Recommended Design Criteria for
Wastewater Stabilization and Pollution Control Ponds...
Supplement to Engineer's Report, Plans and Specifications...
The engineer's report shall contain pertinent information on the location, geology, soil conditions, area for expansion and other factors that will affect the feasibility and acceptability of the proposed treatment facilities. The following information must be submitted in addition to that required by Chapter 10, Recommended Standards for Sewage Works, 1978 or the latest edition :

1. The location and direction of all residences, commercial or business development, and water supplies within one-half mile and information regarding location, construction features and static water levels in all wells within one-fourth mile of the proposed ponds.

2. Soil borings to determine surface and subsurface soil characteristics of the immediate area and their effect on the construction and operation of a pond located on the site. The depth of soil borings shall be at least six feet below the proposed pond bottom elevation, except one shall be a minimum of 25 feet in depth or into bedrock, whichever is shallower. A minimum of one soil boring per acre should be completed.

3. Data demonstrating anticipated percolation rates at the elevation of the proposed pond bottoms.

4. A description, including maps showing elevations and contours of the site and adjacent area suitable for expansion.

5. Sulfate content of the domestic water supply. Where lakes or streams are involved, the existing levels of phosphorus and nitrogen should be considered and the probable effect of nutrient addition to the receiving source should be considered.

6. Meteorological data on evaporation and precipitation in the area.
Basis of Pond Design...
1. Area and Loadings :

a. The maximum design loading on the primary cell(s) shall be 30 pounds of BOD₅ per acre per day.
b. Multiple cells designed for series operation shall be provided in order to meet effluent standards and achieve better nutrient reduction. The design may include facilities for parallel operation for additional flexibility.
c. The area of the primary cell(s) should be approximately 50-60 % of the total surface area of the entire pond system. The total surface area required shall be computed based upon both organic and hydraulic loading, and that which results in the larger surface area shall be utilized.
d. The total organic loading for the total surface area shall not exceed 20 pounds of BOD₅ per acre per day.
e. The design average flow rate shall be used to determine the volume required to provide a minimum storage capacity of 180 days. The 180-day storage of the entire facility shall be provided above the two (2) foot level. The maximum normal liquid depth should not exceed five (5) feet in the primary cell or six (6) feet in the secondary cell. All subsequent cells may have an allowable liquid depth of up to eight (8) feet and shall provide at least 20 days of storage above the two (2) foot level.
f. The net water loss considered in the design resulting from evaporation and seepage shall include the average annual precipitation. Evaporation shall not be considered in the design for those systems primarily operating only during the winter months. Evaporation and precipitation and seepage should be considered when cells are designed for total containment.
g. The seepage rate for the primary cell(s) shall not exceed 1/16 inch per day. An allowable seepage rate of 1/8 inch per day for cells in series following the primary cell(s) may be considered on a case-by-case basis dependent upon underlying soil formations and proximity of water sources in the area.
h. When determining an estimate of the surface area required for non-discharge or controlled-discharge systems, the following formulas may be used :

For total retention :

A = I / WL

For summer months or year-round :

A = I / ( H + WL )

For winter months :

A = I / ( H + S - P )

Where :
A= Estimated surface area in acres
I= Volume of in-flow in acre-feet for the design period
WL= Net water loss (evaporation + seepage - precipitation) in feet for the design period
S= Seepage in feet for the design period
H= Operating depth in feet above the 2-foot level
P= Precipitation

i. All cells should be very nearly balanced volumetrically in order that the 2-foot minimum level and retention time may be maintained. Due to the various configurations and slopes, the average area and depth method is not accurate for water balances. Therefore, to determine the storage volumes of cells for the estimated surface areas at various operating depths the following formula is provided.

V = [ ( 1 / 6 H ) ( B1 + 4 M + B 2 ) ] / 43,560

Where :
V= Volume in acre-feet (total or operating storage)
H= Depth in feet (total or operating) from B1 to B2
B1= Bottom area in square feet of pond level selected
M= Area of mid-section in square feet between levels B1 and B2
B2= Top area in square feet of pond level selected

From these calculations, adjustments could be made in the design for such variables as slopes, operating depths and surface areas to obtain a more accurate volume balance. Allowances for rounded corners should be included in areas of B1, M, B2.

j. Due consideration shall be given to possible future expansion on suitable land when the original land acquisition is made.

