EPA 625/l-81-013a
                     PROCESS DESIGN MANUAL
                       LAND TREATMENT OF
                      MUNICIPAL WASTEWATER
                       RAPID INFILTRATION
                         OVERLAND  FLOW


                         October 1984
                         Published by.

            U. S. Environmental Protection Agency
        Center for Environmental Research Information
                   Cincinnati, Ohio  45268

This  document  is  intended  as  a  supplement   to  the   1981
Technology Transfer Process  Design Manual for Land Treatment  of
Municipal  Wastewater,  (EPA 625/1-81-013).   Throughout  this
document,  the 1981 Process Design Manual will be referred  to  as
the  Manual.   Part I  in this  text  covers design  of  rapid
infiltration  systems   and   Part II  discusses  overland   flow
systems.  A  substantial amount  of new  information  on both _ the
concepts  and  their  performance   has  been  developed  since

Part I  on  rapid infiltration provides additional guidance and
detail  on  planning, design, construction,  and operation  of
rapid infiltration  systems  to avoid problems which  have been
observed  at a few  recently constructed  systems.   The  basic
criteria  in  the 1981  Manual  are still  valid  and are not
repeated in this text.

Part II on overland-flow supplements the 1981 design basis with
information  from operating   municipal  facilities,  as  well  as
additional results from research studies  completed in the
period  December   1980  to   March   1984.     This  information
reinforces   and  strengthens  the  basis   for   this  rapidly
developing technology.


Preparation  of  Part  I  oil  rapid  infiltration  systems  has
involved the participation  of a number of  individuals.   There
were  a team  of. authors,  another group of  individuals  who
deserve  special   recognition  for  their   contributions  and
technical  assistance, and a  group of  invited  experts  who
reviewed the document and provided comments and, suggestions for
its improvement.   Mr. Sherwood  C.  Reed of  USACRREL was  the
principal author of Part I  and coordinated  the  activities of
the other  authors  and groups.   Dr.  James  E. Smith  Jr.,  EPA
CERI was Project Officer of this task.


       Reed,  S. C.;  USACRREL
       Wallace, A.  T.;  University of  Idaho
       Bouwer,  H.;  USDA
       Enfield, C.;  USEPA
       Stein,  C.; Metcalf &  Eddy
       Thomas,  R.;  USEPA

       Special  Contributions and Technical Assistance

       Allen,  D.; New Hampshire  WSPCC
       Aulenbach, D; Rensselaer  Polytechnic Institute
       Crites,  R.;  G. S.  Nolte & Associates
       Dornbush, J.; South Dakota  State University
       Leach, L.; USEPA
       Linstedt, R.  D.; Black &  Veatch
       Rittershaus,  P.; Banner Associates
       Sylvester, K.; ERM, Inc.

       Review Group

       Ariail,  D.; USEPA
       Dean, R.; USEPA
       Deemer,  D. D.; ERM-Southeast, Inc.
       Gilbert, T.;  Wisconsin  DNR
       Hill, G.; Wisconsin DNR
       Larson,  R.; Wisconsin DNR
       Leach, L.; USEPA
       Madancy, R.;  OWR-DOI
       Morgan,  G.; USDA
       Nickleson, M.; USAEHA
       Opfer, W.; U. S.  Forest Service
       Pycha, C.; USEPA
       Schochenmaier, L.; South Dakota DWNR
       Smith, E.; USACERL
       Stark, S.; Minnesota Pollution Control Agency
      Troxler,  R.;  Georgia DNR


Part  II  was developed with the  assistance  of a number of
individuals.  In addition to a team of authors, another group
of experts  were invited to  review the document  and provide
comments  and  suggestions  for  its  improvement.    Certain of
these reviewers also provided additional contributions and/or
technical  assistance.    Mr.    D.  Donald  Deemer  was  the
principal author of Part II and coordinated the activities of
the other authors  and reviewers.    Dr.  James  E.  Smith,  Jr.,
EPA,  CERI was the Project Officer for the development of this

     Deemer, D. D.; ERM-Southeast, Inc.
     Thomas, R. E.;r USEPA
     Reed, S. C.; USACRREL
     Witherow, J. L.; USEPA
     Morgan, G.; USDA, FHA

Special Contributions and Technical Assistance

     Abernathy, A. R.; Clemson University
     Ariail, D.; USEPA
     Clark, P. J.; Clark Engineers
     Ford, J. P.; ERM, Inc.
     Parmelee, D. M. ; Parmelee Incorporated
     Smith, R. G.; University of California-Davis

Review Group

     Aly, O. M.; Campbell Soup Company
     Bledsoe, B. E.; USEPA
     Crites, R. W.; G. S. Nolte & Associates
     Gilde, L. C.; Campbell Soup Company
     Lee, C. R.; USAEWES
     Jones, A. A.,; USEPA
     Opfer, W. J.; USDA, Forest Service
     Overman, A. R.; University of Florida
     Sutherland, J. C.; EDI Engineering & Science
     Zirschky, J.; Clemson University

                     PART I. RAPID INFILTRATION


       1.1  Background
       1.2  Objective and Scope
       1.3  References


       2.1  General
       2.2  Preliminary Screening
            2.2.1  Land Area Requirements
            2.2.2  Economic Factors
            2.2.3  Regulatory Factors
            2.2.4  Site Characteristics
       2.3  Site Selection
       2.4  References


       3.1  General
       3.2  Site Evaluation
       3.3  Soils Investigation
            3.3.1  Soil Texture
            3.3.2  Soil Structure
            3.3.3  Soil Color
            3.3.4  Field Procedures
            Test  Borings
            Test  Pits
            3.3.5  Laboratory  Procedures
            3.3.6  Evaluation  of  Soil Test Results
       3.4  Ground  Water Investigations
       3.5  Infiltration and Permeability Tests
            3.5.1  Infiltration Test Procedures
                   and  Evaluation
            Flooding Basin Test
            Air Entry Permeameter


     3.5.2  Permeability Tests
3.6  References

4.1  General                                         28
4.2  Hydraulic Loading and Basin Area                28
     4.2.1  Land Area Required                       31
     4.2.2  Wet/Dry Ratio                            31
     4.2.3  Application Rate                         31
     4.2.4  Infiltration of Standing Water           34
4.3  Subsurface Flow and Ground Water Mounding       36
     4.3.1  Subsurface Flow    ,                  ,37
     4.3.2  Ground Water Mounding                    39
4.4  RI Basin Configuration and Application
     Scheduling                                      42
4.5  Design Requirements for Winter Operation in
     Cold Climates                                   44
4.6  Design of Seepage Ponds              :           47
4.7  Design of Physical Elements                     47
     4.7.1  Dikes                                    47
     4.7.2  Basins in Fine Textured Soils            48
     4.7.3  Inlet, Distribution, and Transfer
            Structures                               48
     4.7.4  Flow Control                             49
4.8  RI System Performance                           49
     4.8.1  Removal of Toxic Organics                49
     4.8.2  Nitrogen Management in RI Systems        50
     4.8.3  Disinfection in RI Systems               52
4.9  References                ,                      ^3

5.1  General
5.2  Infiltration Surfaces in RI Basins
     5.2.1  Cut and Fill in Coarse Soils
     5.2.2  Cut and Fill in Fine Textured Soils
     5.2.3  Ridge and Furrow Construction
5.3  Dike Construction
5.4  Control of Water
5.5  References
6.1  General
6.2  Wastewater Scheduling
6.3  Maintenance of Infiltration Surfaces
6.4  Monitoring
6.5  Winter Operations
6.6  References

   1-1    Actual  RI  Loading  Rates  versus  Design

   3-1    Moisture Content/Compaction versus
         Permeability  for a Clay  Soil

   3-2    Permeability  versus Void Ratio

   3-3    Typical Subsurface Profile

   4-1    Basin Layout  for Example Calculation

   4-2    Subsurface Profile Section C-C  for
         Example Calculation


   1-1    Rapid Infiltration - Potential  Problems

   2-1    Economic Rating Factors  for Site Suitability

   3-1    Soil Characteristics in  Field Descriptions

   3-2    Textural Properties of Mineral  Soils

   3-3    Vertical Saturated Permeabilities
         from Figure 3-2

   4-1    Design Factors for Hydraulic Loading

   4-2    Porosity of Selected Soils










                      PART II.  OVERLAND FLOW

       1.1  Background
       1.2  Objectives
       1.3  References


       2.1  Introduction
       2.2  Site Selection

     2.2.1 Process Description                       69
     2.2.2 Soil Permeability                         69
2.3  Process Design                                  70
     2.3.1 Design Criteria                           70
     2.3.2 Preapplication Treatment                  70
     2.3.3 Storage                                   71
     2.3.4 Distribution Systems                      71
2.4  Terrace Design and Construction                 71
2.5  Vegetation Selection and Establishment          71
2.6  References                                      72


3.1  Procedures                                      74
3.2  Empirical Method                                74
     3.2.1 Revised Criteria                   •      •74
     3.2.2 Use of Design Ranges                      76
  Selection of Hydraulic
                   Loading Rate                      76
  Determination of Land Area        77
  Selection of Terrace Length       77
  Selection of Application Period   78
3.3  Rational Design Procedure                       78
     3.3.1 Introduction     •                         78
     3.3.2 Procedure                                 79
     3.3.3 Example                                   79
3.4  References                                      83


4.1  Areas of Importance                             85
4.2  Level of Preapplication Treatment               85
4.3  Solids Removal                                  86
4.4  Algal Interference     .                         86
4.5  References                                      86

5.1  Current Practice                                88
5.2  Cold Weather Storage Requirements               89
5.3  Rainfall Considerations                        ,89
     5.3.1 Impact on Effluent BOD Concentration      91
     5.3.2 Impact on Effluent Suspended Solids
           Concentration                 ,      '      91
     5.3.3 Mass Discharges       ,                    91
     5.3.4 Recommended Operating Practices           92
5.4  Storage Reservoir Design                        92
5.5  References                                      92


6.1  Selection                                       94

6.2  Surface Methods
     6.2.1 Gated Pipe
     6.2.2 Slotted or Perforated Pipe
     6.2.3 Bubbling Orifices
6.3  Low Pressure Sprays
6.4  Sprinklers
6.5  Sizing of the Distribution System
6.6  Controls
     6.6.1 Automatic Valves
     6.6.2 Manual Valves
6.7  References


7.1  Importance of Proper Construction
7.2  Design Methods
7.3  Terrace Configurations
     7.3.1 Conventional Terraces
     7.3.2 Step-Up Terraces
     7.3.3 Back-to-Back Terraces
     7.3.4 Step-Down Terraces
     7.3.5 Transitions
7.4  Drainage Channels
     7.4.1 Design
     7.4.2 Runoff Computation
     7.4.3 Channel Types
     7.4.4 Avoiding Erosion Problems
7.5  Land Grading
     7.5.1 Rough Grading
     7.5.2 Topsoil Handling
     7.5.3 Final Grading
7.6  Supervision and Acceptance
7.7  References


8.1  Function
8.2  Selection
     8.2.1 Objectives
     8.2.2 Grass Types
  Reed Canary Grass
  Bermuda Grass
  Nurse Crop
     8.2.3 Combining Grass Species
8.3  Planting
     8.3.1 Density
     8.3.2 Scheduling
     8.3.3 Soil Preparation
     8.3.4 Seeding
     8.3.5 Sprigging
8.4  Vegetation Development
     8.4.1 Start-up Irrigation

            8.4.2 Initial Management
       8.5  Erosion Control
       8.6  References






BOD_ Fraction Remaining versus Distance Down
Slope with Screened Raw Wastewater                81

BOD_ Fraction Remaining versus Distance Down
Slope with Primary Effluent                       82

Recommended Storage Days for Overland Flow
Systems                                           90

Alternative Sprinkler Configurations for
Overland Flow Distribution                        98

Types of Overland Flow Terraces                  103

Types of Drainage Channels                       106




Suggested Overland Flow Design Ranges             75

Summary of Overland Flow Distribution Methods     95

Suitable Overland Flow Grasses                   113

Seeding Density for Overland Flow Systems        116

                  PART I.   RAPID INFILTRATION

                           CHAPTER  1

1.1  Background

Rapid infiltration (RI)  is a ,very successful and cost-effective
method for wastewater management.   RI  systems  can be designed
for wastewater treatment;  or as  one  component in a waste re-use
plan involving recovery of the treated water and/or - storage in
an aquifer.   Municipal RI systems have  been in  successful
operation in the  United States  for  up to  100  years.   In 1981
there were about 320 municipal RI systems in the United States,
either operating or under construction.  Some 30  percent of
these systems have been implemented  since 1971.

The  concept  depends on a  relatively high rate  of wastewater
infiltration into  the soil  followed by  rapid percolation,
either vertically  or  laterally,  away from  the  application
point.   The  best  soils  are relatively coarse  textured,  with
moderate to  rapid  permeabilities.   In  practice,  wastewater
application rates have  ranged from  about 15 m/yr  to  120 m/yr
(50-400  ft/yr)  for  successful RI systems.  For contrast,  the
typical  loading on an  agricultural  system using  wastewater
might  be 1 to  2  m/yr  (3-6  ft/yr)  and the  maximum  loading
typically permitted for an  on-site septic  tank  leachfield
system is about 29 m/yr (95 ft/yr).  Figure  1-1  compares the
actual hydraulic  loading  at several successfully  operating RI
systems to the design range recommended by the 1981 Technology
Transfer Process Design Manual [1].

The  operational  context for  RI systems is  typically earthen
basins   designed    for   a  repetitive   cycle  of  flooding,
infiltration/percolation,  and  drying.  The wet and  dry periods
designed for  these cycles  are  a  function of wastewater and soil
characteristics,  climatic conditions,  and treatment  goals.  The
percolate from cyclic RI  systems  is  typically  suited  for
indirect re-use for many  purposes.   If this percolate emerges
in an  adjacent  surface  water  it should be of  a high quality,
equivalent to  that obtained with complex  and  costly advanced
waste treatment (AWT) systems.

1.2  Objective and Scope

The  Manual [1]  includes basic criteria  and information on the
design,  construction and  performance  of  municipal RI systems.
A large  number of  successfully operating systems have been
designed  using  the  Manual  [1]  (and/or  its  first  edition

                            Range Suggested
                                            for Design
             0.2   0.5   1.5     5     15    50
   Effective  Hydraulic Conductivity of  Soil (cm/hr)
Locations: A-Pilot Basins, Phoenix, AZ
      B-Lake George, NY
      C-Ft. Devens, MA
      D-Boulder, CO
      F-Corvallis, MT
      G-East Glacier, MT
      H-Jackson, WY
      I -Eagle, ID
                         FIGURE 1-1

                             TABLE  1-1
Ground Water
Layers or zones of less permeable
soils not revealed during site
investigation which impede water

Field testing conducted at  dif-
ferent location or different
depth than the final system, so
design may be based on inappropri-
ate data.
Unexpected high seasonal ground
water table which Interferes with
subsurface water movement.
Inadequate capacity to move water
away from the site later-
ally or vertically in the time
allowed by design.
Final surface layer in infiltra-
tion area contains significant
clay or silt.  These "fines" may
segregate during flooding, re-
settle on the surface 'and impede
future water movement.
The subsurface flow from one
basin influences the capacity
of an adjacent basin.
Design Assumptions
Less than design capacity for
water movement because back-
fill operations have reduced
soil permeability (see related
note under Construction).

Actual wastewater characteristics
(algae, suspended solids) differ-
ent than assumed.

Design based on improper use of
criteria or inadequate infil-
tration measurements.

Design ignores potential for
freezing during winter oper-
ations in cold climates.
Excess traffic and inadvertent
compaction of final basin

Failure to remove all of fine
soils in surface layers or zones
of unacceptable soils.

Construction activity in the
basin area when soil moisture
is too high.

Rainfall sorting of fines into
layers of low permeability during
fill operations.

Inadequate specifications for
earthwork and infiltration surface

published  in  1977).    However,  there  are  a  few  recently
constructed  systems,  in a  variety of locations  in  the United
States,   that  are   not   meeting  all   design   expectations,
particularly  with  respect  to the  capability  to  infiltrate and
then percolate wastewater  at the  design  rates.   A preliminary
analysis of these  systems  indicated  that  the  observed problems
could be grouped as shown in Table 1-1.

The basic criteria in the  Manual [1]  are  valid and if properly
applied will  result in successful performance.   It  is  not the
intent  of  this   supplement  to  repeat   all  of  that  basic
information.  This supplement provides additional guidance and,
where necessary,  a stronger emphasis  and more specific detail
on critical  aspects so that the problems listed in  Table 1-1
can be avoided in  future designs.  In addition, this supplement
presents information  developed since  1981 on  performance of RI
systems with respect  to nitrogen removal,  organics removal, and
the need for disinfection.

1.3  References

 1.  U.   S.   Environmental  Protection   Agency.     Technology
     Transfer Process Design  Manual  for Land  Treatment  of
     Municipal Wastewater.  EPA 625/1-81-013.  U.  S.  EPA,  Center
     for Environmental  Research  Information, Cincinnati,  OH.
     October 1981.

                           CHAPTER  2
2.1  General

The -basic  procedures  and  criteria  for  planning   and   site
selection are described  in detail in  Chapter  2  of the Manual
[1] and can also be found in other sources [2,  3,  4,  5].

2.2  Preliminary Screening

The initial procedure to identify suitable sites can be a  desk
top  analysis  of  existing  information.    Numerical  rating
procedures are  described in references  [1,  3,  4] and  include
consideration of soil  and ground water conditions,  grades,
existing  land  use,  and   flood  potential.    However,   the
procedures  in the Manual  [1]  do not  take into  account  the
economic factors related to pumping  from the community to  the
RI site.

       2.2.1  Land Area  Requirements

At the  planning stage  it  is necessary  to  make a preliminary
estimate of  the  land  area  that will be  required  for  the
treatment portion of the RI system using Equation 2-1  (the
basic equation is in  the Manual [13, but is modified here  for
the operating period).
A =  .(.1^9 HOI
where:   A = field area for treatment,  ha
         Q = design daily flow,  m /d
         L = annual design percolation rate,  m/yr
         P = period of operation,  wk/yr

Since  RI systems  typically  operate  on a year-round basis,
Equation 2-1 usually becomes:
                       _  (0.0365HQ)
                       ~      (175

 Figure  2-3  in  the   Manual  [1]  relates   the  clean  water
 permeability of the most restricting  layer  in the soil profile
 to the design wastewater percolation  rate.   That figure can be
 used to estimate the  L value for use  in  equations 2-1 and 2-2
 above.   Figure  2-3 in the  Manual [1] is only  valid for these
 preliminary estimates and is not intended for final RI designs.
 The Manual Ql]clearlystatesthisprecaution,butTts mis-use
 for final  designs has resulted in problems.

        2.2.2  Economic Factors

 Table 2-1  summarizes  the  economic rating factors  [4]  that can
 be used in  conjunction with  the technical  factors  already in
 Chapter 2 of the  Manual  [1]  to evaluate  the influence of
 distance  and elevation on  site suitability.   Both  pumping
 distance  and  elevation  difference  can  have  a  significant
 influence   on  cost-effectiveness  of  site  development.    In
 general,  a site within 10-12  km (6-7 mi) of the community may
 still be competitive with other alternatives.
                            TABLE  2-1
Rating Value
Distance from wastewater source, km

              0- 3
              3- 8
              > 16

Elevation difference,  m

              < 0
              > 60
km x 0.6214 = miles
 m x 3.281  = ft

2.2.3  Regulatory Factors

Although the percolate  from  RI  systems is of high  quality,  it
may not in some cases satisfy all  factors  i  state ground water
quality requirements.   In  these  situations,  there are  two
        Design  for  percolate  recovery,  via  underdrains
        wells, for subsequent re-use or surface discharge.
        Demonstrate via  a hydrogeological survey  and analysis
        that all of the  percolate  will emerge as  base  flow in
        an  adjacent  surface water  or otherwise not  adversely
        impact the in situ aquifer.

       2.2.4  Site Characteristics

Special emphasis is necessary on site topography, and soil type
and soil uniformity as  indicated by  the  soils  and topographic
maps.  Extensive cut and  fill  can  significantly increase costs
for RI construction. Thus,  sites with significant  and numerous,
changes in  relief  over a small  area  are not the  best  choice.
As described in greater detail in  Section 3.3.6,  a significant
clay  fraction  (>10%)  in  the soil  would generally exclude RI
construction on  fill  using  such  materials.   Therefore,  sites
with that type of soil and a topography that would require fill
construction are usually eliminated during  the preliminary
screening process.   Extremely non-uniform soils over the site
area do not absolutely preclude  development for an  RI  system,
but they significantly increase the cost and complexity of site

Most of the common  field  tests are only valid for a relatively
small area  or shallow depth.  Where extreme soil variability is
shown on the soils maps, it  is generally best to consider other
sites.  The alternative may be to construct a large-scale pilot
cell to define  the  hydraulic characteristics of the  site.   If
the  tests   are   successful,  the  pilot  cell  can   then  be
incorporated into the  full-scale system.   The layout  and
construction of  the remainder  of the system then requires
special  care  on   the  part  of   the   designer  and  careful
coordination with those responsible for construction.

2.3  Site Selection

It  is  costly to  conduct the  extensive  field investigations
required  for  a  final  design  at   multiple  sites.    It  is
appropriate to make  a  final screening  and  numerical  rating of
sites to verify feasibility for  a  single site,  or  to determine
which of  several  sites should be  the focus of  detailed field
investigations.  Procedures  discussed in Section 2.2  above can
be used for this purpose.

2.4  References

 1.  U.  S.  Environmental  Protection Agency. Technology Transfer
     Process  Design Manual  for Land Treatment of Municipal
     Wastewater.   EPA 625/1-81-013.  U.  S.  EPA, Center for
     Environmental  Research   Information,   Cincinnati,   OH.
     October 1981.

 2.  Reed,   S.  C.  Design,. Operation and  Maintenance of  Land
     Application  Systems  for Low  Cost Wastewater  Treatment.
     In:   Proceedings  of Workshop on  Low  Cost Wastewater
     Treatment.  Clemson University, Clemson SC. April 1983.

 3.  Ryan,  J.  R. and R. C. Loehr.   Site  Selection Methodology
     for the Land Treatment of  Wastewater. USACRREL  SR  81-28.
     U.  S.  Army Corps of  Engineers,  Cold  Regions  Research and
     Engineering Laboratory, Hanover, NH.  November 1981.

 4.  Reed,  S.  C. and R.  W. Crites.   Handbook  of Land Treatment
     Systems for Industrial and Municipal  Wastes.   Noyes  Data
     Corp.,  Park Ridge, NJ.  1984.

 5.  U.  S.  Environmental  Protection Agency. Generic Facilities
     Plan for  a Small Community:   Stabilization Pond,  Land
     Treatment,  or Trickling Filter. FRD 26.  U. S. EPA,  Office
     of  Water  Program  Operations, Washington,  D. C.   September

 6.  Large,  D.  W.  Land Application of Wastewater and State
     Water   Law,  Vol.  I  and Vol.  II.    U. S.  Environmental
     Protection  Agency.  EPA 600/2-77-232 and EPA 600/2/78-175.
     U.  S. EPA,  Office of Water Program Operations, Washington,
     D.  C.   August 1978.

                       SITE INVESTIGATION
3.1  General

A  basic requirement for  all engineering designs  is that  the
procedure will be used with valid data and information.   For RI
systems, that information comes from a properly conducted field
investigation, coupled with  the careful interpretation ' of  the
field  data  by the designer.    Inadequacies  in these two areas
are  the most common  factors associated with problems in  RI

Problems that should not  have  arisen are listed on  Table  1-1.
These  problems can  be  avoided,  and  it  is  the purpose of  this
section to provide additional guidance and detail  to assist  in
RI  site investigation.    Several  .requirements deserve  special

     . It  is essential   for the  final field  testing  to  be
       conducted on the actual site  and at the actual depth  in
       the soil profile intended  for the  RI  system.   A  series
       of tests may,  therefore,  be  required  as  the design  is
       refined and  the final  basin  configuration determined.
       Extrapolation of  data  from  nearby  sites  is  not  an
       acceptable basis for design.

     . Field  investigation  and   testing  can  be  expensive.
       Cost-effectiveness  and reliable results  are  only  insured
       if the investigative program is planned and  conducted  by
       persons familiar with  soils and ground  water testing,  as
       well  as  having  a  complete  understanding of  the  RI
       concept and the design expectations regarding water

     . Interpretation  of   field  test  results  also requires
       competence  in  soils,  hydrogeology,   and  a thorough
       understanding of the  RI  process.   If suitable in-house
       expertise   does  not   exist,   outside   assistance   is

3.2  Site Evaluation

The first step in the site investigation involves  confirmation
of the feasibility of RI for the  selected  location.   These
procedures  are in  addition to the  screening and  selection
guidance  presented  in Chapter 2.   Several  components  are
included in this  more detailed phase of the evaluation:

Field  examination of exposed  soil  profiles  (on  and
near the site) to include road cuts,  borrow pits,  and
plowed fields.

Field  observation of ground  water  indicators:    Wet
spots, seepage  areas,  vegetation changes,  ponds  and
streams,  and general drainage characteristics such as
standing water after rainfall.

Backhoe test pits, to a  3 m  (10  ft)  depth where  soil
conditions permit,  in  the major soil types on  the
site.  Soil  samples  from critical  layers  (especially
the  layer being considered for  the  future basin
surface)   are  collected  and  reserved  for  future
testing.    Ground water seepage  into the  pit  is
observed  and   the   highest  water   level   obtained
recorded.    Where ground water is   encountered,  a
temporary water  level observation tube  {5 cm (2  in.)
PVC  pipe  with   diagonal  hacksaw  slots}   can   be
installed as the pit is backfilled.

The water level  in  any on-site or adjacent  wells  is
recorded,  in addition  to data  from  any  observation
tubes  installed as  part  of step   3  above.    The
elevations for  all  of  these  observation  points  are
obtained,  as well  as  the elevations of adjacent
surface waters,  and a  preliminary  water table  map
prepared.  , The  evaluation  of these  data includes
consideration  of potential   seasonal  high  water

The  data  obtained  from  steps  1-4  above  allow
preliminary definition  of:

a.  General hydrological setting
b.  Soil  descriptions and water table locations
c.  Proposed soil layer for RI basins
d.  Flow direction,  depth,  and  discharge areas  for
    ground Water and the re-charge  characteristics
    for the site
e.  Possible site modifications including fill  or
    excavation,   underdrains,  or  control  of  natural
    ground water flow

Evaluation of the data  in step  5  results in one  of
three conclusions for the site:

a.  Site  is suitable; proceed with  further detailed
    field  testing.

b.  Site  may be  suitable  with modifications;  proceed
    with   additional  field  testing   and   analysis.

           c.  Site is  unsuitable  for  RI due to  factors not
               revealed  in   preliminary  screening   and   site
               selection;  no  further  testing or  analysis  is

      7.    Ground  water samples  are taken at  a  later  stage  of
           the  detailed site investigation  and analyzed for
           chemical  and biological  constituents to  establish the
           background  characteristics  of the aquifer.

3.3   Soils Investigation

The  soils  investigation  includes  field and  laboratory testing
and  observations  based  on borings and test  pits.    Table 3-1
summarizes  the   factors   that  are   included  in   the   field
description of  all  soil  samples  obtained  from test  pits and
                             TABLE   3-1

     Estimate of percent cobbles,
     gravel, sand, and fines

     Plasticity of fines
     Major textural class

     Soil color

     Wetness and  consistency

     Structural characteristics
     stratigraphy, and geologic
                                       Influences permeability
Permeability and influence
on cut or fill  construction


Presence of minerals,  indi-
cation of seasonal groundwater

Drainage characteristics

Ability to move water  verti-
cally and laterally.

3.3.1  Soil Texture

It is obvious  from the  list  in  Table  3-1  that some  prior  soils
experience  is  essential  for an  effective  and accurate  field
description of soil samples.  Table 3-2 gives an  indication  of
soil type  and  texture based on  its  feeling  and  appearance  in
the field.

A moderately  coarse-textured soil is  the best choice  for RI.
The field  investigator  still looks for layers or  lenses in the
soil profile that could restrict water movement.   Fine-textured
soils,  and even  sandy  soils with a  significant  silt or  clay
content (>10%), are not desirable.  Soils  in this  category tend
to have  relatively low in  situ permeabilities.   In  addition,
the remolding of clay during construction  activities for either
cuts or  fills  can reduce the  permeability to an unacceptable
level  C3].  Figure  3-1, a  typical  density versus moisture
content  plot  for a  clayey soil,  illustrates   this  loss  of

Point A  on the lower curve might represent typical in situ
characteristics in the  soil  profile.   Point  A1 represents the
possible results of construction  activity when higher  moisture
contents  might prevail.   As  shown by the  figure,  the soil
density of A1  is  essentially the same as at point A, but the
permeability has been  reduced by an  order of  magnitude by the
remolding of  the clay.    If  the  site  topography  requires
placement  of fill for infiltration surface construction, clayey
soils are  not recommended.    Experience has  shown  that clayey
sands and  clays exceeding 10% were not successful when  used  in
fill construction  for the infiltration surfaces  in RI basins
C3].  Clayey material can also be a problem for basins entirely
within cut sections and when used as  fill  material for dikes  or
embankments.  These aspects  are discussed  in Chapters 4 and 5.

