Okla. Admin. Code § 252:656-11-3

Current through Vol. 41, No. 19, June 17, 2024

Section 252:656-11-3 - Lagoon construction details

(a)Soil borings. Provide soil boring data conducted by an independent soil-testing laboratory. Borings shall extend at least 5 feet below the proposed lagoon bottom and at least one boring shall be at least 25 feet deep or into bedrock. Borings shall be conducted during the time of highest groundwater level. Provide enough borings to accurately represent the soil characteristics of the entire lagoon site. If bedrock is encountered, describe its general characteristics and identification, and the corresponding geological formation(s). Include a map showing the location of each boring, a log of soil types encountered at each boring, the elevation of the water table where encountered and the permeability of soil samples taken from the same elevation as the proposed lagoon bottom. Fill and seal all borings after testing.

(b)Dikes.

(1)Material. Construct dikes of relatively impervious material and compact them to at least 90% Standard Proctor Density to form a stable structure. Remove vegetation and other unsuitable materials before construction.

(2)Top width. The top of the dike shall be at least 8 feet wide for maintenance vehicles.

(3)Slope. Inner and outer dike slopes shall not be steeper than 1 vertical to 3 horizontal (1:3). Steeper slopes will only be considered where surface construction is of soil cement or other material that will prohibit vegetation growth. Inner dikes shall not be flatter than 1 vertical to 4 horizontal (1:4).

(4)Freeboard. Design the lagoon to maintain at least 3 feet of freeboard above the design maximum water depth at all times.

(5)Lagoon shape. Round, square or rectangular lagoons with rounded corners, with a length not more than three times the width constructed without islands, peninsulas or coves.

(6)Erosion control. Protect inner dikes from wave action and outer dikes from runoff and floodwaters.

(A)Seeding. Where riprap is not used, apply at least 4 inches of fertile top soil to dikes to establish an adequate vegetative cover. Before prefilling, establish vegetation on dikes from the outside toe to 2 feet above the lagoon bottom on the interior as measured on the slope. Specify perennial, low-growing grasses that spread rapidly. Do not use alfalfa or other long-rooted vegetation for seeding since the roots of this type are apt to impair the water holding efficiency of the dikes.

(B)Additional protection. Provide extra protection where inner dikes may be subjected to severe wind action, such as lagoons larger than 5 acres and where the lagoon surface will often be exposed to strong winds. Also, protect areas of turbulence in aerated cells and all pipe penetrations. Install riprap, soil cement or other recognized material. Protect the inner dikes from 1 foot vertically above the high water elevation to 2 feet vertically below the minimum operating elevation. Place riprap on a filter bed at least 6 inches thick, and use material that will stay in place and resist erosion.

(c)Lagoon seal. Construct a soil seal as specified below. If native soils exceed this seepage rate, then a bentonite seal or synthetic liner shall be specified. Use ASTM Method 5084. Analysis of soil shall include how soil will be applied. The seepage rate through the lagoon bottom and inside dike shall not exceed 500 gal/day/acre (5.4 x 10 -7 cm/s) at a hydraulic head of 6 feet for soil and bentonite seal. Synthetic seals shall have no measurable leakage.

(1)Soil seal.

(A) The soil used for sealing shall have a high, uniform content of fine material (clay and silt). Soil containing rock or a high gravel content is not acceptable for a soil seal or for mixing with bentonite.

(B) Soil used to construct the lagoon seal and dike cores shall be relatively incompressible and compacted at a water content up to 4% above the optimum to at least 90% Standard Proctor Density.

(C) The soil used for sealing shall be at least 12 inches thick with the coefficient of permeability (K) no greater than 10 ^-7 cm/s. The soil seal shall be applied in lifts no greater than 6 inches.

(D) Written certification to the effect that the seal was provided and applied in accordance with specifications and that the coefficient of permeability is equal to or less than 10 ^-7 cm/s shall be furnished by the project engineer and independent soils laboratory. The written certification shall include

(i) the number of samples taken;

(ii) a map of the location of the samples taken; and

(iii) a demonstration that the location and number of samples taken are representative of the seal of the lagoon, for both the bottom of the lagoon and all sides of the lagoon dike walls.

(2)Bentonite seal.

(A) The application rate shall be at least 125% of the minimum rate that is determined to be adequate by laboratory tests.

(B) The water content of the soil-bentonite mixture shall be up to 4% above the optimum for maximum compaction. Bentonite shall be applied to soil that is free of all vegetation, trash, roots, frozen soil, snow or ice, stones over 2 inches in diameter or other objectionable material.

(C) Split the material in half and apply in 2 perpendicular 3-inch lifts for a finished compacted blanket thickness of at least 6 inches.

