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= Golder Associates ik 1- / c/1 7 - 3 G/X February 5, 2013 Project No. 103 -81640 Mr. Eric Scott fr Colorado Division of Reclamation Mining and Safety Department of Natural Resources 1313 Sherman St., Room 215 Denver, Colorado 80203 RE: 'ROPOSED CHANGES TO THE ANALYTICAL LIST FOR GROUNDWATER SAMPLING; AT THE BOETTCHER QUARRY Dear Mr. Scott: RECEIVED FEB 0 6 2013 tv Division of Reclamation, Mining & Safety On behalf of Holcim (US) Inc., Golder Associates Inc. (Golder) is submitting this request to modify the suite of constituents included in the groundwater monitoring program for the Boettcher Limestone Quarry located at 3060 West County Road 56, LaPorte, Colorado 80535. The rationale for the proposed changes are presented below with respect to each analyte and supported by references to monitoring data and benchmark levels. Table 1 contains the proposed suite of constituents to be monitored in wells MW -1, MW -2, MW -3 and MW -4. Table 2 contains the proposed suite of constituents to be monitored in recently installed (December 2012) monitoring wells MW -5, MW -6 and MW -7. 1.0 GROUNDWATER MONITORING WELLS MW - 1, MW - 2, MW - 3 AND MW Groundwater was sampled from monitoring wells MW -1, MW -2, MW-3 and MW -4 on a quarterly basis during 2011 and 2012 (i.e. eight quarters of sampling). The laboratory analytical results for all eight quarters were summarized under a separate cover entitled Fourth Quarter Groundwater sampling at the Boettcher Quarry dated January 23, 2013. Golder reviewed analytical results obtained during the last eight quarters in order to determine which constituents have consistently remained below their respective benchmark level and /or not been detected above their respective detection limit. Based upon a review of the data collected over the last two years, the following constituents are recommended to be discontinued from the groundwater monitoring program: • Metals: The metals arsenic, chromium, copper, lead, lithium, manganese, selenium, thallium, uranium, zinc have consistently remained below their respective benchmark levels during the 2011 and 2012 sampling. Of these metals, chromium, copper, lead, thallium, uranium and zinc remained below the laboratory's practical quantitation limit (PQL) for the majority of samples collected in the last eight quarters. • Nutrients: Nitrate as N, Nitrite as N and Nitrate +Nitrite as N have remained consistently below benchmark values, and, for the most part, have not been detected above the laboratory's PQL in the downgradient wells MW -2, MW -3 and MW-4. ■ Radionuclides: Gross alpha and gross beta results have been consistently reported at low or negative concentrations with large uncertainty (e.g., -33 ±18 picocuries per liter (pCi /L)) and vary \10181640\020 prop1changesanayhstgweemplmpboefcher fnL05feb13k hang esanalylre67wsamplingboettcher fn405feb13 docx Golder Associates Inc. 44 Union Boulevard, Suite 300 Lakewood, CO 80228 USA Tel' (303) 980 -0540 Fax (303) 985 -2080 WI golder com Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation