United States
Environmental Protection
Agency
Technology Transfer

Design
Manual
Office of Water Program
Operations
Washington DC 20460
Office of Research and
Development
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Onsite Wastewater
Treatment and
Disposal Systems

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EPA 625/1-80-012
                              DESIGN MANUAL
                       ON SITE WASTBAATER TREATMENT
                          AND DISPOSAL SYSTEMS
                  U.S. ENVIRONMENTAL PROTECTION AGENCY
                   Office of Water Program Operations
                   Office of Research and Development
               Municipal Environmental  Research Laboratory
                              October 1980

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                                NOTICE
The mention  of trade names or commercial  products in this publication is
for  illustration  purposes  and  does   not  constitute  endorsement  or
recommendation  for  use  by the  U.S.  Environmental  Protection Agency.

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                               FOREWORD
Rural  and  suburban  communities are  confronted  with  problems that  are
unique to their  size  and population  density,  and  are  often unable  to
superimpose  solutions  typically  applicable  to  larger  urban  areas.   A
good example of such  problems is the provision of wastewater  services.

In  the past,   priorities  for water  pollution control   focused  on  the
cities,  since  waste  generation  from  these  areas was most evident.    In
such  high-density  development,   the  traditional  sanitary   engineering
approach  was to construct a network of  sewers to convey wastewater  to a
central location for  treatment  and  disposal  to surface  waters.   Since a
large  number of  users  existed  per  unit  length of sewer line, the  costs
of construction and operation could be  divided  among many people,   thus
keeping the  financial  burden  on  each user relatively low.

Within the past several  decades, migration of  the population  from cities
to suburban  and rural  areas  has been  significant.   With  this  shift  came
the   problems   of   providing   utility   services  to  the   residents.
Unfortunately,  in many cases,  solutions  to wastewater problems in  urban
areas  have  been  applied to  rural  communities.    With  the  advent  of
federal  programs  that provide  grants   for   construction  of  wastewater
facilities,  sewers  and centralized  treatment plants were  constructed in
these low-density rural settings.   In many  cases the cost of operating
and  maintaining  such  facilities impose  severe economic  burdens on  the
communities.

Although  wastewater  treatment and disposal systems  serving single  homes
have  been  used  for   many  years,   they  have  often  been  considered  an
inadequate  or  temporary  solution  until  sewers  could  be  constructed.
However,  research has demonstrated  that  such  systems,  if constructed and
maintained  properly,   can provide  a  reliable and  efficient  means  of
wastewater treatment  and  disposal at relatively low cost.

This  document  provides  technical   information  on  onsite   wastewater
treatment and disposal  systems.   It does not  contain standards for  those
systems,  nor does it contain  rules or  regulations  pertaining to onsite
systems.

The  intended  audience for  this manual  includes  those  involved in  the
design,  construction,   operation, maintenance, and  regulation of onsite
wastewater systems.
                                   iii

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                             ACKNOWLEDGMENTS

There were three groups  of  participants  involved  in the preparation of
this manual:  (1) the contractor-authors,  (2) the contract supervisors,
and  (3) the  technical  reviewers.   The manual  was written by personnel
from  SCS  Engineers  and  Rural  Systems  Engineering  (RSE).    Contract
supervision was provided  by U.S.  Environmental  Protection Agency (EPA)
personnel  from the Municipal Construction Division in Washington,  D.C.,
and from the Municipal Environmental Research Laboratory in Cincinnati,
Ohio.   The technical reviewers were  experts  in  certain areas of onsite
waste treatment  and disposal,  and  included  professors,  health officials,
consultants,  and government  officials.    Each  provided technical  review
of a section or  sections  of  the  report.  The  membership  of each group is
listed below.

CONTTRACTOR-^UTHORS:
Direction:   Curtis J. Schmidt,  SCS
            William C.  Boyle, RSE

Senior Authors:   Ernest V, Clements,  Project  Manager,  SCS
                 Richard J.  Otis,  RSE

Contributing Authors:   David H.  Bauer,  SCS
                       Robert L.  Siegrist,  E.  Jerry  Tyler,
                         David E.  Stewart,  James C.  Converse,  RSE

CONTRACT SUPERVISORS:
Project Officers:   Robert M. Southworth, OWPO, EPA,  Washington,  D.C.
                   Robert P. G.  Bowker, MERL,  EPA,.  Cincinnati, Ohio

Reviewers:   James Kretssl, MERL,  EPA, Cincinnati,  Ohio
            Denis Lussier, CERI,  EPA, Cincinnati,  Ohio
            Sherwood Reed,  CRREL,  COE,  Hanover, N.H.

TECHNICAL REVIEWERS:
     1.  Michael Hansel - Minnesota Pollution Control  Agency
     2.  Roger Machmeier - University of  Minnesota
     3.  Jack Abney - Parrott, Ely & Hurt,  Inc.,  Lexington, Kentucky
     4.  William Mellen - Lake County Health  Department, Illinois
     5.  Rein Laak - University of Connecticut
     6.  Gary Plews - Washington Department of Social  & Health Services
     7.  B. L. Carlile - North Carolina State University
     8.  John Clayton - Fairfax County Health Department, Virginia
     9.  William Sharps - Pennsylvania State  University
    10.  Elmer Jones - U.S.  Department of Agriculture
    11.  Edwin Bennett - University of Colorado
    12.  Harry Pence - Virginia Polytechnic Institute
    13.  Briar Cook - U.S.  Department of  Agriculture,  Forest  Service
    14.  Marek Brandes - Ontario Ministry  of  the  Environment  (Retired)
    15.  Michael Nines - Illinois State Department of Public  Health
    16.  John Fancy - John Fancy,  Inc., Waldoboro, Maine
                                  IV

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                                CONTENTS

Chapter                                                           Page


           FOREWORD                                                 tii
           ACWOMEDGBVENTS,                                           v
           CONTENTS                                                 v i i
           LIST CF FIGURES                                           ix
           LIST CF TABLES                                            xv

   1       INTRODUCTION

           1.1  Background                                            1
           1.2  Purpose                                               2
           1.3  Scope                                                 3

   2       STRATEGY FOR ONSITE SYSTEM DESIGN

           2.1  Introduction                                          4
           2-2  Onsite System Design Strategy                         4

   3       SITE EVALUATION PROCEDURES

           3.1  Introduction                                         13
           3.2  Disposal Alternatives                                13
           3.3  Site Evaluation Strategy                             17
           3.4  References                                           48

   4       \AASTE\AATER CHARACTERISTICS

           4.1  Introduction                                         50
           4.2  Residential Wastewater Characteristics               50
           4.3  Nonresidential Wastewater Characteristics            57
           4.4  Predicting Wastewater Characteristics                65
           4.5  References                                           68

   5       WASTEWATER MODIFICATION

           5.1  Introducti on                                         70
           5.2  Water Conservation and Wastewater n o/v Reduction     71
           5.3  Pollutant  Mass  Reduction                             84
           5.4  Onsite Containment - Holding Tanks                   88
           5.5  Reliability                                          88
           5.6   Impacts  on Onsite Treatment and Disposal
                   Practices                                          92
           5.7  References                                          95

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                          CONTENTS (continued)

Chapter                                                            Pa9e


   6       ONSITE TREATMENT METHODS

           6.1            Introduction                                  97
           6.2  Septic Tanks                                         98
           6.3  Intermittent Sand Filters                            113
           6.4  Aerobic Treatment Units                             140
           6.5  Disinfection                                        161
           6.6  Nutrient Removal                                     184
           6.7  Waste Segregation and Recycle  Systems                197
           6,8  References                                          199

   7       DISPOSAL METHODS

           7.1   Introduction                                        206
           7.2  Subsurface Soil Absorption                           207
           7.3  Evaporation Systems                                 300
           7.4  Outfall to Surface Waters                            316
           7.5  References                                          316

   8       APPURTENANCES

           8.1   Introduction                                        321
           8.2  Grease Traps                                        321
           8.3   Dosing Chambers                                     327
           8.4  Flow Diversion Methods for  Alternating Beds          335
           8.5   References                                          337

   9       RESIDUALS DISPOSAL

           9.1   Introduction                                        338
           9.2  Resi dual s Characteristics                            338
           9.3  Resi duals Handl ing Option                            343
           9.4   Ultimate Disposal of Septage                        343
           9.5   References                                          351

  10       MANAGEMENT  CF ONSITE  SYSTEMS

           10.1   Introduction                                       353
           10.2   Theory of  Management                               354
           10.3   Types  of ManagementEnti ties                       355
           10.4   Management Program Functions                       353
           10,5   References                                         366

           APPENDIX-  Soil  Properties  and Soil-Water Relationships  36/

           GLOSSARY                                                382
                                  VI

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                                FIGURES
Number
 2-1       Onsite Wastewater Management Options                        5
 2-2       Onsite System  Design  Strategy                               7
 3-1       Potential  Evaporation Versus Mean Annual
             Precipitation                                            16
 3-2       Example of a Portion  of a  Soil Map as Published
             i n a Detailed  Soil  Survey  (Actual Size)                  20
 3-3       Translation of Typical Soil Mapping Unit Symbol            20
 3-4       Plot Plan Showing  Soil Series Boundaries from
             Soil Survey  Report                                       23
 3-5       Plot Plan Showing  Surface  Features                         25
 3-6       Landscape Positions                                        27
 3-7       Methods of Expressing Land Slopes   -                       27
 3-8       Preparation of Soil  Sample for Field Determination
             of Soil  Texture                                          30
 3-9          1 Texture Determination by Hand:  Physical
             Appearance of  Various      Soil      Textures             32
 3-10      Comparison of  Ribbons and  Casts  of Sandy Loam and
             Clay (Ribbons  Above, Casts Below)                        33
 3-11      Example Procedure  for Collecting Soil  Pit
             Observation  Information                                  34
 3-12      Types of Soil  Structure                                    36
 3-13      Typical Observation  Well for Determining Soil
             Saturation                                              38
 3-14      Construction of  a  Percometer                               42
 3-15      Percolation Test Data Form                                43
 3-16      Compilation of Soils  and  Site  Information
             (Information Includes Topographic,  Soil  Survey,
             Onsite SI ope and Soil P  i t Observations)                  45
                                  vn

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                           FIGURES (continued)


Number                                                              Page


 4-1       Frequency Distribution for Average Daily
             Residential Water Use/Waste Flows                        53

 4-2       Peak Discharge Versus Fi xture Units Present                64

 4-3       Strategy for Predicting Wastewater Characteristics         67

 5-1       Example Strategies for Management of Segregated
             Human Wastes                                             89

 5-2       Example Strategies for Management of Residential
             Graywater                                                89

 5-3       Fl ow Reduction Effects on Pollutant Concentrations         93

 6-1  '     Typical Septic Tank Outlet Structures to Mnimize
             Suspended  Solids in Discharge                           105

 6-2       Septic Tank  Sam and Sludge Clear Spaces                  107

 6-3       Typical Two-Compartment Septi C Tank                       108

 6-4       Four Precast Reinforced Concrete Septic Tanks
             Combined into One Unit for Large Flow
             Application                                             114

 6-5       Typical Buried Intermittent Filter Installation           129

 6-6       Typical Free Access Intermittent Filter                   131

 6-7       Typical Recirculati ng Intermittent Filter System          134

 6-8       Recircul ation Tank                                        134

 6-9       By-Pass Alternatives for Recirculati ng Filters            135

 6-10      Aerobic and Anaerobic Decomposition Products              142

 6-11      Examples of  Extended Aeration Package Plant
             Configurations                                          144

 6-12      Examples of  Fixed  Film Package Plant Configurations       156

 6-13      Stack  Feed Chi orinator                                    171
                                  vi n

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                           FIGURES (continued)

Number                                                              Page
 5-14      Iodine Saturator                                          172
 &-15      Sample Contact Chamber                                    174
 5-16      Typical UV Disinfection Unit                              177
 6-17      Typical UV Steril izing Chamber                            178
 6-18      Qnsite Peni tn~ fi cati on Systems                            190
 f-l       Typical Trench System                                     209
 I-I       Typical Bed System                                        210
 7-3       Alternating Trench  System with Diversion VaUe            218
 /-4       Provision  of a Reserve Area Between Trenches of
             the  Initial System on a Sloping Site                    220
 7-5       Trench System Installed to Overcome a Shallow Water
             Table or Restrictive Layer                              222
 7-6       Typical Inspection  Pipe                                   228
 '-7       Backhoe Bucket with Removable Raker Teeth                 228
 '-8       Methods of Soi 1  fcbsorpti on.Field.Rehabilitation                 232
 7-9       Seepage Pit Cross  Section                                 236
 7-10      Typical Mound Systems                                     240
 7-11      Jetaii sd  Schematic of  a Mound System                      241
 1-12      Proper Orientation of  a Mound System  on a Complex
             Si ope                                                   ?46
 7-13      Mound 31mensi ans                                          ?47
 ?-14      Tiered Mound  System                                      Z57
 7-15      :urtai n 3rai ti to Intercept Laterally ^lovl ig  Perched
              Water Table Caused  by a  Shallow,  Impermeable  Layer     261

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                          FIGURES (continued)
Number                                                             Page
 7-16      Vertical  Drain to  Intercept Laterally Moving
             Perched Water Table Caused by a Shallow,
             Thin,  Impermeable Layer                                 261
 7.-17      Underdrains  Used to Lower Water Table                     262
 7-18      Typical  Electro-Osmosis System                            270
 7-19      Single LI ne  Distribution Network                          273
 7-20      Drop Box Distribution Network                             274
 7-21      Closed Loop  Distribution Network                          276
 7-22      Di stri buti on Box Network                                  277
 7-23      Relief Line  Distribution Network                          279
 7-24      Central  Manifold Distribution Network                     280
 7-25      End Manifold Distribution Network                         281
 7-26      Lateral  Detail - Tee to Tee Construction                  282
 7-27      Lateral  Detail - Staggered Tees or Cross
             Construction                                            283
 7-28      Required Lateral Pipe Diameters for Various Hole
             Diameters,  Hole  Spacings, and Lateral Lengths
             (for Plastic Pipe Only)                                 285
 7-29      Recommended Mam fol d Diameters for Various Manifold
             Lengths,  Number  of Laterals, and Lateral
             Discharge  Rates  (for Plastic Pipe Only)                 286
 7-30      Nomograph for Determining the Minimum Dose Volume
             for a Given Lateral Diameter,  Lateral Length,
             and Number of Laterals                                  287
 7-31      Distribution Network for Example 7-2                      289
 7-32      Distribution Network for Example 7-3                      294
 7-33      Schematic of a Leaching Chamber                           298

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                          FIGURES  (continued)

Number                                                             Page

 7-34      Use of  Metal Holders for the Laying of Flexible
             Plastic  Pipe                                            299
 7-35      Cross Section of Typical ET Bed                           302
 7-36      Curve for  Establishing Permanent Home Loading Rate
             for Boulder,  Colorado Based on Winter Data,
             1976-1977                                               307
 7-37      Typical  Evaporation/Infiltration Lagoon for
             Small  Installations                                     312
 8-1       Double-Compartment Grease Trap                            326-
 8-2       Typical  Dosing Chamber with Pump                          329
 8-3       Level Control Switches                                    331
 8-4       Typical  Dosing Chamber with Siphon                        333
 8-5       Typical  Diversion Valve                                   335
 8-6       Top View of  Diversion Box Utilizing a Treated
             Wood  Gate                                               336
 8-7       Section View of Diversion Box Utilizing
             Adjustable Ells                                         336
 A-1       Names  and  Size Limits of Practical-Size Classes
             According  to Six Systems                                368
 A-2       Textural Triangle Defining Twelve Textural Classes
             of the USDA  (Illustrated for a Sample Containing
             37%  Sand,  451 Silt, and 18% Clay)                       370
 A-3       Schematic  Diagram of a Landscape and Different
             Soils Possible                                          375
 A-4       Upward Movement  by Capillarity in Glass Tubes as
             Compared with  Soils                                     377
 A-5       Soil Moisture Retention  for Four Different Soil
             Textures                                               378
                                   XI

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                           FIGURES (continued)


Number                                                             Page


 A-6       Hydraulic Conductivity  (K) Versus Soil
             Moisture Retention                                     379

 A-7       Schematic Representation of Water Movement Through
             a Soil  with Crusts of Different Resistances             381
                                 XI

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                                 TABLES
Number


 2-1       Selection of Disposal Methods Under Various
             Site Constraints                                          9

 3-1       Suggested Site Evaluation Procedure                        18

 3-2       Soil Limitations Ratings Used by SCS for Septic
             Tank /Soil Absorptian Fields                              22

 3-3       Soil Survey Report  Information for Parcel i n
             Figure 3-4-                                               24

 3-4       Textural Properties of Mineral Soils                       31

 3-5       Grades of Soil Structure                                   36

 3-6       Description of Soil Mottles                                37

 3-7       Estimated Hydraulic Characteristics of  Soil                39

 3-8       Falling Head Percolation Test Procedure                   41

 4-1       Summary of Average  Daily Residential Wastewater
             Fl ovs                                                    52

 4-2       Residential Water Use  by Activity                          54

 4-3       Characteristics  of  Typical Residential  Wastewater          56

 4-4       Pollutant Contributions  of Major Residential
             Wastewater Fractions  (gm/cap/day)                        58

 4-5       Pollutant Concentrations of Major Residential
             Wastewater Fractions  (mg/1 )                              58

 4-6       Typical Wastewater  Flows from Commercial  Sources          60

 4-7       Typical Wastewater  Flows from  Institutional
              Sources                                                  61

 4-8       Typical Wastewater  Flows from Recreational  Sources        62

 4-9       Fixture-Units  per Fixture                                  63

 5-1       Example Wastewater  Fl ow Reducti on Methods                 72
                                  xm

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                          TABLES [continued)
Number                                                             Page

 5-2       Wastewater  Flow Reduction - Water Carriage
             Toilets and  Systems                                      74
 5-3       Wastewater  Flow Reduction - Non-Water Carriage
             Toi1ets                                                  77
 5-4       Wastewater  Flow Reduction - Bathing Devices
             and Systems                                              79
 5-5       Wastewater  Flow Reduction - Miscellaneous Devices
             and Systems                                              82
 5-6       Wastewater  Flow Reduction - Wastewater Recycle and
             Reuse Systems                                            85
 5-7       Example Pollutant  Mass Reduction Methods                   87
 5-8       Additional  Considerations in the Design, Installation
             and Operation of Holding Tanks                           90
 5-9       Potential  Impacts  of Wastewater Modification on
             Onsite Disposal  Practices                                94
 6-1       Summary of  Effluent Data from Various Septic Tank
             Studi es                                                 100
 6-2       Typical  Septic Tank Liquid Volume Requirements            103
 6-3       Location of Top and Bottom of Outlet Tee or Baffle        107
 6-4       Performance of Buried  Intermittent Filters -
             Septic Tank  Effluent                                    121
 6-5       Performance of Free Access  Intermittent Filters           122
 6-6       Performance of Recirculating  Intermittent Filters         123
 6-7       Design Criteria for Buried  Intermittent Filters           124
 5-8       Design Criteria for Free Access  Intermittent Filters       126
 6-9       Design Criteria for Recirculating  Intermittent Filters     128
 6-10      Operation and  Maintenance Requirements for Buried
             Intermittent Filters                                    138
                                 XIV

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                          TABLES  (continued)

Number
 6-11      Operation  and Maintenance Requirements for Free
             Access  Intermittent Filters                             138
 6-12      Operation  and Maintenance Requirements for
             Reel restating  Intermittent Filters                      139
 6-13      Summary  of Effluent Data from Various Aerobic Unit
             Field  Studies                                           146
 6-14      Typical  Operating Parameters for Onsite Extended
             Aeration Systems                                        151
 6-15      Suggested  Maintenance for Onsite Extended Aeration
             Package  Plants                                          153
 6-16      Operational  Problems - Extended Aeration Package
             Plants                                                  154
 6-17      Typical  Operating Parameters for Onsite Fixed Film
             Systems                                                 158
 6-18      Suggested  Maintenance for Onsite Fixed Film Package
             Plants                                                  160
 6-19      Operational  Problems - Fixed Film Package Plants          162
 6-20      Selected  Potential Disinfectants for Onsite
             Application                                             163
 6-21      Halogen  Properties                                        164
 6-22      Chlorine Demand  of Selected Domestic Wastewaters          165
 6-23      Performance of Halogens and Ozone at 25°C                 167
 6-24      Halogen  Dosage Design Guidelines                          168
 6-25      UV Dosage  for Selected Organisms                          180
 6-26      Potential  Onsite Nitrogen Control Options                 186
 6-27      Potential  Onsite Phosphorus Removal Options               194
 6-28      Phosphorus Adsorption Estimates for Selected
             Natural  Materials                                       198
                                  xv

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                           TABLES  (continued)


Number                                                               Page


 7-1       Site Criteria for Trench and Bed  Systems                   212

 7-2       Recommended Rates of Wastewater Application  for
             Trench and Bed Bottom Areas •                             214

 7-3       Typical Dimensions for Trenches and  Beds                   221

 7-4       Dosi ng Frequencies for  Various  Soil  Textures               224

 7-5       Methods of Wastewater Application for  Various
             System Designs and Soil  Permeabilities                   225

 7-6       Si dewall Areas  of Circular Seepage Pits  (ft2)             237

 7-7       Site Criteria for Mound  Systems                            242

 7-8       Commonly Used Fill Materials  and  their Design
             Infiltration  Rates                                       245

 7-9       Dimensions for  Mound Systems                               248

 7-10      Infiltration Rates for  Determining Mound  Basal
             Area                                                     249

 7-11      Drainage Methods  for Various  Site Characteristics          266

 7-12      Distribution Networks  for  Various System  Designs
             and Application Methods                                  271

 7-13      Discharge  Rates for  Various Sized Holes a t Various
             Pressures  (gpro)                                          284

 7-14      Friction Loss  in  Schedule  40  Plastic Pipe,  C=150
             (ft/100  ft)                                              291

 7-15      Pipe Materials  for Nonpressuri zed Distributi on
             Networks                                                297

 7-16       Sample Water Balance  for Evaporation Lagoon Design        314

 8-1       Recommended  Ratings  for Commercial Grease Traps           324

 9-1       Resi duals  Generated  from Ons 1 te  Wastewater Systems        339
                                 xvi

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                          TABLES  (continued)
Number                                                             Page

 9-2       Characteristics of Domestic Septage                       340
 9-3       Indicator Organism and  Pathogen Concentrations
             i n Domestic  Septage                                     342
 9-4       Land Disposal  Alternatives for Septage                    345
 9-5       Independent Septage Treatment Facilities                  348
 9-6       Septage Treatment at Wastewater Treatment Plants          350
10-1       Site Evaluation and System Design Functions               359
10-2       Installation Functions                                    362
10-3       Operation and  Maintenance Functions                       364
10-4       Rehabilitation Functions                                  365
 A-1       U.S. Department of Agriculture Size Limits for
             Soil  Separates                                          367
 A-2       Types and Classes  of  Soil Structure                       372
                                  xvn

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                               CHAPTER  1

                              INTRODUCTION
1.1  Background
Approximately 18 million  housing  units,  or 25% of  all  housing units in
the United  States,  dispose of their wastewater using  onsite  wastewater
treatment and disposal  systems.  These systems include a variety of com-
ponents and  configurations,  the most common being  the  septic tank/soil
absorption  system.   The  number of onsite  systems  is  increasing,  with
about one-half million new systems being installed each year.


The  first onsite  treatment  and  disposal   systems  were constructed  by
homeowners themselves  or  by local entrepreneurs  in accordance with de-
sign criteria  furnished  by federal or  state  health departments.   Usu-
ally, a septic  tank  followed by a soil  absorption  field was  installed.
Trenches  in  the  soil absorption  system  were dug  wide  enough to accommo-
date open-jointed drain tile laid directly on  the exposed trench bottom.
Some health departments suggested that deeper  and wider trenches be used
in "dense"  soils and that the bottom of those trenches be covered with
coarse aggregate before  the  drain tile  was laid.  The  purposes  of the
aggregate were  to  provide a porous media through which  the septic tank
effluent  could  flow  and to provide storage  of the liquid until it could
infiltrate into the surrounding soil.


It has been estimated that only 32% of the total  land  area in  the United
States has soils suitable  for onsite  systems  which  utilize the soil for
final  treatment and disposal  of wastewater.    In areas where there is
pressure  for development, onsite  systems  have  often  been  installed on
land  that  is  not  suitable   for  conventional  soil  absorption systems.
Cases  of  contaminated wells  attributed  to inadequately  treated  septic
tank effluent, and nutrient enrichment of lakes from near-shore develop-
ment are  examples  of  what may occur when  a  soil  absorption  system is
installed  in an  area with   unsuitable  soil  or  geological  conditions.
Alarmed by  the  potential  health hazards of improperly  functioning sys-
tems, public health officials have continually sought methods  to improve
the design and performance of onsite systems.
Unfortunately,  the  great  increases  in population  have  exacerbated the
problems associated with onsite  systems.   The  luxury of vast amounts of
land  for  homesites  is gone;  instead,  denser housing  in  rural  areas is
more common.

                                   1

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In many  areas,  onsite systems  have  been plagued by  poor  public accep-
tance; feelings that those systems were second rate, temporary,  or fail-
ure prone.  This perspective contributed to poorly designed, poorly con-
structed, and inadequately maintained onsite systems.


Recently, the situation has begun  to  change.   Federal,  state, and local
governments have refocused  their  attention  on rural  wastewater  disposal
and,  more  particularly,  on wastewater  systems affordable  by the rural
population.   Onsite systems  are  now gaining  desired recognition  as  a
viable  wastewater  management  alternative  that  can  provide  excellent,
reliable service at a reasonable cost,  while  still  preserving  environ-
mental  quality.    Federal   and  many  state  and  local governments  have
initiated  public  education  programs  dealing  with  the  technical  and
administrative  aspects  of  onsite  systems  and other  less  costly waste-
water handling alternatives for rural  areas.
In this time of  population  movements  to rural  and semi rural  areas, high
costs of  centralized sewage  collection and treatment, and  new funding
incentives for cost  and  energy  saving technologies,  those involved with
rural wastewater  management need more  information on  the planning,  de-
sign, construction,  and  management  of onsite  systems.   This  process  de-
sign manual  provides primarily  technical  guidance on the design,  con-
struction, and maintenance of such systems.
1.2  Purpose
This document provides information on generic types of onsite wastewater
treatment and disposal systems.  It contains neither standards for those
systems nor rules and regulations pertaining to onsite systems.  The de-
sign information presented  herein  is  intended  as  technical  guidance re-
flective of sound, professional practice.  The intended audience for the
manual   includes  those involved in the  design,  construction, operation,
maintenance, and regulation of onsite systems.
Technologies  discussed in  this manual  were  selected  because of  past
operating  experience  and/or because of  the  availability  of information
and  performance  data  on those  processes.   Because a  particular  waste-
water handling option  is not discussed in this manual  does not mean that
it is not  acceptable.   All available technologies  should be considered
when planning wastewater management systems  for rural  and suburban com-
munities.
Groundwater  and  surface  water pollution are major environmental  consid-
erations  when  onsite systems  are used.   All  wastewater  treatment  and
disposal  systems must be designed, constructed, operated, and maintained

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to prevent  degradation of both  groundwater  and surface  water  quality.
For onsite systems designed  and  constructed  using  Environmental  Protec-
tion  Agency  funds,  all  applicable regulations  must be  complied  with,
including requirements  for disposal to  groundwaters (40 R^  6190,  Feb-
ruary 11, 1976).


This manual  is  only a guide.   Before  an onsite system  is  designed  and
constructed,  appropriate local or  state  authorities  should  be contacted
to determine the local  design requirements for a particular system.
1.3  Scope


This manual  includes:


     1.  A strategy for selecting an onsite system

     2.  A procedure for conducting a site evaluation

     3.  A summary of wastewater characteristics

     4.  A discussion of waste load modification

     5.  A presentation of generic onsite wastewater treatment methods

     6.  A presentation of generic onsite wastewater disposal  methods

     7.  A discussion of appurtenances for onsite systems

     8.  An overview of residuals characteristics and treatment/disposal
         alternatives

     9.  A discussion of management of onsite systems
The emphasis of this manual is on systems for single dwellings and small
clusters  of  up to 10  to  12  housing units.  Additional  factors  must be
considered for  clusters  of systems  serving  more than 10  to 12  housing
units.   A brief discussion  of onsite systems  for  multi-home units and
commercial/institutional   establishments  is  also   presented,  when  the
system designs differ  significantly from those for single dwellings.

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                               CHAPTER  2

                   STRATEGY FOR ONSITE  SYSTEM DESIGN
2.1  Introduction
A wide variety  of onsite system designs exist  from  which  to select the
most appropriate  for a given  site.   The  primary criterion  for selection
of one design over another is protection of the public health while pre-
venting environmental degradation.   Secondary criteria are  cost and ease
of operating and  maintaining  the system.   The fate of any  residuals re-
sulting from the treatment and disposal system must be considered in the
selection process.
Figure 2-1 summarizes wastewater management options for onsite systems.
Because of the wide  variety,  selection  of the  system that prevents pub-
lic health hazards and maintains environmental  quality at the least cost
is a difficult task.   The  purpose  of this chapter is to present a stra-
tegy for  selecting  the optimum onsite  system  for  a  particular environ-
ment.  At each step,  the reader is referred to the appropriate chapters
in the  manual  for site evaluation,  and  subsequent  system  design,  con-
struction, operation and maintenance, and residuals disposal.
2.2  Onsite System Design Strategy
Traditionally,  subsurface  soil  absorption  has  been used  almost exclu-
sively for onsite disposal of wastewater  because  of its ability to meet
the  public  health and environmental criteria without  the  necessity for
complex  design  or  high  cost.    A  properly designed,   constructed,  and
maintained  subsurface absorption system  performs reliably over  a long
period  of time with  little  attention.   This  is  because  of  the large
natural capacity of the soil  to assimilate the wastewater pollutants.
Unfortunately, much of the land  area  in  the United States does not have
soils  suited for  conventional  subsurface  soil  absorption fields.   If
soil absorption  cannot  be utilized, wastewater also may  be  safely dis-
posed  of  into surface waters  or evaporated into  the  atmosphere.   How-
ever, more  complex systems  may be  required  to  reliably  meet the public
health and environmental criteria where these disposal  methods are used.
Not  only  are complex systems  often more costly to  construct,  but they
are  also  more difficult and costly to maintain.   Therefore, the onsite
system selection strategy described here is based on the assumption that

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                                          FIGURE  2-1

                            ONSITE  WASTEWATER MANAGEMENT OPTIONS
             WASTEWATER
           MODIFICATION (Ch. 5}
           - Flow Reduction
           - Pollutant Mass
               Reduction
WASTEWATER
    FLOW
    (Ch.4)
      1
RESIDUALS
 DISPOSAL
  (Ch. 9)

1

HOLDING'
TANK

1
PRETRE/
(Ch
- Septit
- Aerob
                             EVAPORATION
                                (Ch. 7)
                               ET
                               ETA
                               Evaporation
                                Lagoon
                               E/l Lagoon
                                              FURTHER TREATMENT
                                                    (Ch. 6)
                                               - Aerobic Unit
                                               - Granular Filter
                                               - Nutrient Removal
                                               - Disinfection
                               SUBSURFACE SOIL
                               ABSORPTION (Ch. 7)
                                - Trenches
                                - Beds
                                - Pits
                                - Mounds
                                - Fill Systems
                                - Artificially Drained
                                  Systems
                                   SURFACE
                                  DISCHARGE

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subsurface soil  absorption  is the preferred onsite  disposal  option be-
cause of its greater reliability with a minimum of attention.Where the
site  characteristicsare  unsuitablefor  conventionalsubsurface  soil
absorption  systems,  other  subsurface  soil  absorption  systems may  be
possible.  Though  these other  systems  may be more  costly  to construct
than  systems  employing  surface water  discharge  or  evaporation,  their
reliable performance under  a minimum  of  supervision may make  them the
preferred alternative.   Figure  2-2  illustrates the onsite system design
strategy discussed in this chapter.


     2.2.1  Preliminary System Screening
The first step in the design of an onsite system is the selection of the
most appropriate components to make up the system.  Since the site char-
acteristics constrain the method of disposal  more than other components-,
the disposal component must be  selected  first.   Selection of wastewater
modification and  treatment components follow.   To select  the  disposal
method properly,  a  detailed  site evaluation is  required.   However, the
site characteristics  that  must  be evaluated may vary  with  the  disposal
method.  Since it is not economical nor practical to evaluate a  site for
every conceivable  system design, the  purpose  of this first  step  is to
eliminate the disposal options  with  the  least  potential  so  that the de-
tailed site evaluation can concentrate on the most promising options.
To effectively screen the disposal options, the wastewater to be treated
and  disposed  must be characterized,  and an  initial  site investigation
made.
         2.2.1.1  Wastewater Characterization
The  estimated  daily  wastewater  volume  and  any  short- or  long-term
variations in flow affect the size of many of the system components.   In
addition,  the  concentrations  of  various constituents  can  affect  the
treatment and disposal options chosen.  Characteristics are presented in
Chapter  4 for  wastewater from  residential  dwellings  as  well  as  from
commercial operations.
         2.2.1.2  Initial Site Evaluation
All useful  information  about  the  site  should be collected.   This may be
accomplished by client contact, a review of available published resource
information and records,  and  an  initial  site visit.   Client contact and
a  review  of published maps  and  reports should  provide  information re-
garding  the  soils,  geology,  topography,  climate,  and  other  physical

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          FIGURE 2-2



ONSITE SYSTEM DESIGN STRATEGY
Waste
Characterization
(Ch. 4)
>
t
Initial
Site
Evaluation
(Sec. 3.3.1. 3.3.2)

>

t
Preliminary
Screening of
Disposal Options
(Table 2-1)
>
t
Detailed
Site
Evaluation
(Ch. 3)

Design System
• Treatment (Ch. 5,6,8)
• Disposal (Ch. 7)
• Residuals (Ch. 9)
S
k
Selection of
Treatment
Component(s)
(Figure 2-1)
;
k
Selection of
Disposal Option
J

k

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features  of  the  site  (See 3.3.1  and  3.3.2).   An  initial  site  visit
should also be made, and  should  include a  visual  survey of the area and
preliminary field testing,  if  required, with a hand  auger (See 3.3.3).
From this site visit, general  site features such as relative soil  perme-
ability, depth and  nature of  bedrock,  depth to water table,  slope, lot
size, and landscape  position should be  identified.   Sources of informa-
tion  and evaluation procedures  for   site  evaluation  are detailed  in
Chapter 3.
         2.2.1.3  Preliminary Screening of Disposal  Options
From  the  wastewater characteristics  and  site  information gathered  in
this  step,  a  preliminary  screening of the disposal  options  can be made
using Table 2-1.   This  table  indicates  the onsite disposal  options that
potentially may  work for the  given  site constraints.   The  potentially
feasible disposal  options are  identified  by noting which ones perform
effectively under all the given site constraints.  Note that with suffi-
cient  treatment  and presence  of  receiving  waters,  surface water dis-
charge is always a potential  disposal  option.
As an example, suppose a site for a single-family home has the following
general characteristics:


     1.  Very rapidly permeable soil
     2.  Deep bedrock
     3.  Shallow water table
     4.  Five to 15 percent slope
     5.  Large lot
     6.  Low evaporation potential


From Table 2-1, the disposal options most applicable to the example site
constraints are:
     1.  Mounds
     2.  Fills
     3.  Surface water discharge
The  design  sections in  Chapter 7 would  be  consulted at this  point to
determine the  specific  characteristics to be  evaluated at the  site in
order to select the most feasible disposal options.

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                                             TABLE  2-1
         SELECTION  OF  DISPOSAL  METHODS  UNDER  VARIOUS SITE  CONSTRAINTS


Method
Trenches
Beds
Pits
Mounds
Fill Systems
Sand-Lined
Trenches or
Beds
Artificially
Drained
Systems
Evaporation
Infiltration
Lagoons
Evaporation
Lagoons
(lined)4-6
ET Beds
or Trenches
(lined) 4-s
ETA Beds
or Trenches4
Site Constraints
Soil Permeability
Very
Rapid



X
X


X








X


X


Rapid-
Moderate
X
X
X
X
X'


X


X


X


X


X

X
Slow-
Very Slow
X2


X
X1


X2





X6


X


X

X
Depth to Bedrock
Shallow
and
Porous



X
X











X


X


Shallow
and
Nonporous



X
X











X


X


Deep
X
X
X
X
X


X


X


X


X


X

X
Depth to
Water table

Shallow



X
X





X





X


X


Deep
X
X
X
X
X


X





X


X


X

X
Slope
0-5%
X
X
X
X
X


X


X


X


X


X

X
5-15%
X

X
X
X


X3


X








X6

X
15%
X

X

X


X3


X3










X
Small
Lot
Size
X"
X
X

X4


X'













X
1  Only where surface soil can be stripped to expose sand or sandy loam material.
2  Construct only during dry soil conditions. Use trench configuration only.
3  Trenches only.
4  Flow reduction suggested.
5  High Evaporation potential required.
6  Recommended for south-facing slopes only.
X means system can function effectively
with that constraint.

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     2.2.2  System Selection
With the potentially feasible  disposal  options  in  mind,  a detailed site
evaluation is performed.   The  information  collected  is  used to identify
the  system  options that meet  the  public health and  environmental  cri-
teria.  If more than one system is feasible, final  selection is based on
results of  a  cost effective analysis.   Local  codes  should be consulted
to determine  which onsite treatment and disposal  methods are permitted
in the area.
         2.2.2.1  Detailed Site Evaluation
A  careful,  detailed  site  evaluation  is  needed  to  provide  sufficient
information to select the most appropriate treatment and disposal system
from the potentially feasible  system  options.   The  evaluation should be
performed in  a systematic  manner  so  as to  insure  that the information
collected is useful and  in  sufficient detail.   A site evaluation proce-
dure is  suggested  in Chapter  3,  including  descriptions of the tests and
observations to be made.  This procedure is based on the assumption that
subsurface soil absorption  is the preferred method of disposal.  If sub-
surface absorption cannot be used, techniques are explained for evaluat-
ing  the  suitability of  a  site for surface  water discharge or evapora-
tion.
         2.2.2.2  Selection of Most Appropriate System
The disposal option selected after the detailed site evaluation dictates
the quality  of  the wastewater required prior  to  disposal.   If suitable
soils exist onsite to employ one of the subsurface soil absorption meth-
ods of disposal,  the  quality  of  the  wastewater applied need not be high
due to the  assimilative capacity of the  soil.   Where  suitable soils do
not exist onsite,  other methods  of disposal  that require a higher qual-
ity of wastewater may be necessary.   These  wastewater quality require-
ments are  established during the  site evaluation (Chapter 3).   Waste-
water reduction and  treatment options  are selected to  meet the required
wastewater quality.
Altering  the  characteristics  of  the  wastewater  generated  can  have  a
major  impact  on  the  design  of  the  treatment  and  disposal  system.
Alteration  can be  beneficial  in reducing the  size or  complexity of the
system.  Chapter 5 describes a variety of wastewater reduction options.
                                   10

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Chapter   6   provides   detailed  information   regarding   the   design,
construction and  operation  of  various treatment options.   Selection  of
the most appropriate treatment  option  is  based on  performance and cost.
Various onsite  systems may  be  synthesized from  the data  presented  in
Chapters  5  and  6.   As  an  example  of the  synthesis of  treatment  and
disposal systems following the detailed site evaluation,  assume that all
three disposal  options selected in 2.2.1.3 proved to be feasible.
Examination  of  the  first  two  disposal   options  indicates  that  only
minimal pretreatment may be required.  Thus, two systems might be:
     1.  Septic tank - mounds
     2.  Septic tank - fill
If groundwater quality is a  constraint,  however,  it may be necessary to
develop other  systems.   Thus, if nitrogen  discharges  from the disposal
system to the groundwater must be controlled, the two treatment-disposal
systems may be revised to include the following:
     1.  Septic tank - mound - denitrifi cation
     2.  In-house toilet segregation/graywater - septic tank - fill


Note that  a  variety  of  other systems  may  be  developed  as well.   The
other  disposal  option  listed in  2.2.1.3  is  surface  water  discharge.
Several  treatment options  exist  if  the  wastewater  is disposed  of  by
discharge  to  surface  waters.     Filtration   and   disinfection  may  be
required as  part  of those  treatment options,  depending  on the  water
quality requirements of the appropriate regulatory agency.


Residuals  produced  from  the  treatment  processes  also  require  safe
disposal.  This must be considered in the selection of  the treatment and
disposal   system.     Chapter  9  provides  information  regarding  the
character,   required  treatment,  and  methods  of  ultimate disposal  of
various residuals produced.
     2.2.3  System Design
Once  all  the  components are  selected,  design  of the  system follows.
Chapters  5,  6,  7, 8, and 9  should be consulted for design information.
                                  11

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     2.2.4  Onsite System Management
Past  experience  has  shown  that onsite  management districts  have  many
benefits,  including  improved site  selection,  system design,  construc-
tion, and  operation and maintenance.   Management  districts  also facili-
tate the use of more complex systems or larger systems servicing a clus-
ter of several homes.  These  districts can  take many forms  with varying
powers.   Chapter  10  provides  an overview of management  options for on-
site systems.
                                    12

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                               CHAPTER 3

                       SITE EVALUATION PROCEDURES
3.1  Introduction
The environment  into  which  the wastewater is discharged  can  be a valu-
able  part  of  an onsite wastewater  and disposal  system.   If  utilized
properly, it can provide excellent treatment at little cost.   However,
if  stressed  beyond  its assimilative  capacity, the  system will  fail.
Therefore, careful  site evaluation  is a  vital part  of onsite  system
design.
3.2  Disposal Options
In general,  facilities designed  to  discharge partially  treated  waste-
water to the soil for  ultimate  disposal  are  the  most reliable and least
costly  onsite  systems.   This  is because  little  pretreatment of  the
wastewater is necessary before  application to  the  soil.   The soil  has a
very large  capacity to transform  and  recycle most  pollutants  found  in
domestic wastewaters.   While the assimilative capacity of  some surface
waters also may be great, the quality of the  wastewater to be discharged
into  them  is   usually  specified by  local   water  quality  regulatory
agencies.


To achieve  the specified quality may require a more costly  treatment
system.    On the  other hand, evaporation of wastewater into  the  atmo-
sphere requires little wastewater pretreatment,  but this  method of dis-
posal is severely limited by local climatic  conditions.   Therefore,  the
soil  should  be  carefully evaluated prior to the investigation  of other
receiving environments.
     3.2.1  Wastewater Treatment and Disposal  by Soil


Soil   is  the  weathered  and unconsolidated  outer layer  of the  earth's
surface.   It is  a  complex arrangement  of primary mineral and  organic
particles  that  differ  in  composition,  size,  shape,  and  arrangement.
Pores or voids between the  particles transmit and  retain air  and water.
Since it  is  through  these pores  that  the wastewater must pass to  be
absorbed and treated, their characteristics are important.  These are
                                  13

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determined largely by the physical properties of the soil.  Descriptions
of some of the more important physical properties appear in Appendix A.


The soil is capable of treating organic materials, inorganic substances,
and pathogens in wastewater  by  acting as  a filter,  exchanger,  adsorber,
and  a  surface  on which  many  chemical  and  biochemical   processes  may
occur.  The  combination  of these processes acting  on  the wastewater as
it passes  through  the soil  produces  a water of  acceptable quality for
discharge into the groundwater under the proper conditions.
Physical  entrapment  of  particulate  matter  in  the  wastewater may  be
responsible  for  much of the  treatment provided  by  soil.   This process
performs  best  when the  soil  is unsaturated.  If  saturated soil  condi-
tions  prevail,  the wastewater  flows  through  the  larger pores and re-
ceives  minimal  treatment.   However, if the  soil  is kept unsaturated -by
restricting  the  wastewater flow  into  the soil,  filtration  is enhanced
because  the  wastewater is  forced  to  flow through  the  smaller pores of
the soil.


Because  most soil  particles and organic  matter  are negatively charged,
they attract and hold positively charged wastewater components and repel
those of like charge.  The  total charge on the surfaces of the soil  sys-
tem is called the cation exchange capacity, and is a good measure of the
soil's  ability  to  retain wastewater  components.   The  charged sites in
the  soil  are able  to sorb bacteria,  viruses, ammonium,  nitrogen,  and
phosphorus,  the  principal  wastewater constituents  of  concern.    The
retention  of bacteria  and viruses  allows  time  for  their die-off  or
destruction  by  other processes, such as  predation  by  other soil  micro-
organisms  (1)(2).   Ammonium  ions  can  be adsorbed  onto clay particles.
Where anaerobic conditions  prevail, the ammonium ions may be retained on
the particles.   If oxygen  is present, bacteria  can quickly nitrify the
ammonium  to  nitrate which is  soluble  and  is  easily  leached to  the
groundwater.  Phosphorus, on the other hand, is quickly chemisorbed onto
mineral  surfaces of  the  soil,  and  as the concentration  of phosphorus
increases  with  time,  precipitates  may form with the  iron,  aluminum, or
calcium  naturally  present  in  most soils.   Therefore, the  movement of
phosphorus through most soils is very slow (1)(2).
Numerous  studies have  shown  that 2  ft  to 4  ft  (0.6  to  1.2  m)  of
unsaturated  soil is  sufficient   to  remove  bacteria  and  viruses  to
acceptable levels and nearly all phosphorus (1)(2).  The needed depth  is
determined  by   the  permeability  of  the   soil.     Soils   with   rapid
permeabilities   may   require   greater  unsaturated   depths   below   the
infiltrative surface than soils with slow permeabilitiers.
                                    14

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     3.2.2  Wastewater Treatment and Disposal  by Evaporation
Wastewater can be returned directly to the  hydrologic  cycle  by evapora-
tion.  This  has  appeal  in onsite wastewater disposal  because  it can be
used in some areas where  site conditions  preclude  soil  absorption or in
areas  where  surface water  or groundwater  contamination  is a concern.
The wastewater can be confined and the water removed  to concentrate the
pollutants within the system.  Little or  no treatment  is  required prior
to evaporation.   However, climatic conditions  restrict the  application
of this method.
Evaporation  can  take  place  from a  free water  surface,  bare  soil,  or
plant canopies.  Evaporation from plants is  called transpiration.   Since
it is often  difficult  to  separate these  two  processes on  partially bare
soil  surfaces,  they are  considered  as a single process called  evapo-
transpiration  (ET).


If evaporation  is  to occur continuously, three  conditions must  be met
(3).    First,  there must be a continuous supply  of  heat to  meet the la-
tent heat requirements of water (approximately 590 cal/gm of water evap-
orated at 15  C).  Second, the vapor pressure in  the atmosphere over the
evaporative  surface  must remain lower than  the  vapor pressure  at the
surface.  This vapor pressure gradient is necessary to remove the mois-
ture either  by  diffusion, convection,  or both.   Third, there must be a
continuous supply  of water to the  evaporative surface.   The first two
conditions are strongly influenced by meteorological factors such as air
temperature,  humidity,  wind velocity,  and   solar  radiation,   while  the
third can be controlled by design.
Successful  use  of  evaporation  for  wastewater  disposal   requires  that
evaporation exceed the total water input  to  the  system.   Rates of evap-
oration  decrease dramatically  during  the cold winter  months.   In  the
case of  evaporative lagoons or evapotranspiration  beds,  input from pre-
cipitation must  also be included.  Therefore, application of evaporation
for wastewater disposal is largely restricted to areas where evaporation
rates  exceed  precipitation  rates.   These areas  occur primarily  in  the
southwestern United States  (see  Figure 3-1).  In  other  areas, evapora-
tion can be used to augment percolation into the soil.


Transpiration  by plants can be used  to augment evaporation in soil-cov-
ered systems (5)(6).   Plants can transpire at high rates, but only dur-
ing daylight hours  of the growing season.   During such periods,  evapo-
transpiration  rates may  exceed  ten times  the  rates  measured in Class A
evaporation pans (7)(8)(9).  However,  overall  monthly evaporation rates
exceed measured  evapotranspiration  rates.  Ratios of evapotranspiration
to evaporation (as measured from Class A  pans) are estimated to be 0.75
                                    15

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                                                     FIGURE  3-1

                            POTENTIAL  EVAPORATION  VERSUS MEAN ANNUAL  PRECIPITATION (4)
                                                     (inches)
CTl
                        + 30
                          + 50
                                                     + 50
                                                         + 3 0
                 ,   Potential Evapotranspiration more than
                    mean annual precipitation

                    Potential Evapotranspiration less than
                    mean annual precipitation

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to 0.8  (6)(7).   Therefore, if covered disposal  systems  are  to be used,
they must be larger than systems with a free water surface.
     3.2.3  Wastewater Treatment and Disposal in Surface Waters


Surface waters  may  be used  for  the disposal of  treated  wastewaters  if
permitted  by  the  local   regulatory  agency.   The  capacity of  surface
waters to assimilate wastewater pollutants varies with the size and type
of the body of water.  In some cases, because of the potential  for human
contact as  well as  the  concern for  maintaining the quality  of lakes,
streams, and wetlands, the use of  such  waters  for disposal  are limited.
Where they  can  be  used,  the minimum  quality of  the wastewater effluent
to be discharged is specified by the appropriate water quality agency.


3.3  Site Evaluation Strategy
The objective of a site investigation is to evaluate the characteristics
of the area  for their potential to  treat  and  dispose  of wastewater.   A
good site evaluation  is one  that  provides  sufficient information to se-
lect the  most  appropriate  treatment and  disposal  system from  a  broad
range of feasible options.  This requires that the site evaluation begin
with  all   options  in  mind,   eliminating  infeasible  options  only  as
collected site  data indicate  (see Chapter  2).   At  the  completion of the
investigation,  final  selection of a system from those feasible  options
is based on costs, aesthetics, and personal preference.


A  site evaluation should be  done  in a systematic manner  to  ensure the
information  collected is useful  and is sufficient  in detail.   A sug-
gested procedure is outlined in Table 3-1 and discussed in the following
section.   This  procedure, which can  be used  to evaluate the feasibility
of sites  for single  dwellings or small clusters of  dwellings (up to 10
to 12), is based  on  the  assumption  that subsurface soil  disposal is the
most appropriate  method of  wastewater disposal.   Therefore,  the suit-
ability  of  the  soils  and  other  site  characteristics  for  subsurface
disposal   are evaluated  first.   If found to  be  unsuitable, then  the
site's suitability for other disposal options is evaluated.
                                   17

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                               TABLE 3-1

                  SUGGESTED SITE EVALUATION PROCEDURE
          Step

  Client Contact
  Preliminary Evaluation
  Field Testing
  Other Site
    Characteristics
  Organization of Field
    Information
       Data Collected

Location and description of lot
Type of use
Volume and characteristics of
  wastewater

Available resource information
  (soil maps, geology,  etc.)
Records of onsite systems in
  surrounding area

Topography and landscape features
Soil profile characteristics
Hydraulic conductivity

If needed, site suitability for
  evaporation or discharge to
  surface waters should be
  evaluated

Compilation of all data into
  useable form
     3.3.1  Client Contact
Before performing any onsite testing, it is important to gather informa-
tion about the site that will be  useful  in evaluating its potential  for
treating and disposing of wastewater.  This begins with the party devel-
oping the  lot.    The  location of the  lot  and the  intended  development
should be established.  The volume and character of the generated waste-
water should  be  estimated.   Any  wastewater constituents that may  pose
potential  problems  in  treatment  and  disposal,  such as  strong  organic
wastewaters,  large  quantities of greases,  fats  or oils,  hazardous  and
toxic substances, etc., should be identified.  This information helps to
focus the site evaluation on the important  site characteristics.
                                   18

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     3.3.2  Preliminary Evaluation
The next step is  to  gather  any  available resource information about the
site.  This includes  soils, geology,  topography,  etc.,  that may be pub-
lished on maps  or in reports.  Local  records  of  soil  tests, system de-
signs, and reported  problems  with onsite systems installed  in  the sur-
rounding area should  also be  reviewed.   This  information may lack accu-
racy, but it can be useful  in identifying potential  problems or particu-
lar features  to investigate.   A  plot plan  of the lot  and  the  land im-
mediately adjacent to it should be drawn to a  scale large enough so that
the information gathered in this and later steps can be displayed on the
drawing.   The  proposed layout of all buildings  and other  manmade fea-
tures should also be sketched in.
         3.3.2.1  Soil Surveys


Soil surveys are usually  found  at  the  local  USDA Soil  Conservation Ser-
vice (SCS) office.  Also,  some  areas of the  country have been mapped by
a  state  agency and these  maps  may be located at  the  appropriate state
office.  In counties  now  being  mapped,  advance  field sheets with inter-
pretive tables often can be obtained from the SCS.


Modern soil survey reports are a collection of aerial photographs of the
mapping  area,  usually a  county, on  which the distribution  and  kind of
soils  are  indicated.   Interpretations  about the potential  uses  of each
soil  for farming,  woodland,  recreation,  engineeering  uses,  and other
nonfarm  uses  are provided.   Detailed  descriptions of each  soil  series
found  in the area are also given.  The maps are usually drawn to a scale
of  4  in.  to  1  mile.  An example of a portion of a  soil  map is shown in
Figure 3-2.


The map  symbols  for each  mapping unit  give the name of the soil  series,
slope, and degree of erosion  (10).  The soil  series name is given a two-
letter symbol, the  first  in upper case, the second in lower case.  Slope
is  indicated by  an  upper  case letter  from A to F.   A slopes are flat or
nearly flat and  F  slopes  are  steep.   The specific  slope range that each
letter represents differs  from survey to survey.  The degree of erosion,
if  indicated,  is  given  a  number  representing  an  erosion class.   The
classes  usually  range from 1  to 3, representing slightly  eroded to se-
verely eroded  phases.  The legend for  the map symbols is found immedi-
ately  preceding and  following  the map  sheets  in  the modern published
surveys.   An  example translation of  a map  symbol  from  Figure  3-2 is
given  in Figure 3-3.
                                   19

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                     FIGURE  3-2

  EXAMPLE  OF  A PORTION  OF  A  SOIL MAP AS  PUBLISHED
      IN A DETAILED  SOIL SURVEY  (ACTUAL  SIZE)
                                                 3 Acres
                                                  100' x 100'
                                                Soil Absorption
                                                    Area
                   FIGURE 3-3

TRANSLATION OF TYPICAL SOIL MAPPING UNIT SYMBOL
                   Dn  C  2
   Soil Series
   Erosion Class
(Moderately Eroded)
                   Slope Class
              (In This Survey 2-6%)
                       20

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Interpretations about potential  uses of each soil series  are  listed in
tables within the text of the report.  The soil's suitabiliy for subsur-
face  soil  absorption systems  and  lagoons  are  specifically  indicated.
Engineering  properties  are also  listed,  often  including  depth  to bed-
rock,  seasonal  high water table, percolation rate,  shrink-swell  poten-
tial, drainage potential, etc.   Flooding hazard  and other important fac-
tors are discussed for each mapping unit with the profile descriptions.


While the soil surveys offer good preliminary information about an area,
it is  not  complete  nor  a  substitute  for  a  field study.   Because of the
scale used, the mapping  units cannot represent areas smaller than 2 to 3
acres (8,100 to 12,100 nr).  Thus, there may be inclusions of soils with
significantly different  character within mapping units that  cannot be
indicated.   For  typical  building lots, the map  loses  accuracy.   There-
fore, these maps cannot be substituted for onsite testing in most cases.
Limitations ratings used  by  SCS  for septic tank-soil  absorption systems
are based on  conventional  trench or bed designs,  and  thus  do not indi-
cate  the  soil's  suitability for  other  designs.   Table 3-2  lists  the
criteria used  in making  the limitation  ratings.   They are based on  a
soil  absorption  system with the  bottom  surface  located 2 ft  (0.6  m)
below the soil surface.   In  many cases,  the limitations can be overcome
through proper  design.   Therefore,  the  interpretations should  be  used
only as a guide.
The information provided by the soil survey should be transferred to the
site drawing along  with  other important information.   An  example for a
parcel is  shown  in  Figure 3-4.   Information  for  each  of  the  soil sites
shown on Figure 3-4 is presented in Table 3-3.


         3.3.2.2  U.S. Geological  Survey Quadrangles


Quadrangles  published  by the  U.S.  Geological  Survey  may  be  useful  in
estimating slope, topography,  local  depressions or  wet areas,  rock out-
crops, and regional  drainage patterns and water table elevations.  These
maps  are  usually drawn  to  a  scale  of  1:24,000  (7.5  minute  series)  or
1:62,500 (15 minute series).   However,  because of their scale, they are
of limited value for evaluating small parcels.
                                    21

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                               TABLE 3-2

                 SOIL LIMITATIONS RATINGS USED BY  SCS
                FOR SEPTIC TANK/SOIL ABSORPTION FIELDS
                          [Modified after (10)]
     Property

  USDA Texture

  Floodi ng
  Depth to Bedrock,
   in.

  Depth to Cemented
   Pan, in.

  Depth to High
   Water Table,  ft
   below ground

  Permeability,
   in./hr
    24-60 in. layer
    layers <24 in.

  Slope, percent

  Fraction >3 in.,
   percent by wt
                                  Limits
 siignt    ModerateSevere
  None,
Protected

   >72
   >72
    >6
 Rare
40-72
40-72
 4-6
  Ice

Common
 Restrictive
   Feature

Permafrost

Floods
  <40     Depth to Rock
  <40     Depth to
            Cemented Pan

   <4     Ponding,
            Wetness
0-6.0
0-8
<25
0.6-2.0
8-15
25-50
<0.6
>6.0
>15
>50
Slow Perc. Rate
Poor Filter
Slope
Large Stones
         3.3.2.3  Local  Records
Soil test reports and records of reported failure of onsite systems from
the surrounding area may be  a  source  of valuable information.   The soil
test reports can provide an indication of soil types and variability.
Performance  of  systems may  be determined  from the  reported  failures.
These  records  are  usually available  from  the local  regulatory  agency.
                                   22

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                FIGURE 3-4

 PLOT PLAN  SHOWING  SOIL SERIES BOUNDARIES
         FROM  SOIL  SURVEY REPORT
Drainage
  Way
   Soil
Boundary
                                              Drainage
                                                 Way
     Adjacent Lot
                                               Property
                                                 Line
                    23

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                                  TABLE  3-3

                      SOIL SURVEY REPORT INFORMATION
                         FOR PARCEL  IN  FIGURE 3-4
                          Soil
                       Absorption          Depth  to
    Map     Soil         Limitation   Flood  High  Water Depth to    Permeability
   Symbol   Sen'es  Slope    Rating    Hazard    Tab! e    Bedrock   Depth	Perm.
                   *                        ftft      in.    in./hr


    DnC2   Dodge    2-6    Moderate     No       >5       5-10     0-40   0.63-2.0
                                                           40-60    2.0-6^3

     TrB   Troxel   2-6     Severe      Yes      3-5       >10      0-60    0.63-20

     PnB   Piano    2-6    Moderate     No       3-5       >10      0-41   0.63-2.0
                                                           41-60    2.0-e!3
     3.3.3   Field Testing
Field  testing begins with a  visual  survey of the parcel  to locate poten-
tial sites  for subsurface soil  absorption.  Soil borings are made in the
potential  sites to  observe  the soil  characteristics.   Percolation tests
may  be conducted  in those  soils  that appear to be  well suited.   If no
potential  sites can be  found from  either the  visual survey,  soil  bor-
ings,  or  percolation  tests,  then  other  means of   disposal  should  be
investigated.


          3.3.3.1  Visual Survey
A visual  survey is made to  locate the areas on the  lot with the greatest
potential  for subsurface  soil absorption.   The  location of  any depres-
sions  gullies,  steep slopes,  rocks  or  rock outcrops, or  other obvious
land and  surface features  are noted  and  marked on  the plot plan.  Vege-
tation  types are also noted that may indicate wetness  or shallow soils.
Locations  and distances from a permanent benchmark to  lot  lines, wells,
surface waters,  buildings,  and  other features  or  structures  are also
marked  on  the plot plan (see  Figure 3-5).  If a suitable area cannot be
                                     24

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                      FIGURE 3-5



          PLOT PLAN SHOWING SURFACE  FEATURES
                        1100
                                                o
                                                CM

                                                CO
               ,1110
B.M.-
I
                       400 Ft.
                 '30 Ft.


                °T
              'Well!
               Ft.
                           25

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found for a subsurface  soil  absorption  system based on this information
other disposal options  must  be considered  (see Chapter 2).   The remain-
der of the field testing can be altered accordingly.
         3.3.3.2  Landscape Position
The  landscape  position and  landform  for each  suitable area  should  be
noted.   Figure 3-6  can be  used  as a  guide for  identifying  landscape
positions.  This information is useful  in estimating surface and subsur-
face  drainage  patterns.   For  example, hilltops  and sideslopes can  be
expected to have good surface and subsurface drainage, while depressions
and foots!opes are more likely to be poorly drained.
         3.3.3.3  Slope
The type and degree of slope of the area should be determined.  The type
of slope indicates what  surface drainage  problems  may  be expected.  For
example, concave  slopes  cause surface runoff  to converge,  while convex
slopes disperse the runoff (see Figure 3-6).
Some treatment  and  disposal  systems are limited by  slopes.   Therefore,
slope measurement is important.  Land slopes can be expressed in several
ways (see Figure 3-7):
     1.  PERCENT OF GRADE - The  feet  of vertical  rise or fall  in 100 ft
         horizontal distance.

     2.  SLOPE  -  The  ratio  of  vertical  rise  or  fall  to  horizontal
         distance.

     3.  ANGLE - The degrees and minutes from horizontal.

     4.  TOPOGRAPHIC ARC  -  The feet  of vertical  rise or fall  in  66 ft
         (20 m) horizontal distance.
Land  slopes  are  usually  determined  by  measuring the  slope of  a  line
parallel to  the ground with an  Abney Level  either at eye height or  at
some other fixed  height above  the  ground.   If an ordinary hand level  is
used, then slopes are determined by  horizontal  line  of  sight which  give
changes in elevation for specific horizontal  distances.   A hand level  is
limited in  use because  it  is best  suited for  slope determinations  up
grade only,  but  has  the  advantage that only  one person is  needed  for
mapping slopes.   Three  methods of  slope  determinations are  discussed
below.
                                   26

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                       FIGURE  3-6

                  LANDSCAPE  POSITIONS
Depression
   /
Ridge Line
                                 Hill Top
 Convex
 Slope
                                            Sideslope
                                                        Foot Slope
                                                   Concave
                                                     Slope
                       FIGURE 3-7

         METHODS OF EXPRESSING LAND SLOPES (10)
                 Horizontal
     Percent of Grade-20
     Slope-1:5
     Angle-11° 19'
     Topographic Arc- 13.2
                           27

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Instrument Supported - Abney  Level:   For accurate slope determinations,
notch two sticks  or  cut  forked sticks so they will  hold  the  level  5 ft
(1.5 m) above the ground.  Rest the level in the notch or fork and sight
to the  notch or  fork  of the  other stick  held  by another person  at a
point on  the  slope.   The land slope  is  read  directly in  percent on the
Abney Level.


Abney  Level:   On  level  ground,  sight the person  working with you  to
determine the  point  of intersection  of  your  line of  sight on  him  when
the instrument is in position  for use as a hand level (zero level  posi-
tion).   When he  is  on the  slope, sight  the  same point on  the person
assisting you and read the slope directly.


Hand Level:  Height of eye must  be determined.   Then sight the point of
interception  with the ground  surface  and determine,  by tape measurement
or pacing, the  ground surface distance  between the  sighting  point and
the point of intercept.  To calculate land slope in percent, divide your
height of eye by the ground surface distance and multiply by 100.


Using one of the  above procedures or  other surveying methods, slopes at
selected sites can be determined  so that  topography  can  be  mapped.   The
number  of  sites  needed will  depend on the  complexity of  slopes.   Slope
determinations should be made at  each  apparent  change in  slope at  known
locations so steep slope areas can be accurately drawn.  Experience  will
be required for proficiency and accuracy  in mapping.   Steep slope  areas
in  natural  topography  have  irregular  form  and  curved  boundaries.
Uniform  boundaries  having  straight lines  and angular  corners  indicate
man-altered  conditions.   For  large areas  it  may be  necessary  to  draw
contour  lines  so that slopes  at  different points in  the  plot can  be
determined.
         3.3.3.4  Soil Borings
Observation  and  evaluation of  soil  characteristics can best  be deter-
mined from  a pit dug by a  backhoe or  other excavating equipment.   How-
ever, an  experienced soil   tester can  do a  satisfactory job by  using a
hand  auger  or probe.   Both methods  are  suggested.   Hand tools can  be
used  to  determine soil variability  over the area and  pits  used to de-
scribe the various soil types found.


Soil  pits  should  be  prepared  at the perimeter  of the  expected  soil
absorption area.   Pits  prepared within the  absorption  area often settle
after the system  has  been installed  and may disrupt  the distribution
network.  If hand augers are used, the holes may be made within the
                                    28

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absorption  area.    Sufficient borings  or  pits  should  be made  to ade-
quately describe  the soils  in  the area,  and  should be  deep  enough  to
assure  that a  sufficient  depth  of  unsaturated  soil  exists  below  the
proposed  bottom  elevation  of   the   absorption   area.    Variable  soil
conditions may require many pits.


Since  in  some  cases subtle differences in color need  to be recognized,
it  is  often advantageous  to prepare  the  soil   pit  so  the  sun  will  be
shining on  the  face during the observation period.   Natural light will
give  true color  interpretations.   Artificial   lighting  should  not  be
used.
         3.3.3.5  Soil Texture
Texture is one of the most important physical properties of soil because
of its close relationship to pore size, pore size distribution, and pore
continuity.   It  refers to the relative proportion  of the various sizes
of solid  particles  in  the soil that are  smaller  than 2 mm in diameter.
The  soil  texture is determined  in  the field by  rubbing  a moist sample
between the thumb and forefinger.  A water bottle is useful for moistur-
izing  the sample.   The grittiness, "silkiness,"  or stickiness  can  be
interpreted as  being caused  by  the soil  separates of  sand,  silt,  and
clay.   It is  extremely helpful to  work with some known samples to gain
experience with field texturing.


While laboratory analysis of soil texture is done routinely by many lab-
oratories,  field  texturing can  give  as good information  as  laboratory
data and  therefore  expenditures  of  time and money for laboratory analy-
ses are not necessary.   To determine  the  soil  texture, moisten a sample
of soil  about one-half to  one inch in diameter.   There  should be just
enough moisture  so  that the consistency is  like  putty.   Too  much mois-
ture  results  in a  sticky  material, which  is hard  to work.   Press  and
squeeze the  sample  between the  thumb  and forefinger.   Gradually press
the  thumb forward  to  try to  form  a  ribbon  from the  soil  (see Figure
3-8).   By using this  procedure,  the  texture of the  soil  can  be easily
described.
Table 3-4  and  Figures 3-9 and 3-10  describe  the  feeling and appearance
of the various soil textures for a general soil  classification.
                                   29

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                  FIGURE 3-8

    PREPARATION OF SOIL SAMPLE  FOR  FIELD
        DETERMINATION OF SOIL TEXTURE
(A) Moistening Sample
(B) Forming Cast
 (C) Ribboning
                       30

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                                TABLE 3-4

                  TEXTURAL PROPERTIES OF MINERAL SOILS
                              Feeling and Appearance
Sand
Sandy Loam
Loam
Silt Loam
Clay Loam
Clay
         Dry Soil

Loose, single grains which
feel  gritty.  Squeezed in
the hand, the soil mass
falls apart when the
pressure is released.

Aggregates easily crushed;
very faint velvety feeling
initially but with continued
rubbing the gritty feeling
of sand soon dominates.

Aggregates are crushed under
moderate pressure; clods can
be quite firm.  When pulver-
ized, loam has velvety feel
that becomes gritty with
continued rubbing.  Casts
bear careful handling.

Aggregates are firm but may
be crushed under moderate
pressure.  Clods are firm to
hard.  Smooth, flour-like
feel domi nates when soi1 i s
pulverized.

Very firm aggregates and
hard clods that strongly
resist crushing by hand.
When pulverized, the soil
takes on a somewhat gritty
feeling due to the harshness
of the very small aggregates
which persist.

Aggregates are hard; clods
are extremely hard and
strongly resist crushing by
hand.  When pulverized, it
has a grit-like texture due
to the harshness of numerous
very small aggregates which
persist.
                                    31
       Moist Soil

Squeezed in the hand, it
forms a cast which crumbles
when touched.  Does not form
a ribbon between thumb and
forefinger.

Forms a cast which bears
careful handling without
breaking.  Does not form a
ribbon between thumb and
forefinger.

Cast can be handled quite
freely without breaking.
Very slight tendency to
ribbon between thumb and
forefinger.  Rubbed surface
is rough.
Cast can be freely handled
without breaking.  Slight
tendency to ribbon between
thumb and forefinger.  Rubbed
surface has a broken or
rippled appearance.

Cast can bear much handling
without breaking.  Pinched
between the thumb and
forefinger, it forms a ribbon
whose surface tends to feel
slightly gritty when dampened
and rubbed.  Soil is plastic,
sticky and puddles easily.

Casts can bear considerable
handling without breaking.
Forms a flexible ribbon
between thumb and forefinger
and retains its plasticity
when elongated.  Rubbed
surface has a very smooth,
satin feeling.  Sticky when
wet and easily puddled.

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                                FIGURE  3-9

              SOIL TEXTURE DETERMINATION  BY  HAND:   PHYSICAL
                   APPEARANCE OF VARIOUS  SOIL TEXTURES
                      Dry
          Moist
Sandy
Loam
               Weak Aggregates
No Ribbon; Non-Plastic Cast
 Silt
Loam
  Clay
                Firm Aggregates
              Hard Aggregates
  Very Slight Ribboning
  Tendency; Moderately
       Plastic Cast
Ribbons Easily; Plastic Cast
                                     32

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                              FIGURE 3-10

             COMPARISON OF RIBBONS AND CASTS OF SANDY LOAM
                 AND CLAY (RIBBONS ABOVE, CASTS BELOW)
If the soil sample ribbons  (loam,  clay  loam,  or clay),  it may be desir-
able  to  determine  if sand  or  silt predominate.   If there is  a  gritty
feel and a lack of smooth talc-like feel, then sand very likely predomi-
nates.  If there is a lack of a gritty feel  but a smooth talc-like feel,
then  silt  predominates.   If there is not a predominance  of  either  the
smooth  or  gritty feel,  then the  sample should not be called anything
other than  a  clay,  clay loam, or  loam.   If  a  sample feels quite smooth
with  little or no grit  in  it, and will  not form a  ribbon,  the sample
would be called silt loam.
Beginning  at  the  top or bottom of  the  pit sidewall,  obvious changes in
texture with  depth  are noted.  Boundaries  that  can be seen are marked.
The texture of each  layer  or horizon is determined and the demarcations
of  boundaries changed  as  appropriate.    When  the textures have  been
determined  for  each layer,  the depth,  thickness,  and texture  of  each
layer is recorded (see Figure 3-11).
         3.3.3.6  Soil Structure


Soil  structure has  a  significant  influence  on  the soil's acceptance and
transmission of water.  Soil structure refers to the aggregation of soil
particles into clusters of particles, called peds, that are separated by
surfaces  of weakness.   These  surfaces  of  weakness  open planar  pores
between the  peds  that are  often seen as  cracks in the soil.   These pla-
nar  pores can greatly modify  the  influence  of  soil  texture  on  water
movement.    Well-structured  soils with  large  voids  between  peds  will
transmit  water more rapidly than  structureless  soils of the  same  tex-
ture,  particularly  if the  soil   has  become  dry before  the  water  is
added.  Fine-textured, massive  soils (soils' with  little  structure)  have
very  slow percolation  rates.
                                   33

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           FIGURE 3-11

EXAMPLE PROCEDURE FOR COLLECTING
SOIL PIT OBSERVATION INFORMATION
Depth
(Ft.)
0
2
4
6
8
10
12
14
Texture Structure Color Soil Saturation
Silt
Loam
Silty
Clay Loan
Clay Loam
Sandy
Loam
1 1
Granular
Platy
Blocky
Platy
Massive
Brown
None
               34

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If a detailed analysis  of  the  soil  structure is necessary, the sidewall
of the  soil  pit should  be carefully examined, using a  pick  or similar
device  to expose  the  natural  cleavages and  planes  of weakness.  Cracks
in the  face  of  the soil profile are  indications  of breaks between soil
peds.  The shapes created by the cracks should be compared to the shapes
shown  in  Figure  3-12.    If cracks  are  not visible,  a  sample  of soil
should  be carefully picked out  and,  by hand,  carefully  separated into
the structural  units until  any further breakdown can only be achieved by
fracturing.
Since the  structure can significantly alter  the  hydraulic characteris-
tics of  soils,  more detailed  descriptions  of soil  structure  are  some-
times desirable.   Size  and grade of durability of the structural  units
provide  useful  information to  estimate  hydraulic conductivities.   De-
scriptions of types and  classes of  soil  structure used by SCS are given
in  Appendix  A.   Grade descriptions  are  given in  Table 3-5.   The  type,
size, and grade of each horizon or zone is recorded in Figure 3-11.
         3.3.3.7   Soil Color
The color and color patterns  in  soil are good indicators of the drainage
characteristics  of the  soil.    Soil  properties,  location in  the land-
scape,  and climate  all  influence  water movement  in the soil.   These
factors  cause  some  soils  to   be  saturated  or  seasonally  saturated,
affecting  their  ability to absorb and treat wastewater.   Interpretation
of soil color aids in  identifying these conditions.
Color  may  be described by estimating the true color for each horizon or
by  comparing the soil  with the  colors  in  a soil  color book.  In either
case,  it is  particularly  important  to note  the colors  or color patterns.
 Pick  up some  soil  and,  without crushing,  observe the  color.    It is
 important  to  have  good  sunlight  and know  the moisture  status  of the
 sample.   If ped  faces are dry,  some water applied from  a mist bottle
 will  allow observation of moist  colors.
 Though  it is often  adequate to speak of  soil  colors in general terms,
 there  is  a  standard method of describing  colors using  Munsell  color
 notation.   This  notation  is used  in  soil survey  reports  and soil  de-
 scription.   Hue is the dominant spectral color and refers  to  the light-
 ness  or darkness  of  the color between black and  white.   Chroma is the
 relative  purity  of  strength of  the color, and  ranges from  gray  to a
 bright  color of  that  hue.   Numbers are given  to  each of the variables
 and  a verbal description  is also given.   For  example, 10YR  3/2 corre-
 sponds  to a color hue of 10YR  value of  3  and  chroma  2.  This is a very
 dark  grayish  brown.

                                    35

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                            FIGURE 3-12

                      TYPES OF SOIL STRUCTURE
          Prismatic
                      Columnar
                   Subangular
          Angular    Blocky
          Blocky
                                              Granular
                             TABLE  3-5

                     GRADES OF  SOIL STRUCTURE
    Grade

Structureless

Weak


Moderate



Strong
      Characteristics

No observable aggregation.

Poorly formed and difficult to  see.
Will  not retain shape on  handling.

Evident but not distinct  in undisturbed
  soil.
Moderately durable on handling.

Visually distinct in undisturbed  soil.
Durable on handling.
                                 36

-------
If a soil color book 1s used to determine soil  colors, hold the soil and
book so  the  sun shines over your  shoulder.   Match the  soil  color with
the color chip  in  the book.  Record the  hue,  chroma  and value,  and the
color name.
Mottling in  soils  is described by the color  of  the  soil  matrix and the
color  or  colors,  size, and  number  of the mottles.   Each color  may  be
given  a Munsell  designation  and name.  However,  it  is  often sufficient
to  say the soil is  mottled.   A  classification  of mottles  used  by the
USDA is shown in Table 3-6.  Some examples of soil mottling are shown  on
the inside back cover of this manual.
                                TABLE 3-6

                     DESCRIPTION OF SOIL MOTTLES (10)
    Character     Class                 Limit

   Abundance      Few            <2% of exposed face
                  Common         2-20% of exposed face
                  Many           >20% of exposed face

   Size           Fine           <5mm longest dimension
                  Medium         5-15mm longest dimension
                  Coarse         >15mm longest dimension

   Contrast       Faint          Recognized only by close observation
                  Distinct       Readily seen but not striking
                  Prominent      Obvious and striking
      3.3.3.8  Seasonally Saturated Soils
 Seasonally saturated soils can usually be detected by  soil  borings  made
 during the wet season or by the presence  of  mottled soils  (see 3.3.3.7).
 For large  cluster systems  or  for developments where  each dwelling  is
 served by an  onsite  system,  the use of observation wells may  be  justi-
 fied.   They are constructed as shown in Figure 3-13.   The  well  should be
 placed in,  but not  extended  through,  the horizon that  is to be moni-
 tored.   More  than one well  in each horizon that may  become  seasonally
 saturated is desirable.  The wells are monitored over  a  normal wet  sea-
 son by observing  the presence  and  duration of water  in  the  well.    If
 water  remains  in the well  for several  days,  the water  level  elevation is
 measured  and  assumed to be  the elevation  of  the  seasonally  saturated
 soil  horizon.
                                    37

-------
                               FIGURE 3-13

                      TYPICAL OBSERVATION WELL FOR
                       DETERMINING SOIL SATURATION
Excavated
(Tamped in
1 "-4'
Solid
1
Soil He
to be Me
^
J^S
t~«—
Soil Material _
when placing)
' Diameter
Wall Pipe
1
)rizon
mitored
r
1
|
, ,«
. ff.'
• *
'oV
• *.*
-
•;»•. :
1
i
g
V/X
.o'.1
•;<
»" .
• > t
••
^f
12" Puddled Clay
.7 or Equal Parts of
Soil and Cement
Mixture

V
,. ^/2"-3/4" Gravel
l!?'"
•> \i.
1" Min.
         3.3.3.9  Other Selected Soil Characteristics
Soil  bulk  density  is  related  to  porosity  and  the movement  of water.
High bulk  density  is an indication of  low  porosity and restricted flow
of  water.   Relative  bulk  densities  of different  soil  horizons can  be
detected in the  field  by pushing a knife or other instrument into each
horizon.   If one horizon offers considerably more resistance to  penetra-
tion than  the others,  its  bulk  density  is  probably higher.  However,  in
some  cases,  cementing  agents  between  soil  grains  or peds may be the
cause of resistance to penetration.


Swelling clays,  particularly montmorillonite  clays, can  seal  off soil
pores when wet.  They can be detected during field texturing of  the soil
by their tendency to be more sticky and plastic when wet.
                                   38

-------
         3.3.3.10  Hydraulic Conductivity


Several methods  of measuring  the  hydraulic conductivity of  soils  have
been developed (1)(11).  The most  commonly  used  test is the percolation
test.   When  run  properly,  the test can give an approximate  measure of
the  soil's  saturated  hydraulic conductivity.  However,  the percolation
of  wastewater  through soil below  soil  disposal  systems  usually  occurs
through unsaturated soils.  Therefore, empirical  factors must be used to
estimate unsaturated  conductivities.   The  unsaturated hydraulic conduc-
tivities can vary dramatically from the saturated hydraulic conductivity
with changes in  soil  characteristics  and moisture  content (see Appendix
A).
The percolation test  is  often  criticized  because  of its variability and
failure to  measure  the  hydraulic conductivity  accurately.   Percolation
tests conducted  in  the  same  soils  can vary by 90% or more (1)(11)(12)
(13)(14).   Reasons  for the  large  variability  are  attributed to the pro-
cedure used,  the  soil  moisture conditions at the  time of the test, and
the  individual  performing  the test.   Despite  these  shortcomings, the
percolation  test  can  be useful  if  used together  with the  soil  borings
data.  The  test can be  used to rank the relative hydraulic conductivity
of  the soil.   Estimated  percolation rates for various soil  textures are
given in Table 3-7.
                                TABLE  3-7

            ESTIMATED HYDRAULIC CHARACTERISTICS OF  SOIL  (15)


      Soil  Texture               Permeabi1ity             Percolation
                                   in./hr                  min/in.


   Sand                               >6.0                     <10

   Sandy loams
   Porous silt loams                0.2-6.0                   10-45
   Silty clay loams

   Clays, compact
   Silt loams                         <0.2                     >45
   Silty clay loams
                                     39

-------
If  test  results agree  with this  table,  the test  and boring  data  are
probably correct and can be used in design.  If not, either the test was
run improperly  or  soil  structure or clay  mineralogy  have  a significant
effect on the hydraulic conductivity.   For example,  if the texture of a
soil is
-------
                                    TABLE  3-8

                FALLING  HEAD PERCOLATION TEST  PROCEDURE
1.  Number and Location  of Tests

    Commonly a minimum of three percolation tests are performed within the area  proposed
    for an absorption system.  They are spaced uniformly throughout the area.   If  soil
    conditions are highly variable, more tests may be required.

2.  Preparation of Test  Hole

    The diameter of each test  hole is 6 in., dug or bored to the proposed depths at  the
    absorption systems or to the most limiting soil horizon.  To expose a natural  soil
    surface, the sides of the  hole are scratched with a sharp pointed instrument and the
    loose material  is removed  from the bottom of the test hole.  Two inches of 1/2 to 3/4
    in. gravel  are placed in the hole to protect the bottom from scouring action when the
    water is added.

3.  Soaking Period

    The hole is carefully filled with at least 12 in. of clear water.  This depth  of
    water should be maintained for at least 4 hr and preferably overnight if clay  soils
    are present.  A funnel with an attached hose or similar device may be used to  prevent
    water from washing down the sides of the hole.  Automatic siphons or float valves may
    be employed to automatically maintain the water level  during the soaking period.   It
    is extremely important that the soil be allowed to soak for a sufficiently long
    period of time to allow the soil to swell if accurate results are to be obtained.

    In sandy soils with  little or no clay, soaking is not necessary.  If, after  filling
    the hole twice with  12 in. of water, the water seeps completely away in less than ten
    minutes, the test can proceed immediately.

4.  Measurement of the Percolation Rate

    Except for sandy soils, percolation rate measurements are made 15 hr but no  more than
    30 hr after the soaking period began.  Any soil that sloughed into the hole  during
    the soaking period is removed and the water level is adjusted to 6 in. above the
    gravel (or 8 in. above the bottom of the hole).  At no time during the test  is the
    water level allowed  to rise more than 6 in. above the gravel.

    Immediately after adjustment, the water level is measured from a fixed reference
    point to the nearest 1/16  in. at 30 min intervals.  The test is continued until  two
    successive water level drops do not vary by more than 1/16 in.  At least three
    measurements are made.

    After each measurement, the water level is readjusted to the 6 in. level.   The last
    water level drop is  used to calculate the percolation rate.

    In sandy soils or  soils in which the first 6 in. of water added after the soaking
    period seeps away in less  than 30 min, water level measurements are made at  10 min
    intervals for a 1 hr period.  The last water level drop is used to calculate the
    percolation rate.