1. Industrial Wastes : Consideration shall be given to the type and effects of industrial wastes on the treatment process.
2. Multiple Units : Flexibility is desirable if one or more cells must be taken out of use for repair, enlargement or for some other reason. This flexibility allows maximum operational capability.
3. Pre- or Post-Treatment : When ponds are used to provide additional treatment for effluents from existing or new primary or secondary wastewater treatment works, the Department will, upon request, review and recommend BOD₅ loading limits for the pond after due consideration of the efficiencies of preceding treatment units.
4. Pond Shape : The shape of the cells shall be such that there are no narrow, L-shaped or elongated portions. Round or square ponds are considered most desirable. Rectangular ponds shall generally have a length not exceeding three times the width. No islands, peninsulas or coves are permitted. Dikes shall be rounded at corners to minimize accumulation of floating material.
Pond Location...
1. Separation Distances : A pond site should be as far as practicable from habitation or any area which may be platted and developed within a reasonable future period. A distance of at least one-half mile from the community and one-fourth mile from a farm home or residence is recommended whenever possible. A pond shall not be located within 1,000 feet of a well used to supply potable water. The high-water line of the pond shall be at least 50 feet from the property line of the adjacent owner. Where an existing pond facility has been established on a site with fixed boundaries, then only the additions and modifications will be subject to the 50 foot separation.

2. Prevailing Winds : If practicable, ponds should be located so that locally prevailing winds will be toward uninhabited areas. Preference should be given sites which will permit an unobstructed wind sweep across the ponds, especially in the direction of the locally prevailing winds. This need not apply to the third cell for ponds operated in series.

3. Surface Runoff : Location of ponds in watersheds receiving significant amounts of runoff water is discouraged unless adequate provisions are made to divert storm water around the ponds and otherwise protect pond embankments. Pond embankments must be above the 100-year floodplain.

4. Groundwater Pollution : Proximity of ponds to water supplies and other facilities subject to contamination and location in areas of porous soils and fissured rock formations should be critically evaluated to avoid creation of health hazards or other undesirable conditions. The possibility of chemical pollution may merit appropriate considerations. The pond bottom should be at least four (4) feet above the high groundwater table and ten (10) feet above rock or impervious soil strata except if synthetic liners are used. The maximum contaminant levels for groundwater affected by ponds and land application techniques shall not be exceeded. In certain areas, lysimeters or monitoring wells will be required; they shall be located and constructed in accordance with the recommendations of the Department. Refer to Chapter XIII for monitoring requirements.
Pond Construction Details...
Embankments and Dikes :

