
plant growth during the winter season (figure 5-11).
Although the macroclimate of an area might be
acceptable for the use of ET systems, evaluation of
the microclimate is often required because it can
significantly influence system performance. In
addition to temperature, precipitation, and pan
evaporation data, exposure position and prevalent
wind direction should be considered as part of the
evaluation process. Southern exposures in the
northern hemisphere provides greater solar radia-
tion. Exposure to wind provides greater drying of
the soil and plant surfaces. Surface drainage
patterns should also be assessed. Well-drained sites
have a lower ambient humidity to enhance evapora-
tion than poorly drained sites.
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5.6 Mapping the site
At the completion of the site evaluation, a site map
or sketch should be prepared to show physical
features, locations of soil pits and borings, topogra-
phy or slopes, and suitable receiver sites. If a map
or aerial photograph was used, field measurements
and locations can be noted directly on it. Otherwise
it will be necessary to take measurements and
sketch the site. The level of effort for developing a
good site map should be commensurate with the
results of the site evaluation and whether the site
map is being completed for a preliminary or
detailed site evaluation.
In addition to the features of the site under consid-
eration, the site map should show adjacent lands
and land uses that could affect treatment system
layout, construction, and system performance.
Maps with a 1- or 2-foot contour interval are
preferred.
5.7 Developing the initial system
design
Developing a concept for the initial system design
is based on integration of projected wastewater
volume, flow, and composition information; the
controlling design boundaries of the selected
receiving environment; the performance require-
ments for the chosen receiving environment; and
the needs and desires of the owner (figure 5-12).
The site evaluation identifies the critical design
boundaries and the maximum mass loadings they
can accept. This knowledge, together with the
performance requirements promulgated by the
regulating authority for the receiving environment,
establishes the design boundary loadings. Once the
boundary loadings are established, treatment trains
that will meet the performance requirements can be
assembled.
Figure 5-11. Potential evaporation versus mean annual precipitation
00
+ Potential Evapotranspiration more than
mean annual precipitation
- Potenial Evapotranspiration less than
mean annual precipitation
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Figure 5-12. Development of the onsite wastewater system design concept
RECEIVER SITE
EVALUATION
DESIGN BOUNDARIES
DELINEATION
PERFORMANCE
REQUIREMENTS
DESIGN BOUNDARY
LOADINGS
IDENTIFICATION OF FEASIBLE
TREATMENT TRAIN ALTERNATIVES
EVALUATION OF ALTERNATIVE TREATMENT TRAINS
AESTHETICS
O&M
REQUIREMENTS
COSTS (CAPITAL &
RECURRING)
RELIABILITY
CONCEPTUAL DESIGN
FINAL DESIGN
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Assembling SWIS treatment trains for a site with shallow,
slowly permeable soils over bedrock
Site description
A single-family residence is proposed for a lot with shallow, finely textured, slowly permeable soil over
creviced bedrock. The depth of soil is 2 feet. The slope of the lot is moderate and is controlled by bedrock.
Ground water is more than 5 feet below the bedrock surface.
Design boundaries
Three obvious design boundaries that will affect the SWIS design are present on this site: the infiltrative
surface, the bedrock surface, and the water table. The site evaluation determined that no hydraulically
restrictive horizon is present in the soil profile above the bedrock.
Performance requirements
The regulatory agency requires that the wastewater discharge remain below ground surface at all times, that
the ground water contain no detectable fecal conforms, and that the nitrate concentrations of the ground water
be less than 10 mg-N/L at the property boundary. In this case study, wastewater modification (reducing mass
pollutant loads or implementing water conservation measures; see
chapter 3) was not considered.
Design boundary mass loadings
Infiltrative surface: Referring to table 5-2, the mass loadings that might affect the infiltrative surface are the
daily, instantaneous, and organic mass loadings. The selected hydraulic and instantaneous (dose volume per
square foot) loading rates must be appropriate for the characteristics of the soil to prevent surface seepage.
Assuming domestic septic tank effluent is discharged to the infiltrative surface and that the surface is placed
in the natural soil, the organic mass loading is accounted for in the commonly used daily hydraulic loading
rates. Typical hydraulic loading rates for domestic septic tank effluent control design. Reducing the organic
concentration through pretreatment will have little impact because the resistance of the biomat created by the
organic content is typically less than the resistance to flow through the fine-textured soil.
Bedrock boundary: The bedrock boundary is a secondary design boundary where a zone of saturation will
form as the wastewater percolates through the soil. This boundary is affected by the daily and linear hydraulic
loadings (table 5-2). If these hydraulic loadings exceed the rate at which the water is able to drain laterally
from the site or percolate to the water table through the bedrock crevices, the saturated zone thickness will
increase and could encroach on the infiltrative surface, reducing its treatment and hydraulic capacity. Because
the site is sloping, the linear, rather than the daily, hydraulic loading will control design.
Water table boundary: The wastewater percolate will enter the ground water through the bedrock crevices.
The daily and linear hydraulic loading and constituent loadings are the mass loadings that can affect this
boundary (table 5-2). Because of the depth of the water table below the bedrock surface and the porous nature
of the creviced bedrock, the daily and linear hydraulic loadings are not of concern. However, nitrate-nitrogen
and fecal conforms are critical design loadings because of the water quality requirements. Table 5-2
summarizes the critical design boundary mass loadings that will affect design.
Assembling feasible treatment train alternatives
Because control of the wastewater is lost after it is applied to the soil, the bedrock and water table boundary
loading requirements must be satisfied through appropriate design considerations at or before the infiltrative
boundary. Therefore, the secondary and water table boundary loadings must be considered first.
Constituent loading limits at the ground water boundary will control treatment requirements. Although the
performance boundary (the point at which performance requirements are measured) may be at the property
boundary, mixing and dilution in the ground water cannot be certain because the bedrock crevices can act as
direct conduits for transporting undiluted wastewater percolate. Therefore, it would be prudent to ensure these
pollutants are removed before they can leach to the ground water. Research has demonstrated that soils
similar to those present at the site (fine-textured, slowly permeable soils) can effectively remove the fecal
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conforms if the wastewater percolates through an unsaturated zone of 2 to 3 feet (Florida MRS, 1993).
Because the soil at the site extends to only a 2-foot depth, the infiltrative surface would need to be elevated 1
foot above the ground surface in a mound or at-grade system. Alternatively, disinfection prior to soil application
could be used. Nitrate is not effectively removed by unsaturated, aerated soil; therefore, pretreatment for
nitrogen removal is required.
Maintaining the linear loading at the bedrock surface below the maximum acceptable rate determines the
orientation and geometry of the infiltrative surface. The infiltrative surface will need to be oriented parallel to
the bedrock surface contour. Its geometry needs to be long and narrow, with a width no greater than the
maximum acceptable linear loading (gpd/ft) divided by the design hydraulic loading on the infiltrative surface
(gpd/ft2). Note: If a mound is used on this site, an additional design boundary is created at the mound fill/
natural soil interface. The daily hydraulic loading will affect this secondary design boundary.
If the perched saturated zone above the bedrock is expected to rise and fall with infiltrative surface loadings,
the instantaneous loading to the infiltrative surface should be controlled through timed dosing to maximize the
site's hydraulic capacity. Failure to control instantaneous loads could lead to transmission of partially treated
wastewater through bedrock crevices, driven by the higher hydraulic head created during periods of peak
system use. Applying the wastewater through a dosing regime will maximize retention time in the soil while
ensuring cyclical flooding of the infiltration trenches, creating optimum conditions for denitrifying bacteria to
accomplish nitrogen removal. The daily and instantaneous hydraulic loadings to the infiltrative surface are
dependent on the characteristics of the soil or fill material in which the SWIS is placed.
Alternative Pretreatment
Dosing
Infiltration
Nitrogen removal Timed dosing
Nitrogen removal with disinfection Timed dosing
Mound with pressure distribution
In-ground trenches with pressure distribution
From this boundary loading analysis, potential treatment train alternatives can be assembled. Table 4-1 and
the fact sheets in chapter 4 should be used to select appropriate system components.
