September 1992

     Wastewater Treatment/Disposal
          for Small Communities
      U.S. Environmental Protection Agency

      Office of Research and Development
  Center for Environmental Research Information
               Cincinnati, OH

               Office of Water
Office of Wastewater Enforcement and Compliance
              Washington, DC
                                             Printed on Recycled Paper

This document has been reviewed in accordance with the U.S. Environmental protection Agency's peer and
administrative review policies and approved for publication. Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.

       1.1  Background	1
       1.2  Types of Small Community Systems	2
       1.3  Use of Small Community Systems	>	2
       1.4  Importance of Proper Planning/Management	2
       1.5  Organization and Use of the Manual	2
       1.6  General References	3

       2.1  Introduction	5
       2.2  Problem Recognition and Mobilization	5
       2.3  Planning	5
       2.4  Design	15
       2.5  Construction	18
       2.6  Startup	21
       2.7  Operation	22
       2.8  References	23

       3.1  Introduction	25
       3.2  Treatment and Disposal of Wastewater in Soil	25
       3.3  Approach to Site Evaluation	,	28
       3.4  Site Identification	30
       3.5  Site Reconnaissance	31
       3.6  Detailed Site Investigations	32
       3.7  Construction Considerations	35
       3.8  References	36

       4.1  Introduction	39
       4.2  Residential Wastewater Characteristics	39
       4.3  Nonresidential Wastewater Characteristics	41
       4.4  Predicting Wastewater Characteristics	44
       4.5  Water Conservation and Wastewater Flow Reduction	45
       4.6  Pollutant Mass Reduction	51
       4.7  Onsite Containment Holding Tanks	>	52
       4.8  Reliability	52
       4.9  Impacts on Soil-Based Treatment and Disposal Practices	53
       4.10 References	55

       5.1  Constructed Wetlands	57
       5.2  Rapid Infiltration	59

                                    Contents (cont.)
5.3  Stabilization Ponds	62
5.4  Overland Flow	66
5.5  Slow Sand Filtration	69
5.6  Slow Rate Land Application	72
5.7  Subsurface Infiltration	75
5.8  Pressure Sewers	79
5.9  Small Diameter Gravity Sewers	82
5.10 Vacuum Sewers	84
5.11 Mechanical Systems for Wastewater Treatment	88
5.12 Extended-Aeration Activated Sludge	88
5.13 Trickling Rlter and Modifications	91
5.14 Oxidation Ditch	94
5.15 Sequencing Batch Reactors	97
5.16 Sludge Handling Alternatives	100
5.17 Septage Handling Alternatives	104
5.18 References	108

                                            List of Figures
2-1    Typical Management Organization for Construction of a Small Community Wastewater Project	18
3-1    Hydraulic Conductivity of Various Soils versus Soil Moisture Tension	26
3-2    Fluid Transport Zones through Soil below Land Application Systems	 27
3-3    Example of Stratigraphic Cross Section Constructed from Soil-Boring Log Data	35
4-1    Frequency Distribution for Average Daily Residential Water Use/Waste Flows	39
4-2    Peak Discharge versus Fixture Units Present	44
4-3    Strategy for Predicting Wastewater Characteristics	45
4-4    Selected Strategies for Management of Segregated Human Wastes	52
4-5    Flow Reduction Effects on Pollutant Concentrations	54
5-1    Capital Costs for Wetland Systems	59
5-2    Schematic of a Rapid Infiltration Facility	60
5-3    Schematic of an Overland Flow System	67
5-4    Schematics of Slow Sand Filters	69
5-5    Schematic of a Slow Rate Land Application	72
5-6    Schematics of Subsurface Wastewater Infiltration Systems (SWISs)	76
5-7    Major Components of a Vacuum Sewer System	87
5-8    Schematic of an Extended-Aeration Process	88
5-9    Schematics of Trickling Filter-Solids Contact Processes	92
5-10   Schematic of an Oxidation Ditch Process	95
5-11   Schematic and Stages for a Sequencing Batch Reactor Process	98
5-12   Sand Drying Bed Details	' 101
5-13   Basic Septage Management Options	105

                                            List of Tables

2-1    Aspects of Wastewater Treatment Management Typically Regulated by the Government	
3-1    Design and Treatment Performance Comparisons for Land
         Application Systems for Domestic Wastewater	
3-2    Typical BOD Loading Rates for Land Application Systems for Treatment of Municipal Wastewater.
3-3    Comparison of Trace Elements in Wastewaters to Recommended Limits for Irrigation Water	
3-4    Typical Soil Textures Suitable for Land Application Systems	....
4-1    Summary of Average Daily Residential Wastewater Flows	
4-2    Typical Residential Water Use by Activity	
4-3    Characteristics of Typical Residential Wastewater	
4-4    Pollutant Contributions of Major Residential Wastewater Fractions	
4-5    Pollutant Concentrations of Major Residential Wastewater Fractions	
4-6    Typical Wastewater Flows from Commercial Sources	
4-7    Typical Wastewater Flows from Institutional Sources	
4-8    Typical Wastewater Flows from Recreational Sources	
4-9    Fixture Units per Fixture	
4-10   Selected Wastewater Row Reduction Methods	
4-11   Wastewater Flow Reduction—^Water-Carriage Toilets and Systems	
4-12   Wastewater Flow Reduction—Nonwater-Carriage Toilets	
4-13   Wastewater Flow Reduction—Showering Devices and Systems	
4-14   Wastewater Flow Reduction—Miscellaneous Devices and Systems	
4-15   Wastewater Flow Reduction—Wastewater Recycle and Reuse Systems	
4-16   Additional Considerations in the Design, Installation, and Operation of Holding Tanks	
4-17   Potential Impacts of Some Wastewater Modification on Disposal  Practices	
5-1    Typical Rapid Infiltration System Performance	
5-2    Suggested  Hydraulic Loading Cycles for Rapid Infiltration Systems	
5-3    Design Criteria—Slow Sand Filters	
5-4    Typical Slow Rate Land Application Treatment Performance	
5-5    Typical Subsurface Wastewater Infiltration System Treatment Performance	
5-6    Typical Site Criteria for a Large SWIS	
5-7    Typical Hydraulic Loading  Rates on Horizontal Soil Infiltrative Surfaces Treating
          Domestic Septic Tank Effluent	
5-8    Average Installed Unit Costs for Pressure Sewer Mains and Appurtenances	
5-9    Average Unit Costs for Grinder Pump Services and Appurtenances	
5-10   Average Unit Costs for STEP Services and Appurtenances	
5-11   Distribution of Causes for Call-out Maintenance on Selected GP
          and STEP Pressure Sewer Projects	
5-12   Main Line Design Parameters	
5-13   Guidelines  for Determining Line Slopes	
5-14   Governing Distances for Slopes Between Lifts	
5-15   Maximum Flow for Various Pipe Sizes	
5-16   Maximum Number of Homes Served for Various Pipe Sizes	
5-17   Average Installed Cost for Vacuum Station (Mid-1990)	
5-18   Summary of Design  Criteria for Extended-Aeration Process	
5-19   Typical Component Sizing for Extended-Aeration Plants	
5-20   O&M Requirements  of Extended-Aeration Facilities	
5-21   Summary of Available Design Criteria for the TFSC Process	
5-22   Typical Component Sizing of TFSC Plants	
5-23   O&M Requirements  of TFSC  Facilities	
5-24   Summary of Design  Criteria for the Oxidation  Ditch Process	
5-25   Typical Component Sizing for Oxidation Ditch Plants	
5-26   O&M Requirements  of Oxidation Ditch Facilities	
5-27   Summary of Available Design Criteria for SBR Process	
5-28   O&M Requirements  of SBR Facilities	



                                           Tables (cont.)
5-29   Summary of Information on Sludge Dewatering Beds	101
5-30   Summary of Information on Aerobic Digestion of Sludge	102
5-31   Summary of Information on Lime Stabilizing of Sludge	103
5-32   Summary of Information on Land Application of Sludge	103
5-33   Suggested Design Values for Septage Characteristics	104
5-34   Summary of Information on Co-treatment of Septage at a Sewage Treatment Plant	106
5-35   Factors to be Considered in Evaluating Cotreatment of Septage	106
5-36   Summary of Information on Lime Stabilization of Septage	107
5-37   Summary of Information on Septage Lagoons	108

The preparation and review of this Handbook was undertaken by many individuals. Contract administration was
provided by the U.S. Environmental Protection Agency's (EPA) Center for Environmental Research Information

Primary Authors:
Robert P. G. Bowker - Bowker & Associates, Inc., Portland, ME
George Frigon - Dames and Moore, Annapolis, MD
James F. Kreissl - USEPA-CERI, Cincinnati, Ohio
Richard J. Otis - Ayres/Associates, Inc., Madison, Wl

Contributing Authors/Reviewers:
Steven Berkowitz - N. C. Dept. of Environment, Health, & Natural Resources, Raleigh, NC
Terry Bounds - Orenco Systems, Inc., Roseburg, OR
Peter A. Ciotoli - Weston Environmental Consultants, Washington DC
Brian J. Cooper - Ontario Ministry of Environment, Toronto, Canada
Fred J. Crates -  Consultant, Findlay, OH
Rfck Dedman - Boals, Brown, & Dedman, Inc., Munford, TN
Stephen P, Dix - National Small Flows Clearinghouse, Morgantown, WV
Alan M. Dunn - Indiana Board of Health, Indianapolis, IN
David Effert - Virginia Dept. of Health, Richmond, VA
James Gidley - West Virginia University, Morgantown, WV
Ian Gunn - University of Auckland, Auckland, New Zealand
Michael T. Hoover - Agricultural Extension Service, Raleigh, NC
Anish Jantrania - National Small Flows Clearinghouse, Morgantown, WV
David Lenning - Thurston County Public Health and Social Services Dept., Olympa, WA
Randy May - Connecticut Dept. of Envir. Protection, Hartford, CN
David A. Pask - National Small Flows Clearinghouse, Morgantown, WV
Diane G. Perley - NY Dept. of Environmental Conservation, Albany, NY
Thomas Peterson - Bioreclamation Assessment Group, Ft. Collins, CO
Sherwood C. Reed - EEC Envir. Engineering Consultants, Norwich, VT
William A. Sack - West Virginia University, Morgantown, WV
Robert L. Siegrist - Oak Ridge National Laboratory, Oak Ridge, TN
Steven J. Steinbeck - NC Dept. of Human Resources, Raleigh, NC
Allan Townshend - Consultant, Gloucester, Ontario, Canada
E. Jerry Tyler - University of Wisconsin, Madison, Wl
Robert C. Ward - Colorado State University, Ft. Collins, CO
Samuel R. Weibel - deceased, Cincinnati, OH
John T. Winneberger - Consultant, Sante Fe, NM
Kenneth C. Wiswall - B H Environmental, Inc., Annapolis, MD
Kevin M. Sherman - Florida Dept. of Health, Tallahassee, FL

Peer Reviewers:
Ronald Frey - Arizona Dept. of Environmental Quality, Phoenix, AZ
Charles Pycha - U.S. EPA-Region V, Chicago, IL
Charles P. Vanderlyn - U.S. EPA-OWEC, Washington, DC
Alfred T. Wallace - University of Idaho, Moscow, ID

Technical Direction:
Randy P. Revetta - U.S. EPA-CERI, Cincinnati, Ohio


                                              CHAPTER 1
1.1   Background

Over the past decade, changes in federal policies have
forced states to play a larger role in financing and admin-
istering public works programs and compelled local gov-
ernments to do more for themselves. A 1990 report by
the U.S. Congress,  Office of Technology Assessment
identified several national  wastewater treatment  prob-
lems common to small communities:

•  Absence of economies of scale and low per capita

•  Low level  of technical expertise of many operating

•  Limited access to existing advanced technologies

Many small communities are without access to the engi-
neering  expertise that would enable them to resolve the
technical problems related to assessing needs,  evaluat-
ing technologies, siting facilities, and deciding on action
plans to meet  regulations.  Furthermore, small,  low-
income  communities have  few alternatives to raising
user fees substantially to cover operating and  mainte-
nance costs and to pay debt service.

In many cases, traditional wastewater treatment strate-
gies have been shown to be inappropriate for the physi-
cal and economic characteristics of the small community.
In the past, when public sewer systems were not  avail-
able, the only practical alternative was to install individual
onsite wastewater systems  that used traditional septic
tank-soil absorption  treatment.  While these individual
systems still represent a viable wastewater management
option for many small communities, not all situations or
community planning strategies are suited for this type of
disposal system. The current trends in wastewater treat-
ment technology and the adoption of innovative manage-
ment strategies  have provided  new alternatives and
options for small communities. When carefully evaluated
against  actual  community  needs  and  available  re-
sources, these alternatives can result in a final selection
and implementation of a wastewater management sys-
tem that is  responsive to the needs of each community
by providing a balanced approach to cost allocation and
operational responsibilities.
The 1977  Clean Water Act  (CWA)  and  subsequent
amendments provided the first federal recognition that
costs are a major problem in the national program to ad-
dress water pollution. This  is especially true for  estab-
lished small communities where failing onsite  systems
and growing rural  population densities necessitate the
development of  wastewater management  programs to
protect public health. Conventional options of providing
gravity sewers and activated sludge treatment are often
excessively  expensive and  require significant manage-
ment costs that  lead to unacceptably  high burdens for
small communities. As a result, the emerging focus for
small community systems has shifted to small-scale sys-
tems that are designed  to fit the  specific needs  of the
community, rather than to provide a standard solution for
all situations. Thus small communities  have found that
development of specialized wastewater systems calls for
a well thought-out strategy in the early stages of  problem
definition and planning, the generation and evaluation of
options pertaining to system selection and costs, and, fi-
nally, the selection of  a management approach that
meets the existing  and future needs of all the identified
small community user groups. The improved levels of treat-
ment and long-term economic  savings of well-designed
small community systems provide engineers and plan-
ners with increasing confidence for reevaluating waste-
water management strategies for existing and developing
communities and give hope to local officials who  formerly
despaired when considering the cost of complying with
environmental regulations.

Historically, although  much of the  initiative  for financing
small community systems had been assumed by the
Federal Construction Grants Program, which provided up
to 85 percent of the funding  for construction of wastewa-
ter systems, most small communities were unable  to ob-
tain funding due to the reliance on  priority lists related to
population. Incentives for development of wastewater
systems were provided primarily through the allocation of
state "set-aside" funds for implementation of small com-
munity wastewater system construction grants. However,
for many communities, the impact of the amendments to
the CWA, the changes in the construction grant program
instituted after 1984, and the implementation of the State
Revolving Fund Program have restricted the  availability
of grant assistance and increased the local share of pro-

j'ect costs. These changes have placed increased pres-
sure on small communities to reduce project costs. This
is usually accomplished through greater use of easy-to-
manage, low-cost technologies and implementation of ef-
fective management strategies with appropriate planning
and operational functions.

1.2   Types of Small Community Systems
Wastewater treatment alternatives for small communities
can be broadly defined under three category groupings
that represent the basic approaches to wastewater con-
veyance, treatment, and/or disposal.
• Natural Systems—that utilize soil as a treatment and
  disposal  medium, including  land  application,  con-
  structed  wetlands, and subsurface infiltration. Some
  sludge and septage handling systems, such as sand
  drying beds, land spreading, and lagoons, are in-
• Alternative Collection Systems—that use lightweight
  plastic pipe buried at shallow depths, with fewer pipe
  joints and less-complex access structures when com-
  pared to conventional  gravity sewers. These include
  pressure, vacuum, and small-diameter  gravity sewer
• Mechanical Systems—that  utilize a combination of
  biological and  physical processes,  employ  tanks,
  pumps,  blowers,  rotating  mechanisms, and/or other
  mechanical components as part of the overall system.
  These include suspended growth, fixed growth, and
  combinations of the two. This category also includes
  some  sludge and  septage management alternatives,
  such as digestion, dewatering, and  composting sys-
  tems and appropriate disposal information.

1.3   Use  of Small Community Systems
The appropriate selection and use of the  various small
community  wastewater management system alternatives
will depend on both the physical characteristics of the site
and the configuration of the service community. There
are many technical alternatives from which small commu-
nities  may  choose in deciding  how to  collect and  treat
wastewater. Each of the various types of wastewater sys-
tems will be affected by the requirements of the service
community  and wastewater treatment system objectives.
Water conservation systems can significantly reduce the
amount of wastewater generated and thus affect the fea-
sibility and  cost of different wastewater alternatives. Re-
ducing water use can also lower the day-to-day operating
costs  for treatment chemicals and other utilities, such as
the drinking water supply system. In some cases, effec-
tive water conservation programs can permit the use of
smaller, less-expensive treatment facilities.
As a preliminary screening tool for system evaluation, it is
often  advantageous  to consider under which circum-
stances systems  are appropriate and  eliminate other
treatment strategies on the basis of inability to meet com-
munity or physical requirements for effective wastewater
treatment. This can be accomplished simply by develop-
ing a generalized list of advantages  and disadvantages
for each alternative to assist in the preliminary decision-
making process and to facilitate understanding of appli-
cations of treatment  alternatives.  To  a  degree,  this
manual assists in this process  by listing only technolo-
gies that are useful in small community wastewater sys-
tems; it generally avoids discussion of technologies that
are rarely appropriate for those applications.
The appropriateness of a given technical alternative will
depend largely on the physical site constraints and the
management  capabilities  of  the  community. Knowing
when and  where to apply a  particular technology will also
involve consideration of the regulatory  requirements for
each collection and treatment system and the capability
of the community to support a management program tai-
lored to the needs of the affected service groups.

1.4   Importance of Proper
Many issues and considerations affect the management
approach  for  small community  systems. These consid-
erations and discussions of the planning and manage-
ment alternatives for wastewater systems are presented
in detail in Chapter 2. There are, however, several over-
riding concerns that will play a  role in the evaluation of
the management options and the selection  of a techni-
cally sound treatment alternative.  These include careful
evaluation of all feasible technical and  management al-
ternatives  against the concerns of the community, treat-
ment objectives,  economic capability, and management
entities and regulatory environments that  provide the
enabling legislation to conduct the  required functions and
activities  of the  system management.  The underlying
theme  that must be addressed here is  to integrate the
selection criteria with all the relevant components that af-
fect  an efficiently functioning wastewater management
program. The management approach must  not assume
that  innovative treatment  alternatives   are  necessarily
more environmentally sound or easier  to operate, nor
that a centralized system will necessarily prove easier to
regulate and manage. The resolution of these issues is
extremely  site-specific and  community-specific, and can
be addressed only through  comprehensive evaluation of
all components of the small community wastewater man-
agement program.

1.5   Organization and Use of the Manual
This manual is designed to guide planners and designers
through the required steps for developing well-conceived
small community wastewater management systems and
to highlight the specific characteristics of the system de-
sign and management functions that lead to the success-
ful implementation of the selected system. The focus of

the manual is to present information  about small-scale
wastewater treatment  systems that are appropriate for
the growing suburban and rural fringe-treatment areas
that characterize the environmental needs of small com-
munities. For the purpose of this manual, small commu-
nities generally refers to rural communities of fewer than
3,500 people; however, the population of small communi-
ties referred to can be as high as 10,000.
One of the major goals of this manual is to highlight the
importance of planning and management considerations
in choosing the appropriate system. This information is
presented so that planners, consultants, local elected of-
ficials, or other organizational groups charged with pro-
viding wastewater management can better evaluate a
broad range of appropriate options for small communities
and understand the  mechanisms for available manage-
ment alternatives. This information is included to assist
those charged with implementation of small community
wastewater management systems in understanding the
basic working principles  and practical limitations of the
various  alternatives. It also is intended to facilitate the
planning and the final selection process.

The manual is organized into five chapters. The succes-
sive chapters span the technical considerations, the con-
cept and planning  stages  of alternative  wastewater
systems evaluation,  and  the  implementation of compre-
hensive wastewater management programs. Chapter 2
discusses the planning  and implementation  of  small
community systems, placing  special emphasis on roles
and  responsibilities  and  the regulatory approvals  re-
quired to  initiate wastewater programs. Site  suitability
and evaluation are discussed in Chapter 3, linking the
characteristics of the physical and chemical conditions of
site soils and hydrogeology to treatment processes. The
specific  characteristics of wastewater (e.g., flow, quality)
and the  capability of the wastewater treatment designs in
addressing these characteristics are presented in Chap-
ter 4. Chapter 5 comprises a technical presentation  of
various alternatives for wastewater treatment and residu-
als management systems and provides  a discussion  of
the applications, factors affecting performance, features
of system design and construction,  and the operation
and maintenance requirements.
The information presented herein is intended  as techni-
cal guidance reflective of sound  professional practice.
Before  any system  is designed and constructed, local
and state authorities should be contacted to  determine
the local design requirements for a particular system.
1.6   General References
Many technical manuals and guidelines, as well as spe-
cific guidance from state and federal programs, are avail-
able  and should be consulted to assist in the evaluation
and selection of a wastewater management system that
is suited to the needs of a particular community. Several
useful resources are listed below; other  more specific
guidance documents are provided in the reference sec-
tions within chapters.

When an NTIS number is cited  in a reference, that refer-
ence is available from:

   National Technical Information Service
   5285 Port Royal Road
   Springfield, VA 22161
   (703) 487-4650
• 1990 Preliminary draft strategy for municipal wastewa-
  ter treatment, Office  of Water and Waste Manage-
  ment, Washington, DC, January 1981.

• A strategy for small  community alternative wastewater
  systems, Office of Waste Program Operations, Wash-
  ington, DC, December 1980.

• Planning wastewater  management facilities for small
  community,  EPA Office  of  Research and  Develop-
  ment,  EPA/600/8-80-030, NTIS No.  PB91-111064,
  August 1980.

• Design manual; on-site wastewater treatment and dis-
  posal systems,  EPA Office of Research and Develop-
  ment,  EPA/625/1-80-012, NTIS No.  PB83-219907,
  October 1980.

• Management of on-site and  small community waste-
  water systems, EPA/600/8-82-009, NTIS No. PB82-
  2C0829, EPA Office of Research and  Development,
  July 1982.

• Reference handbook on small-scale wastewater tech-
  nology, US  Department of Housing and Urban Devel-
  opment, Office of Policy Development and Research,
  Washington, DC, April 1985.

• Rebuilding  the foundations:  state and local public
  works  financing and  management, OTA-SET-447,
  Washington, DC, Government Printing  Office, March

• Handbook of septage treatment and disposal,  EPA
  Office of Research and Development, EPA/625/6-84-
  009, Cincinnati, OH, October  1984.


                                              CHAPTER 2
             Planning and Management of a Small Community Wastewater Project
2.1   Introduction

The planning and management activities of a wastewater
treatment project are so closely intertwined as to make
them  at times  inseparable and  indistinguishable. The
purpose of this chapter is to acquaint the reader with the
planning and management work necessary to complete
the six steps in the typical wastewater treatment  project
and to discuss approaches that may be particularly use-
ful in small communities. The six distinct phases or steps
in a wastewater project are:

• Problem recognition and mobilization

• Planning

• Design

• Construction

• Startup

• Operation
2.2   Problem Recognition and Mobilization

The driving force behind a wastewater treatment project
is usually one or several of the following:

• A  public or private  sector individual or group recog-
  nizes the need for action and rallies a significant seg-
  ment (not necessarily a majority) of the community to
  support the need for a project.

• The courts resolve an action to abate pollution and or-
  der remedial measures.

• State and/or federal agencies enforce pollution  laws
  and/or order remedial measures.

The individual, group,  judge, or  agency responsible for
creating the political or legal pressure that gets the pro-
ject off the ground and who supports it through its evolu-
tion can be called the project's champion. The need for a
champion is apparent when one considers the potential
impediments to any wastewater project, which include
the following:

• Not all community members contribute to or share the
  problem. Those that don't may oppose the project.
•  Several community members may see the absence of
   wastewater collection or treatment facilities as a method
   of growth control.

•  The cost of the project and the resultant annual fees
   may draw substantial opposition.

•  The locations available for a treatment site may draw
   neighborhood opposition.

•  The point of discharge and the perceived negative ef-
   fects downstream may draw opposition from  within
   and outside of the service area.

There is no formal management and planning scenario to
follow in this phase of the project. Judicial and adminis-
trative rulings evolve out of other processes, and private
sector  efforts  are  directed toward  raising  community
awareness of the problem and developing a public outcry
for action. Nonetheless, the energy or the authority of the
project champion  is key for driving the project through
this  phase. The momentum generated and  then sus-
tained  by the  champion through  the  design  phase in
most cases makes the difference between a successful
and unsuccessful project.

2.3   Planning
The formal planning and management of a project begins
at the point where a committee is formed or a governing
body is authorized to study the problem, explore options,
and estimate costs. Management actually precedes plan-
ning  in the sense that a formal plan to allocate resources—
personnel, technical  expertise, time, and funds—and a
mechanism for measuring progress  is required prior to

The objective of the planning phase is to generate a rec-
ommendation to the community that covers the type of
wastewater facilities required, with cost estimates for de-
sign, construction, and operation;  a plan for managing
the design, construction, startup, and operation of the fa-
cilities; and  a  plan  for financing facilities development
and operation. If a comprehensive facility recommenda-
tion cannot be generated, then alternative plans and cost
estimates can be offered; but no more than three alterna-
tives should be put forth. The choice of the number of al-
ternatives is  arbitrary but the reason  for limiting  the

choices is that each option possesses a myriad of im-
pacts for community members to consider. More than a
very few choices will lead to confusion.
At the beginning of the planning phase, three key man-
agement actions must be carried out:
1.  Appoint a person or, more typically, a group to carry
    out the planning effort.
2.  Establish a deadline acceptable to  the  group and
    community for submitting recommendations.
3.  Establish a preliminary planning budget.
Once formed, the group assumes management  respon-
sibility and establishes intermediate tasks, which  may be
in the following sequence:

1.  Assemble or determine the whereabouts of all docu-
    mentation pertaining to the reasons for the project
    and the general area to be served.
2.  Familiarize all  group  members with  the wastewater
    management problem and the reasons for the project.
3.  Determine the need for consultant services.
4.  Solicit and engage consultant services, if needed.
5.  Arrange for public information/feedback.
6.  Document the regulations and laws pertinent to the
7.  Identify and evaluate technical alternatives.
8.  Compare the costs of the most suitable technical al-
9.  Prepare a financing plan.
10. Prepare draft recommendation and a report for public
    and regulatory agency comment.

11. Prepare the final recommendation and report.
With the goals,  schedule, staffing,  and budget estab-
lished, the process of bringing about the small commu-
nity  wastewater  treatment   system can commence.
Accepting as a given the major goal of the planning proc-
ess—the development of  a  recommended wastewater
collection and treatment plan for the community—and
leaving the appointment of the planning group's mem-
bers to local judgment, the remaining discussion in this
chapter focuses on the 11 intermediate tasks.

2.3.1   Assembly of Documentation
The gathering of pertinent documentation concerning the
wastewater treatment project, which  can be  performed
by the planning group or by a consultant, is the founda-
tion of any successful planning effort. The  information
collected must formally document the community's per-
ception of the problem, how the project was conceived,
and who was involved. Supplemental  information should
 • U.S.  Geological Survey quadrangles, tax assessment
   records, flood plain data, and any other maps of the
   planning area

 • Geological studies of the  planning area  (especially
   those concerning  local soils and those that  include
   aerial photography)

 • Government  (state and local) studies of sanitary con-
   ditions in the planning area

 • Local climatological reports  and data

 • Studies of local surface-water and ground-water qual-
   ity and quantity

 • Reports on the history and archeology of the area
 • State, county,  and local planning and development
   studies of the area

 • Any other data or information that  could have an im-
   pact on the project

 All such information is necessary to assist in  document-
 ing the existence and extent of wastewater management
 problems, to evaluate alternative solutions, and to iden-
 tify essential  information that is lacking. The data will be
 used to establish the layout of  sewers and the location of
 treatment  facilities; to identify areas of historical impor-
 tance and flood plains that should be avoided; to charac-
 terize the soil and hydrogeological features of the area to
 determine potential sites for  land-based  systems (i.e.,
 cluster  systems); to establish  the proximity of  future
 roads and  subdivisions; to plan for treatment and  dis-
 charge systems; to identify streams with the greatest flow
 and  the most appropriate stream class designation; to
 make preliminary evaluations of the cost and feasibility of
 acquiring sewer easements; and most important, to es-
 tablish the project's justification. Legal counsel should be
 involved in gathering documentation on the enviromental
 impacts of each alternative treatment method considered
 so that  complete  findings can be reported to state  and
 federal regulatory agencies.

 2.3.2   Familiarization of Planning Group
        Members with the Nature of the
        Wastewater Management Problem
        and the Reasons for the Project
 Although the subject of wastewater problems and poten-
tial solutions can be very technical, the typical small
 community wastewater planner is not expected to have
 had  special training. A general understanding  of  the
 problems and principles involved is all that is necessary.
This is easily acquired if the group receives assistance
from a  regulatory expert  or  a consultant. Unassisted
groups will  require training or  will have to be  composed
of technically competent individuals.
 Familiarization begins during the data assembly process
wherein all members are expected to read the various
documents and reports.  Technical reports may require

interpretation by knowledgeable governmental officials or
consultants. Planning groups with consultant assistance
will usually receive a summation of the existing data in
nontechnical terms.  Ultimately it is important that  all
group members have a firm understanding of existing
conditions to facilitate their review of the implications and
impacts of remedial alternatives.

2.3.3   Determ ination of the Need for a
        Consultant and the Extent of Services
Not  all  wastewater projects require consultants during
the planning stages. Common determinants of the need
for a consultant are as follows:
•  Project size (i.e., the larger the project the more likely
   that consultant services will be necessary)

•  Project complexity (e.g., does the problem definition or
   solution  require a hydrogeologist and/or do the only
   technically feasible treatment methods  require some
   type of treatment plant, etc.)

•  Project schedule (e.g., consultants working full time on
   a project are more efficient than part-time volunteers)

•  Availability of volunteer experts as committee members

•  Capability of existing management agency, if available

It is difficult to establish rules of thumb  regarding the ne-
cessity  for professional  consulting  services during the
planning phase. Advice  on  the matter can be secured
from state, local, and county regulatory  agencies that
have an interest in the project. Communities that can af-
ford to hire consultants will usually benefit from the assis-
tance. However, planning committees must not abdicate
their responsibilities to  a consultant. The group is ulti-
mately responsible for making critical decisions concern-
ing the project, and a consultant should  serve only to
facilitate the work of the group.
Use of a consultant during the planning stages eliminates
potential  liability for the performance of the recom-
mended plan.  More specifically, if an unassisted nonpro-
fessional group develops a recommended plan that is
subsequently used as the basis for a system design and
the  system doesn't work, or it costs substantially more
than anticipated, who is responsible? The use of consult-
ants for final planning and design may provide protection
for the  community against the possibility  of charges of
substantial system nonperformance, failure, or excessive
cost of the preliminary plan.

2.3.4   Soliciting and Engaging Consultant
Of all the intermediate tasks in the planning process, re-
taining a consultant is the most difficult for  small commu-
nities  to  master,   primarily  because  project  group
members will often lack experience in contracting for pro-
fessional services.  The  process is fraught with pitfalls.
For instance,  it can  be difficult to define the work to be
done so that all proposals can be evaluated using a com-
mon measure. And it may not be easy to  identify the
firms with the most experience in technologies pertinent
to a community's wastewater problem.
There is no quick resolution to such issues. The task re-
quires  diligent effort by all members of the planning
group or consultant selection subcommittee.  Where fed-
eral  grants or loans are involved, federal procurement
regulations should be followed closely. Similarly, special
requirements may apply where state funds are used. In
general, five steps should be followed:

1.  Prepare a request for proposals (RFP)

2.  Advertise or  distribute the  RFP to  selected  firms
    (e.g., firms can be selected by issuing a request for
    qualifications  (RFQ))

3.  Collect and review proposals to create a short list of
    firms to be considered

4.  Interview selected consultants from the "short list"

5.  Choose a consultant
Establishing a price for consultant services  can be ap-
proached in several ways. The  fee  may be a required
component  of the proposal, a  separate simultaneous
submittal, or an issue negotiated following consultant se-
lection, or it may be established by a combination of
these methods. Since the legal wording of a contract for
services will vary in form from state to state  and locality
to locality, the discussion below concerns the technical
selection process, with limited reference to the fees and
contract language. The Request for Proposals
A request for proposals (RFP) generally begins with a
brief statement of the problem affecting  the community
and the events  that led the community to initiate the
wastewater planning process. The statement of the prob-
lem and background is  followed by a description  of the
work that would be performed by the consultant.
Drawing up an RFP requires the planning group to have
become as knowledgeable as possible about community
wastewater problems. The description of work also re-
quires  some knowledge  of the possible courses of action.
Information can  be acquired by consulting regulatory
agencies, studying the responses to a request for qualifi-
cations from interested  engineers,  interviewing officials
from nearby communities, and conducting library research.
In general the RFP should request that the consultant:

1.  Search out and review existing data on the wastewa-
    ter project area and the problem

2.   Define the problem using available data and perform
    additional analyses as necessary

3.   Identify alternative technical  solutions and prepare
    cost estimates

 4.   Evaluate  and compare the  various technical  and
     management  alternatives and costs, and prepare
     draft recommendations

 5.   Conduct a public hearing to solicit community, regu-
     latory agency, and planning group comments on the
     draft proposals

 6.   Prepare a final report and recommendation incorpo-
     rating the  comments received
 The statement concerning work to be performed should
 also include instructions regarding interactions between
 the consultant and planning group. For instance, regular
 meetings should be  scheduled for the consultant to re-
 port on progress and findings. A formal report should be
 made to the committee upon completion of each of the
 tasks listed above. These early progress reports, which
 can be  incorporated in whole or in part into the final text,
 will give the planning committee opportunities to provide
 input, and allow it  to perform a quality assurance review
 of the work prior to the final document preparation. The
 RFP should also request or establish a schedule for the
 work. The remainder of the RFP should contain a descrip-
 tion  of other required submrttal contents, such as informa-
 tion  on  insurance,  liability, and  contractual requirements.
 The form of the  RFP, as well as insurance, liability, and
 other legal issues,  should  be reviewed by the community
 lawyer  before the  solicitation is issued. Such a review
 should be relatively brief and inexpensive if the section of
 the solicitation on the scope of the work to be performed
 is well thought out.  Proposal Evaluations
 In general, responses to requests for professional serv-
 ices use the following as a table of contents:
    Description of  the problem (from  the RFP and re-
    The proposer's approach to solving the problem
    Detailed scope of services to be provided
    Schedule of work
    Consulting firm's documented experience with simi-
    lar projects
    Proposed staffing for the project, with resumes
    Staff organization for the project
    Categories of staff to be assigned to the project and
   the  estimated time each will expend  on the project
    (e.g., accounting, engineering, hydrogeology)
    Proposed fee or fee schedule (optional)

In describing an approach  to the problem, the consultant
should be allowed considerable latitude. In reviewing and
comparing  approaches  to the project,  the  reviewers
should look  specifically for clues to the consultants' un-
 derstanding of the project needs. Often consultants have
 their marketing staff  produce promotional statements
 about the company and staff's abilities. The reviewers,
 however, should look for specific language indicating that
 the consultant has  made an effort to understand the
 community's  wastewater  problems,  and  determine
 whether the suggested approach seems reasonable and
 demonstrates the consultant's competence. The  thor-
 oughness of  understanding and completeness of the
 suggested approach should be reflected in the proposed
 scope of services, which is a detailed presentation of the
 consultant's plan of action.

 When comparing the scope of services section of pro-
 posals, reviewers should consider the level of effort pro-
 posed for various stages  of the work. Any emphases
 proposed should be noted to see if plans  correspond to
 the project group's expectations.   .

 The proposed scope of services section, as well as the
 approach section, should also be compared with the sec-
 tion describing the firm's experience with similar projects.
 Does the proposing firm have experience to support its
 statements in the  approach and scope-of-services sec-
 tions? Do the resumes of proposed team members re-
 flect the firm's experience with similar projects? It is
 necessary with proposals  from multilocation firms to de-
 termine  the work location of proposed team members.
 Are they available to perform the work, and how will their
 location  impact the ability  to participate  as required?
 Modern communication technologies reduce, but do not
 eliminate, the need for all team members to be located at
 sites convenient to  the  project. Finally, the proposed
 schedule should   be  evaluated against  the  planning
 group's deadlines and the need to study the various por-
 tions of the completed work prior to taking action. Consultant Interviews
 The selection committee  generally  chooses several of
 the best  proposals to follow up on with further considera-
 tion and consultant  interviews. Interviews are carefully
 scheduled affairs to  help differentiate the best proposal
 from the others. All interviewees are  given the  same
 amount of time. The interview itself usually begins with a
 presentation by the consultant during which he or she is
 asked to embellish  and expand on  the written proposal
 contents. The time allowed for presentations should be
 relayed to consultants with the short list announcement.
 Following the consultant's  presentation,  the  selection
 committee asks questions of the consultant to help it dis-
 tinguish the one best suited to the committee's needs.

 Following the interview  process a consultant  is selected.
 If a fee quote was requested with the proposal and the
 fee is  acceptable the  process can  proceed directly to
 contract execution. If a price quotation was not required
 by the  solicitation, price negotiation  and contract execu-
tion follow the technical  selection process.

2.3.5   Arrange for Public Involvement and
In the past the EPA grants program called this aspect of
the planning  process  public participation.  Because the
primary responsibility  of the individual  or  group desig-
nated to  manage the project's development involves
planning, the  public involvement process consists mainly
of providing information and getting feedback. That is,
the public advises the planners of its knowledge about
the wastewater  problem and provides commentary or
feedback about various proposals as they are developed
and finalized.
It is important to involve the public during the planning
process in order to improve the chance a majority of peo-
ple in the community will accept the planning group's final
recommendations. A plan to encourage public involvement
must  be prepared in  the early stages of the planning
process and managed throughout. The wastewater plan-
ners must establish lines of communication with the pub-
lic. Relying on the local newspapers and radio stations
and flyers is  not enough. The committee  must provide
forums  that  will  draw out the public and  encourage
Successful public  involvement programs  include  the
1.  Scheduled public  meetings that mark important pro-
    ject milestones and provide an opportunity for mak-
    ing  informational  presentations by  the  planning
    committee or its consultants and for soliciting public
    comment. A typical schedule includes advertised
    meetings at the following points:
    - At project kickoff
    - At completion of draft recommendations
    - At completion of final plan recommendations
    - At design-phase kickoff
    - At completion of design
    - At construction contract award
    - At any and all major changes in the projects direction
      of the project
2.  Public outreach to draw diverse individuals or groups
    into the planning process
3.  Regular  news releases or flyers describing the work
    and progress of the committees
Public involvement must  be managed. Since the plan-
ning  committee  is charged with developing a recom-
mended  plan for wastewater management, various
community groups both for and against the project will try
to ensure that their concerns will be addressed fully and
that their viewpoints will be given prominence. Meetings
must be conducted in such a manner that all factions are
given a hearing. Arrangements for day-to-day contacts
with the local citizenry must be made such that the public
is heard and comments acknowledged. Special interest
groups require additional attention to ensure that mem-
bers are given every opportunity to express their con-
cerns and that their concerns are thoroughly addressed.
Special interest groups with a stake in the project that do
not become actively engaged in the  planning  process
dialogue should be approached directly and encouraged
to make concerns known. The degree of  difficulty and
level of effort associated with this task will depend on the
level of controversy generated  by the project. A consult-
ant is often assigned the responsibility of planning public
involvement activities and managing the program.

2.3.6   Document the Regulations and Laws
        Pertinent to the Project
The documentation of pertinent laws and regulations is
usually the responsibility of the consultant, when one has
been retained. The information that is required  early on
in the planning  effort is important  for determining the
technical feasibility, a schedule,  and the estimated cost
of the project. This task includes the collection of all per-
mit applications required and regulatory agency guidance
documents. A listing of  subjects and issues likely to fall
under regulatory control  are listed in Table 2-1.

The list in Table 2-1 is not meant to be all-inclusive and
should only be used as a guide to get the regulation-
gathering  process started. The regulation of wastewater
treatment varies from state to state and locale to locale.
Planners should inquire about the existence of regula-
tions at all levels of government.

Using information on applicable regulations, a flow dia-
gram can be constructed illustrating the steps that need
to be taken to carry out the project. A schedule for the
completion of the various tasks can be prepared based
upon the requirements for the various approval applica-
tions and the need to perform studies and engineering
assessments  as supporting  documentation.  Accurate
completion of this subtask is  important for establishing
design requirements for the next stage of the project.

2.3.7   Identify and Evaluate Technical
With the first six tasks completed or near completion, the
actual planning of the project can begin. The initial array
of options available to the small community is more inclu-
sive than it is for the larger cities. However,  a realistic list
of technologies that can be operated by small communi-
ties is somewhat shorter and includes onsite systems,
cluster approaches, and community-wide options. Even
with this more select variety of  available options, small
communities can expend valuable  time and money pur-
suing and evaluating inappropriate alternatives.  Some
communities have dealt with this problem by only consid-
ering only few options with which they are familiar. While
this approach may produce a solution, it may not be one
that  is best suited for the long-term interests of the

  Table 2-1. Aspects of Wastewater Treatment Management
  Typically Regulated by the Government
 Usual Level of
  National Pollutant Discharge
  Elimination System permit
  Individual septic system regulations
  Ground-water discharge standards
  Receiving stream classification and
  discharge restrictions
  Wetland regulation (sewers and
  treatment plant siting may impact
  Historical preservation (many areas
  require historical and archeological
  evaluations of proposed public works
  Highway construction requirements
  (the regulation or the prohibition of
  road excavation can have enormous
  impacts on the feasibility and cost of
  sewers. Driveway curb cuts for
  treatment facility locations is a lesser
  Flood control (construction and siting
  requirements in or adjacent to flood
  plains can affect feasibility and cost of
  Erosion and sedimentation control
  Navigable waterway construction (the
 Army Corps of Engineers regulates all
 construction within the waters of the
 United States)
 Planning and zoning  impacts
 Procurement standards
 federal, state

 state, local
 state, local

 federal, state
 state, local
state, local
federal, state, local

state, local

federal, state, local
 Note: Local level may include county, township, or parish.

community. Suggested criteria are presented  below to
assist planning groups to narrow down the list of options. Small Community Systems Must Be
        Simple to Operate
Ease of operation is the single most important criterion
for small community wastewater treatment systems. Nu-
merous projects have failed to perform and have cost the
communities they serve large sums expended to  correct
problems  because planners  have overlooked this  re-
quirement. This criteria is particularly  important because
persons with the training required to operate the more
complex or  delicately balanced systems are not  readily
available  in the  general  population. Moreover, once
trained, small community wastewater system operators
are difficult  to retain at rural and suburban pay scales.
Small communities that are situated close to larger cities
and towns may be  able to employ on a part-time basis
 the operators of larger, more complex facilities.  In addi-
 tion, service companies with suitable expertise are more
 likely to be available to communities located in a metro-
 politan area.
 The simplest of all systems is the individual on site septic
 system, and its simplicity is a reason for its attractive-
 ness as a wastewater management option. Persons with
 the skills necessary for onsite system maintenance are
 generally available  even for the most innovative of the
 modern systems.
 Large subsurface, sand filter, and wetland-based  sys-
 tems are examples of  larger systems that are simple to
 operate. Members from the local farming,  electrical  con-
 tracting, plumbing contracting, and excavating contract-
 ing communities collectively have the skills necessary to
 construct and operate these systems.
 Biological  and physical/chemical systems require more
 than a knowledge of the systems' electronics and  me-
 chanics to achieve  and maintain optimum performance
 of all treatment elements.  If systems based  on these
 principles are to be considered, then equal consideration
 must be given to the availability and affordability of the
 required operations staff. Small Community Systems Must Be
 All discharging  systems and large subsurface systems
 must operate within performance standards that  are es-
 tablished by  regulation and are specified in the operating
 permit. Violations of these standards  may expose the
 community to fines  or  legal action. Metropolitan opera-
 tions with seven-day-week, round-the-clock staffing are
 monitored constantly to detect operating aberrations that
 could lead to a permit violation. In contrast, small com-
 munity systems tend to be  monitored  on an intermittent
 basis and therefore  must be designed to be resistant to
 upsets and to provide days  or weeks of advanced warn-
 ing when a problem is developing.
 The type of warning of  impending performance deficien-
 cies provided by a system is somewhat related to the
 system's complexity. Onsite systems  that are properly
 monitored can provide advanced notice of elevated con-
 taminant levels in ground water or  of absorption system
 failure months or years in advance. For instance, sand-
 filter ponding, which  indicates potential problems,  occurs
 weeks or months before critical conditions occur. Wetland
 systems provide days of advanced notice of performance
 failure. Biological and physical/chemical systems provide
 advanced notice of only several hours, at the most, of po-
tential problems.
 Reliability is also an important consideration in the selec-
tion  of alternative  wastewater collection systems.  Many
of the early designs for alternative sewer systems failed
to provide a  level of reliability equal to the reliability of
more conventional systems.  To a degree, the early prob-
lems were due to a general unfamiliarity with the weaker

links in these systems. Problems also resulted from ef-
forts to shave costs. Also,  a consensus has yet to be
reached among the states on corrosion-resistance stand-
ards for  electrical components in  septic tank  effluent
pump systems. Although the atmosphere in these sys-
tems  is extremely corrosive, vulnerable metal compo-
nents are still in use.  The use of  such  materials in
pressure and small diameter gravity sewers can result in
premature failure of system components and necessitate
difficult repairs. Reliability in terms of corrosion protec-
tion, structural durability, ease and access of  mainte-
nance are therefore crucial concerns. Small Community Systems Should
       Be Economical to Construct and
For years onsite systems have been proposed as a low-
cost,  reliable, and simple method of treating wastewater
problems. Experience has shown that the lower cost is
dependent on the perspective of the evaluator. In a com-
munity of 50 homes, for instance, the total capital cost to
replace 10 or even 20 onsite systems is likely to be lower
than to provide collection and treatment facilities for all
50. However, on an individual basis there may be no dif-
ference in capital  cost. That is, the homeowner contract-
ing for an onsite  repair or a replacement may incur as
much capital cost as he or she would have incurred were
a central system  constructed. On the other hand, onsite
systems  have shown  themselves  to  have  lower O&M
costs than community-wide systems with central collec-
tion and treatment facilities.
Sand filter and wetland' systems have also been pro-
moted as low-capital-cost  treatment  options. Unfortu-
nately the cost estimates for these systems are a vestige
of the light-duty designs used during their technological
development. The design standards for working versions
of these systems  are those used for public works that re-
quire rugged and durable facilities  intended for years of
trouble-free  service. They must be equipped with liners
to separate them from the surrounding environment and
with dozens  of performance, operation,  and flow moni-
tors. These added requirements cause these systems to
cost as much if not more to construct than complex bio-
logical or physical/chemical systems; however,  O&M
costs are generally low because of the simplicity of op-
eration and reliability of these systems.
Many of the more complex biological- or physical/chemical-
based systems are available to small communities as
complete prepackaged  units.  Prefabrication  renders
these systems very cost-competitive with those of lesser
complexity. The O&M costs for these systems are gener-
ally higher than the lower technology systems because
they  require daily monitoring to check the balance  and
performance of the various subsystems. The personnel
performing these tasks are required to  be more highly
trained than  operators of simpler systems, thus salaries
for personnel with the required skills are generally higher.
Collection systems should not be left out of any discus-
sion of system capital costs. In unsewered areas, they
can account for  up to 75 percent of the total system's
capital cost, especially if development density is low and
the length of sewer per user is high.

Their attractiveness has been largely attributed to their
eligibility for supplemental funding as alternative collec-
tion systems under the EPA grant program. They remain
attractive in the post-grant era because they offer poten-
tial cost savings in that they require shallower excava-
tions  for  pipes,  smaller pumps,  and  simpler pump
stations than more conventional systems. The lower cost
of construction because of shallow excavations can pro-
vide savings of up to 50 percent depending on the soil,
rock,  and ground-water  conditions in the sewered area.
Savings are the result of reduced requirements for shor-
ing,  dewatering,  and  blasting.  The  small  diameter  of
these sewers  may permit their installation using emerg-
ing methods such as plowing, trenching, and directional
drilling that provide even greater potential  construction
cost savings. There are few direct comparisons regard-
ing the maintenance cost differential between conven-
tional  and small  diameter  gravity  sewers  (SGD).
However, available data indicate that O&M costs can
vary from less to more than,conventional sewer technol-
ogy depending on local conditions (e.g., O&M costs fora
single conventional pump station can equal those of an
SGD system.)

Thus, simplicity of operation, reliability, construction and
operating costs are the considerations to weigh when se-
lecting potential wastewater management alternatives. A
preliminary screening of alternatives will produce a short
list of options deserving of in-depth  consideration. The
planning group consultant will generally perform this task
and report to the committee. Unassisted planners can
seek the assistance of state and federal regulators.

Planning  groups  should be prepared for potential prob-
lems when turning to consultants or regulators for advice.
Very few advisors have had experience with all techno-
logical approaches. As a result, they are prone to recom-
mend familiar processes while questioning the cost and
performance of processes with which they are less famil-
iar. No method guarantees an open-minded assessment
by all evaluators. The planners must be critical in their
consideration  of  recommendations and  representations
to ensure a fair  evaluation. The goal of the alternative re-
view is to produce a list, in order of preference, of the tech-
nically appropriate wastewater management systems.

2.3.8   Compare the Costs and
        Environmental Impact Assessments
        of the Most Suitable Technical
Making system cost comparisons requires that concep-
tual designs be  prepared for all viable alternatives. The
level of detail must be sufficient to permit preparation of

 both a cost estimate and an environmental impact as-
 sessment (EIA) for the construction as well as the opera-
 tion of each  system. Cost estimates and  ElAs at this
 stage are best prepared in concert with public works
 staff, consulting engineers, or other experienced profes-
 sionals. The ElAs will also require input from state and
 federal environmental management  staffs  familiar with
 stream designations and existing environmental regula-
 tions that may restrict the discharge location or even the
 use of certain alternatives.
 The conventional way of reporting and comparing costs
 is in terms of the project's present worth. This approach
 involves calculating  in today's dollars the value of the
 project's  engineering cost, construction  cost, financing
 cost, operating cost, and salvage value for a given plan-
 ning period (e.g., 20 years). Planners are also advised to
 consider the actual construction cost, engineering costs,
 and annual operating cost separately. The ranking of the
 various options by present-worth cost is likely to gener-
 ate a list different from the one generated by a technical
 The objective of the cost comparison is to generate  a
 preliminary  financing plan with projected user costs to
 connect to the system, to amortize long-term debt, and to
 pay for yearly O&M. The financing plan will be of great
 interest to the potential users of the system and will have
 a significant effect on the public acceptability of the plan-
 ners' recommendations.

