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z <br />AS believes that the monitoring result obtained from TDR cable on July 1, 2004, is <br />reliable from the surface to 1000 feet below surface and can be utilized as the baseline for <br />comparisons to future subsidence monitoring. EPA agrees that the July 1, 2004, monitoring data <br />can be used as a baseline for future comparisons of the monthly monitoring of this subsidence <br />monitoring well required by the UIC permit. <br />To explain the three TDR cable monitoring results, AS speculates that pressure of the <br />water in the tubing prior to cementing operations caused the cable to deform and resulted in a <br />short circuit at a depth of 1209 feet. AS further speculates that cementing operations on June 17, <br />2004, again deformed the cable ai a depth of 1000 feet resulting in no signal return from below <br />that depth. <br />EPA agrees that this is one possible interpretation of the data. EPA points out, however, <br />that these data are also consistent with one or more cavity collapses at depths below which there <br />are no signal returns (i.e. cavity collapses at 1209 and 1000 feet below surface). AS did not <br />address this possibility in its July 28, 2004, letter. AS must address this possibility prior to <br />resuming injection at the injection wells surrounding the this TDR cable monitoring well (i.e. <br />injection into cavities 20-2, 20-3, 20-11, 20-12, & 20-14. Until addressing the cavity collapse <br />possibility, injection into these same cavities is not allowed. <br />Within 30 days of your receipt of this letter, please provide a timeline by which AS <br />will address the possibility of cavity collapse at the TDR cable monitoring well #20-12. <br />Failure to comply with a UIC permit or the UIC regulations found at 40 CFR Parts 144 <br />through 148 constitutes one or more violations of the Safe Drinking Water Act, 42 U.S.C. §300h. <br />Such non-compliance may subject you to formal enforcement by EPA, as codified at 40 CFR <br />Part 22. <br />If you have any questions or comments concerning this letter, you may contact Ken <br />Phillips at (303) 312-6405, or Nathan Wiser at (303) 312-6211. Also please continue to direct all <br />- "~ - correspondence to tre atte`nt#on" of I~en I'Yiillips~fNlaiYCode 8ENF=U-FO in our Denver~C7ffic~ - <br />Sincerely, <br />E.c~ ~.t~~x-~~,~,,,~ <br />Elisabeth Evans <br />Duector <br />Technical Enforcement Program <br />cc: Paul Daggat, BLM <br />Erica Crosby, CDMG <br />