I P 0 - W qyQ oa7 NAMM--93/10

May 1993 Water Management

Tennessee Valley Authority

TECHNICAL REPORT SERIES

GENERAL DESIGN, CONSTRUCTION, Resources Group

AND OPERATION GUIDELINES: CONSTRUCTED WETLANDS WASTEVVATER TREATMENT SYSTEMS FOR SMALL USERS INCLUDING INDMDUAL RESIDENCES

SECOND EDITION

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Tennessee Valley Authority. 1 101 Market Street. Chattanooga Tennessee 37402

Requestor:

Enclosed per your request is a copy of the new second edition of “General Design, Construction, and Operation Guidelines: Constructed Wetlands Wastewater Treatment Systems for Small Users Including Individual Residences, TVA/WM--93-19, May 1993.

The new guideline provides increased detail about construction and - - - operation of a system, general tables on sizing a system design, and

guidance on cold weather applications. Information contained in the guideline represents the views of the authors, and revisions from the first edition are based on the experience of the authors, either directly or through sharing information with others.

We appreciate your interest in TVA’s work and the constructed wetlands technology as an alternative wastewater treatment process. If you have any questions, you may contact the authors, Jerry Steiner, 615-751-7314, or James Watson, 615-751-7316. Also they would appreciate any feedback on either positive or negative experience with the constructed wetlands technology.

x y - Gerald R. Steiner, P.E. Manager, Water & Waste Engineering HB 2C-C

ames T. Watson, P.E. enior Environmental Engineer , Water and Waste Engineering B 2C-C

GRS En c 1 os ure

WRC 025LH

References

CONSTRUCTED WETLANDS

Publications Prepared by Water Resources Staff River Basin Operations

Tennessee Valley Authority

Technical Reports and Papers

1. Steiner, G. R., Watson, J. T., Hammer, D. A . , and Harker, D. F., Municipal Wastewater Treatment with Artificial Wetlands - A TVA/Kentucky Demonstration, Aauatic Plants for Water Treatment and Resource Recovery, edited by Reddy, K. R. and Smith, W. H., 923-932, Magnolia Publishing Inc., Orlando, 1987.

c- - 2. Watson, J. T., Diodato, F. D., and Lauch, M., Design and Performance of the Artificial Wetlands Wastewater Treatment Plant at Iselin, Pennsylvania, Aauatic Plants for Water Treatment and Resource Recoverv, edited by Reddy K. R. and Smith, 923-932, W. H., Magnolia Publishing Inc., Orlando, 1987.

3. Steiner, G. R., Watson, J. T., and Hammer, D. A., Constructed Wetlands for Municipal Wastewater Treatment, presented at the Mississippi Water Resources Conference, Jackson, Mississippi, March 29-30, 1988.

4 . Steiner, G. R., Watson, J. T., and Hammer, D. A., Municipal Wastewater Treatment by Constructed Wetlands - A TVA Demonstration in Western Kentucky, Proceedings of Increasing Our Wetland Resources, edited by Zelazny, J. and Feierabend, J. S., 160-167, National Wildlife Federation, Washington, D.C., April 1988

5. Hammer, D. A., Watson, J. T., Agricultural Waste Treatment with Constructed Wetlands, Proceedings of the National Svmuosium on Protection of Wetlands from Apricultural Imuacts, Fish & Wildlife Service, Biological Report 88(16), April 1988.

6 . Rucker, D. J., Wetlands, IMPACT - TVA Natural Resources and the Environment, March/June 1988

7 . Choate, K. D., Steiner, G. R., and Watson, J. T., First Semiannual Monitoring Report: Demonstration of Constructed Wetlands for Municipal Wastewater, March to December 1988, Tennessee Valley Authority, TVA/WR/WQ--89/5, July 1989.

8. Watson, J. T., Reed, S. C., Kadlec, R. H., Knight, R. L., and Whitehouse, A. E., Performance Expectations and Loading Rates for Constructed Wetlands, Constructed Wetlands for wastewater Treatment: Municipal. Industrial. and AEricultural, edited by Hammer, D. A., 319-351, Lewis Publishers, Inc., 1989.

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9. Steiner, G . R . , Freeman, R . J . , Configuration and Substrate Design Considerations for Constructed Wetlands Wastewater Treatment, Constructed Wetlands for Wastewater Treatment: Municipal. Industrial, and Agricultural, edited by Hammer, D. A . , 363-377, Lewis Publishers, Inc., 1989.

10. Watson, J. T., Hobson, J. A . , Hydraulic Design Considerations and Control Structures for Constructed Wetlands Wastewater Treatment, Constructed Wetlands for Wastewater Treatment: Municipal, Industrial. and Agricultural, edited by Hammer, D. A . , 379-391, Lewis Publishers, Inc., 1989.

11. Tennessen, K. J., Painter, M. K., Moscluito Production in Constructed Wetlands for Treatment of Municipal Wastewater, Tennessee Valley Authority, TVA/WR/AB--90/4, March 1990.

12. Watson, J. T., Design and Performance of the Constructed Wetland Wastewater Treatment System at PhilliDs Hip.h School, Bear Creek. Alabama, Tennessee Valley Authority, TVA/WR/WQ--90/5, May 1990.

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13. Choate, K . D., Watson, J. T., and Steiner, G. R., Demonstration of Constructed Wetlands for Treatment of Municipal Wastewater, Monitoring. ReDort for the Period: March 1988 to October 1989, Tennessee Valley Authority, TVA/WR/WQ--90/11, August 1990.

14. Watson, J. T., Choate, K. D. and Steiner, G. R., Performance of Constructed Wetland Treatment Systems at Benton, Hardin, and Pembroke, Kentucky During the Early Vegetation Establishment Phase, Constructed Wetlands in Water Pollution Control, edited by Cooper, P. F. and Findlater, B. C., 171-182, Pergamon Press, Oxford, 1990.

15. Davies, T. H., Watson, J. T., and Jenkins, D. B., Treatability Assessment of.Industria1 Wastes by a Portable Wetland Unit, Constructed Wetlands in Water Pollution Control, edited by Cooper, P. F. and Findlater, B. C., 403-410, Pergamon Press, Oxford, 1990.

16. Edwards, M. E., Preliminary Survey of Vegetative Growth and Survival Factors in Constructed Wetlands, Selected TVA Projects, report prepared for the Tennessee Valley Authority, September 1990.

17. Edwards, M. E., A Study of Soft-stem Bulrush (Scirpus validus) Growth in a Constructed Wetland, Hardin, Kentucky, report prepared for the Tennessee Valley Authority, December 1990.

18. Steiner, G . R., Watson, J. T., General Design. Construction. and Operation Guidelines: Constructed Wetlands Wastewater Treatment Systems for Small Users Includinrr Individual Residences: Second Edition, Tennessee Valley Authority, TVA/WM--93/10, May 1993.

19. Kadlec, R. H., Analysis of Gravel Cell Number Three, Benton, KY Wetlands, report prepared for the Tennessee Valley Authority, April 1991.

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20. Edwards, M. E., Brinkmanri, K . c . , arid Watson, J . T., A Constructed Wetland with a Declining Growth Gradient of Soft-stem Bulrush (Scirpus validus) Plants, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement. Pensacola, Florida, October 21-24, 1991.

21. Kadlec, R. H., Watson, J . T., Hydraulics and Solids Accumulation in a Gravel Bed Treatment Wetland, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

22. Watson, J. T., Danzig, A. J . , Pilot-Scale Nitrification Studies Using Vertical-Flow and Shallow Horizontal-Flow Constructed Wetland Cells, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

23. Steiner, G. R., Watson, J . T., and Choate, K. D., General Design, c- - Construction, and Operation Guidelines for Small Constructed Wetlands

Wastewater Treatment Systems, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

24. Steiner, G. R., Combs, D. W., Small Constructed Wetlands Systems for Domestic Wastewater Treatment and Their Performance, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

25. Choate, K. D., Watson, J. T., and Steiner, G. R., TVA's Constructed Wetlands Demonstration, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

26. Taylor, H. N. Choate, K. D., and Brodie, G. A., Storm Event Effects on Constructed Wetlands Discharges, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

27. Tennessen, K. J., Production and Suppression of Pest Mosquitoes in Constructed Wetlands, presented at the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, Florida, October 21-24, 1991.

28. Knight, R. L., Analysis of Survival and Condition of Planted Vegetation at the Benton, Hardin, and Pembroke, Kentucky Constructed Wetland Treatment Systems, report prepared f o r the Tennessee Valley Authority, CH2MHil1, November 1991.

29. Watson, J. T., Constructed Wetlands for Municipal Wastewater Treatment: State-of-the-Art, presented at the Symposium Epuration Des Eaux Usees Par Les Plants: Perspectives D'Avenir Au Quebec, Montreal, Quebec, Canada, March 2 0 , 1992.

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General and Other Information

1. Steiner, G. R., "Constructed Wetlands--Low Cost, Simple Sewage Treatment for Rural Communities," 4 pages, July 1989 (needs updating)

2. "Constructed/Natural Wetlands," education package, TVA/EPA, 1990. a. 2-page fact sheet b. 8" x 11" copies of 4 large outside display panels c. 11" x 17" copy of Wetlands Are Wonderlands picture f o r coloring d. picture of constructed wetlands system at Chattanooga Nature Center e. 36" x 24" and 19" x 16" colored and b/w copies of 2.b.

3. "Animal Waste Treatment by Constructed Wetlands," color pamphlet, TVA and EPA, 1991.

4. "Wastewater Treatment by Constructed Wetlands," TVA Water Quality Department, 6 pages (needs updating).

5 . Various papers on treatment of acid drainage by constructed wetlands c- - .

prepared principally by TVA Fossil Fuels staff.

6. Agenda for TVA Constructed Wetlands Training Seminar

7. Brooks, R. H., "Statement (on Constructed Wetlands) Before the Subcommittee on Investigations and Oversight, Committee on Public Works and Transportation, United States House of Representatives," August 4 , 1992.

Not included on the reference list are numerous engineering reports for specific wastewater treatment systems.

GRS October 1992

WRC 0186H

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TVA Constructed Wetlands Request Sheet Return sheet to: Water Management Library,

1101 Market Street, Haney Building ZC, Chattanooga, TN 37402-2801

FAX (615) 751-7479 (PLEASE PRINT)

Name: Address:

r- These Numbers Correspond to Title Numbers on the Constructed Wetlands Reference List

I 2 3 4 5 6 7 8 9 IO I 1 12 13

n 15

u I 7

u I 9 u 20 u 21 u 22

23 i 124

25 I 4 26

27 28 29 G I G2a G2b G2c G2d G3 G4 G5 G6 G7

GENERAL DESIGN, CONSTRUCTION, AND OPERATION GUIDELINES

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Tennessee Valley Authority Resource Group

Water Management

CONSTRUCTED WETLANDS WASTEWATER TREATMENT SYSTEMS FOR SMALL USERS

INCLUDING INDIVIDUAL RESIDENCES

SECOND EDITION

Prepared by

Gerald R. Steiner, P.E., and James T. Watson, P.E.

TVA/WM--93/10

Chattanooga, Tennessee

May 1993

Page

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . List of Figures iii

Background iv Purpose of Second Edition . . . . . . . . . . . . . . . . . . . . . . vi

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Water Conservation . . . . . . . . . . . . . . . . . . . . . . . 4 SepticTank . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Septic Tank Effluent Filter . . . . . . . . . . . . . . . . . . . 6 Other Pre-Treatment . . . . . . . . . . . . . . . . . . . . . . . 6

Hydraulic Loading . . . . . . . . . . . . . . . . . . . . . . . . 7 Organic Loading . . . . . . . . . . . . . . . . . . . . . . . . . 7

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 CWType . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Berms/Retaining Walls . . . . . . . . . . . . . . . . . . . . . . 13

Substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Pumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Water Level Control . . . . . . . . . . . . . . . . . . . . . . . 19 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Effluent Disposal . . . . . . . . . . . . . . . . . . . . . . . . 21

Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Planting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . 24

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Septic Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Water Level . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Inlet Distributor . . . . . . . . . . . . . . . . . . . . . . . . 28 Liner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Berms/Retaining Walls . . . . . . . . . . . . . . . . . . . . . . 29 Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Odor Control . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Drain Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Health and Safety . . . . . . . . . . . . . . . . . . . . . . . . 31 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Additional Information . . . . . . . . . . . . . . . . . . . . . . . . 32

Pre-Treatment

Hydraulic and Organic Loading

Basis of CW Design and Construction

* . . Liner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Vegetation

Operation and Maintenance

..

Appendix Design Examples . 4 Options . . . . . . . . . . . . . . . . . . . . 34 Dimensions Guideline Table . . . . . . . . . . . . . . . . . . . 40 Elevation Differences Between System Components . . . . . . . . . 42

I - LIST OF FIGURES

I 1 Number Page

1. Cut-A-Way Perspective of A Constructed Wetlands System . . . . . 2

2. Optional Method f o r Vertical Wall Construction 14 1

. . . . . . . . .

