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Drilling data and 40 years of observation indicate that the bedrock formation above and immediately below the mine workings are dry. Hydrologic communication with the Point Lookout sandstone formation, 275 feet below the seam being mined, is highly unlikely. Therefore, no impact to this ground water resource is anticipated from continued mining. The only ground water source having the potential to be impacted by mining operations is the alluvial aquifer of Hay Gulch. Therefore, the remainder of this analysis will focus on potential impacts to the alluvial aquifer of Nay Gulch. The alluvial aquifer of Hay Gulch averages 20 feet in depth, has a cross- sectional area of 25,200 square feet, a transmissivity valve of 70,400 gpd/ft and a storage coefficient value of 001. Flow through the aquifer was calculated to be about 2,661,120 gpd. Depths to the water table range from 1 to 3 feet, depending upon seasonal variation. The quality of water in the aquifer is poor with total dissolved solids valves of about 2500 mg/1. This poor water quality makes the water unsuitable for domestic and irrigation purposes, but suitable for stock watering. The aquifer appears to be recharged by runoff and from adjacent bedrock strata. The flow direction is downstream, to the southwest. The aquifer appears to provide baseflow for surface water further downstream, where an incised channel exists. Two areas of potential impact to the alluvial aquifer of Hay Gulch exist. They are: 1) further degradation of water quality as a result of leachate infil- tration from the mining bench, and 2) diminution of water quality as a result of ground water withdrawal. As stated above, there is the potential for a further degradation of the water quality of the Nay Gulch alluvial aquifer. Quality could possibly be degraded as a result of leachate from the mine bench entering the aquifer. The operation is so designed that all runoff from the bench is contained by the two sediment ponds located at the northern end of the disturbed area. Leachate from the runoff could enter the aquifer through seepage from the ponds. The Division finds that further degradation is highly unlikely because the amount of leachate entering the ground water system would be negligible when compared to the amount of water flowing through the aquifer. Therefore, rapid dilution would occur and the resulting impact would be insignificant. Addition- ally, the applicant has committed to seal the sediment ponds with an impervious material if water monitoring programs indicate that quality is being adversely affected. The second possible impact is the lowering of water levels in the aquifer of Hay Gulch due to pumping of the mine's production well. This well is a result of an agreement between the applicant, the landowner, and the local Soil Conser- vation Service office. It is hoped that pumping from the well will lower water levels in the aquifer such that the meadow would cease to be waterlogged. An analysis done by the Division using a calculator program developed for OSPf entitled, "Alluvial Valley Floor Aquifers" (OSM, 1981); indicated that the draw- down in the aquifer at a point 600 feet from the pumping well would be about 1.6 feet. This magnitude of drawdown should produce the desired result and still not affect the subirrigation potential of the aquifer. *Sandberg, R., P.B. Sheibach, D. Koch, and T.A. Prickett, 198I, Selected Hand-Held Calculator Codes for the Evaluation of the Probable Cumulative Hydrologic Impacts_ of Mining, Prepared for the Office of Surface Mining, Region V, Denver, Colorado, under Contract No. 55191334.