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GeoScience Services <br />2263 %ingston Road <br />Grnnd junction, CO 81503 <br />(970) 314-3356 <br />values for the Entrada Sandstone are from Lohman (1965) while sandstone and shale unit <br />values are from Freeze and Cherry(1979). Rocks underlying each mine site can be <br />divided into three major groups listed below. Hydraulic conductivity values assigned to <br />each unit in the model was at the mid-to upper range listed in Table 2 of the reports. <br />Rock Tune <br />Entrada Sandstone (Je) <br />Mudstone/Shales (Jms,Js) <br />Jms Sandstones <br />Hvdraulic Conductivity~cm/s) <br />5.0E-OS <br />1.6E-07 <br />1.0E-06 <br />Since the completion of the modeling, additional geotechnical reports were obtained for <br />work involving the Uravan Mill and the associated waste disposal facility located on <br />Club Mesa-on the opposite side of the San Miguel River from mine SM-18. UMETCO <br />(1997) conducted a series of packer test in the Summerville Formation to measwe the <br />hydraulic conductivity. These tests, conducted at 167 to 270 psi, did not introduce any <br />water into the formation indicating that the hydraulic conductivity of the Summerville <br />Formation is no greater than 1.0 E-08 cm/s. This conclusion is supported by laboratory <br />testing that measwed horizontal and vertical permeabilities of less than 9.7 E-10 cm/s. <br />This measwed value represents neazly three orders of magnitude lower permeability than <br />the value used in the model to represent the Summerville Formation and increases the <br />inherent conservatism of the model. <br />Please furnish a more detailed explanation of how faulting in the area of these <br />operations impacts contaminant transport and eapiain what if any consideration <br />was given to those issues in the modeling. <br />Revised cross-sections showing the site geology, including faults, with the model plume <br />of species of concern are attached to this report. As shown in the attached cross sections, <br />only the predicted plume for JD-8 intersects a known fault. However, regarding the <br />implications of subsurface faults on the transport of water and species of concern, faults <br />act as capillary barriers in the unsaturated zone restricting the movement of water. Water <br />in the unsaturated zone would migrate around the faults significantly increasing the travel <br />time. <br />The Division requests a depiction of the water table on the model results and an <br />indication, in the text, of how closely contaminants will travel relative to the water <br />table. <br />The water table has been included in the cross sections for the mine sites where <br />appropriate. For the SM-18 mine site, an up gradient well and the location of the San <br />Miguel River provides reasonable control on the location of the water table. At this site, <br />however, the lower extent of the plume at concentrations ofone-millionth the initial <br />concentration under conditions of no sorption migrated a vertical distance of <br />approximately 400 ft failing to reach the water table that is another 80 ft below the <br />