3. Water Level Control Structures . . . . . . . . . . . . . . . . . 20

Al. Two Cell Constructed Wetlands for a Three Bedroom I

House - Design Example Option 1 . . . . . . . . . . . . . . . . 38

- - - A2. Single Cell Constructed Wetlands for a Three Bedroom House - Design Example Options 1 and 3 . . . . . . . . . . . . . 39

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I 1 I 1 r I f I l 0 I 6 il e m P II

I a

sour

BACKGROUND

The Tennessee Valley Authority ( T V A ) is a federal regional e

development agency.

of the waters of the Tennessee River system. Although great strides have

been made, point source and nonpoint source pollution still affect the

surface water and groundwater quality in the Tennessee Valley and

nationally-

One of T V A ' s major goals i s cleanup and protection

Pollution impairs water uses, causes public health problems, creates

regulatory enforcement headaches, and hinders community and economic

development.

treatment systems or the lack of them. A l s o , a common local problem

faced by homeowners and others in rural and non-sewered areas is poor

site conditions which do not allow installation and satisfactory

performance of conventional on-site systems such as septic tank-drain

fields. Practical solutions are needed, and there is great interest and

desire to abate water pollution with effective, simple, reliable and

affordable wastewater treatment processes.

Causes of this pollution are poorly operating wastewater

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In recognition of this need, TVA began demonstration of the constructed

wetlands technology in 1986 as an alternative to conventional, mechanical processes, especially for small connnunities. As the process is

investigated, its potential to treat various types and volumes of

wastewaters continues to be realized.

Constructed wetlands can be downsized from municipal systems to small

systems, such as for schools, camps and even individual homes. The

systems are effective, simple, affordable, aesthetically pleasing, and

educational. Constructed wetlands "let nature do the dirty work."

These guidelines have been developed by TVA to provide state-of-the-art

and simple instructions for designing, constructing and operating

constructed wetlands for small wastewater flows. They have been

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f i e l d - t e s t e d and shown t o be e f f e c t i v e ; however, they should be

cons idered as on ly “gu ide l ines ,” n o t s t a n d a r d s . F l e x i b i l i t y should

always be al lowed s o t h a t i nnova to r s can tes t p o t e n t i a l l y improved

concepts . Feedback i s encouraged on b o t h p o s i t i v e and n e g a t i v e

expe r i ences s o t h a t TVA can s h a r e t h e informat ion .

The in fo rma t ion conta ined i n t h i s document r e p r e s e n t s t h e views of t h e

a u t h o r s and does n o t n e c e s s a r i l y r e f l e c t W A ’ s o f f i c i a l p e r s p e c t i v e .

V

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c* .

PURPOSE OF S E C O N D EDITION

"General Design, Construction, and Operation Guidelines: Constructed

Wetlands Wastewater Treatment Systems f o r Small Users Including

Individual Residences," TVA/WR/WQ--91/2, was published in March 1991.

Subsequently, there have been iiwnerous presentations at conferences and

meetings, articles published in "Small Flows" by the National Small Flows

Clearinghouse and in other magazines and journals, and local and national

television and press coverage about small systems and the guidelines.

In response to telephone and written requests though April 1993, T V A

distributed approximately 1800 copies of the March 1991 guideline.

Approximately another 1000 copies were distributed by TVA at conferences

and meetings. Additional copies have been distributed through the

National Small Flows Clearinghouse. The authors believe that this large

public response indicates the desire and need for alternative treatment

systems that can provide affordable solutions to environmental and

regulatory compliance problems.

In the introduction to the March 1991 guideline, it was stated that the guidelines may undergo future revisions based on improved information.

Therefore, the purpose of this second edition is to significantly revise,

improve, and expand information in the first edition based on accumulated

TVA experience. Also, an attempt has been made to present some design

information in a more "user friendly" format.

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GENERAL DESIGN, CONSTRUCTION, AND OPERATION GUIDELINES

CONSTRUCTED WETLANDS WASTEWATER TREATMENT SYSTEMS FOR SMALL USERS

INCLUDING INDIVIDUAL RESIDENCES

I. GENERAL

A . Constructed Wetlands Definition

A constructed wetlands wastewater treatment system (CW) may be

defined as "a man-made, engineered, marsh-like area which i s

designed, constructed and operated to treat wastewater by

attempting to optimize physical, chemical, and biological

processes of natural ecosystems." Figure 1 is a cut-a-way c.

perspective of one optional CW configuration. It summarizes

the components of arid processes occurring in a CW. effective, reliable, simple, and relatively inexpensive as

compared to conventional systems.

flow ranges, including sources having relatively small flows

A CW can be

A CW can be built for wide

(e.g., individual homes, small businesses and schools).

B. Discharne and Non-Discharge SYS temc

A CW can be a discharge system (i.e., discharges to a receiving "waters of the U.S.") or a non-discharge system (discharges to

a stream are eliminated by evaporation, transpiration, and/or percolation).

conventional on-site methods are ineffective due to poor site

conditions (e.g., low soil percolation, shallow soils, high

groundwater table, Karst topography).

is classified as "on-site" if it is located within the property

boundaries of the owners producing wastewater.

A non-discharge system is used where

A non-discharge system

a

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C. Size of CW This guideline is generally f o r "small" CW systems , but "small" is not strictly defined. The smallest system designed by T V A

has been for 83 gpd, a one bedroom house with limited

wastewater. "Small" may be considered as systems treating

flows of 20,000 gpd or less. However, a system designed to

treat 100,000 gallons per day for a rural town would also be

"small" compared to a system for one million gallons per day.

The design features of larger systems will follow many of the

guideline criteria.

for "larger" systems . The guideline identifies some differences

D. Reaulatorv Considerations

1. Coordinate planning of all designs with local and state

officials and obtain required approvals. "Small" discharge systems can be reliably designed to meet

"secondary" level permit limits. Large systems also can be

designed to meet secondary limits but additional information is

needed to optimize designs and minimize costs. To meet "advanced" level permit limits for nutrients, such as for

phosphorous and ammonia-nitrogen, loading rates need t o be

relatively small and the CW system should utilize multiple cells in series or stages with each stage designed for specific treatment objectives.

are needed on the reduction of nutrients by a CW before designs

can be developed which will consistently meet advanced level

permit limitations arid also be affordable.

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2.

Additional research and demonstration

3 . Chi-site, non-discharge systems can be reliably designed,

constructed and operated for "small" wastewater flows, depending on wastewater characteristics and siting conditions.

Their best use will be to replace failed adsorption fields or

as an alternative to conventional systems where percolation

rates are low. The technology may also be an alternative to

low pressure mound systems by constructing the CW system on top

of bedrock, impermeable clay, o r high groundwater.

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E.

F.

G.

"CookboQk" Desi- "Cookbook" designing of CW systems is strongly discouraged. The cost-effectiveness of CW's is very site specific. Prepare

and review all designs on a site-by-site basis, and use the

technology only where it has a reasonable chance of performing

acceptably.

An Alternative Technology

Constructed wetlands for an on-site, non-discharge system (such

as for homes) is still considered to be an "alternative"

technology to a conventional septic system.

will be for home owners whose septic systems have failed or for

those building in a location unsuitable for conventional

systems. Consequently, a CW can cost more than a conventional

system. Also, its use normally will require accepting some

degree of r i s k (as with other alternative technologies).

CW option should be compared to other available alternatives so

that the most cost-effective selection is made.

Most applications

The

D-

CW is a relatively new technology. These guidelines may again

be revised as information improves. For example, research may

find that the design hydraulic conductivity can be increased.

This could decrease the required width for larger systems,

which typically would be advantageous.

11. PRE-TREATMENT

A. Water Conserva t ion

1. Water conservation is strongly encouraged. It i s considered a

"pre-treatment" method since it can significantly reduce waste

characteristics. Low-flow plumbing fixtures will help minimize

wastewater flow to the CW system. For example, efficient

ultra-low flush toilets using only 1.6 gallons and less per

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flush versus the common 5 to 6 gallon flush are available.

These fixtures will pay back their cost from water bill savings

and can decrease sewage flow by about one-third or more.

Existing Facilities - Consider replacing standard flush toilets with ultra-low flush toilets. Modify other plumbing fixtures

(e.g., showers, faucets) with water saving devices. Repair any

leaky fixtures as soon as they are noticed.

New Facilities - Require water conserving plumbing fixtures

such as ultra-low flush toilets and flow restricting shower

heads and faucets.

2 .

3 .

B . SeDtic Tank

1. To reduce suspended solids by removing coarse and heavy solids prior to the CW, install a septic tank(s) of appropriate size

and design configuration. Refer to state design criteria for

design, construction, and installation requirements. 2. Use at least one two-cell septic tank. Two tanks in series may

be used if a two-cell tank is not available. Other design

features such as baffling and flow constriction may be used as

an option to a two cell septic tank, if locally available and

approved by regulatory agencies. If minimization of solids and organic load to the CW is a design objective, or if proper maintenance of the tank is questionable, include a septic tank

effluent filter (section 1I.C).

Obtain septic tanks from a manufacturer whose septic tank series is approved by the appropriate state/county health

department. Tanks must be free of any defects. Field repairs

are discouraged and generally should not be acceptable.

Tank failures can be minimized by providing a solid foundation

beneath the entire tank. This is best done by excavating about

2 inches below the final elevation of the tank and backfilling

with small gravel ( 1 / 2 inch or less) or sand. The gravel or sand can be quickly leveled, precluding humps that can cause

stress failure when the tank is filled with water.

3 .

4.

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5. Set the septic tank(s) in place at the location specified by

the plans, backfilling around the sides but leaving the t o p

exposed. Fill.the tank(s1 to overflow and observe for 24 hours

to ensure watertightness. The local health department may

adjust this time so as not to hinder the installation of the

constructed wetlands system. Leave the water in the tank after

the testing period. Properly close the tank after testing.

C . Septic Tank Effluent Filter

1. A filter (with associated vault, access riser and cover, and

other standard accessories) may be installed in the effluent

side of the septic tank. Options include the Zabel Model A100,

Oreiico Models F1248 or F1260, or equivalent. A filter will

further reduce solids and organic load t o the CW system and assure long-term protection of the CW against septic tank upsets and poor maintenance.

cost-effective and low maintenance.

The filters are typically

2. If the septic tank effluent must be pumped to the CW, a combined filter and pump system may be used.

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D. Other Pre-Treatment

Pre-treatment to reduce suspended solids may differ from septic

tanks, especially for larger systems. For example, one

alternative may be a stabilization pond. used to "polish" the effluent of an existing treatment facility

such as a mechanical package plant or a pond.

"pre-treatment" facilities must be operated and maintained to be efficient. Excess suspended solids from a poorly operated

and maintained facility can quickly lead to serious problems in

CW cells (such as surface flow, short-circuiting, odors, and poor effluent quality).

Also, a CW may be

These

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111. HYDRAULIC AND ORGANIC LOADING

A. Hvdraul ic Loadinn

1 . Determine h y d r a u l i c l oad ing t o t h e CW i n g a l l o n s p e r day (gpd) ,

based on t h e r e q u i r e d flow p e r bedroom f o r home systems and

flow p e r person or p e r f i x t u r e f o r o t h e r s m a l l systems. These

rates are e s t a b l i s h e d by each s t a t e . (Typical rates are 120

and 150 g a l l o n s p e r day p e r bedroom; t h e r e f o r e , a t h r e e bedroom

house a t 120 gpd p e r bedroom would have a 360 gpd d e s i g n flow.)

2. Reduced or i nc reased h y d r a u l i c l oad ings may be approved by the

a p p r o p r i a t e r e g u l a t o r y agency based on a c t u a l usage.

B. m a n i c Loadinp;

1. Home Systems - Determine t h e o r g a n i c load ing t o t h e CW i n c- - .

5 pounds BOD5 pe r day ( l b / d ) .

average d a i l y o r g a n i c load ing p e r person and 50 pe rcen t BOD

removal i n t h e s e p t i c t ank , use 0.085 l b BOD p e r day p e r

person.

When assuming 0.17 pounds BOD

5

2. Other Small Users - Use accep ted u n i t l oad ings approved by t h e

state.

Add i t iona l o r g a n i c l o a d r e d u c t i o n s can be t aken i f a s e p t i c

tank e f f l u e n t f i l t e r o r two t anks i n series are used, p o s s i b l y

a t o t a l of 70 p e r c e n t or g r e a t e r . Determine t h e a c c e p t a b l e

r e d u c t i o n through t h e a p p r o p r i a t e r e g u l a t o r y agency.

3 .

I V . BASIS OF CW DESIGN AND CONSTRUCTION

A . General

1. Do n o t "cookbook" des igns . A s p e c i f i c des ign should be

developed for each system based on s i t e c h a r a c t e r i s t i c s and

h y d r a u l i c and o r g a n i c l o a d i n g s . S i t e f a c t o r s t o c o n s i d e r are

s o i l d e p t h and p e r m e a b i l i t y , s e a s o n a l water levels, s u r f a c e

topography, l o t s i z e and shape , shading by trees, and owner

p r e f e r e n c e s and a t t i t u d e s .

-7-

I-

t I I 1 I i 1 I I I I 1 1 E I i I I i

2 . Design Examples - Refer t o t he Appendix f o r c a l c u l a t i o n s of

s u r f a c e a r e a , c ros s - sec t iona l w i d t h , dep th , and l e n g t h f o r fou r

t y p i c a l systems wi th d i f f e r e n t s i t e c o n d i t i o n s .

schematics are included f o r two o p t i o n s .