3.3.2  Soil Structure

Soil structure refers to the aggregation  of soil particles into
clusters of particles called peds.  Well  structured soils with
large voids between peds will transmit water  more rapidly than
structureless  soils of  the  same texture.    Fine-textured  soils
which are well structured, with strong peds, can be  used for  RI
systems.    Field investigation of  such sites  require testing  to
insure  that  the  soil  structure will  not  be   destroyed  by
application of wastewater.  Structure, is best  observed and
evaluated  in the sidewalls of a test  pit.

                                  TABLE  3-2
             Feeling and Appearance
Dry Soil
Moist Soil
Sand       Loose, single grains which
           feel gritty.  Squeezed in
           the hand, the soil mass
           falls apart when the pres-
           sure is released.

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

Loam       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.

Silt       Aggregates are firm, but may
Loam       be crushed under moderate
           pressure.  Clods are firm to
           hard.  Smooth, flour-like
           feel dominates when soil is

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

Clay       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.
                       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 with-
                       out breaking.  Slight tendency
                       to ribbon between thumb and
                       forefinger.  Rubbed surface has
                       a broken or rippled appearance.
                       Case can bear much handling
                       without breaking.  Pinched be-
                       tween 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

                       Casts can bear considerable
                       handling without breaking.
                       Forms a flexible ribbon be-
                       tween thumb and forefinger
                       and retains its plasticity
                       when elongated.  Rubbed surface
                       has a very smooth, satin feel-
                       ing.  Sticky when wet and easily





                                                I	I
                        10          \2         14

                         Moisture Content (%)
              Point A: Density=2000 kg/m3, Moisture=9%, k=2 x 10'8 cm/sec

              Point A': Density=2000 kg/m3, Moisture=13.5%, k=2 x 10'9 cm/sec
                            FIGURE 3-1


     3.3.3  Soil Color

The color and  color  patterns  in a soil  profile  are a good
indicator of the drainage characteristics of  the soil [4].
Reds,  yellows,  and yellow  browns are  representative of well
oxidized   conditions;    an   indication   of    well-aerated,
non-saturated soils.  More  subdued shades  and grays  and  blues
predominate  if  insufficient oxygen  is  present when  saturated
conditions   prevail.      Imperfectly  drained  or   seasonally
saturated soils  show  alternate  streaks or pockets  of oxidized
and reduced soil  elements.   This  condition is  termed soil
mottling.   The  observation of  mottled soils  in the  test  pit
walls is evidence of saturated conditions at that level at some
time in the past.

Some  color  photographs  of  soil  mottling  are  included   in
reference [2].   Experience  is  still  required  for  accurate
interpretation  since  some  mottling  may  have   occurred   in
geological time and may have no reference to the  current status
of  the  soil  profile,  or mineral or organic  stains may  be
mistaken  for mottles.   However,  any mottles  are  suspect  and
should  be taken as a preliminary indicator  of  seasonal high
ground water conditions.

     3.3.4  Field Procedures

Field procedures  for  soils investigations include  borings  and
test pits.  The practical depth for most test pits is about  3 m
(10 ft),  so borings are required for deeper exploration and  for
confirmation in  the  areas between test  pits.   Samples  are
obtained  from borings for soil identification and undisturbed
samplings when necessary for physical and mechanical testing.

  Test Borings

Locating test  borings  in the areas  of the site  that  are
actually to be used for RI basin construction is  essential.   At
least one boring is recommended in every major soil type on  the
site. With generally uniform conditions,  one boring for every 1
to  2 ha (2-5 ac) for continuous  areas of  up to 20 ha (50  ac)
would suffice for large scale systems.   Small scale systems  ( <5
ha) should consider 4-6  shallow borings  spaced over the entire
site.  All borings typically penetrate to below the water table
if  it is  within 10 to 15 m  (30-50 ft) of the ground surface.  A
few borings  should extend  all  the  way  through the  saturated
zone, if  possible,  to define  the thickness of the aquifer  for
use in  subsurface flow calculations.  The drilling methods_most
commonly  used are hollow stem augers and  wet  rotary drills.
Other methods include jetting and churn drilling.  Soil samples
are obtained from all borings using  a  5  cm (2 in.) split-spoon
or  similar device.  Recommended sampling intervals are:

          Borings for monitoring wells;  spoon  samples  at  1.5 m
          (5 ft) intervals

          Borings  for  soils  investigations;  spoon  samples,  2
          each per  1.5 m  (5 ft),  down to 6 m  (20  ft)  then one
          per 1.5 m  (5 ft) thereafter.

The blow counts  to drive  the  sampling spoon  are  recorded for
each sample.  The count for  the  final 30 cm (12 in.) is termed
the standard penetration test  and is used to evaluate  soil
density.  Visual  soil  descriptions of each sample are  made in
the field and samples preserved  in plastic bags  for  chemical
and mineralogical  analysis.   If a  dry  drilling  technique  is
used,  the position of the water  table is observed prior to
closing the hole.  Where soils are relatively uniform in depth,
it is possible to obtain  spoon samples and  undisturbed samples
alternately  from  the same  boring.    When  the   profile  changes
significantly with  depth,  a second boring,  within 3 m  (10 ft)
of the first, is recommended for undisturbed samples to insure
sample continunity.  One  set of undisturbed samples for  every
10 ha (25 ac) of RI basin area is usually sufficient.

An 8 cm  (3 in.) thin wall  Shelby tube is pushed at least  30 cm
(12 in.)  into each  major  soil unit  identified for undisturbed
samples.  At least one tube per  boring  is recommended if the
soil is uniform (isotropic and continuous) and  a maximum of one
tube every 1.5 m (5 ft) above the water table.   The ends of the
tube are  sealed and transported  in an upright  position to the
laboratory for analysis.   It may not be possible to obtain tube
samples from gravelly sands, and loose,  dry, coarse  sands.   In
these cases, a test pit will be necessary.

  Test Pits

Test   pits   are   strongly  recommended   for    all   RI   site
investigations,  since, unlike  borings, they permit  the  direct
observation  of  a relatively large  portion  of  the  subsurface
profile.   Two  or  three  test pits  would  be  considered  the
minimum on even the smallest site.   The various soil  layers can
be  visually  identified   and   the   presence  of   fractured
near-surface rock, hardpan, mottling,  layers or lens of gravel
or clay,  or other anomalies  can  be recorded.  If  the  pit
extends into the ground water, it  can also be  used for  in situ
measurement of hydraulic conductivity  (see Section 3.5).

Soil texture is described  for  each  layer using the  procedures
described in  Section 3.3.1.   Soil  structure  can be  examined
using  a  pick,   or  similar  device,  to  expose  the   natural
cleavages and planes of weakness  in  the profile.   Color  and
mottling can also be observed in the pit wall.   One  end of the
backhoe pit  can be  excavated on a gentle incline.  Following
identification of the soil  layers, benches can be  excavated by


hand at appropriate  levels  to expose undisturbed soils  for  in
situ testing.   These  tests include  in-place  dry density  and
field  or oven-dried moisture content  and, as  described  in
Section 3.5, may include infiltration testing.  Tests  are  made
at  the  depth proposed for  the RI basin  surface  and  at  least
once again, 1 m (3 ft)' deeper  if  the soil is uniform.   Samples
from each  layer are preserved  in plastic bags for  laboratory
analysis and a bag sample of about 40 kg  (90 Ib) of soil at the
proposed    infiltration   surface    collected   for    possible
re-compacted permeability testing in the laboratory.

     3.3.5  Laboratory Procedures

Physical,  chemical,  and  mineralogical tests in the  laboratory
are conducted on the split-spoon and test pit samples described
in  the  previous section.   The minimum  that should be  tested
consists  of the soil  unit that  is  planned for  the  final  RI
basin  infiltration  surface  and  the  soil ' unit  immediately
beneath it.   Composite samples can be assembled  from  the  same
soil unit in different borings or from samples of  the same  soil
unit, if encountered at different depths.  One  set of  chemical
and mineralogical data is  obtained for  each of the  soil  units
tested.   That  would  be  a minimum of  two chemical  and  two
mineralogical tests  (if needed) for  each  10  ha  (25 ac) of  area
intended for use as RI basins.

The  physical testing  of  these samples  include  gradation  and
related procedures  to determine the relative percentage  of
sand, silt, and clay.  The  chemical  tests may  include: percent
organic   matter,   phosphorus,   iron,   manganese,   potassium,
magnesium,  calcium and sodium (exchangeable),  base  saturation,
pH, cation  exchange capacity,  and electrical conductivity (EC).

Mineralogical  tests  are  only  necessary  when  the'  physical
testing indicates the presence  of  clay in the  soil sample.
These  tests are performed on  the less-than-two-micron  size
fraction  to  identify the  clay  minerals.   The analysis  is
typically done by x-ray diffraction.

Additional  testing  for phosphorus adsorption  capacity may  be
necessary in special situations.  Phosphorus may be  a parameter
of  concern for RI in  those cases  where the hydrogeological
analysis  shows that  percolate  will emerge  in an  adjacent
surface water which has stringent phosphorus limitations.   The
Manual [1]  (Section contains procedures for  estimating
phosphorus  removal at  RI  systems.   The  design  equation  in  the
Manual [1]  is based on absolutely-worst-case conditions and,  as
such, is unduly conservative.   The rate  constant  is  the  lowest
possible value, based  on  a  neutral pH.   Most soils  are  either
slightly acidic or slightly alkaline,  and would have  a  higher
rate.  The  equation  is based  on saturated flow  conditions  and',
therefore,  predicts  the  shortest  possible  residence  time  for

 flow from the  basin to the  ground water table.   The  actual
 residence time through  this unsaturated zone will be  much
 longer  and,  therefore, P  removal  will be more  effective  than
 predicted by the equation.

 The  design  example in the Manual [1]  is  also  too  conservative
 with respect  to phosphorus removal  during lateral flow.   The
 example is based  on a most conservative (but  impossible)
 assumption that  the  hydraulic gradient is  equal  to  1  for
 lateral flow,  which again results in the shortest possible
 residence time.  For  example,  if a 10% gradient is  assumed,  the
 0.2  mg/L  P concentration could  be  achieved  in  a lateral
 distance of  20 m (65  ft)   instead  of  the  200  m  (650  ft)
 indicated by the  Manual  [1] (p.5-21).   For the conditions
 specified in that  example,  a  travel distance  of 36 m  (118  ft)
 would be required  for the  phosphorus concentration to approach
 "background" levels (assumed at 0.015 mg/L for  this case).

 If the  calculated concentration  at the distance of concern
 exceeds  specified  limits,  phosphorus  adsorption  tests   are
 performed on the soils through which  the percolate will flow.
 Section  3.7.2  in  the  Manual  [1]  describes these  tests; other
 useful information can be found in references  [6,  7,  8, 9].   It
 is recommended  that the results of the  laboratory  adsorption
 tests be multiplied by a  factor of 5  to account  for the  slow
 precipitation of phosphorus that occurs  over  time in the  soil
 profile [10].

 The  undisturbed soil  samples obtained with the  Shelby tubes are
 tested  for dry unit  weight,  moisture content, and textural
 gradation.  Then,  assuming a  specific gravity of 2.69  (valid
 for  most soils)   the porosity,  void ratio,  and degree  of
 saturation can be calculated using standard procedures [4,  11].
 The   textural   gradations   are  plotted  on   the  standard
 semilogarithmic paper,  and the effective size and uniformity
 coefficients derived  [4, 11].   The same  calculations can  also
 be performed with  results from field  density measurements  in
 the test pits.

 If needed,  laboratory permeability  tests are  conducted using
 the undisturbed samples.  The  basic  procedures  are  described  in
 Soil Science Society of America Journal 46(4):866-880 and ASTM

 The results of laboratory permeability tests are plotted  versus
void ratio on semilogarithmic paper  as shown  in  Figure  3-2. A
 design permeability  for each  hydraulic unit  is  selected near
the lowest end of the void ratio range, as shown on the example
Figure 3-2 and Table 3-3.



.—  O
-O =
O  3
0)  O
       z       r






                             TABLE 3-3
Hydraulic       Permeability       Void Ratio
  Unit        cm/sec      in./h        Range
                       Physical Properties
   K      1.5 x 10
          3-0 x 10
   K      1.0 x 10"
   K      9-0 x 10~4
   K      2.0 x 10
   K-      3.0 x 10~5
21 .26


 1 .42

 1 .27







Medium to coarse sand,
loose, D   0.2-0.3
Fine  to medium sand,
loose, D   0.1-0.1,  less
than  9% fines
Fine  to medium sand,
loose, D   0.1-0.2,
greater than 9% fines

Fine  to medium sand,
dense, D   0.1-0.2

Silty sand,  D  less than

Clayey sand
*These are not general  factors, but are  only valid for the example in
 Figure 3-2

D   is the 10$ soil fraction
 3.3.6  Evaluation  of Soil Test Results

 The results of all  tests  are  reviewed  and  evaluated by an
 experienced  engineer,  geologist,  or  soil  scientist.   This is
 particularly important for  the  chemical and mineralogical  data
 at   sites  where   construction   or operation  may   alter  soil
 reactions or mineral structure (chemical exchange and  leaching,
 cementation, swelling,  etc.).

 If  test results indicate that  a  high percentage of  the  clay is
 montmorillonite,  the relatively high  cation  exchange  capacity
 may result in infiltration problems caused by swelling,  even if
 the total amount  of clay present is small.   Any combination of
 either vermiculities or  montmorillonites  can be  a  problem, if
 the total clay content exceeds  10%.    Soils with  greater  than
 10% clay are  increasingly subject  to  physical changes  and

 chemical leaching,  and  may require  soil amendments  for use as
 RI  application  basins  in  a   cut   section.     As  previously
 indicated,   soils  with  that  much  clay are  not  recommended as
 fill material for infiltration  areas.

 The results of the  field observations and the  laboratory tests
 for physical characteristics are combined and  plotted on a site
 map and on several cross-sections through the  site to provide a
 basis  for  final  design decisions  regarding  basin location,
 water movement, etc.  Figure 3-3 illustrates a typical profile.
I 30
5 20
                      Soil Boring Locations
Distance (m)
                              FIGURE 3-3
                        TYPICAL SUBSURFACE PROFILE

3.4  Ground Water Investigations

Ground water investigations are necessary to determine the
depth to  the ground water table,  the  direction of subsurface
flow, and, in some cases,  to  determine  water quality parameters
for  design  purposes.   The  rate  of   ground  water   flow is
discussed in Section 3.5.   Installation of  at least three wells
is  recommended   during   the   site   investigation.     If  the
preliminary study has identified the general ground water  flow
direction and a tentative location for the RI basins,  then one
well  should be up-gradient,  one in the basin area,  and one
down-gradient on  the  ground  water flow  path near the planned
system boundary.   These  wells can  also  be used later for
operational water quality monitoring.   If little is known about
the area, the three wells are usually spaced in  a  triangle  over
the potential site.  One well per 6-8 ha  (15-20 ac) is usually
sufficient for sites up to 40 ha (100 ac).   The well bottom is
usually between  3 and 10 m  (10-30 ft)  below the  water table.
The lower 1.5 to  2  m  (5-6 ft) of the well  consists of machine
slotted well screen.  A 5 cm  (2 in.) inner  diameter well screen
with  0.25  mm (0.01 in.)  slots is usually satisfactory.   The
bottom of  the hole contains  a medium  to  coarse  sand-pack to
about 1  m (3 ft) above the  well  screen with a bentonite  seal
above the sand pack.  Figure  3-13 in reference  [2] illustrates
a typical shallow monitoring  well.

The  elevation of the top  of  each well  is determined  and the
depth to  ground water in  each  well  periodically observed and
plotted  on maps  and  on  profiles similar to Figure  3-3.  In
general,   the  ground  water   table tends   to  follow  surface
contours  and the flow trends  toward  adjacent  surface waters.
This  may assist in determining location of  the monitoring

It is  strongly  recommended that monitoring wells be installed
prior to the normal "wet" period for the site area and  observed
during this  period  to detect  seasonal  high ground water.   The
use of test pits for detection of  soil mottling (see Section
3.3.3 in this text) is also recommended.

3.5  Infiltration and Permeability Tests

Definition of infiltration capacity and subsurface permeability
is essential for RI system design.  The  infiltration rate is
defined  as  the rate  at  which water enters  the soil  from the
surface.  When  the  soil  profile is saturated,  with negligible
ponding above the surface, the infiltration rate  is comparable
to the effective saturated hydraulic  conductivity of  the  soil
profile  within  the  zone  of influence  for  the tests.   In  both
this   text   and  in  the  Manual   Cl]  the  terms  hydraulic
conductivity  and  permeabilty   are   used   interchangeably.
Definition  of  both  the  vertical  (K  )  and horizontal   (Kh)

permeabilities  in  the  soil  profile are necessary for RI system

     3.5.1  Infiltration Test-Procedures and Evaluation

A number of methods have been developed to measure infiltration
rate or  vertical  hydraulic  conductivity (K ) in the  field.   A
comparison of the  various methods  can  be  fecund in  Table 3-2 in
the Manual [1].   It is the intent  of  each  of  these methods to
define essentially the same parameters, but  their reliability
varies according to individual test conditions.

  Flooding Basin Tests

A flooding  basin  test, with  the test  area  at least 7m2 (75
ft ) is  strongly  recommended  for all RI systems.   Testing the
larger area provides more reliable  data than the smaller-scale
cylinder infiltrometers or air entry permeameters (AEP). A much
larger volume  of  water  is  obviously  required  for  this  test.
The basic procedure is described in detail  in  Section 3.4.1 of
the Manual [1].  For most cases  a  tensiometer  at 15 cm  (6 in.)
and another  at 30  cm  (12  in.)  are  sufficient in  lieu  of the
extensive instrumentation described in the Manual [1].  The use
of  picks  and  shovels  (in lieu  of  special  tools),  and  a
bentonite seal  around  the perimeter  are  also suggested.   The
test  basin   is   flooded   several   times   to   calibrate   the
instrumentation and to insure saturated conditions.  The actual
test,  run is  conducted  within  24 hours  of the  preliminary
trials.  For most  soils with RI  potential,  this  final test run
may require 3 to 8 hours.

Since  it is  the  basic purpose of  the test to  define  the
hydraulic conductivity of the near  surface  soil layers,  the use
of clean water  (with  about the  same  ionic  composition  as  the
expected wastewater) is  acceptable in  most  cases.    There  are
three  major  exceptions  when  the  test utilizes  actual  or
simulated wastewater and/or extends for a longer  period.

         If the  wastewater expected  in the  actual  RI  system
         will have a high  solids   content,   similar  liquid  is
         needed in the test.  High  solids concentrations  might
         come from algae carryover from ponds or from specific
         industrial or commercial components in  the wastewater
         (whey wastes,  pulp and  paper,  food processing,  etc.).
         Such solids clog  the infiltration  surface  and  clean
         water tests would  be  a misleading  basis  for  design.
         In addition,   the  test also extends  for a  sufficient
         period (perhaps  several  weeks)  to model  the actual  wet
         and dry  cycles proposed  for  operation of these RI
         systems.   In  these  situations,  an  appropriate  number
         of standard  flooding  basin  tests  could  be run  with
         clean water to define  the  basic characteristics  of  the

          site.  Assuming that  generally  uniform conditions
          prevail,   one  longer  term test  can then be  run  to
          define  the  influence  of  unique  wastewater  types  on
          infiltration.  The  subsurface flow characteristics are
          still controlled by the clean water K  values in most

      2.   If  the system  is  to  operate  in the continuously,
          flooded "seepage pond"  mode,  it  is best for  a test  to
          simulate that condition for a sufficiently long period
          (perhaps   several months)  to  insure  that  wastewater
          will  percolate  at, expected rates.    The RI  design
          procedures in the  Manual  [1] were  not  intended  for
          permanently  flooded seepage pond designs.  The wet and
          dry periods  described  in the Manual [1]  are intended
          to  restore the  infiltration  capacity  of  the surface
          soils to   near maximum  potential every  cycle through
          bio-oxidation  of  the  filtered  organics.    If  the
          infiltration  surface   is   continuously   flooded,   a
          different  situation prevails  and some other  design
          approach   is necessary and  percolate  water quality
          expectations modified.

      3.   If the borings and related site investigation reveal a
          heterogeneous mixture of soils, a  large  scale RI cell
          {0.5  to 3  ha (1  to  7 ac)}  is  constructed and operated
          as a  pilot RI unit fpr development of design criteria.
          If test results  are appropriate,  the  pilot unit can  be
          incorporated into the full  scale system.

A  minimum of  one basin   infiltration test  on  each major soil
type  in the RI  area is  recommended.   For large continuous
areas,  one test for up  to  10  ha  (25  ac)  of usable land  is
typically sufficient.  The test  is performed on  the  soil layer
j.ntended  for use as the basin infiltration surface in the final
operational system.   Such a requirement seems  self evident,but
it's disregard in the past has resulted in serious problems.

Construction  of RI basins  on  backfilled  material  is  to  be
avoided whenever  possible.   When  construction on  fill  is
absolutely necessary  due  to  site topography,  and if  the  soils
are  within  acceptable   limits  for  clay  content,   a   basin
infiltration test in a test fill area  is  recommended.   The test
fill  is constructed  using  the  same  equipment  and procedures
that would be  used  for  full  scale  construction.  The test fill
should be as deep as  required  by the site  design or 1.5 m  (5
ft), whichever is less.    The top of the fill area  should  be  at
least  5 m  (15 ft) wide  and  5 m  (15  ft) long to  permit  a
standard  flooding basin  test near the  center.   This  approach
was developed, and  used  successfully  to evaluate potential  RI
sites in Maryland [12].

  Air-Entry Permeameter (AEP)

This device was developed by Dr. Herman  Bouwer  [13]  to measure
"point" hydraulic conductivity values in the absence of a water
table.  It has been used in site investigations for a number of
land treatment systems and is described in Section 3.5.2 of the
Manual [1].   The test is useful to verify site  conditions  in
the areas  between the larger  scale flooding basin  tests,  and
also  for  in  situ tests in  the end  wall of  a  test pit  as
described  in  Section  of this text.  An AEP  unit,  used
in this manner can quickly determine the hydraulic conductivity
of all of  the soil layers in  the  profile.  The  device  is not
commercially  available,   but  specifications  and  fabrication
details can be obtained from:

          U. S. Department of Agriculture
          Water Conservation Laboratory
          4332 East Broadway
          Phoenix, AZ  85040
     3.5.2  Permeability Tests
                                         and  horizontal
Definition   of   both   vertical   .                        .
permeability  is  necessary  for  RIV design.     The  vertical
component K  can be inferred from  the field  tests described  in
the  previous  section  or  measured  in  the  laboratory  with
undisturbed soil samples.  Field results are  the  primary basis
for  design  in  all cases.  Laboratory  data  on undisturbed
samples are valuable for confirmation of test basin results and
for   interpolation   for   areas  between   the   field   tests.
Laboratory values  from deeper  soil  borings  also  provide  data
for ground water flow and mounding analysis.

In most soils, 1C  will exceed K  due to soil stratification and
particle orientation.   The relationship for some soils is given
in Table 3-5 in the Manual [1].  The most conservative approach
would be to  assume  that 1C  equals K .  The  direct measurement
of K, in the  field  is  suggested for ^any RI project where there
is a  concern regarding ground water mounding.   A number  of
procedures are  discussed in the Manual [1].   The  auger  hole
test  is recommended  and  complete  details  on procedure  and
calculations  can  be found  in   several  references [1, 10,  13,
14].  A more recent development when the ground water is within
3 m  (10 ft)  of the surface  using a  test  pit  is  described  in
references [15,  16].

3.6  References

 1«  U.   S.   Environmental  Protection  Agency.     Technology
     Transfer Process  Design  Manual  for Land  Treatment  of
     Municipal Wastewater.  EPA 615/1-81-013.    U.  S.  EPA,
     Center for Environmental Research Information,  Cincinnati,
     OH.  October 1981.

 2.  U.   S.   Environmental  Protection  Agency.     Technology
     Transfer Process  Design Manual for On-Site  Wastewater
     Treatment and Disposal Systems.  EPA  625/1-80-012.   U.  S.
     EPA,  Center   for   Environmental   Research   Information,
     Cincinnati, OH.  October 1980.

 3.  Reed,  S.  C.    The   Use   of  Clayey  Sands   for   Rapid
     Infiltration Wastewater Treatment.   USACRREL IR 805.   U.
     S.  Army Corps of  Engineers,  Cold Regions  Research and
     Engineering Laboratory, Hanover,  NH.  December  1982.

 4.  Brady,  J&T.  C.   The  Nature and Properties of  Soil.  8th
     Edition.  MacMillan Publishing Co., New York, NY.  1974.

 5.  U.   S.   Environmental  Protection  Agency.     Technology
     Transfer  Process  Design Manual  for  Land Application  of
     Municipal Sludge.  EPA  625/1-83-016.  U.  S. EPA,   Center
     for  Environmental  Research  Information,  Cincinnati, OH.
     October 1983.

 6.  Enfield,  C.  G.  Evaluation  of   Phosphorus   Models for
     Prediction of Percolate Water Quality in  Land  Treatment.
     In:   Proceedings  of the International  Symposium on  Land
     Treatment of  Wastewater,  Vol.  1.   U.  S. Army Corps  of
     Engineers,   Cold   Regions   Research   and    Engineering
     Laboratory,  Hanover, NH.  August  1978.

 7.  Hill, D. E.  and B.  L.  Sawhney. Removal  of Phosphorus from
     Water by Soil Under  Aerobic  and  Anaerobic  Conditions.
     Journal of Environmental  Quality.  10:401-405.   1981.

 8.  Loehr, R. C.,  et al. Phosphorus Considerations.   In:  Land
     Application of Wastes, Vol 1.  Van  Nostrand  Reinhold Co.,
     New York, NY.  1979.

 9.  Overcash, M.  R.  and   D.  Pal.   Design  of Land  Treatment
     Systems for Industrial Wastes - Theory and Practice.  Ann
     Arbor Science,   Ann Arbor,  MI. 1979.

10.  Reed, S. C. and R.  W.  Cries.   Handbook of Land  Treatment
     Systems for Industrial and Municipal  Wastes.   Noyes  Data
     Corp., Park Ridge,  NJ.   1984.

Terzaghi,  K.  and    R.  B.  Peck.    Soil  Mechanics  in
Engineering  Practice.   John Wiley & Sons, New  York,  NY.

Stein, C. E.  Test Basins in Fill.  Unpublished.  Metcalf &
Eddy Inc., Silver Springs, MD.  May 1983.

Bouwer, H.   Groundwater Hydrology.  McGraw Hill Co.,  New
York, NY.  1978.
U. S. Department of Interior.  Drainage Manual.
Reclamation.  1978.
Bureau of
Healy, K. A.  and  R.  Laak.   Site Evaluation  and  Design of
Seepage  Fields.    Journal  American   Society  of  Civil
Engineers,     Environmental     Engineering     Division.
100(EE5):1133.  October 1974.

Bouwer, H.  and R. C.  Rice.   The  Pit  Bailing Method for
Hydraulic Conductivity  of  Isotropic or  Anisotropic Soil.
Transactions  American  Society of  Agricultural Engineers.
Vol. 26.5, 1435-1439.  1983.

                            CHAPTER  4
 4.1  General

 The basic design procedures in the Manual [1] are still valid,
 so this Chapter only provides additional detail and a stronger
 emphasis on  certain critical  aspects.    Significant advances
 have been made  in  computer sciences in  recent  years  and most
 designers  now  have  access  to  at  least  a  microcomputer.
 Information on the  continuing  development of computer models to
 solve some  of the problems encountered in RI system design can
 be obtained from:

          Holcomb Research Institute
          International Ground Water Modeling Center
          Butler University
          Indianapolis, Indiana  46208

 Determining the design annual  hydraulic  loading  rate  is  one of
 the  most  critical aspects  of RI system design.  The operational
 cycle _(wet/dry periods)   is  another important  factor  and is
 determined  independently.    Combining the annual loading and the
 wet/dry  cycle then  determines the  unit  wastewater application
 rate.  Details  on these factors  are presented  in this  chapter.
 Some   of ^ the  discussion   may  seem  self-evident or  overly
 simplistic,  but a  review  of  problem systems  indicates  that
 these  factors and their inter-relationships may not always have
 been  clearly  understood in  the past.

