Laserfiche WebLink
Section 779.15 (a) Continued. Revised 11/20/80 <br />Mine Plan and Adjacent Area <br />Ground Water Recharge Characteristics The mine plan and adjacent <br />area is located in a semi-arid climate, with average annual preci- <br />pitation of about 11 inches (USDI Bureau of Land Management, 1980). <br />Most precipitation is lost to runoff, evapotranspiration and subli- <br />mation, minimizing the amount available for ground water recharge. <br />The unconsolidated aquifers, including the upland terrace deposits <br />and the stream-laid deposits, are recharged in Lhe spring when <br />snowmelt water infiltrates through the soil. The coal aquifer in <br />the Coalmont Formation is recharged primarily by infiltration in <br />the aquifer outcrop area delineated on Map 15a, Kerr Mine Area <br />Ground Water Hydrology. <br />The rate of ground water recharge is controlled by the amount of <br />precipitation, the infiltration characteristics of the overlying <br />soils, and the horizontal extent of the recharge area. Using an <br />• average annual precipitation of 11 inches (BLM, 1980), and an <br />infiltration capacity of 20% from Soil Conservation Service infor- <br />mation on the soils covering the mine plan area, it follows that <br />2.2 inches per year (0.18 feet per year) should be available for <br />ground water recharge. In the undisturbed condition, the hori- <br />zontal extent of the coal aquifer recharge area was calculated as <br />50 feet wide and 23,000 feet long, covering 26.4 acres. Multi- <br />plying the infiltration capacity of 0.18 feet per year times 26.4 <br />acres, gives a recharge capacity of 4.75 acre-feet per year for the <br />coal aquifer prior to disturbance by mining. <br />Ground Water Storage Characteristics <br />Storage characteristics in the coal aquifer have been determined <br />from pump tests, as listed in Table 9, Kerr Mine Area Aquifer <br />Characteristics. The storage coefficient of the coal aquifer where <br />it is not faulted, is 6.8 x 10 4 (no units). The coal aquifer is <br />faulted in two locations in the mine plan area, both in Section 26, <br />T9N, R78W. The storage coefficient of the coal aquifer in <br />779-34 as <br />