(a) This section applies  to all earthen lagoons and earthen treatment units in a wastewater  treatment facility, including constructed wetlands, facultative  lagoons, aerated lagoons, partially aerated lagoons, stabilization  lagoons, evaporative lagoons, and storage lagoons. Storage lagoons  are considered treatment units for the purposes of this chapter if  they hold wastewater that is not final treated effluent, such as raw  influent or wastewater that has received intermediate treatment.     
      (b) Flow Distribution. The shape and size of a treatment unit  must ensure uniform distribution of the wastewater flow.     
      (c) Windbreaks and Screening.      
        (1) A windbreak or vegetative screening   must  be used if operation of the treatment system could cause spray  to drift off of the property.       
        (2) The use, type, and extent of  windbreaks or vegetative screening must be approved in writing by the  executive director.       
      (d) Maximum Liner Permeability.      
        (1) Except as provided in paragraph (3)  of this subsection, constructed wetlands, facultative lagoons,  aerated lagoons, partially aerated lagoons, stabilization lagoons,  evaporative lagoons, and storage lagoons must be constructed with a  liner material that has a coefficient of permeability less than 1 ×  10                 -7                centimeters per second for a thickness of:                  (A) 2.0 feet for water depths less than  or equal to  8.0 feet;  and                   (B) 3.0 feet for water depths greater  than 8.0 feet.         
        (2) A liner must extend from the lowest  elevation in a lagoon or constructed wetland, up to an elevation of  2.0 feet above normal water elevation in the lagoon or constructed  wetland.       
        (3) If a lagoon is constructed to store  treated wastewater authorized as reclaimed water under Chapter 210 of  this title (relating to Use of Reclaimed Water), the lagoon liner  must comply with §210.23 of this title (relating to Storage  Requirements for Reclaimed Water).       
      (e) Compliance with the Liner  Permeability Requirements. A lagoon must be lined and tested  according to the requirements of this  subsection. The  engineering  report must include the results of all tests required by this  subsection.      
        (1) Sampling Requirements for Soil  Liners.                  (A) Sample Analysis. Soil liner material  must be sampled and analyzed before construction. All samples of the  liner material must meet the following requirements:                      (i) the coefficient of permeability must  be less than 1 × 10                         -7                        centimeters per second;                       (ii) at least 30% of the liner material  must pass through a 200 mesh sieve;                       (iii) the liner material must have a  liquid limit greater than 30%; and                       (iv) the liner material must have a  plasticity index of 15 or greater.                     (B) Preconstruction Sampling for  Unamended In-Situ Liners. Permeability testing for an unamended  in-situ soil liner requires undisturbed core samples of the liner  material. At least one undisturbed core sample must be analyzed for  every 0.25 acre of liner surface area on the bottom of each lagoon or  constructed wetland. At least one additional undisturbed core sample  must be analyzed for every 0.25 acre of liner surface area from each  side of each lagoon or constructed wetland. All undisturbed core  samples must have a coefficient of permeability less than 1 ×  10                     -7                    centimeters per second. The engineering report must  demonstrate that the in-situ soil liner meets the minimum thickness  requirements in subsection (d)(1) of this  section.                   (C) Preconstruction Sampling for  Imported Soil Liners and Amended In-Situ Soil Liners. Four samples  must be tested for every 0.25 acres of liner surface area in each  lift according to subparagraph (A)(ii) - (iv) of this paragraph. At  least one out of every four samples must be tested for permeability  according to subparagraph (A)(ii) of this paragraph. If samples are  collected before compaction, molded samples of the liner material  mixture may be tested instead of undisturbed core samples for  imported soil liners and amended in-situ soil liners.                   (D) Post-construction Sampling. A  minimum of one undisturbed core sample must be analyzed after the  liner is complete for each 0.25 acre of liner surface area on the  bottom  of each  lagoon or constructed wetland. At least one additional  undisturbed core sample must be analyzed for every 0.25 acre of liner  surface area from each side of each lagoon or constructed wetland.  The coefficient of permeability must be less than 1 × 10                     -7                    for each sample. An unamended in-situ liner does not require  post-construction sampling if it meets the pre-construction  requirements in subparagraphs (A) and (B) of this paragraph and the  construction requirements in paragraph (2)(B) of this subsection.         