 4.2   Hydraulic  Loading Rate and Basin Area

 The hydraulic loading rate  is based directly upon the  field and
 laboratory  test  results   for  infiltration,  permeability,  and
 hydraulic conductivity.  Figure 2-3 in the Manual [1]  indicates
 the  general relationship between these factors.  That  figure is
 not  intended  for final design of RI systems.

 If the site investigation  reveals a specific layer of  soil that
 will restrict  flow, the  design  is based  on  the  hydraulic
 conductivity  of that layer regardless  of its  thickness.    In
 many  cases  with a near surface  deposit  of  silts or clays,  it
 may  be cost-effective to remove  the  restricting  layer  and
 locate the  infiltration surfaces  in the underlying soils.   If
 there is not an obvious  restricting layer,  the "effective"
hydraulic conductivity of  the profile is  the mean (arithmetic,
harmonic, or  geometric)  of the values observed (see Section 3.5
 in the Manual [1] for procedures).   A  small percentage of  this

"effective"  hydraulic conductivity is then taken  as the design
loading  rate.   The  percentages used  are based  on historically
successful    RI   performance    and   allow    for   wastewater
characteristics,   soil  reactions,  and   the   need  for  cyclic
operation.   A  further refinement was  added in the Manual Cl] to
allow for a higher  design percentage  for the most  reliable
field  test  procedures.   If  a very  large pilot scale  cell is
constructed and actual wastewater  is  used and applied for
several  months, then test results could  be  used  directly for
design with  little  or no modification.    However, most  of the
commonly used test  procedures require  the adjustments  (safety
factors)  summarized in Table 4-1.
                            TABLE 4-1
      Test Procedure
Adjustment Factor for Annual Loading Rate
  Basin flooding test

  Air entry permeameter and
  cylinder infiltrometers

  Laboratory permeability
     10-15$ of "effective" rate  observed

      2- 4$ of "effective" rate  observed

      4-10$ of "effective" rate  observed,
      or of restricting soil layer.
The hydraulic conductivity defines  the amount  of clean water
that can move  through a unit cross-section  in the soil, at unit
gradient and under saturated  conditions.   For example,  a soil
with an  "effective" vertical conductivity of 5 cm/hr  (2 in/hr)
could  transmit  438 m  /yr (116,000 gal/yr) of  water  through
every 1m   (11 ft ) of horizontal area:

     K  =  5  cm/hr
     hydraulic gradient =  1, because  of saturated  vertical flow

      Clean Water Rate, L
(5  cm/h)(24 h/d)(365  d/yr)(1 m2)
            (100  cm/m)
          =  438 m3/yr  (10,800 gal/yr ft2)

 The loading can also be expressed in terms of  a  depth  of  water
 on a unit area because of  the dimensions  involved,  so:
                 1 m
                        = 438 m/yr (1,437 ft/yr)
 An annual ^ basis  is used  for the  loading  rate  determination,
 since it is  assumed that  wastewater  will  be  applied  on  some
 sort of regular schedule  throughout  the  year,  although the
 specific wet/dry cycle has  not been determined  at  this point in
 the calculations.

 Assuming for the example above,  that basin flooding tests  were
 used  to  determine K  on  a site with deep and uniform soils, it
 would be appropriate to adopt a  factor of  10%  from Table  4-1,
 to determine  the  design  loading rate:

      Annual Wastewater Loading, L
          L T =  (0.10)(clean  water-rate, L  )
            ™ =  (0.10)(438)               cw
              = 44 m/yr  (144  ft/yr)

 It is,  of  course,  possible  to divide  this annual  loading by
 some  other  time  unit and produce  the apparent  "average" weekly
 or daily loading.   In  earlier texts this was  done to provide a
 basis for comparison with the  loading rates  for other  land
 treatment  concepts.   The actual  unit application rate  is not
 derived  in this manner?   Confusion on  this  point has  led to
 problems.   The  10%,  or other safety factors,  are  only  used to
 determine the annual hydraulic loading. It is  not appropriate
 to  adjust  either  Ky or K^ with these factors for  shorter  time
 periods.   Such adjustments do  not  define  the  unit rates for
 infiltration or subsurface flow (see Section 4.2.4 and 4.3).

 Determination  of the  annual  loading  rate is  in  effect  a
 definition of the capacity  of the  site  to  transmit  wastewater
 if  applied  at some undefined, but  regular  schedule  throughout
 the year.   Most RI  systems do  operate  on a  year-round  basis.
 However,  if  some  winter  storage  is  required by the  regulatory
 authorities or there are  seasonal constraints  on operation, the
 annual loading  is  proportionally  reduced to  account  for the
non-operating period.  System operation planned  for nine  months

per year for the sample case would  reduce  the  "annual"  loading
proportionate ly :
                     ^X44 m/yr) = 33 m/yir (108 ft/yr) .
In  some  cases  the  hydraulic   loading   is   limited  by  the
capability to move water away  from  the  application site due to
shallow  confining  layers  or  a  small  hydraulic  gradient (see
Section  4.3.1 in this  text and Section  5.7.1  in the  Manual

     4.2.1  Land Area Required

The required application area  for RI systems  can- be determined
with equations  2-1  and  2-2.   The  area calculated  with these
equations is the  surface area that is  needed for infiltration
in the final system.  There have been cases where the earthwork
design has  allowed  encroachment  for dike  construction  on this
area.   The completed system  in these  cases  has significantly
less than the required infiltration area.

     4.2.2  Wet/Dry Ratio

A  regular  drying  period  is   essential  for  the  successful
performance of RI systems.  The  period required for drying is a
function  of   the   solids  and   degradable   organics  in  the
wastewater and of the climatic influences on aerobic reactions.
The  ratio  of  loading to drying  periods within  a single cycle
for  successful RI  systems  varies,  but  is almost  always less
than 1.   For  primary effluent,  the ratios   are  generally less
than 0.2 to allow for  adequate  drying.   The  ratio  varies for
secondary  effluents in  relation to  the  treatment  objective.
Where maximum  hydraulic loading  and/or  nitirif ioation  are the
objective, the  ratio might  be  0.2 or less.   When nitrogen
removal  is  necess.ary  (see  Section 4.8.2)  the  ratio ranges from
0.5  up to  1.0 12].  Table 5-13 in  the  Manual [1] presents
suggested   hydraulic   loading/drying    periods,   related   to
wastewater  type,  treatment goal, .and climatic season.   In all
cases, to  avoid  excessive  soil clogging,  the hydraulic  loading
period  for  primary,  or  similar,  effluents does  not exceed 1-2
days regardless  of  season  or  treatment  goals.  As discussed in
Section  4.2.4,  additional  time  may be  needed for  all  of the
wastewater  to  infiltrate.

     4.2.3  Application  Rate

The  selected  wet/dry  cycle  is combined with the  "annual"
hydraulic  loading to  determine the  unit application rate.  The
procedure  is   more  complex when different wet/dry  cycles are
                              .  31

 selected  for  summer and winter operations;  an example is given
 Assume:  design  flow = 800  m /d; soil K   =5 cm/hr,  use 9%
 adjustment  factor;  so:  annual hydraulic  loading = 39 m/yr  (128
 ft/yr)  treatment  goals with  primary effluent  are  to maximize
 loading rates, so,  from Table  5-13 in the Manual  [1]:
Summer period  (April - Oct, 214 d)

Winter period  (Nov - March, 151 d)
     Summer period, each cycle = 9 d

            Cycles per season =
    = 24 cycles
     Winter period, each cycle = 14 d

            Cycles per season = —
     = 11 cycles
       Total cycles per year =35
Assuming the  wastewater has similar characteristics  all  year,
the amount applied per  cycle is  the  same  and the summer/winter
drying periods relied on for restoring the infiltration rate.

If the  wastewater has special seasonal  characteristics  (e.g.,
high solids for seasonal industries, etc.) it  may be  necessary
to allow for extra  drying time (or reduced  loading) during
those special periods .

       Wastewater loading per cycle

         =    39  (m/yr)
            ~35 (cycles/yr )
         =  1.1 m/cycle (3.6 ft/cycle)

       Application rate (R) during 2 day wet period
            R  =
                    2 d/cycle
=0.56 m/d
   (1.8 ft/d)

Since  in   this   example  the  wastewater   flow  is  constant
year-round,  and  no storage  is  provided, a  greater  land  area
will be  needed  during the winter  months to maintain  the  same
loading rate.  Using a variation of equation 2-1:
  Summer period,
  A =
                  (800 nr/d) (214 d)
       (1.1 m/cycle)(24 cycles)(10,000 m /ha)
  Winter period,
  A =
                   (800 m /d)(151 d)
       (1.1 m/cycle)(ll cycles)(10,000 m /ha)
                                0.65 ha
                                (1.6 ac)
                                1.0 ha
                                (2.5 ac)
The winter period  would  control the design in this  case.   The
total area needed  is divided  into  multiple  basins.   Table 5-14
in the  Manual  [1]  suggests the number of  basins  required for
various wet/dry ratios.
     For this example, use 7 basins
         basin area =
= (1'°
                                      2 ,.
                              (10, OOOm^ha)
                    = 1428 m2 (15,370 ft2)
         could use 38 m x 38 m square basins (125 x 125 ft)

During the summer months,  four  of the basins could be operated
on  an 8-day cycle,  or  five  basins  on  a 10-day  cycle  to
approximate the 9-day wet/dry,  summer cycle recommended by the
design.   This would allow each  one of the  seven  basins  to be
taken  out of service  for maintenance  for  an  extended period
each summer.

The unit application rate  (R) derived for this example was 0.56
m/d (1.8 ft/d) .  That is compared to the effective steady state
infiltration   rate   for   soil   (K )   to   insure  successful
performance.  As a general "rule-of -thumb" the unit application
rate  is  usually less than 50%  of the K   to allow for initial
clogging by wastewater  solids and organdies,  if optimization of
hydraulic loading is the  design goal.   Even if the application
rate  (R)  is  higher,  ponding will  not typically commence until
the later part  of short flooding cycles.   In  either  case, the
depth  of water remaining  in the basin  at the end of  1-2 day
flooding periods will probably  not exceed 0.3  m.   The depth of
ponding  increases as the flooding period is  extended and/or the
concentration of solids in the wastewater  increases.

      4.2.4  Infiltration of Standing Water

 The  design  approach  is  based  on the  assumption  that  all  of the
 applied water will infiltrate during the very early part  of the
 drying cycle  so that  most  of that  period is  available  for
 aerobic restoration of the  upper soil profile.   This might
 require from 0.5 to  2  days,  depending upon the  organic content
 and  volume of  the  dose.    When  the  restoration  of aerobic
 conditions  takes too long, it. may be necessary to  extend  the
 drying period, perform  maintenance on  the  basin  bottoms, or in
 an extreme  case, perhaps remove and  replace a  given  depth of
 the  surface soils.

 It may  occasionally  be  necessary to estimate either  the depth
 of water  remaining  in the basins  at  some time  after  flooding
 has  stopped or the time necessary to reduce the ponded depth to
 zero.  _There are several alternate approaches to this  problem,
 depending upon  whether a clogging  layer has  formed on  the
 surface or not.  If  surface  clogging  does  not  exist,   the
 equation proposed by Stefan [3] is applicable.
          h = h  - 2.22 (l-n)°'35(n)325 K t°-675
               o                         v
 h = depth of water in basin after time t,  cm

h  = depth at end of flooding period (at t=0),cm

 n = soil porosity (decimal fraction)(see Table 4-2)

KV = saturated vertical hydraulic
     conductivity, cm/h

 t = time, h
In  the application of  this  equation,  it  is  important to
remember that the properties n and K  are  values which apply to
the wetting front, hence they will b^e affected by the presence
of microbial  growth  in this  (near surface)  zone  and  are not
equal   to  the   values    which   existed   before   wastewater
applications  began.     Typical  initial   porosity  ranges  for
various soil textural classes are given in Table 4-2.

                           TABLE 4-2
                 POROSITY OF SELECTED  SOILS  [4]
         Soil Type
Porosity (%}
       Silt and Clay

       Fine sand

       Medium sand

       Coarse sand


       Sand and gravel mix

       Coarse glacial till






Based  upon the studies  of  deVries  [26], both porosity and
hydraulic conductivity can be expected to decrease to the range
of  30  to  60  percent  of  their   initial   values  upon  the
establishment  of biological growth  in  the  near  surface soil
profile,  the  larger decreases  corresponding  to  finer textured
soils.   Using n and K   values equal to  50% of the  original
values will probably give reasonable results.

The basin is  empty when h =  0.  Substitution and rearrangement
of equation 4-1 allows the  estimation of  the time required  to
drain the basin.
                   t  ~

where:  t,  =  time  to drain basin,  h
              all other terms defined above.

For  example,  assuming a medium  sand  with a  KV = 8  cm/h  (3
in./h)' and  a  porosity of 35%, estimate  the drainage time if  40
cm of effluent remain  in the basin at  the end of the  flooding

     Use  50% reductions, so
             K  =(0.5)(8)  =  4 cm/h

              n =  (0.5)(0.36) = 0.18
               0.820'5 0.180'5
                                   = 7.8 h
 In  the  presence of a surface clogging layer  (the  usual  case),
 equations 4-1 and  4-2  are  not  applicable  as  they depend  upon  a
 continuously downward moving saturated front which  never  occurs
 under a thin surface layer of  higher  hydraulic  resistance  than
 the soil  beneath.   An equation  which roughly estimates  the
 decrease in water depth with time is:
where:   d = depth of clogged surface layer,  cm

       KVC = hydraulic conductivity of clogging layer,  cm/h

             all other terms are previously defined.

The  parameters  d and  K   are  obviously  functions  of  both
wastewater suspended soli&i and operating conditions.  As  such,
they are never known  with  certainty.   There are  several
published studies which might be used to deduce probable  values
of these parameters [26,  27,  28].   Of these, the  work of
deVries  [26]   appears   to  simulate  closely   the  operating
conditions of  interest.   From this  study  it appears  that  K
will probably  be  about  0.6 to 1.0  cm/h  (1.5-2.5 in./h)  and V§
will probably  be  about  2 to ,2.5  cm (0.8-1.0 in.).,  Note 'that
when  surface  clogging  controls,  the properties  of  the  upper
soil profile do not enter into equation 4-3  in any way.

The  procedures  outlined  above  are  particularly   useful in
conjunction  with  thermal  calculations  for  RI  .systems  in
northern climates where  winter  freezing and ice  formation  may
cause problems (see Section 4.5  for details).

4.3  Subsurface Flow and Ground  Water Mounding

A proper design insures that the  subsurface soils have  the
capacity to transmit the applied wastewater down and away  from
the  basins  at an acceptable rate  to avoid failure.   .Ground

water  mounding  beneath   the   basin  occurs  when  there  is
insufficient gradient to move water away from beneath the basin
in a lateral direction.  Some temporary mounding is acceptable
as long as it does not interfere with infiltration  at the basin
surface  and dissipates quickly enough to allow  for  aerobic
restoration of the  near surface  profile.  Chapter  5 in the
Manual [1]  discusses these  factors  in detail  and presents a
graphical procedure for  estimating mounding beneath  an RI
basin.   Supplemental information and criteria are included in
Section 4.3.3 in this text.

     4.3.1  Subsurface Flow

Percolate flow  in  the  unsaturated  zone beneath an RI basin is
essentially vertical and K  controls  flow.   If a  ground water
table, impeding layer, or barrier exists at depth,  a horizontal
component is  introduced and  flow  is then  controlled  by  some
combination of K,  and K  within the  ground water  mound or
perched mound.  At the margins  of the ground water mound,  and
beyond, the flow is typically lateral and K,  controls.  Section
3.5.2  in  this  text,  Chapter 3  in  the ManuSl [1],  and similar
sources  [3, 4] discuss K   and K_  and techniques  for  their
The capability for lateral flow away from the  application  site
controls  the  extent of  mounding  that will  occur beneath  the
basins.    The  "space"  available  for  lateral  flow  is   the
underlying  aquifer  and  the  zone between  the  existing  ground
water table or other barrier and whatever point  is  selected as
an acceptable depth beneath the ground surface.   The final
basin  locations  and configurations  should be  plotted on  the
soils/ground  water  maps  and  an analysis  conducted to  insure
that  the  adjacent  profile  has  the   capacity  for   lateral
transmissions  of  the  applied  wastewater.   The  first zone  of
concern  is  the perimeter around the general basin  area,  since
this  may directly influence mounding.   The  analysis  must
consider the  gradients  and potential for  flow  in various
directions away  from the  site,  in  addition  to the loading
schedules  for various  basins  (see  Section 4.3.2)  to  estimate
what  proportion  of the applied  wastewater  will  flow in  a
particular  direction.   The general analysis employs potential
flow theory and is  beyond the  scope of this text.   The  use of
this  theory  to  construct flow  lines  in  the  presence of  a
uniform   flow  field  of  constant   thickness   represents   a
reasonable  approximation  to  what takes place  down-gradient of
the  mound.   The calculations,  if they  are  required by an
approving  agency,  are  described in the  text by  Bear  [29],  or
the computer model by  Daly [44].

In many  cases  the RI percolate emerges as base  flow in adjacent
surface  water and it  is  necessary  to predict  the  position of
the ground  water  table between  the  RI  basins and that point of

 emergence.   This  will  reveal  if seeps  or springs  are likely to
 develop  in the intervening terrain.   In addition,  some  state
 agencies  may specify a residence  time  for the  percolate  in the
 soil to protect  adjacent surface waters,  so it may also  be
 necessary to calculate the travel  time  from  the basin  to the
 surface water.   Equation 4-4  can be  used   to  estimate  the
 saturated  thickness  of   the  water   table   at   any   point
 down-gradient  of the basin  area  [5].   This value  can  be
 converted to an elevation and plotted on maps  and  profiles  to
 identify  potential problem areas.
               h =
where:   h =  saturated thickness of the  unconfined  aquifer  at
              the point of concern,  m

        hQ =  saturated thickness  of  the unconfined aquifer
              beneath the rapid infiltration area,  m

        Q. =  the  lateral  discharge .from the unconfined -flow
              system, per unit width of the flow system,  m /d m

         D =  the  lateral distance from the RI  area to the
              point of concern, m

        1C =  effective horizontal  conductivity  of the  soil
              system, m/d (must have consistent units)

The quantity Q  in equation 4-4 is determined with:
                    Q  =    (h  _
                     i   2D.   o
where:  D.
              distance to seepage face or outlet  point, m
           =   saturated thickness of the  unconfined aquifer at
              point D .

              other terms  defined above
Figures 5-10 and 5-11 in the Manual [1]  and/or  other references
[6, 30,  31,  32] can  also be used  to estimate the  saturated
thickness of the water  table at a  point down-gradient of the
basin  area.     The  answers  from   all   of   these  models  are
meaningless  unless  the  soil  and  hydraulic  parameters  and
boundary conditions  of the site match reasonably well with
those of the model  selected.

The travel time for lateral flow is a function of the hydraulic
gradient, the distance,  the
Equation 4-6 can be used for
gradient, the distance, the  K, ,  and the porosity of  the soil,
                             tnis purpose..
where:  t  = travel time for lateral flow from basin area to
             emergence in surface waters, d

         n = porosity of soils, % (as decimal; calculated from
             field data, see Table 4-2 this section for ranges)

         D = travel distance, m

        h  = saturated thickness of aquifer at RI basin area, m

        h. = saturated thickness of aquifer at point of
         1   emergence

        K  = effective horizontal conductivity of the soil
             system, m/d (units must be consistent)

     4.3.2  Ground Water Mounding

The  material  presented  in the  Manual  [1]  on  mound  height
analysis was  that developed by  Glover C33]  and  summarized by
Bianchi and Muckel C34].  The  Manual [1] did not state  nor
imply that  this  simplified graphical  analysis  would  solve  all
problems relating  to ground  water mounds.   The curves were
developed for  basins  of square or  rectangular  geometry, which
lay  above  level,  fairly   thick,   homogeneous,   aquifers   of
(practically)  infinite extent.   Vertical  re-charge was assumed
uniform  (or nearl'y  so)  and  the height of the  mound was limited
to less  than one-half the thickness of the original unconfined
aquifer.  Many potential RI  sites will  not conform well to
these conditions  and a  certain amount of  ingenuity is required
on the  part of the engineer  who is analyzing  such  sites.   In
the  simplest  cases  the original  curves may be  used with
modifications.     For  example,   a  circular  basin   can   be
approximated by a square one of equal area, allowing the  use of
Figures 5-8 and  5-10 without introducing  significant error
C33].   Also, as the curves  were  developed using unsteady state
equations,  they  necessarily  show  an  ever-increasing  mound
height  with time.   It  is  obvious that during  prolonged resting
periods  (e.g., during annual maintenance), the mound recedes to
a certain  extent.  The  figures  are still applicable,  but  the
principle of superposition in  time must be employed.  If  dosing

is stopped at time t, a  uniform discharge  (from the mound back
to the  basin)  is  assumed  beginning  at  t, thus  effectively
cancelling the  re-charge.   The  algebraic  sum of the two mound
heights  in  time approximates the  mound  shape after re-charge
ends.  More details on the analysis of mound decay can  be found
in references [35,  36, 37].

Other conditions  encountered with reasonable frequency which
may invalidate the use of the curves  in the Manual  [1]  include
the presence of sloped water tables [37],  subsurface layers  of
reduced  conductivity  which  give rise  to  perched mounds [38],
and the  presence of  points  of  withdrawal   (e.g.,  a  stream [39]
or a significant rise in mound height  relative to  the  original
saturated depth  [37, 39]).   Although  there are analytical
solutions and/or dimensionless  plots from  generalized solutions
which satisfy some  of these more  complex  boundary conditions,
the designer would probably be  better  advised to  use a  computer
for  these  complications,  especially  if  the  mound  height
analysis is thought to  be critical to  the success  of  the
project.  There are a number of existing programs  available  to
perform  these calculations,  and improvements are  continuously
forthcoming.  Since most engineering offices have  access to  at
least  a  microcomputer,  and  some  to  larger  systems,  two
applicable programs are discussed here and  sources  given.

An interactive  program  based upon  Glover's analysis  [33]  has
been written  for  the APPLE  II+,  48K  microcomputer  [40].    In
addition  to  calculating the mound  height  ordinates with time
and  distance (which also  solves  the problem discussed   in
Section 4.3.2)  under continuous re-charge,  the program  can also
solve the mound decay problem and  can  handle the  boundary
condition of re-charge to a  stream.  To do this  an "image
basin,"   discharging at  the  same  rate  as  re-charge from the  RI
basin,  is assumed  to be  located  on the opposite  side of the
stream,  equidistance from the real basin.  The technique  borrows
from  the theory  of  well hydraulics using image wells  and
ensures that the (mathematical) mound  intersects the stream  at
its water level, a necessary physical  condition.

The  program  can  also  calculate  the hydrograph of  stream
re-charge, a  computation occassionally required by regulatory
agencies where water quality limiting  stream segments  are
involved.    The  authors  have  designed   the program to   be
"user-friendly," allowing several options,  creating unambiguous
displays,  and  allowing  easy  variation   in  parameters  and
variables.   A  floppy  disk containing the program  and  all
documentation can be purchased  from the authors  at:

          Department of Civil Engineering
          Colorado State University
          Fort Collins,  CO  80523

If  more versatility than  the above  program  can provide  is
required, or more  diverse boundary conditions are encountered,
another interactive program  is  available which seems  to  be
admirably suited.   It was  developed by Dr.  S.  P.  Neuman [41]
and  adapted  for interactive mode  on a  FDP-11/23 minicomputer
(256K)  by Bloomsburg and  Rinker  [42].  The  program  called
UNSAT, can be purchased from:

          Dr. G. L. Bloomsburg
          469 Paradise Drive
          Moscow, ID  83843

This  program   can  treat  non-uniform  flow   regions  having
irregular boundaries,  arbitrary  degrees of  local  anisotropy,
evapotranspiration,  and  percolate  recovery   by   fully-  or
partially-penetrating  wells.      Significant   to   some   more
difficult analyses,  certain time-dependent  boundary conditions
can  be  handled, such as  varying  infiltration  rates  or  stream
levels.  The major drawback to the use  of this program  is the
necessity of knowing (or estimating),  for each soil unit  in the
flow system,  the following relationship:

     1.   Saturated hydraulic conductivity

     2.   Relative  conductivity  (0_
4.4  RI Basin Configuration and Application Scheduling

When the  availability of suitable  land for an  RI  system is
limited  and  preliminary  mounding  calculations  indicate  a
problem,  there is  no alternative to  the use of  subsurface
drainage to control the  rise  of the  water table  (see  sections
5.7.2 to 5.7.4 in the Manual [1]).  This requires  underdrainage
and a  discharge permit  unless  all the recovered percolate is
re-used.  However,  when  land  is not  a limiting factor, it may
often be  possible to  avoid underdrainage  by "optimizing" the
configuration  and  application  scheduling  of  the  RI   basin
system;  for  example,  by arranging  the  basins in  a   strip
configuration and staggering  basin  operation so that no two
adjacent  basins  are  ever  dosed  sequentially.     This was
discussed  in  Section  5.6.1   of  the  Manual  [1].    Further
improvements are  possible  if  the basins are spread  out on the
site,  although this loses the  cost  advantage of  common  dikes.

The mound height analysis, if performed correctly,  usually
points to the best  approach.  By way of illustration,  assume a
system of seven RI  basins  arranged as  shown  in Figure  4-1 in a
hydrogologic setting as shown  in Figure 4-2 .

The average  loading is 1,727  m3/d (60,984 ft3/d) on  a bottom
area of 2.83 ha (7 acres), an  average loading of 0.061  m/d (0.2
ft/d) .   The horizontal hydraulic  conductivity  is 6.1  m/d  (20
ft/d) and the specific yield is 0.20.   It is planned  to operate
the basins  on one  day of dosing and  six  days  rest using the
sequence 1, 4, 7,  2, 6, 2, 5.   Will mounding interfere  with the
operation of this system?   One possible method of analysis is
to  assume  that  the  intermittent loading  to  each basin is
equivalent to  a  continuous  dose, averaged over  the entire
system.  Correcting for  dike  area, this goading is about  0.055
m/d (0.18  ft/d).   Selecting one year  (36S d) as  a trial  value
of t and using Figure  4-9  in  the Manual [1]  with  L/W = 2  and W
- 132 m (432 ft.) .
                   i _ 0.055 _ _
               R ~ V " "072 -- °'
                        (6.1H15.2) _
                   \|(4) (465) (365)
                                    = 0.16
             h   =  (0.08)(0.275)(365) = 8.3 m (26 ft)
Referring to Figure 4-2, this  is  clearly  an unacceptable mound
since  it  would  have intersected the basin  surfaces before  365
days had elapsed.

          I   Direction of
          I Groundwoter Flow
                   276 m (906 ft)
















140 m

                           FIGURE 4-1
^ /J> A ^


•> ^

                           FIGURE 4-2

However,  the previous analysis  does not reflect the actual
operation. Each basin  is loaded at  0.43 m/d  (1.4  ft/d)  for  one
day, then  allowed to drain and rest  for  six days.  At worst,
only basins with  touching corners (not sides)  are dosed  on
consecutive days,  thus,  minimizing  mound  interference.   An
analysis  based upon a single basin  shows  the maximum mound
height is 1.60 m (5.3 ft)  at the end  of one day,  but then
recedes to less than 0.09 m (0.30 ft)  by the end of the seventh
day (using the principle of  superposition  in time discussed in
Section 4.3.2).  Using the principles of  superposition  in time
and space together,  the time history  of mound heights'at a  few
critical points within the space  together, the time  history of
mound heights at  a few critical points within the  system;  for
example, points A or B can be  calculated.   Such a  plot  shows
that  mounding  is  not  a  serious  problem  with  this basin
arrangement  and  application  scheduling.    If  the  analysis
indicated that mounding would  likely  be a problem,  the design
could be  changed  slightly to alleviate it.   For  example,  the
dikes could be made a little wider and/or the basins  could be
changed from square  to rectangular  (long  axis perpendicular to
ground water flow direction), or arranged in a strip.

