2013-08-13_HYDROLOGY - M1977348 (2)

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August 2013 10 103- 81640A installed immediately above the well screen and on approximate 50 -foot intervals on the PVC casings to keep monitoring well MW -7 centered within the borehole for uniform placement of the filter pack and bentonite seal and grout (Appendix D). Monitoring well MW -7 is constructed with two 10 -foot sections of 4 -inch ID, flush threaded, Schedule 40 PVC 20 -slot screen set at a depth interval of about 238.8 feet bls to 258.8 feet bls with the actual perforations between about 239.2 to 258.5 feet bls. Bentonite grout was placed in the annular space above the bentonite seal up to about 24 feet of the ground surface. At 24 feet bls, the bentonite grout was continually lost to the fill, which had to be sealed with bentonite chips to a depth of 3 feet bls. 3.4 Well Development The wells were developed to improve water flow into the wells and reduce turbidity by removing fines from the screen and sand pack. Development was conducted using a combination of surging and bailing /pumping or air lifting methods. During development, the field parameters of pH, electrical conductivity and temperature were measured using a field - calibrated hand -held Hanna HI 98130 Combo water quality meter. Drilling Engineers, Inc. of Fort Collins, Colorado was contracted to develop the three new monitoring wells due to the depths and volumes in monitoring wells MW -6 and MW -7. Monitoring well MW -5 was developed on January 23, 2013 by surging and pumping with a Grudfos Redi- Flow 2 submersible pump until turbidity was not visible and field parameters stabilized. A total of 220 gallons was pumped from monitoring well MW -5 during development with minimal drawdown observed after pumping at an average rate of 1 gallon per minute. Field parameters appeared stabilized and discharge free of visible turbidity at the end of development while pumping at this rate (Appendix D). Monitoring well MW -6 was developed on January 23, 2013, using a 3% -inch diameter surge block and bailing until the well went dry after about 56 gallons were removed. Based on subsequent water levels and field parameters, much of this water is believed to be from drilling operations. On January 31, 2013, Golder returned to monitoring well MW -6 after 1 week of recharge had occurred and hand - bailed about 4 gallons before the well went dry again. The low recharge of formation water to this well impeded the flushing of the screen to considerably reduce turbidity during development. However, field parameters taken during development (Appendix D) on January 31, 2013 indicate the groundwater entering monitoring well MW -6 after the initial 56 gallons were removed were similar to those measured during past sampling events at the upgradient monitoring wells. This suggests that formation water had entered the well. Depth to water below the top of the PVC casing as measured in this well on January 31, 2013 (227.11 feet) and March 5, 2013 (225.42 feet) may indicate that "static" groundwater levels are very deep at this location and are near the bottom of the well. However, these levels may also indicate that recharge is very slow and static conditions had not yet been achieved within this timeframe. Golder 1 h rw llin Ilfi r 9Associates \ \ 081640a \0400 \gwc a e sta I edep_ 09aug13\ gwchanvellinstallfieldrep _09aug13docx