1. (a) Flow Distribution. This section applies to a constructed wetland, a facultative lagoon, an aerated lagoon, a partially aerated lagoon, a stabilization lagoon, and an overland flow process.

   1. (1) The shape and size of a treatment unit must ensure even distribution of the wastewater flow.
   2. (2) The distribution system for an overland flow process must ensure uniform sheet flow of the wastewater onto and across the overland flow terraces.

2. (b) Windbreaks and Screening.

   1. (1) If spray irrigation is used in a location where drift presents a risk of contact with the public, a windbreak or vegetative screening must be used.
   2. (2) The use, the type, and the extent of windbreaks or vegetative screening must be approved by the executive director.

3. (c) Maximum Liner Permeability.

   1. (1) Except as exempted in paragraphs (4) and (5) of this subsection, a constructed wetland, facultative lagoon, earthen aerated lagoon, partially-aerated lagoon, stabilization lagoon, and treated effluent storage lagoon must be constructed with a liner material with a minimum coefficient of permeability of 1x10^-7centimeters per second (cm/sec) with a thickness of 2.0 feet for water depths less than or equal to 8.0 feet and a thickness of 3.0 feet at water depths greater than 8.0 feet.
   2. (2) A liner must extend from the lowest lagoon elevation or lowest constructed wetland elevation up to an elevation of 2.0 feet above normal water elevation in a lagoon or constructed wetland.
   3. (3) The executive director may grant a variance to the liner requirements, in accordance with §217.4 of this title (relating to Variances).
   4. (4) If a lagoon is constructed to store treated wastewater authorized as reclaimed water under Chapter 210 of this title (relating to Reclaimed Water), the lagoon liner must comply with §210.23 of this title (relating to Storage Requirements for Reclaimed Water).
   5. (5) This subsection does not apply to an evaporative lagoon system or an overland flow system. Liner and permeability requirements for these systems are established in §217.208 of this title (relating to Evaporative Lagoons) and §217.209 of this title (related to Constructed Wetlands).

4. (d) Compliance with the Liner Permeability Requirements. Paragraph (1)(A) - (D) of this subsection provides the minimum criteria for ensuring that the liner's permeability will not exceed that allowed in paragraph (3) of this subsection. The report must include the results of any test required in this subsection.

   1. (1) Using Unmodified In-Situ Soils. If the soils that naturally exist at a proposed lagoon or constructed wetland site restrict the movement of wastewater to a degree equivalent to a liner placed as described in subsection (c)(1) of this section. A design must meet the requirements in subparagraphs (A) - (E) of this paragraph to certify the permeability of the in-situ soil layer to ensure that groundwater and surface water quality are protected.

      1. (A) A minimum of one core sample is required for each 0.25 acres of bottom area for each lagoon or constructed wetland.
      2. (B) Each core sample must be sampled to determine the coefficient of permeability, the percent passing a 200mesh sieve, the liquid limit value, and the plasticity index value for the soil that is to serve as a liner.
      3. (C) Each core sample test result must show a coefficient of permeability of less than or equal to 1x10^-7 cm/sec, in compliance with subparagraph (B) of this paragraph.
      4. (D) A liner must be constructed in accordance with one of paragraphs (2), (3), or (4) of this subsection if test results indicate that in-situ soils do not exhibit a hydraulic conductivity of 1x10^-7 cm/sec or less.
      5. (E) An in-situ soil may be used as a lagoon liner or constructed wetland liner if the in-situ soil meets all the requirements in subsection (c)(1) of this section provided that one layer of excavated in-situ material, with the minimum soil characteristic requirements is placed on scarified subgrade in one 8 inch loose lift compacted to no less than 6 inches at 95% standard proctor density in accordance with American Society For Testing And Materials (ASTM) D 698.

   2. (2) Placed Liners. The soil characteristics of the liner material for a placed liner must comply with subparagraphs (A) - (E) of this paragraph. The tests to determine the soil characteristics must conform to standard methods such as ASTM.

      1. (A) At least 30% of the liner material must pass through a 200 mesh sieve;
      2. (B) The liner material must have a liquid limit greater than 30%;
      3. (C) The liner material must have a plastic index of 15 or greater;
      4. (D) The liner material must be placed in four loose lifts that are each a maximum of 8.0 inches in depth and that are compacted to 95% standard proctor density in accordance with ASTM D 698. Each lift must be no less than 6.0 inches thick after compaction resulting in a total vertical thickness of at least 24 inches for a liner; and
      5. (E) An in-situ subgrade must be scarified prior to placement of the lowest lift.

   3. (3) Using Amended In-Situ Soils.

      1. (A) A liner may be constructed from amended soils or blended soils made of imported soils and soils excavated from the proposed lagoon site.
      2. (B) Each sample of amended soil must sufficiently decrease the coefficient of permeability to 1x10^-7cm/sec.

      3. (C) The following samples are required for each liner:

         1. (i) three representative samples from each 6,700 cubic feet of amended soil:
         2. (ii) one field permeability test; and
         3. (iii) one laboratory permeability test.
      4. (D) Each of the permeability tests must verify that the coefficient of permeability is equal to or less than 1x10^-7cm/sec.
      5. (E) When soil permeability is decreased by amending in-situ soil, the liner thickness throughout the lagoon may be decreased to 6.0 inches, if the liner is placed on scarified subgrade in one 8.0 inch loose lift compacted to no less than 6.0 inches at 95% standard proctor density in accordance with ASTM D 698.

   4. (4) Use of a synthetic membrane liner.

      1. (A) A synthetic membrane liner must have a minimum thickness of 40 mils.
      2. (B) A lagoon with a membrane liner must include an underdrain with a leachate detection and collection system.
      3. (C) A liner material must be able to withstand constant sunlight without degrading.
      4. (D) The use of a synthetic membrane liner for a constructed wetland is prohibited.

5. (e) Embankment Design and Construction. This section applies to a constructed wetland, a facultative lagoon, an aerated lagoon, a partially aerated lagoon, a stabilization lagoon, a treated effluent storage lagoon, and an evaporative lagoon.

   1. (1) The top width of an embankment must be a minimum of 10.0 feet.
   2. (2) The report must justify all inner and outer embankment slope steeper than 1.0 foot vertical to 4.0 feet horizontal from the top of an embankment.
   3. (3) Inner and outer embankment slopes steeper than 1.0 foot vertical to 3.0 feet horizontal are prohibited.
   4. (4) All embankments must be protected against erosion by planting grass, paving, riprapping, or other method approved by the executive director.
   5. (5) All embankments must have a minimum cover of 6.0 inches of topsoil if vegetated.
6. (f) Disinfection. Chemical or ultraviolet disinfection is not required if a detention time of at least 21 days is provided in the entire, free-water surface, natural treatment unit, in accordance with §309.3(g) of this title (relating to Disinfection).

7. (g) Sampling Point Significance.

   1. (1) Sizing or design of any treatment unit upstream of the permitted sampling point must not be based on any unit downstream of the permitted sampling point.
   2. (2) A wastewater lagoon downstream of the permitted sampling point is a treated effluent storage lagoon and must comply with the requirements of §210.23 of this title (relating to Storage Requirements for Reclaimed Water).
8. (h) Storm Water Drainage. A natural treatment system must be constructed to prevent storm water from draining into the system.

Source Note:The provisions of this §217.203 adopted to be effective August 28, 2008, 33 TexReg 6843.