2010-12-17_REVISION - C1981019 (153)

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Groundwater 53 Three additional VWPs (VWPC- 04 -17, P1 though P3) were installed in borehole C -04 -17 to monitor hydraulic heads on a more area -wide basis (Plan 5.1). Details of the piezometer construction are provided in Table 5.4. VWP completion diagrams are provided in Appendix 5.E The geophysical log, lithologic log and observations made during drilling of each VWP pilot boring were evaluated to identify the depths of the units targeted for monitoring during the pumping test. The drop weight design electronic transducers were attached to a 1.25" PVC pipe, using several zip ties to hold the arm with the porous element in place while the assembly was lowered into place. Once the entire assembly was lowered down the borehole, the transducers were tested, and then a weighted cutting tool was dropped down the interior of the PVC pipe. This action cut the zip ties, allowing the spring - loaded arms to push the porous element firmly against the side of the borehole. The porous element of each unit is connected via a water - filled tube to a calibrated vibrating wire pressure transducer. After checking that all the transducers were in place, the borehole was tremied with bentonite /cement grout using the PVC pipe. Details of the VWP construction are provided in Table 5.5. Completion diagrams and transducer calibrations are provided in Appendix 5.E. 5.2.6 Hydraulic testing Hydrologic characteristics, including transmissivity, hydraulic conductivity, and storativity C were determined from numerous tests conducted during this investigation and during several previous investigations. These include 31 slug tests, 19 single -well pumping tests, downhole flow meter tests in pilot well C- 04 -16B (Well 16B), a 35 -day pumping test in well 16B and an historic pumping test in well DHSS 80 -1 C. Data from these tests are summarized in Table 5.6, which also specifies the aquifer test, data analysis methods and data source. Table 5.7 and Figure 5.9 summarize the maximum, minimum, and average (geometric mean) of hydraulic conductivity values for units that were tested. Figure 5.9 shows data for those units tested three or more times. In 1980, Utah International performed a 19 -hour pumping test on well DHSS 80 -1C, using five observation wells. Only data from observation well DHSS 80 -4 were reported as usable by Utah International. Data analysis performed by Utah International using the Jacob straight -line method and the Glover approximation of the Dupuit - Forchheimer formula yielded a hydraulic conductivity of 0.06 ft/day for the upper Williams Fork Formation. In 1983, constant -head tests were performed on DH -1 -1, DHH -1 -2, DHH -2 -2, and DHH -4 -3. Water levels were raised to a point near the top of the well casing and maintained for 30 minutes. At the end of this time period, water levels were measured as the water - bearing unit equilibrated. These tests revealed that the J seam had a low hydraulic conductivity (0.002 ft/day), while the G seams were more highly permeable (0.57 ft/day). Results are presented in Table 5.6. In 1996, BDGE performed falling -head slug tests on six valley fill wells and short -term ( -24 hour) pumping tests on six wells screened in discrete units of the Williams Fork Formation and the Trout Creek Sandstone. Reported hydraulic conductivities vary from 0.3 to 197 ft/day. Results for the BDGE wells are provided in Table 5.6. 2572 -R2 Colowyo Coal Company Water Management Consultants