 2.3.9   Prepare a Financing Plan  Overview of Financial Management
 Sound financial management is crucial to the efficient op-
 eration of wastewater systems. It involves estimating ex-
 penses and needed revenues, keeping  comprehensive
 records, and planning for the future. It is not enough for
 small community wastewater systems to break  even.
 Successful systems charge enough so that funds can be
 set aside for the system's future needs,  such as equip-
 ment replacement, line repairs, and emergencies.
 Poor financial management of wastewater systems can
 lead to:
 • Deferred maintenance or repair

 • Inability to replace key system components

 • Inability to operate the system so that it performs as

 • Eventual operational or financial crises

 • Violations of wastewater regulations

The components of financial management include:
 • General utility planning  (anticipating capital and oper-
   ating needs)

 • Rnancial  planning  (meeting capital  and operating
 •  Budgeting

 •  Cost recovery

 •  Accounting and information services

 Several of these components are discussed in more de-
 tail below.

 Financial Planning. Financial planning covers two areas
 of  concern for the small community wastewater system:
 capital improvements  and  operational expenses. The
 costs of capital improvements include not only the costs
 of  materials and construction, but also legal, engineering,
 and certain administrative costs, as well  as other costs,
 such as land acquisition.
 The second area of concern of financial  planning for
 small  communities is  financing operational  expenses,
 which  are the annual expenses associated with the op-
 eration of the facility. These include:

 •  Operations,  maintenance, and most administrative

 • Annual debt service expenses

 •  Financial reserves

 The goal  of financing operational expenses is to make
 the wastewater system self-supporting. Reliable sources
 of  income should be found that will match  existing and
 projected  expenses for operation,  maintenance,  equip-
 ment replacement, and loan repayment costs.
 Budgeting. Most utility budgets are prepared on  an an-
 nual basis. The budget should reflect the major activities
 of the utility, including detailed information regarding the
 revenues and expenses of the facility.
 Typical Revenue Accounts
 • User service charges

 • Hookup/impact fees

 • Taxes/assessments

 • Interest earnings

 Typical Expense Accounts
 • Administration

 • Wages

 • Benefits

 • Electricity

 • Chemicals

 • Fuel and utilities

 • Parts

• Equipment replacement fund

• Principal and interest payments

The budgetary needs of each utility are unique. The in-
formation  contained in the budget should be repre-
sentative of the information  contained in  the  general
utility plan and the financial plan.  Financial statements
should be prepared on a monthly basis and compared to
the budget. The budget should be revised if the projected
costs and revenues are significantly different from the ac-
tual costs and revenues.
Cost Recovery. In order to maintain the facility as a self-
supporting entity, the operating revenues must be suffi-
cient  to meet all system  costs. The following steps are
necessary to develop a cost-recovery system:
•  Identify all system costs
•  Compile system data  as a basis for allocating costs
   among users
•  Classify system users, individually or in groups, to al-
   locate costs in proportion to their use

•  Estimate annual revenue needs
•  Establish rates to meet annual revenue needs
•  Develop billing procedures according to  use, and for
   collection of user charges

A  healthy system will have a positive cash flow as shown on
the annual income  statement. To stay financially healthy, a
wastewater system must:
•  Identify and recover all expenses
•  Institute and maintain an effective financial manage-
   ment system that includes:
    - A utility planning process
    - A financial planning process
    - Effective annual budgeting
    - Effective cost recovery
•  Complete annual  audits and act upon the recommen-
   dations of the auditor Financing Alternatives
Various financing  alternatives exist for small communi-
ties, including:
• Community system reserves
•  Farmers Home Administration loan/grant programs
•  Community development block grants (CDBGs)

•  Municipal facilities revolving  loan funds (also referred
   to as State Revolving Fund loans)

•  Bond issues
•  Local assessments and local option sales taxes

•  Rate increases

When evaluating these financing resources, the impacts
of the financing option upon the system user and future
budgets should be explored. A selection of these financ-
ing mechanisms are discussed below.
User Service Charges. The user charge system is the
central and most important component of a revenue plan,
since it usually accounts  for 80 to 90 percent of  total
revenues. The user charge system has two components:
setting the user rates and  collecting them. The checklist
that follows lists the type of user information that should
be established.
Key  revenue criteria for EPA-funded wastewater treat-
ment facilities include:
•  Charge  each user in proportion  to the quantity and
   quality of the discharge
•  Notify the user of rates annually
•  Impose surcharges for industrial or commercial waste-
   waters that require additional treatment
•  Establish a financial management system to account
   for revenues and expenses

  User Service Charges Checklist   Is This Done at Your
No   Unsure
 All costs are identified
 Costs are allocated proportionately
 based on use
 Flow characteristics are known for
 each customer class
 Each customer's use is known or
 fairly estimated
 Customers are billed in proportion
 to use
 Billing cycle provides timely
 Established procedures ensure
 collection of delinquent bills	
 Federal Grants and Loans. The Farmers Home Admini-
 stration (FmHA) provides loans and grants to rural com-
 munities of up to 10,000 people for wastewater treatment
 facilities. These loans and grants can be used to build,
 repair, improve, or change a facility according to commu-
 nity needs. The loans have a maximum term of 40 years
 (or a shorter term if specified by state law). Interest rates
 may be as low as 5 percent for borrowers that meet spe-
 cific criteria (EPA, 1983; EPA, 1984).

 FmHA loans are intended for communities that are finan-
 cially sound but cannot obtain funds from other sources
 at reasonable rates (EPA,  1983). Grants covering up to
 75 percent of a project's cost may be made to help the
 most financially needy  communities reduce the repay-
 ment burden on the system's users (EPA, 1984). Eligible
 applicants include municipal and  county governments,
 public service districts and authorities, other nonfederal

 public bodies, Native American tribal organizations, and
 broad-based community nonprofit corporations. Priority is
 given to local public bodies providing service to commu-
 nities of 5,500 or less or to projects meeting certain other
 criteria establishing urgent need.
 FmHA  may participate with other federal or public serv-
 ice agencies in jointly funding projects. Community facil-
 ity loans are administered by FmHA district offices, but
 application information is available at local FmHA offices.
 Other federal agencies  such  as the Economic Develop-
 ment Administration and the Department of Housing and
 Urban Development provide grants and/or loans to com-
 munities for various purposes, including wastewater sys-
 tems. County  extension  agents or  regional planning
 agencies are good  sources of information  on  such

 State Revolving Fund (SRF) Loan Program. SRFs are
 available to  towns for  purposes such as constructing
 wastewater treatment facilities.  Loan repayments  go di-
 rectly back into the fund to be loaned to other communi-
 ties (EPA, 1988).

 Under the Federal Water Quality Act of 1987, EPA pro-
 vides each state with startup money to establish a revolv-
 ing loan fund or with money  to add to an existing loan
 fund  for wastewater  facilities. As  of  January 1992 all
 states had established SRF programs.

 Each state's  revolving fund program is slightly different.
 Some programs  limit assistance to communities with
 poor or no credit ratings. Others base their assistance on
 such  factors as the affordability  of the  project,  public
 health benefits, and the potential for economic develop-
 ment. Programs also vary according to maximum loan
 amount, percentage of  total  project  cost eligible  for a
 loan,  interest rate, and duration of the loan. Some states
 simply fund projects on a first-come, first-served basis,
 relying  exclusively on the community's ability to repay.
 Thus  the state must be  contacted to see how its revolv-
 ing loan fund works (EPA, 1988). Each state must estab-
 lish legal mechanisms to  ensure  that the SRF and all
 repayments are used in a manner consistent with  the
 Federal Water Quality Act (EPA, 1989).

 There are several advantages and disadvantages  asso-
 ciated with SRFs. Perhaps the biggest advantage is that,
 if implemented properly, the program can become self-
 sufficient using loan repayments as a source for future
 loans. This reduces future dependence on state funds
 and bonds  as a funding source. In addition, the use of
 loan repayments as a funding source can make a state
 program independent of less-reliable revenue streams,
 such as federal grants and annual state  appropriations
 for which potential problems exist. The state interest-rate
 ceiling,  however, may limit the interest charged to bor-
 rowers,  potentially limiting levels of future loans.  Also,
 loan repayments may not flow back in sufficient amounts
to meet program needs in a timely fashion (EPA, 1984).
 Bond Issues. Bonds  are the most common means of
 securing funds for the construction of wastewater treat-
 ment facilities. Like a home mortgage, bonds extend pay-
 ments for new facilities over a period of 10 to 30 years.
 Bond proceeds are primarily used as a source of funds
 for bond banks or direct loan programs. They have been
 used for leveraging monies in revolving loan funds or
 providing grants and interest rate subsidies.  Leveraging is
 a technique by which bonds are issued to be repaid from
 other financing sources in order to provide project funding
 sooner than would otherwise be possible (EPA, 1984).
 The source of bond payments to investors depends on
 the type of  bond  that has been issued (another term for
 bond payments to investors is debt service,  which simply
 means the  interest payments on the bonds  and bond
 principal as bonds are  retired). The three common bond
 types are:

 • General  obligation bonds, which are secured  by the
   state's full faith and credit and taxing  ability; payments
   are made directly from the state's general fund.

 • Revenue bonds, which are  secured  by the revenues
   generated by project operation. Thus debt  service is
   paid from project revenues. In the case  of  traditional
   revenue bonds issued by communities to build single
   projects,  project revenues are  made  up of  user
   charges.  In the case  of a state program that  funds
   many different  projects, project revenues  may include
   loan repayments from communities and special reve-
   nues such as dedicated taxes and EPA capitalization

 • Double-barreled bonds, where debt service  payments
   may also come from a combination of sources:  taxes
   and project revenues.  In this case, the bonds are se-
   cured first by project revenues, then  by  the full faith
   and credit of the state, should project revenues not be
   sufficient to repay the bonds. This type of  bond is gen-
   erally not available to small communities.

 Regardless of the bond type used, bonds always work in
 combination with  another funding source  that will be
 dedicated to repayment.

 General obligation and revenue  bonds are traditionally
 used by state governments to obtain long-term funds for
 the construction of capital facilities such as wastewater
 projects because they provide statewide benefits for pre-
 sent and future users.  Bonds may not be the appropriate
 source for program startup or operating funds, however, be-
 cause the need for  repayment diverts funds from direct finan-
 cial assistance and  because these costs cannot  be recovered
to make future debt service payments (EPA, 1984).

 State Bond Banks.  Government bonds  are backed
either by the general taxing power of the issuing govern-
 ment  (i.e., general obligation bonds) or by continuing
sources of revenue such as sewer user charges  (reve-
nue bonds) (EPA,  1983).

Most state bond programs act as go-betweens for mu-
nicipalities and the national bond  market. These pro-
grams help many small towns that cannot issue bonds,
or if they can, they must pay high interest rates to attract
investors. A state's typically high credit rating allows it to
issue bonds at relatively low interest rates. Bond banks
act in two ways:  they may either guarantee local bond
issues or they may actually buy local bond issues.
Not all states have bond banks and those that do have a
variety of alternative arrangements. State offices must be
contacted for additional information about eligibility, how
to apply, and terms.

2.3.10   Prepare Draft Recommendation and
        a Report for Public and Regulatory
        Agency Comment
Completion of the preceding steps permits the selection
of a wastewater management approach to recommend to
the community.  All  the previously collected  data and
evaluations should be assembled in a document known
as a facility plan that is released for public and regulatory
agency review. Comments from all parties are solicited.
The usual forum for public comment is a public hearing.
Of the several junctures in the wastewater system plan-
ning process where formal public interaction takes place,
the public hearing on the recommended plan of action is
the most critical. The effort  put into  preparing for this
meeting will be reflected in the ease in which the project
proceeds.  Insufficient preparation can create  mistrust
and doubt among the public and lead to a lengthy and
potentially costly effort to restore support and confidence.
Aspects of the planning process that should be brought
out in the facility plan include:
 • Problem definition
 • Thoroughness in the number of alternatives evaluated

 • Accuracy in the development of conceptual plans

 • Accuracy of cost estimates
 • Justification of all charges
 • Environmental impacts  of  the proposed system (e.g.,
   benefits and potential problems for all media)

 If the plan's foundation is thoroughly established, the rec-
 ommendations usually can be modified or changed read-
 ily in accordance with feedback from the public and from
 agency representatives.

 2.3.11   Prepare Final Recommendation and
        a Report
 Following a well-prepared public hearing on  the facility
 plan, public and  regulatory  agency  comments are ad-
 dressed and a final plan prepared. This is then  released
 for public review. A meeting of the representatives of the
 affected community or the sponsoring community is sub-
 sequently held for the express purpose of voting on ac-
ceptance or rejection of the proposed plan. If the public
hearing on the draft plan was well attended and the plan
well  prepared, it  is likely that public  comment at  this
meeting will be limited.

2.3.12 Summary
The  planning scenario  presented is subject to modifica-
tion  depending on the state  and locality  in which the
wastewater project is intended to be built.  For instance,
the facility plan may be put to a referendum vote  at a
polling station in some communities. Nevertheless, some
expression of community acceptance  is necessary to
complete  all planning phases. If  public participation/liai-
son  has been effective, the likelihood of community  sup-
port is greatly increased.
Many projects never get beyond a majority vote in oppo-
sition to the plan. If the planning process  has imparted
enough momentum to  the project, it is likely to get into
the  next phase. At this point the energy of the project
champion is often essential.
The major reason for a project stalling after the vote is in-
adequate funding to carry on. This  impediment looms larger
now that the federal grant program has been curtailed.

2.4    Design
The first step in the  implementation of planning recom-
mendations is the preparation of a formal engineering
design. From this point in the process on, paid consult-
ants and  contractors are generally used because of the
expertise required to prepare the technical plans, specifi-
cations, and legal papers required to secure regulatory
approval and for use as construction documents.
The primary work of the community during this phase is
the  management of consultant selection, work progress,
 and budgets. Although the formal  planning phase will
 have  been  completed,  during this  and subsequent
 phases the project group must continue to plan for the
 eventual startup and operation of the facility.
 The group given responsibility for these activities may be
 made up of the same or most of the  same people who
 participated in the planning effort or may be an entirely
 different  group depending on the management recom-
 mendations developed in the planning phase. The design-
 phase manager is expected to complete the following  tasks
 in achieving the major goal, the  production of plans and
 • Consultant selection
 • Budget management
 • Schedule management
 • Work quality management
 These tasks are discussed below. Planning for opera-
 tions  is a component of the  work  quality management
 task and  will be dealt with in that discussion.

 2.4.1   Consultant Selection
 The consultant solicitation process for this phase is simi-
 lar to the process followed in the planning phase. How-
 ever, the request for proposals and the response should
 be much more focused. Specific areas on which consult-
 ant's proposals will be evaluated are:
  Scope of
• Schedule
                 What is the firm's experience with the
                 type of project  and technology being
                 proposed,  and what is the experience
                 of employees proposed for the work?

                 This  narrative should provide insight
                 into the depth of a consultant's knowl-
                 edge of the subject and whether there is
                 a sharing of the community's philosophy.

                 This is the consultant's  specific  work
                 proposal. Does it answer the RFP and
                 cover all the known isstfes thoroughly?
                 Does it suggest activities that may have
                 been omitted in the RFP?
                Does it take into account RFP-imposed
                deadlines? Does it allow for community
                review at critical points?  Does it antici-
                pate reasonable times for community
                and regulatory review?

 • Budget and   Is the price  considered  fair  for  the
   Billing        scope of work proposed?  How is pro-
                gress to be measured and billed?
 Other nontechnical requirements such as indemnities, li-
 ability insurance, bonds, and guarantees should be es-
 tablished with advice of the community's counsel.
 Proposal review and final selection are the same  as in
 the planning phase.

 2.4.2   Budget Management
 Management  of  the  project's budget  is  a relatively
 straightforward task, although special emphasis should
 be put on scrupulous recordkeeping. Recordkeeping to
 the specifications of funding agencies is particularly im-
 Assessing the value of the consultant's work and review-
 ing bills  is an important fiduciary responsibility of the
 management team. The manager should be thorough in
 evaluating bills and statements of work. He should bear
 in mind that the relationship with the consultant is defined
 by the contract.
 Requests for change orders from the consultant should
 be compared with the contract to confirm that the  work
was not originally included in the contract.

2.4.3   Schedule Management
Most  project milestones will have been established by
the section in the RFP on the scope of work. However,
practical steps can be taken to ensure that deadlines are
met. The most effective action is the scheduling of regu-
  lar project meetings for monitoring progress and main-
  taining  momentum. Such meetings should be  held at
  least monthly but may need to be held more frequently
  on smaller or fast-paced  projects. The minutes of these
  meetings will serve as a formal record of all parties' ac-
  tivities  and  document  discussions  and  statements,
  should a  record be needed for use in audits or dispute

  2.4.4   Work Quality Management
  Although drawing up construction contract documents is
  the responsibility of the consultant, the community pro-
  ject managers have a responsibility to monitor the quality
  and quantity of the work. Monitoring, however, is not eas-
  ily accomplished by a group that may have limited tech-
  nical expertise and practical experience with wastewater
  systems. There are two reviews that can be performed
  by the project managers, with the help of consultants, to
  ensure that the  principal consultant's work meets the in-
 tent of the design and additional  charges are kept to a
  minimum. These reviews are:
  •  Peer Engineering Review

  •  Constructability Review

 These reviews are generally performed by  outside pro-
 fessionals, at  an added cost to the project. The potential
 long-term  savings in dollars and the benefits in terms of
 peace of mind are more than worth  the  cost.  Potential
 consultants for the peer engineering review can be iden-
 tified by questioning state  and local regulators about the
 recognized experts in the  technologies proposed for the

 The objectives of the peer review are to answer the fol-
 lowing questions:

 • Is the design  capable of performing as intended (i.e.,
   consider present vs. design population analyses)?

 • Has the engineer omitted required treatment steps?

 • Are the design parameters accurate?

 • Are there redundant or needless treatment steps or

 • Does any of the equipment selected lack sufficient du-
   rability to serve the community adequately?

 • Does  the equipment or process require  special or
   costly maintenance?

 • Can the same treatment objectives be met in  a less
   costly manner?

 Even community wastewater management systems em-
 ploying  unsophisticated technologies  can benefit from
 peer review. Consider, for example, a proposal to repair
 or replace individual septic systems in a community.
 Questions the  reviewer may address for a simple septic
tank alone are:

 • How are watertight pipe connections to be made?

• How are tank sections to be sealed?
• Is the cleanout access sufficient for proper mainte-
• Is the chosen tank material the best for the conditions
  in the locality? Would plastic, fiberglass, or concrete
  be better?
• Are any protective coatings required inside or outside
  the tank?
• Are the materials specified for gas baffles, tees, risers,
  or covers durable and not easily corroded by septic
• Will the tank be susceptible to flotation at any time?

• Are the tank backfill requirements suitable?

• What provisions have been made to prevent settling of
  the inlet and outlet pipes.
• Is the tank properly vented?

There are many questions to be asked about the other
septic system components as well. Large or more com-
plex systems have an even greater need for scrutiny.
Such questions may not be obvious to all design consult-
ants. Since money is less available for wastewater sys-
tems for  small  communities and since  lower  system
costs are achieved by  using packaged systems and lo-
cally available  or innovative equipment, financial con-
straints promote the selection of lower cost systems.
There  are few validated national design standards for
small package systems or for equipment,  such as septic
tanks,  commonly used  in small community systems.
Many package systems employ  patented components for
which  performance  data are available  only from the
manufacturer.  Without  third-party  verification,  such data
should be treated with caution.
The septic tank example illustrates the point regarding
design standards. Septic tanks  represent  one of the old-
est wastewater treatment technologies. They are manu-
factured throughout the country, primarily using concrete.
Most states lack a structural standard for concrete septic
tank design. While most sewer piping used today is plas-
tic, plastic pipe does not bond to concrete and few stand-
ards for watertight tank-to-pipe connections are known.
Other septic tank materials also have incomplete struc-
tural design requirements.  Polyethylene  and fiberglass
tank designs, for instance, have had numerous prob-
lems, but thus  far no state has adopted a structural
Peer engineering review then  is  a matter of prudence
and insurance to reduce the risk to the small community
of using less-expensive and untested technologies.
The constructability review  may be performed as part of
the peer review task or separately. It is  recommended,
however, that separate advice from experienced contrac-
tors be secured for maximum benefit.
The object of a constructability review is to determine if
the system plans or specifications contain requirements
that are impossible or too costly to  implement and for
which there are lower-cost or more feasible substitutes.
An example of the kind  of issue addressed by a con-
structability review is the appropriateness of chosen sep-
tic tank construction materials. Assume, for instance, that
the bid date and completion date for an onsite system re-
pair or septic tank effluent collection system project re-
quire  work through the spring or wet season. Assume
also that the soils in the community have a large percent-
age of silt and clay and that the water table is high during
the wet  season. Finally,  assume that concrete  septic
tanks are specified. The  constructability reviewer in this
case might find the following:
• Most yards are likely to be too soft  during the wet sea-
   son to support standard septic tank delivery trucks.

• The construction methods required to  overcome this
   problem are  likely to be  more expensive  than the
   methods required during drier seasons.
• Construction during the wet season is  likely to cause
   greater collateral damage to properties, thus increas-
   ing the cost of restoration.

The constructability reviewer might recommend a longer
contract period with a planned shutdown to overcome the
problem and associated  increased costs, or might rec-
ommend the use  of lighter, more easily handled fiber-
glass or polyethylene tanks.
The potential return on the cost of peer and constructa-
bility  reviews varies from project to  project. In  general,
however, such reviews reduce the potential risk and li-
ability that construction  bidders  associate with projects
involving unfamiliar technologies and conditions.  For ex-
ample, consider the bid prices of septic tank effluent sys-
tems  when they were first introduced. The specifications
usually required that  the private  property on which the
tanks  and service laterals were  placed  be restored to
their original condition or better upon completion. Con-
tractors bidding the projects were faced with the dilemma
of entering into a contract with one party (the community)
to perform work on the land of another party (the home-
owner). The contract requirements were vague in stating
that restoration was to equal preexisting  conditions; the
quality of preexisting conditions, however, was a subjec-
tive requirement and  subjected the contractor's work to
the judgment of a homeowner with whom the contractor
has no contract. Further, the contracts carried no indem-
nification of the contractor from suits resulting from dis-
putes over the adequacy of landscape restoration. There
were other shortcomings in the early  contracts, but these
two glaring omissions resulted  in inflated bids to cover
the cost of the risk the contractors assumed or felt that
they were assuming. As contractor experience grew with

 successive biddings and contracts were  more carefully
 crafted, the bid prices of septic tank effluent system con-
 struction contracts dropped dramatically.
 Had these early projects been peer and constructability
 reviewed many of the contract and design provisions that
 contributed to contractor apprehension would have been

 Concurrent with the management of the design phase, it
 is important that the community management group be-
 gin planning  for the operation of the facility during this
 phase. Although the consultant will be expected to pre-
 pare an  acceptable O&M  manual for the system, input
 and review by the community is important for the follow-
 ing reasons:

 • Wastewater facility operating costs will continue to be
    incurred for years after construction is completed. The
    design and its effect on these  costs should be re-
    viewed constantly to ensure that what is planned as
    an environmental enhancement does  not  lead to a
    chronic fiscal problem.

 • Many operating activities can be designed out of facili-
    ties. The level of operator attention  required affects
    operating   costs.  The  community  representatives
    should have input into this decisionmaking.

 •  The community must develop an understanding of the
    skills  and number of individuals required to operate
    and maintain the facility in order to prepare accurate
    operating cost projections.

 Specific areas that the management committee should
 concern itself with are:

 •  Durability of materials, equipment, finishes

 • Availability/access to spare parts

 • Access to all components

 • Safety provisions and requirements

 * Energy requirements

 • Life expectancy of equipment

 • Requirement for special tools

 • Potential disasters and effects

 • Emergency operations

 • Monitoring and controls

 Special knowledge is not required  to address  these is-
 sues. Questions relative to these issues and about  po-
tential  alternatives to the design should be asked,  the
cost impact evaluated, and guidance given to the  de-
signer so that the constructed facility is appropriate given
the needs, desires, and finances of the community.
 2.5   Construction
 The  construction phase  of  the  project involves  more
 groups and individuals and more money over a short pe-
 riod than all the other phases combined. The participants
 • The community representative
 • The design consultant

 • The construction manager (optional, function may be
   carried out by design consultant)
 • The contractor(s)
 • The subcontractors
 • Funding agencies
 • Regulatory agencies
 Management of this group would be difficult enough were
 they  all  linked contractually.  Unfortunately, they are
 linked in  various ways that could allow for chaos  if the
 group is  not carefully managed.  A typical organization
 chart is presented in Figure 2-1.
Figure 2-1.  Typical Management Organization for Con-
struction of a Small Community Wastewater Project.

The management functions during this phase include:
•  Paying the project bills

•  Maintaining records of funds expended

•  Ensuring that money will be available when needed

•  Functioning as a public liaison

•  Reviewing and approving change orders

•  Making cash-flow projections

•  Monitoring the schedule and status of the work to be
   sure that work complies with the funding  agencies'

•  Monitoring the work to ensure that the terms and con-
   ditions of regulatory approvals are met

•  Preparing  progress reports as may be  required by
   funding and regulatory agencies

•  Monitoring the quantity and quality of the work

•  Resolving disputes as they arise

Even though much of the detailed owner responsibility
may be delegated to a  construction manager, the con-
struction period requires substantial  effort on the part of
the community representative. The primary demands are
processing payment requests, attending periodic (monthly)
job meetings, reviewing  change orders, functioning as a
public liaison, facilitating dispute resolution, and earring out
operational planning.

2.5.1   Functioning as a Public Liaison
Public  liaison responsibilities of the community repre-
sentative include conducting  a preconstruction commu-
nity meeting and responding to questions from the public
throughout the construction period. The use of all avail-
able local  media for providing  progress updates and noti-
fication of public hearings is vital to success.
The preconstruction public meeting can often be com-
bined with the design completion meeting. In relative
terms, the preconstruction public meeting is the more im-
portant of the two  meetings, especially when a sewer
system is to  be constructed or upgraded as part of the
project. Sewer construction brings the public  into direct
contact with the construction contractor since  it involves
working on public roads.  Sewer construction tends to
slow traffic and leaves roads in disrepair for extended pe-
riods. Projects may also  dry up wells and interrupt cable-
TV service, electrical power, or water. Construction also
may require that individuals make arrangements with a
contractor for connection  to  the wastewater  collection
Preconstruction public meetings for treatment systems
primarily serve  to inform the public of project activity and
to maintain a high level of awareness.
The public meeting should include the  following elements:

1.  Summation of project history

2.  Description of the planned facilities and their  ex-
    pected performance

3.  Description of the construction  process,  schedule,
    and anticipated effects on  the community

4.  Introduction  of project participants, including  the
    contractor,  construction manager,  and community
5.  Designation of contact representatives for the vari-
    ous participants. Designation of the types of com-
    plaints  and concerns  for which each participant is
    responsible.  Distribution  of  worksite address and
    phone  numbers  for  responsible  participant  repre-
    sentatives and after-hours emergency phone numbers.

The matter of jobsite contacts for the public deserves ad-
ditional comment. Many communities designate one per-
son or entity as the point of contact to which the public is
directed to  refer all complaints and inquiries. This is rec-
ommended, if only because it permits  the establishment
and maintenance of a tracking system  that ensures a re-
sponse to all public contacts.

2.5.2   Change Order Review
It is rare that a project will  be executed precisely as
planned or as bid, and project changes always have a
cost associated with them. Therefore the evaluation and
negotiation of change orders  are an important manage-
ment  function of the community  representative. If the de-
velopment of change orders is delegated to a construction
manager, then review of the manager's recommendation
is an important function.
Although a detailed discussion  of change order proce-
dures is  beyond the scope of this volume, a  few major
concepts include the following:
« If a change  is unavoidable, don't delay approval.
  Some communities  consume  valuable time trying  to
  associate the change with a regulatory requirement or
  design oversight in order to avoid the cost by transfer-
  ring liability. This process  only delays the  contractor
  and can add more cost to the contract than the value
  of the change because  of the costs of delay. The job
  requirements should be addressed quickly.  Liability or
  other concerns should be addressed separately.

• Get expert help when negotiating costs. Contractors
  generally know their actual costs since their business
  depends on it. Small communities  don't contract for
  wastewater systems everyday and may be at a disad-
  vantage  at the negotiating table. Therefore the com-
  munity is advised to employ  expert assistance when
  valuing changes to the work.  A construction manager
  usually provides this service.  If the manager recom-
  mends a price for a change, be sure backup calcula-
  tions and an explanation are provided.

• Don't let haggling  over the price delay the  work. The
  community should keep in mind that time is money
  and any delay to the project adds cost. When the de-
  lay is caused by the owner, the cost is passed  on by
  the contractor.

Finally,  well-designed  and specified projects will have
fewer unforeseen problems. If the total value  of change
orders exceeds 5 percent of the construction budget, the
planners and designers have not performed well overall.

 2.5.3   Processing Payment Requests
 The prompt review and payment of contractor requisi-
 tions is the single and simplest action the community
 representative can take to ensure a smooth construction
 project. Cutoff dates for contractor billings should be co-
 ordinated with community finance board meetings to en-
 sure quick payment. The community must never transfer
 Its cash-flow problems to the contractor by delaying his
 payment; for instance, when loan payments, grant pay-
 ments, or other funding has not been received. The com-
 munity must  update  cash outflow and inflow  plans
 regularly and take necessary steps to ensure timely con-
 tractor payments.

 2.5.4   Attendance at Progress Meetings
 The job progress meeting is a formal procedure estab-
 lished to bring all project participants together on a regu-
 lar basis to discuss all aspects of the work project. It is
 the main  mechanism by which  the community and its
 representatives keep up with the details of the project.
 The meeting should have a formal agenda and detailed
 minutes should be kept. Attendees should include:
 • The community representative (the owner)
 • The contractor
 • The design consultant(s)
 • The construction manager
 • The funding agency representative (if possible)
 • Regulatory agency representatives (if possible)
 • Utility representatives
 • Traffic control representatives
 • Police
 • Interested citizens

 A typical agenda might include:
 Acceptance of previous meeting minutes
 Schedule review
 1.  Describe work completed since previous meeting
 2.  Compare total work to date against contractor schedu le
3.  Compare contractor payments to date against  pro-
   jected cash flow
4. Agree what action if any is necessary to correct in-
   congruities in the  proposed versus  actual work and
   cash-flow schedules
5. Agree on revised schedules and cash-flow projections

6.  Describe and discuss in detail activities that will oc-
   cur in the next period
Shop drawing review
   All projects have a list of detailed equipment descrip-
   tions and component configurations that are required
    to be submitted and approved before the contractor
    proceeds with certain work. The list of submittals and
    their approval status is compared to the completed
    and  proposed work.  Problems relative to the  ade-
    quacy of the contractor's submissions and the timeli-
    ness  of the review  by  the  design consultant  or
    construction manager are resolved.
 Change order review

    The change orders issued, both pending and antici-
    pated, are reviewed for their content and cost. Al-
    though the monthly meeting is not the proper forum
    for negotiation, it can be used to move intractable is-
    sues because all the interests involved are generally
    represented at the table. Change order review allows
    the owner to keep a current total of the cost of pro-
    ject extras.
 Review of jobsite visitations

    All projects have a constant stream of official and un-
    official visitors and inspectors. These visitors often
    converse with and question the inspectors, foremen,
    laborers, and operators on the job. These informal
    contacts may result in important findings and direc-
    tives being lost or not communicated to the responsi-
    ble individuals.  This  review  attempts to  overcome
    problems caused by lack of communication. One of
    the most  important sources  of comment  is  com-
    plaints or questions from the citizenry.
 Review of jobsite problems

    This  review addresses  past  and  anticipated  con-
    struction problems and is  an advantageous forum for
    their resolution because of the array of interests pre-
    sent. The discussion can  save the owner many dol-
    lars otherwise lost to  lack of productivity and  in
    potential change orders. However,  even more impor-
    tant than the construction-related problems, this  seg-
    ment  of the meeting  permits exposure  of  work
    problems associated with friction among the project
    participants so that they can be  dealt with before
    they turn into full-blown disputes.

2.5.5   Facilitating Dispute Resolution
Disputes arise in all construction  projects. The rapidity
and skill with which they are addressed have a major im-
pact on the cost and outcome  of the project. All construc-
tion contracts  have a dispute resolution clause. These
clauses, however, should be reserved for the most egre-
gious  disputes, after all  efforts to reach a compromise
and conciliation have failed.

Disputes can usually be attributed to some omission, in-
consistency, error, or vagueness in the plans or specifi-
cations for the project. They can also arise from friction
between project participants.

When the community representative becomes aware of a
dispute he or she must take action immediately and  per-

severe until a resolution is achieved. While the art of dis-
pute settlement is beyond the scope of this work, there
are a few pertinent points to consider.

1.   Put the disputed issues in writing and get the oppos-
    ing parties to agree on the points. This single act will
    facilitate dispute resolution by allowing the issues to
    stand out.

2.   Get the disputants to talk with each other to resolve
    their differences.

3.   Set deadlines for action. Don't let the dispute fester
    for a long period.

4.   Get actively involved  in the negotiations only when
    the impasse is judged to be permanent.

5.   Take action. In almost all cases the least costly reso-
    lution is readily available.

6.   Document the actions  taken and the  reasons for

2.5.6  Operational Planning
Operational planning for small community systems con-
tinues through  the construction phase. This effort  has
two main components:

1.   The assembly of a thorough and usable O&M manual.

2.   The preparation of a thorough startup plan.

The technical preparation required for an O&M manual is
usually performed by  the design consultant. The con-
struction contractor supplies the O&M manuals for the fa-
cility's  individual  components,  such  as valves,  flow
meters, and generators.  It  is the  responsibility of the
community representative to review and evaluate these
documents for their accuracy, clarity, and completeness.
Technical  assistance is available from regulatory agen-
cies and operations consultants.  It should not be left to
the system operations staff to  discover O&M manual
shortcomings long after the  consultants and contractor
are gone.
Startup planning is an area that is often overlooked. Most
small community systems are designed to serve pre-
viously unsewered areas. As such, flow to the treatment
plant has usually not begun upon completion of the pro-
ject. As the house-by-house connections to the system
are made, flow increases from zero to approach design
levels. This scenario presents two startup problems:

1.   How is the finished treatment system to be evaluated
    for compliance  with  design requirements without

2.   Since most treatment systems are designed to oper-
    ate within certain flow and contaminant concentration
    limits,  how will performance—compliance with oper-
    ating permits—be achieved with flows and contami-
    nant loads outside the design ranges?
Answers to these questions are as varied as the number
of collection and treatment options. The design consult-
ant should be charged with developing a startup plan, ac-
ceptance criteria, and an interim operating plan for the
connection period. Assistance in evaluating the plan  is
available from regulatory agencies, other utilities, and op-
erating consultants.

The plan for operational startup must address the issues
of performance and permit compliance during what may
be a protracted period. Physical/biological systems, such
as sand filters, have a relatively short startup period and
a  broad operating range. Biological systems using acti-
vated sludge processes have somewhat longer startup
periods; they are dependent upon a supply of wastewa-
ter nutrients to perform properly and  have a much nar-
rower  operating range. Wetland systems, which are
coming into frequent use in small communities' facilities,
have  a very  broad  operating range but may  require a
year or more to develop the necessary plant community.
Sewer systems with small flows may have such long de-
tention times  in pump station wetwells that  offensive
odors are produced.

The design consultant's plan to address such startup is-
sues might be included in the O&M manual or, since it
may be a one-time process, in a separate document. It is
the  community representative's  responsibility  to  be
aware of the requirements for startup and to  make the
necessary staffing and resource commitments to carry
out the plan.
In preparation for conditional acceptance and startup, the
community representative should begin to recruit operat-
ing staff early in the construction period. The number of
staff persons and the training requirements should be es-
tablished in a draft  of the O&M  manual by the design
consultant prior to recruitment.

Once identified, the principal operator should be en-
gaged, placed on the community's payroll, and assigned
to work along with the construction manager and engi-
neers through the end of construction to become familiar
with the physical equipment and the O&M manual. The
earlier the chief operator can be brought onto the project,
the more readily the operator will be able to deal with the
requirements of startup. The need for early engagement
of the operator is dependent on the complexity  of the
system and equipment. Each community must determine
its own needs.

2.6   Startup
The construction phase of wastewater management pro-
jects and the startup phase overlap, with  acceptance
startup commencing at the announcement that the con-
tractor has completed work and is  ready to transfer pos-
session of the facility to the community. At this point all
subcomponents will have  been operationally  checked.
The acceptance startup will check the operation of all

systems as an integrated unit. Operational startup offi-
cially commences on the day that conditional acceptance
of the facility is established, but actually commences with
the recruitment of competent staff, about midway through
the construction period.
Acceptance startup is the responsibility of the community
representative overseeing construction. Assuming that a
reasonable plan for startup testing has been developed,
this phase of the startup should be a straightforward ex-
ercise. The activity should conclude with the preparation
for  the community representative's approval of a startup
and testing report, which compares, on a mechanical per-
formance basis, the requirements of the design report
with the measured performance of the completed facility.
Tank sizes,  pump  sizes,  pump  output, blower sizes,
blower output, weir overflow levels are a few of the items
compared. The performance of biological systems is usu-
ally not compared at this  time because of the need for
seeding and a steady flow of wastewater to encourage
the ecosystem.

The results of testing should be presented in as simple a
form as possible for the community representative to
evaluate prior to acceptance. All deviations from design
requirements should be explained  and an acceptance
recommendation secured  from both the design consult-
ant and construction manager. Prior to acceptance, the
community representative should read the document and
understand the reasons for any variation from the design.
The community representative must be aware that accep-
tance of the facility releases much of the financial leverage
that he possesses to ensure compliance with the design re-
quirements—bonds and guarantees notwithstanding.
Operational startup commences on the date of conditional
acceptance of the completed facility. Conditional accep-
tance is the point at which the facility is completed and
ready to be used for its intended purpose with only minor
items (e.g., touchup painting, grass growth) remaining.

Public information and feedback during the startup phase
are usually  limited to media  announcements  about the
startup of the facility  or a formal open house. Although not
crucial  to the continuance of the project, the open house
provides an appropriate setting to acknowledge the efforts
of the various groups and individuals involved in the project
and to display the fruits of the community's efforts.

2.7  Operation

The operation phase is the long-term continuation of op-
eration after startup. Late in  the  construction  phase or
during  startup, the  permanent community organization
charged with managing the operation of the facility be-
gins its work.

Management responsibilities include:
• Establishment of annual operating budgets
•  Establishment of a preventive maintenance plan

•  Establishment of a long-term capital replacement plan

•  Monitoring of permit compliance and reporting

•  Monitoring of normal O&M

•  Monitoring of staff workloads and needs

Planning responsibilities include:
•  Regular review and updating of emergency operations

•  Preparation and maintenance of capital expansion

Daily operations are carried out by the full- or part-time
operations staff.
The entity responsible for system  management should
establish a formal work plan and schedule. Many small,
and even some large, wastewater systems have failed to
perform or survive through their intended life cycle be-
cause of inadequate management attention or the dele-
gation of responsibilities to the operations staff.
It is often difficult for managers to sustain their attention
to well-designed, simple, and reliable systems because
during the early years,  after stable operations are estab-
lished, they demand little attention. Management alert-
ness  can be maintained  by scheduling, at a  minimum,
quarterly  quality-control  and budget reviews. Larger,
more complex systems will require monthly evaluations.
Sample agenda items are listed below.

A. Facility Performance

1.  Discharge standards versus discharge performance

2.  Establish reasons for noncompliance

3.  Establish a corrective-action plan

4.  Review trends in facility performance (charts or other
    graphics are useful  for presenting trends)
    a. seasonal
    b. long term
    c. corrective-action  plans

5.  Review scheduled maintenance activities

6.  Review major unscheduled maintenance activities

B. Staff

1.  Actual versus planned labor hours

2.  Review training plans
    a. operations
    b. safety

3.   Review licensing status

C. Budget

1.   Planned versus actual cash flow

    a. maintenance appropriations
    b. labor cost
    c. capital expenditures

2.   Prepare requests for supplemental appropriations
D. Planning

1.   Annual budget

2.   Capital improvements

3.   Staff training

4.   System expansion

5.   User charge system review (annually)

The operations management group should retain the de-
sign consultant for guidance at least until it is comfortable
with its task. When the EPA grants program was still in
effect, consultants  were required to be retained for  a
one-year period following startup for the purpose of certi-
fying the successful performance of the project. This ar-
rangement  was useful in that it  maintained a formal
communications link between the community and the de-
signer that helped resolve operations and management
In  summary, planning for system operations begins dur-
ing the preliminary  planning phase  of  the project,
months, if  not years, before  operations commence. The
guiding  principles are  that  small  community  systems
must be simple to operate, reliable, and economical. Ad-
dressing these concerns is then followed by a design ef-
fort during which specific choices are made to implement
the project goals. During construction, an O&M manual is
prepared and operators engaged and trained. Most oper-
ating procedures will have been tested during startup, as
operators are gaining experience. The attention paid and
time devoted to these tasks will greatly enhance the abil-
ity to manage the completed wastewater system.
2.8   References
When an NTIS number is cited in a reference, that refer-
ence is available from:

    National Technical Information Service
    5285 Port Royal Road
    Springfield, VA 22161
    (703) 487-4650

EPA.  1992. Small wastewater systems: Alternative sys-
tems for small communities and rural areas. EPA/F-92-001.

EPA. 1989. Environmental Protection Agency. Water and
wastewater  managers  guide  for  staying  financially
healthy. EPA/430/09-89-004.

EPA. 1988. Environmental Protection Agency. Reference
guide  on  state  financial  assistance   programs.

EPA.  1987. Environmental Protection  Agency.  It's your
choice:   Guide for local officials on  small community
wastewater management options. EPA/430/09-87-006.

EPA.  1986. Environmental Protection Agency. Touching
all bases:  A financial management handbook  for your
wastewater treatment project. EPA/430/09-86-001.

EPA.  1985.  Reducing the  cost of  operating municipal
wastewater treatment  facilities. Available from  the Na-
tional Small Flows Clearinghouse.

EPA.  1984. Is  your  proposed wastewater project too
costly? Options for small communities.  Available from
the National Small Flows  Clearinghouse.

EPA.  1984. User  charge guidance  manual for  publicly-
owned treatment works. EPA/430/9-84-006.

EPA. 1983. Environmental Protection Agency. Managing
small and alternate wastewater system: A planning man-
ual. EPA/430/09-83-008.

EPA.  1979. Environmental Protection Agency. Manage-
ment  of  small-to-medium-sized  wastewater treatment
plants. EPA/430/09-79-013.


                                              CHAPTER 3
       Site Evaluation and Construction Considerations for Land Application Systems
3.1   Introduction

3.1.1   Soil as a Treatment and Disposal
Soil frequently is used to provide both treatment and dis-
posal of wastewaters. It has a  large capacity to retain,
transform, and recycle many of the pollutants found in
municipal  wastewater. As  the wastewater  percolates
through the soil to the ground water, physical, chemical,
and biological  processes occur to provide a high level of
treatment  consistently and reliably. Where properly ap-
plied and  operated, soil-based  or land application treat-
ment  systems have been shown to have relatively low
capital and  operating  costs.  Today several  thousand
such  systems are being used  successfully across the
United States.

Various designs exist for land application systems. They
may apply wastewater either on or below the land  sur-
face.  Surface  application  systems  include  slow  rate,
rapid  infiltration, and overland flow. Subsurface applica-
tion systems include septic tank systems and subsurface
infiltration  systems designed for clusters of homes.  The
selection  of a design depends on the nature of the
wastewater to  be treated, the characteristics of the site,
and regulatory requirements. Except for overland  flow,
these designs  are "zero discharge" systems, where ulti-
mate disposal  of the treated wastewater is to the ground
water, rather than a point discharge to  surface water.
Therefore, to protect ground-water quality, the land appli-
cation site must be carefully selected and the system de-
sign appropriately adapted.

3.1.2   Importance of Site Evaluation in
       System Performance
Hydraulic and treatment performance of land application
systems are related directly to  the soil and site charac-
teristics and the applied wastewater quality. Performance
is  measured by the ability of the system to accept  and
adequately treat the applied wastewater within the de-
fined system boundaries. The system is  commonly de-
fined to include the unsaturated  soil below the infiltrative
surface, the permanent ground-water table, and a portion
of the ground water horizontally extending to the property
line. Typically,  drinking water standards must be met for
 many  pollutants  before the  wastewater/ground-water
 mixture leaves the system boundaries.
 Site evaluation is the most critical factor in successful
 performance of land application systems. It must provide
 sufficient information to predict the capacity of the soil to
 accept and treat the projected wastewater loading and to
 assess how the soil and ground water will respond to that
 loading. Design selection, infiltrative surface area, eleva-
 tion, geometry, and method of system operation are all
 dependent on information gathered during the site evalu-
 ation. Most  failures  of land application systems can be
 attributed to inadequate site evaluation and interpretation
 of the data  collected. It is  necessary that the engineer
 recognize the  importance of a thorough site evaluation
 by experienced, qualified professionals.

 3.1.3   Importance of Construction
        Procedures in System Performance
 Soil is a complex physical, chemical,  and biological sys-
 tem that functions well only when the soil pores remain
 relatively open and continuous. Porosity  and pore conti-
 nuity is essential for the free movement of liquids and
 gases within the soil. Construction activities will  destroy
 many of the pores through compaction, smearing, and
 puddling, all of which reduce the hydraulic and treatment
 capacity of the soil.  Proper construction procedures per-
 formed under the appropriate soil moisture conditions will
 minimize the damage that can occur.
 Soil that has been excessively damaged during construc-
 tion cannot be easily repaired. Usually the system must
 be redesigned to  account for the reduced hydraulic and
 treatment capacity of the soil or to avoid use of the dam-
 aged soil. Often the site  is  no longer suitable and must
 be  abandoned. Therefore, the engineer must consider
 construction procedures  during design and limit the soil
 moisture conditions under which a facility can be built.

 3.2  Treatment and Disposal of
     Wastewater in Soil

 3.2.1    Soil as a Three-Phase System
 Soil is a complex, heterogeneous, porous system of par-
ticulate mineral solids and organic matter in which the in-
terfacial surface area is enormously large. It provides a
three-phase  treatment system: the solid phase consists

of soil particles; the liquid phase consists of water (con-
taining dissolved substances); and the gaseous phase
consists primarily of soil air (and other gases).
The solid matrix of the soil consists of particles differing
in chemical and mineralogical composition as well as in
size, shape, and orientation. The mutual arrangement of
these  particles determines the characteristics  of the soil
pores  in which water and air are transmitted or retained.
The interaction of these phases in the soil directly im-
pacts the capacity of the soil to accept and treat applied

3.2.2   Water Movement in the Soil System
Water moves in soil through the soil pores in response to
a potential energy  gradient. The rate of flow  is propor-
tional to the permeability and the potential gradient. Soil
permeability, a measure of the capability of soil to trans-
mit fluids, is determined by the size, shape, and continu-
ity of the  pores rather than the porosity of the soil.  For
example, clay soil is more porous than sandy soil, but the
sandy soil will transmit much more water under saturated
conditions because "rt has larger, more continuous pores
than the clay soil.
The soil moisture potential consists  of several compo-
nents. The primary components of interest in land appli-
cation systems are the gravitational, hydrostatic (positive
pressure), and the  matric (negative pressure) potentials.
Water will move in the direction of decreasing potential;
however, its path may not be direct because of the avail-
able flow paths in the porous media.
The gravitational potential is the mass of the water times
the acceleration  due  to gravity, or  the  weight  of  the
water. At  any point, it is determined by the elevation of
the point relative to an arbitrary reference level.
The hydrostatic potential is a positive pressure potential
that occurs  below the ground-water surface. It is greater
than atmospheric pressure and increases with depth be-
tow the surface due to the weight of water above.
The matric potential is a negative pressure potential cre-
ated by the physical affinity of water for the soil particle
surfaces and capillary pores. Water attempts to wet the
particle surfaces due  to adhesive  forces between  the
water molecule and the surface. Cohesive force between
water molecules pulls other molecules from the bulk liq-
uid—thus  a negative pressure, or suction, is created, a
phenomenon referred to as capillarity. The movement of
water  stops when  the column of water that  is being
pulled  into a pore is greater than the surface tension at
the air/water surface. Therefore water  is pulled further
and held tighter in small pores than large pores, such
that large pores are the first to empty upon draining.
Under saturated soil conditions (ground water), all  the
soil pores are filled with water and flow occurs in re-
sponse to the gravitational and hydrostatic potentials,
while under unsaturated soil conditions water movement
occurs in response to the gravitational and matric poten-
tials. The most important difference  between saturated
and unsaturated flow is the hydraulic conductivity. Since
all the pores are filled under saturated conditions, flow is
maximal. However, under unsaturated conditions, some of
the pores are air-filled and the conductive cross-sectional
area is reduced. The first pores to empty are the  largest
and, therefore, the most conductive. There can be a dra-
matic difference (several orders of magnitude) between
the  saturated and unsaturated hydraulic conductivity of
the soil (Figure 3-1).
100 —
I  10.


P 1.0-
   0.1 —
             245 ="
                      , Type I (sand)
                             II (sandy loam)
                                      III (silt loam)
                     20  40   60  80   100
                  Soil Moisture Tension (mbar)
                      Drying 	>

Figure 3-1. Hydraulic Conductivity of Various Soils versus
Soil Moisture Tension (EPA, 1980).

