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• Wells are monitored on a monthly basis for water levels. These levels are adjusted to mean sea <br />elevation. Water quality samples, when collected, will be analyzed for the parameters listed in <br />2.04.7.2. Table 2.04.7-1 gives the frequency of water level monitoring, sampling and analysis. <br />PROBABLE HYDROLOGICAL CONSEQUENCES <br />A discussion of the probable hydrologic consequences and reclamation plan are contained in <br />Section 2.05.6(3) and Section 2.05.6(3)(b)(v) of the permit application document. The following <br />discussion is intended to supplement the description of potential impacts of mining and mitigation <br />ofthese potential effects. The determination of significance has been made considering the impact <br />on the quality of the human environment, existing water uses, and the intended post mining land <br />use of the area. <br />Interruption of groundwater flow and drawdown. In order to develop the impact assessment <br />• for groundwater quantity, two different analyses techniques were utilized. First, pit inflow volumes <br />were determined on an annual basis using an analytical approach developed by McWhorter, 1982. <br />The second analysis involved the determination of annual pit inflow rates and annual drawdowns <br />in the adjacent overburden and coal aquifers as a result of the pit inflows. This analysis utilized the <br />USGS 3-dimensional finite-difference groundwater flow model MODFLOW. <br />Transient simulations were performed for alive-year period, using the maximum drawdown <br />estimates for the overburden and coal. These drawdown results are expressed as a maximum at <br />the pit and are expressed as a conical depression which results in decreased drawdown at further <br />distance from the mine. For the overburden, the pit drawdown was 5 feet for years 1 and 2, 8 feet <br />during year 3, 15 feet during year 4, and 30 feet during year 5. The drawdown for the coal <br />simulation was 8 feet during year 1, 5.8 feet during year 2, 6 feet during year 3, 7.3 feet during year <br />4, and 8 feet during year 5. The zero impact contour for the overburden and coal after five years <br />of mining is approximately 4,000 feet. The overburden and coal drawdown contours do not <br />intersect any of the boundaries, therefore, no impact of the San Miguel River from drawdown in the <br />deeper part of the overburden or coal is predicted. Shallow aquifer flow into Tuttle and Calamity <br />Draws in the vicinity of the pit will be decreased, but will be offset by pumpage from the pit. <br />• (REVISED 18 Aug 2003) 2.04.7-45 <br />