5.  Calculation of the Percolation Rate

    The percolation rate is calculated for each test hole by dividing the time interval
    used between measurements  by the magnitude of the last water level drop.  This
    calculation results  in a percolation rate in terms of min/in.  To determine  the
    percolation rate for the area, the rates obtained from each hole are averaged.  (If
    tests in the area  vary by  more than 20 min/in., variations in soil type are
    indicated.  Under these circumstances, percolation rates should not be averaged.)

    Example:  If the last measured drop in water level after 30 min is 5/8 in.,  the
    percolation rate =  (30 min)/(5/8 in.) = 48 min/in.



                                           41

-------
                                      FIGURE  3-14

                             CONSTRUCTION  OF  A  PERCOMETER
Thin Steel
Rod
            ru*—- Yard Stick
                   Eyelets
 Cork
 Float
                   Cross Arm
                   Support
6"-9"
Diameter
                   2" Layer
                   of Gravel
                 When making percolation
                 tests, mark lines here at
                 regular time  intervals.

                     Guide Line^

• Measuring Stick
           Batter Board or
       /— Other Fixed
      r   . Reference Point
 6"-9" Diameter
                                                 «- 2" Layer of Gravel
  (a) Floating Indicator
                                      (b) Fixed Indicator

-------
                          FIGURE 3-15
              PERCOLATION TEST DATA FORM  (17)
Percolation test
Location
                                                ia
Test hole number
Depth to bottom of hole <3 £  inches. Diameter of hole.
   Depth, inches      Soil texture
      0 ~  V
                                                      inches.
 Percolation test by.
 Date of test
Time
t];30
lo:°°
io:*°
10 '^
!l;*D
U-°°
13-3°
I • oo
I-.30



Time
Interval,
minutes
—
3.0
Ao
3o
3o
i-o
30
2.0
3D



Measure-
ment,
inches
w-
+3
Y3
Y3'/f
t3'/,(.
*?'/?
^3L
^3^
^H,



Drop in
water level,
inches
—
/
/
VY
lf/l(o
%
'V/i,
"At,
"k



Percola-
tion rate,
minutes
per inch








W



Remarks












 Percolation rate =   T'T     minutes per inch.
                                 43

-------
Establishing  evaporation  data  at a  speci'fic  location  can  be a  more
difficult problem.   Measurements of Class  A pan evaporation  rates  are
reported  for   all   of   the  states   by   NOAA  in   the   publication,
"Climatological  Data,"  U.S.  Department   of   Commerce,   available   in
depository  libraries  for  government documents  at major  universities  in
each state.   Pan  evaporation measurements are  made at a  few  (5 to  30)
weather  stations  in each  state.   Data  for the winter months  are  often
omitted  because  this  method  cannot  be  used  under  freezing  weather
conditions.   The  critical  period of the year for design  of systems  for
permanent homes is  in the  winter.    Obtaining  representative winter
evaporation data is probably the most difficult part of design analysis.
Application of  evaporation  systems is  most  favorable  in the  warm,  dry
climates  of the  southwestern  United   States.    For   these  areas,  pan
evaporation data are available  for  the  complete year.   The  analysis  of
evaporative potential  for  cooler,  semi-arid regions,  such as  eastern
Washington and  Oregon, Utah, Colorado,  and  similar  areas,  requires  that
winter   data   be  established   by  means  other  than   pan  evaporation
measurements,  since these data  are generally not available.
One method for establishing representative winter evaporation data is to
take measurements on buried lysimeters.  Another method is to use empir-
ical formulations  such  as the Penman  formula  (18).   The Penman formula
has  been  shown  to give  results  comparable to  measured winter  values
(5).
          3.3.4.2  Site Evaluation for Surface Water Discharge


For  surface  water disposal  to be a  viable  option,  access  to a suitable
surface  body of  water  must be  available.   Onsite  investigations  must
locate the body  of water,  identify  it,  and determine the means by which
access can  be gained.   Since  discharges  to surface waters  are  usually
regulated, the local water  quality  agency  must be contacted to learn if
discharge of wastewater into that body of water is permitted and, if so,
what effluent standards must be met.
     3.3.5  Organizing the Site Information
As the  site  information  is  collected,  it is organized so that it can be
easily  used  to check  site  suitability  for any of the  various  systems
discussed  in  this  manual.   One such method of  organization  is shown in
Figure  3-16.    In  this example,  two  soil   observations  have  been  made.
The number of soil  observations varies.  It is important that all  perti-
nent  site  information  be presented  in  a clear fashion to provide suffi-
cient  information  to  the designer  of  the  system without making  addi-
tional  site visits.
                                    44

-------
                              FIGURE  3-16

               COMPILATION  OF SOILS AND  SITE  INFORMATION
            (INFORMATION  INCLUDES TOPOGRAPHIC,  SOIL  SURVEY,
                 ONSITE  SLOPE AND SOIL PIT  OBSERVATIONS)
Name
Address
Site evaluator

Address
Waste water quantity
                                                           -^'. 5
                             o
                             Well
  ^  Soil Pit
  O  Percolation Tests (If Determined)
 — Set Back
 	 Contour
 — Soil Boundary
 .— Drainage Way
                                   45

-------
                      FIGURE 3-16 (continued)
     Name:
     Soil Pit No.
Depth
iTexture
Structure
                                   Color
Soil Saturation
  8
 10
 12
 14
       Silt
          Loam
       Silty
        Clay
         Loam
      Clay Loam
        Sandy
        Loam
Granular
  Platy
 Blocky
  Platy
                                  Brown
                               None
                    Massive
      Soil Map Unit - DnC2
      Slope - 6%
      Landscape Position - Side Slope
      Landscape Type - Plane to Concave
                              46

-------
                    FIGURE 3-16 (continued)
    Name :
    Soil Pit No.
 0
Texture
                  Structure
 Color
Soil Saturation
 8
10
12
14
      Silt
        Loam
     Silty
       Clay
        Loam
     Silt
        Loam
             Blocky
                  Granular
             Blocky
                   Massive
Brown
                           Black
Brown
                         Brown and
                        Grey and Red
                          Mottles
    Soil Map Unit - TrB
    Slope - 4%
    Landscape Position - Footslope
    Landscape Type - Concave
                             47

-------
3.4  References
  1.  Small  Scale  Waste  Management  Project,  University  of  Wisconsin,
     Madison.  Management of  Small Waste  Flows.   EPA 600/2-78-173, NTIS
     Report No. PB 286 560, September 1978. 804  pp.

 2.  Tyler, E. J.,  R.  Laak,  E.  McCoy, and S. S. Sandhu.   The  Soil  as a
     Treatment System.   In:   Proceedings of  the  Second  National  Home
     Sewage  Treatment  Symposium,  Chicago,   Illinois,  December  1977.
     American Society  of Agricultural Engineers,  St.  Joseph,  Michigan,
     1978.  pp. 22-37.

 3.  Hillel, D. I.  Soil and  Water:   Physical  Principles and Processes.
     Academic Press, New York, 1971.   302 pp.

 4.  Flach, K. W.   Land Resources.   In:  Recyclying  Municipal  Sludges
     and  Effluents on Land.   Champafgn,  University of  Illinois,  July
     1973.

 5.  Bennett, E.  R., and K.  D. Linstedt.  Sewage Disposal  by Evaporation-
     Transpiration.    EPA  600/2-78-163,   NTIS  Report  No.  PB  288  588,
     September 1978.  196 pp.

  6.  Pickett,  E.  M.   Evapotranspiration and  Individual  Lagoons.   In:
     Proceedings of Northwest Onsite Wastewater Disposal  Short Course,
     University of Washington, Seattle,  December 1976.   pp. 108-118.

 7.  Pruitt, W.  0.  Empirical Method for Estimating Evapotranspiration
     Using Primarily Evaporation  Pans.   In:   Evapotranspiration and Its
     Role  in Water Resources  ManagementfTonference Proceedings, Ameri-
     can  Society of Agricultural  Engineers,  St.  Joseph,  Michigan, 1966.
     pp. 57-61.

 8.  Beck, A.  F.   Evapotranspiration Pond Design.   Environ.  Eng. Div.,
     Am. Soc. Civil Eng., K)5_ 411-415, 1979.

 9.  Bernhart, A.  P.  Treatment and Disposal  of Wastewater From Homes by
     Soil  Infiltration and  Evapotranspiration.   2nd ed.   University of
     Toronto Press, Toronto,  Canada, 1973.

10.  Soil  Conservation  Service.  Soil  Survey Manual.   USDA Handbook 18,
     U.S.  Government Printing Office, Washington, D.C., 1951.  503 pp.

11.  Studies on Household Sewage Disposal Systems.   Environmental Health
     Center, Cincinnati, Ohio, 1949-3 pts.

12.  Bouma, J.   Evaluation  of the Field  Percolation Test and an Alter-
     native Procedure to Test Soil Potential  for Disposal of Septic Tank
     Effluent.  Soil Sci. Soc. Amer. Proc. 35:871-875,  1971.
                                    48

-------
13.  Winneberger, J. T.  Correlation of Three Techniques for Determining
     Soil Permeability.  Environ. Health, 37:108-118, 1974.

14.  Healy, K. A., and R. Laak.  Factors Affecting the Percolation Test.
     J. Water Pollut. Control  Fed., 45:1508-1516, 1973.

15.  Bouma, J.   Unsaturated Flow  During  Soil  Treatment of  Septic Tank
     Effluent.   J.  Environ.   Eng.,  Am.  Soc.  Civil   Eng.,  101:967-983,
     1975.

16.  Onsite Wastewater Management.   National  Environmental  Health Asso-
     ciation, Denver, Colorado, 1979.

17.  Machmeier, R. E.  How  to  Run  a Percolation Test.  Extension Folder
     261, University of Minnesota,  St. Paul, 1977.

18.  Penman,  H.   L.    Estimating  Evaporation.    Trans. Amer.  Geophys.
     Union, 37:43-46, 1956.
                                   49

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                               CHAPTER  4

                       WASTEWATER CHARACTERISTICS
4.1  Introduction
The effective  management of  any  wastewater flow requires  a  reasonably
accurate knowledge  of its characteristics.   This is  particularly  true
for wastewater flows from rural residential dwellings, commercial  estab-
lishments and  other facilities where  individual  water-using  activities
create an intermittent flow of wastewater that can vary widely in  volume
and degree of pollution.  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  de-
velopment and application of water conservation and waste load reduction
strategies.
For existing developments, characterization of the actual  wastewaters to
be encountered may often times be accomplished.  However,  for many exis-
ting developments, and  for  almost  any  new development,  wastewater char-
acteristics  must  be  predicted.    The  purpose  of  this  chapter is  to
provide  a  basis for  characterizing the wastewater from  rural  develop-
ments.   A  detailed  discussion  of  the  characteristics  of  residential
wastewaters is presented  first,  followed  by  a  limited discussion of the
characteristics  of the wastewaters generated  by nonresidential  estab-
lishments,  including  those of  a commercial,  institutional  and  recrea-
tional nature.   Finally,  a general  procedure  for predicting wastewater
characteristics  for  a  given  residential   dwelling  or  nonresidential
establishment is given.


4.2  Residential Wastewater Characteristics
Residential  dwellings exist in a variety of forms, including single- and
multi-family   households,   condominium  homes,  apartment   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,  generated
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
plumbing  fixtures  and  appliances  present as well as  their  frequency of
use.  Additionally, the  characteristics  of  the residing  family in terms
of number  of family members, age  levels, and  mobility  are  important as

                                   50

-------
is the overall socioeconomic status of  the  family.   The characteristics
of  the   dwelling  itself,   including   seasonal   or   yearly  occupancy,
geographic location,  and method of water supply and wastewater disposal,
appear as additional, but lesser, influences.
     4.2.1  Wastewater Flow


         4.2.1.1  Average Dally Flow
The average daily wastewater flow from a typical  residential  dwelling is
approximately 45  gal/capita/day  (gpcd)  (170 liters/capita/day  [Ipcd])
(Table 4-1).  While  the  average  daily flow experienced at one residence
compared to  that  of another can  vary considerably, it  is typically no
greater than  60 gpcd (227  Ipcd)  and seldom exceeds 75  gpcd  (284 Ipcd)
(Figure 4-1).
         4.2.1.2  Individual Activity Flows
The individual  wastewater  generating activities within a  residence  are
the building  blocks  that serve to produce the  total  residential  waste-
water discharge.  The  average  characteristics  of  several  major residen-
tial water-using  activities  are  presented in Table 4-2.   A water-using
activity that  falls  under  the  category of miscellaneous  in  this  table,
but deserves additional comment,  is water-softener backwash/regeneration
flows.   Water  softener  regeneration  typically occurs  once or twice  a
week, discharging about  30-88  gal  (114  to 333  1)  per regeneration cycle
(11).  On a daily per capita basis, water softener flows have been shown
to average about 5 gpcd (19 Ipcd), ranging from 2.3 to 15.7 gpcd (8.7 to
59.4 Ipcd) (7).
         4.2.1.3  Wastewater Flow Variations
The intermittent occurrence  of individual  wastewater-generating activi-
ties creates  large  variations in the wastewater flow  rate  from a resi-
dence.
             a.  Minimum and Maximum Daily Flows
The daily  wastewater  flow from a specific residential  dwelling  is typ-
ically within  1Q%  and 300% of the average daily  flow at that dwelling,
with the vast majority within 50 and 150% of the average day.   At the
                                   51

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                                                     TABLE 4-1
                               SUMMARY OF AVERAGE DAILY RESIDENTIAL WASTEWATER FLOWS
en
PO
                Studv
Linaweaver, et al. (1)
Anderson and Watson (2)
Watson, et al. (3)
Cohen and Wallman (4)
Laak (5)
Bennett and Linstedt (6)
Siegrist, et al.  (7)
Otis (8)
Duffy, et al.  (9)
No
Resi










. of
dences

22
18
3
8
5
5
11
21
16
Duration
of
Study
months
-
4
2-12
6
24
0.5
1
12
12
Wastewater Flow
Study
Average
gpcd
49
44
53
52
41.4
44.5
42.6
36
42.3
Range of Individual
Residence Averages
gpcd
36 - 66
18 - 69
25-65
37.8 - 101.6
26.3 - 65.4
31.8 - 82.5
25.4 - 56.9
8-71
-
                                                 Weighted Average
                                                                      44

-------
                                FIGURE  4-1

                FREQUENCY DISTRIBUTION  FOR AVERAGE DAILY
                    RESIDENTIAL  WATER USE/WASTE FLOWS
 o
 Q.
 O)
90



80



70
.-?  60
CD
V-i



I
'(/>
0)

    40
30
    20
    10
     0
                  I    I
           I	I
              I	I
I
I   I   I   I   I
I	I
I	I
      1  2    5   10  20304050607080  90  95  9899

         Flow Values Less than or Equal to Stated Flow Value (%)
        Note: Based on the average daily flow measured
        for each of the 71 residences studied in (2) (3) (4)
        (5) (6) (7) (8).
                                  53

-------
                                TABLE 4-2

                  RESIDENTIAL WATER USE BY ACTIVITY*
Acti vi ty
Toilet Flush
Bathi ng
Clotheswashing
Dishwashing
Garbage Grinding
Miscellaneous
Total
Gal /use
4.3
4.0 - 5.0
24.5
21.4 - 27.2
37.4
33.5 - 40.0
8.8
7.0 - 12.5
2.0
2.0 - 2.1
-
"
Uses/cap/day
3.5
2.3 - 4.1
0.43
0.32 - 0.50
0.29
0.25 - 0.31
0.35
0.15 - 0.50
0.58
0.4 - 0.75
-
""
gpcdb
16.2
9.2 - 20.0
9.2
6.3 - 12.5
10.0
7.4 - 11.6
3.2
1.1 - 4.9
1.2
0.8 - 1.5
6.6
5.7 - 8.0
45.6
41.4 - 52.0
a Mean and ranges of results reported in (4)(5)(6)(7)(10).

b gpcd may not equal gal/use multiplied by uses/cap/day due to
  difference in the number of study averages used to compute the
  mean and ranges shown.
                                   54

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extreme, however, minimum and maximum  daily  flows  of 0% and 900% of the
average daily flow may be encountered (2)(3)(12).
             b.  Minimum and Maximum Hourly Flows
Minimum hourly flows of zero are typical.  Maximum hourly flows are more
difficult to  quantify  accurately.   Based on typical  fixture  and appli-
ance usage characteristics, as well as  an  analysis  of residential  water
usage demands, maximum  hourly  flows of 100 gal/hr  (380  1/hr)  can  occur
(2)(13).  Hourly flows  in  excess of this can  occur  due to plumbing fix-
ture and  appliance  misuse  or malfunction (e.g.,  faucet  left  on or worn
toilet tank flapper).
             c.  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 posi-
tion  in  the overall  plumbing  system layout.   The peak  discharge  rate
from  a  given fixture/appliance  is  typically around  5  gal/minute {gpm)
(0.3 liters/sec), with the exception of the tank-type water closet which
discharges  at  a peak  flow of  up  to 25  gpm (1.6 I/sec).   The  use  of
several  fixtures/appliances  simultaneously can increase  the  total  flow
rate from the isolated fixtures/appliances.  However, attenuation occur-
ring in the residential drainage network tends to decrease the peak flow
rates in the sewer exiting the residence.
Although  field  data are  limited,  peak discharge  rates from  a  single-
family dwelling of  5 to  10 gpm (0.3 to 0.6 I/sec)  can be expected.  For
multi-family units, peak rates in excess 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 4.3.1.2.
     4.2.2  Wastewater Quality


         4.2.2.1  Average Daily Flow


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 disposals)  that  collectively generate approximately 45 gpcd (170
Ipcd).
                                    55

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                                TABLE  4-3
           CHARACTERISTICS OF TYPICAL  RESIDENTIAL  WASTEWATER9
         Parameter                  Mass Loading           Concentration
                                     gm/cap/day               mg/1
Total Solids                         115 - 170               680  -  1000
Volatile Solids                       65 - 85                380  -  500
Suspended Solids                      35 - 50                200  -  290
Volatile Suspended Solids             25 - 40                150  -  240

BODs                                  35 - 50                200  -  290
Chemical Oxygen Demand               115 - 125               680  -  730

Total Nitrogen                         6-17                 35  -  100
Ammonia                                1-3                   6-18
Nitrites and Nitrates                   <1                      <1
Total Phosphorus
Phosphate
Total Coliformsb
Fecal Coliformsb
3-5 18 -
1-4 6 -
ioio -
108 -
29
24
1012
ioio
a For typical residential dwellings equipped with standard water-using
  fixtures and appliances (excluding garbage disposals) generating
  approximately 45 gpcd  (170 Ipcd).  Based on the results presented in
b Concentrations presented in organisms per liter.
                                   56

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         4.2.2.2  Individual Activity Contributions
Residential water-using activities  contribute  varying  amounts of pollu-
tants to  the  total  wastewater  flow.   The  individual  activities may be
grouped  into  three major  wastewater  fractions:   (1)  garbage  disposal
wastes,  (2)  toilet wastes,  and (3)  sink,  basin,  and  appliance waste-
waters.  A summary of the average contribution of several  key pollutants
in each of these three fractions is presented in Tables 4-4 and 4-5.
With  regard  to  the  microbiological  characteristics  of  the  individual
waste  fractions,  studies  have  demonstrated  that  the wastewater  from
sinks, basins, and appliances  can  contain  significant concentrations of
indicator  organisms  as  total  and  fecal  coliforms  (14)(15)(16)(17).
Traditionally, high concentrations  of these organisms have been used to
assess the contamination  of  a water  or wastewater  by pathogenic organ-
isms.  One assumes,  therefore, that  these wastewaters  possess  some po-
tential for harboring pathogens.
         4.2.2.3  Wastewater Quality Variations


Since individual water-using activities occur intermittently and contri-
bute  varying  quantities of  pollutants,  the strength of  the  wastewater
generated  from  a residence fluctuates with  time.   Accurate quantifica-
tion  of  these fluctuations is  impossible.   An estimate  of the  type of
fluctuations  possible  can be  derived from  the  pollutant concentration
information  presented  in Table  4-5  considering  that   the  activities
included occur intermittently.
4.3  Nonresidential Wastewater Characteristics
The rural population, as well as the transient population moving through
the  rural  areas,  is  served  by  a  wide  variety 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" non-residen-
tial  establishments   is  a  very  complex  task due  to  several  factors.
First, there is a relatively large number of diverse establishment cate-
gories  (e.g.,  bars,  restaurants, drive-in theaters,  etc.).   The inclu-
sion  of  potentially  diverse  establishments  within  the  same  category
produces  a  potential   for  large  variations in  waste-generating sources
                                     57

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                                TABLE 4-4

              POLLUTANT CONTRIBUTIONS OF MAJOR RESIDENTIAL
                  WASTEWATER FRACTIONS3  (gm/cap/day)
Parameter
BOD5
Suspended
Sol i ds
Ni trogen
Phosphorus
Garbage
Disposal
18.0
10.9 - 30.9
26.5
15.8 - 43.6
0.6
0.2 - 0.9
0.1
0.1 - 0.1
Toi 1 et
16.7
6.9 - 23.6
27.0
12.5 - 36.5
8.7
4.1 - 16.8
1.2
0.6 - 1.6
Basins,
Sinks,
Appliances
28.5
24.5 - 38.8
17.2
10.8 - 22.6
1.9
1.1 - 2.0
2.8
2.2 - 3.4
Approximate
Total
63.2
70.7
11.2
4.0
a Means and ranges of results reported in (5)(6)(7)(10)(14)
                                TABLE 4-5-

              POLLUTANT CONCENTRATIONS OF MAJOR RESIDENTIAL
                     WASTEWATER FRACTIONS*  (mg/1)
Parameter
BOD5
Suspended
Sol i ds
Ni trogen
Phosphorus
Garbage
Di sposal
2380
3500
79
13
Toilet
280
450
140
20
Basins, Sinks,
Appliances
260
160
17
26
Combi ned
Wastewater
360
400
63
23
a Based on the average results presented in Table 4-4 and  the
  following wastewater flows:  Garbage disposal  - 2 gpcd (8  Ipcd);
  toilet - 16 gpcd (61 Ipcd); basins, sinks and  appliances - 29 gpcd
  (110 Ipcd); total - 47 gpcd (178 Ipcd).

                                   58

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and the resultant wastewater  characteristics.   Further,  many intangible
Influences such as location,  popularity, and price  may  produce  substan-
tial  wastewater variations  between  otherwise  similar  establishments.
Finally, there is considerable difficulty in presenting  characterization
data  in units of measurement  that  are easy to apply,  yet predictively
accurate.   (For example, at a restaurant, wastewater flow in gal/seat is
easy  to  apply  to  estimate  total  flow, but  is less  accurate  than  if
gal/meal served were used.)
In this section, limited characterization data for nonresidential  estab-
lishments,  including  commercial  establishments,  institutional  facili-
ties, 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 establishment  in
question, or a similar one in the vicinity, should be obtained.
     4.3.1  Wastewater Flow


         4.3.1.1  Average Daily Flow
Typical  daily  flows  from  a variety  of commercial,  institutional,  and
recreational establishments are presented in Tables 4-6 to 4-8.
         4.3.1.2  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  appli-
ances,  and  to   the  operational   characteristics   of the  establishment
(hours of operation, patronage fluctuations, etc.).


Peak wastewater flows can be estimated utilizing the fixture-unit  method
(19)(20).  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 (21)(22).  One fixture unit was arbitrarily set
equal  to  a  flow rate of 7.5 gpm  (0.5  I/sec),  and various fixtures  were
assigned  a certain  number  of fixture units based  upon  their  particular
characteristics  (Table  4-9).  Based  on probability  studies,  relation-
ships were developed between peak water use and the total  number of  fix-
ture units present (Figure 4-2).
                                    59

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                                TABLE  4-6
          TYPICAL WASTEWATER FLOWS FROM  COMMERCIAL  SOURCES  (18)
         Source

Airport
Automobile Service Station

Bar

Hotel
Industrial Building
  (excluding industry and
  cafeteria)
Laundry (self-service)
Motel
Motel with Kitchen
Office
Restaurant
Rooming House
Store, Department

Shopping Center
                                                       Wastewater Flow
Unit

Passenger
Vehicle Served
Empl oyee
Customer
Employee
Guest
Empl oyee
Empl oyee
Machine
Wash
Person
Person
Empl oyee
Meal
Resident
Toilet room
Empl oyee
Parking Space
Employee
Ran
2.1 -
7.9 -
9.2 -
1.3 -
10.6 -
39.6 -
7.9 -
7.9 -
475 -
47.5 -
23.8 -
50.2 -
7.9 -
2.1 -
23.8 -
423 -
7.9 -
0.5 -
7.9 -
ge
gpd/uni
4.0
13.2
15.8
5.3
15.8
58.0
13.2
17.2
686
52.8
39.6
58.1
17.2
4.0
50.1
634
13.2
2.1
13.2
Typical
t
2.6
10.6
13.2
2.1
13.2
50.1
10.6
14.5
580
50.1
31.7
52.8
14.5
2.6
39.6
528
10.6
1.1
10.6
                                    60

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                                TABLE 4-7

        TYPICAL WASTEWATER FLOWS FROM INSTITUTIONAL SOURCES (18)
           Source



Hospital, Medical


Hospital.Mental


Prison


Rest Home
School, Day:
  With Cafeteria, Gym,
    Showers
  With Cafeteria Only
  Without Cafeteria, Gym,
    Showers

School, Boarding
      Unit
Bed
Employee

Bed
Empl oyee

Inmate
Employee

Resi dent
Employee
       Wastewater Flow
     RangeTypical
          gpd/unit
132
  5.3

 79.3
  5.3

 79.3
  5.3

 52.8
  5.3
251
 15.9

172
 15.9

159
 15.9

119
 15.9
172
 10.6

106
 10.6

119
 10.6

 92.5
 10.6
Student
Student
Student
Student
15.9 -
10.6 -
5.3 -
52.8 -
30.4
21.1
17.2
106
21.1
15.9
10.6
74.0
                                 61

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                       TABLE 4-8



TYPICAL WASTEWATER FLOWS FROM RECREATIONAL SOURCES (18)
                                              Wastewater Flow
Source

Apartment, Resort
Cabin, Resort
Cafeteria
Campground (developed)
Cocktail Lounge
Coffee Shop
Country Club
Day Camp (no meals)
Dining Hall
Dormitory, Bunkhouse
Hotel , resort
Laundromat
Store Resort
Swimming Pool
Theater
Visitor Center
Unit

Person
Person
Customer
Empl oyee
Person
Seat
Customer
Empl oyee
Member Present
Empl oyee
Person
Meal Served
Person
Person
Machine
Customer
Empl oyee
Customer
Empl oyee
Seat
Vi si tor
Range
gpd/un
52.8 -
34.3 -
1.1 -
7.9 -
21.1 -
13.2 -
4.0 -
7.9 -
66.0 -
10.6 -
10.6 -
4.0 -
19.8 -
39.6 -
476 -
1.3 -
7.9 -
5.3 -
7.9 -
2.6 -
4.0 -
74
50.2
2.6
13.2
39.6
26.4
7.9
13.2
132
15.9
15.9
13.2
46.2
63.4
687
5.3
13.2
13.2
13.2
4.0
7.9
Typical
n't
58.1
42.3
1.6
10.6
31.7
19.8
5.3
10.6
106
13.2
13.2
7.9
39.6
52.8
581
2.6
10.6
10.6
10.6
2.6
5.3
                         62

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                                TABLE 4-9

                     FIXTURE-UNITS PER FIXTURE (19)


                     Fixture Type                          Fixture-Units
One bathroom group consisting of tank-operated water
  closet, lavatory, and bathtub or shower stall                   6
Bathtub (with or without overhead shower)                        2
Bi det                                                            3
Combination sink-and-tray                                        3
Combination sink-and-tray with food-disposal  unit                4
Dental unit or cuspidor                                          1
Dental lavatory                                                  1
Drinking fountain                                               1/2
Dishwasher, domestic                                             2
Floor drains                                                     1
Kitchen sink, domestic                                           2
Kitchen sink, domestic, with food waste grinder                  3
Lavatory                                                         1
Lavatory                                                         2
Lavatory, barber, beauty parlor                                  2
Lavatory, surgeon's                                              2
Laundry tray  (1 or 2 compartments)                               2
Shower stall, domestic                                           2
Showers (group) per head                                         3
Sinks
  Surgeon's                                                      3
  Flushing rim  (with valve)                                      8
  Service  (trap standard)                                        3
  Service  (P trap)                                               2
  Pot, scullery, etc.                                            4
Urinal, pedestal, syphon 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 faucets             2
Water closet, tank-operated                                      4
Water closet, valve-operated                                     8
                                   63

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                                                     FIGURE 4-2

                                     PEAK DISCHARGE  VERSUS FIXTURE UNITS  PRESENT (22)
                    450
CTi
                Q_
                co
                0)
                D_
                CD
                _Q
                O
                    400
                    350
                    300
o
u-   250
    200


    150


    100


     50


      0
              I     I      I      I     I     i^   I     I      I|I
          Note:  Curves show probable amount of time indicated peak flow will
                be exceeded during a period of concentrated fixture use.
              System in which flush
               valves predominate
                              System in which flush
                               tanks predominate
                        0
                                        _L
I
I
I
                        6     8    10    12   14    16

                      Fixture Units on System (Hundreds)
                18
                20    22

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     4.3.2  Wastewater Quality
The  qualitative  characteristics of  the wastewaters  generated  by  non-
residential  establishments  can vary  significantly  between  different
types of establishments due  to  the extreme  variation  which can exist in
the waste  generating  sources present.   Consideration of  the waste-gen-
erating sources present at a particular establishment can give a general
idea of  the  character of  the  wastewater,  and serve to  indicate if the
wastewater will  contain any problem constituents,  such as  high grease
levels from a restaurant or lint fibers in  a laundromat  wastewater.
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 pro-
duced may be derived using  the  residential  wastewater  quality data pre-
sented in Tables 4-3 to  4-5.   For establishments where the waste-gener-
ating sources appear significantly different from those in  a residential
dwelling, or where more refined characterization data are desired, a de-
tailed review of the pertinent  literature,  as  well  as  actual  wastewater
sampling at the particular or a similar establishment,  should be conduc-
ted.
4.4  Predicting Wastewater Characteristics


     4.4.1  General Considerations


         4.4.1.1  Parameter Design Units


In characterizing  wastewaters,  quantitative and  qualitative  character-
istics are  often  expressed in  terms  of other parameters.  These para-
meter design units,  as  they may be called, vary  considerably depending
on the  type of establishment  considered.   For  residential  dwellings,
daily flow  values and  pollutant  contributions are  expressed on a  per
person (capita) basis.   Applying  per  capita data  to predict total resi-
dential  wastewater characteristics  requires  that a  second  parameter be
considered,  namely,  the  number of persons residing in  the  residence.
Residential  occupancy typically ranges  from 1.0 to  1.5  persons  per  bed-
room.   Although it  provides  for a  conservative  estimate, the  current
practice is to assume that maximum occupancy  is two  persons per bedroom.


For   nonresidential   establishments,   wastewater   characteristics   are
expressed in terms of a  variety of units.  Although  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.
                                   65

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         4.4.1.2  Factors of Safety
To  account  for the  potential  variability in the  wastewater character-
istics 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  design wastewater characteristics and  the  occupancy  pat-
terns, as well  as  directly through an  overall factor.   For example,  if
an  average  daily  flow  of 75  gpcd  (284 Ipcd) 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.,  45  gpcd  [170 Ipcd]  and  1 .person
per  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  which would yield  an
extremely overconservative estimate.
     4.4.2  Strategy for Predicting Wastewater Characteristics


Predicting wastewater  characteristics  from rural developments  can  be a
complex  task.    Following  a  logical  step-by-step  procedure can  help
simplify  the  characterization process  and render the  estimated  waste-
water characteristics more accurate.  A flow chart detailing a procedure
for predicting wastewater characteristics is presented in Figure 4-3.
                                   66

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                                 FIGURE  4-3

     STRATEGY  FOR PREDICTING WASTEWATER  CHARACTERISTICS
       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  Home. Hours of Operation...)
 Obtain Characterization Data from Literature

• Tables and Text of This Chapter

• Reference and Bibliography Attached
  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)
Conduct Characterization
Field Studies at Facility
in Question or a Very
Similar One
     Apply Overall Factor of Safety as Required
          by Intended Application of Data
               Estimate Wastewater
                 Characteristics
                                    67

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4.5  References
 1.  Linaweaver, F.  P.,  Jr.,  J. C. Geyer, and J.  B.  Wolff.   A Study of
     Residential Water Use.   Department of Environmental Studies, Johns
     Hopkins University, Baltimore, Maryland, 1967.  105 pp.

 2.  Anderson,  J.  S.,  and K.  S.  Watson.  Patterns  of Household Usage.
     J. Am. Water Works Assoc.,  59:1228-1237, 1967.

 3.  Watson, K. S., R. P. Farrell, and J. S.  Anderson.  The Contribution
     from  the  Individual Home  to the  Sewer  System.   J.  Water Pollut.
     Control Fed., 39:2039-2054, 1967.

 4.  Cohen, S.,  and  H.  Wallman.   Demonstration  Of Waste Flow Reduction
     From  Households.    EPA  670/2-74-071,  NTIS  Report No.  PB  236  904,
     1974.  Ill pp.

 5.  Laak,  R.  Relative Pollution  Strengths of  Undiluted Waste Materials
     Discharged  in  Households  and the  Dilution Waters Used  for Each.
     Manual of  Grey Water Treatment  Practice  -  Part II, Monogram Indus-
     tries, Inc., Santa Monica, California, 1975.

 6.  Bennett,  E.  R., and E.  K.  Linstedt.   Individual  Home  Wastewater
     Characterization and Treatment.   Completion  Report Series No.  66,
     Environmental   Resources   Center,  Colorado  State  University,  Fort
     Collins, 1975.  145 pp.

 7.  Siegrist,  R.  L. , M.  Witt,  and  W. C.  Boyle.   Characteristics  of
     Rural  Household  Wastewater.   J.  Env.  Eng.  Div.,  Am.  Soc.  Civil
     Eng.,  102:553-548, 1976.

 8.  Otis,  R. J.  An  Alternative  Public Wastewater Facility for a Small
     Rural  Community.  Small  Scale Waste Management Project,  University
     of Wisconsin, Madison,  1978.

 9.  Duffy, C.  P., et al .   Technical  Performance of the Wisconsin Mound
     System  for On-Site  Wastewater  Disposal  -  An  Interim  Evaluation.
     Presented  in Preliminary Environmental Report for Three Alternative
     Systems  (Mounds) for  On-site  Individual   Wastewater  Disposal  in
     Wisconsin.   Wisconsin   Department of Health  and  Social  Services,
     December 1978.

10.  Ligman,  K.,  N.  Hutzler,  and  W.  C.  Boyle.   Household  Wastewater
     Characterization.   J.   Environ.   Eng.  Div.,  Am.  Soc.  Civil  Eng.,
     150:201-213, 1974.

11.  Weickart,  R. F.  Effects  of  Backwash  Water  and Regeneration Wastes
     From  Household  Water Conditioning Equipment on Private Sewage Dis-
     posal  Systems.  Water Qua! ity Association,  Lombard, Illinois, 1976.
                                    68

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12.  Witt,  M.   Water  Use in  Rural  Homes.   M.S.  study.  University of
     Wisconsin-Madison, 1974.

13.  Jones,  E.  E.,  Jr.   Domestic  Water  Use  in  Individual  Homes and
     Hydraulic Loading  of and Discharge from  Septic Tanks.   In:   Pro-
     ceedings of  the National  Home  Sewage  Disposal Symposium,~~C"hicago,
     December 1974.    American  Society  of  Agricultural  Engineers, St.
     Joseph, Michigan,  pp. 89-103.

14.  Olsson, E.,  L.  Karlgren,  and V.  Tullander.   Household Wastewater.
     National Swedish  Institute  for Building  Research,  Stockholm, Swe-
     den, 1968.

15.  Hypes,  W.  D.,  C.  E. Batten,  and  J.  R.   Wilkins.    The  Chemical/
     Physical and  Microbiological Characteristics  of Typical   Bath and
     Laundry  Wastewaters.   NASA  TN  D-7566,  Langley  Research  Center,
     Langley Station, Virginia, 1974.  31 pp.

16.  Small  Scale   Waste Management  Project,  University  of  Wisconsin,
     Madison.  Management of Small Waste Flows.   EPA 600/2-78-173, NTIS
     Report No.  PB 286 560, September 1978.  804  pp.


17.  Brandes, M.    Characteristics  of  Effluents  From Separate   Septic
     Tanks Treating Grey and Black Waters From the  Same House.   J. Water
     Pollut. Control  Fed., 50:2547-2559, 1978.

18.  Metcalf  and  Eddy,  Inc.    Wastewater  Engineering:    Treatment/
     Disposal/Reuse.   2nd ed. McGraw-Hill,  New York, 1979.  938 pp.

19.  Design  and Construction of  Sanitary and  Storm Sewers.   Manual  of
     Practice No.  9.   Water Pollution  Control  Federation, Washington,
     D.C., 1976.   369 pp.

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

21.  Hunter,  R.  B.   Method of  Estimating  Loads  in  Plumbing Systems.
     Building Materials  and  Structures Report  BMS65,  National  Bureau of
     Standards,  Washington, D.C., 1940.  23 pp.

22.  Hunter, R.  B.   Water Distribution Systems for Buildings.   Building
     Materials and Structures  Report  BMS79,  National  Bureau  of  Stan-
     dards, Washington, D.C., 1941.
                                   69

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                               CHAPTER  5

                        WASTEWATER MODIFICATION
5.1  Introduction
The characteristics of  the  influent wastewater can have  a  major impact
on most any onsite treatment and disposal/reuse system.  To enhance con-
ventional strategies, and to  encourage  new  ones,  methods  can be used to
modify the typical characteristics of the influent wastewater.
Methods  for wastewater  modification  have been  developed  as part  of
three, basic interrelated strategies:  water conservation and wastewater
flow  reduction,  pollutant  mass  reduction, and  onsite  containment  for
offsite disposal.   Each  strategy attempts to reduce  the flow volume  or
to decrease  the mass  of key  pollutants  such as oxygen-demanding  sub-
stances,  suspended  solids,  nutrients,  and pathogenic organisms  in  the
influent wastewater to the onsite disposal system.
Although  the  primary thrust  of this chapter  is directed  toward  resi-
dential  dwellings,  many of  the concepts and  techniques  presented have
equal  or  even  greater  application  to  nonresidential  establishments.
Good   practice  dictates   that  water  conservation/flow  reduction  be
employed  to the  maximum  extent  possible  in  a  dwelling  served  by  an
onsite wastewater system.
At  the  onset,  there  are several  general  considerations regarding waste-
water modification.   First,  there are a  number of methods  available,
including a wide variety of devices, fixtures, appliances, and systems.
Further, the number  of  methods and the diversity of  their characteris-
tics  is ever  growing.    In  many  cases,  the methods  involve equipment
manufactured by one  or  more companies  as  proprietary  products.   In this
chapter,  only  generic  types  of  these products  are considered.   Also,
many methods  and  system components are  presently in  various  stages  of
development and/or application; therefore, only preliminary or projected
operation  and  performance information may  be available.   Finally,  the
characteristics of  many of  the  methods  discussed  may result  in  their
nonconfonuance with existing local plumbing codes.
                                     70

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5.2  Water Conservation and Wastewater Flow Reduction
An extensive array of techniques and devices are available to reduce the
average water use  and  concomitant  wastewater  flows  generated by indivi-
dual water-using  activities  and,  in  turn,  the  total effluent  from the
residence  or  establishment.    The  diversity of present  wastewater flow
reduction  methods  is  illustrated  in  Table  5-1.   As  shown,  the methods
may  be  divided  into  three  major  groups:   (1)  elimination  of  nonfunc-
tional  water  use, (2)  water-saving  devices,  fixtures,  and  appliances;
and  (3) wastewater recycle/reuse systems.


     5.2.1  Elimination of Nonfunctional Water Use
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 shav-
ing,  or operating  a  clotheswasher  or dishwasher with  only  a  partial
load.   Obviously, the potential for wastewater  flow reductions through
elimination  of these  types  of wasteful  use vary tremendously  between
homes,  from  minor to significant  reductions,  depending  on  existing
habits.
         5.2.1.1  Improved Plumbing and Appliance Maintenance


Unseen or apparently insignificant leaks from household fixtures and ap-
pliances can  waste  large volumes of water  and  generate  similar quanti-
ties of wastewater.  Most notable in this regard are leaking toilets and
dripping faucets.   For  example,  a  steadily  dripping faucet can waste up
to several  hundred gallons per day.


         5.2.1.2  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 40 psi (2.8 kg/
cm2)  is  adequate.   Pressure in  excess of this can result in unnecessary
water  use and  wastewater  generation.    To  illustrate,  the  flow  rate
through  a typical faucet opened  fully  is  about  40%  higher  at a supply
pressure  of 80 psi (5.6 kg/cm2) versus  that at 40 psi (2.8 kg/cm2).
                                   71

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                               TABLE 5-1

                EXAMPLE  WASTEWATER FLOW REDUCTION METHODS
  I.   Elimination  of Nonfunctional Water Use
      A.   Improved water  use  habits
      B.   Improved plumbing and appliance maintenance
      C.   Nonexcessive  water  supply  pressure

 II.   Water-Saving Devices, Fixtures, and Appliances
      A.   Toilet
          1.   Water  carriage  toilets
              a.   Toilet  tank inserts
              b.   Dual-flush  toilets
              c.   Water-saving toilets
              d.   Very  low-volume  flush toilets
                  (1) Wash-down flush
                  (2) Mechanically assisted
                     o Pressurized  tank
                     o Compressed air
                     o Vacuum
                     o Grinder
          2.   Non-water carriage toilets
              a.   Pit privies
              b.   Composting  toilets
              c.   Incinerator toilets
              d.   Oil-carriage toilets
      B.   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
      C.   Clotheswashing  devices,  fixtures, and  appliances
          1.   Front-loading washer
          2.   Adjustable  cycle settings
          3.   Washwater recycle feature
      D.   Miscellaneous
          1.   Faucet inserts
          2.   Faucet aerators
          3.   Reduced-flow faucet  fixtures
          4.   Mixing valves
          5.   Hot  water pipe  insulation
          6.   Pressure-reducing valves

III.   Wastewater Recycle/Reuse Systems
      A.   Bath/Laundry  wastewater  recycle for  toilet flushing
      B.   Toilet wastewater recycle  for toilet flushing
      C.   Combined wastewater recycle for toilet flushing
      D.   Combined wastewater recycle for several  uses
                                72

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     5.2.2  Water-Saving Devices,  Fixtures,  and Appliances
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 accomplished without  the use  of  water.   As
presented in  Table 4-2,  over  70% of  a
wastewater  flow  volume  is  collectively
bathing,  and  clotheswashing.    Thus,
wastewater  flow  reductions   should  be
activities.
without
 typical  residential  dwelling's
 generated by  toilet flushing,
 efforts  to  accomplish  major
 directed  toward  these  three
         5.2.2.1  Toilet Devices and Systems
Each flush of a  conventional water-carriage  toilet  uses  between  4 and 7
gal  (15  and 26  1)  of water  depending on  the model  and water  supply
pressure.  On  the  average,  a typical  flush  generates  approximately  4.3
gal  (16 1) of wastewater.   When coupled with  3.5 uses/cap/day,  a  daily
wastewater flow  of approximatley 16  gpcd  (61  Ipcd)  results  (Table 4-2).
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 conventional  water-carriage  toilet are
available, certain  of which use  little  or no water  to  transport  human
wastewater products.  Tables 5-2 and 5-3 present a  summary  of  a  variety
of  toilet  devices  and systems.    Additional  details  regarding  the
non-water carriage toilets  may be found elsewhere (1)(2)(3)(4)(5).
         5.2.2.2  Bathing Devices and Systems
Although great variation exists in the  quantity  of  wastewater  generated
by a  bath  or  shower,  typical  values  include approximatley  25 gal  (95 1)
per occurrence  coupled with a  0.4 use/capita/day  frequency to yield  a
daily per  capita  flow  of about  10 gal  (38 1) (Table 4-2).   The majority
of  devices available  to  reduce  bathing  wastewater  flow  volumes  are
concentrated  around  the  activity of  showering, with their  objective
being to reduce  normal  4-  to 10-gal/min  (0.25 to 0.63 I/sec)  showering
flow  rate.  Several flow reduction devices and systems for  showering are
characterized  in  Table 5-4.    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% of the total wastewater volume.
                                    73

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                                                               TABLE  5-2

                              WASTEWATER  FLOW REDUCTION -  WATER CARRIAGE  TOILETS AND SYSTEMS
Generic Type
     Description
Develop-
 ment
 Stage3
                                                       Application
                                                      Considerations
    Operation  and
     Maintenance
Water Use
Per Event
   gal
    Total  Flow
    Reduction*1
                                                                                                                   gpcd
Toilet with
Tank Inserts
Displacement 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.
  4-5       Device must be
            compatible with
            existing  toilet and
            not  interfere with
            flush mechanism.

            Installation by
            owner.
Post-installation  and
periodic inspections
to insure proper
positioning.
 3.3-3.8
1.8-3.5
4-8
Dual Flush
Toi 1 ets
Devices made for use
with conventional
flush toilets;  enable
user to select  from
two or more flush
volumes based on
solid or liquid waste
materials.

Varieties:  Many
            Device  must be
            compatible with
            existing  toilet and
            not interfere with
            flush mechanism.

            Installation by
            owner.
Post-installation  and
periodic inspections
to insure proper
positioning and
functioning.
 2.5-4.3
3.0-7.0
6-15
Water-Saving
Toilets
Variation of
conventional flush
toilet fixture;
similar in appearance
and operation.
Redesigned flushing
rim and priming jet
to initiate siphon
flush in smaller
trapway with less
water.

Varieties:  Many
manufacturers but
units similar.
            Interchangeable with
            conventi onal  fi xture.

            Requires pressurized
            water supply.
Essentially the same
as for a conventional
unit.
 3.0-3.5
2.8-4.6
6-10

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                                                        TABLE  5-2  (continued)
Generic Type
     Descri pti on
Develop-
 ment
 Stage3
                                                        Application
                                                       Considerations
    Operation and
     Maintenance
            Water Use
            Per Event
               gal
  Total  Flow
  Reductionb
                                                                                                                     gpcd
Washdown Flush
Toilets
Flushing uses only
water, but
substantially less
due to washdown
flush.

Varieties:  Few.
  3-4       Rough-In for unit may
            be nonstandard.

            Drain line slope and
            lateral  run
            restrictions.

            Requires pressurized
            water supply.
Similar to
conventional  toilet,
but more frequent
cleaning possible.
                                                                                                      0.8-1.6
                          9.4-12.2
            21-27
Pressurized
Tank
Specially designed
toilet tank to
pressurize air
contained in toilet
tank.  Upon flushing,
the compressed air
propels water into
bowl at increased
vel oci ty.

Varieties:  Few.
            Compatible with most
            any conventional
            toilet unit.

            Increased noise
            1evel.

            Water supply  pressure
            of 35 to 120  psi.
Similar to
conventi onal
fixture.
                                                                                                      2.0-2.5
                          6.3-8.0
            14-18
toi1et
Compressed
Air-Assisted
Flush Toilets
Similar in appearance
and user operation to
conventional toilet;
specially designed to
utilize compressed
air to ai d in
flushing.

Varieties:  Few
  3-4       Interchangeable with
            rough-in for
            conventional  fixture.

            Requires source of
            compressed air;
            bottled or air
            compressor.

            If air compressor,
            need power source.
Periodic maintenance
of compressed air
source.

Power use - 0.002 KwH
per use.
              0.5
13.3
                                          30

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                                                       TABLE  5-2  (continued)
Generic Type
     Description
Develop-
 ment
 Stage3
 Appl i cati on
Considerations
Operation and
 Maintenance
Water Use
Per Event
   gal
Total Flow
Reduction'5
                                                                                                                    gpcd
Vacuum-
Assisted Flush
Toilets
Similar in appearance
and user operation to
conventional  toilet;
specially designed
fixture is connected
to vacuum system
which assists a small
volume of water in
flushing.

Varieties:  Several.
            Application largely
            for multi-unit  toilet
            installations

            Above floor, rear
            discharge.

            Drain pipe  may  be
            horizontal  or
            inclined.

            Requires vacuum pump.

            Requires power
            source.
                      Periodic maintenance
                      of  vacuum pump.

                      Power  use =  0.002 KwH
                      per use.
                       0.3
                14
            31
a 1 = Prototype developed and under evaluation.
  2 = Development complete,  commercial  production initiated, not locally available.
  3 = Fully developed,  limited use, not locally  available, mail order purchase likely.
  4 = Fully developed,  limited use, locally  available from plumbing supply houses or hardware stores.
  5 = Fully developed,  widespread use,  locally available from plumbing supply houses or hardware stores.
  Compared to conventional  toilet usage  (4.3  gal/flush, 3.5 uses/cap/day, and a total  daily flow of 45 gpcd)

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                                          TABLE 5-3

             WASTEWATER  FLOW REDUCTION  - NON-WATER  CARRIAGE TOILETS
Generic Typea


Pit Privy
     Description
Hand-dug hole in the
ground covered with a
squatting plate or
stool /seat with an
enclosing house.

May be sealed vault
rather than dug hole.
                                        Develop-
                                         ment
             Application
            Considerations
          Requires   same  site
          conditions as for
          wastewater disposal
          (see Chapter 8),
          unless  sealed vault.

          Handles only toilet
          wastes

          Outdoor installation.

          May be  constructed by
          user.
    Operation and
     Maintenance
When full, cover with
2 ft of soil  and
construct new pit.
Composti ng
Privy
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  and
use as soil
amendment.
          Can be  constructed
          independent  of  site
          conditions if sealed
          vault.

          Handles only toilet
          waste and garbage.

          May be  constructed by
          user.

          Outdoor installation.

          Residuals disposal.
Addition of organic
matter after each
use.

Removal and
disposal /reuse of
composted material.
Composti ng-
Small
Small  self-contained
units  accept toilet
wastes only and
utilize the addition
of heat in
combination with
aerobic biological
activity to stabilize
human  excreta.

Varieties:  Several.
3-4       Installation requires
          4-in.  diameter roof
          vent.

          Handles  only toilet
          waste.

          Set  usage capacity.

          Power  required.

          Residuals disposal.
Removal and disposal
of composted material
quarterly.

Power use =2.5
KwH/day.

Heat loss through
vent.
Composti ng-
Large
Larger units 'with a
separated
decomposition
chamber.  Accept
toilet wastes  and
other organic  matter,
and over a long time
period stabilize
excreta through
biological activity.

Varieties:  Several
3-4       Installation requires
          6-  to  12-i n. diameter
          roof vent  and space
          beneath  floor for
          decomposition
          chamber.

          Handles  toilet waste
          and some kitchen
          waste.              »

          Set usage  capacity.

          May be difficult to
          retrofit.

          Residuals  disposal.
Periodic addition of
organic matter.

Removal of composted
material at 6 to 24
month intervals.

Power use = 0.3 to
1.2 KwH/day.

Heat loss through
vent.
                                             77

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                                     TABLE  5-3  (continued)
Generic Type3


Incinerator
     Description
Small  self-contained
units  which
volatilize the
organic components of
human  waste and
evaporate the
liquids.

Varieties:  Several.
Develop-
 ment
 Stageb
 Application
Considerations
            Installation requires
            4-in. diameter roof
            vent.

            Handles only toilet
            waste.

            Power or fuel
            required.

            Increased noi se
            level.

            Residuals disposal.
Operation and
 Maintenance
                                                                            Weekly removal of
                                                                            ash.

                                                                            Semiannual cleaning
                                                                            and adjustment of
                                                                            burni ng assembly
                                                                            and/or heating
                                                                            elements.

                                                                            Power use = 1.2 KwH
                                                                            or 0.3 Ib LP gas per
                                                                            use.
Oil Recycle
Systems use a mineral
oil  to transport
human excreta from a
fixture (similar in
appearance and use to
conventional ) to a
storage tank.  Oil is
purified and reused
for flushing.

Varieties:  few.
            Requires separate
            plumbing for toilet
            fixture.

            May be difficult to
            retrofit.

            Handles only toilet
            wastes

            Residuals disposal.
                      Yearly  removal  and
                      disposal  of  excreta
                      in storage tank.

                      Yearly  maintenance of
                      oil  purification
                      system  by skilled
                      technician.

                      Power use =  0.01
                      KwH/use.
a None 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% of normal  daily flow  (45  gpcd).   Significant
  quantities of pollutants {including N, BODs, SS,  P and pathogens)  are therefore removed from
  wastewater stream.

b 1 = Prototype developed and under evaluation.
  2 = Development complete; commercial production initiated, but distribution  may be restricted;
      mail order purchase.
  3 = Fully developed; limited use, not locally available; mail  order purchase likely.
  4 = Fully developed; limited use, available form local plumbing supply houses  or hardware stores.
  5 = Fully developed; widespread use, available from local  plumbing supply  houses or hardware stores.
                                                 78

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                                     TABLE  5-4

          WASTEWATER  FLOW  REDUCTION - BATHING DEVICES AND SYSTEMS
Generi c Type3
Shower Flow
Control
Inserts and
Restrictors
     Description
Reduce flow rate by
reducing the diameter
of supply line ahead
of shower head.

Varieties:   Many.
Develop-
 ment
 Stageb
 Application
Consi derations
            Compatible with  most
            existing showerheads.

            Installed by  user.
Water Use
 gal /mi n


 1.5-3.0
Reduced-Fl ow
Showerheads
Fixtures similar to
conventi onal,  except
restrict flow rate.

Varieties:   Many
manufacturers, but
units similar.
  4-5       Can match to most
            plumbing  fixture
            appearance schemes.

            Compatible with most
            conventional
            pi umbi ng.
                     1.5-3.0
ON/OFF
Showerhead
Valve
Small valve device
placed in the supply
line ahead of
showerhead, allows
shower fl ow to be
turned ON/OFF without
readjustment of
volume or
temperature.
            Compatible with  most
            conventional  plumbing
            and fixtures.

            May be installed by
            user.
Thermostat-
ically
Controlled
Mi xi ng Val ve
Specifically designed
valve controls
temperature of total
flow according to
predetermi ned
setting.  Valve may
be turned ON/OFF
without readjustment.
            May be difficult to
            retrofit.
                                         79

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                                TABLE  5-4  (continued)
Generic Type3
     Description
Devel op-
 ment
 Stageb
 Application
Considerations
Water Use
 gal /min
Pressure-        Specifically designed
Balanced         valve maintains
Mixing           constant temperature
Valve            of total flow
                 regardless of
                 pressure changes.
                 Single control  allows
                 temperature to be
                 preset.
                                    Compatible  with most
                                    conventi onal  pi umbi ng
                                    and  fixtures.
Air-Assisted
Low-Flow
Shower
System
Specifically designed
system uses
compressed air to
atomize water flow
and provide shower
sensation.
            May be impossible to       0.5
            retrofi t.

            Shower location < 50
            feet of water heater.
                                                     Requires  compressed
                                                     air source.

                                                     Power source
                                                     required.

                                                     Maintenance  of  air
                                                     compressor.

                                                     Power use =  0.01
                                                     KwH/use.
a No reduction in pollutant mass; slight increase in pollutant concentration.

b 1 = Prototype developed and under evaluation.
  2 = Development complete; commercial  production initiated,  but distribution  may  be
      restricted; mail order purchase.
  3 = Fully developed; limited use, not locally available;  mail  order purchase
      likely.
  4 = Fully developed; limited use, available from local  plumbing supply houses or
      hardware stores.
  5 = Fully developed; widespread use,  available from local plumbing supply  houses or
      hardware stores.
                                         80

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         5.2.2.3  Clotheswashing Devices and Systems


The operation of conventional clotheswashers consumes varying quantities
of water depending  on  the manufacturer and model  of the washer and the
cycle selected.  For most, water usage is 23 to 53 gal (87 to 201 1} per
usage.  Based  on home  water  use  monitoring,  an average water use/waste-
water flow volume of approximately 37 gal  (140 1) per use has been iden-
tified, with the clotheswasher contributing about 10.0 gpcd (38 Ipcd)  or
22% of the total daily water use/wastewater flow (Table 4-2).  Practical
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 model  automatic washers can reduce water used
for a comparable load  of  clothes by  up to 40%.  In addition, wastewater
flow reductions may be accomplished  through  use  of a clotheswasher with
either adjustable cycle settings  for  various  load  sizes  or a wash water
recycle feature.
The wash water recycle  feature  is  included  as  an optional  cycle setting
on several  commercially made washers.   Selection of the recycle feature
when washing provides for  storage  of  the  wash  water from the wash cycle
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  comprises  about  45%  of
the total water  use per operation, if  the  wash  water  is recycled once,
about 17 gal  (64 1) will  be  saved,  if twice,  34 gal   (129  1)  ,  and  so
forth.   Actual water savings  and wastewater flow reductions are  highly
dependent on the user's cycle selection.
         5.2.2.4  Miscellaneous Devices and Systems
There  are  a  number  of  additional  devices,  fixtures,  and  appliances
available to  help reduce wastewater  flow  volumes.   These  are directed
primarily toward  reducing the  water  flow rate  through  sink  and  basin
faucets.  Table 5-5 presents  a summary of  several  of these additional
flow  reduction  devices.   Experience  with  these devices  indicates  that
wastewater volume can be  reduced  by  1  to 2 gpcd (4 to 8 Ipcd) when used
for all sink and basin faucets.
     5.2.3  Wastewater Recycle and Reuse Systems
Wastewater  recycle and  reuse  systems  collect  and  process the  entire
wastewater  flow  or  the  fractions  produced  by certain  activities  with
storage  for  subsequent  reuse.    The  performance  requirements of  any
wastewater  recycle   system   are   established   by  the  intended  reuse
activities.    To  simplify  the performance  requirements,  most  recycle
                                   81

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                                TABLE 5-5

      WASTEWATER FLOW REDUCTION - MISCELLANEOUS DEVICES AND  SYSTEMS
Generic Type3
     Description
Develop-
 ment
 Stageb
 Application
Considerations
Faucet
Inserts
Devi ce whi ch i nserts
into faucet valve or
supply line and
restricts flow rate
with a fixed or
pressure
compensating
orifice.

Varieties:  Many.
            Compatible with most
            plumbing.

            Installation simple.
Faucet
Aerators
Devices attached to
faucet outlet which
entrain air into
water flow.

Varieties:  Many.
            Compatible with most
            plumbing.

            Installation simple.

            Periodic cleaning of
            aerator screens.
Reduced-Flow
Faucet
Fi xtures
Similar to
conventional unit,
but restrict flow
rate with a fixed
pressure
compensati ng
orifice.

Varieties:  Many.
                                   or
            Compatible with most
            plumbing.

            Installation
            identical  to
            conventional.
                                  82

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                          TABLE 5-5 (continued)
Generic Type3
     Desert pti on
Develop-
 ment
 Stageb
 Application
Consi derati ons
Mi xi ng
Valves
Specifically
designed valve units
which allow flow and
temperature to be
set with a single
control.

Varieties:  Many.
            Compatible with most
            plumbing.

            Installation
            identical  to
            conventional.
Hot Water
Pipe
Insulation
Hot water piping is
wrapped with
insulation to reduce
heat loss from hot
water standing in
pipe between uses.

Varieties:  Many.
            May be difficult to
            retrofit.
3 No reduction in pollutant mass; insignificant increase in pollutant
concentration.

b 1 = Prototypes developed and under evaluation.
  2 = Development complete; commercial  production initiated, but
      distribution restriced.
  3 = Fully developed, limited use, not locally available; mail  order
      purchase likely.
  4 = Fully developed, limited use, locally available from plumbing
      supply houses or hardware stores.
  5 = Fully developed, widespread use,  locally available from plumbing
      supply houses or hardware stores.
                                  83

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systems process  only the wastewaters  discharged  from bathing, laundry,
and bathroom  sink  usage,  and restrict the use  of the recycled water to
flushing  water-carriage  toilets and  possibly  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 pro-
cesses described  in Chapter 6, complemented by  specially  designed con-
trol  networks.   In  Table  5-6,  several generic  units  are  characterized
according to their general recycle  flow sheet.
5.3  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 elimiriation  of  the pollutant mass  contributed by a
given activity or  the  isolation of the  pollutant mass in a concentrated
wastewater stream.  In  Table 5-7,  several  methods  for  pollutant mass
reduction are outlined.
     5.3.1  Improved User Habits


Unnecessary quantities  of many  pollutants  enter the  wastewater  stream
when materials,  which could  be  readily  disposed of  in  a solid  waste
form,  are  added  to  the wastewater  stream.   A  few examples  include
flushing  disposable  diapers  or  sanitary  napkins down  the toilet,  or
using hot water and detergents to remove quantities of solidified grease
and  food  debris  from pots and  pans to enable their  discharge  down  the
sink drain.
     5.3.2  Cleaning Agent Selection
The use  of certain cleansing agents can  contribute  significant quanti-
ties  of  pollutants.     In   particular,   cleaning  activities,  such  as
clotheswashing and  dishwashing,  can account  for  over 70% of  the  phos-
phorus  in  residential  wastewater  (Table  4-4).   Detergents  are readily
available  that contain  a  low amount  of phosphorus  compared  to  other
detergents.
                                   84

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                                                                 TABLE  5-6

                               WASTEWATER  FLOW REDUCTION  - WASTEWATER RECYCLE AND REUSE SYSTEMS
         Flow  Sheet Description
Develop-
 ment
 Stagea
 Application
Considerations
Operation  and Maintenance
Total  Flow
Reducti onb
gpcd?
Wastewater Quality
	Impacts  	
co
01
       Recycle  bath and laundry
       for  toilet flushing
            Requires  separate toilet
            supply and drain line.

            May  be difficult to
            retrofit  to multi-story
            building.

            Requries  wastewater
            disposal  system for
            toilet and kitchen sink
            wastes.
                     Periodic replenishment  of
                     chemicals,  cleaning  of
                     filters and storage
                     tanks.

                     Residuals disposal.

                     Power use.
                             16     36     Sizable removals of
                                           pollutants, primarily P.
       Recycle  portion of total
       wastewater  stream for
       toilet flushing
            Requires separate toilet
            supply  line.

            May  be  difficult to
            retrofit to multi-story
            building.

            Requires disposal system
            for  unused recycle water.
                     Cleaning/replacement  of
                     filters and other
                     treatment and storage
                     components.

                     Residuals disposal.

                     Periodic replenishment of
                     chemicals.
                             16     36     Significant removals of
                                           pollutants.

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                                                              TABLE  5-6  (continued)
         Flow Sheet Description
Develop-
 ment
 Stage8
 Application
Considerations
Operation and Maintenance
Total Flow
Reduction^
gpcd£
Wastewater Quality
     Impacts 	
       Recycle toilet
       wastewaters for flushing
       water carriage toilets
CO
CTt
            Requires separate toilet
            pi umbi ng network.

            Utilizes low-flush
            toilets.

            Requires system for
            nontoilet wastewaters.

            May be difficult to
            retrofi t.

            Application restricted  to
            high use on multi-unit
            installations.
                      Cleaning/replacement of
                      filters  and  other
                      treatment  components.

                      Resi duals  disposal.

                      Power  use.
                              16      36      Significant  removals of
                                            pollutants.
       Recycle total wastewater
       stream for all water uses
   1-2      Requires major variance
            from State/local  health
            codes for potable reuse.

            Difficult to retrofit.
                      All  maintenance by
                      skilled personnel.

                      Routine service check.

                      Periodic pump out and
                      residuals disposal.

                      Power use.

                      Comprehensive monitoring
                      program required.
                              45    100     No wastewater  generated
                                            for onsite disposal.
         1  = Prototype developed and under evaluation.
         2  = Development complete; commercial  production initiated,  but  distribution may be restricted.
         3  = Fully developed; limited use, not locally  available,  mail  order  purchase  likely.
         4  = Fully developed; limited use, locally available from  plumbing  supply  houses and hardware stores.
         5  = Fully developed; widespread use,  locally available from plumbing supply houses and hardware stores.
         Based on the normal waste flow information presented in Table 4-2.

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                                 TABLE 5-7

                 EXAMPLE POLLUTANT MASS REDUCTION METHODS


           I.  Improved User Habits

          II.  Cleaning Agent Selection

         III.  Elimination of Garbage Disposal  Appliance

          IV.  Segregated Toilet Systems

               A.  Non-Water Carriage Toilets
               B.  Very Low-Volume Flush Toilets/Hoi ding Tank
               C.  Closed Loop Wastewater Recycle Systems
     5.3.3  Elimination of the Garbage Disposal  Appliance
The use of a garbage disposal  contributes substantial  quantities of
and suspended  solids  to  the wastewater load (Table 4-4).   As  a result,
it has  been shown that the use  of a garbage disposal may  increase  the
rate of  sludge and scum  accumulation and produce  a  higher  failure rate
for conventional  disposal  systems  under otherwise  comparable conditions
(6).  For  these  reasons,  as well  as the fact that most waste handled by
a garbage  disposal could  be handled as  solid wastes,  the elimination of
this appliance is advisable.
     5.3.4  Segregated Toilet Systems


Several  toilet  systems  can  be  used  to  provide  for  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  suspended  solids,  nitrogen,  and  pathogenic
organisms (Table 4-4).


A  number  of  potential   strategies  for  management  of segregated  human
excreta  are presented in Figure 5-1.   A discussion of the toilet systems
themselves is presented in  the wastewater flow reduction  section of this
chapter, while  details  regarding the other  unit processes in  the flow
sheet  may be found in Chapter 6.

                                   87

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Wastewaters generated by fixtures other  than  toilets  are often referred
to collectively  as "graywater."   Characterization studies  have  demon-
strated  that  typical   graywater  contains  appreciable  quantities  of
organic matter, suspended solids, phosphorus  and  grease  in  a daily flow
volume  of  29  gpcd  (110 Ipcd)  (7)(8){9)(10)(11)(12)(13)(14)(15)  (see
Table 4-4).  Its temperature as  it  leaves  the residence  is  in the range
of 31° C, with a pH  slightly  on  the alkaline  side.  The organic materi-
als in graywater appear to degrade at a rate not significantly different
from  those  in combined  residential wastewater  (15).   Microbiological
studies have  demonstrated  that significant concentrations  of indicator
organisms as total  and fecal coliforms are  typically  found  in graywater
(7)(11)(12)(13)(14)(15).   One  should assume,   therefore,  that graywater
harbors pathogens.


Although residential  graywater does contain pollutants and must be prop-
erly managed, graywater may be simpler to manage  than total  residential
wastewater due to  a  reduced flow volume.   While diverse  strategies have
been  proposed  for graywater  management (Figure  5-2),  rigorous  field
evaluations have not been conducted  in most cases.  Until  further field
data  become  available,  it is  recommended  that graywater treatment and
disposal/reuse systems be designed as for typical  residential wastewater
(as described in Chapter 6).   Design allowances  should be made only for
the  reductions  in  flow  volume,  as  compared  to typical   residential
wastewater.
5.4  Onsite Containment - Holding Tanks
Wastewaters  may  be  contained on  site using  holding  tanks,  and  then
transported  off  site for  subsequent  treatment and  disposal.    In  many
respects, the design,  installation,  and operation of a  holding  tank  is
similar to that  for  a  septic  tank  (as described in Chapter 6).  Several
additional considerations  do  exist,  as indicated in Table  5-8.   A dis-
cussion regarding the disposal of the pumpage from holding tanks is pre-
sented in Chapter 9 of this manual.
5.5  Reliability


An important  aspect  of  wastewater modification  concerns the reliability
of  a  given  method  to  yield  a  projected  modification  at a  specific
dwelling  or  establishment over  the  long term.   This  is  of particular
importance when designing an onsite  wastewater  disposal  system  based on
modified wastewater characteristics.
                                   88

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                         FIGURE 5-1



EXAMPLE STRATEGIES FOR MANAGEMENT OF SEGREGATED HUMAN WASTES

T T
Privy Compost Toi

i '
Disinfection

i '
Soil Amendme

Human Wastes


let Very Low-Volume
Flush Toilet

I
\
Treatment

i •
nt Onsite
Disposal



*

T
Closed Loop Incinerator
Recycle Toilet Toilet





Holding Tank

i r
Disinfection

1 r

Land Sewage
Disposal Treatment

'


Refuse

                         FIGURE 5-2



 EXAMPLE STRATEGIES FOR MANAGEMENT OF RESIDENTIAL  GRAYWATER
Sediments
*
*
Soil Absorption
Alternatives
tion

1
Further
Treatment
i

Reuse

|
Surface
Water
Discharge
                           89

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                               TABLE 5-8

               ADDITIONAL CONSIDERATIONS  IN THE DESIGN,
              INSTALLATION, AND OPERATION OF HOLDING TANKS
       Item                                Consideration
   Sizing                   Liquid holding capacity  >7 days
                           wastewater flow generation.  Minimum
                           capacity = 1,000 gallons.

   Discharge                There should be no discharge.

   Alarm  System             High water alarm positioned to allow at
                           least 3 days storage after activation.

   Accessibility            Frequent pumping is likely; therefore
                           holding tank(s) must be readily accessible
                           to pumping vehicle.

   Flotation                Large tanks may be subject to severe
                           flotation forces in high groundwater areas
                           when pumped.

   Cost                     Frequent pumping and residuals disposal
                           results in very high operating costs.
Assessing the  reliability  of  wastewater  modification methods is a com-
plex task which  includes considerations  of a  technological,  sociologi-
cal,  economic,  and   institutional  nature.    Major  factors affecting
reliability include:
     1.  The  actual  wastewater  characteristics  prior  to  modification
         compared to the average.

     2.  User awareness and influence on  method performance.

     3.  Installation.

     4.  Method performance.

     5.  User circumvention or removal.
                                    90

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In most situations, projections of the  impact  of  a  wastewater modifica-
tion method  must necessarily be  made,  assuming the  wastewater  charac-
teristics prior  to modification  are  reasonably typical.   If  the actual
wastewater characteristics deviate significantly  from  that of the aver-
age, a projected modification may be inaccurate.
The prospective user  should  be  fully aware of the  characteristics  of a
method considered  for use prior to  its application.  Users  who  become
aware of the characteristics of a method only after it has been put  into
use  are  more  likely  to  be  dissatisfied and  attempt to  circumvent  or
otherwise  alter  the   method and  negate  the  wastewater  modification
expected.
In general, passive wastewater modification methods  or devices  not sig-
nificantly affected by  user  habits tend to be more  reliable  than those
which are subject to user  habits  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.
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 performance data  are necessary
to estimate  the magnitude of the reduction, and  to  predict  the likeli-
hood that  the method will receive long-term user  acceptance.   Accurate
performance data can only be obtained through the results of  field test-
ing and evaluations.  Since many methods and system components are pres-
ently  in  various stages  of  development, only preliminary or projected
operation  and performance data may  be  available.    This preliminary  or
projected data  should be considered cautiously.


The  continued  employment  of a  wastewater modification  method  can  be
encouraged  through  several  management  actions.    First,  the  user(s)
should  be made  fully  aware of  the  potential  consequences if  they should
discontinue  employing  the  modification method  (e.g.,  system  failure,
water  pollution, rejuvenation costs, etc.).   Also, the appropriate man-
agement authority  can approve only  those  methods  whose characteristics
and merits indicate a potential  for long-term user acceptance.  Further,
installation  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.
                                    91

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To help ensure  that a projected modification will  actually  be realized
at a  given site,  efforts  can be  expended to accomplish  the  following
tasks:
     1.  Confirm  that the  actual  wastewater  characteristics prior  to
         modification are typical.

     2.  Make the  prospective  user(s)  of the  modification  method fully
         aware of the characteristics of the method, including its oper-
         ation, maintenance, and costs.

     3.  Determine  if the projected performance  of a given  method  has
         been confirmed through actual  field evaluations.

     4.  Ensure that  any devices or  systems are installed  properly  by
         competent personnel.

     5.  Prevent  user removal  or circumvention of  devices,  systems,  or
         methods.
5.6  Impacts on Onsite Treatment and Disposal Practices


     5.6.1  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%  or more.  The increase in pollu-
tant concentrations in any case may be estimated utilizing Figure 5-3.
     5.6.2  Wastewater Treatment and Disposal Practices
In  Table  5-9,  a  brief  summary  of  several  potential  impacts  that
wastewater  modification  may  have  on  onsite  disposal  practices  is
presented.    It  must  be  emphasized  that  the  benefits  derived  from
wastewater  modification  are  potentially   significant.     Wastewater
modification methods,  particularly wastewater flow reduction,  should be
considered an  integral  part of any onsite wastewater disposal  system.
                                   92

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                           FIGURE  5-3

       FLOW REDUCTION EFFECTS ON POLLUTANT CONCENTRATIONS
CD
O

CD
Q.

0)
(/>
CO
CD
u.
O
c
O
4-1
CD
L_
4— f
C
CD
O
C
O
CJ
•I-'

CO
O
CL
          0        10       20       30        40

           Wastewater Flow Reduction, percent of total daily flow


                 (Assumes Pollutant Contributions the Same
                 Under the Reduced Flow Volume)
                                93

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                                TABLE 5-9

              POTENTIAL IMPACTS OF WASTEWATER MODIFICATION
                      ON ONSITE DISPOSAL PRACTICES
  Disposal System
        Type
                     Modification Practice
   Flow
Reduction
Pollutant
Reduction
Potential  Impact
All Disposal
Surface Di sposal
Evapotranspiration
Onsite Containment
   X


   X


   X


   X
   X

   X

   X
                                    X

                                    X
                                    X

                                    X
            May extend service life of
            functioning system, but
            cannot quantify.

            Reduce water resource
            contamination.

            Simplify site constraints.

            Reduce frequency of septic
            tank pumping.

            Reduce sizing of
            infiltrative area.

            Remedy hydraulically
            overloaded system.

            Reduce component 0 and M
            costs.

            Reduce sizing of components.

            Eliminate need for certain
            components (e.g., nitrogen
            removal).

            Remedy hydraulically
            overloaded system.

            Remedy a hydraulically
            overloaded system.

            Reduce sizing of ET area.

            Reduce frequency of pumping.

            Reduce sizing of containment
            basin.
                                    94

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5.7  References
 1.  Wagner, E. G., and J.  N.  Lanoix.   Excreta Disposal for Rural Areas
     and Small  Communities.   WHO  Monograph 39, World  Health  Organiza-
     tion,  Geneva, Switzerland, 1958.  187 pp.

 2.  Stoner, C. H.  Goodbye  to the Flush Toilet.   Rodale Press, Emmaus,
     Pennsylvania, 1977.

 3.  Rybczynski, W., and A.  Ortega.   Stop the Five Gallon Flush.  Mini-
     mum Coast Housing Group, School of Architecture, McGill University,
     Montreal, Canada, 1975.

 4.  Van Der  Ryn,  S.   Compost Privy.  Technical Bulletin No.  1, Faral-
     lones  Institute,  Occidental, California, 1974.

 5.  Rybezynski, W., C. Polprasert,  and  M.  McGarry.   Low-Cost Technical
     Options  for  Sanitation.  Report  IDRC-102e,  International Develop-
     ment Research Center, Ottawa, Canada, 1978.

 6.  Bendixen, T.  W.,  R.  E.  Thomas, A.  A. McMahan, and  J.  B. Coulter.
     Effect of  Food Waste  Grinders  on Septic Tank  Systems.   Robert A.
     Taft Sanitary Engineering Center, Cincinnati,  Ohio, 1961.  119 pp.

 7.  Siegrist,  R.  L.,  M.  Witt,  and W.   C.  Boyle.  Characteristics  of
     Rural   Housing  Wastewater.  J.  Environ.  Eng.  Div.,  Am.  Soc. Civil
     Eng.,  102:553-548, 1976.

 8.  Laak,  R.  Relative Pollution Strengths of Undiluted Waste Materials
     Discharged in Households  and  the  Dilution of  Waters Used for Each.
     Manual of Grey Water Treatment  Practice - Part  II.  Monogram Indus-
     tries, Inc., Santa Monica, California, 1975.

 9.  Bennett,  E.  R.,   and  E.  K.  Linstedt.    Individual  Home Wastewater
     Characterization  and  Treatment.  Completion  Report  Series No. 66,
   ,  Environmental  Resources  Center,  Colorado  State  University,  Fort
     Collins, 1975.  145 pp.

10.  Ligman,  K.,  N.  Hutzler, and  W.  E.  Boyle.    Household Wastewater
     Characterization.   J.  Environ.  Eng.  Div.,  Am.   Soc.  Civil  Eng.,
     150:201-213, 1974.

11.  Olsson,  E.,  L. Karlgren, and  V.  Tullander.   Household Wastewater.
     National  Swedish  Institute for Building  Research, Stockholm, Swe-
     den, 1968.

12.  Hypes,  W.  D., C. E.  Batten,  and  J.  R.  Wilkins.   The Chemical/
     Physical  and Microbiological  Characteristics of  Bath  and  Laundry
     Wastewaters.   NASA  TN  D-7566,  Langley  Research  Center,   Langley
     Center,  Virginia, 1974.   31 pp.
                                   95

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13.  Small  Scale  Waste  Management  Project,  University  of  Wisconsin,
     Madison.  Management of Small Waste Flows.  EPA-600/2-78-173,  NTIS
     Report No. PB 286 560, September 1978.  804 pp.

14.  Brandes,  M.    Characteristics  of  Effluents  from Separate  Septic
     Tanks Treating Grey and Black Waters From the Same House.  J. Water
     Pollut. Control  Fed., 50:2547-2559, 1978.

15.  Siegrist, R. L.   Management of Residential Grey Water.   Proceedings
     of the Second  Pacific  Northwest  Onsite  Wastwater Disposal  Short
     Course, University of Washington, Seattle, March 1978.
                                   96

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                                CHAPTER 6

                        ONSITE TREATMENT METHODS
6.1  Introduction
This chapter presents  information  on  the component of an  onsite  system
that  provides  "treatment"  of  the  wastewater,  as  opposed  to   its
"disposal"  (disposal   options  for  treated  wastewater  are  covered  in
Chapter 7).  Treatment options  included in this  discussion  are:


     1.  Septic tanks
     2.  Intermittent sand filters
     3.  Aerobic treatment units
     4.  Disinfection units
     5.  Nutrient removal  systems
     6.  Wastewater segregation and recycle systems
Detailed  design,  O&M,  performance, and  construction data are  provided
for  the  first four  components  above.    A more  general  description  of
nutrient  removal  is provided as  these systems  are  not yet in  general
use, and often involve in-house changes in product use and plumbing.   A
brief mention of wastewater segregation and recycle options is  included,
since these also function as treatment  options.
Options  providing  a  combined treatment/disposal  function,  i.e.,  soil
absorption systems, are discussed in Chapter 7.


     6.1.1  Purpose
The purpose of the treatment component is to transform the  raw  household
wastewater into an effluent  suited to  the  disposal  component,  such  that
the wastewater can be disposed of in  conformance with  public health  and
environmental  regulations.  For example,  in a subsurface soil absorption
system, the pretreatment  unit  (e.g.,  septic tank) should  remove  nearly
all settleable solids and floatable  grease and scum so that a reasonably
clear liquid is discharged into the soil absorption field.  This  allows
the  field  to  operate   more  efficiently.    Likewise,  for a  surface
discharge  system,  the treatment  unit should produce  an  effluent  that
will meet applicable surface discharge standards.


                                   97

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     6.1.2  Residuals
No treatment process is  capable  of  continuous  operation without experi-
encing some  type  of residuals buildup.   Removal and  disposal  of these
residuals is a very important and often neglected part of overall system
O&M.
Residuals handling  is  discussed in detail under  each  individual  compo-
nent  in  Chapters 6 and  7.   Final disposal  of residuals is  covered  in
Chapter 9.
6.2  Septic Tanks


     6.2.1  Introduction
The  septic tank  is  the  most  widely  used  onsite wastewater  treatment
option  in the  United  States.    Currently,  about 25%  of the  new  homes
being constructed  in  this country use septic tanks  for  treatment  prior
to disposal of  home wastewater.
This section provides detailed  information  on  the  septic  tank, its sit-
ing  considerations,  performance, design,  construction procedures,  and
operation and maintenance.  The discussion  centers on tanks for single-
family  homes;  tanks for  larger flows are  discussed where  they  differ
from the single-family model.
     6.2.2  Description
Septic tanks are buried, watertight receptacles designed and constructed
to receive  wastewater  from a home, to separate  solids  from the liquid,
to provide  limited  digestion  of  organic  matter,  to store solids, and to
allow the clarified liquid to discharge for further  treatment and dis-
posal.   Settleable  solids  and partially  decomposed sludge  settle to the
bottom  of  the  tank and  accumulate.   A  scum  of  lightweight material
(including  fats and greases)  rises  to  the  top.   The partially clarified
liquid  is  allowed  to  flow through an  outlet  structure just  below the
floating  scum  layer.   Proper use  of  baffles,  tees, and  ells protects
against  scum outflow.    Clarified  liquid can  be  disposed  of  to  soil
absorption  systems, soil   mounds,  lagoons,  or  other disposal  systems.
Leakage  from septic tanks is often considered a  minor  factor; however,
if  tank  leakage causes the  level  of the  scum  layer to drop  below the
outlet  baffle,  excessive  scum discharges can  occur.   In  the extreme
case, the  sludge  layer will  dry and  compact,  and  normal  tank cleaning
                                    98

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practices will not  remove  it (1).   Another problem, if  the  tank  is  not
watertight,  is infiltration into the tank  which  can cause overloading of
the tank and subsequent treatment and disposal  components.
     6.2.3  Application


Septic tanks are normally the first component of an onsite system.   They
must be followed by polishing treatment and/or  disposal  units.   In  most
instances, septic tank effluent is discharged to a soil  absorption  field
where the wastewater  percolates  down  through  the soil.    In  areas  where
soils  are not  suitable  for  percolation,  septic  tank  effluent can  be
discharged  to  mounds  or ET  beds  for  treatment  and  disposal,  or  to
filters or lagoons for further treatment.
Septic  tanks  are  also  amenable  to  chemical  addition  for  nutrient
removal, as discussed later in this manual.
Local  regulatory  agencies  may require  that  the septic tank  be  located
specified distances from home, water well, and water lines to reduce any
risk of disease-causing agents from the septic tank reaching the potable
water  supply.    A  number  of minimum  separation  distances  have  been
developed  for  protecting  water  supplies  and  homes  from  septic  tank
disposal systems, but  these are  largely  arbitrary  and depend to a great
degree  on  the  soil  conditions.    Many  state and  local   building  codes
feature suggested separation  distances  that  should be adhered to in the
absence of any extenuating circumstances.