In layered soils where the hydraulic conductivities of the
layers differ, water that enters  unsaturated soil will move
through alternating unsaturated and saturated soil condi-
tions  as it percolates downward.  Where a coarse  soil
with a higher saturated hydraulic conductivity overlies a
finer textured soil, water will  move through the coarse
soil rapidly to the boundary between the two where it will
be  slowed to the rate the  finer soil can accept.  The
coarse  soil  will  saturate above the boundary  with  the
finer soil, and the rate of water movement through  the
soil profile will be controlled by the saturated conductivity
of the finer soil. Similarly, saturated conditions will occur
above the boundary  when  the finer soil overlies  the
coarse soil. However,  in this case, the soil suction or ma-
tric potential of the finer soil is  greater than the force that
is exerted by the larger pores of the coarse soil.  The

water must saturate the finer soil at the boundary before
the matric potential is reduced sufficiently for the water to
continue its  downward path. Thus in layered profiles
even a thin layer of soil with a higher or lower conductiv-
ity will impede vertical percolation of water and the rate
of movement through the profile will be controlled by the
soil layer with the lowest saturated hydraulic conductivity.
Land-based  systems  have  failed because seemingly
minute texture changes in the soil profile were ignored or
even overlooked.

3.2.3   Hydraulic Capacity of Soils to Accept
Water transport from land  application systems typically
occurs through  three  zones in  the soil:  the infiltration
zone, the vadose (unsaturated zone), and the saturated
zone (Figure 3-2). Wastewater enters the  soil at the sur-
face of the infiltration zone,  a biologically active zone, the
thickness of which will vary with the type of land applica-
tion  system used. It acts  as a physical,  chemical, and
biological filter to remove suspended solids and organics
from the wastewater. The  filtered solids  accumulate on
the infiltrative surface, within the soil pores,  and  on the
soil matrix in this zone providing a source of food and nu-
trients for an active biomass. The biomass and metabolic
by-products also accumulate in this zone. Hydraulically,
the infiltration zone is a transitional zone  where flow
changes from saturated to unsaturated with  a concomi-
tant  sharp decline in hydraulic conductivity because of
the blockage and filling of the soil  pores by the accumu-
lated solids, biomass, and metabolic by-products.

Below the infiltration zone,  the water enters the vadose
zone. In this zone, the water is under a negative pres-
sure potential or matric potential; consequently, flow oc-
curs only in the smaller pores, while larger pores remain
gas-filled. Water transport occurs primarily vertically over
soil particle surfaces and through  capillary pores  due to

Table Surface
—i Capillary
—'  Fringe
Figure 3-2. Fluid Transport Zones through Soil below Land
Application Systems.
the gravitational potential, but the matric potential does
cause some dispersive lateral flow.
Below the vadose zone, the water enters the saturated
zone or ground-water table. All the soil pores are filled in
this zone, and flow occurs vertically and/or horizontally in
response to the gravitational and  hydrostatic pressure
potentials. It is in this zone that the applied wastewater
ultimately leaves the site. The additional water from the
wastewater treatment system causes a  ground-water
mound to  form above the  ground-water  table.  This
mound must be taken into account in the hydraulic de-
sign to ensure that a sufficient vadose zone remains for
treatment below the application area.
Soil  factors that affect hydraulic performance of the land
application systems  include texture, structure, bulk den-
sity, horizonation (stratigraphy, layering),  and soil mois-
ture. Texture, structure, and bulk density relate directly to
the size, shape, and continuity of the soil pores. Texture
is defined by the relative proportion of the various sizes
of the soil particulates or soil "separates" (i.e., sand,  silt,
and  clay), while structure refers to the relative arrange-
ment of the soil particles. Bulk density is the ratio of the
soil mass to its bulk or volume. Finer textured soils such
as silts and clays would  be expected to have  smaller,
less-continuous pores than sands, but because the parti-
cles can agglomerate to  form structural  units or peds,
large interpedal pores can exist to enhance permeability.
Soils with higher bulk volumes tend to have lower perme-
abilities because the pore volume is less.
Horizonation (or layering) and soil moisture distribution in
the soil can impact the rate of water movement through
the  profile.  Soil  layers  of differing  texture, structure,
and/or bulk density can impede vertical percolation  be-
cause of their differing hydraulic conductivities. Zones of
higher soil moisture are indicative of reduced conductivity
due  to lower matric potentials. High moisture conditions
also limit the movement of air through the soil. Soil aera-
tion  is necessary to support  aerobic biochemical reac-
tions for rapid degradation of applied wastes.
Factors in the design of land application systems also af-
fect hydraulic performance. These include geometry and
elevation relative to ground surface of the infiltrative sur-
face, uniformity and periodicity of wastewater application,
and  the quality of the applied wastewater. Each factor
can affect the aeration status of the soil at and below the
infiltrative surface of the soil due to the oxygen demand
exerted by constituents in the applied wastewater. The
hydraulic capacity of the system decreases if anaerobic
conditions are allowed to occur for extended periods.

3.2.4  Wastewater Treatment Capabilities of
Physical, chemical, and biological processes occur in  the
soil providing effective wastewater treatment through re-
tention, transformation,  or  destruction  of  pollutants.
Physical processes include filtration, dispersion, arid dilu-

tion.  Volatilization, adsorption,  complexation  (with  or-
ganic  residues),  precipitation, and photodecomposition
are chemical processes that can occur.  Several biologi-
cal processes including biological oxidation (mineraliza-
tion), nitrification, denitriftcation, immobilization, predation,
and plant uptake can take place depending on the envi-
ronmental conditions. These processes occur most effec-
tively  when  the  soil is  unsaturated  because  the
wastewater is forced to percolate over the soil particle
surfaces where many of the treatment phenomena take
place and air is able to diffuse through the soil. In combi-
nation, these processes can produce a treated water of
acceptable quality for discharge to the ground-water ta-
ble under the proper conditions.

Whether these processes occur and their effectiveness
in treatment depends on the physical characteristics of
the soils  and the environmental conditions of the soil
through which the wastewater percolates. Studies  have
shown that conventional wastewater parameters (e.g.,
biochemical oxygen demand (BODs), suspended solids
(SS), and fecal indicator organisms)  are nearly com-
pletely removed where an aerobic, unsaturated zone of
medium-to-fine textured soil, 0.6 to 1.5 m (2 to 5  ft) in
thickness, with neutral pH is maintained below the infil-
trative surface during system operation. Soils with exces-
sive permeability (coarse texture soil or soil  with large
continuous pores), low organic content, low pH, low cat-
ion exchange capacity and redox potential, high moisture
content, and low temperature have been shown to  have
reduced treatment efficiency.

Other wastewater parameters, such as levels of nitrogen,
phosphorus, heavy metals, toxic organics, and virus, are
removed to varying degrees. Organic or ammonia nitro-
gen is readily and rapidly nitrified biochemically in aero-
bic soil. Because of its high solubility, nitrate leaches to
the ground water. Some biochemical denitrification can
occur in the soil, but without plant  uptake, 60 to 90 per-
cent of the nitrate enters the ground water. Under an-
aerobic soil conditions, nitrification  will not occur, but the
positively  charged ammonium ion  is  retained in the soil
by adsorption onto the soil particles.  The ammonium
may be held until aerobic soil conditions return  allowing
nitrification to occur. Phosphorus and metals can be re-
moved through adsorption, ion exchange, and precipita-
tion reactions, but the capacity of the soil to retain these
tons is finite. The  capacity  varies with  the soil  mineral-
ogy, organic content, pH, redox potential, and cation ex-
change capacity.  The fate and  transport of virus is not
well documented. Limited data suggest some types of vi-
rus are able to leach to ground water; however, when
this occurs their infectivity is soon lost. Fine-textured soil,
aerobic subsoils, and high temperatures favor virus de-
struction. Toxic organics appear to be removed in aero-
bic soils,  but further study  of the  fate  and transport of
these compounds is needed.
 Land treatment system design and operation will also af-
 fect the treatment capability of soil. Systems that main-
 tain unsaturated, aerobic subsoil conditions provide the
 most effective treatment of wastewater. Geometry of the
 infiltrative surface, elevation of the surface relative to fi-
 nal grade, wastewater mass loading rates, and uniformity
 and periodicity of wastewater application influence the
 degree of saturation and aeration status of the subsoil.
 The loading of oxygen-demanding materials per unit area
 must not exceed the rate at which oxygen can be sup-
 plied to the subsoil. Where the infiltrative surface is ex-
 posed to  the atmosphere, mass flow of  air will occur
 behind the wetting front as the wastewater infiltrates the
 soil. Thus the rate of application and the period between
 applications are important operating parameters. In sub-
 surface systems, however, diffusion from  the perimeter
 of the system is the primary pathway of oxygen to the
 subsoil. Therefore  shallow, narrow infiltrative surfaces,
 controlled mass loadings, and uniform, periodic applica-
 tions will enhance aeration.

 The most significant impacts that land  application sys-
 tems are known to have on the quality of ground water
 are  increased concentrations  of nitrogen  (primarily  ni-
 trate), chlorides, and total dissolved solids; temperature
 may also be impacted. Once the treated wastewater en-
 ters the ground water, it does not readily  mix with the
 ground water but remains as a distinct  plume for  as
 much  as  several hundred feet.  Solute concentrations
 within the  plume can remain  above ambient  ground-
 water concentrations. Dilution of the plume  is  dependent
 on the quantity of natural recharge and travel distance
 from the source.

 3.2.5  Hydraulic and Treatment
       Performance of Land Application
 There are significant differences in design and perform-
 ance between the various types of land  application sys-
 tems because of  the  differences in application and
 operation. A comparison  of the systems is  presented in
 Table 3-1.

 3.3   Approach to Site Evaluation
 Successful performance of a land application  system for
 wastewater  treatment depends upon the characteristics
 of the site on which it is built and how  its design and op-
 eration are adapted to those characteristics. The design
 engineer must understand how the soil, ground water,
 vegetation, and other site factors will impact system per-
 formance  so that design features and operation proce-
 dures can be adopted to ensure acceptable  performance.
 Therefore, careful site evaluation is critical.

 The scale and detail of the site evaluation depend on the
quantity and quality of the wastewater and the  charac-
teristics of the site to which the wastewater is to be ap-

 Table 3-1. Design and Treatment Performance Comparisons for Land Application Systems for Domestic Wastewater

 Site Conditions
 Soil texture

 Depth to ground water
 Climatic restrictions

 Design Loadings
 Average daily loading
 Application method
 Disposition of
     Slow Rate

 Sandy loams to clay

  Growing seasond
 Rapid Infiltration     Subsurface Infiltration      Overland Flow
Sands, sandy loams


Sands to clay loamsa    Silt loams, clay loams

   Not applicable
    Not critical0

 Growing seasond
Primary sedimentation'  Primary sedimentation'   Primary sedimentation   Primary sedimentation

 Sprinkler or flooding
Evapotranspiration and

   0.2-4.0 9


Sprinkler or flooding
 Surface runoff and
Treatment Performance
BODs (mg/L)
SS (mg/L)
Total nitrogen as N
Total phosphorus as P
Toxic organicsj
Fecal conforms
(perl 00 mL)
Virus, log removal
Metals (%)


0.1 -0.4

< 10

= 3+



1 -2


= 2


25 -351

0.1 -0.5

< 10

= 3





< 1

 aApplies to single or small cluster household systems; larger systems limited to sands and sandy loams (where significant, depth
 to top of ground-water mound).
 bMinimum separation distance from infiltration surface to highest ground-water mound elevation.
 "Critical only if significant percolation occurs.
 Application during few weeks before and after growing season.
 eMinimum pretreatment requirements.
 fWith restricted public access; crops not for direct human consumption.
 9Loading based on trench bottom area, not total site area.
 hVaries with applied concentration and crop.
 Varies with applied concentration.
 JData are limited, but good removals (>90%) appear to occur at low application rates in aerobic soils for biodegradable organics,
 adsorbed species are removed effectively until the underlying soil column becomes saturated, whereupon removals cease;
 volatiles are removed effectively in the unsaturated soil zone if rates are sufficiently low.
plied. Because of the many factors involved,  site evalu-
ation for land application systems requires the input of a
multidisciplinary team of qualified  engineers,  soil scien-
tists, hydrogeologists, and agronomists experienced  in
the siting, design, and management of such systems. It
may involve extensive,  and in some  cases expensive,
site investigations and testing.

To avoid unnecessary effort and expense, the site evalu-
ation should  focus  on  only the most promising sites.
Therefore, the evaluation  effort should be phased.  A
three-phase approach is suggested.
                                  The first phase includes the identification and screening
                                  of potential sites. Efforts during this phase are limited to
                                  review of available resource materials and the develop-
                                  ment of site screening criteria based on knowledge of the
                                  wastewater source  and its  characteristics. This phase
                                  concludes with the elimination of sites that do not  meet
                                  the established screening criteria.

                                  During phase two, a reconnaissance survey of the poten-
                                  tial sites identified in the first phase is made. A visual sur-
                                  vey and preliminary soil borings are performed to confirm
                                  the potential of each site. This phase also includes a pre-

liminary layout of an appropriate system design to deter-
mine if sufficient suitable area exists to construct the sys-
tem. On the basis  of the findings during this phase, the
sites are ranked according to priority for conducting de-
tailed site evaluations.

The final phase is  the detailed  investigation. It is during
this phase that the critical site characteristics that affect
site suitability and system design and operation are iden-
tified. The investigation typically includes soil profile de-
scriptions, deep soil borings, ground-water assessments
and testing, soil permeability measurements, and topo-
graphic mapping. Only the highest rated site need be in-
vestigated  unless  the  investigation  indicates  that  it
should not be ranked above the others or that it should
be eliminated from consideration. At that point, the next
ranked site should  be investigated. This procedure is fol-
towed until a suitable site is selected.

3.4  Site Identification

3.4.1    Wastewater Characteristics
The projected wastewater volume and characteristics im-
pact both site suitability and  cost. Site suitability is fre-
quently determined by the estimated hydraulic capacity
of the  site to  accept the projected wastewater flows.
Where wastewater flow data are not available, per capita
flows of 200 to 400 L/d (50 to  100 gpd) are typically used
to estimate average  daily flow. A factor of 1.8 to 2.0 is
often used to estimate the peak daily flows. The parame-
ters used to estimate flows for a particular application de-
pend  on  the  characteristics  of  the  community,  the
climate, and the condition of the collection system. If sig-
nificant commercial and/or industrial development exists
in the community, daily wastewater flows  should be esti-
mated  for each establishment and added to the residen-
tial estimate.

Conventional wastewater parameters such as BOD  and
SS seldom limit land application system feasibility or ca-
pacity.  (Typical BOD loading  rates for municipal waste-
water systems  are presented in Table 3-2.)  However,
wastewater constituents such as nitrogen, phosphorus,
potassium,  chlorides, total dissolved  solids,  pH,  and
trace elements may override  hydraulic considerations in
determining land area requirements or selecting a suit-
able land application design.

Table 3-2. Typical BOD Loading Rates for Land Application
Systems for Treatment of Municipal Wastewater3
Slow rate
Rapid Infiltration
Overland flow

44,000 -253,000

Frequently, nitrogen controls system sizing and, hence,
land area requirements. Excessive  nitrogen contamina-
tion of potable ground-water aquifers below land applica-
tion systems often is  a concern, but this threat can be
controlled by limiting the nitrogen loading or promoting
nitrogen removal through system design and operation.
Nitrate nitrogen concentrations in the ground water at the
project property boundary should not exceed the drinking
water standard of 10 mg-N/L. To meet this limit, the total
nitrogen loading rather than the hydraulic loading may
determine system sizing, potentially  increasing land area
requirements. The nitrogen removal  potential of the sys-
tem depends on the crop grown, if any, and system man-
agement practices, which vary with the type of system
In some cases, other  wastewater constituents  such  as
phosphorus or trace elements  control system sizing and
design. For example,  if wastewater trace element con-
centrations exceed the maximum recommended concen-
trations for  irrigation water (Table  3-3), slow-rate land
application systems may not be feasible or may require
special operating  conditions. Most land  application sys-
tems, however, will be controlled by  hydraulic or nitrogen

Table 3-3. Comparison of Trace Elements in Wastewaters
to Recommended Limits for Irrigation Water3


0.11 -0.14
0.002 - 0.044
0.03 - 8.31
for Irrigation
Water0 (ppm)
No standard
* EPA, 1980 and 1981; WPCF, 1990; Reed, 1988.
 aEPA, 1981.
 bRange of reported values. See EPA, 1981.
 cBased on unlimited irrigation at 1 m/yr (3 ft/yr).

3.4.2  Climate

Local climate may affect system selection and land area
requirements.  Precipitation, evapotranspiration potential,
temperature, length of the growing season,  wastewater
application  cycles and storage requirements, and other
factors will impact land area requirements and the type of
system selected. These factors should be considered as
candidate sites are selected because of the influence
they have on the suitability of a site for land application of

3.4.3   Review of Resource Materials
Many resource materials are readily available to assist in
identifying  suitable sites for a land application system.
They should be used to select candidate sites before field
investigations are initiated. The materials include soil sur-
veys, U.S. Geological  Survey  (USGS) quadrangles, well
logs, geologic maps, hydrologic and ground-water maps,
land-use and zoning maps, and National Oceanographic
and Atmospheric Administration (NOAA) climatic data.  In-
terviews with local residents knowledgeable about the area
should also be included in this review.
Soil surveys are available from the local Soil Conserva-
tion Service  (SCS) office.  They  contain a collection of
aerial photographs of the mapping area, usually a county,
on  which the distributions of the various soil series are
shown. The  scales of  the maps usually  range from
1:31,680 to 1:15,840.  A typical profile description to a
depth of 1.5 m (5 ft) for each soil series is provided. The
descriptions include texture, structure, consistency, color,
rooting, estimated permeability, and  thickness of each
horizon. The surveys also provide limited information  on
permeability, slopes, landscape  position, drainage, erosion
potential, flooding potential, chemical properties,  engineer-
ing properties, general suitability for locally grown crops,
and management information. Where published surveys
are not available, field sheets with interpretive tables may
be  available through the local county agent. Typical soil
textures and permeabilities  suitable for land application
systems that can be used in  site identification are pre-
sented in Table 3-4.
USGS quadrangles provide information  on  topography,
landscape  position,  rock outcrops, wetlands,  regional
drainage patterns, and surface water  elevations. These
maps,  which are usually drawn to a  scale  of  1:24,000
(7.5 minute series) or 1:62,000 (15 minute  series), can
help identify potential sites based on landscape position,
slope,  drainage, and separation from the ground water.
Landscape positions best suited for land  application sys-
tems include hilltops, ridge lines, and sideslopes. Depres-
sions and footslopes of hills should be avoided. Slopes
less than 12 percent  are generally preferred. Ground-
water gradients and elevations can be inferred from the
elevations shown for surface water bodies.
                                  Well logs are generally available locally and are an ex-
                                  cellent source of information on soil profile and potential
                                  impermeable layers.
                                  Existing land use also is an important factor in selecting
                                  candidate sites.  Land use of both the identified parcel
                                  and the surrounding parcels should be determined. Land
                                  use can be tentatively determined from the soil survey
                                  maps, USGS quadrangles, and local zoning maps.
                                  The location of the service area relative to potential treat-
                                  ment sites is an important economic  consideration. The
                                  distance and elevation of the treatment site relative to the
                                  service  area  directly  impact wastewater transmission
                                  costs. As a general guideline, sites within 10 to 12 km (6
                                  to 7 mi) and less than 60 m (200 ft) above the elevation
                                  of the pumping station may still be competitive with other
                                  treatment alternatives.

                                  3.4.4    Site Screening
                                  Site screening criteria should be established according to
                                  which potential  sites can be identified and  ranked. The
                                  key criteria may be broken down into environmental-
                                  physical characteristics, economic and  institutional con-
                                  siderations, and other technical and engineering factors.
                                  In  developing  these criteria, federal, state,  and local
                                  regulatory requirements must be considered for any im-
                                  posed limitations such as siting and design requirements,
                                  water quality requirements, and monitoring requirements.
                                  A numerical  approach using qualitative factors for  the
                                  key selection criteria should be  used  to rank sites. This
                                  will focus the following site investigation activities on the
                                  sites with the most potential.
                                  Criteria  should  include  distance  and  elevation from
                                  source,  available area, soils, landscape position, slope,
                                  ownership, and land use. The second phase of evalu-
                                  ation activities should be carried out only with the highest
                                  ranked sites.

                                  3.5  Site Reconnaissance

                                  3.5.1   Visual Inspection
                                  Site reconnaissance begins with a visual survey of each
                                  of the sites identified from a review of the resource mate-
                                  rials. The objective of the visual survey is to  verify  the
                                  site information collected from  the resource  materials
                                  and to note any general features that may affect site suit-
Table 3-4. Typical Soil Textures Suitable for Land Application Systems3
 Soil Parameter
 Textura! class*3

 Unified soil class0
Slow Rate
Clay loams to sandy
Rapid Infiltration
Sand to sandy loams

Subsurface Infiltration  Overland Flow
Sand and sandy loams   Clay and clay loams
                                                                                       GM, GC.SM, SC, CL
                                                                                       OL, CH, OH
aEPA, 1981.
bUSDA-SCS System (SCS, 1951).
cGroup symbols are from ASTM Unified Classification System.

ability or system design. It is important to walk the site
noting  significant features including  topography,  land-
scape position, vegetation, land use surrounding the site,
and others that may affect site suitability or system de-
sign and performance.
Site topography impacts system design and surface and
subsurface drainage. Long, planar slopes or large, level
areas  allow  greater  flexibility in  system layout than
steeply sloping or  hummocky sites.  Sloping sites are
usually better drained than large,  level sites. Drainage is
an important factor when considering  the contribution of
surface runoff to the hydraulic load of the system and the
response of the ground water below  the site to system
Landscape position is an important consideration in site
drainage. Although sites may have favorable topography,
the position of the  site relative to the surrounding land
form may  impact  site suitability.  For example, hilltops
and sideslopes can be expected to have good surface
and   subsurface   drainage,   while   depressions   or
footslopes  are more  likely  to  drain  poorly.  There are
known exceptions to these generalities, such as alluvial
soils in the valleys of arid regions; however, without infor-
mation on  the particular locality, these rules of thumb
serve as effective initial planning tools.
The type and extent of vegetation on  the site provide an
indication of  soil depth and subsurface drainage. It also
may impact site suitability directly. For instance, vegeta-
tion associated with wet soils suggests that subsurface
drainage is not good, and  numerous large  trees  may
make system construction difficult.
Surrounding land use is a necessary consideration. Con-
cerns for the fate of aerosols, odors, and ground-water
drainage from the site must be addressed. Adequate buffer
areas will need to be provided from developed areas.

Other  significant features to observe include areas  of
flooding, surface  water,  rock outcrops,  wells,  roads,
buildings, and buried  utilities. Each of these will help to
determine site suitability or system design. Surface water
bodies, for instance, would suggest the need to investi-
gate the potential water-quality and hydrologic impacts of
the system. Rock outcrops would raise concerns about
soil  depth.  Water  supply  wells  raise concerns about
ground-water flows and  potential  ground-water-quality

3.5.2   Preliminary Soil Borings
Preliminary soil  borings should be performed on sites
that appear to be  suitable following  the visual survey.
The purpose of the borings  is to  provide information re-
garding suitability and variability of the surface soils and
to identify the presence of any shallow, impermeable lay-
ers. The number and density of these borings should be
made to provide sufficient information regarding the soil
properties and variability necessary to  determine whether
more detailed site investigations are warranted. A boring
density of one per 0.2 ha (0.5 ac) is usually adequate to
make this determination. If the soil variability is such that
a greater density of borings is necessary to characterize
the site, consideration should be given to eliminating the
site from further evaluation.
Soil characteristics from the surface to approximately 2 m
(6 ft) below the  anticipated infiltrative surface elevation
should be observed. Important characteristics to note in-
clude soil texture, structure, horizon thickness, moisture
content, color, bulk density, and spatial variability.
A  hand-held soil probe or auger is  sufficient for these
borings unless it is anticipated that the infiltrative surface
of the system will be placed deep within the soil profile. If
a deep system is anticipated, a  truck-mounted soil probe
may be necessary. Excavated  pits or deep soil borings
typically are not  performed during this phase because of
the expense and damage of sites to which no commit-
ment has been made.

3.5.3  Conceptual System  Design
While  on the site, a conceptual layout of the proposed
land application  system should be made based on the
knowledge of the site and projected wastewater flows.
This is done to determine if the site is of sufficient size
and to assess where more detailed site investigation ef-
forts are needed if the site is selected for further consid-

3.5.4  Site Screening
The information  gained  from  the reconnaissance  survey
should be  used  to  revise the site ranking made during
the first phase of the site evaluation.  It is important that
no potential sites be eliminated too early in the process;
however, to limit the expense of the site selection proc-
ess, sites must be carefully ranked so that further investi-
gative  efforts proceed systematically  beginning with the
highest ranked site.

3.6   Detailed  Site Investigations

3.6.1  Soil Profile Descriptions
The soil is a critical factor in determining site suitability
and system design. It is the  primary  determinate of the
hydraulic and treatment capacity of the site. The charac-
teristics of the soil profile must be described in detail to
observe and identify features  that may affect the capacity
of the  site to accept and treat the applied wastewater.
Any soil layer that may affect  vertical percolation of water
should be described even if less than 1 cm in thickness.
The description should include texture, structure, particle
sorting, coarse fragment content, relative  density, macro-
porosity, rooting  patterns, thickness, transition, and conti-
nuity for each identifiable soil  horizon.
The characteristics  of the surface soil  materials  to a
depth of 2 to 5 m (5 to 15 ft)  are the most critical  for de-
termining site suitability. Backhoe-excavated test pits and

 soil borings extending to a depth of 2 to 3 m (6 to 10 ft)
 below the proposed infiltrative surface elevation should
 be used.  Backhoe pits are the most effective for expos-
 ing an undisturbed soil profile. However, unless appropri-
 ate safety precautions can be taken, hollow-stem-auger
 and split-spoon samples may be required.
 Locations  of test pits and borings should be carefully
 planned in advance based on information gained  during
 the resource materials review and  reconnaissance sur-
 vey. The  number and density of test pits and borings
 should be sufficient to enable accurate prediction  of soil
 characteristics and variability, but not so excessive that
 unnecessary damage to the proposed infiltration area re-
 sults. Where spatial variability is not great, a test pit den-
 sity of one per 0.4 ha (1  ac) is usually adequate. Each
 test pit and boring should be carefully located on a plot
 plan and  the surface elevation measured  relative to a
 permanent bench mark.
 A qualified soil scientist familiar with land application sys-
 tems  should describe the soil profile morphology. Par-
 ticular emphasis should be placed on those features that
 affect water movement through the profile.  U.S. Depart-
 ment of Agriculture Soil Conservation Service nomencla-
 ture, rather than the  Unified System, is typically used to
 describe the soil characteristics in the zone of natural soil
 development, typically within 3 m  (10 ft) of the ground
 surface. The USDA system, as described in the SCS Soil
 Survey Manual (1951), provides a more comprehensive
 description to aid in understanding morphological details
 relevant to water movement.

 3.6.2    Characterization of the
        Unconsolidated Substratum
 The deeper unconsolidated materials below the site must
 be  examined also.  Hydraulically restrictive  layers may
 exist that would cause "perched" saturated zones to form
 under system operation. Because these zones could af-
 fect the hydraulic and treatment capacity of the site, they
 must be identified.
 Hollow stem auger borings are used to examine the
 deep unconsolidated materials to depths of 3 to 8  m (10
 to 25 ft) or to bedrock, whichever is shallower. The bor-
 ings should be made near the center and at the perime-
 ters of the proposed infiltration area. A minimum of three
 borings should be made across the site. More may be
 necessary for large  sites or to assess any  suspected
 ground-water boundary zones that  may impact system
 operation, but the maximum  density of borings usually
 need not be more than one per 0.4 ha (1 ac).
 Split-spoon samples should be taken at maximum inter-
vals of 1.5 m (5 ft) and  described sufficiently to assess
 internal drainage. All pertinent details of morphology, li-
thology, and  physical characteristics  should  be  noted.
Characteristic descriptions that are of particular impor-
tance are texture, consistence,  blow counts, moisture
content, estimated permeability, and the presence of free
 water. Borings are typically logged using the Unified Sys-
 tem (ASTM) nomenclature.

 Each boring should be located accurately on a plot plan
 of the site and the surface elevation established relative
 to a permanent bench mark.

 3.6.3   Characterization of the
        Ground-Water Table
 If ground water is present within 8 m (25 ft) of the ground
 surface, the hydraulic response of the water table to pro-
 longed system loading should be evaluated. The primary
 concerns are the direction of ground-water flow from the
 site, potential development of a ground-water mound be-
 low the site that encroaches within the vadose  zone
 needed for treatment, and water-quality impacts.

 Characterization of the ground water to address these
 concerns may be accomplished by the installation  of
 monitoring wells and/or piezometers. A minimum of three
 wells or piezometers that  penetrate the water table by at
 least 1  to 1.5 m (3 to 5 ft) should be installed in the shal-
 lowest  saturated zone in  a triangular pattern across the
 site. After allowing the water surface to equilibrate in the
 well, water elevation measurements are taken and  com-
 pared to establish the horizontal gradient of the ground
 water.  On  large sites, more piezometers  are usually
 needed to allow a better estimate of the gradient. At least
 one nested group  of  three piezometers  at  different
 depths should  be installed and monitored to determine
 the vertical ground-water gradient. All  wells and pie-
 zometers should be fitted with a protective casing with a
 locking cover  to prevent vandalism and foreign  sub-
 stances from entering the well.

 To evaluate the mounding potential, the depth to ground
 water, ground-water  gradient, hydraulic conductivity,  ef-
 fective  porosity or specific  yield, and thickness of the
 saturated zone are needed. The hydraulic  conductivity
 can be determined by performing slug tests or pumping
 tests  in one or more wells on the site (Bouwer, 1978;
 Bouwer and Rice, 1976;  Freeze and Cherry, 1979). In
 some cases, it may be possible to estimate the saturated
 hydraulic conductivity from a particle size analysis of the
 aquifer materials (Bouwer,  1978;  Freeze and Cherry,
 1979). Pumping tests may also be used to determine the
 effective porosity or specific yield of the saturated zone.

 One well should be installed upgradient of the proposed
 system to monitor ambient ground-water quality. The  lo-
 cation  of this  well can  only be determined  after the
 ground-water gradient has been established. At a mini-
 mum, water quality monitoring should include field meas-
 urement of specific conductance,  pH, and temperature,.
 and laboratory  analyses  for total dissolved solids,  total
 organic carbon, nitrogen  species, phosphorus, chloride,
 and alkalinity.  After system construction, this well can
 serve as the background  monitoring well  for assessing
treatment performance.

If the ground water does not occur within 8 m (25 ft) of
the ground surface, it may be appropriate to assume a
"worst case" scenario to avoid the cost of deep well in-
stallation. This can be done by assuming that an imper-
meable  barrier exists at that depth for the mounding
analysis. A similar  assumption can be  made where
ground water is encountered but the  bottom of the aqui-
fer cannot be determined. Again, by assuming an imper-
meable  barrier at this depth, the worst case scenario is
accepted in determining the thickness of the aquifer and
the mounding analysis.
Once installed, the  wells  and piezometers should be
carefully located on an accurate plot plan and the ground
and top of pipe  elevation  measured to  a permanent
bench mark.

3.6.4   Measurement of Hydraulic Properties
        of the Soil
Knowledge of the capacity of the soil to accept and trans-
mit water is critical to the design of land application sys-
tems. Infiltration rates and hydraulic conductivities should
be measured in the field to provide the data necessary
for determining design hydraulic loadings.
The infiltration rate of soil is defined as the rate at which
water enters the soil from the surface, while the hydraulic
conductivity is defined as the rate at  which water moves
through the soil. The initial infiltration rate of a clean, ex-
posed soil surface can equal the saturated hydraulic con-
ductivity of the soil below,  but with time, the infiltration
rate typically declines well below the capacity of the soil
to transmit the water. Infiltration rate decline is caused by
deposition  of wastewater SS  at the infiltrative surface,
growth of active biomass stimulated  by the carbon and
nutrient rich  wastewater,  and changes in the charac-
teristics of the soil. As a result of the decline in the infil-
tration rate, the subsoil  cannot maintain saturation, and
unsaturated conditions prevail. The unsaturated conduc-
tivity of  soil is one to four orders of magnitude less than
the saturated conductivity.  Therefore the  saturated hy-
draulic conductivity of the soil cannot be used directly to de-
termine the long-term infiltration rate for design purposes.
There are both field and laboratory methods for estimat-
ing infiltration rates. Reid  methods provide better esti-
mates  and,  therefore,  are  preferred.  They include
flooding basin, single- or double-ring infiltrometer, sprin-
kler infiltrometer, and air-entry permeameter tests. These
and other test procedures are  described  elsewhere
(Black, 1965a; EPA, 1980; 1981; 1984; ASTM).
Double-ring infiltrometer and basin tests are most com-
monly used for  land application  system design.  Infil-
trometer tests are  small-scale tests  that measure the
hydraulic conductivity of the soil over an  area approxi-
mately 50 cm (1.5 ft) in diameter. Such tests can be eas-
ily used to estimate the saturated  hydraulic conductivity
at several locations and  soil horizons  over the site. Basin
tests are large-scale tests that are typically run over an
area 3 m (10 ft) in diameter. Basin tests provide more ac-
curate measurements of hydraulic conductivity, but re-
quire much larger volumes of  water to  run. Therefore
they are usually run on only the most restrictive soil hori-
zons in the design area.

Laboratory methods for estimating hydraulic conductivity
are  described  elsewhere  (Black,  1965a; ASTM).  Be-
cause only small, disturbed soil samples can be tested,
the results are much less accurate than field tests. Meth-
ods  that minimize disturbance of the soil sample and
best reproduce field operational conditions are preferred.
The concentric-ring permeameter (Hill and King,  1982)
and the cube method (Bouma and Dekker, 1981) are the
most useful techniques.

3.6.5  Analysis of Soil Chemical Properties
Soil  chemical properties can affect permeability and crop
growth potential. Chemical  properties of interest include
pH,  cation exchange capacity (CEC), exchangeable so-
dium percentage (ESP), and electrical conductivity (EC).
Soil  pH has a significant effect on the solubility of various
compounds, microorganism activity,  and  ion exchange
capacity. The  CEC is a measure of  the capacity  of the
soil to adsorb exchangeable cations.  The sum of the ex-
changeable sodium, potassium, calcium, and magne-
sium expressed as a percentage of the CEC is  called
percent-base saturation. There are optimum ranges for
percent-base saturation for various  crop  and soil type
combinations.  Also, high percentages of sodium and po-
tassium will result in significant reductions in permeability
due to soil swelling. ESP should be  kept below 15 per-
cent. EC is a diagnostic tool used to determine salinity of
the soil water. Salinity will affect plant growth and the
type of plants that will thrive. Analytical  procedures for
measuring soil chemical properties can be  found else-
where (Black,  1965b; Jackson, 1958;  Walsh and Beaton,

3.6.6  Topographic Mapping
A topographic survey of the site should be completed in
sufficient detail to produce accurately a topographic map
with 25 to 50 cm (1 to 2 ft)  contour intervals. All soil bor-
ings, soil pits, monitoring wells, and piezometers should
be located on this map with horizontal and vertical posi-
tions established relative to a  permanent bench  mark.
Significant site features such as surface water, rock out-
crops, and large trees that may affect system layout and
design should also be accurately located on this map.

3.6.7  Data Interpretation
Interpretation of the site data collected can be a complex
and difficult task. The interpretation process must  estab-
lish  the elevation of the infiltrative surface and the ac-
ceptable ranges  of wastewater loadings that can be
applied. It must also establish the acceptable boundaries
of the system and its geometry.

 995 -
 985 -
 975 -
 965 -
 955 -
                            Sandy Loam

                            Sandy Clay Loam

                            Gravelly Sand
                 50  100
                                                                              -  995
                                               -  985
                                                                              -  975
                                                   Elev. of
                                                 Lake James
                                               -  955
Figure 3-3. Example of Stratigraphic Cross Section Constructed from Soil-Boring Log Data.
Stratigraphic cross sections of the site are useful to de-
termine the most appropriate elevation of the infiltrative
surface. Using data from borings and pits, enough cross
sections should  be constructed along various transects
of the site to depict the continuity and interrelationships
of key strata affecting system design and operation (Fig-
ure 3.3).

The interpretation process must take into  account the
type of land application design that is proposed for the
site because required site characteristics vary with sys-
tem type. The designer is referred to Chapter 5 for descrip-
tion of the required site conditions for each system type.

Where ground water or a hydraulically restrictive horizon
exists within 8 m (25 ft) of the proposed elevation of the
infiltrative surface, the response  of the ground water to
system loading must be analyzed.  Both analytical and
numerical ground-water mounding models are available.
Because of the  large number of data points necessary
for numerical modeling, analytical models are most com-
monly used. Analytical models have been developed for
various  hydrogeologic conditions  (Brock,  1976;  Fin-
nemore and Hantzshe, 1983; Hantush, 1967; Kahn et al.,
1976).  The assumptions used for each  model must be
compared to the specific site conditions found to select
                        the most appropriate model. (For examples of model se-
                        lection and their computations, see EPA 1981; 1984.)

                        3.7   Construction Considerations

                        Methods used to construct land  application systems are
                        critical to the long-term performance of the installations.
                        Earthmoving operations and  general construction traffic
                        will damage the soil properties that are necessary for fa-
                        vorable wastewater infiltration and percolation.  Careful
                        planning of system construction  can minimize soil dam-
                        age, maintaining the  capacity of the system to accept
                        and treat the applied wastewater.

                        Soils are not equally susceptible to construction damage.
                        The degree of soil compaction, smearing, and puddling
                        that occurs is a function of the soil texture and moisture
                        content. Soil with greater than 25 percent  by weight of
                        clay (all soils excepting sands and loamy sands) is the
                        most susceptible to damage.

                        To limit damage to the soil, a construction plan should be
                        developed  for each  project.  The  plan should  address
                        type of equipment to be used, methods and sequence of
                        construction operations, site traffic and materials stock-
                        piling, site  preparation, and soil conditions during con-
                        struction operations.

Only low-toad-bearing equipment should be used in the
design area. High-flotation tires and track-mounted vehi-
cles are preferred. Scrapers or blades should not be
used near the infiltrative surface because the scraping
action can smear the soil. In areas to be filled with sand,
blades may be used to spread the fill material if a mini-
mum of 30 cm (1 ft) of fill is maintained below the treads
of the vehicle.
Construction methods and the sequencing of operations
must be carefully planned in advance to prevent unnec-
essary damage to the soil. Unlike conventional earthwork
practices, soil  compaction is to be avoided. The number
of passes required to be made over  the design area to
reach the desired grade and elevation should be kept to
a minimum. Once the infiltrative surface is established,
further traffic over  the area should  be avoided. This re-
quires that  the  construction of large  systems be  se-
quenced to limit unnecessary traffic. Testing of the soils
during construction may be included  in the construction
specifications as a  measure of contractor performance.
Site traffic must be controlled at the outset. Site access
and acceptable traffic  lanes and stockpiling areas for
construction machinery and materials delivery should be
delineated on the construction drawings. The site should
be  staked accordingly  before  work commences.  Ap-
proaches  to the design  area should  be made from the
upslope side wherever possible. If the approach must be
made from the downslope side, traffic should be kept to
minimum and routed as far from the area as possible.
Brush and tree removal may be required prior to other
earthwork. Grubbing of  the  site following tree removal
should not be  done since it will damage the structure of
the  soil  and  aggravate soil  compaction during sub-
sequent operations. If the area is  to be filled, the site
should be mowed  and raked before chisel plowing to a
depth of 20 to 30 cm (8 to 12 in.) along  the slope contour.
The soil conditions during construction should be care-
fully monitored. If the soil is near its plastic limit or if the
soil is frozen within 30 cm (1 ft) of the infiltrative surface
finish elevation, construction should  not proceed.
If the soil is damaged to the point that the infiltration rate
is significantly affected,  the  damaged soil must be  re-
moved to expose an undamaged surface. As much as 10
to 15 cm (4 to 6 in.) may have to be removed to restore
the infiltrative capacity of the infiltrative surface. This will
tower the finished elevation and may require adjustments
in the design.

3.8   References
When an NTIS number is cited in a  reference, that refer-
ence is available from:
    National Technical Information Service
    5285 Port Royal Road
    Springfield, VA 22161
    (703) 487-4650
ASTM.  1988. American Society for Testing and Materi-
als. Test method for infiltration rate of soils in field using
double-ring infiltrometers. C3385. Philadelphia, PA.

ASTM.  1974. American Society for Testing and Materi-
als. Test method for permeability of granular soils (con-
stant head). D2434. Philadelphia, PA.

Black, C.A., ed.  1965a. Methods of soil analysis,  part 1:
Physical and mineralogical properties, including statistics
of measurement and sampling. Madison, Wl: American
Society of Agronomy.

Black, C.A., ed.  1965b. Methods of soil analysis,  part 2:
Chemical  and microbiological  properties. Madison, Wl:
American Society of Agronomy.

Bouma, J., and L.W. Dekker. 1981.  A method of measur-
ing the  vertical and horizontal hydraulic saturated con-
ductivity of clay soils with macropores. Soil Sci. Soc. Am.
J. 45:662.

Bouwer, H.  1978. Groundwater hydrology. New York:
McGraw-Hill Book Co.

Bouwer, H., and R.C. Rice. 1976. A slug test for deter-
mining hydraulic conductivity of unconfined aquifers with
completely or partially penetrating wells.  Water  Re-
sources Research 12:423-428.

Brock, R.P. 1976. Dupuit-Forcheimer and potential theo-
ries for recharge  from basins.  Water Resources  Re-
search 12:909.

EPA.  1984.  Environmental  Protection  Agency. Process
design manual:  Land treatment  of municipal  wastewa-
ter—Supplement on rapid infiltration and overland flow.
EPA/625/1-81-013a. Cincinnati, OH.

EPA.  1981.  Environmental  Protection  Agency. Process
design manual: Land treatment of municipal wastewater.
EPA/625/1-81-013. Cincinnati, OH.

EPA.  1980. Environmental Protection  Agency. Design
manual: Onsite wastewater  treatment and disposal sys-
tems.  EPA/625/1-80-012. NTIS No. PB83-219907.

Finnemore, E.J.,  and N.N. Hantzshe. 1983. Ground-water
mounding  due  to onsite sewage disposal. J. Irrigation &
Drainage Am. Soc. Civ. Eng. 109:199.

Freeze,  R.A.,  and J.A.  Cherry.  1979.  Groundwater.
Englewood Cliffs, NJ: Prentice-Hall.

Hantush, M.S.  1967. Growth and decay of ground water
mounds in response to uniform percolation. Water  Re-
sources Research 3:227.

Hill, R.L.,  and L.D. King. 1982.  A  permeameter which
eliminates boundary flow errors in saturated  hydraulic
conductivity measurements. Soil Sci. Soc. Am. J. 46:877.

Jackson, M.L.  1958. Soil chemical  analysis. Englewood
Cliffs,  NJ:  Prentice-Hall.

Kahn, M.Y., D. Kirkham, and R.L. Handy. 1976. Shapes
of steady state perched groundwater mounds. Water Re-
sources Research 12:429.

SCS. 1951. Soil Conservation Service. Soil survey man-
ual. U.S. Department of Agriculture Handbook 18. Wash-
ington, DC.
Walsh, L.M., and J.D. Beaton eds. 1973. Soil testing and
plant analysis. Madison, Wl: Soil Sci. Soc. Am.


                                               CHAPTER 4
                                      Wastewater Characteristics
4.1   Introduction
The effective management of any wastewater flow re-
quires a reasonably accurate knowledge of its charac-
teristics. This is  particularly true  for flows from  rural
residential  dwellings, commercial  establishments, and
other facilities where individual water-using activities cre-
ate an intermittent flow of wastewater that  can  vary
widely in volume and degree of pollution. For small  com-
munities with collection systems, the possibility of a sig-
nificant infiltration  and inflow  (I/I) contribution must  be
taken  into  account for any wastewater planning effort.
Detailed characterization data regarding these flows are
necessary  not  only to facilitate  the  effective design of
wastewater treatment and disposal systems, but also to
enable the development and application  of water conser-
vation and  waste load reduction strategies.
For existing developments, characterization of the actual
wastewaters to be encountered can often be carried out.
However, for many  existing  developments, and for  al-
most all new developments, wastewater characteristics
must be predicted. The purpose  of this chapter is to pro-
vide a basis for characterizing the wastewater from rural
developments.  A  detailed  discussion  of  the charac-
teristics of residential wastewaters is presented first, fol-
lowed by a limited discussion of  the characteristics of the
wastewaters generated by nonresidential establishments,
including those of a commercial,  institutional, and recrea-
tional  nature. Finally, a general  procedure for  predicting
wastewater characteristics for a given residential dwell-
ing or nonresidential establishment is given.

4.2   Residential Wastewater
Residential dwellings exist in a variety of forms, including
single- and  multi-family homes, condominiums, apart-
ment  houses, and cottages or resort residences.  In all
cases, occupancy can occur on a seasonal or year-round
basis. The wastewater discharged from these dwellings
is comprised of a number of individual wastewaters gen-
erated through water-using activities  employing a variety
of plumbing fixtures and appliances. The characteristics
of the wastewater can be influenced by several factors.
Primary influences are the characteristics of the plumb-
ing fixtures and appliances present as  well as their fre-
quency of use. Additionally, the characteristics of the re-
siding  family in terms of the number of resident family
members, age levels, and mobility are important as is the
overall socioeconomic status  of  the family.  The other
characteristics, including seasonal or yearly occupancy,
geographic  location, and  method of water supply  and
wastewater disposal, appear as additional, but lesser, in-

4.2.1   Wastewater Flow  Average Daily Flow
The  average daily wastewater flow  from a typical resi-
dential dwelling is approximately 170 Lpcd (45 gpcd) (Table
4-1). While the average in-house daily flow experienced at
one residence compared to that of another can vary con-
siderably,  it  is typically no greater than 227 Lpcd (60
gpcd)  and seldom exceeds 284 Lpcd (75 gpcd)  (Figure
4-1). Residential water use in arid regions of the  country
can  be significantly greater owing to on-lot demands,
which  nationally average nearly one-half of the residen-
tial (in-house) demand cited above. These figures are
even higher in the Southwest.
          Note: Based on the average daily flow
          measured for each of 71 residences studied.

 f 80
  5 70

 rr 40
 '« Of)
 Q d0
 Table 4-1. Summary of Average Daily Residential Wastewater Flows
                                                                               Wastewater Flow
Number of Residences
Duration of Study
Study Avg. (gpcd)
                                                                  Range of Individual
                                                                  Residence Averages
Linaweaver et al.
Anderson and Watson
Watson et al.
Cohen and Wallman
Bennett and Lfnstedt
Slegrlst et al.
Duffy et al.
Weighted Average


26.3 - 65.4

 aSee References at end of chapter.  Individual Activity Flows
 The individual wastewater generating activities within a
 residence are the building blocks that serve to produce
 the total residential wastewater discharge. The average
 characteristics of  several major  residential water-using
 activities are presented in Table 4-2. A water-using activ-
 ity that falls under the category of miscellaneous in this
 table, but deserves additional comment, is water-softener
 backwash/regeneration  flows.  Water-softener regenera-
 tion typically occurs once or twice  a week, discharging
 about 114 to 333 L (30 to 88 gal)/regeneration cycle (Wel-
 ckart, 1976). On a daily per capita  basis, water-softener
 flows have been  shown to average about 19 Lpcd (5 gpcd),
 ranging from 8.7 to 59.4 Lpcd (2.3 to 15.7 gpcd) (Siegrist et
 al. 1976).

 Tabla 4-2. Typical Residential Water Use by Activity3
Toilet flushing




Garbage grinding
























'Mean and ranges of results reported in Cohen and Wallman,
1974; Laak, 1975; Bennett and Linstedt, 1975; Siegrist et al.,
1976; and Ligman et al., 1974.
 gpcd may not equal gal/use multiplied by uses/cap/d due to
difference in the number of study averages used to compute
the mean and ranges shown.
NA « not applicable
                          Wastewater Flow Variations
                                 The intermittent occurrence  of individual  wastewater-
                                 generating activities  creates  large variations  in  the
                                 wastewater flow rate from a residence.
                                 Minimum and Maximum Daily Flows. The daily wastewa-
                                 ter flow from a specific residential dwelling is typically 10
                                 to 300 percent of the average daily flow at that dwelling,
                                 with the vast majority within 50 and 150 percent of the
                                 average day. At the  extreme,  however, minimum and
                                 maximum daily flows of 0 and  900 percent of the average
                                 daily flow  may be encountered (Anderson and Watson,
                                 1976; Watson et al., 1967; Witt, 1974).
                                 Minimum and Maximum Hourly Flows. Minimum hourly
                                 flows of zero are typical. Maximum hourly flows are more
                                 difficult to  quantify accurately.  On the basis of typical fix-
                                 ture and appliance usage characteristics, as well as  an
                                 analysis of residential water usage demands, maximum
                                 hourly flows  of 380  L (100  hr)/gal can  occur  (Anderson
                                 and Watson, 1967; Jones, 1974). Hourly flows in excess
                                 of this can occur due to plumbing fixture and appliance
                                 misuse or malfunction (e.g., faucet left  on or worn toilet
                                 ball cock).

