Laserfiche WebLink
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 a five-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 intersect <br />any of the boundaries, therefore, no impact of the San Miguel River from drawdown in the deeper <br />part of the overburden or coal is predicted. Shallow aquifer flow into Tuttle and Calamity Draws in <br />the vicinity of the pit will be decreased, but will be offset by pumpage from the pit. Simulated <br />average daily pit inflow for the coal and overburden aquifers varied from 1,255 cubic feet per day <br />in year 1 to 5,604 cubic feet per day in year 5. WFC's approach to these potential impacts is to <br />monitor the aquifers and discharge from the pit to determine the extent of drawdown. The <br />hydrological monitoring program should provide reasonably accurate measurements of effects of <br />mining. Should the monitoring show that impacts to the groundwater aquifers are precluding its use, <br />WFC will provide alternate water sources of comparable quantity and quality. As described in the <br />water augmentation plan, WFC has a 114 acre foot consumptive use right on the Highline Canal <br />which would be used to mitigate the potential 26 acre foot impact on surface water right users from <br />pit inflow drawdown. <br />Impact on groundwater rights No surface or groundwater rights have been identified within the <br />New Horizon 2 mine area. Therefore, there will be no direct impact from the approved mining plan <br />on any local water rights. <br />Impact of spoil material on groundwater flow and recharge The mine pit will remain open only <br />REVISED JULY 2009 2.04.7-50 <br />r. <br />?n <br />i <br />I, <br />i