Alternative 1 elevates the infiltrative surface in a mound of suitable sand fill. With at least a foot of fill and the
unsaturated 2 feet of natural soil below, fecal coliform removal will be nearly complete. The mound would be
designed as long and narrow, oriented parallel to the bedrock surface contours (equivalent to the land surface
contours since the slope is bedrock-controlled) to control the linear loading on the interface between the sand
fill and natural soil or at the bedrock surface. The infiltrative surface would be time-dosed through a pressure
or drip distribution network to distribute the wastewater onto the surface uniformly in time and space.
Alternative 2 places the infiltrative surface in the natural soil. With this design, there would be an insufficient
depth of unsaturated soil to remove the fecal conforms. Therefore, disinfection of the treated wastewater prior
to application to the soil would be necessary. The trenches would be oriented parallel to the bedrock surface
contours (equivalent to the land surface contours since the slope is bedrock-controlled) to control the linear
loading on the bedrock surface. If multiple trenches are used, the total daily volume of treated wastewater
applied per linear foot of trench parallel to the slope of the bedrock surface would be no greater than the
design linear loading for the site. Loadings to the infiltrative surface would be time-dosed through a pressure or
drip distribution network to distribute the wastewater uniformly in time and space.
Note that for the alternatives listed, multiple options exist for each of the system's components (see table 4-1).
Source: Otis, 2001.
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Subsurface wastewater infiltration system design in a restricted area
Often, the available area with soils suitable for subsurface infiltration of wastewater is limited. Because local
authorities usually do not permit point discharges to surface waters, subsurface infiltration usually is the only
option for wastewater treatment. However, a SWIS can perform as required only if the daily wastewater flow is
less than the site's hydraulic capacity.
The hydraulic capacity of the site is determined by the subsurface drainage capacity of the site. The drainage
capacity is defined by the soil profile and the daily hydraulic or linear mass loading to secondary or ground
water boundary surfaces. In some cases, however, the infiltration rate of the wastewater into the soil at the
infiltrative boundary is more limiting. Therefore, it is important to distinguish between the two boundaries if use
of the site is to be maximized. Where hydraulic loadings to secondary boundaries are the principal control
feature, the only option is to limit the amount of water applied to the secondary boundaries. This can be
accomplished through the following:
Orientation, geometry, and controlled dosing of the infiltrative surface
The infiltrative surface should be oriented parallel to and extended as much as possible along the surface
contour of the secondary boundary. Southern, eastern, and western exposures may provide better
evaporation than north-facing slopes. The daily hydraulic loading rate onto the total downslope projection of
"stacked" infiltration surfaces (multiple, evenly spaced SWIS trenches placed on the contour on sloping
terrain) should be limited to the maximum linear loading of the secondary boundary. Timed dosing to the
infiltrative surfaces should be used to apply wastewater uniformly over the full length of the infiltrative
surfaces to minimize the depth of soil saturation over the secondary boundary. Note that the presence of
other SWIS-based treatment systems above or below the site should be considered in load calculations
and design concept development.
Installation of water-conserving plumbing fixtures in the building served
The total daily volume of wastewater generated can be significantly reduced by installation of water-
conserving fixtures such as low-volume flush toilets and low-flow showerheads (see chapter 3). Also,
wastewater inputs from tub spas and automatic regenerating water softeners should be eliminated.
Maximizing the evapotranspiration potential of the infiltration system
Where the growing season is long or use of the property is limited to the summer months,
evapotranspiration can help to reduce the total hydraulic loading to the secondary boundary. The infiltrative
surfaces should be shallow and located in open, grassed areas with southern exposures (in the Northern
Hemisphere).
If the infiltration capacity at the soil's infiltrative surface is the limiting condition, measures to
increase infiltration can be taken. These measures include the following:
Reducing the mass loadings of soil clogging constituents on the infiltrative surface
The mass loadings to the infiltrative surface can be reduced either by increasing the infiltrative surface
area to reduce the mass constituent loading per unit of area or by removing the soil-clogging constituents
before soil application. Where the suitable area for the SWIS is limited, increasing the infiltrative surface
area might not be possible.
Controlled dosing of the infiltrative surface
Timed dosing and alternate "resting" of infiltrative surfaces allow organic materials that might clog the soil
surface to oxidize, helping to rejuvenate infiltrative capacity. Using multiple timed doses throughout the day
with intervals between doses to allow air diffusion maximizes the reaeration potential of the subsoil (Otis,
1997). Dual infiltration systems that can be alternately loaded allow for annual resting of the infiltrative
surfaces to oxidize the biomat. On small lots dual systems are often not feasible because of space
limitations.
Source: Otis, 2001.
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5.7.1 Identifying appropriate treatment
trains
Multiple treatment trains (system designs) are often
feasible for a particular receiver site and expected
wastewater flow. More than one receiving environ-
ment may be suitable for a treated discharge. For
example, subsurface infiltration or a point dis-
charge to surface water might be feasible. Multiple
sites on a property might be suitable as a receiver
site. In addition, more than one treatment train
might meet established or proposed performance
requirements. Each of these alternatives must be
considered to select the most appropriate system for
a given application.
Evaluation of the feasible alternatives is a continu-
ous activity throughout the preliminary design
process. It is beneficial to eliminate as many
potential options as possible early in the prelimi-
nary design process so that time can be spent on the
most probable alternatives. Typically, receiving
environments are the first to be eliminated. For
example, in temperate climates atmospheric
discharges are rarely feasible because there is
insufficient net evaporation to evaporate the
wastewater. Surface water discharges usually can
be eliminated as well because often they are not
permitted by the local regulatory agency. Where
such discharges are permitted, subsurface infiltra-
tion is usually less costly if the site meets the
regulatory agency's requirements because monitor-
ing costs for compliance with point discharge
permit requirements can be substantial.
At the completion of the site evaluation, the
receiving environment has been tentatively selected
(see section 5.5). For each potential receiver site,
the design boundaries have been identified.
Integrating information on physical limitations and
established or proposed performance requirements
helps to define the maximum mass loadings to the
design boundaries (see section 5.3). Defining and
characterizing the controlling design boundaries
and their maximum acceptable mass loadings,
estimating the characteristics of the wastewater to
be treated, and evaluating the site conditions
inform the development of a feasible set of poten-
tial treatment trains. Treatment train assembly is
usually straightforward for surface water dis-
charges because the effluent concentration limits at
the outfall control design. With soil-based systems
such as SWISs, however, treatment train selection
is more complex because multiple design bound-
aries can be involved.
Because direct control of SWIS performance is lost
once the partially treated wastewater enters the soil
at the infiltrative surface, management of the
loadings to any secondary design boundaries and
water table boundaries must be accomplished
indirectly through appropriate adaptations at the
primary infiltrative surface. For hydraulic loadings,
control can be achieved by changing the geometry
or size of the infiltrative surface or the dosing
volume, frequency, and pattern. For organic or
constituent loadings, control is achieved either by
pretreating the wastewater before it is applied to
the infiltrative surface or by increasing the size of
the infiltrative surface.
5.7.2 Treatment train selection
Where multiple treatment trains are feasible and
technically equivalent, each must be evaluated with
respect to aesthetics, operation and maintenance
requirements, cost, and reliability before selection
of the final design concept.
5.7.3 Aesthetic considerations
Aesthetics are an intangible factor that must be
addressed with the owner, users, adjacent property
owners, and regulators. They include consider-
ations such as system location preferences, appear-
ance, disruption during construction, equipment
and alarm noise, and odor potential. It is important
that these and possibly other aesthetics issues be
discussed with the appropriate parties before
selecting the design concept to be used. If the
expectations of the concerned parties are not met,
their dissatisfaction with the system could affect its
use and care.
5.7.4 Operation and maintenance
requirements
Specific and appropriate operation and mainte-
nance tasks and schedules are essential if a waste-
water system is to perform properly over its
intended service life. Important considerations
include
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Chapter 5: Treatment System Selection
• Types of maintenance functions that must be
performed
• Frequency of routine maintenance
• Time and skills required to perform routine
maintenance
• Availability of operation and maintenance
service providers with appropriate skills
• Availability of factory service and replacement
parts
Traditional onsite systems are passive in design,
requiring little operator attention or skill. Unskilled
owners can usually access maintenance services or
be trained to perform basic maintenance tasks.