                                 Instantaneous Peak Flows. The peak flow  rate from a
                                 residential dwelling is a function of the characteristics of
                                 the fixtures and appliances  present and their position in
                                 the overall plumbing system layout. The peak discharge
                                 rate from a given fixture/appliance is typically around 0.3
                                 L/s (5 gpm), with the exception of the tank-type water
                                 closet that discharges a short-duration peak flow of up to
                                 1.6 L/s (25 gpm). The use of several fixtures/appliances
                                 simultaneously can increase the total flow rate over the
                                 rate for  isolated fixtures/appliances. However,  attenu-
                                 ation occurring in the residential drainage network tends
                                 to decrease the peak flow rates in the sewer exiting the
                                 Although field data are limited,  peak discharge rates from
                                 a  single-family dwelling of 0.3 to 0.6 L/s (5 to 10 gpm)
                                 can be expected. For multifamily units, peak rates in ex-

cess of these values commonly occur. A crude estimate
of the  peak flow in these cases can be obtained using
the fixture-unit method described in Section

4.2.2  Wastewater Quality  Average Daily Flows
The characteristics of typical residential wastewater are
outlined in Table 4-3, including daily mass loadings and
pollutant concentrations. The wastewater characterized
is typical of residential dwellings equipped with standard
water-using fixtures and appliances,  excluding garbage
disposal(s),  that collectively generate approximately 170
Lpcd (45 gpcd).  Individual Activity Contributions
Residential  water-using  activities  contribute  varying
amounts of pollutants to the total wastewater flow. The
individual activities may be grouped into three  major

Table 4-3. Characteristics of Typical Residential Wastewater3
Total solids
Volatile solids
Total N
Nitrites and nitrates
Total P
Total coliformsb
Fecal coliformsb
Mass Loading
200 - 290
200 - 290
680 - 730
6 -'12

 aFor typical residential dwellings equipped with standard
 water-using fixtures and appliances (excluding garbage
 disposals) generating approximately 170 Lpcd (45 gpcd).
 Based on the results presented in Laak, 1975; Bennett and
 Linstedt, 1975; Siegristet al., 1976; Ligman et al., 1974; and
 Jones, 1974.
 bConcentrations presented in organisms/L.
wastewater  fractions:  garbage  disposal  wastes, toilet
wastes, and sink,  basin, and appliance wastewaters. A
summary of the average contribution of several key pol-
lutants in each of these three fractions is presented in
Table 4-4.
With regard to the microbiological characteristics of the
individual waste categories, studies have demonstrated
that the wastewater from sinks, basins, and appliances
can contain significant concentrations of indicator organ-
isms as  total  and fecal  conforms (Olsson et al.,  1968;
Hypes et al., 1974; Small Scale Waste Management Pro-
ject, 1978; Brandes,  1978). Traditionally, high concentra-
tions of these organisms have been used to assess the
contamination of a water or wastewater by pathogenic
organisms. One assumes, therefore, that these  waste-
waters possess some potential for harboring pathogens.  Wastewater Quality Variations
Since individual water-using activities occur intermittently
and  contribute  varying  quantities of  pollutants,  the
strength  of the wastewater generated from a residence
fluctuates with time. Accurate quantification of these fluc-
tuations is impossible. An estimate of the type of fluctua-
tions   possible  can  be derived  from  the  pollutant
concentration information presented in Table 4-5 consid-
ering that the activities included occur intermittently.

4.3   Nonresidential Wastewater
The rural population, as well as the transient population
moving through the rural areas, is served by a wide vari-
ety of  isolated commercial establishments and facilities.
For many establishments, the wastewater-generating
sources  are sufficiently similar to those  in  a residential
dwelling  that residential wastewater characteristics can
be  applied.  For  other  establishments,  however,  the
wastewater characteristics can be considerably different
from those of a typical residence.
Providing characteristic wastewater loadings for "typical"
nonresidential establishments is a very complex task due
to several factors.  First, there is a relatively large number
of diverse establishment categories (e.g.,  bars, restau-
 Table 4-4. Pollutant Contributions of Major Residential Wastewater Fractions3 (gm/cap/d)





Garbage Disposals

0.2 - 0.9
0.1 -0.1

0.6 - 1 .6
Basins, Sinks,
24.5 - 38.8
2,2 - 3.4
Approximate Total





 aMeans and ranges of results reported in Laak, 1975; Bennett and Linstedt, 1975; Siegrist et al., 1976; Ligman et al., 1974;
 Olsson et al., 1968

 Table 4-5. Pollutant Concentrations of Major Residential Wastewater Fractions3 (mg/L)

Garbage Disposals


Basins, Sinks,
Approximate Total

 "Based on the average results presented in Table 4-4 and the following wastewaterflows: Garbage disposals—8 Lpcd (2 gpcd);
 toilets—61 Lpcd (16 gpcd); basins, sinks, and appliances—110 Lpcd (29 gpcd); total—178 Lpcd (47 gpcd).
rants, drive-in theaters). The inclusion of diverse estab-
lishments within the same category produces a potential
for large variations in waste-generating sources and the
resultant wastewater characteristics. Further, many intan-
gible  influences, such as location and  popularity, may
produce substantial wastewater variations between oth-
erwise similar establishments. Finally, there is consider-
able difficulty in presenting characterization data in units
of measurement that  are easy to apply yet predictively
accurate (e.g., at  a restaurant,  wastewater flow in vol-
ume/seat is easy  to apply to estimate total flow,  but  is
less accurate than if volume/meal served  were used).
In this section, limited characterization data for nonresi-
dential  establishments,  including commercial  estab-
lishments, institutional facilities,  and  recreational areas,
are presented. These data are meant to  serve only as a
guide, and as such should be applied cautiously. Wher-
ever possible, characterization data for the particular es-
tablishment in question, or a similar one in the vicinity,
should be obtained.

4.3.1    Wastewater Flow   A verage Daily Flows
Typical  daily flows from a variety of commercial, institu-
tional, and recreational establishments are presented in
Tables 4-6 through 4-8.   Wastewater Flow Variation
The wastewater flows from nonresidential  establishments
are subject to wide fluctuations with time. While difficult to
quantify accurately, an estimate of the magnitude of the
fluctuations, including minimum  and maximum flows on
an hourly and daily basis, can be made if consideration is
given to the characteristics of the water-using fixtures
and appliances, and to the operational characteristics of
the establishment (e.g.,  hours of operation, patronage
Tablo 4-6. Typical Wastewater Flows from Commercial Sources9
Automobile service station



Industrial building
(excluding industry and cafeteria)
Laundry (self-service)

Motel with kitchen
Rooming house
Shopping center
Store, department

•"Metcaif and Eddy, 1979.
Vehicle served

Parking space
Toilet room

bDoes not Include all of the facility's wastewater streams,
2.1 -4.0
1 .3 - 5.3
39.6 - 58.0

47.5 - 52.8
23.8 - 39.6
23.8 - 50.1

only those related to customers.



Table 4-7. Typical Wastewater Flows from Institutional Sources'
Hospital, medical

Hospital, mental


Rest home

School, boarding
School, day:
with cafeteria, gym, showers
with cafeteria only
without cafeteria, gym, showers



aMetcalf and Eddy, 1979.

Table 4-8. Typical Wastewater Flows from Recreational Sourcesa
Apartment, resort
Cabin, resort

Campground (developed)
Cocktail lounge
Coffee shop
Country club
Day camp (no meals)
Dining hall
Dormitory, bunkhouse
Hotel, resort
Store resort

Swimming pool
Visitor center
Member present
Meal served
52.8 - 74
34.3 - 50.2
1.1 -2.6
4.0 - 7.9
39.6 - 63.4
476 - 687
1 .3 - 5.3
4.0 - 7.9
aMetcalf and Eddy, 1970.

Peak wastewater flows can  be estimated utilizing the
fixture-unit method (Water Pollution Control Fed., 1976;
Uniform Plumbing Code, 1976). As originally developed,
this method was based on the premise that under normal
usage, a given type of fixture had an average flow rate
and  duration of use (Hunter, 1940; 1941). One fixture
unit was arbitrarily set equal to a flow rate of 0.5 Us (7.5
gpm), and various fixtures were assigned a certain  num-
ber of fixture units based upon their particular charac-
teristics (Table 4-9). On the basis of probability studies,
relationships were developed between peak  water use
and the total number of fixture units present (Figure 4-2).
4.3.2   Wastewater Quality

The qualitative characteristics of the wastewaters gener-
ated by nonresidential establishments can vary signifi-
cantly between different types of establishments due to the
extreme variation that can exist in the waste-generating
sources present.  Consideration of the waste-generating
sources present  at a particular establishment can give a
general idea of the character of the wastewater and serve
to indicate whether the wastewater will contain any prob-
lem constituents, such as high grease levels from a res-
taurant or lint fibers from a laundromat.

 Table 4-9. Fixture Units per Fixture3
 Fixture Type                                 Fixture
 Ona bathroom group consisting of                 6
 tank-operated water closet, lavatory, and
 bathtub or shower stall
 Bathtub (with or without overhead shower)          2
 Bidet                                          3
 Combination sink-and-tray with food-disposal        4
 Combination sink-and-tray                        3
 Dental lavatory                                 1
 Dental unit or cuspidor                           1
 Dishwasher, domestic                           2
 Drinking fountain                                0.5
 Roor drains                                    1
 Kitchen sink, domestic, with food-waste grinder      3
 Kitchen sink, domestic                           2
 Laundry tray (1  or 2 compartments)                2
 Lavatory                                       2
 Shower stall, domestic                           2
 Showers (group) per head                        3
   Surgeon's                                   3
   Flushing rim (with valve)                        8
   Service (trap standard)                         3
   Service (P trap)                               2
   Pot, scullery, etc.                             4
 Urinal, pedestal, siphon jet, blowout                8
 Urinal, wall lip                                   4
 Urinal stall, washout                             4
 Urinal trough (each 2-ft section)                    2
 Wash sink (circular or multiple) each set of          2
 Water closet, tank-operated                       4
 Water closet, valve-operated	8

 "Water Pollution Control Fed., 1976.
If the waste-generating sources present at a particular
establishment are similar to those typical of a residential
dwelling, an approximation of the pollutant mass loadings
and concentrations of the wastewater produced may be
derived using the residential wastewater quality data pre-
sented  in Tables 4-3  to 4-5. For establishments where
the waste-generating sources appear significantly differ-
ent from those in a residential dwelling, or where more
refined  characterization data are desired, a detailed re-
view of the pertinent literature as well as actual wastewa-
ter  sampling at the particular or a similar establishment
should be conducted.
        Note: Curves show probable amount of time indicated peak flow
          will be exceeded during a period of concentrated fixture use.
    400  -  ,—
  | 350

 _ 250

 J> 200
3 150

             System in which flush
             valves predominate
            	System in which flush
               tanks predominate
      0   2
              4   6  8   10  12  14  16  18  20
               Fixture Units on System (hundreds)

 Figure 4-2. Peak Discharge versus Fixture Units Present.

 4.4  Predicting Wastewater

 4.4.1   General Considerations  Parameter Design Units
 In characterizing wastewaters,  quantitative  and qualita-
 tive characteristics are often expressed in terms of other
 parameters. These parameter design units, as they may
 be called, vary considerably depending on the type of es-
 tablishment considered. For  residential dwellings, daily
 flow values and pollutant contributions are expressed on
 a per capita basis.  Applying per capita data to predict to-
 tal residential wastewater  characteristics requires that a
 second parameter be considered; namely, the number of
 persons residing in the residence. Residential occupancy
 is  typically 1.0 to 1.5 persons/bedroom. Although it pro-
 vides for a conservative estimate, the current practice is
 to assume that maximum occupancy is two  persons per

 For  nonresidential  establishments,  wastewater  charac-
teristics are expressed in terms of a variety of units. Al-
though  per  capita units  are employed,   a  physical
characteristic of the establishment such as per seat,  per
car stall, or per square foot is more commonly used.   Factors of Safety
To account for the  potential variability in the wastewater
characteristics at a particular dwelling or establishment,
versus that of the  average, conservative predictions or
factors of safety are typically utilized. These factors of
safety can be applied indirectly through choice of the de-

sign criteria for wastewater characteristics and the occu-
pancy patterns, as well as directly through an overall fac-
tor. For example, if an average daily flow of 284 Lpcd (75
gpcd) and an occupancy of two persons per bedroom
were selected, the flow prediction for a three-bedroom
home would include a factor of safety of approximately 3
when compared to average conditions (i.e., 170 Lpcd (45
gpcd) and 1 person/bedroom). If a direct factor of safety
were also applied (e.g., 1.25), the total factor of safety
would increase to approximately 3.75.
Great care must  be  exercised in predicting wastewater
characteristics so  as not to accumulate multiple factors of
safety that would yield an extremely conservative estimate.

4.4.2   Strategy for Predicting Wastewater
Predicting wastewater characteristics from rural develop-
ments can be a complex  task.  Following  a logical step-
by-step procedure can help simplify  the characterization
process and render  the estimated  wastewater charac-
teristics  more accurate. A flow chart detailing a proce-
dure  for  predicting   wastewater   characteristics  is
presented in Figure 4-3.

4.5   Water Conservation and
      Wastewater Flow Reduction
An extensive array of techniques and devices are  avail-
able to reduce the average water use and concomitant
wastewater flows generated by individual water-using ac-
tivities and, in turn, the total effluent from the residence
or establishment. The diversity of  present wastewater
flow reduction  methods is illustrated in Table 4-10. As
shown, the methods may be divided into three major
groups:  elimination  of nonfunctional water  use; water-
saving devices, fixtures, and appliances; and wastewater
recycle/reuse systems.

4.5.1   Elimination of Nonfunctional Water
Wasteful water-use  habits can occur with most water-
using activities. A few illustrative examples include using
a toilet flush to dispose of a cigarette butt, allowing the
water to run while brushing teeth or shaving, or operating
a clotheswasher or dishwasher with only a partial load.
Obviously, the potential for wastewater flow reductions
through  elimination  of such  wasteful use vary tremen-
dously between homes, from minor  to significant reduc-
tions, depending on habits.   Improved Plumbing and Appliance
Unseen or apparently insignificant leaks from household
fixtures and appliances can waste large volumes of water
and generate similar quantities of wastewater. Most nota-
ble in this regard are leaking toilets and dripping faucets.
For example, a steadily dripping faucet can waste up to
several hundred gallons of water per day.
      Determine primary function of facility
          and classify it accordingly
      (e.g., single-family home, restaurant)
    Identify intended application of wastewater
           characterization data
       Identify wastewater characterization
          data needed (e.g., Q, BODs)
   Determine physical characteristics of facility
    • Wastewater-generating fixtures
     and appliances
    • Parameter design units (e.g., bedrooms,
     seating spaces)
    •Occupancy or operation patterns (e.g.,
     seasonal homes, hours of operation)
   Obtain characterization data from literature

   • Tables and text of this chapter
   • References to this chapter
   • Other sources
   Gather existing measured characterization
          data applicable to facility

   • Water meter records
   • Holding tank pumpage records
   • Other
          Evaluate available data
   • Select data judged most accurate
   • Determine if needed data has
    been obtained
      Calculate waste load characteristics
       (e.g., 45 gpcd x 2 cap/bedroom x
          2 bedrooms =180 gpd)
    Apply overall factor of saftey as required
        by intended application of data
  field studies at
 facility in question
or a very similar one
      Estimate wastewater characteristics
Figure 4-3.  Strategy  for Predicting  Wastewater

 Table 4-10. Selected Wastewater Row Reduction Methods
 Elimination of Nonfunctional Water Use
  • Improved water-use habits
  • Improved plumbing and appliance maintenance and
  • Reduced excessive water supply pressure
 Water-Saving Devices, Fixtures, and Appliances
  • Toltet
      1. Water-carriage toilets
        a. Toilet-tank inserts
        b. Water-saving toilets (3.5 gal.)
        c. Ultra-low flush toilets (ULF) (1.6 gal/flush or less)
          - Wash-down flush
          - Mechanically assisted
          - Pressurized tank
          - Compressed air
          - Vacuum
          - Grinder
      2. Nonwater carriage toilets
        a. Pit privies
        b. Biological toilets
        c. Incinerator toilets
        d. Oil-carriage toilets
  • Bathing devices, fixtures, and appliances
      1. Shower flow controls
      2. Reduced-flow showerheads
      3. On/off showerhead valves
      4. Mixing valves
      5. Air-assisted, low-flow shower system
  • Clotheswashing devices, fixtures, and appliances
      1. Front-loading washer
      2. Adjustable cycle settings
      3. Washwater recycle feature
  • Miscellaneous
      1. Faucet Inserts
      2. Faucet aerators
      3. Reduced-flow faucet fixtures
      4. Mixing valves
      5. Hot water pipe insulation
      6. Pressure-reducing valves
      7. Hot water recirculation
 Wastewater Recycle/Reuse Systems
  • Bath/laundry wastewater recycle for toilet flushing
  • Toilet wastewater recycle for toilet flushing
  • Combined wastewater recycle for toilet flushing
  • Combined wastewater recycle for several uses  Maintain Nonexcessive Water
         Supply Pressure
The water flow rate through  sink  and basin  faucets,
showerheads, and similar fixtures is highly dependent on
the water pressure in the water supply line. For most
residential uses, a pressure of 280 kPa (40 psi) is ade-
 quate. Pressure in excess of this can result in unneces-
 sary water use and wastewater generation. To illustrate,
 the flow  rate through  a typical faucet opened fully is
 about 40  percent higher at a supply pressure of 560 kPa
 (80 psi) versus that at 280 kPa (40 psi).

 4.5.2   Water-Saving Devices, Fixtures, and
 The quantity of water traditionally used by a given water-
 using fixture or appliance is often considerably greater
 than actually needed. Certain tasks may even be accom-
 plished without the use of water. As  presented in Table
 4-2, over 70  percent  of  a typical  residential dwelling's
 wastewater flow volume is collectively generated by toilet
 flushing, bathing, and Clotheswashing. Thus efforts to ac-
 complish  major wastewater flow reductions should be di-
 rected toward these three activities.   Toilet Devices and Systems
 Each flush  of a conventional water-carriage toilet uses
 15-18 L (4-5 gal) of water depending on the model and
 water supply pressure. On average, flushing typically
 generates approximately 16 L (4.3 gal)  of wastewater.
 When coupled with 3.5 uses/cap/d,  a daily wastewater
 flow of approximately  61  Lpcd (16 gpcd) results (Table
 4-2).  Since the mid-1980s 13L  (3.5 gal)/flush (M) has
 been  more common. Recently, several states have man-
 dated that in new construction 6 L (1.6  gal)/flush toilets
 be installed. Nonetheless, the data above are reasonable
 estimates of demand per toilet flush in the United States.

 A variety of devices have been developed for use with a
 conventional flush toilet to  reduce  the volume  of water
 used  in flushing. Additionally, alternatives to the conven-
 tional water-carriage toilet are available,  certain of which
 use little  or no water to transport human wastewater
 products.  Tables 4-11 and 4-12 present a summary of
 various toilet devices  and systems. Additional details re-
 garding the nonwater-carriage toilets may be found else-
 where (Kreissl, 1985; Laak, 1975; Enferadi et al., 1986;
 Molland, 1984).  Bathing Devices and Systems
 Although great variation exists in the quantity of waste-
 water generated by a  bath or shower, typical values in-
 clude approximately 95 L (25 gal)/occurrence coupled
 with a 0.4 use/cap/d frequency to yield a daily per capita
 flow of about 38 L (10 gal) (Table  4-2). The majority of
 devices available to reduce bath ing-waste water flow vol-
 umes are concentrated around the activity of showering,
 with their objective being to reduce the normal 0.25 to
 0.63 L/s (4-10 gpm) showering flow rate. Several flow re-
 duction devices and systems for showering are charac-
terized in Table 4-13. The amount of total wastewater
flow reduction accomplished with these devices is highly
dependent on individual  user habits. Reductions  vary
from a negative value to as much as 12 percent of the to-
tal wastewater volume.

Table 4-11. Wastewater Flow Reduction—Water-Carriage Toilets and Systems
Generic Type
Toilets with tank
 Washdown flush
 air-assisted flush
devices placed into
storage tank of
conventional toilets
to reduce volume
but not height of
stored water

Varieties: Plastic
bottles, flexible
panels, drums or
plastic bags
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 sub-
stantially less due to
washdown flush

Van'eties: Few
 Specially designed
 toilet tank to
 pressurize air
 contained in toilet
 tank. Upon flushing,
 the compressed air
 propels water into
 bowl at increased

 Varieties: Few
 Similar in
 appearance and
 user operation to
 conventional toilet;
 specially designed
 to utilized
 compressed air to
 aid in flushing

 Varieties: Few

Device must be
compatible with
existing toilet and
not interfere with
flush mechanism

Installation by

Reliability low
Post-installation and
periodic inspections
to ensure proper
Water Use Per
  Event (gal)

  Total Flow
1.8-3.5 4-8
with conventional
Essentially the
same as for a
conventional unit
                                                              3.2-13 6-20
 Rough-in for unit    Similar to
 may be nonstandard conventional toilet
 and lateral-run

 Plumber installation
 Compatible with
 most conventional
 toilet units

 Increased noise

 Water supply
 pressure of 35-120

 with rough-in for
 conventional fixture

 Requires source of
 compressed air;
 bottled or air

 If air compressor,
 need power source

 Increased noise
                                                            Cleaning possible

                         (but more
                                                                                                     9.4-12.2 21-27
 Similar to
 conventional toilet
                                                                                  6.3-8.0 14-18
 maintenance of
 compressed air

 0.002 kWh per use
                                             13.3   30

 Table 4-11. Wastewater Flow Reduction—Water-Carriage Toilets and Systems (continued)
Generic Type
Similar in
Application largely
Water Use Per
Event (gal)
Total Flow
14 31
 Hush toilets
appearance and
user operation to
conventional toilet;
specially designed
fixture is connected
to vacuum system
that assists a small
volume of water in

Varieties: Few
for multi-unit
installations, e.g.
vacuum sewer
system. Above
floor, rear dis-
charge. Drain pipe
may be horizontal
or inclined

Requires vacuum
source, usually from
vacuum sewer

Increased noise
maintenance of
vacuum source

0.002 kWh per use
8Compared to conventional toilet usage (4.3 gal/flush, 3.5 uses/cap/d, and a total daily flow of 45 gpcd).

Table 4-12. Wastewater Flow Reduction—Nonwater-Carriage Toilets
Generic Type*
Pit privy
Biological privy
Biological toilets
          Hand-dug hole in the ground
          covered with a seat in an
          enclosed structure

          May be sealed vault rather
          than dug hole
         Similar to pit privy except
         organic matter is added after
         each use. When pit is full it is
         allowed to compost for a
         period of about 12 months
         prior to removal
         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

         Varieties: Several
                   Application Considerations
                   Requires same site conditions
                   as for Wastewater disposal

                   Handles only toilet wastes

                   Outdoor installation

                   Odor potential
                   Can be constructed
                   independent of site conditions
                   if sealed vault

                   Handles only toilet waste and

                   May be constructed by user

                   Outdoor installation

                   Residuals disposal
                   Installation requires 6 to  12 in.
                   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

                   Only units that meet
                   Scandinavian and NSF testing
                   standards should be used
                            When full, cover with 2 ft of soil
                            and construct new pit, unless
                            sealed vault
                            Addition of organic matter after
                            each use

                            Removal and disposal/reuse of
                            residuals may represent health
                            Periodic addition of organic

                            Removal of product material at
                            6 to 24 month intervals should
                            be performed by management

                            Power use: 0.3-1.2kWh/d

                            Heat loss through vent

Table 4-12. Wastewater Flow Reduction—Nonwater-Carriage Toilets (continued)
Generic Type3
Small self-contained units that
volatilize the organic com-
ponents of human waste and
evaporate the liquids

Varieties: Several
Application Considerations   O&M
Installation requires 4-in.
diameter roof vent

Handles only toilet waste

Power or fuel required

Increased noise level

Residuals disposal

Limited usage rate(frequency)

Only units that meet NSF
testing standards should be
Weekly removal of ash

Semiannual cleaning and
adjustment of burning
assembly and/or heating

Power: 1.2 kWh or 0.3 Ib LP
aNone of these devices uses any water; therefore, the amount of flow reduction is equal to the amount of conventional toilet use:
16.2 gpcd or 36 percent of normal daily flow (45 gpcd). Significant quantities of pollutants (including N, BODs, SS, P, and
pathogens) are therefore removed from wastewater stream.

Table 4-13. Wastewater Flow Reduction—Showering Devices and Systems             	
Generic Type3
Shower flow-control inserts
and restrictors
Reduced-flow showerheads
On/off showerhead valve
Mixing valves
Air-assisted, low-flow shower
Reduce flow rate by reducing
the diameter of supply line
ahead of shower head

Varieties: Many
Fixtures similar to con-
ventional, except restrict flow

Varieties: Many manu-
facturers, but units similar
Small valve device placed in
the supply line ahead of
showerhead allows shower
flow to be turned on/off without
readjustment of volume or
Specifically designed valves
maintain constant temperature
of total flow. Faucets may be
operated (on/off) without
temperature adjustment
Specifically designed system
uses compressed air to
atomize water flow and provide
shower sensation
Application Considerations   Water Use Rate (gpm)
Compatible with most existing   1.5-3.0
Installed by user

Compatible with most
conventional plumbing

Installed by user
Compatible with most
conventional plumbing and

Usually installed by plumber

Usually installed by plumber

Compatible with most
conventional plumbing and
May be impossible to retrofit

Shower location <50 ft away
from water heater

Requires compressed air

Power source required

Maintenance of air compressor

Power: 0.01 kWh/use
Unchanged, but duration (and
waste) are reduced
Unchanged, daily duration and
use reduced
aNo reduction in pollutant mass; slight increase in pollutant concentration.

 Table 4-14. Wastewater Flow Reduction—Miscellaneous Devices and Systems
 Generic Type*
 Faucet Inserts
 Faucet aerators
 Reduced-flow faucet
 Mixing valves
 Hot-water system
Device that inserts into faucet valve or supply line and restricts
flow rate with a fixed or pressure-compensating orifice

Varieties: Many
Devices attached to taucet outlet that entrain air into water flow

Varieties: Many
Similar to conventional unit, but restrict flow rate with a fixed or
pressure-compensating orifice

Varieties: Many
Specifically designed valve units that allow flow and
temperature to be set with a single control

Varieties: Many
Hot-water heater and piping is wrapped with insulation to
reduce heat loss

Varieties: Many
Application Considerations
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

Compatible with most plumbing

Installation identical to conventional

May be difficult to wrap entire
hot-water piping system
 "No reduction in pollutant mass; insignificant increase in pollutant concentration.  Clotheswashing Devices and
 The operation of conventional clotheswashers consumes
 varying quantities of water depending on the manufac-
 turer and model of the washer and the cycle selected.
 For most, water usage is 87 to 201 L (23 to 53 gal)/use.
 On the basis of home water-use monitoring, an average
 water-use/wastewater flow volume of approximately 140 L
 (37 gaiyuse has been identified, with the clotheswasher
 contributing about 38 Lpcd (10 gpcd) or 22 percent of the
 total daily water-use/wastewater flow (Table 4-2). Practi-
 cal methods to reduce these  quantities are somewhat
 limited. Eliminating wasteful water-use habits, such as
 washing with only a partial load, is one method. Front-
 loading automatic washers can reduce water used for a
 comparable load of clothes by up to 40 percent. In addi-
tion, wastewater flow reductions may be accomplished
through use of a clotheswasher with either adjustable cy-
 cle settings for various load sizes or a wash-water recy-
cle feature.

The wash-water recycle feature is included  as an op-
tional cycle setting on several commercially made wash-
ers.  Selection  of the  recycle  feature  when  washing
provides for storage of the wash water from the wash cy-
cle in a nearby laundry sink or a reservoir in the bottom
of the machine for subsequent use as the wash water for
the next load. The rinse cycles remain unchanged. Since
the wash cycle accounts for about 45 percent of the total
water use per operation,  if the wash water is  recycled
once, about 64 L (17 gal) will be saved, if twice, about
129 L (34 gal), and  so  forth. Actual water savings and
                                  wastewater flow reductions are highly dependent on the
                                  user's cycle selection.

                          Miscellaneous Devices and Systems
                                  There are a number of additional devices, fixtures, and
                                  appliances available to help reduce wastewater flow vol-
                                  umes. These are directed primarily toward reducing the
                                  water flow rate through sink and  basin faucets. Table 4-
                                  14 presents a summary of several of  these additional
                                  flow reduction devices. Experience with these devices in-
                                  dicates that wastewater volume can be reduced by 4 to 8
                                  Lpcd (1 to 2 gpcd) when used for all sink and basin faucets.

                                  4.5.3   Wastewater Recycle and Reuse
                                  Wastewater recycle and  reuse systems collect and proc-
                                  ess the entire wastewater flow or the fractions produced
                                  by certain  activities  with storage for  subsequent reuse.
                                  The performance requirements of any wastewater recy-
                                  cle system are established by the intended reuse activi-
                                  ties.  To simplify the performance requirements, most
                                  recycle systems process only  the  wastewaters  dis-
                                  charged from bathing, laundry, and bathroom sink usage,
                                  and restrict the use of  the recycled water to  flushing
                                  water-carriage toilets and possibly to lawn irrigation. At
                                  the other extreme, systems are under development that
                                  process the entire wastewater flow and recycle it as  a
                                  potable water source.

                                  The flow sheets proposed for residential recycle systems
                                  are numerous and varied, and typically employ various
                                  combinations of the unit processes described elsewhere
                                  (Bennett and  Linstedt, 1975;  Witt,  1974; Hypes, et al.

Table 4-15. Wastewater Flow Reduction—Wastewater Recycle and Reuse Systems

 Recycle bath and
 laundry for toilet flushing
 Recycle portion of total
 wastewater stream for
 toilet flushing
 Recycle toilet
 wastewaters for flushing
 water-carriage toilets
Application Considerations O&M
Requires separate toilet
supply and drain line

May be difficult to retrofit to
multistory building

Requires separate
wastewater disposal system
for toilet and kitchen sink
Requires separate toilet
supply line

May be difficult to retrofit to
multistory building
Periodic replenishment of
chemicals, cleaning of
filters and storage tanks

Residuals disposal

Power use
Cleaning/replacement of
filters and other treatment
and storage components

Residuals disposal
Total Flow
                       Requires disposal system for  Periodic replenishment of
unused recycle water
Requires separate toilet
plumbing network

Utilizes low-flush toilets

Requires system for
nontoilet wastewaters

May be difficult to retrofit

Application restricted to high
use on multiunit installations
Cleaning/replacement of
filters and other treatment

Residuals disposal

Power use
Foaming is a common
Toilet water has a turbid
Foaming is a common
Toilet water has a turbid
Colorant is usually used to
disguise flush-water

Significant removal of
Limited to high-volume,
commercial installations
Large capital investment
1974; Small Scale Waste Management Project, 1978). In
Table 4-15, generic units are characterized according to
their general recycle flow sheet.

4.6   Pollutant Mass Reduction

A second strategy for wastewater modification is directed
toward decreasing the mass of potential pollutants at the
source. This may involve the complete elimination of the
pollutant mass contributed by a given activity or the isola-
tion of the  pollutant mass in a concentrated wastewater
stream. Several  methods  for pollutant mass  reduction
are available. A few practical ones are described below.

4.6.1    Improved User Habits
Unnecessary quantities  of many  pollutants enter the
wastewater stream when materials that could be readily
disposed of in a solid waste form are added to the waste-
water stream. A  few  examples include flushing dispos-
able diapers or sanitary napkins down the toilet, or using
hot water and detergents to remove quantities of solidi-
fied grease and food debris from pots and pans to enable
their discharge down the sink drain.
                                  4.6.2   Household Product Selection
                                  The use of certain cleansing agents can contribute sig-
                                  nificant quantities of pollutants. In particular, cleaning ac-
                                  tivities,  such as clotheswashing and  dishwashing, can
                                  account for over 70 percent of the phosphorus  in resi-
                                  dential wastewater (Table 4-4). Modern detergents have
                                  reduced this percentage significantly due to lower phos-
                                  phorus content, but very low P content products  can re-
                                  duce the total P content of wastewater to mg/L.  Further
                                  reductions in nutrients, metals, and toxic organic chemi-
                                  cals are possible through product substitution. Additional
                                  details  are available  elsewhere  (Atkins  and Hawley,
                                  1978; Hathaway, 1980).

                                  4.6.3   Elimination of the Garbage-Disposal
                                  The use of a garbage disposal contributes substantial
                                  quantities of BODs and SS to the wastewater load (Table
                                  4-4). As a result, it has been shown that the use of a gar-
                                  bage disposal may increase the rate of sludge and scum
                                  accumulation and  produce a higher failure rate for con-
                                  ventional disposal systems under otherwise comparable
                                  conditions  (Kreissl, 1985). For these  reasons, and be-

                                                Human Waste
Compost Toilet
Very Low Volume
   Flush Toilet
Recycle Toilet
                                       Treatment Plant
Figure 4-4. Selected Strategies for Management of Segregated Human Wastes.
cause most waste handled by a garbage disposal could
be handled as solid wastes, the elimination of this appli-
ance is advisable.

4.6.4   Segregated Plumbing Systems
Several toilet systems provide segregation and separate
handling of human excreta (often referred to as blackwater)
and, in some cases, garbage wastes. Removal of human
excreta from the wastewater stream serves to eliminate
significant quantities of pollutants, particularly SS, N, and
pathogenic organisms (Table 4-4).

A number of potential strategies for management of seg-
regated human excreta are presented in Figure 4-4. A
discussion of the toilet systems themselves is presented
in the wastewater flow reduction section of this chapter.

Wastewaters generated  by fixtures other than toilets  are
often  referred  to  collectively  as graywater. Charac-
terization studies have demonstrated that typical graywa-
ter contains appreciable quantities of organic  matter, SS,
P, and grease in a daily flow volume of 110 Lpcd  (29
gpcd) (Siegrist et al., 1976; Hypes et al., 1974) (see Ta-
ble 4-4). Its temperature as  it leaves the residence is
about 31 °C (88°F), with a pH slightly on the alkaline side.
The organic materials in graywater appear to degrade at
a rate  not significantly different from those in combined
residential wastewater (Hypes et al., 1974). Microbiologi-
cal studies have demonstrated that significant concentra-
tions of indicator organisms as total and fecal conforms
are typically found  in graywater (see References gener-
ally). One should assume, therefore, that graywater har-
bors pathogens.
                            Design allowances  should be  made only for the reduc-
                            tions in flow volume, as compared to typical residential
                            wastewater. Although improved performance has been
                            demonstrated  for graywater-dosed soil absorption sys-
                            tems (SAS) when  compared  to combined wastewater
                            SAS, (Malland, 1984) the variability of local codes dic-
                            tates that SAS size reduction should not exceed the hy-
                            draulic reduction. For example:

                                 SAS Area = QGraywater/Qtotal Wastewater.

                            4.7   Onsite Containment—Holding

                            Wastewaters  may  be  contained  onsite  using holding
                            tanks, and then transported offsite for subsequent treat-
                            ment and disposal. However, this method is expensive
                            and  often aesthetically undesirable and is considered a
                            "last resort" alternative. In many respects,  the design, in-
                            stallation, and operation of a holding  tank is similar to
                            that  for a septic tank. Several additional  considerations
                            do exist, however,  as indicated in Table 4-16. A discus-
                            sion regarding the  disposal of pumpage from holding
                            tanks is presented in Chapter 5.

                            4.8   Reliability

                            An important aspect of wastewater modification concerns
                            the reliability of a given method to yield a projected modi-
                            fication at a specific dwelling or establishment over the
                            long term. Reliability is of particular importance when de-
                            signing an onsite wastewater disposal system based on
                            modified wastewater characteristics.

Table 4-16.  Additional Considerations in the  Design,
Installation, and Operation of Holding Tanks
             Liquid holding capacity >7 days wastewater
             flow generation. Minimum capacity = 1,000 gal
 Discharge    There should be no discharge/exfiltration
 Alarm system High-water alarm positioned to allow at least
             3 days of use after activation
 Accessibility  Frequent pumping is likely; therefore holding
             tank(s) must be readily accessible to pumping
             vehicle and employ proper fittings to minimize
 Flotation      Large tanks may be subject to severe
             flotation forces in high-groundwater areas
             when pumped
 Cost         Frequent pumping and disposal of residuals
	result in very high operating costs	

Assessing the reliability of wastewater modification meth-
ods is a  complex task that includes  considerations of a
technological, sociological, economic,  and institutional
nature. Major factors affecting reliability include:

•  Actual wastewater characteristics prior to modification
   compared to the average

•  User awareness and  influence on method  perform-

•  Installation

•  Method performance

•  User circumvention or  removal

In most situations, projections of the impact of a waste-
water modification method must be made, assuming the
wastewater characteristics prior to modification are rea-
sonably typical.  If the  actual wastewater characteristics
deviate significantly from that of the average, a projected
modification may be inaccurate.

The prospective user  should be fully aware of the char-
acteristics of a method considered for use prior to its ap-
plication.  Users  who  do  not  become  aware of  the
characteristics of a method until after it has been put into
use are more likely to be dissatisfied and attempt to cir-
cumvent  or otherwise  alter the method  and negate the
wastewater modification expected.

In general, passive wastewater modification methods or
devices not significantly  affected by  user habits tend to
be more  reliable than those that are subject to user hab-
its and require a preconceived  active role by the users.
For example, a low-flush toilet is a passive device, while
a  flow-reducing  shower  head  is an  active one. Toilets
that reduce flushing volume yet clean the  bowl equally
well  are  considered  passive  since  additional flushing
would  not be required. Reduced shower flows can result
in  longer showers, thus negating potential savings, and
are considered active devices.
Installation of any devices or systems should be made by
qualified personnel. In many situations, a post-installation
inspection is recommended to ensure proper functioning
of the device or system.
Method performance is extremely important in assessing
the reliability of the projected modification. Accurate per-
formance data are necessary to estimate the magnitude
of the reduction  and to predict the likelihood that  the
method will receive long-term user acceptance. Accurate
performance data can  only be obtained through  field
tests and evaluations. Since many methods and system
components are presently in various stages of develop-
ment, only preliminary or projected  operation and per-
formance  data  may be available. These preliminary or
projected data should be considered cautiously.
The continued employment of a wastewater modification
method can  be encouraged through several manage-
ment  actions. First, the user(s)  should  be made fully
aware of the potential consequences should they discon-
tinue  employing the modification method (e.g.,  system
failure, water pollution, rejuvenation costs). Also, the ap-
propriate management authority can approve only those
methods for which  characteristics and merits indicate a
potential for long-term user acceptance. Further, installa-
tion of a device or system can be made in such a manner
as to discourage disconnection or replacement.  Finally,
periodic inspections  by a  local inspector  within  the
framework of a sanitary district or the like may serve to
identify plumbing  alterations;  corrective orders could
then be issued.
In summary, to help ensure that a projected  modification
will actually be realized at a given site, efforts can be ex-
pended to accomplish the following tasks:
• Confirm that the actual  wastewater  characteristics
  prior to modification are typical.

• Make the prospective  user(s)  of  the   modification
  method  fully aware of  the  characteristics  of  the
  method, including  its operation,  maintenance,  and

• Determine if the projected performance of a given
  method has been confirmed through actual field evalu-
  ations by organizations other than those with  a pro-
  prietary interest.

• Ensure that any device or system is installed properly
  by competent personnel.

• Prevent  user removal or circumvention  of devices,
  systems, or methods.

4.9   Impacts on Soil-Based Treatment
      and Disposal Practices

4.9.1    Modified Wastewater Characteristics
Reducing the household wastewater flow volume without
reducing the mass of pollutants contributed will increase

the concentration of pollutants in the wastewater stream.
The increase in concentrations will likely be insignificant
for most flow  reduction devices with  the  exception of
those producing flow reductions of  20  percent or more.
The effects of such changes on onsite treatment compo-
nents are not considered sufficient to justify design modifi-
cations for single-family homes. The increase in pollutant
concentrations  in  any case may be estimated  utilizing
4.9.2   Wastewater Treatment and Disposal
Table 4-17 presents a brief summary of several potential
impacts that wastewater modification may have on soil-
based disposal practices. It must be emphasized that the
benefits derived from wastewater modification are poten-
tially significant. Wastewater modification methods, par-
ticularly wastewater flow reduction,  should be considered
an integral part of any onsite wastewater disposal system.



                                          Note: Assumes pollutant contributions are the same
                                          under the reduced flow volume.
                                        0      10       20      30      40
                                                 Wastewater Flow Reduction
                                                    (% of total daily flow)

                                Figure 4-5. Flow  Reduction Effects on Pollutant Concen-
Table 4-17. Potential Impacts of Some Wastewater Modification on Disposal Practices
                                                                                      Modification Practice
Disposal System Type

Surface discharge

(holding tank)
Potential Impact

May extend service life of functioning system
Reduce contamination of ground water and surface water
Reduce frequency of septic tank pumping
Reduce sizing of infiltrative area
Partially relieve hydraulically overloaded system
Reduce O&M costs
Reduce sizing and initial cost of components
Eliminate  need for certain components, (e.g., N removal)
Remedy hydraulically overloaded system
Remedy hydraulically overloaded system
Reduce sizing of ET area
Reduce frequency of pumping
Reduce sizing of containment structure
Flow Reduction



4.10  References
When an NTIS number is cited in a reference, that refer-
ence is available from:
    National Technical Information Service
    5285 Port Royal Road
    Springfield, VA 22161
    (703) 487-4650
Anderson, J.S., and K.S. Watson.  1967. Patterns  of
household usage. J. AWWA 59:1228-1237.
Atkins, E.D., and J.R. Hawley. 1978. Sources of metals
and metal levels in municipal wastewater. Environment
Canada/Ontario Ministry  of the Environment  Report No.
Bendixen, T.W., R.E. Thomas, A.A. McMahan, and J.B.
Coulter. 1961. Effect of  food waste grinders on septic
tank systems. Cincinnati, OH:  Robert A.  Taft Sanitary
Engineering Center.
Bennett, E.R., and E.K. Linstedt. 1975. Individual home
wastewater characterization and treatment. Completion
Report Series No. 66. Fort Collins, CO: Environmental
Resources Center, Colorado State University.
Brandes, M. 1978. Characteristics of effluents from sepa-
rate septic tanks treating  grey and black waters from the
same house. J. WPCF 50:2547-2559.
Cohen,  S., and H.  Wallman. 1974.  Demonstration  of
waste flow reduction from households. EPA/670/2-74/071,
NTIS No. PB236 904.
Duffy, C.P., et al. 1978. Technical  performance of the
Wisconsin mound  system for on-site wastewater dis-
posal—An interim evaluation. Presented in  preliminary
environmental   report for three  alternative  systems
(mounds)  for onsite  individual  wastewater disposal  in
Wisconsin. Wisconsin Department of Health  and Social
Enferadi,  K.M., R.C. Cooper, S.C.  Goransow, A.W.
Olivieri,  J.H. Poorbaught, M. Walker, and B.A. Wilson.
1986. A field investigation of biological toilet systems and
grey  water  treatment.  EPA/600/2-86/069,  NTIS  No.
Environment Canada. 1979. Cold climate utilities delivery
design manual. ETR EPS/3-WP-79-2.
Hathaway, S.W., Sources of toxic compounds in house-
hold wastewater.  EPA/600/2-80-128,  NTIS  No.  PB81-
Hunter, R.B. 1941. Water distribution systems for build-
ings. Building Materials and  Structures Report BMS79.
Washington, DC: National Bureau of Standards.
Hunter, R.B. 1940. Method of estimating loads in plumb-
ing systems. Building Materials  and Structures  Report
BMS65. Washington,  DC: National Bureau of Standards.
Hypes, W.D., C.E. Batten, and J. R. Wilkins. 1974. The
chemical, physical and microbiological characteristics  of
typical bath and laundry wastewaters. NASA TN D-7566.
Langley Station, VA: Langley Research Center.
Jones, E.E., Jr. 1974. Domestic water use in individual
homes and hydraulic loading of and discharge from sep-
tic tanks. Proceedings of the National Home Sewage Dis-
posal Symposium, Chicago. Am.  Soc. Agricultural Eng.,
St. Joseph, Ml.

Kreissl, J.F. 1985. North American and European experi-
ences with biological toilets. Proceedings of IAWPRC 1st
Asian conference on treatment, disposal  and manage-
ment of human wastes, Tokyo.
Laak, R. 1975.  Relative pollution strengths of undiluted
waste materials discharged in households and the dilu-
tion  waters used  for each. Manual of grey water treat-
ment practice, part 2, Santa Monica, CA:   Monogram
Ligman, K., N. Hutzler, and W.C. Boyle. 1974.  Household
wastewater characterization. J. Environ. Eng. Div., Am.
Soc. Civil Eng. 150:201-213.

Linaweaver, F.P., Jr., J.C. Geyer, and J.K. Wolff. 1967. A
study of residential water use. Department of Environmental
Studies. Baltimore, MD: Johns Hopkins University.

Maddaus, W.O.  1987. The effectiveness  of  residential
water conservation measures. J. AWWA 79(3):52.

Metcalf and Eddy, Inc. 1979. Wastewater engineering:
Treatment/disposal/reuse. 2d ed.  New York:   McGraw-
Molland, O. 1984. Testing of biological (composting) toi-
lets and practical experiences in Norway. Proceedings of
the  international  conference on  new technology for
wastewater treatment and sewage in rural and suburb ar-
eas. Helsinki, Finland.
Olsson, E., L. Karlgren, and V. Tullander.  1968. House-
hold wastewater. Stockholm, Sweden: National Swedish
Institute for Building Research.

Otis, R.J.  1978. An alternative public wastewater facility
for a small rural community. Madison, Wl: Small-Scale
Waste Management Project, University of Wisconsin.
Proceedings of National Conference on Water Conserva-
tion and Municipal Wastewater Flow  Reduction, Novem-
ber 28 & 29, 1978. Chicago, IL. EPA/430/09-79-015.
Siegrist,  R.L. 1978. Management of residential  grey
water. Proceedings of the second  Pacific Northwest on-
site in wastewater disposal short course. Seattle: Univer-
sity of Washington.

Siegrist, R.L., M.  Witt, and W.C. Boyle. 1976. Charac-
teristics of rural household wastewater. J. Env. Eng. Div.,
Am. Soc. Civil Eng. 102:553-548.

Small-Scale Waste  Management  Project,  University of
Wisconsin, Madison. 1978. Management of small waste
flows. EPA/600/2-78-173, NTIS No. PB286-560.

Tyler, E.J., W.C. Boyle, J.C. Converse, R.L. Siegrist, D.L.
Hargett, and M.R.  Schoenemann. 1985.  Design and
management of subsurface soil  absorption systems.
EPA/600/52-85/070, NTIS No. PB85-216570.

Uniform Plumbing Code. 1976.  International Association
of Plumbing and Mechanical Officials. Los Angeles, CA.

Wagner, E.G., and J.N.  Lanoix. 1958.  Excreta disposal
for rural areas and  small communities. Monograph 39.
Geneva, Switzerland: World Health Organization.

Water Pollution Control Fed. 1976. Design and construc-
tion of sanitary and storm sewers. Manual of Practice No.
9. Washington, DC.
Watson, K., R.P. Farrell, and J.S. Anderson. 1967. The
contribution from the individual  home to the sewer sys-
tem. J. WPCF 39:2039-2054.
Welckart, R.F. 1976. Effects of  backwash water and re-
generation wastes from household water  conditioning
equipment on  private  sewage  disposal systems.  Lom-
bard, IL: Water Quality Association.
Witt, M. 1974. Water use in rural homes. M.S. study. Uni-
versity of Wisconsin-Madison.

                                              CHAPTER 5
                                          Technology Options
The summary of technologies in this chapter is provided
to further aid the process of evaluation and selection of
technologies  by identifying both general  factors  and
those specific to particular locations. Technologies dis-
cussed include soil-based approaches, mechanical  sys-
tems, and collection systems. In an effort to be concise,
not all the evaluation factors that are relevant  to a tech-
nology or other considerations worthy of discussion have
been included.

To facilitate the evaluation and  selection process,  the
discussion  of each technology is presented as criteria
that should be considered to meet a certain need or ap-

The criteria are:

•  Technology Description—the function and operation
   of the  technology, with some discussion of typical ex-
   pected removal rates and modifications.

•  Applicability and Status—the extent of use of  the
   technology, along with typical  flow ranges  and com-
   patibility with other options

•  Advantages/Disadvantages—a relative comparison
   of the  technology in regard to a variety of factors, in-
   cluding power consumption/energy cost, level of  op-
   erator  skill  required,  potential  for odor  nuisance,
   quality of effluent achievable, and sludge production

•  Design  Criteria—presentation  of typical ranges  of
   process  loading rates,  land requirements,  and per-

•  Capital Cost Sensitivity—consideration of the most
   obvious significant costs related to the particular tech-
   nology as well as other costs that should be assessed
   such as pretreatment or transmission to the treatment site

•  O&M Requirements—system complexity and opera-
   tor skill requirements; reliability of  mechanical  equip-
   ment and spare parts needed to maintain operation in
   case of equipment failure

•  Monitoring—frequency  of sampling  and   level   of
   analysis relative  to permit requirements; process con-
   trol monitoring relative to complexity and sensitivity of
   the system
 • Construction  Issues—desired level of operation and
   other considerations related to this phase of the project

 • Residuals—characterization  of residuals  generated
   from the  process, as well as volume relative to other
   processes; options for removal and disposal of sludges

 • Special  Considerations—factors not  covered  by
   other criteria such as special chemical requirements

 5.1   Constructed Wetlands

 5.1.1   Technology Description
 Wetlands are lands where the water  surface is near the
 ground surface for enough of the year to maintain satu-
 rated soil conditions and  promote  related vegetation.
 Constructed wetlands are similar systems specifically de-
 signed for wastewater treatment.

 Constructed wetlands can be considered part of a waste-
 water treatment system, while most natural wetlands are
 considered receiving waters and are therefore subject to
 applicable laws and regulations regarding discharge. The
 influent to currently operating constructed wetland sys-
 tems ranges from septic tanks to secondary  effluents.
 One constructed wetland is included as a component in a
 system designed to treat septage.

 The two different types  of constructed wetlands are char-
 acterized by the flow path of the water through the sys-
 tem. The first, called a free-water surface (FWS) wetland,
 includes  appropriate emergent  aquatic vegetation  in a
 relatively shallow bed  or  channel. The  surface  of  the
 water in such a system is exposed to  the atmosphere as
 it flows through the area. The second type, called a sub-
 surface flow (SF) wetland, includes a foot or more of perme-
 able media—rock, gravel, or course sand—that supports the
 root system of the emergent vegetation. The water in the
 bed or channel in  such  a system flows below the surface
 of the media.

 Both types of constructed  wetlands  typically include a
 barrier to prevent ground-water contamination beneath
the bed or channel; barrier materials range from com-
 pacted clay to membrane liners. A variety of wastewater
 application methods  have been  used with constructed
wetlands, and a number of different outlet structures and

methods have been included to control the depth of
water in the system.