a. Embankments and dikes shall be constructed of relatively impervious and stable material, and compacted to at least 90 percent of Standard Proctor Density (ASTM D698 or AASHTO T99); however, 95 percent of Standard Proctor Density with a moisture content near to 3% wet of optimum is recommended. The compaction and moisture conditions shall be sufficient to limit the seepage through the dike to 1/16 inch per day for all primary cells and shall not exceed 1/8 inch per day for all other cells.
b. All vegetation, roots, and topsoil shall be removed from the area upon which the embankment is to be placed. The embankment material must not contain any organic material, debris, frozen material, large clods or stones larger than 6 inches in diameter. Topsoil shall only be used in the outer portions of the embankment and blended with the other soils. Pond bottom and embankment seals consisting of soils, bentonite, or synthetic liners may be considered provided the permeability, durability, and integrity of the proposed material can be satisfactorily demonstrated for the anticipated conditions.
c. The minimum embankment top width shall be eight (8) feet to permit access of maintenance vehicles. Lesser top widths could be considered for very small installations, one acre or less.
d. Interior embankment slopes should not be steeper than three horizontal to one vertical (3:1) and not be flatter than six horizontal to one vertical (6:1) on the inside. Flatter slopes are sometimes specified for larger installations because of wave action but have the disadvantage of added shallow areas conducive to emergent vegetation and mosquito breeding. The exterior slopes should be three or more horizontal to one vertical for prevention of erosion.
e. Minimum freeboard shall be three (3) feet except for very small installations, one acre or less, where two (2) feet will be permitted.
f. The normal minimum liquid depth in any cell shall not be less than two (2) feet.
g. The embankment exterior shall be covered with at least 4 inches of fertile topsoil.
h. Embankments shall be seeded from the outside toe to the high water line on the interior slope wherever riprap, soil sterilant, and bank stabilization is not utilized. Low growing and spreading perennial grasses that withstand erosion are most satisfactory. In general, alfalfa, clover and other long-rooted vegetation should not be used, since the roots of this type of plant are apt to impair the water holding efficiency of the dikes. For sediment and erosion control, refer to the Department Guide, BMPs "Best Management Practices". The County Agricultural Extension Agent or local Conservation District can usually advise as to hardy, locally suited permanent grasses which would be satisfactory for embankment seeding. Prior to filling or prefilling, the newly seeded vegetation shall be well established if submergence and wave action will occur.
i. A method shall be specified which will prevent vegetation growth over the bottom of the ponds and up to the high water line on the interior embankment slopes. If prefilling is specified before weed growth is established, then soil sterilants may not be necessary up to the prefilled water level.
j. Provisions shall be made for riprapping or bank stabilization of the interior slopes of any cell of five acres or more. Protection for outer embankments (riprap) may be necessary where the dikes are subject to erosion due to severe flooding of an adjacent watercourse. Riprapping or bank stabilization is highly recommended for all cells.
k. Riprap and bank stabilization requirements.
1. The riprap or bank stabilization shall be provided on the interior slopes from the toe to the top of the freeboard. It shall be hard and durable and be stable after placement.
2. The riprap should be approximately 6 to 18 inches in diameter.
3. The riprap shall be placed in depths of 8-18 inches depending upon size, location and configuration of cells.
4. Since riprap is usually placed against fine material, a filter of sand with gravel or spalls shall be placed on the embankment slopes prior to riprapping. The depth of the filter material should be at least four (4) inches. Another alternative available is synthetic filter blankets which shall be securely anchored and shall have been satisfactorily demonstrated by prior use to be suitable and durable for such purposes.
l. Adequate justification is required for not following the foregoing criteria.
Pond Bottom...
1. The pond bottom should be as level as possible at all points. Finished elevations should not vary more than three inches from the average elevation of the bottom.

2. Prior to scarifying, all topsoil shall be removed. In cut areas, the bottom shall then be scarified to a depth of 12 inches and cleared of vegetation and debris. Organic material thus removed shall not be used in the dike core construction. However, suitable topsoil relatively free of debris may be used as cover material on the outer slopes of the embankment. If preliminary tests have determined that the soils exposed on the pond bottom are capable of meeting the allowable seepage limits, a minimum of six (6) inches of the scarified soil shall be removed, the remaining scarified soil shall be brought to the proper moisture content and compacted to the specified density, and then the removed soil shall be uniformly spread and compacted, at the proper moisture content, as specified.

3. Soil boring information and results of percolation, porosity or permeability tests to determine the characteristics of surface soil and subsoil shall be made a part of preliminary surveys to select pond sites and design preparation of plans. Gravel, gypsum and limestone areas must be avoided.

4. The ability to maintain a satisfactory water level in the ponds is one of the most important aspects of design. Removal of porous topsoil and proper compaction of subsoil improves the waterholding characteristics of the bottom. Porous areas within 2 feet of the finished pond floor, such as gravel or sand pockets, shall be removed and replaced with well-compacted clay or other suitable material. Where excessive percolation is anticipated, sealing of the bottom with a clay blanket, bentonite, synthetic liners or other sealing material may be required to achieve a percolation rate not to exceed 1/16 inch per day for all primary cells and shall not exceed 1/8 inch per day for all other cells. The proposed seal should be substantiated by a soils engineering report.

