United States October
Environmental Protection 1984
Agency
SEPA Overland
Flow
An Update
New
Information
Improves
Reliability
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Overland Flow/An Updai
The Process
The 1981 Technology Transfer Process Design
Manual for Land Treatment of Wastewater [1]
provides consulting engineers with a basic
description of the overland flow (OF) process
shown in Figure 1. This manual is now
supplemented by new information on design,
construction, and operation. The objective of this
foldout is to highlight the new information which has
been gained from experience with the OF process.
Design guidance is presented in greater detail in a
1984 supplement [2] to the 1981 Process Design
Manual. Design consultants are encouraged to
obtain this supplement.
Design Tips
Preapplication Treatment
Overland flow systems perform successfully when
preceded by various methods of preapplication
treatment, ranging from screening to conventional
secondary treatment. A minimal degree of
preapplication treatment generally minimizes project
costs without sacrificing treated effluent quality.
Preapplication treatment which is compatible with
OF includes screening/comminution, primary
clarification, or a one-day aerated cell. Designers
and prospective users should be aware that effluent
from OF following a stablization pond may be
comparatively high in suspended solids since algae
is not removed consistently by OF.
Wastewater
Application
By Surface,
Spray, or
Sprinkler
Methods
Limited
Percolation
Figure 1. Overland Flow Schematic
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Application
Preapplication Rate
Treatment m3/h-m
Screening/Primary 0.07 - 0.1 2a
Aerated Cell 0.08 - 0.14
(1 day detention)
Wastewater 0.09-0.15
Treatment Pond0
Secondary"1 0.11 -0.17
a. m3/h-m x 80.5 = gal/h-ft
b. cm/d x 0.394 = in./d
o. Does not include removal of algae
d. Recommended only for upgrading
treatment
Hydraulic
Loading Rate
cm/d
2.0 -7.0b
2.0 - 8.5
2.5 - 9.0
3.0 - 10.0
existing secondary
Table 1. Suggested Overland Flow Design Ranges
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Construction Tips
Terrace Construction
Construction of OF terraces and drainage channels
involves the use of some standard construction
equipment and practices. It also includes certain
specialized equipment and construction practices
which are necessary for achieving uniformly sloping
terraces and satisfactory system performance.
Experience has shown that attempts to reduce
construction costs by use of the wrong equipment
generally results in inferior performance plus higher
O&M costs.
Vegetation Selection
In order to achieve and maintain the desired
smooth sheet flow down the terrace, a
water-tolerant, turf grass is required. The most
commonly used grasses have been Reed canary
grass, fescue, and in warm climates, Bermuda.
Planting a mixture of several grasses has been
found to be most successful. Inclusion of a fast
growing nurse crop such as rye grass will provide a
temporary protective cover until the primary grasses
become established.
Operating a System
The observation of several operational municipal
OF facilities has highlighted some good operating
practices to optimize treatment performance. Some
tips are provided below:
• There is always a period of time (several months
to one year) necessary for the vegetation to
become established and the system to be
capable of treating the design wastewater flow
effectively.
• The cut vegetation should not be harvested for
the first one to two years. Leaving it on the
terrace as mulch will help to accelerate system
acclimation and improve start-up performance.
• Best long-term performance has been found with
application periods of 6 to 12 hours per day.
• Part of an OF system can accept hydraulic
loading rates higher than the design for short
periods (two to four weeks) to rest other parts for
maintenance.
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Current Use
Over a dozen municipal OF systems are currently
in operation. Table 2 shows a selected list of
municipal OF systems including those which are
currently operational, those which are in the desfgn
or construction stage, and recently completed or
currently active research projects.
Operational
Location
Chico, TX
Cleveland, MS
Corsicana, TX
Davis, CA
Easley, SC
Estherwood, LA
Falkner, MS
Kenbridge, VA
Lamar, AR
Morse, LA
Mt. Olive, NJ
Raiford, FL
Sumrall, MS
Size
(MGD)
0.07
3.00
1.00
5.00
0.10
0.08
0.04
0.30
0.10
0.08
0.02
1.30
0.20
Design/Construct
Location
Alma, AR
Arcadia, LA
Castor, LA
Glendora, MS
Gretna, VA
Hall Summit, LA
Luttrell, TN
Morton, MS
Parchman, MS
Pooler, GA
Vinton, LA
Size
(MGD)
1.27
0.50
0.03
0.82
0.26 -
0.056
0.20
1.44
0.08
1.00
1.00
Research Projects
Location
Ada, OK
Baton Rouge
Carbondale,
Davis, CA
Easley, SC
Hanover, NH
Harriman, NY
, LA Laramie, WY
L Logan, UT
Pauls Valley, OK
Paw Paw, Ml
Vicksburg/Utica, MS
Table 2. Selected Municipal Overland Flow Facilities
Further Reading
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. U.S. Environmental Protection Agency. Technology
Transfer Process Design Manual for Land Treatment of
Municipal Wastewater-Supplement on Rapid Infiltration
and Overland Flow. EPA 625/1-81-013a. U.S. EPA,
Center for Environmental Research Information, Cincinnati,
OH. October 1984.
3. Thomas, R.E. Overland Flow: A Decade of Progress.
Presented at the Missouri Water Pollution Control
Association 1984 Annual Meeting. U.S. EPA, Office of
Water Program Operations, Washington, D.C. February
1984.
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For More Information
On Overall Technical Information
EPA-OWPO(WH-547) EPA-Robert S. Ken Research
401 M Street, SW
Washington, DC 20460
(202) 382-7370/7369
Laboratory
P.O. Box 1198
Ada, OK 74820
(405) 332-8800
On Operating Facilities
Contact state I/A coordinators in states listed in Table 2.
Note: CA, LA, MS, and TX have at least two operational
OF facilities.
On Grant Processing
EPA Region 1
John F. Kennedy Federal Building
Boston, MA 02203
EPA Region 2
26 Federal Plaza
New York, NY 10278
EPA Region 3
6th & Walnut Streets
Philadelphia, PA 19106
EPA Region 4
345 Courtland Street, NE
Atlanta, GA 30365
EPA Region 5
230 South Dearborn Street
Chicago, IL 60604
EPA Region 6
1201 Elm Street
Dallas, TX 75270
EPA Region 7
324 East 11th Street
Kansas City, MO 64106
EPA Region 8
1860 Lincoln Street
Denver, CO 80295
EPA Region 9
215 Fremont Street
San Francisco, CA 94105
EPA Region 10
1200 6th Avenue
Seattle, WA 98101
Mention of trade names or commercial products
does not constitute endorsement.
Prepared by Environmental Resources Management, Inc.
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