United States
 Environmental Protection
Office of Water
Program Operations (WH-546) ,
Washington DC 20460   I
February 1984
Overland Flow:
A Decade of Progress

February 1984
                      OVERLAND FLOW: A Decade of Progress
                            Richard E. Thonas
                        Municipal Technology Branch
                    U.S. Environmental Protection Agency
                          Washington, D.C.  20460
                Presented at Missouri Water Pollution Control
              Association, Annual Meeting, February 26-28, 1984


This report has been reviewed by the
Environmental Protection Agency and approved for
publication.  Approval does not signify that the
contents necessarily reflect the views and policies
of the Environmental Protection Agency, nor does
mention of trade names or conmerical products
constitute endorsement or recommendation for use.


              Overland Flow:   A Decade of Progress
                              by R.  E. Thomas
      Treatment of wastewater by allowing it to flow as a thin sheet over
 gently sloping ground is cotitionly referred to as  "spray runoff,"  "gratis
 filtration" or "overland flow. "  The term overland flow has been
 by the United States Environmental Protection Agency  (U.S. EPA) and
 be used in this discussion.  Overland flow is not a new technology  for
 disposal of wastewater.   It  has been in use for many  decades for
 disposal of industrial wastewaters and municipal wastewater on a limited
 basis.  Conversely,  the  concept of overland flow as a treatment process
 is relatively new.   Research to understand the removal mechanisms and
 the control of these mechanisms by design  and operation is a rapidly
 advancing science.

     Research on treating domestic wastewaters by overland flow in  the
 United States started about  12  years ago at the EPA research labbfStBry
 in Ada, Oklahoma .   Many other  Federal, State and private sources Hive
 contributed to the rapid development of this promising technology during
 the ensuring decade.   Those wishing to delve into the results Of irflisfe
 research efforts should  look for the proceedings of periodic workshops
 such as the one held at  Dallas, Texas in September  1980 .  ThoSe who are
 more interested in current design  information should  refer to a design
 manual ,  or to project specific information available on the rapidly
 increasing number of systems in design, under construction or now
 operating .

     Research and limited operational data available  to date show
 overland flow to offer an energy saving and simply  operated wastewater
 management concept with  substantial  cost saving potential for smaller
 communities.   Overland flow has potential  to treat  raw sewage without
 sludge production.   It can be used to upgrade existing treatment
 facilities inculding primary plants,  treatment ponds, and even secondary
 plants.   It will achieve good removal of oxygen demand  (BOD) , suspended
 solids (SS) ,  and nitrogen without  energy input or chemical addition.
 EPA; like others; recognizes the benefits which can be achieved if  the
 results demonstrated by  research can be achieved routinely in actual

     In this context, overland flow  is an excellent example of the
 innovative and alternative technology thrust of the Clean Water Act of
 1977.  The definition of land treatment in the Act, as extended in the
EPA operating guidance for the Construction Grants  Program, includes
overland  flew in the category of alternative technology which makes it
eligible  for the financial incentives of this program.

      Our knowledge of overland flow technology is very dynamic.  We are
 at an important transition point as a decade of research results are
 about to be verified and improved with performance data from operational
 facilities. Any state of the  art summary becomes rapidly dated in such
 a period of rapid transition.   I will highlight sources of past, present
 and future information with the objective of guiding interested parties
 to the best source of information for their needs.


      Research on overland flow in the United States started about
 25 years ago when a slow-rate  land  treatment system treating food
 processing wastewater was modified  to become an overland flow system.
 Other food processors adopted  the concept and overland flow became
 established as  a reliable and  low cost process serving many food
 processing facilities in the 1960's.  Research staff at the Robert S.
 Kerr Environmental Research Laboratory of the EPA initiated a decade of
 research on treatment of municipal  wastewater in 1971.  Other Federal,
 State and several university teams  have contributed to a substantial
 body of  information on design  and performance.  Major sources of key
 research results are identified in  Table 1.

