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Non-Tributary Support: Cash Mine Borehole AdrianBrown <br />The average far field elevation of the groundwater table is taken to be equal to the original groundwater <br />table elevation at the mine collar. The elevation of the mine shaft collar is 8050.29 feet (above mean sea <br />level). The depth to water in the vicinity (at wells approximately 1000 feet northwest of the mine shaft - <br />Plate 2) has been measured to average 30.20 feet in the period 1987-2006. Thus the average far field <br />elevation of water table is 8020.09 ft. <br />The water elevation in the mine is 7788.99 ft. Thus, the average head loss resulting from flow to the <br />mine is: <br />Average head. loss (H) Average far field elevation - Average elevation at mine <br />= 8020 ft - 7789 ft = 231 ft <br />2.5.4 Radius of Influence <br />The radius of influence of the well flow is the distance from the well that is affected by drawdown to the <br />well. In this case the spread of the drawdown cone around the well is controlled by the infiltration of <br />water from precipitation, which ultimately (at steady state) provides the water that enters the mine. <br />The equation for infiltration flow to a circular area is: <br />Q=nR2q <br />where: Q = volumetric infiltration flow [L3T"I] <br />R = radius of influence of well [L] <br />q = infiltration rate [LT-11 <br />The infiltration rate to the mine area can be estimated by consideration of the baseflow in streams in the <br />area. Stream baseflow is that flow that is not contributed to by surface runoff, and enters the stream <br />system from deep groundwater flow. It is present 'in the stream year-round, but is essentially all of the <br />stream flow during periods of low rainfall or periods when precipitation occurs as snow. <br />The mine area drains to Gold Run, which is a tributary of Fourmile Creek. Fourmile Creek flow has <br />been monitored at Orodell, Boulder County, Colorado, approximately 7.1 miles downstream of the mine <br />(direct distance). The flow results from the station for the more recent period of record (1985-1996) are <br />presented in Figure 25. The baseflow is clearly evident as the low flow period, which in this case extends <br />from August through the following February. <br />5 USGS, 2007. Streamflow information for USGS 06727500, Fourmile Creek at Oradell, Colorado. Downloaded from <br />http://waterdata.usgs.gov/nwis/, January 15, 2007. <br />1601A-20070125