4.5  Design Requirements for Winter Operation in Cold

Rapid  infiltration  systems  can  operate  successfully on  a
year-round basis  in cold climates.   Systems  in  Massachusetts,
New York,  Michigan, Wisconsin,  South Dakota,  Montana,  and Idaho
have  all  operated  through  the  winter  without  significant
difficulty.  Proper thermal protection for the pipes, pump
stations,   valves   and  related  plumbing   is  essential   for
wintertime operation.  This is covered in other  references [7].
The  unique  concern  for RI  is  prevention  of  a  permanent,
impermeable ice barrier  at,  or in, the  near surface  soils  in
the basin.  Two possible problems can develop:

     .  The standing water in the basin freezes  into a layer of
        ice that,  because of entrapped vegetation, cannot float
        to  the  surface.   If the  next  increments  of  applied
        wastewater are not warm enough to melt through  the  ice
        layer, the  basin can be  in the  failure  mode  for  the
        rest of the winter.

        If  at  the  end  of the  infiltration  period,  the .soils
        drain too slowly, the water remaining in the soil pores
        may freeze, rendering the surface impermeable.   If this
        frozen, saturated  soil  layer  is not thawed, the basin
        is in the failure mode.

The successfully operating systems in northern climates tend to
have relatively coarse, rapidly drained soils and operate with
dilute  raw  sewage   or  relatively   warm  wastewater  from

conventional primary or secondary treatment systems.   Suggested
operating procedures  to  deal with  some  of these problems  are
discussed in  Chapter 6.   Design  features  which  have been
successful include:

     1. Ridge  and furrow  configuration on the  basin bottom
        combined  with a floating  ice  sheet.  The  ice gives
        thermal protection, and rests on the ridge tops  in  the
        final infiltration  stage.

     2. Inducing snow  drifting  with snow fences  in  the  basins
        and  then  flooding  beneath  the  snow cover.   The  snow
        retards  freezing,  but the water  equivalent  of  the
        melted  snow  is  a  negligible  contribution  to   the
        hydraulic load in the basin.

     3. By-pass some  of  the  final  cells in  a long  detention
        facultative   lagoon   to  retain  some   of  the  heat
        originally present  in the wastewater.

     4. Design one or more  of the RI cells  for winter operation
        in the seepage pond mode with continuous flooding and a
        floating ice cover.  These cells can be drained,  dried,
        and restored each spring.   Any  special  nitrogen  limits
        or other water quality limits must be considered,  since
        removal efficiencies are reduced at low temperatures.

     5. Based on thermal and hydraulic calculations,  adjust  the
        wet/dry ratio  during  the  critical  periods so the  near
        surface soil never  irreversibly freezes (see  discussion
        below and reference [8] for details).

Wastewater storage for winter conditions is not included  in  any
of the alternatives listed above.   Storage  may  be necessary to
equalize flow variations,  and storage may be  provided  for
emergencies, but winter storage is  not  an  absolutely necessary
component in RI system design for the contiguous United States.
A cost-effective  design  attempts  to understand and  adjust  for
the low temperature conditions  rather than  increasing  costs by
including long-term storage.

Storage may be needed  during the winter  in  cold climate  areas,
however, if high nitrogen removal is a system requirement.
Ice  starts to  form as  soon as  the surface layer  of water
reaches 0°C  (32°F)  and  the latent heat is withdrawn.  The  ice
thickness that will develop can be predicted with equation 4-7,
which  is valid  for ponds and  for the  standing water in  a
wet/dry RI operation.

                    I = C N(AT) (t)
where:   I = ice thickness,  cm

         C = coefficient, depending on environmental conditions

           = 1.7 for snow cover on basin or snow on top of ice

           = 3.0 for no snow.
              (see reference 7 for other conditions)
        AT =
  (0 C - TA)

= average air temperature over period t,   C

=  time,  days  (this  is  the time,  in 'wet/dry  RI
  operations after the water  at the  surface  reaches
  ObC (32°F)
The factor (AT)(t) in equation 4-7 is called, the freezing index
and  is  an  environmental   characteristic '  for  a  particular
location.  It can be calculated from weather records or .typical
values  can  also  found  in reference  [7]  and similar  sources.
The design calculations are based on the  coldest winter  of
record  in 20  years,  or  even longer  if data  are available.
Equations 4-2 or 4-3 and 4-7 can be solved for winter operating
systems to determine how long it takes for  infiltration  to  be
complete and if  any ice. will form.   Any ice formed has  to  be
melted by the  next  increment of wastewater., . The  energy input
required is given by equation 4-8.
                  E  =
 = energy required to melt the ice,  cal
                              6     ,3
 = latent heat of ice, 80 X 10   cal/m
          I = ice thickness, cm
          A = surface area of ice, m"
The  energy available in  the next  increment  of wastewater  is
dependent on the incoming  liquid temperature.   Only a fraction
of the heat released in  cooling  the  incoming water to  0 C
(32°F)  is  available  for  ice melting,  since there will  also  be
significant heat losses to the atmosphere.  The situation where
both the soil and the water  in  the  soil pores freeze is a more

complex,   two-phase  problem   and   reference
[8]  should  be
A -design based on  a floating  ice layer  is recommended for
critical situations.   Even under  wet/dry  operations when the
ice is resting on the basin bottom, it provides'insulation and
retards freezing of  the  soil.   Absence  of  the ice layer  would
require  a  more  frequent  flooding  cycle  to  prevent  soil
freezing.  Stefan [8] shows that the presence of a  floating ice
layer protects the  soil  from  freezing  for  a period of over  27
days as  compared  to 2.5  days  for freezing  to  commence   in  an
unprotected soil  under  the same  conditions.   It  is. essential
that the ice layer re-float at every flooding cycle.

4.6  Design of Seepage Ponds

The Manual  [1] presents  criteria  for  RI  design that  are  based
on the assumption that the system will be operated  on a wet/dry
cycle  so  that the  near  surface  soils  can be  aerobically
restored.   Those  criteria were not intended  for  basins  or
infiltration ponds  expected to  be permanently flooded.   It
should be understood that the  percolate  from seepage  ponds will
not be  comparable  in quality to  a properly managed  RI  system
designed for  a  regular wet/dry cycle.    Seepage  ponds   in
suitable soils 'can  infiltrate large  volumes  of  water  where
water quality  is  not an issue.   Specific criteria   for  their
design is not included in this text.

4.7  Design of Physical Elements

Most of the physical  elements for RI  basins  are similar  to
wastewater .lagoons.   These include dikes,  access  ramps,  inlet
and transfer structures,  and  flow control  devices.   Chapter 4
in reference Cll] provides  details on some  of  these features,
as well as Section 5.9 in the Manual [1].

     4.7.1  Dikes.

The dikes of RI basins intended for wet/dry cyclic  operation  do
not need to be more than 1 m (3 ft) high and could  be even less
in many  cases.  Extra  freeboard is not recommended for  routine
wastewater  containment.   If a basin does not infiltrate  at the
expected rate, restoration of the surface  is necessary and
extra  freeboard  in that  basin  does not  solve the problem.
Dikes that  are higher than necessary can actually contribute  to
operating  problems  through the extra runoff and potential  for
erosion of  soil fines.   Some  of  the basins in  a system,
however, can be designed for  emergency storage  and these dikes
can be higher.   In these  cases  the  dike  includes  sufficient
freeboard  and  incorporates wave  protection • at  the  water line
zone.   All basins  designed for  flooding  for more than  a  few
weeks  duration  might  include  an outlet or  other positive

drainage features  'so  the basin can be  drained quickly when
maintenance is necessary.  This is because the  time period
required for natural drainage  through  the  basin bottom may be
unacceptably long.

The dikes are  compacted  to prevent  seepage through them.  The
top of  the  dike often is a road for  vehicle access  and,  if
possible, should be pitched to the outside  so that  all  drainage
and runoff goes away from the basin.   Erosion control for the
inner dike  surface  is  necessary,  both during construction and
during system  operation.   The  washout  of soil fines from this
source has  sealed  the  basin surfaces  in a number  of  systems.
Grass,  or  similar  vegetation, may  eventually stabilize the
slope, but the use of a silt fence or similar porous barrier at
the toe  of  the slope is  suggested  during construction and may
still be necessary  during operation.   It is also necessary to
provide a ramp or  other  easy access for maintenance equipment
to enter the basins.

     4.7.2  Basins in Fine-Textured  Soils

If the soils in the basin bottom contain  a  significant  fraction
of fines (silts and/or  clay >10%), then  stabilization with
grass may be necessary  C12].  Flooding  the  bare  surface of such
soils may suspend some of  the fine soil  fraction in the water.
The repetitive sorting and re-deposition of those fines on the
surface   can   eventually   reduce   the   infiltration   rate
significantly.   A surface  layer  of  gravel  or similar material
may hold the fines in place, but the interface may  not dry
properly and a clogging,  biological  layer  may develop.  Other
mixed-in amendments  (sand, gravel,  lime,  woodchips)  have not
been  effective [12H-   A  grass  cover is  the only  effective
treatment for  this  condition known to  date.   These RI systems
tend to be  near the low  end of the range of hydraulic loading
and the grass  cover may actually improve the infiltration
capacity of the basin surface.

     4.7.3   Inlet,  Distribution and  Transfer Structure

Small basins with low velocity, low volume wastewater flow may
only  require  a simple splash  block  at the discharge  pipe.
Large basins may require  a more complex arrrangement to dampen
the entering flow  to prevent erosion  of the basin and/or the
adjacent dike.   In all  cases,  uniform wastewater application
over  the  entire  basin   surface  is  necessary.     This  may
automatically  occur with  a  high  application rate  on  finer
textured soils, but may  require some  structural assistance on
coarse soils to insure uniform distribution.  The distribution
system  might  range from  a network of  pipes and troughs  to
sprinklers in the extreme case.

In many cases, several basins or sets of basins may be  flooded
at the  same  time  so interbasin transfer structures  may be
necessary.   In general,  these  are  similar to  those used  for
lagoons  [11].  Figure 5-4  in  the Manual [1]  illustrates  a
transfer structure with removable rings  to control the depth of
water in  a basin.    A device of this  type gives  the operator
greater control and permits optimization of basin use.

     4.7.4  Flow Control                      .

Depending on the size of the system,  the design can provide for
a control  system ranging  from simple  manual valves to  a  fully
automated  operation involving  time  switches,  float  switches,
tensiometers, and  automatic valves.   In either case, it is
necessary for  regular visits to  all of  the basins  by  the
operator to observe conditions and make necessary adjustments.

It is essential that  the design provide sufficient flexibility
so that adjustments in loading and  application rate for  a
particular basin can  be made by the operator.   The  adjustable
transfer structure  discussed  above is one  example.   It  is  also
absolutely essential  that  particular  attention be paid to the
preparation of the O & M Manual for the system?It is critical
for  theoperatortounderstand clearly  theRI  concept,  what
controls   and  adjustments   are  available,   and   what   the
consequences  of these adjustments might be.

4.8  RI System Performance              •

Basic information on the performance of RI systems can be found
in Chapters 1, 2, and 5 of the Manual [1] and other sources [2,
4, 14, 20, 24, 25].  The percolate after a few meters of travel
in the  soil  is of such a quality that  recovery  and  re-use for
unrestricted  agricultural irrigation is acceptable.  The system
can  be  managed to  satisfy nitrogen  and  other  drinking  water
limitations  in the percolate, but the  direct  on-site recovery
and  re-use   as  potable   water  is   not  recommended  without
extensive  further treatment.

There has  been additional  research and  study  on the  removal of
toxic organics  and  nitrogen  in  RI  systems since publication of
the  Manual [1] and  the need for disinfection is still a concern
for  many.  Further details  on these  three  topics  are  given

     4.8.1 Removal of Toxic  Organics

The  discussion on  organics  in the Manual Cl] was  limited to
removal efficiencies  for pesticides and BOD.  The  confidence in
BOD   removal  efficiency  is   based  on   a  reasonably  large
historical data base.  A  few researchers  have since monitored
specific  organic chemicals in  rapid  infiltration systems [13,

14, 15, 16, 17] and have demonstrated significant reductions in
many toxic organic chemicals.  Analysis of organic chemicals is
expensive  and the  analytical techniques  are  relatively  new,
resulting  in  a  limited  data  base  for  specific  compounds
identified    in    municipal    wastewaters.        Therefore,
"rule-of-thumb" removal efficiencies are not  available and are
not expected  to be available  in  the foreseeable future.   For
this  reason,  the  engineer  needs  to  forecast  the  removal
efficiency based  on  an understanding of the processes  in  a RI

A  model  has been  developed  [16] which  separates a  RI system
into  three computation compartments involving the  standing
water, the  surficial soils,  and the  deeper soil layers.   The
model was developed in the laboratory, but not tested on a full
scale RI system.

An interactive  computer  aided design code has  been  written in
Fortran 77 along with a user's guide.  The code can run on most
64K byte microcomputers having Fortran 77 compilers.   Copies of
the information are  available in  Simulation  Waste  Access  to
Groundwater:  A User's Guide  [19]  which can be  obtained  from
the   International   Groundwater   Modeling   Center,   Butler
University, Indianapolis, Indiana,  46208.

     4.8.2  Nitrogen Management in Rapid Infiltration Systems

The discussion in Sections 5.2.2 and  in the  Manual [1]
describes   the   nitrification/denitrification  mechanisms   in
rapid-infiltration  systems   for   nitrogen  removal.       The
importance  of temperature,  pH,  and the  necessity  of organic
carbon (as  an energy source  for the denitrifying bacteria)  is
discussed.  Equation 5-1 estimates the amount of total nitrogen
that may be removed based  on the total  organic  carbon (TOC)  in
the applied wastewater.   Nitrogen  removal  versus infiltration
rate is shown in  Figure  5-2  and hydraulic  loading rates versus
percent nitrogen  removal is  provided in Table  5-2 (all  in the
Manual  [1]).   Research on  RI systems  has combined new  and
former design and  operaion  techniques  for improved  nitrogen
control.    If high nitrates  are  not objectionable,  the design
develops the maximum hydraulic loading potential.  However,  if
the objective is to maximize total nitrogen removal,  maximizing
hydraulic   loading   is  sacrificed   to   design  for   optimum

In systems designed for maximum hydraulic loading, high nitrate
concentrations will  be experienced in  the percolate  near  the
beginning of  each loading  period.   These short pulses of  high
nitrate-nitrogen may peak  up to  an order  of  magnitude greater
than the  average.   The pulse  is  a result of nitrification  of
the ammonium  stored in  the  soil profile  during the  previous
loading period.   This high nitrate  water is  released as a  slug

when the capillary water  is  displaced during the next  loading
period.   Four to  five days  drying has been shown  to be an
adequate  time  to   provide   ample  soil  re-oxygenation   for
nitrification of this applied ammonium.   After the high  nitrate
pulse, the nitrate-nitrogen concentration drops to a much lower
value (see Section 5.2.2 of the Manual [1]).   The average total
nitrogen concentration, including  the high peaks,  will  likely
range between 9 and 20 mg/L.

When  the objective  of design is  to  maximize  total  nitrogen
removal, a more detailed procedure is used.   Loading  schedules
directly  affect  ammonium  adsorption  during  wetting,   while
drying schedules affect oxygen mass transfer  and diffusion into
soil.   To  achieve  complete  nitrification  of the  ammonium
nitrogen,  the  amount  of  ammonium  nitrogen  applied   during
loading  is balanced  against  the  amount of oxygen entering  the
soil  profile  during drying.   Otherwise, ammonium  nitrogen
accumulates in the soil  until its  adsorption capacity  for
ammonium nitrogen is saturated, and then ammonium nitrogen, as
well as nitrate-nitrogen,  appears in the reclaimed water.

Loading periods  must  be long  enough  to maximize  ammonium
adsorption   and   develop  an   anoxic  environment   to   allow
denitirification.    The organic carbon source provided  must be
sufficient to support adequate denitrification.   The  small
amount  of available carbon  in secondary effluent  can be  a
limiting factor.   Drying  periods  must be  long  enough to allow
near  ultimate  soil re-oxygenation.  This  period is determined
by the infiltration rate and the moisture release capability of
the  soil at the site.  The  design procedure is summarized in
these six steps:

      1.  Determine  the mass  of ammonium that can be  stored in
         the  soil profile per unit  area  for  the  unsaturated
         depth using the  published equations  [21] to  calculate
         the   ammonium   adsorption   ratio   and  exchangeable
         ammonium, percentage.

      2.  Calculate  the length of  the loading  period  required
         for    maximum   ammonium    adsorption,    using   the
         infiltration  measurement  described  in  Section  5.4 of
         the Manual  [1] and the known ammonium concentration of
         the applied effluent.

      3.  Estimate the mass  flow  of oxygen and the mass of
         diffused  oxygen  that can be accumulated  in the soil
         profile   for   a   specific  drying  period,   using  the
         published  technique  [23].

      4.  Balance  the  ammonium adsorption with the  available
         oxygen to establish the  length of  loading and drying
         periods   for  optimum nitirification  of  the  system.

Practical lengths of loading and  drying  periods  might
also  be   considered   to  fit   the   operation   and
maintenance   schedule   of   the   municipal   system
operators; i.e., five to nine days  loading and two  to
five days drying, respectively.

Balance nitrate-nitrogen produced against the mass  of
organic carbon entering the soil.

Optimize denitrification by reducing  the infiltration
rate in the flooded basin.
Using  these  six steps,  the designer  can  expect  total nitrogen
removal in excess of 60% and the discharge of total nitrogen to
be below 10 mg/L, for typical municipal wastewaters during warm

The   infiltration   rate   can  be   fine-tuned   to   enhance
denitrification by operating at reduced depth of  ponding  or by
adding  suspended  solids.     However,  this  will  result  in
additional sacrifice of loading  and will increase the  land
areas  required.   Selecting  a site  which naturally has  low
infiltration  rates  or compacting  the soil surface  can  assure
high  total nitrogen  removal  rates,   but  either  increases  the
land area  needed.   Reducing  the   infiltration rate,  increases
contact   time   between    the   soil  micro-organisms,    and
nitrate-nitrogen,  and more  efficient  denitrification  can  be
accomplished.  One of the most important  factors  for producing
denitrification  is  to have near-saturated conditions  in  the
soil media [20H.

Thus/ optimum total nitrogen removal  in land  treatment  systems
can  be achieved by adjusting the loading period  to insure
complete nitrification of  the  ammonium nitrogen  in  the  sewage
and adjusting the infiltration rate to provide the needed  level
of denitrification.  The use of primary effluent allows  maximum
total nitrogen removal at higher infiltration rates  due to  its
higher organic carbon content.   Nitrification  reaction rates in
the  soil will be significantly reduced in the  winter in  cold
climate areas.   Winter  storage,  similar   in  duration to  that
described in Part II of this supplement,  is necessary for  those
RI systems designed for maximum nitrogen removal.

     4.8.3  Disinfection in RI Systems

The  need  for disinfection and  the effectiveness  of  virus  and
pathogen removal in RI systems is  discussed in the  Manual  [1]
(Chapter 5) and in more recent texts  [2,  24,  25].  Each one of
these  references discusses numerous projects,  studies,  and
evaluations.    In general,  they show  that RI system percolate
can be of very high quality with respect to viral  and bacterial
content.  There have been some  studies where  some viruses  were

detected in  the  percolate when high virus  concentrations  were
present in the  wastewater,  rainfall, during drying  periods was
heavy, and the  wastewater was  applied at  high rates  to  very
coarse  soils.   There has  never  been any  evidence  of  any
water-related disease  problem related  to the  operation of any
land treatment system in the United States.

Chlorination of wastewater  can  reduce the  concentration of
bacteria and virus  significantly.  Chlorination  of wastewater
can also significantly increase the number and concentration of
refractory toxic  organic compounds which  can then  reduce the
effectiveness of RI treatment for their removal.   Since the RI
system itself will remove bacteria and virus effectively, there
is  no need  for wastewater  Chlorination prior  to application.
In the general case,the ground water sources for down-gradient
water supplies  will be  protected.   On-site  recovery  of water
for  drinking purposes is  not recommended  without  appropriate
treatment.   The  worst case for down-gradient  impacts  might be
high wastewater loading  rates or  seepage ponds on coarse soils
with  a  shallow water  table  and  nearby recovery  for  drinking
water.   These conditions  are typically identified  during the
site investigation and design.  In some cases, with such ground
water use  very close  to the RI  system,  it may  be  prudent to
provide   standby   disinfection    for   the    recovered   water.
Disinfection at that point will be more effective and provide a
greater degree  of overall health  protection  than Chlorination
of wastewater prior to application on the RI basin.

4.9  References

 1.  U. S. Environmental Protection Agency.  Technology Transfer
     Process Design  Manual  for  Land Treatment of Municipal
     Wastewater.   EPA 625/1-81-013.   U.  S.  EPA, Center for
     Environmental   Research   Information,    Cincinnati,   OH.
     October 1981.

 2.   Reed, S. C.  and  R.  W.  Crites.  Handbook of Land Treatment
      Systems for  Industrial and  Municipal Wastes.   Noyes Data
      Corp.,  Park Ridge,  NJ. 1984.

 3.   U.  S.  Department of Interior. Drainage  Manual,  Bureau of
      Reclamation. USGPO  Stock No.  024-003-00117-1. 1978.

 4.   Bouwer,  H.  Groundwater  Hydrology.   McGraw  Hill  Co., New
      York, NY. 1978.

 5.   Sylvester,  K.    Land Treatment  by Rapid  Infiltration,
      Unpublished.   ERM,  Inc., West Chester, PA, April 1984.

 6.  Motz,  L.   H.     Hydrogeology  in  Land  Application   of
     Wastewater.  In:  Proceedings of  Water Forum  "81,  Vol  1.
     American Society  of Civil  Engineers.  San Francisco, CA.
     August 1981.

 7.  U.  S.  Environmental Protection Agency.  Cold Climate
     Utilities Delivery Design Manual.   EPA 600/8-79-027.  U.  S.
     EPA,  Center   for  Environmental  Research   Information,
     Cincinnati, OH.  September 1979.

 8.  Stefan,  H.  G.  Heat Loss  from Rapid Infiltration Basin  in
     Winter.   Journal  American Society of Civil Engineers,
     Environmental Engineering Division.  Vol.  108,  EE1, p.141.
     February 1982.

 9.  Eckenfelder, W.  W.   Industrial  Water Pollution Control,
     McGraw Hill Co.,  New York, NY.  1966.

10.  Healy,  K. A.  and  R.  Laak.  Site Evaluation and Design  of
     Seepage  Fields.   Journal  American   Society  of   Civil
     Engineers,      Environmental     Engineering      Division.
     100(EE5):1133. October 1974.

11.  U. S. Environmental Protection Agency.  Design Manual for
     Municipal    Wastewater     Stabilization    Ponds.    EPA
     625/1-83-015.    U.  S.   EPI,  Center  for  Environmental
     Research Information,  Cincinnati,  Ohio.  October  1983.

12.  Reed,  S.  C.     The   Use  of   Clayey  Sands  for   Rapid
     Infiltration Wastewater Treatment.   USACRREL IR 805.   U.
     S. Army  Corps of  Engineers, Cold  Regions Research and
     Engineering Laboratory,  Hanover,  NH.   December 1982.

13.  Bouwer,  E.  J., P. L.  McCarty, and J.  C. Lance.   Trace
     Organic Behavior in Soil  Columns  During Rapid  Infiltraion
     of  Secondary  Wastewater.    Water   Resources   Research.
     15:151-159.  1981.

14.  Bouwer,  H. ,  R. C.  Rice,  J. C. Lance,  and R.  C. Gilbert.
     Rapid-Infiltration System for Wastewater  Renovation and
     Beneficial  Re-use.  EPA 600/2-82-080.   PB  82-256941.   U.
     S. Environmental  Protection Agency.  1981.

15.  Bouwer,  H.  and R. C.  Rice.   Renovation  of Wastewater  at
     the 23rd Avenue Rapid Infiltration Project.  Journal  Water
     Pollution Control Federation.   56:76-83.   1984.

16.  Enfield,  C. G.,  D. M.  Walters, J.  T.  Wilson,  and  M.
     Piwoni.   Behavior of Organic Pollutants during Rapid
     Infiltration   of   Wastewater   into   Soil:      Part   II
     Mathematical Description of Transport and Transformation.
     Journal of  Environmental  Quality.  (In  Press).

Hutchins, S. R.,  M.  B. Tomson,  and C.  H.  Ward.   Trace
Organic   Contamination  of   Groundwater   from   a   Rapid
Infiltration  Site:   A Laboratory-Field Coordinated Study.
Environmental Toxicology and Chemistry.  Vol. 2, No. 2, pp
195-216.  1983.

Tomson,  M.  B.,  J. Dauchy, S.  Hutchins,  C.  Curran,  C. J.
Cook,  and C.  H.  Ward.   Groundwater  Contamination by Trace
Level Organics  from a Rapid Infiltration  Site.   Water
Resources Research.  15:1109-1116.  1981.

Walters,  D. M. and C.  G.  Enfield.   Simulated Waste Access
to  Groundwater:    A  User's  Guide.  Butler  University,
Indianapolis, IN.

Bennett,  E.  R.  and L. E.  Leach.   Field Studies  of Rapid
Infiltration Treatment of Primary Effluent.   American
Society   of   Civil  Engineers  Specialty  Conference   on
Environmental Engineering.  Boulder, Colorado.  July 1983.

Lance,  J. C.    Land  Disposal of  Sewage Effluents  and
Residue.  Groundwater Pollution Microbiology.  pp. 197-224
Gabriel  Britton  and Charles P. Gerba,  eds.   John Wiley &
Sons,:Inc.,  New York,  NY.   1984.

Leach,  L. E. and C.  G.  Enfield.   Nitrogen Control in
Domestic  Wastewater  Rapid Infiltration Systems.   Journal
Water Pollution  Control Federation.   Vol.  55, No.  9,  pp.
1150-1157.  September 1983.

Lance,  J. C.,  F. D.  Whisler,  and R.  Bouwer.    Oxygen
Utilization in Soils  Flooded  with Sewage Water.   Journal
of Environmental Quality.    Vol. 2.    November 1973.
Middlebrooks,  E.  J.,  ed.    Water
Publishers, Ann Arbor,  MI.  1982.
                                           Re-Use.  Ann   Arbor
Page,  A.  L.,  T. J.  Gleason,  J.  E.  Smith, Jr.,  I.  K.
Iskandar,  and L. E.  Sommers.   Proceedings of the  1983
Workshop on Utilization of Municipal Wastewater  and  Sludge
on Land.  University of California,  Riverside, CA.   1983.

deVries, J.   Soil Filtration  of Wastewater- Effluent  and
the Mechanism of Pore Clogging.  Journal Water  Pollution
Control Federation.   44:565-573.  1972.

Ripley, D.  P.  and Z.  A.  Saleem.   Clogging in  Simulated
Glacial  Aquifers  due  to  Artificial  Recharge.    Water
Resources Research.    9:1047-1057.   1973.

28.  Behnke,   J.  J.    Clogging  in  Surface  Operations  for
     Artificial  Ground  Water   Recharge.     Water  Resources
     Research.  5:870-876.   1969.

29.  Bear,  J.   Hydraulics  of  Groundwater.   McGraw  Hill Book
     Co., New York,  NY.   pp. 282-299.   1979.

30.  Singh,  R.   Prediction of Mound  Geometry Under  Recharge
     Basins.   Water Resources Research.   12:775-780.  1976.

31.  Marino,  M.A.   Artificial Ground  Water  Recharge,   1.
     Circular   Recharging   Area.     Journal   of   Hydrology.
     25-201-208.  1975.
     Khan,  M.  Y.  and D. Kirkham.   Shapes  of Steady  State
     Perched Groundwater  Mounds.   Water  Resources Research.
     12:429-436,   1976.

33.  Glover, R. E.   Mathematical Derivations as Pertaining to
     Ground  Water  Recharge.    USDA,  Agricultural  Research
     Service, (mimeo.) 81 pp.  1961.
     Bianchi,  W. C.:  and C. Muckel.  Ground Water  Recharge
     Hydrology.   USDA,  Agricultural  Research Service.   ARS
     41-161.  December 1970.
35.  Hantush, M. S.  Growth and Decay of Ground Water Mounds in
     Response   to  Uniform   Percolation.     Water   Resources
     Research.  3:227-234.  1967.

36.  Haskell,  E.  E.,  Jr. and  W.  C. Bianchi.   Development and
     Dissipation of Ground Water Mounds beneath Square Recharge
     Basins.     Journal  American  Water   Works  Association.
     47:349-353.   1965.
     Bauman,  P.     Technical  Development  in   Ground   Water
     Recharge.  Advances in  Hydroscience.    2:209-279.   V.  T.
     Chow,  (Ed.).  1965.

