(a) Except as provided in subsection (b) of this section, the rules pertaining to groundwater monitoring and response apply to owners and operators of facilities that process, store, or dispose of hazardous waste.
  (1) The owner or operator must satisfy those requirements of paragraph (2) or (3) of this subsection for all wastes (or constituents thereof) contained in any such waste management unit at the facility, regardless of the time at which waste was placed in the units.
  (2) Except as provided in paragraph (3) of this subsection, all solid waste management units must comply with the requirements in §335.167 of this title (relating to Corrective Action for Solid Waste Management Units). A surface impoundment, waste pile, land treatment unit, or landfill that receives hazardous waste after July 26, 1982, (hereinafter referred to as a regulated unit) must comply with the requirements of §§335.157 - 335.166 of this title (relating to Required Program; Groundwater Protection Standard; Hazardous Constituents; Concentration Limits; Point of Compliance; Compliance Period; General Groundwater Monitoring Requirements; Detection Monitoring Program; Compliance Monitoring Program; and Corrective Action Program) in lieu of §335.167 of this title for purposes of detecting, characterizing, and responding to releases to the uppermost aquifer. The financial responsibility requirements of §335.167 of this title apply to regulated units.
  (3) The commission may replace all or part of the requirements of §§335.157 - 335.166 of this title with alternative requirements for groundwater monitoring and corrective action for releases to groundwater set out in the permit or in a post-closure order where the commission determines that:
    (A) a regulated unit is situated among solid waste management units or area of concern, a release has occurred, and both the regulated unit and one or more solid waste management unit(s) or area of concern are likely to have contributed to the release; and
    (B) it is not necessary to apply the groundwater monitoring and corrective action requirements of §§335.157 - 335.166 of this title because the alternative requirements will be protective of human health and the environment.
  (4) If a permitted facility obtains an order setting out alternative requirements provided in §335.151(e) of this title (relating to Purpose, Scope, and Applicability), then the alternative requirements shall also be referenced in the facility's permit.
(b) The owner or operator's regulated unit or units are not subject to regulation for releases into the uppermost aquifer under this section and §§335.157 - 335.166 of this title if:
  (1) he is exempted under 40 Code of Federal Regulations (CFR) §264.1;
  (2) he operates a unit which the commission finds:
    (A) is an engineered structure;
    (B) does not receive or contain liquid waste or waste containing free liquids;
    (C) is designed and operated to exclude liquid, precipitation, and other run-on and run-off;
    (D) has both inner and outer layer of containment enclosing the waste;
    (E) has a leak detection system built into each containment layer for which continuing operation and maintenance will be provided during the active life of the unit and the closure and post-closure care periods; and
    (F) to a reasonable degree of certainty, will not allow hazardous constituents to migrate beyond the outer containment layer prior to the end of the post-closure care period.
  (3) the commission finds, in accordance with 40 CFR §264.280(d), that the treatment zone of a land treatment unit that qualifies as a regulated unit does not contain levels of hazardous constituents that are above backgrounds levels of those constituents by an amount that is statistically significant, and if an unsaturated zone monitoring program meeting the requirements of 40 CFR §264.278 has not shown a statistically significant increase in hazardous constituents below the treatment zone during the operating life of the unit. An exemption under this paragraph can only relieve an owner or operator of responsibility to meet the requirements of this subchapter relating to groundwater monitoring and response during the post-closure care period;
  (4) the commission finds that there is no potential for migration of liquid from a regulated unit to the uppermost aquifer during the active life of the regulated unit (including the closure period) and the post-closure care period specified under 40 CFR §264.117. This demonstration shall be certified by a licensed professional geoscientist or geotechnical engineer. In order to provide an adequate margin of safety in the prediction of potential migration of liquid, the owner or operator shall base any predictions on assumptions that maximize the rate of liquid migration; or
  (5) he designs and operates a pile in compliance with 40 CFR §264.250(c).
(c) Sections 335.157 - 335.166 of this title apply during the active life of the regulated unit (including the closure period). After closure of the regulated unit, these sections:
  (1) do not apply if all waste, waste residues, contaminated containment system components, and contaminated subsoils are removed or decontaminated at closure;
  (2) apply during the post-closure care period under 40 CFR §264.117 if the owner or operator is conducting a detection monitoring program under §335.164 of this title; or
  (3) apply during the compliance period under §335.162 of this title if the owner or operator is conducting a compliance monitoring program under §335.165 of this title or a corrective action program under §335.166 of this title.

Source Note: The provisions of this §335.156 adopted to be effective May 28, 1986, 11 TexReg 2347; amended to be effective July 14, 1987, 12 TexReg 2106; amended to be effective October 19, 1998, 23 TexReg 10878; amended to be effective January 30, 2003, 28 TexReg 715; amended to be effective September 1, 2003, 28 TexReg 6915