1. (a) Nonconforming technology. An integrated facultative lagoon is nonconforming technology and is subject to review in accordance with §217.7(b)(2) of this title (relating to Types of Plans and Specifications Approvals).

2. (b) Integrated Facultative Lagoon Design.

   1. (1) The length-to-width ratio of an integrated facultative lagoon must be 3.0 to 1.0, unless the report justifies other dimensions more suitable to the site.
   2. (2) A pit must not be less than 0.40 acre in total surface area.
   3. (3) The outer lagoon area must not be less than 10 times the surface area of the pit.

   4. (4) A pit must have adequate volume to contain:

      1. (A) 0.1 cubic foot per capita per year sludge storage for a minimum of 20-years ; and
      2. (B) a two-day hydraulic retention time above the sludge storage area.
   5. (5) The maximum up-flow velocity in the pit is 2.0 feet per day at design flow.
   6. (6) If an integrated facultative lagoon has more than one pit, each pit must receive an amount of wastewater influent equivalent to the size of a pit.
   7. (7) An inlet must be located in the pit portion of a lagoon.
   8. (8) An outlet must be able to maintain the water level within 1.0 foot of a constant level.
   9. (9) A design must locate an integrated facultative lagoon in a central location with regard to the surrounding secondary lagoons and meet the buffer zone requirements specified in §309.13 of this title (relating to Unsuitable Site Characteristics).

   10. (10) Depth.

       1. (A) The depth of an inlet pit must not be less than 15 feet deep from the water surface elevation during normal operating conditions to the influent inlet point within the pit.
       2. (B) An integrated facultative lagoon must have berms or other deflection devices around the pit.
       3. (C) The berm height must be at least the lesser of 5.0 feet or one-half the depth of the outer lagoon.
       4. (D) The minimum distance from the water surface elevation during normal operating conditions to the top of the berm around a pit is 5.0 feet.
   11. (11) Organic Loading. The maximum organic loading into a pit is 300 pounds of ultimate five-day biochemical oxygen demand (BOD₅) per acre of total lagoon area per day.

   12. (12) Odor Control.

       1. (A) An inlet to a pit must be 3.0 feet above the bottom of a lagoon and the flow must be directed downward.
       2. (B) A design must allow water from a lagoon following an integrated facultative lagoon must be recirculated to the surface of the integrated facultative lagoon.
       3. (C) An integrated facultative lagoon must be capable of recirculating at least 50% of the design flow from an outlet of the downstream lagoon.
       4. (D) An integrated facultative lagoon must not siphon lagoon contents through a submerged inlet.

   13. (13) Removal Efficiency.

       1. (A) A design may be based on the removal efficiency of the pit of an integrated facultative lagoon no more than 60% of the influent BOD₅.
       2. (B) A design may be based on subsequent removal efficiency of BOD₅ in the outer portion of the integrated facultative lagoon no more than 50% of the remaining BOD₅, which is 20% of the original BOD₅.
   14. (14) Detention Time. An integrated facultative lagoon must provide a minimum of 21 days hydraulic retention time.

Source Note:The provisions of this §217.213 adopted to be effective August 28, 2008, 33 TexReg 6843.