1. (a) Non-conforming technology. An integrated facultative lagoon is a non-conforming technology and is subject to the requirements of §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.
   2. (2) A pit must not be less than 0.25 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 of sludge storage for a minimum of 20 years; and
      2. (B) two days of design flow above the sludge storage area.
   5. (5) The up-flow velocity in the pit must be less than 2.0 feet per day at design flow.
   6. (6) If an integrated facultative lagoon has more than one pit, influent flow must be split proportional to the pit volumes.
   7. (7) An inlet must be located in the pit portion of a lagoon.
   8. (8) An outlet must be at a depth of 1.0 foot from the lagoon surface.
   9. (9) An integrated facultative lagoon must meet the buffer zone requirements specified in §309.13 of this title (relating to Unsuitable Site Characteristics).

   10. (10) Depth.

       1. (A) A pit must be at least 15 feet deep during normal operating conditions, measured from the water surface to the influent inlet point.
       2. (B) An integrated facultative lagoon must have berms around the pit.
       3. (C) The berm height must be at least 5.0 feet or one-half the depth of the outer lagoon, whichever is greater.
       4. (D) The distance from the water surface elevation during normal operating conditions to the top of the berm around a pit must be at least 5.0 feet.
   11. (11) Organic Loading. The organic loading into a pit must not exceed 300 pounds of five-day biochemical oxygen demand 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 the lagoon and the influent flow must be directed downward.
       2. (B) An integrated facultative lagoon must be capable of recirculating at least 50% of the design flow from an outlet of the downstream lagoon.
       3. (C) Oxygenated water from a downstream stabilization lagoon must be recirculated to the surface of the integrated facultative lagoon.
       4. (D) An integrated facultative lagoon must prevent siphoning of lagoon contents through a submerged inlet.

   13. (13) Removal Efficiency.

       1. (A) The design of an integrated facultative lagoon must not be based on more than 60% organic removal efficiency in the pit.
       2. (B) The design of an integrated facultative lagoon must not be based on a subsequent organic removal efficiency of more than 50% in the outer portion of the integrated facultative lagoon.
       3. (C) The design organic removal efficiency for the entire integrated facultative lagoon must not exceed 80%.
   14. (14) Detention Time. An integrated facultative lagoon must provide a minimum of 21 days hydraulic retention time at design flow.

Source Note:The provisions of this §217.213 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254.