1. (a) A wetted subsurface media must allow adequate root penetration and be identified in the report.

2. (b) The operational water depth of a Subsurface Flow System (SFS) wetland must not exceed the lesser of:

   1. (1) 18 inches at design flow; or
   2. (2) the maximum normal root depth of the emergent plant species used in an SFS wetland.
3. (c) Seasonal draw down of the water level must be performed to encourage deeper root penetration into the wetted media.
4. (d) Plant spacing must be sufficient to allow maturity of a wetlands flora ecosystem, but must not exceed 36 inches on center.

5. (e) Configuration. An SFS wetland must include the following minimum configuration standards:

   1. (1) Multiple cells. An SFS wetland must include multiple cells that can be operated independently, allowing individual cells to be removed from service while maintaining system operations.
   2. (2) Cell Size. The size of a cell must meet permit effluent limitations with any single cell removed from service.

   3. (3) Hydraulic profile.

      1. (A) An SFS wetland must maintain minimum 6.0 inches of dry media cover at design flow, at least 2.0 inches of upstream media cover during peak flow conditions, and not more than 12.0 inches of upstream media cover during diurnal low flow conditions.
      2. (B) An SFS wetland hydraulic profile must be based on the following figure, unless the report justifies an alternate design method, includes the source of the method, and all supporting calculations and documentation.
         Attached Graphic
         
         Attached Graphic
         

   4. (4) Maximum depth.

      1. (A) The maximum wetted media depth of an SFS wetland is the lesser of:

         1. (i) 24 inches at design flow; or
         2. (ii) the maximum normal root depth for a planned primary population emergent plant species.
      2. (B) An SFS wetland must have a dry media cover depth of at least 6.0 inches and not more than 9.0 inches above the design flow hydraulic gradient.
   5. (5) Minimum slope. An SFS wetland cell must have an adequate bottom slope to facilitate drainage for maintenance and to maintain media water depth over the entire cell length under all anticipated operational flow conditions.
   6. (6) Parallel trains. An SFS wetland must have parallel treatment trains to increase operational flexibility.

6. (f) Flow Distribution. A constructed wetland must have effective flow distribution and collection to efficiently treat wastewater. An SFS wetland must include the following minimum flow distribution standards:

   1. (1) Flow distribution.

      1. (A) The inlet and outlet system of an SFS wetland cell must assure uniform distribution of influent flow and uniform collection of effluent flow across an entire cell.
      2. (B) The inlet and outlet devices must not cause locally high velocities to avoid the movement of wetland media.
      3. (C) Each inlet and outlet system must be adjustable to allow variation in operational water level and flooding of a cell for weed control.
   2. (2) Submergence. Each inlet and outlet of an SFS wetland must be below the media surface.
   3. (3) Maintenance. The design of an inlet and outlet device must allow inspection and cleaning.
   4. (4) Staged influent feed. If a high influent BOD₅load is anticipated, the design must allow for staged influent fee to improve process control.

7. (g) SFS Organic Loading and Treatment Efficiency.

   1. (1) A constructed wetland process may be based on organic loading design for typical municipal wastewater primary or secondary effluent.
   2. (2) A design must be based on the organic removal treatment efficiency for an SFS wetland on the areal loading equation found in the following figure unless the report justifies an alternate method to determine the organic removal treatment efficiency and all supporting calculations.
      Attached Graphic
      
8. (h) Temperature. A design must be adequate to treat wastewater in the range of temperatures of the wastewater in the facility.
9. (i) Vector Control. Vegetation maintenance, including removal of excessive plant litter and detritus, is required to prevent mosquito breeding opportunities.

10. (j) Media Design. SFS wetland media must meet the following minimum requirements:

    1. (1) The media must be hard rock, slag, or other clean, comparable media material.
    2. (2) The media must contain less than 0.1% by weight of clay, sand, and other fine materials.
    3. (3) The media materials must have a Mohs hardness of at least 5.0.
    4. (4) Media must be resistant to acidic conditions.
    5. (5) Synthetic media is nonconforming or innovative technology and is subject to §217.7(b)(2) of this title (relating to Type of Plans and Specifications Approvals).
    6. (6) Media gradation and uniformity must be used to determine the wetland's hydraulic conductivity.
    7. (7) The media must be placed in an SFS wetland by light equipment to avoid introduction of clay or other undesirable materials, to avoid compaction, and to avoid creating ruts in the subgrade.
    8. (8) If an SFS wetland has gravel media larger than 1.5 inch diameter, the design must specify a top layer of small gravel to encourage healthy plant rooting. The gravel layer must be above the normally saturated media zone. The design must specify a transitional (medium grade) layer between small gravel and coarse gravel to minimize small gravel migration into lower void spaces.

Source Note:The provisions of this §217.211 adopted to be effective August 28, 2008, 33 TexReg 6843.