Engineering

3 . General Guidel ine f o r Dimensions - The Appendix inc ludes a

t a b l e which l is ts , as a gene ra l g u i d e l i n e , v a r i o u s design

dimensions f o r twu, t h r e e , and f o u r bedroom houses and l a r g e r

small systems f o r t y p i c a l s ta te h y d r a u l i c l oad ing c r i t e r i a .

4 . Eleva t ion Di f f e rences between System Components - System

components should have e l e v a t i o n d i f f e r e n c e s t o provide f o r t h e

most e f f e c t i v e ope ra t ion .

provided i n t h e Appendix.

Suggested re la t ive d i f f e r e n c e s are

B. CW Tvue

1. There are two b a s i c types of CWs - subsu r face flow and s u r f a c e

flow (or f r e e water s u r f a c e ) .

2. Subsurface Flow - These systems c o n t a i n porous s u b s t r a t e and

are designed and ope ra t ed t o prevent v i s i b l e s t a n d i n g water.

For r e s i d e n t i a l u se , a subsu r face flow system i s recommended t o

minimize p o t e n t i a l odor , v e c t o r , and p u b l i c h e a l t h problems.

3. Sur face flow (or f r e e water s u r f a c e ) - These systems have

v i s i b l e s t a n d i n g water.

gu ide l ine .

f o r l a r g e r systems and i n c r e a s e w i l d l i f e b e n e f i t s , b u t t h e r e

are a l s o disadvantages such as p o t e n t i a l mosquito problems.

s u r f a c e f low CW could be used i n whole o r p a r t t o enhance a

"water garden" concept f o r a small system, b u t p o t e n t i a l

problems must be considered and managed.

The i r des ign is n o t covered by t h i s

They have t h e p o t e n t i a l t o b e mo-e c o s t - e f f e c t i v e

A

C . Configurat ion

1. A small CW c o n f i g u r a t i o n may c o n s i s t of a s i n g l e c e l l , two

c e l l s i n series, o r m u l t i p l e ce l l s i n para l le l and /o r series.

2. S i n g l e C e l l System - A s i n g l e c e l l t y p i c a l l y should be used f o r

s i tes where ( a ) wastewater w i l l n o t p e r c o l a t e (i.e., high

groundwater t a b l e , shallow s o i l above impermeable rock, o r v e r y

impermeable c l a y ) , ( b ) topography i s r e l a t i v e l y f l a t ( p r e f e r r e d

-8-

1

I 1 i 1 I I f I I I f 1 I I I 1 1 I ! t

e l e v a t i o n d i f f e r e n c e s between major system components cannot be

r e a d i l y o b t a i n e d ) , and ( c ) d r a i n f i e l d s fo l lowing t h e CW a r e

r e q u i r e d by s t a t e or l o c a l h e a l t h department.

Two-Cell System - Two c e l l s i n series may be used a t s i t e s with

s o i l which w i l l marg ina l ly p e r c o l a t e t r e a t e d w a s t e w a t e r . The

f i r s t c e l l is l i n e d t o a s s u r e s u f f i c i e n t water f o r maintenance

of h e a l t h y wetland p l a n t s . The second c e l l i s u n l i n e d to al low

p e r c o l a t i o n of t h e t r e a t e d wastewater and p rec lude or minimize

s u r f a c e d i s c h a r g e s . I f p e r c o l a t i o n r a t e s are h igh , t h e second

c e l l may b e too d r y t o maintain h e a l t h y v e g e t a t i o n .

riot n e g a t i v e s i n c e i t i n d i c a t e s t h a t t h e system i s f u n c t i o n i n g

w e l l . )

s u b s t r a t e i n t h e second ce l l i f v e g e t a t i o n cannot be s u s t a i n e d .

M u l t i c e l l System - Use p a r a l l e l and /o r series ce l l s t o p rov ide

des ign and o p e r a t i o n a l f l e x i b i l i t y f o r l a r g e r systems.

s p e c i f i c advantages of modular ce l l s i n c l u d e d e s i g n

s i m p l i f i c a t i o n ( t o l i m i t t h e dimensions of g r a v e l c e l l s t o less

than 200 f e e t wide, 100 f e e t long, and 2-1/2 f e e t deep ) ,

a d d i t i o n of cel ls as system load increases w i t h t i m e ,

o p t i m i z a t i o n of t r ea tmen t p rocesses (BOD removal i n f i r s t s t a g e

cel ls and n u t r i e n t removal i n subsequent ce l l s ) , a d a p t a t i o n t o

s i t e shape o r topography (al low cel ls t o b e t e r r a c e d i n

p a r a l l e l o r series t o reduce and b a l a n c e c u t and f i l l ) , and

f l e x i b i l i t y t o t empora r i ly remove i n d i v i d u a l cells from service

or l oad d i f f e r e n t l y .

3 .

(Th i s i s

A l a y e r of d e c o r a t i v e mulch may b e ma in ta ined on t h e

4 . c. -

Some

D. Dimensions

1. Sur face Area

a. To determine CW s u r f a c e area, m u l t i p l y s u r f a c e h y d r a u l i c

l oad ing c r i t e r i o n i n squa re f e e t of t o t a l s u r f a c e area p e r

g a l l o n p e r day ( f t /gpd) by t h e h y d r a u l i c l o a d ( s e c t i o n

1II.A) i n g a l l o n s p e r day (gpd).

2

b. U n r e s t r i c t e d Area - Use a s u r f a c e h y d r a u l i c l o a d i n g c r i t e r i o n 2 of 1 .3 f t /gpd.

c . R e s t r i c t e d Small Area - Use a s u r f a c e h y d r a u l i c l oad ing 2 c r i t e r i o n of 0.87 f t /gpd.

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I

I I t I I I I E I I t 1 1

-* -

d. Cold Climates - Use a surface hydraulic loading criterion of at n L least 1.3 ft /gpd.

2. Cross-section Area

a. Calculate the cross-section area based on hydraulic loading and

organic loading rates. Select the larger value.

b. Hydraulic Loading - Calculate area based on the hydraulic

loading (section 1II.A) and Darcy's Law (Appendix). Use a

relatively low hydraulic gradient (assume equal to bed slope)

up to 1 percent and a conservative long-term hydraulic

conductivity (850 feet per day). For a flat bottom (0% slope),

assume a low hydraulic gradient for the calculation (typically

0.5 percent). higher can be used t o minimize cut and fill.

receiving secondary or higher quality wastewater, a higher

hydraulic conductivity may be used (up to a 10-fold increase,

i.e., 8500 ft/day). This will normally be advantageous for

larger systems to reduce the total inlet width needed.

(NOTE - The design values for hydraulic conductivity are still considered conservative. As more experience and data are

acquired, the design values may be increased, resulting in

improved dimensional flexibility for larger flows. The actual

hydraulic gradient is expected to vary with distance down the

cell due to the partial but differential filling of substrate

pore spaces with time. It may be greater than design value in the inlet area and less than design value in the outlet area.

Darcy's Law is used to design the cross-section area to assure

that the flow is subsurface, and also is considered t o be a

conservative approach. Darcy's Law applies to laminar flow

regimes. Flow in clean gravel can range from laminar to turbulent, depending on flow rates and gravel sizes. Use of

low, long-term hydraulic conductivities and small gravel sizes

assures flow regimes that are either laminar or in the

transitional region, thus assuring practical applicability of

Darcy's Law.

For sloping lots, bed slopes of 2 percent or

For cells

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c . Organic Loading - Calcu la t e area based on t h e o rgan ic loading

( s e c t i o n 1II.B) and an o rgan ic loading c r i t e r i o n of 1 f t per

0.05 l b BOD p e r day.

where a reduced i n l e t width i s advantageous, an o r g a n i c loading

c r i t e r i o n of 1 f t pe r 0.10 l b BOD p e r day may b e used w i t h a

r i s k of o c c a s i o n a l s u r f a c e flow i n i n l e t area ove r long t e r m .

2

For l a r g e r systems o r s t e e p s l o p i n g l o t s

2

3 . S u b s t r a t e Depth

a. For c a l c u l a t i o n , s e l e c t i n l e t end s u b s t r a t e dep th of 12 inches

o r 18 inches.

b . U n r e s t r i c t e d Area - Use a 1 2 inch dep th t o p rov ide t h e b e s t

t reatment by a s s u r i n g flow i s through t h e most e f f e c t i v e

p o r t i o n of t h e p l a n t r o o t zone. Aerobic microorganisms t h a t

degrade waste o rgan ic s o b t a i n oxygen from t h e p l a n t r o o t s .

Most r o o t biomass w i l l be i n t h e t o p 1 2 i n c h e s of t h e c e l l s .

c. R e s t r i c t e d Small Area - Use 18 inch depth i f a v a i l a b l e s u r f a c e

area i s l i m i t e d by t h e l o t s ize o r shape.

Cold climates - A deeper c e l l should be used t o a l l o w f o r

g r e a t e r water dep ths du r ing extreme c o l d weather t o p reven t

d.

f r e e z i n g .

cri teria of a t least 1.3 f t Igpd.

F l a t beds (0% s l o p e ) - Determine t h e o u t l e t end dep th based on

t h e c a l c u l a t e d dep th and an assumed low h y d r a u l i c s l o p e

( t y p i c a l l y 0.5%).

equa l t o t h e o u t l e t end depth, which w i l l s i m p l i f y bed

c o n s t r u c t i o n for s m a l l systems.

Use 18 i n c h dep th w i t h t h e s u r f a c e h y d r a u l i c l oad ing 2

e.

Make t h e dep th f o r t h e e n t i r e ce l l l e n g t h

f . Sloped beds - A s loped bed and a f l a t s u r f a c e w i l l r e s u l t i n a

deeper e f f l u e n t end than i n f l u e n t end. The d i f f e r e n c e between

the i n f l u e n t and e f f l u e n t s u b s t r a t e dep ths should b e less than

6 i nches p r e f e r a b l y and no g r e a t e r than 1 2 inches .

(NOTE - For a r e l a t i v e l y long c e l l , t h e g r a v e l in t h e o u t l e t

area could b e d r y f o r a depth equa l t o t h e d i f f e r e n c e between

t h e i n l e t and o u t l e t depths . Th i s is due t o t h e a c t u a l

h y d r a u l i c s l o p e , and could make maintenance of h e a l t h y

v e g e t a t i o n i n t h i s area more d i f f i c u l t . An o p t i o n f o r a long

c e l l i s t o s l o p e both t h e bed bottom and t o p of s u b s t r a t e

-11-

I

4 .

a.

b.

C .

5.

a.

b .

C .

according t o the hydrau l i c g r a d i e n t ; however, t he r i s k of

s u r f a c e flow would i n c r e a s e s i n c e t h e hydrau l i c g r a d i e n t w i l l

v a ry wi th time and d i s t a n c e down the c e l l . )

Width

To c a l c u l a t e e f f e c t i v e width (width of c e l l bottom i f s i d e

s l o p e s are u s e d ) , d i v i d e c r o s s - s e c t i o n a l area ( s e c t i o n IV.D.2)

by depth ( s e c t i o n IV.D.3).

I t is suggested t h a t t h e width of c e l l s w i th b u r i e d i n l e t

d i s t r i b u t o r s be r e s t r i c t e d t o a m a x i m u m of about 14 f e e t t o

reduce s h o r t - c i r c u i t i n g p o t e n t i a l . As an alternative, wider

c e l l widths can be used w i t h flow s p l i t t e r s and corresponding

segmented b u r i e d i n l e t d i s t r i b u t o r s .

For l a r g e r f lows, a p r a c t i c a l upper l i m i t on t h e width of each

c e l l u s ing s u r f a c e d i s t r i b u t o r s i s about 200 f e e t .

Leng’h

To c a l c u l a t e t he e f f e c t i v e system l eng th (bottom of c e l l ) ,

d i v i d e s u r f a c e area ( s e c t i o n IV.D.1) by width ( s e c t i o n IV.D.4).

S i n g l e C e l l System - The l e n g t h of a c e l l (bottom) i n a

s i n g l e - c e l l system i s t h e e f f e c t i v e system l e n g t h ( s e c t i o n

IV.D.5.a). The a c t u a l cq l l l e n g t h w i l l be r e s t r i c t e d by

c r i t e r i o n f o r s loped beds i n s e c t i o n IV.D.3.f i n combination

wi th t h e design h y d r a u l i c g r a d i e n t . For example, f o r a

h y d r a u l i c g r a d i e n t of 1.0%, t h e l e n g t h of a ce l l should n o t

exceed 100 f e e t s i n c e t h e d i f f e r e n c e between i n l e t and o u t l e t

s u b s t r a t e dep ths would exceed 1 2 inches.

important f o r l a r g e r systems, r e q u i r i n g series ce l l s t o provide

t h e t o t a l e f f e c t i v e c e l l l e n g t h .

Two-Cell System - I f t h e i n - s i t u s o i l type w i l l p rov ide an

e s t ima ted p e r c o l a t i o n rate of 120 minutes/ inch or b e t t e r , a

two-cell system may be used t o ach ieve e i t h e r z e r o or minimal

d i scha rge due t o water loss through p e r c o l a t i o n and

e v a p o t r a n s p i r a t i o n from t h e system. The s u r f a c e area of t h e

system i s d iv ided e q u a l l y between each c e l l , and t h e second

c e l l i s unl ined ( s e c t i o n IV-F). The l e n g t h of each c e l l i s

one-half t he system l e n g t h ( s e c t i o n IV.D.5.a).