5.1.2   Applicability and Status
As of 1991 a total of 143 communities were known to be
using or considering the feasibility of using a constructed
wetland system for wastewater management (Brown and
Reed, 1991). Systems in use include 31 FWS and 26 op-
erating SF wetlands. The range in size is from 2.2 to 880
Us (0.05 to 20 mgd) for FWS systems and from 0.04 to
132 L/s (0.001 to 3  mgd) for SF systems. (Because the in-
formation gathered to date is incomplete, the data that fol-
low may not contain  information for all of the wetlands.)
Wastewater treatment using constructed wetlands has
come into wider use only since the late 1980s, although
a few FWS systems were in operation earlier. Although
currently there are slightly more FWS than SF systems in
operation, SF systems are projected to outnumber FWS
systems over time.
The majority of constructed wetland systems (70 percent
of FWS and 90 percent of SF) treat less than 44 Us (1
mgd). Smaller systems tend  to be SF configurations
(mean - 13 L/s (0.3 mgd), median = 2 Us (0.04 mgd)).
Larger systems tend to be FWS configurations that range
in size from 2.3 to 880  Us (0.05-20 mgd) (mean = 85 L/s
(1.9 mgd), median « 20 L/s (0.5 mgd)).

5.1.3   Advantages/Disadvantages
Constructed wetlands offer the following advantages for
wastewater management:
•  Low construction cost
•  Passive system easily managed by small community
   with O&M personnel
•  Excellent  removal of biochemical oxygen  demand
   (esp. BODs) and suspended solids (SS) from primary
   or septic/lmhoff tank effluents
•  Generally attractive  systems with secondary ecologi-
   cal benefits in terms of wildlife habitat enhancement

The following disadvantages should be taken in account
when considering a constructed wetland system:
•  Lack of generally agreed-upon design factors, result-
   ing in several unproven approaches to design of land-
   intensive systems, especially FWS types where up to
   4 ha/L/s (450 ac/mgd) have been required
•  SF systems remain unproven for other than BODs and
   SS removal

5.1.4   Design Criteria
No generally accepted consensus has been established
in the United States regarding design of constructed wet-
land systems. There  are  several schools  of thought
concerning design approaches, ranging from unsubstan-
tiated empirical to  semirational  models  based on very
limited  data. Also, no consensus has been reached on
system configuration and other system details such as
aspect ratio, depth of water or media, type of media,
slope of surfaces and bottoms of beds, and inlet and out-
let structures. Moreover, pretreatment varies widely, with
facultative lagoons the most common form of  pretreat-
ment. These are used at 41 percent of the FWS and 44
percent of the SF systems. Septic tanks are used  at 24
percent of the SF systems. Aerated lagoons, secondary
treatment, and advanced treatment have also been used.
About one-third of the systems in operation use a mixture
of plant species; the other two-thirds use bulrush, cattail,
or reeds alone. One-third of the FWS  systems  use only
cattails, and 40 percent of the SF systems use  only bul-
rush.  Canna lilies, arrowhead,  duckweed, reed canary
grass, and torpedo grass have also been used in con-
structed wetland systems.
The broad ranges in the following parameters for SF sys-
tems illustrate the lack of consensus  regarding system
design:  hydraulic loading rates varying from 0.02 to 0.4
m3/m2 x d surface area (0.5 to 10 gpd/sq ft) and 1 to 110
m3/m2 x d vertical facial area perpendicular to flow (25 to
2,700 gpd/sq ft); organic loading rates of 2 to 160 kg
BOD/ha x d (0.2 to 140 Ib/ac x d); gravel sizes of 6 to
130 mm (0.25 to 5 in.); and depths of 30 to 76 cm (1.0 to
2.5 ft). For comparison, the data below presents design
parameters for state-of-the-art systems used in  Europe,
where over 500 constructed wetland sites  have  been es-
Areal requirement = 5 m2/PE
1 PE = 56gpd(200L/d)
   BODrem:  80-90 percent
   total Nrem:   <30 percent
   total Prem:   <15 percent
Plants: Common reed (Phragmites australis)
Pretreatment: Primary clarification or septic/lmhoff tanks
Bed slopes:  top = 0 percent
             bottom = 1 percent toward outlet
Bed depth:   average = 0.6 m (2 ft)
             at inlet > 0.3m (1  ft)
Containing walls: slope = as vertical as possible
Freeboard: >0.5m
Liner: yes
Media: 3-10 mm (rounded)
Inlet: maximize horizontal distribution
Outlet: variable water level control (20 cm (8 in.) above
rock surface to bed bottom)
Width: determined by following Darcy's equation:

    Ac = Qs /kt (dh/ds)
    Ac = facial area perpendicular to flow (m2)
    Qs = design flow (m3/s)
    kf = hydraulic conductivity (with gravel sizes recom-
    mended = 3 x IO"3 m/s)
    dh/ds = slope of bed bottom (m/m)
 Design parameters  are similarly broad for FWS systems:
 hydraulic loadings are 10 to 40 L/m2 surface area (0.2 to
 1.0 gpd/sq ft) for BOD and SS removal (as high as 120
 L/m2 x d (3 gpd/sq ft) for nitrification) and organic loadings
 are 10 to 20 kg BOD/ha  x d (9 to 18 Ib/ac x d) for BOD
 and SS removal (as low  as  1 kg/ha x d (0.9 Ib/ac/d) for
 nitrification).  Hydraulic residence time of FWS systems
 should be at least 7 days, but as many as 365 days have
 been used.

 5.1.5  Capital Costs
 Capital costs per unit of flow for both types of con-
 structed wetlands in the United  States are shown in Fig-
 ure 5-1. The most sensitive costs are for land, earthwork,
 liners, vegetation planting,  and, for SF systems, fill media.

                                        -I  $3.00/gpd
 Designed  AWT  NBj    Sec
 Purpose:	Removal Treatment
            Free Water Surface
 Region VI  TVA  Other  Designed
                               Subsurface Flow
                    CW Type
Figure 5-1. Capital Costs for Wetland Systems.

5.1.6   O&M Requirements/Costs
Constructed wetland  systems should  be inspected at
least weekly. This O&M requirement includes inlet and
outlet inspection and flow  recording. Overall experience
has not yet allowed quantification of these costs, but they
are considered negligible in comparison to treatment al-
ternatives. Sidewall maintenance is also required.

5.1.7   Monitoring
With constructed wetlands, vegetation growth should be
monitored and standard sampling and  analysis require-
ments of the permit should be fulfilled.

5.1.8 Construction Issues
Considerations concerning the construction of wetlands
for wastewater treatment include:
 • Media for SF systems should be rounded and washed
   prior to placement

 • Vertical sidewalls for SF systems ensure proper vege-
   tation at edge of bed

 • Use of gabions and large slopes at the inlet simplifies
   construction and ensures good horizontal distribution
   of flow in SF systems

 5.1.9   Residuals
 Although not  generally practiced, harvesting of an  SF
 system's vegtetation would enhance removal of nutrients
 at the cost of increased O&M and residuals  disposal
 problems.  It is also possible that eventual dislodging may
 be required, but quantification of this measure is not  yet
 available.  SF systems should not be  immediately pre-
 ceded by facultative lagoons since algae will aggravate
 any clogging problems.

 5.1.10  Special Considerations
 The role of plants in a constructed wetland system is at
 present undefined. Moreover, the hybrid designs of con-
 structed wetlands will evolve such that their present  ca-
 pabilities will be upgraded. At this time, however, the  SF
 systems and small FWS systems should not be expected
 to remove  more than  BOD and SS in significant quanti-
 ties; however, very large (very lightly  loaded)  systems
 may also accomplish nitrification.

 5.2   Rapid Infiltration

 5.2.1    Technology Description
 Rapid  infiltration is a  soil-based wastewater treatment
 method that typically consists  of a series of earthen ba-
 sins with exposed soil  surfaces designed for a repetitive
 cycle of flooding, infiltration/percolation, and drying (Fig-
 ure 5-2). The method depends on a relatively high rate of
 wastewater infiltration into the  soil  and  percolation
 through a vadose or unsaturated soil zone below the infil-
 trative surface before recharge to the ground-water table.
 System design is based on the capability of soils to pro-
 vide  acceptable  treatment before the percolate reaches
 the ground water.

 5.2.2    Applicability and Status
 Rapid infiltration is a  proven technology for year-round
 treatment  of domestic,  municipal, and  other organic
 wastewaters. Its  application is limited  primarily by soil
 characteristics, ground-water impacts, and land costs. It
 is not well suited for inorganic industrial wastewaters.

 5.2.3   Advantages
 Rapid infiltration  is a method of land application providing
very  favorable removal of the conventional wastewater
 parameters—including ammonia—that is simple to oper-
 ate and requires only a minimum of operator intervention.
 Moreover, it requires less  land area than other land appli-
cation methods and may  be operated year round. It is a

                                      (a)  Hydraulic Pathway
                                                                           Flooding Basin
                                           GW Mound
                            (b) Natural Drainage into Surface Waters
Figure 5-2. Schematic of a Rapid Infiltration Facility (EPA, 1981).
"zero-discharge" method that provides ground-water
recharge rather than requiring an outfall for direct dis-
charge to surface water. Frequently, renovated wastewa-
ter is recovered via wells for reuse in irrigation.

5.2.4   Disadvantages
Use of rapid infiltration is limited by site and soil charac-
teristics that affect the capability of the soil to accept and
treat the applied  wastewater. Potential ground-water im-
pacts  from nitrate nitrogen  are a serious concern and
may also limit its  application.

5.2.5   System Design  Site Selection
Site selection is  based on the treatment capacity of the
soils and the availability of sufficient land area of suitable
topography. The treatment capacity of the soil is depend-
ent primarily on texture, structure, and unsaturated thick-
ness. No soil type provides optimum conditions for the
removal of all wastewater constituents.  Fine-texture soil,
such as silt and clay loams, has a relatively low hydraulic
conductivity and is therefore unsuitable for rapid infiltra-
tion.  Coarse soil, such as sand, has a higher rate of hy-
draulic  conductivity  and  reaeration  to allow  higher
hydraulic and organic loading and shorter cycles for ba-
sin resting,  which can permit rapid infiltration. However,
coarse soil can be a less-effective physical filter, have a
lower cation exchange capacity, and  allow more rapid
percolation  of wastewater through the vadose  zone
where most treatment occurs. Typically, sites with sand
to sandy loam soils are selected. A summary of typical
treatment performance data is presented in Table 5-1.

Unsaturated depth of soil is another critical site-selection
criterion. A minimum of 1.5 to 2.5 m (5 to 8 ft) of unsatu-
rated soil with relatively uniform hydraulic conductivity is
necessary below the infiltrative surface to provide neces-
sary treatment. Greater unsaturated thicknesses are usu-
ally required in coarse, granular soils to provide longer
residence times. Ground-water mound height analysis
must be performed to determine  if the separation dis-
tance can be maintained during system operation. If the
desired separation distance cannot be maintained, the
hydraulic loading can be reduced, basin geometry can be
changed to have a  high-aspect ratio in relation to the
ground-water gradient, basin spacing can be increased,
or ground-water drainage can be provided.  Hydraulic Loading Rate
The design hydraulic loading rate is determined by soil
characteristics, ground-water mounding potential,  treat-
ment requirements, applied wastewater quality, and pre-
cipitation. The maximum hydraulic  loading is established
by the hydraulic conductivity of the least permeable soil
horizon in the vadose zone. Typically, 4 percent of the
measured saturated  hydraulic conductivity is used as a
preliminary estimate. This rate  may be adjusted down-
ward to limit the BOD loading to within 21 to  126 kg/ha/d
(19 to  112 Ib/ac/d) to control infiltrative surface clogging.
Primary treatment is the minimum level of pretreatment
suggested, but where the public has even limited access,
secondary treatment is required. If there is concern about
nitrogen contributions to the ground water below the sys-
tem, nitrogen rather than BOD may control the hydraulic
loading (pattern and total rate) and pretreatment. Poten-
tial for excessive ground-water mounding and other site-
specific issues may require the hydraulic loading to  be
reduced further. Typical average hydraulic loading rates
are 1.5 to 35.0 cm/d. To assist in selecting  appropriate
hydraulic loading rates, loadings used by systems oper-
ating under similar conditions should be compared (EPA,
1981,1984; Reed & Crites, 1984; Overcash & Pal, 1979;
WPCF, 1990).

Table 5-1. Typical Rapid Infiltration System Performance3  Application Patterns
The selected application pattern for basin operation will
determine the number and size of the basins and the
land area required. The pattern is selected to control infil-
trative surface clogging and/or to  promote nitrogen re-
moval (Lance et al., 1976; Lance, 1984). Typical ratios of
application periods to  drying  periods  vary from 0.2,
where maximum hydraulic loading is the objective, to 1.0
for maximum nitrogen removal. Suggested loading cy-
cles are presented in Table 5-2.

5.2.6   Design Modifications
Underdrains or extraction wells may be used to lower the
water table to increase the unsaturated depth of soil be-
low the infiltrative surface or to reclaim the renovated
water. Information on  the design of underdrain systems
can be found elsewhere (USDA, 1971; U.S. Dept. of Inte-
rior,  1973; Luthin, 1973). Some states require an aquifer
Table 5-2. Suggested Hydraulic Loading Cycles for Rapid














aEPA, 1981.
" A rvrtll/^otlrtrt r-ii-M'ti-ijrJrt -Fj-tt- rvKii^ri <-tfi J i»i£flrmn4> nliAi ild-J L^M I ! wi !+ ** ,*J *j«
1-2 days to prevent excessive clogging. Periods maybe
affected by the rate of ground-water mounding (rise).


Toxic organics

Fecal coliforms


Loading (kg/ha x d) Removal







Varies with
2-6 logs

2-4 logs

Lower removals associated with high loading rates on coarse soils
Removal depends on preapplication treatment, BOD:N, climate,
hydraulic loading, and wet/dry cycle
Removal correlates with soil texture, time of service, soil
mineralogy, and travel distance
Favorable removal of volatile and biodegradable organics appears
to occur where the subsoil remains aerobic
Removals correlate with soil texture, travel distance, and resting
Limited data suggest favorable removals with low loadings,
fine-texture soil, aerobic subsoil, and high temperatures
aWPCF, 1990; Nilsson, 1991.
NA = not applicable

protection permit, which calls for demonstration of non-
degradation and,  in some cases, upgrading of pretreat-
ment and monitoring requirements.
Continuously flooded  infiltration basins  are  a modified
operation method that has been used where high-rate in-
filtration is desired. Treatment performance of such sys-
tems is unfavorable  because of the rapid percolation and
the elimination of subsoil reaeration and aerobic conditions.

5.2.7  Capital Cost Sensitivity
Capital costs of rapid infiltration projects are controlled
primarily by land costs and earthwork. Earthwork includes
infiltration surface  preparation and dike construction. If the
topography is not favorable for basin construction, site
grading may add a significant cost. Other associated
costs that may be  significant are  installation of under-
drains, if  needed,  transmission of  wastewater to the
treatment site, and pretreatment.

5.2.8  O&M Requirements
The primary O&M requirements of rapid infiltration sys-
tems include basin cycling, infiltration surface mainte-
nance, winter operations, nitrogen  management,  and
monitoring.  Other O&M  tasks include maintenance of
pumps and other equipment  and basin dikes. These
tasks are easy to perform and require little specialized
training. No special  equipment is necessary except for a
tractor and harrow for infiltration surface maintenance.  A
useful description of these tasks is provided by EPA (1984).

Costs of O&M are associated primarily with labor costs.
Other costs include  power costs for wastewater pumping
and equipment depreciation. Total labor requirements,
excluding maintenance of the pretreatment works, should
not exceed 10 to 15 hr/wk. O&M costs are in the range of
5 to 10 cents/1,000 gal of wastewater treated.

5.2.9  Construction Issues
Construction activities include infiltration, surface prepa-
ration, dike construction,  and installation of basin piping,
inlet structures, and, where needed, basin underdrains.
These construction activities are as important  as site
evaluation  in achieving  successful  performance  of  a
rapid infiltration system. Infiltration surface preparation  is
the most critical factor. The surface must be carefully lev-
eled to within 5 cm (2 in.) of the specified finished eleva-
tion in  each basin  with  a  minimum  of  surface
compaction. Once the surface is fine-graded, it should be
ripped and cross-ripped to a depth of 60 cm (2 ft). Con-
struction practices should minimize equipment  travel  in
the direction of ground-water movement. The dikes be-
tween  the basins must prevent leakage from the basins
and provide vehicular access to  each basin,  and they
must be graded such that erosion of the embankments
does not occur. Proper construction procedures are dis-
cussed elsewhere (EPA, 1984; WPCF, 1990).
5.2.10  Monitoring
Monitoring requirements cover wastewater volumes ap-
plied to each basin, daily wastewater ponding levels in
each basin, basin cycle times, applied wastewater qual-
ity, and ground-water elevations and quality.

5.2.11  Residuals
No  residuals are usually  produced with  rapid infiltration
systems. Occasional surface scrapings and residual al-
gae, for instance, may be  buried onsite given the minimal
volume of such residuals.

5.3   Stabilization Ponds

5.3.1   Technology Description
Facultative lagoons, or ponds, are the  most frequently
used  form of municipal  wastewater treatment in the
United States, with over  5,000 systems  currently in op-
eration. These lagoons are usually 1.2 to 1.8 m (4 to 6 ft)
in operating depth and are not  mechanically  mixed or
aerated.  The layer of  water near the surface is aerobic
due to atmospheric reaeration and  algal  respiration. The
layer at the bottom of the  lagoon  is anaerobic and  in-
cludes sludge deposits. The intermediate layer, termed
the  facultative zone, ranges from aerobic near the top to
anaerobic at the bottom.  The layers may be indistinct or
be  clearly  defined due  to temperature-related water-
density variations. Disruptions can occur  in the spring
and fall of each year when the surface layer of melted ice
may have a higher density than lower layers. This higher
density water induces vertical  movement,  mixing the
pond contents and producing objectionable odors due to
the  release of anaerobically formed gases during these
unstable periods.

The presence of algae in the near-surface water is es-
sential to several  aspects of treatment  performance of
facultative ponds.  In the  presence of sunlight the  algal
cells take up carbon dioxide from the water and release
oxygen. On warm, sunny days the  oxygen concentration
in the near-surface water  can exceed saturation levels. In
addition, because  of  the temporary  carbon dioxide re-
moval, the pH of the near-surface water can exceed 10.
This results in conditions favorable for ammonia removal
via  volatilization, and long-detention-time facultative ponds
have been  shown  to be  very effective for ammonia re-
moval. This photosynthetic activity by the algae occurs
on a diurnal basis so that  both oxygen and pH levels shift
from a maximum during daylight hours to their minimums
at night.

The oxygen  produced by  the  algae and  by surface
reaeration is used  by aerobic bacteria to stabilize the or-
ganic material in the upper layer  of water. Anaerobic fer-
mentation is the dominant activity in the bottom layer in
the  lagoon. Both of these reaction  rates  are significantly

 reduced during the winter and early spring months in
 cold climates.  Effluent quality may be reduced  to  the
 equivalent of long-detention-time  settling when  an  ice
 cover  persists on the  water  surface. For this reason,
 many states in the northern United States and in Canada
 prohibit discharge  from facultative lagoons during  the
 winter months.
 Typical detention times range from 20  to 180 days for
 continuously discharging  facultative lagoons.  Detention
 times can approach 200 days  in northern climates where
 discharge  restrictions  prevail. Effluent  BOD  <30/mg/L
 can usually be achieved; effluent  TSS may range from
 <30 mg/L to over 100 mg/L depending on the algal con-
 centrations. Many existing facultative  lagoons are large,
 single-cell  systems, with the  inlet constructed near  the
 center of the cell. That configuration can result in  under-
 mining the design volume of the system. A multiple-cell
 system, with at least three cells,  is recommended with
 appropriate inlet and outlet structures to  maximize  the
 utilization of the design volume.

 Although the concept  is somewhat land-intensive, par-
 ticularly in northern climates,  stabilization  ponds offer a
 reliable, easy-to-operate process that  makes it attractive
 for small, rural communities where sufficient land is often
 available.   Aerated Lagoons
 Aerated lagoons are smaller and deeper than facultative
 lagoons  and are  designed  for biological treatment of
 wastewater on a continuous basis. In contrast to stabili-
 zation  ponds, which obtain oxygen from photosynthesis
 and surface reaeration, aerated lagoons  typically employ
 devices that supply supplemental oxygen to the system.
 Aerated lagoons evolved from stabilization ponds when
 aeration devices were added to counteract odors arising
 from anaerobic conditions. The aeration  devices may be
 mechanical (i.e., surface aerator) or diffused air systems
 using submerged or overhead pipes. Surface aerators
 are divided into two types: caged aerators and the more
 common turbine and vertical shaft aerators. Diffused  air
 systems  utilized in lagoons typically  consist of plastic
 pipes supported near the bottom of the lagoon cells with
 regularly spaced sparger holes drilled in the tops  of the
 pipes,  although overhead air  headers and finer bubble
 systems have recenty been applied. Because aerated la-
goons  are  normally designed  to achieve partial  mixing
only,  aerobic/anaerobic  stratification  may occur, and
 large fractions of incoming solids and  the biological sol-
ids produced from waste conversion can settle to the bot-
tom of the lagoon cells.   Controlled Discharge
A  common operational modification  is  the  controlled-
discharge mode where pond discharge is prohibited dur-
ing the winter months in cold climates and/or during the
peak algal growth periods in  all  climates. In this ap-
proach, each cell in the system is isolated  and then dis-
 charged sequentially. A common operational modification to
 aerated and facultative lagoons is the controlled-discharge
 pond system. Sufficient storage capacity is provided in the
 lagoon system to allow wastewater storage during winter
 months, peak algal growth periods, or receiving-stream
 low-flow periods. In this approach, each cell in the sys-
 tem is isolated and then discharged sequentially. In the
 Great Lakes states of Michigan, Minnesota, and Wiscon-
 sin, as well as in the province of Ontario, many pond sys-
 tems are designed to discharge in the spring and/or fall
 when water quality effects  are minimized. As a  secon-
 dary  benefit, operational costs are lower than for a con-
 tinuous  discharge  lagoon  because  of  reduction  in
 laboratory monitoring requirements and the need for less
 operator control. A similar modification  is called a hy-
 drograph controlled release lagoon (HCRL) where water
 is retained in the pond until flow volume and conditions in
 the receiving  stream are adequate for discharge,  thus
 eliminating the need for costly additional treatment.  Modifications
 A recently developed physical modification to upgrade
 the performance of existing one-  or two-cell systems in-
 volves dividing existing lagoons into multiple cells to im-
 prove hydraulic  conditions.  Another  recent patented
 development uses  a floating plastic grid to prevent the
 transport of duckweed (Lemna sp.) plants on the surface
 of the final cell(s) in the lagoon system.  This duckweed
 cover restricts the  penetration of light to destroy algae
 and improve effluent SS quality. With sufficient detention
 time (>30 days) and intensive harvesting, significant nu-
 trient removal may be possible. Some systems also have
 the capability  to draw effluent from several  levels and
 thereby avoid the  high  algal concentrations near the
 water surface during discharge.

 The rock filter, used as an alternative means of removing
 algae  from lagoon  effluents,  consists  of a submerged
 bed of rocks (5 to 20 cm (2 to 8  in.) diameter) through
 which the lagoon effluent is passed vertically or horizon-
 tally, allowing the algae to be removed in the rock filter.

 The basic simplicity of O&M is the key advantage of this
 process. The effluent quality achievable and the depend-
 ability of long-term  operation, however, have not been
 well documented yet. Rock filtration following treatment
 in single-cell lagoons has been problematic and therefore
 is not recommended.  Sand Filter
 The intermittent sand filter is an outdoor, gravity-actuated,
 slow rate  filtration system that capitalizes on the avail-
 ability  of  land area.  It  is a  biological  and physical
 wastewater treatment  mechanism  consisting  of  an
 underdrained bed of granular material, usually sand. The
 filter surface is flooded intermittently with  lagoon effluent
 at intervals that permit the surface to drain between ap-
 plications. It is recommended that  the flow be directed to
one filter for 24 hours. That filter is then allowed to drain

and dry for one to two days, and the flow goes to an adja-
cent filter. It  is preferable to have three filter beds where
good operation and treatment can be accomplished over a
three-day cycte. (This technology is described in more de-
tail in Section The system can remove suspended
solids (algae) and BOD  as  well as convert ammonia  to

5.3.2   Applicability and Status
Lagoon (wastewater stabilization pond) technology, the
most common  means  of  wastewater treatment in the
United States, is primarily  used in smaller communities.
The concept is well-suited for rural communities and in-
dustries where land is readily available but skilled mainte-
nance  is not. Lagoons that discharge to larger receiving
streams have been designated as "equivalent to secon-
dary treatment" by the EPA. However, many existing la-
goons will require upgrading by methods such as those
described above if they  cannot meet stream effluent re-
quirements or if they are leaking into the ground water.

5.3.3   Advantages/Disadvantages
The advantages of stabilization ponds include the follow-
• Minimum  operational skills required
• Low capital cost requirements
• Many means of upgrading available, minimizing capi-
   tal outlays where lagoons already exist
• Sludge disposal required only at 10- to 20-year intervals

Disadvantages of this technology include:
• Large land area requirements
* Continous flow  (traditional)  facultative ponds cannot
   meet stringent effluent  standards during  warm  sea-
   sons without upgrading
• Lagoons can negatively impact ground water if an inade-
   quate liner is installed or if an existing liner is damaged
• Most lagoons discharge to smaller, water-quality-limited
   streams and may, therefore, require upgrading
• Several upgrading techniques  are not fully  charac-
   terized, making their adoption speculative

5.3.4   Design Criteria  Facultative Lagoons
Every system should have a series of at least three cells.
Most states  have design criteria that specify the areal or-
ganic  loading (Ib/ac/d)  and hydraulic  residence time.
Typical organic loading for the system is 22 to 67  kg
BOD/ha/d (20 to 60 Ib/ac/d).  Overall typical detention
times range from 20 to 180 days or more, depending on
A number of empirical models exist for design of faculta-
tive lagoons. These include first-order plug flow, first-
order complete mix, and  models proposed  by  Gloyna,
Marais, Oswald, and Thirumurthi. None of these have been
shown to be clearly superior to the others. All will provide a
reasonable design  if the proper parameters are selected
and if the hydraulic characteristics of the system are known.
Depth is normally 1.5 to 1.8 m (5 to 6 ft), although a
range of 0.9 to 2.4 m (3 to 8 ft) is often suggested. Typi-
cal removals of BODs are 75 to 95 percent, but SS may
vary from negligible to 90 percent. A high degree of toxic
organics and metals are generally removed. Ammonia
conversion (20  to 80 percent)  and phosphorus removal
(10 to 50 percent) can be significant in warm, algae-con-
trolled periods.  Likewise, fecal coliform reductions are
dependent on the detention time and are quite significant
during these periods.  Aerated Lagoons
Every system should have a series of at least three cells
that  are lined (or similarly secured)  to prevent adverse
ground-water impacts. Many states have design criteria
that  specify the design loading, the  hydraulic residence
time, and the aeration requirements. Pond  depths range
from 1.8 to 6 m (6 to 20 ft),  with 3 m (10 ft) being typical
(the  shallow depth systems are usually converted  facul-
tative lagoons).  Detention times range from 3 to 20 days,
with  10  days being typical (shorter detention times use
higher intensity aeration). The design of these systems
for BOD removal is based on first-order, complete-mix ki-
netics. Even though the system is  not completely mixed,
a conservative  design will result. The model commonly
used is:
    Ce = effluent BOD
    Co = influent BOD
    KT = temperature-dependent rate constant 12.51"1 at
    t = total detention time in system
    n = number of equal-size cells in system
Oxygen requirements are typically 30 to 40 hp/Mgal ca-
pacity; they may range as  high as 100 hp/Mgal where
complete mixing is desired.
BOD  removal can range from 80 to 95 percent. Effluent
total suspended solids (TSS) can  range from  20 to 60
mg/L  depending on the concentration of algae  in the ef-
fluent. Removal of ammonia nitrogen is usually less ef-
fective  than  in facultative  lagoons.  Nitrification  of
ammonia can occur in underloaded aerated lagoons or if
the system is  specifically  designed for that  purpose.
Phosphorus removal is also less effective than in faculta-
tive lagoons due to the more  stable  pH  and  alkalinity
conditions. Phosphorus removals of about 10 to 20 per-

cent might be expected. Removal of conforms and fecal
conforms can be effective, depending on detention time
and temperature. Disinfection will be necessary to meet
effluent limits consistently. Rock Filters
Key considerations for rock filters include:
• Hydraulic loading rates (HLR): 0.3 to 0.9 m3/m3/d (7.5
   to 22 gpd/sq ft)
• Submerged inlets
• 7.5 to 15 cm (3 to 6 in.) rock

• SS removal (percent) = 100 - 66H (H=HLR in m3/m3/d)

• At least three cells are required in the system that pre-
   cede the rock filter  Hydrograph Controlled Release
         Lagoon (HCRL) Systems
An HCRL  system has three principal components:  a
stream-flow monitoring system, a storage cell, and an ef-
fluent discharge system. The stream-flow monitoring sys-
tem measures the flow rate in the stream and transmits
this data to the effluent discharge system. The effluent
discharge  system consists of a controller and a  dis-
charge structure. The controller operates  a discharge de-
vice (e.g.,  a motor-driven  sluice gate)  through  which
wastewater is discharged from the storage lagoon; how-
ever, these tasks can be manually performed.
Key considerations for HCRLs include:
• Need release  model keyed to flow (as measured by
   depth) in receiving stream

• Outlets should be capable of drawing from different
   depths to ensure best quality
• Storage  cells sized by use of water-balance equations  Duckweed Systems
The key considerations for duckweed systems include:
• A 30-day retention time  with shallow depth and fre-
   quent harvesting required (= every 1 to 3 days at peak
   season)  if nutrient removal sought
• Plan must be in place on fate of harvested plants (i.e.,
   processing on site, transportation, and ultimate fate)
• Manageability  by local authorities is yet to be estab-
   lished (need contract management)
• May need post-aeration  to meet  effluent  dissolved
   oxygen (DO) requirements Intermittent Sand Filters
The preferred design (EPA, 1980) for lagoon upgrading
is as follows:
• 3 cells in series, all 76 to 91 cm (30 to 36 in.) deep
• Progressively finer sands (e.g., effective sizes of 0.72
   mm, 0.40 mm, and 0.17 mm)
• Effluent quality = 10 mg/L of BODs and SS

• Complete  nitrification expected, except under  ex-
   tremely cold conditions

This configuration is considered to provide the most ef-
fective approach  (in terms of achieving the most favor-
able effluent quality attainable) for lagoon upgrading.

5.3.5   Capital Costs   Facultative Lagoons
a. Assumptions

1.  Design basis:
    Areal  loading method, 45 kg BOD/ha x d (40 Ib/ac x d)
    in warm climates, 22 kg BOD/ha x d (20 Ib/ac x d) in
    the primary cells only in cold climates
    Water depth 1.5m (5 ft)
    Effluent BOD  = 30 mg/L
    Effluent TSS = 60 mg/L

2.  Costs based on November 1990 prices (ENR = 4780)

3.  Construction costs include excavation, grading, berm
    construction,  and inlet and  outlet structures. Costs
    do not include a lagoon  liner, purchase of the land,
    or delivery of wastewater to the site.

4.  The construction cost equations below are valid for a
    preliminary estimate for  design flows up to 440  Us
    (10mgd), where
    C = Costs (in millions of dollars)
    Q = Wastewater flow (mgd)
b. Construction Costs
    Warm climates: C = 0.750(Q)°-729
    Cold climates: C = 1.800(Q)a711   Aerated Lagoons
a. Assumptions

1.  Design basis:
    Influent BOD = 210 mg/L
    Effluent BOD = 30 mg/L
    Depth = 3m(10ft)
    Detention time = 10 days
    Floating mechanical aerators at 10 hp/Mgal

2.  Costs based on November 1990 prices (ENR = 4780).

3.  Construction costs include excavation, grading, berm
    construction,  and inlet and  outlet structures, and
    membrane liner. Costs do not include purchase of
    the land or delivery of wastewater to the site.

4.  The construction cost equations below are valid for a
    preliminary estimate for design flows up to 440 Us
    (10 mgd), where
    C = Costs (millions of dollars)
    Q = Wastewater flow (Mgal/a)

a. Construction Costs


    1-1 Omgd:C = 0.31 0(Q)  Rock Filters and Intermittent Sand
Information on costs is  currently  insufficient to provide
firm estimates, but construction costs of $1.00/gpd of
capacity should be considered quite conservative.  Duckweed and HCRL
Cost information  is currently insufficient  to serve as a
basis for providing estimates.

5.3.6  O&M Costs   Facultative Lagoons (All Climates)
 C = 0.016(Q)°-496  Aerated Lagoons
0-1 mgd: C « 0.025 (Q)  "'"
1-10mgd:C = 0.025(Q) Upgrading Systems
A range of 50 to 75 cents per year per gallons per day of
capacity is a reasonable estimate of O&M costs for inter-
mittent sand filters.
Controlled discharge, HCRL, and duckweed and  rock
filters: No valid data.

5.4   Overland  Flow

5.4.1  Technology Description
Overland flow is a land application method of wastewater
treatment with a point discharge to a surface water. The
technology consists of a  series of uniformly sloped, vege-
tated terraces with a wastewater distribution system lo-
cated at the top  of the terrace and a runoff collection
channel at the bottom (Figure 5-3). Facilities for waste-
water storage during wet or freezing weather are also
provided. In overland flow, wastewater is applied inter-
mittently across the top of the  terraces and allowed to
sheet flow over the vegetated surface to the runoff  col-
lection channel. The system  is not designed for soil per-
colation, though some percolation may occur.

Treatment is achieved primarily through  sedimentation,
filtration,  and  biochemical activity  as the wastewater
flows through the vegetation on the terraced slope. SS
settle or  are filtered from the flow to be degraded or in-
corporated into the soil. Effluent TSS concentrations of
less than 10 mg/L are possible.  However, algae removal
is not consistent because many algal cells are buoyant or
motile  and resist  removal by sedimentation or filtration.
Organics are degraded  by biological films attached on
the plant and soil  surfaces. BODs removals of 90 percent
are often achieved. Total nitrogen removals of up to 80
percent can be achieved, but will vary with the  mass
loading, ambient  temperature, and other environmental
factors and are more comrrjonly much lower. The princi-
pal removal mechanism is biological denitrification,  but
some plant uptake and ammonium volatilization may oc-
cur.  Phosphorus may be  partially removed  by soil  ad-
sorption (in the early operational stage) and plant uptake.
Removal efficiencies as high as 50 percent are possible,
but 20 to 60 percent is common). Overland flow is not ef-
fective in pathogen  removal,  however. Little is  known
about treatment performance for metals and toxic organics
removals. Because treatment  is dependent on active
biomass  and vegetation,  the terraces are operated on
wet/dry cycles and applications are ceased during freezing
periods. Further information on treatment performance is
available elsewhere (WPCF, 1990).

5.4.2  Applicability and Status
Overland flow first gained  widespread use in the early
1970s. It was developed for areas where soils are poorly
suited for other land application  methods dependent on
ground-water  recharge for ultimate disposal  of  the
treated wastewaten Today, overland flow i$ successfully
used by many small communities, primarily in the south-
ern half of  the United States. Its use is limited primarily
by land suitability, climate, and  land costs.

5.4.3  Advantages
Overland flow is well suited for wastewater treatment by
rural  communities  and seasonal industries with organic
wastes.  It  provides secondary or advanced secondary
treatment, yet is relatively simple and inexpensive to op-
erate. If the vegetative cover can be harvested and sold
(e.g., as  forage), overland flow can provide an economic
return from the reuse of water  and nutrients.  Of the land
application  methods  of wastewater treatment, overland
flow  is  the approach  least restricted by soil  charac-
teristics;  however,  this method does  require a relatively
impermeable soil for conventional operation.

5.4.4  Disadvantages
Overland flow is primarily limited by climate, crop water
tolerances, and land slope. Application is restricted dur-
ing wet weather and can be limited when temperatures re-
main below freezing. Application rates may be  restricted by
the type  of crop grown. Steeply sloping or flat terrain is
not well suited for this  method of treatment.  Disinfection
is required  in order to meet effluent permit requirements
prior to discharge (unique to land application processes).

5.4.5  Design Criteria

5.4.5.?   Site Selection
Topography is the most important site-selection criterion
because of its impact on the costs of earthwork.  Terrace
slopes should be between 2 and 8 percent and relatively
uniform,  with sufficient length to  provide adequate travel
time for treatment. Flatter slopes may result in wastewa-
ter ponding on the terraces, and erosion may be signifi-
cant on steeper slopes. Terrace lengths are  typically 30
to 60 m (100 to 200 ft). South-facing slopes are preferred

    by Surface
     Spray, or
                               Overland Flow
                                                Sprinkler Circles

Figure 5-3. Schematic of an Overland Flow System.

in cold climates to  extend the operating season (EPA,
1984; WPCF, 1990).
Soil  type  and  permeability are  of limited importance.
Overland flow was  developed for use on soils with low
permeabilities. Therefore, detailed soil evaluation is only
necessary if significant wastewater percolation  into the
soil is expected. Where the soil  is permeable, it should
meet the same criteria used for slow-rate land application
if ground-water protection is to be provided.  Preapplication Treatment
Secondary treatment levels (30 mg/L BODs and 30 mg/L
TSS or greater) can easily be achieved by overland flow
systems with primary pretreatment. Whether higher lev-
els of pretreatment are required depends on local regula-
tions  and aesthetics.  The  most  common  method of
pretreatment used in the United States is lagoons, which
effectively remove grit and other solids that may damage
or clog the pumps and distribution system. However, in
lagoons with long retention times, such as facultative or

aerated ponds, algae growth can be significant, adversely
affecting effluent quality from overland flow systems. There-
fore, primary treatment or lagoon stabilization with retention
times limited to 1 to 2 days are suggested (WPCF, 1990).
Where climatic restrictions obtain, storage facilities must
also be provided that are sufficient to hold the flow during
extented periods.  Hydraulic Loading Rate
The rate of wastewater application is dependent on the
effluent discharge  limitations,  level  of  pretreatment,
length  and slope of the terrace, and climate. The degree
of treatment provided is directly proportional to the length
of the slope and the ambient temperature, and inversely
proportional to the  hydraulic loading  rate and terrace
slope. The degree of pretreatment primarily affects  nitro-
gen removal.  Low BODs concentrations in the applied
wastewater enhance nitrification,  while  higher BODs
concentrations  enhance denitrification.  Typical  hydraulic
loading rates for primary pretreated wastewater are 0.2 to
0.4nr?/h x m of terrace width (16 to 32 gal/h x ft). For sec-
ondary  pretreated wastewater, hydraulic  loadings  may
reach 0.6 m3/h x d (48 gal/h x t). The design rate selected
for a particular site should take into account the influence of
each of the factors above (EPA, 1981; 1984; WPCF, 1990).  Operating Cycle
Overland flow systems have performed best when appli-
cations of wastewater are alternated with drying periods.
Common practice is to toad a terrace for 12 hr followed by
a 12-hr drying period. Lower ratios enhance nitrification.  Distribution
Uniform application of wastewater across the width of the
terrace is critical  to system performance. Wastewater is
applied at  the  top of each terrace by  sprinklers or weir
overflow methods. Because  weir overflow methods re-
quire precise leveling of the device used, they are  sug-
gested for small  systems only. Sprinklers are the most
commonly used method. They are located either at the
top of  the  terrace or within the top one-third of the ter-
race. Where sprinklers are used, terrace lengths should
be increased, with 45 m (150 ft) the minimum length. The
stope length should be at least 20 m (65  ft) greater than the
diameter of the sprinkler pattern. Distribution types and their
design are described elsewhere (EPA, 1984; WPCF, 1990).  Vegetation Selection
Perennial,  water-tolerant  grasses are best suited for
overland flow systems. Suitable cool-season grasses in-
clude reed canary grass, fescue, and rye grass. Suitable
warm-season grasses include common and coastal Ber-
muda,  Dallis,  and Bahia. Local agricultural extension
agents should be consulted for further guidance.  Runoff Collection
The runoff collection channel must be designed with suf-
ficient capacity and grade to prevent water from ponding
at the base of the terrace. At a minimum, it should be de-
signed to handle the 10-year,  1-hour rainfall event for the
area.  The channel may be lined or unlined, but unlined
ditches require more maintenance to control weed growth.  Storage
Sufficient storage is needed to hold wastewater during
periods when applications cannot be made.  In cold cli-
mates, the storage  requirements are determined by the
number of days the temperature is below freezing. In the
United States, storage  requirements can reach 160 days
(EPA,  1984; WPCF, 1990). In climates where freezing is
not a significant factor, sufficient storage should be pro-
vided to allow flexibility in operation and crop  harvesting,
typically 2 to 5 days.

5.4.6   Capital Cost Sensitivity
Land  and earthwork costs are the most significant capital
costs of overland  flow  systems. Distribution network con-
struction may also be significant depending on the type used
and the topography. Typical capital costs vary from  $1.40
(0.1 mgd) to $14.00 (0.01 mgd) per gallon of dailycapacity.

5.4.7   O&M Requirements
O&M requirements of overland flow systems include har-
vesting of the cover crop, maintenance of the distribution
and collection systems, and pest control.  Periodic mowing
is necessary to maintain a healthy growth of grass. An an-
nual minimum of 4 to 6 mowings per year is suggested. Re-
moval  of the grass is necessary for high-level nitrogen and
phosphorus control. Mosquitoes and weed control through the
use of pesticides or microbiological agents may be necessary.

Costs of O&M are associated  primarily with labor costs.
Almost no  special equipment other than the appropriate
agricultural equipment is required.  Total  labor  require-
ments, excluding maintenance of the pretreatment works
and effluent disinfection system, should not exceed 10 to
15  hr/wk.  O&M  costs typically  range from $1.40  to
$2.80/1,000 gal treated wastewater (at 10,000 gal/d)  to
$0.35 to $0.70/1,000 gal (at 100,000 gal/d).

5.4.8   Construction Issues
Terrace grading  is critical  to achieving  sheet flow for
successful  operation. The slopes should be final graded
with a land plane to within 1.5 cm (0.6 in.)  of the pre-
scribed slope. Soil compaction is not a critical factor ex-
cept as it relates to establishment of the vegetative cover
or to prevention of ground-water contamination. The ter-
races  should be irrigated after seeding, but wastewater
applications should be limited until the vegetation is well
established;  the acclimation  period  is typically 3  to 4
months in duration.

5.4.9   Monitoring
Monitoring  requirements cover volumes,  rates, frequen-
cies, and patterns of wastewater applications and influent
and  effluent  quality monitoring dictated  by the permit.
Where significant infiltration of wastewater into the soil
occurs, ground-water monitoring may also be required.

5.4.10  Residuals
Residuals produced by overland flow systems are limited
to harvested crops.

5.5  Slow Sand Filtration

5.5.1 Technology Description
Slow sand  filters are used for both small communities
and individual homes. They consist of one or more beds
of granular  material, typically graded sand, 60 to 90 cm
(2 to 3 ft) deep, underlain with collection drains imbedded
in gravel. Pretreated wastewater is intermittently applied
                                 to the surface of the sand bed and allowed to percolate
                                 through the bed where  it receives treatment. The filter
                                 media  remains unsaturated and is vented to the atmos-
                                 phere,  such that an aerobic environment is maintained in
                                 the filter. The percolate is usually collected by the under-
                                 drains, which  remove it from the filter for further treat-
                                 ment or disposal.

                                 Three  types of slow sand filters  are commonly  used.
                                 They include buried, open, and recirculating configura-
                                 tions (Figure 5-4). While all three are somewhat similar in
                                 design, they may differ in method of operation, perform-
                                 ance, access, and filter media specifications.
                            Distribution Box
                                             Inspection/Disinfection Tank •
                                                   (if required)

                                             (a) Buried (Single-Pass) Sand Filter
                              Vent Pipes
                  Splash Plate
                   Pea Gravel

                                              Insulated Cover
                                                (if required)
                                             Distribution Pipe
                                               Collection Pipe
Graded Gravel —/    >—
1/4 to 1-1/2 in.
                  (b) Open (Intermittent) Sand Filter
Perforated or Open Joint
                   Raw Waste
                          Sump Pump

                                          (c) Basic Recirculating Sand Filter
                                                                       Sand Filter
Figure 5-4. Schematics of Slow Sand Filters.

-------   Buried Sand Filters
Buried sand filters are single-pass filters constructed be-
low grade in an excavation lined with an impermeable
membrane and covered with backfill  material.  Distribu-
tion piping is imbedded in gravel or crushed rock placed
on top of the filter media. A geotextile  fabric over the top
of the gravel prevents the backfill material  from piping
into the filter. To  provide venting of  the filter, the up-
stream ends of the underdrains are extended vertically
above grade. The distribution piping  may also be ex-
tended above grade for venting. These systems have been
used primarily for individual home wastewatertreatment.  Open or Intermittent Sand Filters
Open sand filters are single-pass (intermittent) filters ex-
posed to the surface  to  allow inspection and  periodic
maintenance of  the infiltrative surface.  Wastewater  is
usually distributed over the surface by flooding. The fil-
ters are typically exposed, although  removable covers
may be used depending on climatic conditions.  Recirculating Sand Filters
Recirculating sand filters are  open sand filters designed
to recirculate the  filtrate. The recirculation tank  receives
pretreated wastewater and a portion of the  filtrate. The
pump, which is engaged by a submersible  pump  oper-
ated by a timer, regularly doses the filter with the mixture
of the pretreated wastewater and return filtrate. Modifica-
tions to recirculating filters that provide substantial nitro-
gen removal have been successfully applied (Lamb  et
al., 1990;  Piluk and Hao, 1989;  Sandy et al., 1988).

The mechanism of treatment is a  combination of bio-
chemical and physical filtration and chemical adsorption.
Slow sand filters operate as aerobic, fixed-film biological
reactors capable of producing a high-quality effluent con-
sistently. The treatment process is very stable  and reli-
able, but dependent on temperature. It is able to accept
variations in  hydraulic  and organic loading with little  ef-
fect on effluent quality.

Performance will vary with the media used, temperature,
hydraulic and organic loadings, and method of operation
(EPA, 1985; Oregon DEQ, 1982). Recirculating  sand fil-
ters typically provide a  high-quality effluent similar to sin-
gle-pass  (open) filters. Typically effluent BODs and SS
concentrations below 10 mg/L are achieved. The effluent
is very low  in turbidity. Nearly complete nitrification  is
also achieved by  all filters except in cold-temperature
conditions. Denitrification has  been shown to occur in  re-
circulating filters; varying with modifications in design and
operation, removals of 50 percent or more of the applied
nitrogen may be achieved. Phosphorus may be removed
initially through chemical adsorption on the media grains,
but removals decline with time as the adsorption  capacity
Is reached. Fecal coliform removal accomplished with  re-
circulating filters is less efficient than  single-pass filters,
but removal of two to three logs is commonly achieved.
5.5.2  Applicability and Status
Sand filters are a proven method for providing advanced
secondary wastewater treatment. They have been used
for  treatment  of  municipal  wastewater  since the  late
1800s. They are well suited to rural communities, small
clusters of homes,  individual residences, and business
establishments. The life  cycle costs are lower than for
extended aeration package  plants for small community
treatment. Their use  is limited by land availability  and
capital cost, but they are easy to operate, requiring  per-
sonnel with a minimum of skills.

5.5.3  Advantages
Sand filters are  moderately inexpensive to construct,
have low energy requirements, and do not require highly
skilled personnel  to operate. They produce high-quality
effluents,  significantly  better than those produced by
extended-aeration  package  plants   or  stabilization
lagoons. The treatment process  is extremely stable, re-
quiring  limited  intervention  by  operating personnel.
Through modular design, treatment capacity can easily
be expanded.

5.5.4  Disadvantages
Sand filters require somewhat more land area than pack-
age plants, but their land  requirements are lower than for
lagoons. The amount of head required by the filters typi-
cally exceeds  1 m  (3.25 ft), possibly requiring pumping
for  effluent disposal where available land relief is insuffi-
cient. Odors from open, single-pass filters treating pri-
mary or septic/lmhoff tank effluent do  occur  and  may
require buffer zones from inhabited areas. Suitable filter
media may not be available locally.

5.5.5  Design Criteria  Preapplication Treatment
The minimum  of primary treatment of wastewater is re-
quired before  application to sand filters. Either septic
tanks or Imhoff tanks are commonly used. Higher levels
of treatment can  reduce  filter size requirements  or  pro-
long filter  life,  but such cost savings  must be weighed
against the increased costs of pretreatment. For larger
flows, stabilization ponds may be used (see Section 5.3).  Media Characteristics and Depth
Filter media are described by the effective size  (Dio or
particle diameter with 10 percent of grains by weight or
smaller) and uniformity  coefficient  (Deo/Dio)  or some
other measure of the grain size  range. The smaller the
effective size, the higher the  level of treatment, the lower
the hydraulic loading, and the more frequent the need for
maintenence.  The  lower the uniformity coefficient, the
longer the filter's life span. In practice, effective sizes are
0.10 to 1.5 mm, but the requirements differ for each type.
Uniformity coefficients are typically less than 4.0.
Sand is the most  commonly used media, but anthracite,
garnet, mineral tailings, and bottom ash have been used.
Alternative media  must  be  durable  and insoluble in

water. The media used should have a total organic con-
tent of less than 1 percent, total acid soluble matter of
less than 3 percent, a hardness greater than 3 on the
Moh's scale, and be generally round in shape.
Media depths commonly used are 0.6 to 0.9 m (2 to 3 ft).
Deeper beds tend to provide more complete treatment
and more constant effluent quality. Greater depths are
suggested where the media have smaller effective sizes,
because the smaller media retains more moisture, which
reduces  aeration  of  the  media  necessary for  effective
biochemical activity.   Loading Rates
Hydraulic loading rates vary with the characteristics of
the media, the type of filter design, and the wastewater
strength.  Rates are typically 3 to 40 cm/d (0.75 to 10
gpd/sq  ft). Buried filters  usually have the lowest hy-
draulic  loadings, while  recirculating  filters have the
highest (Table  5-3). Higher rates generally reduce the
effluent quality and increase the frequency  of mainte-
nance  for a given media  and  filter  design.  Organic
loading rates have  not  been  widely used  in  current

Table 5-3. Design Criteria—Slow Sand Filters3
Design Factor
Media specifications
Effective size (mm)
Uniformity coefficient
Depth (m)
Hydraulic loading

Dosing frequency

Recirculation ratio
k XimTrvti

0.7-1 .00


Open Recirculating
im of ^rvHimr>ntTt'inn

0.40-1.00 1.0-1.50
<4.0 <4.0
0.60-0.90 0.60-0.90
5-10 12-20
1-4/d 5-10min/
30 min
NA 3:1-5:1
aEPA, 1985.
NA = not applicable  Wastewater Application
The manner in which wastewater is applied to the sur-
face is critical to performance. Doses of wastewater must
be applied uniformly to the filter surface at sufficient inter-
vals for the wastewater to infiltrate completely. This al-
lows ample aeration of the filter media to effect aerobic
treatment. Distribution methods commonly used involve
surface flooding, spray nozzles, and interlaced pipe later-
als (gravity and pressure).