        (2) Soil Liner Construction.                  (A) Amended In-situ or Imported Soil  Liner Construction. All amended in-situ or imported soil liners must  comply with the following requirements:                      (i) liner  material must be placed in  loose lifts that are each no more than 8.0 inches in thickness;                       (ii) each lift must be compacted to at  least 95% standard proctor density at -1% to +3% optimum moisture  according to American Standards for Testing and Materials (ASTM) D  698;                       (iii) each lift must be no more than 6.0  inches thick after compaction and the completed liner must meet the  minimum thickness requirements in subsection (d)(1) of this section;  and                       (iv) the in-situ subgrade must be  scarified before placement of the lowest lift.                     (B) Unamended In-situ Soil Liner  Construction. All unamended in-situ soil liners must comply with the  following requirements.                      (i) The liner must include at least one  8.0 inch loose lift of excavated in-situ material that is compacted  to no more than 6.0 inches at 95% standard proctor density at -1% to  +3% optimum moisture according to ASTM D 698.                       (ii) The in-situ subgrade must be  scarified before placement of the lowest lift.           
        (3) Synthetic Membrane Liner  Construction. All synthetic membrane liners must comply with the  following requirements.                  (A) A synthetic membrane liner must have  a minimum thickness of 40 mils.                   (B) A synthetic membrane liner must  include an underdrain with a leachate detection and collection  system.                   (C) Synthetic membrane  liner material   must be able to withstand constant sunlight without degrading.                   (D) Soil compaction beneath a synthetic  liner must meet the liner manufacturer's requirements.         
      (f) Embankment Design and Construction.      
        (1) The top of an embankment must be at  least 10.0 feet wide.       
        (2) The engineering report must justify  all inner and outer embankment slopes steeper than 1.0 foot vertical  to 4.0 feet horizontal from the top of the embankment.       
        (3) Inner and outer embankment slopes  steeper than 1.0 foot vertical to 3.0 feet horizontal are prohibited.       
        (4) All embankments must be protected  against erosion by establishing  grass, paving,  riprapping, or any  other method approved in writing by the executive director.       
        (5) All vegetated embankments must have  a minimum cover of 6.0 inches of topsoil.       
      (g) Disinfection. Unless otherwise  specified in the wastewater treatment facility's wastewater permit,  chemical or ultraviolet disinfection is not required if a detention  time of at least 21 days is provided in the plant-free water surface  with full sun exposure in accordance with §309.3(g) of this  title (relating to Application of Effluent Sets).     
      (h) Sampling Point Significance. The size or design of a treatment unit  upstream of the permitted sampling point must not be based on the  design of any storage  lagoon or other  structure downstream of the  permitted sampling point.     
      (i) Stormwater Drainage. A natural  treatment system must be designed and constructed to prevent  stormwater from draining into the system.     
      (j) Piping. A natural system must have  piping that allows water in each lagoon or wetland cell to be  re-routed to a different lagoon or wetland cell for maintenance.     
      (k) Freeboard.      
        (1) A lagoon must have a minimum of 2.0  feet of freeboard above the normal operating level if the lagoon's  normal water surface area is less than 20 acres.       
        (2) A lagoon must have a minimum of 3.0  feet of freeboard above the normal operating level if the lagoon's   normal water  surface area is 20 acres or more.       
        (3) A constructed wetland cell must have  at least 2.0 feet of freeboard above the normal operating level, or  the freeboard required to manage the selected wetland plant  population, whichever is greater.       
      (l) Prohibition of Synthetic Liners for  Constructed Wetlands. The use of a synthetic membrane liner for a  free water surface constructed wetland is prohibited.     
     Source Note:        The provisions of this §217.203 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254