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Site - Specific Values of Hydraulic Conductivity in Surrounding Bedrock Containing C -Pit <br />The following discussion written by Brown and Caldwell is in support of CEMEX's proposal to no <br />longer sample groundwater at monitoring well CEM -001. <br />At the May 12, 2011 meeting held at DRMS' offices, David Bird suggested that CEMEX should <br />determine site - specific values for the hydraulic conductivity of the various bedrock units containing <br />C-Pit, to support the contention that pit water is effectively contained within the pit. The following <br />discussion summarizes the available information on this subject. <br />Monitoring well CEM -001 is located approximately 650 feet southeast of C -Pit, and screened across <br />the Fort Hays Limestone and approximately 10 feet above and below the limestone into the two <br />shale units that contain the Fort Hays. As summarized in the Technical Revision NO. 8- August 31, <br />2007 Brown and Caldwell hydrogeologic report, CEM -001 is 141.5 feet deep with a 40 -foot well <br />screen. The water data summarized in the August 2007 report and collected since then clearly <br />demonstrate that a hydraulic connection exists between C -Pit and CEM -001. This connection does <br />not, however, reflect the transmission of water, as proven by the lack of water in down gradient well <br />CEM -005, located 2,700 feet southeast of CEM -001 and also screened across the Fort Hays at 378 <br />to 398 feet below ground surface (bgs). We have concluded from these data that the rising and <br />falling head in CEM -001 that coincides with the pit water elevation in C -Pit indicates the presence <br />of fractures and bedding planes in the Fort Hays and the shale units above and below the <br />limestone. Although these fractures do transmit changes in head (pressure) from C -Pit to CEM - <br />001, they apparently pinch out and close off with increasing depth as the Fort Hays dips to the <br />southeast. <br />As summarized on page 2 -7of the August, 2007 C -Pit Hydrologic Investigations report, on March 9, <br />2007 Brown and Caldwell investigators installed an In -Situ Multi- Parameter Troll 9500 transducer <br />in CEM -001 after first purging the 4 -inch diameter well dry. The transducer was placed in the <br />empty well bore at approximately 50 -feet bgs in the 141.5 -foot deep well (the placement was <br />limited by the length of cable that came with the transducer). The transducer data show that it <br />took 14.5 hours for the groundwater level in CEM -001 to rise up into the well bore approximately <br />92 feet to first reach the transducer level, and from that point, it took approximately 68 additional <br />hours for it to rise another 30 feet until it stabilized as it equilibrated to reflect the head off of the C- <br />Pit water at that time. The attached plot (Attachment 1) was prepared from the transducer data; <br />the pink curve depicts the head on the transducer (the vertical axis reflects pressure as feet of <br />water). <br />Using the transducer data, Brown and Caldwell was able to perform analyses to determine site - <br />specific hydraulic conductivity values in the CEM -001 area. In each analysis the formation(s) <br />surrounding the well screen are stressed by adding or removing water (in this case, removing by <br />pumping) and the water levels are measured while they recover. Each test carries with it certain <br />assumptions about other aquifer conditions, well construction, and test execution. For this reason, <br />four different analyses were conducted to ensure the most representative results. <br />The analytical results for hydraulic conductivity range from 2.25x10 cm /sec to 2.69x10 cm /sec. <br />Since CEM -001 is screened across three geologic formations (the Smokey Hill Shale, the Fort Hays <br />Limestone, and the Carlile Shale), these K values represent a superposition of the individual K <br />