     Khan,  M.  Y.  and  D.  Kirkham.   Shapes of  Steady  State
     Perched  Groundwater  Mounds.    Water Resources  Research.
     12:429-436.  1976.
 39.   Brock,  R.  P.   Dupuit-Forchheimer  and  Potential Theories
      for Recharge from Basins.   Water  Resources  Research.
      12:909-911.  1976.
      Molden,   D.   J.,  D.   K.   Sunada,   and  J.   W.   Warner.
      Microcomuter   Model   of   Artificial    Recharge.      In:
      Proceedings of First National Conference on Microcomputers
      in Civil Engineering.   pp. l-5a.   W.  E.  Carroll (Ed.).
      Orlando,  FL.  November  1983,

41.  Neuman,  S. P.,  R.  A.  Feddes, and  E.  Bresler.   Finite
     Element   Analysis   of   Two-Dimensional  Flow   in   Soil
     Considering Water  Uptake by Plants:   I-Theory.    Soil
     Science  Society of American  Proceedomgs.   39:224-230.
     March-April 1975.

42.  Bloomsburg, G. L. and R. E.  Rinker.   Ground  Water Modeling
     with an Interactive Computer.  Ground Water.   21:208-211.
     March-April 1983.

43.  Brooks, R. H.  and A. T.  Corey.  Properties of Porous  Media
     Affecting Fluid  Flow.   In:   Proceedings American  Society
     of  Civil  Engineers,   Journal  Irrigation   and   Drainage
     Division.   92:1R2.   1966.

44.  Daly,  C.  J.  A Procedure for Calculating Ground Water Flow
     Lines,   USACRREL SR 84-9.  U.  S. Army Corps  of Engineers,
     Cold Regions Research and Engineering Laboratory,  Hanover,
     NH.  April 1984.

                           CHAPTER  5

5.1  General

The most  critical  elements during construction  of RI  systems
are the infiltration surfaces,  earthwork for  dike construction,
and control of surface  and subsurface flow when necessary.
Special attention to all these factors is required to insure a
successful system.

5.2  Infiltration Surfaces in RI Basins

An appropriate  design locates the  basins in the "best"  soil
materials on the site.  In some existing systems  this  principle
was sacrificed to obtain gravity flow to  and among the  basins.
Gravity flow is desirable, but is not  the priority requirement
for site  development.   The  design,  if  at  all  possible,  also
avoids basin construction on backfilled materials.  If  fill  is
absolutely necessary, then a test fill is used as  described  in
Chapter  3 and  criteria  developed  from that experience for
construction of the full scale system.

The construction of RI systems utilizes  the  standard  equipment
and machinery used  for conventional earthwork.    However,  most
construction contractors have  little or no experience  with  RI
basin  construction.   It may be  necessary to  overcome the
traditional  attitudes  that  "successful"  earthwork   requires
maximum   compaction,   maximum  soil  density  and  structural
stability of the soil.  At a very early stage in the project  it
is  necessary   to   insure  that  all   construction   personnel
understand the RI concept and the need to avoid  any action that
will  unnecessarily  reduce  the hydraulic  conductivity of the
basins.   In addition, the  contract  specifications have  to  be
very  explicit  regarding  the procedures and  limitations  on
earthwork.  Any soil layers or zones to  be  removed and wasted
are  carefully  delineated on plans and profiles,  and  then
rigorously controlled during the actual excavation and disposal

     5.2.1  Cut and Fill in Coarse Soils

The field density test is  the  normal quality control  procedure
for   placement   of  fill   and  related  earthwork   for   most
construction.  There have been examples where field density was
the  only control  on placement of  fill for RI  basins.  The
specifications  might require  that the  density  of the  fill  in
the basin area should not exceed some  percentage  (75-80%)  of
the optimum density.   In one project with such  specifications,
the basins  failed.

The  field  density test is  not  by itself  sufficient  to insure
adequate quality  control  during RI construction.  As  shown in
Figure 3-1(this text),if the field moisture happened to be on
the  "wet"  side of  optimum  for  a  particular  soil it  would be
possible to  achieve a specified density limit and at  the same
time  reduce  the permeability significantly.   Placement of all
fill  in  the  infiltration  area  of  a  basin~ or  excavation
activities within  0.3 m  (1 ft)  of the final basin  surface is
only  recommended when the soil moisture content is on the "dry"
side  of  optimum.   Since the construction contractor has no
control over natural rainfall events, the  contract  is written
to be sufficiently flexible to  allow for  this downtime.   The
grading plan includes measures  to prevent  surface runoff from
entering the basin  area and even sprinkling for dust  control is
avoided in the same area when equipment is operating  at or near
the final grade.

The  final  infiltration  surface  in  the  basin needs to  be
uniformly  graded  to  allow  distribution  of  wastewater  and
utilization  of  the  entire soil  profile for treatment.   Small,
apparently insignificant depressions  need  to  be  avoided,  since
these  will  be  the  last  to  drain,  resulting  in  a  local
accumulation of solids leading to infiltration failure in those
areas.  Basins  with a slight grade  have been  successful,  and
when  positive drainage features  are  used,  they are  located at
the lowest spot in  the basin.   The normal  construction efforts
to achieve  the required uniform grades  {+5 cm (2  in.)  is
typical} can, with many soils, result in some"" compact ion of the
surface  layer.   The following procedures  are  recommended:
Fill Areas



Cut Areas

     1.  ,

Bring fill to specified elevation.

Fine grade to specified tolerance.

Both 1 a,nd 2 are only done when soil is on "dry" side
of optimum moisture.

Rip the surface  to  a depth of at least 0.6 m  (2  ft)
and cross rip in a perpendicular direction.

Break up clods and other consolidated material  thrown
up by the ripper.   Disk-harrow with  light tractor  or
other  vehicle with low  ground  pressure  tires  is
usually suitable.
Cut to specified elevation.

Fine grade to specified tolerance.

     3.    Steps 1 and 2  when  soil moisture is on the "dry" side
          of optimum,  for  the last  0.3 m  (1 ft) of cut.

     4.    Rip the surface  to  a depth of 0.6 m  (2 ft).

     5.    Disk and harrow surface using low ground  pressure

     5.2.2  Cut and Fill in Fine-Texture  Soils

The same basic precautions given in  the  previous section also
apply  to  fine-textured  soils.    The   requirements  for  low
moisture content during  earthwork activities are even more
important in this case.   It is assumed that the design has
avoided  basin fills  (see Chapter 4) when  clay and/or, silt
content  exceeds  about 10%, so this  section  is only  concerned
with cut sections and fills of acceptable materials.

As described  in  Chapter 3 and 4,  the presence of significant
silt and clay  in the  surface  layer of RI basins may eventually
result  in  infiltration  problems   due  to  the  sorting  and
deposition on  the  surface of these fine  fractions.   The only
surface  treatment that  has been shown to be  effective  is the
establishment  of  a  grass   cover  on  such  soils   [IJ.    A
combination of Coastal Bermuda (11  kg/ha) (10  Ib/ac) and  Dallis
grass (22 kg/ha)  (20  Ib/ac) was recommended for one project in
the Southern  United  .States.    Local  agronomic experts  can be
consulted for recommendations.   Seeding is only done  at an
appropriate season  for  the locality,  and temporary sprinklers
may be  needed to establish  grass in dry areas.   Wastewater
flooding  does   not   then start   until   the  grass  is  well

     5.2.3  Ridge and Furrow Construction

Ridge  and furrow  construction can offer  advantages  for both
grass  covered and  bare  soil basins.   A  ridge and  furrow
configuration  provides  some  increase in  the  infiltration area
available at  the surface.    It  also allows for more  rapid
aeration of  the soils,  since  the  ridge  tops  are dry when the
last increments  of wastewater are infiltrating in the furrow.
A  ridge and  furrow  basin bottom  can  extend  the time between
maintenance operations, since solids  will tend to accumulate in
the  furrow  bottoms,   leaving  the  ridges  clean.    A   final
situation where ridges and  furrows are suggested  are those
locations in  extreme  cold  climates where  the design is based on
maintaining a floating  ice cover in  the  winter.   The  ice  layer
rests  on the ridge  tops and infiltration continues  in the

Special  equipment  may  be  available  for  ridge  and  furrow
construction if the site is in an area where surface irrigation
is normally practiced.   A cross-section With  furrows  at least
30 cm  (12  in.)  deep was recommended for one RI  project  in the
Southern United States.  Whatever configuration is constructed,
it is  necessary  that it be easily reproduced  by the  system
operator,  since  reconstruction  of  the  ridges  is  required

5.3  Dike Construction

Basic construction procedures and controls used for embankments
are suitable for  RI  dikes.   Erosion control for  dike  soils  is
necessary  during  construction and  the use of silt fences  or
other barriers is recommended.

5.4.  Control of Water

The design and  the grading plan  includes consideration  of
surface  runoff requirements during construction,  and these
elements (i.e., ditches,  temporary berms,  etc.)  are  typically
installed  at  a  very  early  stage  of  construction.    Such
temporary  elements  are  then  removed  when  construction  is
complete, if not  incorporated in the final site  drainage plan.,
The,surface runoff from site roads  and outer dike slopes is  no
different than normal precipitation runoff,  so  special  measures
for water quality control are not required.

The design may include trenches or underdrains  to intercept and
re-direct native ground water in the vicinity of the RI basins.
These features typically require a  surface outlet, but are not
designed to intercept wastewater  percolate.     Therefore, a
discharge permit is not necessary.   These drains should also  be
installed  at a very  early .stage  of construction,  as  should
monitoring wells  where the final  location  will  not  interfere
with construction activities.   The routine  observation  of these
wells and drainage features during construction may indicate  if
additional work of this nature  is necessary.  In one  situation,
even though some  ground water  diversion was installed,  it was
observed to be insufficient to prevent basin interference  by a
seasonally high ground water table.

5.5  References

 1.  Reed,   S.   C.     The   Use   of  Clayey  Sands  for  Rapid
     Infiltration Wastewater Treatment, USACRREL  IR 805, U.  S.
     Army  Corps  of  Engineers,  Cold  Regions   Research  and
     Engineering Laboratory,  Hanover, NH.  December 1982.

                           CHAPTER  6

6.1  General

In  some cases,  the design of  existing RI  systems  did not
provide sufficient flexibility for operational adjustments and
basin optimization.  This is often compounded by an inadequate
O & M Manual so that  the operator may  not know how  to make
adjustments or understand their significance.   There have been
cases where all basins  were loaded at  the same time in  what was
supposed to be a cyclic operation, or where each basin in turn,
was loaded until it was "full" before flow was switched to the
next.   It  is absolutely essential that  the  operator  be given
sufficient   information   and   resources   so   that   design
expectations can  be  realized.ThemajorconcernsforRT
systems  are  wastewater   scheduling,   maintenance   of  basin
bottoms, and winter  operations  [1,  2].   The O  & M procedures
for pumps and other equipment, dikes,  and similar features are
not unique to RI systems and can  be found elsewhere.

6.2  Wastewater Scheduling

In  some  cases,  the design  may  specify  different loadings for
various  basins in the system if their  soils are distinctly
different.    In the typical  case,  however,  the design  is based
on  a  uniform application for  all basins as  derived  from the
field and laboratory test results.  It is not unusual  for some
of the basins to have  a higher capacity than the design rate,
or some less.  The operator observes and records the volume of
water  applied  to  each  basin  and  the  time  required  for
infiltration to be complete for every cycle.  A staff  gauge or
a similar  marker  in  each basin  is  also  recommended.   The
operator can then  observe the actual rate  of infiltration in
the final stages after  flooding has been  stopped.  The  operator
also notes the location of wet spots and small areas of ponded
water during the drying  period  so these can  receive special
attention at the next scheduled maintenance.

A routine evaluation of these data permits optimization of the
basins by adjusting the application schedules  and loadings on a
regular basis.  It  is not often possible to alter  the pump
capacity to  increase or  decrease  flow rate,  so the adjustment
requires a change  in  the  flooding period for a particular
basin.   These  data also give  warning of  when clogging  is
reaching an unacceptable level.   Definition of a  generally
applicable   rule  is   not   possible,    but   a   preliminary
"rule-of-thumb" suggests that all standing water at the end of
the flooding period  should  infiltrate within  the first 1/3 of
the drying period.   If the final infiltration takes more than

 one-half of the drying period,  then maintenance is necessary.
 In all but  the  coarsest  soils,   it is  recommended  that each
 bas"\n .in  tlrie  sYstem be  allowed  to dry and  then the  bottom
 scarified  or the crust removed once  a  year  during the warmest
 and driest season of the year,  regardless  of  its infiltration
 capacity at  the  time.

 In many systems  the  actual wastewater  flow in  the  first few
 years  of operation  may  be significantly less than the ultimate
 design  capacity,   and  ' an  appropriate  operation  program  is
 needed.  The best approach  is  to rotate operation among basins
 or sets  of basins,  using  only the  number needed for the current
 flow.   These are loaded  at the full design rates.   This will
 also provide an  early confirmation that all  of the basins have
 the capability  to  function  at design  rates.   Operational
 flexibility  to  make   these   types  of.  adjustments  requires
 multiple  cell   RI  systems.    A minimum of  three  cells  is
 suggested  for  even the smallest RI system.    The operator may
 also have to' make  adjustments, or install additions  to any
 distribution network   in  the  basin,   if  it   appears  that
 wastewater infiltration is not uniform.

 6.3  Maintenance of Infiltration Surfaces

 Regular maintenance of the infiltration surfaces in  the  RI
 basin  is  required  and  a  useful O  & M  manual  contains  a
 tentative  schedule  and   procedure.    Once  the   system  is
 operational,  the   evaluation   of   the   routine   observations
 discussed  above  will  allow optimization  of  this  maintenance
Equipment for  routine maintenance typically
tractor,  or  other  towing  vehicles, with  low
tires  and disk/harrow, or  similar devices,
surface  soil  layer.   The  number and  sizes  of
varies with  the size of the  RI  system.   Small
contract annually, for these services unless
other municipal uses for the  equipment.  Since
seldom required,  it is not  necessary to  have
dedicated for RI maintenance.
 consists  of a
ground pressure
to  scarify the
 this equipment
 RI systems may
there  are some
deep ripping is
 such equipment
These maintenance activities are only conducted when  the  basin
is dry and the moisture content in the surface soil  layer  is  on
the dry side of optimum, as described in Chapter  5.   The  first
step is to  remove  any thick deposits of organic  material  that
may have accumulated in the low spots and re-grade to  eliminate
the low spots.  Any deposits of soil  eroded  from  the  dikes are
also removed.   The final step is  scarification  of  the entire

Maintenance of  grass  covered  surfaces is  similar, but  instead
of disking, the  surface can be aerated when necessary with a

spiked drum or similar device.   The grass  is  cut and removed at
least once  a  year.   Experience may  show, however,  that more
frequent mowing is necessary at a particular  location.

Emergency maintenance  should also be restricted  to dry  soils.
If positive drainage  elements  do not exist  in a  basin,  it is
necessary to excavate a small sump with a backhoe or dragline,
pump out any standing water, and allow the surface to dry prior
to access with heavy equipment.

Deep  ripping  loosens  a   consolidated  soil.    However,  if
deposition  of  organics is  the  cause of reduced  permeability,
ripping  cannot provide long-term  benefits,  since the ripping
only re-distributes the material.  When acceptable permeability
cannot  be  restored,  then  removal  and   replacement  of  the
affected   soil   layer   is   recommended.      Fort   Devens,
Massachusetts, restored  their  basins in  this  manner  after 20
years of operation [3].   Approxmately 1 m (3 ft) of the upper
soil  was removed  and  replaced with  similar  material  from an
adjacent borrow pit.

6.4  Monitoring.

The  water  quality  monitoring  requirements  are established by
the  regulatory  authorities.   It is assumed that  the  design
provided appropriate sampling points and  the O  &  M  Manual
defined  appropriate techniques.  The  water levels in all  of  the
observation  wells  incorporated  in  the   final   system   are
routinely observed and  recorded.   The  O  & M Manual_ (or  a
similar  document)  explains  what  the operator should do with the
data  and how to  interpret it.

A regular  tour  of the  site  and  the  general vicinity is
recommended to insure the  integrity  of the  dikes and to  look
for  seeps  or  springs  in unexpected  locations.  These may  not
occur for months or even years after system start-up,  depending
on  soil  conditions and topography.   Small  seeps can  often be
corrected  with  additional fill  material.   In  some  cases,
cut-off  trenches and/or subsurface drainage may  be necessary.
The  appearance of  a seep  in an unexpected location  is  evidence
that  lateral  flow  is  occurring in a direction not predicted by
the  design.   Additional monitoring  wells  may,   therefore, be
required on such a flow path.

6.5   Winter Operations

The presence  of  weeds and  other  random vegetation  is  not
typically  a problem  for  many RI  systems  in either winter or
summer.   Ft.  Devens,  Massachusetts  operates on a year-round
schedule,  but there is no  special effort to manage  or  remove
the vegetation.   However, the Ft.  Devens  system  receives
relatively  warm primary effluent and  the  soils  are relatively

 coarse  and infertile.   Any ice that forms in  the winter  is
 melted by ^the next application and the basins  drain  rapidly.
 Any  location in  a cold region  that  does  not have  similar
 conditions needs  to  pay special attention  to the  vegetation,
 and either cut it close  to  the  surface or burn it off in  late
 fall.   Basins in more  fertile soils may require  vegetation
 management during  the warm season  as well.

 Those systems designed  for a floating  ice  cover will require
 special  operation early in each  winter to develop  the ice
 sheet,  and then will have to  rely on  flow meters or  other
 remote sensing devices  for operation since  the  basin surface
 cannot then be seen beneath the  ice  layer.

 Formation of the  ice  layer requires continuous flooding,  after
 the onset  of low temperature  winter conditions,  to maintain
 some  standing water in the  basin.  The initial ice layer should
 be  8  to 10 cm (3-4 in.)  thick for  ridge and furrow basins, to
 bridge the gap between ridges.   Equation 4-7 can be rearranged
 and solved for the  time required  to produce a  specified ice
 thickness under particular  temperature conditions,  as shown in
 the example below.
                          - -(I)'
 (see  equations 4-7 for definition of terms)

 Assuming  10 cm (4 in.) of ice is required, and that the ambient
 air temperaure remains at about  -10°C  (14°F)  the time required
 to  form the  ice,  when no snow  cover  is present  (C = 3)  would
                      t =
To) = 1-1 day
The predicted  time  of  1.1 day assumes the water is  already  at
0 C (32 F).  Since it is likely that warmer wastewater is used,
there will be  additional  time required for cooling.   Assuming
for this  example  that  the total  time required would  be  about
two days, it would be necessary to maintain a  depth of standing
water over the entire  basin for  that  period.   Since  water  is
also  infiltrating  at a relatively high rate  during  the  same
period,  maintaining several centimeters of standing water might
be difficult if the system has rapidly  permeable  soils and  a
low application rate.

6.6  References

 1.  U. S.  Army Corps  of  Engineers.   Land Treatment  Systems
     Operation and Maintenance, EM 1110-2-504.  Washington,  D.
     C.  November 1983.

 2.  Reed,  S.  C.   Design,  Operation and  Maintenance of  Land
     Application  Systems  for  Low Cost  Wastewater  Treatment.
     In:  Proceedings  of  Workshop  on  Low   Cost  Wastewater
     Treatment.  Clemson University,  Clemson,  SC.   April 1983.

 3.  Satterwhite, M.  B.,  B.  J.  Condike,  and  G.  L. Stewart.
     Treatment   of   Primary   Sewage   Effluents   by   Rapid
     Infiltration.   USACRREL  TR  87-48.   U.  S.  Army Corps  of
     Engineers,   Cold   Regions   Research   and   Engineering
     Laboratory, Hanover,  NH.   1976.

                    PART II.  OVERLAND FLOW

                           CHAPTER  1

 1.1  Background

 When the second  edition of the  Technology  Transfer Process
 Design  Manual  for Land  Treatment  of Municipal Wastewater  [1]
 was  published  in  October 1981,  the overland  flow  (OF)  process
 was  just  beginning  to gain  recognition   as   an  effective
 wastewater treatment  alternative.    The experience gained  and
 successes reported from  these  early OF projects  have led to  a
 substantial  increase  in  the  use of the OF process  for  smaller
 communities.    As of  March  1984,   there were approximately  48
 municipal OF systems in operation or in some stage of design or

 Overland  flow  treatment  of  municipal  wastewater  has  finally
 moved   from   the  research/demonstration   stage   to   routine
 implementation.   The  guidance  provided in the 1981 Manual  [1]
 has  been instrumental  in  giving the  design engineers  and
 owner/operators a sound  basis upon which to design  and  operate
 OF  systems.   However,  as  with  any  new  and/or  unfamiliar
 process, the guidance can be improved as additional  information
 is gained from construction  and operational  experience.

 1.2 Objectives

 The  overall  objective of this  chapter is to update and  refine
 the  information  contained in  the Manual  [1] with  the more
 recent experiences gained during the  design,  construction,  and
 operation of an  increasing number  of municipal  OF systems.
 This supplement is. not intended to replace the Manual  [1] which
 continues to provide a firm  base of  understanding  for  the
 technology.   Therefore, the  Manual  [1] will be  referenced
 extensively  in  this  document with existing sections repeated
herein only when necessary to clarify a point.

 The information provided in  Part II is based principally  on  two
 sources of new information:   (1) field investigations of  six OF
 systems  which were placed  into operation  in 1983  and 1984,
ranging in size from  265 to  11,356 m /d (0.07 to 3.0 MGD)  and
 three systems which were under  construction in early 1984;  and
 (2)   recently   available  data  from   research/demonstration

Although it is  premature to  assess  adequately  the effectiveness
of the municipal  OF  facilities, it appears that  most,  if not

all,  of them  will  be capable of  meeting  their  discharge
criteria.  The field investigations also uncovered a number of
design,  construction,  and operational  factors  which could be
modified to  improve  their performance and reliability.   These
factors are organized by  subject matter in this text.  _ As  long
term   operating   experience  is   gained   from  municipal  OF
facilities, it will be possible to develop  further  refinements
and to optimize engineering criteria.

1.3  References

 1.  u.  S.  Environmental  Protection  Agency.     Technology
     Transfer  Process  Design  Manual  for  Land  Treatment of
     Municipal Wastewater.  EPA  625/1-81-013.   U.  S.  EPA,
     Center for Environmental Research Information,  Cincinnati,
     OH.  October 1981.

                            CHAPTER  2

                         CURRENT  STATUS
 2.1   Introduction

 There has been  considerable experience  gained  regarding site
 selection, design,  construction,  and operation of municipal OF
 systems  since publication of the Manual  [1].  This is organized
 by subject matter into  individual chapters within this text and
 briefly  summarized  in this chapter.

 2.2   Site Selection

 Experience has  indicated two areas where the  Manual Hi] needs
 clarification.  These are  the  use of  the  terms "slope"  and
 "terrace, " and  the  use of soil permeability data in selecting

      2.2.1  Process Description

 The OF process  consists of  applying wastewater along the upper
 portions  of  sloping,  grass  covered fields  and  allowing  it  to
 flow  over the  vegetated surface to runoff  collection ditches.
 Throughout this chapter,  the uniformly sloped areas  which
 receive  wastewater  for treatment  will  be  called   "terraces."
 The runoff  collection  ditches into which the  treated effluent
 flows will be  called  "drainage channels."   In  the  Manual [1],
 the term  "slope" was used to describe a terrace, but the latter
 term   is  more  appropriate   and   is  more   compatible   with
 conventional agricultural engineering terminology.

 The OF  process  was developed to overcome  the  limitations --to
 land  treatment  which   are  created  by soil   types   of  low
 permeability.   OF  differs  from the  other  two  principal  land
 treatment processes, slow rate and  rapid infiltration,  in that
 it is not dependent on  infiltration and the treated effluent is
 discharged  as   a   point  source.     As continued   operating
 experience is gained from municipal OF systems,  it  is  expected
 that  the  consideration and  use of  the process  will increase.
 Furthermore,  as  already experienced in some  states where  OF  is
 in use,  both designers  and  regulatory  officials are taking  a
 less conservative attitude towards the process design criteria.

     2.2.2  Soil Permeability

Although  the   OF   process   was  developed  to   overcome   the
restrictions of  low permeability soils,  it can also  be used on
 sites which do  not  contain heavy clay and  silt soils [2,  3].
Table 2-9 of  the Manual  [1] suggests that  the most suitable

soils for OF  are those with  permeabilities  of less  than  0.5
cm/h  (0.2  in./h).   However,  both designers  and regulatory
personnel have used that  value as an inflexible  limit.   This
can result in sites being eliminated from consideration for OF
when they are,  in fact,  suitable.

OF can be designed successfully on sites where the surface soil
permeability is  greater than 0.5 cm/h.   Consideration  for
potential ground water contamination (particularly nitrates) is
necessary if significant  percolation  is  likely to  occur (see
Section  4.5.2 of  the Manual  [1]).  Although an artificial
barrier can be constructed on  sites where  no natural barriers
exist [2, 3],  it is usually not cost-effective to do so.

2.3  Process Design

     2.3.1  Design Criteria

The recently constructed municipal OF systems have utilized the
design guidance  provided  in the  Manual  [1]  in a conservative
fashion.  Although these facilities have  not  yet generated much
performance data,  observation  of  a .number  of  them  indicates
they will be capable of performing according  to their  discharge
criteria.  Since the publication of the Manual  [1], a  number of
independent research and  demonstration projects have  al.so been
conducted to study the OF process.  Most of these  projects
either have been completed or are in their  final stages  of work
after up to  ten  years of evaluations.   In general, these
projects have  verified  and/or  expanded the  data  base for
treatment and the experiences from many  of  them were considered
in  the development of this document.  It  is worthy to  note  that
some  of  the  more  recent  studies  contain  initial  results
regarding topics not studied  prior  to  the publication  of the
Manual  [1],  such as the  removal  of toxic  organics  [4,  5, 6].
Overall, these  new  sources  of  information support  changes
regarding preapplication  treatment and storage.

      2.3.2  Preapplication Treatment

The OF experience to date, as discussed in Sections  3  and  4,
leads to the following  conclusions:

          OF  systems are capable  of  performing  satisfactorily
          with    only   minimal   levels   (i.e.,    screening,
          comminution)  of preapplication treatment  [1,  7,   8,
          9, 10].

          For   certain  treatment  objectives  (e.g.,   nitrogen
          removal),  OF systems using minimal preapplication
          treatment  perform  better than those  using  higher
          levels of  preapplication  treatment [1,  7,  11,  12,

          Algal solids are  difficult  to remove  in  OF systems
          [7,  10,  14,  15,  16]  and preapplication  treatment
          processes  which encourage  algal growth  frequently
          result in greater  discharge  of suspended solids.

          Inadequate  screening,  resulting   in   clogging  of
          distribution systems,   is  a  common  problem found in
          municipal OF systems.

     2.3.3  Storage

OF systems often  require  less storage than slow  rate land
treatment systems for the same climatic  conditions (see Chapter
5).   In  most cases,  there  is no need  for storage  during
rainfall   events.     Because  of  the   potential   for  algae
production,  storage cells  should  be  designed as  off-line,
rather than on-line,  components  of the treatment  system.

     2.3.4  Distribution  Systems

Most municipal OF  systems designed to date use surface or low
pressure  distribution methods  to minimize energy  costs and
aerosol  generation.    Although these   methods  can  be  used
effectively,  it is  difficult  to  balance the hydraulics to
achieve uniform flow to all  terrace areas.   Consequently, it is
also difficult to achieve and maintain uniform sheet flow down
the terraces.  These factors  do not lessen the  advantages of
using   surface  and   low   pressure   systems   for   municipal
wastewaters,  provided  they   are  considered during  design and
construction as discussed in Chapter 6.

2.4  Terrace Design and Construction

Observation of recently  completed municipal OF facilities has
shown  that terrace  construction has  not  always  achieved the
design goal of uniform  sheet flow.  In efforts to conserve
costs, or because -of a lack of understanding of the  importance
of  grading,  many  OF  terraces  have not   been  designed  and
constructed in a   manner  and  to  the  tolerances which will
provide uniform sheet flow.   Detailed recommendations for
improving    terrace  design  and construction  practices  are
provided in Chapter 7.

2.5  Vegetation Selection and Establishment

The OF  process requires  water-tolerant  turf grass.   Thus, the
options of vegetation selection  are not nearly as flexible as
for  slow  rate land  treatment.   The  more  intensive operating
schedule of an OF  system diminishes the  significance and value
of harvesting the grass crop.   It is  best to  leave  the cut
grass  on  the  terrace for the first year or two  to  build up a
mulch layer,   thereby accelerating system  acclimation and

providing better overall performance.   Moreover,  since the
primary purpose  of  the OF  system  is  wastewater treatment .and
not crop production, the cash value of the grass should not be
given more  importance  than it deserves.   An over-emphasis on
cash  value  can  lead  to  operating  procedures  which  are
counter-productive  to  good wastewater  treatment performance.
Recommended procedures  for vegetation  selection,  establishment,
and management are discussed in Chapter  8.

