SECTION 252:616-7-1. Construction and maintenance

  All industrial surface impoundments must comply with the construction and maintenance requirements of this section.

(1)   Stormwater. All surface impoundments, except those designed specifically for stormwater runoff, shall be constructed to prevent the entrance of runoff waters.

(2)   Slope. Inner and outer dike slopes shall not be steeper than 1 vertical to 3 horizontal (1:3). Steeper slopes will be considered where surface construction is of material, such as soil cement, that will prohibit the growth of vegetation. Concrete or rock face surface impoundments may be exempted from this requirement by the DEQ on a case by case basis.

(3)   Berms and dikes. Construct berms and dikes to provide a flat surface wide enough to provide safe access for inspection and maintenance of the surface impoundment.

(4)   Depth to groundwater. The bottom of any surface impoundment shall be a minimum of 15 feet above the historic maximum groundwater table.

(A)   Perched water is considered groundwater.

(B)   If a distance of (15) feet is not physically possible, a lesser distance may be approved by the DEQ depending on the wastewater and impoundment classification, use of liners or other means which will protect waters of the state.

(5)   Erosion control. Protect all earthen surface impoundment dikes and berms against erosion by using soil, gravel, concrete pads, shallow-root vegetation or other methods. Trees and deep-root vegetation shall not be used as erosion control and shall be removed in a timely manner to maintain the integrity and stability of the impoundment. 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 surface impoundment bottom on the interior as measured on the slope. Specify perennial, low-growing grasses that spread rapidly. Alfalfa or other long-rooted grasses should not be used 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 surface impoundments larger than 5 acres and where the surface impoundment 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.

(6)   Holding capacity. Total retention surface impoundments shall be sized to contain the design flow of wastewater (including sludge) plus expected rainfall plus 3 feet of freeboard. Where total retention is obtained by surface evaporation, the required area shall be based on design flow plus 90^th percentile rainfall less the pan evaporation rates for the area where the impoundment will be located. See supplemental information Table of Rainfall and Evaporation Data.

(7)   Freeboard. Maintain at least 3 feet of freeboard on all surface impoundments unless otherwise specified in a permit.

(8)   Liner systems. All surface impoundments shall be constructed with a liner system appropriate for the classification of wastewater from normal daily operation and when applicable, wastewater due to spill, by-pass or unit process failure.

(9)   Liner materials. The chemical and physical properties of liner materials must ensure that such structures and barriers do not fail to contain or control seepage or release of waste and wastewater because of:

(A)   pressure gradients;

(B)   physical contact with wastewater;

(C)   chemical reactions with wastewater;

(D)   the stress of installation;

(E)   the stress of daily operation and maintenance; and

(F)   exposure to sunlight, temperature and climatic extremes, freeze/thaw cycles, and wet/dry cycles.

(10)   Total retention. Total retention surface impoundments shall not have outfall structures which may allow or cause the release of wastewater to the environment (such as pipes, man-made trenches, erosion-induced trenches, or impoundment overflow).

(11)   Flow-through. Flow-through surface impoundment systems shall have a device that can immediately shut-off influent or effluent flows in the event of a spill, bypass, unit process failure or other emergency.

[Source: Added at 17 Ok Reg 1925, eff 6-12-00; Amended at 22 Ok Reg 1468, eff 6-15-05]