5. Clay for liners shall be placed and compacted in at least two (2) lifts, the depth of any lift shall not exceed 8 inches.

6. The suitability of sealing the pond with bentonite will depend on the type of soil and conditions encountered in the field. Application rates for an effective seal can be determined by the use of a particle size analysis and the Atterburg limits tests. The application rate shall be specified in terms of pounds per square foot. The blanket application method is preferred to the soil-bentonite mix application because it provides a complete seal using approximately one-half of the amount for a mix application.

a. Bentonite should be applied only on well packed and smooth surfaces.
b. After bentonite has been applied, at least two (2) inches of soil should be placed on top of the bentonite and moderately packed to insure that bentonite material will remain in place until the pond is put into operation.

7. Prior to putting the ponds into operation, percolation tests shall be conducted and submitted to DWNR. Suggested methods for conducting percolation tests are double ring infiltrometer, laboratory permeability tests on thin wall tube samples, with the neutron method supplement weighing lysimeters or seepage tests on the entire pond in which the pond is filled and the water level and pan evaporation rate are monitored daily. If tests indicate seepage limits are exceeded, the seal shall be modified and retested until it meets those limits as required.

8. Prefilling the pond should be considered in order to protect the liner, to prevent weed growth, to reduce odor, and to maintain moisture content of the seal.
Influent Lines...
1. Any generally accepted pipe material for underground sewer construction will be given consideration for the influent line to the pond. The pipe material selected should be adapted to local conditions. Special consideration must be given to the character of the wastes, possibility of septicity, corrosion, exceptionally heavy external loadings, abrasion, the necessity of reducing the number of joints, soft foundations and similar problems. Surcharging of gravity flow sewers upstream from the inlet manhole is not permitted.

2. A manhole shall be installed at the terminus of the gravity line or force main to the primary cell and located as close to the dike as topography permits. The invert of this manhole should be at least six (6) inches above the maximum operating level of the primary cell to provide sufficient hydraulic head without surcharging the manhole. Flow distribution structures shall be designed to effectively split hydraulic and organic loads equally to multiple primary cells.

3. Influent lines shall be located along the bottom of the primary cell and shall be securely anchored to the bottom of the pond so that the invert elevation is near the bottom of the pond. This line can be placed at zero grade. The use of an exposed dike to carry the influent line to the discharge point is prohibited, as such a structure will impede circulation and cause localized deposition of sludge. Influent lines shall not be located within or below the seal.

4. Influent piping should be located to minimize short-circuiting within the cell. Each primary cell of a multiple-celled pond operated in parallel shall have a separate inlet but this does not apply to those cells following the primary cell when series operation alone is used. Influent lines or interconnecting piping to secondary cells of multiple-celled ponds operated in series may consist of pipes through the separating dikes. Influent lines to rectangular ponds should terminate at approximately one-third of the length from the upstream end of the cell and its outlet structure, except that it shall be at approximately the mid-point for cells without an outlet.

5. The end of the influent line shall be provided with a concrete headwall and shall rest on a suitable concrete apron that is at least four (4) feet by four (4) feet. The influent line shall discharge horizontally into a shallow, saucer-shaped depression.
Control Structures and Interconnecting Piping...
1. Interconnecting piping and overflow piping should be of cast iron, corrugated metal, or other suitable materials of at least eight (8) inches in diameter. Piping shall have capacity to permit transfer of water at a minimum rate of six (6) inches of pond water depth per day at the available head.

2. Control structures shall be provided for each cell. No discharge structure will be permitted for a single cell installation. The control structure should provide a positive visual means of directing and controlling the flow and be accessible for maintenance and adjustment of controls. The control structure should consist of a manhole or box equipped with multiple-valved pond drawoff lines or an adjustable overflow device so that the liquid level of the pond can be adjusted to permit operation between the minimum and maximum operating levels. At least one drawoff line shall be located at the two (2) foot level. The lowest of the drawoff lines to such structure should be 12 inches off the bottom to control eroding velocities and avoid pickup of bottom deposits. Erosion protection should be provided at the inlet and discharge end of the piping. The overflow from the pond during ice-free periods should be taken near, but below, the water surface to release the best effluent and insure retention of floating solids. A locking device should be provided to prevent unauthorized access to and use of the level control facilities. The outlet structure should be located to minimize short-circuiting within the cell, if possible, on the windward side. Consideration must be given in the design of all structures to protect against freezing or ice damage under winter conditions.

