2014-02-24_REVISION - M1986015 - Laserfiche WebLink

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Timothy A. Cazier, P.E. February 24, 2014 Page 2 If this construction period does not coincide with the lower groundwater elevation, please provide an explanation for the observed data. a. Response: From discussions with Transit Mix and review of historical DRMS filings, construction of the slurry wall began in October 2008, and was completed January 2009. The approximate timeline for the beginning of construction is documented in the November 2008 Annual Report submitted to the DRMS (available on DRMS Image Documents and attached here as Figure 6). Dewatering associated with mining processes was initiated inside of the slurry wall at about this time, which accounted for the drop in water levels inside of the slurry wall observed in Well Nos. MW -1, MW -2, MW -3 and MW -5. b. Also, mining and dewatering was occurring outside of the slurry wall in the northeast corner of Phase 2 from approximately September 2008 through June 2009. These mining and dewatering activities account for the drop on water level observed in MW -6 and in the residential wells along 25th Lane. Note that the water levels in the residential wells began to recover in about July 2009 when those mining and dewatering activities stopped in the northeast corner of Phase 2 outside of the slurry wall. By July 2009, MW -6 had been mined out and water levels were no longer recorded from this monitoring well. 3) Comment: There is another precipitous drop (—]Oft) in groundwater elevation for four of these same wells (e.g., MW -1, MW -2, MW -3, and MW -5) beginning about July 2009. Please provide an explanation for the observed data. a. Response: More aggressive dewatering inside of the slurry wall was initiated in about July 2009 in preparation for the 90 -day liner performance test, which was conducted between January and April 2010. Prior to the 90 -day test the pit was dewatered starting in about July 2009, which accounts for the second drop in water levels observed in MW -1, MW -2, MW -3 and MW -5 located inside of the slurry wall. It should be noted that starting in June 2009; additional monitoring wells (MW- 101, MW -102, MW -103 and MW -105) were constructed outside of the slurry wall which document the difference in water level inside and outside of the slurry wall. These wells were used to document the difference in ground water level as part of the liner performance test. 4) Comment: The data for MW -6 ends about March 2009. Is this well still functional? Was it abandoned properly? Please provide abandonment documentation. a. Response: MW -6 was located in an area that has been mined through, and therefore the well no longer exists. Documentation of the abandonment status of MW -6 has been filed with the Division of Water Resources to document that the well no longer exists. The abandonment report is attached for your reference. www.bbawater.com _-