Th i s may become

-1 2-

6 . Balancing Aspect (Length t o W i d t h ) Rat ios - Genera l ly , des ign

should minimize s h o r t - c i r c u i t i n g p o t e n t i a l which i n c r e a s e s wi th

smaller a s p e c t r a t i o s .

narrow as p o s s i b l e while cons ide r ing a l l o t h e r f a c t o r s

a f f e c t i n g t h e f i n a l a s p e c t r a t i o . In p r a c t i c e , t r a d e - o f f s must

be c a r e f u l l y considered and balanced wi th in the recommended

l i m i t s s e t f o r t h i n these g u i d e l i n e s . For example, h i g h e r

h y d r a u l i c g r a d i e n t s dec rease c e l l width ( p o s i t i v e f a c t o r ) , b u t

i n c r e a s e c e l l l e n g t h and depth (nega t ive f a c t o r ) . M u l t i p l e

c e l l s should b e used t o s t a y w i t h i n recommended l i m i t s .

O p t i o n a l l y , less conse rva t ive design v a l u e s f o r long-term

h y d r a u l i c c o n d u c t i v i t y and/or u n i t o rgan ic loading can b e used,

b u t t h e corresponding r i s k of a t least i n t e r m i t t e n t s u r f a c e

flow i n t h e i n l e t area must be accepted. A s more o p e r a t i o n a l

expe r i ence and performance information become a v a i l a b l e , r i s k

can b e b e t t e r a s s e s s e d and des ign c r i te r ia can be upgraded t o

reduce conservat ism.

I t i s be l i eved t h a t c e l l s should be as

E. 1.

2.

3 .

a.

b.

4 .

a .

Berms/Retaininq Walls

Surround t h e CW cel ls w i t h e a r t h e n berms o r a r e t a i n i n g w a l l t o

r e t a i n wastewater i n t h e t r ea tmen t system and p reven t s u r f a c e

runoff from e n t e r i n g t h e system.

The t o p of t h e b e n d r e t a i n i n g w a l l should b e a minimum of 6

i nches above t h e CW bed s u r f a c e ( t o p of mulch) and a m i n i m u m of

6 i n c h e s above t h e e x i s t i n g ground s u r f a c e .

Earthen B e r m s - E x t e r i o r s l o p e s should b e 3 H : l V o r f l a t te r .

I n t e r i o r s l o p e s may be ver t ical o r s loped up t o 2H:lV,

determined based on e x i s t i n g s o i l c h a r a c t e r i s t i c s , c o n s t r u c t i o n

t echn iques t o be used, and landscaping o b j e c t i v e s . Plywood can

be used t o shape i n t e r i o r v e r t i c a l w a l l s (F igu re 2 ) .

Re ta in ing w a l l s - Use i n s t e a d of e a r t h e n berms t o conserve space o r f o r t e r r a c i n g

needs. Bui ld w i t h conc re t e b l o c k s , c r o s s t i e s , l andscap ing

t imber s , o r o t h e r materials t h a t are s t r o n g and d u r a b l e ( e . g . ,

Plia-Dike, o r e q u i v a l e n t ) .

-1 3-

45 mil EPDM liner (or equivalent)

NOTE: Treated landscape limbers may be substituted for R.R. crossties. (one row of 6x6 timbers or two rows and columns of 3x5 limbers)

Pea gravel base for liner if needed

- -.------.-'

Topsoil - - S * (Compact all fill dirt in 6" increments to minimize long- term settling under ' crosslies or timbers)

1.- 318" or 112" plywood wall supported by treated 2x4's at ends and middle of each full sheet (cover plywood joints and all nails on inside wall of cell with 2 layers of duct tape - do not nail through liner)

Figure 2. Optional Method for Vertical Wall Construction

t

i

L,. Line o r s e a l r e t a i n i n g w a l l s t o prevent seepage ( s e c t i o n 1 V . F ) .

5. Cap - For s m a l l (home) systems, t h e top of t h e berms o r

r e t a i n i n g w a l l s may be capped wi th 6" X 6" landscape t imbers o r

r a i l r o a d c r o s s t i e s t o s e c u r e t h e l i n e r , p reven t s u r f a c e runoff

from e n t e r i n g the c e l l , and improve t h e appearance of t he

c e l l . For l a r g e r s y s t e m s wi th an e a r t h e n berm, a minimum t o p

width of t h r e e f e e t would f a c i l i t a t e g r a s s c u t t i n g .

F. L i n e r

1. I n s t a l l an impermeable l i n e r i n s i d e b e r m / r e t a i n i n g w a l l on the

bottom and s i d e w a l l s of c e l l . The primary purpose of t h e

l i n e r is t o prevent e x f i l t r a t i o n of wastewater from t h e c e l l

and i n f i l t r a t i o n of groundwater i n t o t h e c e l l . With

e x f i l t r a t i o n , a s u f f i c i e n t water l e v e l could n o t be a s s u r e d f o r

maintenance of wetland v e g e t a t i o n . With i n f i l t r a t i o n ,

r e t e n t i o n t i m e needed f o r wastewater t r ea tmen t would be reduced.

2. Type

a. Materials - Use a type of heavy du ty s y n t h e t i c 30-45 m i l

membrane, such as e t h y l e n e propylene d i e n e monomer (EPDM)

rubber , po lyv iny l c h l o r i d e , o r po lye thy lene , o r compacted

c l a y . Use W r e s i s t a n t materials.

b . With a s y n t h e t i c l i n e r , remove a l l rocks , r o o t s and d e b r i s t h a t

might puncture t h e l i n e r . A 1 t o 2 i n c h l a y e r of sand o r round

pea g r a v e l between t h e bed bottom and t h e l iner would p rov ide

a d d i t i o n a l p r o t e c t i o n and should be r e q u i r e d f o r a l l

i n s t a l l a t i o n s where bedrock must be excavated.

3 . S i n g l e C e l l System - I n s t a l l an impermeable l i n e r on t h e bottom

and s i d e s of t h e c e l l .

t a b l e or bedrock n e a r t he ground s u r f a c e , t h e CW may be b u i l t

on the ground s u r f a c e w i t h impermeable l i n e r and a p p r o p r i a t e

In areas having a h i g h groundwater

p rov i s ions f o r e f f l u e n t d i s p o s a l .

4 . Two-Cell System

a . C e l l 1 - Line as i n a s i n g l e c e l l system.

b . C e l l 2 - Do n o t l i n e t y p i c a l l y . However, i f i n s t a l l e d on

s l o p i n g t e r r a i n , downhill s i d e s of t h e second c e l l may need t o

-15-

be l i n e d t o prevent w a t e r s eepage a t the i n t e r f a c e between the

f i l l m a t e r i a l and the o r i g i n a l ground s u r f a c e . I f t h i s i s t h e

c a s e , d i g through t h e f i l l m a t e r i a l and extend the s i d e w a l l

l i n e r a t least 6 inches i n t o t h e o r i g i n a l s o i l below t h e f i l l

material i n the c e l l bottom.

5 . Provide leakproof seal between the l i n e r and piping which

e n t e r s and ex i t s t h e c e l l f o r i n l e t and o u t l e t d i s t r i b u t o r s .

For example, use Tank Adaptors o r e q u i v a l e n t .

G. S c b s t r a t e

1. Type and S i z e

a . Type - The most common s u b s t r a t e i s s i z e d , washed g r a v e l . A

p r e f e r r e d s u b s t r a t e t o reduce compaction i s a g r a v e l w i th

rounded s u r f a c e s such as r i v e r pea g rave l . Do n o t use crushed

l imestone u n l e s s i t is the orily a v a i l a b l e a l t e r n a t i v e ; i t can

compact more due to i t s a n g u l a r shape and has a g r e a t e r

p o t e n t i a l t o puncture a l i n e r .

b . S i z e - For t h e main s u b s t r a t e , use A.H.D. s i z e s 8 through 9

(average diameter 1 /4 i n c h and 1/8 inch, r e s p e c t i v e l y ) . Larger

s i z e s (e.g., A.H.D. s i z e s 6 , 67, o r 7 - 1 / 2 t o 3/8 i n c h ) may b e

used i f more r e a d i l y a v a i l a b l e i n c e r t a i n l o c a t i o n s , b u t t h e

smaller s i z e is p r e f e r r e d . Also, t h e l a r g e r s i z e should b e

used i f t h e s e p t i c tank e f f l u e n t is pumped t o t h e CW. c. I n f l u e n t d i s t r i b u t i o n and e f f l u e n t c o l l e c t i o n - I n t h e f i r s t

and last two f e e t of t h e c e l l ( s ) , use 2 t o 4 i n c h s t o n e around

t h e i n f l u e n t d i s t r i b u t o r and e f f l u e n t c o l l e c t o r p i p e s t o reduce

i n f l u e n t and e f f l u e n t c logg ing p o t e n t i a l . One f o o t i n s t e a d of

two f e e t may be used f o r v e r y s m a l l systems (e.g., one bedroom

house) w i th a s h o r t c e l l l e n g t h .

2. C l e a n l i n e s s - The s u b s t r a t e should be washed t o minimize f i n e s

which w i l l p lug t h e pore spaces of t h e s u b s t r a t e and p o s s i b l y

cause s u r f a c e flowing.

Depth - The e f f e c t i v e s u b s t r a t e depth is t h a t s e l e c t e d i n

s e c t i o n IV.D.3.

3 .

-16-

4 .

5 .

H.

1.

2.

3 .

a.

b.

S u b s t r a t e Surface - The s u b s t r a t e bed s u r f a c e should be f l a t t o

f a c i l i t a t e water l e v e l c o n t r o l , v e g e t a t i o n p l a n t i n g and growth,

and prevent s t a g n a n t poo l s . Allowable t o l e r a n c e s should be

0.04 f e e t (0 .5 i n c h ) o r less a t any p o i n t on t h e s u r f a c e f o r

s m a l l systems (1 /4 a c r e o r l e s s ) , and 0.08 f ee t (1.0 i n c h ) f o r

l a r g e r systems ( g r e a t e r than 1 / 4 a c r e ) .

Su r face Mulch - For s m a l l systems, apply a 3-inch l a y e r of

mulch on top of s u b s t r a t e t o h e l p c o n t r o l p o t e n t i a l odor s ,

p reven t r e f l e c t i v e sun s c a l d i n g of v e g e t a t i o n and f o r v i s u a l

a e s t h e t i c s . Mulches may inc lude b a r k , p i n e s t r a w , t r e e c h i p s ,

composted l e a v e s , e t c . (Mulch i s g e n e r a l l y n o t used on l a r g e r

systems where water levels can be t empora r i ly r a i s e d above the

g r a v e l s u r f a c e f o r p l a n t i n g and s p e c i a l maintenance o p e r a t i o n s . )

P i p i n g

Complete necessa ry replumbing on house s a n i t a r y plumbing t o

connect a l l household wastewater t o t h e s e p t i c tank.

Use approved plumbing s t a n d a r d s ( e .g . , The Southern Plumbing

Code), t o determine house replumbing needs, t ype of p ipe , and

l o c a t i o n and spacing of c l eanou t s between t h e house and s e p t i c

tank.

I n f l u e n t D i s t r i b u t i o n

Use a header p ipe t o provide uniform wastewater d i s t r i b u t i o n .

D i s t r i b u t i o n can e i t h e r b e on or below t h e s u r f a c e of the

s u b s t r a t e . Use a b u r i e d o r covered d i s t r i b u t o r f o r smaller

systems where a c c e s s i b i l i t y t o t h e wastewater needs t o b e

c o n t r o l l e d , such as f o r an i n d i v i d u a l home where c h i l d r e n can

be p r e s e n t . Use a s u r f a c e d i s t r i b u t o r f o r l a r g e r f lows (above

abou t 2,000 gpd).

Buried D i s t r i b u t o r - This method is used f o r smaller g r a v i t y

flow systems t o l i m i t a c c e s s t o t h e wastewater. Use 2-inch

d i ame te r pipe f o r homes,with up t o t h r e e bedrooms w i t h t y p i c a l

water use. Use 3-inch d i ame te r p ipe f o r a fou r bedroom house.

P l ace i n l e t d i s t r i b u t o r s a t mid-depth i n 2 t o & i n c h s t o n e .

D r i l l ho l e s 5 / 8 i nch d i ame te r , spaced 6 i n c h e s a p a r t on t o p ,

bottom, and each s i d e of p ipe (4 rows).

