Okla. Admin. Code § 252:656-13-4

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

Section 252:656-13-4 - Wet weather flow equalization basins

(a)Basin type. For gravity inlet systems, provide flow splitting or automated flow diversion devices to divert excess flows to the flow equalization basin(s). Design shall include a method to return contents to primary basins. For pumped systems, installation of control valves or dedicated pumps to handle wet weather flow shall be used to divert wet weather flow to the basin. Depending on the elevation of the basin, it may be possible to return the flow to the plant's primary units by gravity. If not, a pump return system will be necessary.

(b)Design criteria. The design of basins requires a thorough evaluation of flow patterns and volumes. Items to be considered are basin geometry, construction materials, storage capacity and operational controls.

(c)Basin layout. Basins designed for storage of five million gallons or more require a minimum of two compartments designed to operate in series. All flow must be diverted to a lined basin where solids can settle and, at a predetermined elevation, overflow to additional basins. A single basin equipped with an impervious liner is acceptable where the required storage capacity is less than five million gallons. Provisions are required for returning the contents of the basins to the treatment plant and for removal of settled solids.

(d)Basin construction. Basin construction must be in accordance with OAC 252:656-11-3 and OAC 252:656-11-4 with the following exceptions:

(1) Top of dikes may be reduced to a width of 6 feet.

(2) Bottoms of lagoon cells shall be adequately sloped to allow drainage to waste return structure(s).

(3) For basins with two compartments, the first basin must be lined below the maximum design water elevation with concrete, asphalt, or equivalent material. Single compartment basins must be lined as above.

(e)Storage capacity. Design minimum storage to contain the anticipated excess flow during the largest seven-day wet weather period in 10 years, with the capability to be emptied in a timely manner. Actual flow data shall be used to develop flow balance or mass diagrams for determining basin capacity. Base the frequency and duration of storms on field data and weather service records.

(f)Aeration requirements. Where oxygen is required to prevent the wastewater from becoming anaerobic provide air at the rate of 1.25 to 2.0 cfm per 1,000 gallons basin volume. Where mechanical aerators are used, 7.5 horsepower per million gallons of basin capacity is required.

(g)Pumps and flow control methods. Controls are required to regulate flow to the basin and return flow to the plant. Adequate controls with measuring devices are required to divert all flow in excess of the plant hydraulic capacity to the basin. Provisions and controls are required to return the basin contents to the plant after the wet weather event has passed and influent flow returned to normal. Return flow may be manual or automatic, but sufficient flow measurement and instrumentation devices must be included to determine the actual flow to the first treatment unit. Where basin return flow is automatic, control equipment must limit the combination of plant influent plus the basin return flow to the hydraulic capacity of the plant.

Okla. Admin. Code § 252:656-13-4

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