      A decade of work has contributed a firm understanding of the basic
 concept.   It is well understood that microbial populations on the soil
 surface play a  key role in the treatment process.  I prefer to visualize
 overland flow as a batch reactor.   The flat reactor surface is rough and
 gently sloping  to produce variable  liquid depth and residence time.
 Liquid depth may range  from one to  twenty-five millimeters while
 residence time  may vary by as much  as plus or minus 50 percent of the
 design time of  about 30 to 60 minutes.  Overland flow is typically
 operated with feed periods of  6 to  12 hours per day for 5 to 6
 consecutive days.  The  12 to 18 hour daily rest periods provide time for
 biooxidation of the more  resistent  fraction of the settled solids and
 reareation of the surface reaction  sites.  The extended rest after 5 to
 6 consective days of feed provides  sufficient drying to control insect
 breeding  cycles as well as to  return the microbial population to the
 rapid growth stage.   It is important to keep the active microbial
 population lean, mean and hungry to get the most out of them.

      Results to date show that the  combination of settling, filtration,
microbial degradation and interactions with the soil combine to produce
better treatment  than conventional  suspended growth or fixed-film
biological treatment processes.  The biochemical oxygen demand (BOD) and
 total suspended solids  (TSS)  in overland-flow effluent usually average
 10 to 20 mg/1 with maximum values seldom exceeding 30 mg/1.  Nitrogen is
 also removed through microbial nitrification - deritrification, crop
uptake and ammonia volatilization.   Nitrification - denitrification
dominates  at recommended  loading rates while crop uptake will become a
major factor as the total annual nitrogen load drops toward that needed
to satisfy the  crop demand.  For example, nitrification - denitrifi-
cation will clearly dominate when the total annual nitrogen load is

 2,000 pounds per acre; the annual crop demand is 100 pounds per acre;
 and the system is achieving 85 percent (1700 pounds)  mass removal.
 Conversely, crop uptake will be a major factor if the total annual
 nitrogen load is 800 pounds per acre;  the annual crop demand is 300
 pounds per acre; and the system is achieving 90 percent (720 pounds)
 mass removal.  It is comparatively easy to design and operate to achieve
 total nitrogen removals in the range of 70 to 90 percent based on total
 mass removal.  It is more meaningful to use total mass removal as
 opposed to concentration reduction because there is substantial water
 loss to evapotranspiration and seepage.  The effluent discharged
 (excluding rainfall input runoff)  is usually 50 to 80 percent of the
 wastewater applied to the system.

      Soil interactions with the clayey soils which make the best sites
 provides 40 to 60 percent phosphorus removal.   The amount of removal may
 decline with time in service and varies according to the properties of
 the site soils.   Several researchers have shown that phosphorus removal
 can be improved by chemical addition.   One would predict that the
 accepted principals of phosphorus  removal by chemical precipitation
 would apply to this fixed-film batch reactor as well as any other witii
 one basic difference.   The precipitated phosphorus is deposited on the
 soil surface to be incorporated into the soil  rather than being removed
 as a sludge to be further processed for disposal.

      We are also at a significant  transition stage in the support and
 conduct of research on overland flow as a treatment technology.
 Laboratory, pilot and demonstration type studies are  on the decline.  It
 appears that we  have sufficient confidence in  our understanding of the
 basic concept to shift our attention to the  gathering of information
 from full-scale  operational facilities.   One approach is use of "field
 tests" as established by the 1981  amendments to the construction grants
 provisions of the Clean Water Act.   In my roles as National Coordinator
 of the innovative and alternative  technology program,  I have initiated
 an effort evaluate our current  reservoir of  design and operating
 information and  to incorporate  it  into a supplement to the EPA design
 manual on land treatment.   This effort is well underway and the
 supplement to the design manual should be available in October 1984.