Dosing frequencies are related to the type of filter, me-
dia size, and wastewater strength. Smaller, more fre-
quent  doses  are  preferred  for  coarse  media to
increase residence time in the media. Typical dosing
frequencies  for intermittant filters range from 1 to 4
times daily. Recirculating filters are dosed for 5 to 10
minutes every half hour.
Multiple sand filters are suggested to provide standby ca-
pacity and allow filter loading and  resting cycles. Typi-
cally, two or four cells are provided.

Dosing tanks are sized for the maximum size dose to be
used. The dosing tank for recirculating filters must be sized
for at least five times the forward-flow dose volume.

5.5.6    Capital Cost Sensitivity
Filter media availability will have the most significant im-
pact on construction costs. Other associated costs that
may be significant  relate to land, earthwork, pretreatment,
and transmission of wastewater to the treatment site.

5.5.7    O&M Requirements
Slow sand filters require relatively little operational control
or maintenance. Primary O&M tasks include filter surface
maintenance, dosing equipment servicing, and influent
and effluent monitoring. With  continued use, sand filter
surfaces will become clogged with organic biomass and
solids.  Once operating  infiltration rates fall below the hy-
draulic loading rate,  permanent ponding of the filter sur-
face will occur indicating that the filter should be taken
off-line for "resting" and surface tilling  or removal. Buried
filters are designed to  operate without maintenance for
their design life. Filters exposed to sunlight may develop
algae mats, which may require control by shading the
surface. For community systems, disinfection will be re-
quired  prior to discharge, but disinfectant quantity re-
quirements are low due to their high  quality.

5.5.8    Construction Issues
Filter media placement  and underdrain construction are
the most critical construction issues.  The filter media is
usually placed in lifts. Filter performance is best when the
filter media is homogeneous. The  surface of the filter
must be graded carefully to ensure  uniform treatment.
The underdrains must  also be sufficiently sloped to en-
sure adequate drainage.

5.5.9    Monitoring
Monitoring requirements cover wastewater volumes and
quality applied to each filter, dosing frequencies, and sur-
face infiltration  rates. All discharge permit requirements
must also be met.

5.5.10   Residuals
Small quantities of  residuals are  usually produced. In
most intermittent  sand filtration facilities,  sand must be
periodically removed from the surface as a method of fil-
ter rejuvenation. The sand  may be stockpiled onsite and
later washed and reused, or landfilled. Other filters gen-
erally do not generate solids in quantities sufficient to re-
quire utilization of  a  disposal method, except at the end
of their service lives.

 5.6  Slow Rate Land Application

 5.6.1   Technology Description
 Slow rate land application  is a soil-based wastewater
 treatment  method  designed  to   apply  intermittently
 unchlorinated primary or secondary treatment effluent at
 a controlled rate to a vegetated soil surface of moderate
 to slow permeability (Rgure 5-5). The wastewater is ap-
 plied via sprinklers or flooding of furrows. Following appli-
 cation,  the  wastewater infiltrates the land surface  and
 percolates through the soil profile to the ground-water ta-
ble. A tailwater return system is usually provided to con-
tain and recycle wastewater runoff from the site due to
excessive application or precipitation. It consists of a col-
lection pond, pump, and return pipeline. A storage reser-
voir must also be provided for adverse weather conditions,
crop cultivation and harvesting, and emergencies.

The relatively low application  rates on natural vegetated
soil surfaces provide the potential for slow rate systems
to produce the highest treatment levels of the land appli-
cation methods. Wastewater constituents are removed in
the soil matrix by filtration, adsorption, ion exchange, pre-

                                       (a) Application Pathway
 GW Mound
                                       (b) Subsurface Pathway

Flgum 5-5. Schematic of a Slow Rate Land Application System.

cipitation, microbial  action, and  plant uptake (WPCF,
1990). Part of the water is lost to evaporation and plant
transpiration. Organics  are removed by  soil adsorption
and biochemical oxidation. Nitrogen is removed primarily
by crop uptake, but denitrification  can also be significant.
Chemical immobilization  and plant uptake are mechanisms
of phosphorus removal. Metals, certain toxic organics, and
pathogens are also effectively removed. Typical treatment
performance data are presented in Table 5-4.

Table 5-4. Typical  Slow  Rate  Land Application
Treatment Performance3


(kg/ha xd)
Removal Comments
 0.3-2.4    65-95
 Phosphorus     0.1-3.0    75-99
Percolate typically <1
Removal efficiency
depends on crop and
crop management
Plant uptake accounts
for approximately 25
Limited data suggest
effective removals are
provided for volatile
and biodegradable
Nearly complete
 aEPA, 1981; WPCF, 1990.
 NA = not applicable

Vegetation is an important component that serves to ex-
tract nutrients, control erosion, and  maintain soil perme-
ability. It should be selected and  managed according to
the site conditions and treatment objectives.

Either cultivated or forested sites are used. In cold cli-
mates, wastewater storage is required during most of the
nongrowing seasons; however, year-round application is
often employed on forested sites.

5.6.2   Applicability and Status
Slow rate land application for wastewater treatment is a
proven  technology  for  municipal  and  other  organic
wastewaters. Used for over one  hundred years, it has
evolved from  a "disposal" method  to one that  can be
used to recycle wastewater  onto agricultural crops, for-
ests, or park lands. Its use is limited primarily by  land
suitability, climate, and land costs.

5.6.3   Advantages
Slow rate land application is well  suited for treatment of
wastewater from rural communities  and seasonal indus-
tries such as vegetable canning.  It  can provide an  eco-
nomic  return from the reuse of water and nutrients for
irrigation of landscaped areas or production of market-
able,  commercially processed crops.  It also provides
ground-water  recharge. Of the various  land  treatment
methods, slow rate land application is the least limited by
surface slopes.

5.6.4  Disadvantages
Because of the vegetation component, slow rate land ap-
plication  is limited by climate and nutrient requirements
of the vegetation. Climate affects the growing  season
and will  dictate the period of wastewater application and
storage  requirements.  Crop  water  tolerances,  nutrient
requirements,  and nitrogen  removal  capacity  of the
vegetation-soil complex limit the  hydraulic loading  rate.
Application must be suspended during wet periods or frozen
soil  conditions. Because of the limits on the hydraulic
loading rate, the  area  of land necessary is significantly
larger than for other land application methods.

5.6.5  Design Criteria  Site Selection
Important  site-selection criteria  include  soil  charac-
teristics,  ground-water conditions, and topography. Soil
characteristics are important for wastewater  treatment
and crop management. Generally,  loamy soils (loamy
sands to clay loams) are  best  suited for slow rate land
application systems. Finer texture  soils  (clays) do not
drain well, retaining water for long periods, which makes
crop  management more  difficult. Coarse texture soils
(sands) can accept higher application rates and do not
retain water, which may be important where crops with
low  moisture tolerance are used. In addition to  texture,
unsaturated depth of  the  soil is important.  Adequate
depth must be provided for root development and waste-
water treatment. An unsaturated depth greater than 1.0  m
(3.3 ft) to the top of any ground-water mound is usually
necessary. Greater depths may be necessary for deep-
rooted crops.  In some cases, subsurface drainage can
be   provided  where  shallow  ground   water  occurs.
Ground-water mound height  analysis is  usually neces-
sary to determine if the required  unsaturated depth can
be maintained during system operation.

Slope, relief, and susceptibility to flooding are important
topographic features to consider.  Where crop cultivation
is to be practiced, slopes greater than 15 percent should
be avoided. Uncultivated crops, such as pasture, can be
irrigated on slopes of 15 to 20 percent. Woodlands have
been irrigated successfully with sprinklers on  slopes  of
up to 40 percent.  Site relief, or the differences in  surface
elevations across the site, is  an important consideration
for wastewater distribution to the  points of irrigation and
wastewater  ponding in depressions. Flood-prone areas
should be avoided unless the land application system is de-
signed to be an integral part of the flood management plan.

Land area requirements range from 25 to 220 ha (60 to
550  ac) for treatment  of 3,780 m3/d (1  mgd). Land for
pretreatment facilities,  storage,  roads, and buffer zones
is additional.

-------  Crop Selection
 Important criteria for crop selection are climate, soil char-
 acteristics,  wastewater  characteristics  and application
 rate, and available management skill, labor, and  equip-
 ment. On sites where wastewater treatment rather than
 crop water requirements  are the objective, the vegetation
 selected should have high nitrogen uptake capacity, high
 consumptive use  or evapotranspiration potential, high
 soil-moisture tolerance,  low sensitivity  to  wastewater
 constituents, and  minimum management requirements.
 Crops meeting these requirements include various per-
 ennial forage grasses, turf grasses, some tree species,
 and some field crops. These include reed canary grass,
 tall fescue,  Bermuda grass, perennial rye grass,  Italian
 rye  grass,  and orchard grass.  Mixed  hardwoods and
 pines are the most common tree crops for systems with
 higher application rates. Where the  wastewater is  for
 crop irrigation, the crops listed above  may be grown, as
 well as other crops such as legumes, cotton, soybeans,
 safflower, grains, and some fruit crops  including  citrus,
 apples, and grapes. Crop selection guidance can be ob-
 tained from local agricultural extension agents and avail-
 able texts (CSWRCB, 1984; EPA, 1981; WPCF, 1990).  Preapplication Treatment
 The degree of  pretreatment required for slow  rate land
 application is dependent  on public health considerations,
 nuisance control, soil and  crop considerations, nitrogen
 concentration, and distribution method.  In general, primary
 treatment is acceptable for isolated, restricted-access sites
 where the crops are not intended for human consumption.
 State requirements vary  for controlled agriculture irriga-
 tion for various crops, for turf irrigation in parks, and  on
 golf courses. Where nitrogen loading is critical  or  where
 other wastewater  constituents can affect plant growth,
 additional pretreatment may be required.  Hydraulic Loading Rate
 The design  hydraulic loading rate is controlled by either
 the hydraulic conductivity of the soil, nitrogen loading, or
 the water requirement of the crop. Local rates of precipi-
 tation and evapotranspiration potential of the crop must
 also be considered. The  maximum daily application rate
 must not exceed the  soil percolation rate. Typically, the
 maximum application rate used is  2 to 4 percent  of the
 saturated hydraulic conductivity  of the least permeable
 soil  horizon within 2.4 m (8 ft) of the  surface.  This rate
 must be adjusted for precipitation and evapotranspiration
 during the application period. Where  nitrogen  contribu-
 tions to the ground water must be controlled, the nitrogen
 mass loading will control  the hydraulic  loading rate. Crop
 requirements for water or tolerances to  salinity or other
 wastewater constituents may also be a controlling factor.
 Methods  for estimating the  design hydraulic loading rate
 may be found elsewhere (EPA, 1981; WPCF, 1990).

 The application period must also be determined. Applica-
tions cannot be made during very wet  periods, during
freezing weather, or during  crop harvesting  activities.
These periods must be estimated to determine the total
land area requirements.   Wastewater Distribution
Common methods of  wastewater  distribution used in
slow  rate land application systems include  sprinkling,
flooding, and drip irrigation. Sprinkling is the most com-
mon method because is can be adapted to a wide range
of soil and topographic conditions and is suited to a vari-
ety of crops. Either fixed, portable, center  pivot, or trav-
eling gun systems are used. Flooding of furrows or other
bermed areas is  used where it is compatible with con-
ventional agricultural irrigation practices. Drip irrigation
requires that the applied wastewater have a high level of
pretreatment and be low in iron, hydrogen sulfide, and to-
tal  bacteria  to prevent emitter clogging. Therefore,  this
method is restricted to systems where the resource value
of the wastewater is high. Guidance for distribution sys-
tem design can be found elsewhere  (EPA,  1981; WPCF,
1990;  Booher, 1974; Hart, 1975; SCS, 1983; Irrigation
Association, 1983).  Storage Requirements
Storage of wastewater must be provided during periods
when applications cannot be made.  A water balance for
each  month of operation should  be  calculated to estab-
lish these requirements (EPA, 1981).

5.6.6    Capital Cost Sensitivity
Land, earthwork,  distribution system, and storage facili-
ties are the  most significant capital costs. The land area
required is dependent on the nature  of the irrigated crop,
soil characteristics, and acceptable  application periods.
Distribution costs can be affected by the type of system
selected and site  topography. In cold, wet climates, stor-
age requirements can be significant. Other costs that
should  be  considered  are  underdrain  installation, if
needed, transmission of wastewater to the treatment site,
and pretreatment.

5.6.7    O&M Requirements
The primary O&M requirements of slow rate land appli-
cation systems are crop management and servicing of
the distribution  tailwater return  systems. Agricultural
crops require the  most intensive management, while for-
est application requires the least  management. Manage-
ment   tasks  may  include  soil  tillage, planting  and
harvesting of crops, nutrient control,  pH adjustment, tail-
water return  system maintenence, and sodium and salin-
ity control (EPA, 1981). No special equipment other than
the appropriate agricultural equipment is required. Costs
of operation are  associated primarily with  labor costs.
Other costs  include power for wastewater pumping and
equipment depreciation.  Total labor requirements,  ex-
cluding maintenance of the pretreatment works, are esti-
mated to be approximately 15 to 20 cents/1,000 gal of
applied water.

5.6.8  Construction Issues
Construction factors include site preparation and installa-
tion of runoff controls, irrigation piping, a tailwater sys-
tem,  return  systems,  and  storage  facilities.  Since
sustained wastewater infiltration is an important compo-
nent of successful system operation, it is critical that con-
struction  activity be limited on the application site. Where
storm-water runoff can be  significant, measures must be
taken to prevent excessive erosion including terracing of
steep slopes, contour plowing, no-till farming, and the es-
tablishment of grass border strips and installation of sedi-
ment control basins.

5.6.9  Monitoring
Monitoring requirements may cover volumes,  rates, fre-
quencies,  and  patterns  of  wastewater   applications,
ground-water quality  and elevations, soil  fertility, and
plant tissue. Ground-water monitoring may be  required
by the local regulatory agency  to evaluate system per-
formance. Soil fertility should be evaluated periodically to
determine if soil amendments are necessary. Trace ele-
ments should also be analyzed  to avoid toxic accumula-
tions. Plant tissue analysis is used to determine whether
there are deficient or toxic levels of elements.

5.6.10 Residuals
Residuals produced  by slow rate land application sys-
tems are limited to harvested crops and crop residues.

5.7  Subsurface Infiltration

5.7.1  Technology Description
Subsurface wastewater infiltration systems  (SWISs) are
subgrade land  application systems. The soil  infiltration
surfaces  are exposed in buried excavations that are gen-
erally filled with porous media. The media maintains the
structure of the excavation, allows the free flow of pre-
treated wastewater over the infiltrative surfaces, and pro-
vides storage of wastewater  during  peak flows. The
wastewater enters the soil where treatment is provided
by filtration, adsorption, and biochemical reactions. Ulti-
mately, the treated wastewater enters and flows with the
local ground water.

Various SWIS designs have been developed for use de-
pending on the site and soil conditions encountered. The
designs differ primarily in where the  infiltrative surface is
placed (Figure 5-6). The surface may be exposed within
the natural soil  profile (conventional) or at  or above the
surface of the natural soil (at-grade on mound systems).
The elevation of the infiltrative surface is critical because
of the need to provide an adequate depth of unsatu rated
soil between ,the infiltrative surface and a limiting condi-
tion (i.e.,  bedrock or ground water).

The geometry of the infiltrative surface also varies. Long,
narrow infiltrative surfaces  (trenches) are preferred. Wide
infiltrative surfaces (beds)  and deep infiltrative surfaces
(pits and deep trenches) do  not perform as well, even
though they require less area.
Subsurface infiltration systems are capable of high levels
of treatment for most domestic wastewater pollutants of
concern (Table 5-5). Under suitable site conditions, re-
moval of biodegradable organics, SS, phosphorus, heavy
metals, and virus and fecal indicators is nearly complete.
The fate of toxic organics and metals has  not been as
well documented, but limited  studies suggest that many
of these constituents do not travel far from the system.
Nitrogen is the most significant wastewater parameter
that is not readily removed by the soil. Nitrate concentra-
tions above the drinking water standard of 10 mg-N/L are
commonly found in ground water below SWISs.

Table 5-5. Typical  Subsurface  Wastewater Infiltration
System Treatment Performance	
Parameter      Applied   Removal  References
           Concentration   (%)
BOD5         130-150     90-98  Siegristetal., 1986
                                  Univ. Wis., 1978
Nitrogen         45-55     10-40  Reneau, 1977
                                  Sikora & Corey, 1976
Phosphorus       8-12     85-95  Sikora & Corey, 1976
                                  Tofflemire & Chen,
Fecal               NA  99-99.99+  Gerbaetal., 1975
coliforms                          Univ. Wis., 1978

NA = not applicable

5.7.2  Applicability and Status
Subsurface infiltration systems are well suited for treat-
ment of small wastewater flows.  Small SWISs, com-
monly called  septic tank systems, are traditionally used
in unsewered areas by individual residences, commercial
establishments, mobile home parks, and campgrounds.
Since the late 1970s, larger SWISs have been increas-
ingly used  by clusters of homes  and small communities
where wastewater flows are  less than 1.1  L/s (25,000
gpd). They are a proven technology, but require specific-
site  conditions to be successfully implemented. SWISs
are often preferred over mechanical treatment facilities
because of their consistent performance with few O&M
requirements, lower  life cycle costs, and less aesthetic
impact on the community.

5.7.3  Advantages
Because subsurface  infiltration systems are buried, they
are ideally suited for decentralized treatment of wastewa-
ter. For rural  homes  and  business establishments,  they
are often the only method of wastewater treatment avail-
able. Some communities choose subsurface infiltration
systems to avoid costly sewer construction. Where indi-
vidual lots  are not  suited for their construction, suitable
remote sites may be used to cluster  homes onto a single
SWIS, thereby limiting the extent  of sewers. Alterna-

           (a) Conventional SWIS
                                                             t---.-A         Jw£8fe>-<&--
              >T-** -?•=' •45V£:^VAf?:Kf ;w:f?£?^/-J:V^;v-;".:':
                       «•"-**"   "••*•''*   * "
(b) At-Grade SWIS

            Barrier Material
       Sand Fill

           3sa?lr==P"l^g.'  -^sg^sr. _Rgck Strata oxlmpemTeable^Soil Layer S-=
           (c) Mound SWIS
Figure 5-6. Schematics of Subsurface Wastewater Infiltration Systems (SWISs).

tively,  wastewater from  entire  communities may  be
treated by an SWIS. Because the system is buried, the
land area can be used as green space or park land. In
addition, SWISs provide ground-water recharge.

5.7.4   Disadvantages
Use of SWISs are limited by site and soil conditions. Be-
cause  the infiltrative surface is buried, it can be managed
only by taking it out of service every 6 to 12 months to
"rest."  This  requires that standby cells  be constructed
with alternating loading cycles. Therefore larger SWISs
are usually  restricted to well-drained sandy  soils to re-
duce land area requirements. Because nitrogen is not re-
moved effectively  by  SWIS, pretreatment  to remove
nitrogen  may be necessary to prevent nitrate contamina-
tion above the drinking water standards in the underlying
ground water.

5.7.5   Design Criteria  Site Selection
Site selection is based on the treatment capacity of the
soils and the availability of sufficient land area of suitable
topography. The treatment capacity of the soil depends
primarily on texture, structure,  and unsaturated thick-
ness. No soil type provides optimum conditions for the
removal  of all wastewater constituents. Fine-texture soil,
such as  silt loams and clay loams, provides particularly
favorable removal of conventional constituents. However,
fine-texture soil has a relatively low hydraulic conductivity
and  reaeration rate. Therefore the hydraulic loading and
infiltration basin rest cycle will control system sizing, and
a large land area may be required. Coarse soil, such as

Table 5-6. Typical Site Criteria for a Large SWIS3
                               sand, has a higher hydraulic conductivity and reaeration
                               rate to allow higher hydraulic  and organic loading and
                               shorter cycles for basin "resting," which can reduce the
                               required  land area. However, coarse soil can be a less
                               effective  physical filter, have a lower cation exchange ca-
                               pacity, and allow  more rapid percolation of wastewater
                               through the vadose zone where  most treatment occurs.
                               Thus the treatment objectives may control system de-
                               sign. For large SWISs serving clusters of homes or com-
                               munities  (Table 5-6), sites with sand to sandy loam soils
                               are typically selected. Site selection for individual home
                               SWISs are regulated by local onsite system codes, which
                               should be consulted before site investigations are made.

                               Unsaturated depth of  soil  is another critical site-selection
                               criterion.  A minimum of 1.5 to 2.5 m (5 to 8 ft) of unsatu-
                               rated soil with relatively uniform hydraulic conductivity is
                               necessary below the  ground surface to provide neces-
                               sary treatment.  For large SWISs, ground-water mound
                               height analysis  must  be  performed to determine if the
                               separation distance can be maintained during system op-
                               eration.  If the  desired  separation distance cannot be
                               maintained, the hydraulic loading can  be reduced. For
                               large SWISs, the system should be located along a con-
                               tour perpendicular to the ground-water gradient. Basin
                               spacing can be increased or ground-water drainage pro-
                               vided in areas where limiting conditions place restrictions
                               on conventional designs.

                               Topography should also  be considered in site selection.
                               Depressions, footslopes,  concave slopes,  flood plains,
                               and other areas that exhibit poor  surface and subsurface
                               drainage should  be avoided. Mild planar slopes,  ridge
                               lines, and shoulder slopes are best suited for an SWIS.
 Landscape position

Soil Characteristics

 Bulk density


 Depth to phreatic
 Flow boundaries
Typical Application

Ridge lines, hill tops, shoulder slopes
Planar, mildly undulating, slopes
< 12 percent

Sands, sandy loams
Granular, blocky
<20 percent expansive (2:1) clays
Moderate, rapid

Slight to moderate resistance to
Moderately well, well, somewhat poorly

>1.5 m (4.5 ft)

Near discharge point
Applications to Avoid

Depressions, footslopes, concave slopes, flood plains
Complex slopes, slopes >18 percent
Clay loams, clays
Platy, prismatic, columnar
>20 percent (2:1) clays
Very rapid, moderately slow to very slow,
hydraulically restrictive horizons
Moderate to strong resistance to penetrometer

Extremely well, very poorly, excessively well drained
<1.5 m (4.5 ft), sole source aquifers

Near no-flow boundary
aSWISs serving individual homes are adaptable to a broader range of soil and site conditions. Local codes should be consulted.

-------   Hydraulic Loading Rate
The design hydraulic loading rate is determined by soil
characteristics, ground-water  mounding  potential,  and
applied  wastewater  quality. Clogging of the infiltrative
surface  will occur in response to prolonged wastewater
loading, which will reduce the  capacity of the soil to ac-
cept the wastewater. However, if the loading is control-
led,  biological  activity  at the  infiltrative  surface will
maintain waste accumulations in relative equilibrium so
that reasonable infiltration rates can be sustained.
Selection of the design hydraulic loading rate must con-
sider both soil and system design factors. Typically, de-
sign rates for larger SWISs are based on detailed soil
analyses and experience,  rather than measured hydrau-
lic conductivities. Commonly used loading  rates are pre-
sented  in Table 5-7; however,  these  rates  should be
adjusted up or down depending on the specific site con-
ditions,  design concept, and applied wastewater quality
(WPCF, 1990).   Wastewater Pretreatment
The minimum of primary treatment is required of waste-
water before application to an SWIS. Septic tanks are
commonly used for smaller sources and Imhoff tanks for
larger ones. Higher levels of treatment can reduce SWIS
size or  prolong system life, but this must be weighed
against  the increased costs of pretreatment and potential
damage from poor maintenance of the system. Where
pretreatment  is desirable,  aerobic  biological treatment
processes are generally used.   Design Concept
SWIS designs should be adapted to the specific site and
soil conditions and wastewater characteristics. The initial

Table 5-7. Typical Hydraulic Loading Rates on Horizontal
Soil Infiltrative Surfaces Treating Domestic Septic Tank
Soil Texture
Gravel, very coarse sand
Coarse to medium sand
Fine sand, loamy sand
Sandy loam, porous loam
Loam, silt loam
  (moderate to strong blocky structure)
Clay loam
  (moderate to strong blocky structure)
Clay loams and clays with appreciable
shrink-swell potential or weak,
columnar, or prismatic structure
Hydraulic Initiative
Surface Hydraulic
Loading Rate
  Not recommended


  Not recommended
"Adjustments to these rates may be necessary for specific
applications to account for other soil factors and design
concepts. See WPCF, 1990.
"Conversion: 1 cm/d = 0.24 gal/ft2 d
design concept should strive to include the following
•  Narrow trenches, 0.2 to 1.0 m (0.5 to 3.0 ft) wide, ex-
   cavated parallel to surface or ground-water piezometric
   surface contours (based on analysis  or ground-water
   mounding potential) with level bottom surfaces

•  Shallow placement  of  the infiltrative surfaces, less
   than or equal to 0.6 m (2 ft) below final grade

•  Pretreatment  capability to  remove  organics,  sus-
   pended solids, grease, oils, etc. to concentrations less
   than or equal to typical domestic septic tank effluent

•  Uniform dosing of infiltrative surfaces one to four times
•  Multiple cells (3 to 4 minimum) to  allow annual or
   semiannual resting  and standby capacity  for opera-
   tional flexibility

•  Devices for monitoring daily wastewater flows, infiltra-
   tive surface ponding, and ground-water elevations
Modifications to this design concept are usually required
if  site limitations  cannot be  removed.  Guidelines for
adapting SWISs to common site limitations encountered
are presented elsewhere (Converse & Tyler, 1990; Con-
verse et al.,  1989;  EPA,  1980; Siegrist et al.,  1986;
WPCF, 1990).

5.7.6  Capital Cost Sensitivity
Land and  earthwork  are the  most  significant capital
costs. Where select fill must be used to bed the primary
infiltrative surface, the cost of transporting the material
also becomes significant. Other costs that should be con-
sidered  are pretreatment costs and transmission of the
wastewater to the treatment site.

5.7.7  O&M Requirements
A well-designed SWIS requires limited  operator attention.
Management functions primarily involve tracking system
status, testing for solids accumulation, evaluating pump
performance, and monitoring system controls. Monitoring
performance of pretreatment units, mechanical compo-
nents, and wastewater ponding levels above the filtration
surface are essential. If a change in status is noted, op-
erator intervention may be required. Routine servicing of
SWIS may be limited to annual or semiannual alternating
of the infiltration cells.

5.7.8  Construction Issues
A frequent cause of early SWIS failure is poor construc-
tion. If the soil structure is damaged during construction,
the system may not be able to accept the design hydrau-
lic loading rates.  To avoid damage, a construction plan
should be  developed that addresses the type of con-
struction equipment, construction  procedures,  site ac-
cess, site preparation, and existing soil conditions (Univ.
Wis., 1978; WPCF, 1990). Compaction of the infiltrative
surface  should be avoided by using proper procedures

and low load-bearing construction equipment. After exca-
vating to grade, the infiltrative surface should be carefully
scarified. Construction should not proceed if the soil mois-
ture is near the plastic limit or frozen conditions exist.

5.7.9    Monitoring
Monitoring requirements cover applied wastewater flows
and quality, ponding levels above the infiltrative surfaces,
ground-water elevations below the system, and, if appro-
priate,  ground-water quality. Flows should be recorded
daily.  Ponding levels  should  be measured biweekly or
monthly. Water quality  measurements  should be  per-
formed at least quarterly.

5.7.10   Residuals
No residuals are produced from subsurface  infiltration
systems. In an individual home SWIS (septic tank  sys-
tems),  where the septic tank is considered an integral
part of the system, septage is generated within the tank.
Septage should be removed  every three to five years.
The septage is typically treated  at a municipal treatment
plant or is land spread (EPA, 1984).

5.8   Pressure Sewers

5.8.1    Technology Description
Pressure sewer systems generally use smaller pipe di-
ameters than conventional sewers and are operated with
pumping instead of gravity. In less populated  areas  they
usually result in lower construction costs relative to  con-
ventional sewer systems. Pressure sewers are consider-
ably independent  of  slope,  and  systems  have been
developed and applied to reduce the high capital cost of
sewer  systems that have been  designed in accordance
with accepted design parameters, namely slope and ve-
locity. Pressure sewer systems involve a number of pres-
surizing inlet points and an outlet to a treatment facility  or to
a downstream gravity sewer, depending on the application.

The two major types of pressure sewer systems are the
grinder pump (GP) system and the septic tank effluent
pump (STEP) system. The major difference between the
two systems is in the onsite equipment and layout.  Nei-
ther pressure sewer system alternative requires  any
modification of household plumbing.

In both designs household wastes are collected  in the
sanitary sewer and conveyed by gravity to the pressuri-
zation facility. The onlot discharge piping arrangement in-
cludes at least one check valve and one gate valve to
permit isolation of each pressurization  system from the
main sewer. GPs can be installed in the basement  of a
home  to provide easier access for maintenance  and
greater protection from vandalism.

A GP pressure sewer has a pump at each service  con-
nection. The pumps are 0.75 kW (1 hp) or more, require
110V or 220V, and  are equipped with a grinding mecha-
nism that macerates the solids. The head provided by
the pumps are typically about 15 to 30 m (50 to 100 ft)
and flow rates vary widely. The pumps discharge into a
pressurized pipe system that terminates at a treatment
plant or a gravity collector. Because the mains are pres-
surized there is no infiltration into them; however, infiltra-
tion and inflow in the house sewers and the pump wells
can occur. In areas where the GP sewer system has re-
placed septic tank and leaching field systems, these may
be retained for  emergency overflow, but they should be
separated from the pump well  by a  gate valve that  is
opened only when necessary to accommodate emer-
gency  overflow from the GP  unit; otherwise, the septic
tank and leaching field can become sources of large vol-
umes of infiltration.

Electrical service is required at each service connection.
The pipe network typically has no closed loops. The
sewer  profile often parallels  the ground surface profile.
Horizontal  alignment can be curvilinear. Plastic pipe  is
typically used. Service connection diameters are typically
1 1/4 in. (30 mm). Cleanouts are used to provide access
for flushing. Automatic air release  valves are required  at
and slightly downstream of summits in the sewer profile.
Because of the small diameters and curvilinear horizontal
and vertical alignment, excavation depths  and volumes
are typically much  smaller for a GP pressure sewer than
for conventional sewers,  sometimes requiring only  a
chain trencher.

Centrifugal and positive displacement pumps have been
used in GP systems. Positive displacement pumps have
a discharge nearly independent of head. Although this
may simplify some design problems, it results in  some
additional operational ones. The choice is typically up  to
the design engineer's preference.

Several dwelling units or other service locations can be
clustered to a single pump well, which should have an in-
creased working volume depending on the total popula-
tion equivalent  it serves. Clustered service connections
have often led to disputes over billing and responsibility
for nuisance  conditions and service calls. Duplex pump
wells  are often used on clustered, commercial, institu-
tional, or other larger services.

A STEP pressure sewer typically has a septice tank and
a  pump at each  service  connection. The pumps dis-
charge septic tank effluent into a pressurized pipe sys-
tem that  terminates  at  a treatment  plant or a gravity
sewer. Because the mains are pressurized, there will be
no infiltration into them, but infiltration and inflow into the
house sewers and the septic/interceptor tanks should be
minimized during the construction of onlot facilities. The
volume of these tanks is usually  about 3,800 L (1,000
gal). They remove  grit, settleable solids, and grease. The
pumps typically are 0.25 to 0.37 kW (1/3 to 1/2 hp) and
require 110 to 120  V. The head provided by the pumps is
typically about 9 to 15 m (30 to 50 ft) and 1  L/s (15 gpm),
but flow rates vary widely. The working volume of the

 pump well is typically 150 to 230 L (40 to 60 gal). The
 discharge line  from the pump is equipped with at least
 one check valve and one gate valve. Electrical service is
 required at  each service connection. The pipe network
 can contain closed loops but typically does not.  The
 sewer profile typically parallels the ground surface pro-
 file, and the horizontal alignment can be curvilinear. Plas-
 tic pipe is typically used. The service lateral diameter is
 typically 11/4 in. (30 mm). Cleanouts are used to provide
 access for flushing. Automatic air release valves are re-
 quired at and slightly downstream of summits in all pres-
 sure  sewer  profiles. Because  of the small  diameters,
 curvilinear horizontal and vertical alignments,  excavation
 depths and volumes are typically much smaller for pres-
 sure sewers than for conventional sewers, sometimes re-
 quiring only a chain trencher.

 A service connection at an elevation higher than the hy-
 draulic guide line may be served by gravity, avoiding the
 need for a pump. The use of a gravity connection  in this
 situation is  advantageous  because a pump would be
 subject to siphoning and air-binding. Hybrid designs are
 common in current practice. Septic tanks  with integral
 pump vaults  are available; they reduce onlot excavation.
 Existing septic tanks are not used owing to their propen-
 sity to leak and be  a source of infiltration and inflow.

 5.8.2   Applicability and Status
 Pressure sewer systems are most cost-effective  where
 housing density is  low, where the terrain has undulations
 with relatively high relief, and where the system  outfall
 must be at a  higher elevation than most or all of the serv-
 ice area. They can also be effective where flat terrain  is
 combined with high ground  water or bedrock, making
 deep cuts and/or multiple lift stations excessively expen-
 sive. They can be cost-effective even in densely  popu-
 lated  areas  where the terrain  will not  accommodate
 gravity sewers.

 Since pressure systems do not have the large excess ca-
 pacity typical of conventional gravity sewers,  they must
 be designed with  a balanced approach keeping  future
 growth and internal hydraulic performance in mind.

 Where pressure sewers are indicated, the choice be-
 tween GP and STEP systems depends on two main fac-
 tors: First, the costs of onlot facilities will be typically over
 75 percent of the total system cost. Thus there will be a
 strong incentive to  use a system with less expensive on-
 lot facilities for  a particular project.  STEP systems may
 allow  some  gravity service connections,  thus lowering
 onlot costs. GP systems must have a pump at each serv-
 ice connection to grind the solids.

 Second, GP  systems require a higher velocity because
they carry heavy solids and grease. STEP systems will
 better tolerate the low flow conditions that occur in loca-
tions with a highly fluctuating seasonal occupancy and in
 locations with slow buildout from a relatively small initial
 population to the ultimate design population.
 GP units are preferable for use at individual homes that
 discharge  into a conventional gravity sewer at a higher
 elevation, while  STEP systems are most compatible with
 small-diameter gravity sewers.

 5.8.3   Advantages/Disadvantages
 Key advantages of pressure sewer systems include:
 • Pressure sewer systems are less expensive than con-
   ventional gravity sewerage, due to the fact that the
   cost of on-property facilities represents a major portion
   of the capital cost of the entire system. This can be-
   come an economic advantage since on-property com-
   ponents are not required until the house is constructed
   and then borne directly by  the homeowner. Low front-
   end investment makes the present-value cost of the
   entire system lower than that of conventional gravity
   sewerage, especially  in new development divisions
   where it may take many years before homes are built
   on all lots.

 • Due to the fact that the wastewater is pumped, gravity
   flow is not necessary, and the strict  alignment  and
   slope restrictions for conventional gravity sewers can
   be discarded. Network layout does not  depend  on
   ground contours: pipes can be laid in any location,
   and extensions can be  made in the street right-of-way
   at a relatively small cost without damage to existing
   structures or to the natural environment.

 • Because the pipe size and  depth requirements are re-
   duced, material and trenching costs are significantly

 • Manholes  are eliminated;   low-cost clean outs and
   valve  assemblies are  used instead and are spaced
   further apart than manholes in a conventional system.

 • Infiltration  is greatly reduced  or may even  be elimi-
   nated, resulting in reductions in pipe size.

 • The user pays for the electricity used  to operate the
   pump unit. The resulting increase in the user's elec-
   tricity bills is  small, but this small increase often re-
   places  large  bills  for  central  pumping,  which  is
   eliminated by the pressure system. In other words, the
   responsibilities for installation and paying for pumping
   are transferred from the authorities to  the users; the
   authorities are involved in pump and collection mainte-
   nance only.

• Final treatment may be substantially reduced,  both in
   hydraulic and organic loading in the case of STEP sys-
   tems. For GP systems hydraulic loadings are reduced.

• More flexibility is allowed in siting final treatment facili-
   ties, and this  may help reduce long outfall lines. The
   location can be chosen to facilitate site work.
Key disadvantages of pressure sewer systems include:

• A high level of institutional involvement is required,
  since the pressure system has many mechanical com-
  ponents located all over the area served.

• The O&M cost for a pressure system is often higher
  than that of a conventional gravity system due to the
  high number of pumps in use. However, the existence
  of lift  stations in  a  conventional gravity sewer can
  quickly reverse this situation.

• Yearly  preventive  maintenance  calls are  usually
  scheduled for onlot 'components at pressure sewers,
  and STEP systems also  require pumpout of intercep-
  tor tanks at prescribed (3 to 5 yr) intervals.

• Public education is necessary so that the user knows
  how to deal with emergencies and how to avoid block-
  ages or other emergency maintenance initiators.

• Malodors and corrosion are potential problems since
  the wastewater in the collection sewers is usually an-
  aerobic. Proper ventilation and odor control must be
  provided for in the design, and noncorrosive  compo-
  nents  should  be used. Air  release valves  are often
  vented to soil beds to minimize odor problems, and
  special discharge and treatment designs are required
  to avoid terminal discharge problems.

5.8.4 Design Criteria
A wide  variety of design flows has been used. When
positive displacement GP units are used, the design flow
is obtained by multiplying  the pump discharge by the
maximum number of  pumps expected to be operating si-
multaneously.  When centrifugal pumps  are used, the
equation used  is: Q = 20 + 0.5D, where Q is the flow in
gpm and  D is the number of equivalent  dwelling units
served. The operation of the system under various as-
sumed conditions should be simulated by computer as a
check on the adequacy of the design. No allowances for
infiltration and inflow should be required. No minimum
velocity  is generally  used  in design,  but GP systems
must attain 3-5 fps at least once per day. A Hazen-Wil-
liams coefficient  (C)  =  130 to  140 is suggested for hy-
draulic analysis.  Pressure mains generally use 5 cm (2
in.)  or larger PVC pipe (SDR 21), although at least 7.6
cm  (3 in.) pipe is preferred owing to the availability of
standard tapping equipment. Rubber-ring joints are pre-
ferred over solvent welding  due to the high coefficient of
expansion for  PVC pipe.  High-density  polyethylene
(HOPE) pipe with fused joints is widely used in Canada.
Electrical requirements, especially for GP  systems, may
necessitate rewiring and  electrical service upgrading of
dwellings  served. Pipes are generally buried to  at least
the winter frost penetration depth; in far northern sites in-
sulated and heat-traced pipes  are generally buried at a
minimal depth. GP and STEP pumps are sized to ac-
commodate the hydraulic grade requirements of the sys-
tem.  Discharge  points must employ drop  inlets  to
minimize odors  and  corrosion. Air  release valves are
placed at high points in the sewer and often are vented
to soil beds. GP effluent is generally about twice the
strength of conventional  sewer wastewater  (e.g., BOD
and TSS of 350 mg/L). STEP effluent  is, of course, pre-
treated and has a BODs of 100 to 150 mg/L and SS of 50
to 70 mg/L.  Both can be assumed to  be anaerobic and
potentially odorous if subjected to turbulence (stripping of
gases such as HaS).

5.8.5  Capital Costs
Pressure sewers are generally more cost-effective than
conventional  gravity sewers  in  rural  areas. However,
even though capital cost savings  of  90 percent have
been achieved, no universal statement of savings is pos-
sible owing to the site specificity of each system. Recent
evaluations of the actual costs of pressure sewer mains
and  appurtenances (essentially  the same for GP and
STEP) and items specific to each type  of pressure sewer
have yielded the following data: Average  installed unit
costs for pressure sewer mains and appurtenances are
presented in Table 5-8. Average unit costs for GP serv-
ices  and appurtenances are presented in Table 5-9. Av-
erage unit costs for STEP services and appurtenances
are presented in Table 5-10.

Within Table 5-8 the linear cost of mains can vary by a fac-
tor of 2 to 3, depending on the type of trenching equipment
and local costs of high-quality backfill and pipe.

5.8.6 O&M Requirements/Costs
Energy costs are borne by the homeowner. For GP sys-
tems this cost may vary from about $1.00 to $2.50/month
depending on the horsepower of the unit. For STEP units
the costs are almost always less than $1.00/month.

Preventive system  maintenance  is normally  carried out
annually for each unit with monthy maintenance of other
mechanical components. STEP systems also require pe-
riodic pumping of tanks. Total O&M costs include trou-
bleshooting,  inspection   of  new  installations,   and

Table 5-8. Average  Installed Unit  Costs for Pressure
Sewer Mains and Appurtenances (Mid-1991 )a
Item                                   Unit Cost ($)
2 in.  mains                                  7.50/LF
3 in.  mains                                  8.00/LF
4 in.  mains                                  9.00/LF
6 in.  mains                                 11.00/LF
8 in.  mains                                 14.00/LF
Extra for mains in asphalt concrete pavement      5.00/LF
2 in.  isolation valves                          250/each
3 in.  isolation valves                          275/each
4 in.  isolation valves                          350/each
6 in.  isolation valves                          400/each
8 in.  isolation valves                          575/each
Automatic air release stations                1,500/each

aEPA, 1991
LF = linear feet

 Table 5-9. Average Unit Costs for Grinder Pump Services
 and Appurtenances (Mid-1991)
 2 hp centrifugal GP
  List price
  Quantity price
 Simplex GP package
  List price with 30 in. vault
  Quantity price with 30 in. vault

 4 in. building sewer
 1.25 in. service line
 Abandon septic tank
                                      Unit Cost ($)



Table 5-10. Average Unit Costs for STEP Services and
Appurtenances (Mid-1991)
 Effluent pump list price
 Effluent pump quantity price
 Simplex factory package list price
 Quantity package price w/extemal vault
 Quantity package price w/intemal vault
 New septic tank
 Installation (retrofit of existing tank)
 Installation (with new septic tank)
 4 in. building sewer
 1.25 in. service line
 Abandon septic tank
                                    Unit Cost ($)
                                    4-8 /LF
 LF = linear feet

responses   to   problems  are  estimated   at  $100-
200/yr/un'rt. The breakdown on emergency service calls
on selected GP and STEP sewer projects are presented in
Table 5-11.

Mean time  between service calls (MTBSC) data vary
greatly,  but values of 4 to 10 yr for both GP and STEP
units are reasonable estimates for quality installations.

5.8.7    Construction Issues
It Is very important for the engineer to ensure that the
building sewer and ail onlot piping and structures are free

Table   5-11.  Distribution   of  Causes  for  Call-out
Maintenance on Selected GP and STEP Pressure Sewer
                              (% of occurrences)
                         GP Projects   STEP Projects
                            25-40          40-60
                            20-25          10-30
                            20-30          20-40
                             5-15             1-5
                             5-15            1-10
Electrically related
Pump related
Pump vault or tank related
Piping related
of infiltration and inflow (I/I) and sump pump/foundation
drain connections,  via  proper testing prior to hookup.
Proper  bedding of  PVC pipe  is also particularly  impor-
tant, and accurately prepared  "as built" plans must be
provided to the system owner,  including lot facility plans
showing the onlot component  locations. Each  section of
pipe and all tanks should be tested prior to covering with
backfill  to ensure water-tight conditions. Videotaping be-
fore and after onlot construction will  resolve most resto-
ration claims.

5.8.8   Monitoring
Detailed daily records of maintenance and annual sum-
maries should be provided. Also specific records for each
unit should be kept with the lot facility plan in order to
permit maintenance staff to evaluate potential problems
prior to  arrival at the site of the emergency call. On larger
flow sources, cycle counters may be useful to track any
trends, just as periodic line-pressure checks can alert the
O&M staff to impending needs.

5.8.9   Residuals
STEP systems incorporate septic (interceptor) tanks, and
therefore  need  periodic  pumping  to remove trapped
grease and solids. Usually this is required every 3 to 5 yr,
but some systems attempt to lengthen this pumping fre-
quency by requiring biannual inspections to avoid unnec-
essary  pumping. Heavy  grease generators, such as
commercial sources, may need to be pumped out annu-
ally or semiannually.
Owing to their tendency to accumulate grease in their
tankage, GP units are often pumped as part of the an-
nual preventive maintenance check.

5.9   Small Diameter Gravity Sewers

5.9.1   Technology Description
A small diameter gravity (SDG) sewer collects effluent
from septic tanks at each service connection and trans-
ports it by gravity to a treatment plant or a gravity sewer.
Such systems are also known as diameter effluent sew-
ers,  effluent drains, and small  bore sewers. The volume
of the septic tanks in these systems is often 1,000 gal but
varies widely. The tanks remove grit, settleable  solids,
and  grease, and they attenuate peak flows. Both the
horizontal and vertical alignments of the  pipes can be
curvilinear. The pipe network includes no closed loops.
Uphill sections can be  used provided there  is enough
elevation head upstream to maintain flow  in the desired
direction and there is no backflow into any service con-
nection. Minimum diameters are usually 10 cm (4 in.),
but smaller sizes have been used successfully. Plastic
pipe is typically used since it is economical in small sizes
and  resists  corrosion  by   the  septic  wastewater.
Cleanouts are used to provide access for flushing. Man-
holes are used  infrequently,  usually  only at the major
junctions of main lines. Air release risers may be re-

quired at or slightly downstream of extreme summits in
the sewer profile. Because of the small diameters and
flexible slope and alignment, excavation depths and vol-
umes are typically much smaller than with conventional
sewers, sometimes requiring only a chain trencher.
Two varieties of SDG systems  have been used in the
United States: variable grade and minimum grade. Vari-
able  grade systems follow surface contours  rather
strictly, taking advantage of the flexibility of horizontal
and  vertical alignment when there  is enough elevation
head to maintain flow in the desired direction and there is
no backflow into any service connection at design flow.
For minimum grade systems, minimum downward slopes
are imposed. Recent designs blend both of these ap-
proaches, allowing  variable grade but minimizing the
number of flooded sections.
Individual service connections can  be equipped with a
septic tank effluent pump (STEP) unit, creating a hybrid
of the STEP pressure sewer. The use of STEP connec-
tions is advantageous when excavation costs can be re-
duced enough to offset increased onlot  costs. Hybrid
designs are common in current practice.  Inline lift sta-
tions can also be used if required by the terrain, but their
use may signal a need to reevaluate the cost-effectiveness
of an SDG system vs. other alternative sewer systems. Use
of hybrid systems should be considered before evaluating
high-cost lift stations.

While two-compartment septic tanks may be more effi-
cient at retaining solids, single-compartment tanks have
performed well. Also, several dwelling units or other serv-
ice  locations can be clustered to a single septic tank,
which should have an increased volume  depending on
the total population equivalent it serves.

Other variations  of SDG  sewers—known  as "simplified
sewer systems," "steep slope sewers," and  "flat-grade
sewers"—are in  use in Nebraska as well as in  South
America, Africa,  and  Asia.  These  systems employ
smaller diameter pipes, simplified manhole requirements,
shallower depths, and other cost-saving features in com-
parison to conventional gravity sewers.

5.9.2  Applicability and Status
Approximately 250 SDG sewers have been financed in
the United States by the EPA Construction Grants Pro-
gram. Many more have been financed with private or lo-
cal funding in North America.

SDG sewer systems are likely to be most cost-effective
where the housing density is low, the terrain has undula-
tions of low relief, and the elevation of the system termi-
nus is lower than all or nearly  all of the service area.
They can also be effective where the terrain is too flat for
conventional gravity sewers without deep excavation.

SDG sewer systems do not have the large excess ca-
pacity typical of conventional gravity sewers. Therefore
they must be designed with an  adequate  allowance for
future growth if that is desired. These systems were in-
troduced in the United States in the mid-1970s, but have
been used in Australia since the 1960s.

5.9.3  Advantages/Disadvantages
Key advantages of SDG systems include:
•  Construction is faster than for conventional sewerage,
   requiring less time to provide service.

•  O&M can be carried out by unskilled personnel.

•  Any required lift and pumping station can be reduced
   in size and simplified owing to the nature of the waste-

•  Elimination of manholes helps to further reduce inflow
   (further reducing the sizes of pipes),  lift/pumping sta-
   tions, and final treatment.

•  Reduced  excavation costs: Trenches for  SDG  sewer
   pipelines are typically narrower and not as deep as in
   conventional sewers.

•  Reduced  material costs: As the name indicates, SDG
   sewer pipelines are smaller than conventional sewers,
   reducing pipe and filling costs.

•  Power requirements are negligible or low.

•  Final treatment requirements are not only  reduced hy-
   draulically but are also scaled down in terms  of or-
   ganic loading since partial treatment is performed at
   the source.

•  Reduced  depth of  mains minimizes additional con-
   struction costs due to high ground water or rocky con-

While SDG systems have no major disadvantages spe-
cific to temperate climates, some restrictions  exist gener-
ally that limit their application:
•  SDG sewers are  not suitable to serve as combined
   sewers, even if pipe size could  be  increased. Due to
   the nature of variable grades and relatively flat slopes,
   solids drawn to SDG sewers will block them.

•  For  the same  reason, SDG  sewers cannot handle
   commercial  wastewater having high grit or settleable
   solids levels. Restaurants may be  hooked up if they
   are equipped with effective grease traps. Laundromats
   could be a constraining factor for SDG in small com-
   munities. There has been no report on the  use of SDG
   as a commercial wastewater collection option.

