(a) Any surface impoundment that is not covered by subsection (c) of this section or 40 Code of Federal Regulations (CFR) §265.221 must have a liner for all portions of the impoundment (except for existing portions of such impoundments). The liner must be designed, constructed, and installed to prevent any migration of wastes out of the impoundment to the adjacent subsurface soil or groundwater or surface water at any time during the active life (including the closure period) of the impoundment. The liner may be constructed of materials that may allow wastes to migrate into the liner (but not into the adjacent subsurface soil or groundwater or surface water) during the active life of the facility, provided that the impoundment is closed in accordance with §335.169(a)(1) of this title (relating to Closure and Post-Closure Care (Surface Impoundments)). For impoundments that will be closed in accordance with §335.169(a)(2) of this title, the liner must be constructed of materials that can prevent wastes from migrating into the liner during the active life of the facility. The liner must be:
  (1) constructed of materials that have appropriate chemical properties and sufficient strength and thickness to prevent failure due to pressure gradients (including static head and external hydrogeologic forces), physical contact with the waste or leachate to which they are exposed, climatic conditions, the stress of installation, and the stress of daily operation;
  (2) placed upon a foundation or base capable of providing support to the liner and resistance to pressure gradients above and below the liner to prevent failure of the liner due to settlement, compression, or uplift; and
  (3) installed to cover all surrounding earth likely to be in contact with the waste or leachate.
(b) The owner or operator will be exempted from the requirements of subsections (a) and (j) of this section if the commission finds, based on a demonstration by the owner or operator, that alternate design and operating practices, together with location characteristics, will prevent the migration of any hazardous constituents (see §335.159 of this title (relating to Hazardous Constituents)) into the groundwater or surface water at any future time. In deciding whether to grant an exemption, the commission will consider:
  (1) the nature and quantity of the wastes;
  (2) the adopted alternate design and operation;
  (3) the hydrogeologic setting of the facility, including the attenuative capacity and thickness of the liners and soils present between the impoundment and groundwater or surface water; and
  (4) all other factors which would influence the quality and mobility of the leachate produced and the potential for it to migrate to groundwater or surface water.
(c) The owner or operator of each new surface impoundment unit on which construction commences after January 29, 1992, each lateral expansion of a surface impoundment unit on which construction commences after July 29, 1992, and each replacement of an existing surface impoundment unit that is to commence reuse after July 29, 1992, must meet the requirements of 40 CFR §264.221(c), as amended through July 14, 2006 (71 FR 40254).
(d) The executive director may approve alternative design or operating practices to those specified in subsection (c) of this section if the owner or operator demonstrates to the executive director that he meets the requirements of 40 CFR §264.221(d), as amended through January 29, 1992 (57 FR 3462).
(e) The double liner requirement set forth in subsection (c) of this section may be waived by the commission for any monofill which contains only hazardous wastes from foundry furnace emission controls or metal casting molding sand, and such wastes do not contain constituents which would render the wastes hazardous for reasons other than the toxicity characteristics in 40 CFR §261.24, and is in compliance with either of the following requirements:
  (1) the monofill:
    (A) has at least one liner for which there is no evidence that such liner is leaking. For the purposes of this subsection, the term "liner" means a liner designed, constructed, installed, and operated to prevent hazardous waste from passing into the liner at any time during the active life of the facility, or a liner designed, constructed, installed, and operated to prevent hazardous waste from migrating beyond the liner to adjacent subsurface soil, groundwater, or surface water at any time during the active life of the facility. In the case of any surface impoundment which has been exempted from the requirements of subsection (c) of this section on the basis of a liner designed, constructed, installed, and operated to prevent hazardous waste from passing beyond the liner, at the closure of such impoundment, the owner or operator must remove or decontaminate all waste residues, all contaminated liner material, and contaminated soil to the extent practicable. If all contaminated soil is not removed or decontaminated, the owner or operator of such impoundment will comply with appropriate post-closure requirements, including, but not limited to, groundwater monitoring and corrective action;
    (B) is located more than 1/4 mile from an underground source of drinking water (as that term is defined in §331.2 of this title (relating to Definitions)); and
    (C) is in compliance with groundwater monitoring requirements of this subchapter; or
  (2) the owner or operator demonstrates that the monofill is located, designed, and operated so as to assure that there will be no migration of any hazardous constituent into groundwater or surface water at any future time.
(f) The owner or operator of any replacement surface impoundment unit is exempt from subsection (c) of this section if:
  (1) The existing unit was constructed in compliance with the design standards of Resource Conservation and Recovery Act, §3004(o)(1)(A)(i) and (o)(5); and
  (2) There is no reason to believe that the liner is not functioning as designed.
(g) A surface impoundment must be designed, constructed, maintained, and operated to prevent overtopping resulting from normal or abnormal operations, overfilling, wind, and wave action; rainfall; run-off, malfunctions of level controllers, alarms, and other equipment; and human error.
(h) A surface impoundment must have dikes that are designed, constructed, and maintained with sufficient structural integrity to prevent massive failure of the dikes. In ensuring structural integrity, it must not be presumed that the liner system will function without leakage during the active life of the unit.
(i) The commission will specify in the permit all design and operating practices that are necessary to ensure that the requirements of this section are satisfied.
(j) A surface impoundment (except for an existing portion of a surface impoundment) that will be closed in accordance with §335.169(a)(2) of this title must have an additional liner to that required in subsection (a) of this section which:
  (1) prevents any migration of wastes out of the impoundment to the adjacent subsurface soil or groundwater or surface water at any time prior to the end of the post-closure care period; and
  (2) minimizes the rate of migration of wastes out of the impoundment to the adjacent subsurface soil or groundwater or surface water so as not to pose a substantial present or potential hazard to human health and the environment.

Source Note: The provisions of this §335.168 adopted to be effective May 28, 1986, 11 TexReg 2347; amended to be effective March 18, 1991, 16 TexReg 1369; amended to be effective November 23, 1993, 18 TexReg 8218; amended to be effective February 26, 1996, 21 TexReg 1142; amended to be effective November 15, 2001, 26 TexReg 9135; amended to be effective February 21, 2013, 38 TexReg 978