Section 217.203 - Design Criteria for Natural Treatment Units(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 x 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 x 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 x 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 x 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.30 Tex. Admin. Code § 217.203
The provisions of this §217.203 adopted to be effective August 28, 2008, 33 TexReg 6843; Amended by Texas Register, Volume 40, Number 47, November 20, 2015, TexReg 8329, eff. 12/4/2015