(a) Areas of emergent vegetation in a free water surface (FWS) wetland must have a maximum water depth less than or equal to 24 inches at design flow.
(b) Plants.
  (1) Emergent plant spacing must be no more than 66 inches on center.
  (2) If floating plants are used in a FWS wetland, the wetland must also contain emergent plants.
(c) Multiple Cells. An FWS wetland must include multiple cells that can be operated independently, allowing an individual cell to be removed from service while maintaining system operations.
(d) System Size. An FWS wetland system must be sized to meet permit effluent limits, even when any single cell is removed from service.
(e) Bottom slope.
  (1) An FWS wetland cell must have adequate bottom slope, or other means such as strategically placed deep-water zones, to facilitate drainage for maintenance.
  (2) Plants selected for an FWS wetland cell shall be compatible with the water depths under all anticipated operational flow conditions.
(f) Parallel trains. An FWS wetland must have parallel treatment trains to increase operational flexibility.
(g) Wind protection. An FWS wetland cell must either be oriented to avoid prevailing winds perpendicular to the process flow direction, or must use elevated berms or vegetative windbreaks.
(h) Inlets and Outlets.
  (1) The inlets and outlets of an FWS wetland cell must ensure uniform distribution of influent flow and uniform collection of effluent flow across the entire cell cross section.
  (2) An FWS wetland must have multiple inlet and outlet devices designed to minimize scouring of wetland substrate caused by locally high velocity effluent flow.
  (3) Each inlet and outlet device in an FWS wetland must be adjustable to allow variations in the operational water level.
  (4) Submergence. An FWS wetland inlet must be submerged under normal operational conditions.
  (5) Inspection and Cleaning. An FWS wetland must be designed to allow for the inspection and cleaning of inlet and outlet devices.
(i) Organic Loading and Treatment Efficiency.
  (1) The design of an FWS wetland must be based on the design organic loading of the influent to the FWS wetland.
  (2) Organic removal efficiency for FWS wetlands must be calculated from the area-based loading rate equation found in Figure: 30 TAC §217.210(i)(2), unless the engineering report justifies an alternate method to determine the organic removal efficiency by identifying a method, the sources of the method, and all supporting calculations.
Attached Graphic
(j) Vector Control.
  (1) The design of an FWS wetland must include mosquito control by:
    (A) using mosquito fish (Gambusia spp.) or other natural predators;
    (B) maintaining aerobic conditions; or
    (C) using other biological controls.
  (2) A design must minimize the potential for damage to wetlands caused by mammals such as nutria and muskrats.

Source Note: The provisions of this §217.210 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254