Septage removal usually requires professional
services, but these are readily available in most
areas. More complex wastewater systems, however,
require elevated levels of operator attention and
skill. The designer must weigh the availability of
operator services in the locale of the proposed
system against the consequences of inadequate
operation and maintenance before recommending a
more complex system. The availability of factory
service is also an important consideration. Where
operation and maintenance services are not locally
available and the use of alternative systems that
have fewer operation and maintenance require-
ments is not an option, the prospective system
owner should be advised fully before proceeding.
5.7.5 Costs
Costs of the feasible alternatives should be arrayed
based on the total cost of each alternative. Total
costs include both the capital costs incurred in
planning, designing, and constructing the system
and the long-term costs associated with maintaining
the system over its design life (20 to 30 years in
most cases; see table 5-8). This method of cost
analysis is an equitable method of comparing
alternatives with higher capital costs but lower
annual operating costs to other alternatives with
lower capital costs but higher annual operating
costs. Often, owners are deceived by systems with
lower capital costs. These systems might have much
higher annual operating costs, a shorter design life,
and possibly higher replacement costs, resulting in
much higher total costs. Systems with higher capital
costs might have lower total costs because the
recurring operation and maintenance costs are less.
Choosing between alternatives with varying total
cost options is a financing decision. In some cases,
capital budgets are tighter than operating budgets.
Therefore, this is a decision the prospective owner
must make based on available financing options.
Table 5-8 is an example of such a comparative
analysis.
The USEPA Office of Wastewater Management
posts financing information for onsite wastewater
treatment systems or other decentralized systems
(cluster systems not connected to a wastewater
treatment plant) on the Internet at http://
www.epa.gov/owm/decent/funding.htm. Links are
available at that site to financing programs sup-
ported by a variety of federal, state, and other
public and private organizations.
5.7.6 Reliability
The reliability of the proposed system and the risks
to the owner, the public, and the environment if
malfunctions or failures occur must be considered.
Potential risks include public health and environ-
mental risks, property damage, personal injury,
medical expenses, fines, and penalties. Where these
or other potential risks are significant, contingency
plans should be developed to manage the risks.
Contingencies include storage, pump and haul
(holding tank), redundant components, reserve
capacity, and designation of areas for repair or
replacement components (e.g., replacement leach
field). These come at additional cost, so their
benefit must be weighed against the potential risks.
5.7.7 Conceptual design
After evaluating the feasible options, the prelimi-
nary treatment train components can be selected. At
this point in the development of the design, the unit
processes to be used and their sequence are de-
fined. A preliminary layout should be prepared to
confirm that the system will fit on the available site.
Sufficient detail should be available to prepare a
preliminary cost estimate if needed. It is recom-
mended that the conceptual system design and
preliminary layout be submitted to the regulatory
agency for conditional acceptance of the chosen
system. Final design can proceed upon acceptance
by the owner and regulatory agency.
5-30
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Chapter 5: Treatment System Selection
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L/SER4 0/7srte Wastewater Treatment Systems Manual
5-31
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Chapter 5: Treatment System Selection
Table 5-9. Common onsite wastewater treatment system failures
Type of failure
Evidence of failure
Hydraulic failure
Pollutant contamination of
ground water
Microbial contamination of
ground and surface water
Nutrient contamination of
surface water
Untreated or partially treated sewage pooling on ground surfaces, sewage backup in plumbing fixtures,
sewage breakouts on hill slopes
High nitrate levels in drinking water wells; taste or odor problems (e.g., sulfur, household cleaners) in well
water caused by untreated, poorly treated, or partially treated wastewater; presence of toxics (e.g., solvents,
cleaners) in well water
Shellfish bed bacterial contamination, recreational beach closures due high bacterial levels, contamination of
drinking water wells with fecal bacteria or other fecal indicators
Algae blooms, high aquatic plant productivity, low dissolved oxygen concentrations
5.8 Rehabilitating and upgrading
existing systems
Onsite wastewater treatment systems can fail to
meet the established performance requirements.
When this occurs, corrective actions are necessary.
Successful rehabilitation requires knowledge of the
performance requirements, a sound diagnostic
procedure, and appropriate selection of corrective
actions.
5.8.1 Defining system failure
Failure occurs when performance requirements are
not met (see table 5-9). Under traditional prescrip-
tive rules, onsite wastewater systems must comply
with specific siting and design requirements,
maintain the discharged wastewater below ground
surface, and not cause backup in fixtures. Typi-
cally, failures are declared when wastewater is
observed on the ground surface or is backing up in
the household plumbing. However, systems also
may be declared as failed if they do not comply
with the prescriptive design rules. Thus, except for
hydraulic failures, systems can be declared failed
based on their design, but rarely based on treatment
performance to date.
When failure is strictly a code compliance issue
rather than a performance issue, enforcing correc-
tive actions can be problematic because corrective
actions for code-based compliance might not
reduce (and might even elevate) the potential risk
to human health or the environment. Also, code
compliance failures can be much more difficult to
correct because site or wastewater characteristics
might prevent compliance with the prescriptive
requirements. In such instances, variances to the
rule requirements are needed to remove the
noncompliant condition. Performance codes, on the
other hand, define failures based on performance
requirements consisting of specific and measurable
criteria. Usually, treatment options are feasible to
achieve compliance, though costs can be a signifi-
cant impediment.
5.8.2 Failure diagnosis
Wastewater system failures occur at the design
boundaries when the acceptable boundary loadings
are exceeded. Prescribing an effective corrective
measure requires that the failure boundary and the
unsuitable boundary loading be correctly identified.
The manifestations of boundary failures can be
similar in appearance despite different locations or
causes of failure. For example, the primary infiltra-
tive surface might fail to accept the daily wastewa-
ter load, causing the discharged wastewater to seep
onto the ground surface. The cause of failure might
be that the daily hydraulic capacity of the infiltra-
tive surface was exceeded, the instantaneous
hydraulic loading (dose volume) was too great, or
the organic load was too high. In other instances,
the linear loading on a site might be exceeded,
causing a saturated zone above a secondary restric-
tive horizon to rise and encroach on the infiltrative
surface (effluent mounding). The potential gradient
across this surface is reduced in this situation, and
the reaeration of the subsoil is inhibited. As a result
of the reduced gradient and increased clogging, the
infiltrative surface can no longer accept the daily
5-32
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Chapter 5: Treatment System Selection
Figure 5-13. Onsite wastewater failure diagnosis and
correction procedure
REPORTED WASTEWATER SYSTEM
FAILURE
INITIAL DATA GATHERING
• System layout and boundary loadings
• Soil test reports
• Age of system
• Description of failure symptoms
• Daily flow estimates
• Visusal observation
CAUSE OF FAILURE DETERMINATION
• Develop failure hypothesis considering
Failure boundary
Boundary loadings
HYPOTHESIS TESTING
• Soils Testing
• Wastewater metering
• Wastewater sampling
• Component testing/monitoring
DESIGN CORRECTIVE ACTION
• Change boundary loadings
Water conservation
Wastewater segregation
Additional infiltrative surface area
Pretreatment
Subsurface drainage diversion
Infiltrative surface orientation and
geometry
• Change receiver site
• Change receiving environment
loading and allows wastewater to back up in the
trenches and possibly to surface. Though the causes
of failure in these two instances are different, the
symptoms are similar. Thus, it is important that a
systematic approach to failure diagnosis be used.
Failures occur for a reason. The reason for failure
should be determined before corrective actions are
implemented; if not, failures can recur. The
diagnostic procedure should be comprehensive, but
based on deductive reasoning to avoid excessive
testing and data gathering (figure 5-13). Another
example of a failure diagnosis, Failure Analysis
Chart for Troubleshooting Septic Systems (FACTS)
is provided in Adams et al., 1998.
In addition to specific design boundary failures,
failures can be caused by system age. Tanks and
pipes buried in the ground begin to deteriorate after
20 or more years of use and may require repair or
replacement. In addition, the treatment capabilities
of soils below infiltration fields that have been in
use for several decades might not be adequate for
continued use. Years of treatment use can cause the
interstitial spaces between soil particles to become
filled with contaminants (e.g., TSS, precipitates,
biomass). Soil structure can also be affected after
many years of use. Finally, changes in design and
construction practices in the past 25 years have led
to marked improvements in system performance
and treatment capacity. These issues make consider-
ation of system age a vital component of the
overall failure investigation.