     6.2.4  Performance
Table 6-1 summarizes  septic  tank  effluent quality.   In  addition  to the
tabulated  results,  bacterial  concentrations  in   the  effluent are  not
significantly changed since septic tanks cannot be relied upon to remove
disease-causing microorganisms.   Oil  and  grease  removal  is typically 70
to 80%, producing  an  effluent of about 20-25 mg/1.   Phosphorus removal
is slight, at about  15%,  providing  an effluent quality of about 20 mg/1
total P.
Brandes  (7)  studied  the  quality  of  effluents  from septic tanks treating
graywater and  blackwater.   He found that without  increasing  the volume
of  the septic  tank,  the efficiency of the blackwater (toilet wastewater)
treatment  was   improved  by  discharging  the  household  graywater  to  a
separate treatment disposal system.
                                   99

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                                                     TABLE 6-1



                              SUMMARY OF EFFLUENT DATA FROM VARIOUS SEPTIQ TANK STUDIES
o
o


Parameter
BOD5
Mean, mg/1
Range, mg/1
No. of Samples
COD
Mean, mg/1
Range, mg/1
No. of Samples
Suspended Solids
Mean, mg/1
Range, mg/1
No. of Samples
Total Nitrogen
Mean, mg/1
Range, mg/1
No. of Samples

Ref. (2)
7 Sites

138
7-480
150

327
25-780
152

49
10-695
148

45
9-125
99

Ref. (3)
10 Tanks

1383
64-256
44

--
—
—

1553
43-485
55

—
—

Source
Ref. (4) Ref. (5)
19 Sites 4 Sites

140 240&
70.385
51 21

—
—
--

101 95b
48-340
51 18

36
—
51

Ref. (6)
1 Tank

120
30-280
50

200
71 -360
50

39
8-270
47

--
—

      a Calculated from the average  values  from  10  tanks,  6  series of tests.


      b Calculated on the basis of a log-normal  distribution of  data.

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Factors affecting  septic tank  performance  include geometry,  hydraulic
loading,   inlet  and   outlet   arrangements,   number  of   compartments,
temperature,  and  operation and  maintenance  practices.    If  a tank  is
hydraulically overloaded, retention time may  become too  short and  solids
may not settle or float properly.


A   single-compartment  tank  will  give acceptable performance.   However,
multi-compartment tanks  perform somewhat  better  than  single-compartment
tanks of the same total capacity,  because they  provide better protection
against solids carry-over into discharge  pipes during-periods  of  surges
or upset due to rapid digestion.


Improper design  and  placement of  baffles can  create  turbulence  in  the
tank,  seriously  impairing  settling  efficiency.    In  addition,  poor
baffles or outlet devices may promote scum or  sludge  entry to discharge
pipes.   Obviously,  improper  operation  and  maintenance  will   impair
performance.     Flushing  problem   wastes  (paper  towels,  bones,   fats,
diapers,  etc.) into  the system can  clog  piping.   Failure to pump  out
accumulated  solids  will   eventually   lead  to   problems   with   solids
discharge in the effluent.
     6.2.5  Design


         6.2.5.1  General
Septic  tanks  for  single-family  homes  are usually  purchased  "off  the
shelf," ready for installation, and are normally  designed  in  accordance
with local codes.
The tank  must be designed  to  ensure removal  of  almost all  settleable
solids.  To accomplish this, the tank must provide:

     1.   Liquid volume sufficient for  a  24-hr fluid retention  time  at
         maximum sludge depth and scum accumulation  (8).

     2.  Inlet and outlet devices to prevent the  discharge  of  sludge  or
         scum in the effluent.

     3.  Sufficient  sludge  storage  space  to prevent  the   discharge  of
         sludge or scum in the effluent.

     4.  Venting  provisions to  allow  for   the  escape  of  accumulated
         methane and hydrogen sulfide gases.
                                  101

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             6.2.5.2  Criteria
The first  step  in selecting  a  tank volume is to  determine  the average
volume of wastewater produced per day.   Ideally,  this  is done by meter-
ing wastewater  flows  for a  given  period;  but that  is  seldom feasible,
particularly if  a septic tank  system  is being selected  for  a building
still  under construction.
In the  past,  the  design capacity of most  septic  tanks  was  based on the
number of bedrooms  per  home and the average  number  of  persons per bed-
room.   Chapter 4  showed  that  the  average  wastewater contribution  is
about 45 gpcd  (170  Ipcd)  (2).  As  a safety  factor,  a value  of 75 gpcd
(284 Ipcd)  can  be  coupled with a potential maximum  dwelling density of
two  persons per  bedroom, yielding  a  theoretical  design  flow of  150
gal/bedroom/day (570 1/bedroom/day).  A theoretical  tank  volume of 2 to
3  times  the  design  daily  flow  is  common,  resulting  in  a  total  tank
design  capacity of 300 to 450 gal  per bedroom  (1,140  to  1,700  1  per
bedroom).
While not ideal, most state and local codes rely on some version of this
method by assigning required septic tank capacities solely by the number
of bedrooms (see Table 6-2).  Unfortunately, hourly and daily flows from
the home can vary greatly.  During high flow periods, higher solids con-
centrations are  discharged from  the septic tank.   Well-designed,  two-
compartment tanks reduce the effect of peak hour loads.
Another key  factor  in  the  design  and performance of septic tanks is the
relationship  between  surface area,  surge  storage, discharge  rate,  and
exit  velocity.    These parameters  affect  the hydraulic  efficiency  and
sludge retention capacity of the tank.


Tanks  with  greater surface  area  and  shallower  depth  are  preferred,
because increased liquid surface  area increases  surge storage capacity;
a  given  inflowing  volume  creates a  smaller  rise  in  water depth  and a
slower discharge  rate  and  exit velocity.   These  surges of flow through
the tank  are dampened  as surface area  increases.   This allows a longer
time for  separation of sludge  and scum  that  are  mixed by turbulence re-
sulting from  the influent surge (8).


In addition  to increasing the surface area, there are two other means of
reducing  the exit velocity and reducing the  opportunity  for  solids  and
scum to escape through the  outlet.   These  are:  1) increase the size of
the outlet riser; and  2)  reduce  the size of  the  final  discharge pipe.
The use of a  6-in.  (15-cm)  outlet riser instead of a 4-in. (10-cm)
                                    102

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o
OJ
                                                     TABLE  6-2
                                  TYPICAL  SEPTIC TANK  LIQUID  VOLUME  REQUIREMENTS
Minimum, gal
1-2 bedrooms, gal
3 bedrooms, gal
4 bedrooms, gal
5 bedrooms, gal
Additional bedrooms  (ea), gal
Federal
Housing
Authon' ty
750

750

900

1,000

1,250

250
U.S. Public
Health
Servi ce
750

750

900

1,000

1,250

250
Uni form
PI umbl ng
Code
750

750

1,000

1,200

1,500

150

Range of State
Requirements (9)

500 - 1,000

500 - 1,000

900 - 1,500

1,000 - 2,000

1,100 - 2,000


-------
outlet riser  will  reduce the exit  velocity from 0.025  ft/sec  to 0.011
ft/sec (0.76 cm/sec to 0.34 cm/sec)  a reduction of 56% (8).
Use of garbage grinders increases both the settleable and floatable sol-
ids in the  wastewater  and their accumulation rates  in  the  septic tank.
U.S. Public Health Service (USPHS) studies indicate that the increase in
the sludge  and scum accumulation  rate is about  37% (10).    This means
either more frequent pumping  or a larger tank  to  keep  the  pumping fre-
quency down.   A  common expedient is to add 250 gal  (946  1)  to the tank
size when garbage grinders are used, although this volume is arbitrary.
It  is  generally  a good idea  to avoid the use of  garbage grinders with
onsite systems.
         6.2.5.3  Inlet and Outlet Devices
The flow out  of  a septic tank should carry  only  minimal  concentrations
of settleable solids.  Higher concentrations can occur if:
     1.  The inlet turbulence in a single-compartment tank causes mixing
         of the sludge with the wastewater in the clear space.

     2.  The rise velocity of the water  in  the  vertical  leg of the out-
         let tee resuspends previously captured solids.

     3.  The rising gases produced by anaerobic digestion interfere with
         particle-settling  and   resuspend   previously  captured  solids,
         which then are lost in the effluent.
The inlet to a septic tank should be designed to dissipate the energy of
the incoming  water,  to minimize  turbulence,  and to  prevent  short-cir-
cuiting.  The  inlet  should preferably be either  a  sanitary tee or baf-
fle.   The baffle  should be small enough so that  it  is  flushed out each
time,  and yet keeps floating solids from blocking the inlet.   The invert
radius in a tee helps dissipate energy in the transition from  horizontal
to  vertical flow,  and  prevents dripping that, at the  proper  frequency,
can amplify water  surface oscillations  and  increase intercompartmental
mixing.   The  vertical  leg of the  inlet  tee should  extend   below  the
liquid  surface.    This  minimizes induced  turbulence by  dissipating  as
much energy in the inlet as possible.


The outlet structure's  ability to retain sludge and  scum in  either the
first  or  second  compartment   is   a  major   factor  in   overall   task
performance.    The  outlet of a  septic  tank can  be  a tee, a  baffle,  or
some  special   structure  (see   Figure  6-1).   The outlet  must  have  the
proper submergence and  height  above liquid  level  such that  the  sludge
                                   104

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                             FIGURE 6-1

             TYPICAL SEPTIC TANK OUTLET STRUCTURES TO
            MINIMIZE SUSPENDED SOLIDS IN DISCHAR6E(11)
       Liquid Level
                                          Tank Outlet Pipe
               Gas Deflection /
                    Baffle
Liquid Level
 Outlet Scum
    Baffle—*
Liquid Level
                                 Gas Deflection
                                     Device
                Gas Deflection
                 Configuration
                                 105

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and  scum  clear spaces  balance,  and proper  venting of sludge  gases  is
provided  (see  Figure  6-2).     Although  the Manual of  Septic  Tank  Prac-
tices recommends an outlet submergence equal  to 40% of the liquid depth,
other  studies  have shown  that  shallower  submergence decreases  solids
discharges and allows for greater sludge accumulation, and thus for less
frequent  pumping   (8).    Table  6-3  summarizes  the   results  of  these
studies.
As  shown  in  Figure  6-1,  various  types of  gas deflection  baffles  and
wedges have been developed to prevent gas-disturbed sludge from entering
the rising leg of the outlet.
         6.2.5.4  Compartmentation
Recent trends in septic tank  design  favor  multiple,  rather than single,
compartmented tanks.  When a tank is properly divided into compartments,
BOD  and  SS  removal are  improved.   Figure  6-3  shows  a  typical  two-
compartment tank.
The benefits of compartmentation are due largely to hydraulic isolation,
and to the reduction or elimination  of  intercompartmental  mixing.   Mix-
ing  can  occur  by  two means:   water  oscillation and  true  turbulence.
Oscillatory mixing  can be minimized by making compartments  unequal  in
size  (commonly  the  second  compartment is  1/3  to 1/2  the size of  the
first),  reducing  flow-through  area,  and  using  an  ell  to  connect
compartments (1).
In the first compartment, some mixing of sludge and scum with the liquid
always occurs due to induced turbulence from entering wastewater and the
digestive process.  The second compartment receives the clarified efflu-
ent from  the  first  compartment.   Most of the  time  it receives  this hy-
draulic  load  at  a  lower rate and  with less  turbulence than  does the
first compartment, and, thus, better  conditions  exist for settling low-
density solids.   These conditions lead  to longer working periods before
pump-out of solids is necessary and improve  overall  performance.
         6.2.5.5  Access and Inspection
In order to provide access and a means to inspect the inside of the sep-
tic tank, manholes should be provided.  Manholes are usually placed over
both  the  inlet and  the  outlet  to  permit cleaning behind  the baffles.
The manhole cover should extend above the actual septic tank to a height
not more than  6 in.  (15  cm)  below the finished grade.  The actual  cover
can extend to the ground surface if a proper seal is provided to prevent
                                   106

-------
                              FIGURE 6-2

             SEPTIC TANK SCUM AND SLUDGE CLEAR SPACES (8)
            Liquid
            Level"
j    . Sc
Scum
                           Scum Clear
                              Space
           Total Clear Space  Sludge Clear
                                Space



                                 •Outlet
                                TABLE 6-3

          LOCATION OF  TOP  AND BOTTOM OF OUTLET TEE OR BAFFLE (12)
               Tank  Receiving  Sewage
                           Tank Receiving Sewage
                                and Garbage
Total
Liquid
Tank
Capacity
gal
500
750
1,000
Projection3
Above
Liquid Level
12
12
12
Penetration3
Below
Liquid Level
22
24
26
Projection3
Above
Liquid Level

18
18
Penetration3
Below
Liquid Level

38
41
3 Percentage of liquid depth.   See Figure 6-2 for diagram.
                                  107

-------
                         FIGURE 6-3

            TYPICAL TWO-COMPARTMENT SEPTIC TANK







_









__ _ 	



l~ 1>
! i



_



• — 	 	 1 r
= 	 	 	 14=
—i * *
\ i
l|

— \ I'
Access iQi ~ ]~F
Manholes ' .1*
^ -ty


( '
i ;
_j

. .. -_ _,.. ,


~i


i — i
^sT^
^__ 	 !

















i_










b







                            Plan
Sanitary
  Tee
 Inlet

-
A*

., V Ul 11 r
Liquid Level
^
(r
"
~.
*


~l


JJ
•Outlet
                     Longitudinal Section
                             108

-------
the escape  of odors and accidental  entry into the tank.   In addition,
small  inspection pipes can be placed  over the  inlet and outlet to allow
inspection without having to remove the manhole.


         6.2.5.6  Materials
The most  commonly  used construction material  for septic tanks  is con-
crete.  Virtually all  individual-home septic tanks  are  precast for easy
installation in the  field.  The walls have  a  thickness  of 3 to 4 in. (8
to 10 cm), and the tank is  sealed  for watertightness after installation
with two coats of bituminous coating.  Care  must be taken to seal around
the inlet and  discharge pipes  with a bonding compound  that will adhere
both to concrete and to the inlet and outlet pipe.
Steel is another  type  of  material  that has been used  for  septic tanks.
The  steel  must  be  treated  so  as  to  be able  to  resist  corrosion  and
decay.     Such   protection   includes   bituminous   coating  or   other
corrosion-resistant  treatment.   However, despite  a  corrosion-resistant
coating, tanks deteriorate at the  liquid level.   Past  history indicates
that  steel tanks  have  a  short operational  life  (less than  10 years)  due
to corrosion (3).
Other  materials  include  polyethylene  and  fiberglass.    Plastic  and
fiberglass tanks  are  very  light, easily  transported,  and resistant  to
corrosion and  decay.    While  these  tanks have  not  had a good  history,
some manufacturers are  now producing an  excellent  tank with  increased
strength.  This minimizes  the chance of  damage during installation  or
when heavy machinery  moves  over it after burial.
     6.2.6  Installation Procedures
The  most  important  requirement of  installation  is  that  the tank  be
placed on  a level grade  and  at a depth that  provides  adequate gravity
flow from  the  home and matches  the  invert  elevation of the house sewer.
The tank should be placed  on  undisturbed soil  so that settling does not
occur.   If the excavation  is dug  too deep, it  should  be  backfilled to
the  proper elevation  with  sand  to  provide an adequate bedding for the
tank.  Tank performance can be impaired if  a level position is not main-
tained, because inlet and outlet structures will  not function properly.
                                 109

-------
Other considerations include:
     1.  Cast iron  inlet  and outlet structures  should  be used  in  dis-
         turbed soil areas where tank settling  may  occur.

     2.  Flotation collars should be used in areas  with  high  groundwater
         potential.

     3.  The tank should be placed so that the  manhole is  slightly below
         grade to prevent accidental  entry.

     4.  The tank should be  placed  in an  area  with  easy access to alle-
         viate pump-out problems.

     5.  During  installation,   any   damage   to  the  watertight  coating
         should  be  repaired.   After installation,  the tank  should  b.e
         tested for watertightness by filling with  water.

     6.  Care  should  be  taken  with  installation   in  areas  with  large
         rocks to prevent undue  localized stresses.

     7.  Baffles,  tees,  and elbows should be  made  of  durable  and
         corrosion-proof  materials.     Fiberglass  or   acid-resistant
         concrete  baffle  materials  are  most suitable.    Vitrified  clay
         tile, plastic, and cast iron are best  for  tees  and ells.
     6.2.7  Operation and Maintenance
One of the major  advantages  of  the  septic  tank  is that it has no moving
parts and,  therefore,  needs very little routine  maintenance.   A well-
designed  and  maintained  concrete,  fiberglass,  or  plastic tank  should
last  for  50 years.  Because of corrosion  problems, steel tanks  can  be
expected to last  no more  than 10 years.  One cause of septic  tank prob-
lems involves a failure to pump  out the sludge solids when required.   As
the  sludge  depth  increases,  the  effective liquid volume  and detention
time  decrease.    As  this occurs,  sludge  scouring  increases,  treatment
efficiency  falls  off,  and more solids  escape through the outlet.   The
only way to prevent this is by periodic pumping  of the tank.
Tanks should be inspected at  intervals  of  no  more than every 2 years to
determine  the  rates of  scum and  sludge  accumulation.    If  inspection
programs are not carried out, a  pump-out frequency  of once every 3 to 5
years is  reasonable.   Once the characteristic  sludge  accumulation rate
is  known,  inspection  frequency  can be adjusted accordingly.   The inlet
and  outlet structures and  key joints  should  be  inspected for  damage
after each tank pump-out.
                                  110

-------
Actual inspection of  sludge and scum  accumulations  is the  only  way to
determine definitely when a given tank needs  to  be pumped.   When  a tank
is inspected,  the  depth of sludge  and scum  should  be measured  in  the
vicinity of  the outlet  baffle.   The  tank  should be  cleaned  whenever:
(1) the  bottom  of  the scum layer is within  3 in. of  the bottom  of  the
outlet device; or (2) the sludge level is within 8  in. of the bottom of
the outlet device.   The efficiency  of suspended solids removal  may start
to decrease before  these conditions  are reached.
Scum  can  be measured  with  a stick  to which a  weighted flap  has been
hinged, or  with  any device that can be  used to  feel the bottom  of the
scum  mat.   The stick  is  forced  through  the mat, the hinged  flap falls
into  a  horizontal  position,  and  the  stick  is  raised  until  resistance
from  the bottom  of  the scum is felt.  With  the  same tool,  the distance
to the bottom of the outlet device can  be determined.
A long stick wrapped with  rough, white  toweling  and lowered to the bot-
tom of the  tank will  show the  depth  of sludge and the liquid  depth of
the tank.  The stick should be lowered behind the outlet device to avoid
scum particles.  After several  minutes, the  sludge  layer  can be distin-
guished by sludge particles clinging to the toweling.
Other methods for measuring sludge  include connecting  a  small  pump to a
clear plastic line  and lowering the line until  the  pump starts to draw
high solids concentrations.


Following  is  a  list of considerations pertaining to septic  tank opera-
tion and maintenance:
     1.  Climbing into septic tanks can  be  very  dangerous,  as the tanks
         are  full of toxic gases.   When using  the manhole,  take every
         precaution  possible, i.e., do not  lower an  individual  into the
         tank without a  proper  air supply,  and  safety  rope  tied around
         chest or waist.

     2.  The  manhole, not  the inspection  pipe, should  be used for pump-
         ing  so as to minimize  the risk  of  harm  to the inlet and outlet
         baffles.

     3.  Leaving solids in the septic tank to aid in starting the system
         is not necessary.

     4.  When  pumped,  the septic  tank must not  be disinfected, washed,
         or scrubbed.
                                   Ill

-------
     5.  Special  chemicals are not needed to start  activity  in  a septic
         tank.

     6.  Special   additives  are  not  needed  to improve  or  assist  tank
         operation once  it is  under way.   No  chemical  additives  are
         needed  to  "clean"  septic  tanks.    Such  compounds may  cause
         sludge bulking and decreased sludge digestion.   However,  ordi-
         nary  amounts  of bleaches,  lyes,  caustics,  soaps,  detergents,
         and drain cleaners do not harm  the  system.   Other preparations,
         some of which claim to eliminate the need for septic tank  pump-
         ing, are not  necessary for proper  operation and are  of  ques-
         tionable value.

     7.  Materials not  readily  decomposed (e.g.,  sanitary napkins,  cof-
         fee grounds, cooking  fats,  bones, wet-strength  towels, dispos-
         able diapers,  facial  tissues, cigarette  butts)  should  never be
         flushed into a septic tank.   They will  not  degrade in the  tank,
         and can clog inlets,  outlets, and the  disposal  systems.


     6.2.8  Considerations for Multi-Home and Commercial  Wastewater


         6.2.8.1  General
In some  instances,  a  septic  tank can serve several  homes,  or a commer-
cial/institutional  user such  as a school,  store,  laundry, or restaurant.
Whereas septic tanks for single-family homes must handle highly variable
flows (i.e., approximately 45% of the total  household flow occurs in the
peak four hours), commercial  systems must  also be able to treat continu-
ous wastewater flows for 8-16  hours  a day as  well  as peak loadings.  In
addition, commercial wastewaters may present  special  problems that need
to be  handled prior to discharge  to the  septic tank  (i.e.,  grease re-
moval  for  restaurant  wastewaters,  and  lint removal for  laundry waste-
water).
As explained  previously,  septic tanks  of two compartments  give  better
results  than  single-compartment  tanks.    Although  single-compartment
tanks are  acceptable  for  small  household installations,  tanks  with  two
compartments should be provided for  the larger  institutional  systems.
Tanks with more than two compartments  are not used frequently.
Multiple-compartment  tanks   for  commercial/institutional  flows  should
have  the same  design features  as single-family  home  tanks  discussed
above.   These  include:   compartments  separated  by walls with  ports  or
slits at proper elevations,  proper  venting,  access to all  compartments,
and proper inlet and outlet design and submergence.
                                  112

-------
The effect  of  a multiple-compartment tank can be  accomplished  by using
two or  more tanks in  series.   A better  construction  arrangement,  par-
ticularly for medium or large  installations,  is  to connect special  tank
sections together  into  a  unit having single  end-walls  and  two  compart-
ments.  A unit of four precast tank sections forming two compartments is
shown in Figure 6-4.
         6.2.8.2  Design
Larger tanks for commercial/institutional flows or for clusters of homes
must be  sized  for the  intended  flow.    Whenever  possible  with existing
facilities, the  flow should be metered  to obtain accurate  readings  on
average daily flows  and  flow peaks.   For housing  clusters, if the total
flow cannot be  measured,  the  individually  metered  or  estimated flows
(based on the expected population and the generation  rate of 45 gal/cap/
day (170 1/cap/day)  from each house  must be  summed to determine the de-
sign flow.   For commercial/institutional  applications,  consult Chapter
4.  For  flows  between 750 and 1,500 gal  per day  (2,840 to  5,680 1  per
day),  the  capacity  of the tank  is  normally  equal to  1-1/2  days  waste-
water flow.   For  flows  between  1,500 and 15,000 gpd (5,680  to  56,800
Ipd),  the minimum effective tank  capacity can be calculated at 1,125 gal
(4,260 1) plus 75% of the daily flow; or

                           V = 1,125 + 0.75Q

     where:

        V = net volume of the tank (gal)
        Q = daily wastewater flow (gal)


If garbage grinders  are  used, additional  volume or extra sludge storage
may be desired to minimize the  frequency  of pumping (10).
6.3  Intermittent Sand Filters


     6.3.1  Introduction
Intermittent  sand  filtration  may  be  defined  as   the   intermittent
application  of  wastewater  to  a  bed  of   granular  material  which  is
underdrained to  collect and  discharge the  final  effluent.   One of  the
oldest  methods   of   wastewater  treatment  known,   intermittent   sand
filtration,  if  properly  designed,   operated,   and  constructed,   will
produce effluents  of very high  quality.    Currently,  many  intermittent
sand filters are used throughout the United States  to treat wastewater
from small commercial and institutional  developments and from individual
                                   113

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                                                FIGURE 6-4

                         FOUR PRECAST REINFORCED CONCRETE SEPTIC TANKS COMBINED
                              INTO ONE UNIT FOR LARGE FLOW APPLICATION (10)
                 		T
                                  	    I
	J_
                                                   Plan
                                          12" Dia. Inspection Hole-
Influent
                                                 Section
                                 Vent
                                                   Joints to be Grouted
                                                                                                  Effluent

-------
homes.  The use of intermittent sand filters  for  upgrading  stabilization
ponds has also become popular (13).


Intermittent  sand  filtration  is  well   suited   to  onsite  wastewater
treatment and disposal.   The process is  highly  efficient, yet  requires  a
minimum  of  operation and maintenance.   Normally,  it  would be used  to
polish effluents  from septic  tank  or aerobic treatment  processes and
would  be  followed  by  disinfection  (as  required)  prior   to  reuse  or
disposal  to land or surface  waters.
     6.3.2  Description


Intermittent sand filters are  beds of granular  materials  24 to 36  in.
(61 to  91  cm)  deep  and underlain  by  graded  gravel  and  collecting  tile.
Wastewater is applied  intermittently  to  the  surface of the  bed  through
distribution  pipes  or  troughs.     Uniform   distribution   is  normally
obtained by dosing so as to flood the entire  surface of  the bed.


Filters may be designed to provide free access (open filters), or may be
buried  in  the ground  (buried  filters).    A   relatively  new  concept  in
filtration  employs  recirculation  of  filter  effluent  (recirculating
filters).
The mechanisms of purification attained by intermittent sand filters are
complex  and  not  well understood  even  today.   Filters  provide  physical
straining and  sedimentation  of  solid materials within  the media grains.
Chemical  sorption also  plays a  role in  the removal of  some  materials.
However,  successful  treatment  of  wastewaters  is  dependent  upon  the
biochemical  transformations  occurring  within the  filter.  Without the
assimilation  of  filtered and  sorbed  materials  by biological  growth
within the filter, the process would fail to operate properly.   There is
a  broad  range of trophic  levels  operating within  the  filter,  from the
bacteria  to annelid worms.
 Since  filters  entrap,  sorb,  and assimilate materials  in the wastewater,
 it is  not surprising to find that the interstices between the grains may
 fill,  and the  filter  may eventually clog.   Clogging may  be  caused by
 physical,  chemical,  and  biological  factors.    Physical  clogging  is
 normally  caused by  the accumulation  of  stable solid materials  within or
 on the surface  of the  sand.   It is  dependent  on  grain size and porosity
 of the filter media, and  on wastewater suspended solids characteristics.
 The  precipitation,  coagulation, and adsorption of a vareity of materials
 in wastewater may also contribute to the clogging problem in some filter
 operations  (14).    Biological  clogging  is  due primarily  to an improper
                                   115

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balance of the intricate biological  population within the filter.  Toxic
components in the wastewater, high organic loading,  absence of dissolved
oxygen, and  decrease  in  filter temperatures are the most  likely causes
of  microbial  imbalances.    Accumulation  of  biological   slimes  and  a
decrease  in  the  rate  of decomposition of  entrapped  wastewater contami-
nants within the filter accelerates filter  clogging.   All  forms of pore
clogging  likely  occur  simultaneously  throughout the  filter  bed.   The
dominant  clogging  mechanism is  dependent upon wastewater  characteris-
tics, method and rate of wastewater application, characteristics of the
filtering media,  and filter environmental  conditions.
     6.3.3  Application
Intermittent sand  filtration  is well adapted  to  onsite disposal.   Its
size  is  limited by  land availability.   The  process  is applicable  to
single homes and clusters of  dwellings.   The  wastewater applied  to the
intermittent filters  should be  pretreated  at  least by  sedimentation.
Septic tanks should  be  required as a minimum.  Additional  pretreatment
by  aerobic  biological  processes normally results in higher  acceptable
rates of wastewater application and longer filter  runs.   Although  exten-
sive field experience is lacking to  date, the  application of  pretreated
graywaters to intermittent sand filters may  be advantageously  employed.
There is some evidence that higher loading  rates  and longer filter runs
can be achieved with pretreated graywaters.
Site constraints  should  not limit the application of  intermittent  sand
filters, although odors from open filters receiving septic  tank effluent
may require isolation of the process  from  dwellings.   Filters  are often
partially (or completely)  buried  in  the ground, but may be  constructed
above  ground  when dictated  by shallow  bedrock or  high  water  tables.
Covered filters are required in areas with extended periods of  subfreez-
ing weather.  Excessive long-term rainfall and  runoff  on submerged  fil-
ter  systems may  be  detrimental   to  performance,   requiring  appropriate
measures to divert these sources  away from the system.
     6.3.4  Factors Affecting Performance
The  degree  of  stabilization  attained by an intermittent sand  filter  is
dependent upon:  (1) the type and biodegradability of wastewater applied
to  the  filter,  (2) the environmental conditions within the  filter,  and
(3)  the  design characteristics of the filter.


Reaeration  and  temperature are  two of the most  important  environmental
conditions  that  affect the degree  of wastewater  purification through  an
intermittent  sand  filter.    Availability  of  oxygen within the  pores
                                  116

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allows  for  the  aerobic  decomposition of  the wastewater.   Temperature
directly  affects  the  rate  of  microbial  growth,  chemical  reactions,
adsorption  mechanisms,  and   other   factors   that   contribute  to  the
stabilization of wastewater within the sand media.
Proper selection of process design variables also  affects  the  degree of
purification of wastewater by  intermittent  filters.   A brief discussion
of those variables is presented below.
         6.3.4.1  Media Size and Distribution
The successful use of a granular material  as a filtering media is depen-
dent upon the proper choice of  size  and uniformity  of the grains.   Fil-
ter media size and uniformity are expressed in terms of "effective size"
and "uniformity  coefficient."    The  effective size  is  the size of  the
grain, in millimeters,  such that 10% by weight are smaller.  The unifor-
mity coefficient  is  the  ratio  of the grain size  that has 60% by weight
finer than itself to the  size which  has 10% finer than  itself.  The ef-
fective size  of  the granular media  affects the quantity  of  wastewater
that may be  filtered,  the rate of filtration, the  penetration depth of
particulate matter,  and  the quality of the filter effluent.   Granular
media that is too coarse lowers the retention time of the applied waste-
water through the filter to a point where  adequate biological  decomposi-
tion is  not  attained.   Too  fine  a media  limits the  quantity of waste-
water that may be successfully  filtered,  and will  lead  to early filter
clogging.  This  is  due to the  low hydraulic  capacity and the existence
of capillary  saturation, characteristic of  fine materials.   Metcalf and
Eddy (15) and Boyce  (16)  recommended that  not more  than 1% of the media
should be finer  than 0.13 mm.   Many suggested values for the effective
size and uniformity coefficient exist in the literature (10)(17)(18)(19)
(20).   Recommended filter media effective  sizes range from a  minimum of
0.25 mm  up  to approximately 1.5  mm.   Uniformity coefficients (UC)  for
intermittent filter media normally should  be less  than 4.0.
 Granular  media  other than sand that have  been  used include anthracite,
 garnet,  ilmenite,  activated  carbon, and mineral  tailings.    The  media
 selected  should  be  durable and insoluble in water.  Total organic matter
 should be less than  1%,  and  total  acid soluble  matter should not exceed
 3%.   Any  clay,  loam, limestone,  or  organic material  may  increase the
 initial  adsorption  capacity  of  the sand,  but  may  lead  to  a  serious
 clogging  condition as the filter ages.


Shapes of  individual media grains  include round,  oval,  and  angular  con-
figurations.  Purification  of wastewater infiltrating  through granular
media is  dependent  upon  the  adsorption and oxidation of organic  matter
in the wastewater.   To a limiting extent, this is dependent on the shape
                                   117

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of the grain; however, it is more  dependent  on  the  size  distribution  of
the grains, which is characterized  by the UC.


The arrangement or placement of different sizes  of grains throughout the
filter bed is also an important design consideration.   A  homogeneous bed
of one  effective size media  does  not  occur often due  to  construction
practices and variations in  local materials.   In a bed  having  fine media
layers placed above coarse layers,  the downward  attraction of  wastewater
is not as great  due  to the  lower amount of cohesion of the  water in the
larger pores (21).   The coarse media  will not draw  the water  out of the
fine media,  thereby  causing the bottom  layers  of the fine material  to
remain saturated with water.  This saturated zone acts as a water seal,
limits oxidation, promotes clogging,  and reduces the action of  the  fil-
ter to  a  mere  straining mechanism.  The use of media  with  a  UC of  less
than 4.0 minimizes this problem.
The media  arrangement  of coarse over  fine  appears theoretically to  be
the most favorable, but it may be difficult  to operate  such  a  filter  due
to internal clogging throughout the filter.
         6.3.4.2  Hydraulic Loading Rate


The  hydraulic  loading  rate may be  defined  as the volume of liquid  ap-
plied to the surface area of the sand filter over a  designated  length of
time.   Hydraulic loading is normally  expressed  as  gpd/ft , or  cm/day.
Values  of  recommended loading  rates  for  intermittent sand filtration
vary  throughout  the literature and  depend  upon  the  effective size  of
sand  and the type of wastewater.   They normally range from 0.75 to 15
gpd/ft2 (0.3 to 0.6 m3/mz/d).


         6.3.4.3  Organic Loading Rate
The  organic  loading rate  may  be defined as  the  amount of  soluble  and
insoluble organic  matter  applied per unit  volume  of filter bed over  a
designated length of time.  Organic loading  rates  are not often  reported
in the literature.   However, early  investigators found  that  the perfor-
mance of  intermittent  sand filters was dependent upon  the  accumulation
of stable organic  material  in  the filter bed  (14)(21).   To  account  for
this,  suggested hydraulic  loading  rates today are often  given for  a
particular type of wastewater.   Allowable  loading  rates increase with
the  degree   of  pretreatment.    A  strict relationship  establishing  an
organic loading rate,  however,  has not yet been clearly  defined in  the
literature.
                                  118

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         6.3.4.4  Depth of Media


Depths of intermittent  sand  filters  were initially designed to  be  4  to
10.feet;  however, it  was soon  realized at  the  Lawrence  Experimental
Station (21) that most of the purification of wastewater occurred within
the top 9 to 12  in.  (23 to 30 cm)  of the bed.   Additional  bed  depth did
not improve the wastewater purification to any significant degree.  Most
media depths used today range from 24 to 42 in.  (62 to 107 cm).   The use
of  shallow  filter beds helps  to keep  the cost  of installation  low.
Deeper beds  tend to  produce  a  more  constant effluent  quality,  are not
affected  as severely  by  rainfall  or snow  melt  (22),  and permit the
removal of more media before  media replacement becomes necessary.


         6.3.4.5  Dosing Techniques and Frequency
Dosing techniques refer  to  methods  of application of wastewater to  the
intermittent sand filter.  Dosing of intermittent filters  is  critical  to
the performance of the process.   The  system must be designed  to insure
uniform distribution of  wastewater  throughout  the  filter  cross-section.
Sufficient  resting  must  also be  provided  between  dosages  to obtain
aerobic conditions.   In small filters,  wastewater  is  applied  in  doses
large enough to entirely flood the filter surface with  at  least 3 in.  (8
cm) of water,  thereby  insuring adequate  distribution.   Dosing  frequency
is dependent upon media  size,  but should be greater with  smaller  doses
for coarser media.
Dosing methods that have been used include ridge and furrow application,
drain tile distribution, surface  flooding,  and  spray  distribution  meth-
ods.   Early sand  filters  for municipal  wastewater were  surface  units
that  normally  employed  ridge and furrow or spray  distribution  methods.
Intermittent filters in use  today are  often built  below the ground sur-
face and employ tile distribution.
The   frequency   of  dosing  intermittent  sand   filters   is  open   to
considerable  design judgement.   Most  of the  earlier  studies  used  a
dosing  frequency  of I/day.   The Florida studies  investigatged  multiple
dosings  and  concluded  that the BOD  removal  efficiency of  filters  with
media effective  size greater than 0.45  mm  is  appreciably  increased  when
the  frequency  of loading  is increased beyond twice  per  day  (23).   This
multiple  dosing  concept  is  successfully  used  in  recirculating  sand
filter  systems in  Illinois (24), which employ  a dosing frequency of  once
every 30 min.
                                    119

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         6.3.4.6  Maintenance Techniques


Various techniques to maintain  the  filter bed may be employed  when  the
bed becomes clogged.  Some of these  include:   (1)  resting  the bed for a
period of time,  (2)  raking  the  surface layer and thus breaking  the  in-
hibiting crust, or  (3)  removing the top surface media and  replacing it
with  clean  media.   The effectiveness  of each  technique  has not been
clearly established in the literature.


     6.3.5  Filter Performance
A  summary  of  the performance  of  selected  intermittent  sand  filters
treating household wastwaters appears  in Table  6-4,  6-5,  and  6-6.   These
tables  illustrate   that   intermittent   filters  produce  high-quality
effluents  with  respect  to  BODs  and   suspended  solids.     Normally,
nitrogen is transformed almost  completely  to  the nitrate form  provided
the  filter  remains  aerobic.    Rates  of nitrification may  decrease  in
winter months  as temperatures fall.  Little or  no denitrification  should
occur in properly operated intermittent  filters.
Total  and  ortho-phosphate  concentrations can be reduced up  to  approxi-
mately 50% in clean  sand;  but  the  exchange  capacity  of  most of  the sand
as well as phosphorus removal  after maturation  is  low.   Use of  calcare-
ous sand or other high-aluminum or iron  materials  intermixed within the
sand  may  produce  significant  phosphorus  removal.   Chowdhry  (28)  and
Brandes, et  al.  (23),  reported  phosphorus removals  of up  to  90% when
additions of 4% "red mud" (high in A1203 and Fe203) were made to a medi-
um sand.   Intermittent  filters are capable of  reducing  total and fecal
coliforms by 2 to 4  logs,  producing effluent values  ranging from 100 to
3,000  per  100 ml  and 1,000 to 100,000/100 ml for  fecal  and total  coli-
forms, respectively (2)(19)(28).
     6.3.6  Design Criteria


         6.3.6.1  Buried Filters
Table  6-7  summarizes design  criteria  for subsurface intermittent  sand
filters.
Hydraulic loading of these filters is normally equal  to  or less  than 1.0
gpd/ft2  (0.04  m3/m2/d)  for  full-time  residences.     This   value  is
similar  to  loading rates  for  absorption systems  in  sandy soils  after
                                  120

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                                                       TABLE 6-4



                           PERFORMANCE OF BURIED INTERMITTENT FILTERS - SEPTIC TANK EFFLUENT
                      Filter Characteristics
Effluent Characteristics
IV3
Effecti Me
Size
mm
0.24
0.30
0.60
1.0
2.5
0.17
0.23 - 0.36
Urn" f ormi ty
Coefficient

3.9
4.1
2.7
2.1
1.2
11.8
2.6 - 6.1
Hydraulic
Loading
gpd/ft2
1
1
1
1
1
0.2
1.15
Depth
in.
30
30
30
30
30
39
24
BOD
mg/1
2,0
4.7
3.8
4.3
8.9
1.8
4
SS
mg/1
4.4
3.9
4.3
4.9
12.9
11.0
12
NHjN
mg/1
0.3
3.8
3.1
3.7
6.7
1.0
0.7
N03N
mg/1
25
23
27
24
18
32
17
Reference

25
25
25
25
25
22
19

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                                                              TABLE 6-5


                                         PERFORMANCE  OF FREE  ACCESS  INTERMITTENT  FILTERS
                           Filter Characteristics
Effluent Quality
ro
ro
Source
Effective Unif.
Size Coeff.
mm

Septic Tank
Septic Tank
Trick. Filter
Trick. Filter
Primary
Primary
Primary
Primary
Septic Tank
Extended Aer.
La goon (Summer)
Lagoon (Winter)

0.23
0
0
0
0
0
1
1
0
0
0
0

-0.26
.41
.27
.41
.25
.25
.04
.04
.45 3.0
.19 3.3
.19 9.7
.19 9.7
Hydraulic
Loading
gpd/ft2

4.5
2.3
11.4
14.0
2.75
4.7
-
14
5
3.8
9.1
9.1
Depth
in.

60
60
60
60
30
30
30
30
30
30
36
36
Dose
Freq.
per
day
-
-
-
-
1
2
2
24
3-6
3-6
1
1
BOD
mg/1

233
113
173
183
6
3
28
4
8
3
2
9.4
SS
mg/1

-
-
-
-
6
8
36
9
4
9
3
9.6
NHjN
mg/1

8
3
2
2
5
2
10
3
3
0.3
0.5
4.6
N03M
mq/1

32
46
29
33
19
22
13
17
25
34
4.0
1.0
Filter
Run
months

6 - 9b
6 - 9b
6b
12b
4.5
36
>54
>54
3
12
1
4
Ref.


21
21
21
21
23
23
23
23
2
2
13
13
      a  Estimated from "oxygen consumed."


      b  Weekly raking 3 inches deep.

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                                                               TABLE  6-6


                                       PERFORMANCE OF RECIRCULATING INTERMITTENT FILTERS9
                 Filter Characteristics
Effluent Quality
ro
CO
Effective
Size
ran
0.6 - 1.0

0.3 - 1.5

1.2

Unif.
Coeff.

2.5

3.5

2.0

Hydraulic
Loading
gpd/ft2


3.0 - 5.0b

3. Ob


Depth
in.
36

24

36

Recir culation
Ratio
r/Q
4:1

3:1 - 5:1

4:1


Dose BOD
mg/1
5-10 min every 4
30 min
20 min every 15.8C
2-3 hr
5 mi n every 4
30 min

SS NHsN Mtnce. Ref.
mg/1 rnq/1
5 - Weed/Rake 24
as Req'd
10. DC 8.4C Rake 26
Weekly
3 - Weed 27
as Req'd
      a Septic tank effluent.

      b Based on  forward flow.


      c Average for 12 installations (household flow to 6,500 gpd plant).

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                             TABLE 6-7

          DESIGN CRITERIA FOR BURIED INTERMITTENT FILTERS
       Item
        Design Criteria
Pretreatment
Hydraulic Loading
  All year
  Seasonal

Media
  Material

  Effective size
  Unif. Coeff.
  Depth

Underdrai ns
  Material
  Slope
  Beddi ng

  Venti ng

Di stri buti on
  Material
  Beddi ng

  Venti ng

Dosi ng
Minimum level - sedimentation (septic
  tank or equivalent)
<1.0 gpd/ft2
<2.0 gpd/ft2
Washed durable granular material (less
  than 1 percent organic matter by weight)
0.50 to 1.00 mm
<4.0 (<3.5 preferable)
24 to 36 inches
Open joint or perforated pipe
0.5 to 1.0 percent
Washed durable gravel  or crushed stone
  (1/4 to 1-1/2 in.)
Upstream end
Open joint or perforated pipe
Washed durable gravel or stone (3/4 to
  2-1/2 in.)
Downstream end

Flood filter; frequency greater than
  2 per day
                                   124

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equilibrium conditions  are obtained.   When  filters are  designed  for
facilities with seasonal occupation, hydraulic  loading  may  be  increased
to   2.0   gpd/ft2   (0.08   m3/m2/d)   since  sufficient   time  will   be
available for drying and restoring the infiltrative  surface  of the bed.


The effective size of  media  for subsurface filters  ranges  from 0.35 to
1.0 mm with  a UC less  than  4.0, and preferably  less than  3.5.   Finer
media will tend to clog more readily, whereas  coarser  media may result
in  poorer distribution  and  will   normally  produce a  lower  effluent
quality.
Distribution and underdrains are  normally  perforated  or  open-joint pipe
with a minimum 4-in.  (10-cm) diameter.   The  distribution and underdrain
lines  are  surrounded by  at least  8 in.  of washed  durable gravel  or
crushed stone.   For  distribution  lines,  the gravel or stone is  usually
smaller than  2-1/2  in.  (6 cm) but  larger  than  3/4 in.  (2  cm),  whereas
the size range of the gravel or stone for  the underdrains is between 1-
1/2 to  1/4  in.  (3.8 to 0.6 cm).   Slopes of underdrain  pipe range from
0.5 to  1%.   With dosing,  there  would be  no requirement for slopes  on
distribution piping.


Proper dosing to the filter is critical  to  its  successful  performance.
The dosing system is designed  to  flood the  entire filter  during  the dos-
ing cycle.  A dosing frequency of  greater than two times  per day  is rec-
ommended.   Details on design and  construction of dosing  chamber  facili-
ties appear in Chapter 8.


         6.3.6.2  Free Access  Filters (Non-Recirculating)


Design criteria  for free access filters  are presented  in  Table 6-8.
Hydraulic loading  to  these filters depends  upon  media size and  waste-
water characteristics.  Septic tank effluent may be  applied  at  rates  up
to 5 gpd/ft2  (0.2  nr/nr/d),  whereas a higher quality  pretreated  waste-
water may be applied at rates as  high  as  10 gal/d  ftz (40  cm/d).   Selec-
tion of hydraulic loading will also be influenced  by desired filter run
times (see Section 6.3.8).  Higher  acceptable loadings on  these  filters
as compared to subsurface filters relates primarily to the accessibility
of the filter surface for maintenance.
Media characteristics and underdrain systems for free access filters are
similar to those for subsurface filters.   Distribution is  often provided
through pipelines and directed on splash  plates located at the center or
corners of the sand surface.   Occasionally,  troughs or spray nozzles are
                                  125

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                                TABLE  6-8

          DESIGN CRITERIA FOR FREE ACCESS INTERMITTENT FILTERS
       Item
        Design Criteria
Pretreatment
Hydraulic Loading
  Septic tank feed
  Aerobic feed

Medi a
  Material

  Effective size
  Unif. Coeff.
  Depth

Underdrains
  Material
  Slope
  Beddi ng

  Venting

Distribution

Dosi ng
Number
  Septic tank fe,ed
  Aerobic feed
Minimum level - sedimentation (septic
  tank or equivalent)
2.0 to 5.0 gpd/ft2
5.0 to 10.0 gpd/ft2
Washed durable granular material (less
  than 1 percent organic matter by weight)
0.35 to 1.00 mm
<4.0 (<3.5 preferable)
24 to 36 inches
Open joint or perforated pipe
0.5 to 1.0 percent
Washed durable gravel or crushed stone
   (1/4 to 1-1/2 in.)
Upstream end

Troughs on surface; splash plates at center
  or corners; sprinkler distribution

Flood filter to 2 inches; frequency greater
  than 2 per day

Dual filters, each sized for design flow
Single filter
                                  126

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employed as well, and  ridge  and furrow application has  been  successful
during winter operation  in  severe climatic  conditions.   Dosing of  the
filter should provide  for flooding  the bed to a  depth  of  approximately
2 in.  Dosing frequency is usually greater than two times  per day.   For
coarser media (greater than  0.5 mm),  a dosing frequency greater than  4
times per day is desirable.   Design  criteria  for dosing  chambers, pumps,
and siphons are  found in  Chapter 8.


The properties of the wastewater  applied affect the clogging  character-
istics of the filter and, therefore, the methods  of filter  maintenance.
Dual filters, each designed  to carry the design flow rate,  may be desir-
able  when  treating  septic  tank  effluent  to  allow  sufficient resting
after clogging (see Section  6.3.8).
         6.3.6.3  Recirculating Filters


Proposed design criteria for recirculating intermittent sand filters  are
presented in  Table 6-9  (24)(26).   These  free access filters employ  a
recirculation  (dosing)  tank between  the pretreatment  unit and  filter
with  provision for  return of  filtered  effluent  to the  recirculation
tank.


Hydraulic loading  ranges  from  3 to  5 gpd/ft2  (0.12 to 0.20 m3/m2/d)
depending on  media  size.   Media size  range  is from 0.3 to  1.5 mm,  the
coarser  sizes  being  recommended (23)(26).   Underdrain  and  distribution
arrangements are similar  to  those  for free access  filters.   Recircula-
tion is  critical to effective operation,  and  a 3:1  to 5:1  recirculation
ratio  (Recycle:   Forward Flow)  is  preferable.  Pumps should be  set by
timer  to dose  approximately  5  to  10 min  per 30  min.   Longer  dosing
cycles may be  desirable  for larger installations -  20 min  every  2 to 3
hr.   Dosing  should be at  a  rate high  enough  to insure  flooding  of  the
surface  to greater than  2 in.  (5 cm).   Recirculation chambers are nor-
mally sized at 1/4 to 1/2 the volume of the septic  tank.
     6.3.7  Construction Features


         6.3.7.1  Buried Filters
A  typical  plan  and  profile of  a buried  intermittent sand  filter  are
depicted in  Figure 6-5.   The filter is placed within  the  ground with a
natural topsoil cover in excess of 10  in.  (25 cm)  over the crown of the
distribution  pipes.    The   filter  must be  carefully  constructed  after
excavation and the granular  fill  settled by  flooding.   Distribution and
underdrain lines should be  constructed of  an  acceptable material  with a
minimum diameter of 4 in.  (10 cm).   The  tile is normally laid with open
                                   127

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                                TABLE  6-9

         DESIGN CRITERIA FOR RECIRCULATING  INTERMITTENT  FILTERS
       Item
        Design Criteria
Pretreatment
Hydraulic Loading

Media
  Material

  Effective size
  Unif. Coeff.
  Depth

Underdrai ns
  Material
  Slope
  Beddi ng

  Venti ng

Distribution
Recirculation Ratio

Dosing



Recirculation Tank
Minimum level - sedimentation (septic
  tank or equivalent)

3.0 to 5.0 gpd/ft2 (forward flow)
Washed durable granular material  (less
  than 1 percent organic matter by weight)
0.3 to 1.5 mm
<4.0 (<3.5 preferable)
24 to 36 inches
Open joint or perforated pipe
0.5 to 1.0 percent
Washed durable gravel or crushed stone
  (1/4 to 1-1/2 in.)
Upstream end

Troughs on surface; splash plates at center
    or corners; sprinkler distribution

3:1 to 5:1 (5:1 preferable).

Flood filter to approx. 2 inches; pump 5
  to 10 min per 30 min; empty recirculation
  tank in less than 20 min

Volume equivalent to at least one day's raw
  wastewater flow
                                  128

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                                        FIGURE 6-5



                 TYPICAL  BURIED  INTERMITTENT FILTER  INSTALLATION
          Distribution
House Sewer?
                                                                                ^tjaDischarge
                                                              Inspection  Manhole

                                                                and Disinfection

                                                                  Contact Tank

                                                                   (If Required)
                                          Profile
               Top Soil Fill

              Drainage
    Marsh  Hay or

   Drainage Fabric
                      XXX
            vxxxxxxxxxVxxx!
            xxxxxxxxxxxxxx
            xxxxxxxxxxxxxx
            xxxxxxxxxxxxxx
            xxxxxxxxxxxxxx
            xxxxxxxxxxxxxx
..,,XXXXXyVXX
XXXXXXXXXXjiX
XXXXX XXX XX^'X
xxxxxxxxxxxxx
xxxxxxxxxxxxx
xxxxxxxxxxx>^
xxxxxxxxxi? ""^
xxxxxxxx^r-
XXXXXXXX/jfl
            xxx	
•xxxxxxxxxxxxxxxxxxxxxxxxxxx.
'XXXXXXXXXXXXXXXXXXXXXXXXXXX.
'XXXXXXXXXXXXXXXXXXXXXXXXXXX
'XXXXXXXXXXXXXXXXXXXXXXXXXXX,
L-*^xxxxxxxxxxxxxxxxxxxxxxx  -
Z^vxxxxxxxxxxxxxxxxxxxx
   Vxxxxxxxxxxxxxxxxxxx
   k.Vxxxxxxxxxxxxxxxxxx'
XXX	-
XXXXXXXXX, - , ™
xxxxxxxxxxxxx.
 xxxxxxxxxxxx,
 • -xxxxxxxxxx,
   •xxxxxxxxx.
   vxxxxxxxx-
    • -xxxxxxx.
     'XXXXXXX,
     •  x/./x-
             _.._

  Graded Gravel 3/4" to 21/2"
             ,,,,
            ////// S//S///S
            XXXXXXX>XXXXXX,
          Perforated or Open

           Joint Distributors
                                     xxxxx
                                     xxxxx
                                     xxxxx
                                     xxxxx
                                     xxxxx
                                     xxxxx
                                     xxxxx
                                     xxxxx
                            xxxxxxxxxxxxxxx
            xxxxxxxxxxxxxx
            xxxxxxxxxxxxxx?
            xxxxxxxxxxxxxx xxxx ............ .
            XXXXXXXXXXXXXXXXXXXXXXXXXXX XXX, .
            ' XXXXX XXXX XX XXXXXX/XXXXXXXXXXVX






                           '''-
?5«^
^1
xxxx
xxxxx •
XXXXX
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
XXXXX
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
xxxxx
                                                                                       in.
                                              >8 in.
                                                                               24-36 in.
                  XXXXXXXXXXXXXXXXXXXXXXXXXXX
                  'XXXXXXXXXXXXXXXXXXXXXXXXXXX
                  'XXXXXXXXXXXXXXXXXXXXXXXXXXX
                 X'^^/^/xxxxxxxxxxxxxxxxxxxxx
                 v\xxxxxxxxxxxxxxxxxxxxx/xxxx
                                              > 8  in.
     Graded Gravel 1/4" to 11/2"
                          Perforated or Open

                         Joint Pipe, Tarpaper

                           Over Open Joints
                                       Section A-A
                                           129

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joints with  sections  spaced not less  than  1/4 in. (0.6 cm)  or greater
than  1/2  in.  (1.3 cm) apart.   If continuous pipeline is  used, conven-
tional perforated pipe will  provide adequate distribution and collection
of wastewater within the filter.
The underdrain lines are laid  to  grade  (0.5  to 1%)  and one line is pro-
vided for each 12 ft  (3.6 m) of  trench  width.   Underdrains are provided
with a  vent pipe at  the  upstream end extending to  the  ground surface.
The bedding material  for underdrain lines is  usually a minimum of 10 in.
(25  cm)  washed graded  gravel  or stone  with  sizes  ranging from  1/4  to
1-1/2 in.  (0.6 to  3.8 cm).   The gravel   or stone may  be  overlain  with a
minimum  of  3  in.  (8 cm) of  washed  pea  gravel  (1/4-  to  3/8-in.  [0.6  to
1.0 cm] stone) interfacing with the filter media.
The distribution  lines  should be level  and are  normally  spaced at 3-ft
(0.9 m) centers.  Distribution lines  should be  vented at  the downstream
end with  vertical  risers to  the ground surface.   Approximately  10 in.
(25 cm) of  graded gravel (3/4-  to  2-1/2-in.  [1.9- to  6.3-cm]  size)  is
usually employed  for  bedding  of  distribution  lines.  Marsh  hay,  washed
pea  gravel,  or  drainage fabric   should  be placed  between  the  bedding
material and the natural topsoil.
The  finished  grade over the  filter  should be mounded so  as  to provide
drainage of rainfall away from the filter bed.  A grade of approximately
3 to 5%, depending upon topsoil characteristics, would be sufficient.
Any washed, durable granular material that is  low  in  organic  matter may
be  used  for  filter  medium.    Mixtures  of  sand,   slag,  coal,  or  other
materials have  been  used  to  enhance the removal of selected  pollutants
and to extend filter life.  Care must be taken, however, to insure  that
the media does not stratify with fine layers  over  coarse.
Design  and  construction of  the dosing chamber  and pump or  siphon  em-
ployed for proper application of wastewater  to  the  filter are described
in Chapter 8 of this manual.
         6.3.7.2  Free Access Filters
The  plan  and profile of  a  typical  free access filter  appear  in Figure
6-6.   These filters  are  often built within  the  natural soil,  but  may
also  be  constructed  completely  above  the ground  surface.   They  are
usually surrounded by sidewalls,  often  of  masonry construction,  to pre-
vent earth from washing into the filter media and to confine the flow of
wastewater.  Where severe climates  are  encountered,  filter  walls should
                                   130

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                               FIGURE 6-6



                  TYPICAL FREE ACCESS  INTERMITTENT FILTER

                  Splash Plate
          •——OT—"™
                    t  j
                                  Plan
                                                                Discharge
                                               From

                                               Pretreatment
 //^\^
Graded

Gravel

  to 11/2"
                             Insulated Cover

              Splash

               Plate
            fl
Vent

Pipe
         **•:
A 4 «
 4» ' *
»!••
 *:/.«•
         -:.•••i

         1 4 » »

         ' » 't.

         •«••*•
         « *< » •
          » ft  »

         » ' .' - « *
   ft 4

    «
                                 Distribution

                                 Pipe

             0
I
>\; .v.v.:-...:.'.'—::::^
* S •.»»•••••«»•. »•,... • -, K *•
 t\ -•.•.":/-•/;/.-.;::;-..»»
1 •  ;.V-V.  Media   »/.« ."^V
;.:--.v,v.-.-.-..-//.-.-.--.-/--/.--

^':vi-\V:X-:::.v:-:v/.^'>
5*7" "  ^—-~r   "  -   n J~ - - ~-----
                                     ^v^>^\
                                      24"-36"
                       Collection Pipe



                                 Profile
                                      Perforated or Open Joint
                                  131

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be insulated if exposed directly to the air.   The  floor of the filter is
often constructed of  poured  concrete  or other masonry, but may  consist
of the natural  compacted  soil.   It is  usually sloped  to  a  slight grade
so  that   effluent can  be  collected  into  open   joint  or  perforated
underdrains.
Free access  filters may be  covered to  protect  against severe  weather
conditions, and to  avoid encroachment  of weeds or animals.    The  cover
also serves  to reduce  odor  conditions.   Covers  may be constructed  of
treated wooden  planks, galvanized  metal,  or  other  suitable  material.
Screens or  hardware cloth mounted  on  wooden  frames  may also serve  to
protect  filter surfaces.    Where  weather  conditions  dictate,  covers
should be  insulated.   A space of 12 to  24  in. (30 to 61 cm)  should  be
allowed between the insulated cover  and sand surface.
The  underdrain  lines should  be constructed of  an acceptable  material
with a minimum diameter of 4  in.  (10  cm).   The tile  is  normally laid  so
that joints  are  spaced  not less  than  1/4  in.  (0.6 cm)  or  greater  than
1/2 in.  (1.3  cm)  apart.   Conventional  perforated  pipe  may also be em-
ployed  for  distribution  and  collection.   The underdrain  lines may  be
laid directly on  the  filter  floor,  which should be  slightly  pitched  to
carry  filtered  effluent to  the drain  line.   In  shallow  filters, the
drain line may be laid within a shallow  trench within the  filter floor.
Drain lines  are  normally  spaced at  12-ft (3.6-m) centers and  sloped  at
approximately 0.5 to  1%  grade  to discharge.   The  upstream end  of  each
drain line should be  vented  with  a vertical vent pipe  above  the filter
surface, but within  the  covered  space.


The bedding material for underdrain lines should be  a minimum  of 10 in.
(25 cm) of washed graded gravel  or  stone with sizes  ranging from 1/4  to
1-1/2 in. (0.6 to 3.8 cm).   The gravel or stone may be overlain with a
minimum of 3 in.  (8  cm)  of washed  pea  gravel  interfacing with  the filter
media.
Distribution to the  filter  may be by means of troughs laid  on  the  sur-
face, pipelines discharging  to splash plates located  at the center  or
corners  of  the filter,  or  spray distributors.   Care  must be  taken  to
insure  that  lines discharging  directly  to  the  filter  surface do  not
erode the  sand surface.  The  use  of curbs around the splash plates  or
large  stones   placed  around the  periphery of  the  plates  will  reduce
scour.   A  layer of washed  pea  gravel  placed over the filter media  may
also be  employed  to  avoid surface  erosion.   This practice  will  create
maintenance difficulties; however,  when  it is time to rake  or  remove a
portion of the media  surface.
                                  132

-------
Filter media employed in free access filters may be  any  washed,  durable
granular material free of  organic  matter.   As indicated previously  for
buried filters, mixtures of sand, slag, coal, or other materials may be
employed, but with caution.
The design and construction features of the dosing chamber and pumps,  or
siphon systems for these filters,  are described  in Chapter 8.
         6.3.7.3  Recirculating Filters
A profile  of  a typical recirculating  intermittent  sand filter is  pre-
sented  in  Figure 6-7.   Recirculating  filters are  normally  constructed
with  free  access to  the  filter surface.   The  elements of  filter  con-
struction  are  identical  to  those  for the  free  access filter  (Section
6.3.6.3 above).   A  schematic  of a  recirculation  tank is presented  in
Figure 6-8.
The basic  difference  between  the recirculating filter and the  free  ac-
cess filter is the recirculation chamber (dosing chamber)  which  incorpo-
rates  a  pump to  recycle  filter effluent.   The recirculation  tank  re-
ceives the overflow from a septic  tank,  as well  as  a portion of  sand
filter effluent.   A pump, controlled  by  a time clock mechanism,  pumps
the wastewater mixture to the  filter surface.   The  recirculation tank is
of equivalent strength and material to  the  septic  tank.   It  is  normally
1/4 to 1/2 the size  of  the  septic tank  (or  a volmw equivalent to at
least  one  day's  volume of raw  wastewater  flow).   The tank must be  ac-
cessible for maintenance  of pumps,  timers,  and control valves.   Covers
should be  provided and insulated as required by climatic  conditions.


Recirculation ratios may  be controlled by a variety of methods.   These
include  splitter  boxes,  moveable  gates,   check  valves,  and  a  unique
"float valve" arrangement (Figure 6-9).   The  "float valve"  incorporates
a  simple  tee and  a rubber ball suspended  in  a wire  basket.   The  ball
will float up and  close off the inverted tee when the  water level  rises.
Recirculation ratios are normally established between  3:1  to  5:1 (26).
Recirculation pumps are normally submersible pumps  rated  for 1/3 horse-
power.   They should  be  sized to empty  the  recirculation tank  in  less
than  20  min.   The recirculation pump  should  be controlled by a  time
clock  to  operate between  5 to 10 min  every  30 min (26), and  should be
equipped with a float shut-off and  high water override.   Details on  pump
and control specifications may be found in Chapter 8.
                                   133

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                                 FIGURE 6-7

              TYPICAL RECIRCULATING INTERMITTENT FILTER SYSTEM
 Raw Waste
             Pretreatment
                 Unit
       To Discharge
Float Valve  t {
                                                      i^,*44»jifc.'ijji ,y
Recirculation
    Tank
                                                Pump
                                                         Free Access
                                                         Sand Filter
                                  FIGURE  6-8

                              RECIRCULATION TANK
    From
Pretreatment
                                Discharge
                        Liquid Level
                                           Float
                                          Valve
                                                 fir
                                                           fl
                                                                  From Filter
                                                                  To Filter
                                                                  Pump
                                    134

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                              FIGURE 6-9


            BY-PASS ALTERNATIVES FOR RECIRCULATING FILTERS
     Discharge
            Filter ^
            Return
                                    Sanitary Tee
Filter

Return
                                             Open Basket
                                           Floating Ball
                                  t
                               Discharge
                                 n
                            Moveable Gate
                                 u
                               To Filter
 To Filter —
Discharge
::JD

:.--0
r
-(
r
^
7
M




^Adjustable
A. Filtel"
Return


Weirs
                                135

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     6.3.8  Operation and Maintenance


         6.3.8.1  General


Intermittent sand filters require relatively little  operational  control
or maintenance.   Once wastewater is  applied to  the  filter,  it  takes  from
a few days to two weeks before the  sand has matured (2)(28).   BOD and SS
concentrations  in  the  effluent  will  normally  drop  rapidly  after
maturation.  Depending upon  media size, rate of application, and ambient
temperature,  nitrification  may  take  from 2 weeks up  to 6  months  to
develop.  Winter  start-up should be avoided  since  the  biological  growth
on the filter media  may not  properly develop (14).


As discussed above,  clogging of the filter eventually occurs  as the  pore
space between the media  grains  begins  to  fill  with inert and  biological
materials.  Once  hydraulic  conductivity falls  below  the  average hydrau-
lic  loading,  permanent  ponding  occurs.   Although  effluent quality may
not  initially  suffer,  anaerobic conditions within  the filter  result in
further rapid clogging and a cessation of  nitrification.   Application of
wastewater  to the filter should be  discontinued when continuous ponding
occurs at levels  in  excess  of 12 in.  (30  cm)  above the sand  surface.  A
high water alarm located 12  in. (30 cm) above the sand surface serves to
notify the owner of a ponded condition.


Since  buried filters  cannot  be easily  serviced,  the  media  size  is
normally  large  and  hydraulic  application  rates are  low  (usually  less
than 2 in./d [5 cm/d]).  Proper pretreatment maintenance  is- of  paramount
importance.   Free access filters,   on  the other hand,  may be  designed
with finer  media  and at  higher  application  rates.  Experience  indicates
that intermittent sand filters  receiving septic  tank influent  will  clog
in approximately  30  and  150 days for  effective  sizes of 0.2 mm and 0.6
mm,  respectively  (2).    Aerobically treated  effluent can be applied  at
the same rates for up to 12  months  if suspended solids  are  under 50  mg/1
(2)(23).   Results with  recrrculated filters using coarse  media  (1.0  -
1.5 mm) indicate filter runs in excess of  one year  (27).
         6.3.8.2  Maintenance of Media
Maintenance  of  the media  includes  both routine maintenance  procedures
and media  regeneration  upon clogging.   These  procedures apply  to  free
access  filters  only.   The effectiveness of routine raking  of the media
surface has  not been  clearly established,  although employed  in  several
studies (2)(14)(21)(24).   Filters  open  to  the air require  weed  removal
as well.   Cold  weather maintenance  of media may  require different meth-
ods of wastewater application, including ridge and furrow and continuous
                                  136

-------
flooding.  These  methods are designed  to  eliminate ice  sheet  develop-
ment.  Use of insulated  covers permits  trouble-free  winter  operation  in
areas with ambient temperatures  as low as -40° F (2).


Eventually, filter clogging requires media regeneration.  Raking  of  the
surface will  not  in  itself eliminate the need  for more  extensive reha-
bilitation (2)(14).   The removal of the top  layer  of sand, as well  as
replacement with  clean  sand  when sand depths are depleted  to less than
24 to  30 in.  (61  to  76 cm), appears  to  be  very effective  for  filters
clogged  primarily by a  surface  mat.   This  includes filters  receiving
aerobically treated  effluent (2).   In-depth  clogging,  however,  often
prevails  in many  intermittent filters requiring oxidation of the clog-
ging materials.   Resting of the  media for a period of time has proven  to
be very  effective in  restoring  filter hydraulic conductivity (2).   Hy-
drogen peroxide treatment  may also  prove to  be effective,  although  in-
sufficient data are available on long-term application of this oxidizing
agent.
         6.3.8.3  Other Maintenance Requirements
The successful  operation  of filters is dependent on  proper maintenance
of  the  pretreatment processes.  The  accumulation  of scum,  grease,  and
solid materials on  the  filter surface  due  to inadequate  pretreatment
results in  premature filter failure.   This  is especially  critical  for
buried  filters.   Grease  traps,  septic tanks,  and other  pretreatment
processes should be routinely maintained in accordance with requirements
listed in other sections of this manual.
Dosing chambers,  pumps,  and  siphons  should  receive  periodic maintenance
checks as  recommended  in Chapter 8.    If electronic  sensing devices  are
employed to warn  owners  of filter  ponding,  these  devices should also be
periodically checked as well.
         6.3.8.4  Summary


The maintenance and operational requirements for buried, free access and
recirculating  filters  are  summarized  in Tables  6-10,  6-11, and  6-12.
Routine maintenance  requirements  have not been well documented  for in-
termittent filtration onsite,  but visits should be made  four times per
year  to check  filters  and their appurtenances.   Based  on a  meager data
base, unskilled manpower requirements for buried filter  systems  would be
less  than  2 man  days  per  year for examination  of dosing  chamber and
appurtenances  and  septic  tank.   Free access filters may  require from 2
to 4 man days  per year for media maintenance and replacement and examin-
ation  of  dosing  chamber,  septic  tank,  and appurtenances.   Additional
                                    137

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                            TABLE  6-10

              OPERATION AND MAINTENANCE  REQUIREMENTS
                  FOR BURIED INTERMITTENT  FILTERS
         Item                               0/M  Requirement
Pretreatment                       Depends  upon  process

Dosing Chamber
  Pumps and controls               Check  every 3 months
  Tinier sequence                   Check  and  adjust  every  3 months
  Appurtenances                    Check  every 3 months

Filter Media                       None
                            TABLE 6-11

              OPERATION AND MAINTENANCE REQUIREMENTS
               FOR FREE ACCESS INTERMITTENT FILTERS
         Item                               0/M Requirement


Pretreatment                  Depends upon process

Dosing Chamber
  Pumps and controls          Check every 3 months
  Timer sequence              Check and adjust every 3 months
  Appurtenances               Check every 3 months

Filter Media
  Raking                      Every 3 months,  3 in.  deep
  Replacement
    Septic tank feed          Replace when ponded more than  12  in.  deep;
                                replace top 2  to 3 in. sand; rest while
                                alternate unit in operation  (60 days)
    Aerobic feed              Replace when ponded more than  12  in.  deep;
                                replace top 2  to 3 in. sand; return to
                                service

Other                         Weed as required
                              Maintain distribution  device as required
                              Protect against  ice sheeting
                              Check high water alarm


                                 138

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time would  be required by  analytical  technicians for effluent  quality
analysis as  required.   Power requirements would be  variable,  depending
upon the dosing  method employed, but  should  be less than 0.1  kWh/day.
The  volume   of  waste  media from  intermittent  filters  may  amount  to
approximately 0.25 ft3/ft2  (0.08 m3/mz) of surface area  each  time media
must be removed.
                               TABLE 6-12

                 OPERATION AND MAINTENANCE REQUIREMENTS
                 FOR RECIRCULATING INTERMITTENT FILTERS
            Item                          0/M Requirement


   Pretreatment             Depends upon process

   Dosing Chamber
     Pumps and controls     Check every 3 months
     Timer sequence         Check and adjust every 3 months
     Appurtenances          Check every 3 months

   Filter Media
     Raking                 Every 3 months,  3 in.  deep
     Replacement            Skim sand when heavy incrustations occur;
                              add new sand when sand depth falls
                              below 24 in.

   Other                    Weed as required
                            Maintain distribution device as required
                            Protect against ice sheeting
      6.3.9  Considerations for Multi-Home and Commercial Wastewaters


         6.3.9.1  Applicability


 Intermittent  filtration  processes  have  been  successfully  employed in
 larger  scale installations to achieve high levels of treatment of waste-
 water.
                                   139

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         6.3.9.2  Design Criteria
Intermittent filters for larger installations may be designed  in  accor-
dance with  similar criteria used  for onsite systems  (20).    Submerged
filters  should  be avoided.   The  biggest difficulty  with  larger  flow
units is  adequate wastewater distribution.   Troughs,  ridge and  furrow
spray distributors, and  multiple  pipe apron  systems may be used.   Si-
phons or pumps should be employed  to  achieve  from 2  to 4 doses per day.
Filter  flooding  to approximately  2  in.  (5 cm)  should be achieved  per
dose.
Multiple beds are desirable instead of one large filter unit.   Allowance
should be made  for  60-day  resting periods for  filters  receiving  septic
tank effluent.
         6.3.9.3  Construction Features
Construction features for large intermittent sand filters  are  similar to
those of smaller units.  Distribution and collection systems are normal-
ly more elaborate.  Covering is desirable in very cold climates.
         6.3.9.4  Operation and Maintenance
Day-to-day operation and maintenance of larger filter  systems  are  mini-
mal.  Sand surfaces should be raked and leveled on a weekly basis.   Dis-
tribution troughs  should  be kept level;  pumps  or siphons  and  controls
must be  periodically maintained.  Unskilled manpower requirements  of 10
to 15 man-hours per week may be expected for  larger installations.   Pow-
er requirements depend on dosing systems employed.
6.4  Aerobic Treatment Units


     6.4.1  Introduction
Biological wastewater treatment processes are employed to transform dis-
solved and colloidal pollutants into gases, cell  material,  and metabolic
end  products.   These processes may occur  in  the  presence  or  absence of
oxygen.   In the  absence of  oxygen  (anaerobic  process),  wastewater mate-
rials may be hydrolyzed and  the  resultant  products  fermented  to produce
a variety of alcohols,  organic acids, other  reduced  end products,  syn-
thesized  cell  mass, and  gases including carbon dioxide,  hydrogen,  and
methane.  Further treatment of the effluents from anaerobic processes is
                                   140

-------
normally required in order to achieve an  acceptable quality for surface
discharge.    On  the other  hand, aerobic  processes  will  generate  high-
quality effluents containing a  variety  of oxidized  end products, carbon
dioxide, and metabolized biomass.   Figure 6-10 summarizes the basic dif-
ferences in these processes.


Biological  wastewater treatment is normally carried out in an open cul-
ture whereby a great variety  of microorganisms exist symbiotically.  The
system  is,  therefore, very versatile in carrying out  a variety of bio-
chemical reactions in response to variations in input pollutants as well
as other environmental  factors.
An important  feature  of biological  processes is the  synthesis  and sub-
sequent separation of microbial cells  from  the  treated liquid.   In con-
ventional  aerobic  processes,  new biological  growth may be  expected to
range  from 30 to 60% of the  dry  weight of organic matter added  to the
system.   As  the  residence time  of microbial  cells  in the  system in-
creases, the net cell  synthesis decreases, but never reaches  zero due to
the  presence  of  a certain  amount  of inert material  in the  influent
wastewater as well as nondegradable solids  synthesized by  the microbes.
It  is  necessary,  therefore,  to  waste  these solids  as  they  build up
within  the  system.   Yet, it is equally  as  important to maintain within
the  system an active population  of microbes to carry out  the desired
biochemical reactions.
Aerobic biological treatment  processes  can  be employed onsite to remove
substantial amounts of BOD  and  suspended  solids  that are not removed by
simple sedimentation.  A  secondary  feature  of the process is nitrifica-
tion  of  ammonia  in  the  waste  (under  appropriate  conditions)  and  the
significant reduction of pathogenic organisms.
Despite their advantageous treatment capabilities, aerobic units for on-
site  treatment  are susceptible to upsets.   Without regular supervision
and maintenance, the aerobic unit may produce low-quality effluents.  To
avoid the problems associated with operation and maintenance, some manu-
facturers have  incorporated various  features  into the  design  of these
package units in order to reduce the need for frequent surveillance.
At least two process schemes are commercially available today for onsite
application.   These are:   (1)  suspended  growth and  (2)  fixed growth.
Each  system has  its own  unique operational characteristics  and design
features,  but  all  provide  oxygen  transfer to  the  wastewater,  intimate
contact between  the microbes and  the  waste,  and solids  separation and
removal.
                                   141

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                                FIGURE 6-10



                AEROBIC AND ANAEROBIC DECOMPOSITION PRODUCTS
                              CO
                 CELLS
NONDEGRADABLE
                        (ORGANICS,  INORGANICS)
                                                         NONDEGRADABLE
                                                    CELL MASS
                                    142

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Anaerobic biological  treatment processes may also be employed for onsite
wastewater treatment.  Septic tanks provide anaerobic  treatment  as  dis-
cussed more fully in Section 6.2.   Septic  tank  designs,  however, do not
normally incorporate considerations  to optimize  anaerobic decomposition.
Anoxic  denitrification  of nitrified  wastewaters  may also be  practiced
onsite.  Details of this  process are  described  in  Section 6.6.   Anaero-
bic packed beds  have  been proposed  for onsite  treatment of  wastewaters
(29),  but there  has  been  no  long-term  field experience  with  these
processes.
     6.4.2  Suspended Growth Systems - Extended Aeration
         6.4.2.1  Description
Extended  aeration  is  a modification  of the  activated sludge  process
whereby  a high  concentration  of  microorganisms are  maintained in  an
aeration tank, followed by separation and recycle of all  or a portion of
the biomass back to the aeration tank.   There  are a variety of proprie-
tary extended aeration  package plants available  on  the market today for
onsite application.   Figure 6-11  depicts  two typical  package  extended
aeration  systems.  The  process may be operated in a batch  or continuous
flow  mode,  and  oxygen is  supplied  by  either  diffused or  mechanical
aeration.   Positive  biomass  return  to  the aeration  tank  is  normally
employed, but  wasting of excess  solids  varies widely  between  manufac-
tured units.
         6.4.2.2  Applicability
Extended  aeration  processes  are  necessarily more  complex than  septic
tanks, and require regular operation and maintenance.  The plants may be
buried or  housed  onsite,  but must be readily accessible.   The aeration
system requires  power,  and some  noise  and odor may be  associated with
it.   There are no  significant  physical  site conditions  that  limit its
application,  although local  codes may  require  certain   set-back  dis-
tances.   The process is temperature-dependent, and  should be  insulated
and covered as climate dictates.
         6.4.2.3  Factors Affecting Performance
 In extended aeration package plants, long hydraulic and solids retention
 times (SRT) are maintained to ensure a high degree of treatment at mini-
 mum  operational control,  to  hedge  against  hydraulic  or organic overload
 to the  system,  and  to  reduce net sludge production (20).  Since wasting
 of accumulated  solids  is  often  not routinely  practiced in many of these
                                   143

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                           FIGURE 6-11

     EXAMPLES OF EXTENDED AERATION PACKAGE PLANT CONFIGURATIONS



                       Batch - Extended Aeration
      Influent
Pump Shut-off
  Elevation
                          Blower
High Water
  Alarm
           •   ,   !
           «   «  i
           o    « A
                               .Effluent
           •'r)  >
                                       Diffuser
                                                      -Pump
  Influent
                                          Mechanical or
                                        Diffused Aeration
                                                         Settling
                                                         Chamber
                                                     Sludge
                  Flow-Th'rough Extended Aeration
                              144

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units, SRT increases to a point where the clarifier can no longer handle
the solids, which will  be uncontrollably wasted in the effluent.   Treat-
ment  performance  (including nitrification)  normally improves with  in-
creasing hydraulic  retention  time and  SRT to  a  point where  excessive
solids build-up will result in high  suspended  solids  washout.   This is
one of  the biggest operational  problems with  extended aeration  units,
and is often the reason for reports of poor performance.


Dissolved  oxygen concentrations   in  the  aeration  tank  should  exceed
2 mg/1 in order to insure a high degree of treatment and a good settling
sludge.  Normally,  onsite  extended aeration plants  supply an  excess of
dissolved  oxygen  due  to minimum  size  restrictions on blower  motors or
mechanical  drives.  An  important element of most aeration  systems is  the
mixing  provided by  the aeration  process. Most  package  units  provide
sufficient mixing to ensure good  suspension of  solids  and mass transfer
of nutrients and oxygen to the microbes.


Wastewater characteristics  may also   influence  performance  of the  pro-
cess.   Excess  amounts  of  certain  cleaning  agents,  greases,  floating
matter,  and  other  detritus  can  cause  process   upsets  and  equipment
malfunctions.    Process  efficiency   may  be  affected  by  temperature,
generally improving with increasing temperature.
The clarifier is an  important  part  of  the  process.   If the biomass can-
not be  properly separated  from  the treated  effluent,  the process  has
failed.   Clarifier  performance  depends upon  the settleability of  the
biomass, the hydraulic overflow rate,  and  the  solids  loading  rate.  Hy-
draulic  surges  can result  in  serious  clarifier malfunctions.   As men-
tioned previously, high solids loadings caused  by accumulation  of  mixed
liquor solids result in eventual  solids carryover.  Excessively long re-
tention  times for  settled  sludges in the clarifier may  result  in  gasi-
fication and  flotation of  these  sludges.   Scum  and  floatable  material
not  properly  removed  from the  clarifier surface  will  greatly  impair
effluent quality as well.


The  field  performance of  onsite extended  aeration package  systems  is
summarized in Table  6-13.   Results  presented in this summary  indicate
that performance is  variable  due  to the wide  diversity  of factors that
can  adversely  affect  extended  aeration systems.   Shock  loads,  sludge
bulking, homeowner abuse   or  neglect,  and  mechanical malfunctions  are
among  the  most  common reasons  for  poor  performance.    In  general,  the
uncontrolled  loss  of  solids  from  the  system  is  the  major cause  of
effluent deterioration.
Generally, extended aeration  plants produce  a  high  degree  of nitrifica-
tion since hydraulic and solids retention times are  high.   Reductions of
                                   145

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                                                    TABLE 6-13



                          SUMMARY OF EFFLUENT DATA FROM VARIOUS AEROBIC  UNIT FIELD  STUDIES





                                                                Source
Parameter
BOD5
Mean, mg/1
Range, mg/1
No. of Samples
Suspended Solids
Mean, mg/1
Range, mg/1
No. of Sampl es
Ref. (2)

37
<1-208
112

39
3-252
117
Ref. (30)

37
1-235
167

62
1-510
167
Ref. (31)

47
10-280
86

94
18-692
74
Ref. (32)

92
-
146

94
-
146
Ref. (33)

144
10-824
393

122
17-768
251
Ref. (34)

31
9-80
10

49
5-164
10
Ref. (35)

36
3-170
124

57
4-366
132
en

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phosphorus are  normally less than 25%.   The removal  of  indicator bac-
teria in onsite  extended  aeration processes is highly  variable  and not
well documented.  Reported values  of  fecal  coliforms  appear to be about
2  orders  of  magnitude lower  in  extended  aeration  effluents than  in
septic tank effluents (2).


         6.4.2.4  Design
A discussion of  some  of  the  important features of onsite extended aera-
tion package plants  in light of current operational  experience  is pre-
sented below.
             a.  Configuration


Most  extended  aeration package plants designed  for  individual  home ap-
plication range  in capacity from  600 to 1,500 gal  (2,270  to  5,680 1),
which  includes  the aeration compartment, settling chamber,  and  in some
units, a pretreatment compartment.  Based upon average flows from house-
holds,  this volume  will  provide  total  hydraulic  retention  times  of
several days.
             b.  Pretreatment
Some  aerobic  units provide a  pretreatment step to  remove  gross solids
(grease,  trash,  garbage  grindings,  etc.).   Pretreatment devices include
trash traps, septic tanks, comminutors, and aerated surge chambers.  The
use of a  trash  trap  or septic  tank preceding the extended aeration pro-
cess  reduces problems with floating'debris in the final clarifier, clog-
ging  of flow lines, and plugging of pumps.
             c.  Flow Mode
Aerobic  package  plants  may  be designed as continuous flow or batch flow
systems.   The simplest continuous flow units  provide  no flow equaliza-
tion  and depend  upon aeration tank  volume  and/or baffles to reduce the
impact of hydraulic surges.  Some units  employ  more sophisticated flow
dampening  devices,  including air lift or  float-controlled mechanical
pumps to  transfer  the wastewater from aeration tank to clarifier.  Still
other  units  provide  multiple-chambered tanks to attenuate  flow.   The
batch  (fill  and  draw)  flow system eliminates the  problem  of hydraulic
variation.   This unit collects and  treats  the wastewater over a period
of time  (usually one day),  then discharges the settled effluent by pump-
ing at the end of  the cycle.
                                   147

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             d.  Method of Aeration
Oxygen  is  transferred  to  the mixed  liquor by  means  of  diffused  air,
sparged turbine, or surface entrainment devices.   When  diffused air  sys-
tems are employed, low head blowers or compressors are  used to force the
air through the diffusers placed on the bottom of the tank.  The sparged
turbine employs both a  diffused  air  source  and external  mixing, usually
by means  of a  submerged flat-bladed  turbine.   The sparged  turbine  is
more complex than  the  simple diffused air  system.   There  are a variety
of mechanical aeration  devices employed  in  package  plants  to  aerate and
mix the  wastewater.   Air  is entrained and circulated within the mixed
liquor through violent agitation from mixing or pumping action.


