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Permit #: M ~ ~QQQ• ~~. Confidental?: tU <br />AMERICAN <br />SODA, L.L.. <br />Class: - Type-Seq.: <br />From: To: <br />Doc. Name: <br />Doc. Date (if no dat tam ' <br />Celina Akin <br />~, ~~,,,,,,, ~ rental Engineer <br />2717 County Road 215 <br />Parachute, CO 81635 <br />Wednesday, October 13, 2004 <br />Ms. Erica Crosby <br />Colorado Division of Minerals and Geology <br />1313 Sherman Street, room 215 <br />Denver. CO 80203 <br />Dear Erica: <br />Telephone (970) 285-6500 <br />Facsimile (970) 285-6393 <br />RECEIVED <br />OCT 1 42044 <br />ENV234.04 <br />Dirisinn of Minerals and Geolelry <br />This letter is in response to both your letter dated October 7, 2004 regarding the adequacy of <br />submitted Technical Revision #4 to Permit No. M-1999-002 proposing to modify the ground water <br />monitoring program for both the interim status and for commercial production operations and your <br />letter dated October 13, 2004 regarding clarification of data supporting TR-#4. We have discussed <br />some of these issues by phone and I will reiterate that discussion as it pertains to your written <br />questions. <br />1. Possible exceedances with newly established Numeric Protection Levels (NPL) and Early <br />Warning Indicators (EWI) standards: <br />Response: The Division suggests the use of the 15-month baseline data set and the Dixon calculation <br />to determine the cutoff concentration for what would or would not be an outlier, and the use of these <br />calculation results to establish the EWIs and NPLs at that cutoff concentration for the parameters <br />selected for on-going monitoring. The NPLs and EWIs specified in the TR-#4 submittal were <br />calculated using the 15-month baseline data and the Dixon calculation. As pointed out in the <br />numerous bulleted locations and constituents listed in the Division letter, there are a number of <br />locations and constituents which periodically exceed these NPL and EW I levels in the 48 months of <br />operational monitoring subsequent to the 15-month baseline period. Paging through Appendix B <br />shows the natural variation in the data and gives a visual comparison of values observed during the 15 <br />month baseline period as compared to the subsequent 48 months of operational monitoring. As is <br />pointed out in the Division letter, "the natural fluctuations in ground water chemistry result in <br />concentrations of certain constituents that are higher than the NPLs and EW Is for those constituents". <br />The NPLs and EW Is based on the 15-month baseline period are generally very conservative and do <br />not seem to be the best representation of the data in several instances. <br />As we have discussed over the last few days, I have calculated a possible compliance level based <br />upon one sigma using only the 48 months of operational data. In light of the variations observed in the <br />baseline period in some of these graphs, it is apparent that the operational data is more representative <br />of the monitoring wells than the baseline data seems to be. I will offer an explanation of this in <br />response to item one of your second letter later in this correspondence. These graphs are provided to <br />you with this letter. The one sigma level is not influenced by baseline data. It is only operational data. <br />There are still a number of points that vary slightly over this level from time to time throughout the 48 <br />month monitoring period represented. It is expected that this will be the case because we are still <br />Natural Sodium Products for A Cleaner Environment <br />