5.8.3 Initial data gathering
When a failure is reported, relevant information
regarding the system should be gathered.
• Visual observation. A visual observation of the
failure should be made to confirm the informa-
tion provided. Also, the owner should be
interviewed regarding the owner's observations,
use of the building, and other relevant informa-
tion. Each of the system components should be
inspected and mechanical components (e.g.,
float switches, flow diverters) tested.
• Past operation and maintenance practices.
Assessing operation and maintenance actions
taken over the past 3 to 5 years can often aid in
detecting relatively simple problems. Perhaps
the tank has not been pumped, the tank filter (if
used) has not been cleaned, the electrical supply
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 5: Treatment System Selection
to the pumps has not been checked, or the
switches have not been examined.
System layout and boundary design loadings.
The system layout can be obtained from the
design drawings or from a site survey. From the
layout, the design boundary loadings should be
determined or estimated based on the original
design flow.
Soil test reports. Soil test reports should be
obtained. If none are available, soil auger
testing between the trenches or just outside the
SWIS perimeter might be necessary to provide a
simple description of the soil profile to deter-
mine whether any significant secondary design
boundaries might be present.
Age of system. If the system age is less than 2
years, it is likely the design boundary loadings
were in error or improper construction tech-
niques (e.g., operation of heavy equipment on
SWIS area, installation during wet conditions)
that significantly altered the soil characteristics
were used. If the age of the system is greater
than 2 years, it is likely that the design condi-
tions changed. Changed conditions could
include changes in the building's use, increased
wastewater flows, infiltration and inflow into the
system, surface runoff over the system, im-
proper maintenance, compaction of SWIS soils
by vehicle traffic, and others.
Description of failure symptoms. The symptoms
of failure are important. Historically, reported
failures have usually been hydraulic in nature
and tended to be manifested by surface seepage.
Information on the location and frequency of
the surface seepage helps to determine the
specific design boundary at which the failure
occurred and possible causes of the failure. For
example, surface seepage above the infiltration
system suggests that the infiltrative surface is
overloaded, either hydraulically or organically.
Seepage downslope from the system suggests
that a secondary design boundary exists and is
overloaded hydraulically. If the failure is
seasonal, wet weather conditions are likely to be
the cause; that is, clear water is infiltrating into
the system or causing inadequate subsurface
drainage.
Daily flow estimates. Estimates of daily waste-
water flows derived from water meter data or
other sources are needed to compare the design
loadings with actual loadings. In the absence of
data, water use should be estimated (see chapter
3) with the caveat that such estimates are seldom
accurate. Where practical, water meters should
be read or installed as soon as the failure is
reported so that metered data can be collected.
Initially, daily flow estimates might need to
suffice for the purposes of failure analysis.
Leaking plumbing fixtures, such as improperly
seated toilet tank flapper valves, should be
investigated.
5.8.4 Determining the cause of failure
From the gathered data, hypotheses of potential
causes of failure should be formulated. Formulat-
ing hypotheses is an important step in diagnosing
the problem because the hypotheses can be tested to
provide a systematic and efficient analysis of
possible causes of failure (see case study). Testing
can take many forms (see table 5-10 as an example
of a local approach) depending on the hypotheses
to be tested. It may include soil profile descrip-
tions, soil hydraulic conductivity testing, wastewa-
ter characterization, equipment testing and monitor-
ing, and other tests.
5.8.5 Designing corrective actions
If the design boundary failure can be identified and
its cause identified, selecting an appropriate
corrective action is straightforward. Table 5-11 can
be used to select the appropriate corrective action
for a given boundary failure. This table presents
classes of corrective actions and the impacts they
can be expected to have on boundary mass load-
ings. Several options typically exist for each class
of corrective action. Specific actions will be
determined by the particular needs of the system
and site.
The failure diagnosis and correction procedure
outlined in figure 5-13 provides a summary of
activities required to identify and characterize the
cause of failure. As noted in the previous discus-
sion, data collection, failure cause determination,
and testing of hypotheses (e.g., as in the case study
above) provides key information needed to develop
corrective actions. Failures at design boundaries
(e.g., exceeding mass pollutant or hydraulic load
limits) can be rectified by changing boundary
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Chapter 5: Treatment System Selection
Table 5-10. General OWTS inspection and failure detection process3
Inspection process steps
Field procedures
General site review
Notification of inspection / Owner is sent a notice of inspection 1 month before inspection date indicating time and date of
inspection (waived for failure investigations)
/ Information and requirements concerning provision of access to system are included with notice
File review / Review system design features
/ Review prior inspection reports
/ Review other relevant file information
/ Note unusual circumstances on inspection form
/ Walk property to confirm location of tank, SWIS, other system features, water resources, wells (if
present), drainage patterns (relative to SWIS)
/ Check tank and SWIS area for effluent surfacing, odors, graywater bypass, selective fertility,
unusual conditions
/ Check diversion valves (if present); confirm location of operating SWIS (if more than one)
/ Open tank; examine for structural problems (cracking, settling, decay)
/ Check inlet and outlet ports for positioning, scum accumulation, rocks, root matter, obstructions
/ Check liquid level in tank; measure scum/sludge levels
S Inspect risers (if present) for structural integrity and watertightness
/ Check pump basins for structural integrity
/ Check pumps and switches (if present); operate float switches to confirm operation
SWIS inspection / Visually inspect SWIS for signs of wetness, odor, effluent pooling, selective fertility, presence of
shrubs or trees, settling, signs of vehicles driving over SWIS, new structures (driveways,
outbuildings) encroaching on SWIS, runoff across SWIS surface
/ Conduct hydraulic load test to assess SWIS operation (see table 5-11)
' Inspection program requirements of The Sea Ranch in California. See table 5-11.
Source: Adapted from Hantzsche, 1995.
Table 5-11. Response of corrective actions on SWIS boundary mass loadings.
Inspection of septic tank and
appurtenances
CORRECTIVE ACTION
Water conservation
Wastewater segregation
Elimination of I/I
Surface drainage diversion
Subsurface drainage
diversion
Timed dosing
Additional infiltration area;
resting existing SWIS
Pretreatment
Infiltration surface
orientation and geometry
BOUNDARY LOADINGS
INFILTRATION BOUNDARY
Daily
hydraulic
(gal/d-ft2)
1
1
1
Wo Impact
No Impact
No Impact
1
Wo Impact
No Impact
Instantaneous
hydraulic
(gal/dose-ft2)
Wo Impact
No Impact
No Impact
No Impact
No Impact
1
1
Wo Impact
No Impact
Organic
(Ib cBOD/fl2)
Wo Impact
4
No Impact
No Impact
No Impact
No Impact
1
1
Wo Impact
SECONDARY BOUNDARY
Dally hydraulic
(gal/d-ft2)
1
1
*
1
1
Wo Impact
1
Wo Impact
1
Linar
hydraulic
(gal/d-ft)
1
1
1
1
1
Wo Impact
1
Wo /mpacf
1
WATER TABLE BOUNDARY
Daily
hydraulic
(gal/d-fl2)
I
1
1
1
1
Wo Impact
1
Wo Impact
1
Linear
hydraulic
(gal/d-ft)
1
*
*
^
*
Wo Impact
4
No Impact
^
Constituent
(Ibxyz/ft2)
Wo Impact
4
No Impact
No Impact
No Impact
No Impact
1
1
Wo Impact
Notes: Assumes uniform application of wastewater over the infiltrative surfaces for the action to have a significant impact.
X indicates reduced loading rate.
Source: Otis, 2001.
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Chapter 5: Treatment System Selection
Failure hypothesis testing at a system serving a highway rest area
A wastewater system serving a highway rest area used a drip distribution system for final treatment and
dispersal of the wastewater. After the first summer of use, water was observed above the dispersal system.
The original soil test results indicated that the soils were deep, loamy sands with no apparent secondary
boundaries. The system design appeared to use appropriate loadings on the infiltrative surfaces.