(D) After mixing and compacting, analyze a sample of the soil/bentonite mixture for permeability. If the coefficient of permeability exceeds 10 ^-7 cm/s, the depth of the mixture or content of bentonite shall be increased as necessary to obtain the required seal.

(E) Compact the mixture at the proper water content to at least 90% Standard Proctor Density (specifically excluding use of a sheepsfoot roller).

(F) Cover the completed seal with at least 4 inches of soil in addition to necessary erosion control.

(G) Hydrate with fresh water and keep at or above the optimum water content until the pond is prefilled.

(H) Written certification to the effect that the seal was provided an applied in accordance with specifications and that the coefficient of permeability is equal to or less than 10 ^-7 cm/s shall be furnished by the project engineer and independent soils laboratory. The written certification shall include:

(i) the number of samples taken;

(ii) a map of the location of the samples taken; and

(iii) a demonstration that the location and number of samples taken are representative of the seal of the lagoon, for both the bottom of the lagoon and all sides of the lagoon dike walls.

(3)Synthetic liner.

(A) The synthetic liner shall be at least 30 mils (0.030 inch) thick, unless the lagoon is subject to heavy traffic, in which case the liner shall be at least 60 mils (0.060 inch) thick.

(B) Remove or cover sharp objects in the subsoil with a bedding of 4 inches of clean soil or sand.

(C) Use 4-inch perforated pipe to allow venting and draining of the soil to reduce gas and hydrostatic pressures and facilitate monitoring for leakage.

(D) The synthetic liner panels shall be laid out in a longitudinal direction and sealed with an overlap of 4 to 6 inches.

(E) The anchor trench shall be a 6-inch minimum depth and placed at least 9 to 12 inches beyond the slope break of the dike.

(F) Take adequate measures to protect the integrity of the liner including UV protection.

(4)Uniformity. The bottom shall be as level as possible. Finished elevations shall not deviate more than 3 inches from the average elevation.

(5)Prefilling. Protect the integrity of the liner by hydrating with fresh water until the lagoon is used.

(d)Influent lines. Influent lines shall terminate in a flow distribution manhole or control structure with the invert at least 6 inches above the maximum design high water elevation of the lagoon. Design the control structure to proportionally split the flow to the primary cells.

(1)Placement. Raw sewage distribution lines may be placed on the surface of the lagoon bottom. Anchor pipe to prevent floating or settling. Soil shall not be mounded over the distribution lines. The method of construction shall not alter the integrity of the lagoon seal.

(2)Point of discharge. To minimize short-circuiting in primary cells, terminate influent lines at the lesser of either the center of the cell or a point at least 100 feet from the inside toe of any dike. Install multiple inlets when the distance from any inlet to the toe of an adjacent dike exceeds 250 feet. Terminate influent lines for aerated cells within the mixing zone of the aeration equipment.

(3)Discharge apron. To control erosion of the lagoon bottom, influent lines shall discharge horizontally into shallow, saucer-shaped depressions and terminate on a concrete apron. The apron shall be at least 2 feet square or 2 feet in diameter. Provide additional energy dissipating devices where influent will enter the lagoon at a high velocity.

(e)Miscellaneous construction standards. All pipes entering and exiting the seal shall be constructed with a seepage collar.

(f)Control structures and interconnecting piping.

(1)Structure. Provide structures to control water depth in cells, route water through the system, and measure flow at discharging facilities. Control structures in primary cells shall be capable of controlling the operating depth between a minimum of 3 feet and the maximum design operating depth. For suspended solids control, the discharge structure should allow the withdrawal point to vary below the surface to obtain the best quality effluent. Valves, slide tubes, dual slide gates or removable interlocking boards are recommended, and they shall:

(A) be accessible for maintenance and adjustment of controls;

(B) control water level and flow rate, and complete shutoff;

(C) be constructed of non-corrosive materials; and

(D) be located to minimize short-circuiting within the cell.

(2)Discharge piping. Pipe meeting ASTM standards for sanitary sewers shall be adequately anchored but not interrupt the integrity of the seal.

(A)Hydraulic capacity. The hydraulic capacity for continuous discharge structures and piping shall allow for a minimum of 250% of the design flow of the system.

(B)Minimum pipe size. All piping within the lagoon shall be at least 12 inches in diameter for facilities serving 100 PE or more and at least 8 inches for facilities serving less than 100 PE. Design influent pipe for rodding. Protect all piping between the lagoon cells from the entrance of turtles.

Okla. Admin. Code § 252:656-11-3

Added at 17 Ok Reg 1140, eff 6-1-00; Amended at 23 Ok Reg 937, eff 6-15-06; Added at 28 Ok Reg 1282, eff 7-1-11

Amended by Oklahoma Register, Volume 31, Issue 24, September 2, 2014, eff. 9/12/2014

Amended by Oklahoma Register, Volume 32, Issue 23, August 17, 2015, eff. 9/15/2015