1. (a) Primary treatment must remove the settleable and floatable solids in the influent prior to the wastewater entering a stabilization lagoon.

2. (b) Odor Management.

   1. (1) A stabilization lagoon must be located so that the local prevailing winds will be toward a less populated area.
   2. (2) If uncontaminated water is available, a stabilization lagoon must be pre-filled to the 2.0 foot level at start-up.
   3. (3) A stabilization lagoon system must include a piping arrangement that allows the recirculation of effluent from a final lagoon to the influent side of an initial stabilization lagoon.
   4. (4) A stabilization lagoon may return recirculation water by surface spray to assist in maintaining aerobic conditions at the lagoon surface and reduce potential odor.
3. (c) Minimum Number of Wastewater Stabilization Lagoons. A minimum of two stabilization lagoons is required to comply with secondary treatment limits. The stabilization lagoons must be operated in series with each other following the primary treatment unit.

4. (d) Lagoon Design.

   1. (1) The minimum length-to-width ratio of a stabilization lagoon is 3.0 to 1.0.
   2. (2) Islands, peninsulas, and coves within a stabilization lagoon are prohibited.
   3. (3) A stabilization lagoon must have a depth of at least 3.0 feet but not more than 5.0 feet under design operating conditions.
   4. (4) Inlet and outlet structures must be adjustable to allow for raising and lowering water level a minimum of 6.0 inches to assist in controlling vegetative growth.
   5. (5) A stabilization lagoon must have a minimum of 2.0 feet of freeboard above the normal operating level if the lagoon's normal water surface area is less than 20 acres.
   6. (6) A stabilization lagoon must have a minimum of 3.0 feet of freeboard above the normal operating level if the lagoon's normal water surface area is 20 acres or more.

5. (e) Pipe and Hydraulic Equipment.

   1. (1) All structures and pipes in a stabilization lagoon must be sized to transport at least 250% of the facility's design flow.
   2. (2) The inlet and outlet structures must be sized to transport the volume of water found in the top 6.0 inches of a lagoon during normal operating depths per day at the available head.
   3. (3) A pipe and recirculation system must allow a stabilization lagoon system to comply with the facility's permitted effluent limitation with any one lagoon of service.

6. (f) Maximum Surface Organic Loading Rate for Stabilization Lagoons.

   1. (1) The maximum surface organic loading rate on the stabilization lagoon series is 35 pounds (lbs) of five-day biochemical oxygen demand (BOD₅) per acre per day.
   2. (2) The maximum surface organic loading rate on the first lagoon in a stabilization lagoon series is 75 lbs of BOD₅ per acre per day.
   3. (3) The surface organic loading rate applied to the stabilization lagoon series is equal to the total influent organic loading minus any reduction in organic load provided by the primary treatment units.

7. (g) Inlet and Outlet Structures.

   1. (1) A stabilization lagoon outlet must include removable baffles to prevent floating material from being discharged, and must be constructed to operate correctly as the level of the lagoon surface varies under normal operating conditions.
   2. (2) An outlet must be at least 18 inches but not more than 24 inches below the lagoon surface to control the discharge of algae.
   3. (3) A multipurpose control structure may be used to facilitate a normal operational function such as drawdown, flow distribution, flow depth, measurement, sampling, pump for recirculation and chemical addition; and to minimize the number of construction sites in a lagoon.
   4. (4) A pipe embankment penetration must have a seep water-stop collar.
   5. (5) A stabilization lagoon must have a drainpipe to allow emptying for maintenance and may use a pump as part of a drainage system. If not permanently installed, a temporary pipe suction station must be provided.

Source Note:The provisions of this §217.207 adopted to be effective August 28, 2008, 33 TexReg 6843.