A visual inspection and interviews with the maintenance staff at the rest area provided important clues:
/ The site of the dispersal system had been significantly regraded after the soil testing had been
completed. Up to 5 feet of material had been removed from the site.
/ The system was a replacement for another system that had also failed. The existing septic tanks were used
in the new system.
/ Water use was metered and recorded daily.
/ The rest area had a sanitary dump station that discharged into the wastewater system. The dump station
received very heavy use on weekends during the summer. This load was not accounted for in the metering
data.
From these clues, several hypotheses were formulated fortesting.
a. Water discharges to the system exceed the hydraulic and constituent design loadings.
This hypothesis can be tested by estimating daily wastewater discharges. The recorded water meter data
provide an accurate estimate of water use at the rest area. The metered data would need to be corrected for
turf irrigation at the rest area. Turf irrigation can be estimated from staff interviews of irrigation schedules.
Unaccounted water from the sanitary dump station must be estimated. Counting the number of vehicles
using the dump station and assuming an average volume of wastewater discharged per vehicle would
provide a reasonable estimate. Because of the strength of the dump station wastewater, wastewater
samples at the septic tank outlets should be taken to determine organic loadings.
Another issue that might need to be considered is load inputs from disinfectants or other chemicals used in
holding tanks that are discharged into the dump station. Significant concentrations of these chemicals could
affect biological processes in the tank and infiltrative zone.
b. Infiltration/inflow of clear water into the system or into the SWIS is excessive.
Only the septic tanks were left in place during the reconstruction of the existing system. All new
components were leak tested during construction. It can be assumed that the new portion of the system
does not leak if inspection records exist and can be verified. The existing septic tanks could be expected to
be the source of any inflow or infiltration. Infiltration of surface runoff from the area over the septic tanks,
revealed by the existence of saturated soils around the tanks, could result in significant infloinfiltration
contributions. If there is evidence that such conditions exist, the septic tanks should be pumped and tested
for leakage. Runoff of storm water onto the SWIS surface could also cause ponding and might require
regrading of the surrounding site or a diversion to route runoff elsewhere
c. The actual soil characteristics at the receiver site are different from the soil test results.
The characteristics of the soils after regrading might be different from those reported by the original soil
tests because of the depth of soil removed. Also, the regrading operations might have compacted the
subsoil, creating a secondary design boundary that was not anticipated. Soil tests could be performed to
determine if the existing profile below the dispersal system is different in texture, structure, and bulk density
from that reported earlier. Also, the source of the surface seepage should be investigated. If the seepage
occurs immediately above a dripperline but the soil is not saturated between the lines, the infiltrative surface
surrounding the dripperline is hydraulically or organically overloaded. If the soil between the lines is
saturated, a secondary boundary that is hydraulically overloaded probably exists. If such a boundary is
present, the soil below the boundary would be unsaturated.
By developing these hypotheses, determination of the failure can be systematic and efficient. The most probable
hypothesis can be tested first, or appropriate tests for all the hypotheses formulated can be performed at one time
for later evaluation.
Source: Otis, 2001.
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Chapter 5: Treatment System Selection
loadings to accommodate the hydraulic or mass
pollutant assimilative capacities at the design
boundary. Loading adjustments may require
lowering water usage through water conservation
measures, eliminating clear water inputs, or
separating graywater; increasing the area of the
infiltrative surface; or diverting precipitation and/
or shallow ground water from the SWIS with berms
or curtain drains.
Approaches for lowering mass pollutant loads
include improving pretreatment by upgrading the
existing system and/or adding treatment units,
improving user habits (e.g., removing food,
kitchen, or dishwashing wastes from the wastewater
stream), reducing or eliminating inputs of cleaners
or other strong chemical products, and reducing
solid waste in the wastewater stream (e.g., ground
garbage from garbage disposals). If measures to
correct failures within the existing receiver site are
not possible, corrective actions may involve
changing the receiver site or changing the receiver
site conditions. These options include adoption of
different treatment technologies, physical alteration
of the receiver site, and installation of a new
infiltration system, thereby resting the existing
system for future alternate dosing.
Attention to established performance requirements
and the design boundaries where they are measured
helps to ensure that corrective actions meet the
overall goals of the management entity and protect
human health and the environment. Implementation
of corrective actions should follow the same
processes and procedures outlined in the preceding
sections for new or replacement OWTSs.
References
Adams, A., M.T. Hoover, W. Arrington, and G.
Young. 1998. FACTS: Failure Analysis Chart for
Troubleshooting Septic Systems. In Onsite
wastewater Treatment: Proceedings of the Eighth
National Symposium on Individual and Small
Community Sewage Systems. American Society
of Agricultural Engineers, St. Joseph, MI.
American Society for Testing and Materials
(ASTM). 1996a. Standard Practice for Surface
Site Characterization for Onsite Septic Systems.
ASTM Practice D5879-95 el. American
Society for Testing and Materials, West
Conshohocken, PA.
American Society for Testing and Materials
(ASTM). 1996b Standard Practice for
Subsurface Site Characterization of Test Pits
for Onsite Septic Systems. ASTM Practice
D5921-96 el. American Society for Testing and
Materials, West Conshohocken, PA.
American Society for Testing and Materials
(ASTM). 1997. Standards Related to On-Site
Septic Systems. ASTM publication code 03-
418197-38. American Society for Testing and
Materials, West Conshohocken, PA.
American Society for Testing and Materials
(ASTM). 2000. Standard Practice for
Classification of Soils for Engineering
Purposes (Unified Soil Classification System).
ASTM D 2487-00. American Society for
Testing and Materials, West Conshohocken,
PA.
Ayres Associates. 1993. Onsite Sewage Disposal
System Research in Florida—An Evaluation of
Current OSDS Practices in Florida. Report to
the Department of Health and Rehabilitative
Services. Ayres and Associates, Tallahassee,
FL.
Black, C.A., ed. 1965. Methods of Soil Analysis.
Part 1: Physical and Microbiological
Properties, Including Statistical Measurement
and Sampling. American Society of Agronomy,
Madison, WI.
Bouma, J., and L.W Dekker. 1981. A method of
measuring the vertical and horizontal hydraulic
saturated conductivity of clay soils with
macropores. 5*0/7 Science Society of America
Journal 45:662.
Bouwer, H. 1978. Groundwater Hydrology.
McGraw-Hill Book Company, New York, NY.
Bouwer, H., and R.C. Rice. 1976. A slug test for
determining hydraulic conductivity of
unconfmed aquifers with completely or
partially penetrating wells. Water Resources
Research 12:423-428.
Brock, R.P. 1976. Dupuit-Forcheimer and potential
theories for recharge from basins. Water
Resources Research 12:909.
USEPA Onsite Wastewater Treatment Systems Manual
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Chapter 5: Treatment System Selection
Finnemore, E.J., and N.N. Hantzshe. 1983.
Ground-water mounding due to onsite sewage
disposal. Journal of the American Society of
Civil Engineers Irrigation and Drainage
Division 109:999.
Florida Department of Health and Rehabilitative
Services (Florida HRS). 1993. Onsite Sewage
Disposal System Reseach in Florida.
Tallahassee, FL.
Freeze, R.A., and J.A. Cherry. 1979. Groundwater.
Prentice-Hall, Englewoods Cliffs, NJ.
Fredrick, J.C. 1948. Solving disposal problems in
unsewered areas. Sewage Works Engineering
19(6):292-293, 320.
Glegg, G.L. 1971. The Design of Design.
Cambridge University Press, London, England.
Hantush, M.S. 1967. Growth and decay of ground
water mounds in response to uniform
percolation. Water Resources Research 3:227.
Hantzsche, N.N. 1995. Data Management System
for On-Site Wastewater Inspection Program at
The Sea Ranch, California. In Proceedings of
the Sixth International Symposium on
Individual and Small Community Sewage
Systems. American Society of Agricultural
Engineers, St. Joseph, MI.
Hill, R.L., and L.D. King. 1982. A permeameter
which eliminates boundary flow errors in
saturated hydraulic conductivity measurements.
5*077 Science Society of America Journal
46:877.