•  Corrosion has been a problem in some SDG systems
   in the United States. Noncorrosive  materials must be
   incorporated in the design.

•  Desludging  interceptor tanks and  disposing of col-
   lected  septage  are probably the most complex as-
   pects of the SDG system. This should be carried out
   by the local  authorities. Contracting the private sector

   to carry out these tasks is an  option,  provided the
   authorities have enforceable power for hygiene control.

• The most common problem has been related to odors.
   Many early systems utilized an  onlot balancing tank
   that promoted stripping of HaS  from the interceptor
   (septic) tank effluent. Other odor problems have been
   due to  inadequate  house ventilation systems  and
   mainline manholes or venting structures.  In all cases,
   appropriate engineering can control these problems.

5.9.4   Design Criteria
Peak flows  are based on the formula Q = 20 + 0.5D,
where Q is  gpm and D  is the number of dwelling units
served by the system. A determination of peak flows is
used for design instead of actual flow data. Each seg-
ment of the sewer is analyzed by the Hazen-Williams or
Manning equations. Roughness  coefficients of 120 to
140 (H-W)  and 0.013 (M) are common. No minimum
velocity is required and PVC pipe (SDR 35) is commonly
employed for  all gravity segments.  But stronger pipe
(e.g.,  SDR 21) may be  dictated where several STEP
units feed the system. Also, check valves may be used in
flooded or  other sections on  service  laterals  where
backup from the main is possible (surcharging).

All components must be  corrosion-resistant and all dis-
charges (e.g., to a  conventional gravity interception or
treatment facility) must be made  through drop inlets be-
low the liquid level to minimize odors. The system is ven-
tilated  through service-connection  house  vent  stacks.
Other atmospheric openings should be directed to soil
beds for odor control, unless they are located away from
the populace.

Interception tanks are generally sized in accordance with
local septic tank codes. STEP units employed for below-
grade services are covered under pressure sewers. It is
incumbent on the engineer to ensure that onlot infiltration
and inflow  (I/I)  be eliminated through proper  testing of
building sewers and pre-installation testing  of intercep-
tion tanks.

Mainline cleanouts are generally spaced at 120 to 300 m
(400 to 1,000 ft) apart. Septic (interceptor) tank effluent
is generally assumed to contain 100 to 150 mg/L BODs
and 50 to 75 mg/L SS. Treatment is normally by stabili-
zation pond or by subsurface infiltration.

5.9.5   Capital Costs
The installed costs  of the collector mains and  laterals
and the interceptor tanks constitute more than 50 percent
of total construction  cost. Average unit costs for 12 pro-
jects (adjusted to January 1991) were:  10 cm (4 in.)
mainline, $12.19/ft  ($3.71/m); cleanouts,  $290 each;
service connections, $9.08/ft ($2.76/m); and 440 L (1,000
gal) interceptor tanks, $1,315. The average cost per con-
nection was $5,353 (adjusted to January 1991).
5.9.6   O&M Requirements/Costs
The major O&M  requirement for SDG systems is the
pumping of interceptor tanks, usually at 3 to 5 yr inter-
vals. Other O&M activities include line repairs from exca-
vation damage, supervision of  new connections,  and
inspection  and  repair of mechanical components. Most
SDG system users pay $10 to  20/month for manage-
ment, including  O&M and administrative costs.

5.9.7   Construction Issues
As with all alternative sewer systems, onlot construction is a
major part of the project. All sites should be videotaped prior
to and after construction to minimize claims from home-
owners. Onlot facility plans should be developed at this
time and used  throughout the project  by maintenance
personnel.  Testing of all piping installed should be per-
formed, and as-built drawings of the installation should
be created and submitted  to the local authority. Where
possible, trenching  machines should be considered for
substantial  (=50 percent) cost savings.  Granular backfill
is preferred, as  are rubber-ring joints, given the nature of
PVC pipe. Magnetic tape above the installed pipe is con-
sidered extremely cost-effective to prevent  future dam-
age.  In some  cases, the authority  has  included the
building sewer in  the project  to ensure I/I  control. Ease-
ments are required for O&M tasks and usually are in the
form of a wide  strip centered on  the service lateral and
interceptor tank.

5.9.8   Monitoring
Some management schemes involve biannual tank in-
spection and pumping only  when needed. Most have
merely dictated a pumping schedule (e.g., 3 to 5 yr for
residential users and every year  for  commercial users).
Otherwise,  no monitoring plan is typically established.

5.9.9   Residuals
SDG  systems,  like STEP systems,  require interceptor
tank pumping. Septage treatment and disposal are de-
scribed elsewhere.

5.10  Vacuum Sewers

5.10.1  Technology Description
A vacuum  sewer system has three  major subsystems:
the central  collection station,  the collection network, and
the onsite facilities. Vacuum pressure is generated at the
central collection station and  is transmitted by the collec-
tion network throughout the area to be served. Wastewa-
ter from conventional  plumbing fixtures  flows by gravity
to an onsite holding tank. When about 38 to 57 L (10 to
15 gal) of wastewater has been collected, the vacuum in-
terface valve opens for a few (3 to 30) seconds allowing
the wastewater  and a volume of air to be sucked through
the service pipe and into the main.  The difference be-
tween the atmospheric pressure behind the wastewater

 and the vacuum ahead provides the primary propulsive
 force. The fact that both air and wastewater flow simulta-
 neously produces high velocities that prevent blockages
 under  normal operating conditions. Following the valve
 closure, the system returns to equilibrium and the waste-
 water reaches the central collection tank, which is under
 vacuum. When the wastewater in that  tank  reaches  a
 certain level, a conventional nonclog wastewater pump
 discharges it through a force main to a treatment plant or
 gravity interceptor.

 The vacuum interface valve is the unique component of a
 vacuum sewer system. It operates automatically using
 pneumatic controls; thus, the onsite facilities do not use
 any electricity. The  valve is placed in a  valve pit that is
 usually buried above the holding tank. Plastic pipe is
 used throughout a  vacuum sewer system. The gravity
 flow house sewer is usually 10 cm (4 in.)  pipe. It normally
 incorporates an external vent to admit air when the valve
 cycles, thus preventing the house plumbing traps from
 being sucked dry. Typical service laterals are 7.6 cm (3 in.)
 pipe, and  mains range from 10 to 25 cm  (4 to 10 in.) de-
 pending on the flow and layout. Joints are either solvent-
 welded or (preferably) vacuum-certified rubber-ring type.

 The profile  of the collection network makes use of the
 limited ability of vacuum propulsion to flow upward in or-
 der to avoid excessive excavation. Where the ground
 slopes in  the flow direction more than 0.2 percent, the
 pipe parallels the ground. Otherwise the  pipe is laid with
 a downward slope of 0.2 percent until the depth becomes
 excessive. When this occurs, a lift formed by two 45 de-
 gree elbows and a short length of pipe is inserted to gain
 elevation. The typical lift raises the pipe by 0.6 m (2 ft) or
 less. Division valves are usually placed at main junctions
 and at 450 m (1,500 ft)  intervals to facilitate troubleshoot-
 ing and repairs. Service lines or tributary mains always
join  the  continuing main from above  through a wye

 Several mains may  be  served by a single collection sta-
tion. Each main is  connected directly to the collection
tank through a division valve. Air usually flows from the
collection tank through a vacuum reserve tank to the vac-
uum pumps, which  discharge  to the atmosphere. Dual
vacuum pumps are provided to improve reliability. Both
liquid ring and sliding vane vacuum pumps  have been
used. Automatic controls cycle the vacuum pumps alter-
nately to maintain the vacuum in the desired range, usu-
ally  5.5 to  7.0 m  (18 to  23  ft) of water.  A  backup
diesel-generator set is  used to maintain service during
electrical outages. An autodialing telephone alarm is pro-
vided to summon the operator in case of malfunctions.

Detailed design recommendations differ among manu-
facturers and engineers. A single interface  valve may
serve several  houses,  a school, or a small business
area. A few systems use vacuum toilets, which require
about 1 to 2  L (0.25 to 0.5 gal)/flush, contain their own in-
terface valves, and have their own vacuum service lines.
Cleanouts are provided as access to mains.
The vacuum reserve volume may be provided in the col-
lection tank rather than in a separate vacuum reserve
tank. One manufacturer offers an ejector-type vacuum
pump in which wastewater from the collection tank is re-
circulated by a centrifugal  pump as the primary fluid in a
multiphase jet pump. Another manufacturer provides  a
factory-assembled, skid-mounted central collection sta-
tion that can handle design sewage flows of up to 10 Us
(150 gpm). In addition to residential applications, vacuum
plumbing  is used in office buildings,  hospitals, factories,
and marinas.

5.10.2  Applicability and Status
On January 1,  1990, there were  42 residential vacuum
sewer systems operating  in 12 states, including Alaska
and Florida. These systems served more than 50,000
persons using 100 central collection  stations, more than
10,000 vacuum interface valves, and about 160 vacuum
toilets. The first of these systems  has operated  since
1970. All but three systems use the same brand of inter-
face valves.
Vacuum sewers are most likely to be cost-effective when
excavation costs are high, population densities are mod-
erate to high (but isolated), and the topography is flat to
moderately  rolling. They are well suited for combined
sewer  separation  projects in finite  urban areas where
prohibitive costs  of  construction must be  minimized.
Other factors favoring vacuum sewers are the need for
water conservation and the need to minimize the risk of
sewage spills.

5.10.3  Advantages/Disadvantages
Key advantages of vacuum sewers include:
•  Low cost of mains

•  No electricity required at service locations

•  Shallow depth of mains

•  Single valve can serve several homes (sources)

•  With backup  generator,  complete independence from
   local power outages

•  Well suited for dense but isolated housing develop-

Key disadvantages of this type of system include:
»  Requires large (>75 generally) numbers of homes for

•  Somewhat more mechanically sophisticated than other
   alternative systems

•  Requires fast response to malfunctions and greater
   O&M skill level than other alternative systems

•  Slightly  more difficult  to install  main lines  than other

5,10.4 Design Criteria
Although there  are no universally accepted criteria, the
following are widely used:

The maximum capacity of a 7.6 cm (3 in.) interface valve
is 2 Us (30 gpm). The minimum vacuum head needed to
operate an interface valve is 1.5 m (5 ft) of water.

Vacuum sewer design rules have been developed largely
by  studying operating  systems. Important design pa-
rameters are presented in Tables 5-12 and 5-13.

Table 5-14 shows at what length the 0.2 percent slope
will govern vs.  the percentage of pipe diameter for the
slopes between lifts.

The AIRVAC company has developed a table recommend-
ing maximum design flows for each pipe size (Table 5-15).

The maximum number of homes served for various pipe
sizes is presented in Table 5-16.

The sum of frictional and lift losses should not exceed
about 4 m (13 ft) of water. Frictional  losses may be esti-
mated using  a modified Hazen-Williams formula. The
recommended height of a lift is 30 cm (1 ft) in 10 cm (4 in.)
pipe and 46 to 70 cm (1.5 to 2.3 ft) in larger pipes. The
loss due to a lift is taken as the invert to invert rise less
the internal pipe diameter.

Table 5-12. Main Line Design Parameters	
Minimum distance between lifts                      20 ft
Minimum distance of 0.2 percent slope prior to         50 ft
a series of lifts
Minimum distance between top of lift and any            6 ft
service lateral
Minimum slope                                  0.2%
 Table 5-13. Guidelines for Determining Line Slopes3
 Line Size        Use Largest of:
 4 in. Mains       -0.2%
                - Ground slope
                -80% of pipe dia. (between lifts only)
 Bin. Mains       -0.2%
                - Ground slope
                -40% of pipe dia. (between lifts only)

 "Assuming minimum cover at top of slope.

 Table 5-14. Governing Distances for Slopes Between Lifts
 Pipe Diameter  Distance (ft)  Governing Factor
       4           <135
       4           >135
      >6           <100
      >6	>100
                            Table 5-15. Maximum Flow for Various Pipe Sizes3
80% of pipe diameter
0.2% slope
40% of pipe diameter
0.2% slope	
                                Pipe Diameter (In.)
                             Maximum Flow (gpm)
                            aBMCI, 1989.

                            Table  5-16. Maximum
                            Various Pipe Sizes3
                      Number of Homes  Served  for
                                Pipe Diameter (in.)
                                Homes Served
aBMCI, 1989.
bThe recommended maximum length of any 4-in run is 2,000
ft, which may limit the amount of homes served to a value
less than 70.

Use dual vacuum pumps; size each to handle airflow at
design conditions. Use dual sewage pumps; size each to
handle design flow. The collection tank volume is at least
three times the working volume. Choose the working vol-
ume that allows a sewage pump to start every 15 min-
utes at design flow. A 1,500 L (400 gal) vacuum reserve
tank is normally  used. The vacuum  pump run time
should be 1 to 3 minutes.

5.10.5   Environmental Impact
Construction impacts may be much less than conven-
tional sewers because of reduced excavation. Risk of
sewage spills is minimal since pipes are under vacuum.
Aeration of sewage in mains  nearly  eliminates odor

5.10.6   Capital Cost Sensitivity
Costs are highly site-specific. The following data are gen-
eralized estimates based on  a  1989 telephone survey
concerning 32 out of 42  U.S. vacuum systems, on bid
tabulations and information from manufacturers and de-
sign engineers. All costs  are in  December 1989 dollars
(ENR Construction Cost Index = 4679). On the basis of
data from 17 systems, the total  construction cost of a
vacuum  sewer system  may range  from  $7,000 to
$18,000/valve. Note that one valve may serve more than
one house. A more detailed estimate can be based on
the following typical installed unit costs, but wide vari-
ations from these values are to be expected.
3 in. interface valve, pit, cover $2,000-2,300 each
4 in. auxiliary vent                  50-60 each
4 in. gravity flow house sewer                5/ft
3 in. vacuum service pipe                    7/fl
4 in. vacuum main                       8-11/ft

 6 in. vacuum main                     11-14/ft
 8 in. vacuum main                     14-17/ft
 10 in. vacuum main                       1 9/ft
 4 in. division valve                    350 each
 6 in. division valve               400-500 each
 8 in. division valve               550-700 each
 10 in. division valve                 1,000 each
 4 in. cleanout                         150 each
 6 in. cleanout                         180 each
 Gauge taps                           50 each
 Lifts                                  50 each
 Cycle counter                         125 each
 Table 5-17 gives average installed prices for both custom-
 designed stations as well as for package stations. The
 prices include the equipment (including the generator for
 all stations),  station piping, electrical,  excavation, site
 restoration, and labor.
 5.10.7 O&M Requirements/Cost Range
 Power consumption varies  with design flow, length  of
 mains, lift, and quality of maintenance. On the basis of
 records from six systems,  annual power consumption
 ranges from  150 to 600 kWh/valve.  A value of 200
 kWh/valve/yr is recommended for preliminary estimates.
 A study of six systems yielded a MTBSC from 1 to 22
 years. A planning value of 6 to 8 years is reasonable for
 new vacuum valve designs.
 Preliminary O&M cost estimates can be derived with the
 following formula:
 C = (2,430 x NS) + (205 x LR x NS) + (0.5 x LR x NDV)
 + (5.1 x NIV) + (1.2 x LR x NIV) + (500 x NIV x ER)
C    =  annual O&M cost in December 1989 dollars
 NS  =  number of central collection stations
LR   =  labor rate including fringe benefits and overhead
        in December 1989$/hr
NDV =  number of division valves
 NIV  =  number of vacuum interface valves
 ER   =  electric power rate in December 1989$/kWh
 Major components of a  vacuum sewer system are pre-
 sented in Figure 5-7.
 5.10.8  Construction Issues
 Vacuum system manufacturers generally  include assis-
 tance to engineers and communities during the construc-
 tion phase of the project. One key difficulty arises due to
 the common practice of using two separate phases of in-
                   Main #2
Main #3
                                      Main #1
                                  3 in. Vacuum
                                  Service Line
          Vacuum Station

          Division Valve
          Valve Pit
          Building Sewer

Figure 5-7. Major Components of a Vacuum Sewer System.
Table 5-17. Average Installed Cost for Vacuum Station (Mid-1990)

Package station
Package station
Package station
Custom station
Custom station
Custom station
Number of
Customers ($)
Equipment Cost3
Building Cost ($)

Installed Cost ($)

Total Cost ($)

 Includes generator.

stalling onsite services, with subsequent main-line instal-
lation and hookup. Careful coordination of these activities
is  necessary.  Vacuum testing  of all  sewer segments
must be performed daily during construction. During con-
struction of a vacuum sewer system there is potentially
less noise impact, fewer problems with fugitive dust, and
less erosion than with  conventional sewers because of
smaller equipment requirements.

5.10.9  Monitoring
In addition to operating tasks  discussed  above, cycle
counter readings and spot checks of vacuum pressure at
various locations in  the piping network should  be in-
cluded in any monitoring program to anticipate potential

5.11  Mechanical Systems for
      Wastewater Treatment
Mechanical systems utilize a combination of biological
and physical processes for the treatment of wastewater,
employing tanks, pumps, blowers, rotating  mechanisms,
and/or other mechanical components as part of the over-
all  wastewater treatment  system. Mechanical systems
are frequently used for medium to large municipal waste-
water treatment plants, but also have been widely ap-
plied for the treatment of wastewater associated  with
small,  sewered communities or clusters  of residential
housing  and  commercial establishments.  For very low
flows (<2 L/s  (<50,000 gpd)), preengineered "package
plants" are the mechanical systems normally used. Efflu-
ent from mechanical systems can either be  discharged to
surface water or applied to the land.

Virtually  all mechanical  systems  employ suspended-
growth  or  attached-growth (fixed-film) biological proc-
esses or a combination of the two. In suspended-growth
systems, microorganisms responsible for the breakdown
of the organic matter are suspended in liquid by mixing.
In attached-growth systems, microorganisms become at-
tached to an inert medium, such as rock or plastic. Oxy-
gen is  provided  mechanically in  suspended-growth
systems and naturally  in  attached-growth  systems.  The
biological process is followed by a clarification step to al-
low separation of the biological solids from the treated
wastewater. Suspended-growth treatment approaches
discussed in this section include the  sequencing batch
reactor, oxidation ditch, and extended-aeration  system.
The trickling filter process is discussed as an example of
an attached-growth system.

Mechanical  systems  have potential advantages over
some "natural"  alternatives in  that they can provide a
high-quality effluent, and they are generally very land-ef-
ficient. Disadvantages include the need for close skilled-
operator supervision,  high maintenance requirements,
and high power consumption compared to natural waste-
water treatment systems.

5.12  Extended-Aeration Activated

5.12.1  Technology Description
The extended-aeration process is a widely used modifi-
cation of the conventional suspended-growth, activated-
sludge process characterized by low loading rates and
long hydraulic and solids  retention times. Hydraulic re-
tention times are typically 24 hours, with solids retention
times of 20 to 40 days. Because of the low BOD loading,
the process operates in the endogenous  respiration
phase of the microbial growth cycle, resulting in partial
oxidation of biological solids.  Some extended-aeration
processes operate in a completely mixed regime, with
the contents of the aeration basin being  nearly homoge-
neous. Some technologies are designed to operate in a
plug-flow mode. The high solids retention times associated
with the process promote nitrification. In a well-operated
facility, BOD and SS removals can be expected to range
from 85 to 95 percent. A properly designed and operated
extended-aeration facility can be expected to produce an
effluent with BOD  and SS levels less than 30  mg/L 90
percent of the time and less than 20 mg/L 50 percent of
the time. Because  of the long aeration times, biodegrad-
able toxic compounds are likely to be removed.  A flow
diagram of the process is shown in Figure 5-8.

An extended-aeration process typically consists of coarse
screening or comminution, activated-sludge aeration us-
ing course air diffusers or mechanical aerators,  secon-
dary  clarification using surface skimming and   return
sludge pumping, disinfection often  with chlorine storage
and  feed facilities, and  transport  to a contact basin.
Sludge is typically  wasted to an aerobic holding or aero-
bic stabilization compartment. Sludge  disposal  varies
widely.  Primary clarification is rarely used.
Screened and/or Complete Mix
Raw Wastowator
^ *• AeranonranK >

Return Sludge
^ Clarifler I ^

Excess Sludge


Effluent ^

To Disposal

Aerobic Holding Tank
or Aerobic Digester
 Figure 5-8. Schematic of an Extended-Aeration Process.

 5.12.2  Applicability and Status
 Extended-aeration processes are used widely throughout
 the  United  States for municipal wastewater flows less
 than 2 L/s (50,000 gpd). Most of these are preengineered
 package plants that serve residential subdivisions, small
 clusters of homes,  commercial or institutional  estab-
 lishments, or individual homes. Such package plants are
 largely  preassembled, allowing rapid installation with a
 minimum of site preparation.  For  this reason,  package
 plants are sometimes used for temporary or emergency
 applications. Package plants generally utilize steel tank-
 age, but  precast concrete is also used. Preengineered
 extended-aeration systems are available for flows up to
 about 40 L/s  (1  mgd). However, the extended-aeration
 process has been used to treat wastewater flows of 220
 L/s (5 mgd) and greater.

 Most package plants discharge to  surface waters, al-
 though  they have been utilized  for treatment prior to land
 application or even subsurface disposal. However,  the
 mechanical complexity  of  such plants  is generally  not
 compatible  with  low-maintenance,  land-based  disposal

 Extended-aeration processes  and  package plants  are
 considered a fully developed technology, having been in
 wide use since the 1950s.

 5.12.3  Advantages/Disadvantages
 Key advantages of the  extended-aeration  process in-
 • Lowest  sludge production   of  any activated-sludge

 • High-quality effluent achievable

 • Preengineered package plants  quickly installed with
   minimal site preparation

 • Favorable reliability with sufficient operator attention

 • Nitrification  likely at wastewater temperatures  >15°C

 • Relatively minimal land requirements

 • Relatively low initial cost

 • Can  handle moderate-shock hydraulic loadings with
   minimal problems

 Key disadvantages of this type of system include:

 • High  power consumption and energy cost compared
   to land-based or natural systems

 • High  O&M requirements compared to land-based or
   natural systems; skilled operator necessary

• Susceptible to excursions in effluent SS  and associ-
   ated  BOD due to high  flow variations and operator in-

• Potential freezing problems in cold climates
• Possibility of poor settleability of  mixed liquor  sus-
   pended  solids (MLSS) due to formation of "pinpoint"

• Potential for rising sludge due to dentrification in final
   clarifier in warmer months

• Blower noise and sludge handling odor potential

• Preengineered plants may require additional components
   or modification to meet specified effluent limitations

5.12.4  Design Criteria
Table  5-18  summarizes the  design  criteria for the
extended-aeration process. For package plants, compo-
nents such as aeration basins and clarifiers are preengi-
neered, and system selection for domestic wastewater
applications typically is based solely on flow. The size of
the system selected should be conservative to account
for peak flow conditions.  Table 5-19 provides typical siz-
ing of  unit  processes  at  average design flows of 0.4 to
4.0 L/s (0.01 to 0.1 mgd).

For engineered plants using the extended-aeration proc-
ess, final clarifier design should be conservative  to ac-
count  for  high MLSS  and  poor  settleability  of the
biological solids. Since the process lacks primary  clarifi-

Table  5-18. Summary of Design  Criteria for  Extended-
Aeration Process
Parameter                                  Range
Volumetric loading (Ib BODs/d/1,000 cu ft)           8-15
MLSS (mg/L)                             2,500-6,000
F/M (Ib BODs/d/lb MLVSS)                    0.05-0.15
Aeration detention time (hr)  (based on daily         18-36
Air requirements (scf/lb BODs applied Ib Oa/lb  3,000-4,000
BODs applied)                                2.0-2.53
Solids retention time (days)                       20-40
Recycle ratio (R)                             0.75-1.5
Volatile fraction of MLSS                        0.6-0.7

aBased on 1.5 Ib Oa/lb BODs removed + 4.6 Ib O2/lb
Table 5-19.  Typical  Component  Sizing for Extended-
Aeration Plants

                                 At Average Design
                                     Flow (mgd)
Unit Process
Raw sewage pumping (mgd)
Aeration basin volume (cu ft)
Secondary clarifier area (sq ft)
Chlorinator capacity (Ib/d)
Chlorine contact chamber volume (cu ft)
Drying bed area (sq ft)
Site area (ac)

cation and due to the potential for rising sludge, secon-
dary clarifiers must be equipped with surface skimming
devices to remove grease and floating solids.  Surface
aerators are not recommended  for  extended-aeration
processes in cold   climates because of  potential for
freezing problems.
Design life of a wastewater treatment plant using the
extended-aeration process can be expected to vary de-
pending on whether it is a preengineered system or one
employing cast-in-place concrete tanks. Steel package
plants may have an effective service life as short as 10
years if the maintenance program is inadequate, but as
long as 20 years with regular and  effective maintenance.
Larger,  custom-engineered systems may have a design
life of 20 years or  more. Mechanical equipment used in
either type is likely to have a service life of 5 to 15 years,
depending on the type and quality of the equipment.

Because of concerns for blower noise and odors associ-
ated with handling of residuals, adequate  buffer zones
are necessary between the facility and residential areas.
This distance should be at  least 200 ft. In addition, ade-
quate fencing is necessary to restrict access to the site.

Small  mechanical  plants  typically are unattended at
night. For this reason, plants should be designed with an
alarm system to alert emergency  personnel, such as a
police or fire department dispatcher.

5.12.5   Capital Cost Sensitivity
Package  plants are  relatively economical since  site
preparation and engineering costs are minimized. Some
units are installed  above ground  on  a concrete slab. In
general, package plant costs  are sensitive to flow, with larger
units required to adequately handle peak flow conditions.

Costs of engineered systems or package plants may be
affected by site conditions such as geology, climate, and
surrounding aesthetics.  Larger treatment plants may re-
quire buildings  to house operations and control centers,
laboratories, and sludge dewatering facilities. In general,
preengineered  package  systems  are less costly than
custom-designed systems  employing cast-in-place con-
crete tankage.

5.12.6   O&M Requirements
O&M requirements for an extended-aeration facility are
high because of the need for skilled and regular operator
supervision to ensure performance, and the general me-
chanical complexity of the components. O&M  require-
ments  are summarized in  Table  5-20. An inventory of
spare parts must be maintained  in case  of equipment
failure,  which  eventually will occur.  Inventories should
include pump  packing and seals,   bearings,  motors,
diffusers,  chlorinator  components, and  flow  metering
equipment. In many cases, lack of spare parts and the
long lead times to procure parts and equipment  have re-
sulted in long periods of poor performance.
Table 5-20. O&M  Requirements  of  Extended-Aeration
  • Effluent quality monitoring required by NPDES permit
  • Operation assessment analyses (e.g., MLSS, DO, sludge
   blanket, settleability)
  • Regular cleaning of screens, weirs, skimmer
   mechanisms, diffusers, and other components
  • Regular adjustment of sludge return rate and air injection
  • Regular wasting of solids
  • Sludge dewatering and disposal
  • Control of disinfectant dosage
  • Administration and recordkeeping
  • Blowers or mechanical aerators
  • Influent and return sludge pumps
  • Electrical equipment and instrumentation
  • Mechanical dewatering equipment
  • Laboratory equipment such as pH, DO meters, chemicals
  • Disinfection system
Many small communities lack the skilled personnel nec-
essary to operate properly and maintain a mechanical fa-
cility of this type. Thus an extended-aeration plant may
not be the system  of choice for flows less than 2 L/s
(50,000 gpd). If such a system already exists, the munici-
pality may wish to procure, under contract, the services
of an individual or firm qualified to operate and maintain
the facility, relieving the municipality of this burden.

Energy consumption for an extended-aeration facility is
high relative to other mechanical treatment alternatives,
primarily due to mixing and the high oxygen requirement
associated with the long solids retention time.  Energy is
consumed by aeration of the  activated  sludge basin (as
well  as the  aerated sludge holding tank or aerobic di-
gester, if applicable), influent pumping (if applicable), return
sludge pumping,  mechanical  dewatering  (if applicable),
building heating,  cooling,  and lighting, and by operating
other miscellaneous processes such as clarification and
disinfection.  However, the aeration/mixing step accounts
for the overwhelming majority of power demand. Electri-
cal energy requirements may be  expected to be approxi-
mately 15,000 kWh/yr for a 0.4 L/s (10,000 gpd) facility,
40,000 kWh/yr for a 2 L/s (50,000 gpd) plant, and 60,000
kWh/yr for a 4 L/s (100,000 gpd) facility.

5.12.7 Monitoring
Monitoring consists of sampling and conducting analyses
as required by the National Pollutant Discharge Elimina-
tion System  (NPDES) or other permits,  and as is neces-
sary to ensure optimum plant performance. NPDES
requirements will vary substantially depending  on the
size of the facility and the characteristics of the receiving
waters. NPDES monitoring requirements may include in-

 fluent flow, influent BOD and SS, and effluent BOD, SS,
 chlorine residual, and nutrients (i.e., ammonia, phospho-
 rus). Sampling frequency may range from  daily to bi-
 monthly. Operational monitoring generally includes MLSS,
 aeration basin, dissolved oxygen (DO), pH, settleability, al-
 kalinity,  effluent chlorine  residual,  influent  flow,  return
 sludge flow, and sludge waste rate.

 5.12.8  Residuals
 Residuals generated from an  extended-aeration facility
 include screenings and waste sludge. Grit is  also gener-
 ated if the  plant is equipped with a separate grit cham-
 ber. Grit and screenings must be removed and disposed
 of promptly because of their  putrescible nature. If no
 separate grit chamber is provided, grit accumulates in the
 aeration tank, eventually requiring draining and cleaning.
 Due to the long solids-retention time, waste  sludge pro-
 duction is somewhat less than for conventional activated
 sludge. Sludge may be wasted to a sludge holding tank
 or stabilization process such as an  aerobic digester and
 removed  from the plant  as a  liquid, or may be sub-
 sequently dewatered  by sand bed or other technologies
 and hauled away as a solid. Options for the  handling of
 waste sludge from mechanical wastewater treatment sys-
 tems are discussed in greater detail later in this chapter.

 5.13 Trickling Filter and Modifications

 5.13.1  Technology Description
 The trickling filter process is an attached-growth process
 in which wastewater that has undergone primary clarifi-
 cation is distributed periodically over an inert  media such
 as rock or plastic. Organisms contained in biological slimes
 attached to this media are responsible for the  breakdown
 of organic matter. Periodically, portions of this slime layer
 "slough off" the inert media and are removed by gravity,
 settling in  a secondary clarifier. A  typical trickling filter
 process consists of screening, grit removal, primary clari-
 fication, biological treatment with the trickling filter, sec-
 ondary clarification, and disinfection.
 Conventional, standard-rate trickling filters were at one
 time one  of the most popular methods  of  wastewater
 treatment,  with many such facilities constructed from
 1930 to 1950. The conventional trickling filter process is
 simple and easy to operate. The early plants used stones
 as the media for biological growth and were designed for
 discharge of the secondary sludge  or "humus" back to
 the primary clarifier for co-settling.  The  combined pri-
 mary and secondary sludge was typically dewatered on
 sand drying beds, particularly at the smaller facilities.
 The conventional trickling filter process is limited with re-
 spect to performance. Many older facilities are unable to
 meet secondary treatment standards (30 mg/L BOD; 30
 mg/L SS) on a year-round basis. Finely divided panicu-
 late matter with poor settling properties, characteristic of
the trickling filter process, often contributes to high SS
 levels in the effluent. Attention to the design of the final
 clarifier can overcome this problem.  In 1984,  EPA re-
 laxed performance standards for existing trickling filter
 plants, allowing discharge of an effluent containing no
 more than 45 mg/L SS and  45 mg/L BOD. A conven-
 tional existing trickling filter plant would be expected to
 produce an effluent with less than 40 mg/L BOD and SS
 90 percent of time, and less than 30 mg/L BOD and SS
 50 percent of the time.

 Several modifications to the conventional standard  rate
 of trickling have been  developed to overcome  the per-
 formance  limitations of the original process. These in-
 clude "high-rate" processes and the trickling filter-solids
 contact (TFSC) process.  High-rate trickling filters typi-
 cally employ higher hydraulic and organic loading rates
 to the trickling filters and continuous recirculation of efflu-
 ent through the filter at 50 to  300 percent of the influent
 flow. Many high-rate systems employ plastic media con-
 sisting of  either random-dump packing or prefabricated
 plastic modules that are set in place. Considerable devel-
 opment has occurred in the manufacture of such  modular
 plastic media for trickling filter applications.

 The TFSC process is a relatively innovative approach to
 the trickling filter process. In this process, discharge from
 the trickling filter is "contacted" with secondary return
 sludge in an aerated, short-detention-time tank.  This  al-
 lows  flocculation and agglomeration of the trickling  fil-
 ter "fines," improving SS and associated BOD removal
 in the final clarifier.  In some cases, round, secondary
 clarifiers equipped with a central flocculation well  are
 used to improve flocculation and settleability of the bio-
 logical solids.  The process  is capable of consistently
 meeting secondary  and  some advanced  secondary
 treatment standards.

 Another modification is the coupled trickling filter-activated-
 sludge  approach, which employs both attached-growth
 and suspended-growth biological processes. In this vari-
 ation,  discharge from the  trickling filter enters an acti-
 vated-sludge aeration basin for additional carbonaceous
 removal and nitrification before  final  clarification. This
 modification may be used where ammonia removal (nitri-
 fication)  is required.  The process is particularly stable
 and capable of consistently achieving a high-quality efflu-
 ent having  BOD and SS levels less than 20 mg/L.

 Flow  diagrams  of  the  various  TFSC processes  are
 shown in Figure 5-9.

 5.13.2 Applicability and Status
 Because of the inability to meet secondary treatment
 standards consistently, conventional  trickling filter facili-
ties are  no longer being  built. However,  many such
plants are still in operation, having been constructed to
treat wastewater from both small and large communi-
ties. Some of these have been abandoned,  while oth-
ers have been upgraded to the  TFSC  process  to
improve performance.


                                                                       Center Well
                                   Aerated Solids
                                   Contact Tank
    Waste Sludge

                                                                    Return Sludge
                   Waste Sludge  •<-

               Mode 2
                                            Return Sludge
                                            Aeration Tank
                                                    Return Sludge
                                   Aerated Solids
                                    Contact Tank
                                                                       Center Well
                   Waste Sludge

                                                                                               >• Treated
                             Return Sludge
                             Aeration Tank
                                                    Return Sludge
Figure 5-9. Schematics of Trickling Filter-Solids Contact Processes.
High-rate trickling filters are also rarely used today for
secondary  treatment because of these same perform-
ance limitations. However they are applicable for use as
"roughing" filters ahead of activated-sludge processes to
reduce the organic loading to the aeration basin. Such
roughing filters are particularly applicable for reduction of
high  organic loadings  resulting from  industrial dis-

In 1991, it was estimated that over 50 TFSC plants were
in design construction or operation.  Eleven plants were
                                         known to be in operation. Although the process was only
                                         recently developed (late 1970s), its relatively widespread
                                         application  allows  consideration  as a fully developed
                                         technology. The TFSC process is clearly appropriate as
                                         a  mechanical wastewater  system  for small,  sewered
                                         communities, both  for new  systems and  as a  retrofit to
                                         existing trickling filter plants. Features that make TFSC
                                         well suited for such applications include its relative sim-
                                         plicity, consistently  favorable performance, and  low O&M
                                         requirements compared  to  other  mechanical treatment

 5.13.3  Advantages/Disadvantages
 Advantages of the TFSC process include:
 • Applicable for new facilities or upgrading existing trick-
   ling filter plants

 • Capable of consistently achieving very high-quality ef-
   fluent (<20 mg/L BOD & SS)

 • Relatively simple process

 • Low cost and reliable upgrading technique for trickling

 • Can be designed to provide nitrification

 Key disadvantages of this process include:
 • Primary clarification required

 • Pumping required to douse trickling filter

 • Potential for  nuisance odors from  primary  clarifiers,
   trickling filter,  sludge handling

 • Moderate  O&M requirements; skilled operator neces-

5.13.4  Design Criteria
Available design criteria for the TFSC  process  are sum-
marized in Table 5-21. Definitive design criteria have not
been established, and as a result,  a wide variation exists
in some design  parameters. Table 5-22 provides typical
sizing criteria for components of the TFSC process.
There are several design considerations that must be ad-
dressed for a successful operation. It is essential to es-
tablish conditions in the aerated solids' contact  tank and
final clarifier that promote favorable flocculation. For this

 Table 5-21. Summary of Available Design Criteria for the
 TFSC Process
Hydraulic loading (mgd/ac)
BOD loading (lb/1 ,000 cu ft/d)
Recirculation ratio
Media depth (ft)
Detention time (hr)
Solids retention time (days)
MLSS (mg/L)
DO (mg/L)
Overflow rate based on total area
Sidewater depth (ft)
Flocculatorcenterwell (% of total
Trickling Filters
Low rate High rate
1-4 10-40
5-25 30-60
0 0.5-3
6-8 4-6
Solids Contact/
Aeration Tank
Low rate High rate
0.3-1.5 6-12
0.5-2.0 >6
700-3,00 1,500-3,500
1 .5-3.5 2.0-4.0
Secondary Clarifier
71 ,500
  370   1,850   3,700

  330   1,750   3,500
   50    250     500
1,200   5,600  11,100

  1.5      3       5
 Table 5-22. Typical Component Sizing for TFSC Plants
                                  At Average Design
                               	Flow (mgd)
 Unit Process
 Primary clarifier area (sq ft)
 Primary effluent pumping (mgd)
 Trickling filter volume (cu ft)
 Recirculation pumping  (mgd)
 (for high-rate systems)
 Solids contact basin volume (cu ft)
 (30-min contact time w/33%
 return rate)
 Secondary clarifier area (sq ft)
 Chlorinator capacity (Ib/d)
 Chlorine contact chamber volume
 Site area (ac)

 reason, fine bubble diffusers are typically used in the sol-
 ids contact tank to provide sufficient dissolved oxygen and
 gentle mixing without excessive turbulence that might shear
 the floe. Channels  or pipes  leading to the final clarifier
 should not  impart turbulence to the liquid. Some of the
 early designs for the  process employed flocculating  cen-
 ter wells that could  be  gently  mixed using mechanical
 paddles or air spargers. However, it was found that hy-
 draulic conditions in the  center well were such that addi-
 tion of mixing devices was not necessary.

 Design life for a trickling filter plant is 20 years or more.
 However, mechanical equipment  used in the plant is
 likely to have a service life of 5 to 15 years depending on
 the type and quality of the equipment.

 Trickling filter plants,  because of the presence of a pri-
 mary clarifier, accumulation  of  biomass on the trickling
 filter, and the handling of primary sludge, have greater
 potential for release of objectionable odor than extended-
 aeration facilities. "Filter flies" may also be a localized
 nuisance. Buffer distance around the facility should be at
 least 60 m (200 ft). Fencing  must  be provided to restrict

 Mechanical plants serving small communities are typi-
 cally unattended at night. Plants should be equipped  with
 an alarm system to alert emergency dispatch personnel.

5.13.5  Capital Cost  Sensitivity
 In general, new TFSC processes are more costly than
 either custom-designed  extended-aeration  plants  or
package plants. This  is  attributable mainly to  the addi-
tional costs associated  with primary clarification  and
sludge handling. However, use  of the TFSC process is
probably the most  economical  means of upgrading an
existing trickling filter plant to meet secondary standards.
Costs of TFSC plants may be affected by site conditions
such as climate, geology, and surrounding aesthetic con-

ditions. Relatively high costs are likely to be associated
with sludge dewatering and stabilization.

5.13.6 O&M Requirements
O&M  requirements for a TFSC facility are relatively high
due to the need for skilled and regular operator supervi-
sion and the general mechanical complexity of the com-
ponents. However,  performance  is less dependent  on
operator skill and supervision than the extended-aeration
process. O&M requirements are summarized in Table 5-
23. An inventory of spare parts must be maintained in
case of equipment failure, which eventually will occur. In-
ventories should  include pump packaging and  seals,
bearings, motors, diffusers, chlorinator components, and
flow metering  equipment. In many cases, lack of spare
parts  and the long lead times to procure parts  and equip-
ment  have resulted in long periods of poor performance.

Table 5-23. O&M Requirements of TFSC Facilities	
  • Effluent quality monitoring required by NPDES permit
  • Operation assessment analyses (e.g., MLSS, DO, sludge
    blanket, settleability)
  • Regular cleaning of screens, weirs, filter media, skimmer
    mechanisms, diffusers and other components
  • Regular adjustment of trickling filter recirculation rate,
    sludge return rate and air injection rate
  • Regular wasting of solids
  • Sludge dewatering, stabilization, and disposal
  • Control of disinfectant dosage
  • Administration and recordkeeping
  • Blowers
  • Primary effluent and return sludge pumps
  • Trickling filter distribution system
  • Electrical equipment and instrumentation
  * Mechanical dewatering equipment
  • Laboratory equipment such as pH, DO meters, chemicals
  • Disinfection system
 Many small communities lack the skilled personnel nec-
 essary to operate properly and maintain a mechanical fa-
 cility of this type. Thus the TFSC process is unlikely to be
 the system of choice for flows less than 2 L/s  (50,000
 gpd). If such a system already exists, the municipality
 may wish to procure, under contract, the services of an
 individual or firm qualified to operate and maintain the fa-
 cility, relieving the municipality of this burden.

 Energy consumption for a TFSC facility is  higher than a
 trickling filter plant, but less than an activated sludge fa-
 cility due to the low power requirement to supply oxygen
 to the contact tank. This may increase substantially if ni-
 trification is required.  Energy is consumed by trickling fil-
 ter influent and  recirculation pumping,  aeration of the
 solids  contact  or activated-sludge  basin,  return  sludge
pumping, mechanical dewatering (if applicable), sludge
stabilization, the  heating, cooling, and lighting of the
building housing  the  system,  and other miscellaneous
processes such as clarification and disinfection. Pumping
energy may be estimated using the equation:
    kWh/yr = 1900 x (flow, mgd) x (discharge head, ft)

5.13.7  Monitoring
Monitoring consists of sampling and conducting analyses
as required by NPDES or other permits, and as is neces-
sary to  ensure optimum plant performance.  NPDES re-
quirements will vary substantially depending on the size
of the facility and the characteristics of the receiving wa-
ters. NPDES monitoring requirements may include influ-
ent flow, influent BOD and  SS,  and effluent BOD, SS,
chlorine residual, and nutrients (i.e., ammonia, phospho-
rus). Sampling frequency may range from  daily to bi-
monthly.  Operational  monitoring  generally  includes
MLSS,  aeration basin DO, pH, settleability, alkalinity, ef-
fluent chlorine residual,  influent flow, trickling filter recir-
culation flow, return sludge flow, and sludge waste rate.

5.13.8  Residuals
Residuals generated from a typical TFSC system include
grit and both  primary and secondary sludge.  Grit and
screenings must  be removed  and disposed of promptly
because of their putrescible nature.
Secondary sludge may be blended with primary sludge in
the primary tank or pumped  to a stabilization process
such as an aerobic or anaerobic digester. Sludge may be
removed from the plant  as a liquid or may be dewatered
by sand bed or mechanical devices and hauled away as
a solid. Options  for the handling of waste sludge  from
mechanical wastewater treatment systems are discussed
in greater detail later in Section 5.16.

5.14 Oxidation Ditch

5.14.1  Technology Description
The oxidation  ditch process is a closed-loop variation of
the extended-aeration activated-sludge process. As with
extended aeration, the  process  is characterized by hy-
draulic  retention times of 18 to 30 hours,  and solids re-
tention  times  of  10 to  33 days. The process is highly
stable and  reliable, and is suitable for relatively small
wastewater flows  associated  with  small  communi-
ties or subdivisions.
An oxidation ditch process typically consists of coarse
screening, grit removal,  one or more closed-loop aerated
channels, secondary clarification, and disinfection.  Pri-
mary clarification is rarely used. A typical means of aera-
tion is  the use of horizontally mounted rotating brush,
cage, or disc  aerators,  which operate at 60 to 110 rpm
and provide transfer of oxygen as well as  impart velocity
to the wastewater. Another common aeration system as-
sociated with  a proprietary  oxidation  ditch process is  a
vertical turbine, nonsparged aerator mounted at 180 de-

  gree bends in the channel near the dividing wall. Several
  novel aeration and mixing devices have also been used
  with varying degrees of success in regard to oxygen trans-
  fer and maintaining solids in suspension. A schematic of
  the oxidation ditch process is provided in Figure 5-10.
  Screened and
  Degritted Raw
               f   Dividing Strip

                   Return Sludge
Excess Sludge
 Figure 5-10. Schematic of an Oxidation Ditch Process.

 Oxidation ditch loops are generally oval in shape. Some
 larger plants have employed "folded loop" or horseshoe
 configurations to make efficient use of space. For small
 facilities, a single channel, 1.2 to 1.8 m (4 to 6 ft) deep
 with 45 degree sloping sidewalls, is typically used. This
 configuration  allows  several  options  for construction.
 Often, cast-in-place reinforced concrete is used to form
 the ditch. However, gunite and asphalt lined ditches have
 been successfully constructed.  Lining is necessary  to
 prevent erosion from the moving wastewater. Experience
 has shown the cost of gunite lining to be higher than rein-
 forced concrete for  this  application.  Deeper ditches
 (>3m) (but smaller in area) with common vertical, con-
 crete walls are also used for larger facilities.

 In the 1980s, a number of "in channel" clarifier designs
 were marketed for oxidation ditch plants. Here a clarifica-
 tion device is placed within the channel to  provide a qui-
 escent settling zone,  with  solids returned back to the
 ditch through ports or slots at the bottom of the clarifier.
 These systems eliminate the need for separate final clari-
 fiers and  return sludge pumping; however,  there are
 trade-offs: lack of the ability to waste a thickened sludge
 from a separate clarifier (requiring wasting  of a relatively
 dilute mixed  liquor);  lack  of operational  flexibility  in
 adjusting sludge  return rates; and the need to increase
 mixing to overcome additional headloss through the ditch
 resulting  from the restriction of flow  around  the in-
 channel clarifier.

 The oxidation  ditch is capable of  reliably  producing a
 very high-quality effluent. A1978 study by EPA that com-
 pared the performance of 29 oxidation ditch plants with
 competing biological  processes demonstrated that the
 oxidation ditch systems outperformed conventional  acti-
 vated sludge,  package plants, trickling filters, and  rotat-
 ing biological contactors. Average annual effluent quality
was  less than  15 mg/L BOD  and SS. A 20-20  effluent
was  achieved 85 to 90 percent of the time and a 30-30
effluent was achieved 95 percent of the time.
  Oxidation ditch plants are capable of substantial nitrogen
  removal, with 40 to 80 percent nitrogen removal achiev-
  able. This favorable performance results from the devel-
  opment of zones  of low dissolved oxygen or  anoxic
  conditions  between aerators  where denitrification can
  take place. Achieving high nitrogen removal efficiency in-
  volves  careful placement of aerators and  adjustment  of
  variables such as aerator speed, immersion depth, and
  on/off cycling frequency.

  5.14.2  Applicability and Status
  The oxidation ditch was  developed in  the Netherlands,
  with the first plant constructed in 1953 for a community  of
  400 people. Because of its high performance and reliabil-
  ity it now is used widely throughout the United States. It
  is well  suited for wastewater flows in excess of 0.4 L/s
  (10,000 gpd). In 1980, over 650 oxidation ditch  plants
  were in use in the  United States and Canada. Where a
  mechanical system  is desired that  will provide excellent
  performance, high reliability,  and relatively minor opera-
  tor attention, the oxidation ditch should be considered.

  5.14.3  Advantages/Disadvantages
  Key advantages of the oxidation ditch process include:
  •  Low sludge production

  •  Excellent performance
  •  High  reliability

  •  Nitrogen removal likely
 •  Relatively low initial cost

 •  Can be designed  for biological phosphorus and nitro-
    gen removal

 Key disadvantages of this process include:
 •  Protection from aerator freezing  problems necessary
    in cold climates

 •  Relatively high maintenance requirements for aerators
 •  Potential for rising sludge due to denitrification in final

 • Requires good operator  skills and  routine  monitoring

 5.14.4  Design Criteria
 Table 5-24 summarizes the design criteria for the oxida-
 tion ditch process. These criteria would  apply to a con-
 ventional  ditch   (extended  aeration)   designed  for
 carbonaceous BOD removal, without specific considera-
 tions for nutrient  (i.e., nitrogen, phosphorus)  removal.
 Typical sizing of components of an oxidation ditch plant
 is summarized in Table 5-25.
 Manufacturers  of  aeration  equipment  for  oxidation
 ditches have developed design criteria  and suggested
 plant layouts to meet a wide range of performance and
 site requirements. Some ditches have been designed as
a single reactor that operates as both aeration basin and
clarifier. The  most common oxidation ditch configuration

Table 5-24. Summary of Design Criteria for the Oxidation
Ditch Process
Volumetric loading (Ib BODs/lb/1,000 cu ft)
MLSS (mg/L)
F/M (Ib BODs/d/lb MLVSS)
Aeration detention time (hr)
(based on average daily flow)
Solids retention time (days)
Recycle ratio (R)
Volatile fraction of MLSS
Channel velocity (fps)
Oxygen transfer efficiency for horizontal
aerators (Ib Oa/hp-hr/LF)

 Table 5-25. Typical Component Sizing for Oxidation Ditch
 Unit Process
 Aeration basin volume (cu ft)
 Aerator, installed (hp)
 Secondary clarifier area (sq ft)
 Return sludge pumping (mgd)
 Chtorinator capacity (Ib/d)
 Chlorine contact chamber volume
 Site area (ac)
 At Average Design
    Flows (mqd)
   0.1     0.5    1.0
13,400  66,400 134,000
   7.5      40     60
   400   2,000  4,000
   0.2     1.0    1.5
    50     250    500
 1,200   6,000 11,000
 in the United States is a continuous-flow, single-channel
 ditch followed by a final clarifier.  Another arrangement
 comprises  multiple concentric channels  connected  by
 submerged ports. Such plants allow flexibility in operating
 mode.  For example,  some  four-channel plants  are de-
 signed to allow operation in  the extended-aeration mode,
 conventional  activated sludge-aerobic digester mode, or
 contact stabilization mode simply by adjustment of gates
 and valves.
 The procedure for design of an oxidation ditch plant is
 approximately the same  as for an extended-aeration
 activated-sludge  plant.  Some low-alkalinity waste-
 waters may require  pH adjustment when subjected to
 long detention times in the aeration basin. Calculation of
 oxygen requirements should assume that nitrification will
 occur. Design life of an oxidation ditch plant is 20 years
 or more,  however,  mechanical  equipment  is  likely to
 have a service life of 5 to 15 years depending on the type
 and quality of the equipment.