-1 7-

I c.

c. Small Systems With Pump - Make the 2 t o 4 i nch s t o n e depth

about 3 i nches deeper; place the pipe ( s i z e d t o ma in ta in a f l o w

v e l o c i t y of 2 f t l s e c o r h i g h e r ) on top of t h e s t o n e (above

water l e v e l ) ; d r i l l o r i f i c e ho le s 1/8 inch d i a m e t e r , spaced 6

inches a p a r t , i n s e r i e s of 3 holes f a c i n g up and 1 h o l e f a c i n g

down ( t o a l low the pipe t o d r a i n between pump c y c l e s ) ; p l a c e

o r i f i c e s h i e l d s made of 3 inch PVC caps over each 1/8 inch

o r i f i c e f a c i n g up; and cover t h e d i s t r i b u t o r assembly w i t h a

m a t e r i a l such as a p i ece of f i l t e r f a b r i c , f i b e r g l a s s s c r e e n ,

o r l i n e r , and then followed by mulch.

d. Su r face D i s t r i b u t o r - This method is p r e f e r r e d f o r l a r g e r

s y s t e m s , b o t h g r a v i t y flow and pumping from t h e pre- t reatment

u n i t .

t e e s which can be swivel led t o d i s t r i b u t e t h e flow even ly from

each tee. Tees w i l l have l u b r i c a t e d s l i p f i t t i n g s . P r e f e r r e d

tee spac ing on the header i s 4-6 f o o t c e n t e r s f o r heade r s less

than 100 fee t long and 5-8 f o o t c e n t e r s f o r heade r s between 100

f e e t and 200 feet long.

plug o r cap which can be removed f o r f l u s h i n g accumulated

Use a 3 inch minimum ( s i z e d f o r f low) header p i p e having

A t t h e end of each header w i l l b e a

s o l i d s .

prevent movement during adjustment of tees.

The p ipe needs t o be f i r m l y anchored between tees t o

4 . E f f l u e n t C o l l e c t i o n

a. Use a header p ipe t o provide uniform wastewater c o l l e c t i o n .

b. Use 2 i n c h d i ame te r , o r l a r g e r , p ipe , s i z e d f o r flow. A 2-inch

diameter p i p e i s adequate f o r homes w i t h up t o f o u r bedrooms

wi th t y p i c a l water use. D r i l l ho l e s 518 i n c h i n c h d i ame te r ,

spaced 6 i nches a p a r t on top, bottom, and each s i d e of p ipe ( 4

rows ) . Place p i p e on the c e l l bottom i n t he 2 t o 4 i n c h s t o n e .

Cleanouts - I n s t a l l a capped c l eanou t on each end of t h e i n l e t

d i s t r i b u t o r and o u t l e t c o l l e c t o r . Locate c l e a n o u t s a t t h e

i n s i d e edge of each c e l l and extend above t h e t o p of t h e

mulch. Extend the i n l e t d i s t r i b u t o r c l e a n o u t s a t least 12

inches above the mulch t o a l low obse rva t ion lmon i to r ing of

i n c r e a s e i n head due t o p a r t i a l p i p e l g r a v e l c logg ing w i t h t i m e .

c.

5 .

-18-

I. Pumuin_g

1. I d e a l l y , a g r a v i t y flow system i s d e s i r e d . However, if

wastewater cannot g r a v i t y flow from house plumbing t o t h e

s e p t i c tank and CW, t h e s e p t i c tank e f f l u e n t must be pumped.

2. S e l e c t t h e r equ i r ed pump based on flow and t o t a l head, working

w i t h t h e pump manufacturer .

3. Always inc lude e i t h e r a s e p t i c tank f i l t e r (Orenco, Zabel, o r

e q u i v a l e n t ) o r a second s e p t i c tank t o minimize s o l i d s pumped

t o t h e CW ( s e c t i o n s 1 I . B and 1I .C) .

Restr ic t t h e pumping rate by a valve t o p reven t o r minimize

s u r f a c e flow i n t h e CW. S e t t h e dosing volume s o t h a t i t does

n o t exceed one-fourth the d a i l y des ign flow. Also, adjustments

( i n c r e a s e s ) may be needed i n t h e i n f l u e n t c r o s s - s e c t i o n a l area

based on in s t an taneous pumping rates.

4 .

5. Sur face su rg ing which may e v e n t u a l l y occur d u r i n g pumping may

b e m i t i g a t e d by reducing dosing volume, f low rates, and /o r

lowering c e l l water dep th t o p rov ide a d d i t i o n a l s u r g e c a p a c i t y .

6. A d d i t i o n a l information is needed t o be t te r i d e n t i f y minimum

a p p r o p r i a t e pumping rates, dosing volumes, and c e l l des ign .

Th i s w i l l b e developed through experience.

J. Water Level Control

1. Water level c o n t r o l and adjustment is c r i t i ca l t o e s t a b l i s h m e n t

and s u r v i v a l of t h e p l a n t s . Roots of emergent p l a n t s must b e

k e p t w e t and t h e p l a n t s w i l l n o t s u r v i v e i f t h e y are completely

covered w i t h water f o r extended p e r i o d s . Also, i f water i s

allowed t o s t a n d i n o r above t h e mulch, s u r f a c e odor may occur .

2. I n s t a l l a s u i t a b l e d i scha rge s t r u c t u r e i n c o r p o r a t i n g a n

a d j u s t a b l e water l e v e l c o n t r o l d e v i c e a t t h e e f f l u e n t end of

t h e ce l l ( s ) us ing e i t h e r t h e s w i v e l l i n g s t a n d p i p e o r

c o l l a p s i b l e tub ing o p t i o n s as shown i n F igu re 3.

a. For a home system, the s t r u c t u r e may c o n s i s t of an 18 i n c h PVC

p i p e s e c t i o n , embedded v e r t i c a l l y i n a 6 i n c h c o n c r e t e f l o o r

pad. For l a r g e r systems t o accommodate l a r g e r p i p i n g , t h e

s t r u c t u r e may c o n s i s t of a l a r g e r PVC p i p e s e c t i o n o r a

c o n c r e t e b lock box.

-19-

I

h) 0 1

2'-4'Stone - *

Perforated Collector Pipe

/

Plan View of Outlet Structure with Swivel Standpipe

?

Tight fining lid

Watertight box - pe section or concrete box

6" concrete pad Secure 90 deg. elbow of standpipe with collar so that it can be rotated but not Come Off. Control Device with Swiveling Standpipe

6" concrete pad ]

Control Device with Collapsible Standpipe

NOT TO SCALE

Figure 3. Water Level Control Structures

I

I 1 I I I 1 I f

I 1 1 I I

c-

I J

b . The discharge pipe from the effluent collection header will

enter the control structure.

c. Place a valve on the discharge pipe from the cell into the

water level control structure immediately in front of the water

level control device. The valve will allow flow to be stopped

if the standpipe ever needs servicing.

d. Connect the adjustable water level control device after the

valve. For smaller systems, the water level control device may

be a length of flexible/collapsible tubing such as super heavy

duty sewer hose used for travel trailers. For larger systems,

a swivelling standpipe is suggested. Refer to Figure 3 .

e. The standpipe/tubing should allow manipulation of the water

level from draining the beds to 2 inches over the surface of

the gravel substrate.

f. Provide a tight fitting lid for the water level control

structure to prevent escape of possible odors, keep out leaves

and other objects, discourage vandalism of the valve and

piping, and preclude possible safety considerations.

K. Miscellaneous

1. Rainfall Runoff - Slope or trench the area around the CW to divert surface water away from the system.

Safety - The entire CW area may be enclosed with a suitable fence. This is especially encouraged with larger systems where the substrate is flooded for planting and operational

measures. Fences will also discourage trespassing and prevent

possible sanitary problems. Also, water level control box lids

may be secured and locked.

2.

L. Effluent DisDosa 1 1. No discharge from CW cells - For sites with good to marginal

soil percolation, a small system (e.g., individual home)

utilizing an unlined second cell typically has no discharge due

to water loss by evaporation, transpiration, and percolation of

treated water from the unlined cell.

-21-

2. Discharge f r o m CW cells a. When all water cannot be eliminated in the CW cells or local

health department policy requires drainfields as a

precautionary measure, route excess water to a drainfield of

gravel-less leach bed tubing (or equivalent) installed

according to manufacturer instructions. The size of the

drainfield is typically much smaller than that required

following septic tanks because of the improved long-term

percolation rates of the higher quality CW effluent. One

successful sizing criterion is 50 feet of 8 inch gravel-less pipe per bedroom.

should be at least 12 inches above bedrock, impermeable clay,

or seasonally high groundwater level. If necessary, use a "mound" design incorporating permeable top soil f o r the

drainf ield.

Land application or drip irrigation - The highly treated

discharge could be land applied to an area planted with

landscaping plants or with wetlands or water tolerant grasses.

Consult with the local health department or regulatory agency

for applicable design criteria.

Nonpoint source discharge - A discharge for the highly treated

wastewater could be designed as a nonpoint source discharge to an appropriate approved area.

The bottom of the gravel-less pipe typically

b.

c.

d. Point source discharge - Larger systems requiring point source effluent disposal to a receiving stream must be approved by the appropriate state agency and designed to meet all limitations.

V. Vegetation

A. Svecies 1. Use plant species that grow naturally within the region.

2. Select species which have extensive vertical and lateral root

growth. Preferred species include, but are not limited to:

TYDhaceae (cattail family), cvpe racaea (sedge family), Graminear (grass family), and Junacaen (rush family). ScirDus

-22-

2 .

v a l i d u s ( so f t s t em b u l r u s h ) has been used s u c c e s s f u l l y a t

s e v e r a l municipal systems. Phraqmites a u s t r a l i s ( g i a n t r e e d )

i s a ve ry good s p e c i e s f o r wastewater t r e a t m e n t , b u t i s

considered a "noxious" p l a n t i n some a r e a s due t o i t s

a g g r e s s i v e growth.

Sun l igh t - F u l l s u n l i g h t f o r most of t h e day du r ing t h e growing

season i s needed f o r most s p e c i e s . For shady l o c a t i o n s , s e l e c t

shade t o l e r a n t s p e c i e s such as f e r n s .

3 . Ornamental s p e c i e s - Flowering and o t h e r t ypes of ornamental

s p e c i e s can a l s o be used f o r a e s t h e t i c a t t r a c t i v e n e s s ,

e s p e c i a l l y around t h e pe r ime te r of t h e c e l l ( s ) .

s p e c i e s i n c l u d e , b u t are n o t l i m i t e d t o : canna l i l y (Canna

f l acc ida , ) , e l ephan t ear (Co locas i a e s c u l e n t a , cal la l i l y

(Zantedeschia a e t h i o p h ) , v a r i o u s water i r i s ( I r i s

pseudacorug), arrowhead ( S a g i t t a r i a l g L i f o l i a ) , arrow arum

(Pe l t andra v i r n i n i u ) , pickerelweed (Pon tede r i a c o r d a t a ) , and

s w e e t f l a g (Acorus a.).

S e v e r a l

B .

1.

2.

3.

4 .

5 .

6.

_ _ P 1 an t i n g

I d e a l l y , p l a n t v e g e t a t i o n du r ing s p r i n g to e a r l y summer t o

o b t a i n as much growth as p o s s i b l e p r i o r t o w i n t e r . This

reduces w i n t e r m o r t a l i t y .

weeks p r i o r t o e a r l y f r o s t d a t e .

Adjust t h e water l e v e l i n a s i n g l e c e l l system o r t h e f i r s t

c e l l i n a two-cell system t o t h e t o p of t h e g r a v e l s u b s t r a t e .

Space p l a n t s on no less than a one f o o t c e n t e r s g r i d p a t t e r n

f o r small systems ( l e s s t han 1 / 4 a c r e ) and two f o o t c e n t e r s f o r

l a r g e r systems ( g r e a t e r t han 1 / 4 a c r e ) . This p l a n t i n g d e n s i t y

should provide a uniform v e g e t a t i o n cover i n one t o two growing

seasons.

Use p l a n t s w i th a 6 t o 1 2 inch s t a l k above t h e r o o t s ; prune i f

necessa ry .

P l a n t through t h e mulch s o t h a t r o o t p o r t i o n i s i n t h e water

and t h e s t a l k above water.

In the second c e l l of two-cell systems, u se s p r i n k l e r t o water

p l a n t s u n t i l they have a t least 1 f o o t of new growth.

Do n o t p l a n t v e g e t a t i o n a f t e r 2

-23-

E I

C . M i a l l a n e v m 1. A t t h e completion of cons t ruc t ion a c t i v i t i e s , d r e s s t h e s i t e .

Rake any r u t s and bare a r e a s made during c o n s t r u c t i o n t o

e q u i v a l e n t o r i g i n a l cond i t ion .

2. Minimize e r o s i o n on ea r then berms by sowing a s u i t a b l e cover

crop ( e . g . , Kentucky 31 Fesque) and cover wi th a straw mulch.

3 . If w e t c o n d i t i o n s occur a t t h e CW d i scha rge p o i n t , p l a n t reed

canary g r a s s o r o t h e r water t o l e r a n t s p e c i e s as a cover crop.

I V I . OPERATION AND MAINTENANCE

I 1 E

A . General

1. Constructed wetland t reatment systems f o r small w a s t e w a t e r

f lows r e q u i r e minimal ope ra t ion and maintenance. However, some

c a r e by the owner i s r equ i r ed t o maintain an e f f e c t i v e and

a t t r a c t i v e system. Casual obse rva t ions are needed t o preclude

problems o r minimize i d e n t i f i e d problems.

2. The l e n g t h and d e t a i l of t hese g u i d e l i n e s should n o t alarm t h e

use r . P o t e n t i a l problems are addressed t h a t are n o t expected

t o occur u n l e s s t he system i s abused.