2.6  References

 1.  U.   S.   Environmental  Protection   Agency.     Technology
     Transfer  Process Design Manual for  Land Treatment of
     Municipal Wastewater.  EPA  625/1-81-013.   U.  S.  EPA,
     Center for Environmental Research Information, Cincinnati,
     OH.  October 1981.

 2.  Reed S. C.  and R. W.  Crites.   Handbook of Land  Treatment
     Systems for Industrial and  Municipal Wastes.   Noyes  Data
     Corporation, Park Ridge,  NJ.  1984.

 3.  Ketchum, L.  H.  et al. Overland Flow Treatment of  Poultry
     Processing   Wastewater   in    Cold   Climates.      EPA
     600/52-81-093.    U.  S.  Environmental  Protection  Agency,
     Robert  S.  Kerr Environmental  Research  Laboratory,    Ada,
     OK.  July 1981.

 4.  Jenkins, T.  F., et al. Assessment  of the  Treatability of
     Toxic Organics by Overland  Flow.    CRREL Report '83-3.  U.
     S. Army Corps of Engineers  Cold  Regions Research and
     Engineering Laboratory, Hanover,  NH.   1983.

 5.  Zearth, M.,  et al.  'Removal of Toxic Organics by Overland
     Flow.   Department of Civil  Engineering,  University of
     California  Davis  - Davis, CA.   1984.

 6.  Enfield,  C.  G.,   et'al.   Mathematical   Description of
     Volatile  Toxic  Organics   on  Overland  Flow.     U.  S.
     Environmental   Protection  Agency,     Robert   S.   Kerr
     Environmental  Research Laboratory>  Ada,  OK. '1984.

 7.  Smith,  R.  G. and  E.  D.  Schroeder.   Demonstration of the
     Overland Flow Process  for the  Treatment  of  Municipal
     Wastewater  - Phase II Field Studies.  Department of  Civil
     Engineering,  University of  California,  Davis - Davis,
     California.  1982.

 8.  Thomas, R.  E.,  K. Jackson,  and L.  Penrod.   Feasibility of
     Overland  Flow  for  Treatment  of  Raw Domestic  Wastewater.
     EPA  660/2-74-087.  U. S. Environmental Agency,  Robert S.
     Kerr Environmental Research Laboratory,   Ada,  OK.   1974.

 9-  Bledsoe,   B.  E.   Development  Research  for Overland  Flow
     Technology.    EPA 600/9-31-022.   In:    Proceedings  of
     National Seminar on Overland Flow Technology for Municipal
     Wastewater.  U. S. Environmental Protection Agency,  Robert
     S.  Kerr  Environmental  Research  Laboratory,   Ada,  OK.

10.  Abernathy, A.  R.   Overland Flow  Treatment of  Municipal
     Sewage at Easley, SC.   EPA 600/2-83-015.   1983.

11.  Martel,  C.  J.,  T.  F.  Jenkins,  and   A.   J.   Palazzo.
     Wastewater Treatment  in  Cold  Regions by Overland  Flow.
     CRREL  Report 80-7.   U.   S.  Army Corps of  Engineers,  Cold
     Regions Research and Engineering Laboratory,  Hanover,  NH.
     1980.                     ;

12.  Thomas, R. E.   Preapplication Treatment for Overland Flow.
     In:   Proceedings of International  Symposium  of State  of
     Knowledge in Land Treatment of Wastewater.  Volume  I,  pp.
     305-312.   U.  S. Army  Corps of Engineers,  Cold Regions
     Research and Engineering Laboratory, Hanover,  NH.   1978.

13.  Smith,  R. G.,   et  al.    Performance of Overland Flow
     Wastewater Treatment Systems  Summary Report.   Department
     of  Civil  Engineering,  University  of  California,  Davis  -
     Davis, California.   1982

14.  Witherow,  J.  L.  and B.  E.  Bledsoe.  Algae Removal by  the
     Overland  Flow  Process.    U. S.  Environmental  Protection
     Agency,  Robert S.  Kerr  Environmental  Research Laboratory,
     Ada, OK.   1982.

15.  Hall, D.  H.,  et al.   Municipal  Wastewater Treatment  by  the
     Overland     Flow    Method     of    Land     Application.
     EPA-600/2-79-178.  1979.

16.  Peters,  R. E.,  C.  R.   Lee,   and  D.  J.  Bates.   Field
     Investigations  of  Overland  Flow  Treatment  of   Municipal
     Lagoon Effluent.   Technical Report EL-81-9.  U. S. Army
     Engineer   Waterways  Experiment  Station,   Vicksburg,   MS.
     September 1981.

                           CHAPTER  3

                        DESIGN CRITERIA
3.1  Procedures

The Manual [1] describes two procedures for the design of an OF
system.  The most commonly used method is an empirical approach
which  was  developed  from successfully  operating  OF  systems.
The alternative presented in the Manual  [1]  is  the  preliminary
development of a rational design procedure [2,  3,  4].   Advances
in both of these methods are presented below.

3.2  Empirical Method

     3.2.1 Revised Criteria

Most,  if  not all,  of the  recently  constructed OF  facilities
were designed  using the  empirical method.   Hydraulic  loading
rates,  application  rates, terrace  lengths,  and other  variables
were selected to be within .the  range  of  design criteria listed
on Table 6-5 of the Manual  [1].  Recent  studies [5, 6,  7] have
shown  excellent  performance   with   hydraulic  loading1  rates
greater than  the  upper limit of the  ranges  shown on  Table 6-5
of the Manual [1],  thereby  implying  that the  ranges  given in
Table  6-5 [1]  are conservative.   However,  these high rate
application projects have been  research/demonstration projects
with near  ideal construction and operational control.   The use
of high loading  rates has not yet been  observed  on full-scale
systems  which are  operated and controlled exclusively by a
municipality.  Most of the  municipal  systems were  designed and
are  currently operating at  the low end  of  the range  given in
Table  6-5  of the Manual  tl]•  Therefore, major modifications to
Table  6-5  [1]  cannot ,be  supported by the  results  from current
operating  systems.  However, on the basis of current knowledge,
most municipal  OF  systems can  operate successfully at loading
rates  nearer to the median of the design ranges^Conservative
designs near  the  low  end of the range may negate the  advantage
of  using  the OF process.    Such conservatism  can  result in  a
non-discharging  slow  rate  land  treatment system  which  is
unnecessarily  costly  due   to  the   extensive  preparation  of
terraces.   It  may also result  in an  intermittent overland  flow
system Which produces a poorer quality effluent  because the
terraces often become  too dry for good performance.

Table  3-1  is  a revised version of  Table 6-5 of the Manual  [1].
Table   3-1  shows  a  range  of   values   for  each   type  of
preapplication   treatment  based  on  successfully  operating
systems.     The   relationship   between  application  rate  and
hydraulic  loading  rate  is   discussed  in Section 6.4.2  of the
Manual [1].   These  ranges allow the designer to select  specific

                        TABLE  3-1

  m /h m
Loading Rate
Screening/Primary    0.07 - 0.12'
                   2.0 - 7.0
Aerated Cell         0.08 - 0.14
  (1 day detention)
                   2.0 - 8.5
Wastewater Treat-
  ment pond°
0.09 - 0.15
  2.5 - 9.0
0.11 - 0.17
  3.0 -10.0
a. m /h m x 80.5 = gal/h ft

b. cm/d x 0.394 = in./d

c. Does not include removal of algae

d. Recommended only for upgrading existing secondary

design  values  on the  basis of  several inter-related  factors
such as effluent discharge requirements, climate, and  the  type
of distribution system used.   Rates  near the upper end of  the
range may be used during warm months,  while values near the low
end are suggested if soil temperatures drop below approximately
10°C or  if maximum  removal efficiency  is  desired [!]•   Slope
lengths  and application periods are  discussed  in Sections and, respectively.

     3.2.2 Use of Design Ranges

  Selection of Hydraulic Loading Rate

The suggested design ranges shown on Table 3-1 are divided into
four categories  on  the  basis  of the  level of  preapplication
treatment  provided.   Within each of  the  four categories,  the
specific design criteria are shown as ranges, rather than  as  a
single number.   The  range is  provided  to account for  the
variable conditions which  may be encountered  at different OF
sites throughout the country.  The principal variables  are the
climatic environment of the project and  the effluent discharge
limitations imposed on the system.

The first  step in using Table  3-1 is  to establish the level of
preapplication treatment  which  will  be provided.   Next,  the
hydraulic  loading rate can be  selected  on  the basis  of climate
and effluent  limitations.    For  use  with  Table   3-1,  climatic
conditions can be divided into three categories as follows:

     Cold  climates  -  Those  which require  the  same number of
        storage days for OF as for slow rate  systems.   This is
        explained   in   more   detail   in   Chapter   5.     The
        geographical areas  defined by this category  are  those
        at  and above  the 80 day storage line shown  on Figure
        5-1 of this document.

     Moderate climates - Those locations between the 40 day and
        80 day storage lines shown on Figure 5-1.

     Warm  climates -  Those where the OF  system will not be
        affected by short duration freezing temperatures.   The
        warm climate  zones  are  defined  as those at  and  below
        the 40 day storage line shown on Figure 5-1.

Also  for use with  Table  3-1,  the effluent discharge criteria
can be divided into three categories as follows:

     Least  stringent  -  Defined as  EPA's  secondary treatment
        quality for trickling  filters and wastewater treatment

      Moderately  stringent  -  Intermediate levels  of BOD and
         suspended solids  (between  10/10  and  secondary  limits
         defined above), but  no nutrient  limitations.

      Most  stringent - High ,levels  of  BOD and suspended  solids
         removal  (i.e.,  10/10 or better)  and/or the inclusion of
         nutrient  limitations.

When the project location  is in a warm climate zone (at or
below the  40 day storage line on Figure 5-1)  and the  effluent
discharge  limitations  fall  into  the  least stringent  category
(as  defined  above),  the highest application rate  (and hydraulic
loading  rate) in  a  particular  preapplication treatment  category
can  be selected.   Conversely, when the project  is  in a cold
climate  (at  or above the 80 .day storage  line on Figure  5-1) and
the   effluent  discharge  limitations  fall  into   the . most
restrictive  category (as defined  above), the lowest rates in a
particular preapplication treatment category can be  considered.
If  both  variables  (climate  and discharge  limitations)  are in
the  moderate categories,  rates near  the  median  of  a  specific
range are   suggested.     Using  the   same  logic,   all  other
combinations  of  the   two   principal  variables  (climate  and
discharge  limitations)  will  fall  somewhere within the range of
application  rates and  hydraulic loading rates in Table 3-1.

   Determination of Land Area

The  land area is  determined by combining the  facility design
flow,  the hydraulic loading  from Table  3-1, and  the number of
operating days for  the  system. The equations  in Section 6.4.8
in the Manual [1]  can be used  for this purpose.   The operating
days  for a particular facility are based on the storage factors
in  Chapter  5 of  this .text  and  the designer's best judgement
regarding any other non-operating periods.   It  should be noted
that  once  the hydraulic loading rate  is selected and the land
area calculated,  the designer still may have  the  option of
selecting  a  surface, low  pressure, or  high pressure  system,
provided the application rates are maintained within the ranges
presented in Table 3-1.

  Selection of Terrace Length

The  length  of individual OF, terraces  is controlled by  the
choice  of  distribution  system  and  the  effluent  discharge
limitations.   Surface  and  low  pressure  distribution  systems
require terrace lengths of 20 to 30 meters, while high pressure
sprinkler distribution  systems require a  terrace length  of 10
to  20 meters  greater  than the diameter  of the   sprinkler
pattern.   The three  categories of discharge criteria listed in
Section  also influence  selection  of  terrace  length.
When  the  discharge  limitations fall  into the least stringent
category, the shortest length can  be considered,  while the most

stringent category will  require the  longest length
lowest application rate.
and the
  Selection of Application Period

Table 6-5 of the  Manual [1] suggests that  application periods
can be  from 8 to  12  hours per day,  and that the application
frequency can  be  from  5  to 7 days per  week.   Although these
remain   as  good  guidelines   for   satisfactory  treatment
performance,   they are not rigid  boundary  conditions.   Of
particular importance is the fact that the  application periods
(at the rates shown in Table 3-1)  can be  increased  up to  24 h/d
for periods of two to,  four weeks during warm weather  with no
adverse  impact on treated  effluent BOD  and  suspended  solids
concentrations.  Continuous application  (using 0.03 m /h-m) at
24 h/d,  7 d/wk was  successful  for  over  a  year using primary
effluent at a  pilot project in New York State [8]. At3another
project,  with  a  higher   application  rate   (0.18  m /h • m) ,
continuous  operation  for  24 h/d  for  extended periods  of time
(i.e., greater than two weeks),  even during warm  weather, was
found  to result  in  decreased  performance,  particularly with
respect to nitrogen removal C2] .

The capacity for accepting longer application  periods for a few
weeks allows portions  of  a system  to  be shut down completely
for mowing and/or maintenance while  the remainder of the  system
continues to treat the design volume of wastewater  at hydraulic
loading rates  higher than  the  design average.   It also  allows
stored wastewater  to be added  to  the daily design flow  and be
satisfactorily  treated  without  adding  to  the  total land

Based on previous  experiences, it follows  that  the application
periods can be flexible,  but  they usually fall within a range
of 6  to 12 hours, regardless of  the  climate and  discharge
categories used  for  selecting the design hydraulic  loading
rate.  Selecting a specific application period between  6  and 12
h/d for individual terraces has not  been found to be a  critical
part  of the design  procedure.   However,  there  are  certain
advantages  (explained in Section 6.5) to operating a system 24
hours  a day,   while  still maintaining a  6-12 h/d application
period for the individual  terraces.

3.3  Rational Design Procedure

     3.3.1 Introduction

A rational  design procedure is presented in Section 6.11.2 of
the Manual [1] as a  model which describes BOD removal as  a
function of terrace  length and  application  rate,  where the
application rate  has  the units m /h.m of  slope  width.   This

procedure  was  developed   by  Smith  and  Schroeder   at  the
University of  California-Davis  [2]  as an  alternative to  the
empirical design approach.

     3.3.2  Procedure

The rational design equation is presented in the following form
Cl, 2]:
               c -c   A    -kz/qn
                z  =  A exp   ' ^

= concentration of BOD,, in applied wastewater,  mg/L
     C  =  concentration  of BOD_  at a distance (z) down the
          terrace, mg/L

      c = minimum   achievable   effluent   concentration,   mg/L
           (determined to be 5 mg/L BOD [2])
      A = empirically determined coefficient dependent on the
          value of q

      z = distance down terrace, m
      k = empirically determined rate constant

      q = application rate,  m /h.m terrace width, the  valid
          range for model shown on Figures 3-1 and 3-2

      n = empirically determined coefficient, exponent

The  preceding equation has  been developed further [4]  as a
family of  curves  of (C -c/C ) vs z for  different  values  of q.
These curves, as  shown1 on figures 3-1 and 3-2 for screened
wastewater and primary  effluent,  respectively,  can be used for
selecting  design  application  rates  to  achieve  needed  BOD

      3.3.3  Example

The  following example was developed by Smith and Schroeder [2].
It  is presented here  only  to illustrate  the  design procedure
just described.

Assume the following information is known:

     1.  Applied  wastewater  =   screened  raw  municipal

     2.  Plow (Q) = 3,000 m3/day

     3.  Influent BOD5 (CQ) = 150 mg/L

     4.  Required effluent BOD_ (C) = 20 mg/L

The necessary design calculations are:

     1.  Compute the required removal ratio C-5/C
                          = 0.10
         Select application rate (q) in valid range of
Select q = 0.37 m /h
         Determine required value of terrace length (z),
         referred to as distance down-slope in Figure 3-1.

               z = 41 .5m

         Select application period (P) .

               P = 12 h/d

         Compute q for area calculation, applying a safety
         factor of 1.5 [2].
                     0.37 nr/h.m
                   = 0.25 m /h-m

          APPLICATION RATES, (m3/h-m)q.
                  10              20             30             40

                             DISTANCE DOWN SLOPE, m

                                    FIGURE 3-1
                       WITH SCREENED RAW WASTEWATER (4)

         APPLICATION RATES, (m3/h-m)q
                                20             30

                            .  DISTANCE DOWN SLOPE, m

                                    FIGURE 3-2
                            WITH PRIMARY EFFLUENT (4)

          6.   Compute required total  area.
              application frequency.
                    Area =
Assume 7 d/wk
                    Area =
                         - (3,000  m3/d)(41.5 m)
                           (0.25  m /h.m)(12 hr/d)
                    Area = 41,500 m = 4.2  ha (10.4  ac)

The rational design  procedure  presented above has been  tested
on  several  OF  research  systems  [2, 3,  9,  10].     Field
investigations at Ada,  OK £9] verified the design equation  with
respect to terrace length and expanded  it to  determine terrace
length  for desired concentrations of suspended  solids and
ammonia.  Those field investigations [9] ran  from  July through
October  when   maximum   and  minimum  average   monthly  air
temperatures were  35°C  (95°F)  and  9  C  (48 F),  respectively.
Use of the equation  for other than warm weather  conditions was
not tested.  Field investigations at Easley,  SC  [10] partially
validated the BOD removals defined by Equation 3-1.

As more experience is gained, this model,  or some similar first
order relationship, may become the basis  for  all designs.  One
of  the  major  present  benefits  is  the  support  that  this
procedure  provides  for  the safety and  conservatism of the
criteria  in  Table  3-1,   and  the  related  empirical   method
described in this Chapter.   It shows that the empirical  design
procedure  (Table  3-1)  has  an  adquate  safety factor and  that
additional  safety  factors  are  not  needed  when  using  the
empirical method.

3.4  References

 1.  U.  S.   Environmental  Protection  Agency.      Technology
     Transfer  Process  Design  Manual  for  Land Treatment  of
     Municipal Wastewater.  EPA 625/1-81-013.   U.  S.  EPA,
     Center for Environmental Research Information,  Cincinnati,
     OH.  October 1981.

 2.  Smith, R.  G.  and E.  D.  Schroeder.  Demonstration  of the
     Overland Flow  Process  for the  Treatment of Municipal
     Wastewater - Phase II  Field  Studies.   Department  of Civil
     Engineering, University of  California, Davis -  Davis,
     California.  1982.

 3.  Martel, C. J.,  et al.   Development  of a Rational  Design
     Procedure for Overland  Flow Systems.  CRREL  Report  82-2.
     U. S. Army Corps  of Engineers,  Cold Regions  Research  and
     Engineering Laboratory,  Hanover,  NH.   1982.

 4.  Smith, R. G.  Development  of a Rational Basis  for  Design
     and  Operation  of   the  Overland  Flow  Process.     EPA
     600/9-31-022.   In:    Proceedings of  National Seminar  on
     Overland Flow Technology for Municipal Wastewater,  Dallas,
     TX.  1981.

 5.  Ketchum, L.  H.  et al.  Overland Flow Treatment  of  Poultry
     Processing   Wastewater    in   Cold   Climates.       EPA
     600/52-81-093.    U.   S.   Environmental  Protection  Agency,
     Robert S. Kerr Environmental Research Laboratory,  Ada,  OK.
     July 1981.

 6.  Wightman,  D., et al.   High-Rate Overland  Flow.  Water
     Resources Research,  Volume 17,  No. 11, pp.  1679-1690.
     Pergamon Press Ltd.   1983.

 7.  George, D. B.,  D. Wightman, and J.  Witherow.   High-Rate
     Overland Flow Treatment of Municipal Wastewater.   LCC
     Institute of Water Research, Lubbock, TX.   1983.
8.  Clark,  P.  J.
    Project Report,
                       Marsh  Pond/Overland Flow  Pilot Plant
                      Clark Engineers,  Rochester, NY.    1983.
 9.  Witherow, J. L. and  B.  E.  Bledsoe.   Design Model for  the
     Overland Flow  Process.    U.  S.  Environmental  Protection
     Agency, Robert S. Kerr  Environmental  Research  Laboratory,
     Ada, OK.  1984.

10.  Abernathy,  A. R.,  J. Zirschky, and M. B. Borup.   Overland
     Flow  Wastewater  Treatment   at   Easley,   SC.     Clemson
     University, Clemson,  SC.  1984.

                           CHAPTER 4

4.1  Areas of Importance

Experience with OF  technology continues to show  several  areas
of preapplication treatment  to be especially important to  the
cost-effectiveness and performance of the process.  These  are:

          The level of preapplication treatment

          Effective solids removal  to prevent clogging of  the
          distribution system

          The effect of algae on suspended solids  removal

4.2  Level of Preapplication Treatment

Section 6.3  of the Manual  [1] recommends that preapplication
treatment consisting  of  screening and comminution  is  adequate
for OF systems.  Where the treatment site is  not well isolated,
aeration  is  also  recommended  to  control odors  during  storage
and/or application.   Data  from research studies [2, 3, 4,  5,3
continue  to  confirm the ability  of OF  systems  to produce  an
effluent  superior to  secondary effluent  when  applying  screened
raw  municipal  wastewater.     Thus,   it  is  generally   not
cost-effective to provide high levels of treatment prior to  OF.
Ynfact,IncaseswherenitrogenremovalIsa   major
consideration, high  levels of preapplication treatment  can
actually  interfere with  this objective.   Greater nitrogen
removal  can be achieved  when the  applied wastewater has  a
higher carbon  to nitrogen  ratio  [6].   Thus,  better  nitrogen
removal can  be expected when  applying  screened raw wastewater
than when applying either primary or secondary effluent.

Presently, many regulatory authorities require higher levels of
preapplication treatment than screening or comminuting.   A
single-cell   aeration   pond   with   a   detention   time   of
approximately  one  day  is  an  approach  which   is   gaining
acceptance.   These short  detention  time aerated  cells are in
use  in several  recently  constructed  OF  systems.   Limited
performance  data  are  available from these  systems.   However,
this method offers the following potential advantages:

          A  level  of  preapplication  treatment   which  often
          satisfies those state guidelines which require higher
          levels of preapplication  treatment  than screening or

     Positive odor control.

     Minimal   sludge   management    (as    compared   to
     conventional   primary   and.   secondary   treatment

     Relatively  simple  and inexpensive  construction and

     Reduced potential for .algal  growth.

Solids Removal
A common problem with some  newly  constructed municipal OF
systems has  been solids clogging  of the distribution  system.
The result  is  poor wastewater  distribution  onto the  terraces
and increased maintenance time for opening clogged orifices in
the distribution  system.   Although  this  problem can never be
completely eliminated, it can be  substantially reduced by
providing   an   adequate   screening   system   as   part   of
preapplication treatment.

4.4  Algal Interference
The Manual ClD indicates that algal solids have been difficult
to remove from some  stabilization pond effluents .   Further
experience C2, 5,  7, 8, 9] has confirmed that algal solids are
not reliably  removed  by OF systems .   Preapplication treatment
that generates algae  (i.e., stabilization ponds) increases the
effluent  suspended   solids   concentration   from  OF  systems
compared to preapplication treatment  which  does not encourage
algal   growth.     Appropriate   selection   of  preapplication
treatment processes,  coupled with appropriate  design of storage
facilities,  is  an  important  consideration  when  designing to
minimize algal solids in system discharges.

4.5  References

 1.  U.  S.   Environmental  Protection   Agency.     Technology
     Transfer Process  Design Manual for  Land Treatment of
     Municipal  Wastewater.   EPA  625/1-81-013.   U. S.  EPA,
     Center for Environmental  Research Information, Cincinnati,
     OH.  October  1981.

 2.  Smith,  R. G. and E.  D.   Schroeder.    Demonstration  of the
     Overland Flow  Process   for  the Treatment of  Municipal
     Wastewater -  Phase II Field Studies.  Department of Civil
     Engineering,  University of California,  Davis -  Davis,
     California.   1982.

3.  Thomas, R. E., K. Jackson,  and  L.  Penrod.   Feasibility of
    Overland  Flow for Treatment  of Raw  Domestic  Wastewater.
    EPA 660/2-74-087.  U.  S.  Environmental  Protection Agency,
    Robert  S.  Kerr Environmental  Research  Laboratory, U.  S.
    EPA, Ada,  OK.  1974.

4.  Bledsoe,  B.  E.   Development Research  for Overland  Flow
    Technology.    EPA  600/9-31-022.     In:   Proceedings  of
    National Seminar on Overland Flow Technology for Municipal
    Wastewater.   U.S. Environmental Protection Agency, Robert
    S. Kerr Environmental Research Laboratory,  Ada, OK.  1980.

5.  Abernathy, A.  R.   Overland  Flow  Treatment of  Municipal
    Sewage at Easley, SC.   EPA 600/2-83-015.  1983.

6.  Smith,  R. G.,  et  al.   Performance  of   Overland  Flow
    Wastewater Treatment  Systems  Summary Report.   Department
    of  Civil  Engineering,  University  of  California,  Davis  -
    Davis, California.  1982

7.  Witherow,  J.   L.  and B.  E.  Bledsoe.  Algae  Removal by the
    Overland  Flow Process.   U.  S. Environmental  Protection
    Agency, Robert S. Kerr  Environmental  Research  Laboratory,
    Ada, OK.  1982.

8.  Hall,  D. H.,  et al.   Municipal Wastewater Treatment by the
    Overland  Flow   Method   of  Land   Application.        EPA
    600/2-79-178.  1979.

9.  Peters,  R.  E.,   C.  R.  Lee,  and   D.  J.  Bates.   Field
    Investigations of Overland  Flow  Treatment of  Municipal
    Lagoon Effluent.   Technical Report EL-81-9.   U.  S.  Army
    Engineer  Waterways   Experiment  Station,   Vicksburg,   MS.
    September 1.981.

                           CHAPTER 5

5.1  Current Practice

Section 6.5.1 of  the Manual [1] states  that  the EPA computer
programs  C2]  EPA-1  and  EPA-3  (storage  programs  based  on
freezing   temperatures,   rainfall,   and   snow  accumulation
constraints) may  be used  to  estimate,  conservatively,  the
winter storage requirements for OF systems.   It  further states
that in areas of  the country below the 40-day storage contour
shown on Figure 2-5 of the Manual [1],  OF systems can generally
operate  all year  without storage.   One example is  a  large
industrial  OF  system  in  Texas   [3J   which  has  operated
successfully for 20 years without any storage.

Using EPA-1 and EPA-3 produces  a conservative design of storage
facilities for municipal OF systems.   This conservatism is
fostered by several factors,  including:

          EPA-1 and EPA-3 were  developed primarily  for slow
          rate land treatment systems.

          Lack of  operating experience with OF operation in
          various  geographical  areas.

          Concern  by state regulatory authorities over cold and
          wet weather performance.

          The use  of storage  facilities  for  other objectives
          (e.g., preapplication treatment, reduction of the
          length of the operating days, weekend  shutdown, etc.)
          in  addition  to non-operation  only  during inclement

A small amount of  storage does  provide considerable operational
flexibility to  a  system.   Even  where climatic  conditions are
mild enough to avoid cold weather storage, two to five days of
storage  capacity   will   allow  the   convenience  of  weekday
operation,  if desired.   It will also provide added flexibility
for  terrace  maintenance  and  mowing.   This  flexibility is
especially  important  for  small  to  moderate   size   systems.
However, a large   percentage of recent  designs  are combining
storage as an inseparable part of the  preapplication treatment
process (e.g., the  storage  volume  is added  to  the volume of a
stabilization pond).    Such designs  have  limited operational
flexibility to allow control of algal production or to remove
the algae prior to application  to the OF  system.

5.2  Cold Weather Storage Requirements

Experience has been mixed  regarding  the ability of OF  systems
to operate during cold weather conditions.   Studies  in New
Hampshire [4], Wyoming [5], and Indiana [6]  have shown that OF,
operated in'the  typical  cyclic pattern,  could not always meet
secondary effluent requirements.   On the other  hand, an OF
system  treating primary effluent in  New York  State  [7] has
operated successfully through  two  winters without storage and
met secondary effluent  requirements  by operating  continuously
for 24  hours a day,  7  days per week.  That  system operated
under very severe climatic conditions,  yet  consistently met or
exceeded secondary treatment quality.

General guidance  for  storage at  overland  flow systems is
provided in Figure 5-1  which  is a  revised  storage contour map
similar to Figure 2-5 found  in the Manual  [1].  Figure 5-1 is
only a general guide,  based on the  following conditions:

          Storage equivalent  to that  required for  slow rate
          land  treatment  systems   is   shown  for  systems  in
          moderate and  cold  climates  (i.e.,  at and  above the
          40-day contour line on Figure 5-1).

          Storage for cold weather  operation is not shown for
          systems  in warm climates  (i.e.,  those  below the
          40-day contour line on Figure 5-1).

          A minimum of two to  five days storage  is recommended
          for systems in warm climates to  provide operational
          flexibility and convenience.

