(a) During the closure period, the owner or operator must:      
        (1) continue all operations (including pH control) necessary to maximize degradation, transformation, or immobilization of hazardous constituents within the treatment zone as required under §335.171(1) of this title (relating to Design and Operating Requirements (Land Treatment Units)), except to the extent such measures are inconsistent with paragraph (8) of this subsection;       
        (2) continue all operations in the treatment zone to minimize run-off of hazardous constituents as required under §335.171(3) of this title;       
        (3) maintain the run-on control system required under §335.171(3) of this title;       
        (4) maintain the run-off management system required under §335.171(4) of this title;       
        (5) control wind dispersal of hazardous waste if required under §335.171(6) of this title;       
        (6) continue to comply with any prohibitions or conditions concerning growth of food-chain crops under 40 Code of Federal Regulations (CFR) §264.276;       
        (7) continue unsaturated zone monitoring in compliance with 40 CFR §264.278, except that soil-pore liquid monitoring may be terminated 90 days after the last application of waste to the treatment zone; and       
        (8) establish a vegetative cover on the portion of the facility being closed at such time that the cover will not substantially impede degradation, transformation, or immobilization of hazardous constituents in the treatment zone. The vegetative cover must be capable of maintaining growth without extensive maintenance.       
      (b) For the purpose of complying with 40 CFR §264.115, when closure is completed, the owner or operator may submit to the executive director certification by an independent licensed professional geoscientist, in lieu of an independent licensed professional engineer, that the facility has been closed in accordance with the specifications in the approved closure plan.     
      (c) During the post-closure care period, the owner or operator must:      
        (1) continue all operations (including pH control) necessary to enhance degradation and transformation and sustain immobilization of hazardous constituents in the treatment zone to the extent that such measures are consistent with other post-closure care activities;       
        (2) maintain a vegetative cover over closed portions of the facility;       
        (3) maintain the run-on control system required under §335.171(3) of this title;       
        (4) maintain the run-off management system required under §335.171(4) of this title;       
        (5) control wind dispersal of hazardous waste if required under §335.171(6) of this title;       
        (6) continue to comply with any prohibition or conditions concerning growth of food-chain crops under 40 CFR §264.276; and       
        (7) continue unsaturated zone monitoring in compliance with 40 CFR §264.278, except that soil-pore liquid monitoring may be terminated 90 days after the last application of waste to the treatment zone.       
      (d) The owner or operator is not subject to regulation under subsections (a)(8) and (c) of this section if the commission finds that the level of hazardous constituents in the treatment zone does not exceed the background value of those constituents by an amount that is statistically significant when using the test specified in paragraph (3) of this subsection. The owner or operator may submit such a demonstration to the executive director at any time during the closure or post-closure care periods.      
        (1) The owner or operator must establish background soil values and determine whether there is a statistically significant increase over those values for all hazardous constituents specified in the facility permit under 40 CFR §264.271(b).                  (A) Background soil values may be based on a one-time sampling of a background plot having characteristics similar to those of the treatment zone.                   (B) The owner or operator must express background values and values for hazardous constituents in the treatment zone in a form necessary for the determination of statistically significant increases under paragraph (3) of this subsection.         
        (2) In taking samples used in the determination of background and treatment zone values, the owner or operator must take samples at a sufficient number of sampling points and at appropriate locations and depths to yield samples that represent the chemical make-up of soil that has not been affected by solid waste or leakage from the treatment zone, and the soil within the treatment zone, respectively.       
        (3) In determining whether a statistically significant increase has occurred, the owner or operator must compare the value of each constituent in the treatment zone to the background value for that constituent using a statistical procedure that provides reasonable confidence that constituent presence in the treatment zone will be identified. The owner or operator must use a statistical procedure that:                  (A) is appropriate for the distribution of the data used to establish background values; and                   (B) provides a reasonable balance between the probability of falsely identifying hazardous constituent presence in the treatment zone and the probability of failing to identify real presence in the treatment zone.         
      (e) The owner or operator is not subject to regulation under §§335.156 - 335.166 of this title (relating to Applicability of Groundwater Monitoring and Response; Required Programs; 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); if the commission finds that the owner or operator satisfied subsection (d) of this section and if unsaturated zone monitoring under 40 CFR §264.278 indicates that hazardous constituents have not migrated beyond the treatment zone during the active life of the land treatment unit.     
     Source Note:        The provisions of this §335.172 adopted to be effective May 28, 1986, 11 TexReg 2347; amended to be effective November 15, 2001, 26 TexReg 9135; amended to be effective September 1, 2003, 28 TexReg 6915