Oxygen transfer efficiencies for these small package plants are normally
low (0.2  to 1.0 Ib  Oo/hp  hr)  (3.4 to 16.9 kg 02/MJ)  as  compared  with
large-scale  systems  due primarily  to  the high  power  inputs to  the
smaller units  (constrained by minimum motor sizes  for these  relatively
small  aeration tanks) (2).   Normally,  there is sufficient  oxygen trans-
ferred  to  produce high  oxygen  levels.   In an attempt to  reduce power
requirements or  to enhance  nitrogen  removal,  some  units  employ cycled
aeration periods.  Care must be taken to avoid  the development of  poor
settling biomass when cycled aeration is used.


Mixing of the aeration  tank  contents  is  also  an  important  consideration
in the  design  of oxygen transfer  devices.   Rule of thumb requirements
for mixing  in  aeration  tanks range  from 0.5  to  1  hp/1,000  ft3  (13  to
26 kw/1,000 nr) depending upon reactor geometry.   Commercially available
package units jire reported to deliver  mixing  inputs rangi-ng from 0.2 to
3 hp/1,000  ft3  (5  to  79  kw/1,000 m3)  (2).   Deposition   problems  may
develop in those units with the lower mixing intensities.


             e.  Biomass Separation


The clarifier is critical  to the successful  performance  of the extended
aeration  process.    A  majority  of the  commercially available package
plants provide simple gravity separation.   Weir  and baffle designs  have
not been  given much  attention   in package  units.   Weir  lengths af  at
least 12 in. (30 cm)  are preferred (10,000  gpd/ft at 7 gpm) (127 nr/d/m
at 0.4 I/sec) and sludge deflection baffles should be included as a  part
of the  outlet  design.   The  use  of gas deflection  barriers is a simple
way to keep floating solids away from the weir area.


Upflow clarifier devices have also been  employed to improve separation.
Hydraulic surges must be avoided in these systems.  Filtration devices
                                    148

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have also been employed  in  some  units.   While filters may produce high-
quality  effluent,  they   are  very   susceptible  to  both  internal  and
external clogging.  The behavior of clarifiers is dependent upon biomass
settling properties, solids loading rate, and hydraulic overflow rates.
Design peak hydraulic overflow rates should be less than 800 gpd ft2 (32
nr/d/m2); and at  average flow design values  normally  range  from 200 to
400 gpd/ftz  (8  to 16 nr/d/nr).   Solids loading rates  are  usually less
than 30 lb/ftz/d  (145 kg/mz/d) based upon  average  flow and  less than 50
lb/ftz/d (242 kg/mz/d) based upon peak flows.
             f.  Biomass Return
Once separated from the treated wastewater, the biomass must be returned
to the aeration tank or be  wasted.   Air lift pumps, draft tubes working
off  the  aerator,  and gravity  return  methods are normally  used.   Batch
units  and plants  that employ  filters  do not  require sludge  return.
Rapid  removal  of  solids  from the clarifier  is  desirable  to avoid deni-
trification and subsequent floatation of solids.  Positive sludge return
should be employed in  package plants  since  the use of  gravity return
systems has generally proved ineffective (2)(20).


Removal of floating solids  from  clarifiers has  normally been ignored in
most  onsite  package  plant  designs.    Since this  material  results  in
serious deterioration of the effluent, efforts should be made to provide
for  positive removal of this  residue.   Reliance on the owner  to remove
floating  scum is unrealistic.


             g.  Biomass Wasting


Most onsite package plants  do  not  provide  for routine wasting  of solids
from the  unit.   Some  systems,  however, do  employ an  additional  chamber
for  aerobic  digestion  of wasted sludge.   Wasting  is  normally  a manual
operation whereby  the  operator  checks  mixed liquor  solids and  wasted
sludge when  mixed liquor  concentrations  exceed a  selected value.   In
general,   wasting should be  provided  once every 8 to  12 months  (2)(35).


             h.  Controls and Alarms
Most aerobic units are supplied with some type of alarm and control  sys-
tem to detect mechanical breakdown and to control the operation of elec-
trical  components.    They  do  not  normally  include  devices  to  detect
effluent quality or biomass deterioration.  Since the control systems
                                   149

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contain electrical  components, they are subject to corrosion.  All  elec-
trical  components   should  be  waterproofed  and  regularly  serviced  to
ensure their continued operation.
         6.4.2.5  Additional Construction Features
Typical  onsite  extended  aeration  package  plants are  constructed  of
noncorrosive  materials,  including reinforced  plastics and  fiberglass,
coated steel, and reinforced  concrete.   The  unit  may  be  buried provided
that there is easy access to all  mechanical  parts  and  electrical  control
systems, as  well  as appurtenances requiring maintenance such  as  weirs,
air lift pump lines, etc.  Units may also be installed above ground,  but
should be properly housed to protect against severe climatic conditions.
Installation of the units should be in accordance  with specifications of
the manufacturers.
Appurtenances  for the  plant  should  be  constructed  of  corrosion-free
materials  including  polyethylene plastics.   Air diffuser  support  legs
are   normally   constructed   from   galvanized  iron   or   equivalent.
Large-diameter  air  lift units  should  be  employed  to avoid  clogging
problems.    Mechanical   units  should  be properly  waterproofed  and/or
housed from  the elements.
Since blowers, pumps,  and  other  prime  movers  are abused by severe envi-
ronment, receive  little attention, and are often  subject  to  continuous
operation, they  should be  designed for heavy duty  use.   They should be
easily  accessible for  routine  maintenance and  tied into  an effective
alarm system.
     6.4.2.6  Operation and Maintenance


             a.  General Plant Operation
Typical  operating  parameters for  onsite  extended aeration  systems  are
presented in  Table 6-14.   The activated  sludge  process  can  be operated
by controlling only  a  few parameters  -  the aeration  tank dissolved oxy-
gen,  the  return  sludge rate, and  the sludge wasting rate.   For onsite
package  plants,  these  control techniques  are normally fixed  by mechani-
cal  limitations  so  that  very little  operational  control is  required.
Dissolved oxygen is normally high and cannot  be practically controlled
except by "on or off"  operation.  Experimentation with  the  process  may
dictate a desirable cycling arrangement employing a simple time clock
                                    150

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                               TABLE 6-14
     TYPICAL OPERATING PARAMETERS FOR ONSITE  EXTENDED AERATION  SYSTEMS
             Parameter9

MLSS, mg/1
F/M, Ib BOD/d/lb MLSS
Solids Retention Time, days
Hydraulic Retention Time, days
Dissolved Oxygen, mg/1
Mixing, hp/1,000 ft3
Clarifier Overflow Rate, gpd/ft2
Clarifier Solids Loading, Ib/d/ft2
Clarifier Weir Loading, gpd/ft2
Sludge Wasting, months
   Average

 2,000-6,000
 0.05 -  0.1
    20-100
     2-5
    >2.0
   0.5-1.0
   200-400
    20-30
10,000-30,000
     8-12
Maximum
 8,000
  800
   50
30,000
a Pretreatment:  Trash trap or septic tank.
  Sludge Return and Scum Removal:   Positive.
                                   151

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control  that results in power savings and may also achieve some nitrogen
removal  (Section 6.6).
The return  sludge  rate is normally  fixed  by pumping capacity  and  pipe
arrangements.   Return  sludge  pumping rates often range from  50 to  200%
of forward flow.  They  should  be  high  enough to reduce  sludge retention
times in the clarifier  to a minimum  (less  than  1 hr), yet low enough to
discourage pumping of excessive amounts of water with the sludge.   Time
clock controls may be used to  regulate return pumping.


Sludge wasting is manually accomplished in  most  package  plants.   Through
experience, the  operator  knows when mixed liquor  solids  concentrations
become excessive, resulting in excessive clarifier loading.   Usually 8-
to 12-month intervals  between  wasting is satisfactory, but this  varies
with  plant  design and  wastewater  characteristic.   Wasting is  normally
accomplished by  pumping mixed liquor  directly  from  the  aeration tank.
Wasting  of  approximately 75%  of  the  aeration   tank  volume   is  usually
satisfactory.   Wasted sludge must be handled  properly (see Chapter 9).
             b.  Start-Up
Prior to actual  start-up,  a dry checkout should be  performed  to  insure
proper installation.   Seeding of the  plant  with bacterial cultures  is
not required as  they  will  develop within a 6-  to 12-week  period.   Ini-
tially, large  amounts of  white  foam may develop,  but will subside  as
mixed liquor solids increase.   During start-up, it  is  advisable  to re-
turn  sludge at  a  high  rate.    Intensive  surveillance- by  qualified
maintenance personnel  is desirable during the first  month of start-up.
             c.  Routine Operation and Maintenance
Table 6-15 itemizes suggested routine maintenance performance for onsite
extended aeration  package plants.   The  process is  labor-intensive  and
requires semi-skilled personnel.  Based upon field experience with these
units, 12  to  48  man-hr per yr  plus  analytical  services  are  required to
insure  reasonable  performance.   Power requirements  are variable,  but
range between 2.5 to 10 kWh/day.
             d.  Operational Problems
Table 6-16  outlines  an abbreviated listing of  operational  problems  and
suggested remedies for them.  A detailed discussion of these problems
                                    152

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                               TABLE 6-15

                    SUGGESTED MAINTENANCE FOR ONSITE
                   EXTENDED AERATION PACKAGE PLANTS3
      Item
                Suggested Maintenance
Aeration Tank

Aeration System
  Diffused air

  Mechanical
Clarifier
Trash Trap

Controls


Sludge Wasting

Analytical
Check for foaming and uneven air distribution.
Check air filters, seals, oil  level,  back  pressure;
  perform manufacturer's required maintenance.
Check for vibration and overheating;  check oil
  level, seals; perform manufacturer's required
  maintenance.

Check for floating scum; check effluent appearance;
  clean weirs; hose down sidewalls and appurtenance;
  check sludge return flow rate and adjust time
  sequence if required; locate sludge blanket;
  service mechanical equipment as required by
  manufacturer.

Check for accumualted solids;  hose down sidewalls.

Check out functions of all controls and alarms;
  check electrical control box.

Pump waste solids as required.

Measure aeration tank grab sample for DO,  MLSS, pH,
  settleability, temperature;  measure final  effluent
  composite sample for BOD, SS, pH (N and P if
  required).
a Maintenance activities should be performed about once per month.
                                   153

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                               TABLE  6-16

         OPERATIONAL PROBLEMS—EXTENDED AERATION PACKAGE  PLANTS
     Observation
        Cause
        Remedy
Excessive local
  turbulence in
  aeration tank

White thick billowy
  foam on aeration
  tank

Thick scummy dark
  tan foam on
  aeration tank

Dark brown/black foam
  and mixed liquor in
  aeration tank

Billowing sludge
  washout in
  clarifier
Clumps of rising
  sludge in clarifier
Fine dispersed floe
  over weir, turbid
  effluent
Diffuser plugging
Pipe breakage
Excessive aeration

Insufficient MLSS
High MLSS
Anaerobic conditions
Aerator failure
Hydraulic or solids
overload

Bulking sludge

De nitrification
Septic conditions
in clarifier

Turbulence in
aeration tank
                          Sludge age too
                          high
Remove and clean
Replace as required
Throttle blower

Avoid wasting solids
Waste solids
Check aeration system,
aeration tank D.O.
Waste sludge; check
flow to unit

See reference (37)

Increase sludge return
rate to decrease
sludge retention time
in clarifier

Increase return rate
Reduce power input
                         Waste sludge
                                    154

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for larger, centralized systems can  be  found  in the "Manual  of Practice
- Operation  of  Wastewater Treatment  Plants"  (36) and  "Process  Control
Manual  for Aerobic  Biological  Wastewater  Treatment Facilities"  (37).
Major  mechanical  maintenance problems  for onsite  treatment  units  are
with  blower  or  mechanical  aerator  failure,   pump  and pipe  clogging,
electrical  motor failure,  corrosion and/or  failure of  controls,  and
electrical  malfunctions  (35).     Careful   attention  to  a  maintenance
schedule  will  reduce  these problems   to  a   minimum,  and  will   also
alleviate  operational   problems  due  to the  biological  process  upset.
Emphasis  should  be  placed on  adequate maintenance  checks  during  the
first  2 or 3 months of operation.


         6.4.2.7  Considerations for Multi-Home Application


The extended  aeration  process may be well  suited  for  multiple-home or
commercial applications.  The same requirements listed for single onsite
systems generally  apply to  the  larger  scale  systems  (20)(36)(37)(38).
However, larger package plant systems may be  more complex  and  require a
greater degree of operator attention.
     6.4.3  Fixed Film Systems


         6.4.3.1  Description


Fixed  film  systems employ  an inert media  to which microorganisms  may
become attached.   The  wastewater comes in contact with  this fixed film
of microorganisms either by  pumping  the water past  the media or by mov-
ing the media past the wastewater to be treated.   Oxygen may be supplied
by natural ventilation or by mechanical or  diffused  aeration within the
wastewater.  Fixed film reactors are normally constructed as packed tow-
ers or as rotating plates.   Figure 6-12 depicts three  types of onsite
fixed  film  systems - the trickling  filter  (gravity flow  of wastewater
downward),  the  upflow  filter   (wastewater  pumped   upward  through  the
media), and the rotating biological  contractor.
The trickling  filter  has been used to  treat  wastewater  for many years.
Modern filters today consist of towers of media constructed from a vari-
ety of plastics, stone, or redwood laths into a number of shapes (honey-
comb  blocks,  rings, cylinders, etc.).   Wastewater is distributed  over
the surface of the  media and  collected  at the bottom through an undrain
system.   Oxygen is normally  transferred by  natural  drafting,  although
some  units employ  blowers.   Treated effluent  is  settled  prior  to being
discharged or partially recycled back through the filter.
                                    155

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                               FIGURE 6-12

            EXAMPLES OF FIXED  FILM PACKAGE PLANT CONFIGURATIONS
                                 Motor
                                               ROTATING
                                        BIOLOGICAL CONTACTOR
          UPFLOW FILTER
                                Effluent
 TRICKLING F1LTFR

     Influent Distributor
	J'
  *"•»"**"*» '  »"
Vr Under Drain 'v/a
Fixed
Media
r

	
h Pump
TJ __
I v I
— j"»-tt
V
^ ^
I^^^^^^illil^iCS'udge 1
                                         Clarifier
                                          Timer
                                          Control
                                          Valve
                                              Influent
                                                                   Septic
                                                                    Tank
      •Effluent to Clarifier or Septic Tank
                                   156

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In  an  upflow  filter,  wastewater  flows  through  the  media  and  is
subsequently collected at  an  overflow weir.   Oxygen may  be  transferred
to the biomass by means  of diffusers  located  at the bottom of the tower
or by surface entrainment  devices  at  the top.  One of  the commercially
available units  of  this  type  (built  primarily  for shipboard  use)  does
not  require  effluent  sedimentation  prior to  discharge  (Figure  6-12).
Circulation  of  wastewater through this particular unit promotes  the
shear of  biomass from the media  and  subsequent  carriage  to the  tank
bottom.
The  rotating  biological  contactor  (RBC)  employs a  series of  rotating
discs  mounted on  a  horizontal  shaft.   The  partially submerged  discs
rotate  at rates  of  1  to  2 rpm  through  the  wastewater.   Oxygen  is
transferred to the biomass as the disc rotates from the air to the water
phase.  Recirculation of effluent is not normally practiced.


         6.4.3.2  Applicability
There has been little long-term  field  experience  with  onsite  fixed film
systems.  Generally, they  are less complex than  extended  aeration sys-
tems and should require less attention; if designed properly they should
produce an effluent of  equivalent quality.
There  are  no  significant  physical   site  constraints  that  should  limit
their  application,  although local  codes may  require certain  set-back
distances.   The  process is  more  temperature  sensitive than  extended
aeration  and  should  be  insulated   as  required.   Rotating  biological
contactors  should  also  be  protected from  sunlight to  avoid  excessive
growth of algae which may overgrow the plate surfaces.


         6.4.3.3  Factors Affecting Performance
Limited  data are  currently  available  on  long-term  performance  of  onsite
fixed  film systems.   Detailed  description  of  process  variables  that
affect fixed film process perfomrance appear in  the  "Manual  of Practice
for Wastewater Treatment Plant Design"  (20).   Low  loaded  filters  should
also  achieve  substantial  nitrification, as  well  as  good  BOD and  SS
reductions.
         6.4.3.4  Design


Onsite  fixed film  systems include  a variety  of proprietary  devices.
Design  guidelines  are,  therefore, difficult  to prescribe.   Table  6-17
                                   157

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presents suggested design ranges for two generic fixed film systems, the
RBC and the fixed media processes.
                               TABLE 6-17

       TYPICAL OPERATING PARAMETERS FOR ONSITE FIXED FILM SYSTEMS


              Parameter9                 Fixed Media         RBC


  Hydraulic Loading, gpd/ft2                25-100        0.75-1.0

  Organic Loading, Ib BOD/d/1000 ft3         5-20          1.0-1.5

  Dissolved Oxygen, mg/1                    >2.0            >2.0

  Overflow Rate, gpd/ft2                   600-800         600-800

  Weir Loading, gpd/ft2                 10,000-20,000   10,000-20,000

  Sludge Wasting, months                     8-12            8-12
  a Pretreatment:  Settling or screening.
    Recirculation:  Not required.
All fixed  film  systems  should be preceded by  settling  and/or  screening
to  remove  materials that  will  otherwise  cause  process  malfunction.
Hydraulic loadings are normally constrained by biological  reaction rates
and mass  transfer.
Organic loading is primarily dictated by oxygen transfer within the bio-
logical film.   Excessive organic  loads may cause  anaerobic  conditions
resulting in odor and  poor  performance.   Dissolved  oxygen  in  the liquid
should be at  least  2 mg/1.   Recirculation  is  not normally practiced in
package fixed film systems since it adds to the degree of complexity and
is  energy and  maintenance   intensive.    However,  recirculation may  be
desirable  in  certain  applications where  minimum  wetting  rates  are
required for optimal  performance.
The production  of  biomass  on fixed film systems  is  similar  to  that for
extended aeration.   Very  often,  accumulated sludge  is directed  back  to
the septic tank for storage and partial  digestion.
                                   158

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         6.4.3.5  Construction Features
Very few commercially  produced fixed film systems are  currently  avail-
able for onsite  application.   Figure 6-12 illustrates  several  flow  ar-
rangements  that  have been  employed.   Specific construction  details  are
dependent on  system  characteristics.  In general, synthetic  packing  or
attachment  media  are  preferred  over naturally occurring materials  be-
cause they are  lighter,  more durable, and provide better void  volume -
surface area characteristics.  All fixed  film  systems  should be covered
and  insulated  as  required  against  severe  weather.    Units  may be  in-
stalled at  or below grade depending upon site topography and  other  adja-
cent treatment  processes.   Access to  all  moving parts  and  controls  is
required, and  proper  venting  of the unit  is  paramount, especially  if
natural ventilation is being used  to supply  oxygen.   Underdrains,  where
required, should  be  accessible  and  designed to provide sufficient  air
space  during  maximum  hydraulic  loads.   Clarification  equipment  should
include  positive  sludge and  scum handling.   All  pumps,  blowers,  and
aeration devices,  if required,  should  be  rugged,  corrosion-resistant,
and built for continuous duty.
         6.4.3.6  Operation and Maintenance


              a.  General Process Operation
Fixed film  systems  for  onsite  application  normally  require very minimal
operation.  Rotating biological contactors are  installed  at fixed rota-
tional  speed  and submergence.   Flow to  these  units is  normally fixed
through the use of an integrated pumping system.  Sludge wasting is nor-
mally controlled  by a  timer setting.  Through  experience,  the  operator
may  determine  when  clarifier  sludge should  be  discharged in  order  to
avoid sludge flotation (denitrification) or excessive build-up.


Where aeration is provided, it is normally designed  for continuous duty.
On-off cycling of aeration equipment may be practiced for energy conser-
vation if shown not to cause a deterioration  of effluent quality.
              b.  Routine Operation and Maintenance


Table 6-18 itemizes suggested routine maintenance performance for onsite
fixed film  systems.   The process is  less  labor-intensive  than extended
aeration  systems  and  requires semi-skilled personnel.   Based  upon  very
limited field experience with these units, 8 to 12 man-hr per yr plus
                                    159

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                               TABLE  6-18
                    SUGGESTED MAINTENANCE  FOR ONSITE
                      FIXED FILM PACKAGE PLANTS*
      Item
             Suggested Maintenance
Media Tank
Aeration System
RBC Unit

Clarifier
Trash Trap
Controls
Analytical
Check media for debris accumulation,  ponding,
  and excessive biomass - clean as  required;
  check underdrains - clean as required;  hose
  down sidewalls and appurtenances; check
  effluent distribution and pumping - clean as
  required.
See Table 6-15
Lubricate motors and bearings; replace seals as
  required by manufacturer.
See Table 6-15
See Table 6-15
See Table 6-15
Measure final effluent composite  sample for
  BOD, SS, pH (N and P if required).
a Maintenance activities should be performed about once  per month.
                                   160

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analytical services are required  to  ensure  adequate performance.   Power
requirements depend upon  the device employed,  but may range  from  1  to
4 kWh/day.
              c.  Operational Problems


Table  6-19  outlines  an  abbreviated  list  of  potential   operational
problems  and suggested  remedies  for onsite  fixed  film systems.    A
detailed  discussion  of  these may be  found in  the  "Manual  of Practice -
Operation  of Wastewater  Treatment Plants"  (36) and  "Process  Control
Manual  for Aerobic  Biological   Wastewater  Treatment Facilities"  (37).
         6.4.3.7  Considerations for Multi-Home Applications
Fixed film  systems  may be well  suited for multiple-home  or  commercial
applications.   The  same  requirements for  single-home onsite  systems
apply  to the  large-scale systems  (20)(29)(37)(38).   However,  larger
systems  may  be more  complex  and require  a greater degree of  operator
attention.
6.5  Disinfection


     6.5.1  Introduction
Disinfection of wastewaters  is  employed  to  destroy pathogenic organisms
in the wastewater stream.  Since disposal of wastewater to surface water
may result in potential contacts between individuals and the wastewater,
disinfection  processes  to  reduce  the   risk  of  infection  should  be
considered.
There are a number of important waterborne pathogens found in the United
States  (39)(40)(41)(42).  Within  this  group  of  pathogens,  the protozoan
cyst is generally  most  resistant  to disinfection  processes,  followed by
the virus  and, the vegetative bacteria (43).   The  design  of the disin-
fection process  must necessarily  provide effective control  of  the  most
resistant pathogen likely to  be present in the  wastewater  treated.   Up-
stream  processes may effectively reduce some  of these pathogens,  but
data are  scant on the  magnitude  of this reduction for  most pathogens.
Currently, the effectiveness  of  disinfection is measured  by  the use of
indicator  bacteria (total  or  fecal  coliform)  or disinfectant  residual
where  applicable.    Unfortunately,  neither  method guarantees  complete
destruction of the pathogen,  and  conservative values  are often  selected
to hedge against this risk.
                                   161

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                               TABLE  6-19

             OPERATIONAL PROBLEMS—FIXED FILM PACKAGE  PLANTS
    Observation
      Cause
             Remedy
Filter Ponding
Filter Flies
Odors
Freezing
Excessive Biomass
  Accumulation
Poor Clarification
Media too fine

Organic overload




Debri s
Poor wastewater
  distribution
Poor ventilation/
  aeration
Improper
  insultati on

Organic overload
Low pH; anaerobic
  conditions

Denitrifi cation
  in clarifier

Hydraulic overload
Replace media

Flush surface with  high  pressure
  stream; increase  recycle rate;
  dose with chlorine (10-20 mg/1
  for 4 hours)

Remove debris; provide
  pretreatment

Provide complete wetting of
  media; increase recycle rate;
  chlorinate (5 mg/1  for 6 hours
  at 1 to 2 week intervals)

Check underdrains;  maintain
  aeration equipment,  if
  employed; insure  adequate
  ventilation; increase  recycle

Check and provide sufficient
  insulation

Increase recycle; flush  surface
  with high pressure stream;
  dose with chlorine;  increase
  surface area (RBC)

Check venting; preaerate
  wastewater

Remove sludge more often
                                         Reduce recycle;  provide  flow
                                           buffering
                                   162

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Table  6-20  presents  a listing  of potential  disinfectants for  onsite
application.   Selection of  the  best disinfectant is dependent  upon  the
characteristics   of   the   disinfectant,   the  characteristics   of   the
wastewater and the treatment processes preceding  disinfection.   The most
important  disinfectants  for  onsite application  are chlorine,  iodine,
ozone,  and  ultraviolet  light,   since   more  is  known   about  these
disinfectants and equipment is available  for their application.
                               TABLE 6-20

        SELECTED POTENTIAL DISINFECTANTS FOR  ONSITE  APPLICATION
     Disinfectant
Formula
                                      Form Used
Equipment
Sodium Hypochlorite      NaOCl

Cal ci um Hypochl ori te   Ca (OC1);

Elemental  Iodine          12


Ozone                     03


Ultraviolet Light
                                       Li qui d

                                       Tablet

                                      Crystals


                                        Gas
                                    Electromagnetic
                                      Radiation
                              Metering Pump

                             Tablet Contactor

                              Crystal/Liquid
                                Contactor

                             Generator, Gas/
                             Liquid Contactor

                              Thin Film
                                Radiation
                                Contactor
Disinfection processes  for  onsite disposal  must necessarily be  simple
and safe  to operate,  reliable, and  economical.   They normally are  the
terminal  process in the treatment flow sheet.
     6.5.2  The Halogens - Chlorine and Iodine
         6.5.2.1  Description
Chlorine and  iodine  are powerful  oxidizing agents capable  of  oxidizing
organic matter,  including  organisms, at  rapid  rates in relatively  low
concentrations.  Some of the characteristics of  these halogens  appear in
Table 6-21  (20)(44)(45).
                                  163

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                                 TABLE 6-21

                           HALOGEN PROPERTIES (27)
    Sodi urn
      Hypochlorite
                  Form
Liquid
    Calcium        Tablet
      Hypochlorite   (115 gm)
    Iodine
                 Crystal s
                         Commercial
                          Strength
                         Available
                          12 - 15
                            70
                           100
                   Sped fi c
                   Gravity
                                   1.14 - 1.17
                                     4.93
   Handling
   Materials
Ceramic, Glass,
 Plastic,
 Rubber
                            Glass, Wood,
                              Fiberglass,
                              Rubber

                            Fiberglass,  Some
                              Plastics
   Characteristics


Deteriorates rapidly at
 high temperatures, in
 sunlight, and at high
 concentrations.

Deteriorates at
 3-5%/year
              Stable in water;
               solubility:
                 10° - 200 mg/1
                 20° - 290 mg/1
                 30° - 400 mq/1
Chlorine may be added  to  wastewater as  a  gas, Clp-  However,  because the
gas  can  represent  a  safety hazard and  is  highly  corrosive,  chlorine
would  normally be  administered as  a solid or liquid for onsite applica-
tions.   Addition of  either  sodium  or calcium hypochlorite to wastewater
results  in an  increase in  pH and  produces the  chlorine compounds hypo-
chlorous acid, HOC!, and  hypochlorite ion,  OC1", which are designated as
"free"  chlorine.    In  wastewaters  containing reduced  compounds  such as
sulfide, ferrous  iron,  organic  matter,  and  ammonia,  the  free  chlorine
rapidly  reacts in nonspecific side  reactions  with the reduced compounds,
producing chloramines,  a  variety of chloro-organics, and chloride.  Free
chlorine is the most powerful disinfectant, while chloride has virtually
no  disinfectant capabilities.  The other chloro-compounds, often called
combined chlorine,  demonstrate  disinfectant  properties  that  range from
moderate to  weak.    Measurement  of  "chlorine  residual" detects  all  of
these  forms  except chloride.   The  difference between  the chlorine dose
and  the  residual,  called "chlorine demand,"   represents the  consumption
of  chlorine  by reduced materials in the  wastewater (Table 6-22).  Thus,
in  disinfection  system  design,  it is  the chlorine residual  (free  and
combined) that is of importance  in  destroying pathogens.
                                     164

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                               TABLE 6-22

           CHLORINE DEMAND OF SELECTED DOMESTIC WASTEWATERS3
                                                             Chlorine
                       Wastewater                             Demand
   Raw fresh wastewater                                        8-15

   Septic tank  effluent                                       30  - 45

   Package biological  treatment plant effluent                10  - 25

   Sand-filtered effluent                                      1-5
   a Estimated concentration  of  chlorine  consumed  in  nonspecific
     side reactions with 15-minute contact  time.
Iodine is normally used in the elemental  crystalline form, Io,  for water
and wastewater disinfection.  Iodine hydrolyzes in water to form the hy-
poiodus forms, HIO and 10", and  iodate,  I03.   Normally, the predominant
disinfectant species in water  are I2,  HIO, and 10",  as little  I03 will
be found at normal wastewater pH values (less than pH 8.0).  Iodine does
not appear  to  react very rapidly  with organic compounds  or ammonia  in
wastewaters.   As  with  chlorine, however, most wastewaters will  exhibit
an iodine demand due to nonspecific side  reactions.  The reduced form of
iodine, iodide, which is  not an  effective  disinfectant, is not detected
by iodine residual analyses.


         6.5.2.2  Applicability


The halogens  are  probably  the most practical  disinfectants for  use  in
onsite  wastewater treatment applications.   They  are  effective against
waterborne  pathogens,  reliable,  easy  to  apply,  and  are  readily  avail-
able.
                                   165

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The  use  of chlorine as  a  disinfectant may result in  the  production of
chlorinated by-products  which  may be  toxic  to aquatic life.   No toxic
by-products have been identified for iodine at this time.
         6.5.2.3  Performance
The  performance  of halogen disinfectants is dependent  upon  halogen  re-
sidual concentration  and  contact time,  wastewater  characteristics,  na-
ture of the  specific  pathogen,  and  wastewater  temperature  (20).   Waste-
water characteristics may effect the selection of the halogen as  well  as
the  required dosage  due  to  the nonspecific  side reactions  that  occur
(halogen  demand).    Chlorine  demands  for  various wastewaters are  pre-
sented  in Table 6-22.   The  demand of  wastewaters  for iodine  is  less
clear.   Some investigators have reported  iodine demands 7  to 10  times
higher  than  those  for chlorine  in wastewaters  (46)(47)  while  others
indicate  that  iodine  should  be relatively  inert to reduced  compounds
when compared  to chlorine (48).  Design of  halogen  systems  is normally
based upon dose-contact relationships  since  the  goal of disinfection  is
to  achieve  a  desired level  of pathogen  destruction  in  a  reasonable
length of time with  the  least  amount  of disinfectant.   Because of  the
nonspecific  side  reactions that occur,  it is important to  distinguish
between halogen dose  and  halogen residual  after  a given contact period
in evaluating the disinfection process.


Table 6-23 provides a summary of halogen residual-contact  time informa-
tion  for  a variety of organisms  (43).  These are average values  taken
from a number of studies and should be  used with  caution.   Relationships
developed  between  disinfectant  residual,  contact time, and  efficiency
are empirical.  They  may  be linear  for certain organisms,  but are  often
more complex.   Thus,  it is not  necessarily  true that doubling the con-
tact time will  halve  the  halogens  residual  requirements for  destruction
of certain pathogens.  In the absence of  sufficient data  to make  these
judgements,  conservative  values  are normally employed for  residual-dose
requirements.


The  enteric  bacteria are more  sensitive to the   halogens than cysts  or
virus.   Thus,  the  use of indicator  organisms  to judge  effective disin-
fection must be cautiously employed.


Temperature effects also vary with pathogen and halogen, and  the  general
rule of thumb indicates that there should be a two to threefold decrease
in  rate  of  kill  for  every  10° C  decrease  in  temperature  within  the
limits of 5 to 30° C.
                                   166

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                               TABLE 6-23

         PERFORMANCE OF HALOGENS AND OZONE AT 25°C [After (43)]
                                 Necessary Residual After 10 Min. to
                                 Achieve 99.999% Destruction (tng/1)
                                Amoebi c        Enteric        Enteri c
          Halogen                Cysts         Bacteria        Virus


    HOC1  (Predominates             3.5            0.02           0.4
      @ pH <7.5)

    OCL-  (Predominates              40            1.5            100
      6 pH >7.5)

    NH2Cla                          20              4              20

    12 (Predominates               3.5            0.2             15
      (? pH <7.0)

    HIO/IO-  (Predominates            7            0.05           0.5
      6 8.0>pH>7.0)

    03                         0.3->1.8        0.2-0.3        0.2-0.3
    a  NHCl2:NH2Cl Efficiency  =  3.5:1
         6.5.2.4  Design Criteria


The design  of  disinfection processes requires the  determination  of the
wastewater characteristics,  wastewater  temperature, pathogen to  be de-
stroyed, and disinfectant  to be employed (20).   From  this  information,
the required  residual-concentration relationship may  be developed  and
disinfectant dose may be calculated.


Wastewater characteristics  dictate  both halogen demand  and  the  species
of the disinfectant that predominates.   In  effluents from  sand  filters,
chlorine demands would be  low  and,  depending  upon pH,  hypochlorous acid
or hypochlorite would prevail  if chlorine is  used.   (The effluent would
be  almost  completely nitrified,  leaving little  ammonia available  for
reaction).   At pH values below 7.5,  the more  potent free chlorine form,
                                     167

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HOC!, would predominate.   It is clear from Table 6-23 that  pH  plays an
important  role  in the  effectiveness of  chlorine disinfection  against
virus and cysts (10 to 300 fold differences).
The effect of temperature is often ignored except to ensure that conser-
vatively long contact  times  are  selected  for  disinfection.   Temperature
corrections are necessary for estimating  iodine  doses  if  a  saturator  is
employed, since the solubility of iodine in water decreases dramatically
with decreased temperature.
Design of onsite wastewater  disinfection  systems must  result in  conser-
vative dose-contact time values, since careful  control  of the process is
not feasible.   Guidelines  for chlorine and iodine disinfection  for  on-
site applications are presented in Table  6-24.   These  values are guide-
lines only,  and more definitive analysis may  be warranted  in  specific
cases.
                               TABLE 6-24

                    HALOGEN DOSAGE DESIGN GUIDELINES


                                       Dose3
                   Septic Tank     Package Biological     Sand Filter
   Disinfectant     Eff1uent        Process Effluent      Effluent
                      mg/1                imjTI               mg/1
   Chiori ne
     pH 6            35-50               15-30              2-10
     pH 7            40-55               20-35             10-20
     pH 8            50-65               30-45             20-35

   Iodineb
     pH 6-8         300-400              90-150            10-50
   a Contact time = 1 hour at average flow and 20°C; increase
     contact time to 2 hours at 10°C and 8 hours at 5°C for similar
     efficiency.

   b Based upon very small data base, assuming iodine demand from
     3 to 7 times that of chlorine.
                                    168

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The  sizing  of halogen  feed  systems is dependent  upon  the  form of  the
halogen used  and  the method of  distribution.   Sample calculations  are
presented below.

Sample calculations:
Estimate of sodium hypochlorite dose -  liquid feed
    Halogen:  NaOCl  - trade strength 15% (150 g/1)
    Dose required:  20 mg/1  available chlorine
    Wastewater flow:  200 gpd average
1.  Available chlorine =
    (150 g/1) x (3.785 1/gal) x (1.0 lb/453.6 g)  =  1.25  Ib/gal
2.  Dose required =
    (20 mg/1) x (3.785 1/gal) x (1 lb/453.6 g)  x  (10"3 g/mg)
    = 1.67 x 10"4 Ib/gal
3.  Dose required =
    (1.67 x 10~4 Ib/gal) x (200 gal/d)  = 3.34 x 10"2  Ib/d
4.  NaOCl dose =
    (3.34 x 10"2 Ib/d) + (1.25 Ib/gal) = 0.027 gal/day

Estimate of halogen  design - tablet feed
    Halogen:  Ca(OCL)o tablet - 115 g;  commercial  strength 70%
    Dose Required:  20 mg/1  available chlorine
    Wastewater Flow:  200 gpd (750 1/d)
    1.  Available chlorine in tablet =  0.7 x 115(g) = 80.5 g/tablet
    2.  Dose required = 20 (mg/1) x 750 (1/d) = 15  g/d
    3.  Tablet consumption = QQ g^g/tablet) = °'19 tablets/day
             or:  5.4 days/tablet
                                  169

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         6.5.2.5  Construction Features


             a.  Feed Systems
There  are basically  three  types  of  halogen feed  systems  commercially
available for onsite application:   stack  or  tablet  feed  systems,  liquid
feed  systems,  and  saturators.    Tablet  feed  devices  for  Ca(OCl)2
tablets (Figure 6-13) are constructed of durable,  corrosion-free plastic
or  fiberglass,  and are  designed  for in-line installation.   Wastewater
flows  past  the tablets  of  Ca(OCl)2, dissolving  them  in proportion  to
flow  rate (depth  of  immersion).   Tablets  are added  as requried  upon
manual inspection  of  the unit.   One commercial  device  provides  29-115
g/tablet  per  tube  which  would require  refilling  in approximately  155
days  (5.4 days/tablet x 29).


Halogens may  also  be  fed to the  wastewater  by an aspirator  feeder  or a
suction feeder.   The  aspirator feeder operates  on a simple  hydraulic
principle that  employs the  use of the vacuum created when  water flows
either through a venturi tube  or  perpendicular to a nozzle.   The vacuum
created draws the disinfection solution from a container  into the disin-
fection unit,  where  it  is  mixed with wastewater  passing  through  the
unit.   The  mixture  is then injected  into the main wastewater stream.
Suction feeders  operate  by pulling  the  disinfection  solution  from  a
container by  suction  into  the disinfection unit.   The  suction  may  be
created by either a pump or  a siphon.
The storage reservoir containing the halogen should provide  ample  volume
for several weeks of operation.   A 1-gal  (4-1) storage tank would  hold
sufficient  15%  sodium  hypochlorite  solution  for approximately 37  days
before  refill  (see  sample  computation).    A 2-gal  (8-1)  holding  tank
would  supply  50  days  of   10%  sodium  hypochlorite.    A  15%  sodium
hypochlorite  solution  would   deteriorate  to   one-half  its   original
strength  in 100 days  at 25°C  (49).   The  deterioration rate of  sodium
hypochlorite  decreases  with   decreased  strength;   therefore,   a   10%
solution would decrease to one-half strength in about 220  days.


If liquid  halogen  is dispersed  in this  fashion, care must be  taken  to
select  materials  of construction that are  corrosion-resistant.    This
includes storage tanks, piping, and appurtenances as well  as the pump.


Iodine  is  best applied  to  wastewater by means  of a  saturator whereby
crystals of  iodine  are dissolved in carriage water  subsequent  to being
pumped  to  a  contact  chamber   (Figure 6-14).    Saturators  may  be  con-
structed or purchased commercially.  The  saturator consists  of  a tank of
fiberglass  or other  durable  plastic  containing a supporting base  medium
                                  170

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                            FIGURE 6-13

                      STACK FEED CHLORINATOR
         Feed Tubes
Water Inlet
                                                       Water Outlet
                                                        ^3(001)2
                                                        Tablets
                                171

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                        FIGURE 6-14

                     IODINE SATURATOR
Wastewater
                           Tank
                             I
                                              Iodine Solution
                                              Iodine Crystals
                            172

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and iodine crystals.  Pretreated wastewater  is  split,  and  one  stream is
fed to the saturator.  The dissolution of iodine is dependent upon water
temperature,  ranging  from 200  to 400  mg/1  (Table 6-21).   The  iodine
solution from the saturator is  subsequently  blended with the wastewater
stream,  which is  discharged  to  a  contact chamber.    Depending  upon
saturator size and dosage requirements,  replenishment  of iodine every  1
to 2 yr may be required (assumes a dosage of 50  mg/1  for 750  I/day using
a 0.2-cu-ft saturator).
             b.  Contact Basin
Successful disinfection  depends  upon the  proper  mixing and contact  of
the disinfectant  with the wastewater.   If  good  mixing is achieved,  a
contact time of 1 hour  should  be  sufficient  to  achieve  most onsite dis-
infection objectives  when  using  doses presented  in  Table 6-24.   Where
flows are low (e.g., under 1,000  gal  per day) (3,785  1 per day), contact
basins may be  plastic,  fiberglass,  or a length of concrete pipe placed
vertically and outfitted with  a  concrete base (Figure 6-15).   A 48-in.
(122-cm)  diameter concrete  section  would theoretically  provide  6  hr  of
wastewater detention  for an  average  flow of 200 gal  per  day (757  1  per
day) if the water depth were only approximately  6  in. (15  cm).   A 36-in.
(91-cm) diameter  pipe section  provides  6 hr detention  at approximately
12 in.  (30 cm) of water depth  for the same flow.   Therefore, substanti-
ally longer theoretical detention times  than necessary  for  ideal  mixing
conditions are  provided using 36-  or 48-in. (91- or 122-cm)   diameter
pipe.     This  oversizing  may  be   practically   justified  for  onsite
applications with  low  flows,  since  good  mixing  may be  difficult  to
achieve.
Contact  basins  should  be  baffled in  order to  prevent serious  short-
circuiting within the basin.  One  sample baffling  arrangement  is  illus-
trated in Figure 6-15.
         6.5.2.6  Operation and Maintenance
The  disinfection  system  should  be designed  to  minimize operation  and
maintenance  requirements,  yet  insure  reliable  treatment.     Routine
operation  and  maintenance  of  premixed liquid  solution  feed  equipment
consists of  replacing  chemicals,  adjusting  feed rates, and maintaining
the  mechanical  components.    Tablet  feed  chlorination  devices  should
require  less  frequent attention,  although  recent  experience  indicates
that  caking  of  hypochlorite tablets occurs  due  to the moisture  in  the
chamber.  Caking may result in insufficient dosing of  chlorine,  but  may
also  produce  excessive dosage  due to cake  deterioration and  subsequent
spillage into the wastewater stream.   Dissolution  of  chlorine may also
be erratic, requiring routine adjustment of  tablet  and  liquid  elevation
                                   173

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(experience with  some units  indicates  that dissolution  rates  actually
increase  with  decreased  flow rates).    Routine  maintenance of  iodine
saturators  includes  replacing  chemicals,  occasionally  adjusting  feed
rates,  redistributing   iodine   crystals  within  the   saturator,   and
maintaining mechanical components.
                              FIGURE 6-15

                         SAMPLE CONTACT CHAMBER
   Wastewater
       with
   Disinfectant
                                              J
Concrete Pipe Section
                                          Wooden Baffles
Process control  is  best  achieved  by periodic  analysis of halogen resid-
uals  in the  contact chamber.  The  halogen  residuals  can be measured by
unskilled  persons  using a  color  comparator.    Periodic  bacteriological
analyses  of  treated  effluents   provide actual  proof  of  efficiency.
Skilled technicians are  required to  sample  and analyze  for  indicator
organisms or pathogens.
                                    174

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 It  is  estimated  that tablet feed  chlorinators  could  be operated with
approximately  6 unskilled man-hr per yr  including monthly chlorine re-
sidual  analyses.   Iodine saturator  systems  and  halogen  liquid feed sys-
tems may require 6 to  10 semi-skilled man-hr per yr.   Electrical power
consumption would be highly variable  depending  upon  other process pump-
ing  requirements,  as well  as the  use  of metering pumps and controls.
Chemical requirements will  vary,  but are  estimated fo be  about  5  to
25 I b  (2 to 11 kg)  of  iodine  and 5 to 15 I b (2 to  7 kg)  of available
chlorine per yr for  a family of four.
         6.5.2.7    Other  Considerations
In making a final  decision on halogen disinfection,  other considerations
must be  included  in addition to cost,  system effectiveness,  and relia-
bility.    Without  a dechlorination  step,  chlorine  disinfection  may be
ruled out administratively.   Currently,  there is no  evidence that iodine
or its compounds are toxic to aquatic life.
     6.5.3    Ultraviolet  Irradiation


         6.5.3.1    Description


The germicidal properties of ultraviolet (UV)  irradiation  have been rec-
ognized for many years  (50)(51).  UV  irradiation has been used for the
disinfection  of  water  supplies  here  and abroad,   and  currently  finds
widest application for small water  systems for  homes, commercial estab-
lishments,  aboard ship,  and in  some industrial water purification sys-
tems.    The  use of UV irradiation for wastewater disinfection has only
recently been seriously  studied (52)(53).


Ultraviolet is germicidal  in the  wave  length  range  of 2,300 to 3,000  A,
its greatest  efficiency  being  at 2,540  A.    Currently,  high-intensity,
low-pressure mercury  vapor lamps emit a major  percentage of their energy
at this wave  length,  making them most efficient for use.   The primary
mode of  action of UV is the  denaturation of nucleic  acids,  making  it
especially effective  against virus.
In  order  to  be  effective,  UV  energy  must  reach  the organism  to  be
destroyed.   Unfortunately, UV energy is rapidly  absorbed in water and by
a variety  of organic  and  inorganic molecules in  water.  Thus,  the trans-
mittance or absorbance properties  of the water  to be treated are criti-
cal to  successful  UV  disinfection.   To achieve disinfection,  the water
to be treated is  normally exposed inathinfilmtotheUV source.   This
may  be  accomplished  by enclosing  the  UV  lamps within a  chamber,  and
                                  175

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directing  flow  through and  around  the lamps.   It  may  also be  accom-
plished by exposing a thin film of water  flowing over  a  surface  or  weir
to a bank of lamps suspended above and/or  below the water surface.


The lamps  are encased  within a clear, high transmittance, fused  quartz
glass sleeve in order to protect them.  This also  insulates  the lamps  so
as  to  maintain an  optimum  lamp  temperature  (usually about  105° F  or
41° C).  To ensure maintenance of a very  high  transmittance  through  the
quartz  glass  enclosure,  wipers  are  usually  provided with  this equip-
ment.   Figures  6-16 and  6-17 depict  a  typical   UV disinfection  lamp
arrangement currently being  used.   There are  a number  of commercially
available  units  that may  be applicable  to onsite  wastewater applica-
tions.
         6.5.3.2  Applicability
Site conditions should not restrict the use of  UV  irradiation  processes
for onsite application,  although  a  power  source is required.   The  unit
must be  housed  to protect it  from  excessive  heat, freezing,  and dust.
Wastewater characteristics limit the applicability  of  UV equipment since
energy transmission is dependent  upon the absorbance  of  the  water to  be
treated.   Therefore,  only  well-treated wastewater can be  disinfected
with UV.
         6.5.3.3  Factors Affecting Performance
The effectiveness of UV disinfection is dependent upon UV power,  contact
time, liquid  film thickness, wastewater absorbance,  process  configura-
tion, input voltage, and temperature (50)(51)(52).


The UV power output for a lamp is dependent upon the input voltage,  lamp
temperature,  and  lamp characteristics.  Typically,  UV output may  vary
from as  low as 68% of rated capacity at 90 volts to  102%  at  120 volts.
Lamp temperatures  below  and  above about 104° F  (40°  C)  also  results  in
decreased output.   The use of quartz glass enclosures  normally  ensures
maintenance of optimum temperature within the  lamp.
Since disinfection by UV requires that  the  UV  energy  reaches  the organ-
isms, a  measure of wastewater  absorbance  is  crucial  to proper  design.
Transmissability  is  calculated as an  exponential  function of depth  of
penetration and the absorption coefficient of the wastewater:

                                T = e-ad
                                   176

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                                  FIGURE  6-16

                         TYPICAL UV DISINFECTION UNIT
 [ Outlet
n
	I     Flow Control Valve
                                         Mounting Brackets for Easy
                                       Installation Vertical or Horizontal
                                                                  Removeable
                                                                 Flanged head
c
Drain Plug
           Q-
        Warning
     Sterlizing Chamber
     (see Figure 6-17)
                                                                        Wipers
                           Fail-Safe Monitor


                              Solenoid Shut Off Valve
                  Extension
                                                             Inlet

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                           FIGURE 6-17

                 TYPICAL UV STERILIZING CHAMBER
                                  Ultraviolet light rays  are emitted from
                                  high intensity  ultraviolet lamps and
                                  pass through the quartz sleeves.
       Baffles force the water to travel
       tangetially through the chamber in a
       spinning motion around quartz sleeves.
Sterlizing Chamber
Quartz Sleeve
                           Typical sterilizers employ one to
                           twelve lamps per sterilizing chamber.
                              178

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where T is the fraction  transmitted,  a  is the absorption coefficient in
cm"1 at  2,537 A,  and  d is  the  depth in  cm.   Typically, a  very  high-
quality distilled  water will  have  an absorption coefficient  of  0.008,
where tap water would normally vary from 0.18 to 0.20.   Wastewaters pol-
ished  with  sand  filtration  should produce  absorption  coefficients  of
from 0.13 to  0.20, whereas septic  tank  effluents  may be as high as 0.5.
Currently, rule  of thumb requirements for UV  application  indicate that
turbidities should be less than  10  JTU  and color  less  than 15 mg/1.  (1
Jackson Turbidity Unit [JTU] is about equivalent to 1 Formazin Turbidity
Unit [FTU]).
The relationship between  UV  power and contact time  is  still  uncertain.
Empirical relationships have been used to  express  the  performance  of UV
equipment.  Currently^ the empirical  term, microwatt seconds  per square
centimeter (mw sec/cm2),  is used (50)(51).
The required contact time for a given exposure is dictated by the waste-
water  absorbance,  film  thickness,  and  the  pathogen  to be  destroyed.
Typical values of UV dosage for selected organisms appear in Table 6-25.


This  tabulation  indicates  that a wide  spectrum of organisms  are  about
equally sensitive to UV irradiation.  There are exceptions to this, how-
ever;  Bacillus spores  require  dosages in excess of 220,000  mw sec/cm2,
and protozoan as high as 300,000 mw sec/cm .
One characteristic trait of UV disinfection of water has been the photo-
reactivation  of  treated organisms  within  the wastewater.   Exposure  of
the  wastewater to  sunlight  following UV  disinfection  has  produced  as
much  as  1.5  log  increase  in  organisms  concentration.    This  phenomena
does  not  always  occur,  however,  and  recent  field tests  indicate  that
photoreactivation may not be of significant concern (52).
         6.5.3.4  Design
There  has  been  little  long-term  experience with wastewater UV disinfec-
tion  (2)(52)(53).   Therefore, firm  design criteria are  not  available.
One may draw  upon  water  supply disinfection criteria,  however,  for con-
servative design (50)(51).
                                    179

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                               TABLE 6-25

                    UV DOSAGE FOR SELECTED ORGANISMS


      Organi sm                        Dosage for 99% Kill  at a  = 0.0

                                                nw sec/cm^


   Shi gel la                                      4,000

   Salmonella                                    6,000

   Poliovirus                                    6,000

   IH Viral Form                                 8,000

   E. Coli                                       7,000

   Protozoan                                 180-300,000a

   Fecal Coliform                               23,000b
   a For 99.9% inactivation.

   b Field studies corrected to a = 0; 99.96% inactivation.
Wastewater should be pretreated to a quality such that turbidity is less
than 10 JTU and color  is  less  than 15  mg/1.  Intermittent sand filtered
effluent  quality  will  generally  not  exceed these limits  when properly
managed.   It  would  be  desirable to provide measurement  of UV transmit-
tance in  the  wastewater on  a continuous  basis  to ensure  that sufficient
UV power  reaches  the organism  to  be  treated.    Dosage values  should  be
conservative  until more data are  available.  Therefore,  a desired mini-
mum UV  dose of .16,000  mw sec/cnr or kw  sec/nr  should be applied  at all
points throughout the disinfection chamber.  A maximum depth of penetra-
tion should be  limited to about 2 in. (5  cm)  to allow for variation  in
wastewater absorption.    The  UV  lamps  should  be  enclosed in  a  quartz
glass sleeve  and  appropriate-automatic cleaning devices  should be pro-
vided.  A UV  intensity meter should be installed at a point of greatest
water depth from the UV tubes,  and  an  alarm provided to  alert the owner
when values fall below on acceptable level.
                                     180

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         6.5.3.5  Construction Features
Commercially available  UV  units sold primarily for water  supply  disin-
fection  are applicable  for onsite  wastewater disinfection.   Most  of
these units are  self-contained  and  employ  high-intensity  UV irradiation
over a thin film of water for short contact times.
The self-contained unit should be installed following the last treatment
process in  the  treatment sequence,  and  should be protected  from  dust,
excessive heat, and  freezing.   It should be accessible  for maintenance
and control.  As  described in the previous  section,  the unit should be
equipped with a cleaning  device  (manual  or automatic) and  an intensity
meter  that  is properly  calibrated.   Flow to  the unit  should  be  main-
tained relatively constant.  This  is often achieved  by means of a  pres-
sure compensated flow control  valve.
Some larger  UV  modules  are available that consist of  a  series of lamps
encased within quartz glass enclosures.   The module may be placed within
the flow stream such that all  water passes through the  module.  UV lamps
positioned over discharge weirs,  and  therefore out of  the  water,  are
also  available.   These  systems  are  not as  efficient as  flow through
units since only a  fraction of  the lamp  arc  intercepts the water.  Con-
trol of the water film over the weir plate (V-notch or  sharp crested)  is
difficult  to maintain unless  upstream  flows  are carefully  regulated.
Cleaning and metering devices are required for both of  these systems.
Depending on upstream processes and  the  UV  unit employed,  the UV system
may be  operated  on a continuous flow or intermittent  basis.   For small
flows,  self-contained  tubular units  and  intermittent flow  would  be
employed.   Influent  to  the  unit could  be pumped to the UV  system from a
holding tank.  In  order to  obtain  full-life expectancy of  the UV lamps,
they  should be  operated continuously regardless  of  flow  arrangement.
Where  UV modules  are  employed,   continuous  flow  through  the  contact
chamber may be more practical.
         6.5.3.6  Operation and Maintenance
Routine  operational  requirements include quartz glass  enclosure clean-
ing, lamp replacement, and  UV  intensity  meter  reading.   Since UV disin-
fection  does  not  produce  a  residual,  the only  monitoring required would
be periodic bacterial analyses by skilled technicians.  Periodic mainte-
nance of pumping  equipment  and controls, and cleaning of quartz jackets
during lamp replacement, would also be required.
                                   181

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Cleaning of quartz glass enclosures  1s  of  paramount Importance  since UV
transmittance is severely  impaired by the  accumulation  of  slimes  on  the
enclosures.   Cleaning  is required at least  3  to 4 times per year at a
minimum, and  more  often  for systems employing  intermittent  flow.    If
automatic wipers are employed,  the frequency of manual cleaning  may be
reduced to  twice per year.  Expected lives  of  lamps  are  variable, nor-
mally ranging from 7,000 to 12,500 hours.  It is good practice,  however,
to replace lamps every 10 months, or when metered UV intensity falls  be-
low acceptable  values.   A complete cleaning of  quartz  glass  enclosures
with  alcohol  is required  during  lamp  replacement.   Based on  limited
operational experience, it is estimated  that 10  to 12 man-hr  per  yr  are
required  to maintain  the UV  system.    Power  requirements  for  the  UV
system for design flow rates up to 4 gpm (0.25  I/ sec) are approximately
1.5 kWh/day.
     6.5.4  Ozonation


         6.5.4.1  Description


Ozone,  Oo,  a pale blue  gas with pungent odor, is  a  powerful  oxidizing
agent.   It is only  slightly  soluble in water, depending  upon  tempera-
ture, and is highly unstable.  Because of its instability,  ozone must be
generated on site.


Ozone  is  produced by the  dissociation  of molecular oxygen  into  atomic
oxygen with  subsequent formation of  Oo.   It  is produced commercially by
passing an oxygen-containing feed gas between electrodes separated by an
insulating material  (54)(55).   In  the presence of  a high-voltage,  high-
frequency  discharge, ozone  is  generated from oxygen  in  the  electrode
gap.
Ozone  is a  powerful  disinfectant  against  virus,  protozoan cysts,  and
vegetative bacteria  (54)(55)(56)(57).   It is normally sparged  into  the
water to be treated by means of a variety of mixing and contact devices.
Because  of its  great reactivity,  ozone will interact  with  a variety of
materials in  the  water,  resulting in an  ozone  demand.   The short half-
life of ozone also results in the rapid disappearance of  an ozone resid-
ual in the treated water.
         6.5.4.2  Applicability
Ozone is currently used to disinfect water supplies in the United States
and  Europe,  and is  considered  an excellent  candidate  as an  alternate
wastewater  disinfectant (54)(55)(56)(57).   The major  drawback to  its
                                   182

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widespread use to date has  been  the  expense  of generation.   There is no
documented long-term field experience with ozone disinfection onsite.


Since ozone is a highly  corrosive  and toxic  gas,  its generation and use
onsite  must  be  carefully  monitored  and controlled.    The  generator
requires  an  appropriate  power  source,  and must  be properly  housed to
protect it  from  the elements.   Wastewater characteristics will  have an
impact  on  ozone  disinfectant efficiency  and  must be considered  in  the
evaluation of this process.
Data  on  the  effectiveness  of  ozone  residuals  against pathogens  are
scant.  Employing the  same  criteria  as  used  for halogens,  ozone appears
to be  more  effective against virus and amoebic  cysts  than  the halogens
(Table 6-23).
The  literature  indicates that ozone action  is  not  appreciably affected
by pH variations between 5.0  and 8.0  (58).   Turbidity above values of 5
JTU  has  a  pronounced  effect upon ozone  dosage requirements,  however
(47)(58).   Limited field  experience  indicates that  ozone  requirements
may  approximately  double  with  a doubling of  turbidity  to  achieve
comparable destruction of organisms (47).


Currently, with  very limited  operating  data,  prescribed ozone  applied
dosages  recommended  for wastewater disinfection vary from  5 to  15 mg/1
depending upon contactor efficiencies and pathogen to be destroyed.
         6.5.4.3  Construction Features
The  ozone  disinfection  system  consists  of  the  ozone gas  generation
equipment,  a  contactor,  appropriate  pumping  capacity  to  the  contactor
and  controls.   There are two basic  types  of  generating equipment.   The
tube-type  unit  is  an  air-cooled  system  whereby  ozone  is  generated
between  steel  electrode plates  faced with ceramic.   Oxygen-containing
feed  gas may  be pure oxygen,  oxygen-enriched air, or air.  The  gas is
cleaned,  usually  through  cartride-type inpingement  filters,  and  com-
pressed  to  about 10  psi.   The compressed gas  is subsequently cooled and
then  dried  prior to being reacted in the ozone contacting chamber.  Dry-
ing  is essential to prevent serious corrosion  problems within the gener-
ator.
The  generated  ozone-enriched  air is intimately mixed with wastewater in
a  contacting  device.   Ozone  contactors  include  simple  bubble diffusers
in  an  open tank, packed columns, and  positive pressure injection (PPI)
devices.   Detention times within these  systems range  from  8-15  min in
                                     183

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the bubble diffuser units to 10-30 sec in packed columns and PPI  systems
(59)(60).   Limited data  are currently  available on  long-term  use  of
these contactor  devices  for onsite systems.   There are  relatively  few
field-tested, small-capacity systems commercially available.


         6.5.4.4  Operation and Maintenance
The ozone  disinfection system  is a  complex series  of mechanical  and
electrical  units, requiring  substantial maintenance,  and  is  susceptible
to a  variety  of malfunctions.   Since data on long-term  experience  are
relatively unavailable,  it  is  not possible  to  assess maintenance  re-
quirements on  air cleaning  equipment,  compressors,  cooling and  drying
equipment, and contactors.  It is estimated that  8 to 10 kWh/lb of ozone
generated will  be required (54).  Monitoring requirements  are similar to
those for  UV  disinfection, including occasional   bacterial analyses  and
routine ozone monitoring.
6.6  Nutrient Removal


     6.6.1  Introduction


         6.6.1.1  Objectives
Nitrogen and  phosphorus  may have  to  be removed from wastewaters  under
certain circumstances.   Both are plant  nutrients and may  cause  undesir-
able  growths  of plants  in  lakes  and  impoundments.   Nitrogen may  also
create problems as a toxicant to fish (free ammonia), as well  as  to  ani-
mals and humans (nitrates).   In addition, the presence  of reduced nitro-
gen may create a significant oxygen demand in surface waters.
Nitrogen may  be found in  domestic  wastewaters as organic  nitrogen,  as
ammonium,  or  in the  oxidized  form as nitrite  and  nitrate.   The  usual
forms of phosphorus in domestic wastewater include orthophosphate,  poly-
phosphate, pyrophosphate,  and  organic  phosphate.   Sources  of wastewater
nitrogen and phosphorus from the home are presented in Table 4-4.
The removal or  transformation of  nitrogen  and  phosphorus  in  wastewaters
has been  the  subject of  intensive  research and demonstration  over  the
past  15  to 20 yr.   Excellent  reviews of the status of these  treatment
processes  can  be  found  in  the  literature  (61)(62).   As discussed  in
Chapter  7, the  soil  may also  serve  to  remove  and/or  transform  the
nitrogen and phosphorus in wastewaters percolating through them.
                                    184

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The  treatment  objective  for  nitrogen and  phosphorus in  wastewater  is
dependent upon  the  ultimate means of  disposal.   Surface  water  quality
objectives  may  require  limitations  of  total   phosphate,  organic  and
ammonia  nitrogen,   and/or  total  nitrogen.   Subsurface  water  quality
objectives  are  less well  developed,  but may restrict nitrate-nitrogen
and/or total phosphate.
         6.6.1.2  Application of Nutrient Removal  Processes to Onsite
                  Treatment
There are  a  number of  nutrient  removal  processes applicable  to onsite
wastewater treatment, but there are very little  data  on long-term field
applications of  these  systems.   In-house  wastewater  management through
segregation  and  household  product  selection  appears  to  be  the  most
practical and cost-effective method  for  nitrogen and  phosphorus control
onsite.   Septic  tanks  may remove a portion of these  nutrients as flot-
able  and settleable solids.   Other  applicable  chemical,  physical,  or
biological  processes may  also be employed to  achieve  a  given level  of
nutrient removal.    Although  these supplemental  processes may  be  very
effective  in  removing  nutrients, they  are normally complex and energy
and labor intensive.
Since  the  state-of-the-art  application  of onsite  nutrient removal  is
limited, the  discussion  that follows  is  brief.   Processes  that  may  be
successful   for onsite application  are described.   Acceptable  design,
construction, and operation data are presented where they are available.
     6.6.2  Nitrogen Removal


         6.6.2.1  Description
Table 6-26  outlines  the potential  onsite nitrogen control  options.   In
many instances, these options also achieve other treatment objectives as
well,  and  should  be evaluated  as  to  their  overall  performance.   The
removal or  transformation  of  nitrogen  within  the soil  absorption system
is described fully in Chapter 7.
         6.6.2.2  In-House Segregation
Chapter  4  provides a  detailed description of  the  household wastewater
characteristics and sources of these wastewaters.  Between 78 and 90% of
the nitrogen in the wastewater discharged from the home is from toilets.
Separation of toilet wastewaters would result in average nitrogen levels
                                   185

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                                                   TABLE 6-26

                                  POTENTIAL ONSITE NITROGEN CONTROL OPTIONS*
         Option
  Description
    Effectiveness
       Comments
  Onsite
Techno! ogy
  Status
oo
cr>
      In-House
      Segregation
     Biological
     Ni tri f i cati on
     Biological
     Denitrification
      Ion  Exchange
Separate toilet
wastes from other
wastewater

Granular Filters
                        Aerobic package
                        plants
Anaerobi c
processes
f ol 1 owi ng
nitrification

Cationic
exchange-NH4

Anionic
exchange-N03
78-90% removal  of N
in blackwater
>90% conversion to
ni trate

85-95% conversion to
nitrate
80-95% removal of N
>99% removal of
or
Management of residue
requi red
Achieves high level of
BOD and solids removal

May achieve good levels
of BOD and solids
removal; labor/energy
i ntensi ve; resi due
management

Requires carbon source;
labor intensive; high
capital cost
   Good



   Good


   Good
 Tentati ve
Very high operation costs     Tentative
      a  Not  including  the  soil absorption  system—see Chapter 7.

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of about  0.004  Ib/cap/day (1.9 mg/cap/day)  or  17 mg/1  as N  in  the re-
maining graywater (Tables 4-4 and 4-5).   Chapter 5 describes  the process
features,  the  performance,  and  the operation  and maintenance  of  low-
water  carriage  and  waterless toilet  systems.   The  resultant residuals
from toilet segregation,  whether  they be  ash, compost,  chemical  sludge,
or  blackwater,  must  be considered in this  treatment strategy.   A  dis-
cussion of residuals disposal is presented in Chapter 9.


The success of this method of nitrogen removal  is dependent  upon appro-
priate management of  the  in-house segregation fixtures  and the disposal
of the residues  from  them.   These devices must be considered a  part of
the treatment system  when developing  appropriate  authority for institu-
tional  control.
         6.6.2.3  Biological Processes


Nitrogen  undergoes  a variety  of biochemical  transformations  depending
upon  its  form  and the environmental conditions  (61).   Organic nitrogen
in  domestic  wastewaters readily  undergoes  decomposition to  ammonia  in
either  aerobic  or anaerobic conditions.   In an aerobic  environment,  a
select  group of  bacteria  oxidize  ammonia  to  nitrite and  ultimately
nitrate.   Nitrates  may  be reduced by a  variety of organisms to various
nitrogen  gas  under  anaerobic conditions.  Depending  upon  the treatment
objectives, one or several of these processes may be employed to achieve
the desired end product.


             a.  Applicability
A  number  of  biological  processes  for nitrogen conversion are applicable
to  onsite treatment.   Domestic  wastewater  characteristics  should  not
limit  application  of these processes,  provided  the nitrogen  is  in  the
appropriate  form  for conversion.   Since biological processes  are tem-
perature-sensitive, such systems should be covered and insulated in cold
climates.  Covering also contains odors, should problems occur.
             b.  Process Performance
Although data are sketchy, about 2 to 10% of the total nitrogen from the
home may be  removed  in  the septic  tank  with septage  (63)(64).  Approxi-
mately  65  to 75% of  the  total  nitrogen in septic  tank  effluents  is in
the  ammonia-nitrogen  form, indicating a significant level  of decomposi-
tion of organic nitrogen (2).
                                  187

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Nitrification of  septic  tank effluents occurs  readily  within  intermit-
tent sand  filters (see Section 6.3).   Field experience  indicates  that
intermittent sand  filters  loaded  up to 5  gpd/ft2 (0.02  orr/nr/d),  and
properly maintained to avoid excessive ponding  (and  concomitant  anaero-
bic conditions), converts up to 99%  of the  influent  ammonia  to nitrate-
nitrogen  (2).   Aerobic biological  package  plants also provide a  high
degree  of  nitrification,  provided solids retention  times are long  and
sufficient oxygen is available  (see Section  6.6).


The biological  denitrification (nitrates to  nitrogen  gases)  of  waste-
water follows a nitrification  step (61).  There has  been  little  experi-
ence with  long-term  field  performance of  onsite denitrification  pro-
cesses.   Ideally,  total  nitrogen removal  in  excess of  90%  should  be
achievable, if the system is properly operated and maintained (61).


             c.  Design and Construction  Features
Septic Tanks:  There are no septic tank design requirements specifically
established  to  enhance  high levels of  nitrogen  removal.   Designs  that
provide excellent solid-liquid separation ensure lower concentrations of
nitrogen associated with suspended solids.


Nitrification:   Biological  nitrification is achieved by a  select group
of aerobic microorganisms referred to as  nitrifiers  (61).   These organ-
isms  are  relatively  slow-growing  and  more  sensitive to  environmental
conditions than  the broad  range  of  microorganisms found  in  biological
wastewater treatment  processes.   The  rate of growth  of  n-itrifiers  (and
thus  the  rate of nitrification) is dependent upon a number  of  parame-
ters,  including temperature,  dissolved oxygen, pH,  and certain  toxi-
cants.   The  design and  operating  parameter used to  reflect  the growth
rates of  nitrifiers is  the  solids  retention  time (SRT).   Details of the
impact of temperature, dissolved oxygen, pH, and toxicants  on  design SRT
values  for  nitrification systems  are  outlined  in  reference  (61).   In
brief, biological nitrification systems  are  designed  with  SRT values in
excess of 10 days;  dissolved oxygen concentrations should  be in excess
of 2.0 mg/1;  and pH values  should  range between 6.5 and 8.5.   Toxicants
known to  be troublesome are discussed in reference (61).
Details of the  design  and  construction  of intermittent  sand  filters  and
aerobic package plants are found in Sections 6.3  and 6.4.   In general,
designs normally  employed  for onsite application  of these processes  to
remove BOD and  solids are sufficient to encourage nitrification as well.
Denitrification:  Biological denitrification is carried out under anoxic
conditions  in  the  presence of facultative, heterotrophic microorganisms
                                    188

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which convert  nitrate  to nitrogen gases  (61).   Numerous microorganisms
are capable of  carrying  out this process, provided  there  is  an organic
carbon source available.   These organisms are less sensitive to environ-
mental conditions  than the nitrifiers, but the  process  is temperature-
dependent.  Process  design  and  operational  details for conventional  de-
nitrification processes are discussed in reference (61).


Design and operational  experience with onsite biological  denitrification
systems is limited at this  time (2)(65)(66).   Several  systems have been
suggested for  onsite application, two  of which are shown  in Figure 6-
18.   One  employs a  packed  bed  containing approximately 3/8-in.  (1-cm)
stone that  receives, on  a  batch basis,  effluent from  a  nitrification
process.  The  nitrified  wastewater flows to a  dosing  tank, where  it is
held  until a  predetermined  volume is obtained.   Methanol  (or other or-
ganic carbon  source) is  then added  to provide a  C:N  ratio of approxi-
mately  3:1.   After  approximately 15 min,  the wastewater is  pumped up
through the anoxic packed stone bed.   Effluent flows from the  top of the
bed.   Liquid  retention times in  the packed bed  (based  on void volume)
varying from  12 to  24 hours  have been employed  with  good results (2).
Pumping may  be  provided by  a  1/3-hp  submersible  pump  actuated by  a
switch float within  the  sump.   A small  chemical  feed pump  controlled by
a  timer  switch may  be  used  to feed the  organic carbon  source  to  the
sump.  A  30% methanol solution  may be used as the carbon source.  Other
organic  carbon  sources  include  septic  tank  effluent,  graywater,  and
molasses.   Metering of organic carbon source to the nitrified  wastewater
requires  substantial  control to ensure a proper C:N ratio.   Insufficient
carbon results in decreased denitrification rates, whereas  excess carbon
contributes to  the final effluent BOD  (61).   The use of  an  easily  ob-
tainable,  slowly  decomposable,  solid carbon  source could also  be con-
sidered.  Peat,  forest litter,  straw,  and paper mill sludges, for exam-
ple,  could be  incorporated  as a  portion  of  the  upflow filter.   Control
of the denitrification process using these solid carbon sources would be
difficult.
Another onsite  nitrification-denitrification  system  that has  been field
tested employs  a  soil  leach field (66)  (Figure  6-18).   Septic  tank  ef-
fluent is distributed  to  a  standard  soil  absorption  field.   An  imperme-
able shield of fiberglass is placed approximately 5 ft (1.5  m) below  the
distribution line.  The location of this collector should be deep enough
to ensure complete nitrification within the overlying unsaturated soil.
The  nitrified  wastewater is collected on  the  sloped fiberglass shield,
and directed to a 24-in.  (61-cm) deep bed of pea gravel  contained within
a  plastic  liner (denitrifying  reactor).   The gravel bed is  sized deep
enough to  provide a hydraulic  detention  time of approximately  10 days
(based on  void  volume).   Methanol or  other  energy source is  metered to
the  gravel  bed through  a  series  of distributors.    The gravel  bed  is
vented with  vertical  pipes to  allow escape of  nitrogen gas  evolved in
the  process.    Short-term experience  with  this  system  has  been  good.
Total nitrogen  concentrations  of less than 1 mg/l-N  were achievable in
                                   189

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                             FIGURE 6-18

                   ONSITE  DENITRIFICATION SYSTEMS
Effluent
             a a . 
-------
effluent samples during summer months.   Higher values (5-10 mg/l-N)  were
observed during the colder winter months.


Although no  studies have  been  reported  in the  literature for  onsite
applications,  intermittent  or  cycled  extended  aeration  processes  are
potentially promising  (61)(67)  for  the  nitrification-denitrification of
wastewater.   This  process  makes use of  existing proprietary  extended
aeration package plants where aeration  is  cycled to provide both aerobic
and anoxic environments.   In this mode of  operation,  sufficient  solids
retention time  (SRT) is  provided to insure nitrification,  and  a  suffi-
cient period  of anoxic  holding  is  provided to  insure  denitrification.
The biomass serves  as  the energy source for denitrification.   The cycle
times vary dependent on  temperature and wastewater characteristics.   A
typical  cycle, using a SRT  of  20 days,  aerates 180 min and holds  anoxic
for 90 min (67).  Nitrogen removals in  excess of 50% are attainable with
this system  (2)(67).   Operation of the cyclic  aeration  system  requires
substantial supervision for a period of time until  proper sequences have
been selected.
             d.  Operation and Maintenance
Nitrification  Systems:     Operation  and  maintenance  requirements  to
achieve  nitrification  in  either  intermittent sand  filters or  aerobic
package  units  are not  significantly  different from those  discussed  in
Sections 6.3 and  6.4.   In both systems,  the  process  must be maintained
in an aerobic condition at all  times to ensure effective nitrification.
Denitrification  Systems;    Operation and  maintenance requirements  for
denitrification  systems  are  normally  complex and  require  semi-skilled
labor  for proper performance.   In  addition  to routine maintenance  of
pumping systems, mixers, and timer controls, the addition and balance  of
a carbon  source is required.
Routine analyses of nitrogen compounds and biological  solids is also im-
portant.   Rough  estimates for semi-skilled labor for maintenance  of an
onsite  denitrification  system varies from  15  to 30 man-hr per yr.   If
methanol is used as a carbon  source,  it is estimated  that from 33 to 55
Ib/yr  (15  to 25 kg/yr)  are  required for  a  family  of four.   Power re-
quirements for methanol  feed and pumping are about 15 to 25 kWh/yr.
         6.6.2.4  Ion Exchange


 Ion exchange  is  a  process  whereby ions of a given species are displaced
 from  an  insoluble  exchange material  by ions of  a  different  species in
                                   191

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solution.  It can be  used  to  remove either ammonium or nitrate nitrogen
from wastewaters.   This process has  been employed in  full-scale  water
and  wastewater  treatment  plants  for several  years   (61)(67)(68),  but
there is no  long-term experience with the process  for nitrogen  removal
in onsite applications.
Nitrogen removal  by  ion exchange has potential  for  onsite application,
since it is very effective and is simple to operate.  Unfortunately, per-
iodic replacement of the exchange media is expensive  and regeneration of
the media  onsite does not  appear  to be  practical at this time.   Site
conditions and climatological factors should not limit its application.
             a.  Ammonia Removal
Ammonia removal may be achieved by employing the naturally occurring ex-
change media, clinoptilolite, which has a high affinity for the ammonium
ion (61).   Laboratory experience has shown that  packed  columns of cli-
noptilolite resin  (20 x 40  mesh)  will  effectively remove  ammonium ion
from septic tank effluent without serious clogging problems (2).  Regen-
eration with 5% NaCl  was successful  over numerous trials.   Breakthrough
exchange capacity of  this  resin  was  found to  be about 0.4 meq NH4 /gram
in  hard  water at  application  rates of  10 bed volumes  per hr.   (This
value will vary, increasing  with  decreased hardness.)   Very large quan-
tities of  resin are  required  to treat  household  wastewaters  (approxi-
mately 10 Ib per day).  Treatment of segregated graywaters substantially
lower in ammonium concentration decreases the amount of resin needed.
This process  employs  a packed column or bed  of  the  exchange resin fol-
lowing a septic tank.   The  waste  is  pumped from  a sump to the column in
an upflow or down flow mode on a periodic basis.  Once the resin has been
exhausted, it  is  removed  and replaced by  fresh  material.   Regeneration
occurs offsite.
Operation and  maintenance of this  process  requires  routine maintenance
of the  pump  and occasional  monitoring of ammonium levels  from the pro-
cess.   Replacement of  exhausted  resin  is  dictated  by wastewater charac-
teristics and  bed  volume.   There are  insufficient data  at this time to
delineate labor, power, and resin requirements.
             b.  Nitrate Removal
Nitrate removal from water may be achieved by the use of strong and weak
base ion exchange resins (68)(69).  There are very little data available
                                    192

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on  long-term  performance of  these nitrate  removal  systems for  waste-
water.  Numerous anions in water compete with nitrate for sites on these
resins; therefore, tests  on  the specific wastewater to  be  treated need
to be performed.


This process has potential for onsite application,  where it  would  follow
a  nitrification process  such  as intermittent  sand filters.   As  with
ammonia resins, regeneration is performed off site.
There is insufficient information on nitrate exchange to provide design,
construction, operation, and maintenance data at this time.


     6.6.3  Phosphorus Removal


         6.6.3.1  Description
Table 6-27  outlines the  most  likely treatment processes  available  for
onsite removal  of phosphorus in wastewater.   In many  instances,  these
processes will also achieve other treatment objectives as well,  and must
be evaluated as to their overall  performance.
         6.6.3.2  In-House Processes
Review of  Chapter 4 indicates  that  the major sources of  phosphorus  in
the  home  are laundry,  dishwashing,  and toilet wastewaters.   Contribu-
tions of phosphorus in the home could be reduced from approximately 4  to
2 gm/cap/day through the use of 0.5% phosphate detergents.


Segregation  of  toilet wastewaters   (blackwater)  from household  waste-
waters reduces phosphorus levels  to  approximately 2.8  gm/cap/day  in the
graywater  stream.   Chapter  4  describes  the process  features,  perfor-
mance, and operation and maintenance of low-water carriage  and waterless
toilet systems that would be employed  for this  segregation.   Note that
the  resultant residues  from  these toilet systems must be  considered  in
this treatment strategy.  A  discussion  of residuals  disposal  appears  in
Chapter 9.
As with any in-house measure to reduce pollutional  loads, the success of
the  process  is dependent upon owner commitment  and  appropriate  manage-
ment of the alternative plumbing equipment.
                                   193

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                                              TABLE 6-27

                              POTENTIAL ONSITE PHOSPHORUS REMOVAL OPTIONS
   Opti on
  Descrlpti on
Effectiveness
      Comments
  Onsi te
Technology
  Status
In-House
Segregation
Chemical
Precipitation:
  Iron, Calcium
  and Aluminum
  Salts
Laundry detergent
substi tuti on

Separate toilet
wastes from other
wastewaters
Dosing prior to
or following
septic tanks
Sorpti on
Processes:
  Calcite or Iron   Beds or columns
  Alumi na
Beds or columns
     50% P
   removal

    20-40% P
   removal
 Up to 90% P
   removal
 Up to 90% P
   removal

   90-99% P
   removal
0.5% P detergents
available

Management of residues
required; achieves
significant BOD, SS
reduction

Increases quantity of
sludge; labor intensive
                                            Replacement required
High cost for material,
labor intensive
Excellent
                                                                                               Good
  Fair
Tentati ve


Tentati ve

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         6.6.3.3  Chemical  Precipitation


Phosphorus in wastewater may be rendered insoluble by  a  selected  number
of metal  salts,  including  aluminum, calcium,  and  iron (62).   Although
the  reactions  are complex, the  net result  is  the precipitation of  an
insoluble  complex that  contains  phosphate.   Phosphorus  precipitation
methods  normally  include   the  addition  of  the  chemical,  high-speed
mixing, and slow agitation  followed by sedimentation.
There  has  been little long-term  experience  with phosphorus removal  of
wastewaters onsite (2)(70).  Precipitation of  phosphates  is  less  easily
accomplished for  polyphosphates  and organic phosphorus than for  ortho-
phosphate.   Therefore,  precipitation within the  septic tanks,  although
simpler  to  manage,  may  not  remove a  significant portion of the  phos-
phate, which is in the poly and organic form.  Substantial  hydrolysis of
these  forms may occur in  the septic  tank,  however,  producing the  ortho-
form.  Thus, precipitation following the septic  tank  may  achieve  higher
overall removals of total phosphorus.
Performance  is  dependent  on  the point  of chemical addition,  chemical
dosage,  wastewater  characteristics, and  coagulation and  sedimentation
facilities.   Dose-performance  relationships  must  be  obtained  through
experimentation, but  one should  expect  phosphorus removals between  75
and 90%.   Improvement in this performance may be  achieved if  intermit-
tent sand  filters follow the  precipitation/sedimentation  process.   Side
benefits are achieved with the addition of the precipitating chemicals.
Suspended  and  colloidal  BOD  and  solids will  be carried down with  the
precipitate, producing a higher quality effluent than would otherwise be
expected.


Chemical  precipitation  of wastewaters  generates  more  sludge than  do
conventional systems  due to both  the insoluble end product of  the added
chemical and the excess suspended and colloidal  matter  carried  down with
it.  Estimates  of  this increased quantity are very  crude  at this time,
but may range from 200 to 300%  by  weight in excess of  the  sludge nor-
mally produced from a septic tank system.
             a.  Process Features
The  chemicals  most often used for phosphate  precipitation  are  aluminum
and  iron compounds.   Calcium  salts may  also  be  used,  but require pH ad-
justment prior to  final  discharge to  the  environment.   Aluminum is gen-
erally added as alum  (A^SO^'n H20).   Ferric  chloride and ferric sulfate
are  the most commonly used iron salts.
                                   195

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Anionic polyelectrolytes  can be  used  in combination with  the aluminum
and iron salts to improve settling, but may overly complicate the onsite
treatment system.


The required  dosages  of aluminum  and  iron compounds are  generally  re-
ported as molar ratios of trivalent metal  salt to phosphate phosphorus.
Molar ratios  currently  used  in practice today  range  from  1.5:1  to 4:1,
depending upon  wastewater characteristics,  point of addition,  and  de-
sired phosphorus removal (20)(62).