B. S t a r t -up

1. Delayed Organic Loading - P r e f e r a b l y , p l a n t s should grow f o r

one growing season be fo re con t inuous ly sending w a s t e w a t e r t o

t h e system. This w i l l enhance good root development throughout

t h e s u b s t r a t e . Although most systems are t y p i c a l l y p l aced i n

service as soon as they are completed, p l a n and conduct an

extended s t a r t - u p per iod under reduced load ing c o n d i t i o n s , i f

p o s s i b l e . Add water o r wastewater t o t h e system t o m a i n t a i n

the water l e v e l and l i q u i d f e r t i l i z e r f o r good p l a n t growth.

2. Flow D i s t r i b u t i o n - For s u r f a c e d i s t r i b u t i o n , a d j u s t each

swivel tee on the d i s t r i b u t i o n p ipes t o o b t a i n equa l f low from

each tee. This i s accomplished by t r i a l and e r r o r . I n s e r t a

l e v e r ( s h o r t s e c t i o n of l i k e s i z e p i p e ) i n t o t h e tee and then

g e n t l y r o t a t e the t e e t o the proper e l e v a t i o n . S e t t h e

-24-

3 .

4 .

5 .

C.

1.

2.

3 .

a.

overf low e l e v a t i o n s from the t e e s S O t h a t t h e d i s t r i b u t o r pipes

w i l l b e about ha l f f u l l of wa te r .

Water Level - Maintain water level about 1 i n c h above t h e

g r a v e l s u b s t r a t e s u r f a c e u n t i l t h e p l a n t s have abou t 1 t o 2

f e e t of new growth (may n o t be p o s s i b l e i n an u n l i n e d c e l l ) .

Grass Mowing - Do n o t mow t h e newly p l a n t e d g r a s s u n t i l i t i s

a t least 4 inches high. Do n o t c u t i t any lower than 3 inches

unti l i t i s f u l l y e s t a b l i s h e d ( f o r a t least t h e f i r s t two

growing months a f te r p l a n t i n g ) .

i n t o t h e wetland c e l l s t o reduce t h e need f o r weeding t h e c e l l s .

S p r i n k l e r Use - For systems w i t h a second wet land c e l l , check

t h e water l e v e l i n t h e second c e l l a t least once a week. I f

t h e water level i s more than two inches below t h e t o p of t h e

g r a v e l (or deeper than t h e r o o t dep th of t h e p l a n t s ) , water the

c e l l w i t h t h e s p r i n k l e r a t least weekly d u r i n g d r y p e r i o d s of

t h e growing season f o r a t least 2 hour s , o r more f r e q u e n t l y i f

t h e p l a n t s ace n o t growing good.

Do n o t blow g r a s s c l i p p i n g

Seutic Tank

Do n o t a l low s e p t i c tank t o f i l l w i t h s o l i d s s o t h a t s o l i d s

c a r r y ove r i n t o t h e CW. S o l i d s can plug t h e d i s t r i b u t o r p ipes

and t h e g r a v e l i n t h e CW. I f t h i s does o c c u r , sewage can back

up i n t o t h e plumbing and s u r f a c e i n t h e CW. Also, odor and

a e s t h e t i c problems can r e su l t . These can become c o s t l y and

time-consuming problems t o m i t i g a t e .

Check t h e dep th of accumulated s o l i d s i n t h e s e p t i c t ank a f t e r

t h e f i r s t 5 yea r s of o p e r a t i o n , and eve ry two t o f o u r y e a r s

t h e r e a f t e r . When t h e sum of t h e dep ths of t h e bottom s ludge

and f l o a t i n g scum is one-third of t h e d i s t a n c e from t h e tank

bottom t o t h e o u t l e t p ipe , a p r o f e s s i o n a l s e p t i c t ank pumper

should c l e a n t h e t ank and d i s p o s e of t h e s e p t a g e as approved by

t h e l o c a l h e a l t h department.

Tanks w i t h f i l t e r s (Zabel , Orenco, o r e q u i v a l e n t )

Clean f i l t e r s whenever the tank is pumped. Th i s should be done

-25-

by t h e p r o f e s s i o n a l s ep f i l t e r by

sp ray ing wi th clean water according t o t h e m a n u f a c t u r e r ' s

i c t a n k pumper. Clea

i n s t r u c t i o n s . D i rec t t he wash w a t e r back t o t h e s e p t i c tank.

b. I f t h e house plumbing becomes clogged t o t h e e x t e n t t h a t none

of t h e plumbing f i x t u r e s a r e d r a i n i n g p r o p e r l y , t h e f i l t e r i s

one l i k e l y source of t he d ra inage problem. I t should be

in spec ted and cleaned as necessa ry . I f t h i s o c c u r s , i t

i n d i c a t e s an upset of t he s e p t i c tank caused by excessive flow

or d i s p o s a l of harmful chemicals t h a t should be p reven tab le .

D. Water Level

1. Normal Operation - Maintain water l e v e l i n t h e f i r s t c e l l about

one inch below the g rave l s u b s t r a t e s u r f a c e a t t h e i n l e t end.

Adjust water l e v e l using the p ipe / tub ing i n t h e water level

c o n t r o l s t r u c t u r e . For a swivel s t a n d p i p e , g r a d u a l l y r o t a t e i t

down t o lower the level and up t o raise t h e level. For the

f l e x i b l e tubing, lower o r raise t h e top of t h e tub ing w i t h t h e

notched cha in and hook on t h e w a l l . To conven ien t ly check t h e

water level r e l a t i v e t o the g r a v e l s u r f a c e , remove t h e caps of

t h e obse rva t ion s t andp ipes a t each end of t h e i n l e t

d i s t r i b u t o r , o r remove a s m a l l area of mulch and d i g a shal low

h o l e i n t h e g rave l ( f i l l h o l e a f t e r checking) . Water levels

w i l l temporar i ly i n c r e a s e wi th flow su rges .

r- -

2. Extended No Flow Periods (e.g., long v a c a t i o n s ) - Maintain

water level i n the bed. Without f low, water i n t h e c e l l w i l l

evapora t e i n hot weather and f r e e z e du r ing severe c o l d weather

cond i t ions . Both extremes w i l l damage r o o t s and t u b e r s over a

prolonged per iod. Plan t o have w a t e r added to t h e system as

needed.

3 . Pump Systems - Adjust t he pump f l o a t s , pump o u t l e t valve, and

t h e water l e v e l so t h a t t he pump c y c l e does n o t r e su l t i n

wastewater surging above the mulch l a y e r . P e r i o d i c adjustments

may be needed as the system matures t o keep t h e s u r g e s below

t h e mulch or grave l .

-26-

I

c.

1

4 . Leaking J o i n t s - Check a d j u s t a b l e s t andp ipe or hose i n the

water l e v e l c o n t r o l s t r u c t u r e f o r leaks f r o m j o i n t s . R e p a i r t o

s t o p any leaks .

f r o n t of a d j u s t a b l e s t andp ipe o r hose.

r e p a i r i s completed.

F i r s t , s h u t o f f f low us ing v a l v e l o c a t e d i n

Open va lve as soon as

5. Surface Ponding

a . I f s u r f a c e ponding i n a wet land c e l l can n o t be c o n t r o l l e d by

water l e v e l adjustment , i t may be caused by e i t h e r excess ive

flows above t h e design b a s i s o r c logg ing of the s u b s t r a t e by

excess ive s o l i d s from t h e s e p t i c tank o r by microbe growth due

t o excess ive o rgan ic loads .

b . Determine i f s o l i d s are c o l l e c t i n g i n i n l e t d i s t r i b u t o r by

c l e a n i n g wi th a homemade c l e a n i n g g i g c o n s t r u c t e d w i t h a wire

and sponge. Snake t h e w i r e from one end of t h e d i s t r i b u t o r

p ipe through t h e o t h e r end. Wrap one end of t he w i r e around a

sponge o r o t h e r material t h a t i s l a r g e enough t o be compressed

when p u l l e d through t h e p ipe . Clean t h e p ipe by p u l l i n g sponge

through t h e pipe several t i m e s . A l a r g e amount of s o l i d s i n

t h e pipe i n d i c a t e s plugging of t h e wet land by excess ive s o l i d s

d i scha rg ing from t h e s e p t i c tank.

Draining and d ry ing t h e c e l l for a week o r more may t empora r i ly

h e l p t h e problem, b u t c o r r e c t i o n w i l l probably r e q u i r e

replacement of t h e g r a v e l from t h e i n l e t t o t h e p o i n t where

flow. r e e n t e r s t h e g r a v e l .

c.

d. I d e n t i f y and implement a c t i o n s t o p reven t t h e problem from

r e c u r r i n g , such as pumping t h e s e p t i c tank more f r e q u e n t l y ,

i n s t a l l i n g a s e p t i c tank f i l t e r o r a n o t h e r s e p t i c tank i n

series, and e l i m i n a t i n g t h e u s e of any t o x i c chemicals t h a t

have the p o t e n t i a l t o "upset" t h e s e p t i c tank.

e. I f c l e a n i n g of t he i n l e t d i s t r i b u t o r reveals l i t t l e o r no

s o l i d s bu'ildup i n t h e p i p e , ponding is probably caused by

excess ive water flow which exceeds t h e h y d r a u l i c c a p a c i t y of

t h e s u b s t r a t e . C o r r e c t i v e a c t i o n s i n c l u d e use of water

conserving f i x t u r e s o r i n s t a l l a t i o n of a n o t h e r p a r a l l e l

wetlands c e l l .

-27-

I I I

f . Water levels may temporar i ly i n c r e a s e w i t h f l o w s u r g e s . D o n o t

make major c o r r e c t i o n s un le s s t h e water l e v e l remains above the

g r a v e l o r mulch s u r f a c e f o r an extended per iod .

E . I n l e t D i s t r i b u t o r

1. Buried D i s t r i b u t o r - P e r i o d i c a l l y check t h e water l e v e l i n t h e

c l eanou t s on each end of t h e i n l e t d i s t r i b u t o r . If t h e water

l e v e l i n the c l eanou t s i s obvious ly h ighe r than t h e top of t h e

g r a v e l , ho le s i n the d i s t r i b u t o r p ipe o r t h e l a r g e s t o n e around

t h e p ipe are clogging.

c l ean ing g i g descr ibed above.

t h e problem, the l a r g e s t o n e can be cleaned by c a r e f u l l y

pouring ox id iz ing chemical such as b leach o r hydrogen peroxide

i n t o t h e d i s t r i b u t o r p ipe c l eanou t s .

p l a n t s t h a t may be k i l l e d i n t h e i n l e t area.

Small Systems With Pump - Clean t h e d i s t r i b u t o r p ipe once per

season ( sp r ing , summer, f a l l , and w i n t e r ) by removing t h e end

caps and running t h e homemade g i g desc r ibed above through t h e

p ipe several times.

Clean t h e p ipe us ing a homemade

I f p ipe c l ean ing d o e s n ' t c o r r e c t

Replace any wet land

2 .

3 . Sur face D i s t r i b u t o r - Check and main ta in t h e d i s t r i b u t o r tees

SO t h a t t h e flows are about equal . A tee may become p a r t i a l l y

blocked by s o l i d s , a l g a e , or o t h e r a r t ic les . F lush s o l i d s o u t

of t h e d i s t r i b u t o r p ipe by t empora r i ly removing an end cap/p lug

o r t u r n i n g a n end tee down one a t a time.

should f l u s h most s o l i d s . Use a garden hose t o remove

remaining s o l i d s . Remove any ar t ic les such as pape r , s t i c k s ,

o r r a g s t h a t may b lock a tee. P e r i o d i c a l l y b r u s h each tee t o

remove accumulated a l g a l growth.

The f low of water

F. L ine r

1. Maintain cover over t h e s i d e s of s y n t h e t i c l i n e r s (e .g . , EPDM,

po lye thylene , P V C , hypalon, neoprene, b u t y l rubbe r , e t c . ) which

ex tend above the s u b s t r a t e and water l e v e l t o p reven t W

degrada t ion .

-28-

I

c- t

2. P e r i o d i c a l l y check f o r l i n e r l eaks . Dyes should be used t o

v e r i f y suspec ted l e a k s . Drain c e l l , remove g rave l i n the

suspec ted l e a k area, l o c a t e l e a k , and patch the l i n e r fol lowing

manufac tu re r ’ s i n s t r u c t i o n s . Leaks around t h e i n l e t and o u t l e t

p ipes may be caused by caulk ing p u l l i n g away from t h e l i n e r .

If s o , r ecau lk a s necessa ry . Draining and r e p a i r i n g l eaks

should be accomplished wi th in one day t o reduce r i s k of k i l l i n g

the wet lands v e g e t a t i o n .

G. Berms/Retainine. Wa 11s

1. Repair any e a r t h e n berm e r o s i o n as soon a s i t i s noted .

2 . Repair l e a k s around be rms / re t a in ing w a l l s as soon as noted by

plugging, s e a l i n g , e t c .

3 . Mow e a r t h e n berms o r around r e t a i n i n g d ikes t o main ta in an

a t t r a c t i v e s i t e .

li. Pumps

I f a pump i s p a r t of t h e system, main ta in t h e pump and any

alarm system accord ing t o manufac tu re r ’ s s p e c i f i c a t i o n s .