 5.14.5  Capital Cost Sensitivity
 Oxidation ditch plants are  competitive with  other acti-
 vated sludge processes in the range of 4 to 440 L/s (0.1
 to 10.0 mgd) and appear to be particularly cost-effective
 in the larger size ranges. However, local factors and spe-
cific process design can have a major impact on relative
construction costs.
Ditch configuration can  affect construction costs.  For
small plants, the shallow ditch with 45 degree sloped
sidewalls appears most cost-effective. For plants over 44
L/s (1  mgd), the deep channel with straight sidewalls is
cost effective. Ditch construction techniques can also af-
fect capital costs, as discussed elsewhere. As with other
mechanical plants, capital costs  are influenced by site,
geological, and local aesthetic conditions.

5.14.6  O&M Requirements
O&M requirements for the oxidation ditch process are
summarized in Table 5-26. O&M costs are high relative
to natural systems for wastewater treatment. Successful
performance requires skilled operators and regular in-
spection, monitoring, and maintenance.

 Table 5-26. O&M Requirements of Oxidation Ditch Facilities
  • Effluent quality monitoring required by NPDES permit
  • Operation assessment analyses (e.g., MLSS, DO, sludge
    blanket, settleability)
  • Regular cleaning of screens, weirs, skimmer
    mechanisms, tank walls, and other components
  • Regular adjustment of sludge return rate and oxygenation
  • Regular wasting of solids
  • Sludge dewatering and disposal
  • Control of disinfectant dosage
  • Administration and recordkeeping
  • Mechanical aerators
  • Influent and return sludge pumps
  • Electrical equipment and instrumentation
  • Mechanical dewatering equipment
   • Laboratory equipment such as pH, DO meters,  chemicals
   • Disinfection system	

 In oxidation ditch plants, aerators and aerator drives ac-
 count for  a major portion of mechanical problems. In an
 EPA study of oxidation  ditch plants, many plants experi-
 enced the following aerator-related problems every 2 to 5
 •  Loss of "teeth" from brush-type aerators
 •  Bearing problems in gear drives, line shafts, and aera-
    tor shafts
 •  Failure of flexible couplings between line shafts
 •  Failure of gear reducer and gear reducer shaft seals
 • Corrosion of  bearings, couplings, and  drive units due
    to continuous wetting from aerator spray

 In cold climates, spray from aerators will freeze on equip-
 ment, structures, and walkways. Aerators should be cov-

  ered in moderately cold areas, and also heated in very
  cold areas.

  Many small communities lack the skilled personnel nec-
  essary to operate properly and maintain a mechanical fa-
  cility  of this  type. Thus the oxidation ditch  process  is
  unlikely to be the system of choice for flows less than 2
  Us (50,000 gpd). If such a system already exists, the mu-
  nicipality may wish to procure, under contract, the services
  of an individual or firm qualified to operate and maintain the
  facility, relieving the municipality of this burden.

  Energy requirements for an oxidation ditch facility include
  drives for aerators and pumps, sludge dewatering (if ap-
  plicable), heating, lighting, and miscellaneous uses. An-
  nual electrical energy requirements may be expected to
  be approximately 72,000 kWh/yr for a 4 Us  (0.1 mgd) fa-
  cility, 280,000 kWh/yr for a 22 Us (0.5 mgd)  plant, and
  500,000 kWh/yr for a 44 Us (1 mgd) facility.

  5.14.7 Monitoring
  Monitoring consists of sampling and conducting analyses
  as required by NPDES or other permits, and as is neces-
  sary to ensure optimum plant performance. NPDES re-
 quirements will vary substantially depending on the size
 of the facility  and the characteristics of the receiving wa-
 ters. NPDES  monitoring requirements may  include  influ-
 ent flow,  influent BOD  and SS, and effluent  BOD, SS,
 chlorine residual, and nutrients (i.e., ammonia, phospho-
 rus). Sampling frequency may range  from daily to bi-
 monthly.  Operational   monitoring   generally  includes
 MLSS, aeration basin DO, pH, settleability, alkalinity, ef-
 fluent chlorine residual,  influent flow, return  sludge  flow,
 sludge waste  rate, and dewatered sludge solids content.

 5.14.8  Residuals
 Residuals generated from  an oxidation  ditch facility
 include screenings, grit, and waste sludge.  Grit  and
 screenings must  be removed and disposed of promptly
 because of their putrescible nature. If no separate grit
 chamber  is provided, grit accumulates  in the oxidation
 ditch, eventually requiring draining and cleaning.

 Due to the long solids retention time, waste sludge pro-
 duction is the same as for an extended-aeration system
 and somewhat  less than  for conventional  activated
 sludge. Sludge may be wasted to a sludge holding  tank
 or stabilization process such as an aerobic digester and
 removed from the plant as a liquid, or may be dewatered
 by  sand bed  or  other devices and hauled  away  as a
 solid. Options  for  the handling of waste sludge  from me-
 chanical wastewater treatment systems are discussed in
 greater detail later in this chapter.

 5.15  Sequencing Batch Reactors

 5.15.1  Technology Description
 The sequencing batch reactor (SBR) process is  a form of
the activated-sludge process in which aeration, sedimen-
tation, and decant functions are combined in  a single re-
  actor. Most municipal SBRs consist of two or more paral-
  lel tanks. The process employs a five-stage cycle: fill, re-
  act,  settle,  draw,  and  idle.  During the fill  stage,
  wastewater enters the tank and mixes with the settled
  biological solids remaining from the previous cycle. The
  tank  is  mixed during the fill stage and may be aerated.
  During the react stage, the wastewater and mixed liquor
  are subjected to aeration, causing oxidation of organic
  matter.  Aeration and mixing are stopped during the settle
  stage, allowing solids to settle.  Clarified supernatant is
  decanted during the draw stage. After decanting, solids
  are removed from the bottom of the tank during the idle
  stage. By this stage the first reactor will have finished its
  cycle and the other reactor(s)  will continue filling. When
  the second reactor completes its fill stage, it begins its
  react cycle and influent wastewater is directed to the first

  Modifications to the process include systems that con-
 tinually accept influent flow, and oxidation ditch  systems
 that function as SBRs without the use of external clarifiers.

 A  typical SBR  process consists of  screening,  grit re-
 moval, SBR cycling,  and disinfection. The disinfection
 system must be designed so that it is either large enough
 to  accommodate the high periodic flow during decanting
 or  preceded by flow equalization. Primary clarification is
 not commonly practiced. A schematic diagram that in-
 cludes the five stages of an SBR cycle is provided in Fig-
 ure 5-11.

 Critical components of an SBR system include the aera-
 tion/mixing  system, the decant system, and the control
 system.  Aeration/mixing systems include jet aeration,
 fine and coarse bubble diffusers, and mechanical turbine
 aerators. Of these, the jet aeration system appears to be
 most common. It has the advantage of being able to mix
 independently of aeration. This may be important if bio-
 logical nutrient removal is desired.

 A well-designed and reliable decant system is critical to
 ensuring a high-quality effluent  by avoiding discharge of
 floating solids or MLSS. At least five different proprietary
 designs are available through vendors of SBR systems.
 Development of SBR technology in the United  States
 has progressed rapidly since 1980, resulting in many im-
 provements to decanter designs. Decanters include me-
 chanically activated surface skimmers, floating decanters
 with hydraulically activated valves, floating pipes and ori-
 fices equipped with flapper valves operated by air pres-
 sure, and fixed-position siphons.

 Process  control  is  provided by a programmable logic
controller (PLC),  which along with associated software is
provided  by the manufacturer. Programs are typically de-
veloped and modified by the vendor to suit the intended
application.  PLC  hardware  is generally reliable. Con-
struction is modular, and troubleshooting and module re-
placement are straightforward.

              Bar Screen
 Raw Wastewate
SBR Tank No. 1
                             SBR Tank No. 2
   Stream Discharge
                           Waste Sludge to
                       Sludge Handling System
] Fill
_J Aeration
1 Settle
[ Effluent 4— L


- t]
1 ^ Waste

Figure 5-11. Schematic and Stages for a Sequencing Batch Reactor Process.
Sludge wasting is accomplished by wasting either aer-
ated MLSS or settled solids. Often, submersible pumps
are used to waste solids.
SBRs are capable of producing a high-quality effluent.
Data collected by EPA from 13 secondary plants using
SBR technology showed effluent average BOD levels of
3.3 to 21.0 mg/L, average SS levels of 3 to 25 mg/L, and
average NHs-N levels of 0.3 to 12.0 mg/L. These data
are average values representing 7 to 12 months of oper-
ating data.
SBRs are also capable of  both  biological  nitrogen and
phosphorus removal, which is accomplished by proper
reactor sizing and selection of stage lengths and aeration
times to achieve the desired distribution of aerobic, an-
oxic, and  anaerobic conditions. Scant data on  full-scale
operations are available to document the  effectiveness
for nitrogen and phosphorus removal, yet phosphorus re-
moval appears quite easily achievable.

5.15.2  Applicability and Status
The SBR process has widespread application where me-
chanical treatment of small wastewater flows is desired.
Because it provides batch treatment of wastewater, it is
ideally suited for the wide variations in flow rates that are
typically associated with small communities. Operation in
the "fill  and draw" mode prevents the "washout"  of bio-
logical solids  that often occurs  with extended aeration
systems subjected to wide flow variations.

Another advantage of SBR systems for small communi-
ties is that they require less operator attention than most
mechanical treatment  alternatives, yet in most cases
they provide a very high-quality effluent. With rare excep-
tion, operators of SBR systems  are enthusiastic about
                         the technology, preferring it to conventional activated-
                         sludge systems.
                         Although most municipal applications of SBR technology
                         have been online only since 1980, the concept is well es-
                         tablished. Many full-scale fill-and-draw systems were op-
                         erated between  1914 and 1920, but most were  later
                         converted to the continuous-flow mode. The  Pasveer
                         ditch was a variation implemented during the early 1960s
                         that employed continuous feeding of wastewater, with in-
                         termittent settle and discharge. The system was intro-
                         duced in Denmark, and 250 plants were in operation by
                         1980. Similar systems were constructed in Australia be-
                         ginning in 1965, all employing continuous-feed and inter-
                         mittent discharge processes.
                         The first  application of  SBR technology in the  United
                         States was in  1980. Since that time, SBR systems have
                         become  more widespread. In 1989, approximately 150
                         SBR plants were in design or operation; at least 90 facili-
                         ties were known to be operating. Nearly half of these had
                         design flows less than 11 Us (0.25 mgd), and a third had
                         flows less than 4 Us (0.1 mgd).

                         5.15.3  Advantages/Disadvantages
                         Key advantages of the SBR process include:
                         • Simple, reliable
                         • Ideally suited for wide flow variations
                         • Capable of very high and consistent effluent quality
                            due to quiescent batch settling

                         • Requires less operator attention than most other me-
                            chanical systems
                         • High operational flexibility allowing capability for nutri-
                            ent removal, filamentous growth control

 The disadvantages of this process include:
 •  Some problems reported with decant systems
 •  Improvements  to hardware continue to be  made as
    the technology develops
 •  Requires skilled operator and regulator inspection and

 5.15.4 Design Criteria
 Available design criteria for the SBR process  are sum-
 marized in  Table  5-27. Vendors of SBR equipment typi-
 cally  provide  substantial  technical assistance  in  the
 design of the particular SBR system. Some vendors offer
 preengineered SBR package plants. No standard proce-
 dures have been developed for sizing an SBR system.

 Table 5-27. Summary of Available Design Criteria for SBR
 Total tank volume
 Number of tanks
 Tank depth (ft)
 SRT (days)
 Aeration system
 Cycle times (hr)
0.5-2.0 times average daily flow
Typically 2 or more
Sized to deliver sufficient oxygen during
aerated fill and react stage; 02
requirements similar to conventional
activated sludge (with nitrification as
4-12 (typical)
 5.15.5  Capital Cost Sensitivity
 SBR systems are likely to be extremely cost-competitive
 with other  mechanical wastewater  treatment  systems
 over a wide range of flows. Unfortunately, scant historical
 data have been compiled comparing the capital cost of
 SBR systems with other competing mechanical systems.
 Clearly, the lack of need for an external secondary clari-
 fier  and  return sludge pumping system offers potential
 savings in construction costs. In addition, primary clarifi-
 cation  is normally not employed. Design considerations
 regarding the disinfection system (see Section 5.15.1),
 however,  have the potential to offset some of the inher-
 ent advantages of SBR systems.

 As with other mechanical systems, capital costs may be
 affected by site conditions such as climate, geology, and
 surrounding aesthetics. Costs for sludge stabilization and
 dewatering may account for a significant percentage of
 construction costs.

 5.15.6  O&M Requirements
 O&M requirements for an SBR system are expected to
 be among the lowest  of any  mechanical wastewater
treatment plant. Experience with operating SBR proc-
 esses has shown excellent reliability and relatively low
 maintenance. As  with other mechanical systems, how-
 ever, a more skilled operator is necessary. Sludge stabili-
 zation and dewatering are likely to constitute a substan-
 tial portion of the operating and maintenance costs. O&M
 requirements of an SBR plant are summarized in Table 5-28.

 Table 5-28. O&M Requirements of SBR Facilities

   • Effluent quality monitoring required by NPDES permit
   • Operation analyses (e.g., MLSS, DO, settleability)
   • Cleaning of screens, weirs, decant mechanisms,
    diff users, and other components
   • Adjustment of cycle times as required to optimize
   • Regular wasting of solids
   • Sludge dewatering and disposal
   • Control of disinfectant dosage
   • Administration and recordkeeping
   • Blowers, mechanical aerators, or mixing pumps
   • Waste sludge pumps
   • Electrical equipment, including programmable logic
   • Mechanical dewatering equipment
   • Laboratory equipment such as pH, DO meters, chemicals
   • Disinfection system
 Energy consumption for an SBR facility is expected to be
 similar to that for an extended-aeration or oxidation ditch
 plant, but slightly greater than for a TFSC facility. This
 variability in energy requirements for the various systems
 is primarily due to the differences in energy required to
 transfer oxygen  into the wastewater.  Energy  is con-
 sumed  by aeration, mechanical sludge dewatering, pre-
 liminary treatment,  heating, cooling, and lighting of the
 building housing the system, and  other miscellaneous

 5.15.7  Monitoring
 Monitoring consists of sampling and conducting analyses
 as required by NPDES or other permits, and as is neces-
 sary to  ensure optimum plant performance.  NPDES  re-
 quirements will vary substantially depending on the size
 of the facility and the characteristics of the receiving wa-
 ters. NPDES monitoring requirements may include influ-
 ent flow, influent BOD and  SS, and effluent BOD, SS,
 chlorine residual, and nutrients (i.e., ammonia, phospho-
 rus). Sampling frequency may range from daily to  bi-
 monthly.  Operational  monitoring  generally   includes
 MLSS, aeration basin DO during react stage, pH, settle-
 ability, alkalinity, effluent chlorine residual, influent flow,
 and sludge waste rate.

5.15.8   Residuals
 Residuals generated from an SBR facility include screen-
ings and waste secondary sludge. Grit is also generated
if the plant is equipped with a separate grit chamber. Grit

and  screenings must be removed  and disposed  of
promptly because of their putrescible nature.
Due to the long solids retention time associated with
many SBR facilities and the lack of primary clarification,
waste sludge production is relatively low. Sludge may be
wasted to a sludge holding tank or stabilization process,
such as an aerobic digester, and removed from the plant
as a liquid, or may be dewatered by sand bed or other
devices and hauled away as a solid. Options for the han-
dling of waste sludge from mechanical wastewater treat-
ment systems are discussed in  greater detail later in this

5.16 Sludge Handling Alternatives

5.16.1  Introduction
Treatment and disposal of sludge generated from the
mechanical treatment of wastewater is a major problem
facing small communities. Sludge handling can account
for 50 percent of the cost of  operating a wastewater
treatment plant. Many sanitary  landfills refuse or are re-
luctant to accept sewage sludge, and suitable areas for
land spreading of stabilized sludge are becoming difficult
to find in some urbanized areas  of the country.
Regulations promulgated by EPA are quite specific with
regard to the degree of stabilization  required  before
sludge can be applied to the land. At a minimum,  agricul-
tural use of sludge requires the sludge to be pretreated
by aerobic digestion, air drying, anaerobic digestion, or
lime stabilization.  Additional sludge stabilization  can be
accomplished by utilizing composting, heat drying, heat
treatment, thermophilic aerobic  digestion, dry lime stabili-
zation, and other processes described by the EPA.
Sludge handling approaches that have the widest appli-
cation in small communities are as follows:
   Holding Tank mm
Aerobic or

                        Hauling             Larger POTW
 Liming or digestion followed by land application is gener-
 ally the most simple and economical  means of handling
 and disposing of sewage sludge. It does require, how-
 ever, the availability of land for application within a rea-
 sonable proximity  of the sewage treatment plant. A
 significant number of communities employ landfill dis-
 posal instead. Virtually all landfills now require sludge to
 be dewatered to a minimum solids content of 20 to 25

 5.16.2 Sludge Holding Tank
 The first component of many  small  community sludge
 management schemes  is a holding  tank.  The holding
 tank should be conservatively sized to hold sludge during
periods of inclement weather, when dewatering capacity
is  not  available, or should any other problem arise; a
volumetric capacity sufficient to accommodate 30 days of
sludge wasting is recommended.  Most sludge holding
tanks are aerated to prevent septic conditions and en-
train  solids in  suspension  when required.  Diffusers
should be of the coarse-bubble type with the capability to
be removed  for cleaning.  They should  provide a
minimum  of 0.4 L of air per m3 of tank volume(s) (25
cfm/1,000 cu ft).  Depending on the application, holding
tanks should be designed to allow periodic  sludge set-
tling and decant of supernatant, increasing solids content
and reducing the volume for dewatering and/or disposal.
Even if septic  conditions are prevented with aeration,
odor emissions may be a problem. Simple offgas biofil-
ters composed of soil, compost, or a combination of such
materials  can provide an economical  means of control-
ling such emissions.

5.16.3  Dewatering Beds
Dewatering beds remove sludge moisture by drainage
and by evaporation. Underdrainage is collected and re-
turned to the plant headworks. Drying beds typically con-
sist of 15 to 25 cm (6 to 10 in.) of sand placed over 20 to
46 cm (8 to 18 in.) of gravel or stone. Effective size of the
sand is 0.3 to 1.2 mm,  and uniformity coefficient is less
than 5. Gravel  is generally graded from 1/8  to 1  in. Un-
derdrains are vitrified clay with open joints or perforated
PVC pipe with  a  minimum diameter of 10 cm (4 in.) and
minimum slope of 1 to 2 percent. A  cross section of a
typical sand drying bed is shown in Figure 5-12.

Sludge is preferably applied to the beds in 20 to 25 cm (8
to 10 in.)  lifts. Drying beds are partitioned into sections 3
to 6 m (10 to 20 ft.) wide and 6 to 30 m (20 to 100 ft.)
long.  Partitions  may  be constructed using  pressure-
treated wooden planks, earthen dikes, or concrete walls.
Concrete foundations  are  required  around the  drying
area if it is to be covered (in colder climates).

Feed  piping may be ductile iron  or PVC. It should be
sized to prevent  clogging yet maintain adequate cleans-
ing velocities. Provision should be made  for  flushing and
draining the line. Diversion  boxes or valves are used to
feed the desired bed. Splash plates are  usually em-
ployed in order to minimize erosion of the sand and im-
prove sludge distribution.

After the sludge has dried to a minimum solids content of
20 to 25 percent, it is removed from the bed. For small op-
erations this is typically done manually, although small
front-end  loaders are preferable.  Sand that may be re-
 moved in the process will eventually require  replacement.
 Modern beds are designed with longitudinal concrete strips
 allowing access by a truck or front-end loader.

 For cold  or wet  climates, glass enclosures  can be con-
 structed  to  improve drying during  inclement weather.
 Ventilation is necessary for moisture control.


 Figure 5-12. Sand Drying Bed Details.
 Modifications to traditional sand drying beds include use
 of  wedgewire  or plastic block bottoms,  paved  drying
 beds, vacuum-assisted drying beds,  and special mixing
 devices for areas of intense sunlight. All but the paved
 bed require chemical (usually polymer) conditioning prior
 to sludge application, thus limiting these particular modifi-
 cations to systems operated by skilled O&M staffs. All of
 the alternative systems  can be cleaned by mechanical
 means, substantially  reducing labor costs associated
 with dewatered sludge removal. Field experience indi-
 cates that  the  use of totally and partially paved drying
 beds result in shorter drying time than with conventional
 drying beds. Experience with polymer treatment followed
 by drying on plastic- or wedgewire-bottom beds has been
 limited in the United States, but indications are promis-
 ing. Final solids vary from about 12 percent with immedi-
 ate  removal,  to  higher percentages  with  continued

 Vacuum-assisted sludge drying (VASD) beds are a rela-
 tively recent innovation developed in the mid-1970s. This
technology consists of an array of specially made porous
 blocks or plates  with  sealed  joints.  After the polymer-
treated sludge  has drained supernate, a pump applies a
 vacuum to  the bottom,  pulling additional moisture from
 polymer-conditioned,  gravity-drained  sludge  until it cracks.
The major   advantage of these alternative systems is
shorter drying times. The normal VASD cycle time for di-
gested sludges is considerably less than 24 hours. Final
 solids are generally 13 to 15 percent, unless dried further
 before disposal.
 Table 5-29 provides a summary of information on sludge
 dewatering beds.

 Table 5-29. Summary of Information on Sludge Dewatering
                                                         Applicability and
                                                         Design criteria
 Capital cost
Simple, widely-used, effective system

Minimal skill and operator attention
required; low construction costs;
effectiveness, variable and subject to site
Sludge removal is labor intensive;
covering may be required in cold or wet
climates; odor and vector potential; land
requirements are considerable
Open beds:  2.0 - 2.5 sq ft/capita
Closed beds: 60 - 75 percent of open
            bed area
Capital cost may be substantially
increased if covering is required
Sludge removal is labor intensive, but
overall operating costs are low compared
to mechanical dewatering. Energy costs
are minimal; operation is simple
As required by disposal or end-use permit;
operational monitoring consists of cake
solids content measurement
Odors, flies may be a problem, particularly
if the sludge is not well stabilized
 5.16.4  Sludge Conditioning Aerobic Digestion
 Aerobic digestion of sewage sludge is commonly used
 by small communities as a means of stabilization prior to
 land  application. If  application  sites are in reasonably
 close proximity to the source of sludge, direct application
 of liquid sludge is clearly the most economical approach.
 If not, dewatering via sand drying beds may be used to
 reduce the volume of sludge to be hauled away.

 Aerobic digestion as practiced by small communities is
 typically performed in an open tank. Continuous introduc-
 tion of air allows biological oxidation  of organic matter
 under aerobic conditions. Aerobic digestion results in a
 reduction  in biodegradable volatile solids, improved de-
 waterability, and odor reduction. Oxygen may be sup-
 plied by mechanical aerators or diffusers.

 Solids retention times (SRTs) in aerobic digesters may
vary from 30 to 60 days depending on the ambient tem-
peratures of the site and the sludge. Minimum retention
times are likely to be dictated by state regulations that

specify the degree of stabilization necessary prior to agri-
cultural  utilization. EPA guidelines  indicate 60 days  at
158C (59°F) to 40 days at 20°C (68°F), with a volatile sol-
ids reduction of at least 38 percent. Actual operating ex-
perience would suggest that 40 percent VSS reduction
can be  achieved at lower  SRTs and that the minimum
SRT to  achieve such reduction is dependent on the type
of sludge. For example, extended aeration and oxidation
ditch sludges typically contain  no  primary sludge and
have already undergone partial  stabilization from endo-
genous respiration.
For small  operations, single-tank  digesters are  com-
monly used. Periodically, aeration is stopped and solids
are allowed to settle for 6 to 12 hours. Clarified super-
natant is then decanted and returned to the plant. This
procedure maximizes the solids  capacity of the digester,
and also allows a thickened  sludge to  be removed,
thereby reducing the volume to be hauled away. Gener-
ally, supernatant quality from an aerobic digester is fa-
vorable, and  impacts on  the  plant from supernatant
decant are minimal.
A recent development from Germany is the autothermal
thermophilic aerobic digestion process (ATAD). It is just
now  being  introduced into North  America.  European
studies indicate a superior  stabilization with greater cost-
effectiveness: greater  destruction of organisms and re-
duction of VSS at a price  competitive with conventional
aerobic digestion (EPA, 1990).
Table 5-30 provides  a summary of information on  the
aerobic digestion process. Anaerobic Digestion
Anaerobic digestion is  nearly as common among existing
small U.S. community systems as aerobic digestion. Like
the latter, subsequent processing may be a function of
proximity of the disposal site. When dewatering is  called
for, sand beds are the most frequent choice. However,
the use of anaerobic digesters for new treatment facilities
is becoming far less popular now that designers are rec-
ognizing the value of operational simplicity in new facilities.
When used, modern anaerobic digesters are generally
designed as two-stage systems, to maximize the stabili-
zation process and  gas production.  The recovery and
use of this gas  (primarily methane) is considered the
most attractive  feature of anaerobic digesters, but the
complexity of the recovery and use process makes their
feasibility marginal for wastewater systems with capaci-
ties in the range of 100,000 to 1 million gpd and unlikely
in  smaller systems,  unless regional energy recovery fa-
cilities are in place.  In these cases, the sludge from the
wastewater treatment plant becomes an additional energy-
producing raw material that must merely be transferred
from the treatment facility  to the energy recovery facility
 along with the responsibility for disposal.
Table 5-30. Summary of Information on Aerobic Digestion
of Sludge	
Applicability and Simple, widely used process for sludge
status           stabilization
Advantages      Minimal operator attention; low odor
                potential; simple process; resistant to
                upset; no chemical required
Disadvantages   Very high power consumption; aeration
                system requires high maintenance; larger
                volume tank required for cold climate
                application; foaming potential
Design criteria   SRT:           40 days at 20°C
                VSS loading:     0.1-0.4 Ib/cuft/d
                Diffused air req'd: 20-60 cfm/1,000 cu ft
                Mech. aeration:   0.75-1.25 HP/1,000 cu ft
                Minimum DO:    1-2 mg/L
Capital cost      Detention times, digester volumes, and
sensitivity      construction costs increase with
                decreasing sludge temperatures
Operation and   Relatively little operator attention for
maintenance    process except for monitoring and
                decant/sludge withdrawal operations; high
                maintenance for mechanical or diffused
                aeration system; high power requirements
                for oxygen transfer
Monitoring      As required by end-use permit;
                operational monitoring consists of DO,
                VSSin, VSSout, temperature Lime Stabilization
The addition of lime to sledges in sufficient quantities to
raise the pH above 12 for 30 minutes has been employed
by small municipalities in Europe and in the United States
for  many years. Lime treatment has several advantages
over biological conditioning including  low capital cost,
ease of use, and improved pathogen  reduction. It also
serves as an ideal temporary or interruptable supplemen-
tal  process  for periodically overloaded  existing  digester
systems.  The chief disadvantages of lime stabilization
are the inability of the process to reduce volatile solids (or
sludge  mass)  and the large increase in additional inert
solids for dewatering and disposal. Also, subsequent loss
of the  advantages of  alkaline  status upon storage must
be  accounted for in the subsequent sludge processing
steps (e.g., odors, slower dewatering rates). Design crite-
ria and other information on lime stabilization in small com-
munity treatment plant sludges is provided in Table 5-31.

In recent years, much has been made of new commercial
processes for  the  alkaline treatment  of waste sludge
"cake." Most of these processes have been  applied to
larger municipal facilities (>5 mgd capacity). It is doubtful
that these systems will have a significant impact on small
facilities unless they contribute to a  regional sludge man-

  Table 5-31. Summary of Information on Lime
  Stabilization of Sludge
  Applicability and


  Design criteria
 Capital cost
 Simple process

 Low capital cost; favorable pathogen
 destruction; on/off capability; low
 maintenance requirements.
 Large increase in sludge solids; no
 destruction of volatile SS; loss of benefits
 after storage > 2 wk.
 Dosage = attainment of pH >12 for 30
 minutes after mixing; mixing by aeration
 (preferred) or mechanical means;
 high-calcium lime yields faster reaction
time (hydrated lime preferred)
Lime dosage to meet pH/time
requirements, storage time, and mixing
requirements directly affect operating
costs. Higher calcium content of lime
reduces cost. Capital costs of
< $150,000 can be anticipated for STPs
of mgd.
Lime costs of < than $50/day; total O&M
costs are  primarily in range of $10 to
20/metric tone of solids, the great
majority being lime and labor;
maintenance of lime feeding and mixing
equipment is greatest demand
pH is the primary parameter for
 agement facility. In this case the responsibility for such
 processing would be transferred to the regional facility.

 5.16.5  Land Application of Sludge
 Application of stabilized sludge to the land is commonly
 practiced by small, rural communities. It is a simple proc-
 ess and provides substantial benefit to agricultural  and
 marginal  lands  given  the value of sewage  sludge as a
 soil conditioner and source of organic matter and nutrients.

 Sludge can  be applied as a liquid  or  as a  dewatered
 cake. Many small municipalities favor applying sludge as
 a liquid since it eliminates the dewatering step and stabi-
 lized sludge can be taken directly from'the plant to the
 land. Liquid sludge can be applied by tank truck, subsur-
 face injection, or spray irrigation. Dewatered sludge  can
 be  applied by a manure spreader and incorporated  into
 the soil by disking or plowing.

 Using the same tank truck both  to haul and apply sludge
 is a simple and economical approach, but it can cause
 compaction and rutting of the soil.  To overcome  this
 problem,  spray irrigation is recommended.  Equipment
 used for spray irrigation of sludge is simple and reliable.
 Another approach is to use specially designed applicator
trucks with flotation tires, but such equipment is costly for
 small communities to purchase and maintain unless they
 offset costs by receiving sludges from neighboring com-

 One of the major drawbacks of land application is the
 need to store .sludge when weather or soil conditions do
 not permit application.  Sludge is not applied when the
 soil is wet or frozen. In certain areas of the country, this
 restriction requires the capability to store sludge for long
 periods of time.

 The  rate of sludge application to land may be governed
 by nutrient loadings  or loadings of trace elements such
 as cadmium.  In  general, application rates  depend on
 sludge composition,  soil/hydrogeological characteristics,
 climate, vegetation, and cropping practices. Annual appli-
 cation rates have varied from 1 to over 220 t/ha (0.5 to
 100  tons/ac)  per year. For most small  municipalities
 treating sewage of domestic origin, sludge metals levels
 are generally low, and application rates are often based
 on supporting the nitrogen needs of  the crop. Typically
 900 dry kg (1 ton) of sludge provides  27 kg (60 Ib) of ni-
 trogen (50 percent of which is available), 18 kg (40 Ib) of
 phosphate, and 2 kg  (5 Ib) of potash.

 Table 5-32 provides  a summary of information on  land
 application of sludge.

 Table 5-32. Summary of Information on Land Application
 of Sludge
                                        Applicability and
                  Simple, widely used process of sludge
                  disposal for small communities
                  Simple; low cost; utilizes sludge as soil
                  conditioner, source of organic  matter and
Disadvantages    Storage requirements may be
                  considerable to accommodate sludge
                  generation during wet, frozen soil
                  conditions; odor potential; local
                  opposition possible; close monitoring
Design criteria    Dependent on sludge composition, soil
                 characteristics, vegetation, cropping
Capital cost      Costs may increase substantially if large
sensitivity        storage volumes required; cost of
                 specialized application vehicles high,
                 service life is approximately 10 yr
O&M             Costs sensitive to distances between
                 sludge source and application points;
                 maintenance of vehicles and application
                 equipment required; monitoring costs
                 may be high
Monitoring       Monitoring requirements dictated by state
                 regulations; requirements increase with
                 size of operation; monitoring required for
                 sludge soil, ground water, crops

5.17  Septage Handling Alternatives

5.17.1  Introduction
Providing  adequate treatment and disposal alternatives
for septic  tank pumpings (septage) is a major challenge
for small  communities. Raw  septage is a highly putre-
scible  material that may  contain high  levels of grit,
grease, and debris. It is difficult to dewater, and the char-
acteristics are highly variable. In addition, daily septage
generation rates are unpredictable, with substantial sea-
sonal variations occurring  due to changes  in soil and
ground-water conditions. In the past, septage has been
commonly applied to the land in a raw state. However,
many states are now implementing more stringent regu-
lations requiring stabilization of septage prior to land ap-
plication in order to minimize the potential for disease
transmission, vector attraction, and odor emissions. In
some areas, high densities of septic systems, lack of
available  land,  and lack of available sewage treatment
plant capacity have justified the construction of high-cost,
independent facilities dedicated solely to the treatment of

5.17.2 Septage Characteristics
Septage characteristics are highly variable depending on
such factors as tank size and design, user habits, pump-
ing frequency, climate and seasonal weather conditions,
and presence of appliances  such as garbage grinders,
washing machines,  and water softeners. Table 5-33 pro-
vides recommended design  values for  various charac-
terization  parameters.
Ratios of  peak monthly to average monthly septage vol-
ume that can be expected at  a treatment site range from
1.5 to 2.5. Ratio of peak daily to average daily volume
can be expected to range from  3.0 to 5.0. Annual sep-
tage volumes can be estimated from historical records, if
available; by assuming  a generation rate of 230 to 380
L/cap/yr (60 to 100 gal/cap/yr); or by assuming a typical
tank volume of 3,800 L (1,000 gal) and  a pumpout fre-
quency of every three to five years.

5.17.3  Overview of Septage Handling
Rgure 5-13 provides an  overview of septage  handling
options available to a small community. The most com-
mon approach  is  land application; co-treatment at a sew-
age treatment  plant is also widely employed.  For  small
communities, independent facilities are1 usually limited to
simple, low-cost approaches such as  stabilization la-
goons or lime stabilization systems.

5.17.4  Land Application
Land application of septage employs the same  tech-
niques used for land application of liquid sewage sludge
discussed earlier in this chapter. Where stabilization of
liquid septage  is required prior to land application, lime
stabilization should be considered, since it is one of the
Table 5-33. Suggested
Total P
Heavy metals
Toxic organics
Methyl alcohol
Isopropyl alcohol
Methyl ethyl ketone
Design Values for Septage
Value (mg/L)b


b Except for pH
TS = total solids
TVS = total volatile solids
TSS = total suspended solids
VSS = volatile suspended solids
COD=chemical oxygen demand
BOD = biochemical oxygen demand
TKN = total kjeldahl nitogen
NH4-N = ammonia nitogen
P = phophate
LAS = linear alkyl sulphonate

most simple and economical techniques to meet applica-
ble stabilization criteria. Lime  stabilization involves addi-
tion and mixing of sufficient lime to achieve a pH of 12 for
at least 30 minutes. To achieve pH of 12, lime dosages
can be expected to be 1,500 to 3,500 mg/L as Ca(OH)2,
which is hydrated lime. (Lime stabilization is discussed in
more detail earlier in this chapter.)

5.17.5  Co-treatment at a Sewage Treatment
Many septage haulers dispose of septage at wastewater
treatment plants. This is an acceptable alternative if the
plant  has sufficient  capacity and is  equipped to handle
the material.

The most common approach is to add the septage to the
headworks of the plant. In many plants,  this allows the
septage to undergo screening and grit removal, which is

                               Land Spreading
                               Trench/Landfill Burial
                               Subsurface Incotporalion
                               Addition to Liquid Stream
                               Addition to Sludge Stream
                               Addition to Both Streams
                               Stabilization Lagoon
                               Conventional Biological Treatment
                               Aerobic Digestion
                               Anaerobic Digestion
                               Lime Stabilization
 Figure 5-13. Basic Septage Management Options.

 important to remove debris and grit that can foul equip-
 ment or cause excessive wear  on pump components.
 Larger  plants (> 88 Us (2 mgd)) often allow  haulers to
 discharge directly to an influent channel or manhole im-
 mediately  upstream of  the  headworks.  However, for
 small plants, this can result in a substantial "shock load"
 to the  biological system, particularly if the plant is not
 equipped with a primary clarifier. Primary clarifiers allow
 removal of many of the organic septage solids, damping
 the  organic  loading to  the aeration  basin.  For  small
 plants lacking primary clarifiers or for larger facilities re-
 ceiving high  volumes of  septage, a septage  hold-
 ing/equalization tank is strongly recommended. The tank
 should  be sized to handle twice  the peak daily volume
 and should be  equipped with an air mixing system to
 maintain solids in suspension. A solids handling pump is
 then used to transfer septage to the headworks at a pre-
 determined rate. A timer and level control system can be
 used to establish these feed patterns. Because odor
 emissions from a septage holding tank are a major con-
 cern, provisions should be made for a  biofilter or other
 simple odor-control device.

 Details  of a septage receiving pad may be found else-
 where (EPA, 1984; Rezek and Cooper,  1980).  However,
 provision should be made for a trash rack and washdown
 facilities. It is important that a log be maintained of all
 septage deliveries; at a minimum, entries should include
 hauler's name, time of delivery, volume, and  source of
 septage. Also, a sample of each load received at the fa-
 cility should be taken.

 Septage may also be treated as a sludge, and handled
 as part of the solids management  scheme at the sewage
treatment plant. This can be accomplished effectively by
adding septage upstream of a primary clarifier;  however,
for small extended-aeration plants or oxidation ditches
 without primary clarification, handling septage in the sol-
 ids handling train deserves consideration. Septage may
 be added to the stabilization process, such as an aerobic
 digester, or to the sludge holding tank prior to  dewater-
 ing.  Separate screening and  grit removal is recom-
 mended  for either approach, however. Septage  is not
 easily dewatered, and  blending  with  treatment  plant
 sludge prior  to  dewatering may  have major  adverse
 impacts on the dewatering unit's performance. For this
 reason, addition of septage to the stabilization process
 is the preferred method of handling this waste  in the
 solids train.

 Table 5-34 provides a summary of information on sep-
 tage handling at a wastewater treatment plant.  Table 5-
 35  lists specific  factors to be evaluated for co-treatment
 of septage and watewater.

 5.17.6 Independent Septage Treatment
 Independent facilities for the treatment of septage may
 be warranted if land  is not available for land spreading,
 or if adequate treatment plant capacity is not available
 within a reasonable proximity (16 to 32 km  (10 to 20 mi))
 to the sources of septage. Independent facilities can vary
 in scope  from simple lime stabilization  systems to com-
 plex  mechanical septage treatment plants comprising
 multiple physical and biological processes.

 Independent septage treatment facilities using  technol-
 ogy compatible with the capabilities of a small  commu-
 nity would  most  likely utilize  aerobic  digestion,  lime
 stabilization, or lagoons. Aerobic Digestion
 Aerobic digestion of septage is very similar to aerobic di-
 gestion of sewage sludge (see discussion of the aerobic
 digestion process, earlier in this chapter).

 An independent septage treatment facility using the aero-
 bic digestion process should employ screening  and grit
 removal as part of a  preliminary treatment  scheme. Re-
 siduals from these processes require regular disposal.
 Although  the aerobic digestion  process is a relatively
 simple means of stabilization, there are several important
 concerns  related  to its  use at an independent septage
 treatment facility.  First, power costs are likely to be quite
 high to accomplish  the  transfer of oxygen. Second, su-
 pernatant decanted from the digester must be disposed
 of properly. Supernatant may require additional treatment
 prior to introduction to a subsurface disposal system as
 well as storage prior to use in an irrigation system. Vari-
 ous options for an independent aerobic  digestion facility
 are shown in Figure 5.14. Lime Stabilization
 Lime stabilization is likely to be among the most cost-
effective options for stabilization of septage  to meet land
application criteria and/or conditioning of septage prior to

Table 5-34. Summary of Information on Co-treatment of
Seplage at a Sewage Treatment Plant
Applicability and
Design criteria
Capital cost

Commonly used technique for septage
Sewage treatment plants generally
equipped to handle such waste;
compatible with sewage for biological
treatment; maintains waste treatment
operations at one location
Some plants may have insufficient
capacity to handle large volumes;
increases aeration, scum, and sludge
handling requirements; requires
adequate preliminary treatment systems;
may increase odor emissions
Screening and grit removal should be
provided; organic loading capacity of
plant must be evaluated; primary
clarification desirable to minimize impact
on biological system; separate receiving
station and equalization recommended
Additional capital cost may be only for
receiving station,  equalization/holding
tank, odor control system
Additional O&M costs likely for increased
aeration, sludge and scum handling
requirements, grit and screenings
disposal, cleanup
Septage volumes, characteristics, normal
wastewater plant monitoring
dewatering. The process is simple and requires a mini-
mum of operator skill and attention.
The process involves  addition of sufficient lime or other
alkaline material to raise the pH to 12 for a period of 30
minutes. This destroys pathogenic organisms, improves
dewaterability, and  reduces  objectionable  odors. Lime
can be added in the form of quicklime, CaO, or Ca(OH)2.
Table 5-35. Factors To Be Considered in Evaluating Co-
treatment of Septage	

Design Factors
  • Types of unit processes  at wastewater treatment plant
  • Design capacity (hydraulic and organic) of the plant
  • Proposed location of septage input
  • Volume of septage (average, peak)
  • Mode of addition (slug or continuous loading)
  • Ratio of existing loadings to design loadings (hydraulic
   and organic)
Potential Impacts
  • Increased organic loading to biological process
  • Increased solids loading to sludge handling processes
  • Increased hydraulic loading
  • Scum buildup on primary clarifier surfaces
  • Foaming problems in aeration basins
  • Increased odor emissions from headworks, primary
  • Potential upsets due to toxic substances present in
   nondomestic septage
  • Potential to exceed effluent limitations for BOD, TSS,
In addition, other alkaline materials such as lime kiln dust
or cement kiln dust can be used to elevate the pH.

Lime stabilization of septage is typically conducted on a
batch basis using a single- or two-tank system.  For small
operations, lime is added manually to the tank containing
screened, degritted septage. The tank contents are then
mixed; air mixing appears to be the most effective means
of mixing lime with liquid septage. The pH of the liquid is
monitored several  times during the lime addition process.
When a pH of 12 is reached, the contents are maintained
at that pH for a period of 30 minutes.  At this pH, release
of ammonia (NHs) can be expected.

'-H ,
nings Grit

Supernatant ^


— ^ Surface Water
— ^- Irrigation

                                       Land Application
                                     of Dewatered Sludge
                                       Land Application
                                       of Liquid Sludge
Figure 5-14. Alternatives for an Independent Aerobic Digestion Facility for Septage Treatment.

 The stabilized sludge may be applied to the land as a liq-
 uid or dewatered first, using sand drying beds.  If dewa-
 tered, treatment  and disposal of the filtrate  must  be

 Information on lime stabilization of septage is  summa-
 rized in Table 5-36.

 Table 5-36. Summary of Information on Lime Stabilization
 of Septage	
 Applicability    Simple, fully developed technology with
 and status     broad application for small communities
 Advantages    Simple batch processes; minimal operator
                skills; economical; meets EPA pathogen-
                reduction criteria; reduces objectionable
                odors; improves dewatering
 Disadvantages No organic destruction; increases mass of
                solids to be handled; mechanical lime feed
                systems, if used, require high degree of
                operator attention; dusty operation;
                potential ammonia releases
 Design criteria  Screening, grit removal recommended. Air
                mix tank, batch process
                pH = 12.0 for 30 minutes
                Dosage: 1,500-3,500 mg/L as Ca(OH)2
 O&M           Generally low O&M for small batch
                operations; larger, mechanized operations
                may have high O&M requirements;
                relatively low power consumption
 Construction   If dewatering is part of treatment scheme,
 issues          facilities must be constructed to
                treat/dispose of filtrate
 Monitoring     As required by disposal permit; operational
                monitoring consists of pH measurement;
                solids content of cake, if applicable Lagoons
 Lagoons are commonly  used for the treatment of sep-
 tage, particularly in the northeastern United States. Prop-
 erly  designed  and  sited, lagoons   provide  consistent
 performance and  are  easy to operate. The simplest sys-
 tem consists of two earthen basins in a  series. Raw sep-
 tage  is  discharged  into  the  primary  lagoon.  Partially
 clarified  effluent from the first  cell  is discharged into a
 second lagoon that also acts as a percolation pond. Liq-
 uid is disposed of through  a combination of infiltration
 and  evaporation.  Figure 5-15 shows various configura-
 tions for septage lagoons, including those that discharge
 to the ground water using percolation ponds or infiltration
 basins and those that produce an effluent that is sub-
jected to further treatment and/or is  applied to the land.
 Depending upon State regulations and  subsurface geo-
 logical and ground-water conditions, lining of the lagoons
 may be required, and the type that discharges to ground
water may be prohibited.  Concrete, asphalt, or clay liners
 are recommended over membrane liners due to the po-
tential for damage to membrane liners during removal  of
accumulated  solids.  Lagoons  are  often  constructed
 above grade with earthen embankments to minimize ex-
 cavation costs.

 Although performance data are limited, existing data sug-
 gest that septage be treated  in two lagoons in a series
 prior to treatment in infiltration  beds and  percolation
 ponds, and  before land application or further treatment
 and surface discharge.  One of the major operating con-
 siderations with septage lagoons is accumulation of sol-
 ids.  Lagoons  may  require  periodical  dredging,  and
 percolation ponds may  require draining and  cleaning to
 restore infiltrative capacity. For these reasons, use of two
 parallel lagoon systems  is recommended.

 To minimize odor emissions during the discharge of sep-
 tage from hauler trucks,  the material should  be dis-
           One-Cell Lagoon with Percolation Pond (Controlled Discharge)
            Two-Cell Lagoon with Percolation Pond (Controlled Discharge)

                                         ' Recircuiating
                                         Sand Filter
                                         ' Spray Irrigation
                                         ' Overland Flow
               Two-Cell Lagoon with Surface Discharge or
                Land Application (Controlled Discharge)
          Two-Cell Lagoon with Percolation Pond (Continuous Discharge)

                                        > Recircuiating
                                         Sand Filter
                                        1 Spray Irrigation
                                        1 Overland Flow
                Two-Cell Lagoon with Surface Discharge or
                 Land Application (Continuous Discharge)

Figure 5-15. Septage Lagoon Variations.

charged into a concrete chamber with a tight-fitting man-
hole or hatch. Septage then flows by gravity into the first
cell of the lagoon, below the water surface to avoid turbu-
lence. Because of the large exposed surface area, odor
emissions may be a problem. Large buffer zones (300 ft
(90 m)) are recommended. Addition of lime to maintain a
pH 7 may help reduce objectionable odors.
A summary of information on  septage lagoons  is  pro-
vided in Table 5-37.

5.18  References
When an NTIS number is cited  in a reference, that refer-
ence is available from:
    National Technical Information Service
    5285 Port Royal Road
    (703) 487-4650
Argaman, Y. 1988.  Continuously  fed  intermittently de-
canted activated  sludge:  A  rational basis for  design.
Water Res. 22:303.
Arora, M.L., E.F. Barth, and M.B. Umphres. 1985. Tech-
nology evaluation of sequencing batch reactors. WPCF
ASAE. 1980. Design and operation of farm  irrigation sys-
tems. M.E. Jensen ed. Monograph No. 3. St. Joseph, Ml.
American Society of Agricultural Engineers.
BMCI. 1989. AirVac vacuum sewage system design man-
ual. Rochester, IN.
Booher, L.J. 1974. Surface irrigation. FAO  Agricultural
Development Paper No. 94. United Nations. Rome, Italy:
Food and Agricultural Organization.
Borrelli, J. 1984. Overland flow treatment of domestic
wastewater in northern climates. EPA/600/2-84-161. En-
vironmental  Protection Agency.  Ada,  OK. R.S. Kerr Envi-
ronmental Research Laboratory.
Carlson, C.A., et al. 1974. Overland  flow treatment  of
wastewater. Misc Paper Y-74-3. U.S. Army Corps of En-
gineers. Vicksburg, MS. Waterways Experiment Station.
Condren,  A.J. 1978. Pilot-scale evaluations  of septage
treatment  alternatives. EPA/600/2-78-164,  NTIS  No.
Condren,  A.J., A.T.  Wallace,  I.A.  Cooper,  and  J.  F.
Kreissl. 1987. Design, operational and cost considera-
tions for  vacuum-assisted sludge dewatering bed  sys-
tems. J. WPCF, 59(4):228-234.
Converse, J.C., and E.J. Tyler. 1990.  Wisconsin  mound
soil  absorption system siting,  design and construction
manual. Madison,  Wl: University of  Wisconsin Small
Scale Waste Management Project.
Converse, J.C., E.J. Tyler, and J.O. Peterson. 1989. Wis-
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Table 5-37. Summary of Information on Septage Lagoons
Applicability     Suitable for septage disposal where
                geological conditions, buffer areas are
Advantages      Relatively low construction cost; consistent
                performance; simple operation
Disadvantages   Potential for ground water contamination
                and odor problems; large land area
                required; ground-water monitoring
                essential; eventually, dredging required to
                remove accumulated solids
Design criteria   Minimum 2 lagoons in series followed by
                percolation beds, land application,
                Two parallel systems recommended
                Percolation bed loading: 1 gpd/sqft
                Minimum ground-water separation
                distance: 4 ft (to top of ground-water mound)
                Detention time  (min.): 20 days in lagoons
                Lagoon depth (min.): 3 ft
                Lining: as required by state: concrete,
                asphalt, clay
                pH control: 6.8  - 7.2 using lime
Capital cost      Cost increase with lagoon lining
sensitivity       requirements and need for further
                treatment prior to surface discharge
O&M           Does not require skilled operator;
                dredging/cleaning operations are labor
                intensive; ground-water monitoring
                necessary; lime addition may reduce odor
Monitoring      Ground water monitoring required; effluent
                monitoring may be necessary depending
                on final disposal; minimal operational
Residuals       Lagoon dredgings; scrapings from
                infiltration basins
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