Hoover, M.T. 1997. A Framework for Site
Evaluation, Design, and Engineering of On-
site Technologies Within a Management
Context. Marine Studies Consortium, Waquoit
Bay National Esturarine Research Reserve, and
ad hoc Task Force for Decentralized
Wastewater Management. Marine Studies
Consortium, Chestnut Hill, MA.
Kahn, M.Y., D. Kirkham, and R.L. Handy. 1976.
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mounds. Water Resources Research 12:429.
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GretagMacbeth LLC, New Windsor, NY.
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Health, and Natural Resources (North Carolina
DEHNR). 1996. On-Site Wastewater
Management: Guidance Manual. North
Carolina Department of Environment, Health,
and Natural Resources, Division of
Environmental Health, On-Site Wastewater
Section, Raleigh, NC.
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Soils. Version 1.1. U.S. Department of
Agriculture, Natural Resources Conservation
Service, National Soil Survey Center, Lincoln,
NE. .
Otis, R.J. 1997. Considering Reaeration. In Ninth
Northwest On-Site Wastewater Treatment Short
Course and Equipment Short Course,
University of Washington, Seattle.
Otis, R.J. 1999. Designing on the Boundaries: A
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NOWRA Conference and Exhibit. National
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Otis, R.J. 2001. Boundary Design: A Strategy for
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Chapter 5: Treatment System Selection
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Glossary
Glossary
Absorption: The process by which one substance is
taken into and included within another substance,
such as the absorption of water by soil or nutrients
by plants.
Activated sludge process: A biological wastewater
treatment process in which biologically active
sludge is agitated and aerated with incoming
wastewater. The activated sludge is subsequently
separated from the treated wastewater (mixed
liquor) by sedimentation, and most of it is returned
to the process. The rest is wasted as needed.
Adsorption: The increased concentration of
molecules or ions at a surface, including exchange-
able cations and anions on soil particles. The
adherence of a dissolved solid to the surface of a
solid.
Aerobic: Having molecular oxygen as a part of the
environment, or growing or occurring only in the
presence of molecular oxygen, as in "aerobic
organisms."
Aerobic treatment unit (ATU): A mechanical
onsite treatment unit that provides secondary
wastewater treatment by mixing air (oxygen) and
aerobic and facultative microbes with the wastewa-
ter. ATUs typically use a suspended growth treat-
ment process (similar to activated sludge extended
aeration) or a fixed film treatment process (similar
to trickling filter).
Alternative onsite wastewater treatment system:
An onsite treatment system that includes compo-
nents different from those used in a conventional
septic tank and drain field system. An alternative
system is used to achieve acceptable treatment and
dispersal/discharge of wastewater where conven-
tional systems may not be capable of meeting
established performance requirements to protect
public health and water resources, (e.g., at sites
where high ground water, low-permeability soils,
shallow soils, or other conditions limit the infiltra-
tion and dispersal of wastewater or where addi-
tional treatment is needed to protect ground water
or surface water quality). Components that might be
used in alternative systems include sand filters,
aerobic treatment units, disinfection devices, and
alternative SWISs such as mounds, gravelless
trenches, and pressure and drip distribution.
Anaerobic: Characterized by the absence of
molecular oxygen, or growing in the absence of
molecular oxygen (as in "anaerobic bacteria").
Anaerobic upflow filter: A high-specific-surface
anaerobic reactor filled with a solid media through
which wastewater flows; used to pretreat high-
strength wastewater or to denitrify nitrified waste-
water.
Biochemical oxygen demand (BOD): A commonly
used gross measurement of the concentration of
biodegradable organic impurities in wastewater.
The amount of oxygen, expressed in milligrams per
liter (mg/L), required by bacteria while stabilizing,
digesting, or treating organic matter under aerobic
conditions is determined by the availability of
material in the wastewater to be used as biological
food and the amount of oxygen used by the micro-
organisms during oxidation.
Biomat: The layer of biological growth and
inorganic residue that develops at the wastewater-
soil interface and extends up to about 1 inch into
the soil matrix. The biomat controls the rate at
which pretreated wastewater moves through the
infiltrative surface/zone for coarse- to medium-
textured soils. This growth may not control fluxes
through fine clay soils, which are more restrictive
to wastewater flows than the biomat.
Blackwater: Liquid and solid human body waste
and the carriage waters generated through toilet
usage.
Centralized wastewater treatment system: A
wastewater collection and treatment system that
consists of collection sewers and a centralized
treatment facility. Centralized systems are used to
collect and treat wastewater from entire communities.
Chemical oxygen demand (COD): A measure of
oxygen use equivalent to the portion of organic
matter that is susceptible to oxidation by a strong
chemical oxidizing agent.
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Glossary
Chlorine residual: The total amount of chlorine
(combined and free available chlorine) remaining in
water, sewage, or industrial wastes at the end of a
specified contact period following disinfection.
Clarifiers: Settling tanks that typically remove
settleable solids by gravity.
Class V injection well: A shallow well used to
place a variety of fluids at shallow depths below the
land surface, including a domestic onsite wastewater
treatment system serving more than 20 people.
USEPA permits these wells to inject wastes below
the ground surface provided they meet certain
requirements and do not endanger underground
sources of drinking water.
Clay: A textural class of soils consisting of particles
less than 0.002 millimeters in diameter.
Cluster system: A wastewater collection and
treatment system under some form of common
ownership and management that provides treatment
and dispersal/discharge of wastewater from two or
more homes or buildings but less than an entire
community.
Coliform bacteria: A group of bacteria predomi-
nantly inhabiting the intestines of humans or other
warm-blooded animals, but also occasionally found
elsewhere. Used as an indicator of human fecal
contamination.
Colloids: The solids fraction that is described as the
finely divided suspended matter that will not settle
by gravity and is too large to be considered dis-
solved matter.
Compliance boundary: A performance boundary
with enforceable performance limits (through an
operating permit).
Consistence: Attribute of soil expressed in degree
of cohesion and adhesion, or in resistance to
deformation or rupture. Consistence includes the
resistance of soil material to rupture; resistance to
penetration; the plasticity, toughness, or stickiness
of puddled soil material; and the manner in which
the soil material behaves when subjected to com-
pression. General classifications of soil consistence
include loose, friable, firm, and extremely firm.
Constructed wetland: An aquatic treatment system
consisting of one or more lined or unlined basins,
some or all of which may be filled with a treatment
medium and wastewater undergoing some combina-
tion of physical, chemical, and/or biological
treatment and evaporation and evapotranspiration
by means of macrophytes planted in the treatment
medium.
Construction permit: A permit issued or autho-
rized by the regulatory authority that allows the
installation of a wastewater treatment system in
accordance with approved plans and applicable
codes.
Continuous-flow, suspended-growth aerobic
system: A typical activated sludge process.
Conventional onsite system: A wastewater treat-
ment system consisting of a septic tank and subsur-
face wastewater infiltration system.
Decentralized system: Onsite and/or cluster
wastewater systems used to treat and disperse or
discharge small volumes of wastewater, generally
from dwellings and businesses that are located
relatively close together. Decentralized systems in a
particular management area or jurisdiction are
managed by a common management entity.
Denitrification: The biochemical reduction of
nitrate or nitrite to gaseous molecular nitrogen or an
oxide of nitrogen.
Digestion: The biological decomposition of organic
matter in sludge, resulting in partial gasification,
liquefaction, and mineralization.
Disinfection: The process of destroying pathogenic
and other microorganisms in wastewater, typically
through application of chlorine compounds, ultra-
violet light, iodine, ozone, and the like.
Dissolved oxygen (DO): The oxygen dissolved in
water, wastewater, or other liquid, usually expressed
in milligrams per liter (mg/L), parts per million
(ppm), or percent of saturation.
Dissolved solids: The fraction of solids dissolved in
water.
Drain field: Shallow, covered, excavation made in
unsaturated soil into which pretreated wastewater is
discharged through distribution piping for applica-
tion onto soil infiltration surfaces through porous
media or manufactured (gravelless) components
Glossary-2
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Glossary
placed in the excavations. The soil accepts, treats,
and disperses wastewater as it percolates through
the soil, ultimately discharging to groundwater.