I. Veveta t ion

1. Check t h e v e g e t a t i o n f o r s i g n s of d i s e a s e o r o t h e r stress

(yel lowing o r browning, w i t h e r i n g , s p o t s , e t c . ) . Some of t hese

symptoms may occur n a t u r a l l y as t h e p l a n t s mature , e s p e c i a l l y

a f t e r s eeds have matured. I f t h e water level is s a t i s f a c t o r y ,

o b t a i n guidance from a l o c a l a g r i c u l t u r a l e x t e n s i o n a g e n t , or

knowledgable garden c e n t e r .

2. Manually p i ck l a r g e i n s e c t s (e .g . , c a t e r p i l l a r s , s l u g s ) caus ing

damage t o t h e wet land v e g e t a t i o n . For s e r i o u s i n s e c t

i n f e s t a t i o n which i s des t roy ing t h e v e g e t a t i o n , a chemical

agent may be a p p l i e d a f te r o b t a i n i n g guidance from a

knowledgable person (e.g. a g r i c u l t u r a l ex tens ion a g e n t , o r good

garden c e n t e r ) f o r proper chemical and a p p l i c a t i o n ra te .

3 . If v e g e t a t i o n does n o t appear h e a l t h y and w a t e r levels a r e

c o r r e c t l y main ta ined , add a balanced l i q u i d f e r t i l i z e r

-29-

I

1 I I 1 I I I I I I 8 6 I a I

II I a

c.

m

4 .

5.

6 .

7 .

a . a.

b.

9 .

p e r i o d i c a l l y ( t h r e e times a growing season) t o t h e wastewater

by f l u s h i n g down a t o i l e t . "Normal" domestic sewage may no t

c o n t a i n a l l t he t r a c e n u t r i e n t s and elements r e q u i r e d by the

v e g e t a t i o n i n a gravel s u b s t r a t e .

Replace dead p l a n t s as necessa ry t o f i l l v o i d s .

p u l l up "volunteer" weeds, t r e e s and shrubs from the wet lands.

These s p e c i e s w i l l shade a n d crowd the d e s i r a b l e wetland p l a n t s .

Prevent excess ive shadiIig of wetland v e g e t a t i o n by c o n t r o l l i n g

growth of t r e e s o r h i g h shrubs n e a r t h e wetland ce l l s . Most

wetland p l a n t s need a t least s i x hours of sunsh ine each day.

Remove mature wetland v e g e t a t i o n a f t e r t he p l a n t s have browned

i n the f a l l if des i r ed f o r v i s u a l a e s t h e t i c s . However, only

c u t approximately two-thirds of t he he igh t of t h e p l a n t s . The

removed m a t e r i a l may be l a i d on t h e bed s u r f a c e as a mulch.

Deep r o o t growth

Encourage deep r o o t growth by lowering t h e water level over

s e v e r a l weeks during the dormant v e g e t a t i o n pe r iod . Do n o t

drop t h e water l e v e l too low, too q u i c k l y and leave t h e r o o t s

w i thou t w a t e r .

Suggested procedure - A f t e r f r o s t has k i l l e d t h e t o p of t he

p l a n t s , drop the water l e v e l below t h e g r a v e l s u r f a c e t o

one-third the g rave l depth (e .g . , 4 i nches for a 12 i n c h depth)

f o r a week; r a i s e the level back t o 1 i n c h below t h e s u r f a c e

f o r a week; drop the l e v e l two-thirds t h e d e p t h ( e . g . , 8 inches

for a 1 2 inch dep th ) f o r a week; a g a i n raise t h e level t o 1

inch below t h e s u r f a c e f o r a week; drop t h e level t o 1 inch

above t h e c e l l bottom (11 inches f o r a 1 2 i n c h d e p t h ) f o r a

week; r a i s e the l e v e l t o 1 inch. Repeat t h i s c y c l e once more.

Divide and r e p l a n t d e c o r a t i v e f lower ing s p e c i e s ( e .g . , i r i s ) t o

enhance the system a t t r a c t i v e n e s s .

3 . Qdo r Control

1. Standing water on the s u b s t r a t e s u r f a c e i s t h e probable cause

of o b j e c t i o n a b l e odor . Level any low and h igh s p o t s on the

s u b s t r a t e s u r f a c e which c r e a t e small s t a n d i n g pools by raking

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I

and /o r f i l l i n g w i t h a d d i t i o n a l s u b s t r a t e . I f a too high water

l e v e l i s causing s t a n d i n g water on most o f t he s u b s t r a t e

s u r f a c e . lower the l e v e l u s ing the water l e v e l c o n t r o l device

so t h a t i t i s about one inch below the s u b s t r a t e s u r f a c e .

2 . Odors w i l l a l s o occur from water s t a n d i n g o r f lowing w i t h i n the

water l e v e l c o n t r o l s t r u c t u r e a n d open o b s e r v a t i o n s t a n d p i p e s .

Odors from these s t r u c t u r e s should be n o t i c e a b l e on ly when the

caps o r covers a r e removed o r l oose . Secure t h e caps and l i d s

i n p l ace t o prevent t h e s e odors from escap ing .

K . Brain F i e l d

1. Mow t o keep the a r e a a t t r a c t i v e .

2. F i l l i n any low areas where s u r f a c e water ponding occur s .

3 . I f wastewater s u r f a c e s above t h e d r a i n f i e l d f o r extended

p e r i o d s , check risers t o e n s u r e t h a t a l l e x t e n s i o n s are

r e c e i v i n g water . If any s e c t i o n is n o t r e c e i v i n g water, a pipe

may be s e p a r a t e d o r crushed. Repair as n e c e s s a r y .

4. I n s t a l l a t i o n of water conse rv ing plumbing f i x t u r e s o r

a d d i t i o n a l d r a i n f i e l d area may be n e c e s s a r y .

L. Heal th and S a f e 2

1. Prevent c h i l d r e n from p l a y i n g i n t h e system t o avo id c o n t a c t

w i th p o t e n t i a l l y i n f e c t i o u s microorganisms.

2. The t i g h t f i t t i n g l i d on t h e w a t e r level c o n t r o l s t r u c t u r e may

be secu red w i t h a l a t c h and lock i f a p o t e n t i a l s a f e t y problem

i s a s t r o n g c o n s i d e r a t i o n .

M. Miscellaneous

1. Leaky Plumbing F i x t u r e s - Repair f a u l t y plumbing f i x t u r e s as

soon as they are n o t i c e d . Leaky o r s t u c k commode f l a p s can

p a r t i c u l a r l y reduce t r ea tmen t e f f e c t i v e n e s s of a small CW due

t o the l a r g e q u a n t i t y of water t h a t can b e l o s t i n a s h o r t time

pe r iod .

2. Household Chemicals - Do n o t empty s t r o n g chemicals ( e . g . , some

d r a i n c l e a n e r s , f l o o r c l e a n e r s , b l e a c h ) i n t o t h e s a n i t a r y

-31-

I

I I I 1 I I I I I I I 1 I I 1 I I 1 I

c* -

V I I .

- 3 2 -

3 .

4 .

5 .

6 .

7 .

8.

system. Chemicals can upse t t h e s e p t i c tank causing excess ive

s o l i d s t o w a s h ou t o f t he s e p t i c tank and p o s s i b l y plug the

s u b s t r a t e . A l s o , chemicals can damage and k i l l t h e v e g e t a t i o n .

Pipe Clogging - Prevent o r minimize p ipe c logging by

r e s t r i c t i n g f l u s h i n g of g r e a s e , food p a r t i c l e s , and tampons and

o t h e r personal hygiene p roduc t s . Use c l e a n o u t s i n s t a l l e d

b e f o r e the s e p t i c tank and t h e wet land c e l l s t o unclog p ipes .

H e r b i c i d e s f p e s t i c i d e s - Do n o t apply h e r b i c i d e s and p e s t i c i d e s

which can damage v e g e t a t i o n e i t h e r on o r n e a r t h e system.

Mulch - Maintain a three- inch mulch l a y e r on t o p of t h e

s u b s t r a t e , e i t h e r with l i t t e r from t h e wet land v e g e t a t i o n , pine

straw o r ba rk , o r o t h e r s u i t a b l e material .

Su r face Drainage - Reroute any s u r f a c e dra ihange e n t e r i n g t h e

CW around o r away from t h e cell(s).

Animals - Prevent animals from digging i n CW, d e s t r o y i n g

v e g e t a t i o n and making h o l e s i n the s u b s t r a t e and mulch.

Unusual Problems - Contact your l o c a l county h e a l t h department

f o r guidance i f any unusual problem i s no ted .

ADDITIONAL INFORMAT I O N

Questions about t h e g u i d e l i n e s may b e d i r e c t e d t o t h e a u t h o r s ,

Tennessee Val ley Au thor i ty , Water Management, Haney Bui ld ing 2C,

1101 Market S t i e e t , Chattanooga, Tennessee 37402-2801, o r

te lephone 615 /751-3164 .

I

, . 'ir

f d a,

APPENDIX

Design Examples for Four Optional Residential Constructed Wetlands Systems

Table of Design Dimensions for Selected Systems

Table of Relative Elevation Differences Between System Components f o r Constructed Wetlands

Wastewater Treatment Systems

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1 B I I I 0 I I I l I i I I I I I I

Design Examples

Res iden t i a l ISmal l Constructed Wetlands Systems With S e p t i c Tank (ST) Primary Treatment

Note: C a l c u l a t i o n s are n o t rounded. Dimensions are rounded ( u s u a l l y t o the n e a r e s t whole number) a f te r a l l c a l c u l a t i o n s are completed.

Assume 3 bedroom house occupied by 4 people.

Hydraulic Load, Q = 120 gpd p e r bedroom * 3 rooms = 360 gpd (48.132 f t 3 / d )

Organic Load = 0.17 l b l d l p e r s o n * 4 people * 50% ST ca r ryove r = 0.34 l b l d

Hydraulic Loading Criteria = 1 .3 f t2 /gpd

Organic Loading Criteria = 1.0 f t2 /0 .05 l b BODId

Determine CW c e l l s u r f a c e area, As:

As = 360 gpd * 1 .3 f t2 /gpd = 468 f t 2

Option 1:

S i t e cond i t ion - Yard is r e l a t i v e l y f l a t and area is n o t cons t r a ined . The i n - s i t u - s o i l p e r c o l a t i o n rate i s between 90 and 120 m i d i n .

Use f l a t bed. Assume h y d r a u l i c g r a d i e n t , S = 0.5%, or 0.005, and h y d r a u l i c c o n d u c t i v i t y , Ks = 850 f t / d ( conse rva t ive rate based on long-term clogging of t h e g r a v e l ) .

Determine ce l l c ros s - sec t ion area, &, based on h y d r a u l i c l o a d , Q, and Darcy's Law:

A, = Q/(Ks * S ) , where Ks = s u b s t r a t e h y d r a u l i c c o n d u c t i v i t y ( long term) S = h y d r a u l i c g r a d i e n t (assume e q u i v a l e n t t o bed s l o p e )

A, = 48.132/(850 * .005) = 11.325 f t 2

Determine c e l l c ros s - sec t ion area, A,, based on o r g a n i c load:

A, = 1.0 f t2 /0 .05 l b BOD/d * 0.34 l b BOD/d = 6.8 f t 2

A, i s l a r g e r by h y d r a u l i c loading; t h e r e f o r e , use 11.325 f t 2 .

Use 1.0 f t f o r c e l l depth, D ( f r o n t of c e l l )

Determine c e l l width: W = A,/D

= 11.32511.0 = 11.325 f t

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i

4

1 I 1 ! i 1 I c 1

System c e l l l e n g t h . L = A,/W = 468/11.325 = 41.325 f t

Rounding t o t h e n e a r e s t whole number r e s u l t s i n c e l l dimensions of 11 f t wide and 41 f t long. fas te r , t h e wet lands system may be d iv ided i n t o two e q u a l l y s i z e d c e l l s (each c e l l 11 f t wide arid 20.5 f t long w i t h t h e second c e l l u n l i n e d ) i f t he l o c a l h e a l t h department does n o t r e q u i r e a subsequent d r a i n f i e l d . If a d r a i n f i e l d i s r e q u i r e d , one l i n e d c e l l (11 f t w i d e and 41 f t l o n g ) w i l l be more c o s t e f f e c t i v e .

S ince t h e s o i l p e r c o l a t i o n rate i s 120 min/ in o r

S u b s t r a t e depth: one c e l l system:

c e l l i n l e t : 1.0 f t c e l l o u t l e t : 1.0 f t + (0.005 * 41.325) = 1.2066 f t = 14.479 i n

two c e l l system: c e l l i n l e t : 1.0 f t c e l l o u t l e t : 1.0 f t + (0.005 * 68.824/2) = 1.1033 f t = 13.240 i n

-. - . Use a f l a t c e l l bottom ( t o s i m p l i f y c o n s t r u c t i o n ) and a c e l l dep th of 14 i n f o r a one c e l l system and 1 3 i n f o r a two c e l l system.

Refer t o F igu re A 1 f o r t h e two c e l l system and F igure A2 f o r t h e s i n g l e c e l l system o p t i o n s .

ODtion 2:

S i t e c o n d i t i o n - Yard is r e l a t i v e l y f l a t ; however, t h e homeowner d e s i r e s a more narrow system which f i t s i n t o t h e landscaping a l o n g one s i d e of t h e yard as much as p o s s i b l e . between 90 and 120 min / in .

The i n - s i t u s o i l p e r c o l a t i o n rate is

Assume bed s l o p e , S = 1.0%, o r 0.01.

