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iolder <br />sociates <br />RECEIVED <br />OCT 1 '__' 2015 <br />DIVISION OF RECLAMATION <br />MINING AND SAFETY <br />October 18, 2016 Project No. 1547675 <br />Mr. Eric Scott <br />Colorado Division of Reclamation Mining and Safety <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />RE: REQUEST FOR TECHNICAL REVISON OF PERMIT M-1977-348: CHANGES TO THE <br />GROUNDWATER SAMPLING FREQUENCY AT THE BOETTCHER QUARRY <br />Dear Mr. Scott: <br />On behalf of Holcim (US) Inc., Golder Associates Inc. (Golder) is submitting this request for a technical <br />revision to permit M-1977-348 to modify the sampling frequency of the groundwater monitoring program for <br />the Boettcher Limestone Quarry located at 3060 West County Road 56, LaPorte, Colorado 80535. <br />Changes to the sampling frequency were discussed in the October 4, 2016 conference call between Golder, <br />Holcim (US) Inc. and the Division of Reclamation Mining and Safety (DRMS). A reduction in sampling <br />frequency is requested because monitoring wells MW -2, MW -3, MW -4, MW -6, and MW -7 are being purged <br />dry during quarterly sampling events and, due to low hydraulic conductivity in surrounding subsurface <br />materials do not recover to static conditions between events. Without stabilization of the groundwater <br />elevations between events, the wells cannot be considered fully recharged to static levels and quarterly <br />samples are not considered independent measurements from previous samples. Golder reviewed pressure <br />transducer (transducer) data from monitoring wells MW -2 and MW -7 in order to determine if the water levels <br />stabilize between sampling events. Water level measurements recorded by transducers deployed in these <br />wells between August 26th and November 81" 2013 are plotted in Figure 1 and Figure 2. The third quarter <br />sampling event was conducted on August 26th and the fourth quarter purge event on November 71'. Based <br />upon review of the data collected in 2013, the groundwater elevations in both MW -2 and MW -7 steadily <br />increased from the time of quarterly sampling to the time of purging for the following quarter. It is concluded <br />that these wells did not reach groundwater equilibrium conditions during the monitoring period shown on <br />Figures 1 and 2. <br />Figure 3 presents a graph of the monitoring well water elevations measured during each sampling event <br />from 2013 to the present. Wells MW -1 and MW -5 exhibit minimal drawdown during sampling and are <br />relatively stable through time. However, the water elevations in the deeper wells (MW -2, MW -3, MW4, <br />and MW -6, and MW -7) typically show similar fluctuations with time to one another. These variations in <br />water level elevation overtime (Figure 3) correlate to the number of days elapsed between sampling events <br />(Figure 4), in which the amount of recharge observed in these well increases with elapsed time. Considering <br />the 2013 transducer data for MW -2 and MW -7 and the general correlation between water level responses <br />in these and the other deep wellsr it is inferred that the majority of the site wells do not recharge to static <br />levels between quarterly events. <br />Based on the presented data, Golder is requesting a reduction in sampling frequency from quarterly to <br />semi-annually. The intent of this request is to allow for complete well recharge between sampling events <br />and true independent measurements based on groundwater equilibrium conditions. <br />IlIS73iT67S5o110a.—NnMirtwKwur4r�tkyiti�7!17Ta d!.npnh�.n�.�amx!.+�.n�!.r �h,MteocN6.dacir <br />Golder Associates Inc. <br />44 Union Boulevard, suite 300 R <br />Lakewood, CO 80228 USA <br />Tel (303) 9800540 Fax: (303) 985-2080 www Bolder cam <br />Golder Associates: Operations In Africa, Asia, Australasia, Europe, North America and South America <br />Golder, Golder Associates and the GA globe design are trademarks of Go der Associates Corporadon <br />