The designer  and operator must  recognize that,  if storage is
provided according to Figure 5-1, the  storage  facility  must be
reserved  for  those  days  which actually  require  storage.   In
moderate  climate regions,  there are frequently a significant
number   of   favorable   application  days   intermixed  with
unfavorable  days during the  winter.   During these favorable
days, it may  not be  possible to apply the  full  design  loading
rate, but  it  may very well be possible to apply at a  reduced
loading   rate   without   violating  the    effluent  discharge
limitations.  This procedure can be  used  to reduce the  storage
requirements  for systems  located  between  the  40- and 80-day
contour lines.   On  the  other  hand,  in the cold climate  zones
(those  above  the 80-day storage line), it may not be possible
to  use  intermittent   operation  during  the  winter   without
violating the effluent discharge limitations.

5.3  Rainfall Considerations

There continues  to  be  a common misconception that OF  systems
cannot  be  operated during  rainfall  events.    However, since OF


500	I OOP
                        FIGURE 5-1

systems   are  specifically   designed   for  surface   runoff,
arbitrarily prohibiting wastewater  application  during  rainfall
will  serve  no  purpose  unless  the  discharge  violates  the
conditions of the discharge permit and impairs water quality in
the receiving stream.

     5.3.1 Impact on Effluent BOD Concentration

Experience has shown that rainfall  of  any  intensity has little
effect on  effluent  BOD concentrations.  Studies  with  screened
raw and primary effluent municipal  wastewaters  showed  effluent
BOD concentrations  during  rainfall  events to be  only  slightly
eleyated above normal  operating  values,  but-well below the 30
mg/L secondary treatment standard [8, 9].  Similar results have
been  found at  several industrial  OF systems  treating  food
processing  [10],  textile  [11],   and   pulp  and  paper  [12]
wastewaters.   Most  of the  industrial experiences  showed  that
the  effluent  BOD   concentration   increased   slightly  during
moderate rainfall intensities and/or short duration storms, but
actually decreased  below normal operating values  during  high
intensity and/or long  duration rainfall  events.   This  decrease
can most likely be attributed to dilution.

     5.3.2 Impact on Effluent Suspended Solids Concentration

The impact of rainfall on the suspended solids concentration of
the treated effluent can be more significant than the influence
on BOD.  Increased concentrations of suspended solids have been
found to  consist  principally of non-volatile solids resulting
from varying degrees of soil  erosion [8, 13].   Elevated levels
of suspended solids  are typically found  in the  rainfall runoff
from newly constructed systems where the vegetation has not had
sufficient  time  to  provide thorough coverage of  the terraces,
where runoff  channels  have not  been stabilized,  or where the
design/construction  practices   did  not   follow  sound  soil
conservation and  agricultural principles.   Mature  OF systems
with stable soils and  established vegetation  show little or no
increase  in suspended  solids concentrations.   In  one project
where the  impact of rainfall was  studied  [14],  the suspended
solids  concentration  in  the discharge  resulting  solely  from
rainfall of  approximately  1.5  cm was  similar to  the following
day's discharge  resulting  solely from applied wastewater.   In
some cases, erosion protection (e.g., rip-rap, concrete lining,
and other  soil stabilization procedures)  of  drainage  channels
may be necessary to further reduce suspended solids discharges.

     5.3.3 Mass Discharges

Even   though   the    effluent   BOD   and   suspended    solids
concentrations  during rainfall are  similar to dry  weather
conditions, the mass discharge  of these  constituents obviously
increases proportionally to both the intensity  and  duration of

the  rainfall  event.   For  systems  with discharge  limitations
which are  specified in mass  units,  heavy* rainfall events  can
cause a violation of the mass discharge  limitations during  the
actual event C14, 15].   However, it is unlikely that the 30-day
average limits in the discharge permit will be violated.

     5.3.4 Recommended Operating Practices

While rainfall increases the mass of most pollutants discharged
from an OF system, it also results in increased stream flow  and
minimal  impact  on  receiving water quality.   Therefore,  the
operating permits for OF systems  need  not  prohibit  application
of wastewater  during  rainfall events.   Recognizing this, some
state regulatory agencies and EPA regions have  written permits
based on flow  which increase the mass discharge  limits during
rainfall and/or  replace them with a concentration  limit.   The
U.   S.   Army   Engineer  Waterways   Experiment  Station   has
recommended a  detailed  procedure for developing  permits  which
take the above factors into consideration [9].

5.4 Storage Reservoir Design

To minimize the  impact  of algae  on  treatment performance,  the
storage reservoir should  be designed as an  off-line  component
of the system  and used  only as  the  need  dictates.  The storage
reservoir should be emptied as soon as possible by blending  the
stored wastewater containing  algae  with  pre-treated wastewater
prior to its application to the OF system.

5.5  References

 1.  U.  S.   Environmental   Protection  Agency.     Technology
     Transfer Process  Design  Manual for Land  Treatment  of
     Municipal Wastewater.  EPA 625/1-81-013.    U.  S. EPA,
     Center for Environmental Research Information,  Cincinnati,
     OH.  October 1981.

 2.  Whiting, D. M.  Use of Climatic Data in Estimating Storage
     Days for Soil Treatment Systems.  EPA-600/1-76-250.  U. S.
     Environmental  Protection Agency, Office of Research  and
     Development.  1976.

 3.  Thornthwaite, C.  W.   An  Evaluation  of Cannery Waste
     Disposal by Overland Flow  Spray Irrigation.   Publications
     in Climatology 22.   1969.

 4.  Martel,  C.  J.,   T.   F.   Jenkins,  and  A.  J.   Palazzo.
     Wastewater  Treatment  in  Cold   Regions  by Overland  Flow.
     CRREL  Report  80-7.  U.  S.  Army  Corps  of Engineers Cold
     Regions Research and Engineering Laboratory, Hanover,  NH.





Borelli, J., et  al.   Overland Flow Treatment  of  Domestic
Wastewater in Northern  Climates.   University  of  Wyoming,
Laramie, WY.  1984.

Ketchum, L. H. et  al.  Overland Flow Treatment  of Poultry
Processing   Wastewater    in   Cold   Climates.       EPA
600/52-81-093.    U.  S.   Environmental  Protection  Agency,
Robert S. Kerr Environmental Research Laboratory,  Ada,  OK.
July 1981.

Clark,  P. J.     Marsh Pond/Overland Flow  Pilot  Plant
Project Report.   Clark Engineers,  Rochester,  NY.   1983.

Figueiredo,  R.  F.,  R.   G.  Smith,  and E. D.  Schroeder.
Rainfall and Overland Flow  Performance.   Journal  American
Society  of  Civil  Engineers,  Environmental  Engineering
Division, Vol.  110, No.  3,  p. 678.  June 1984.

Peters,  R.  E.,  C.  R.   Lee,  and D.  J.  Bates.    Field
Investigations  of  Overland  Flow  Treatment  of  Municipal
Lagoon Effluent.   Technical  Report EL-81-9.   U.  S. Army
Engineer  Waterways  Experiment  Station,   Vicksburg,  MS.
September 1981.

Gilde,  L.  C. and  O.  M. Aly.   Personal  Communications.
Campbell Soup Company,  Camden, NJ.  1984.

Deemer, D. D.    Overland  Flow Treatment of Textile Mill
Wastewater.    In:   Proceedings   of  the  1984  Triangle
Conference on Environmental  Technology.   Duke  University,
Durham, NC.  1984.
Deemer,  D.  D.  Personal  Notes.
Marietta, GA. 1984.
                ERM-Southeast,   Inc.,
Witherow,  J. L.   Overland Flow in Warm  Climates.   In:
Proceedings  of  the  44th Annual  Louisiana Conference  on
Water Supply, Sewage, and Industrial Waste.  1981.

Witherow, J. L. et al.   Meat  Packing Wastewater  Treatment
by  Spray  Runoff  Irrigation.   EPA  600/2-76-224.    In:
Proceedings  of  the  Sixth  National  Symposium   on  Food
Processing Wastes. 1976.
Witherow,  J.  L.
Systems  - II.   In:
Waste  Conference.
Small  Meat-Packers  Waste  Treatment
Proceedings of the  30th Industrial
 Purdue  University,   Lafayette,   IN.

                           CHAPTER 6

                      DISTRIBUTION SYSTEMS
6.1 Selection

OP  achieves  treatment primarily  through contact  between the
applied wastewater and  the soil medium.   Other factors being
equal, the distribution  method which achieves  the best sheet
flow pattern  will  produce the  best  quality of  effluent.   As
stated  in   Section   6.6   of  the  Manual   [1],   wastewater
distribution  on OF systems can be achieved by surface methods,
low pressure sprays,  and moderate to  high pressure  impact
sprinklers.    Observation of  recently constructed  systems has
added considerable knowledge about the importance  of selection
and design.   A summary  of the advantages  and  limitations of
various types of distribution systems is  provided in Table 6-1.

6.2 Surface Methods

Surface distribution  methods  are  favored by  many regulatory
authorities and engineers because they offer potentially lower
operating costs and minimal aerosol  generation.  Because of the
low aerosol potential,  state regulations usually require less
buffer zone  area  for surface  systems,  especially  compared to
high pressure  sprinkler methods
Achieving and  maintaining
uniform  flow  onto  and  across  the  OF   terraces  can  be
limitation of  surface distribution systems
             They require
careful  installation to achieve the  leveling required for
uniform  flow  through  each  orifice,  and  periodic maintenance
thereafter.        Hydraulically  balancing   and  maintaining
distribution becomes  increasingly difficult  as  the elevation
differences within  the system  increase,
       Uniform  sheet  flow
over the terraces can;generally be accomplished  in the presence
of  a  thick cover  crop.  Spreading can  also be improved by
applying the wastewater onto a gravel  layer and/or  splash
blocks.   The gravel layer  is often underlain by  a  plastic
membrane.   Sufficient  grade  must be provided at  the point of
application to  prevent backflow  under  the distribution pipes
and resulting non-uniform distribution.

     6.2.1 Gated Pipe

Gated  pipe  is  probably  the  best  choice  of  the   surface
application methods.    However, because the  gated pipe is
located above  ground, it has a potential  for  freezing and
settling in addition to the limitations previously  mentioned.
Pipe-runs exceeding 100 m (300 ft),  make it difficult to attain
uniformity  of   discharge   between  gates   without   careful
individual  gate adjustment.     Reasonably  good  results  can be
attained for longer  runs  by  feeding from the high side of the

                                   TABLE   6-1
 Surface Methods (6.2)*

 General (6.2)
 Low energy costs
 Minimize  aerosols
 and wind  drift
 Small buffer zones
 Difficult to  achieve
 uniform distribution
 Moderate erosion
 Gated Pipe  (6.2.1)
 Same  as  General
 Easy  to  clean
 Easiest  of surface
 methods  to balance
 Same  as General plus
 Potential  for
 freezing and settling
 Slotted or perforated
       pipe  (6.2.2)
Same as General
Same as Gated Pipe plus
Small openings clog
Most difficult to
balance hydraulically
Bubbling Orifices (6.2.3)
Same as General plus
Not subject to
Only the orifice
must be leveled
Same as General plus
Difficult to clean
when clogged
Low Pressure Sprays (6.3)
Better distribution
than surface methods
Less aerosols than
sprinkler systems
Low energy costs
Nozzles subject
to clogging
More aerosols and wind
drift than surface
Sprinklers (6.4)
Most uniform
                                                      High energy costs
                                                      Aerosol and wind drift
                                                      Large buffer zones
a.  Section where discussed

terrace and balancing the pressure  gain  from the elevation drop
across the terrace against the  pressure loss  generated by the
friction  of the  wastewater  moving  through the  pipe.   The
advantages of gated pipe are  that the  movable gates  allow
relatively easy flushing  of  debris which tend to  build  up in
the openings.  The use  of a  surge  flow wastewater feed method
has been  found to minimize  the amount of gate  plugging [2].
With  careful  adjustment, the  gates  can be used_ to  attain
reasonable uniformity of  discharge along  the  pipe  in  spite of
minor local height variations.

     6.2.2 Slotted or Perforated Pipe

The grade of  slotted or perforated pipe must be carefully
established and regularly maintained  since there  is  no other
adjustment possible.   Small  slots  and/or perforations are not
as easily  cleaned as  the  gated  pipe  openings, and it  is often
necessary to cut large openings  in  the top of the  pipe for
purposes  of  maintenance.    Recommendations  to use  slotted or
perforated pipe are limited to  small  systems having relatively
short pipe-runs which are easy to adjust.

     6.2.3 Bubbling Orifices

Bubbling  orifices are  essentially small riser pipes (often
1-inch   diameter)    connected   to   underground   distribution
laterals.   Typically, they discharge  onto some type of  concrete
dispersion pad.  Bubbling orifices  have  the same limitations as
other  surface  distribution systems except for pipe settlement
and freeze damage,  since only  the orifice,  not the pipeline,
must be carefully leveled.

6.3 Low Pressure Sprays
Low pressure sprays {i.e., fixed nozzles <1.38 kg/cm   (20 psi)}
are  essentially  a variation  or  extension  of the  bubbling
orifice.  They are available  in many types and variations.  The
principal  limitation  of low pressure sprays  is  plugging from
particles  too  large  to  pass  the orifice and partial  plugging
from  the  buildup  of smaller particles.   Fine  screening or
double comminution before the distribution system or  straining
within the system can  be used to prevent plugging  by large
particles.  Flush  outlets  on  the ends of  the  distribution
laterals   are  helpful  in clearing  the lines  of any  large
particles.   It is usually necessary  to open these outlets for
only  a few minutes, with  the  discharge  applied to the  terrace.
The pulsation  caused by the  flushing also tends  to clear the
fixed  spray nozzles of  accumulated small  debris that has built
up and partially plugged them.

The  principal  advantages  of  low  pressure spray  systems over
surface methods are better distribution  of the wastewater onto

the  terrace  and  less  sensitivity  to   local  variations  in
elevation.    While they produce  less mist  than  high pressure
sprinklers,  they produce more mist  than  surface  methods.   Low
pressure   spray   systems    can   usually  provide   adequate
distribution of  municipal  wastewater on  OF terraces.   Splash
blocks and/or gravel layers are often used to prevent erosion.

6.4 Sprinklers
Medium  {1.38 to  3.45  kg/cm  (20 to 50  psi)}  to high  {>3.45
kg/cm   (50  psi)}  pressure  impact and gear  driven agricultural
type sprinklers have been used extensively  to apply industrial
wastewaters to OF  systems, but only to a limited  extent on
municipal  OF systems.  The  potential  limitations of those
sprinklers   are   non-uniform   distribution   during   windy
conditions, the  risk of  aerosol generation  and the  higher
energy requirements associated with  pumping.  State regulations
usually require  a greater buffer  zone  area  for  sprinkler
systems than for surface and low  pressure distribution methods.
Gear  driven  sprinklers   produce   less   mist   than   impact-
sprinklers,  but generally have a  higher initial cost.  They are
also  more  subject to  clogging  if the  wastewater  contains
stringy-type solids.

Sprinklers provide the most uniform  distribution of wastewater
onto the terraces, thereby making it easier to achieve  uniform
sheet flow  with  less  maintenance.   Minor variations in height
have little effect on discharge and  major variations in height
between terraces  can be  easily overcome  in design.   Medium to
high pressure sprinklers have less  tendency to collect debris
and become plugged, but will be plugged by  particles too large
to pass  the nozzle.   Screening  should be  used  to  reduce the
particle size within the distribution system to one which will
readily pass through the nozzles.  As with low pressure  sprays,
flush outlets on  the  ends  of the laterals are quite effective
in clearing the pipe of any large particles.

Sprinkler distribution  systems have not been shown to  provide
higher  levels of  performance than surface and  low pressure
spray methods when treating municipal wastewaters.  However, on
several industrial OF systems treating higher concentrations of
BOD and suspended solids  than typically found  in  municipal
wastewater,  high pressure sprinklers were found to be the only
satisfactory distribution method  [3].

Vertical distribution risers connected to the lateral pipeline
through  a  flexible coupling allow  easy  cleanout  of any riser
stoppages and protect the buried  lateral pipe from breakage due
to vibration  and  impact.   The piping configurations in Figure
6-1  show both  the effective and  non-effective methods for
placing  lateral  lines  and  sprinklers on  the terrace.   The use
of part-circle sprinklers as shown in Figures 6-1(b) and 6-1(f)

                           RUNOFF COLLECTION
                                                                      (HALF CIRCLE).

                                                      ,  SPRAY DIAMETER  „
C                                                             SPRINKLER
                                                             (FULL CIRCLE)
                            (FULL CIRCLE)
                                                !_ RADIUS
                               RUNOFF COLLECTION
                                                                         (HALF CIRCLE)
                         WOT RECOMMENDED
                              FIGURE 6-1

is not recommended because they will have the tendency to allow
some wastewater  to  drift back, untreated, into  the  collection
channel  (b) or  road (f)  from the  adjacent terrace.  Also,
part-circle sprinklers sometimes have a  tendency  to  rotate  out
of their specific part-circle pattern.   A very slight wind will
cause the configuration shown in Figure 6-1(d) to spray most of
the water on one terrace,  thereby causing an overload  of that
terrace and little or no wetting of the other one.

6.5  Sizing of the Distribution System

A majority  of  the  full-scale  municipal overland  flow systems
have been sized to apply the  full daily design flow  to  the
system  over a six  to twelve hour period,  five  days a week.
This mode of operation minimizes the labor required  to operate
the system,  but  it  may  increase  both  the capital  and  energy
costs for the  system.   For example, if  the  24-hour  wastewater
volume is applied  to the  system  during an 8-hour period each
day, the  piping  distribution  system must be  sized  for  three
times the design flow,  and greater  yet  if the system  is only
operated five days a week.  Additionally, pumping capacity must
also be  increased  by the same order  of magnitude.  Minimum
capital and energy  costs are usually achieved by  designing  for
seven-day,  24-hour  operation of  the pumping and .distribution
system  with no  terrace  receiving  wastewater  for  more than
twelve hours  at  any  one  time,  followed by  at  least  a  twelve
hour  rest  (see  Section    The  designer  and  the
municipality should consider these  factors  during  the  design
and planning stage  and select  the  operating  mode  which is best
for their particular situation.

There has been a tendency to design OF systems with large zones
controlled  by  remotely  operated  valves.   This  increases  the
size of the distribution system compared to  the  use  of smaller
zones with  additional,  but smaller, remotely operated valves.
Large zones can also limit operational flexibility.

6.6  Controls

Both manual and  automatic  controls  have  been used successfully
for operating  OF systems.   The advantages of manual controls
are their simplicity and the fact that  the  operator will have
frequent  contact with and opportunity  for observation  of  the
system.  These advantages must be balanced against the need  for
more operator time and  full  dependency on the operator  to
control the application periods.  Such demands on an operator's
time frequently result in the overwatering of some terraces  and
the underwatering of others.   Totally manual controls  are  not
recommended for  pumped distribution systems.   As  a  minimum,  a
low level cutoff switch should be provided for pump protection.

The primary advantages of automation are better  utilization of
operator time, and in some cases, more accurate  control of the
application  periods.    Automation  can  range  from  a  pump
protection cutoff  switch to  a programmable control system
capable  of  making  decisions  based  on  feedback  from  the
operating system.  The best system is a compromise  which allows
the operator to program any portion of the  system to  operate at
any time for any pre-selected length of time.   This flexibility
is very  helpful  in providing  the desirable  short application
and rest periods during start-up (see Section 8.4), while still
maintaining the capability of  providing  longer application and
rest periods during routine operation (see  Section

The  controls  should also provide  minimum  safety  detection
features to protect against damage.  In  addition,  the  operator
should have  the  capability of  manually  bypassing  the control
system in  case of failure and  for  maintenance purposes.   The
advantages of automatic controls increase with larger systems.

     6.6.1  Automatic Valves

Both pneumatic and hydraulic remote  controls have proven to be
quite dependable  for field  installations.    Pneumatically and
hydraulically  operated diaphragm  valves  (requiring pressure to
close) have given good service  for many  years on numerous  land
treatment  systems  under  all  climatic conditions  with  few
operational problems.   Electric controls located in the field
are  generally not  suitable because they can be  affected by
lightening and are  a safety hazard. Piloted valves  have been
unsatisfactory in all cases  where  the wastewater  was used as
the  operating  medium because of clogging,  even  when  strainers
are  used.  The use  of a clean, pressurized,  external  fluid as
an operating  medium  generally provides satisfactory  service.
Ball,  butterfly,  and  plug   valves  with   external   cylinder
operators, closed by air pressure and opened by spring  tension,
provide satisfactory on/off service.

     6.6.2  Manual Valves

Ball, plug,  and  gate valves  all provide  satisfactory manual
on/off service.  Butterfly valves are also  capable  of providing
satisfactory   service   for   primary  effluent,   but   are  not
recommended  for use with raw wastewater  since solids can
interfer with the  valve operation.  Globe  and angle valves
generally  permit  close  regulation of  flow,  and are  therefore
satisfactory  for  throttling  purposes.   Other types  of valves
should be  used for  throttling  only  if specifically recommended
for  that purpose by the manufacturer.

6.7  References

 1.  U.   S.   Environmental   Protection  Agency.     Technology
     Transfer Process  Design  Manual for  Land Treatment of
     Municipal Wastewater.   EPA  625/1-81-013.   U.  S. EPA,
     Center for Environmental Research Information, Cincinnati,
     OH.   October 1981.      .  .:

 2.  Borelli,  J., et al.   Overland Flow Treatment of  Domestic
     Wastewater in Northern  Climates.   University of  Wyoming,
     Laramie,  WY.  1984.                     ,

 3.  Gilde, L.  C.,  and O.  M. Aly.   Personal  Communications.
     Campbell Soup Company,  Camden,  NJ.   1984.

                           CHAPTER  7

7.1  Importance of Proper Construction

The primary purpose of  land grading,  also called land  forming
and land  leveling,  is> to re-shape the  soil  surface to assure
the  uniform  movement   of   water  across  the  OF  terraces.
Attainment and maintenance  of smooth  sheet flow  down each
terrace is necessary to achieve optimum OF process performance.
Observation of  current  practices  indicates   that  grading and
finishing  require  more  attention  in   design  and  during
construction.   The purpose  of this  chapter is to provide more
detail than that found in the Manual  [1].

7.2  Design Methods

The design of OF  terraces and drainage channels utilizes many
conventional agricultural  engineering principles.    There are
four basic methods which are  used for land grading design [2,
3]:   (1)  the  plane method,  (2) the  profile method,  (3) the
plan-inspection method,  and (4) the contour adjustment  method.
In all methods,  the designer must  provide a 10 to 40% excess of
cut in  relation to fill to compensate for  the shrink-swell
potential of the soil.  With  some soils,  the  percentage can be
even higher. Experience with  a specific type of soil  is the
only way to determine the  actual percentage   of  excess cut
required.  The  local  ;USDA Soil Conservation  Service personnel
can often provide advice in this area.

It is  beyond the  scope of this  text  to provide  a detailed
description  of  the  various   land   grading  design  methods.
However,  since  these  techniques are  not  commonly used in
munxcipal wastewater  treatment engineering,  the consultant is
encouraged  to   seek   assistance,   if   necessary,   from  an
agricultural engineer or other  qualified  professional for this
portion of the design.

7.3  Terrace Configurations

There are four basic types of terrace configurations  used  in OF
design.  These  are:     (1)   conventional,  (2)  step-up,  (3)
back-to-back,  and  (4)  step-down.   The four configurations are
shown  on Figure 7-1  and  described  in more  detail  in the
following sections.  The choice of which configuration to use
should  be based on  the  existing  site  conditions and the
economics of construction.  More  than one type   of terrace can
be used on the same site.

(2-8%) \
                 ORIGINAL GROUND
                 SURFACE (2-8%)
                       ORIGINAL GROUND
                       SURFACE (< 2%)
     SURFACE (<1%)
. SURFACE (> 8%)

                                FIGURE 7-1

     7.3.1  Conventional Terraces

Conventional terraces are used  where  the existing field grade
generally meets  the criteria  (2  -  8%)  for  overland  flow
presented in the Manual [1].  Localized cutting and filling_is
accomplished  as  necessary  to  fully  meet  grade  criteria.
Individual  terraces  are  then  formed  by  drainage  channel

     7.3.2  Step-Up Terraces

Step-up  terraces  are used  where  the  existing  field  grade is
less than that  desired  for  OF (i.e.,  <2%)  and it is necessary
to increase existing  field grades.   The  front  slope of the
adjacent lower terrace provides one side of a v-channel, while
the terrace itself  provides the other side.   If  additional
channel  depth  is required,  it  may be  attained by additional
excavation,  by construction of a ridge on the  upper  edge of  the
lower terrace, or a combination of these two methods.

     7.3.3  Back-to-Back Terraces

Back-to-back  or "humpback"  terraces  are also  used where  the
existing field grades are less  than that desired  for OF  (i.e.,
<2%).  They  are  most economical when  the existing field grades
are very flat  (<0.3%!).  When  the  existing field  grades  are
between 0.3%  and 2.0%,  step-up  terraces  are  usually more
economical to  construct than back-to-back  terraces.   However,
on  sites   where  land  availability  is  extremely   limited,
back-to-back terraces may be  justified when the  existing  field
grades  are  up to 1.0%  because,  although they  will  not be as
economical   to   construct,   they  will  provide  higher   land
utilization  (i.e., greater terrace area) than  step-up terraces.

Back-to-back terraces do not require construction of individual
terrace drainage channels because  the entire area of  the
terraces  where the  lower  portions  intersect acts  as  a  broad
triangular channel.  Where  the  lower portions intersect at
appreciably  different heights,  the,lower portion  of the higher
terrace  should be cut back on a 4:1 or flatter slope to prevent
erosion  and  facilitate mowing.

      7.3.4   Step-Down Terraces

Step-down  terraces   are  used to reduce  field  grades  on  sites
where  the existing  grades  are greater than that desired  for OF
 (i.e.,  >8%).   The drainage  channel  is constructed at the  lower
edge  of  the  adjacent higher  terrace before the step-down to the
lower terrace  is started.   The upper terrace backslope, or
step-down,  is  typically constructed on a 4:1 slope.

          7.3.5  Transitions

The  overall   grading   plan  must  include  transitions  from
individual terraces  to  adjacent,  unused areas,  as  well as to
other terraces and runoff channels.   Safety in  construction and
future maintenance operations (e.g.,  mowing)  must be considered
in  designing  these  transitions.    Using  ordinary   caution,
equipment is  generally  considered safe  to operate on 4:1 or
flatter slopes [4].

7.4  Drainage Channels

     7.4.1  Design

Drainage channels  and discharge  structures should  be  designed
to handle the  discharge from the entire area  which they will
drain,  not just the area of the OF terraces.' Drainage  channels
should have enough discharge  capacity to handle the peak rate
of runoff from a  25-year/24-hour  frequency storm,  plus 0.1 to
0.2 m  (4-8  in.)  freeboard.   Channels are  ordinarily  designed
using the Manning formula.   For unlined channels, an n  value of
0.06 is normally used to design for capacity and an n  value of
0.03 to compute  for velocity.    Channel  velocities  do not
ordinarily  exceed 1.5  m/s (5 ft/s),  although  this  limit is
influenced by  factors such  as  soil type and vegetation in the
channel.  Design of drainage channels  and  discharge structures
involves several  steps,  including  runoff computation, selection
of channel type,  erosion control,  and consideration of  specific
grading techniques.

     7.4.2  Runoff Computation

Various satisfactory  methods  are available  for estimation of
design  runoff.  The  Rational method [3]  is one of  the most
commonly  used and various  charts,   nomographs, tables,  and
computer  programs  are available to expedite  design runoff
computations.   A  C value of 0.50 to  0.55  is satisfactory for
most overland flow systems.  Cook's method [3] is  somewhat
simpler and gives  similar  results to the  Rational  method when
the  above  C  value  is  used.     Channels  must be   designed
specifically for  each   site  in  order to  effect  economy of

     7.4.3  Channel Types

Drainage channels are of three basic  types:   1)  the ridge type,
2) the more common ridge and trough type]  and 3) the trough or
ridgeless  type.   These are shown on Figure 7-2.   The ridge
front slope provides one side of  the V-channel and the  terrace
provides the other side  for ridge  type channels.  The ridge and
trough type channel is  constructed by excavating a trough and
using the  excavated  soil  to form the ridge.    The trough or

              RIDGE CHANNEL
                                       BACK SLOPE
                             GROUND SURFACE
              TROUGH CHANNEL
                 FIGURE 7-2

ridgeless type channel is usually constructed by  excavating the
channel  and  disposing  of  the  excavated  soil  in  another
location.   For  erosion  protection  and ease  of mowing (if
grass-lined channels  are  used),  it is  generally best to keep
the  ridge front  and back  slopes  at a 4:1  slope  and  never
steeper than a 3:1 slope.