Adding aluminum or  iron salts  to  the  raw wastewater prior to the septic
tank has the  advantage of using the existing septic tank for sedimenta-
tion (70).  Aluminum  or iron salts may be metered to the raw wastewater
with a chemical  feed pump activated by electrical  or mechanical impulse.
Mixing of the chemical with the wastewater is provided in the sewer line
to the septic tank.   The  quantity of  metal  salt added to the wastewater
is dependent  upon wastewater characteristics.   Since  the impulse to the
feed pump may come  from any of a  number of  household events,  it is not
possible  to   precisely  adjust  metal   dosage.    An  average dose  of salt
based on estimated phosphorus discharge is most practical.
Addition of iron or aluminum salts following the septic tank may also be
considered.   A  batch  feed  system  could be  employed whereby  a  preset
chemical dose is provided when the wastewater reaches a preset volume in
a holding tank.  Mixing may be provided by aeration or mechanical  mixer,
followed  by  a  period  of  quiescence.    Additional  raw wastewater  flow
would be  diverted  to a holding  tank  until  the precipitation-sedimenta-
tion cycle is  completed.   This  system may  be employed after the  septic
tank and preceding the intermittent sand filter.


The processes briefly described above represent a few of the many  chemi-
cal treatment  processes  that might be considered  for onsite treatment.
They may  be  designed and  constructed  to fit the  specific  needs  of the
site, or  purchased  as  a  proprietary  device.   Storage and  holding  of
chemicals must be considered in the design of these systems.  Details on
chemical  storage,  feeding,  piping,  and  control  systems  may  be  found
elsewhere  (20)(62).   Attention  must  be given  to  appropriate materials
selection,  since many  of  the  metal   salts employed  are   corrosive  in
liquid  form.


             b.  Operation and Maintenance
Every effort should be made  to  select equipment that is easily operated
and  maintained.    Nonetheless,   chemical  precipitation  systems  require
semi-skilled labor  to maintain chemical  feed  equipment,  mixers,  pumps,
                                    196

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and electronic or mechanical controls.   More  frequent pumping  of waste-
water sludge  or  septage is  also  required.   A rough  estimate  for semi-
skilled labor is 10 to 25 man-hr per yr depending upon the complexity of
the equipment.   Conservative  estimates  on sludge  accumulation  dictate
sludge  or  septage pumping  every  0.5  to 2 years  for an  average home.
Chemical requirements would vary widely,  but are  estimated to range from
22 to 66 Ib/yr Al  (10  to 30 kg/yr)  or 11 to 33 Ib/yr Fe (5 to  15 kg/yr)
for a family of four.
         6.6.3.4  Surface Chemical Processes
Surface chemical  processes,  which  include  ion exchange,  sorption,  and
crystal growth  reactions,  have  received  little application in  treatment
of municipal wastewaters,  but hold  promise  for onsite  application  (62).
These  types  of  processes are easy to control  and  operate; the effluent
quality is not influenced by fluctuations in influent concentration;  and
periods of disuse between applications should not affect subsequent per-
formance.  Phosphorus removal on selected anion exchange resins has been
demonstrated, but control  of the  process  due  to sulfate competition  for
resin sites has discouraged its application (71).   Phosphorus removal  by
sorption  in  columns  or beds of calcite or  other  high-calcium,  iron,  or
aluminum minerals is feasible;  but long-term experience with these  mate-
rials  has  been  lacking (2)(25)(72).   Many  of  these  naturally  occurring
materials  have  limited capacity to  remove phosphorus,  and  some investi-
gations  have demonstrated the development of  biological  slimes  that
reduce  the capacity of  the  mineral  to  adsorb phosphorus.  Table 6-28
lists  a range  of phosphorus adsorption capacities of  several  materials
that may be  considered.   The use  of locally available  calcium, iron,  or
aluminum  as naturally occurring  materials, or as wastewater  products
from industrial  processing,  may prove to be cost-effective; but trans-
port of these materials any distance normally rules out their widespread
application.     Incorporation   of  phosphate-sorbing   materials  within
intermittent sand filters is discussed more fully in  Section 6.3.5.


The use of alumina ^203), a plentiful  and naturally occurring material
for sorption of phosphorus, has been demonstrated in  laboratory studies,
but has not yet been  employed  in long-term field tests (75).   Alumina
has a  high affinity for phosphorus, and  may be regenerated with sodium
hydroxide.  Application of an alumina sorption process  is similar to  ion
exchange,  whereby a  column or bed would  be  serviced  by replacement on a
routine basis.   Costs for this  process are high.
6.7  Wastewater Segregation and Recycle Systems
Chapter 5  discusses  in  detail  in-house methods that may  be  employed to
modify the  quality of the  wastewater.   These  processes  are  an important
                                   197

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component  of  the  onsite treatment  system  as  they  remove  significant
quantities of pollutants from the  wastewater prior to further treatment
and/or disposal.
                               TABLE 6-28

              PHOSPHORUS ADSORPTION ESTIMATES FOR SELECTED
                    NATURAL MATERIALS (73)(74)(75)a
                Media                                  Adsorption
                                                  (mg P/100 gm media
   Acid Soil Outwash                                     10 - 35

   Calcereous Soil Outwash                                5-30

   Sandy Soils                                            2-20

   F-l Alumina (AleOa), 24-48 mesh                      700 - 1500
   a Based on maximum Langmuir isotherm values.
      6.7.1  Wastewater  Segregation


Among the wastewater  segregation components  which  significantly alter
wastewater  quality are the non-water  carriage toilets (Table 5-3), and
the  very low water flush  toilets  (Table  5-2)  with blackwater  contain-
ment.    Impacts of wastewater  modification  on  onsite disposal practices
are  outlined  in Table 5-9.
 The graywater resulting  from  toilet segregation practices normally re-
 quire  some treatment  prior  to disposal (Tables  4-4  and 4-5 -  "Basins,
 Sinks,  and Appliances").   Treatment methods  for  graywater  are similar to
 those  employed  for  household wastewaters (Sections  6.2 to  6.6 and Figure
 5-2),  but performance  data are lacking.
                                    198

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Residuals resulting  from the  treatment  or holding of  segregated waste
streams must  be  considered when evaluating  these  alternatives.  Details
of  the  characterization  and  disposal  of  these   residuals  appear  in
Chapter 9.
     6.7.2  Wastewater Recycle


In-house  wastewater  recycle systems  are  treatment  systems  employed to
remove specific pollutants  from one  or  more  wastewater streams in order
to meet  a specific water  use  objective (for example,  graywater may be
treated to a  quality  that is acceptable for  flushing  toilets, watering
lawns, etc.).  These systems are summarized in Table 5-6.
The impact of  recycle  systems on the quality  of  wastewater  to be ulti-
mately disposed is difficult to assess at this time owing to the absense
of long term experience with  these  systems.   It is likely that substan-
tial pollutant mass reduction will occur in addition to flow reduction.
As with  segregated systems, the  disposal  of residuals  from  these pro-
cesses must be considered in system evaluation.
6.8  References
 1.  Jones, E. E.  Septic Tank - Configuration versus Performance.  Pre-
     sented  at the  2nd Pacific  Northwest  On-Site  Wastewater  Disposal
     Short Course, University of Washington, Seattle, March 1978.

  2.  Small  Scale  Waste Management  Project,   University  of  Wisconsin,
     Madison.  Management of Small Waste  Flows.   EPA 600/2-78-173,  NTIS
     Report No. PB 286  560,  September 1978.  804  pp.

  3.  Weibel,  S.  R.,  C.  P.  Straub, and J. R.  Thoman.   Studies on House-
     hold Sewage Disposal Systems, Part I.  NTIS  Report No.  PB  217  671,
     Environmental Health Center, Cincinnati,  Ohio, 1949.  279 pp.

  4.  Salvato,  J.  A.   Experience  with  Subsurface  Sand  Filters.   Sewage
     and  Industrial Wastes, 27(8):909, 1955.

  5.  Bernhart,  A.  P.   Wastewater from Homes.    University  of  Toronto,
     Toronto,  Canada, 1967.

  6.  Laak,  R.   Wastewater Disposal  Systems in Unsewered  Areas.   Final
     Report   to   Connecticut   Research  Commission,  Civil  Engineering
     Department, University of Connecticut, Storrs, 1973.
                                  199

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  7.  Brandes,  M.    Characteristics  of Effluents  from  Separate  Septic
     Tanks Treating Gray and Black Waters from the Same House.  J. Water
     Pollut. Control Fed., 50:2547-2559, 1978.

  8.  Weibel,  S.  R.,  T.  W.  Bendixen,  and  J.  B.  Coulter.    Studies  on
     Household Sewage  Disposal  Systems, Part  III.   NTIS  Report  No.  PB
     217 415, Environmental  Health Center,  Cincinnati,  Ohio,  1954.   150
     pp.

  9.  Plews,  G.  D.    The  Adequacy   and  Uniformity  of  Regulations  for
     On-Site  Wastewater  Disposal  -  A  State  Viewpoint.   JJT;   National
     Conference on  Less  Costly Wastewater  Treatment Systems  for Small
     Communities.    EPA 600/9-79-010, NTIS Report No.  PB  293  254, April
     1977.  pp. 20-28.

10.  Manual  of  Septic  Tank  Practices.   NTIS  Report  No.  PB  216  240,
     Public Health Service, Washington, D.C., 1967.  92 pp.

11.  Baumann, E.  R., E.  E. Jones,  W.  M.  Jakubowski, and M. C. Notting-
     ham.   Septic  Tanks.  In:  Proceedings  of the Second National  Home
     Sewage  Treatment  Symposium,   Chicago,  Illinois,  December  1977.
     American Society  of Agricultural  Engineers,  St.  Joseph, Michigan,
     1978.  pp. 38-53.

12.  Weibel,  S.  R.   Septic  Tanks:    Studies  and Performance.   Agric.
     Eng., 36:188-191, 1955.

13.  Harris,  S. E.,  J. H. Reynolds,  D. W.  Hill,  D.  S.  Filip, and E.  J.
     Middlebrooks.   Intermittent  Sand Filtration  for  Upgrading Waste
     Stabilization Pond Effluents.  J.  Water Pollut. Control Fed. 49:83-
     102, 1977.

14.  Schwartz, W.  A.,  T.  W.  Bendixen,  and R. E. Thomas.  Project Report
     of Pilot Studies  on  the Use  of  Soils as Waste Treatment Media; In-
     house  Report.   Federal  Water Pollution Control  Agency, Cincinnati,
     Ohio, 1967.

15.  Metcalf, L.,  and H. P. Eddy.   American Sewerage Practice.  3rd ed.,
     Volume III.   McGraw-Hill, New York, 1935.  892 pp.

16.  Boyce, E.  Intermittent Sand Filters for Sewage.  Munic. Cty. Eng.,
     72:177-179,  1927.

17.  Recommended Standards for  Sewage  Works.   Great Lakes-Upper Missis-
     sippi  River  Board of State  Sanitary Engineers,  Albany,  New York,
     1960.  138 pp.

18.  Filtering Materials  for Sewage  Treatment Plants.   Manual  of Engi-
     neering  Practice  No.  13, American Society of  Civil  Engineers, New
     York, 1937.   40 pp.
                                    200

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19.  Salvato, J. A., Jr.  Experience With Subsurface Sand Filters.  Sew.
     Ind. Wastes, 27:909-916, 1955.

20.  Wastewater Treatment Plant Design.  Manual of Practice No. 8, Water
     Pollution Control Federation, Washington, D.C., 1977.  560 p.

21.  Clark, H. W. and  S.  Gage.   A Review of Twenty-One Years of Experi-
     ments upon  the  Purification  of  Sewage  at the Lawrence Experimental
     Station.   40th Annual   Report,  State  Board of  Health  of Massachu-
     setts, Wright E. Potter, Boston, Massachusetts, 1909.  291 pp.

22.  Brandes, M.  Effect of  Precipitation and Evapotranspiration on Fil-
     tering Efficiency  of Wastewater Disposal  Systems.   Publication No.
     W70, Ontario Ministry of Environment, Toronto, Canada, May 1970.

23.  Emerson,  D.  L., Jr.    Studies  on  Intermittent Sand  Filtration  of
     Sewage.   Florida  Engineering and  Industrial  Experimental  Station
     Bulletin  No.   9,   University of  Florida  College  of  Engineering,
     Gainesville, 1954.

24.  Mines,  J.,  and  R.  E.  Favreau.   Recirculating Sand  Filter:   An
     Alternative to  Traditional   Sewage  Absorption  Systems.   In:   Pro-
     ceedings  of the National  Home  Sewage  Disposal  Symposium, Chicago,
     Illinois, December 1974.    American Society of  Agricultural  Engi-
     neers, St. Joseph, Michigan,  1975.  pp. 130-136.

25.  Brandes,  M., N.  A. Chowdhry, and W. W.  Cheng.   Experimental Study
     on  Removal  of  Pollutants  From Domestic Sewage by Underdrained Soil
     Filters.   In:    Proceedings   of  the  National  Home  Sewage Disposal
     Symposium,  Chicago,  Illinois, December 1974.   American  Society of
     Agricultural Engineers, St.  Joseph, Michigan, 1975.  pp. 29-36.

26.  Teske,  M. G.    Recirculation -  An  Old Established  Concept Solves
     Same  Old  Established  Problems.   Presented at the  51st Annual  Con-
     ference of  the Water Pollution  Control  Federation,  Anaheim, Cali-
     fornia, 1978.
27.  Bowne, W. C.   Experience in Oregon With the Hines-Favreau Recircu-
     lating Sand  Filter.   Presented at  the  Northwest States Conference
     on Onsite Sewage Disposal,  1977.

28.  Chowdhry, N.  A.   Underdrained Filter  Systems  - Whitby Experiment
     Station.    Ministry   of  the   Environment  Interim  Report Part  2.
     Toronto, Canada, 1973.

29.  Kennedy, J.  C.   Performance of Anaerobic  Filters  and Septic Tanks
     Applied  to  the Treatment of Residential  Wastewater.   M.S. Thesis,
     University of Washington, Seattle,  1979.
                                   201

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30.  Bernhart, A.  P.    Wastewater From Homes.   University  of  Toronto,
     Toronto, Canada,  1967.

31.  Voell, A. T.  and R.  A.  Vance.    Home  Aerobic  Wastewater Treatment
     Systems - Experience in a Rural  County.  Presented at the Ohio Home
     Sewage Disposal Conference, Ohio State University, Columbus, 1974.

32.  Tipton, D. W.  Experiences of a County Health Department with Indi-
     vidual Aerobic Sewage Treatment  Systems.   Jefferson  County Health
     Department,  Lakewood, Colorado, 1975.

33.  Brewer,  W.  S.,  J.  Lucas, And  G. Prascak.   An Evaluation  of  the
     Performance of Household Aerobic Sewage Treatment  Units.   Journal
     of Environmental  Health, 41:82-85, 1978.

34.  Glasser, M.  B.  Garrett  County  Home  Aeration  Wastewater Treatment
     Project.  Bureau of Sanitary Engineering, Maryland State Department
     of Health and Mental Hygiene, Baltimore, 1974.

35.  Hutzler, N. J.,  L.  E.  Waldorf,  and J.  Fancy.  Performance of Aero-
     bic Treatment  Units.   In:   Proceedings of  the  Second National Home
     Sewage  Treatment  Symposium,  Chicago,  Illinois,  December  1977.
     American Society  of Agricultural Engineers, St.  Joseph, Michigan,
     1978.  pp. 149-163.

36.  Operation of  Wastewater Treatment Plants.    Manual  of Practice  No.
     11, Water Pollution  Control  Federation,  Washington,  D.C.,  1976.
     547 pp.

37.  Tsugita, R. A.,  D.  C.  W.  Decoite, and L, Russell.   Process Control
     Manual  for  Aerobic  Biological   Wastewater  Treatment  Facilities.
     EPA 430/9-77-006,  NTIS Report No. PB  279  474,  James  M. Montgomery
     Inc.,  1977.   335 pp.

38.  Process  Design Manual,  Wastewater Treatment Facilities for Sewered
     Small  Communities.  EPA-625/1-77-009,  U.S.  Environmental Protection
     Agency, Cincinnati, Ohio, 1977.

39.  Craun, C. F.  Waterborne Disease - A Status Report Emphasizing Out-
     breaks in Ground Water Systems.  Ground Water,  17:183-191,  1979.

40.  Craun, C. F.  Disease Outbreaks Caused by Drinking Water.  J. Water
     Pollut. Control Fed., 50:1362-1375, 1978.

41.  Jakubowski,  W.,  and J. C.  Hoff,  eds.    Waterborne  Transmission  of
     Giardiasis.    EPA 600/9-79-001,  NTIS  Report  No. PB 299  265,  U.  S.
     Environmental  Protection Agency, Health Effects Research  Labora-
     tory,  Cincinnati, Ohio, June 1979.  306 pp.

42.  Berg,  G., ed.  Transmission  of  Viruses by  the Water Route.  Wiley,
     New York, 1967.  502 pp.
                                   202

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43.  Chang, S. L.  Modern Concept of Disinfection.  J. Sanit. Eng. Div.,
     Am. Soc. Civil Eng., 97:689-707, 1971.

44.  White, G. C.  Handbook of  Chlorination.   Van Nostrand Reinhold, New
     York, 1972.   751 pp.

45.  Morris, J.  C.  Chlorination  and  Disinfection:    State  of  the Art.
     J. Am. Water Works Assoc., 63:769-774, 1971.

46.  McKee, J. E. Report on the Disinfection of Seattle Sewerage.  Cali-
     fornia Institute of Technology, Pasadena, California, April 1957.

47.  Budde, P. E., P. Nehm, and W. C. Boyle.  Alternatives to Wastewater
     Disinfection.  J. Water Pollut. Control Fed., 49:2144-2156, 1977.

48.  Black,  A.  P.   Better  Tools  for  Treatment.   J.  Am.  Water Works
     Assoc., 58:137-146, 1966.

49.  Baker,  R.  J.   Characteristics of Chlorine  Compounds.    J.  Water
     Pollut. Control  Fed., 41:482-485,  1969.

50.  Jepson, J.  D.   Disinfection  of Water  Supplies by Ultraviolet Irra-
     diation.  Water Treat. Exam., 22:175-193, 1973.

51.  Huff, C. B., H.  F. Smith, W. D. Boring, and N. A. Clarke.  Study of
     Ultraviolet  Disinfection  of Water  and Factors  in  Treatment Effi-
     ciency.  Pub. Health Rep., 80:695,705, 1965.

52.  Scheible, 0.  K.,  G.  Binkowski, and  T.  J.  Mulligan.    Full  Scale
     Evaluation  of  Ultraviolet  Disinfection  of  a Secondary  Effluent.
     In:  Progress in Wastewater Disinfection Technology,  EPA 600/9-79-
     UT8,  NTIS  Report No. PB  299  338,  Municipal  Environmental  Research
     Laboratoty, Cincinnati, Ohio, 1979.  pp. 117-125.

53.  Kreissl, J. F.,  and  J.  M. Cohen.   Treatment Capability of a Physi-
     cal Chemical Package Plant.  Water Res., 7:895-909, 1973.

54.  Rosen,  H.  M.    Ozone  Generation and  Its  Economical  Application in
     Wastewater Treatment.  Water Sew.  Works, 119:114-120, 1972.

55.  Johansen, R.  P.,  and  D.  W. Terry.   Comparison  of  Air and Oxygen
     Recycle  Ozonation  Systems.   Presented at the Symposium on Advanced
     Ozone Technology, Toronto, Canada, November 1977.

56.  Majumdar, S.  B.,  and 0.  0.  Sproul.  Technical and Economic Aspects
     of Water and  Wastewater Ozonation:  A Critical Review.  Water Res.,
     8:253-260, 1974.

57.  McCarthy, J. J., and C. H. Smith.  A  Review of Ozone and Its Appli-
     cation  to  Domestic  Wastewater Treatment.    J.  Am.   Water Works
     Assoc., 66:718-725, 1974.
                                   203

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58.  Poynter, S. F., J.  S.  Slade,  and H.  H.  Jones.  The Disinfection of
     Water  with Special  Reference  to Viruses.    Water Treat.  Exam.,
     22:194-208, 1973.

59.  Scaccia, C.,  and  H.  M.  Rosen.    Ozone  Contacting:   What  is  the
     Answer?  Presented at the Symposium on  Advanced  Ozone Technology,
     International  Ozone Institute, Toronto, Canada, November 1977.

60.  Venosa,  A.  D.,  M. C.  Meckes,  E.  J.  Opatken,  and  J.  W.  Evans.
     Comparative Efficiencies  of  Ozone  Utilization  and  Microorganism
     Reduction  in   Different   Ozone  Contactors.    In:   Progress   in
     Wastewater Disinfection Technology,  EPA 600/9-79^018,  NTIS  Report
     No. PB 299 338, MERL,  Cincinnati, Ohio,  1979.  pp.  141-161.

61.  Process  Design Manual  for Nitrogen Control.   EPA  625/1-75-007,
     United   States  Environmental   Protection   Agency,   Center   for
     Environmental  Research Information, Cincinnati, Ohio,  October 1975.
     434 pp.

62.  Process  Design  Manual  for Phosphorus  Removal.  EPA  625/1-76-001,
     United   States  Environmental   Protection   Agency,   Center   for
     Environmental   Research  Information,  Cincinnati,  Ohio,  April  1976.

63.  Brandes, M.   Accumulation Rate  and  Characteristics of Septic Tank
     Sludge  and Septage.   J.  Water  Pollut. Control Fed., 50:936-943,
     1978.

64.  Laak, R.,  and  F. J. Crates.   Sewage  Treatment by Septic Tank.  In;
     Proceedings of the Second Home Sewage Treatment Symposium, Chicago,
     Illinois,  December 1977.   American  Society  of  Agricultural  Engi-
     neers, St.  Joseph,  Michigan,  1978.  pp. 54-60.

65.  Sikora,  L.  J., and D.  R. Keeney.  Laboratory Studies on Stimulation
     of  Biological  Denitrification.   In:   Proceedings of  the National
     Home  Sewage Disposal  Symposium, Chicago,  Illinois,  December 1975,
     American Society of Agricultural  Engineers,  St.  Joseph,  Michigan,
     1975.  pp. 64-73.

66.  Andreoli,  A.,  N. Bartilucci,  R,  Forgione,  and R.  Reynolds.   Nitro-
     gen Demand in  a  Subsurface Disposal  System.   J.  Water Pollut. Con-
     trol Fed., 51:841-854, 1979.

67.  Goronszy,  M.  C.   Intermittent Operation of  the  Extended Aeration
     Process  for Small  Systems.  J.  Water Pollut. Control  Fed.,  51:274,
     1979.

68.  Clifford,  D. A., and W. J. Weber, Jr.  Multicomponent  Ion Exchange:
     Nitrate  Removal Process with  Land Disposal  Regenerant.  Ind. Water
     Eng., 15:18-26, 1978.
                                   204

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69.  Beulow, R. W., K. L. Kropp, J. Withered, and J. M. Symons.  Nitrate
     Removal by  Anion Exchange  Resins.   Water  Supply  Research Labora-
     tory,  National   Environmental  Research  Center,  Cincinnati,  Ohio,
     1974.

70.  Brandes, M.   Effective  Phosphorus  Removal  by Adding Alum to Septic
     Tank.  J.  Water Pollut. Control Fed., 49:2285-2296, 1977.

71.  Midkiff, W. S.,  and  W.  J.  Weber,  Jr.  Operating Characteristics of
     Strong  Based  Anion  Exchange  Reactor.    Proc.  Ind.   Waste  Conf.,
     25:593-604, 1970.

72.  Erickson,  A.  E., J. M. Tiedje, B.  G.  Ellis, and  C.  M.  Hansen.   A
     Barriered Landscape  Water  Renovation System for Removing Phosphate
     and Nitrogen  from Liquid Feedlot  Waste.   In:  Livestock Waste Man-
     agement Pollution Abatement;  Proceedings "of the International  Sym-
     posium on Livestock  Wastes, St.  Joseph, Michigan,  1971.   pp.  232-
     234.

73.  Ellis, B. G., and A. E. Erickson.   Movement and Transformation of
     Various Phosphorus  Compounds  in  Soils.   Michigan Water Resources
     Commission, Lansing, 1969.

74.  Tofflemire, T. J.,  M.  Chen, F. E.  Van  Alstyne, L. J. Hetling, and
     D. B.  Aulenbach.   Phosphate Removal by  Sands  and Soils.  Research
     Unit Technical Paper 31, New York State Department of  Environmental
     Conservation, Albany, 1973.  92 pp.

75.  Detweiler, J. C.  Phosphorus  Removal  by Adsorption  on  Alumina as
     Applied to  Small  Scale Waste  Treatment.  M.S.  Report.  University
     of Wisconsin, Madison,  1978.
                                    205

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                               CHAPTER  7

                            DISPOSAL METHODS
7.1  Introduction
Under the  proper  conditions,  wastewater may be safely  disposed  of onto
the land,  into  surface waters, or  evaporated  into the atmosphere by a
variety  of methods.   The most  commonly used  methods  for  disposal  of
wastewater from single dwellings and  small  clusters of  dwellings may be
divided into three  groups:  (1) subsurface  soil  absorption systems, (2)
evaporation systems, and (3)  treatment systems  that discharge to surface
waters.  Within each of these groups, there are various  designs that may
be selected based upon the site factors encountered and  the characteris-
tics of  the  wastewater.   In some cases,  a  site  limitation may be over-
come by employing flow reduction or wastewater  segregation devices (see
Chapter 6).   Because of  the  broad  range of possible alternatives, the
selection  of  the most appropriate  design  can  be difficult.   The site
factor versus system design matrix presented in Chapter  2  should be con-
sulted to aid in this selection.
Onsite disposal methods discussed in this chapter are:
     1.  Subsurface soil absorption systems
         - trenches and beds
         - seepage pits
         - mounds
         - fills
         - artificially drained systems
         - electro-osmosis

     2.  Evaporation systems
         - evapotranspiration and evapotranspiration-absorption
         - evaporation and evaporation-percolation ponds

     3.  Treatment systems that .discharge to surface waters


Performance  data  and  design,  construction, operation,  and  maintenance
information are provided for each of these methods.
                                   206

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7.2  Subsurface Soil  Absorption
     7.2.1  Introduction

Where  site conditions  are  suitable,  subsurface  soil  absorption  is
usually  the  best  method of  wastewater  disposal  for  single  dwellings
because of its  simplicity,  stability,  and low  cost.    Under the  proper
conditions,  the soil  is  an   excellent  treatment  medium and  requires
little  wastewater  pretreatment.    Partially   treated  wastewater  is
discharged below ground surface where it  is  absorbed  and treated  by the
soil as  it percolates  to  the groundwater.   Continuous  application  of
wastewater causes  a  clogging  mat  to  form at the  infiltrative  surface,
which slows the movement of water into the soil.  This can be beneficial
because  it helps  to  maintain  unsaturated  soil  conditions below  the
clogging mat.   Travel  through  two to four  feet of unsaturated soil  is
necessary to provide adequate  removals of pathogenic organisms  and other
pollutants  from the  wastewater   before  it  reaches  the  groundwater.
However,  it  can  reduce the  infiltration rate of soil  substantially.
Fortunately,   the  clogging  mat   seldom  seals  the   soil   completely.
Therefore, if  a subsurface  soil  absorption  system is  to  have  a  long
life,  the  design must  be  based  on  the  infiltration  rate   through  the
clogging  mat  that  ultimately  forms.   Formation  of  the clogging  mat
depends primarily on loading patterns,  although  other factors may  impact
its development.

         7.2.1.1  Types of Subsurface Soil Absorption Systems


Several  different  designs  of  subsurface  soil absorption systems  may be
used.   They include trenches and beds,  seepage  pits,  mounds, fills, and
artificially drained  systems.   All are covered excavations  filled with
porous  media with  a means  for introducing and  distributing the  waste-
water  throughout the  system.    The  distribution  system  discharges the
wastewater into the voids of the porous media.  The voids maintain expo-
sure  of the soil's  infiltrative  surface and  provide  storage for the
wastewater until it can seep away  into the surrounding  soil.


These  systems  are  usually  used to treat  and dispose  of septic tank ef-
fluent.  While  septic tank effluent rapidly forms a clogging mat in most
soils,  the clogging mat seems  to reach an equilibrium condition through
which  the  wastewater  can flow at  a  reasonably  constant rate,  though it
varies  from  soil  to  soil  (1)(2)(3)(4).   Improved pretreatment  of the
wastewater does not  appear to reduce the  intensity of clogging,  except
in  coarse granular soils such as  sands (4)(5)(6).
                                    207

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         7.2.1.2  System Selection
The type  of subsurface soil  absorption  system selected depends  on the
site characteristics  encountered.    Critical  site  factors  include soil
profile characteristics  and permeability, soil depth  over  water tables
or bedrock, slope, and the  size  of the acceptable area.   Where the soil
is  at  least moderately  permeable  and remains  unsaturated  several  feet
below  the system  throughout the  year,  trenches or  beds  may  be used.
Trenches  and beds  are excavations  of relatively large areal  extent that
usually rely on the upper soil horizons to absorb the wastewater through
the bottom and sidewalls of the excavation.  Seepage pits are deep exca-
vations  designed  primarily for lateral  absorption  of  the  wastewater
through the  sidewalls  of the  excavation;  they are used only where the
groundwater level  is  well   below the bottom of the pit, and  where beds
and trenches are not feasible.
Where the  soils  are  relatively  impermeable  or remain saturated near the
surface, other designs can be used to overcome some limitations.  Mounds
may be  suitable  where  shallow bedrock,  high water table,  or slowly per-
meable  soil  conditions exist.   Mounds  are beds constructed  above  the
natural   soil  surface  in  a  suitable fill  material.   Fill  systems  are
trench or bed systems constructed in fill material brought in to replace
unsuitable soils.  Fills  can be used to overcome some of the same limi-
tations as mounds.   Curtain  or  underdrain designs sometimes can be used
to  artifically  lower groundwater tables  beneath  the  absorption area so
trenches or  beds may  be  constructed.   Table 2-1 presents  the general
site conditions  under which the various designs discussed in this manual
are best suited.  For specific site criteria appropriate for each, refer
to the individual design sections in this chapter.
     7.2.2  Trench and Bed Systems


         7.2.2.1  Description
Trench  and bed  systems  are  the most  commonly  used method  for onsite
wastewater treatment and disposal.   Trenches are shallow,  level  excava-
tions,  usually  1  to 5  ft (0.3 to 1.5 m) deep  and  1  to  3  ft (0.3 to 0.9
m)  wide.   The  bottom  is filled with 6 in.  (15 cm) or more  of washed
crushed  rock  or gravel over  which  is laid  a  single line  of perforated
distribution  piping.   Additional rock  is  placed over  the  pipe  and the
rock covered  with  a suitable  semi permeable barrier to prevent the back-
fill from  penetrating  the  rock.  Both  the bottoms and  sidewalls of the
trenches are  infiltrative  surfaces.   Beds  differ  from  trenches  in that
they are wider  than 3 ft (0.9 m) and may  contain  more  than one  line of
distribution  piping (see Figures 7-1 and 7-2).  Thus, the bottoms of the
beds are the  principal  infiltrative surfaces.
                                    208

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     FIGURE  7-1

TYPICAL TRENCH  SYSTEM
                          Backfill
Perforated
Distribution
Pipe
                                Barrier
                                Material
                               3A - 2-1/2 in. Rock
 Water Table or
Creviced Bedrock
           209

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                      FIGURE 7-2

                 TYPICAL  BED SYSTEM
      Distribution
          Box
       ,-^v.vv*<

k-Nl '. .S-« c^SkT^—-. »r---   >.?•>
 Perforated
Distribution
    Pipe
         2-4 ft. min
               Water Table or
              Creviced Bedrock
J6-12 in. of
  3/4-21/2 inch
   dia. Rock
                          210

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         7.2.2.2  Application
Site criteria  for trench and  bed  systems are summarized  in  Table 7-1.
They are  based upon factors necessary to maintain  reasonable infiltra-
tion rates  and adequate treatment  performance  over many years  of con-
tinuous service.   Chapter 3 should  be consulted for  proper  site  eval-
uation procedures.
The wastewater  entering the  trench  or bed  should be nearly  free  from
settleable  solids,  greases,   and  fats.    Large  quantities  of  these
wastewater  constituents hasten  the  clogging  of  the  soil   (9).    The
organic strength of the wastewater has not been well  correlated with the
clogging mat resistance except in granular soils (4)(5).   Water softener
wastes have not been found  to  be  harmful  to  the system even when signi-
ficant amounts of  clay are present (9)(10).   However, the  use of water
softeners can add  a  significant hydraulic  load to  the absorption system
and should  be taken  into  account.   The  normal use  of  other household
chemicals and detergents have  also been shown to have no ill  effects on
the system (9).
         7.2.2.3  Design


             a.  Sizing the Infiltrative Surface
The design of soil absorption systems begins at the infiltrative surface
where  the  wastewater enters  the  soil.   With continued  application  of
wastewater, this  surface clogs and the rate  of  wastewater infiltration
is  reduced below the  percolative  capacity  of  the  surrounding  soil.
Therefore, the  infiltrative surface must be  sized on the  basis  of the
expected  hydraulic  conductivity of  the  clogging mat  and  the estimated
daily wastewater  flow (see Chapter 4).


Direct measurement of  the expected wastewater infiltration rate through
a mature clogging mat in a specific soil  cannot be done prior to design.
However,  experience  with  operating  subsurface soil  absorption systems
has  shown  that design  loadings can  sometimes  be correlated with  soil
texture  (3).(4)(11)(12).    Recommended  rates of  application  versus  soil
textures and  percolation rates are presented in  Table 7-2.   This table
is meant  only as a guide.   Soil  texture  and measured percolation rates
will not always be correlated as indicated, due to differences in struc-
ture, clay mineral content, bulk densities, and other  factors in various
areas of the country (see  Chapter 3).
                                    211

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                                TABLE 7-1

                SITE CRITERIA FOR TRENCH AND BED SYSTEMS
             Item
                Criteria
Landscape Position3
SI opea
Typical Horizontal Separation
  Distancesb

    Water Supply Wells
    Surface Waters, Springs
    Escarpments, Manmade Cuts
    Boundary of Property
    Building Foundations
Soil
    Texture
    Structure
    Color
Level, well  drained areas, crests of
slopes, convex slopes most desirable.
Avoid depressions, bases of slopes and
concave slopes unless suitable surface
drainage is  provided.

0 to 25%.   Slopes in excess of 25% can
be utilized  but the use of construction
machinery may be limited (7).   Bed
systems are  limited to 0 to 5%.
             50
             50
             10
              5
             10
100 ft
100 ft
20 ft
10 ft
20 ft
Soils with sandy or loamy textures are
best suited.  Gravelly a'nd cobbley
soils with open pores and slowly
permeable clay soils are less
desirable.

Strong granular, blocky or prismatic
structures are desirable.  Platy or
unstructured massive soils should be
avoided.

Bright uniform colors indicate
well-drained, well-aerated soils.
Dull, gray or mottled soils indicate
continuous or seasonal saturation and
are unsuitable.
                                    212

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                          TABLE 7-1  (continued)


             Item                                 Criteria
Layering                          Soils exhibiting layers with distinct
                                  textural  or structural  changes  should
                                  be carefully evaluated to insure water
                                  movement will  not be severely
                                  restricted.

Unsaturated Depth                 2 to 4 ft of unsaturated soil should
                                  exist between the bottom of the system
                                  and the seasonally high water table or
                                  bedrock (3)(4)(8).

Percolation Rate                  1-60 min/in. (average of at least 3
                                  percolation tests).0  Systems can be
                                  constructed in soils with slower
                                  percolation rates, but soil  damage
                                  during construction must be avoided.
a Landscape position and slope are more restrictive for beds because
  of the depths of cut on the upslope side.

b Intended only as a guide.  Safe distance varies from site to site,
  based upon topography, soil permeability,  ground water gradients,
  geology, etc.

c Soils with percolation rates <1 min/in. can be used for trenches and
  beds if the soil is replaced with a suitably thick (>2 ft) layer of
  loamy sand or sand.
                                    213

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                             TABLE 7-2

            RECOMMENDED RATES OF WASTEWATER APPLICATION
           FOR TRENCH AND BED BOTTOM AREAS (4)(!!){12)*
Soil Texture

Gravel , coarse sand
Coarse to medium sand
Fine sand, loamy sand
Sandy loam, loam
Loam, porous silt loam
Silty clay loam, clay loamd
Percolation Application
Rate Rateb
min/in. gpd/ft^
<1 Not suitable0
1-5 1.2
6-15 0.8
16 - 30 0.6
31 - 60 0.45
61 - 120 0.26
a May be suitable estimates for sidewall infiltration rates.

b Rates based on septic tank effluent from a domestic waste
  source.  A factor of safety may be desirable for wastes of
  significantly different character.

c Soils with percolation rates <1 min/in. can be used if the
  soil is replaced with a suitably thick (>2 ft) layer of loamy
  sand or sand.

d Soils without expandable clays.

e These soils may be easily damaged during construction.
                                   214

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Conventional trench or bed designs should not be used for rapidly perme-
able  soils  with percolation  rates  faster than  1  min/in.  (0.4  min/cm)
(11).  The  rapidly  permeable  soils  may  not provide the necessary treat-
ment  to  protect the groundwater quality.  This  problem  may be overcome
by replacing the native soil with a suitably thick (greater than 2 feet)
layer of loamy  sand or sand textured soil.  With the liner in place, the
design of the  system  can  follow the design of conventional  trenches and
beds  using  an  assumed percolation  rate  of 6 to 15 min/in.  (2.4 to 5.9
min/cm).
Conventional trench or bed designs  should  also  be avoided in soils with
perc'olation rates  slower  than 60 min/in.  (24 min/cm).   These  soils can
be easily  smeared  and  compacted  during  construction, reducing the soil's
infiltration rate  to  as  little as half  the  expected  rate (12).   Trench
systems  may be  used  in  soils with  percolation  rates  as  slow  as 120
min/in (47 min/cm), but only if great care is exercised during construc-
tion.   Construction should proceed  only when the  soil  is  sufficiently
dry to resist compaction  and  smearing during excavation.   This point is
reached  when  it crumbles when trying to roll a  sample  into  a wire be-
tween the palms of the hands.  Trenches  should be installed so that con-
struction machinery need  not  drive  over the  infiltrative surface.  A 4-
to 6-in.  (10-  to 15-cm)   sand  liner  in  the bottom of  the trench may be
used to  protect  the soil  from compaction during placement of the aggre-
gate and to expose  infiltrative  surface that would otherwise be covered
by the aggregate (11)(13).


             b.  Geometry of the Infiltrative Surface


Sidewalls as Infiltrative Surfaces:   Both the horizontal  bottom area and
the vertical sidewalls of trenches and beds can act as infiltrative sur-
faces.   When a  gravity-fed  system  is first put into service, the bottom
area  is the  only  infiltrative  surface.   However,  after  a  period  of
wastewater  application,  the  bottom  can become sufficiently  clogged to
pond  liquid above it, at which  time the  sidewalls  become  infiltrative
surfaces as well.   Because  the  hydraulic gradients  and  resistances of
the clogging mats  on  the bottom and  sidewalls  are not likely  to be the
same, the  infiltration  rates may be  different. The  objective  in design
is  to maximize  the area of  the surface  expected to have  the  highest
infiltration rate  while  assuring  adequate treatment  of  wastewater and
protection  of the groundwater.


Because  the sidewall  is  a vertical  surface,  clogging may not be as se-
vere  as that  which occurs at the bottom surface,  due  to  several fac-
tors:   (1) suspended  solids  in  the  wastewater  may not be a significant
factor in  sidewall clogging;  (2) the  rising and falling liquid levels in
the  system allow alternative  wetting and drying  of  the  sidewall  while
the bottom may remain continuously inundated;  and (3)  the  clogging mat
                                   215

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can  slough  off the sidewall.   These factors  tend  to  make the sidewall
clogging less  severe  than the  bottom  surface.   However,  the hydraulic
gradient across the  sidewall  mat is also  less.   At the bottom surface,
gravity, the  hydrostatic pressure  of  the  ponded water above,  and the
matric  potential  of  the soil  below  the  mat  contribute  to  the  total
hydraulic gradient.  At the.sidewall, the gravity potential is zero, and
the  hydrostatic potential diminshes  to  zero at the liquid surface.  Be-
cause  the  matric  potential  varies  with  changing soil  moisture  condi-
tions,  it  is  difficult  to  predict  which  infiltrative  surface  will  be
more effective.
In humid  regions where percolating rainwater  reduces  the matric poten-
tial  along the sidewall,  shallow  trench  systems are suggested (4).  The
bottom  area  is  the  principal  infiltrative  surface in  these systems.
Shallow trenches often are best because the upper soil  horizons are usu-
ally more  permeable and  greater  evapotranspiration can occur.   In dry
climates, the sidewall area may be used to a greater extent.  The bottom
area may be  reduced  as  the  sidewall  area is increased.  Common practice
is not  to  give  credit to the first 6  in.  (15  cm)  of sidewall  area mea-
sured from the  trench bottom, but any exposed sidewall  above 6  in. (15
cm) may be  used  to reduce the bottom area (3) (11).   The infiltration
rates given  in Table 7-2 may be used for sidewall areas.


Trench versus Bed Design:   Because beds  usually require less total land
area and are less costly  to construct, they are often installed instead
of trenches.   However,  trenches are generally  more desirable  than beds
(4)(11)(12)(13)(14).  Trenches  can  provide up  to  five  times more side-
wall   area  than  do  beds  for  identical  bottom areas.    Less  damage  is
likely  to  occur  to  the soil  during construction because the excavation
equipment can straddle  the  trenches  so it  is  not necessary to drive on
the infiltrative  surface.   On  sloping  sites,  trenches can  follow the
contours to  maintain  the  infiltrative  surfaces in  the  same soil  horizon
and keep excavation to a minimum.   Beds may be acceptable where the site
is relatively level  and the soils are sands and loamy sands.


Shallow versus Deep Absorption Systems:  Shallow soil absorption systems
offer several  advantages  over deep systems.    Because  of  greater plant
and animal activity  and less  clay due  to eluviation, the upper soil ho-
rizons  are usually  more  permeable than  the deeper  subsoil.   Also, the
plant activity helps  reduce the loading on the system during the growing
season  by  transpiring significant amounts  of liquid and  removing some
nitrogen and phosphorus from the waterwater.  Construction delays due to
wet soils are also reduced because the upper horizons dry more quickly.


On the  other hand,  deep systems have  advantages.   Increased depths per-
mit increased sidewall area exposure for the same amount of bottom area.
They also  permit  a  greater depth of liquid ponding which increases the
                                  216

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hydraulic gradient across  the  infiltrative  surface.   In some instances,
deep systems can be used  to  reach  more permeable soil  horizons when the
proximity of groundwater tables do not preclude their use.


Freezing of shallow absorption  systems  is not a problem if kept in con-
tinuous operation  (4)(11).   Carefully constructed systems with  6  to 12
in. (15 to 30 cm) of soil  cover, which are in continuous operation, will
not freeze even in areas where frost penetration may be as great as 5 ft
(1.5 m) if the distribution pipe is gravel  packed and header pipes insu-
lated  where  it is necessary  for  them to pass  under driveways  or other
areas usually cleared of snow.
Alternating Systems;  Dividing the soil absorption system into more than
one field to allow  alternate  use  of  the individual  fields over extended
periods of time can  extend  the  life  of the absorption system.  Alterna-
ting operation of the fields  permits  part of the system to "rest" peri-
odically  so  that  the infiltrative surface can  be rejuvenated naturally
through biodegradation of the clogging mat (4) (11)(12)(13)(15)(16).  The
"resting" field also acts as a standby unit that can be put into immedi-
ate service  if  a  failure occurs  in the other part  of the system.   This
provides a period of time during which the failed field can be rehabili-
tated or rebuilt without an unwanted discharge.
Alternating systems commonly consist of two fields.  Each field contains
50 to 100% of  the  total  required  area  for a single field.  Common prac-
tice is to switch  fields  on  a  semiannual  or annual schedule by means of
a diversion valve  (see Figure 7-3 and Chapter 8).  Though it has not yet
been proven,  such  operation  may permit a  reduction  in the total  system
size.  In sandy soils with a shallow water table, the use of alternating
beds may increase  the chance of groundwater contamination because of the
loss of treatment  efficiency when the clogging mat  is decomposed after
resting.


             c.  Layout of the System


Location:    Locating the  area  for the soil absorption system  should be
done with  care.   On undeveloped  lots, the site should be located prior
to locating  the  house, well,  drives,  etc., to ensure  the  best area is
reserved.    The   following   recommendations  should  be considered  when
locating the soil  absorption system:


     1.  Locate  the system where the  surface  drainage is  good.   Avoid
         depressions and bases of slopes and areas in the path of runoff
         from  roofs, patios, driveways, or other paved areas unless sur-
         face  drainage is provided.
                                  217

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                             FIGURE 7-3

           ALTERNATING TRENCH SYSTEM WITH DIVERSION VALVE
                                     Septic
                                     Tank

                                     Diversion
                                       Valve
    2.
     3.
In areas with  severe  winters,  avoid areas that are  kept clear
of snow.   Automobiles, snowmobiles, and  other  vehicles  should
not  be  allowed on  the area.   Compacted or cleared  snow will
allow frost  to penetrate  the  system,  and compacted  soil  and
losf of vegetation  from  traffic over  the system will  reduce
evapotranspiration in the summer.

Preserve as  many trees as  possible.   Trenches may  be run be-
tween trees.  Avoid damaging the trees during construction.

is £e>erable°nto a single trench because of the flexibility ,t offers  in
wastewater application.


nn  lots  with insufficient area  for  trenches or on  sites  with granular



?he excUJaY iSn becomes too deep on the upslope side.  In such instances,
                                  218

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deep trenches with  a  greater depth of rock  below  the  distribution pipe
to increase the sidewall  area is more suitable.
Reserve Area:  When planning and locating the absorption system, consid-
eration should be given to reserving a suitable area for construction of
a second system.  The  second  system would  be added if the first were to
fail  or  if the  system required expansion  due to  increased  wastewater
flows.   Care must be used  in  constructing  the second system so that the
original  system is not damaged by the construction equipment.


The reserve area should be  located  to facilitate  simultaneous  or alter-
nating loading of both systems.  If the reserve area is used because the
initial system has failed,  the  failing  system should not be permanently
abandoned.   With time, the  initial  system  will  be naturally rejuvenated
and can be used  alternately with the reserve system.  Reserve areas can
be provided very easily with trench systems by reserving sufficient area
between the initial  trenches as shown in Figure 7-4.
Dimensions:  The absorption system should be dimensioned to best fit the
lot while maintaining separation distances and avoiding excessive depths
of excavation.  Commonly used dimensions are given in Table 7-3.
The depth of excavation is determined by the location of the most perme-
able soil  horizon  and flow  restricting  layers or the  high  water table
elevation.  Unless a  deep, more  permeable  horizon exists,  the trench or
bed bottom  elevation  should  be maintained at  about  18  to  24 in. (46 to
61 cm)  below the natural  ground surface.   To prevent  freezing  in  cold
climates, 6  to  12  in. (15 to  30 cm) of  cover  should be backfilled  over
the aggregate (11).
If  the  water table  or a  very  slowly permeable  layer  is too  near the
ground surface to construct  the  system at  this depth,  the system can be
raised.  Very shallow trenches 6 to 12 in.  (15 to 30 cm) deep can be in-
stalled and  the  area backfilled with additional  soil  (see  Figure 7-5).
Adequate separation  distance must  be  provided between  the trench bottom
and  the  seasonally  high  groundwater  level  to  prevent  groundwater
contamination.
The length of  the  trench  or bed system depends on the site characteris-
tics.  The length of the distribution laterals is commonly restricted to
100 ft  (30  m).  This is  based  on  the  fears of root penetration, uneven
settling, or pipe breakage which could disrupt the flow down the pipe to
render  the  remaining downstream  length  useless.   However,  these fears
are unwarranted  because the aggregate transmits  the  wastewater (4)(13)
(17).     To   assure  adequate   transmission  and  distribution  of  the
                                  219

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                         FIGURE  7-4

        PROVISION OF A RESERVE AREA  BETWEEN TRENCHES
           OF THE INITIAL SYSTEM ON  A  SLOPING SITE
                                              From
                                           Pretreatment
         Reserve
         System
    Drop
    Box
Trenches
Following
Contours
Primary
System
Diversion
  Valve
                                                  Drop Box
                           220

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wastewater through   the aggregate,  extreme  care must be  taken  to con-
struct the.trench  bottom at  the  same elevation throughout  its  length.
The overriding considerations  for  determining  trench  or  bed lengths are
the site characteristics.
Spacing between  trench  sidewalls  could be as  little  as  18  in.  (46 cm).
A  spacing  of 6  ft (1.8 m)  is suggested,  however,  to  facilitate  con-
struction and to provide a reserve area between trenches.
                            TABLE 7-3

             TYPICAL DIMENSIONS FOR TRENCHES AND BEDS
                                   Bottom     Cover
    System     Wi dth   Lengthb     Depthc   Thickness  Spacingd
                 FF~     ft          FETTu        fl
   Trenches    1-3*      100       1.5-2.0    6 (min)       6

   Beds         >3       100       1.5-2.0    6 (min)       6
   a Excavations generally should not be less than 1 ft wide
     because the sidewall may slough and infiltrate the aggregate(lO)

   b Length of lateral from distribution inlet manifold.  May be
     greater if site  characteristics demand.

   c May  be deeper if a more suitable horizon exists at greater
     depth and sufficient depth can be maintained between the bottom
     and  seasonably high water table.

   d From sidewall to sidewall.  Trench spacing may be decreased
     because of soil  flow net patterns, specifically for shallow
     trenches in sandy soils.
                                    221

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                                  FIGURE 7-5

              TRENCH SYSTEM INSTALLED TO OVERCOME  A SHALLOW  WATER
                    TABLE OR RESTRICTIVE LAYER  [AFTER  (11)]
                Diversion for
               Surface Water
              12-18 in.  Soil Backfill Over Area
                         6-12 in.
2-4
Seasonally High Water Table
or Flow Restrictive Layer
                                           Drainfield
                                           Trenches
                                      ft.
                    Original.
                    Ground
—1		 Surface
               d.  Effluent Distribution
  Methods of  Application;   To ensure that  the  absorption system performs
  satisfactorily over a reasonably long lifetime, the method of wastewater
  application to the  infiltrative  surface must  be compatible with the ex-
  isting soil and site characteristics.  Methods of wastewater application
  can be grouped into three categories:  (1) gravity flow; (2) dosing; and
  (3) uniform application.  For designs of distribution networks employing
  these methods, see Section 7.2.8)
       1.  Gravity flow  is  the  simplest and most commonly employed of the
           distribution  methods.   Wastewater is allowed  to  flow into the
           absorption system directly from  the treatment unit.  With time,
           a  clogging  mat usually develops  on  the bottom surface  of the
           absorption  system  and continuous  ponding  of the  wastewater
           results.   This may  lead  to  more severe clogging  of the soil,
           reducing  the  infiltration rate.   However, this  effect  may be
           offset  by the greater effective  infiltrative  area provided by
           submerging  the  sidewalls  of  the system, particularly in trench
           systems.   The  ponding also  increases  the  hydraulic gradient
                                      222

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    across the  clogging mat, which  can increase  the  infiltration
    rate (2)(18).

    If  adequate  treatment  is  to  be achieved  in coarse  granular
    soils such  as sands,  wastewater application  by gravity  flow
    requires that a clogging mat exist at the infiltrative surfaces
    to prevent  saturated  conditions  in  the underlying soil  and  to
    prevent groundwater contamination.   The mat  develops  with  con-
    tinued application, but groundwater  contamination by  pathogenic
    organisms and viruses can be a danger at first.

2.  Dosing can be employed  to provide intermittent aeration  of the
    infiltrative surface.   In  this method, periods  of loading are
    followed by periods of  resting,  with cycle  frequencies ranging
    from hours to  days.   The resting phase  should be  sufficiently
    long to allow  the  system to drain and expose  the  infiltrative
    surface to air, which encourages rapid  degradation of the clog-
    ging materials by aerobic bacteria.

    This method of operation may increase the rate of infiltration,
    as well as  extend the  life  of the   absorption system,  because
    the clogging mat resistance is  reduced  (1)(4)(6)(15)(17).   In
    sands or  coarser  textured  materials,  the  rapid  infiltration
    rates can lead to  bacterial  and  viral  contamination  of shallow
    groundwater, expecially  when first  put  into  use (4).   There-
    fore, systems  constructed  in these   soils should be  dosed  with
    small volumes  of  wastewater several  times a day  to  prevent
    large saturated  fronts moving through  the soil.   In  finer  tex-
    tured  soils,  absorption,  rather than  treatment, is the  con-
    cern.   Large,  less frequent  doses  are more suitable  in these
    soils to provide longer  aeration times between doses  (4).   See
    Table 7-4 for suggested dosing frequencies.

3.  Uniform Application means applying the  wastewater in  doses  uni-
    formly over  the  entire  bottom area  of the system to minimize
    local overloading and the depth of ponding following  each dose.
    This is usually  achieved with a  pressure distribution network.
    In this manner,  the soil is more likely  to  remain  unsaturated
    even during  initial  start-up when no clogging mat is present.
    The minimum  depths of ponding during  application permit rapid
    draining  and  maximum  exposure  of  the bottom surface  to air
    which reduces  the  clogging  mat resistance.   The sidewall  is
    lost as  an infiltrative surface, but  this may  be  compensated
    for by the maintenance of higher infiltration rates  through the
    bottom  surface.    See  Table  7-4 for suggested dosing frequen-
    cies.
                                 223

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                               TABLE 7-4

             DOSING  FREQUENCIES FOR VARIOUS  SOIL TEXTURES



    Soil Texture                                Dosing Frequency


   Sand                                     4 Doses/Day

   Sandy Loam                               1 Dose/Day

   Loam                                     Frequency Not Critical3

   Silt Loam                                1 Dose/Daya
   Silty Clay Loam

   Clay                                     Frequency Not Critical9
   a  Long-term  resting  provided by alternating fields may be
     desirable.
Selection of Application Method:  The selection of an appropriate method
ofwastewater  applicationdepends  on  whether  improved  absorption  or
improved  treatment  is the  objective.   This  is determined by  the  soil
permeability and the  geometry  of the infiltrative surface.   Under  some
conditions, the method  of  application  is not critical, so  selection  is
based on  simplicity of  design, operation,  and cost.   Methods of appli-
cation for  various  soil  and site conditions are  summarized  in  Table  7-
5.   Where more than  one may  be appropriate,  the methods are listed  in
order of preference.
             e.  Porous Media
The function  of  the  porous media placed below  and  around the distribu-
tion pipe  is  four-fold.   Its  primary  purposes  are to support  the  dis-
tribution pipe and to  provide  a media through  which  the  wastewater can
flow from the distribution pipe  to reach the  bottom and  sidewall  infil-
tration areas.   A second function is to provide  storage  of peak  waste-
water flows.   Third,  the media dissipates any  energy  that the  incoming
wastewater  may   have   which   could  erode   the  infiltrative  surface.
Finally, the  media  supports  the  sidewall of  the excavation  to prevent
its collapse.
                                    224

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                                TABLE 7-5

      METHODS OF WASTEWATER APPLICATION FOR VARIOUS SYSTEM  DESIGNS
                       AND SOIL PERMEABILITIES9
       Soil
   Permeabi11ty
(Percolation Rate)
   Trenches or Beds
    (Fills, Drains)
    On Level  Site
Trenches (Drains)
    On SI opi ng
    Site (>5%)
Very Rapid
(<1 min/in.)

Rapi d
(1-10 min/in.)
Moderate
(11-60 min/in.)
Slow
(>60 min/in.)
Uniform Application15
        Dosi ng

 Uniform Application
        Dosing
        Gravity

        Dosi ng
        Gravity
 Uniform Application

      Not Critical
     Gravity
     Dosi ng

     Gravity
     Dosing
     Gravity
     Dosing
   Not Critical
a Methods of application are listed in order of preference.

b Should be used in alternating field systems to ensure adequate
  treatment.
                                   225

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The depth  of the  porous  media may  vary.   A minimum  of 6 in.  (15 cm)
below the distribution  pipe  invert and 2 in.  (5  cm) above the crown of
the pipe  is  suggested.    Greater  depths may  be used  to  increase the
sidewall area  and to  increase  the  hydraulic  head  on  the infiltrative
surface.
Gravel or crushed rock is usually used as the porous media, though other
durable porous materials may be  suitable.   The  suggested  gravel  or rock
size is 3/4 to 2-1/2 in. (1.8 to 6.4 cm) in diameter.  Smaller sizes are
preferred because  masking  of  the  infiltrative  surface by the  rock  is
reduced (13).   The rock should  be durable  and  resistant  to slaking and
dissolution.  A hardness of  3  or greater on the Moh's Scale of Hardness
is suggested.  Rock  that can scratch  a  copper penny without leaving any
residual   rock  meets  this  criterion.    Crushed  limestone   is  unsuitable
unless dolomitic.   The  media should be  washed  to  remove  all  fines that
could clog the infiltrative surface.
To maintain  the porous nature  of  the media, the media must  be covered
with a material  to  prevent backfilled soil  from entering  the media and
filling  the  voids.   Treated  building paper was once used  but has been
abandoned in favor of  untreated building  paper,  synthetic  drainage fab-
ric, marsh hay  or straw.   These materials do not create a  vapor barrier
and permit some moisture to pass through  to the soil  above where it can
be removed through evapotranspiration.  All  these materials,  except for
the drainage  fabric,  will  eventually  decay.   If they  decay  before the
soil has stabilized, the value  of  the materials is  lost.   To ensure the
barrier  is not  lost  prematurely, heavy duty building paper of 40 to 60
Ib (18 to 27 kg) weight or a 4 to 6 in. (10 to 15 cm)  layer of marsh hay
or straw should be  used.  In dry sandy  soils,  a 4 in.  (10  cm)  layer of
hay or straw covered with  untreated  building paper  is suggested to pre-
vent the backfill from filtering down into the rock.


             f.  Inspection Pipes
Inspection  pipes  located in the subsurface  soil  absorption  system pro-
vide limited  access to  observe  the  depth of ponding, a measure  of the
performance of the  system, and a means of locating the subsurface field.
If used, the inspection pipes should extend from the bottom infiltrative
surface of  the system  up to or  above final  grade.  The bottom should be
open and  the top  capped.    The  portion of  the  pipe within  the  gravel
should be perforated to permit a free flow of water (see Figure 7-6).
                                   226

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         7.2.2.4  Construction
A frequent cause of early  failure  of  soil  absorption systems is the use
of poor construction techniques.  The following should be considered for
construction of a soil  absorption system:
             a.  Layout
The system should be laid out to facilitate the maneuvering of construc-
tion equipment so that damage to the soil  is minimized.
     1.  Absorption  system  area  should  be  staked  out  and roped  off
         immediately  after  the  site  evaluation  to  keep  construction
         equipment and other vehicles off the area until  construction of
         the system begins.

     2.  Trenches rather than beds are preferable in soils with signifi-
         cant clay  content (greater than 25% by  weight)  because equip-
         ment can  straddle  the  trenches.   This  reduces  the compaction
         and smearing at the exposed infiltrative surface.

     3.  Trenches should be spaced at least 6 ft (1.8 m)  apart to facil-
         itate the  operation of the construction equipment  if  there is
         sufficient area.

     4.  To minimize  sidewall  compaction, trench widths  should be made
         larger than  the  bucket  used for excavation.  Buckets  are made
         to compact the  sidewall  to prevent caving  during  excavation.
         If the excavation is wider than the bucket, this effect is min-
         imized.   An  alternative is  to  use modified buckets with side
         cutters or raker teeth (see Figure 7-7).

     5.  Trenches  should  follow the  contour  and be  placed  outside the
         drip lines of trees to avoid root damage.
             b.  Excavation
Absorption of waste effluent by soil requires that the soil pores remain
open at the  infiltrative  surface.   If  these are sealed during construc-
tion by compaction, smearing, or puddling of the soil, the system may be
rendered  useless.   The  tendency  toward compaction,  smearing,  and pud-
dling depends upon the soil type, moisture content, and applied force.
                                    227

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                  FIGURE 7-6

            TYPICAL  INSPECTION  PIPE
                   Vent Cap,
Distribution
Pipe
            ^K<$i^-%-
             *&f#'* GRAVE"!? o$
4" Perforated
Inspection Pipe
                                 -Open Bottom
                  FIGURE 7-7

  BACKHOE BUCKET WITH REMOVABLE RAKER TEETH (11)
                                  in. Rods or Bolts
                               Approximately 1-1/2 in. Long
                               Spaced Approximately 3 in. on
                               Center
                     228

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Soils with  high clay  contents  (greater  than 25%  by weight)  are  very
susceptible to  damage, while  sands are  rarely  affected.  Careful  con-
struction techniques minimize this soil  damage.  They include:


     1.   Excavation may proceed  in clayey soils only when  the moisture
         content is below the soil's plastic limit.   If a sample of soil
         taken at the depth of the proposed bottom of the system forms a
         "wire"  instead of crumbling when  attempting  to  roll  it between
         the hands, the soil  is too wet.

     2.   A backhoe  is  usually used to  excavate  the  system.   Front-end
         loaders or bulldozer  blades   should  not be  used because  the
         scraping action of  the  bucket  or blade can  smear  the soil  se-
         verely,  and   the  wheels  or  tracks   compact   the  exposed
         infiltrative surface.

     3.   Excavation equipment  must not  be  driven  on the bottom  of  the
         system.   If trenches  are used, the equipment can  straddle  the
         excavation.   If a bed is used, the  bed  should  be divided into
         segments so the machinery can always operate  from undisturbed
         soil.

     4.   The bottom  of each trench or  bed must be  level  throughout to
         ensure more uniform distribution of effluent.  A level and tri-
         pod are essential  equipment.

     5.   The bottom and sidewalls  of the excavation  should  be left with
         a  rough open  surface.    Any  smeared  and   compacted surfaces
         should be removed  with care.

     6.   Work should be scheduled only when the infiltrative surface can
         be covered in one day,  because wind-blown silt  or  raindrop  im-
         pact can clog the  soil.


             c.   Backfilling


Once  the  infiltrative  surface  is properly  prepared,   the  backfilling
operations must be done carefully to avoid any damage to the soil.


     1.   The gravel or crushed rock used as the  porous  media is laid in
         by a  backhoe  or  front-end  loader  rather  than  dumped  in  by
         truck.   This should be done from the sides of the system rather
         than driving out  onto the exposed bottom.   In  large beds,  the
         gravel  or rock should be pushed out ahead of a small  bulldozer.

     2.   The distribution  pipes  are covered with a minimum of 2  in. (5
         cm)  of gravel  or  rock  to  retard  root growth,  to  insulate
                                   229

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         against  freezing  and  to  stabilize  .the  pipe  before  backfill-
         ing.   Procedures for constructing  the  distribution  network  are
         discussed in Section 7.2.8.

     3.  The gravel  or rock is  covered  with untreated building  paper,
         synthetic drainage  fabric, marsh  hay  or  straw to  prevent  the
         unconsolidated soil cover  from  entering the media.   The  media
         should be covered  completely.   If untreated building  paper  is
         used,  the seams  should overlap at least  2 in. (5  cm) and  any
         tears  covered.   If marsh  hay  or  straw is used,  it  should  be
         spread uniformly to a  depth  of 4  to 6  in. (10 to  15  cm).   In
         bed construction,  spreading  a  layer of  hay  or  straw covered
         with untreated building paper is good practice.

     4.  The backfill material  should  be  similar to the  natural  soil  and
         no more permeable.   It should be mounded above  natural  grade to
         allow  for settling  and to channel  runoff away  from the system.
         7.2.2.5  Operation and Maintenance


             a.  Routine Maintenance
Once installed,  a  subsurface soil  absorption system requires  little  or
no attention as long as the wastewater discharged into  it is  nearly free
of settleable  solids,  greases,  fats,  and oils.   This  requires that the
pretreatment unit be maintained  (see  Chapter 6).  To  provide  added in-
surance that  the system  will  have a  long,  useful  life,  the  following
actions are suggested:


     1.  Resting of the system by  taking  it  out  of  service for a period
         of time  is an effective  method of restoring  the infiltration
         rate.  Resting allows the absorption field  to gradually drain,
         exposing  the   infiltrative  surfaces  to air.   After  several
         months, the  clogging mat is  degraded   through  biochemical  and
         physical  processes   (1)(4)(6)(13)(15).    This  requires that  a
         second  absorption  system exist to  allow  continued  disposal,
         while  the  first  is  in the  resting  phase.   The  systems  can  be
         alternated on a yearly basis by means of a  diversion valve (see
         Figure 7-3).

     2.  The  plumbing  fixtures  in  the home  should be  checked  regularly
         to repair any leaks  which can add  substantial  amounts of water
         to the system.

     3.  The  use  of special  additives such as  yeast,  bacteria,  chemi-
         cals, and enzyme preparations is not necessary and is of
                                   230

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         little value  for the  proper function  of the soil  absorption
         system (3)(4).

     4.  Periodic  application of oxidizing agents, particularly hydrogen
         peroxide, are being tried as  a  preventative  maintenance proce-
         dure (19).    If  properly applied, the agents oxidize  the clog-
         ging mat to restore much of  the  system's infiltration capacity
         within a day or two.   Handling  of these agents is very danger-
         ous,  and therefore  the treatment  should be  done by  trained
         individuals  only.    Experience  with  this treatment  has  been
         insufficient  to determine  its  long-term effectiveness in  a
         variety of  soil  types.
             b.  Rehabilitation
Occasionally,  soil  absorption  systems  fail,  necessitating  their  reha-
bilitation.  The  causes  of failure can be complex,  resulting  from poor
siting,  poor  design,  poor  construction, poor  maintenance,  hydraulic
overloading, or a  combination  of these.  To  determine  the most approp-
riate method of rehabilitation, the cause of failure must be determined.
Figure 7-8  suggests  ways  to determine the cause of  failure and corres-
ponding ways of rehabilitating the system.
The  failure  frequency  should be determined before  isolating  the cause.
Failure may occur occasionally or continuously.  Occasional  failure man-
ifests  itself  with occasional  seepage  on the ground  surface,  sluggish
drains,  or  plumbing backups.   These usually  coincide with  periods  of
heavy rainfall  or  snowmelt.   Continuous  failure  can have  the  same symp-
toms  but on a  continuous  basis.   However,  some systems may seriously
contaminate the  groundwater  with no surface manifestations of  failure.
These failures are detected by groundwater sampling.
Occasional Failure:   The cause of occasional  failure  is  much easier to
determine, and rehabilitation  can  be  more  simple.   Since  the  system
functions  between  periods of  failure,  sizing and  construction  usually
can  be eliminated  as the cause.   In  these  instances,  failure  is  the
result  of poor siting,  poor  maintenance,   or  hydraulic  overloading.
Excessive  water use,  plumbing  leaks,  or foundation  drain  discharges are
common reasons for hydraulic overloading.  These can be corrected by the
appropriate action as indicated in Figure 7-8.
The  next  step  is  to  investigate  the  site  of  the  absorption  system.
Occasional  failure  usually is  due  to poor drainage  or  seasonally high
water  table conditions.    The  surface  grading  and  landscape  position
should  be checked  for poor  surface drainage conditions.    Local  soil
conditions  should also be  investigated  by borings  for  seasonally high
                                    231

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                                                       FIGURE  7-8


                                    METHODS OF SOIL ABSORPTION FIELD REHABILITATION
                                                         Failure Noted
oo
ro
Determine Failure Frequency
Periodic




Determine Cause
^—-"T^
*--^ \
Siting Overloading
Check Check:
• Landscape * Plumbing




Within 1




—- - — -
Year
Continuous
1
Determine Age of System When
Failure First Occurred
^ 	 ^^
^^ ^^—
Determine Cause
- — ^^^ Siting/
~~ — •— ^^_ Design/


Maintenance Construction
Check: Check:

• Ma.ntenance . So,l Type (Tex-
Position Record ture Hydraulic
• Excessive Water
Use Conductivity)
* Surface Grading


• Condition of • Unsati

rated
• Foundation Dram Treatment Depth of Soil
. .. !!• L. Discharge
• Depth to High 3
Groundwater

* Neighboring Systems
Conditions
1
Corrective Actions Corrective Act
Unit

_^-—
„—- 	
Overloading
Check:
• Plumbing
• System Loading

* Waste Character-
istics





— 	 	
After 1 Year
Determine Cause
.--— "

Maintenance
Check:
• Maintenance Record
• Condition of Tank

• Condition of Field

• System Age
* Landscape
Position



• Building Lateral

' System Size
(Tank and Field)
ons Corrective Actions

Corrective Actions
Corrective Actions
* Distribution of
• Draining • Repair Plumbing • Pumping Effluent
• Regrading/Filling • Flow Reduction • Repair
• Holding Tank (when • Eliminate Clear * Infiltra
lion Rate
necessary) Water Discharges
• Reconstruction


• Neighboring Sys-



tern
Corrects
• Dosin
s Conditions
e Actions
g
• Repair Plumbing
• Flow Reduction
• Eliminate Clear
Water Discharges
. Waste Segregation
• Improved Pretreatment



• Pumping
m Hydrogen Peroxide
• Resting






• Addition
• Reconstruct
Conventional
Alternate
Holding Tank
Community Facility

-------
water  tables  (see  Chapter 3).   Corrective  actions include  improving
surface drainage  by  regrading or filling  low areas.   High  water  table
conditions may be corrected in some  instances by  installing  drains (see
Section 7.2.6).
Lack of maintenance of the  treatment  unit  preceding  the  soil  absorption
field may also  be a  cause  of occasional  failure.   The  unit  may be  a
point of infiltration and inflow during wet periods.   The unit should be
pumped and leaks repaired.


Continuous Failure:  The causes of continuous failure are more difficult
to  determine.However,  learning the  age of  the  system when  failure
first occurred is very useful  in isolating  the cause.


If  failure  occurred within the  first year  of operation, the cause  is
probably due  to  poor  siting,  design,  or construction.   It  is  useful  to
check  the  performance  of  neighboring  systems  installed  in  similar
soils.   If  they  have similar loading  rates  and  are working  well,  the
failing system should be  checked  for  proper  sizing.   A small  system  can
be  enlarged  by  adding new  infiltration  areas.  In  some  instances,  the
sizing may  be adequate but the  distribution of the wastewater  is poor
due to improper construction.   Providing dosing may  correct  this  problem
(see Section  7.2.8).   Damage  to  the  soil  during construction may also
cause failure,  in  which  case  the  infiltrative area is  less  effective.
Reconstruction or an addition  is necessary.  Alternate systems  should be
considered  if the  site is  poor.   This  includes investigating the fea-
sibility of  a cluster or community  system  if surrounding  systems  are
experiencing similar problems.


If  the system had  many years  of  useful  service before failure occurred,
hydraulic overloading  or poor maintenance is usually the  cause.   The
first  step  is  to  find out as much  about the system as possible.    A
sketch  of  the  system  showing the   size,   configuration, and location
should be made.   A soil  profile  description should also  be  obtained.
These items may be  on  file  at the local  regulatory  agency but their  ac-
curacy should be  confirmed  by an onsite visit.  If  the  system provided
several  years of  useful  service,  evidences  of overloading   should  be
investigated  first.   Wastewater  volume  and characteristics  (solids,
greases, fats, oil) should  be determined.   Overloading may  be  corrected
by  repairing  plumbing,  installing flow  reduction fixtures  (see  Chapter
5), and eliminating any discharges from  foundation drains.   If the vol-
ume reductions are insufficient for acceptance by the existing infiltra-
tive surface,  then additional  infiltrative  areas  must  be  constructed.
Systems  serving commercial  buildings  may fail  because  of the  wastewater
characteristics.  High solids concentrations or large amounts  of  fats,
                                  233

-------
oils, and greases, can cause failure.  This is. particularly true of sys-
tems serving restaurants and laundromats.  These failures can be correc-
ted  by  segregating  the wastewaters to eliminate  the  troublesome waste-
waters (see Chapter 5), or by improving pretreatment (see Chapter 6).


Lack of  proper maintenance of  the  treatment unit may have  resulted  in
excessive clogging due to  poor  solids  removal  by  the  unit.   This can  be
determined by  checking  the maintenance record and the condition  of the
unit.  If this appears to  be  the  problem,  the unit should be pumped and
repaired, or replaced if necessary.  The infiltrative  surface of the ab-
sorption field should  also be checked.  If  siting, design,  or mainten-
ance do  not appear  to be the  cause  of  failure, excessive  clogging  is
probably the problem.  In such cases, the infiltrative surface can some-
times be rejuvenated by oxidizing the clogging mat (4)(9)(13)(16).  This
can be done by allowing  the  system  to  drain  and rest  for several  months
(4).   To permit  resting,  a new  system  must be constructed  with means
provided for switching back  and forth.  Alternatively,  the  septic  tank
could  be operated as  a holding  tank  until   the  clogging mat  has  been
oxidized.  However,  this involves frequent pumping,  which may be costly.
Another  method,   still  in the  experimental   stage,  is  the  use  of the
chemical  oxidant, hydrogen peroxide  (16).  Because  it is new, it is not
known if it will  work well in all  soils.   Extreme care should be used  in
its application because  it is a strong oxidizing  agent.   Only individu-
als trained in its use should perform the treatment.
         7.2.2.6  Considerations for Multi-Home and Commercial
                  Wastewaters
Design of trench and bed soil absorption systems for small  institutions,
commercial establishments,  and  clusters of dwellings  generally  follows
the same  design principles  as for  single  dwellings.   In cluster  systems
serving more than about five homes,  however,  peak  flow estimates  can be
reduced because of flow attenuation, but contributions from infiltration
through the  collection system  must be included.   Peak flow  estimates
should be based on the  total number of people to be served (see  Chapter
4).   Rates  of  infiltration  will vary with  the  type  of collection sewer
used (19M20).
With commercial  flows,  the  character of the wastewater  is  an  important
consideration.   Proper  pretreatment  is necessary  if  the  character  is
significantly different than domestic wastewater.


Flexibility in operation should  also  be  incorporated into  systems  serv-
ing larger  flows since  a failure can  create  a  significant problem.  Al-
ternating bed systems should be considered.  A three-field system can be
constructed in which each field  contains 50% of  the required absorption
                                  234

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area (19).   This  design allows flexibility in  operation.   Two  beds are
always in operation, providing 100%  of  the  needed infiltrative  surface.
The  third  field  is  alternated in  service  on  a  semi  annual or  annual
schedule.   Thus,  each  field  is  in  service  for one  or two years  and
"rested" for 6  months  to one year to rejuvenate.   The third field also
acts as  a standby unit in case one  field fails.  The  idle  field  can be
put  into service  immediately while a  failed  field  is  rehabilitated.
Larger  systems  should  utilize some dosing or uniform application  to
assure proper performance.
     7.2.3  Seepage Pits


         7.2.3.1  Description
Seepage pits or dry wells  are  deep  excavations  used for subsurface dis-
posal  of pretreated  wastewater.   Covered  porous-walled  chambers  are
placed in the  excavation  and surrounded by gravel  or  crushed rock (see
Figure 7-9).   Wastewater enters  the chamber where  it is stored until  it
seeps out through  the chamber wall  and infiltrates  the sidewall  of the
excavation.
Seepage pits are generally discouraged by many local regulatory agencies
in  favor  of trench  or bed  systems.   However,  seepage pits  have  been
shown to be an  acceptable  method  of disposal  for small  wastewater flows
(21).   Seepage  pits  are used where land  area  is too limited for trench
or  bed  systems;  and  either the groundwater level  is deep  at all times,
or  the  upper  3  to 4 ft (0.9 to 1.2 m) of the  soil  profile is underlain
by  a more permeable unsaturated soil material  of great depth.
         7.2.3.2  Site Considerations
The  suggested  site criteria for  seepage  pits are  similar  to  those for
trench  and  bed systems summarized  in  Table 7-1 except  that  soils with
percolation rates  slower  than  30 min/in.  (12 min/cm)  are  generally ex-
cluded.   In  addition, since  the  excavation  sidewall  is  used as  the
infiltrative surface,  percolation tests are run in each soil  layer en-
counted.   Maintaining sufficient  separation  between  the bottom of the
seepage  pit and the  high  water  table  is a  particularly important con-^"
sideration  for protection of groundwater quality.
                                    235

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                                  FIGURE 7-9

                           SEEPAGE PIT CROSS SECTION
                   4" Inspection Pipe
  Influent,
                 Reinforced Concrete Cover
                   Extended to Solid  Earth

                       Effluent

              Brick, Block, Ring, or
             .Precast Chamber
              with Open Joints

             6" to 12" of 3/4-21/2"
                  Clean Rock
      Water Table
       or Impervious Layer
4' min.  Unsaturated Soil
  i	
         7.2.3.3  Design
             a.  Sizing the Infiltrative Surface
Since the  dominant infiltration surface of  a seepage pit  is  the side-
wall, the  depth and diameter  of  the pit is  determined  from  the perco-
lation rate and thickness of each  soil  layer exposed by  the excavation.
A  weighted average of  the  percolation  test results (sum  of  thickness
times percolation rate of each  layer divided by  the total  thickness) is
used.   Soil  layers with  percolation rates  slower than 30 min/in.  (12
min/cm)  are excluded from this computation (3).
The weighted percolation rate is used to determine the required sidewall
area.   Infiltration rates  presented previously  in  Table 7-2  are  used
with  the  estimated daily  wastewater  flow  to  compute  the  necessary
sidewall area.
                                   236

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Table  7-6  can be  used  to determine the  necessary seepage pit sidewall
area for various effective depths below the seepage pit inlet.
                                 TABLE 7-6

              SIDEWALL  AREAS OF  CIRCULAR  SEEPAGE  PITS  (ft2)3
   Seepage15
     Pit
   Pi ameter
      ft

       1
       2
       3
       4
       5
       6
       7
       8
       9
      10
      11
      12
Thickness of Effective Layers Below Inlet (ft)
                                                  10
3.1
6.3
9.4
12.6
15.7
18.8
22.0
25.1
28.3
31.4
34.6
37.7
6
13
19
25
31
38
44
50
57
63
69
75
9
19
28
38
47
57
66
75
85
94
104
113
13
25
38
50
63
75
88
101
113
126
138
151
16
31
47
63
79
94
110
126
141
157
173
188
19
38
57
75
94
113
132
151
170
188
207
226
22
44
66
88
110
132
154
176
198
220
242
264
25
50
75
101
126
151
176
201
226
251
276
302
28
57
85
113
141
170
198
226
254
283
311
339
31
63
94
126
157
188
220
251
283
314
346
377
   a Areas for greater depths can be found by adding  columns.   For
     example,  the area of a 5 ft diameter pit, 15 ft  deep  is equal  to
     157 + 79, or 236 ft.

   b Diameter  of excavation.
             b.  System Layout
Seepage pits may be any diameter or depth provided they are structurally
sound and can be constructed without seriously damaging the soil.  Typi-
cally, seepage pits are 6  to  12  ft (1.8 to 3.6 m) in diameter and 10 to
20 ft (3 to 6 m)  deep  but  pits 18 in. (0.5 m) in diameter and 40 ft (12
m) deep have been constructed (22).  When more than one pit is required,
experience has shown that  a separation distance  from  sidewall  to side-
wall equal  to  3 times the diameter of the largest  pit  should  be main-
tained (3).
                                 237

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The same  guidelines  used  in locating trenches and  beds  are  used to lo-
cate  seepage  pits.   Area  should be  reserved for  additional   pits  if
necessary.
         7.2.3.4  Construction
Pits may  be dug  with  conventional excavating  equipment or with  power
augers.  Particular care must  be  exercised  to  ensure  that the  soils are
not too wet before starting  construction.   If  powered bucket augers are
used, the pits should be reamed  to a  larger diameter  than the  bucket to
minimize compaction and smearing of the soil.  Power screw augers should
only be used in granular soils because  smearing  of the sidewall  is dif-
ficult to prevent with such equipment.
To maximize  wastewater  storage, porous walled chambers  without bottoms
are usually  used.   Precast  concrete  seepage  chambers  may be used or the
chambers  may be  constructed  out  of  clay or  concrete brick,  block  or
rings.   The  rings  must have  notches  in them  to provide  for  seepage.
Brick  or block  are laid without  mortar, with  staggered  open  joints.
Hollow block may  be laid on its side but a  4-in. (10-cm) wall thickness
should be maintained.    Large-diameter  perforated pipe  standing  on  end
can be used in  small  diameter pits.   Six  to 12 in.  (15 to 30  cm)  of
clean gravel or  3/4 to  2-1/2  in.  (1.8  to 6.4 cm) crushed rock is placed
at the  bottom of the excavation  prior to placement  or  construction  of
the  chamber.   This  provides  a  firm  foundation for  the chamber  and
prevents bottom soil from being removed if the pit is pumped.


The chamber  is constructed  one  to  two  feet  smaller  in diameter than the
excavation.  The  annular space  left  between  the  wall  of the chamber and
the excavation is filled with clean gravel or crushed rock to the top of
the chamber.
Covers  of  suitable strength to  support the soil cover  and  any antici-
pated  loads are  placed over  the  chamber  and  extend at  least 12  in.
beyond  the excavation.  Access to the pit for inspection purposes can be
provided by a manhole.   If a manhole is used,  it should be covered with
6  to  12 in. (15  to 30 cm)  of soil.  An inspection  pipe  can  extend to
ground  surface.   A noncorrosive, watertight cap  should  be  used with the
inspection pipe.
                                   233

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         7.2.3.5  Maintenance
A well-designed and constructed  seepage  pit  requires no routine mainte-
nance.   However,  failure ocassionally occurs.   Pumping and  resting  is
the only reasonable rehabilitation technique  available.
     7.2.4  Mound Systems


         7.2.4.1  Description


The mound  system was originally  developed  in North Dakota  in  the late
1940's where  it became  known  as the NODAK  disposal  system  (23).   The
mound was designed to overcome  problems  with slowly permeable soils and
high water tables in rural  areas.  The absorption bed was constructed in
coarse gravel  placed over the  original  soil after the  topsoil  was re-
moved.   Monitoring  of these systems  revealed  that  inadequate treatment
occured  before  the  groundwater was reached,  and  seepage often  occurred
during wet periods of the year.   Successful  modifications of the design
were made to overcome these limitations (4).  Mound systems are now used
under a variety of conditions.
A mound  system is a  soil  absorption system that  is  elevated  above the
natural  soil  surface  in a  suitable  fill  material.   The  purpose  of the
design is to overcome site restrictions that prohibit the use of conven-
tional soil  absorption systems  (4)(24).    Such  restrictions are:   (1)
slowly permeable  soils,  (2)  shallow permeable  soils over  creviced  or
porous bedrock,  and  (3)  permeable  soils  with  high  water tables.   In
slowly permeable  soils, the mound  serves  to improve absorption  of the
effluent  by  utilizing  the  more  permeable  topsoil  and  eliminating con-
struction in the wetter and more slowly permeable subsoil, where smear-
ing  and   compaction  are  often  unavoidable.   In  permeable soils  with
insufficient  depth  to  groundwater  or  creviced  or porous  bedrock, the
fill  material  in  the  mound  provides  the  necessary  treatment  of the
wastewater (see Figure 7-10).


