(a) The commission adopts by reference 40 Code of Federal Regulations (CFR) §257.95 (Assessment monitoring program) as amended through the April 17, 2015, issue of the             Federal Register            (80 FR 21301) subject to the additions in this section.     
      (b) The owner or operator of the coal combustion residuals (CCR) unit must establish a groundwater protection standard for each constituent in Appendix IV adopted by reference in §352.1431 of this title (relating to Appendix IV - Constituents for Assessment Monitoring) detected in the groundwater. The groundwater protection standard shall be one of the following.      
        (1) For constituents for which a maximum contaminant level (MCL) has been established under 40 CFR §141.62 (Maximum contaminant levels for inorganic contaminants) and §141.66 (Maximum contaminant levels for radionuclides), the MCL for that constituent.       
        (2) For constituents for which an MCL has not been established, the background concentration for the constituent established from wells in accordance with §352.911 of this title (relating to Groundwater Monitoring Systems).       
        (3) For constituents for which the background level is higher than the levels identified under paragraphs (1) and (2) of this subsection, the background concentration.       
      (c) The owner or operator may return to detection monitoring only after satisfying the conditions of 40 CFR §257.95(e), and after obtaining written approval from the executive director.     
      (d) If one or more constituents in Appendix IV adopted by reference in §352.1431 of this title are detected at statistically significant levels above the groundwater protection standard established in subsection (b) of this section in any sampling event, the owner or operator shall notify the executive director, and any local pollution agency with jurisdiction that has requested to be notified, in writing within 14 days of this determination.     
      (e) If any of the constituents listed in Appendix IV adopted by reference in §352.1431 of this title have been detected at a statistically significant level exceeding the groundwater protection standards, then the owner or operator may submit an alternative source demonstration in accordance with 40 CFR §257.95(g)(3) to the executive director for review. In making a demonstration under this subsection, the owner or operator must, within 90 days of detecting a statistically significant level above the groundwater protection standard of any constituent listed in Appendix IV adopted by reference in §352.1431 of this title, submit a report prepared and certified in accordance with §352.4 of this title (relating to Engineering and Geoscientific Information) to the executive director, and any local pollution agency with jurisdiction that has requested to be notified, demonstrating that a source other than a CCR unit caused the exceedance or that the exceedance resulted from error in sampling, analysis, statistical evaluation, or natural variation in groundwater quality.     
      (f) If the owner or operator does not make an alternative source demonstration under this section satisfactory to the executive director, then the owner or operator shall initiate assessment of corrective measures as required in 40 CFR §257.95(g)(4). The executive director may require the owner or operator to install additional monitoring wells to determine whether the demonstration is satisfactory. If the owner or operator does make an alternative source demonstration under this section that is satisfactory to the executive director, then the owner or operator may continue to monitor in accordance with the assessment monitoring program established under this section.     
     Source Note:        The provisions of this §352.951 adopted to be effective May 28, 2020, 45 TexReg 3464