1. (a) Design.

   1. (1) If evaporative lagoons are used, a facility must have a minimum of two lagoons.
   2. (2) The primary evaporative lagoon must provide at least 60% of the total surface area of an evaporative lagoon system.
   3. (3) The number and size of evaporative lagoons must provide adequate evaporation for design flow during periods of low evaporation.
2. (b) Odor Management. An evaporative lagoon must be located so that the local prevailing winds will be toward a less populated area.

3. (c) Synthetic Membrane Liners.

   1. (1) A synthetic membrane for an evaporative lagoon must be at least 40 mils thick.
   2. (2) A lagoon with a synthetic membrane liner must have an underdrain leak system consisting of at least a leachate collection system and a detection system.
   3. (3) The liner manufacturer's specifications may require proper compaction of soil beneath the liner.
   4. (4) A liner material must withstand constant sunlight without degrading.

4. (d) Configuration, Depth, and Loading.

   1. (1) An evaporative lagoon may be constructed in a round, square, or rectangular shape. The corners of a square or rectangular shaped evaporative lagoon must be rounded in order to minimize accumulation of floating materials.

   2. (2) The depth of an evaporative lagoon is dependant on its location within the lagoon system.

      1. (A) The maximum operating depth for a primary lagoon is 5.0 feet, but the area around an inlet must be designed for solids deposition according to the criteria in §217.205 of this title (relating to Facultative Lagoons).
      2. (B) The maximum operating depth for a secondary lagoon is 8.0 feet.

   3. (3) Evaporation and Organic Loading.

      1. (A) An evaporation lagoon system must be sized based on the evaporation rate for the site and a maximum allowable organic loading rate.
      2. (B) The evaporation loss must be calculated by using the Penman-Monteith method or a comparable, established method.
      3. (C) An evaporative lagoon system must be sized to account for the influent flows and precipitation from a 25-year frequency, one-year rainfall event in accordance with §309.20(b)(3)(B) of this title (relating to Land Disposal of Sewage Effluent), unless the report includes an alternate method of disposing of the wastewater and the supporting documentation.
      4. (D) The maximum organic loading rate must be calculated based on an evaporative lagoon system that is sized using the evaporation rate as required by subparagraph (C) of this paragraph.
      5. (E) The five-day biochemical oxygen demand (BOD₅) loading on a primary evaporative lagoon must not exceed 150 pounds of BOD₅ per acre of surface area per day.
5. (e) Embankment. The embankments for an evaporative lagoon must be constructed in accordance with §217.203(e) of this title (relating to Design Criteria for Natural Treatment Facilities).

6. (f) Inlet and Outlet Structures.

   1. (1) An influent line for an evaporative lagoon must terminate into a manhole located along the embankment edge.
   2. (2) An inlet manhole invert must be a minimum of 6.0 inches above the maximum high water level of a primary evaporative lagoon.
   3. (3) A submerged discharge pipe must extend from a manhole along and anchored to the bottom of an evaporative lagoon.

   4. (4) An inlet discharge pipe must discharge on to concrete apron in a depression near the center of the primary evaporative lagoon to prevent scour.

      1. (A) A concrete apron must be at least 2.0 square feet in surface area, at least 8.0 inches thick, and resistant to the corrosive effects of a wastewater environment.
      2. (B) The report must justify the use of any material other than concrete for a discharge apron.
   5. (5) Inlet and outlet structures for an evaporative lagoon must be constructed in a manner that allows the water surface elevation to be varied during normal operating conditions.

Source Note:The provisions of this §217.208 adopted to be effective August 28, 2008, 33 TexReg 6843.