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<br />best available data. <br /> <br />Response: As explained in Comment 5 and in the previous comment, EPA believes that <br />these ground-water quality data are sufficient to establish Permit requirements that will minimize <br />negative impacts from the operation of nahcolite extraction wells covered by this Permit. The <br />injection takes place in a unit (the Saline Zone) which is not an aquifer and the operator is <br />required to cement all wells to the surface and to carry out on-going mechanical integrity testing <br />to demonstrate that the wells have mechanical integrity. EPA believes that the Final Permit, as <br />modified in response to comments and additional EPA review of the various documents, provides <br />adequate control to ensure protection of USDWs and other aquifers in the mining area. <br />As a result of the review of this comment and the associated information, EPA has <br />determined that no changes to the Permit are needed in response to this specific concern. <br />Comment 17: There aze concerns relating to the need for corrective action associated <br />with the under ound injection portion of the project. <br />The following two (2) paraphrased comments discuss issues and concerns relating to <br />corrective action. <br />1. No corrective action (Page 13, SOB) -suggest that the option for corrective action be left <br />open so that any identified problems can be properly corrected. <br />2. Well 20-1 could be providing a pathway for aquifer communication <br />Response: There appears to be a misunderstanding regarding the corrective action referred to in <br />the SOB. The discussion on page 13 of the SOB refers only to the need for corrective action <br />relating to existing wells within the area of review, which presently penetrate the injection zone <br />(see 40 CFR 144.55). As mentioned in the Apri122, 1999 Water Monitoring plan, American <br />Soda had determined that well ZO-1 would not be utilized for the commercial mining phase and <br />would be eliminated. EPA also indicated in the SOB that there were concerns regarding the seal <br />in well 17- I. After reviewing the report on the results of an analysis of the site ground-water data <br />done for the applicant by Dr. Sauhuer ("Groundwater Quality in Piceance Creek Basin", G..J. <br />Saulnier, Jr. September, 1999), EPA has determined that we1120-1 may have historically allowed <br />communication between several aquifer zones and may present a future problem, which, at a <br />minimum, may affect sample results. There is no information that allows judgements to be made <br />regarding well 17-1 (located in the vicinity of the proposed mine panel for yeazs 25-30 of the <br />project). <br />As a result of the review of the information, EPA has decided to require that well <br />20-1 must be properly plugged and abandoned prior to commencement of injection <br />activities. Additionally, EPA will require submittal of a plan for determining if the <br />construction of we1117-1 is adequate to prevent communication between aquifers. This <br />plan must be submitted within siz (6) months of the effective date of this Permit. The <br />activities outlined in the well 17-1 study plan must be carried out within one (1) year of the <br />33 <br />