The mound system consists  of:   (Da suitable fill material, (2) an ab-
sorption  area,  (3)  a  distribution network,  (4)  a  cap,  and (5)  top soil
(see  Figure 7-11).  The effluent is pumped or siphoned into the absorp-
tion  area through  a  distribution network  located  in the  upper part of
the coarse  aggregate,  it  passes through  the  aggregate and infiltrates
the  fill  material.   Treatment  of  the wastewater occurs as  it passes
through the fill material  and the unsaturated zone  of the natural soil.
The cap,  usually a finer textured material  than the fill, provides  frost
protection, sheds precipitation, and retains moisture for a good vegeta-
tive  cover.  The topsoil provides a growth medium  for the vegetation.
                                   239

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                            FIGURE 7-10

                       TYPICAL MOUND  SYSTEMS
Strayv, Hay or Fabric

           Fill
 Topsoil
                                          Distribution Lateral

                                                     Absorption Bed
                                                      Layer of Top Soil
               Strata or Impermeable Soil Layer ;-:^~r=r ~s^
        (a) Cross Section of a Mound System for Slowly Permeable
                         Soil on a Sloping Site.
   Straw, Hay or Fabric

           Fill
Topsoil
                                               Distribution Lateral
                                                        Absorption Bed
                                                  Plowed Layer of Top Soil
                                                     "
                           ^

              Water Table or Creviced Bedrock |

        (b) Cross Section of a Mound System for a Permeable Soil,
           with  High Groundwater or Shallow Creviced Bedrock
                               240

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                              FIGURE 7-11

                 DETAILED SCHEMATIC  OF  A MOUND SYSTEM
                 Layer of Straw
                  or Marsh Hay
          Sandy Loam
11/4" Perforated
   Laterals
 Inlet Pi
                                                  :.*>$& Surface Water
        " - 21/2" '
      Clean Rock
                    QG
         7.2.4.2  Application
             a.   Site Considerations
Site criteria  for  mound systems are  summarized  in  Table 7-7.    These
criteria reflect current  practice.   Slope limitations for mounds are
more restrictive than for conventional systems, particularly  for  mounds
used on sites  with  slowly  permeable  soils.   The  fill  material and na-
tural  soil  interface can represent an abrupt  textural change that re-
stricts downward percolation, increasing the chance for surface seepage
from the base  of the mound.
                                  241

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                               TABLE 7-7

                    SITE CRITERIA FOR MOUND SYTSTEMS
            Item
            Cri ten' a
Landscape Position
Slope
Typical Horizontal Separation
Distances from Edge of Basal Area

   Water Supply Wells
   Surface Waters, Springs
   Escarpments
   Boundary of Property
   Building Foundations
Soil
   Profile Description
   Unsaturated Depth
Well  drained areas, level  or
sloping.  Crests of slopes or
convex slopes most desirable.
Avoid depressions, bases of slopes
and concave slopes unless  suitable
drainage is provided.

0 to 6% for soils with percolation
rates slower than 60 min/in.a

0 to 12% for soils with percolation
rates faster than 60 min/in.a
            50
            50
            10
             5
            10
to
to
to
to
to
100 ft
100 ft
20 ft
10 ft
20 ft
                                      (30 ft when located upslope from a
                                      building in slowly permeable
                                      soils).
Soils with a well developed and
relatively undisturbed A horizon
(topsoil) are preferable.  Old
filled areas should be carefully
investigated for abrupt textural
changes that would affect water
movement.  Newly filled areas
should be avoided until proper
settlement occurs.

20 to 24 in. of unsaturated soil
should exist between the original
soil surface and seasonally
saturated horizons or pervious or
creviced bedrock.
                                    242

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                          TABLE  7-7  (continued)
   Depth to Impermeable  Barrier        3 to 5 ftb

   Percolation Rate                   0 to 120 min/in. measured at 12 to
                                      20 in.c
a These are present limits used  in Wisconsin established to coincide
  with slope classes used by  the Soil Conservation Service in soil
  mapping.  Mounds have been  sited on slopes greater than these, but
  experience is limited (25).

b Acceptable depth is site dependent.

c Tests are run at 20 in. unless water  table 1s at 20 in., in which
  case test is run at 16 in.   In shallow  soils over pervious or creviced
  bedrock, tests are run at 12 in.
                                  243

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The acceptable depth to an impermeable layer or rock strata is site spe-
cific.   Sufficient depth must  be  available to channel  the  percolating
wastewater  away  from  the  mound (see  Figure  7-10).   If not,  the  soil
beneath the mound  and  the  fill  material  may become saturated, resulting
in seepage  of  effluent on the  ground  surface.   The suggested depths to
an impermeable layer given in  Table  7-7 may be  adjusted  in  accordance
with  the  site  characteristics.   Soil  permeability,  climate,  slope,  and
mound  layout determine  the  necessary  depth.   Slowly  permeable  soils
require a  greater  depth to  remove  the liquid than  do permeable soils.
Frost  penetration  reduces the  effective  depth  and  therefore  a greater
depth  is  required  in areas with severe winters.   Level  sites require a
greater depth  because  the hydraulic gradients in  the  lateral  direction
are less  than  on sloping sites.  Finally,  mound  systems extended along
the contour of a  sloping  site  require less depth  than  a  square mound.
Not enough  research information is available to give specific  depths for
these  various  conditions.    Until  further  information is  available,
mounds  on  slowly  permeable  soils  should be  made as  long  as possible,
with the restricting layer at least 3 ft (0.9 m)  below the natural  soil.
             b.  Influent Wastewater Characteristics
The wastewater entering the mound system should be nearly free from set-
tlcable  solids,  greases,  and fats.   Septic  tanks  are  commonly used for
pretreatment and have  proved  to  be  satisfactory.   Water softener wastes
are not  harmful  to  the system nor is the use of common household chemi-
cals and detergents (9)(10).
         7.2.4.3  Design


             a.  Fill Selection
The mound design must begin with the selection of a suitable fill mater-
ial because its infiltrative capacity determines the required absorption
bed area.  Medium texture sands, sandy loams, soil  mixtures, bottom ash,
strip  mine  spoil  and slags  are  used or are being  tested  (24).  To keep
costs  of construction  to  a minimum,  the  fill  should be  selected from
locally  available  materials.    Very  permeable  materials  should  be
avoided, however, because their  treatment  capacity  is  less and there is
a  greater risk  of surface seepage from the  base of the  mound when used
over the more  slowly  permeable soils.   Commonly used fill  materials and
their  respective design infiltration rates are presented in Table 7-8.
                                   244

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                                 TABLE 7-8

                  COMMONLY USED FILL MATERIALS AND THEIR
                      DESIGN INFILTRATION RATES (24)
    Fill Material
   Characteristics3
                        Design
                     Infiltration
                         Rate

                       gpd/ft2
    Medium Sand
    Sandy Loam

    Sand/Sandy Loam
      Mi xture
    Bottom Ash
>25%
<30-35%
0.25-2.0 mm
0.05-0.25 mm
0.002-0.05 mm
 5-15%    Clay Content
88-93%
 7-12%
Sand
Fi ner Grai ned
  Material
1.2



0.6

1.2



1.2
    a Percent by weight.
             b.  Geometry of the Absorption Bed
The  absorption  area within the  mound system can  either  be a bed  or a
series of trenches.   Beds are typically used  for  single  homes or other
small systems  because  they are  easier  to  construct.  The  shape  of the
bed, however,  depends  on the  permeability  of the natural  soil  and the
slope of  the  site.   In most  instances,  a  rectangular  bed with the long
axis parallel to the slope  contour  is preferred to minimize the risk of
seepage from the base  of  the  mound.  If the natural  soil  has a percola-
tion rate  slower than  60 min/in.  (24 min/cm),  the  bed  should  be made
narrow and extended along the contour as far as possible (see Figure 7-
12).    In soils  with  percolation   rates  faster  than 60  min/in.  (24
min/cm), the bed  can  be  square  if  the water table is  greater than 3 ft
(0.9 m)  below the natural ground surface (4)(25).
                                   245

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                              FIGURE 7-12

         PROPER  ORIENTATION  OF A MOUND  SYSTEM ON A COMPLEX SLOPE
                                         Mound Shaped to Conform to
                                         the Contour and to Shed Runoff
                  Avoid Concave Slopes
                  to Prevent Convergence
                  of Flow
             c.  Sizing the Filled Area
The dimensions of  the  mound are dependent on the size and shape of  the
absorption bed, the  permeability  of the natural  soil, the slope of  the
site, and the depth of fill  below the bed (see  Figure 7-13).   Depths  and
dimensions are presented in  Table 7-9.


The downslope setback (I) in Figure 7-13 is dependent on  the  permeabili-
ty of the natural  soil.  The basal area of the  mound must be  sufficient-
ly large to absorb the wastewater before it reaches  the perimeter of  the
mound or surface seepage will  result.   On  level  sites, the entire  basal
area  (L  x  W) is used  to determine  I.   However,  on  sloping  sites, only
the area below and downslope  from the  absorption bed is  considered [(B)
x  (A  +  I)].   The  infiltrative  rates  used  for  the  natural soil to size
the downslope setback are given  in  Table 7-10.   These rates  assume that
a  clogging mat  forms at the fill/natural soil  interface, which may  not
be true.   Since  the  percolating wastewater can and  does move laterally
from this area, these values  are  conservative.   However,  for soils with
percolation  rates  faster than  60 min/in.  (24 min/cm),  the   side  slope
criteria determine the  basal  area  instead  of  the  infiltration rate  of
                                  246

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                     FIGURE  7-13

                  MOUND DIMENSIONS
  Straw or Marsh Hay
Medium Sand Fill
                               Perforated
                     f4V:«raag!tegvhK:tMCTai
  'Subsoil      Plowed Surface  ^3A-2V2 in. Rock
                 (A) Cross Section
                          W
X
1

Distribution
Laterals "==:


;
Bed of
3A"-2V2" Rock-"-*



V
A
*

\
	 ., |
___^--*.
' — ~-_^
1 ^
1 i '
i
1
I
,
Slope







•• >












'



i


^v
J





/
B




K
J






*












L






                (B) Plan View
                         247

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                                TABLE 7-9

                  DIMENSIONS FOR MOUND SYSTEMS3 (25)
             Item
        Dimension
Mound Height

  Fill Depth (D), ft
  Absorption Bed Depth (F), in.
  Cap at Edge of Bed (G), ft
  Cap at Center of Bed (H), ft

Mound Perimeter

  Downs!ope Setback (I)
  Upslope Setback (J), ft
  Side Slope Setback (K), ft

Si de SI opes
        1 (inin)b
        9 (min)
        1C
         1.5C
Depends on Soil  Permeability
        10d
No Steeper Than 3:1
a Letters refer to lettered dimensions in Figure 7-13.

b On sloping sites, this depth will increase downs!ope to maintain a
  level bed.  In shallow soils where groundwater contamination is a
  concern, the fill depth should be increased to 2 ft.

c A 4-6 in. depth of quality topsoil is included.  This depth can be
  decreased by 6 in. in areas with mild winters.  If depths less than
  1 ft are used, erosion after construction must be avoided so
  sufficient soil covers the porous media.

d Based on 3:1 side slopes.  On sloping sites,  (J) will be less if
  3:1 side slope is maintained.
                                   248

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the top soil.  It is only in the more slowly permeable soils where addi-
tional basal area  is  required,  and a conservative  design  may be appro-
priate for these situations.
                               TABLE 7-10

         INFILTRATION RATES FOR DETERMINING MOUND BASAL AREA (4)
        Natural Soil Texture
Percolation
   Rate
  mi n/i n.
Infiltration
    Rate
    Sand,  Sandy Loam

    Loams,  Silt Loams

    Silt Loams, Silty  Clay Loams

    Clay Loams, Clay
    0-30

   31-45

   46-60

   61-120
     1.2

     0.75

     0.5

     0.25
             d.  Effluent Distribution
Although both  gravity  and  pressure  distribution networks  have been used
in mound  systems, pressure  distribution  networks are  superior (4)(24)
(25).  With pressure distribution, the effluent is spread more uniformly
over the entire  absorption area to minimize saturated  flow  through the
fill  and  short  circuiting,  thus  assuring  good  treatment   and  absorp-
tion.   Approximately  four  doses per day  is  suggested  (25).   The design
of pressure distributed networks is found in Section 7.2.8.
             e.  Porous Media
The porous  media  placed in the absorption bed  of  the  mound is the same
as described in Section 7.2.2.3.
             f.  Inspection Pipes
Inspection pipes are not necessary, but can be useful in observing pond-
ing depths in the absorption bed (see Figure 7-6) of the mound.
                                    249

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Example 7.1:   Calculation of Mound Dimensions and Pumping Requirements

Design a mound for a 3 bedroom house with the following site conditions.
Letter notations used in Figure 7-13 are used in this example.

    Natural  Soil Texture:                  Clay loam

    Percolation Rate at 20 in depth:       110 min/in.

    Depth to Seasonally High Water Table:  20 in.

    Slope:                                 6%

    No bedrock or impermeable layers
Step 1:  Select the  Site.   The mound  site  should be selected prior  to
         locating the  house  and the road when  possible.    Consider  all
         criteria listed  in  Table 7-7  for  possible mound  locations  on
         the  lot.    Consider the  difficulties  in  construction  of  the
         mound at  the various  locations.   Evaluate all criteria,  then
         pick the best site.

Step 2:  Select Suitable Fill Material.   It may be necessary to make a
         subjective  judgement  on  the  quality of  fill  material  versus
         transportation  costs.    The  ideal   fill  material  may  not  be
         readily available and thus selection of lesser  quality fill  may
         be practical.   If  finer,  the  loading rates used to  design  the
         absorption bed may have to be  reduced.   Assume  a medium  texture
         sand  for  this example.   The  design infiltration  rate  is  1.2
         gpd/ft^ (Table 7-8).

Step 3:  Estimate Design Flow.  Peak flow is  estimated  from the  size  of
         the  building.In  this  instance,  150  gpd/bedroom is  assumed
         (see Chapter 4).

Step 4:  Size Absorption Bed.


         Absorption Bed Area =   45° gpd ,  =375 ft2
                               1.2  gpd/fr

Step 5:  Calculate Absorption Bed Dimension.  The bed must  parallel  the
         site contour.Since  the  natural  soil  is  slowly permeable,  it
         is desirable to run the bed along  the contour  as far as possi-
         ble.  In this example, assume sufficient area  exists for  a  65-
         ft length bed.

                                  O7C ff£
                  Bed Width (A)  =  Jir I; =  5.8  ft or 6  ft
                                   oo it
                                   250

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                  Bed Dimensions:   A =  6  ft
                                   B =  65 ft
Step 6:   Calculate Mound Dimensions.
         a.   Mound Height
             Fill  Depth  (D)  =  1  ft (Table 7-9)
             Fill  Depth  (E)  =  D  +  [(Slope)  x  (A)]
                            =  1  ft + [(0.06)  x  (6)]
                            =  1.4  ft (This is only approximate.  Criti-
                              cal  factor  is  construction of  level  bed
                              bottom.)
             Bed Depth (F)  =  9  in. (min) (Table 7-9).  (A minimum of 6
                              in.  must be below the inverts of the dis-
                              tribution laterals.)
             Cap at Edge of  Bed  (G)    = 1 ft  (min)  (Table 7-9)
             Cap at Center of  Bed  (H)  = 1-1/2 ft (min)  (Table 7-9)
         b.   Mound Perimeter
             Downslope Setback (I):   The  area below and downslope of the
             absorption  bed  and  sloping sites must  be  sufficiently large
             to absorb  the  peak  wastewater flow.    Select  the proper
             natural  soil infiltration rate  from  Table 7-10.   In this
             case, the natural soil  infiltration rate  is 0.25 gpd/ft .
             Upslope Setback (J) = (mound height at upslope edge of bed)
                                   x (3:1 slope)
                                   = [(D) + (E)  +  (G)]  x (3)
                                   = (1.0 + 0.75 +  1.0)  x  (3)
                                   = (2.75) x (3)
                                   = 8.25 ft (This will be less because
                                     of natural  ground  slope, use 8 ft.)
            Side Slope Setback (K) = (mound height  at  bed center) x (3:1
                                     slope)
                                       (D)  +  (E) ^  lc\  ^ /in  x (3)
                                  251

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                       =  M.£-Id + 0.75 + 1.5 |  x (3)
                       = (3.5)  x (3)
                       = 10.5 ft,  or 11 ft
Basal  Area Required    = (B)  x [(I)  + (A)]
                       ,     450 gpd   = Ij800ft2
                          0.25 gpd/fr
             (I) MA)  =
                   (I)=  If|°°- (A)
                          1,800   (•
                       =      --
                       = 21.7 ft, or 22 ft
    Check  to  see  that  the  downslope  setback  (I)  is  great
    enough so as not to exceed a 3:1 slope:
    (mound height at downslope edge of bed)  x (3:1 slope)
                       = C(E) + (F) + (G)] x (3)
                       = (1.4 + 0.75 + 1.0)  x (3)
                       = 9.5 ft
    Since  the distance  needed  to maintain  a  3:1  slope  is
    less  than  the distance  needed  to  provide  sufficient
    basal area, (I) = 22 ft
    Mound Length (L)   = (B) + 2(K)
                       =65+2 (11)
                       = 87 ft
    Mound Width (W)    = (J) + (A) + (I)
                       =8+6+22
                       = 36 ft
                            252

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Step 7:     Design Effluent Distribution Network.  See Section 7.2.8(f).


         7.2.4.4  Construction


             a.  Site Preparation
Good construction techniques  are  essential  if the mound  is  to function
properly.  The following techniques should be considered:


Step 1:  Rope off the  site to  prevent  damage to the area during other
         construction activity  on  the lot.   Vehicular  traffic over the
         area should be prohibited to avoid soil  compaction.

Step 2:  Stake out  the  mound perimeter  and  bed  in the proper orienta-
         tion.  Reference  stakes set  some distance  from the  mound peri-
         meter are  also required  in case  the corner  stakes  are  dis-
         turbed.

Step 3:  Cut and remove  any  excessive vegetation.  Trees  should  be cut
         at ground surface and the stumps left in place.

Step 4:  Measure the average  ground elevation along the upslope edge of
         the bed to determine the bottom elevation of the  bed.

Step  5:  Install   the  delivery  pipe  from  the  dosing  chamber  to  the
         mound.  Lay the pipe below the frost line or slope it uniformly
         back to the dosing chamber  so  it may drain after dosing.  Back
         fill and compact the soil  around the pipe.

Step 6:  Plow the area within the  mound  perimeter.   Use a two bottom or
         larger moldboard  plow,  plowing  7 to 8  in. (18 to  20 cm)  deep
         parallel to the contour.   Single bottom plows should not be us-
         ed, as  the trace wheel  runs in every  furrow, compacting the
         soil.  Each furrow should be thrown upslope.   A chisel plow may
         be  used in  place  of a moldboard plow.   Roughening  the surface
         with backhoe  teeth  may be  satisfactory, especially  in  wooded
         sites with  stumps.   Rototilling is  not  recommended because of
         the damage it does to the soil  structure.  However,  rototilling
         may be used in granular soils,  such as sands.

         Plowing should not be  done when  the soil  is  too  wet.  Smearing
         and compaction of the soil will  occur.  If a  sample  of the soil
         taken from the plow  depth forms  a  wire  when  rolled  between the
         palms,  the soil  is  too  wet.    If it  crumbles,   plowing may
         proceed.
                                    ?53

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             b.  Fill Placement
Step  1:  Place  the  fill material  on  the  upslope  edges  of  the  plowed
         area.   Keep  trucks off the  plowed area.   Minimize  traffic on
         the downslope side.

Step  2:  Move  the  fill material  into  place  using  a  small  track  type
         tractor with a blade.   Always  keep a  minimum  of 6 in. of mate-
         rial  beneath  the  tracks of the tractor  to minimize  compaction
         of  the  natural  soil.   The fill  material  should  be  worked in
         this manner until  the  height  of the  fill  reaches the elevation
         of the top of the absorption bed.

Step 3:  With  the blade of the tractor, form  the  absorption  bed.   Hand
         level the bottom  of the bed,  checking it for  the proper eleva-
         tion.  Shape the sides to the desired slope.
             c.  Distribution Network Placement


Step 1:  Carefully place the coarse aggregate in the bed.  Do not create
         ruts  in  the  bottom of  the  bed.    Level  the  aggregate  to  a
         minimum depth of 6 in.  (15 cm).

Step 2:  Assemble the distribution network on the aggregate.   The mani-
         fold  should  be placed so  it will  drain between  doses,  either
         out the laterals  or back into the pump chamber.   The laterals
         should be laid level.

Step 3:  Place additional  aggregate  to  a  depth  of at  least 2 in.  (5 cm)
         over the crown of the pipe.

Step 4:  Place a suitable backfill barrier over the aggregate.


             d.  Covering


Step 1:  Place a finer  textured  soil  material  such  as clay or silt loam
         over the top of the bed to a minimum depth of 6 in. (15 cm).

Step 2:  Place 6  in. (15  cm)  of  good  quality topsoil  over  the  entire
         mound surface.

Step 3:  Plant grass over  the entire mound  using  grasses adapted  to the
         area.   Shrubs  can be planted  around the base and up the side-
         slopes.  Shrubs  should  be somewhat moisture  tolerant since the
         downslope  perimeter may become  moist  during early  spring and
         late  fall.   Plantings  on top of  the mound  should  be drought
                                    254

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         tolerant,  as  the  upper  portion  of the  mound  can  become  dry
         during the summer.
         7.2.4.5  Operation and Maintenance


             a.  Routine Maintenance
A properly  designed  and constructed mound should operate satisfactorily
with virtually no regular maintenance.
             b.  Rehabilitation


Three failure  conditions  may occur within the mound.   They are (1) se-
vere clogging  at the bottom  of the absorption area, (2) severe clogging
at the fill material and natural soil interface, and (3) plugging of the
distribution network.  Usually these failures can be easily corrected.


If severe clogging occurs at the bottom of the absorption bed, its cause
should first  be determined.   If it is  due  to failure  to  maintain the
pretreatment unit, hydrogen peroxide to oxidize the accumulated organics
at the infiltrative  surface  could  be used.   The chemical can be applied
directly to the bed  or through the dosing chamber.  Because of the dan-
ger  in  handling this  strong  oxidant,  this treatment  should  be done by
professionals.


If  the  clogging  is due  to  overloading  or  unusual wastewater charac-
teristics,  efforts  should be  made to  reduce  the wastewater  volume or
strength.   It may  be  necessary  to enlarge the  mound.  The  mound cap
should be  removed and  the  aggregate in  the absorption  bed stripped out.
The  area  down si ope  of the mound  should be plowed  and additional  fill
added to  enlarge  the mound to the  proper size.   The absorption bed can
then be reconstructed.
Severe clogging  at the fill and  natural  soil  interface will cause sur-
face seepage at the base of the mound.  This area should be permitted to
dry  and  the downslope area plowed.   Additional  fill  can then be added.
If this does not correct the problem, the site may have to be abandoned.
Partial plugging of the distribution piping may be detected by extremely
long dosing  times.   The  ends of the distribution laterals should be ex-
posed and the pump activated to flush out any solid material.  If neces-
sary, the pipe can be rodded.
                                  255

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         7.2.4.6  Considerations for Multi-Home and Commercial
                  Wastewaters
Designs of  the mound  system for  larger flows  follow the same  design
principles as  for  smaller  flows.   In cluster systems  serving more  than
five homes, however, peak flow estimates can be  reduced  because  of  flow
attenuation, but contributions from  infiltration  through  the collection
system must be included.  Peak flow estimates should be based on  the to-
tal  number of  people  to be served (see Chapter 4).   Rates  of  infiltra-
tion vary with the type of collection sewer used  (19)(20).


With commercial flows,  the  character of the wastewater is  an  important
consideration.   Proper  pretreatment is necessary  if the  character  is
significantly different than domestic wastewater.


Modifications  to  the  design  of  the mound  system may be desirable for
larger  flows  on sloping  sites or in slowly permeable soils.    In  both
instances,  the absorption  area  should be  broken up  into  a  series  of
trenches or  smaller beds.   This  is  beneficial  on  sloping sites  because
the beds can be tiered to reduce  the amount of  fill required (see Figure
7-14).  Depths of  fill  material  below beds should not exceed 4  to  5  ft
(1.3 to 1.7 m)  because  differential  settling will  cause  the bed  to  set-
tle unevenly.  If the  system is tiered,  each trench or bed must be dosed
individually.   This can be  done  by automatic  valving  or alternating
pumps or siphons.


In sites with  slowly permeable soils, breaking the absorption  area  into
smaller trenches or beds helps  distribute  the effluent over much wider
areas.  Spacing of the beds or trenches should  be sufficient so that the
wastewater contributed from one trench or bed is  absorbed  by the  natural
soil  before  it reaches  the lower  trench or bed  (see Table 7-10).   The
beds or trenches should be as long as the site  allows.  A long  bed,  bro-
ken  into  several  shorter systems, each  served  by a pump or siphon,  is
preferred  over two or  more  short  parallel beds,  especially  in soils
where the effluent moves downslope.
Flexibility in operation  should  also  be  incorporated  into  systems serv-
ing  larger  flows,  since  a  failure  can  create  a significant  problem.
Alternating bed  systems  should  be  considered.   A three-bed system  is
suggested where  each  bed contains 50% of  the required absorption  area
(19).   Two  beds are  always  in operation,  providing 100%  of  the  needed
infiltrative  surface.   The  third  bed is  alternated  into  service  on  a
yearly  schedule.    Thus,  each field  is  in  service for two years  and
"rested"  for  one  year  to rejuvenate.   The  third bed also  acts  as  a
standby  unit  in  case one  bed  fails.   The  idle  fields can be  put  into
service immediately while the failed bed  is rehabilitated.
                                   256

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                               FIGURE  7-14

                           TIERED  MOUND  SYSTEM
                                      Gravel-Filled
                                     Absorption Bed
     7.2.5  Fill Systems
         7.2.5.1  Description
Fill systems may be  used  on  sites with slowly permeable soils overlying
sands and sandy loams where  construction  of a conventional  system below
the  tight  soil  horizons may  be ruled out.   If the depth  from  the top
surface  of  the underlying  sand  or sandy  loam  to the  seasonally high
water table or  bedrock  is inadequate  to  construct a  trench or bed sys-
tem, the slowly permeable soil  may be stripped away and replaced with a
sandy fill material  to  provide 2  to  4 ft (0.6 to  1.2  m) of unsaturated
soil.  A trench or bed system may then be constructed within the fill.
Mound  systems  would also be  suitable designs for  these  conditions and
may be less  expensive to construct,  but  fill  systems  offer some advan-
tages.   If the  soils  overlying  the sands or sandy loams are very slowly
permeable, the size of a fill  system may be smaller than that of a mound
permitting their installation in smaller areas.  Also, fill systems usu-
ally have less  vertical  relief above the  natural  grade  than do mounds.
This may be desirable for landscaping purposes.
                                   257

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         7.2.5.2  Application


             a.  Site Considerations
The use  of  fills is restricted to  sites  where unsuitable surface soils
may be stripped  away without  damaging  the underlying soils.   Therefore,
fills are limited to sites where the underlying soils are sands or sandy
loams  and  the  seasonally  high water  table or  bedrock surface  is  not
within 1 ft  (0.3 m)  of the sand or sandy loam surface.  If the depth to
the seasonally  high water table  or bedrock is  greater than 3 to  5 ft
(0.9 to  1.5 m)   from the sandy  or sandy loam  surface,  a  fill  system is
not necessary.   A deep  trench or  bed  system can be constructed directly
in the more permeable underlying area.
Once the fill is placed, the site must meet all the site and soil  crite-
ria required for trench or bed systems (see Table 7-1).
             b.  Influent Wastewater Characteristics
The  influent wastewater must  be free  of  settleable solids,  fats,  and
grease.  Water softener wastes are not harmful, nor is the normal  use of
household chemicals and detergents.
         7.2.5.3  Design
Since fill  systems  differ  from  trench and bed systems only in that they
are constructed  in  a  filled  area,  the design of fill  systems is identi-
cal  to  trenches and  beds.   The only unique  features are  the sizing of
the area  to be filled and the  fill  selection.   Uniform distribution of
the wastewater  over the  infiltrative surface through  a  pressurized net-
work is suggested to maintain groundwater quality (11).
             a.  Sizing of the Filled Area
A minimum  separation  distance of 5 ft  (1.5  m)  between the sidewalls of
the  absorption  trenches  or bed, and the  edge  of the filled area should
be maintained.  This allows for sidewall absorption and lateral movement
of the wastewater.
                                   258

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If a perched water table  condition  occurs  in the surface soils that are
to be moved, provisions should  be made  to  prevent this water from flow-
ing into the  filled  area.  Curtain drains,  perimeter drains or barrier
trenches may  be  necessary upslope  or  around the filled  area  to remove
this water (see Section 7.2.6).
             b.  Fill Selection
The fill material should be similar in texture to the underlying sand or
loamy  sand.   The backfill material  used to cover  the  system should be
finer textured to shed surface runoff.  It may be the original soil that
was removed.
         7.2.5.4  Construction
Care should be exercised  in  removing  the unsuitable soil  prior to fill-
ing  to prevent  excessive disturbance  of  the  sandy  soil  below.   The
machinery  should  always  operate  from unexcavated  areas.   The  top  few
inches of  the  sand or sandy loam  soil  should  be  removed  to ensure that
all the unsuitable soil is stripped.
The exposed surface should be harrowed or otherwise broken up to a depth
of 6 in. (15 cm) prior to filling.  This eliminates a distinct interface
forming between the fill  and  the natural  soil  that would disrupt liquid
movement.
Once the fill has been placed, construction of the absorption system can
proceed as for trenches or beds in sands.  However, if the fill depth is
greater than  4  ft (1.2 m), the  fill  should  be allowed to settle before
construction begins.   This  may require a year to settle naturally.  To
avoid  this  delay,  the fill  can be  spread  in shallow lifts and each me-
chanically  compacted.   This  must be  done  carefully, however,  so that
layers  of  differing density  are  not created.  The  fill  should be com-
pacted to a density similar to the underlying natural soil.
         7.2.5.5  Operation and Maintenance
The operation  and  maintenance  of fill  systems are identical to trenches
and beds  constructed in sands.   The  fill  system lends itself very well
to treatment with  chemical oxidants or reconstruction in the same area.
                                   259

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     7.2.6  Artificially Drained Systems


         7.2.6.1  Description


High water  tables  that limit the use of  trenches,  beds  or seepage pits
can sometimes be artificially lowered to  permit  the use  of these dispo-
sal methods.   Vertical  drains,  curtain drains and  underdrains  are com-
monly  used  subsurface  drainage  techniques.   Soil  and  site  conditions
determine which method is selected.
Curtain  drains and  vertical   drains  are  used to  lower perched  water
tables.   These methods  are  most effective  where the perched  water is
moving laterally under the soil  absorption site.   The drains are placed
upstream of the absorption area to intercept the groundwater as it flows
into the area.
Curtain drains  are  trench  excavations  in which perforated drainage pipe
is  placed.   These  are  placed  around the upslope perimeter  of  the soil
absorption  site  to  intercept the groundwater moving  into  the  area (see
Figure 7-15).   If the  site has  sufficient slope,  the drains are brought
to  the surface  downsi ope to allow free drainage.   On level sites, pumps
must be  used to remove  the collected  water.   If the restrictive layer
that creates the water table is thin and overlies permeable soil, verti-
cal drains  may  be  used.   These  are  trench  excavations  made through the
restrictive layer into the more permeable soil below and backfilled with
porous material  (see Figure 7-16).   Thus,  water moving  toward the ex-
cavation is able to drain  into the underlying soil.   Vertical drains are
susceptible to sealing by  fine sediment transported by the water.


Underdrains  are  used where water tables exist  4 to  5 ft  (1.2  to 1.5 m)
below the surface in permeable soils.  The drains are similar to curtain
drains in construction, but several drains may be necessary to lower the
water  table sufficiently  (see Figure  7-17).   Depth  and  spacing of the
drains are  determined by the soil and water table characteristics.
         7.2.6.2  Site Considerations
Successful  design  of artificially  drained systems depends upon the cor-
rect  diagnosis  of  the drainage problem.   The  source of the groundwater
and  its flow characteristics  must be  determined to select  the proper
method  of  drainage.   Particular  attention must be given to soil strati-
fication and groundwater gradients.
                                  260

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                                FIGURE 7-15

         CURTAIN DRAIN TO  INTERCEPT LATERALLY MOVING PERCHED  WATER
               TABLE CAUSED  BY A SHALLOW, IMPERMEABLE LAYER
     Curtain
      Drain


 Material
Perched
 Water
 Table
Gravel Filled
Above High
Water Table
  -^.Drainage Pipe
                                          ^Absorption
                                           Trenches
                                                   Impermeable Layer
                                FIGURE  7-16

       VERTICAL DRAIN TO INTERCEPT LATERALLY MOVING PERCHED WATER TABLE
                CAUSED BY A SHALLOW,  THIN, IMPERMEABLE LAYER
          l?gpK^^^^
          $&$	Fl11        '             ^^^^,
          *kfe#  i\/i-,+—;-,i      I                     y
                Material
                             i
                  Gravel Filled
                  Above High
                  Water Table
                Permeable
                   Soil
                                    Impermeable Layer

                                   Absorption Bed
                                                        Backfill
                                   261

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                                 FIGURE 7-17

                    UNDERDRAINS USED TO LOWER WATER TABLE
                                Underdrains
                                                                   Fill
                                                                 Material
Absorption
 Trenches
 1        I
                    Gravel Filled
                    Above High
                    Water Table
                                          Drainage Pipe
             a.  Subsurface Drainage Problems
There is  an  unlimited variety of  subsurface  drainage problems but  the
most  common  ones can  be  grouped into four general  types (26).   These
are:   (1)  free water  tables,  (2)  water tables over  artesian  aquifers,
(3) perched water tables,  and (4) lateral  groundwater flow problems.


Free  water tables typically  are  large, slow moving bodies of  water  fed
by  surface waters,  precipitation,  and  subsurface  percolation from  other
areas.   In the lower elevations  of the drainage  basin,  the groundwater
is  discharged  into  streams,  on  the  ground  surface in low areas,  or  by
escape  into  other   aquifers.    The   groundwater  elevation  fluctuates
seasonally.   The slope of a  free  water table surface is  usually  quite
gentle.
                                   262

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Where the soil is permeable,  underdrains can  be  used to lower the water
table sufficiently to permit  the  installation of  trench or bed disposal
systems.  In  fine textured  soils  of  slow permeability,  however, subsur-
face drainage is impractical.


An  artesian  aquifer  is  a  groundwater  body  confined  by  an  impervious
layer over the  aquifer.   Its  pressure surface (  the elevation to which
it  would  rise in a well  tapping  the aquifer) is higher  than  the local
water table,  and may even  rise  above the  ground surface.   Pressure  in
the aquifer  is  caused by the  weight  of a  continuous body of water that
is  higher than the local  water table.   Leaks  at  holes or weak points  in
the  confining layer  create  an  upward flow,  with  the  hydraulic  head
decreasing  in the  upward  direction.   The  groundwater  moves in  the
direction  of the  decreasing  gradient  and escapes  as  seepage at  the
ground surface or moves laterally into other aquifers.
Areas with this problem  are  impractical  to  drain.   The water removed is
continually replenished from the aquifer.  This requires relatively deep
and  closely  spaced drains and  pumped  discharges.   Onsite  disposal  op-
tions other than soil absorption systems should be investigated in areas
with shallow artesian aquifers.
In  stratified  soils,  a water  table may develop that  is  separated from
the free water table  by a  slowly permeable layer,  i.e., a perched water
table.   This  occurs  when  surface sources of  water saturate  the soil
above the layer due to slow natural drainage.   Methods employed to drain
perched water tables depend upon the particular site conditions.  Verti-
cal drains, curtain drains or underdrains may be used.
Lateral  groundwater  flow  problems  are  characterized  by  horizontal
groundwater  movement  across  the  area.   This  flow  pattern  is  usually
created by soil stratification or other natural barriers to flow.
The  depth, orientation  and  inclination  of the  strata or barriers deter-
mine the drainage method used and its location.  Curtain drains or vert-
ical drains  are  usually employed  to  intercept  the water upstream of the
area to be drained.
             b.  Site Evaluation
Soils  with high water  tables  that may be practical to  drain  to make a
site  suitable for  a  trench or bed  system are ones having  (1)  shallow
perched  water tables,  (2)  lateral  groundwater flow, or  (3)  free water
tables in  coarse textured soils.   Soils that are saturated for prolonged
                                   263

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periods, particularly on level  sites, are not practical  to drain.   Other
disposal methods should be investigated for such sites.


Because each of  these  drainage  problems  require different solutions,  it
is important that  the site evaluation  be done in sufficient  detail  to
differentiate between  them.   Where the need for  subsurface  drainage  is
anticipated, topographic  surveys,  soil  profile descriptions  and estima-
tion of the  seasonally  high groundwater  elevations and  gradients  should
be emphasized.   Evaluation of  these site characteristics must be done  in
addition to other characteristics that are evaluated  for subsurface dis-
posal (see Chapter 3).


Topographic Surveys:   Topographic  maps of the  site with  1 to  2 ft (0.3
to 0.6  m)  contour  intervals are useful as base maps  on which  water and
soils information can be referenced.  Water table elevations, seep areas
and areas with  vegetation indicative of seasonal or prolonged high water
tables should be locaf   >n the map.  Elevations of ridges,  knolls, rock
outcrops and natural drainage ways  should  also be noted.   This informa-
tion is useful  in establishing the source of the groundwater, its direc-
tion of flow, and the placement of the drainage system.
Soil Profile Descriptions:  The  soil  profile  must  be carefully examined
toidentify  the  type  of drainage  problem and  the  extent of  seasonal
water table  fluctuations.   Soil  stratification and  soil color  are used
to make these determinations.


Soil stratification or layering may or may not be readily visible.  Soil
texture, density, color, zones of saturation and root penetration aid in
identifying  layers  of varying  hydraulic  conductivity  (see Chapter  3).
The thickness and slope of each layer should be described.   Deep uniform
soils indicate that the drainage problem must be handled as a  free water
table  problem.    Stratified  soils  indicate  a  perched  or lateral  flow
groundwater problem.


The soil color helps to identify zones of periodic  and continous satura-
tion.  Soil mottling occurs when the soil  is periodically saturated,  and
gleyed soil  indicates continuous  saturation (see Chapter 3).   The high-
est  elevation  of the mottling  provides  an estimate of the  seasonally
high water table, while the top of the gleyed zone  indicates the season-
ally low water table elevation.   It is  particularly  important to estab-
lish the extent of the seasonal  fluctuations to determine if drainage is
practical.   If the  seasonally low water table is above the elevation to
which  the  soil  must  be drained  to make the  site acceptable,  drainage
must be  provided  throughout  the year.   If  pumps are used  to  remove  the
water,   costs  may  be   excessive  and   other  alternatives   should   be
investigated.
                                  264

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Groundwater. Elevation  and Gradients:   To  accurately  determine ground-
water  elevations  and  gradients,  observation  wells  or  piezometers  are
used.   Observation  wells are  used  to observe  groundwater flutuations
throughout a year  or more.   If several  are  strategically  placed about
the  area,  the  local  gradient  can  also be  established  by measuring  the
water  surface  elevation  in each well.    Piezometers differ  from obser-
vation wells in  that they are constructed so that  there is no leakage
around the pipe.   The water surface elevation measured establishes  the
hydrostatic pressure at  the bottom  of the well.  If  placed at several
depths, they can be used to establish whether artesian conditions exist.
For construction of piezometers and interpretation of results, see USDA,
"Drainage of Agricultural  Land" (26).


The  measured  or estimated water  table elevations  for  a  specific  time
period are plotted on  the topographic map.   By  drawing the contours of
the  water  table  surface  from these plots,  the direction of groundwater
movement is determined,  since movement is  perpendicular to the ground-
water  contours.   This helps  locate  the source of the  water and how to
best place the drainage network.
         7.2.6.3  Design


             a.  Selection of Drainage Method
In  designing a  subsurface  drainage  system,  the site characteristics are
evaluated  to  determine which  method of  drainage  is most  appropriate.
Table   7-11   presents   the   drainage   method   for   various   site
characteristics.   In  general,  shallow,  lateral flow  problems  are  the
easiest drainage problems to correct for subsurface wastewater disposal.
Since the  use  of  underdrains for onsite disposal  systems has  been very
limited, other  acceptable  disposal  methods  not requiring  drains should
first be considered.
             b.  Curtain Drains
Curtain drains  are  placed some distance upslope  from  the proposed soil
absorption system to intercept the groundwater, and around either end of
the  system  to prevent  intrusion.   On sites  with sufficient slope, the
drain is extended downslope until it surfaces, to provide free drainage.
The  drain is  placed slightly into the restrictive  layer to ensure that
all  the groundwater is  intercepted.  A separation distance from the soil
absorption  system  is  required to  prevent  insufficiently treated waste-
water from entering the drain.  This distance depends on the soil perme-
ability and  depth  of drain  below the bottom  of  the absorption system;
however, a separation distance of 10 ft is commonly used.
                                   265

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                               TABLE 7-11

            DRAINAGE METHODS FOR VARIOUS SITE CHARACTERISTICS
        Site Characteristics
  Drainage
  Problem
Drainage Method
Saturated or mottled soils above a
restrictive layer with water source
located at a higher elevation; site
usually sloping

Saturated or mottled soils above a
restrictive layer; soil  below
restrictive layer is unsaturated;
site is level or only gently sloping

Deep uniform soils mottled or
saturated

Saturated soils above and below
restrictive layer with hydraulic
gradients increasing with depth
Lateral flow
Perched water
table
Free water
table

Artesian-fed
water table
Curtain drain
Vertical  drain3
Underdrai nb
Vertical  drain3
Underdrai


Avoi d
3 Use only where restrictive layer is thin and underlying  soil  is
  reasonably permeable.

b Soils with more than 70% clay are difficult to drain and should  be
  avoided.
                                   266

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The size of the drain  is  dependent upon the soil  permeability, the size
of the area drained, and the gradient of the pipe.  Silt traps are some-
times  provided  in the  drain  to  improve  the quality of  the  discharged
drainage.  These units may require infrequent cleaning to maintain their
effectiveness.
             c.  Vertical Drains
Vertical drains  may be  used to intercept  a laterally  flowing  perched
water table.   Separation distances between the drain  and  the bottom of
the soil absorption  system are the same as  for  curtain drains to main-
tain an unsaturated zone under the absorption system.


The size and placement of the drain depends upon the relative permeabil-
ities of the  saturated  soil  and  the  soil  below  the restrictive layer,
and the size of the area to be drained.  The infiltration surface of the
vertical drain (sidewalls  and bottom  area) must  be  sized  to absorb all
the water  it  receives.   The  width and depth  of  the  drain  below the re-
strictive layer  is  calculated by  assuming an infiltration  rate  for the
underlying  soil.   If clay and silt are  transported  by the groundwater,
the infiltration  rate  will be less  than the saturated  conductivity of
the soil.   Clogging of the vertical  drain by silt can be  a significant
problem.    Unfortunately,  experience  with  these  drains in  wastewater
disposal is lacking.
             d.  Underdrains
Underdrains  must be  located to  lower the water  table to  provide the
necessary  depth  of unsaturated  soil  below the  infiltrative  surface of
the soil absorption system,  and  to  prevent poorly  treated effluent from
entering the drain.  Sometimes, a network of drains is required through-
out the area where the soil absorption system is located.  The depth and
spacing of  the  drains is determined by  the  soil  permeability, the size
of the area to be drained, and other factors.  Where necessary, however,
see USDA Drainage of Agricultural Land (26) for design procedures.
         7.2.6.4  Construction


             a.  Curtain Drains and Underdrains
To  maximize  infiltration  of  the groundwater  into  the pipe,  a coarse,
porous  material  such as  gravel, crushed  rock,  etc., should  be placed
under  and above  the  pipe.   The  porous  material  is  extended  above the
                                   267

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high  water table  elevation.    To  prevent  silt  from entering  the pipe
while the  disturbed area  is  stabilizing,  the  tops of the joints or per-
forations  should  be covered  with waterproof building paper  or the pipe
jacketed with mesh.   Natural  soil  material  is  used for  the remainder of
the backfill (27).
The  outlet must  be  protected from  small  animals.   The outlet  may be
covered with  a porous  material  such as rock  or gravel.   Various com-
mercial outlet protection devices are also available (26).


             b.  Vertical Drains
Vertical  drains  are dug to  the  desired depth and width,  and are back-
filled with  a  coarse,  porous media such as  coarse  sand,  1/4- to 1/2-in
(0.6  to  1.3  cm)  gravel, or  similar material,  to a  level  above the high
perched water  table elevation.   Natural  soil  materials are used for the
remainder of the backfill.
         7.2.6.5  Maintenance
A well-designed  and  constructed drainage system requires little mainte-
nance.    The  outlets  should  be  inspected  routinely  to  see  that free
drainage  is maintained.   If  a silt trap is used, it should be inspected
annually  to determine the need for cleaning.
     7.2.7  Electro-Osmosis


         7.2.7.1  Description
Electro-osmosis is a technique used to drain and stabilize slowly perme-
able  soils during excavation.   A direct current  is  passed  through the
soil,  which  draws  the  free  water  in  the  soil   pores  to  the  cathode
(28).   The water  collects  at  the cathode and is pumped out.   Steel  well
points  serve  as  cathodes,  and steel  rods driven  between  wells are used
as  anodes.  Common  practice is  to  install  the  electrodes approximately
15  ft (4.6 m) apart,  and  apply  a  30- to 180-volt potential.   Current
flow  is 20 to 30  amps (28).
Recently, a  similar technique has been applied to onsite wastewater dis-
posal  in  soils  with  percolation  rates  slower  than 60  min/in.  (24
min/cm).  A  galvanic  cell is constructed out of natural materials, which
requires no  external  power source.  This cell is capable of generating a
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0.7- to  1.3-volt potential  (29).  Conventional  absorption  trenches  are
constructed and  a mineral  rock-filled anode  is  installed  immediately
adjacent to the  trench.  Coke-filled  cathodes with graphite  cores  are
installed some distance from the trench  (see  Figure 7-18).   The  water
that moves to  the cathode is claimed to be removed by evapotranspiration
(30).   These  systems have  been  used successfully in California,  Iowa,
Minnesota, and Wyoming (29).
         7.2.7.2  Site Considerations
Electro-osmosis systems were  developed  to  enhance wastewater absorption
in  slowly  permeable  soils.    They  are used  in  soils with  percolation
rates slower than 60  min/in.  (24 min/cm).   Criteria for  soil absorption
trench or bed are presented in Table 7-1.
         7.2.7.3  Design and Construction
The electro-osmosis system is patented.   Design and construction of sys-
tems are done by licensees.
         7.2.7.4  Operation and Maintenance
Once  installed,  no routine maintenance of  the electrodes has  been  re-
ported.   Maintenance  techniques  for the. soil  absorption  trench  are
presented in Section 7.2.2.5.
     7.2.8  Effluent Distribution Network for Subsurface
            Soil Absorption Systems
Several  different  distribution  networks are  used  in  subsurface  soil
absorption systems.  They include single line,  closed loop,  distribution
box,  relief  line,  drop  box,  and pressure  networks.   The  objective  of
each  is  to   apply  the  pretreated  wastewater  over  the  infiltrative
surface.
The  choice  of one  network  over another depends  on the type of  system
proposed and the method of wastewater application desired.   Networks for
the various types of systems versus the method of wastewater application
are given in  Table  7-12.  Where more than  one network is suitable,  they
are listed in order of preference.
                                    269

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               FIGURE 7-18

   TYPICAL ELECTRO-OSMOSIS SYSTEM  (30)
       Anodes
                   Anodes
From
Anode /
V
Septic Tank g^H
u_ - —

Absorption
/f8"
/

Trenches
Wide Dike

a Anode

\
i

Q.
CO
Cathode
4" Graphite Cores
               Cathode
              4" Vents

                Plan View
                    A*-1
                  Slope
 .Cathode (+)
             Absorption
               Trench
                     Anode (-),
               Distribution
            Coke
                      Mineral
                        Rock
                Section A-A
                    270

-------
                                                    TABLE  7-12

                    DISTRIBUTION NETWORKS FOR VARIOUS SYSTEM  DESIGNS AND APPLICATION METHODS*
         Method
           of
      Application  Single Trench
                               Mul ti-Trench
                              (Fills,  Drains)
                               On Level  Site
                     Multi-Trench
                       (Drains)
                    On Sloping Site
                            Beds
                      (Fills,  Drains)        Mounds
ro
      Gravity
      Dosing
             Single line
             Single line
             Pressure
Uniform      Pressure
Application
Drop box
Closed loop
Distribution box

Closed loop
Pressure
Distribution box

Pressure
Drop box
Relief line
Distribution boxb

Distribution box
                                                      Pressure0
Closed loop        Not applicable
Distribution box
Closed loop
Pressure
Distribution box

Pressure
Not applicable
                                        Pressure
      a Distribution networks are listed in order of preference.

      b Use limited by degree of slope (see Section 7.2.8.1  d)

      c Because of the complexity of a pressure network  on a sloping  site,  drop  boxes  or  relief lines are
        suggested.

-------
         7.2.8.1  Design


             a.   Single Line
Single-line  distribution  networks  are trenches  loaded by  gravity  or
dosing.   The distribution line is a  3- to  4-in.  (8- to 10-cm)  diameter
perforated pipe laid level  in the center of the  gravel-filled  excavation
(see Figure 7-19).   The pipe is usually laid such that the holes are  at
or  near  the  invert of  the pipe.   Where  the  length  of  single  lines
exceeds 100 ft  (30 m), it  is preferable to locate the wastewater  inlet
toward the center of the line.
             b.  Drop Box
Drop  box  networks  are typically  used for  continuously ponded  multi-
trench systems on level  to maximum sloping lots.   It  is  a  network  that
serially loads each trench to its full  hydraulic capacity.
A drop  box  is a small, circular  or  square box with a  removable  cover.
It has  an inlet, one or two distribution  lateral  outlets,  and  an over-
flow.   The  lateral  outlet  inverts are located at  or near the bottom  of
the box, all of the  same diameter pipe.   The  overflow  invert can  be the
same elevation as the crown of the lateral  outlet, or  up to 2 in. above
it, to cause the full depth of the trench to flood.  The inlet invert of
the drop box  may  be at the same  elevation as the overflow  invert  or a
few inches  above.   An  elevation  difference of 1  to 2 in.   (3 to  5 cm)
between trenches is  all that is  needed  to install a  drop  box  network.
The boxes may be buried,  but  it is  suggested  that the covers be  left
exposed for periodic inspection  and maintenance (see Figure  7-20).
Drop boxes  are  installed at the  wastewater  inlet of each trench.   The
inlets may  be  located anywhere along  the  trench length.  A  solid  wall
pipe connects the overflow from the higher  box to the inlet of the lower
box.   The  first box  in  the  network receives all the effluent  from the
pretreatment tank  and distributes it  into the  first trench.   When the
first  trench  fills,  the box  overflows into  the  next  trench.  In  this
manner, each trench in the system is used successively  to its full  capa-
city.   Thus, only  the  portion  of the  system   required  to   absorb  the
wastewater is used.  During periods of high flow or low absorptive capa-
city of  the soil,  more  trenches  will  be used.    When  flows  are  low or
during the hot dry summer months,  the  lower  trenches may not be needed,
so  they  may drain  and  dry  out,   automatically  resting more  trenches,
which rejuvenates their infiltrative surfaces (11).
                                    272

-------
                            FIGURE  7-19

                 SINGLE LINE DISTRIBUTION NETWORK
\A
P

Z2 C


/atertight
ipes and
Joints
*5 ft.H
Min 1

— * B A
, 	 \
—-R
       Pretreatment
            Unit
:•• K^M^i^fTTT^Tr??^.'..i....... .   in.,..	

	IT-ITI '•••- *  'f?           Perforated Pipe'^:;;^--'^S:>
'	  ^-1       ft  ^"—-~;;r—_'.. J".'.".'; ;^_""  "     """	•.'"  ~—^1
                       ^"Level or 2 in. to 4 in.
                           per 100 ft.  Slope
                            Section A-A
                   Overfill to Allow
                    for Settlement
                   Distribution Pipe
                      Crushed Stone
                         or Gravel
I 6 in. min
                                         Section B-B
                              273

-------
                          FIGURE 7-20

          DROP BOX DISTRIBUTION NETWORK  ([AFTER  (22)]
      Inlet From
     Pretreatment
      or Previous
       Drop Box
Outletto
 Trench
           Overflow
            to Next
           Drop Box
                          Outlet to
                           Trench
                     Plan
                                     - Inlet
                                          Outlet to
                                           Trench
             Distribution \\\
                Pipes
Pretreatment
    Unit     Water-Tight
                Pipes
                               Plan
                   Extra Trenches
                j      Can be
             ._!.Li_  Added If
                     Necessary
                            Covers May be Exposed at
                            Surface if Insulated in
                            Cold Climates
                                Drop Boxes

                              Section A-A
                             274

-------
The liquid level in the  trenches  is  established  by the elevation of the
overflow invert leading to the succeeding drop box.  If the elevation of
this invert is near the top of the rock in the trench,  the entire trench
sidewall will  be utilized, maximum hydrostatic head will  be developed to
force  the  liquid into the  surrounding soil, and  evapotranspiration by
plants during the growing season will be maximized by providing a supply
of liquid to the overlying soil.


The drop  box  design  has several  advantages  over single  lines,  closed
loop,  and distribution box networks for continuously ponded systems.   It
may be  used on  steeply sloping sites without surface  seepage  occurring
unless  the  entire  system  is  overloaded.    If the system  becomes  over-
loaded, additional  trenches can  be  added easily without  abandoning or
disturbing the existing system.   Drop  box networks  also  permit unneeded
absorption  trenches  to  rest  and rejuvenate.   The  lower trenches  are
rested  automatically  when  flows  are  low or  infiltration capacity  is
high.    The  upper trenches may be rested  when necessary  by plugging  the
drop box lateral  outlets.
             c.  Closed Loop
In  absorption  systems  where the entire  infiltrative  surface is at  one
elevation, such  as  in  beds or  multi-trench  systems on level or nearly
level sites, closed loop networks may be used.   The distribution pipe is
laid level over  the gravel  filled  excavation and  the  ends  connected  to-
gether  with  additional pipe  with  ell or  tee  fittings.   In beds,  the
parallel lines are usually  laid  with  3 to  6  ft (0.9 to 1.8 m)  spacings.
A tee, cross, or distribution box may be used at the inlet  to the closed
system (See Figure 7-21).
             d.  Distribution Box
Distribution box  networks  may be  used  in  multi-trench systems or  beds
with independent distribution laterals.  They are  suitable  for  all  gra-
vity-flow systems.


The distribution laterals in the network extend  from a common watertight
box called  the  distribution  box.   The box may  be  round  or  rectangular,
with a  single  inlet, and  an  outlet for each distribution  lateral.   It
has an exposed, removable  cover.   Its  purpose is  to divide  the  incoming
wastewater equally between each lateral.  To achieve this objective, the
outlet inverts must  be at  exactly  the  same  elevation.   The  inlet  invert
should  be  about 1 in.  above  the outlet inverts.   Where dosing  is em-
ployed or where the  slope  of  the  inlet pipe  imparts a significant velo-
city to  the  wastewater  flow,  a baffle should be placed  in  front  of the
inlet to prevent short-circuiting.

                                  275

-------
                             FIGURE 7-21

                  CLOSED LOOP DISTRIBUTION NETWORK
    Watertight Pipe & Joints,
                                             Tight Joints
                                             at All Ends
                                     «—^—    Perforated
                                       /    Distribution Pipe
                                      ' ^ I  H I  fl  I  TTT  .  I   I" I I .  <
                     Pretreatment   lv '  »   *  *' «   »  « •»  «  <  <   » ••>  »
                          Unit
Distribution  box  networks  are  suggested  only  for absorption  systems
located on  level  or gently  sloping  sites,  where the system can  be in-
stalled so  that  the  ground  surface elevation  above  the  lowest  trench is
above the box outlets  (11).   This  is because  it is difficult to prevent
the  distribution box  from  settling  (11)(17)(31).   If  the box were to
settle unevenly  so that the  lowest  trench  received a  greater  share of
the  effluent, wastewater  would seep  onto the  ground  surface unless the
distribution lateral of the lowest trench were at  a  high enough  eleva-
tion to back up  the  wastewater into  the box,  where it could flow into a
different lateral.   Therefore,  to  utilize  the  full  capacity of  each
trench in  the  system, distribution  box  networks  should be used  only
where each  trench  can  back  up into  the  distribution  box  (see  Figure 7-
22).   On  steeply  sloping sites,  other networks  should be  used,  unless
great  care   is   used   to  construct  the  distribution  box  on  a  stable
footing.    If used for dividing  flow between  independent trenches, any
combination  of   trenches  can  be  rested by   plugging  the  appropriate
outlets.
             e.  Relief Line
Relief  line  networks  may  be  used in  place  of  drop  box  networks  in
continuously  ponded multi-trench  systems  on  sites  up  to  the  maximum
permissible slopes.  The network provides serial  distribution  as  in drop
                                  276

-------
                          FIGURE 7-22

                   DISTRIBUTION BOX NETWORK
Distribution Box
Firmly Supported
in Level Position
      All Pipe Inverts
      at Same Elevation
                                 Central Feed
Perforated
Distribution
Pipe
n
Distribution i
Box \ j
T u'^ ii -4*. <—
\ \\
n|
I fa ^••ff /X "^
\ \\
\ \
i \
I J
Water-Tight-^* ^/
Pipes Distributic
Pipes
^
h
in
                                    End Feed
                   Ground Surface at Lowest
                   Trench Higher Than Outlets
                   of Distribution Box.
                    Trenches'
                  •Distribution
                       Box
                         Section A-A

                                277

-------
box  networks  (see  Figure 7-23).   However, .the design  makes  it  more
difficult to add trenches to the system and it  does  not  permit the  owner
to manually rest the upper trenches.


The  network uses  overflow or relief lines between  trenches  in  place  of
drop boxes.   The  invert of the overflow  section  should be located near
the  top  of  the  porous media to use the maximum  capacity  of  the trench,
but  it should be  lower than the septic tank outlet invert.  The  invert
of  the overflow from the  first absorption trench should be at least 4
in.  lower than  the  invert of the pretreatment  unit  outlet. Relief lines
may  be located  anywhere along  the  length  of the  trench,  but successive
trenches  should be separated 5 to 10 ft (1.3 to 3.0  m) to  prevent  short-
circuiting.
             f.  Pressure Distribution
If uniform distribution of wastewater over  the  entire  infiltrative  sur-
face  is  required,  pressure distribution networks are  suggested.  These
networks may  also  be used in  systems that  are  dosed since the mode  of
the network operation is intermittent.


To achieve  uniform distribution,  the volume  of water  passing out  each
hole  in  the  network  during  a dosing cycle must be nearly equal.    To
achieve this, the  pressure  in each segment of  pipe must  also  be  nearly
equal.  This is accomplished by balancing the head losses  through  proper
sizing of  the  pipe  diameter, hole  diameter and hole  spacing.   Thus,
approximately 75  to 85%  of  the total  headloss incurred  is across  the
hole  in  the  lateral, while the remaining 15 to 25% is incurred  in  the
network delivering the  liquid to  each  hole.  The networks  usually  con-
sist of 1- to 3-in.  (3-  to 8-cm)  diameter laterals,  connected  by  a  cen-
tral or end manifold of larger diameter.  The laterals  are perforated at
their inverts with 1/4  to 1/2 in. (0.6 to  1.3  cm) diameter holes.   The
spacing between holes is  2 to 10  ft  (0.6 to 3.0 m)  (see Figures 7-24 to
27).
Pumps are  used  to pressurize the network, although siphons may  be  used
if the dosing chamber  is  located  at  a  higher  elevation  than the  lateral
inverts.   The  active dosing volume is about  10  times the  total  lateral
pipe volume.  This ensures more uniform distribution since  the laterals,
drained after each  dose,  must fill  before the network  can become  prop-
erly pressurized.  (See Section 8.3 for dosing chamber design.)
                                    278

-------
                            FIGURE 7-23

                 RELIEF LINE DISTRIBUTION NETWORK
Distribution Pipe
                          rFlow
                          V
From Pretreatment Unit
       A
Absorption
Trenches
Follow Contours
            L
                                                 JEnds Capped
                              Relief
                               Line
                                  L*-A Distribution Pipe and
                              •Relief   Trencn to be Level
                                Line
            Distribution Pipe
                                       Relief
                                        Line
                Section A-A
                                279

-------
«*   CO
cvi   >-<
1 t I
OH
00
I—I
O
O
O
                                                   280

-------
                  FIGURE ?-
r
    End Cap
 From
 Dosing
Chamber
                                     Distribution
                                       Lateral
                                    281

-------
                                                    FIGURE 7-26

                                      LATERAL  DETAIL - TEE TO TEE CONSTRUCTION
                                    Reducing Coupling
ro
CO
ro
                          Manifold
                                             Holes Spaced
                                             2 ft to 10 ft
.Lateral
i-Cap
                     ~Q<-Hole in Cap Near
                           Crown for Air
                           Venting in
                           Larger Systems

-------
                                                     FIGURE 7-27

                                 LATERAL DETAIL  -  STAGGERED TEES OR CROSS CONSTRUCTION
             .Staggered Tees or Cross,
ro
CO
GO
                                                 Lateral
Cap

d ?
                                                     N Holes Spaced
                                                      2 Ft. to 10 Ft.
         w   Hole in Cap
           Near Crown for
           Air Venting in
           Larger Systems

-------
To simplify the design of small  pressure distribution networks,  Table 7-
13, and Figures 7-28, 7-29,  and 7-30, may be used.   Examples 7-2 and 7-3
illustrate their  use.    Other  design methods  may  be equally  suitable,
however.
                               TABLE 7-13

                DISCHARGE RATES FOR VARIOUS SIZED HOLES
                       AT VARIOUS PRESSURES (gpm)
       Pressure                     Hole Diameter (in.)
     ftpsT


      1      0.43

      2      0.87

      3      1.30

      4      1.73

      5      2.17
1/4
0.74
1.04
1.28
1.47
1.65
5/16
1.15
1.63
1.99
2.30
2.57
3/8
1.66
2.34
2.87
3.31
3.71
7/16
2.26
3.19
3.91
4.51
5.04
1/2
2.95
4.17
5.10
5.89
6.59
Example 7-2:  Design of a Pressure Distribution Network for a Trench
Absorption Field'
Design  a pressure network  for an  absorption  field consisting of  five
trenches, each  3  ft  wide  by 40 ft long,  and spaced 9 ft apart center to
center.
Step  1:  Select  lateral  length.   Two  layouts are  suitable for  this
         system: central  manifold (Figure 7-24) or end manifold  (Figure
         7-25).  For  a central  manifold  design, ten  20-ft laterals  are
         used;  for an end  manifold  design,  five 40-ft  laterals  are
         required.  The end manifold design is used in this example.

Step  2:  Select  hole  diameter  and hale spacing for laterals.   For  this
         example,  1/4-in.  diameter  holes spaced every 30  in. are used,
         although other combinations could be used.
                                   284

-------
                                         FIGURE 7-28

REQUIRED LATERAL  PIPE  DIAMETERS FOR VARIOUS HOLE DIAMETERS,  HOLE SPACINGS,  AND  LATERAL LENGTHS'
                                   (FOR PLASTIC PIPE ONLY)
ro
CO
en
.c
O)
c
-£
CD —
w
0)
CD

10
b
25-
30-
OK
OO

45
RO
LATERAL DIAMETER (IN)
Hole Diameter
1/4
in)
Hole Spacing (ft)
2

(\
V
2"
3

H-E
11
[)
>^
IV
4

5
1"
Exampl
/ // 	 "
/4
S^

6

7

e7-3
Example
7-2
Hole Diameter (in)
5/16
Hole Spacing (ft)
2


\w
2
3"
3



1!
"
4
5
1"

/ "


1V4
6

rt
1Y2"
7


Hole Diameter
3/8
Hole Spacing
2


1J4-

.3"
3



2"

4
5
r

11/

1
^"
(ft)
6

in)

7

1/4"




Hole Diameter ( n)
7/16
Hole Spacing (ft)
2
3


r/r

3

r/,"

ir
4


5
1
6
7
;r
1 1/4"
m-
2"




v/


it
Hole Diameter (in)
1/2
Hole Spacing (ft)
2



i3
4


Vh"




1»"
2
3"
567
1"
1 V*"


, 11/2"



  a Computed for plastic pipe only. The Hazen-Williams equation was used to compute headlosses
 through each pipe segment (Hazen-Williams C= 150). The -orifice equation for sharp-edged orifices
 (discharge coefficient = 0.6) was used to compute the discharge rates through each orifice.
 The maximum lateral length for a given hole and spacing was defined as that length at which the
 difference between the rates of  discharge from the distal end and the supply end orifice reached
 10 percent of the distal end orifice discharge rate.

-------
                                                           FIGURE 7-29

                     RECOMMENDED MANIFOLD DIAMETERS FOR VARIOUS MANIFOLD  LENGTHS, NUMBER OF LATERALS,
                                      AND LATERAL  DISCHARGE RATES (FOR PLASTIC PIPE ONLY)
                                                  MANIFOLD DIAMETER (IN)
ro
co
Flow
Late
(gp
-a'
Central Manifol
per
:ral •
m)
5
10
15
20
25

Manifold Length (ft)
5

4
-
;!
3
2
6
3
*
CM
^
rn
3
10

4 6
1 'a"
f 2

8
i-
••
10
^

« — Exam
3"
r
2 3

4 1 5
	 15

4
*
2

6
*
»
a|io|i2
2"

ale 7-3
3"
,,P
2|3|4 | 5


it
6
20

6



8

10|12
2"
'S.
3J4
56
...

14
r
7
25
30
35
40
Number of Laterals with Central Manifold
6J8
2"
jJ
IOJ12|l4


si 4|5l 6 1 7
6| 8
2"
3
10J12|14
r
3I4J5
Number

-------
                                  FIGURE 7-30

NOMOGRAPH FOR DETERMINING THE MINIMUM  DOSE VOLUME FOR A GIVEN LATERAL DIAMETER,
                    LATERAL LENGTH, AND  NUMBER OF LATERALS
• 4,000 r 1
• 3,500 I
• 3,000
- 2,500
1 2,000
"5 EXAMPLE 7-3 — i
05 V,
•1.500 ^ 7
.3 /
0 EXAMPLE 7-2 /
- 1 ,000 ^ . . — y
•900 ^ /X \
•800 W
• 700 Q
-600 ^
3
• 500 ^
1 450 H
•400 ^
350
s
300 x^x v
^200 ^
150 /
F20 / V
• / "
- / x
-10 < .' ^''
UJ xX
• t? '
• 5^5
/. U-
'4 0
•3 DC
J UJ
CO
•2 ^
3
z
• 1
/
•100



MO
\
\ -15 *:
•3 \ -c
\ -20 1-
\ "25 Z
•^ --^^ ^-30 a
6 , ^^'!«N<
05 50 LU s.^^
•6 'uJ < X "*^^

,7 1 ^ ^N
-I \
•8 ^ \
9 S X\
•10IE


-15
9O
                                                                         3
                                                                              U5
                                                                              01
                                                                              O
                                                                              c
                                                                             UJ
                                                                             QC
                                                                             UJ
                                                                         1V.
                                                                        • 1
                                       287

-------
Step 3:  Sel ec t 1 ateral  di ameter •    For 1/4-in.  hole  diameter, 30-in.
         hole spacing, and 40-ft length, Figure 7-28 indicates either a
         1-1/4-in.  or 1-1/2-in. diameter lateral could be used.  The 1-
         1/2-in.  diameter is  selected for this  example.

Step  4: Calculate   lateral   discharge  rate.    By  maintaining  higher
         pressures  in  the  lateral,  small  variations in elevation along
         the length of the lateral and  between  laterals do not  signifi-
         cantly affect  the rates of discharge from  each hole.   This
         reduces construction costs, but increases pump size.  For this
         example,  a 2-ft head is  to  be maintained  in the lateral.  For a
         1/4-in.  hole  at 2 ft of head, Table  7-13  shows  the hole dis-
         charge rate to be 1.04 gpm.


                of  hoHs/Utera!  .
                                 = 16

         Lateral  discharge rate  = (16 holes/lateral)  x  (1.04 gpm/hole)

                                 = 16.6 gpm/1 ateral

Step 5:  Select manifold  size.   There are to be five laterals spaced 9
         ft apart.  A manifold length of 36 ft is therefore required.

         For  five  laterals  and 16.6  gpm/lateral, Figure 7-29  indicates
         that a 3-in. diameter manifold is required.

Step 6:  Determine minimum dose volume (Figure 7-30).

         With:  lateral  diameter   = 1-1/2 in.
                lateral  length     = 40 ft
                number of laterals = 5
         Then:  pipe volume        = 3.7 gal
         Minimum dose volume       = approx.  200 gal

         The  final dose volume may be larger than this minimum  depending
         on the desired number of doses per day (see Table 7-4).

         See  Figure 7-31 for completed network design.

Step 7:  Determine minimum discharge rate.

         Minimum discharge rate = (5 laterals) x (16.6 gpm/lateral)

                                = 83 gpm
                                   288

-------
                                                 FIGURE  7-31

                                    DISTRIBUTION NETWORK FOR  EXAMPLE 7-2
                                                              3ft
CD
                           40ft
           9ft.
                    9ft
                               9ft.
                                         9ft
                                                                                    3 in. Manifold
                                                                                          From Dosing
                                                                                           Chamber
          Hole Spacing

             30 in.
y2 in. Laterals

-------
Step 8:   Select proper pump or siphon.

         For a pump  system,  the  total pumping head of  the  network must
         be  calculated.    This  is equal  to  the  elevation  difference
         between  the  pump and  the distribution  lateral  inverts,  plus
         friction loss in the pipe that delivers the wastewater from the
         pump  to  the network  at  the  required rate,  plus  the  desired
         pressure to be maintained in  the  network  (the  velocity  head is
         neglected).   A pump is  then  selected  that is  able  to discharge
         the minimum rate (83 gpm) at the calculated pumping head.

         For a siphon system, the siphon discharge  pipe must be elevated
         above the lateral inverts at a distance  equal to  the friction
         losses and velocity head in  the pipe that delivers  the waste-
         water from the siphon to the network at the required rate, plus
         the desired pressure to  be maintained in  the  network.

         For this example, assume  the  dosing  tank  is  located  25  ft from
         the network inlet, and  the difference  in  elevation between the
         pump and the inverts of  the  distribution  laterals is 5 ft.

         a.  Pump (assume 3-in.  diameter delivery  pipe)

             1.  Friction loss in 3-in. pipe at 83  gpm (from Table  7-14)

                                           = 1.38 +   -  (1.73  - 1.38)
                                           = 1.49 ft/100 ft

                 Friction loss in 25 ft

                                           = (1.49 ft/100 ft)  x (25 ft)

                                           = 0.4 ft

             2.  Elevation Head            = 5.0 ft
             3.  Pressure to be maintained = 2.0

                 Total  pumping head        = 7.4 ft


         Therefore, a pump capable of delivering at least 83 gpm against
         7.4 ft of head is required.

         b.  Siphon (assume 4-in. diameter delivery pipe)

             1.  Friction loss in 4-in. pipe at 83 gpm (from Table 7-14)

                                  = 0.37 + -j| (0.46 - 0.37)

                                  = 0.4 ft/100 ft
                                  290

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                    TABLE 7-14

FRICTION LOSS IN SCHEDULE 40 PLASTIC PIPE, C = 150
                    (ft/100 ft)
Flow 1
gpm
1 0.07
2 0.28
3 0.60
4 1.01
5 1.52
6 2.14
7 2.89
8 3.63
9 4.57
10 5.50
11
12
13
14
15
16
17
18
19
20
25
30
35
40
45
50
60
70
80
90
100
150
200
250
300
350
400
450
500
600
700
800
900
1000
1-1/4


0.07
0.16
0.25
0.39
0.55
0.76
0.97
1.21
1.46
1.77
2.09
2.42
2.74
3.06
3.49
3.93
4.37
4.81
5.23
























1-1/2



0.07
0.12
0.18
0.25
0.36
0.46
0.58
0.70
0.84
1.01
1.17
1.33
1.45
1.65
1.86
2.07
2.28
2.46
3.75
5.22






















_2






0.07
0.10
0.14
0.17
0.21
0.25
0.30
0.35
0.39
0.44
0.50
0.56
0.62
0.68
0.74
1.10
1.54
2.05
2.62
3.27
3.98


















_3 _4 _6 8















0.07
0.08
0.09
0.10
0.11
0.12
0.16
0.23
0.30 0.07
0.39 0.09
0.48 0.12
0.58 0.16
0.81 0.21
1.08 0.28
1.38 0.37
1.73 0.46
2.09 0.55 0.07
1.17 0.16
0.28 0.07
0.41 0.11
0.58 0.16
0.78 0.20
0.99 0.26
1.22 0.32
0.38
0.54
0.72



1£




































0.07
0.09
0.11
0.14
0.18
0.24
0.32
0.38
0.46
                       291

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                 Friction loss  in 25 ft
                                  =  (0.4 ft/100 ft)  x  (25  ft)
                                  =  0.10 ft
             2.   Velocity head in delivery  pipe
                   Discharge rate =  83 gpm =  0.185  ft  /sec
                   Area           =(1/4)7T ()2  =  0.087  ft2
                   Velocity       = 0-185 ft3/sec  =  2>13  ft/$ec
                                      0.087 ftT

                   Velocity head  . (Velocity)2


                                  _ ([2.13] ft/sec)2
                                     2(32.2 ft/sec2)

                                  = 0.07 ft

             3.  Pressure to be maintained

                                  = 2.0 ft

             Total                   2.2 ft

         Minimum  elevation of  the  siphon  discharge  invert  above  the
         lateral inverts must be 2.2 ft.

In summary, the final network  design  consists of  five  40-ft laterals 1-
1/2 in.  in diameter connected with  a 36-ft end manifold 3-in.  in  dia-
meter, with  the inlet from the  dosing  chamber  at one end  of the  mani-
fold.    The inverts  of  the laterals  are perforated with 1/4-in.  holes
spaced every 30 in.
Example 7-3:  Design of a Pressure Distribution Network for a Mound
Design a pressure distribution network for the mound designed in Example
7-1.
                                  292

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Step 1:   Select 1ateral  1ength.   A  central manifold  (Figure 7-24) design
         is used in  this example.


         Lateral length  = 65,ft  - 0.5  ft  (for manifold)
                        =  32 ft
Step 2:  Select hole diameter and hole  spacing  for  laterals.   For this
         example,  1/4-in. diameter holes spaced  every  30 in.  are used,
         although  other combinations  could be used.

Step 3:  Select lateral  diameter.    For 1/4-in. hole  diameter,  30-in.
         hole spacing,  and  32-ft  lateral  length, Figure 7-28 indicates
         that either a 1-1/4-in. or 1-1/2-in. diameter lateral could be
         used.  The 1-1/4-in.  diameter  is selected for  this example.

Step  4:  Calculate  lateral  discharge  rate.    A 2-ft  head  is  to  be
         maintained in the lateral.

         For  1/4-in.  hole at 2 ft  of  head,  Table  7-13  shows the hole
         discharge rate to be  1.04 gpm.
                of holes per lateral  =  A  g  i


                                     =  13


         Lateral  discharge rate =  (13 holes/lateral) x (1.04 gpm/hole)


                                =  13.5  gpm/lateral


Step 5:  Select manifold  size.   There  are to  be  four  laterals (two on
         either  side  of  the  center manifold)  spaced  3  ft apart.   A
         manifold length  of  less  than  5 ft  is required  (see Figure 7-
         32).

         For four laterals,  13.5  gpm/lateral,  and manifold length less
         than  5  ft,  Figure 7-29  indicates  that a  1-1/2-in.  diameter
         manifold is required.
                                   293

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                                 FIGURE 7-32

                    DISTRIBUTION NETWORK FOR EXAMPLE 7-3
           1-1/2 in.
          Manifold
Hole Spacing
    30 in.
                                                  1-1/4 in
                                                  Laterals
                                      294

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Step 6:   Determine minimum dose  volume  (Figure  7-30).

               With:   lateral  diameter    =  1-1/4  in.
                      lateral  length      =  32 ft
                      number of  laterals  =  4

               Then:   pipe volume   =  2  gal
               Minimum dose volume  =  <100 gal

         From Table  7-4,   for a medium  texture  sand, 4  doses/day are
         desirable.  Therefore,  the dose  volume is:


                                       =  112 gal/dose
Step 7:   Determine minimum discharge  rate.

         Minimum discharge rate =  (4  laterals)  x  (13.5  gpm/lateral)
                                =  54  gpm

Step 8:   Sel ec t proper pump .   For this  example,  assume the dosing tank
         is located  75 ft  from the  network  inlet, the  difference  in
         elevation between the pump and the inverts of the distribution
         laterals is 7 ft, and a  3-in.  diameter delivery pipe is to be
         used.

              Friction loss in 3-in.  pipe  at 54 gpm  (from Table 7-14)


                              = 0.58  + --  (0.81 - 0.58)
                              =  0.67 ft/100  ft


              Friction loss in 75 ft

                                        =  (0.67  ft/100  ft)  x  (75 ft)

                                        =  0.5 ft

              Elevation head            =  7.0 ft
              Pressure to be maintained  =  2.0 ft

              Total  pumping head        =  9.5 ft

         Therefore,  a pump capable of delivering at  least 54  gpm against
         9.5 ft of head is required.
                                  295

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In summary, the final network design  consists  of  four 32-ft laterals 1-
1/4 in. in  diameter  (two on each side of  a  3-in.  diameter  center mani-
fold.   The inverts  of  the laterals  are perforated with 1/4-in.  holes
spaced every 30 in.


             g.  Other Distribution Networks
Several other distribution network designs are occasionally used.   Among
these  are  the  inverted network  and  leaching  chambers.  While  users  of
these networks claim they are superior to conventional  networks, compre-
hensive evaluations of their performance have not been made.
Inverted Network:  This network uses  perforated  pipe  with  the  holes lo-
cated in the  crown  rather than near  the  invert  (32).   This arrangement
is designed  to  provide more uniform  distribution  of wastewater over  a
large area, and  to prolong  the  life  of  the field by collecting any set-
tleable solids passing out of the septic tank in  the bottom of  the  pipe.
Water-tight sumps are located at both ends of  each inverted line to fa-
cilitate periodic removal  of the accumulated solids.
Leaching Chambers:   In  place of perforated pipe and  gravel  for distri-
bution and  storage  of the wastewater,  this  method employs  open  bottom
chambers.  The chambers interlock to form an  underground cavern over the
soils' infiltrative surface.   The wastewater  is discharged into the cav-
ern through a central weir,  trough,  or  splash  plate  and allowed to flow
over  the  infiltrative surface  in  any direction.   Access holes  in  the
roof  of  the  chamber  allow  visual  inspection  of  the soil  surface  and
maintenance as necessary.  A large number of  these  systems have been in-
stalled in the northeastern United States (see  Figure 7-33).
          7.2.8.2  Materials
Three to 4-in. (8- to 10-cm) diameter pipe or tile is typically used for
nonpressurized networks.  Either perforated pipe or 1-ft (30 cm)  lengths
of  suitable  drain tile may be  used.   The perforated pipe  commonly has
one  or  more  rows  of 3/8- to 3/4-in.  (1.0-  to 2.0-cm)  diameter  holes.
Hole  spacing  is  .not critical.   Table 7-15 can be  used as  a  guide for
acceptable materials for nonpressurized networks.


Plastic pipe  is  used for pressure distribution networks because  of the
ease of drilling  and assembly.   Either PVC  Schedule 40  (ASTM D 2665)  or
ABS  (ASTM 2661) pipe may be used.
                                  296

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                               TABLE  7-15

         PIPE MATERIALS FOR NONPRESSURIZED DISTRIBUTION NETWORKS
     Type of Material
 Specification
       Class
Clay Drain Tile

Clay Pipe
    Standard and Extra-
      Strength Perforated

Bituminized Fiber Pipe
    Homogeneous
      Perforated
    Laminated-Wall
      Perforated

Concrete Pipe
    Perforated Concrete

Plastic
    Acryloni tri1e-
      Butadiene-
      Styrene  (ABS)

    Poly vi nyl
      Chloride (PVC)
ASTM C-4


ASTM C-211



ASTM D-2312

ASTM D-2313
ASTM C-44 (Type 1
  or Type 2)

ASTM D-2751&
ASTM D-2729b
D-3033b D-3034b
Standard Drain Tile
Standard
ASTM C-143
    Styrene-Rubber
      Plastic (SR)

    Polyethylene (PE)
    o Straight Wall
    o Corrugated (Flexible)
ASTM D-2852b
  D-3298b
ASTM D-1248b
ASTM F-405-76b
a Must be of quality to withstand sulfuric acid.

b These specifications are material  specifications only.   They do not
  give the location or shape of perforations.
                                   297

-------
                                 FIGURE 7-33

                       SCHEMATIC OF A LEACHING CHAMBER
                                             Fresh Air
                                             Vent-
                                                               -»;•-• .... At^ *au- _-- «-£.