A, = Q/(Ks * S) = 48.132/(850 * -01) = 5.6626 f t 2

Since o rgan ic load wid th (same as Option 1) i s l a r g e r , u s e 6.8 f t 2 .

The e q u i v a l e n t bed s l o p e is: S = 48.132/(850 * 6 .8 ) = 0.0083273 o r 0.833%

Use 1.0 f t f o r c e l l d e p t h , D ( f r o n t of c e l l )

Determine c e l l width: W = A,/D

= 6.8/1.0 = 6.8 f t

System c e l l l e n g t h , L = As/W = 468/6.8 = 68.824 f t

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I-

C.

Rounding t o the n e a r e s t whole number resul ts i n c e l l dimensions of 7 f t wide and 69 f t long. Since the s o i l p e r c o l a t i o n ra te i s 120 min i in o r f a s t e r , t he wetlands system may be d iv ided i n t o two e q u a l l y s i z e d c e l l s (each c e l l 7 f t wide and 34:5 f t long w i t h t h e second c e l l u n l i n e d ) i f t he l o c a l h e a l t h department does n o t r e q u i r e a subsequent d r a i n f i e l d . I f a d r a i n f i e l d i s r equ i r ed , one l i n e d c e l l ( 7 f t wide arid 69 f t long) w i l l be more c o s t e f f e c t i v e .

S u b s t r a t e depth: one c e l l system:

c e l l i n l e t : 1.0 f t c e l l o u t l e t : 1.0 f t + (0.0083273 * 68.824) = 1.5731 f t = 18.877 i n

t w o c e l l system: c e l l i n l e t : 1.0 f t c e l l o u t l e t : 1.0 f t + (0.0083273 * 68.824/2) = 1.2866 f t = 15.439 i n

Use a f l a t c e l l bottom ( t o s i m p l i f y c o n s t r u c t i o n ) and a c e l l depth of 19 i n f o r a one c e l l system and 15 i n f o r a two c e l l system.

For Options 1 and 2 , i f p r a c t i c a l , c o n s t r u c t t h e second c e l l a t a lower e l e v a t i o n than t h e f i r s t c e l l t o a l low independent water level c o n t r o l i n each c e l l . I d e a l l y , t he top of t he second c e l l should b e a t o r below the bottom of t h e f i r s t c e l l . I f t h i s i s n o t p r a c t i c a l , lowering t h e water level i n t h e f i r s t c e l l may be r e s t r i c t e d by t h e water level i n the second c e l l .

Option 3 :

S i t e c o n d i t i o n - S i t e has shal low s o i l , ave rag ing only 3 i n c h e s deep, above a s i l t y sandstone bedrock w i t h low pe rmeab i l i t y .

S ince t h e r e w i l l be no p e r c o l a t i o n , t h e o p t i o n of two ce l l s is e l i m i n a t e d . Use a f l a t bed and one c e l l .

Use Option 1 dimensions f o r one ce l l (11 f t wide and 41 f t l ong) .

Refer t o F igu re A 2 .

Qption 4:

S i t e c o n d i t i o n - Avai l ab le s i t e has 25% s l o p e ; t h e r e f o r e , a r e l a t i v e l y wide bed would r e q u i r e c o s t l y c u t and f i l l f o r berms. A l s o , f r a c t u r e d rock w i l l r e q u i r e a system l i n e r .

Use a m u l t i c e l l system w i t h p a r a l l e l beds which are f l a t . Te r race the paral le l c e l l s on t h e s lope . Use a flow s p l i t t e r t o d i v i d e t h e flow e q u a l l y between two p a r a l l e l beds.

S ince t h e des ign o b j e c t i v e i s t o minimize c e l l width, f o l l o w the procedure used i n op t ion 2. Organic loading r e q u i r e s an i n l e t a r e a of a t l ea s t 6.8 f t 2 , which corresponds t o a bed s l o p e of 0.833%. Divide t h e

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I

s i n g l e c e l l ob ta ined i n op t ion 2 i n t o two p a r a l l e l c e l l s t h a t are 3 f t wide, 69 f t long , and 1 9 i n deep. Dimensions could be reduced f u r t h e r u s ing a des ign dep th of 18 i n and a h y d r a u l i c loading c r i t e r i o n of 0.87 f t 2 / g p d . f t long , and 25 i n deep.

For a one c e l l system t h e dimensions would be 5 f t wide, 69

(W = 6.811.5 = 4.5333 f t ) ( L = 313.2/4.5333 = 69.089 f t ) ( D = 1.5 + [0-00833 * 69.0891 = 2.0755 f t = 24.906 i n )

I f needed, two p a r a l l e l c e l l s could be used t h a t w e r e each 2.5 f t wide, 69 f t long , and 25 i n deep.

C e l l w a l l s need t o be designed t o a s s u r e long-term s t a b i l i t y on t h e s t e e p s lope .

Design a mounded d r a i n f i e l d below t h e wet land ce l l .

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- 39 -

DIMENSIONS GUIDELINE - RESIDENThL SYSTEMS BASED ON HYDRAULIC AM> ORGANIC: LOADINGS~

One Cel 1 sys tem Two Se ries Ce 115

Hydraulic Loading Hydraulic2 Cell Area Substrate Depth3 Width Length Substrate Depth3 Width Length aDd Slope. z ft2 Inlet/Outlet.in ft f t Inlet/Outlet,in f t f t

TWO BEDROOM HOUSE - 3 PEOPLE: 240 0.50 240 0.50 240 0.726 240 0.726 300 0.50 300 0.50 300 0.907 300 0.907

312 20 9 312 20 9 3 90 26 1 390 26 1

THREE BEDROOM HOUSE - 4 PEOPLE: 360 0.50 468 360 0.50 313

0 360 0.833 468 313 I 360 0.833

450 0.50 585 450 0.50 392 450 1.04 585 450 1.04 392

I

0

FOUR BEDROOM HOUSE - 5 PEOPLE: 480 0.50 6 24 480 0.50 418 480 0.888 6 24 480 0.888 418 600 0.50 780 600 0.50 522 600 1.11 780 600 1.11 5 22

12/14 18/20 12/17 18/23 12/14 18/20 12/20 18/26

12/14 18/20 12/19 18/25 12/14 18/20 12/23 18/30

12/14 18/20 12/20 18/26 12/14 18/20 12/24 18/30

41 41 60 60 41 41 75 75

11 41 8 41 7 69 5 69 14 41 9 41 7 86 5 86

154 41 10 41 9 73 6 73 194 41 13 41 9 92 6 92

12/13 18/19 12/15 18/21 12/13 18/19 12/16 18/22

12/13 18/19 12/15 18/21 12/13 18/19 12/17 18/24

12/13 18/19 12/16 18/22 12/13 18/19 12/18 18/24

20.5 20.5 30 30 20.5 20.5 37.5 37.5

11 20.5 8 20.5 7 34.5 5 34.5 14 20.5 9 20.5 7 43 5 43

154 20.5 10 20.5 9 36.5 6 36.5 1g4 20.5 13 20.5 9 46 6 46

I/ Dimensions are rounded t o the nearest whole number based on unrounded calculations. Slightly different dimensions may be obtained for other methods of rounding.

- 2/ Hydraulic Slopes - Larger values for each hydraulic loading scenario provide the minimum cross-section area, which is equal to the cross-section area controlled by the organic load.

;1/ Inlet/Outlet Substrate Depth - Cell bed(s) can be sloped from inlet to outlet, or the bed(s) can be made flat and use the deeper outlet depth.

- 4/ Not recommended for a buried distributor without splitting flow equally t o a segmented distributor.

DIMENSIONS GUIDELINE - 2,000 TO lO!,OOO GPD SYSTEMS BASED ON HYDRAULIC LOADING^

I e I c

Hydraul ic Loading nDd

2,000 2,000 2,000 2,000

5,000

5,000 5,000

5,000

10,000 10,000 10,000 10,000

Hydraul ic Cel l Area Slope . % f t 2

0.50 2,600 0.50 1,740, 1 .o 2,600 1 .o 1,740

0.50 6,500 0.50 4,350 1 .o 6,500 1 .0 4,350

0.50 13,000 0.50 8,700 1 .o 13,000 1 .o 8,700

One Cel l Svs tem Two S e r i e s Cells

S u b s t r a t e Depth2 Width Length S u b s t r a t e Depth2 Width Length I n l e t /Out l e t , iq f t f t I n l e t /Out l e t . i n f t f t

12/14 18/20 12/22 18/28

12/14 18/20 12/22 18/28

12/14 18/21 12/22 18/28

63 41 42 41 31 83 21 83

15 7 41 105 41

79 83 52 83

3153 41

15 7 83 105 83

2103 41

12/13 18/19 12/17 18/23

12/13 18/19 12/17 18/23

12/13 18/19 12/17 18/23

63 42 31 2 1

157 105

79 52

3153

15 7 106

2103

20.5 20.5 41.5 41.5

20.5 20.5 41.5 41.5

20.5 20.5 41.5 41.5

I/ DIMENSIONS BASED ON ORGANIC LOAD MUST ALSO BE CHECKED AND USED I F CONTROLLING. Dimensions a r e rounded t o the n e a r e s t whole number based on unrounded c a l c u l a t i o n s . methods of rounding. A l l i n l e t d i s t r i b u t o r s should be above ground.

S l i g h t l y d i f f e r e n t dimensions may be obta ined f o r o ther

- 2 / I n l e t I O u t l e t S u b s t r a t e Depth - Cell b e d ( s ) can be s loped from i n l e t t o o u t l e t , o r t he b e d ( s ) can be made f l a t and use t h e deeper o u t l e t depth .

a / Not recommended wi thout s p l i t t i n g e q u a l l y between two p a r a l l e l c e l l s ,

WRC 0803H

\ Re la t i ve E leva t i on D i f fe rences Between System Components f o r Constructed Wptlands (CW) Wastewater Treatment Systems.

ComDonenb Re la t i ve E leva t ion D i f fe rence

Pre fer red Acceotable Comments

House d ra ins t o s e p t i c tank ( S T ) > 1% slope 1% slope A l l p ipes and the sep t i c tank need a t l e a s t 6" o f t o p s o i l cover; per fe rab ly 12". i n l e t Mounding may be used i f necessary.

ST o u t l e t t o top o f CW g rave l . 12" o r l a r g e r 6" ( w i t h 6" d i f f e rence increases p o t e n t i a l f o r f l ood ing ST i f c logg ing o f CW i n l e t a r e a occurs f i l t e r o r This p o t e n t i a l is considered t o be low. 2 ST'S)

Top o f CW g rave l t o n a t u r a l ground surface on h igh s ide o f s lope

I 6 h, I

Bottom o f g rave l ( 1 s t CW c e l l ) and top o f g rave l (2nd CW c e l l ) between twa CW c e l l s i n se r ies ( i f app l i cab le )

Bottom o f CW c e l l t o bottom o f 8" grave l l ess d r a i n

0" up t o 6" Having the top o f the g rave l l e v e l w i t h the u p h i l l slope assures that the c e l l is higher/ lower ne i the r too h igh nor low for the t e r r a i n . Runoff is e a s i l y d iver ted . Cut and f i l l

i s genera l l y balanced on moderate slopes wh i le excess f i l l r e s u l t s on small slopes (which i s genera l l y no t a problem). The acceptable range ( 6 " higher or lower) provides f l e x i b i l i t y to ad jus t c u t and f i l l f o r a c t u a l s i t e cond i t ions so long as the preceding c r i t e r i o n concerning the e leva t i on d i f f e rence between the ST o u t l e t and top o f grave l is met. The c e l l should be o r ien ted so tha t the c e l l leng th p a r a l l e l s the s i t e ' s n a t u r a l contour. ,

0" or l a r g e r l e s s than 0" (up t o same e leva t i on f o r than i t s p e r c o l a t i o n ra te . top o f g rave l f o r bo th c e l l s )

P a r t i a l f l ood ing o f the water l e v e l c o n t r o l s t r u c t u r e f o r the f i r s t c e l l may occur under the "acceptable" c r i t e r i o n when water en ters the second c e l l a t a r a t e greater

12" or grea te r 3" Any d i f f e rence l e s s than 8" w i l l r e s u l t i n p a r t i a l f l ood ing o f the CW w a t e r l e v e l c o n t r o l s t r u c t u r e i f the d r a i n p ipe f i l l s w i t h w a t e r . Although t h i s cond i t ion should be avoided i f p rac t i cab le , i t ' s pr imary e f f e c t would be to l i m i t w a t e r l e v e l adjustments i n the CW c e l l . The minimum acceptable d i f f e rence o f 3" w i l l a l l o w water t o i n f i l t r a t e i n t o the s o i l and no t f l o o d the water l e v e l c o n t r o l s t ruc tu re u n t i l the f l ow r a t e exceeds the pe rco la t i on capac i ty o f the system a t a head o f about 1" above the d r a i n holes i n the g rave l l ess d r a i n p ipe .

The suggested r e l a t i v e e l e v a t i o n d i f f e rences assume tha t the var ious components are loca ted c lose t o one another. consldered (added t o the suggested values) i f components are separated by l a rge distances. l e a s t 1%.

F r i c t i o n losses may need to be The grade f o r a l l p i p i n g between components should be at

WRC 1032H