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mile target distance limit extends 3 miles through the reservoir to its outfall, then another <br /> 5 mites downstream in the Blue River to a point approximately 3 miles downstream of <br /> the town of Silverthorne(CDPHE,2002), <br /> No stream-discharge station exists for the Swan River near the site. The nearest active <br /> gauging station(USGS Station 09046600)is located on the Blue River below the <br /> confluence with the Swan River. it measures discharge from a 121-square-mile <br /> drainage area. The mean annual discharge for water years 1958 through 1996 for the <br /> Blue River at this gauging station is 107 cubic feet per second (cfs)(USGS, 1997). <br /> Mean annual precipitation as totaled from the University of Delaware(UD)database is <br /> 18.22 inches. The two-year, 24-hour rainfall event is 1.5 inches(Dunne and Leopold, <br /> 1978). The net annual precipitation as calculated from precipitation and <br /> evapotranspiration data is 3.98 inches(CDPHE,2002). <br /> 7. NATURE AND EXTENT OF CONTAMINATION <br /> Mine wastes may generate three major types of pollutants: Acid drainage, <br /> concentrations of heavy metals, and sediments derived from erosion of tailings and <br /> waste-rock piles(CDPHE, 2002). CDPHE and ABC in separate investigations collected <br /> samples of sediments,soils, waste rock, tailings,and water to characterize the nature <br /> and extent of contamination at the site. The following paragraphs summarize the results <br /> of these investigations. <br /> 7.1 Source Dimensions and Volumes <br /> On October 20,2000 CDPHE measured the dimensions of each waste-rock or tailings- <br /> pile source identified during the sampling event. Field data consisted of Global <br /> Positioning System(GPS)measurements of pile areas,and height estimates using a <br /> hand-held clinometer. Based on the field measurements. CDPHE calculated the <br /> volumes for each waste source shown in Table 1 (CDPHE,2002). <br /> Waste sources associated with the IXL/Royal Tiger site consist of an on-site,fine- <br /> grained tailings pile,stream-side tailings located to the west of the site along the south <br /> side of the Swan River valley,waste rock dumps,and a draining adit attributable to <br /> mining of ore from the site(CDPHE,2002). As shown in Table 1,the waste-rock dumps <br /> have a total volume of about 67,235 cubic yards(cu.Yd.). They are located on the hill <br /> overlooking the Swan River drainage and appear well removed from the flood plain <br /> (CDPHE,2002). <br /> The on-site tailings pile,at approximately 5,700 cu.Yd.,is the largest of several discrete <br /> tailings deposits. This tailings pile was the subject of a previous in-place closure by B&B <br /> Mines,which consisted of grading the pile,covering the graded tailings with river <br /> cobbles from the adjacent dredge tailings,placing a thin topsoil layer, and planting <br /> vegetation. The covered tailings pile remains located in the lower reaches of the mill <br /> area immediately adjacent to the Swan River Valley. CDPHE (2002)indicates that the <br /> cover over the on-site tailings pile is thin or absent in places. CDPHE collected samples <br /> of exposed fine-grained materials at the base of the former mill structure and on the <br /> eastern periphery of the rock cover(CDPHE,2002). The remaining stream-side tailings <br /> deposits total approximately 4,669 cu.Yd. <br /> lXLlRoya{T+ger VCUP Application w - Page 15 of 33 <br />