      The consideration of  overland flow in facility planning presents a
 specific and rather unique set  of  circumstances.  As  already mentioned,
 it is a developing technology and  there  is very little operational
 experience.   Because of this  lack  of operating experience,  State
 regulatory agencies may not have established criteria and guidance on
 design and operation.   The fact that overland  flow shows excellent
 capability to treat raw sewage presents a  further complication.
Application of raw sewage  to the land  is contrary to  accepted environ-
mental engineering practice.  The idea of applying raw sewage to the
 land conjures up the historical health incidences associated with raw
 sewage farming with food crops in the  19th century.  This practice of

 irrigating human food crops with raw sewage was justifiably abandoned
 because of unacceptable health risks.  An educational and adjustment
 period is needed to provide operational experience for establishment of
 State criteria and to determine  an appropriate match-up of preappli-
 cation treatment with the overall  objective of specific projects.  It is
 the cannon dilemma of which comes  first  the horse or the cart  and
 it demands a position of flexibility for case-by-case determinations.
 This position  allows  simultaneous  development of State guidance and
 adoption of developing technology  as mandated by the innovative/alterna-
 tive provisions of the Clean Water Act of 1977.

      EPA guidance for preapplication treatment for overland flow which
 will qualify a project for construction grant funding is divided into
     general levels that provide  this needed flexibility.
     The two  levels of preapplication treatment recognize proximity of
residents in  an urban setting as an important factor in site selection.
The  lesser  level of preapplication treatment specifies simple screening
or comminution for overland flow in isolated areas without public
access.  The  second level specifies a sufficient level of biological
treatment to  control odors and nuisance conditions in more urban
locations with closer proximity of human habitation.

     This EPA decision to set screening or comminution as a minimum
level of preapplication treatment is based on results of several
research and  demonstration projects.  There is a substantial amount of
long term operational experience showing the excellent capability of
overland flow to treat raw wastewater.  Many operating facilities
produce effluents with BOD and SS values of less than 20 mg/1 when the
applied raw wastewater has a BOD of more than 500 mg/1 and SS in excess
of 250 mg/1.

     State guidance for overland flow is at an early stage of infor-
mation and varies substantially from state to state.  It is only within
the  last four or five years that many States have formulated a written
policy on overland flow technology.  In those States, overland flow is
gaining acceptance as a practical, cost-effective and environ-
mentally-sound alternative.  Other States are looking at overland flow
systems on a  case-by-case basis until a larger data base is developed
from first-hand experiences with overland flew systems within the State.
It is important to be avare of the status of current state criteria when
considering overland flow in facility planning.


     Transfer of research and demonstration results to practical design,
operation and maintenance usually adds new dimensions to acceptance and
implementation of a new technology.  The initial group of full-scale
systems serves as a field test to verify performance and to identify
design features that facilitate better construction and easier oper-
ation.  We are at that transition stage in the long range implementation

 of overland flow technology.   There are seme 35 to 50  systems in design,
 under construction or already in operation.   A partial list of these
 systems is presented in Table 2.   Systems listed were  selected to show
 the distribution of geographic and climatic  conditions represented by
 this initial group of full-scale systems.

      Several of the eight systems which are  listed as  operational have
 already been studied to evaluate actual performance in relation to that
 projected at the time of design.   Results from these studies are
 positive.   Performance is consistent with design projections and
 previous research results.  Reports of  design features needing
 improvement to facilitate better construction and easier operation are
 comparatively minor and readily correctible with current knowledge.  The
 fact that operators are very  pleased with the ease that the systems rteet
 discharge criteria is also encouraging.  This encouraging result is
 countered by reports that systems do not discharge or  discharge only
 part of the year.   This may be the result  of overly conservative design
 with the resulting high cost  of excessive  reserve capacity.  The
 information gathered to date  warrants an indepth study of design,
 construction and performance  to ensure  the appropriateness of future


      My perspective for overland  flow treatment of domestic wastewaters
 is  a position of controlled optimism.   Research results and limited
 operational data identify simplicity/ energy  savings,  and low operating
 costs, as major benefits.  Overland flow is a good example of a
 developing technology which addresses the  innovative/alternative aspects
 of  the  Clean Water Act of 1977.   EPA continues to encourage consider-
 ation of overland  flow in this context.  Workshops such as this one and
 the continued research evaluation of newly constructed facilities will
 provide EPA, State agencies,  and  applicants up-to-date knowledge for
 improved design  and operational reliability.  Technical assessment of
 overland flow  systems now operating, under construction or scheduled for
 construction will  assist state agencies and applicants to keep pace with
 this rapidly developing tehcnology.  EPA is confident  that overland flow
will become a popular and reliable wastewater treatment process.  It is
uniquely attractive to  smaller communities who stand to benefit most
 from its simplicity lower cost and energy  saving features.