                                                              •*K.--"*J
                x-^'	 j,," -2k~- ":;" •*• —. jit-.""  - ^"--a-~ .sffc ,.~^'-y- ^--.•>!*-- •r_A""~^L"".^
                                                               - ~"'^ --..•~'^" 7~~i. -?
                                                               -• -«M'I.  -"• _jjft. "^ _ -
                                                              .-.f--.-;;-^*::
                                                              '^.- j$£- _~3^.—*_-
                                                              . '--••"  -*.. _ — J,
                                                              ..-•a- -- — *«.—_;=
                                                                 .*;:'Jt-~-"..*.--
                                                               ife- -_fc-^-,5C- t
                                                              .-;*-. ~^-i."-*
             «/"
          7.2.8.3   Construction
              a.   Gravity  Network Pipe Placement
To  insure  a  free  flow of  wastewater,  the  distribution pipe should be
laid  level  or  on  a  grade  of  1  in.  to 2  in. per 100  ft  (8.5 to  16.9
cm/100  m).   To maintain  a  level  or uniform  slope, several  construction
techniques can  be  employed.   In  each case a  tripod level  or  transit is
used  to   obtain  the   proper  grade  elevations.    Hand  levels  are  not
adequate.
                                       298

-------
The rock  is  placed in the  excavation  to the elevation of  the  pipe  in-
vert.   The rock  must  be  leveled by hand  to  establish  the  proper grade.
Once the pipe is laid, more rock is carefully placed over the top of the
pipe.   Care must also be taken  when  flexible corrugated plastic pipe is
used,  because  the  pipe  tends to "float"  up  as rock is placed  over  the
top of the pipe.   One method is to employ special  holders  which can be
removed once all  the rock is in  place (see Figure 7-34).
                                  FIGURE 7-34

                         USE OF METAL HOLDERS FOR THE
                        LAYING OF FLEXIBLE PLASTIC PIPE
       Metal Holder	
       (Removed After
       Rock Placement)
4" Flexible
Perforated
Plastic Pipe
             b.  Pressure Network Pipe Placement
Pressure  distribution  networks  are usually fabricated  at  the  construc-
tion  site.   This may  include  drilling holes in  distribution  laterals.
The  holes must be  drilled  on  a straight  line  along the length  of the
pipe.  This can be  accomplished  best  by  using 1-in.  by 1-in.  angle iron
as a  straight-edge  to  mark  the  pipe.   The holes are then drilled at the
proper spacing.   Care  must be used to drill  the  holes perpendicular to
the  pipe  and  not at an  angle.   All  burrs left around  the  holes inside
the  pipe  should  be removed.   This  can  be done  by sliding a  smaller
diameter  pipe or rod down the pipe to knock the burrs off.
Solvent weld joints are  used  to  assemble  the  network.   The laterals are
attached to the manifold such that the perforations lie at the bottom of
the pipe.
                                    299

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Since the network  is  pressurized,  small  elevation  differences along the
length of the  lateral do  not  affect the uniform  distribution  signifi-
cantly.  However,  these  variations should be held within  2  to  3  in.  (5
to 8 cm).  The  rock  is  placed  in the absorption area first,  to  the ele-
vation of  the  distribution  laterals.   The rock  should be  leveled  by
hand, maintaining  the same elevation  throughout the  system,  before lay-
ing  the  pipe.   After the  pipe is laid, additional  rock is  placed over
the pipe.
             c.  Distribution Boxes
If used,  distribution  boxes should be installed level  and  placed in an
area where  the  soil  is  stable  and remains reasonably  dry.   To protect
the box  from  frost heaving, a 6-in.  (15-cm)  layer  of 1/2-  to 2-1/2-in.
(1.2- to 6.4-cm) rock should be placed below and around the  sides of the
box.  Solid wall pipe should be used to connect the box with the distri-
bution laterals.  Separate connections should be made for each lateral.
To insure  a more equal  division  of flow, the  slope  of each connecting
pipe should be  identical  for at least 5 to 10  ft  (1.3 to 3.0 m) beyond
the box.
7.3  Evaporation Systems


     7.3.1  Introduction


Two basic types of onsite evaporation systems are in use today:


     1.  Evapotranspiration beds (with and without infiltration)

     2.  Lagoons (with and without infiltration)
The advantages of these systems are that they utilize the natural  energy
of  the sun  and,  optionally,  the  natural  purification  capabilities  of
soil  to  dispose of the  wastewater.   They must, however,  be  located  in
favorable  climates.   In some  water-short  areas  where  consumptive water
use is forbidden (e.g., Colorado), they may not be allowed.
Mechanical  evaporators  are  in the experimental stage, and  are  not com-
mercially  available.    For  this  reason, they  are not included  in this
discussion.
                                   300

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     7.3.2  Evapotranspiration and Evapotranspiration/Absorption Beds


         7.3.2.1  Introduction
Evapotranspiration (ET) beds can be used to dispose of wastewater to the
atmosphere so that  no  discharge to surface or groundwater  is  required.
Evapotranspiration/absorption (ETA) is  a modification  of  the  ET concept
in which  discharges  to both the  atmosphere and to  the groundwater are
incorporated.  Both ET and  ETA  have been  utilized  for onsite  wastewater
disposal  to the extent that several  thousand of these systems  are in use
in the United States (33).
         7.3.2.2  Description
Onsite ET disposal  normally  consists of a sand  bed  with  an  impermeable
liner and wastewater distribution piping (see Figure 7-35).   The surface
of the sand bed may be planted with vegetation.  Wastewater  entering the
bed  is  normally pretreated  to  remove settleable and  floatable  solids.
An ET  bed  functions by  raising  the wastewater to the upper  portion  of
the bed by capillary action  in  the  sand,  and then evaporating it to the
atmosphere.  In addition, vegetation transports water from the root zone
to the leaves,  where  it is  transpired.   In  ETA  systems,  the  impervious
liner  is  omitted,  and  a portion  of the wastewater  is  disposed  of  by
seepage into the soil.
Various  theoretical   approaches  are  used  to  describe the  evaporation
process.   This  suggests that  there  may be some  uncertainty  associated
with a  precise  quantitative description of the process.   However,  cur-
rent  practice is  to limit the uncertainties  by basing  designs on  a
correlation  between  available pan  evaporation  data  and  observed  ET
rates,  thereby minimizing assumptions  and  eliminating  the  need  to aver-
age long-term climatic data.  References (33)(34)(35) and (36) provide a
more detailed discussion of the correlation method.
         7.3.2.3  Application
Onsite systems utilizing ET disposal are primarily used where geological
limitations prevent  the  use  of  subsurface  disposal,  and where discharge
to  surface  waters  is not permitted or  feasible.   The geological  condi-
tions that tend to favor the use of ET systems include very shallow soil
mantle,  high  groundwater,  relatively  impermeable  soils,  or  fractured
bedrock.   ETA systems are generally  used  where  slowly  permeable  soils
are encountered.
                                   301

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                              FIGURE 7-35

                    CROSS SECTION OF TYPICAL ET BED
         Slope
 Impervious
   Liner
                                                      Topsoil (Varies 0-4")
'Filter Cloth or Equivalent
                  Rock
                                           Perforated'
                                            Pipe (4")
Although ET systems may be used where the application of subsurface dis-
posal systems  is limited,  they  are not  without limitations.   As  with
other disposal  methods that require area-intensive construction, the use
of ET systems  can  be constrained by limited  land  availability and  site
topography.  Based on experience to date with ET disposal  for year-round
single-family homes, approximately 4,000 to 6,000 ft2 (370 to 560 nr)  of
available land is typically required.   The  maximum slope  at which an  ET
system is applicable has not been established, but use on  slopes greater
than 15%  may be possible  if  terracing, serial  distribution,  and other
appropriate design features are incorporated.
By far the most  significant  constraint  on  the use of ET systems is cli-
matic conditions.  The evaporation  rate  is  controlled  primarily by cli-
matic factors such as  precipitation,  wind  speed,  humidity,  solar radia-
tion, and temperature.   Recent  studies  indicate that essentially all  of
the  precipitation that  falls on an ET bed  infiltrates  into the bed and
becomes  part  of the  hydraulic  load that requires  evaporation  (33)(34)
(37).  Provisions for long-term storage of effluent and precipitation in
ET systems  during  periods of negative  net evaporation, and  for subse-
quent evaporation during periods of positive net evaporation, are expen-
sive.  Thus, the year-around use of nondischarging ET systems appears to
be feasible  only in the  arid  and semiarid portions of  the western and
southwestern United  States where  evaporation  exceeds precipitation dur-
ing  every month  of operation, so  that long-term  storage capacity is not
                                   302

-------
required.  ET systems for  summer homes may  be  feasible in the  more tem-
perate parts of the country.   For  ETA systems,  the  range  of  applicabil-
ity is less well  defined, but the soils must be capable of accepting all
of the influent wastewater if net evaporation is zero  for any signifi-
cant periods of the year.


In  addition  to  climate  and  site  conditions,  the characteristics  of
wastewater discharged to an onsite disposal  system may affect its  appli-
cation.   For ET disposal,  pretreatment  to remove settleable and  float-
able solids is necessary to  prevent physical clogging  of  the wastewater
distribution piping.   The relative advantages of aerobic  versus  septic
tank  pretreatment  for  ET  and ETA  systems  have  been  discussed  in  the
literature (33)(35)(37)(38).  Although  each  method has been supported by
some  researchers,  reports  of well-documented, controlled  studies indi-
cate that septic tank pretreatment is  adequate (33)(34)(37).


         7.3.2.4  Factors Affecting Performance


The following factors affect the performance of ET and ETA systems:
     1.  Cl imate
     2.  Hydraulic loading
     3.  Sand capillary rise characteristics
     4.  Depth of free water surface in the bed
     5.  Cover soil  and vegetation
     6.  Construction techniques
     7.  Salt accumulation (ET only)
     8.  Soil permeability (ETA only)
As noted previously, climate has a significant effect on the application
and  performance  of ET and  ETA  systems.   Solar  radiation,  temperature,
humidity, wind speed, and precipitation all  influence performance.  Since
these parameters  fluctuate  from day to day,  season  to  season,  and year
to year, evaporation rates  also  vary  substantially.   To insure  adequate
overall   performance,  these  fluctuations   must  be  considered  in  the
design.
The hydraulic loading rate of an ET bed affects performance.   Too high a
loading rate  results  in  discharge from the bed;  too  low  a loading rate
results in a lower gravity (standing) water level  in the bed  and ineffi-
cient  utilization.    Several  researchers  noted  decreased  evaporation
rates  with  decreased water  levels  (33)(34)(35).    This problem  can  be
overcome by sectional construction in  level areas  to  maximize  the water
level  in  a  portion of the  bed, and by serial  distribution  for sloping
sites.
                                   303

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The capillary rise characteristic of the sand used to fill the ET bed is
important since this mechanism is responsible for transporting the water
to the  surface of the  bed.   Thus, the  sand needs to  have  a capillary
rise potential at least as great as the depth of the bed, and yet should
not  be  so   fine  that  it  becomes clogged  by  solids  in  the  applied
wastewater (33).
Significant seasonal  fluctuations  in  the  free  water surface are normal,
necessitating  the  use of  vegetation  that is  tolerant to  moisture  ex-
tremes.  A variety of vegetation, including grasses, alfalfa, broad-leaf
trees, and evergreens, have been reported to increase the average annual
evaporation rate from an  ET  bed to above that for bare soil (35).  How-
ever,  grasses  and  alfalfa  also result  in  nearly  identical  or reduced
evaporation rates as  compared  to bare soil  in  the winter and the spring
when  evaporation rates  are normally at a minimum  (33)(34).   Similarly,
top  soil  has  been  reported to  reduce  evaporation  rates.   Certain ever-
green  shrubs,  on the other  hand,  have  been shown  to  produce  slightly
greater  evaporation  rates than  bare  soil  throughout  the year  (33).
Thus,  there  are conflicting  views on the  benefits  of cover  soil  and
vegetation.
Although  ET  system performance is generally affected  less  by construc-
tion  techniques  than most subsurface disposal  methods,  some  aspects of
ET construction  can  affect performance.  Insuring  the  integrity  of the
impermeable liner  and  selecting the  sand to provide  for maximum  capil-
lary  rise properties  are  typically  the most  important considerations.
For ETA  systems,  the effects of construction  techniques  are  similar to
those discussed previously with reference to subsurface disposal systems
in slowly permeable soils.
Salt accumulation in ET disposal systems occurs as wastewater is evapor-
ated.   Salt accumulation is  particularly  pronounced at the  surface of
the bed  during  dry  periods,  although  it is redistributed throughout the
bed by  rainfall.    Experience  to date indicates  that  salt accumulation
does  not interfere with  the  operation  of nonvegetated  ET systems (39)
(40).   For  ET  systems with  surface  vegetation,  salt  accumulation  may
adversely affect performance after a long period of use, although obser-
vations  of  ET  systems  that have been in  operation  for 5 years indicate
no  significant  problems  (33).   In order  to minimize  potential  future
problems associated with  salt  accumulation,  the ET  or  ETA piping system
may be designed to  permit flushing of the bed.


Since ETA  systems  utilize seepage into the  soil  as well as evaporation
for wastewater  disposal,  soil  permeability  is also  a factor in the per-
formance of  these  systems.   Discussion of  this factor relative to sub-
surface  disposal systems  (Section 7.2) applies here.
                                    304

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Data that  quantitatively  describe performance are not available  for  ET
or ETA  disposal.   However, the technical  feasibility  of  nondischarging
ET disposal  has  been  demonstrated under  experimental  conditions  (33)
(34).  In addition, observations of functioning ET systems indicate  that
adequate  performance can  be achieved  at  least  in  semi arid  and  arid
areas.    The  performance of  ETA  systems depends primarily on  the rela-
tionship  between  climate  and soil  characteristics,  and  has  not  been
quantified.  However, the  technical feasibility of such systems  is  well
accepted.


         7.3.2.5  Design
ET and ETA systems must  be  designed  so  that they are acceptable in per-
formance and  operation.   Requirements  for  acceptability  vary.   On  one
hand, acceptable  performance can  be defined for  an ET system  as zero
discharge for a  specified  duration such as 10 years, based  on  the wea-
ther  data  for a similar period.   Alternatively, occasional  seepage  or
surface overflow during periods of heavy rainfall  or snowmelt may be al-
lowed.  In addition, physical appearance requirements for  specific  types
of vegetation and/or a firm  bed  surface for normal  yard use (necessita-
ting  a  maximum  gravity water level  approximately 10 in.  [25 cm]  below
the surface)  may also be incorporated in the criteria.


Appropriate acceptance criteria  vary with  location.   For  example,  occa-
sional discharge may  be acceptable in  low-density  rural  areas,  whereas
completely nondischarging systems are more appropriate in  higher density
suburban areas.   Thus, acceptance  criteria  are usually  defined  by  local
health officials to reflect local conditions (33).
Since the size  (and thus  the  cost)  of ET and ETA systems are  dependent
on  the  design hydraulic  loading  rate,  any  reduction  in flow to  those
systems is beneficial.  Therefore,  flow reduction  devices and  techniques
should  be  considered  an  integral  part  of  an  ET   or  ETA  system.


The design hydraulic loading rate is the principal  design feature affec-
ted  by  the acceptance  criteria.    Where  a total  evaporation  system  is
required, the  loading rate must be low enough  to prevent the bed  from
filling  completely.   Some  discrepancy  in acceptable loading  rates  has
been reported.  Although reports of system designs based on  higher load-
ing  rates  have been  presented  in  the  literature (35)(37), other  data
obtained under controlled  conditions  indicate that  pan  evaporation  must
exceed  precipitation  in  all  months of a  wet year  (based on at least 10
years of data) if a total, year-round evaporation  system is  used.  Under
these conditions,  loading  rates between 0.03 and 0.08  gpd/ft^ (1.2  and
3.3  1/nr/day)  were  found to be appropriate in  western  states  (Colorado
and Arizona) (33)(34).
                                   305

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The hydraulic loading  rate  is determined by an  analysis  of the monthly
net ET  ([pan  evaporation x a  local  factor] minus  precipitation)  expe-
rienced  in  the  wettest  year  of a  10-year  period.   Ten years  of data
should be  analyzed,  as  very  infrequent but large  precipitation events
may be experienced over the life of the system that would result in very
infrequent discharge.   Where  occasional  discharge from an  ET  system  is
acceptable, loading rates may be determined  on a less restrictive basis,
such as  minimum monthly net ET in  a dry year.   If  the  unit is used for
seasonal application,  then  only those months of  occupancy  will  consti-
tute the basis for design.
The loading  rate  for  ETA systems is determined  in  the  same manner,  ex-
cept that  an additional  factor  to  account for  seepage in the  soil  is
included.  Thus, the loading rate for an ETA system is generally greater
than the loading rate for an  ET  system  in  the same climate.  The avail-
able data  indicate  that ETA  systems can be used with  a wider  range of
climatic conditions.  For example,  if soil can  accept  0.2 gpd/ft  (8.1
1/nr/day), and the minimum monthly  net  ET  is  zero (determined as neces-
sary according to ±he acceptance criteria), the  loading rate  for design
is also 0.2 gpd/ftz (8.1 l/mVday).


In addition  to loading  rates,  the designer must  also  consider selection
of fill material, cover soil, and vegetation.   The role  of  vegetation in
providing  additional  transpiration  for  ET  systems  is uncertain  at this
time.   During  the  growing   season,  the impact  of vegetation could  be
significant.  However, during the nongrowing season, the effect of vege-
tation has not been well  documented.  Sand available  for ET and ETA bed
construction should be  tested  for capillary rise height and rate before
one is selected.   In  general,  clean and uniform  sand  in the size of DCQ
=  0.1  mm (50% by weight  smaller than or equal  to  0.1  mm)  is desirable
(33).
The assumptions for a sample ET bed design are given below:
     1.  Four occupants of home
     2.  45-gpcd design flow (no in-home water reduction)
     3.  Location:  Boulder, Colorado
     4.  Critical months:  December 1976 (see Figure 7-36)
     5.  Precipitation:  0.01 in./day (0.25 mm/day)
     6.  Pan evaporation:  0.07 in./day (1.7 mm/day)
An ET bed must  be  able  to evaporate  the household wastewater discharged
to  it  as well  as  any  rain  that falls on  the  bed surface.   Thus,  the
design of an  ET system  is based  on  the estimated flow from the home and
the difference  between the precipitation rate and the evaporation rate
                                   306

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                              FIGURE 7-36

CURVE FOR ESTABLISHING PERMANENT HOME LOADING  RATE FOR BOULDER, COLORADO
                  BASED ON WINTER DATA, 1976-1977(33)
        10
  mm/day
         0
                         JJ
                        1976
DJ
 J J
1977
                                  307

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during the critical months of the year.   In  this  example,  we are assum-
ing  an  average  household flow  of  4  persons  x  45  gcpd,  or  180  gpd
total.  Past work has shown that actual  evaporation  from an ET system is
approximately the  same  as the measured  pan  evaporation rate in  winter
(33).  Summer rates  are approximately  70% of the measured pan  evapora-
tion rates in this area,  but excessive evaporation potential more  than
offsets this condition.   Therefore,  the  design  is based on pan  evapora-
tion (in./day) minus precipitation (in./day).   In  this example,


             (0.07 in./day) - (0.01 in./day)  = 0.06  in./day


This equates to  a rate of 0.04 gpd/ft2.


In this example, then,  the required  area  for  the  ET bed is finally  cal-
culated:


                          180 gPd  , =  4,500 ft2
                        0.04 gpd/fr

To allow  a  factor  of safety, the size could be increased  to  as  much as
7,500 ft2 based  on 75  gpcd.   A more realistic  size  would be  5,000 to
6,000 ft2,  which would insure no  overflows.    If water conservation is
practiced,  direct  significant   savings   in  size  and  costs  could  be
achieved.


         7.3.2.6  Construction Features
A  typical  ET  bed installation  was shown  previously  in  Figure  7-35.
Characteristics of  an ETA  bed  are identical  except  that the liner  is
omitted.   Limited data are  available  on optimum construction  features
for ET and ETA disposal units.   The following  construction  features are
desirable:
     1.  Synthetic liners should have a thickness of at least 10 mil;  it
         may be  preferable  to  use  a double thickness of liner  material
         so that the seams can be stagqered if seams are unavoidable.

     2.  Synthetic liners should be cushioned on both  sides  with layers
         of sand at least 2 in.  (5  cm)  thick  to prevent puncturing dur-
         ing construction.

     3.  Surface runoff  from  adjacent  areas  should be diverted around
         the system by berms or drainage swales.
                                  308

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     4.   Crushed stone  or gravel  placed  around the  distribution  pipes
         should be 3/4 to 2-1/2 in. (2 to 6 cm).

     5.   Filter cloth or equivalent should be used  on top of the rock or
         gravel to prevent  sand  from settling  into  the  aggregate,  thus
         reducing the void capacity.

     6.   Care  should  be exercised in assembling the perforated distri-
         bution pipes (4 in. [10 cm]) to prevent pipe glues and solvents
         from contacting the synthetic liner.

     7.   The bed surface should be sloped for positive drainage.

     8.   A relatively porous topsoil, such  as loamy  sand or sandy  loam,
         should be  used  if  required to  support vegetation to  prevent
         erosion, or to make the appearance more acceptable.

     9.   The bed  should be located  in  conformance  with local   code  re-
         quirements.

    10.   Construction  techniques  described previously  for  subsurface
         disposal  systems,  where soil  permeability may  be  decreased by
         poor  construction  practices,  should  be used  for  ETA  systems
         (39WOH41).
         7.3.2.7  Operation and Maintenance
Routine operation and maintenance of an ET or ETA disposal  unit consists
only of typical yard maintenance activities such as vegetation trimming.
Pretreatment units and appurtenances require maintenance as described in
Chapter  8.    Unscheduled maintenance  requirements are  rare, and  stem
mainly from poor operating practices such  as  failure  to  pump  out septic
tank solids.
         7.3.2.8  Considerations for Multi-Home and Commercial
                  Wastewaters
ET  systems may  be  applicable  to  small  housing  clusters  and  commer-
cial/institutional establishments, but large area requirements may limit
their practicality.  Adjustments in the type of pretreatment used may be
required  depending  on the  wastewater  characteristics.   For  example,  a
grease trap is normally  required  prior to  septic tank  or aerobic treat-
ment of restaurant wastewater disposed of in an ET system.
                                   309

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     7.3.3  Evaporation and Evaporation/Infiltration Lagoons


         7.3.3.1  Description


Lagoons  have  found widespread  application for  treatment of  municipal
wastewater from  small  communities,  and have occasionally been  used  for
wastewater treatment  in onsite  systems prior  to  discharge to  surface
waters.  A more common application in onsite systems has been for treat-
ment and subsequent disposal by evaporation, or  a  combination  of evapo-
ration and infiltration.
A discussion of evaporation and evaporation/infiltration lagoons is  pro-
vided, since  thousands  are currently in  use  across the  United  States.
However,  performance data are very limited.   The information provided  in
this  section  is  based on  current  practice  without assurance that  such
practice is optimal.
         7.3,3.2  Application
In the United  States,  an  evaporation  or evaporation/infiltration  lagoon
could be used  in  most locations that have enough  available land.   How-
ever, local  authorities typically  prefer or  require the use of  subsur-
face disposal systems where conditions permit.   Thus,  actual application
of these lagoons  is generally  limited  to rural  areas where  subsurface
disposal  is  not possible.   In  addition,  use  of evaporation/infiltration
lagoons is  not appropriate in areas where wastewater  percolation  might
contaminate  groundwater supplies,  such  as in areas of shallow or  crev-
iced bedrock, or high water tables.  Use of both types of lagoons,  espe-
cially evaporation lagoons, is favored by the  large net  evaporation  po-
tentials found in arid regions.


Data on the  impact of influent wastewater characteristics on evaporation
and evaporation/infiltration lagoons are  very  limited.   Pretreatment  is
desirable,  especially if a garbage grinder discharges  to  the system.
         7.3.3.3  Factors Affecting Performance
The  major climatic  factors  affecting  performance  of  evaporation  and
evaporation/infiltration lagoons include sunlight,  wind  circulation,
                                   310

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humidity, and  the  resulting  net evaporation potential.   Other  features
that affect performance include:


     1.  Soil   permeability (evaporation/infiltration  only)--lagoon  size
         and soil  permeability are inversely proportional

     2.  Salt  accumulation  (evaporation  only)—results   in   decreased
         evaporation rate

     3.  Hydraulic loading—size must accommodate peak flows

     4.  Inlet configuration—center  inlet  tends to  improve mixing  and
         minimize odors

     5.  Construction techniques


         7.3.3.4  Design
Lagoons can be circular or rectangular.  The maximum wastewater depth is
normally 3 to 5 ft (0.9 to 1.5 m) with a freeboard of 2 or 3 ft, (0.6 to
0.9 m),  although  depths greater than  8  ft (2.4 m) have  also  been  used
(42)(43)(44)(45)(46)(47).   The  minimum wastewater depth  is  generally  2
ft  (0.6  m).    This  may necessitate  the  addition  of fresh  water  during
high-evaporation summer  months.   Figure 7-37 shows the  dimensional  re-
quirements for  a  typical onsite lagoon.   The size ranges from 3 to 24
ftVgpcd  (0.07  to  0.57  nr/lpcd),  depending  primarily on  the type  of
lagoon  (evaporation  or  evaporation/infiltration),  soil  permeability,
climate, and loc'al  regulations.


Lagoon design is usually based on locally available evaporation and  pre-
cipitation data, soil percolation rates (evaporation/infiltration  only),
and an  assumed wastewater flow.   Since runoff is excluded  by  the  con-
tainment berms, evaporation  lagoons  need only  provide  adequate surface
area  to  evaporate  the  incident precipitation  and the  influent  waste-
water.   Calculations may be made initially  on an  annual  basis, but  must
then  be  checked to  insure that adequate volume is provided for storage
during periods  when liquid inputs exceed  evaporation.   A  brief  design
example  is outlined below.
Assumptions:

     1.  Four occupants of home
     2.  45-gpcd wastewater flow
     3.  Annual precipitation:  15.3 in.
     4.  Annual evaporation:  46.7 in.
                                   311

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                            FIGURE 7-37



 TYPICAL  EVAPORATION/INFILTRATION LAGOON FOR SMALL INSTALLATIONS
Inlet -*£>:
                                                           Min
                  3:1  Slope
Min. Freeboard
                        -iz.    Winter
                            - 3  Operating Depth,
                     Inlet
                                312

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Design flow:.

                     4 persons x 45 gpcd = 180 gpd

Net evaporation per year:

                     46.7  in. - 15.3 in.  =  31.4 in.

     (31.4 in.)(144 in.2)  = 4,522 in.3 of water/ft2 water surface

     (4,522 in.3)(ft3/l,728 in.3)(7.48 gal/ft3)  =  19.6 gal of water/ft2
                                                      water surface
Lagoon area required:

             (180 gpd){365 days)/(19.6  gal/ft2)  =  3,352  ft2

This can be provided by a  round lagoon, 65.3-ft diameter.
At  this  point, we  need to  ensure  that the  lagoon  will  have  adequate
storage capacity  to  allow accumulation of water  to  a depth of no more
than 4 or 5 ft  in  low-evaporation months  (usually  winter),  and  to allow
sufficient surface  area for evaporation  of  the accumulated water plus
new influent flows  during  the  months when evaporation rates exceed  the
monthly wastewater flow (usually summer).   This  is  done by comparing  the
wastewater flow against the evaporation  rate for each  months, and  by
performing a water  balance  (i.e.,  calculating the gain or  loss in gal-
lons for each months).  Table 7-16 shows such a  balance.
From October through  April,  the  lagoon will  gain 35,443 gal of  volume.
This is equivalent to a gain of 1.4 ft:


                    (35,443 gal)(	L-^)(? 48\a1)  =  1.4  ft
                                3,352  fr  /tW 9al

Beginning with a 2-ft minimum depth, the depth  of  the  lagoon varies  from
2 ft to 3.4 ft.
Some  sources  indicate that  BOD  loadings should  also  be considered  in
lagoon sizing  for  odor control.   Loadings  in  the range  of 0.25 to  0.8
#BOD/day/l,000 ft*  (1.2  to  3.9  kg/day/1000 m*)  have been  recommended,
but supporting data  for  onsite systems are not  available  (43)(45)(46).
If  infiltration  is  permitted and feasible considering local soils,  the
size  of  the lagoon can be  reduced  by  the amount of water  lost  through
percolation.
                                  313

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                                                 TABLE 7-16

                             SAMPLE WATER BALANCE FOR EVAPORATION  LAGOON  DESIGN
Preci pi tati ona Net"
Month

October
November
December
January
February
March
oo April
£ May
June
July
August
September

Influent
gal
5580
5400
5580
5580
5040
5580
5400
5580
5400
5580
5580
5400
SBTTKJ
Preci p .
in.
1.1
1.4
1.8
1.6
1.6
1.4
1.4
1.2
1.2
0.8
0.8
1.0
T573~
Evap.
in.
2.2
1.8
1.7
0.7
0.9
1.2
3.1
5.3
6.1
9.4
9.0
5.3
"5577
-Evaporation
in.
-1.1
-0.4
0.1
0.9
0.7
0.2
-1.7
-4.1
-4.9
-8.6
-8.2
-4.3

gal
- 2299
- 836
209
1881
1463
418
- 3553
- 8569
-10241
-17974
-17138
- 8987

Flow
gai
3281
4564
5789
7461
6503
5998
1847
- 2989
- 4841
-12394
-11558
- 3587

Cum.
Vol ume
gal
3281
7845
13634
21095
27598
33596
35443
32454
27613
15219
3661
74

a [Precip. - Evap. (gal)] = [Precip. - Evap. (in.)] x (3352 ft2) x (7.48 gal/ft3) x (1/12)
                          = 2090 x [Precip. - Evap. (in.)]

b Net Flow = (Influent) + (Precip. - Evap.)

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Other design features which are frequently incorporated include fencing,
center  inlet,  specific  berm  slopes,  and buffer  zones.   Five- or  6-ft
(1.5- to 1.8-m) high  fencing  is  preferred to  limit animal  and human in-
trusion.  Submerged center  inlets  are  recommended  to  facilitate mixing,
to provide even solids deposition, and to minimize odors.   Interior  berm
slopes,  steep  enough to  minimize rooted  aquatic plant  growth in  the
lagoon, but  resistant to  erosion,  are desirable.  Slopes  sufficient to
accomplish this objective have been reported  to  be between  3:1 and  2:1,
depending primarily  on  height and soil  characteristics.    Buffer zones
are normally controlled  by local  regulations, but typically  range  from
100 to 300 ft (30 to 91  m).
         7.3.3.5  Construction Features
To prevent seepage through the berm in unlined lagoons, a good interface
between the berm  and  the native soil is necessary.   In  areas where  the
use of subsurface disposal systems is restricted due to slowly permeable
soils, B-horizon soils are frequently appropriate for berm construction.
Excavation of  the  topsoil  prior to berm placement  (so that the base of
the berm rests on  the  less  permeable  subsoils)  reduces the incidence of
seepage, as does compaction of  the  berm material  during  placement.   For
evaporation lagoons,  care during construction to insure  placement of a
leak-free liner reduces the need for impermeable berm material and asso-
ciated construction precautions.


         7.3.3.6  Operation and Maintenance
Start-up of  a  lagoon  system requires filling the lagoon  from a conven-
ient freshwater  source  to a depth of at least 2 ft  (0.6  m).   This ini-
tial filling helps to prevent rooted plant growth and septic odors.
Solids  removal  is required periodically for evaporation  lagoons.   Data
are  not available  to  indicate  the  exact frequency  of  solids  removal
required, but intervals of  several years  between  pump-outs  can be anti-
cipated.
The  reported  need  for  chemical   addition  to  control  odors,  insects,
rooted plants, and microbial growth  varies on  a case-by-case  basis  with
climate,  lagoon  location and configuration,  and loading  rate.   Mainte-
nance of a minimum 2-ft  (0.6-m) wastewater depth in the lagoon,  and  fre-
quent trimming of vegetation on the  berm  and  in the vicinity of the la-
goon, are suggested.  No other maintenance is  required.
                                    315

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         7.3.3.7  Seasonal, Multifamily, and Commercial  Applications
Use of evaporation and evaporation/infiltration lagoons for summer homes
would result in somewhat  reduced  area  requirements  per gallon  of waste-
water handled,  since  storage would not  need to be  provided during  the
winter  months.    Otherwise,  application  of  these  systems to  seasonal
dwellings is comparable to year-round residences.


Evaporation and evaporation/infiltration  lagoons  are also applicable to
multifamily and  commercial  applications, although  additional  pretreat-
ment may be required depending on the wastewater characteristics.
7.4  Outfall to Surface Waters
Direct discharge  of  onsite treatment system effluent  is  a  disposal  op-
tion if  an  appropriate receiving water is available  and  if the regula-
tory agencies permit  such  a  discharge.   The  level  of treatment required
varies,  depending on  local  regulations,  stream water  quality  require-
ments, and other  site-specific conditions.  In general, onsite treatment
system effluent disposed by  surface  discharge  must  at least meet secon-
dary treatment  standards for publicly  owned  treatment works.   Depending
on  site-specific  conditions, more  stringent  BOD  and SS discharge  re-
quirements and/or limitations on N and P discharges may be applicable.
The  performance,  operation, and  maintenance  requirements, and  the  en-
vironmental  acceptability  of  the  surface discharge depend predominantly
on the preceding treatment system.  Operation and maintenance associated
specifically  with  the surface discharge  pipe  are minimal in  a  gravity
situation.   If the effluent  must be pumped, then  routine pump  mainte-
nance will be required.
Discharge pipes should be made of corrosion- and crush-resistant materi-
als such as cast iron or rigid plastic pipe.  For single-family systems,
the pipe  should  range from 2 to 4 in.  (5  to  10 cm)  in diameter, should
be buried,  and  should be moderately  sloped (between  0.5  and 3%).  Steep
slopes may cause washout at the discharge point.
7.5  References
  1.  Bendixen, T. W., M.  Berk, J.  P.  Sheehy,  and S.  R.  VJeibel.   Studies
     on Household Sewage  Disposal Systems, Part  II.   NTIS  Report No.  PB
     216  128,  Environmental  Health Center, Cincinnati,  Ohio, 1950.   96
     pp.
                                   316

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 2.  Bouma,  J.   Unsaturated Flow During  Soil  Treatment of  Septic  Tank
     Effluent.   J.  Environ.  Eng.  Div.,  Am. Soc.  Civil  Eng.,  101:996-983,
     1975.

 3.  Manual  of Septic Tank Practice.   Publication No.  526,  Public Health
     Service,  Washington,  D.C.,  1967.   92 pp.

 4.  Small   Scale Waste  Management  Project,  University  of  Wisconsin,
     Madison.   Management of Small Waste  Flows.   EPA  600/2-78-173,  NTIS
     Report No. PB  286 560,  September 1978.  804  pp.


 5.  Laak,  R.    Pollutant  Loads  From Plumbing Fixtures  and  Pretreatment
     to Control Soil  Clogging.   J.  Environ.  Health,  39:48-50, 1976.

 6.  Winneberger, J.  H.,  L. Francis,  S.  A.  Klein,  and P.  H.  McGauhey.
     Biological Aspects of  Failure  of Septic Tank  Percolation Systems;
     Final  Report.   Sanitary Engineering  Research Laboratory, University
     of California,  Berkeley,  1960.

 7.  Winneberger, J.  T., and J.  W.  Klock.  Current and Recommended Prac-
     tices  for Subsurface Waste Water  Disposal  Systems  in  Arizona.   En-
     gineering Research Center Report  No.  ERC-R-73014,  College of Engi-
     neering Service, Arizona State  University,  Tempe, 1973.

 8.  Subsurface  Wastewater  Disposal  Regulations.   Plumbing Code,  Part
     II.  Department  of Human Services,  Division of  Health  Engineering,
     Augusta,  Maine,  1978.

 9.  Weibel, S.  R.,   T.  W.  Bendixen,  and J.  B. Coulter.   Studies  on
     Household Sewage  Disposal  Systems,  Part III.   NTIS  Report  No.  PB
     217 415,  Environmental Health Center, Cincinnati,  Ohio, 1954.   150
     pp.

10.  Corey, R.  B.,  E. J. Tyler,  and  M.  V. Olotu.  Effects  of Water Soft-
     ener Use  on the Permeability of  Septic  Tank Seepage  Fields.   In:
     Proceedings of the Second National Home Sewage  Treatment Symposium,
     Chicago,  Illinois, December 1977.   American Society of Agricultural
     Engineers, St.  Joseph, Michigan, 1978.   pp. 226-235.

11.  Machmeier, R.  E.  Town and  Country Sewage Treatment.   Bulletin 304,
     University of Minnesota, St. Paul,  Agricultural  Extension Service,
     1979.

12.  Otis,  R.   J., G.  D.  Plews,  and D. H. Patterson.   Design of Conven-
     tional  Soil Absorption Trenches and  Beds.   In:   Proceedings of the
     Second National  Home Sewage Treatment Symposium,  Chicago,  Illinois,
     December  1977.    American  Society  of  Agricultural Engineers,  St.
     Joseph, Michigan, 1978.  pp. 86-99.
                                   317

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13.   McGauhey, P. H.,  and J. T. Winneberger.  Final Report on a Study of
     Methods of  Preventing  Failure of  Septic  Tank Percolation Systems.
     SERL Report No.  65-17,  Sanitary  Engineering  Research  Laboratory,
     University of California, Berkeley, 1965.   33 pp.

14.   Bendixen, T. W., J. B. Coulter,  and  G.  M. Edwards.  Study of Seep-
     age Beds.   Robert  A. Taft Sanitary Engineering Center,  Cincinnati,
     Ohio,  1960.

15.   Bouma,  J.,  J.  C.  Converse, and F. R.  Magdoff.   Dosing  and Resting
     to  Improve  Soil  Absorption  Beds.   Trans.  Am.  Soc.  Civ.  Eng.,
     17:295-298, 1974.

16.   Harkin, J. M., and M.  D.  Jawson.  Clogging and Unclogging of Septic
     System Seepage Beds.   In:   Proceedings  of the Second Illinois Pri-
     vate Sewage  Disposal  system, Champaign,  Illinois,  1977.   Illinois
     Department of Public Health, Springfield,   pp. 11-21.

17.   Otis,  R.  J.,  J.  C. Converse, B. L.  Carlile,  and J.  E.  Witty.   Ef-
     fluent Distribution.   In:   Proceedings  of the Second National  Home
     Sewage  Treatment  Symposium,  Chicago,   Illinois,  December  1977.
     American  Society  of Agricultural   Engineers,  St.  Joseph,  Michigan,
     1978.   pp. 61-85.

18.   Kropf,  F. W.,  R.  Laak, and K.  A.  Healey.   Equilibrium Operation of
     Subsurface  Absorption  Systems.    J.  Water  Pollut.  Control  Fed.,
     49:2007-2016, 1977.

19.   Otis,  R. J.   An  Alternative Public Wastewater Facil-ity  for a Small
     Rural  Community.   Small  Scale  Waste  Management Project, University
     of Wisconsin, Madison,  1978.

20.   Alternatives for Small  Wastewater Treatment Systems.   EPA 625/4-77-
     011, NTIS Report No. PB  299 608,  Center for Environmental  Research
     Information, Cincinnati,  Ohio, 1977.

21.   Bendixen,  T.  W.,  R. E.  Thomas, and  J.  B. Coulter.   Report  of  a
     Study  to  Develop Practical Design Criteria  for Seepage Pits  as  a
     Method for  Disposal of Septic  Tank Effluents.   NTIS Report  No.  PB
     216 931, Cincinnati, Ohio,  1963.  252 pp.

22.   Winneberger, J. T.  Sewage Disposal System for the Rio-Bravo Tennis
     Ranch,  Kern County, California.  1975.

23.   Witz,  R. L., G. L. Pratt, S. Vogel, and C. W.  Moilanen.   Waste Dis-
     posal  Systems  for Rural  Homes.   Circular No. AE  43,  North  Dakota
     State University Cooperative Extension Service, Fargo,  1974.

24.   Converse, J. C.,  B. L.  Carlile, and G. W.  Peterson.  Mounds for the
     Treatment and  Disposal of Septic Tank Effluent.   In:   Proceedings
     of  the  Second National  Home  Sewage  Treatment  Symposium,  Chicago,
                                  318

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     Illinois, December  1977.   American Society  of Agricultural  Engi-
     neers, St. Joseph, Michigan, 1978.  pp. 100-120.

25.  Converse, J.  C.    Design  and  Construction  Manual  for Wisconsin
     Mounds.   Small  Scale Waste Management  Project,  University of Wis-
     consin, Madison, 1978.  80 pp.

26.  Soil  Conservation  Service.   Drainage of  Agricultural  Land.   Water
     Information  Center, Port Washington, New York, 1973.  430 pp.

27.  Mellen, W. L.   Identification of  Soils  as a Tool for the Design of
     Individual Sewage Disposal Systems.  Lake County Health Department,
     Waukegan, Illinois, 1976.  67 pp.

28.  Casagrande,  L.   Electro-Osmotic  Stabilization of Soils.  J. Boston
     Soc. Civ. Eng., 39:51-82, 1952.

29.  On-Site Wastewater Management.  National Environmental Health Asso-
     ciation, Denver, Colorado, 1979.  108 pp.

30.  Electro-Osmosis, Inc., Minneapolis, Minnesota.

31.  Bendixen, T. W.,  and J.  B. Coulter.   Effectiveness at the Distri-
     bution Box.   U.S. Public Health Service, Washington, D.C., 1958.

32.  Sheldon, W.  H.   Septic Tank  Drainage  Systems.  Research Report No.
     10,  Farm Science  Agricultural  Experiment  Station,  Michigan  State
     University,  East Lansing, 1964.

33.  Bennett, E.  R. and K. D.  Linstedt.  Sewage Disposal  by Evaporation-
     Transpiration.   EPA  600/2-78-163, NTIS  Report  NO.  PB   288  588,
     September 1978.  196 pp.

34.  Rugen,  M. A.,  D. A.  Lewis,  and  I. J.  Benedict.   Evaporation  - A
     Method  of Disposing of Septic Tank Effluent.   Edwards Underground
     Water District, San Antonio, Texas, (no date).  83 pp.

35.  Bernhardt, A.  P.   Treatment and  Disposal of  Wastewater from Homes
     by Soil  Infiltration and Evapotranspiration.  University of Toronto
     Press, Toronto, Canada, 1973.  173 pp.

36.  Pence, H. J.  Evaluation of Evapotranspiration as a Disposal System
     for Individual Household Wastes (A Seven-State Test); Draft Report.
     National Science Foundation, Washington, D.C., 1979.

37.  Lomax, K. M., P.  N.  Winn,  M.  C.  Tatro, and L. S. Lane.  Evapotran-
     spiration Method  of Wastewater disposal.   UMCEES  Ref.  No.  78-40,
     University of Maryland Center for Environmental and Estuarine Stud-
     ies, Cambridge, 1978.  42 pp.
                                   319

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38.   Bernhart, A. P.  Return  of  Effluent Nutrients to the Natural Cycle
     Through  Evapotranspiration   and   Subsoil-Infiltration  of  Domestic
     Wastewater.  In:  Proceedings  of  the National Home Sewage Disposal
     Symposium, Chicago,  Illinois,  December 1974.   American  Society of
     Agricultural  Engineers, St.  Joseph, Michigan, 1975.  pp.  175-181.

39.   Land Treatment of Municipal  Wastewater Effluents. EPA 625/4-76-010,
     NTIS  Report  No.  PB  259 994,  Center  for  Environmental  Research
     Information,  Cincinnati,  Ohio,  1976.

40.   Jensen, M. E., H. G. Collins, R.  D. Burman, A. E. Cribbs, and A. I.
     Johnson.   Consumptive Use  of  Water and  Irrigation  Water Require-
     ments.   Irrigation Drainage Division,  American Society  of Civil
     Engineers, New York, 1974.  215 pp.

41.   Priestly, C. H. B., and R. J. Taylor.  On the Assessment of Surface
     Heat  Flux  and  Evaporation  Using  Large-Scale  Parameters.    Mon.
     Weather Rev., 100:81-82,  1972.

42.   Witz,  R.  L.   Twenty-Five Years with  the  Nodak Waste Disposal Sys-
     tem.   In:  Proceedings of the  National  Home  Sewage Disposal  Sympo-
     sium,  Chicago,  Illinois,  December 1974.   American Society of Agri-
     cultural Engineers, St. Joseph, Michigan, 1975.  pp. 168-174.

43.   Standards for Designing a Stabilization Lagoon.  North Dakota State
     Department of Health, Bismarck, (No date).   3 pp.

44.   Pickett,  E.  M.   Evapotranspiration  and  Individual Lagoons.   In:
     Proceedings  of  Northwest Onsite  Wastewater  Disposal  Short Course,
     University of Washington, Seattle, December  1976.  pp. 108-118.

45.   Standards  for  Subsurface  and  Alternative  Sewage and  Non-Water-
     Carried Waste  Disposal.   Oregon  Administrative Rules, Chapter 340,
     Division 7,  May 1978.  p 97.

46.   Hines,  M.  W.,  E.  R. Bennett,  and  J.  A.  Hoehne.  Alternate Systems
     for Effluent Treatment and  Disposal.   In:  Proceedings of the Sec-
     ond  National  Home  Sewage  Disposal  Symposium,  Chicago,   Illinois,
     December  1977.    American Society  of Agricultural  Engineers,  St.
     Joseph, Michigan, 1978.  pp. 137-148.

47.  Code  of Waste  Disposal Regulations - Part III.  Utah State Depart-
     ment  of Health, Sewers  and Wastewater Treatment  Works,  Salt Lake
     City,  1977.  41 pp.
                                   320

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                                CHAPTER  8

                              APPURTENANCES
8.1  Introduction
This chapter discusses  several  types  of  equipment used in onsite waste-
water  treatment/disposal  systems that have  general application  to  the
components previously presented.  The following items are covered:


     1.  Grease traps (or grease interceptors)
     2.  Dosing chambers
     3.  Flow diversion methods
Grease  traps  are used  to remove  excessive  amounts of grease  that may
interfere with subsequent treatment.  Dosing chambers are necessary when
raw  or partially treated  wastewater must be  lifted or dosed  in  large
periodic volumes.   Flow diversion valves are used  when  alternating use
of treatment  or  disposal  components is employed.   These  components are
described as  to  applicability, performance, design criteria,  construc-
tion features, and operation and maintenance.


8.2  Grease Traps


     8.2.1  Description


In some instances, the accumulation of grease can be a problem.  In cer-
tain commercial/institutional  applications,  grease  can  clog sewer  lines
and  inlet and outlet structures in septic tanks, resulting in restricted
flows and poor septic tank performance.  The purpose of a grease trap is
simply to remove grease from the wastewater stream prior to treatment.
Grease  traps  are small  flotation  chambers where  grease floats  to  the
water surface and is retained while the clearer water underneath is dis-
charged.  There  are  no moving  mechanical  parts,  and the design is simi-
lar to that of a septic tank.
                                   321

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The grease  traps  discussed  here are the  large,  outdoor-type  units,  and
should  not  to be  confused  with  the  small grease  traps  found  on  some
kitchen drains.
     8.2.2  Application


Grease traps are very  rarely  used  for individual  homes.   Their main ap-
plication  is  in treating  kitchen  wastewaters from  motels,  cafeterias,
restaurants, hospitals,  schools, and  other  institutions  with large vol-
umes of kitchen wastewaters.
Influents to  grease traps usually contain  high  organic  loads including
grease, oils, fats, and dissolved  food  particles,  as  well  as detergents
and suspended solids.   Sanitary wastewaters are not  usually treated by
grease  traps.    Wastewaters  from  garbage  grinders should  not be  dis-
charged to  grease traps,  as  the  high solids loadings can  upset  grease
trap performance  and greatly  increase both  solids  accumulations  and the
need for frequent pumpout.
     8.2.3  Factors Affecting Performance


Several factors can affect the performance of a grease trap:  wastewater
temperature,  solids  concentrations,  inlet  conditions, retention  time,
and maintenance practices.


By placing the grease trap close to the source of the wastewater (usual-
ly the kitchen) where the wastewater is still hot, grease  separation and
skimming (if  used) are  facilitated.   As  previously mentioned,  high sol-
ids concentrations can impair grease flotation and cause a solids build-
up on  the bottom, which necessitates frequent  pumpout.    Flow control
fittings should be installed  on  the  inlet side of smaller traps to pro-
tect against  overloading or  sudden  surges  from the  sink  or  other fix-
tures.  These surges can cause agitation in the trap, impede grease flo-
tation, and allow  grease  to  escape  through  the outlet.  Hydraulic load-
ing and retention  time  can also affect performance.   High loadings and
short  retention times may  not allow  sufficient time for grease to sepa-
rate fully, resulting  in poor -removals.   Maintenance  practices are im-
portant,  as  failure to  properly clean the  trap and  remove  grease and
solids can result  in excessive  grease buildup that can lead to the dis-
charge of grease in the effluent.
                                   322

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     8.2.4  Design


Sizing of grease traps is based on wastewater flow and can be calculated
from the number and kind of sinks and fixtures discharging to the trap.
In addition, a grease trap should be rated on its grease retention capa-
city, which is  the  amount of grease  (in  pounds)  that  the trap  can hold
before its average efficiency drops below 90%.  Current practice is that
grease-retention capacity in pounds should equal  at least twice  the flow
capacity in gallons per minute.   In  other words, a trap rated at 20 gpm
(1.3 I/sec) should  retain at least  90% of the  grease  discharged  to  it
until it holds at least 40 Ib (18 kg) of grease (1).  Most manufacturers
of  commercial  traps  rate  their  products  in   accordance  with  this
procedure.
Recommended minimum flow-rate capacities of traps connected to different
types of fixtures are given in Table 8-1.


Another design method has  been  developed  through  years  of field experi-
ence  (3).    The  following  two  equations  are  used for restaurants  and
other types of commercial kitchens:
     1.  RESTAURANTS:
                      UD
 (D) x (GL) x (ST) x (££) x (LF) = Size of Grease Interceptor, gallons3

     where:

          D = Number of seats in dining area
         GL = Gallons of wastewater per meal, normally 5 gal
         ST = Storage capacity factor -- minimum of 1.7
                                         onsite disposal -2.5
         HR = Number of hours open
         LF = Loading factor — 1.25 interstate freeways
                                1.0  other freeways
                                1.0  recreational areas
                                0.8  main highways
                                0.5  other highways

     2.  HOSPITALS,  NURSING  HOMES,  OTHER TYPE  COMMERCIAL  KITCHENS WITH
         VARIED SEATING CAPACITY:

 (M) x (GL)  x (ST) x (2.5)  x  (LF)  =  Size  of  Grease  Interceptor,  gallons3

     where:

         M = Meals per day
        GL = Gallons of wastewater per meal, normally 4.5
                                    323

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                                TABLE 8-1

           RECOMMENDED RATINGS FOR COMMERCIAL GREASE TRAPS (1)
   Type of Fixture
Restaurant kitchen
  sink

Si ngle-compartment
  scullery sink

Double-compartment
  scullery sink

2 single-compartment
  sinks

2 double-compartment
  sinks

Dishwashers for
  restaurants:

     Up to 30 gal
       water capacity

     Up to 50 gal
       water capacity

     50 to 100 gal
       water capacity
Flow
Rate
gpm
15
20
25
25
35
15
25
40
Grease
Retenti on
Capacity
Rating
Ib
30
40
50
50
70
30
50
80
Recommended
Maximum Capacity
Per Fixture Connected
to Trap
gal
50.0
50.0
62.5
62.5
87.5
50.0
62.5
100.0
                                   324

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        SC =. Storage capacity factor — minimum of 1.7
                                        onsite disposal  - 2.5
        LF = Loading factor — 1.25 garbage disposal  &
                                    dishwashing
                               1.0  without garbage disposal
                               0.75 without dishwashing
                               0.5  without dishwashing
                                    and garbage disposal

     a Minimum size grease interceptor should be 750 gal


Thus, for a restaurant with a 75-seat dining area, an 8  hr per day oper-
ation, a typical discharge of  5  gal  (19  1)  per meal, a  storage capacity
factor of 1.7 and a loading factor of 0.8, the size of the grease inter-
ceptor is calculated as follows:


         (75) x (5) x (1.7) x (|) x (0.8) = 2,040 gal (7,722  1)


Other design considerations include:   facilities  for insuring that both
the  inlet and  outlet are  properly  baffled;  easy  manhole   access  for
cleaning; and inaccessibility of the trap to insects and vermin.
     8.2.5  Construction Features


Grease traps are generally made  of  pre-cast  concrete,  and  are purchased
completely assembled.  However,  very large units may be  field construc-
ted.   Grease  traps come  in  single-  and double-compartment  versions.
Figure 8-1 shows a typical  pre-cast double-compartment  trap (2).


Grease traps are  usually buried so as to  intercept  the  building sewer.
They must be level,  located  where they are easily  accessible  for clean-
ing,  and  close to  the  wastewater  source.   Where efficient  removal  of
grease is  very important, an  improved two-chamber  trap has  been  used
which has a  primary (or grease-separating)  chamber and  a  secondary (or
grease-storage) chamber.   By  placing the  trap as close as  possible  to
the  source  of  wastewaters,  where  the  wastewaters are  still  hot,  the
separating grease at the surface of the  first  chamber  can  be removed  by
means  of  an  adjustable weir  and  conveyed  to  the  separate  secondary
chamber, where  it accumulates,  cools, and  solidifies.  This  decreases
the requirement for  cleaning and allows  better grease  separation in the
first chamber.
                                   325

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                                  FIGURE 8-1

                        DOUBLE-COMPARTMENT GREASE TRAP
            Removable Slab
                                               Gas Tight Manhole Frame
                                               and Cover for Traffic
                                               Duty Anticipated
         Inlet —
                 Outlet
                                Top View
Tee with
Cleanout Plug
         Inlet
Precast Concrete
Tank
                      Grade
                            ~v
Manhole Cover

    •^Concrete Pad
                                                                 Outlet
                Tee with
                Cleanout Plug
                                    Section
                                      326

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The inlet, outlet, and baffle  fittings  are  typically  of "T"  design with
a  vertical  extension 12  in.  (30 cm) from  the tank  floor and  reaching
well above the water line (3).
To  allow  for proper maintenance, manholes  to finished grade  should  be
provided.    The  manhole covers should  be of gas-tight  construction  and
should be designed to withstand expected loads.
A check of  local  ordinances and codes should  always  be  made  before the
grease trap is designed or purchased.
     8.2.6  Operation and Maintenance
In  order  to be  effective,  grease traps  must be operated  properly  and
cleaned regularly  to  prevent  the escape  of appreciable quantities  of
grease.  The frequency of cleaning at any given installation can best be
determined  by  experience  based  on  observation.   Generally,  cleaning
should  be  done  when  75%  of  the  grease-retention capacity  has  been
reached.  At restaurants, pumping  frequencies  range from  once  a week to
once every 2 or 3 months.
8.3  Dosing Chambers


     8.3.1  Description
Dosing chambers  are tanks that  store  raw or pretreated  wastewater  for
periodic  discharge  to  subsequent  treatment  units  or disposal  areas.
Pumps or siphons with appropriate switches and alarms are mounted in  the
tank to discharge the accumulated liquid.
     8.3.2  Application
Dosing chambers are used where it is necessary to elevate the wastewater
for  further  treatment or disposal, where intermittent  dosing  of treat-
ment  units  (such  as sand filters) or  subsurface  disposal  fields is de-
sired, or  where pressure distribution networks are used  in subsurface
disposal  fields.  If the dosing chamber is at a lower elevation than the
discharge  point,  pumps must  be  used.   If  the  dosing  chamber  is  at a
higher elevation,  siphons  may be  used,  but only if the settleable and
floatable solids have been removed from the  wastewater  stream.
                                  327

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     8.3.3  Factors Affecting Performance


Factors that must be considered in design of dosing chambers are (1) the
dose volume, (2) the total dynamic head,  (3)  the  desired  flow  rate,  and
(4) the wastewater  characteristics.   When pumps are  used,  they must be
selected  based  on  all  three  factors.    If  raw  wastewater with  large
solids  is pumped,  grinder  pumps  or  pneumatic ejectors  must  be  used.
Siphons are chosen on the basis of the  desired  flow  rate  and their dis-
charge  invert elevations  determined  from the total  dynamic  head.   Only
wastewaters free  from  settleable  and flotable solids can  be discharged
by  siphons.   If corrosive wastewaters  such as  septic tank effluent are
being discharged, all  equipment  must be selected  to  withstand  the cor-
rosive atmosphere.
     8.3.4  Design


         8.3.4.1  Dosing Chambers with Pumps
A pumping  chamber consists  of  a tank,  pump,  pump controls,  and  alarm
system.  Figure  8-2  shows a cross  section  of  a typical  pumping chamber
used for pumping pretreated wastewater.  The tank can be a separate unit
as shown, or  it  can  have  common  wall  construction with the pretreatment
unit.
The  tank  should have  sufficient volume  to  provide the  desired  dosing
volume, plus a  reserve volume.   The  reserve  volume is the volume of the
tank  between  the high water  alarm  switch and  the invert of  the inlet
pipe.   It  provides  storage during  power outages  or  pump failure.   A
reserve capacity equal to the estimated  daily wastewater  flow is typi-
cally used for residential application (4).  In large flow applications,
duplex pump units can be used as an alternative to provide reserve capa-
city.  No reserve capacity is necessary when  siphons are used.
Pump  selection  is based on the  wastewater  characteristics,  the desired
discharge  rate,  and the pumping  head.   Raw wastewater  requires  a pump
with  solids-handling  capabilities.   Grinder pumps,  pneumatic ejectors,
or  solids-handling  centrifugal  pumps  are  suitable  for  these  applica-
tions.   While pneumatic ejectors may  be used  in  other  applications as
well,  submersible centrifugal  pumps  are  best  suited  where large volumes
are to be  pumped in each dose.
The pump size is determined from pump performance curves provided by the
manufacturers.  Selection is based on the flow rate needed and the pump-
ing  head.   The  specific application  determines  the flow  rate  needed.
                                  328

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                                                   FIGURE 8-2

                                        TYPICAL  DOSING CHAMBER WITH PUMP
          Influent
CO
ro
10
                                        Relay in Weather Proof
                                              Enclosure
                                      Manhole Cover
           High Water
          Alarm Switch
Reserve Capacity
After Alarm Sounds
                                    	Level

                                    Level Control Switch

                                             Shut-Off Level
                                                         Level
                                                        Control
                                                        Switch
Hanger Pipe
for Pump Removal


Quick Disconnect
Sliding Coupler
                                                                                   -*• Effluent

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The pumping  head  is calculated by  adding the, elevation  difference be-
tween the  discharge outlet  and  the average or  low water level  in the
dosing chamber  to  the friction losses  incurred  in the  discharge pipe.
The velocity head can be neglected in most applications.


If the liquid  pumped is to be free  from  suspended  solids,  the pump may
be set on  a pedestal.   This provides a  quiescent  zone below  the  pump
where any  solids entering  the  chamber can  settle, thus avoiding  pump
damage or malfunction.  These solids must be removed periodically.


In cold climates where  the  discharge pipe is not buried below the frost
line, the  pipe should be  drained  between doses.   This  may be  done  by
sloping the  discharge pipe back to  the  dosing chamber  and  eliminating
the check valve at  the  pump.   In  this manner,  the pipe is able to drain
back  into  the dosing  chamber  through the  pump.   The dosing  volume  is
sized to account for  this  backflow.   Weep holes  may also be used if the
check valve is left in place.


The  control  system  for the pumping chamber  consists  of a  "pump  off"
switch, a "pump on" switch, and a high water alarm switch.  The pump off
switch is set  several  inches above  the  pump intake.  The pump on switch
is set above  the pump  off  switch  to provide  the proper  dosing volume.
Several inches  above the pump on  switch, a high water  alarm  switch  is
set  to  alert  the  owner of  a  pump  malfunction  by  activating  a visual
and/or audible  alarm.  This switch  must be on a circuit  separate  from
the pump switches.
The  switches  should  withstand the humid and  other  corrosive atmosphere
inside the tank.  Pump failures can usually be traced to switch failures
resulting in pump burn out,  so  high  quality switches are a good invest-
ment.  Some types are:
         Mercury:   Two  basic  types  are  available.   One is  an  on-off
         switch  sealed  within  a  polyethylene  float suspended  from  the
         top of  the chamber by  its  power  cord.   Two switches are neces-
         sary to operate the pump  (See  Figure 8-3).   The elevations  are
         adjusted individually.   Differential  switches  are  also  avail-
         able  to turn the  pump  on and off  with one switch,  but  these
         lack the ability to adjust the dosing volume.
                                   330

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                          FIGURE  8-3

                    LEVEL  CONTROL SWITCHES
          Relay
      Pump-on Level
Vent Tube
in Cord
\ Pump-off Level  	/\ Pump-off Level

->                    C—-*\ Switch

                b) Pressure Diaphragm
                                                     Switch

                                                 Pump-on Level
a) Mercury Float
                                                      Pump-off Level
               c) Weighted Float
2.  Pressure Diaphragm:   The pressure diaphragm switch is a micro-
    switch mounted behind  a neoprene diaphragm.   The microswitch
    side of the diaphragm is vented to the atmosphere by means of a
    vent tube imbedded in the  power  cord.   The other side is sub-
    merged in the liquid.  As the liquid level rises and falls, the
    pressure on  the diaphragm  activates the  switch  (See  Figure 8-
    3).   Thus,  one  switch is  sufficient to  operate  the  pump; but
    the differential in liquid  levels is usually limited to about 6
    in, although  switches  with larger  differentials can  be pur-
    chased.   If used  in  pumping  chambers,  the vent  tube  must be
    located outside the pumping chamber  or the humid atmosphere in
    the chamber can cause the switch  to corrode.

3.  Weighted Float:   The  switch is mounted  above  the water with 2
    weights attached to a single cable hanging from the switch (See
    Figure 8-3).  When the weights are hanging free, the switch is
    held  open;  but as  the  liquid  level  rises,  the weights are
    buoyed up,  closing the  switch  when  the  second  weight  is sub-
    merged.   The switch   is  held  closed by  a magnet; but  as the
                              331

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         liquid level  drops,  the weights  lose their buoyancy  and  open
         the switch when the bottom weight  is  exposed.   The dosing  vol-
         ume can be changed by adjusting the spacing between the floats.
All  electrical contacts  and. relays must be mounted outside  the  chamber
to protect  them  from corrosion.   Provisions  should be made  to  prevent
the gases from following the electrical  conduits into  the  control  box.
         8.3.4.2  Dosing Chambers with Siphons
Siphons may be used in place  of  pumps  if the point of discharge is at a
lower elevation than the outlet of the pretreatment unit.  A chamber em-
ploying siphons consists  of  only a tank and  the  siphon.   No mechanical
or  electrical  controls  are   necessary,  since  the  siphon operation  is
automatic.  A typical siphon  chamber  is  illustrated  in Figure 8-4.  Two
siphons may be placed in a tank and automatically alternate,  providing a
simple method of  dividing the wastewater flow  between  two treatment  or
disposal units.
The design  of the dosing  chamber  is determined by  the  siphon selected
and the  head  against  which it must operate.   The  size of  the siphon is
determined by the average flow rate desired.  The manufacturer specifies
the "drawing depth," or  the  depth  from  the bottom  of the siphon bell to
the high water level  necessary  to  activate  the siphon (See  Figure 8-
4).   The length and width of the  chamber are determined  by  the dosing
volume desired.
Siphon  capacity is  rated when  discharging  into  the open  atmosphere.
Therefore, if the discharge is into a long pipe or pressure distribution
network, the headlosses must  be  calculated  and the invert at the siphon
discharge  set  at that  distance  above the  outlet.   For  high  discharge
rates  or  where  the  discharge  pipe  is  very  long,  the  discharge  pipe
should be one nomimal pipe size larger than the siphon to facilitate air
venting.
The  siphons  may be cast iron or  fiberglass.   Cast iron siphons are the
most  common.    Their  advantage  is  that  the bell  is  merely set  on the
discharge  pipe  so they may  be  easily removed and  inspected.   They are
subject  to corrosion,  however.   Fiberglass siphons do  not  corrode, but
because  of their light weight, they must be bolted to the chamber floor.
                                   332

-------
                                                       FIGURE 8-4

                                          TYPICAL DOSING CHAMBER WITH SIPHON
                Influent
CO
CO
CO
                                                Manhole
                                                                           Vent


->!























t
Drawing Depth
1
/
s
^inhr^n Roll*^^^
W/Vent r-
Siphon Leg -^
T=


f
\



1





=^

'



->
^





1

/
I

u
^v 	 .





i


/

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i
i




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-------
     8.3.5  Construction
The  tank  must  be watertight  so  groundwater does  not  infiltrate  it.
Waterproofing consists of adequately  sealing  all  joints with asphalt or
other  suitable  material.   Coating  the  outside  of  the tank  prevents
groundwater from seeping into the  tank.   Asphalt  coating the inside and
outside of  steel  tanks  helps  retard  corrosion.   Application  of  4-mil
plastic to  the  wet  asphalt  coating  protects  the  coating when  back-
filling.
At high  water table sites,  precautions  should be taken  so  the chamber
does not  float  out of  position due  to hydrostatic pressures on a near-
empty tank.   This  is not normally a problem for concrete tanks, but for
the  lighter-weight materials,  such  as  fiberglass,  it could  present  a
problem.   The manhole  riser pipe should  be  a  minimum  of 24  in. (61 cm)
in diameter  and  should extend 6  in.  (15  cm) above ground level  to keep
surface-water from entering the chamber.
If plastic pipe is used for the inlet or discharge, precaution should be
taken  to ensure  that  the pipe  does not break  as the  backfilled  soil
around  the  tank  settles.   A  cast iron pipe  sleeve  or  other  suitable
device  can be  slipped  over the plastic  pipe  extending  from the tank to
unexcavated soil to provide this protection.


     8.3.6  Operation and Maintenance
Little  routine  maintenance of  dosing chambers is  required.    The  tank
should  be  inspected periodically,  and any  solids  that accumulate on the
floor  of  the tank  should  be removed.   If  pumps  are used,  the system
should  be cycled  to  observe operation  of the switches  and  pump.   If
siphons are  used,  the water  level  in the  tank  should be noted  over  a
period  of  time to determine if the siphon is operating properly.  If the
siphon  is  working properly, the water level will  fluctuate from the bot-
tom  lip of the  siphon bell  to several  inches  above the bell.   If the
water  elevation  does  not change  despite water addition, the  siphon  is
"dribbling,"  indicating  that  the   vent  tube  on  the  bell  requires
cleaning.
                                  334

-------
8.4  Flow Diversion Methods for Alternating Beds
     8.4.1  Description
Under some circumstances, it is desirable to  divert  the  wastewater  flow
from one soil absorption area to another to provide  long-term  alternate
resting periods (see Chapter 7).  Flow diversion may be  accomplished  by
the use of  commercially available diversion  valves  (Figure 8-5) or  by
diversion  boxes (Figures 8-6 and 8-7).
                               FIGURE 8-5

                         TYPICAL  DIVERSION VALVE
                                         Water-Tight Access Cap
                                      Valve Direction Handle
                                         Valve Body
                                 335

-------
                         FIGURE 8-6

   TOP VIEW OF DIVERSION BOX UTILIZING A TREATED  WOOD  GATE
                     LjJ    Ljj    LJJ
                                             Wood Gate
                         FIGURE 8-7

   SECTION VIEW OF DIVERSION BOX UTILIZING  ADJUSTABLE ELLS
 90° Ell in
zontal Po
  (Open)
n
isition
^--^
-A

I Cover



Inlet
U


^n O I
Liquid Level


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** — •
Nipp





„. —
le


— — - — .
^-90
Vertic
(C
tf

                                                  (Closed)
                Open
Closed
                             336

-------
     8.4.2  Design
Diversion boxes can  be  made from conventional distribution  boxes.   One
type of  diversion  box shown in  Figure  8-6 uses  a treated wood  gate  to
divert the flow to the desired outlet pipe (5).


Another, shown in  Figure  8-7,  uses 90° ells  that  can  be  moved from the
horizontal  to the vertical position to shut off flow.  Caps or plugs can
be used  in  place of  elbows.   Elbows,  however, provide a  freer  flow  of
air  into  the resting  system.    Insulated  covers  must be  provided  with
diversion boxes when installed in cold climates.
     8.4.3  Construction
Construction  follows  manufacturers  recommendations  or the  procedures
outlined for distribution boxes (Chapter 7).
     8.4.4  Maintenance
Maintenance of  diversion valves  involves  little more than  turning  the
valve at the desired frequency.  Any accumulated solids in the diversion
box or valve should be removed periodically.
8.5  References
1.  Manual of Septic Tank Practice.  NTIS Report  No.  PB  216  240,  Public
    Health Service, Washington, D.C., 1967.   92 pp.

2.  Hogan, J. R.  Grease Trap Discussion.  Plumb Eng., May-June 1975.

3.  HYGI Design Manual.  M.  C. Nottingham Company, Pasadena,  California,
    1979.

4.  Converse,  J.   C.    Design  and  Construction  Manual  for  Wisconsin
    Mounds.    Small  Scale   Waste  Management  Project,   University  of
    Wisconsin, Madison, 1978.  80 p.

5.  Machmeier,  R.   E.   Home  Sewage Treatment Workbook.   Agricultural
    Extension Service, University of Minnesota, St.  Paul, 1979.
                                   337

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                                CHAPTER 9

                           RESIDUALS DISPOSAL
9.1  Introduction
Proper maintenance  of onsite  treatment systems  requires  periodic dis-
posal of  residual  solids, sludges,  or  brines.    In  some  areas,  finding
environmentally  sound techniques  for disposal   of  these  residuals  has
been very difficult.   Because of the possible  presence  of pathogens in
many of  these wastewaters,  proper  handling and  disposal  are important
from a  public health  perspective.    The  homeowner's role  in residuals
handling is  to  ensure that residuals from  his  system  are removed peri-
odically at  the  appropriate  interval so that proper system performance
is maintained.
This chapter  discusses the characteristics of  residuals,  and describes
treatment and disposal options  for  septage  (septic  tank  pumpings).   The
chapter is  intended  to be merely an overview  of  residuals handling op-
tions.   The  reader  is referred to  publications that  discuss particular
alternatives in greater detail.
9.2  Residuals Characteristics
Table  9-1  summarizes  the  residuals  that  may be  generated by  onsite
wastewater handling  systems.   Typical  characteristics,  removal  frequen-
cies,  and  disposal  modes are  presented.   Many of  the  residuals  listed
may contain  significant  amounts  of pathogenic  organisms,  nutrients,  and
oxygen-demanding materials; thus,  they  require proper handling  and dis-
posal to protect public health and to prevent degradation of groundwater
and surface water quality.
In general,  residuals  generated  by  onsite  wastewater systems are highly
variable in  character.   This is due  to  several  factors,  including type
and number of  fixtures,  number  and  age of  occupants, type of wastewater
treatment system, and user habits.
The wastewater removed from septic tanks,  commonly  referred  to  as  sept-
age, is  the  most common  residual  generated from  onsite  wastewater  sys-
tems.  The  characteristics  of septage are  presented  in Tables  9-2  and
9-3.    While  information  on  septage  characteristics  and  treatment
/disposal alternatives is relatively  abundant,  data on  other  residuals
listed in Table 9-1 are limited.

                                   338

-------
                                                          TABLE 9-1

                                  RESIDUALS  GENERATED FROM ONSITE WASTEWATER SYSTEMS (1)
           Resi dual
      Source
 Frequency of
    Removal
    Characteristics
      Disposal3
CO
CO
         Septage
          Sludge
          Sewage
         Blackwater
          Recycle
            Residuals
          Compost
          Ash
          Scum
   Septic  tank
   Aerobic  unit
   Holding  tank
   Holding tank
 Recycle systems
 Compost toilet;
   large
   small

Incinerator toilet
   Sand filters
  2 to 5 yr      High BOD and SS;  odor,
                 grease,  grit,  hair,
                 pathogens
     1  yr
High BOD and SS;
grease, hair, grit,
pathogens
week to months   Strong septic sewage;
                 odor, pathogens
6 months-1 yr    High BOD and SS; odor,
                 pathogens
6 months-1 yr    Variable depending on
                 unit processes employed
6 months-1 yr
   3 months

   weekly
   6 months
Relatively stable, high
organics, low pathogens
Dry, sterile, low
volume
Odor, pathogens, low
volume
Pump out by professional
hauler for off-site
disposal.

Pump out by professional
hauler for off-site
disposal.

Pump out by professional
hauler for off-site
disposal.

Pump out by professional
hauler for off-site
disposal.

Pump out by profesisonal
hauler for off-site
disposal.

Homeowner performs
onsite disposal; garden
burial.

Onsite burial by
homeowner or di sposal
with rubbish to landfill

Onsite burial by
homeowner or off-site
disposal
         a Approval  by  state  or local  regulatory agency  necessary.

-------
                                TABLE 9-2

                   CHARACTERISTICS OF DOMESTIC SEPTAGE


         Parameter                     Mean Value
                                          mg/1
                      Reference
Total Solids
Total Volatile Solids
Suspended Solids
Volatile Suspended Solids
BOD
COD
PH

Alkalinity (CaCOs)
TKN
NH3-N
22,400
11,600
39,500

15,180
 8,170
27,600

 2,350
 9,500
21,120
13,060

 1,770
 7,650
12,600
 8,600

 4,790
 5,890
 3,150

26,160
19,500
60,580
24,940
16,268

  6-7 (typical)

   610
 1,897

   410
   650
   820
   472

    59
   100
   120
    92
   153
  2
  3
  4

  2
  3
  4

  2
  3
  5
  6

  2
  3
  5
  6

  2
  3
  6

  2
  3
  4
  5
  6

2,3,4

  3
  5

  3
  4
  5
  6

  2
  3
  4
  5
  6
                                    340

-------
                          TABLE 9-2 (continued)
         Parameter                     Mean Value              Reference
Total Phosphorus

Grease
Alumi num
Arsenic
Cadmium

Chromium
Copper
Iron

Mercury
Manganese

Nickel

Lead
Sel eni urn
Zinc
mg/1
190
214
172
351
3,850
9,560
48
0.16
0.1
0.2
9.1
0.6
1.1
8.7
8.3
210
160
190
0.02
0.4
5.4
4.8
0.4
<1.0
0.7
2.0
8.4
0.07
9.7
62
30

3
4
5
6
3
4
6
6
3
4
6
3
6
3
6
3
4
6
4
6
4
6
3
4
6
3
6
6
3
4
6
                                   341

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                                TABLE 9-3

             INDICATOR ORGANISM AND PATHOGEN CONCENTRATIONS
                           IN DOMESTIC SEPTAGE
        Parameter                   Typi cal  Range              Reference
                                    counts/100 ml


Total Coliform                       10?  - 10$                      5

Fecal Coliform                       106  - 108                    4,5,7

Fecal Streptococci                   106  - 107                    4,5,7

Ps. aeruginosa                       IQl  - 103                    4,5,7

Salmonella sp.                        
-------
Accumulation rates of residuals differ for the same reasons that account
for their  variability  in characteristics:  that  is, type  and  number of
fixtures, occupancy characteristics, type of wastewater system, user ha-
bits, etc.   The figures presented in  Table  9-1  for frequency  of resid-
uals  removal  reflect  typical   ranges  found  in  practice,  although  the
range of actual  values may be greater.


9.3  Residuals  Handling Options
Residuals  that  potentially may be  disposed of onsite  by  the homeowner
include compost from compost toilets, ash from incinerating toilets, and
the  solids mat  from sand  filters.   Assuming  proper operation  of the
unit, ash  from  incinerating toilets  is  sterile and  can be  safely dis-
posed by mixing it with soil on the homeowner's property, or by handling
with household  solid wastes.   Residuals from compost toilets are rela-
tively stable, but may contain pathogenic bacteria and virus, especially
if  the  system has  not been properly  operated and maintained.   Onsite
burial is approved in some states but not in others, due to the possible
health hazards of handling the waste.  The same conditions  hold for dis-
posal of the scum that must be periodically raked off filtration units.
Pathogens may be present in the scum layer, and approval for onsite dis-
posal  varies  with locale.   The appropriate  state or  local  regulatory
agency should be consulted for the requirements in a particular area.
As Table  9-1  indicates,  the residues from septic  tanks,  aerobic  treat-
ment  units,  holding tanks,  and  recirculating toilets must  be  periodi-
cally pumped  out and  disposed  of by  professional  haulers.   The  home-
owner's responsibility should be to ensure that this service  is  provided
before residuals buildup impairs performance of the treatment unit.
9.4  Ultimate Disposal of Septage
By far  the  most common waste material generated  from  onsite systems is
septage.   The following discussion provides  a brief overview  of  tech-
niques  for  disposal  of this waste.   For  a  more complete description of
these processes, the reader is referred to the list of references at the
end of this chapter.
There  are  three basic  methods  for disposing  of septage:   disposal  to
land,  treatment  and disposal at  separate septage  handling  facilities,
and treatment at existing wastewater treatment plants.
                                   343

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     9.4.1  Land Disposal
Four  methods can  be used  for disposing of  septage to  land:   surface
spreading,  subsurface  disposal, trenching, and  landfilling.   Table 9-4
summarizes  the main  characteristics of these disposal techniques.


Land  spreading  is the most frequently used septage  disposal  method in
the  United States.   Surface  spreading  of septage  is  generally accom-
plished  by the  same techniques  as  municipal  liquid wastewater sludge
spreading.   This may simply  involve  the  septage pumping truck emptying
its  contents  on the field  while slowly driving  across  the site.   This
technique  has  very low operation and  maintenance requirements.   A more
controlled  approach  is to  use a holding tank  to receive septage loads
when  the soil is not suitable  for spreading.  A  special vehicle (tractor
.or  truck  with flotation  tires)  can  then be used to spread the septage
when  weather and soil conditions permit.
 Subsurface disposal techniques  have  gained wide acceptance as  alterna-
 tives for disposal  of  liquid sludge and,  to some  extent,  septage.   Three
 basic approaches to subsurface disposal  are available:


      1.   Incorporation using  a  farm  tractor  and  tank  trailer with  at-
          tached subsurface injection  equipment.

      2.   Incorporation using a single,  commercially available  tank  truck
          with subsurface injection equipment.

      3.   Incorporation using tractor-mounted subsurface injection equip-
          ment in conjunction  with a  central holding facility and  flex-
          ible "umbilical  cord."   Liquid  sludge  is continually' pumped
          from the holding tank to the injection  equipment.


 Disposal  of  septage by burial  in  excavated trenches is another common
 disposal  technique.   Trenches are typically  3  to 6 ft  (0.9  to 1.8  m)
 deep and  2  to 3 ft  (0.6 to  0.9  m)  wide,  with dimensions varying  with
 site location.   Space  between  trenches should  be sufficient to  allow
 movement of  heavy  equipment.   A series of  trenches  is usually  dug  by a
 backhoe to allow sequential loading  and  maximum  dewatering.   Septage is
 usually applied in 6-  to  8-in.  (15 to  20 cm)  layers.  When the  trenches
 are  full, the  solids  can be excavated and  placed  in a  landfill if they
 have dewatered  sufficiently,  or the trenches can  be covered with  2 ft
 (0.6 m)  of  soil.  A  thorough site  evaluation  is  essential   to prevent
 groundwater contamination with this disposal technique.
                                   344

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                                                    TABLE 9-4

                                     LAND DISPOSAL  ALTERNATIVES FOR SEPTAGE
      Alternative
                  Design Considerations
Advantages
Di sa dvantages
CO
-pi
en
Subsurface   Septage volume /character!" sties
Disposal      Climate
(1)(2)(8)    Site characteristics
(9)(17)      - Soil  type/permeability
(19)         - Depth to groundwater
               or bedrock
             - Aquifer size, flow
               characteristics, use
             - Slope
             - Proximity to dwellings,  etc.
             - Crop and crop use
             - Size of site
             - Site protection
             Equipment selection
             Application rate
             Winter storage or
               contingency plan
             Mom" tori ng wel 1 s

Surface      Septage volume/character!sties
Spreading    Application rate  (N loading)
(1)(2)(8)    Climate
(9)(17)      Storage facilities
(19)         Site characteristics (same
               as subsurface disposal)
             Equipment selection
             Moni tori ng wel1s
                                                   Low  human contact potential
                                                   Low  incidence of odors
                                                     and  vectors
                                                   Aesthetically more
                                                     acceptable than surface
                                                     spreading
                                                   Good soil amendment
                                                    Small  labor  requirement
                                                    Minimum  equipment  required
                                                    Benefit  from fertilizer -
                                                      soil amendment value
                                                    Low  cost
                                                    Simple Operation
                       Large land requirements
                       Storage may be required
                         during inclement weather -
                         wet or frozen ground
                       Need more equipment than for
                         surface spreading
                       Possible odor and aesthetic
                         nuisance
                       Spreading restricted by wet
                         or frozen soil
                       Storage may be required
                         during inclement weather
                       Pretreatment may be required
                         for deodorization and
                         pathogen destruction
                       Possible human contact or
                         vector attraction

-------
                                               TABLE 9-4 (continued)
      Alternative
     Desi gn Consi derati ons
      Advantages
       Disadvantages
      Trench
      Disposal
      (18)
GO
*.
CPi
      Sanitary
      Landfill
      Disposal
Septage volume/characteristics
Si te characteri sti cs
- Soil  type/permeability
- Depth to groundwater or
  bedrock
- Aquifer size,  flow
  characteristics, use
- Proximity to dwellings, etc.
- Proximity to septage sources
Site protection
Equipment selection
Design life
Monitoring wells

Septage/refuse ratio
Leachate collection/treatment
Monitoring wells
Simple operation
Low labor requirement
Minimal  equipment required
Low cost
Less land required than
  surface or subsurface
  spreading operations
No new equipment needed
Low odor and pathogen
  problems due to daily
  soi1 cover
Low cost
Higher potential for
  groundwater contami nati on
Odors and vectors
Limited design life -
  usually cannot use same
  land repeatedly
Limited application due to
  leachate generation
Good operating procedures
  required - refuse/septage
  mi xi ng
Extensi ve moni tori ng
  required - leachate,
  runoff, groundwater
May not be approved in some
  states

-------
Sanitary landfills in the United  States  generally  accept a  multiplicity
of materials such as refuse,  industrial  wastes,  and  sometimes  hazardous
or toxic wastes.   All  of these wastes are compiled  on  a daily basis at
the landfill and  buried  under a soil cover.   The  acceptance of septage
at a landfill depends chiefly on  the ratio  of the  mixture of  septage to
refuse to maintain moisture  control.   However, a  few  states  do  not allow
landfill disposal  of  septage, and some  others do not  recommend  it  be-
cause of potential runoff and leachate problems.
     9.4.2  Independent Septage Treatment Facilities


In some  areas  of the country,  facilities  have been constructed  exclu-
sively for  handling septage.   These systems  vary from  simple  holding
lagoons to sophisticated, mechanically based plants.  The latter  systems
are generally more  capital  intensive, and may also have  greater  opera-
tional requirements.  Such systems have  been  found to  be cost effective
in areas of significant  septic  system density,  such as Long  Island, New
York.   In rural  areas, simpler,  less  expensive  alternatives  may  be more
economically favorable.   Of the independent  facilities  listed in Table
9-5,  lagoons are  the most  common and  among the least  expensive indepen-
dent  septage handling  alternatives.   All of  the  other independent sys-
tems  have been  implemented to some degree, although  in  most cases, not
widely.


