2013-04-10_PERMIT FILE - C1981019A (11)

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RULE 2 PERMITS season, and discharge from the valley -fill aquifers also supports stream baseflow. At the northern, downgradient boundary of the Collom permit expansion area, because the bedrock aquifers do not continue north past the north limb of the syncline, nearly all groundwater outflow from the permit expansion area occurs through the valley -fill aquifers. The elevation of the valley floors where they cross the northern limb of the syncline is about 6,500 ft amsl. Groundwater Quantity — WMC (2006) estimated of groundwater flux through the general area from Good Spring Creek on the east to Morgan /Straight Gulch on the west in conjunction with development of a regional hydrogeologic model. The calculations used water - balance methods based on average hydraulic conductivities, saturated thicknesses and aquifer widths for both bedrock and valley -fill aquifers. The methods are described in detail in WMC's 2006 report Colloin Pit Hydrogeologic Model, included as Exhibit 7, Item 22. The results were broken down by drainage and included recharge, loss to evapotranspiration, groundwater outflow as stream base flow, and groundwater outflow through the valley fill at the north boundary of the area. The flux estimates are summarized in Table 2.04.7 -43. For the Collom Gulch and Jubb Creek drainages, which encompass the Collom permit expansion area, the total flux of groundwater through the valley fill and bedrock units above the KM bed was estimated to be about 31,000 cubic feet per day (ft3 /day). About 65 percent of the outflow of groundwater at the northern boundary of the Collom permit expansion area was through the valley -fill aquifers, and the remaining 35 percent was outflow as stream baseflow. The groundwater flux through the Collom Gulch and Jubb Creek drainages comprises about 11 percent of the total groundwater flux through the area included in the calculations. The bulk of the flow (about 86 percent) occurs in the Morgan /Straight Gulch, Wilson Creek and Good Springs Creek drainages. Groundwater Quality — Baseline monitoring was conducted in 1996 -1997 of the bedrock and valley -fill aquifers and during 2004 -2006 of the valley -fill and bedrock aquifers in the Collom permit revision area. The data are summarized in Tables 2.04.7 -41 and 2.04.7 -42. The Colorado Mined Land Reclamation Division's ( CMLRD) Guidelines for the Collection of Baseline Water Quality and Overburden Geochemistry Data were utilized during the baseline monitoring, and the proposed sampling plan was reviewed and approved by the CMLRD prior to completion of the baseline monitoring program. Water quality sampling and laboratory analyses were conducted in accordance with Rule 2.03.3(4). The depth to water in each of the wells and field measurements for pH, electrical conductivity, and temperature were monitored monthly. Quarterly monitoring included a full suite of analyses on each well. Water samples from the wells were filtered in the field and preserved for analysis of dissolved metal concentrations. Groundwater samples were also collected in Collom permit expansion area wells in 1984 -1985, 1996- 1997, and 1999 -2000 as part of earlier studies; pertinent data from those data sets are included in the discussion presented in this section. Figures 2.04.7 -36 and 2.04.7 -37 present trilinear diagrams illustrating water quality for representative bedrock and valley fill monitoring wells from the data collected during baseline monitoring in 2004 -2006. Groundwater samples for water quality analysis were collected from the bedrock and monitoring wells in 2004 to 2006. Water samples were also collected from well C- 04 -16B, constructed for use in a long -term aquifer test in the proposed Collom Lite pit area, to characterize the groundwater that would be produced during Collom Lite pit dewatering operations. Additional data collected in 1996 and 1997 from wells UL- 95-01, W -95 -11 and UL -95 -40 were also available. The locations of these wells are shown on Map l OB. A summary of the sampling history and results is provided in Table 2.04.7 -42 for the bedrock wells. Table 2.04.7 -42 also lists the Federal drinking water maximum contaminant levels (MCLs) and secondary drinking water quality criteria. Although these criteria are not specifically applicable, they provide a basis for comparison. Collom— Rule 2, Page 39 Revision Date: 9/28/11 Revision No.: PR -03