1.   Thomas, R. E., K. Jackson, and L. Penrod.  Feasibility of Overland
     Flow for Treatment of Raw Domestic Wastewater.   Robert S. Kerr
     Environmental Research Laboratory.  EPA Series No. 660/2-74-087,
     July 1974.  31p.

2.   National Seminar on Overland Flew Technology for Municipal
     Wastewater.  EPA-600/9-81-022, U.S. Environmental Protection
    1 Agency, Center for Environmental Research Information,
     Cincinnati, OH, 1981.

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

4.   Innovative and Alternative Technology Projects:  A Progress Report.
     U.S. Environmental Protection Agency, Office of Water Program
     Operations, Washington, D.C., 1983.

                                      Table 1:  A Synopsis of Major Research Efforts
Project             Study
Location/Scale      Team
               Principal Findings and Garments
Ada, OK
Laboratory and
field plot
Hanover, NH
laboratory and
field plot
P.O. Box 1198
Ada, OK 74820
72 Lyme Road
Hanover, NH 03755
Vicksburg,  MS
and Utica,  MS
laboratory at
WES and field
plot at Utica,  MS
P.O. Box 631
Vicksburg, MS 39180
 and lagoon
Overland Flow is a dependable technology
to provide low-cost advanced treatment.
Excellent removal of BOD, TSS and nitrogen.
Moderate removal of phosphorus easily improved
with chemical addition.  Best results when
applying raw wastwater.  SS as algae is most
difficult to remove.  Bacterial indicators are
reduced by 90 to 99% by overland flow.
Comment;  Up to 12 years of continuous use for
          some plots through sequential studies.

Two years of study with erophasis on hydraulic
detention time were used to advance a design
theory.  The theory represents other published
data well.  Study also provided good infor-
mation regarding low temperature reduction
of BOD removal under severe winter conditions.
Also includes sane initial information on
removal of trace organics.  Favorable removals
were observed for a number of organics.

Laboratory studies at the Waterways Experiment
Station addressed removal mechanisms for laboratory at
nitrogen, phosphorus and selected metals using
amended secondary effluent from a package plant.
                                                          Field plot studies with lagoon effluent at the
                                                          Utica, MS site demonstrated that slopes ranging
                                                          from 2 to 8% had little effect on treatment.  SS
                                                          as algae cells was effectively rerooved by using
                                                          lower instanteous application rates.   Reported
                                                          80 to 90% removals for cadmium,  nickel, copper
                                                          and zinc at these slower rates.

                                      Table 1:  A Synposis of Major Research Efforts
Principal Findings and Comments
Easley, SC
Field Demonstration
and full-scale
Davis, CA
indoor piolt
studies and field
Moodna Basin
Hariman, NY
field plots
SC-DHEC and Environ-
mental Systems
Engineering Depart-
Clemson University
Clemson, SC, 29631
Department of Civil
University of
California, Davis
Davis, CA,
Phillip J. Clark
Engineers and
Consultants, PC
New York, NY, 12205
Raw           Demonstrated overland flow for treatment of raw
lagoon        caiminuted sewage (25,000 gpd) and lagoon effluent
Effluent      (75,000 gpd).  Both systems met or exceeded
              typical secondary systems with consistent quality
              of effluent.  Best removals when raw sewage was
              the source and removal of algae SS was most
              Comment;  The system is scheduled to continue as
                        a full-scale operational system treating
                        lagoon effluent.

synthetic    Semicontrolled pilot studies in the laboratory
primary      were coupled with a follow up field demonstration
secondary    to develop design theory and verify design for the
             full-scale facility to treat 5 mgd.  Design theory
             is based primarily on detention time as influenced
             by slope dimensions and application procedures.

primary      A facility plan pilot test to verify design of
secondary    overland flow as one of the alternatives under
             consideration for an expansion and upgrade of
             existing facilities.  Fifteen months of data on
             BOD, SS, nitrogen and bacteria in a cold climate
             including winter operation led to conclusion that
             overland flow could be operated successfully to
             meet secondary in winter and achieve tertiary in