Effluent: Sewage, water, or other liquid, partially
or completely treated or in its natural state, flowing
out of a septic tank, subsurface wastewater infiltra-
tion system, aerobic treatment unit, or other
treatment system or system component.
Effluent filter (also called an effluent screen): A
removable, cleanable device inserted into the outlet
piping of the septic tank designed to trap excessive
solids due to tank upsets that would otherwise be
transported to the subsurface wastewater infiltration
system or other downstream treatment components.
Effluent screen: See Effluent filter.
Engineered design: An onsite or cluster system
that is designed to meet specific performance
requirements for a particular site as certified by a
licensed professional engineer or other qualified
and licensed or certified person.
Environmental sensitivity: The relative suscepti-
bility to adverse impacts of a water resource or
other environments that may receive wastewater
discharges.
Eutrophic: A term applied to water that has a
concentration of nutrients optimal, or nearly so, for
plant or animal growth. In general, nitrogen and
phosphorus compounds contribute to eutrophic
conditions in coastal and inland fresh waters,
respectively.
Evapotranspiration: The combined loss of water
from a given area and during a specified period of
time by evaporation from the soil or water surface
and by transpiration from plants.
Fixed-film wastewater treatment system: A
biological wastewater treatment process that
employs a medium such as rock, plastic, wood, or
other natural or synthetic solid material that will
support biomass on its surface. Fixed-film systems
include those in which the medium is held in place
and is stationary relative to fluid flow (tricking
filter), those in which the medium is in motion
relative to the wastewater (e.g., rotating biological
disk), and dual process systems that include both
fixed and suspended biomass together or in a
series.
Graywater: Wastewater drained from sinks, tubs,
showers, dishwashers, clothes washers, and other
non-toilet sources.
Hydraulic conductivity: As applied to soils, the
ability of the soil to transmit water in liquid form
through pores.
Laminar: Used to describe flat, sheet-like ground
water flows that migrate laterally along the upper
surface of a confining layer of soil or rock.
Management entity: An entity similar to a
responsible management entity, but managing a
limited set of management activities (e.g.,
homeowners' association, contracted provider of
management services).
Management services: Planning, design, permit-
ting, inspection, construction/installation, opera-
tion, maintenance, monitoring, enforcement, and
other services required to ensure that the wastewa-
ter treatment performance requirements established
by the regulatory authority are achieved. Manage-
ment services should be provided by properly
trained personnel and tracked by means of a
comprehensive management information system.
Mineralization: The conversion of an element
from an organic form to an inorganic state as a
result of microbial decomposition.
Mottling: Spots or blotches of different colors or
shades of color interspersed with the dominant soil
color caused in part by exposure to alternating
unsaturated and saturated conditions.
Nitrification: The biochemical oxidation of
ammonium to nitrate.
Nonconventional onsite wastewater treatment
system: System using technologies or combinations
of technologies that are used where conventional
onsite treatment systems cannot meet established
performance or prescriptive requirements because
of limiting site conditions. Also referred to as
Alternative onsite wastewater treatment systems.
Onsite wastewater treatment system (OWTS): A
system relying on natural processes and/or me-
chanical components that is used to collect, treat,
and disperse/discharge wastewater from single
dwellings or buildings.
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Glossary
Operating permit: A renewable and revocable
permit to operate and maintain an onsite or cluster
treatment system in compliance with specific
operational or performance requirements.
Organic nitrogen: Nitrogen combined in organic
molecules such as proteins and amino acids.
Organic soil: A soil that contains a high percentage
(more than 15 to 20 percent) of organic matter
throughout the soil column.
Package plant: Term commonly used to describe
an aerobic treatment unit serving multiple dwell-
ings or an educational, health care, or other large
facility.
Particle size: The effective diameter of a particle,
usually measured by sedimentation or sieving.
Particle-size distribution: The amounts of the
various soil size fractions in a soil sample, usually
expressed as weight percentage.
Pathogenic: Causing disease; commonly applied to
microorganisms that cause infectious diseases.
Ped: A unit of soil structure such as an aggregate,
crumb, prism, block, or granule, formed by natural
processes.
Perched water table: The permanent or temporary
water table of a discontinuous saturated zone in a soil.
Percolation: The flow or trickling of a liquid
downward through a contact or filtering medium.
Performance-based management program: A
program designed to preserve and protect human
health and environmental resources by focusing on
the achievement of specific, measurable perfor-
mance requirements based on site assessments.
Performance boundaries: The point at which a
wastewater treatment performance requirement
corresponding to the desired level of treatment at
that point in the treatment sequence is applied.
Performance boundaries can be designated at the
discharge point of the pretreatment system (e.g.,
septic tank, package plant discharge to surface
waters), at physical boundaries in the receiving
environment (impermeable strata, ground water
table), at a point of use (ground water well), or at a
property boundary.
Performance requirement: Any requirement
established by the regulatory authority to ensure
future compliance with the public health and
environmental goals of the community. Perfor-
mance requirements can be expressed as numeric
limits (e.g., pollutant concentrations, mass loads,
wet weather flows, structural strength) or narrative
descriptions of desired performance, such as no
visible leaks or no odors.
Permeability: The ability of a porous medium such
as soil to transmit fluids or gases.
pH: A term used to describe the hydrogen ion
activity of a system.
Physical boundaries: Points in the flow of waste-
water through the treatment system where treatment
processes change. A physical boundary can be at
the intersection of unit processes or between
saturated and unsaturated soil zones. A physical
boundary may also be a performance boundary if
so designated by the regulatory authority.
Plastic soil: A soil capable of being molded or
deformed continuously and permanently by
relatively moderate pressure.
Platy structure: Laminated or flaky soil aggregate
developed predominantly along the horizontal axes.
Prescriptive-based management program:
Program that applies predetermined requirements
such as site characteristics, design standards, and
separation distances to permit or otherwise allow
the operation of onsite wastewater treatment
systems. This type of program requires that proposed
sites meet preset specifications that are perceived
to protect public health and the environment.
Prescriptive requirements: Standards or specifica-
tions for design, siting, and other procedures and
practices for onsite or cluster system applications.
Proposed deviations from the specified criteria,
procedures, or practices require formal approval by
the regulatory authority.
Pretreatment system: Any technology or combina-
tion of technologies that precedes discharge to a
subsurface wastewater infiltration system or other
final treatment unit or process before final dissemi-
nation into the receiving environment.
Glossary-4
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Glossary
Regulatory authority (RA): The level of govern-
ment that establishes and enforces codes related to
the permitting, design, placement, installation,
operation, maintenance, monitoring, and perfor-
mance of onsite wastewater treatment systems.
Residuals: The solids generated and retained
during the treatment of domestic sewage in treat-
ment system components, including sludge, scum,
and pumpings from grease traps, septic tanks,
aerobic treatment units, and other components of an
onsite or cluster system.
Responsible management entity (RME): An entity
responsible for managing a comprehensive set of
activities delegated by the regulatory authority; a
legal entity that has the managerial, financial, and
technical capacity to ensure the long-term, cost-
effective operation of onsite and/or cluster water
treatment systems in accordance with applicable
regulations and performance requirements (e.g., a
wastewater utility or wastewater management
district).
Sand filter: A packed-bed filter of sand or other
granular materials used to provide advanced
secondary treatment of settled wastewater or septic
tank effluent. Sand/media filters consist of a lined
(e.g., impervious PVC liner on sand bedding)
excavation or structure filled with uniform washed
sand that is placed over an underdrain system. The
wastewater is dosed onto the surface of the sand
through a distribution network and allowed to
percolate through the sand to the underdrain
system, which collects the filter effluent for further
processing or discharge.
Septage: The liquid, solid, and semisolid material
that results from wastewater pretreatment in a
septic tank, which must be pumped, hauled, treated,
and disposed of properly (i.e., in accordance with
40 CFR Part 503).
Septic tank: A buried, preferably watertight tank
designed and constructed to receive and partially
treat raw wastewater. The tank separates and retains
settleable and floatable solids suspended in the raw
wastewater. Settleable solids settle to the bottom to
form a sludge layer. Grease and other light materi-
als float to the top to form a scum layer. The
removed solids are stored in the tank, where they
undergo liquefaction in which organic solids are
partially broken down into dissolved fatty acids
and gases. Gases generated during liquefaction of
the solids are normally vented through the
building's plumbing stack vent.