3. Interconnecting piping for multiple unit installations operated in series should be valved or provided with other arrangements to regulate flow between structures and permit flexible depth control. Interconnecting piping to secondary cells should discharge horizontally near the pond bottom to minimize the need for erosion control measures and should be located as near the dividing dike as construction permits. Consideration must be given in the design of all piping to protect against freezing or ice damage under winter conditions. Interconnecting piping shall be provided with splash pads. Anti-seep collars may be necessary on pipes penetrating the dikes, to discourage seepage and scouring.

4. The outlet end of the discharge pipe should be screened to prevent the entrance of wildlife.
Miscellaneous...
1. Access Roads : An all-weather access road to the pond site shall be provided to carry out the routine inspections and maintenance which are required year-round on even the smallest installations. A minimum 30 foot easement is recommended and not less than 20 feet should be provided. This minimum easement will permit light shaping and gravel surfacing for a ten foot roadway. Such minimums may only be satisfactory where the drainage is good and the distance from a maintained roadway is less than one-half mile. Minimum access fulfilling these requirements should be provided in all cases.

2. Fencing : The entire pond area shall be enclosed with a suitable fence to provide for public safety, to exclude livestock, and to discourage trespassing. The pond area should be fenced with at least 4 foot woven wire and two strands of barbed wire at the top. Where ponds are located near schools, parks, trailer courts, etc., the pond area shall be entirely enclosed with 6 foot high non-climbable chain-link fence. A vehicle access gate of minimum 12 foot width to accommodate mowing equipment should be provided unless the installation is small; then 8 foot will be satisfactory. All access gates shall be provided with locks. Fences shall be located away from the outside toe of the dike to facilitate dike mowing and maintenance operations.

3. Warning Signs : Appropriate signs should be provided along the fence around the pond to inform the public of the facility and advise against trespassing. A minimum size of 20 inches by 12 inches with a minimum size letter of two inches is recommended. There shall be at least one such sign on each side of the pond and every 500 feet along the fence.

4. Flow Measurement : Provisions for flow measurement devices shall be provided at the inlet and outlet of controlled-discharge systems. Flow measurement devices shall be capable of measuring the maximum anticipated flows. Recording equipment shall be protected from the weather and flow conditions.

5. Depth Measurement : Pond depth indicators shall be provided. Due to ice conditions, a calibrated, inclined concrete section anchored into the dike slope is the most desirable. The outlet structure of each cell may also be utilized if properly and permanently calibrated. The depth indicator shall allow easy observation and shall be permanent. It is recommended that the depth indicators be permanently etched in the concrete.

6. Synthetic Liners : ( a ) The minimum lining thickness shall be 30 mils. The liner material shall be resistant to sunlight and organic materials typical of wastewater. ( b ) Where the bottom of pond is below the seasonal high groundwater, the liner shall be stabilized to prevent it from rising. An air-release system may be required. ( c ) Liners shall be installed and securely anchored to resist movement from wave and ice conditions.

7. Laboratory Equipment and Service Building : Equipment for wastewater analyses should be provided as outlined in Chapter 40, Recommended Standards for Sewage Works, 1978 or the latest edition. A minimum amount of equipment may be provided if the owner utilizes the wastewater analyses provided by the Municipal Effluent Sampling Program (MESP) of the South Dakota Department of Water and Natural Resources or any other acceptable public or private wastewater laboratory. Consideration in design should be given to a service building to house laboratory and maintenance equipment.

8. Deviations from Design Criteria : The Department may consider and allow deviations where adequate documentation is provided to prove the need for such deviation.