                                      Table 1:  A Synposis of Major Research Efforts
Project             Study
Location/Scale      Team
                                          Principal Findings and Contents
Carbondale, XL
full-scale for
trailer park
Pauls Valley, OK
Field demon-
Baton Rouge,
       School of                lagoon
       Engineering and          effluent
       University of
        Southern Illinois
       Carbondale, IL, 62901
                                raw and pond
State Health
Oklahoma City,
OK 73152
and Health Sciences
University of Oklahoma
Oklahoma City, OK 73190
Center for Wetland       simulated
Louisiana State
Baton Rouge,
  LA 70803
 Studies assessing the effects of high hydraulic
 loading and slope lengths showed 60 to  85 percent
 removal of BOD after 60 to 100 minutes  of
 retention time.
 Comment?  The results of this study show the same
           comparatively broad peak of good
           performance at loadings  of  10 to
           50 inches per week as  others  observed  at
           loadings as low as 2 inches per week.

Treatment of raw wastewater demonstrated the
ability to achieve BOD and SS removals better than
conventional secondary under winter and  summer
operation.  Temperature was shown to have a direct
effect on removal efficiency.  Treatment of the
lagoon effluent provided limited  benefits as an
advanced treatment process.  There  was 100% virus
removal for the raw system.  Airborne  bacteria
were greater in downwind samples  but no  viruses
were isolated in air samples.

These carefully controlled studies  showed that
ammonia volatization was a minor mechanism in
nitrogen removal as it accounted for  about 5% of
the removal.  Nitrification - denitrification and
crop uptake could dominate depending  on the total
nitrogen load to the system.

                                      Table 1:  A Synposis of Major Research Efforts
Project             Study
Location/Scale      Team
                 Principal Findings and Ccnments
Logan, UT
field plots
Laramie, WY
field plots
Paw Paw, ME
field test and
 Utah Water 'Research
 Utah State University
 Logan, UT, 84322
 Department of
University of Wyoming
Laramie, WY, 82070

William & Works
P.O. Box 6510
Grand Rapids,
 MI, 49506
lagoon         This brief three month study on newly established
effluent       plots during the fall season showed no BCD or SS
               removal at loading rates of 2 to 6 inches per

               Comment;  Work at other locations has demonstrated
                         the need for several months of system
                         conditioning to ensure stable conditions
                         for evaluating performance.

               Preliminary results from the first year of study
               support previous work which had projected that
               start up and operation in cold climate winter
               conditions could present formidable design

               Field site for study has been prepared and is
               being conditioned with wastewater applications.
               applications.  Spring of 1984 will initiate
               period of wastewater application under
               stabilizing conditions for evaluation of
 pond effluent

                    Table 2:  A Selected List of Overland Flow Systems
Conrnmity, State

 Alma, AR
* Alpine, AZ
 Arcadia, IA
 Castor, IA
 Cleveland, MS
 Corsicana, IX
*Davis, CA
*Easley, SC
 Esterwood, LA
*Falkner, MS
 Forrest Hill, IA
 Franklinton, IA
 Hall Summit, IA
 Heavener, OK
 Kenbridge, VA
*Lamar, AR
 Morse, LA
*Mt. Olive, NJ
*Newrnan, CA
 Norwalk, IA
 Norwood, LA
 Oppelo, AR
*Santa-Fernwood, ID
 Vinton, IA
 Wabbaseka, AR



                    Consulting Firm
Ellis, Murphy & Holgate
Ralar and Assoc.
S.M. Cothren
Clark Dietz Engineers
Gilbreth & Assoc.
Brown & Caldwell

Alex Iheriot, Jr. & Assoc.

Alex Theriot, Jr. & Assoc.
N-Y & Assoc.
Alex Teriot, Jr. & Assoc.
Alford Engineering Co.
Environmental Technology Consultants, Inc.
Burrough, Verling, Braswell, Inc.
Alex Theriot, Jr. & Assoc.

Brown & Caldwell

US Environmental Planners
Affiliated Engineers
Roy F. Weston
Affiliated Engineers
 * systems reported to be operational