Laserfiche WebLink
Non-Tributary Support: Cash Mine Borehole AdrianBrown <br />2.5.5 Well Radius <br />Inflow to a well is controlled by the open area of the well, which is equal to the perimeter multiplied by <br />the open length. For the case of a tabular mine operating as a well, the effective well radius is <br />considered to be equal to the radius of a circle that has a perimeter equal to that of the mine. <br />Accordingly: <br />Well radius of mine (r) = Mine perimeter / (2 n) <br />The mine perimeter in this case, with a largely tabular mine, is taken to be equal to twice the average <br />width of the mine. Based on the mine sections on Plate 4, the average width of the mine is 500 feet. <br />Thus: <br />Well radius of mine = (2 * 500 ft) / (2 * n) = 159 ft <br />2.5.6 Hydraulic Conductivity <br />The hydraulic conductivity can be computed from the above parameters, as follows: <br />K = Q ln(R/r) / (2 7E L H) <br />where: Q = volumetric flow [1.56 gpm or 109,617 cu.ft./yr] <br />L = length of open interval of well [647.80 ft] <br />H = head loss of flow to well [231 ft] <br />R = radius of influence of well flow [733 ft] <br />r = radius of well [159 ft] <br />Thus: <br />K = 109617 cu.ft./yr * ln(733 ft /159 ft) / (2 n * 647.80 ft * 231 ft) <br />= 0.178 ft/yr = 1.7x10"' cm/sec <br />This is a low hydraulic conductivity, consistent with relatively unfractured and/or healed Boulder Creek <br />Granodiorite host rock, and consistent with the very small inflow that has been observed to this mine. <br />2.6 Porosity <br />The effective porosity of the bedrock materials is an important parameter for evaluation of water <br />resource and water flow issues. The effective porosity of the bedrock is difficult to directly measure in <br />low permeability fractured bedrock, so a literature-based value is used. <br />2.6.1 Porosity of Bedrock <br />The bedrock at the Cash Mine site is Boulder Creek Granodiorite, which is relatively intact. <br />Literature review shows-the porosity of igneous rockmasses to generally fall between 0 and 5 percent by <br />volume, with a summary of estimates of porosity being presented in Table 3. Based on these results, the <br />porosity of intact granodiorite averages approximately 1%. All of the tests reported in Table 3 derive <br />from the testing of intact rock samples, so the porosity reported is primary porosity; that is porosity in <br />the rockmass itself. Actual granodiorite rockmassses also derive porosity from discontinuities, including <br />fractures and joints. The fracture porosity is estimated at a further 1% for this material, resulting in a <br />1601A-20070125 6