2016-11-07_REVISION - M1977348 - Laserfiche WebLink

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- RECEIVED — - Golder Nov 0 7 2016 Associates TR= ��)1ti1��j�1:I�) DIVISION OF RECLAMATION 11Nr,.&SAFFrY L'iolcrtion: Mti'1992060 October 18, 2016 Project No. 1547675 Mr. Eric Scott Colorado Division of Reclamation Mining and Safety Department of Natural Resources 1313 Sherman St., Room 215 Denver, Colorado 80203 RE: REQUEST FOR TECHNICAL REVISON OF PERMIT M-1977-348: CHANGES TO THE GROUNDWATER SAMPLING FREQUENCY AT THE BOETTCHER QUARRY Dear Mr. Scott: On behalf of Holcim (US) Inc., Golder Associates Inc. (Golder) is submitting this request for a technical revision to permit M-1977-348 to modify the sampling frequency of the groundwater monitoring program for the Boettcher Limestone Quarry located at 3060 West County Road 56, LaPorte, Colorado 80535. Changes to the sampling frequency were discussed in the October 4, 2016 conference call between Golder, Holcim (US) Inc. and the Division of Reclamation Mining and Safety (DRMS). A reduction in sampling frequency is requested because monitoring wells MW-2, MW-3, MW-4, MW-6, and MW-7 are being purged dry during quarterly sampling events and, due to low hydraulic conductivity in surrounding subsurface materials do not recover to static conditions between events. Without stabilization of the groundwater elevations between events, the wells cannot be considered fully recharged to static levels and quarterly samples are not considered independent measurements from previous samples. Golder reviewed pressure transducer(transducer)data from monitoring wells MW-2 and MW-7 in order to determine if the water levels stabilize between sampling events. Water level measurements recorded by transducers deployed in these wells between August 26th and November 8th 2013 are plotted in Figure 1 and Figure 2. The third quarter sampling event was conducted on August 26th and the fourth quarter purge event on November 7th. Based upon review of the data collected in 2013, the groundwater elevations in both MW-2 and MW-7 steadily increased from the time of quarterly sampling to the time of purging for the following quarter. It is concluded that these wells did not reach groundwater equilibrium conditions during the monitoring period shown on Figures 1 and 2. Figure 3 presents a graph of the monitoring well water elevations measured during each sampling event from 2013 to the present. Wells MW-1 and MW-5 exhibit minimal drawdown during sampling and are relatively stable through time. However, the water elevations in the deeper wells (MW-2, MW-3, MW-4, and MW-6, and MW-7) typically show similar fluctuations with time to one another. These variations in water level elevation over time(Figure 3)correlate to the number of days elapsed between sampling events (Figure 4), in which the amount of recharge observed in these well increases with elapsed time. Considering the 2013 transducer data for MW-2 and MW-7 and the general correlation between water level responses in these and the other deep wells, it is inferred that the majority of the site wells do not recharge to static levels between quarterly events. Based on the presented data, Golder is requesting a reduction in sampling frequency from quarterly to semi-annually. The intent of this request is to allow for complete well recharge between sampling events and true independent measurements based on groundwater equilibrium conditions. i.\15\1547675\0110\samplingfrequencyreduction fnl-18octl6\1547675changesfrequencygwsamplingboe8cher fnl-18oc116.docx Golder Associates Inc. 44 Union Boulevard,Suite 300 4r Lakewood,CO 80228 USA Tel: (303)980-0540 Fax: (303)985-2080 www.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