Sequencing batch reactor: A sequential sus-
pended-growth (activated sludge) process in which
all major steps occur in the same tank in sequential
order. Sequencing batch reactors include intermit-
tent-flow batch reactors and continuous-flow
systems.
Settleable solids: Matter in wastewater that will not
stay in suspension during a designated settling
period.
Silt: A textural class of soils consisting of particles
between 0.05 and 0.002 millimeters in diameter.
Soil horizon: A layer of soil or soil material
approximately parallel to the land surface and
different from adjacent layers in physical, chemi-
cal, and biological properties or characteristics
such as color, structure, texture, consistence, and
pH.
Soil map: A map showing the distribution of soil
types or other soil mapping units in relation to the
prominent physical and cultural features of the
earth's surface.
Soil morphology: The physical constitution,
particularly the structural properties, of a soil
profile as exhibited by the kinds, thickness, and
arrangement of the horizons in the profile and by
the texture, structure, consistence, and porosity of
each horizon.
Soil structure: The combination or arrangement of
individual soil particles into definable aggregates,
or peds, which are characterized and classified on
the basis of size, shape, and degree of distinctness.
Soil survey: The systematic examination, descrip-
tion, classification, and mapping of soils in an area.
Soil texture: The relative proportions of the various
soil separates (e.g., silt, clay, sand) in a soil.
Soil water: A general term emphasizing the
physical rather than the chemical properties and
behavior of the soil solution.
Subsoil: In general, that part of the soil below the
depth of plowing.
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Glossary
Subsurface wastewater infiltration system
(SWIS): An underground system for dispersing and
further treating pretreated wastewater. The SWIS
includes the distribution piping/units, any media
installed around or below the distribution compo-
nents, the biomat at the wastewater-soil interface,
and the unsaturated soil below.
Topsoil: The layer of soil moved in agricultural
cultivation.
Total Kjeldahl nitrogen (TKN): An analytical
method for determining total organic nitrogen and
ammonia.
Treatment system: Any technology or combination
of technologies (treatment trains or unit processes)
that discharges treated wastewater to surface
waters, ground water, or the atmosphere.
Unsaturated flow: Movement of water in a soil that
is not filled to capacity with water.
Vegetated submerged bed: A constructed wetland
wastewater treatment unit characterized by anaero-
bic horizontal subsurface flow through a fixed-film
medium that has a growth of macrophytes on the
surface.
Water quality-based performance requirement: A
specific, measurable, and enforceable standard that
establishes limits for pollutant concentrations or
mass loads in treated wastewater discharged to
ground water or surface waters.
Water quality criteria: A set of enforceable
requirements under the Clean Water Act that
establish measurable limits for specific pollutants
based on the designated use(s) of the receiving
water body. Water quality criteria can be expressed
as numeric limits (e.g., pollutant concentrations or
mass loads) or narrative descriptions of desired
conditions (e.g., no visible scum, sludge, sheens, or
odors).
Water quality standards: A set of enforceable
requirements under the Clean Water Act that
include classification of receiving waters in
accordance with their federal or state designated
use(s), use-based water quality criteria that estab-
lish measurable limits for specific pollutants, and
antidegradation provisions to ensure that water
quality is maintained or improved.
Water table: The level in saturated soil at which
the hydraulic pressure is zero.
Glossary-6
USEPA Onsite Wastewater Treatment Systems Manual
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Resources
Resources
USEPA Office Web Sites:
• Home Page - http://www.epa.gov/
• Office of Water - http://www.epa.gov/ow/
• Office of Wastewater Management - http://
www.epa.gov/owm/
• Office of Science and Technology - http://
www.epa.gov/waterscience/
• Onsite/Decentralized Treatment Site - http://
www.epa.gov/owm/decent
• Environmental Technology Verification - http://
www.epa.gov/etv/
• Nonpoint Source Pollution - http://www.epa.gov/
owow/nps/
• Source Water Protection - http://www.epa.gov/
safewater/protect.html
• Surf Your Watershed - http://www.epa.gov/surf/
• Total Maximum Daily Load Program (TMDL) -
http://www.epa.gov/owow/tmdl/
• Underground Injection Control Program (UIC) -
http://www.epa.gov/safewater/uic.html
USEPA Documents:
• Guidelines for Management of Onsite/Decentral-
ized Wastewater Systems - http://www.epa.gov/
owm/decent/downloads/guidelines.pdf
• Constructed Wetlands for Wastewater Treatment
and Wildlife Habitat - http://www.epa.gov/owow/
wetlands/construc/content. html
• Onsite Wastewater Treatment and Disposal
Systems (1980) - http://www.epa.gov/cgi-bin/
claritgw?op-Display&document=clserv:epa-
cinn: 5 276;rank=3 &template=epa
• Response to Congress on the Use of Decentral-
ized Wastewater Treatment Systems - http://
www.epa.gov/owm/decent/response/index.htm
• Small Community Wastewater Systems - http://
www.epa.gov/oia/tips/scwsint.htm
• Wastewater Treatment publications (OWM) -
http://www.epa.gov/owm/secttre.htm
Other Links of Interest:
• American Society of Agricultural Engineers -
http://asae.org/
• American Water Works Association - http://
www.awwa.org/
• American Society of Civil Engineers - http://
www.asce.org/
• Association of State and Interstate Water Pollu-
tion Control Administrators - http://
www.asiwpca.org/
• Clean Water Network - http://www.cwn.org/
• Conservation Technology Information Center -
http://www.ctic.purdue.edu/CTIC/CTIC.html
• Consortium of Institutions for Onsite/Decentral-
ized Wastewater Management - http://
www.dal.ca/%7Ecwrs/cdwt/
• Council of State Governments - http://
www. state snews. org/
• Environmental Council of the States - http://
www.sso.org/ecos/
• Groundwater Foundation - http://
www.groundwater.org/
• National Association of Counties (NACo) - http://
www.naco.org/
• National Association of County and City Health
Officials (NACCHO) - http://www.naccho.org/
• National Association of Home Builders - http://
www.nahb.com/
• National Association of Regional Councils -
http://www.narc.org/
• National Association of Towns and Townships
(NATaT) - http://natat.org/natat/Default.htm
USEPA Onsite Wastewater Treatment Systems Manual
Resources-1
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Resources
National Environmental Health Association
(NEHA) - http://www.neha.org/
National Environmental Training Center for
Small Communities (NETCSC) http://
www.nesc.wvu.edu
National Center for Small Communities - http://
natat.org/ncsc/Default.htm
National Onsite Wastewater Recycling Associa-
tion (NOWRA) - http://nowra.org/
National Small Flows Clearinghouse (NSFC) -
http://www.nesc.wvu.edu
New England Interstate Water Pollution Control
Commission (NEIWPCC) - http://
www.neiwpcc.org
National Sanitation Foundation (NSF) - http://
www.nsf.org
Rural Community Assistance Program (RCAP) -
http://rcap.org
USDA-Rural Utilities Service (RUS) - http://
www.usda.gov/rus/
USEPA Onsite/Decentralized Wastewater
Toolbox - http://www.epa.gov/owm/decent/
tool_right.htm
Fact Sheets:
• Onsite/Decentralized Treatment Technologies
Fact Sheets - http://www.epa.gov/owm/decent/
tech_right.htm
• Barnstable County, Massachusetts, Department
of Health and Environment - http://
www.capecod.net/alternativeseptic/
• City of Austin, Texas - http ://www. ci. austin.tx.us/
wri/fact.htm
• The Municipal Technologies Branch of EPA -
http://www.epa.gov/owmitnet/mtbfact.htm
• National Small Flows Clearinghouse - http://
www.estd.wvu.edu/nsfc/NSFC_ETI.html
• University of Rhode Island Onsite Wastewater
Training Center - http://www.edc.uri.edu/
homeasyst/pagel l.htm
• University of Minnesota Extension Septic
System Owner's Guide - http:/
www. extension .umn. edu/distribution/
naturalresources/DD65 83 .html
Resources-2
USEPA Onsite Wastewater Treatment Systems Manual
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