Any  of  the  channel  types  may  be   used  with  any  terrace
configuration   except   the   back-to-back   terrace.      The
characteristics of the site determine  the relative  desirability
of the channel types.  When working with flat cross  slopes,  it
may be of  value to combine the three  types of channels in the
same terrace, phasing  from the ridge type to  the  ridge and
trough type to the trough type.   This increases the channel's
gradient, thereby improving drainage.

     7.4.4  Avoiding Erosion Problems

Observation of  operating  systems  indicates that  many runoff
channels suffer  from excessive erosion before  an adequate
vegetative cover is established.   One cause of this  erosion  is
excessively steep  channel sides where  water,  especially from
the  terraces, drains into the  channel.  Such  grades should
never be steeper than 4:1.

A second cause  of erosion is water from a tributary  drainage
channel  entering  a  larger  drainage  channel  at  a  higher
elevation than the  invert of  the larger  channel.   In such
cases,  the depth of the tributary channel should be  lowered  to
the invert of the  larger  channel through a  transition  section.
The  transition  section  should be long enough so that the
velocity does not  exceed 1.5 m/s  (5  ft/s)  within  it,  and the
side slopes should be cut back at 4:1.  If such a transition  is
impractical,  a  concrete  flume or some other  type  of  drop
structure  should be  used to convey the  water  safely into the
lower channel.

Another  cause of  erosion  is excessive velocity before the
vegetation becomes established.   All  drainage channels having
flow velocities greater than 0.9  m/s (3.0 ft/s) when  calculated
using a Manning n of 0.25 should be protected with  some type  of
cover material such as  staked down jute or nylon matting with
wood fiber.  Concrete lined channels,  rip-rap, and  straw or hay
mulch using an injected  asphaltic  or  other  binder may also  be
suitable.   Finally,  pipes may be  used  to  convey the  drainage
water  from the OF terraces  to  the  discharge  or some  point
within the  system  where  it  can  be  safely released.  Pipes are
particularly  suitable when  step-down terraces  must  be   used.
Piped-drainage also provides highly efficient land  utilization.

7.5  Land Grading

Although the construction of OF  terraces  and  drainage channels
involves the  use of  some  standard construction equipment  and
practices,  it  is unique  in  that it  also  includes certain
equipment (i.e., a land plane)  and construction practices which
are not commonly used by many  of the  contractors who  bid on OF
projects.  The  following is a  discussion  of certain aspects of
the land grading operations which are specific to OF  systems.

     7.5.1  Rough Grading

Settlement of the soil after rough  grading  is a  major cause of
failure  to  achieve  uniform  terrace  surfaces.    Where  the
construction schedule will  allow,  the  soil  should be left to
settle for three months  to  a  year  following  the rough grading
operation.   The terraces  should  then be  checked for  excessive
settlement and  corrections made,   if  necessary.   Recognizing
that this length of interruption to  the  construction schedule
usually  is  not practical,  the  following procedure  has been
found to provide satisfactory results.

During terrace  construction, the earth should be placed  in 15
cm  (6 inch) layers  (or  lifts)  and compacted,  as a minimum,  to
the density  of  the  adjacent  undisturbed soils.   Excavation,
fill,  and compaction should be accomplished with a dozer, pan,
scraper,  or other appropriate  pieces of earth  moving equipment.
Clods,  if any, should  be crushed before  they  are buried.
Because  it  is  necessary   to  avoid  excessive  compaction,
equipment  operators   should   be   instructed  to   avoid   a
follow-the-leader route, but rather distribute the wheel  load
over as much  of the tract  as  possible without increasing  the
earth moving distance.   A lift should be built  all the  way
across a fill area before the  next  lift begins, except when an
existing  depression  occurs within the fill  area.   Existing
depressions should be brought  level with adjacent areas  using
15 cm (6 in.)  lifts before beginning the normal fill procedure.

     7.5.2  Topsoil Handling

Observation of  construction practices on OF  sites shows that
topsoil is frequently stripped,  stockpiled,  and then replaced
as the last step in  the grading operation.   While this  may be
necessary in some  cases,  it can  be an unnecessary and  costly
activity  in other  cases.    Utilization of the  subsoil  may
require only the application of the proper fertilizer, which is
generally  a  much   less   expensive  operation  than  topsoil
preservation.    Fertilization has proven to be  an effective  and
economical  method  of utilizing exposed subsoil in several
industrial overland flow systems.   Soil samples, to  the  depth
of the expected excavation,  can be obtained  and sent to a soils
laboratory for  analysis. The  laboratory can  recommend whether

the subsoil can support plant growth and the  type  and  amount of
fertilizer and/or other soil amendments required.

If the  subsoil  cannot support plant  growth, even  with the
addition of fertilizers,   the  topsoil is stockpiled,  the  cuts
over-excavated, and the topsoil replaced.  The fill areas  must
also be stripped, the  fills partially made with  the  materials
available,  and the topsoil replaced.   This  is  an expensive
procedure, and it increases the difficulty of the  final  grading
operations because the roots and other matter  contained in the
topsoil often interfere with achieving a smooth surface  finish.
When topsoil  preservation  is essential,  the topsoil  from one
terrace should be stockpiled on an area requiring  little cut or
fill.   The  cuts and fills  in  this  terrace are then  completed
and the topsoil from the adjacent terrace stripped and used for
dressing the  surface of  the first terrace.   Then,  progressing
across the field, the topsoil should be moved from the adjacent
terrace as the terrace forming  is  completed until  the  last
terrace is dressed with  the stockpile from  the first terrace.
This  procedure  minimizes  the time and  expense  of topsoil
removal and replacement.

     7.5.3  Final Grading

A  land plane,  also  called a  land  leveler  or  long frame
bottomless scraper, is  the ideal equipment  for final grading.
It  is  only effective on  loose  soil.   The soil  is usually
loosened  by disking with a heavy  disk.  If  large clods are
turned  up, the area  is  re-worked  with a  lighter disk or
sheepsfoot roller to break up the clods.   The   land plane is
then  passed  over each  terrace  as a   finishing  operation.
Integrity  of the terrace must be maintained during the  planing
operation.  The  first two  passes  of  the  land plane  are  usually
made at opposite 45° angles  to the long  axis of the  terrace
with the  last pass  being parallel to it.  The purpose  of  this
cross  planing  is  to  prevent  the   development  of   a   long
sinusoidal wave approximately twice the length of  the  land
plane.  If any portion  of  the  terrace  is scraped  bare of  loose
soil  during   the  planing   operation,   that  area  should be
re-scarified  and the  terrace  completely  re-planed.    Surface
deviations not  exceeding  1.5  cm (0.05 ft)  from the planned
slopes  can be  achieved with three passes of the land plane.

There  are various types  and  sizes of land planes and the
selection of  one  for  a specific  site is important.  A  land
plane capable  of doing  excellent work  on a  field  1.6  by 1.6 km
(1 mi by 1 mi) probably cannot be turned around on a terrace 30
m  (100  ft) long by 60 m (200 ft) wide.  A laser controlled land
plane,  the ultimate in finish grading equipment,  can be  used if
the  terrace  was  designed  as  a  plane.    Planing  need be
accomplished  only in the  direction  of the longest axis of the
terrace.   The many turns  required  in  cross planing  can be

eliminated if a laser controlled land plane is,used.

Although other equipment can be used for final grading, it  is
usually with greater difficulty and/or poorer results  than  with
the use of  a  land plane.   Laser equipped dozers are  efficient
for finishing  some  terraces.   Motor  graders  can  also be  used
for final grading.  The use of  a landscape  box  is  suggested  to
smooth out the tracks and other irregularities  left by  a motor
grader.   These alternatives are  recommended  only  if a  land'
plane is not available.

7.6  Supervision and Acceptance

Although  it is beyond  the scope  of this chapter to provide
detailed instructions for supervising  the  terrace  construction
operations,  the following is a  check list of some items which
are critical to the  satisfactory completion of  the terraces:




The  specified  lift  depth  (max.  15   cm)   is   not

The   specified   compaction   (to   pre-construction
density) is maintained in each lift.

The specified grades are attained on  the edges of the

The specified channel depth and width are maintained.

The channel  transitions  are constructed as shown  on
the plans.

Terrace areas  which are scraped  bare  of loose  soil
during  the  land planing operation, are  re-scarified
and the terrace completely re-planed.
          The  pipeline   backfill
                          is   properly  placed   and
Stumps, concrete, and other materials are  not  buried
within the overland flow site.
7.7  References

 1.  U.  S.   Environmental   Protection  Agency.     Technology
     Transfer Process  Design Manual for  Land Treatment of
     Municipal Wastewater.   EPA  625/1-81-013.   U.  S.  EPA,
     Center for Environmental Research Information, Cincinnati,
     OH.  October 1981.

2.  Land Leveling Irrigation.   Chapter 12.   SCS  National
    Engineering Handbook.   Section  15.   U.S.  Department of
    Agriculture,  Soil Conservation Service.  March 1959.

3.  Frevert,  R.  K.,  et al.   Soil  and  Water Conservation
    Engineering.    John  Wiley and  Sons,  Inc.,  New  York,  NY.

4.  American  Society  of  Agricultural  Engineers  Standard.
    Design,  Layout,  Construction,  and  Maintenance  of Terrace
    Systems.  A.S.A.E.  S268.2,  Revised and reclassified as a
    Standard.   A.S.A.E.,  Saint  Joseph, MI.  December 1978.

                           CHAPTER 8


8 . 1  Function

A well established vegetative cover  is essential  for  the
efficient performance of  OF  systems.  The  purpose  of  this
chapter is  to provide greater  detail  on vegetation selection
and establishment than found in Sections 6.8.3 and of
the Manual
8.2 Selection
     8.2.1 Objectives
The Manual  Cl3  lists the desirable  characteristics  for  an OF
cover crop.  However,  a high  percentage of new OF systems appear
to be  placing  great  emphasis  on  cash crop production  to the
detriment of slope protection  and wastewater  treatment.   This
is especially important in the  early stages of cover  crop
establishment and in the start-up  of  wastewater treatment.
Some grasses, most notably  some of the  improved Bermuda grass
varieties,  are  established only  by   sprigging  or  sodding.
Sodding is  usually too expensive,  while sprigging at standard
agricultural rates does  not provide adequate  initial coverage
for either slope  protection  or  the start-up of wastewater
treatment.   The  problem is  further  compounded  when  the early
cuttings are removed as hay  rather than being allowed to remain
on the terraces as a protective mulch.

     8.2.2 Grass Types

Grasses suitable for  use  in OF systems  are described in Table
8-1.  Additional information on these grasses  can be found in
various  references  on forage grasses  C2, 3].   The primary
purpose  of  the vegetation  in  an overland flow system  is to
facilitate  the treatment of wastewater.    The  market value of
the crop is only of secondary importance.   If a grass will not
grow under  a particular set of OF  conditions,  no matter what
its other desirable characteristics, it  is  of  no benefit.   The
most common grasses  used on OF systems have  been Reed  canary
grass and various Bermuda grass varieties.

  Reed Canary  Grass

While Reed  canary grass is  sometimes slow in establishment, it
forms a very tough, dense sod,  spreading by seed,  rooting from
the  joints  of stems in soil contact,  and  vigorous  thick
rhizomes  which push  out from  the  crown.   It has one  of the
longest  growing seasons of all the cool  season grasses and



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continues growing throughout hot  summers  if adequate moisture
is available.  It is  one  of the most drought-resistant of the
cool season grasses  and may be expected to become the dominant
grass on many OF sites.

The market value of  Reed canary grass  is often described as low
by many references which show it to have relatively low protein
values.  Under normal growing  conditions,  it  is  raised on wet
land where it  is  usually  past  its  prime before  it  can be
harvested as a hay crop.  However, some research [4] has shown
that Reed  canary grass  grown  on  an  OF system can  exceed the
commonly reported  values  for alfalfa  in both protein  and
nutrient content.

 Bermuda Grass

Common Bermuda grass becomes readily established  from seed
during warm weather  and  may establish  an initial  dominance
during  the  warm season.  Unless  used as  a summer  nurse crop
(see Section, however, Bermuda should be planted only
as far  north as  it  grows  naturally.    This  is  true  for any of
the warm season grasses.   If planted in the fall  or early
spring in a mixture of  cool  season grasses, only unhulled seed
should be  planted,  since  unhulled seed  (as opposed  to hulled
seed) is more likely to  survive during conditions which  are not
conducive  to  germination.   The  various  Bermuda  grasses will
generally become dormant  after  the  first  hard frost, but will
continue to provide  the  thick turf  needed for satisfactory
treatment performance.   If an  improved  Bermuda  grass  variety
which  requires  sprigging  (e.g.,  Coastal  Bermuda)  is  selected,
overseeding with  a nurse  crop  is  required  to establish a
satisfactory   cover  until   the  sprigged   grass    is  well

 Nurse  Crop

When the primary grass  selected is  a slow starting  species or
one with a low initial density, a number  of other varieties may
be used  as  a nurse  crop to  provide the initial density  needed,
even though  some  of these nurse crops may last no longer than
the  first  growing  season.   Various warm  season  varieties of
grass  could be  selected  for this purpose, including common
Bermuda, which will provide rapid cover when planted  during hot
weather and will eventually be  crowded out by the improved
variety  Coastal.  If  the  time of year is  suitable;   annual rye
grass or another quick growing cool  season grass will serve the
same purpose.

     8.2.3 Combining Grass Species

Planting a mixture  of  several  grasses generally achieves the
most satisfactory results by providing a  high initial  density

and the capability to apply wastewater as  quickly  as  possible.
The selection of grasses  to  include in a  mixture  is  dependent
on the climate, the  time  of  planting,  and the  availability  of
irrigation water during start-up.   In areas where warm  season
grasses such as Bermuda will  grow,  a mixture of warm season and
cool  season grasses  is  recommended.   In cooler  climates,  a
mixture of all cool season grasses  is best.

Recommendations from local grass specialists can be helpful  in
the selection process.  Such'specialists  might be found through
the  local  USDA Soil  Conservation   Service,  county agents,  or
other  local agricultural specialists.    However,  when using
agricultural  advisors,   it  is  very  important  for   them  to
understand  that  the  primary  objective  of  the   project  is
wastewater treatment and the  grasses selected must  adapt  to the
imposed  wastewater  application conditions.   If.  this is not
done, inappropriate recommendations may result.

8.3 Planting

     8.3.1 Density

The  amount of  seed to plant depends on the type  of grass
selected,  expected  germination,  water  availability,  and  time
available  for  cover crop development.   Table 8-2  provides
general guidelines  for  seed  densities which  can be  used  when
constructing a  new OF system.   The low density rates  are  used
for temporary stabilization and erosion control or  if  water for
cover  crop  development  is in  short supply.   These  rates  are
equivalent to  commonly  used  seeding rates for pastures.   The
moderate density  rates  represent  a typical  range of  seeding
when planting  at  the optimum  time for development by  natural
rainfall.   The high  density rates will  provide  the fastest
development of  a dense  cover  crop, but these rates require  an
adequate   supply   of  irrigation  water   whenever   sufficient
moisture for germination and growth is not provided by natural

It is necessary to convert the density values in Table 8-2  to a
seeding  rate (kg/ha  or Ib/ac) by dividing by the  number  of
seeds per kilogram (or per pound)  for  a  specific grass.  These
latter values can be provided by suppliers or found in standard
references [2,3].   If a mixture of  several grasses  is  used,  the
seeding rate for each grass must be adjusted proportionally.

     8.3.2 Scheduling

Planting time  is  affected by location,  climate,  variety  of*
grass,.   availability  of  irrigation   water,   capability   of
sprinkler irrigation, construction  schedule,  expected  rainfall,
and other  factors.   In  general,  cool season grasses  should  be
planted from spring through early  summer  or  early  fall through

late  fall.   The availability  of water and  the  capability of
sprinkler  irrigation  adds  considerable  flexibility  to  these
planting times.  For  example, with  proper irrigation,  cool
season grasses  can  even be  started  in the  middle  of summer.
However,  this requires considerable attention to detail and is
not a  recommended practice.  Warm season grasses  generally
should be planted from late spring through  early fall, although
this can vary according to area and climate.
                           TABLE  8-2
                         (seeds/m  )
     Low Density
                        1,450 -  2,690
     Moderate Density
                        4,300 -  8,600
     High Density
                       15,500 - 20,450
Local  agricultural  advisors can  give advice  regarding  the
optimum time as well as the limits of time for grass planting.
The timing of the planting  schedule  is  complicated  when it is
desired to plant both cool  and  Warm  season  grasses.  However,
there  are time  overlaps  in  both spring and  fall for  most
grasses.  Also,  some varieties of grass  seed, if planted out of
season  and protected by  a growing cover, simply will  lie
dormant  until  climatic   conditions   are  suitable  for  their
germination and growth.   A second option is to plant  the  two
seed types  separately  at  the optimum planting  time for each.
The second planting (commonly called overseeding)  will require
a seeder  which  will not damage the  initial stand  or  mar  the
soil surface.

In order to have the greatest potential  for establishing a good
vegetative cover, it is  important  to  plan the construction
schedule  so  that completion   of  the  final grading of  the
terraces  coincides  with  the optimum  time  for planting  the

selected  grasses.   If  this cannot  be accomplished,  it is
necessary to plant a nurse  crop  which will germinate and  grow
at the time construction is  completed  and then to  pverseed  with
the primary  grasses  at  their  optimum planting time.   If  the
construction is completed at a time when even  a nurse  crop  will
not germinate,  the terraces and drainage channels will  require
protection  (straw  mulch  or  other  suitable  covering)   from
erosion.   The  construction and  planting  schedule  is  most
critical in  cold climates where there  is  generally less  time
available for establishing vegetation.

     8.3.3 Soil Preparation

At  the completion of  finish grading, fertilizer  and  soil
amendments (e.g., lime) are applied according  to soil  test
recommendations  and immediately  incorporated  to a depth of  10
cm  (4  in.)  or more.   Any standard equipment can be used for
applying this material provided it  gives uniform  spreading and
does  not  damage the  slopes.  A smoothing harrow  is usually
pulled behind the  disk  harrow to eliminate ridges  and  provide
additional cultivation  in  forming  a  seed bed.   Additional
passes of the  same  or  other equipment may  be  necessary  to
prepare an  adequate  seed bed.   Any procedure  is  satisfactory
provided it  leaves the  soil  surface in a  smooth  condition and
does not create ridges or leave vehicle tracks.

     8.3.4 Seeding

Brillon seeders  have been found  to be  very effective  planters
for OF systems.  This equipment distributes the seed and covers
it  with a  small amount of soil  (commonly  called  cultipacking)
in  the same operation.    Although,  other planters can be  used
satisfactorily,  the  best results  are generally achieved  when
the seed  is cultipacked  into the  soil.   Only light  tractors
should  be  used  for  seeding  or  other  operations  such  as
cultipacking and there  should be no  wheel tracks left  on the
terraces.   The  seeding  and  cultipacking operations should  be
carried out parallel to the steepest terrace  slopes,  even
though this  is  clearly contrary to  the  conventional  wisdom for
         control.    If  contour  planting  is  followed,  the
depressionsareso shallow  that the  slightest  runoff breaks
through the minute depressions  or  weak spots,  creating a rill
or wash.  Up and downslope planting prevents the  concentration
of water  so that  only sheet  erosion  or  that from raindrop
splash takes place.  Actual  soil movement  may be greater, but
the smooth  uniform surface  is  not as  likely  to be  destroyed.
Areas other than terraces may  be seeded according to the best
operating characteristics of the planting equipment.

     8.3.5 Sprigging

Broadcast planting is the perferred method  of  sprigging  an OF
terrace.   The  soil is prepared in  the same  manner as  for
seeding.   Then  3.5 to ^4.4  m /ha (40-50 bu/ac) of  sprigs  are
broadcast.  Sprigs are pressed into the  soil  using  a weighted
disk harrow with the disks  set straight.  The soil is firmed by
cultipacking up  and down  the slope.   One cm ( 0.5 in.)  of
irrigation water  should be applied  by a  sprinkler  system
immediately.  Broadcasting freshly cut stems is an alternative
method  of propogating Coastal Bermuda  grass.  The  quantity
should be increased to 7.8 to 8.7 in /ha  (90-100 bu/ac) but the
same procedure as for sprigging is used.  Immediate irrigation
is  even more critical  when  using  stems .than sprigs  and no
delays  should  be  allowed  between  cutting  the  stems  and

Other planting  methods  are  satisfactory, provided  they leave
the soil  surface in a smooth  condition and, do not leave ridges
or  vehicle tracks.   If less than  2.4  m /ha   (27 bu/ac)  are
planted,  the terraces require overseeding with a nurse crop to
provide cover until a permanent sod  forms.   A nurse crop should
also be overseeded if the planting islate jn the season when a
sod may not have time to form before frost.

Certain  precautions  are necessary  in planting sprigs.   Only
live, freshly dug sprigs should be planted.   If they cannot be
planted immediately following  digging, they  should be kept
moist  and cool.   They  must be  wet down and turned  often to
prevent heating.  Sprigs must be well  covered during hauling to
prevent  drying  by sun and  wind.   Allowing sprigs  to dry out
before  planting  is  probably the  most  common cause of failures
to  obtain stands.  The tips of sprigs  should be above  ground as
sprigs buried more than two inches deep may  not grow.  The area
from which  sprigs  are dug  should be free of weeds,  soil borne
diseases, and insect pests.

8.4 Vegetation Development

When seeding  and/or  sprigging is used,  a period of growth and
acclimation  is  necessary between planting  the vegetation and
the application of  wastewater at  full  design loading rates.
Certain management practices can  be used to  accelerate the
development  of  the vegetation and to minimize  the  acclimation

     8.4.1  Start-Up Irrigation


Grass  growth on seeded systems can  usually  be  started with
natural precipitation by  selecting  the appropriate planting

time.    However,  irrigation  is  strongly  recommended  when
sprigging an OF system.  In either case, the use of  irrigation
will almost  always  provide more rapid  grass  development than
relying  on  natural precipitation.   Since-  irrigation  can add
considerable cost  to  the development of  the system,  it is
usually used only  when the construction and start-up  schedule
does not provide  sufficient  time for  grass development by

Either fresh water  or wastewater  can  be used  to  promote the
growth of  vegetation,  with  the  irrigation rates  selected to
provide sufficient moisture for grass growth, but not enough to
create runoff from the system.  On seeded systems using medium
to high pressure sprinkler distribution systems, the sprinkler
system can be   used for the  application  of irrigation water.
Surface and  low pressure distribution systems  cannot  be used
for such purpose because they  do not provide uniform  coverage
of irrigation water.  A temporary system  of  portable  irrigation
pipe with medium to high pressure  sprinklers  is  required for
these systems.   Temporary irrigation pipe  and sprinklers are
required  for   sprigged  terraces,   even   if  the   wastewater
distribution system consists of high pressure sprinklers.  The
temporary system is required  to  wet the  lower  portion of the
terrace beyond the reach of the sprinkler patterns.


The following irrigation procedures have been used successfully
in providing rapid  vegetative  growth on  new OF systems.   They
have been found  to  be  applicable in many areas of  the country
and with many types of grasses  C5].

The  first  watering is initiated  as soon  as possible  after
planting the grass,  but is not started unless there  is an
adequate water (or wastewater)  supply to  continue irrigation as
needed.   The  first watering of  each terrace lasts  for 15
minutes.   Subsequent waterings of 15 minutes each are  repeated
hourly up to the point of runoff within the sprinkler  pattern.
Irrigation  is  stopped as  soon as  a  surface  film of  water
appears within  the sprinkler  pattern  of a terrace.   Fifteen
minute waterings,  repeated  hourly,  are re-started as  soon as
the  soil surface  appears dry.    The  sprinklers   should be
operated  at   pressures  recommended  by   the  manufacturer.
Whenever rainfall occurs to the extent that it serves the same
purpose as the  irrigation,  the irrigation can be discontinued
until the  soil  surface  within the  sprinkler  pattern appears

When the grass within the sprinkler pattern reaches  an average
height  of 2.5  cm  (1  in.), the irrigation  schedule  can be
changed to one  watering per day for one week.   The following
week, the irrigation schedule  can be reduced to  one application

of  water  every  other  day and  then  twice a  week  for the
following week, each time applying water long enough to achieve
total wetting  of the  soil, but allowing  no runoff.   Upon
completion of the above schedule, water should continue  to  be
applied to  achieve a  steady  growth  pattern.    Application
frequency will  vary with daily temperatures and  rainfall, but
watering to  the point of runoff should  not be needed more than
twice per week.

When  the  terraces  are irrigated  only  by  the   wastewater
distribution system  (with medium  to high pressure sprinklers),
the same procedure is used until the grass  within  the sprinkler
pattern reaches an average  height of approximately 2.54  cm  (1
in.).   At this point,  the number  of  watering cycles can  be
successively increased to force water downslope  toward the
bottom  of the  terrace.    Extreme  caution is  necessary at this
point, as runoff must never be allowed  to the extent of causing
applications of irrigation water.   As the  grass  development
proceeds to  the extent  that the entire terrace can be  wetted,
the irrigation schedule  can be changed to one watering per day
for one week.  The following week, the  irrigation schedule can
be reduced to every other day and then to twice a week  for the
following week,  each time applying water long enough to achieve
total wetting of  the terrace, but  stopping irrigation just
before runoff into the terrace channel  occurs.

     8.4.2  Initial Management

The initial  level  of treatment  at new  OF  systems  may not meet
the   effluent   discharge  limitations,   particularly  if  the
hydraulic loading  rate is at the  full design rate.  The  system
begins  to become  acclimated during the  first few months  of
wastewater application,   and treated effluent quality continues
to improve during this  period.

One practice which has been found to improve the  efficiency  of
an OP system during  the start-up  and  acclimation  period  is  to
allow at least  the first three  cuttings of grass  to remain  on
the soil surface.   This mulch  layer helps  to prevent  erosion,
and increases  the organic  and  nutrient content  of the  soil,
thereby providing  improved  conditions for biological activity.
If wastewater must be  treated at the  earliest possible  time,
the terraces can  be sodded  or  seeded at  the  highest density
shown on  Table 8-2 and irrigated according to  the guidance
provided in  Section  8.4.1 in order to accelerate development.
The use of wastewater for irrigation to hasten the  development
of  the  vegetative cover not  only shortens the  OF  system
acclimation  period and   produces  a  higher  initial  quality  of
effluent,  but also reduces  alternate  treatment  and/or storage

Short  application  periods with short rest  periods,  such as  15
to  30  minutes of wastewater application with  45 to 90  minutes
rest,  will also produce  a better  initial  quality of  effluent
and may further  shorten the acclimation period.   This  technique
also reduces  or  prevents  damage from erosion,  since it  reduces
flow velocities  while  still allowing the soil  microorganisms  to
become  acclimated  to  the waste.    These  short application and
rest  cycles can be  gradually increased over  several weeks  to
the regularly planned  application periods.

8.5  Erosion  Control

The  first several months after seeding  is the  time  that the
system  is  most  susceptible  to   erosion  damage.     Frequent
inspections are  necessary during this period to  note and repair
erosion damage.  The inspection is  especially  important  after a
heavy  rainfall.    Small  channels  can be  corrected easily with
hand labor by filling or by  making small  coffer dams of soil
and/or mulch  in  the  channels,  and re-seeding or  sodding.  More
extensive  damage may necessitate repair with equipment (i.e.,  a
land plane or other device),  but  the  use  of  equipment on the
terraces after seeding should be avoided except when absolutely

8.6  References

1.   U.   S.   Environmental  Protection  Agency.     Technology
     Transfer Process Design Manual  for Land Treatment  of
     Municipal  Wastewater.   EPA  625/1-81-013.   U.  S.  EPA,
     Center for  Environmental Research Information, Cincinnati,
     OH.  October  1981.

 2.  McBickar, M.  H. and  J. S. McBickar.  Approved Practices  in
     Pasture  Management.   Second  Edition.   Interstate Printers
     and Publishers, Inc., Danville, IL.  1963.

 3.  Heath,   M.  E.,   D.   S.   Metcalfe,  and   R.  F.   Barnes,
     Forages/The  Science of  Grassland  Agriculture.    Third
     Edition.   The Iowa  State University  Press,   Ames, Iowa.

 4.  Thornthwaite,  C. W.   An  Evaluation of  Cannery Waste
     Disposal by Overland Flow Spray Irrigation.  Publications
     in Climatology 22.   1969.

 5.  Ford, J. P.   Grass  Development on  Overland  Flow  Terraces.
     Unpublished.  ERM-Southeast, Inc. Marietta,  GA.   1984
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