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June 16, 2011 <br />Michael Cunningham <br />Environmental Protection Specialist <br />Colorado Division of Reclamation, Mining and Safety <br />1313 Sherman Street — room 215 <br />Denver, Colorado 80203 <br />Dear Mr. Cunningham: <br />MW No. 1 Min. 159 — Max 191 <br />No. 2 Min. 6 — Max 166 <br />No. 3 Min. 171 — Max. 237 <br />No. 4 Min. 229 — Max. 343 <br />No. 5 Min. 110 — Max. 188 <br />No. 6 Min. 55 — Max. 127 <br />No. 7 Min. 36 — Max. 90 <br />No. 8 Min. 15 — Max. 51 <br />No. 9 Min 1 — Max. 97 <br />No. 10 Min. 22 — Max. 100 <br />ilig7C" <br />NORINERN COLORADO (ONSJRU(UORS, INC, <br />9075 WCR 10 * Fort Lupton, CO 80621 <br />303 - 857 -175.1 <br />FAX: 303 - 857 -2933 <br />RE: NCCI Pit #1, Technical Revision No. 5, Updated Monitoring Wells, Groundwater Monitoring <br />Data, Established Bench Marks, and Adequacy Review Response. <br />Response to Letter Dated May 20, 2011, To Address Comments As Required <br />File No. M- 2001 -107 <br />NCCI offers the following response to the five (5) items that the Division requires be addressed for <br />our request for Technical Revision No. 5. <br />Item No. 1 — NCC began monitoring the wells as per Technical Revision No. 3 in January, 2007. <br />Item No. 2 — Establishing base line monitoring well levels based on standard deviation calculations <br />for each monitoring well using the data collected from January, 2007 through December, 2010. <br />Attached you will find NCC's established standard deviations for monitoring well No. 1 through No. <br />10. The standard deviation for the minimum and the maximum probability is as follows: <br />Item No. 3 — NCC will notify the Division in writing within 48 hours in the event the monthly <br />averages of any of the monitoring well exceeds the upper and lower baseline levels by 24 inches for <br />three consecutive months. <br />