      9.4.3  Septage Handling at Wastewater Treatment Plants
Two methods  exist for handling septage at  wastewater  treatment facili-
ties:   addition  to  the liquid stream  (near the headworks  or upstream
from the  plant),  or  addition  to the  solids  handling train (see Table 9-
6).   Both have advantages  under  appropriate conditions.   For example,
addition to the headworks (screens, grit chamber) is desirable where the
plant  employs  primary clarification, since  this effectively introduces
the septage  solids directly  into  the  sludge handling scheme.   For ex-
tended aeration plants, however, septage addition to the wastewater flow
may have  a severe impact  on the aeration  capacity of the system.  Thus,
introducing  the  septage into the  sludge stream  may  be desirable.   Con-
sideration of  plant aeration and solids handling capacity  is necessary
to  determine whether either  scheme  is  feasible.   Under  either mode of
addition,  solids  production increases with  increased  septage addition.
Septage  holding  facilities  allow  controlled addition  of  the septage to
the wastewater treatment plant.
For additional information on the capability of wastewater treatment fa-
cilities  to  handle  septic tank pumpings, the  reader  is  referred to the
publications list in Section 9.5 (3)(11).
                                  347

-------
                                                                             TABLE 9-5

                                                       INDEPENDENT  SEPTAGE  TREATMENT  FACILITIES
          Process
Description
                                                                   Design Considerations
                                                                  Advantages
                                                                                                                                  Disadvantaoes
       Lagooning        Usually  anaerobic  or  facultative
       (1)(13)(14)      Inlet on bottom for odor  control
       (161(17)         Liquid disposal  by percolation
                          and evaporation  in  lagoon  or by
                          separate infiltration bed
                        pH adjustment to pH 6-8 may  be
                          necessary for odor  control
       Lime             Collection,  mixing,  and reaction
       Stabilization      with lime  to pH 12 (hold 1  hour)
to     (1)(4)(5)        Dewatering optional
-p>                      Odors eliminated, pathogens greatly
00                        reduced
       Chlorine         Chlorine and septage mixed in
       Oxidation          pressurized reaction  chamber
        (1)(9)(15)       pH 1.2 - 2.5
                        Chlorine dosage 700-3,000 mg/1
       Aerobic          Similar to aerobic digestion  of
       Digestion          sewage sludge
       (1)(9)(13)       Often accomplished at  existing
                          wastewater treatment plant
                            Septage volume/characteri sties
                            Site  location
                            -  Distance to dwellings, etc.
                            -  Depth to groundwater or
                              bedrock
                            -  Distance to surface water
                            Depth  of liquid, surface area
                            Climate
                            Aquifer characteristics
                            Moni tori ng we! 1 s
                            Solids removal and disposal

                            Septaqe volume/characteristics
                            Septage receiving/holding
                            Mixing (air  or mechanical)
                            Lime  handling and feeding
                            Final  disposal
                            Septage  volume/characteristics
                            Equipment  sizing
                            Septage  receiving/holding
                            Dewatering facilities
                            Final  solids  disposal
                            Chlorine storage/safety
                            Septage  volume/characteristics
                            Seotage  receiving/holding
                            Organic  loading
                            Solids retention time (20-30
                              days)
                            Climate  (temperature)
                            Mixino and DO level
                            Fi nal di soosal
Low cost
Simple operation
Odor problems if pH not  maintained
Cannot use in areas with hiqh
  water table
Possible vector orohlem
Soil cloaqlng may stop percolation
Odor eliminated
Good pathogen
  reduction
Low land requirement
Enhanced solids
  dewatering

Stable, odor-free
  sludge produced
High pathogen
  destructi on
Enhanced solids
  dewatering
Low land requirement


SS reduction
BOD reduction
Reduction of odor and
  pathogens
May enhance solids
  dewa ten" no
Low land requirement
No reduction in oraanic matter
Lime increases Quantity for
  final disposal
H1nh cost for labor and lime
Unknown effects of long-term
  storage

High operating costs dependent on
  chlori ne cost
Neutralization may be required
Question of harmful chlorinated
  organics
Underdrainage liquor ream'res
  further treatment
Biolooical operation not simple
Subject to ornanic overloadina
Requires mom'tori no and lab
  analysis
Can have foaming problems

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                                                                     TABLE  9-5  (continued)
          Process
                            Descrlpti on
                                                                    Desian  Considerations
                                                                                                     Advantaoes
                                                                                                                                   Disadvantaqes
CO
J5.
UD
       Composting       May be natural  draft or forced air
       (1)              Septage mixed with bulking material
                        High temperature/pathogen
                          destruction
                        Storage/di stri buti on
Anaerobic        Often accomplished in combination
Digestion          with sewage sludge
(9)(11)          Demonstrated on pilot-scale
                 Identical  to sludge digestion
                   technology
       Chemical          Chemical  coagulation
       Treatment        - Mixing  and settling
       (1)(9)(10)       - Supernatant collection,
                          treatment/di sposal
                        - Sludge  hoi di ng/dewatering/di sposal
                        Acidification ^SO^)
                        - Mixing  and settling
                        - Additional  coagulation possible
                          with lime
                                                        Septage  volume/characteristics
                                                        Septage  receiving/hoi ding
                                                        Bulking  agent availability
                                                        Dewatering
                                                        Materials handling capability
Septage volume/characteri sties
Septage receiving/holding
Gri t removal
Soli ds retenti on ti me
Maintenance of digester
  temperature
No toxic materials input
Final disposal

Septage volume/characteristics
Septage receiving/holding
Chemical  feed equipment and
  dose levels
Mixing,  reaction time,  settling
  time
Fi nal  di sposal
                                  Provides pathogen
                                    destruction and
                                    stabilization
                                  Produces soil
                                    amendment
                                  Operationally simple
                                  Low energy
                                    requi rements

                                  Methane recovery/
                                    utilization
                                    possible
                                  Stabilized product
                                  Can handle variety of
                                    organic wastes
                                                                                         Low land reauirement
                                                          High  bulking  agent  reoiiirement if
                                                            not dewatered
                                                          Product  market must be  established
                                                          Mav he labor-intensive
                                                                                                                        Bioloaical process reouires close
                                                                                                                          operator control
                                                                                                                        Subject to upset bv toxics
                                                                                                                        Reouires  continuous supply of
                                                                                                                          organic materials
                                                                                                                 Hinh labor reauirement
                                                                                                                 Hiqh costs
       Dewateri ng
                 Dryi ng  beds
                 Pressure  filtration
                 Vacuum  filtration
                 Drying  lagoons
                 Centrifugation
Septage volume/characteristics
Septage receiving/holding
SS concentrations
Filterability
Pretreatment-chemi cal
  conditioning
Final  disposal
                                  Reduced  hauling  costs
                                  Reduces  area  required
                                    for  disposal
                                                                                                                        Hiqh cost for some alternatives
                                                                                                                        Hiqh operation and maintenance
                                                                                                                          requi rements
                                                                                                                        Mechanical dewaterino devices
                                                                                                                          require an enclosure

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                                                                           TABLE  9-6

                                                 SEPTAGE  TREATMENT  AT  WASTEWATER TREATMENT PLANTS
             Process
                           Description
     Design Considerations
     Advantages
                                                                                                                                   Disadvantages
oo
01
o
          Liquid Stream    Septage placed in storage  tank at
          Addition           plant
          (3)(6)(11)(12)   Pretreatment (screening, grit
                            removal)
                          Controlled bleed into headworks  to
                            prevent shock overload
Sludge Stream     Septage placed in storage tank
Addition         Fed directly into sludge stream with
(6)(11)(12)        or without separate conditioning/
                  handling
Septage  volume/characteristics
Plant capacity  (aeration and
  solids handling)
Receiving station
- Truck  transfer
- Storage
- Pretreatment  (optional)
- Controlled  discharge to plant
Sludge production
O&M (power, labor, chemicals)

Septage  volume/characteristics
Septage  receiving /hoi dinn
Organic  and solids loading on
  each sludqe handling unit
Pumping  and storage  capacity
Additional mixing and feedina
  equipment
Increase in chemical usaae
                                                                                       Easily implemented
                                                                                       Low capital cost
                                                                                       Public acceptance
                                                                                         good
                                                                                       Particularly
                                                                                         desirable at. plants
                                                                                         with orimary
                                                                                         clarification
Avoids overloading
  secondary  and
  tertiary  systems
Avoids oossihility of
  final  effluent
  degradation
                       Additional sludqe Generation
                       May organically overload  plant
                       Increased nw
                       Final disposal  site and sludqe
                         eouipment exoansion  may he
                         needed
Additional  sludge  oeneration
Final  disposal  site and sludne
  eauipment expansion >nay he
  needed

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9.5  References
 1.  Bowker, R. P. G.,  and  S.  W.  Hathaway.  Alternatives for the Treat-
     ment  and  Disposal  of  Residuals  from On-Site  Wastewater  Systems.
     Municipal   Environmental  Research  Laboratory,  Cincinnati,  Ohio,
     1978.

 2.  Kolega,  I.  0.,  A.  W.  Dewey,  B.  J.  Cosenza,  and R.  L.  Leonard.
     Treatment  and Disposal  of  Wastes  Pumped from  Septic  Tanks.  EPA
     600/2-77-198,  NTIS  Report   No.   PB  272  656,   Storrs  Agricultural
     Experiment Station, Connecticut,  1977.  170 pp.

 3.  Segal 1, B. A.,  C.  R. Ott, and  W. B.  Moeller.   Monitoring Septage
     Addition to Wastewater Treatment  Plants, Volume I:  Addition to the
     Liquid  Stream.   EPA  600/2-79-132,  NTIS  Report No.  PB  80-143613,
     1979.

 4.  Feige,  W.  A.,  E.  T.  Oppelt,  and J.  F.  Kreissl.   An Alternative
     Septage Treatment Method:   Lime Stabilization/Sand-Bed Dewatering.
     EPA  600/2-75-036,  NTIS Report  No.  PB 245 816,  Municipal  Environ-
     mental Research Laboratory,  Cincinnati, Ohio, 1975.  64 pp.

 5.  Noland, R. F., J. D. Edwards, and M. Kipp. Full Scale Demonstration
     of  Lime  Stabilization.   EPA  600/2-78-171,  NTIS Report  No.  PB  286
     937, Burgess  and Niple Ltd., Columbus, Ohio, 1978.  89 pp.

 6.  Bennett, S. M.,  J.  A.  Heidman,  and J. F.  Kreissl.   Feasibility of
     Treating Septic  Tank  Waste  by  Activated Sludge.  EPA 600/2-77-141,
     NTIS  Report  No.  PB  272  105,  District of Columbia,  Department of
     Environmental Services, Washington, D.C., 1977.  71 pp.

  7.  Deninger,  J.  F.    Chemical   Disinfection Studies  of  Septic  Tank
     Sludge  with   Emphasis  on  Formaldehyde and  Glutaraldehyde.   M.S.
     Thesis.  University of Wisconsin, Madison, 1977.

  8.  Maine  Guidelines  for   Septic  Tank  Sludge Disposal  on the  Land.
     Miscellaneous Report  155. Life Sciences and Agriculture Experiment
     Station  and   Cooperative  Extension  Service,  University of Maine,
     Orono, Maine  Solid and Water Conservation Commission,  1974.

 9.  Cooper,  I.  A.,  and J.  W. Rezek.   Septage  Treatment and Disposal.
     Prepared  for the EPA  Technology  Transfer Seminar Program  on Small
     Wastewater Treatment Systems, 1977.  43 pp.

10.  Condren,  A.   J.    Pilot  Scale  Evaluations   of  Septage  Treatment
     Alternatives.   EPA  600/2-78-164,  NTIS Report No.  PB 288 415, Maine
     Municipal Association, Augusta, Maine, 1978.  135 pp.
                                   351

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11.   Bowker, R. P. G.  Treatment and Disposal of Septic Tank Sludges.  A
     Status Report.  May 1977.   In:   Small  Wastewater Treatment Facili-
     ties.   Design  Seminar  Handout.   Environmental  Protection  Agency
     Technology Transfer, Cincinnati, Ohio, 1978.

12.   Cooper,  I.  A.,  and J.  W.  Rezek.   Septage Disposal  in Wastewater
     Treatment Plants.   In: Individual On-Site Wastewater Systems.  Pro-
     ceedings of the Thfrcl National  Conference.   N.  McClelland, ed. Ann
     Arbor Science, Ann Arbor, Michigan, 1977.  pp. 147-169.

13.   Jewell, J. W.,  J.  B.  Howley, and  D.  R.  Perrin.  Design Guidelines
     for  Septic Tank Sludge  Treatment and Disposal.   Prog.  Water Tech-
     nol., 7, 1975.

14.   Guidelines for  Septage  Handling and Disposal.   New England Inter-
     state  Water  Pollution  Control  Commission,  Boston,  Massachusetts,
     August 1976.

15.   Wise,  R.  H.,  T. A. Pressley,  and B. M. Austern.   Partial Charac-
     terization  of Chlorinated  Organics  in Superchlorinated  Septages
     and  Mixed  Sludges.   EPA 600/2-78-020, NTIS Report  No.  PB  281 529,
     USEPA, MERL, Cincinnati, Ohio, 1978.  30 pp.

16.   Brown, D.  V., and  R.  K. White.   Septage Disposal Alternatives for
     Rural  Areas.    Research  Bulletin  1096,   Ohio   State  University,
     Columbus, 1977.

17.   Barlow,  Gill  and  E.  Allan Cassell.   Technical Alternatives  for
     Septage  Treatment  and Disposal  in Vermont.   Draft.   Vermont Water
     Resources Research Center, University of Vermont, Burlington, 1978.

18.   Walker,  J.  M.,  W. D. Burge,  R. L.  Chaney,  E.  Epstein, and  J.  D.
     Menzies.   Trench  Incorporation  of Sewage Sludge  in  Marginal  Agri-
     cultural  Land.    EPA  600/2-75-034,  NTIS  Report No.  PB   246  561,
     Agricultural Research Service, Beltsville,  Maryland, 1975.   252 pp.

19.   Sommers,  L.  E.,  R. C.  Fehrmann,  H. L.  Selznick, and  C.  E.  Pound.
     Principles  and  Design  Criteria for  Sewage Sludge  Application  on
     Land.  In:  Sludge Treatment and Disposal Seminar Handout,  Environ-
     mental Research Information Center, Cincinnati, Ohio, 1978.
                                  352

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                               CHAPTER 10

                      MANAGEMENT OF ONSITE SYSTEMS
10.1  Introduction
Onsite systems offer  a  viable means for controlling  public  health  haz-
ards,  environmental   degradation,  and  nuisances  that  might  otherwise
arise from wastewater generated  in unsewered areas.  If  onsite systems
are to perform successfully over a  reasonable  lifetime, a sound manage-
ment  program  with  sufficient technical assistance  and  enforcement  cap-
abilities is needed.
Management programs may take many  forms.   A good program,  at a minimum,
performs the following functions:
     1.  Site evaluation validation
     2.  System design review
     3.  Construction supervision
     4.  Operation and maintenance certification
     5.  Rehabilitation assistance
     6.  Monitoring and enforcement
     7.  Public education activities
Most  states  perform  some  or all  of these functions  with  much  of  the
responsibility  often  delegated  to  local  units of  government.    These
programs are  very diverse (1).   At one end of the  spectrum,  the state
may limit its responsibility to the promulgation of minimum  standards to
be adopted by local jurisdictions, which may have the right  to establish
stricter  standards.    At  the  other  end, the state  may  retain  all
management functions over onsite systems.


Thus,  the  management  programs  used  in  various  jurisdictions  differ
greatly as do their effectiveness.  Therefore,  the  following examination
of approaches and  techniques  that may be  used  to  manage  onsite  systems
is intended to:
     1.  Provide a means of evaluating the existing management program.

     2.  Suggest techniques used  to  improve  an  existing  management pro-
         gram or to establish a new one.

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Some of  the  techniques discussed  may  not be .readily  incorporated into
existing management  programs  due  to different  state  constitutional  and
statutory  provisions and  legal  interpretations.   Some  techniques  may
require  the  enactment of  enabling legislation  granting  the management
entity necessary authority to manage onsite systems.


10.2  Theory of Management
An effective  management program provides  technical  assistance together
with strong regulation  enforcement.   Both  aspects  are directed at major
control points.


     10.2.1  Principal Control Points
There are  several  distinct phases in the life  of an onsite system that
require control.  These are:
     1.  Installation
     2.  Operation
     3.  Maintenance
During  the  "installation"   phase,  the  management  program must  limit
installation  to  suitable  sites,   and  assure  the  proper  design  and
construction  of  all  onsite  systems.   It  is  during  this phase  that
management  programs  can be  most  effective in minimizing  the  potential
threat to public health and water quality.
During  the  "operation"  phase,  the management program must assure proper
operation of an  onsite  system  through  periodic  monitoring.   While there
are  very  few  operational  requirements  for a septic tank-soil absorption
system, some of  the  onsite  systems  have  more extensive requirements.   A
good  management  program imposes controls  during  this  phase whether the
system's operation is straightforward or elaborate.
Finally, in the "maintenance" phase, the management program must provide
for adequate maintenance of  an  onsite  system,  e.g.,  periodic pumping of
septic tanks.  It also must detect any onsite system that fails to func-
tion  properly.   This may  be done through  systematic  or random inspec-
tions.  A good program takes the necessary action to assure that repair,
replacement, or abandonment of failed systems is completed.
                                    354

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     10.2.2  Authority Needed by Management Entities


If  adequate management  is  to  be  provided  at  the  principal  control
points,  management entities  should  have  the  authority to  perform the
functions listed below.  The optional  functions become imperative if the
management entities own the onsite systems.


     Suggested Functions               Optional Functions

     1.  Site evaluation               1.  Planning
     2.  System design                 2.  Legal functions
     3.  Installation                  3.  Financing
     4.  Operation and Maintenance     4.  Public education
     5.  Rehabilitation
     6.  Monitoring


The authority to  perform  these functions does not need to be granted to
a  single management entity.   In fact,  it is  unlikely  that one entity
will have all the  program responsibility.  However, the total management
program  should  have  the combined  authority  to perform  the necessary
functions.


In  each  jurisdiction,  the authority  of each  management entity should be
examined.    Statutory  authority,  judicial   decisions,  and the   state
constitution must  be carefully reviewed.  Often existing programs may be
adapted  and/or  utilized  to  aid  in   management.    For  example,  the
management  entities may  require  that certain  onsite systems  be designed
by  registered professional engineers even though the entities themselves
do  not  register engineers.    In  the  event that  additional  authority is
needed,  enabling  statutory language will be required.


10.3  Types of  Management Entities
There  are  several  types of entities  that have the authority to perform
the management functions previously described.  These include:
      1.  State agencies
      2.  Local governmental/quasi-governmental units
      3.  Special purpose districts
      4.  Private institutions  (profit, nonprofit)
                                    355

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     10.3.1  State Agencies


Except for the limitations contained in its own constitution, each state
retains complete authority  to  protect the general welfare  of  its citi-
zens,  including  the  management  of  onsite  systems.    The  state  health
agency and/or agency responsible for water quality are the agencies most
likely to exercise the state's authority.
The  degree  of  control  exerted  by  state  agencies  over onsite  systems
varies from state to state.  Many states set design standards for onsite
systems.   Those that do  not  set standards delegate  authority  to local
governments  to  do  so.    Several  states  retain  the  responsibility  for
administrative/technical portions of the onsite management program.
A  state  management program is often  considered  more  effective,  because
local  pressures  to weaken  onsite regulation are  not thought to  be  as
effective at the  state  level.   In addition,  since states typically have
more resources to hire or retain experienced individuals than most local
units  of government,  state  agencies  are  in  a  better  position  to take
responsibility for many of  the  regulatory and  administrative require-
ments.
     10.3.2  Local Governmental/Quasi-Governmental Units
In some states, a portion or most of the responsibility of onsite system
management is delegated by the legislature to units of local government.
In other  states  with strong "home rule" powers,  the  local  unit of gov-
ernment has the authority to manage onsite systems even without being so
delegated by the state legislature.   The various  types of local govern-
mental units are:
         Municipalities  -  Incorporated  units of  government  have  full
         responsibility  for the general  welfare  of its  citizens;  have
         broad  financing  authority,  including  the authority to  levy
         property  taxes,  to  incur  general  obligation  debts,  to  use
         revenue  bonding and  to  impose special  assessments  upon  bene-
         fitted property; and are legal  entities authorized to contract,
         commence law suits, and own property.

         Unincorporated  Government  (e.g.,  County)  - Unincorporated gov-
         ernmentalunits often have authority equal  to municipalities;
         however, these units may not have the authority for some onsite
         program  management responsibilities,  i.e.,  ownership of onsite
         systems which do not serve county institutions. Typically,
                                    356

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         these units  have financial  authority  and legal  entity  status
         similar to municipalities.

     3.  Quasi-Governmental  Units - These units include regional  (multi-
         county)water  quality  boards,  regional   planning  commissions,
         local or  regional  health departments/boards, councils of gov-
         ernment, and other agencies  with  the  exception  of special  pur-
         pose entities.   Their authority varies with  the  intended pur-
         pose of each unit;  however,  the  financial  authority is  typi-
         cally less than  that of municipalities  and  unincorporated gov-
         ernmental  units.
     10.3.3  Special Purpose Districts
Special purpose  districts depend  entirely  on enabling  legislation  for
their authority and extent of services.  These districts are independent
units of  government,  created to  provide  one or more  services,  such  as
water and wastewater services to those within their boundaries.   If per-
mitted  by  the enabling  legislation,  services may  also be provided  to
others outside their boundaries.   The  boundaries  are  often permitted  to
cross local governmental  boundaries so  that  services  can be provided  to
all  those in  need, despite  the  fact that  residents  of  the  district
reside on either side of local governmental  boundaries (counties, towns,
villages, etc.).
Nearly all special purpose districts have sufficient financial  authority
to impose service charges, collect fees, impose special  assessments upon
property  benefitted,  and  issue  revenue and/or special  assessment bonds.
In addition,  some special purpose districts  receive the  same  financing
authority  enjoyed by  municipalities,  including  the  authority to  levy
taxes and  incur  general obligation  debt (i.e.,  general  obligation bonds
backed by taxing authority).  These districts are usually legal entities
that may enter into contracts, sue, and be sued.
     10.3.4  Private Institutions
Private  institutions  do  not  rely  on  enabling  legislation,  but  are
founded upon the right of individuals or corporations to enter into con-
tracts.   However,  they  are often  subject to  review or  regulation  by
state public service or utility commissions.
                                   357

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         10.3.4.1  Private Nonprofit Institutions (Associations
                   and Corporations)


These  entities  include homeowners' associations,  private  cooperatives,
and  nonprofit  corporations  that  provide  services  for onsite  systems.
The  range  of  services may  vary  from merely  providing maintenance  to
complete ownership of  the system.   The  freedom  of  the contract permits
this complete range of services; however, the association or corporation
may be regulated by the state public service or public utility laws.
         10.3.4.2  Private-for-Profit Institutions
This type of  entity may be a  sole  proprietorship,  partnership,  or cor-
poration that provides  services  for onsite  systems.   The homeowner or a
group of owners  (homeowners'  associations)  typically  enters  into a con-
tract with  this private  entity  for the  provision of services.   These
services could  include  maintenance and operation of  the owner's onsite
system,  or  the  private  entity  could own  the  systems  and charge  the
homeowner for the  use  of  the systems.    The  state  public service  or
public utility commission may regulate the private entity.
10.4  Management Program Functions


A  good  management program consists  of  many functions that may  be per-
formed by one entity only or shared among several  entities.  The  user of
this manual  is urged to  review the range  of  functions  discussed here,
and  to  select entities that  are  best able to  perform  those  functions.
For  a more complete  discussion  of the  various  functions, see  References
(2)  and (3).
     10.4.1  Site Evaluation and System Design
In  developing  a management program,  a  choice can be made  between  per-
forming  the  site  evaluation  and  system  design  functions within  the
entity itself or reviewing  work  done  in the  private  sector.  Table 10-1
summarizes  the  suggested activities  that  should be performed  for  both
options.
                                   358

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                                    TABLE 10-1

                 SITE EVALUATION AND  SYSTEM  DESIGN FUNCTIONS
Scope of Activities
               Adml ni strati ve/Techni cal
                     Activities
                                    Regulatory/Enforcement
                                         Activities
Perform all
evaluations
provide system
designs
site
and
a.  Conduct site evaluations
    for each lot to  be
    devel oped
                        b.   Identify and evaluate
                            feasible (or permitted)
                            system designs

                        c.   Design selected system
Review all site
evaluations and
system designs
            a.
    Verify site evaluation
    procedures and data
    collected for each lot
                        b.
                Review and approve or
                disapprove plans
a.  Establish guidelines and
    procedures for
    identifying sites
    suitable for development

b.  Develop cost-effective-
    ness guideli nes and
    evaluation procedures

c.  Establish design
    standards, construction
    specifications, and
    performance standards

            and

    Issue construction permit

a.  Develop guidelines and
    procedures for
    identifying sites
    suitable for development

            and

    Develop training,
    certification, or
    licensing program for
    site evaluators

b.  Establish design
    standards, construction
    specifications, and
    performance standards

            and/or

    Develop training
    certification  or
    licensing program for
    system  designers

            and

    Issue  construction
    per mi t
                                        359

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         10.4.1.1  Standards for Site Suitability, System
                   Design, and Performance


A  state  agency with  appropriate  authority may establish  minimum stan-
dards for site suitability, system design, and performance.  This may be
preferred over  each management entity  establishing its  own  standards.
The  advantages  are  (1)  more uniformity  of regulations  throughout  the
state (although the local management entity may choose to be more strin-
gent if  it  has  the power to do so), and  (2)  more resources and experi-
enced personnel at the state level to develop appropriate standards.
         10.4.1.2  Site Evaluation and System Design
It may be desirable to include site evaluation and system design activi-
ties as part of the management  program.   These activities could be per-
formed by  any  of the  entities  making up the  management  program.   How-
ever, if the local management entity proposes to own and operate systems
within its  jurisdiction,  this would be the  preferred  entity  to perform
these  activities.   Legal  advice  should  be sought  regarding  liability
which may result from undertaking this activity.


As an  alternative  to  performing site evaluations and  system  designs as
part of  the management program, these activities could  be performed by
site evaluators and system designers  licensed  or  registered by the man-
agement entity.  Licensure or registration is suggested to assure quali-
ty.   However,  such assurances  can only  be  obtained if  the  license or
registration is  subject  to  suspension or revocation.   Random  or preap-
proved site  inspections by the  management entity  are suggested to check
compliance with established procedures and standards, particularly where
site limitations are anticipated.


         10.4.1.3  Plan Approval and Construction Permits


The management process should be initiated either by submission of plans
for  review and approval   or  by  application  for a permit  to construct a
system.   Either  requirement  for plan approval  or   permit  issuance  for
construction of a  system  provides  the management  entity with a conveni-
ent method of obtaining information about the site evaluation and system
design.  Site suitability and design standards may be easily enforced by
refusing to approve plans or issue permits.


Plan approval or  permit  programs at the  state level may be more desira-
ble  than  at the local level   because  of  greater technical resources and
isolation  from  local  political  pressures  to allow development on poorly
                                   360

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suited sites.  As  an  alternative to the review of all applications, the
state agency could review  a  random  sample of the plans approved or per-
mits issued by the local management entity.  The state agency would have
the authority to countermand  local  approval.   However, it would be nec-
essary to  limit  the  period of time that  the  state  agency has  to act on
the local action.
     10.4.2  Installation
As with site evaluation and system design, the management entities could
choose to  install  all  new  systems  themselves.    This  would  be particu-
larly desirable if ownership were to be retained by the entity.  If not,
the  entity  may choose  to  control   installation through  inspections.
Table 10-2  summarizes  the  suggested  activities  that  should be performed
for both options.
         10.4.2.1  Construction Inspections
A  program  to inspect  the onsite  system  at each critical  stage during
construction is very desirable to prevent improper construction and pre-
mature  failure  of the system.   The inspection may be  performed by any
entity  involved in the total  management  program, but  it  would  be most
appropriate  for the entity that has responsibility for the rehabilita-
tion or abandonment of improperly functioning systems.


If the management entity does not perform the inspections, they could be
performed by licensed or registered inspectors.  A state agency would be
the most likely entity to  develop  a program to train  inspectors in pro-
per design  and  construction  techniques  for  all  acceptable types of sys-
tems.  This would assure more uniform quality of inspections statewide.
To further assure uniformity and thoroughness of inspections, checklists
of  specific  items  to  be  inspected  for  each  type of  permitted  design
could  be  developed.  The  inspectors would be  required  to  certify that
the checklist was completed after the inspector's personal  inspection of
the  installation,  and  that all  entries contained on the checklist are
correct.   To  insure that inspections are  timely,  the management  entity
may require the system installer to give notice as to when  the construc-
tion of the system  is to commence.
                                   361

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                                  TABLE  10-2

                            INSTALLATION  FUNCTIONS
  Scope  of Activities
   Admi ni strati ve/Techni cal
        Activities
                             Regulatory/Enforcement
                                  Activities
  Perform inspection/
  supervision of
  construction
a.   Perform construction
    inspection and/or
    supervision during
    various phases of
    construction

b.   Prepare as-built drawing
  Review  construction
  inspection/
  supervi sion
a.
Revi ew certifi ed
inspection by  licensed/
registered inspectors
                        b.  Require as-built  drawing
                             Develop guidelines and
                             specifications for
                             construction
b.  Record as-built drawing
   and issue system use
   permit

a.  Develop specifications
   for construction and
   checklists for inspection

            and

   Develop training,
   certification or
   licensing program for
   inspectors

b.  Record as-built drawing
   and issue system use
   permit
          10.4.2.2  As-Built Drawings
It  is  not  unusual  for the  system installed to be  quite different from
the  drawings  originally  approved  because  of  changes  necessary  during
construction.   As-built drawings become very valuable when  inspection or
servicing  of the  system is  required.   Therefore,  a requirement for as-
built  drawings  is  a  good  practice.   These plans  could  be indexed by
street,  address,  name of  original owner,  installer,  and legal  descrip-
tion.
          10.4.2.3  Training and Licensing  of Installers
To reduce  the reliance  on  good construction  supervision and  inspections,
a  program to train  and license  or register installers could  be estab-
lished.   Training  would include  presentation of design and  construction
techniques of all  approved system  types.  To be effective,  this program
would  have to be coupled with  a  strong enforcement program  in  which the
license  to install  systems could be suspended or revoked.
                                     362

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     10.4.3  Operation and Maintenance


Traditionally, the  responsibility  for operation and maintenance  of on-
site systems has been left to the owner.   This has  been less than  satis-
factory.  As an alternative, management entities are beginning to  assume
this responsibility.   The program adopted  may either be  compulsory or
voluntary.   If voluntary,  the  management entities perform  the mainte-
nance or  issue operating  permits  on receipt  of an assurance that the
proper maintenance  was  performed.   Table 10-3  summarizes  the suggested
activities that should be performed for both options.
         10.4.3.1  Standards for Operation and Maintenance


A  standard  for  the  operation  and  maintenance of  each type  of  system
used,  stating  the procedures  to  be used  and the  frequency  with  which
they are to  be  performed,  is desirable.   These  standards would include
those necessary to regulate the hauling and disposal of residuals gener-
ated by onsite systems as well.  The state agency would be the preferred
entity to set  these  standards.  The advantages  of  having the state set
the  standards  include more uniformity  in  the regulations and  more re-
sources and experienced personnel  to develop appropriate standards.
         10.4.3.2  Operating Permits
Rather than  the  management entities  providing services,  compliance with
operation and  maintenance  standards  could be assured  through  an opera-
ting permit program.  The type and frequency of maintenance required for
each type of system would  be  established by the entity.   An  operating
permit allowing the owner to use the system would be renewed only if the
required maintenance is  performed.   The system owner  would  be notified
when the  permit  is about  to  expire, and told what  maintenance must be
performed to obtain a renewal.   The  owner would  be required to have the
necessary maintenance performed  by an  individual  licensed or registered
to  perform  such  services  within a  specified  period of  time  (e.g.,  60
days).  This individual  would sign  and  date  one  portion of the owner's
permit, thereby certifying that the service was performed.


The  enabling ordinance or  statutory language establishing  this permit
program must indicate that  it  is unlawful  to  occupy a home served by an
onsite system unless the owner holds a valid operating permit.   Thus, if
the permit were not renewed, the owner would be in violation of the ord-
inance or statute.  From  a legal viewpoint,  enforcement of this type of
violation is straightforward.
                                   363

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                                    TABLE 10-3

                      OPERATION AND  MAINTENANCE  FUNCTIONS
Scope of Activities
   Administrative/Technical
         Activities
                                Regula tory/Enforcement
                                     Activities
Perform necessary
operati on/
maintenance
a.
                        b.
Provide routine and
emergency operation/
maintenance of each
system

Determine if operation/
maintenance program is
voluntary or compulsory
Admi ni ster
operation/
maintenance
a.
Establish an operation
and maintenance program
            program
                        b.
    Determine if operation/
    maintenance program is
    voluntary or compulsory
                        c.
    Develop policies for
    regulating operation/
    maintenance activities
a.  Develop guidelines  and
    schedules for  routine
    operati on/mai ntenance
b.  Establish operation/
    maintenance program

              and

    Obtain legal  authority
    for right of access to
    private property

a.  Develop guidelines and
    schedules for routine
    operati on/mai ntenance

              and

    Impose standards for
    hauling and disposal of
    resi duals

b.  Develop system for
    notifying owner of
    required operation/
    maintenance

              and

    Issue a regularly renewed
    operating permit after
    certification that proper
    operati on/mai ntenance
    has been performed

c.  Develop training,
    certification, or
    licensing program for
    those contracting to
    perform operation/
    maintenance activities
                                        364

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         10.4.3.3  Li censure/Registration


To provide  assurance that onsite systems are  properly operated and main-
tained, licensing or registering of qualified individuals  is  desirable.
This  could  be done  at the  state level.    If  licensure/registration pro-
grams  for  individuals, such  as plumbers,  residual  waste  haulers, sani-
tarians,  etc.,  already exist,  and if  these  individuals have  sufficient
knowledge of onsite systems,  an additional  program may  not be necessary.


      10.4.4  Rehabilitation


Because onsite systems are  usually located on private property and below
ground,  system  failures  are  difficult to  detect.   If  a management pro-
gram  is  to  effectively  prevent  public   health  hazards,   environmental
degradation,  and nuisances,  identification  and correction of  failures
are  a necessary part of the  management  program.   Table 10-4  summarizes
the suggested activities that should be performed.
                                 TABLE  10-4

                          REHABILITATION FUNCTIONS
                          Administrative/Technical         Regulatory/Enforcement
   Scope of Activities       	Activitles	             Activities	


   Detect and correct     a.  Develop  procedures for      a.  Develop performance
   improperly                identifying improperly          standards
   functioning systems        functioning systems
                           (Sanitary surveys,                     and
                           presale  inspections,
                           etc.)                        Obtain legal  authority
                                                       for right of  access to
                                                       private property

                       b.  Rehabilitate system        b.  Issue order requiring
                                                       rehabilitation

                                                               or

                                                       Rehabilitate  system as
                                                       part of operation/
                                                       maintenance program
                                     365

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         10.4.4.1  Inspections


Inspections could be performed  as  part of a sanitary survey of the area
or  through  presale  inspections during  real  estate transactions.   The
latter  option may  require  enabling  legislation.   Constitutional  re-
straints regarding  the inspection  of  private property and  the limita-
tions on the  sale of  property  have to  be  considered  prior to enacting
such legislation.
         10.4.4.2  Orders and Violations
The management entity  needs  the  authority  to issue orders requiring the
repair, replacement, or abandonment of improperly functioning systems if
the systems  are  not owned  by  the entity.   Various  state agencies have
this authority.   If  the  owner  does not comply with  the  order  to repair
or  rehabilitate  the  system,  the  management entity could  require that
copies  of all violations  be  filed  with  the registrar  of  deeds  or  a
similar official.   The effect of  such  a  filing  requirement would be to
give notice of the violation in  the  chain  of title whenever an abstract
or  a  title insurance  policy is  prepared.    Any  potential  mortgagee or
buyer would thereby be alerted to  the violation.
 10.5   References
 1.   Plews,  G.  D.   The Adequacy  and Uniformity  of  Regulations for On-Site
     Wastewater Disposal  - A  State Viewpoint.   In:  National Conference
     on Less Costly Wastewater  Treatment  Systems  for Small Communities.
     EPA 600/9-79-010,  NTIS  Report No.  PB  293  254,  April 1977.   pp.
     20-28.

 2.   Small   Scale   Waste  Management Project,  University  of Wisconsin,
     Madison, Management of  Small   Waste  Flows.   EPA 600/2-78-173,  NTIS
     Report  No.  PB 286 560,  September 1978.

 3.   Interim Study Report,  Management of  On-Site  and  Small   Community
     Wastewater Systems.   M687,   U.S.  Environmental  Protection Agency,
     Municipal  Environmental  Research Laboratory,  Cincinnati, Ohio,  1979.
                                   366

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                               APPENDIX A

              SOIL PROPERTIES AND SOIL-WATER RELATIONSHIPS
A.I  Introduction
An understanding  of  how water moves into  and  through soil is necessary
to predict  the  potential  of  soil  for wastewater  absorption  and treat-
ment.  Water moves through the voids or pore spaces within soil.  There-
fore, the size,  shape, and continuity of the pore spaces are very impor-
tant.  These characteristics are dependent on the physical properties of
the soil and the characteristics of water as well.
A.2  Physical Properties of Soil


     A.2.1  Soil Texture
Texture is one of the most important physical properties of soil because
of its close relationship  to  pore  size,  pore size distribution and pore
continuity.   It  refers to the  relative  proportion  of the various sizes
of solid  particles  in the soil that are smaller than 2 mm in diameter.
The particles are commonly divided into  three size fractions called soil
"separates."  These separates are given  in Figure A-l.  The U.S. Depart-
ment of Agriculture (USDA) system is used in this manual (Table A-l).
                                   TABLE A-l

     U.S. DEPARTMENT OF AGRICULTURE  SIZE LIMITS FOR  SOIL  SEPARATES
                                                       Tyler Standard
         Soil Separate               Size Range             Sieve No.
                                       mm
    Sand                               2-0.05             10-270 mesh
        Very coarse  sand              2-1                10-16  mesh
        Coarse sand                   1-0.5              16-35  mesh
        Medium sand                  0.5-0.25             35-60  mesh
        Fine sand                  0.25-0.1              60-140 mesh
        Very fine  sand               0.1-0.05             140-270 mesh

    Silt                            0.25-0.002

    Clay                               <0.002

                                   367

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                                                                        FIGURE A-l

                                                     NAMES AND  SIZE LIMITS  OF  PRACTICAL-SIZE
                                                      CLASSES ACCORDING  TO  SIX  SYSTEMS  (1)
OO
cr>
CO
                     SYSTEM

                   1. US. Bureau of
                     Reclamation and
                     Corps of Engineers (U.S
                     Dept. of the Army)
                    2. American Association
                      of State Highway
                      Officals
                    3. American Society for
                      Testing and Materials
                    4. Wentworth
                    5  U.S Department of
                      Agriculture
                    6 International Society
                     of Soil Science

1
	 M
i • •
1
1
Silt and Clay
(distinguished on the
basis of plasticity)

Colloid

Colloid

Cl"
>

3
i
V 	
3V 	

Clay


Clay
Clay





1
+•
*•
Silt
sm

Silt

Silt
Silt
1 1 1 1 1 1 f







11 1 I
'
Fine sand
Fine sand
Fine sand

Very
fine
sane

Very
fine
sand


Fine
sand

Fine
sand
Fine sand
i t i
f
,nl


v mi

Medium
sand
Coarse
sand
Medium
sand

Medium
sand JCoars
sand

Medium
sand Coar;
sand
Very
coars
sand
3
Very
coarse
sand
e
Coarse sand
i i i 1 1 1 1
1
1 '
Coarse
sand
i i in
1

Fine gravel
Fine gravel
Coarse
sand


Mediun
gravel
i 1 I
Coarse
gravel
Coarse
gravel



Gravel





Pebbles
Granules

Fine gravel





M '
Cobbles
Boulders
	

Cobbles

Coarse gravel

Cobbles
Gravel
i i i i i i
I


i i i
...1
                                         0.000
                                                   0.002
                                                                    0.02             02

                                                                             P;ti(icle diameter, mm
                                                                                                      20
                                                                                                                       20
                                                                                                                                        200
                      Used in soil engineering

                    h
                      Used in geology.


                      USDA system used in this manual


                      Used in soil science.

-------
Twelve textural classes  are defined by the relative  proportions  of the
sand,  silt  and clay separates.   These are represented  on  the textural
triangle (Figure A-2).   To  determine  the  textural  class  of a soil hori-
zon, the percent  by weight of the  soil separates  is  needed.   For exam-
ple, a sample  containing  37%  sand,  45% silt and 18% clay has a textural
class of loam.  This is illustrated in Figure A-2.
Soil  textural  classes are  modified if  particles  greater than 2  mm in
size are present.  The adjectives "gravelly," "cobbly," and "stoney" are
used  for particles  between 2 and 75 mm,  75 and 250 mm,  or  250 mm, re-
spectively,  if  more than  15%  to  20% of the soil  volume  is  occupied by
these fragments.
 Soil  permeability,  aeration  and  drainage  are  closely  related  to  the  soil
 texture  because of  their influence  on  pore size  and pore  continuity.
 They  are  also  related  to the  soil's  ability to  filter particles and
 retain  or adsorb pollutants  from the waste  stream.   For example,  fine
 textured or clayey  soils do  not transmit water  rapidly or drain  well
 because  the pores  are  very  small.   They  tend  to  retain water  for  long
 periods  of time.   However,  they act as  better filters and can  retain
 more  chemicals  than soils of other textures.  On the  other hand,  coarse
 textured or sandy soils have  large, continuous  pores  that can accept and
 transmit large  quantities of  water.   They  retain  water for only short
 periods  of time.   The capacity to retain  chemicals is generally low and
 they  do  not filter wastewater as well  as finer textured soils.   Medium
 textured or loamy soils have  a balance between wastewater absorption and
 treatment capabilities.   They  accept and  transmit  water  at  moderate
 rates,  act as  good  filters,  and  retain  moderate amounts  of  chemical
 constituents.
      A.2.2  Soil  Structure


 Soil structure has a significant  influence on. the  soil's  acceptance  and
 transmission of water.   Soil  structure refers to the aggregation  of soil
 particles into clusters of particles, called peds,  that are separated by
 surfaces of weakness.  These surfaces  of  weakness  open  planar  pores  be-
 tween the peds that are often  seen  as  cracks in the soil.  These planar
 pores can  greatly  modify  the  influence  of  soil texture  on  water  move-
 ment.  Well structured soils with large voids between peds will  transmit
 water more rapidly than structureless soils  of the  same texture,  partic-
 ularly if the  soil has become  dry before  the water is added.  Fine tex-
 tured, massive soils  (soils  with  little structure) have  very  slow per-
 colation rates.
                                    369

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                           FIGURE A-2

   TEXTURAL  TRIANGLE  DEFINING TWELVE TEXTURAL CLASSES OF THE  USDA
(ILLUSTRATED  FOR A SAMPLE CONTAINING 37% SAND, 45% SILT, AND 18% CLAY)
                          100%
                          Clay Loam
               Loam	
                  A
          30/-Sandy clay:
                Loam  \
               V    V
              \     \
            \~A~~A~
             Silt Loam
           —r	r-
                 \ /  \
              -Sandy Loam
   100%
   sand
60   50   40
Percent Sand
  by Weight
                                                      100%
                                                        silt
                               370

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The  form,  size and  stability  of the aggregates  or peds depend  on  the
arrangement of the  soil  particles  and the bonds  between  the  particles.
The four major types of  structures  include  platy, blocky, prismatic  and
granular.  Detailed descriptions of types and  classes  of  soil  structure
used by SCS are given in Table A-2.
Between the peds are voids which are often relatively large and continu-
ous compared to the voids or  pores  between  the  primary particles within
the peds.   The type  of  structure determines the  dominant direction of
the pores and, hence, water movement  in  the soil.   Platy structures re-
strict vertical percolation of water because cleavage faces are horizon-
tally oriented.   Often,  vertical flow  is so restricted that  the upper
soil  horizons  saturate,   creating  a  perched  water  table.   Soils  with
prismatic  and  columnar  structure  enhance  vertical  water flow,  while
blocky  and  granular  structures enhance  flow  both  horizontally  and
vertically.


The soil's permeability by air  and  water is also influenced by the fre-
quency and degree  of expression  of the  pores created by  the  structual
units.  These characteristics depend upon the size of the peds  and their
grade or  durability.   Small   structural  units create more  pores  in the
soil  than large structural  units.    Soils with  strong structure  have
distinct  pores between peds.   Soils with very weak structure, or soils
without  peds  or  planes  of   weakness,   are  said  to be  structureless.
Structureless  sandy  soils are called single  grained  or  granular, while
structureless clayey soils are called massive.
Structure  is  one  soil  characteristic  that  is  easily  altered or  de-
stroyed.   It is  very  dynamic,  changing  in  response to moisture content,
chemical composition  of soil  solution,  biological  activity,  and manage-
ment practices.  Soils containing minerals  that  shrink and swell  appre-
ciably,  such  as  montmorillonite  clays,   show  particularly  dramatic
changes.   When the  soil peds  swell  upon wetting, the large pores become
smaller, and water  movement through the soil is  reduced.   Swelling can
also  result if  the  soil   contains  a high  proportion of  sodium  salts.
Therefore,  when  determining  the  hydraulic  properties  of  a  soil  for
wastewater  disposal,   soil  moisture  contents and  salt  concentrations
should  be  similar  to  that expected in  the  soil  surrounding  a soil  dis-
posal system.
     A.2.3  Soil Color
The color and color patterns in soil are good indicators of the drainage
characteristics  of  the soil.   Soil properties,  location in  the  land-
scape, and climate all influence water movement in the soil.  These fac-
tors cause some soils to be saturated or seasonally saturated, affecting
                                   371

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                                                      TABLE  A-2

                                   TYPES  AND CLASSES OF  SOIL  STRUCTURE
                                            TYPE (shape and arrangement of peds)
 Class
Platelike, with
one dimension
(the vertical)
limited and
greatly less
than the other
two; arranged
around a hori-
zontal plane
faces mostly
horizontal
Prismlike, with two dimensions
(the horizontal) limited and con-
siderably less than the vertical; '
arranged around a vertical line;
vertical faces well defined;
vertices angular
                                                           Blocklike, polyhedronlike, or spheroids, or with three dimensions of
                                                           the same order of magnitude, arranged around a point.

                                                           Blocklike; blocks or polyhedrons    Spheroids or polyhedrons having
                                                           having plane or curved surfaces    plane or curved surfaces which
                                                           that are casts of the molds formed  have  slight or no accommodations
                                                           by the faces of the surrounding    to the faces of surrounding peds
                                                           peds
                              Without        With rounded  Faces flattened, Mixed rounded Nonporous
                              rounded caps   caps          most vertices   and flattened     peds
                                                           sharply angular faces with many
                                                                          rounded vertices
                                                                         Porous peds
Platy
Prismatic
Columnar
(Angular)
Blocky*
(Subangular)
Blockyt
Granular
Crumb
Very
very
Fine
fine or
thin
or thin
Very
platy
Thin
to 2
thin
; < 1 mm
platy; 1
mm
Very fine pris-
matic;
<10 mm
Fine prismatic;
10 to 20 mm
Very fine
columnar;
<10 mm
Fine Columnar;
10 to 20 mm
Very fine angu-
lar blocky;
^ 5 mm
Fine angular
blocky; 5 to
10 mm
Very fine sub-
angular blocky;
<5 mm
Fine sub ang
blocky; 5 to
10 mm
Very fine
angular;
<1 mm
Fine
1 to
granular;
2 mm
Very fine
crumb; <
1 mm
Fine crumb;
1 to 2 mm
 Medium        Medium platy;  Medium pris-   Medium colum-Medium angu- Medium sub-   Medium granu-Medium crumb;
                2 to 5 mm     matic, 20 to    nar; 20 to 50  lar blocky; 10   angular blocky;  lar; 2 to 5 mm  2 to 5 mm
                              50mm         mm           to 20 mm      10 to 20 mm


 Coarse or thick Thick platy;    Coarse pris-    Coarse colum- Coarse angular Coarse sub-    Coarse granu-
                5 to 10 mm    matic, 50 to    nar; 50 to     blocky, 20 to   angular; 20     lar; 5 to 10 mm
                              100 mm        100 mm       50 mm        to 50 mm


 Very coarse or  Very thick     Very coarse    Very coarse    Very coarse    Very coarse    Very coarse
 very thick      platy; >  10 mm prismatic;      columnar;     angular blocky; Subangular     granular;
                              > 100 mm     > 100 mm     >50mm      blocky;         >10  mrn
	>50 mm	

 Source: Soil Survey Staff 1960
 •(a)Somelimes called nul. (bl The word "angular" in the name can ordinarily be omitted
 tSometimes called nuciform, nut, or Subangular nut  Since the size connotation of these terms
     is a source of great confusion to many,  they are not recommended.
                                                          372

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their ability  to  absorb and  treat  wastewater.    Interpretation  of  soil
color aids in identifying these conditions.
Soil colors are  a  result of the color  of  primary soil  particles,  coat-
ings of iron and manganese  oxides,  and  organic  matter on the particles.
Soils that  are  seldom or never  saturated  with water and  are  well  aer-
ated, are usually  uniformly red,  yellow or brown  in  color.   Soils  that
are  saturated  for  extended  periods or all the  time  are  often  grey  or
blue in  color.   Color charts have  been  developed for  identifying  the
various soil colors.
Soils that are saturated or nearly saturated during portions of the year
often have spots or streaks of different colors called mottles.  Mottles
are useful to determine zones of saturated soil that may occur only dur-
ing wet periods.  Mottles result from chemical  and biochemical  reactions
when  saturated  conditions,  organic matter, and temperatures above  4°  C
occur together in the  soil.   Under these conditions,  the bacteria pres-
ent rapidly deplete any oxygen present while feeding on the organic mat-
ter.  When  the  oxygen is depleted, other  bacteria  continue the organic
decomposition using  the oxidized  iron  and manganese  compounds,  rather
than oxygen, in their metabolism.  Thus, the insoluble oxidized iron and
manganese, which  contribute much  of  the color to  soil,  are  reduced to
soluble compounds.  This causes  the  soil  to lose  its  color, turning the
soil  grey.   When  the soil  drains,  the soluble iron  and  magnesium are
carried by the water to the larger soil  pores.   Here they are reoxidized
when  they come  in contact with  the oxygen  introduced  by the air-filled
pores, forming  insoluble compounds once again.  The result is the for-
mation of red,  yellow  and  black  spots  near  surfaces, and the  loss of
color, or greying,  at the  sites where  the  iron and manganese  compounds
were  removed.   (Examples  of  mottled soils  are shown  in  Figure 3-20).
Therefore, mottles  seen in unsaturated  soils  can  be  interpreted  as an
indication that the soil is periodically saturated.  Periodic saturation
of soil  cannot always be identified by mottles, however.  Some  soils can
become saturated  without the formation  of mottles, because one  of the
conditions needed  for mottle  formation  is not  present.   Experience and
knowledge of  moisture  regimes  related  to landscape position  and other
soil  characteristics  are necessary  to  make  proper interpretations  in
these situations.
Also, color  spots  and  streaks  can be present in soils for reasons other
than soil saturation.  For example, soil parent materials sometimes cre-
ate  a  color  pattern  in the soil  similar  to mottling.   However,  these
patterns  usually  can  be  distinguished from  true  mottling.    Some very
sandy soils  have uniform  grey  colors because there are no surface coat-
ings on  the  sand grains.   This color can mistakenly be interpreted as a
gley or  a poor draining color.  Direct measurement of zones of soil
                                   373

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saturation may be necessary  to  confirm  the soil moisture regimes if in-
terpretations of soil colors are not possible.
     A.2.4  Soil Horizons
A  soil  horizon is  a layer of  soil  approximately parallel  to  the soil
surface with  uniform characteristics.   Soil horizons  are  identified by
observing changes  in soil  properties with depth.   Soil  texture,  struc-
ture, and color changes are some of the  characteristics  used to  deter-
mine soil  horizons.
Soil horizons are commonly  given  the  letter  designations of A,  B, and C
to  represent  the surface  soil,  subsoil, and  substratum,  respectively.
Not all  soils have all  three  horizons.   On the other  hand,  many soils
show variations within each master horizon and are subdivided as Al, A2,
A3, and  Bl,  etc.   Some example soils and  their horizons  are  shown  in
Figure A-3.


Each horizon  has  its  own set of characteristics and  therefore  will re-
spond differently  to  applied wastewater.  Also, the  conditions created
at the boundary between soil horizons can significantly influence waste-
water flow and treatment through the  soil.   Therefore,  an evaluation  of
a  soil  must  include  a  comparison  of the  physical  properties  of  each
horizon that influences absorption and treatment of wastewater.


     A.2.5  Other Selected Soil Characteristics
Bulk density and clay mineralogy are other soil  characteristics that can
significantly  influence water  infiltration and  percolation  in  soils.
Soil bulk density is the ratio of the mass of soil  to its bulk or volume
occupied by the  soil mass  and  pore  space.   There is not a direct corre-
lation  between bulk density  and soil  permeability, since  sandy  soils
generally have a higher bulk density and permeability than clayey soils.
However, of  soils with  the same texture,  those soils with  the  higher
bulk densities are more compact with less pore volume.  Reduced porosity
reduces the hydraulic conductivity of  the  soil.   Fragipans are examples
of  horizons  that have  high bulk densities  and  reduced permeabilities.
They are very  compact  horizons rich in  silt and/or  sand but relatively
low in clay, which commonly interferes with water and root penetration.


The mineralogy of clay  present in the  soil  can  have a very significant
influence on water movement.  Some clay minerals shrink and swell  appre-
ciably with changes  in  water content.   Montmorillonite is the most com-
mon of  these swelling clay minerals.   Even if  present in small amounts,
                                   374

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           FIGURE A-3

SCHEMATIC  DIAGRAM OF A LANDSCAPE
  AND DIFFERENT  SOILS POSSIBLE
                                 DnC2
                                      A - Surface Soil -
                                      B - Subsoil
                                      C - Substratum
                                      A - Surface Soil
              375

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the porosity  of soils containing  montmorillonite  can vary dramatically
with varying  moisture content.   When  dry,  the clay  particles shrink,
opening the cracks between peds.  But when wet, the clay swells, closing
the pores.
A.3  Water in the SoiTSystem


     A.3.1  Soil Moisture Potential
Soil  permeability,  or the capability  of soil to  conduct water, is not
determined by  the  soil  porosity but,  rather,  the  size,  continuity, and
tortuosity of  the  pores.   A  clayey soil  is  more porous  than  a  sandy
soil, yet  the sandy  soil  will conduct  much more water  because it has
larger, more continuous  pores.   Under natural drainage conditions, some
pores in the soil are filled with water.  The distribution of this water
depends upon the characteristics of  the  pores, while its movement is de-
termined by  the  relative energy status  of  the  water.   Water flows from
points of higher energy  to points of lower  energy.  The energy status is
referred to as the moisture potential.
The  total  soil  moisture potential has  several  components,  of which the
gravitational and matric potential are the most important.  The gravita-
tional  potential  is  the  result  of  the attraction of  water  toward the
center of  the earth  by a  gravitational  force and is equal to the weight
of water.   The  potential  energy of the water at any point is determined
by the elevation  of  that  point relative to some reference level.  Thus,
the  higher  the water  above this reference, the greater  its gravitational
potential.
The  matric  potential  is produced by  the  affinity of water molecules to
each  other  and to  solid  surfaces.    Molecules within  the body of water
are  attracted  to  other molecules by  cohesive  forces,  while water mole-
cules  in  contact  with  solid surfaces are more strongly attracted to the
solid  surfaces by  adhesive  forces.   The  result  of these forces acting
together  draws water into the pores of the soil.  The water tries to wet
the  solid surfaces of the  pores  due  to  adhesive forces and pulls other
molecules with it due to cohesive forces.   This phenomenon is referred
to  as capillary rise.  The rise  of water is  halted  when the weight of
the  water column is equal to the  force of capillarity.  Therefore, water
rises  higher and  is held tighter in  smaller pores than in larger pores
(see  Figure  A-4).   Upon draining, the largest pores empty first because
they  have the weakest hold  on  the  water.    Therefore,  in unsaturated
soils, the water is held in the finer pores  because they are better able
to  retain the  water against the forces of gravity.
                                   376

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                              FIGURE  A-4

               UPWARD MOVEMENT BY  CAPILLARITY  IN  GLASS
                  TUBES AS COMPARED WITH SOILS (2)

                                Air Spaces
                                            Soil Particle

                                                  Capillary Water
                                                  Adsorbed Water
The ability of the soil  to draw or pull  water into its pores is referred
to as  its matric  potential.   Since the water  is  held against the force
of gravity,  it has  a pressure  less  than  atmospheric.   This  negative
pressure is often referred to as  soil  suction  or  soil moisture tension.
Increasing suction or tension is associated with soil  drying.
The moisture content of soils with similar moisture tensions varies with
the nature of the pores.   Figure  A-5  illustrates  the change in moisture
content versus  changes in  moisture  tensions.  When the soil  is  satu-
rated,  all  the  pores  are  filled with water  and no capillary  suction
occurs.  The  soil  moisture tension is zero.   When drainage occurs, the
tensions increase.  Because the sand has  many relatively large pores, it
drains  abruptly  at relatively  low  tensions, whereas the clay releases
only a  small  volume  of water over a wide  tension range because  most of
it  is  strongly  retained  in very fine pores.  The  silt loam  has more
coarse  pores  than  does the clay, so its curve  lies  somewhat below that
of  the  clay.   The sandy loam has more finer pores than the sand so its
curve lies above that of the sand.
                                   377

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                          FIGURE A-5

               SOIL MOISTURE RETENTION FOR FOUR
                  DIFFERENT SOIL TEXTURES (3)
                       20   40   60   80   100
                  Soil  Moisture Tension (MBAR)
                     Soil Drying	^
A.3.2  Flow of Water in Soil
The flow of water  in  soil  depends  on  the soil's ability to transmit the
water and the  presence  of a force to  drive  it.   Hydraulic conductivity
is defined  as  the soil's  ability  to  transmit water, and  is  related to
the number,  size,  and  configuration  of the  pores.   Soils with  large,
continuous water-filled pores can  transmit water  easily  and have  a high
conductivity, while  soils with  small,  discontinuous  water-filled pores
offer a high resistance to  flow, and,  therefore,  have low conductivity.
When the soil  is  saturated, all  pores
tivity depends on all the soil  pores.
or dries (see Figure  A-5),  the larger
smaller water-filled  pores  may  transmit the water.   Therefore, as seen
in Figure  A-6,  the  hydraulic  conductivity decreases  for all soils  as
they dry.  Since clayey soils have more fine pores than sandy  soils, the
hydraulic conductivity  of a clay  is  greater than a  sand  beyond  a soil
moisture tension of about 50 mbar.
                                  are water-filled  and the conduc-
                                  When the soil  becomes unsaturated
                                  pores  fill  with air, and only the
                              378

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                               FIGURE A-6

                    HYDRAULIC  CONDUCTIVITY (K)  VERSUS
                         SOIL  MOISTURE  RETENTION (4)
                   1000-
CD
\100-

u
>-
'>
s
                  T3
                  C
                  O
                  o
                     10-
                    1.0-3
                     0.1-
        245 r
                                LType I (sand)
                   Type II,
                       (sandy loam)
                                20 40  60  80  100
                            Soil Moisture Tension (MBAR)
                                 Drying 	>-
Water movement in  soil  is  governed by the total moisture potential  gra-
dient and the soil's  hydraulic  conductivity.  The direction of movement
is from a point of higher potential (gravity plus matric potential)  to  a
point of lower potential.  When the soil  is  saturated, the matric  poten-
tial  is  zero,  so  the water moves  downward  due to gravity.   If the  soil
is unsaturated,  both  the  gravity  and matric  potentials  determine  the
direction of flow, which may  be upward, sideward, or downward depending
on the difference  in total  potentials  surrounding the area.  The greater
the  difference  in  potentials between  two   points,  the  more  rapid  the
movement.  However, the volume of water moved  in  a given time  is propor-
tional  to the  total  potential gradient and  the soils hydraulic conduc-
tivity at the given moisture  content.  Therefore, soils with greater
hydraulic conductivities transmit  larger  quantities  of water at the same
potential gradient than soils with  lower  hydraulic conductivities.
                                    379

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     A.3.3  Flow of Water Through Layered Soils
Soil  layers  of  varying  hydraulic  conductivities  interfere with  water
movement.  Abrupt changes in conductivity can cause the soil to saturate
or  nearly  saturate  above  the boundary regardless of  the  hydraulic  con-
ductivity  of  the underlying layer.   If the upper layer  has  a signifi-
cantly greater hydraulic conductivity, the water ponds because the lower
layer cannot transmit the water  as  fast as the upper layer delivers it.
If the upper layer has a lower conductivity, the underlying layer cannot
absorb  it  because  the  finer pores  in  the  upper  layer hold  the  water
until the matric potential is reduced to near saturation.
Layers  such  as these may  occur  naturally  in soils or as  the  result of
continuous wastewater application.   It is common to  develop  a clogging
mat  of  lower  hydraulic  conductivity at the  infiltrative surface  of  a
soil disposal  system.  This  layer  forms  as a result of suspended solids
accumulation, biological  activity, compaction by construction machinery,
and  soil  slaking  (3).   The clogging mat may restrict water  movement to
the  point where water is  ponded above,  and the soil  below  is unsatur-
ated.   Water  passes  through  the  clogging  mat  due to  the  hydrostatic
pressure  of  the ponded water  above  pushing the water through,  and the
soil suction of the unsaturated soil  below pulling it through.


Figure  A-7  illustrates  three columns  of  similar  textured  soils  with
clogging  mats  in  various  stages  of development.    Water is  ponded at
equal heights above the infiltrative surface of each column.


Column  A  has no clogging mat  so the water is able to pass  through all
the  pores, saturating the  soil.   The moisture tension in this column is
zero.   Column B  has  a  permeable  clogging mat developed  with moderate
size pores.  Flow into the underlying soil  is restricted by the clogging
mat  to a  rate less than the soil  is able to transmit it.   Therefore, the
large pores  in the soil  empty.  With increasing intensity of the mat, as
shown in  Column C, the flow rate through the soil  is reduced  to very low
levels.   The water is  forced to  flow through  the  finest pores  of the
soil, which  is a very tortuous path.   Flow rates through  identical clog-
ging mats developed on different soils will  vary  with the soil's capil-
lary characteristics.
A.4   Evaluating Soil Properties


To  adequately predict how soil  responds  to  wastewater application, the
soil  properties  described  and  other  site  characteristics  must  be
identified.   The  procedures  used  to evaluate  soils are  described  in
Chapter  3 of  this manual.


                                  380

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                                 FIGURE A-7

             SCHEMATIC REPRESENTATION OF WATER MOVEMENT THROUGH
                 A SOIL  WITH CRUSTS OF DIFFERENT RESISTANCES
          M Water
Clogging Layer
Qpore
Particle
                             <.•••: s-_-
A.5  References
1.  Black,  C.  A.   Soil  Plant Relationships.   2nd  ed.  Wiley, New York,
    1968.  799 pp.

2.  Brady, N.  C.  The Nature  and  Properties of Soils.   8th ed. MacMil-
    lan, New York, 1974.  655 pp.

3.  Bouma, J. W., A.  Ziebell,  W.  G.  Walker, P. G. Olcott, E. McCoy, and
    F. D.  Hole.   Soil Absorption of  Septic Tank  Effluent.  Information
    Circular 20,  Wisconsin  Geological  and Natural History Survey, Madi-
    son, 1972. 235 pp.

4.  Bouma, J.    Unsaturated  Flow During  Soil  Treatment of  Septic Tank
    Effluent.  J. Environ. Eng., Am.  Soc. Civil Eng., 101:967-983, 1975.
                                   381

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                                GLOSSARY
A horizon:   The horizon formed  at or near the surface,  but  within  the
     mineral soil, having properties that reflect the influence of accu-
     mulating organic matter or eluviation, alone or in combination.

absorption:   The process by which one substance is taken  into  and  in-
     cluded within another substance, as the absorption of water by soil
     or nutrients by plants.

activated  sludge process:   A biological  wastewater  treatment  process in
     which a mixture of  wastewater and  activated  sludge  is  agitated  and
     aerated.   The  activated  sludge  is  subsequently separated  from  the
     treated  wastewater  (mixed liquor)  by sedimentation and  wasted or
     returned to the process as needed.

adsorption:  The increased  concentration of molecules  or ions at a sur-
     face, including exchangeable cations and anions on soil particles.

aerobic:   (1) Having molecular oxygen as a part of the  environment.  (2)
     Growing or occurring only in  the presence of molecular oxygen, such
     as aerobic organisms.

aggregate, soil:  A group of soil  particles cohering so as to  behave me-
     chanically as a unit.

anaerobic:  (1) The absence of molecular oxygen.  (2) Growing  in the ab-
     sence of molecular oxygen (such as anaerobic bacteria).

anaerobic  contact process:    An   anaerobic waste  treatment  process in
     which  the  microorganisms responsible  for waste  stabilization  are
     removed  from the  treated  effluent  stream by sedimentation or other
     means, and  held  in  or returned  to  the process  to enhance the rate
     of treatment.
           o
angstrom  (A):    one  hundred millionth of  a  centimeter.
B horizon:   The  horizon  immediately  beneath  the A horizon characterized
     by  a higher  colloid  (clay or  humus)  content, or  by a  darker  or
     brighter color than the  soil  immediately  above or below,  the color
     usually  being  associated  with  the  colloidal  materials.    The
     colloids may be of alluvial origin, as clay or humus; they may have
     been  formed  in  place (clays, including sesquioxides); or they may
     have  been derived from a texturally layered parent material.

                                 382

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biochemical  oxygen demand (BOD):   Measure of the concentration of organ-
     ic impurities in wastewater.   The amount of oxygen required by bac-
     teria while  stabilizing organic  matter under aerobic  conditions,
     expressed in  mg/1,  is  determined  entirely by the  availability  of
     material  in  the wastewater  to be  used as biological food,  and  by
     the  amount  of  oxygen  utilized   by   the  microorganisms  during
     oxidation.

blackwater:    Liquid  and solid human  body waste and the carriage waters
     generated through toilet usage.

bulk density, soil:   The mass of dry  soil   per unit bulk volume.   The
     bulk volume  is  determined   before drying  to constant weight  at
     105°C.

C horizon:  The horizon that normally lies beneath the B horizon but may
     lie beneath the A horizon, where the only significant change caused
     by  soil   development   is an  increase   in  organic  matter,  which
     produces an A  horizon.   In  concept, the  C horizon  is unaltered  or
     slightly altered parent material.

calcareous soil:   Soil  containing  sufficient  calcium  carbonate  (often
     with magnesium  carbonate)  to effervesce  visibly  when treated with
     cold 0.1N hydrochloric acid.

capillary attraction:    A  liquid's movement over, or  retention  by,  a
     solid surface,  due  to  the  interaction  of  adhesive and  cohesive
     forces.

cation  exchange:    The  interchange  between  a cation  in solution  and
     another cation  on the  surface of any surface-active material, such
     as clay or organic colloids.

cation-exchange capacity:  The sum total  of exchangeable cations that a
     soil can adsorb; sometimes  called total-exchange, base-exchange ca-
     pacity, or cation-adsorption  capacity.   Expressed  in milliequiva-
     lents per  100  grams  or per  gram  of soil  (or of  other exchanges,
     such as clay).

chemical  oxygen  demand  (COD):   A measure  of the  oxygen  equivalent  of
     that portion of  organic  matter that is  susceptible  to oxidation  by
     a strong chemical oxidizing  agent.

chlorine  residual:    The total  amount  of chlorine (combined  and  free
     available  chlorine)  remaining   in  water,  sewage,  or  industrial
     wastes  at  the end   of a   specified  contact   period  following
     c hi ori nation.

clarifiers:    Settling tanks.   The purpose  of a clarifier is to remove
     settleable solids by gravity, or colloidal solids by coagulation
                                   383

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     following chemical  flocculation;  will  also remove floating oil  and
     scum through skimming.

clay:  (1) A  soil  separate consisting of particles <0.002 mm in equiva-
     lent diameter.  (2) A textural class.

clay mineral:   Naturally  occurring inorganic  crystalline  or amorphous
     material   found  in  soils  and  other earthy deposits,  the particles
     being predominantly  <0.002 mm in diameter.    Largely  of secondary
     origin.

coarse texture:  The texture  exhibited by sands,  loamy sands, and sandy
     loams except very fine sandy loams.

coliform-group bacteria:   A group  of  bacteria predominantly inhabiting
     the intestines of man  or  animal,  but also occasionally found else-
     where.  Used as an indicator of human fecal contamination.

colloids:  The finely divided  suspended matter which will  not settle,
     and the  apparently dissolved matter which may be transformed into
     suspended matter by contact with  solid  surfaces or precipitated by
     chemical   treatment.   Substances  which are soluble as judged by or-
     dinary physical tests,  but will  not pass  through  a  parchment mem-
     brane.

columnar structure:   A soil  structural  type with  a vertical  axis much
     longer than the horizontal axes and a distinctly rounded upper sur-
     face.

conductivity,  hydraulic:   As  applied to  soils, the ability of the soil
     to transmit water in liquid form through pores.

consistence:   (1)  The  resistance  of a material  to deformation or rup-
     ture.  (2) The degree of cohesion or adhesion of the soil mass.

     Terms used for describing consistence at various soil moisture
     contents  are:

       wet soil:   Nonsticky,  slightly sticky, sticky, very sticky, non-
       plastic, slightly plastic, plastic, and very plastic.

       moist  soil:   Loose, very friable, friable,  firm,  very firm, and
       extremely firm.

       dry soil:   Loose,  soft, slightly  hard,  hard,  very hard, and ex-
       tremely hard.

       cementation:  Weakly cemented, strongly cemented, and indurated.

crumb:   A  soft,  porous, more  or less rounded ped from 1 to 5 mm in dia-
     meter.
                                   384

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crust:  A surface layer on soils, ranging in thickness from a few milli-
     meters to  perhaps  as much  as  an  inch, that is  much  more  compact,
     hard, and  brittle  when  dry, than the  material  immediately beneath
     it.

denitrification:   The  biochemical  reduction of  nitrate or  nitrite  to
     gaseous molecular nitrogen or an oxide of nitrogen.

digestion:   The biological  decomposition  of organic matter  in sludge,
     resulting in partial  gasifiction,  liquefaction, and  mineralization.

disinfection:   Killing  pathogenic  microbes on or in  a material without
     necessarily sterilizing it.
disperse:  To break up compound  particles,  such  as aggregates,  into the
     individual  component particles.

dissolved oxygen  (DO):   The oxygen dissolved in  water, wastewater,  or
     other liquid,  usually expressed  in milligrams  per liter  (mg/1),
     parts per million (ppm),  or percent of saturation.

dissolved solids:   Theoretically,  the anhydrous  residues  of the  dis-
     solved constituents in water.  Actually, the term is defined by the
     method used in determination.

effluent:    Sewage,  water,  or  other  liquid,  partially or  completely
     treated or in its natural  state, flowing out of a reservoir, basin,
     or treatment plant.

effective size:   The size  of  grain such that  10% of the  particles  by
     weight are smaller and 90% greater.

eutrophic:   A  term applied to water that has a  concentration of nutri-
     ents optimal, or nearly so, for plant or animal growth.

evapotranspiration:   The  combined loss of water from  a  given area, and
     during  a  specified period  of  time, by  evaporation from the  soil
     surface and by transpiration from plants.

extended aeration:  A modification of the activated sludge  process which
     provides for aerobic sludge digestion within the aeration system.

filtrate:  The liquid which has passed through a filter.

fine texture:   The texture exhibited by soils having  clay  as a  part of
     their textural class name.

floodplain:   Flat or nearly  flat land on  the  floor of a  river valley
     that is covered by water during floods.
                                  385

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floodway:  A channel  built to carry excess water from a stream.

food to  microorganism  ratio  (F/M):   Amount of  BOD applied  to the  acti-
     vated  sludge  system per  day per  amount  of MLSS in  the  aeration
     basin, expressed as Ib  BOD/d/lb  MLSS.

graywater:  Wastewater generated by water-using fixtures and appliances,
     excluding the toilet and possibly the garbage disposal.

hardpan:   A hardened soil layer,  in the lower  A or  in  the B  horizon,
     caused by cementation of soil  particles with organic matter or with
     materials such as  silica,  sesquioxides,  or calcium carbonate.   The
     hardness does not  change appreciably with  changes in moisture con-
     tent, and pieces of the hard layer do not slake  in water.

heavy soil:   (Obsolete  in scientific use.)   A  soil  with  a  high content
     of  the  fine  separates,  particularly  clay,  or  one  with  a  high
     drawbar pull  and hence  difficult to cultivate.

hydraulic conductivity:  See conductivity, hydraulic.

impervious:  Resistant to penetration by fluids or by roots.

influent:  Water, wastewater, or other  liquid flowing  into  a  reservoir,
     basin, or treatment plant.

intermittent filter:   A natural  or artificial  bed of  sand or other  fine-
     grained material to  the surface of which wastewater  is applied in-
     termittently in flooding doses  and through which  it passes;  oppor-
     tunity is  given  for filtration and  the  maintenance of an  aerobic
     condition.

ion:  A charged atom,  molecule, or  radical,  the migration  of which af-
     fects the transport  of  electricity through  an electrolyte  or,  to  a
     certain extent, through  a  gas.   An  atom or molecule that  has lost
     or  gained  one  or  more electrons;  by such  ionization it  becomes
     electrically charged.  An example is the alpha particle.

ion  exchange:   A chemical  process involving reversible  interchange of
     ions  between  a  liquid and  a  solid  but  no  radical  change in
     structure of the solid.

leaching:  The removal  of materials in solution from  the soil.

lysimeter:  A device for  measuring percolation  and leaching losses from
     a column of soil under controlled conditions.

manifold:   A  pipe fitting with  numerous  branches to  convey fluids be-
     tween  a  large  pipe and several  smaller  pipes,  or to permit choice
     of  diverting flow  from  one of several  sources or  to one  of several
     discharge points.
                                  386

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mapping unit:   A soil  or combination of  soils  delineated  on  a map and,
     where possible, named to show the taxonomic unit or units included.
     Principally,  mapping  units  on maps  of soils  depict soil  types,
     phases, associations, or complexes.

medium texture:  The texture exhibited  by very  fine  sandy  loams, loams,
     silt loams, and silts.

mineral soil:   A soil  consisting predominantly of,  and having its pro-
     perties  determined  by,   mineral   matter.    Usually  contains  <20
     percent organic matter, but may contain an  organic surface layer up
     to 30 cm thick.

mineralization:  The conversion of an element from an organic  form to an
     inorganic state as a result of microbial decomposition.

mineralogy, soil:  In practical use, the kinds and proportions of miner-
     als present in soil.

mixed  liquor suspended  solids  (MLSS):   Suspended  solids in a  mixture of
     activated  sludge   and  organic matter  undergoing  activated  sludge
     treatment in the aeration tank.

montmorillonite:   An aluminosilicate clay mineral with  a  2:1 expanding
     structure;  that  is,  with two  silicon  tetrahedral  layers enclosing
     an aluminum octahedral layer.  Considerable expansion  may be caused
     by water moving between silica layers of contiguous units.

mottling:   Spots or blotches of different  color  or  shades of color in-
     terspersed with the dominant color.

nitrification:  The biochemical oxidation of ammonium to nitrate.

organic nitrogen:   Nitrogen combined in  organic molecules  such as pro-
     teins, amino acids.

organic soil:   A soil  which contains a high percentage (>15  percent or
     20 percent) of organic matter throughout the sol urn.

particle size:  The effective diameter  of a particle usually measured by
     sedimentation or sieving.

particle-size  distribution:   The amounts of  the  various soil separates
     in a soil  sample,  usually expressed as weight percentage.

pathogenic:   Causing disease.   "Pathogenic"  is also  used  to designate
     microbes  which commonly cause  infectious  diseases,  as  opposed to
     those which do so  uncommonly or never.
                                   387

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ped:   A  unit  of  soil  structure  such  as an  aggregate, crumb,  prism,
     block, or granule, formed by  natural  processes  (In  contrast  with a
     clod, which is formed artificially).

pedon:  The smallest volume  (soil  body)  which  displays  the  normal  range
     of variation  in properties of  a soil.   Where properties such  as
     horizon thickness vary  little along  a lateral  dimension,  the  pedon
     may occupy an area of a square yard or less.  Where such a property
     varies substantially along a  lateral  dimension, a  large pedon sev-
     eral  square yards in area may be required to show the full range  in
     variation.

percolation:  The  flow or trickling  of  a liquid downward through  a con-
     tact or filtering medium.  The liquid may or may not fill  the pores
     of the medium.

permeability, soil:  The ease  with which gases, liquids, or plant roots
     penetrate or pass through soil.

pH:  A term used to describe the hydrogen-ion activity of a  system.

plastic soil:   A soil  capable of  being  molded or deformed  continuously
     and  permanently,  by  relatively  moderate  pressure,  into  various
     shapes.  See consistence.

platy structure:  Soil  aggregates that are developed predominantly along
     the horizontal axes; laminated;  flaky.

settleable  solids:   That matter  in wastewater which  will   not stay  in
     suspension during a preselected  settling  period, such  as  one  hour,
     but either settles to the bottom or floats to the top.

silt:   (1) A  soil  separate consisting  of  particles  between 0.05  and
     0.002 mm in diameter.   (2) A soil textural class.

single-grained:   A nonstructural  state normally  observed in soils con-
     taining a preponderance of large particles,  such as sand.  Because
     of a lack of  cohesion,  the  sand grains  tend not to assemble  in ag-
     gregate form.

siphon:   A closed conduit  a portion of which  lies  above the  hydraulic
     grade  line,  resulting  in  a pressure  less  than  atmospheric and re-
     quiring a  vacuum  within the conduit  to start  flow. A siphon uti-
     lizes  atmospheric pressure to effect  or increase the flow of  water
     through the conduit.

slope:  Deviation of a plane surface from the horizontal.

soil  horizon:   A layer of soil or soil  material  approximately parallel
     to the land surface and differing from adjacent genetically related
                                   388

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     layers in physical, chemical,  and  biological  properties or charac-
     teristics such as color, structure, texture, consistence, pH, etc.

soil  map:   A map  showing  the  distribution of soil types  or other soil
     mapping  units  in relation  to  the  prominent  physical  and  cultural
     features of the earth's surface.

soil  morphology:   The physical  constitution, particularly the structural
     properties,  of a soil  profile as exhibited by the kinds, thickness,
     and arrangement of the horizons in  the profile, and by the texture,
     structure, consistence, and porosity of each horizon.

soil  separates:  Groups of mineral particles separated on the basis of a
     range in size.  The principal separates are sand, silt, and clay.

soil  series:   The  basic  unit of  soil classification,  and consisting of
     soils which are essentially alike in all major profile characteris-
     tics, although the texture of the A horizon may vary somewhat.  See
     soil type.

soil  solution:   The  aqueous liquid phase  of  the soil  and  its solutes
     consisting of  ions  dissociated from the surfaces of  the soil  par-
     ticles and of other soluble materials.

soil  structure:  The  combination  or arrangement  of individual soil  par-
     ticles into definable  aggregates,  or peds,  which are characterized
     and classified on the basis of size, shape,  and degree of distinct-
     ness.

soil  suction:  A measure of the force of water retention in unsaturated
     soil.  Soil  suction is  equal  to a  force per unit area that must be
     exceeded  by  an  externally  applied suction  to initiate water flow
     from  the soil.   Soil  suction is  expressed  in  standard  pressure
     terms.

soil  survey:   The  systematic  examination,  description,  classification,
     and mapping of soils in an area.

soil  texture:  The relative proportions of the various soil  separates in
     a soil.

soil  type:    In mapping  soils,  a subdivision of a  soil  series  based on
     differences in the texture of the A horizon.

soil  water:    A  general  term  emphasizing  the physical  rather  than the
     chemical properties and behavior of the soil solution.
                                    389

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solids:  Material  in the solid state.

     total:    The  solids  in  water,  sewage,  or other  liquids;  includes
     suspended and  dissolved  solids; all material  remaining  as residue
     after water has been evaporated.

     dissolved:  Solids present in solution.

     suspended:  Solids physically suspended  in water,  sewage,  or other
     liquids.   The quantity  of  material deposited  when a quantity  of
     water,  sewage, or  liquid is filtered through an  asbestos  mat in a
     Gooch crucible.

     volatile:  The quantity of solids in water,  sewage, or other liquid
     lost on ignition of total solids.

solids retention time  (SRT):   The  average  residence  time  of suspended
     solids in a biological  waste treatment system, equal  to the total
     weight  of suspended  solids  in  the system  divided  by  the  total
     weight  of  suspended  solids leaving  the  system  per  unit  time
     (usually per day).

subsoil:   In  general  concept, that part  of the soil  below the  depth  of
     plowing.

tensiometer:  A device for measuring the negative hydraulic pressure (or
     tension) of water  in  soil in situ;  a porous,  permeable ceramic cup
     connected through a tube to a manometer or vacuum gauge.

tension,  soil water:  The expression, in positive  terms, of the negative
     hydraulic pressure of soil water.

textural  class, soil:   Soils grouped on  the  basis  of  a specified range
     in texture.   In  the United  States,  12 textural  classes  are recog-
     nized.

texture:   See soil  texture.

tight  soil:   A compact,  relatively  impervious  and tenacious  soil  (or
     subsoil), which may or may not be plastic.

Total  Kjeldahl  Nitrogen  (TKN):   An  analytical  method  for determining
     total organic nitrogen and ammonia.

topsoil:   (1)  The  layer of soil  moved  in cultivation.   (2) The A hori-
     zon.   (3) The  Al  horizon.    (4) Presumably fertile  soil  material
     used to topdress roadbanks, gardens, and lawns.

uniformity coefficient  (UC):   The ratio of that size  of grain  that has
      60% by weight finer  than itself,  to the size which has 10% finer
     than itself.
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unsaturated flow:  The  movement of water in a  soil which  is  not filled
     to capacity with water.

vapor  pressure:    (1)  The pressure  exerted by  a vapor  in a  confined
     space.  It is a  function of the temperature.  (2)  The  partial  pres-
     sure of water vapor in the atmosphere.   (3) Partial  pressure of any
     liquid.

water table:  That level  in  saturated  soil  where the  hydraulic pressure
     is zero.

water table, perched:  The water table of a  discontinuous saturated zone
     in a soil.
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EXAMPLES OF SOIL MOTTLING (EXAMPLES A, B & C INDICATE
   SEASONAL SOIL SATURATION, EXAMPLE D DOES NOT)
           (A)
Extremely Prominent Mottling
      in a Clayey Soil
                                              (B)
                                    Mottling in a Loamy Soil
         (C)
Mottling in a Sandy Soil
                                                 (D)
                                          Mottling Inherited
                                        from Geologic Processes

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