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The lower and upper coals of the upper Williams Fork formation produce <br />marginally potable wa~er of limited quantity. Hydraulic conductivity values <br />range from 1.6-175 ft /day. The excavation of the recharge area will change <br />its physical properties and the quality of water which can be recharged. As <br />there are no users of the aquifer downdip of the Hayden Gulch Mine, any <br />impacts will be insignificant. <br />The Twentymiie Sandstone lies below the Lower Coal of Hayden Gulch and is <br />separated by 200-300 feet of interbedded sandstones and shales. The <br />Twentymile Sandstone stratigraphically lies 525 feet above the Wadge Coal (the <br />principal seam to be mined at Seneca II-W), but it has been eroded over much <br />of the Seneca II-W area. This regional aquifer will not be disturbed by <br />either mining operation, and hence its water quality and quantity will not be <br />affected. <br />The sediments associated with the Lennox and Wadge coal seams may contain <br />perched aquifers as Wadge Coal. The strata does not contain or transport <br />significant volumes of water in this area, although it has been known to in <br />other locations. <br />The Wolf Creek coal seam, which lies 150 to 170 feet below the Wadge coal <br />seem, is the first significant aquifer below the mined seam at Seneca II-W. <br />This seam, which is up to twelve (12) feet thick, appears to be saturated in <br />this area. Due to the dip of the unit and the confining nature of the over <br />and underburden, the Wolf Creek has as much as 770 feet of artesian head in a <br />well. It should be noted that the amount of head is aerially variable as the <br />aquifer's conditions change from water table (unconfined) near outcrops to <br />confined conditions at depth. <br />The aquifer characteristics of the Wolf Creek (low transmissivity and <br />storativity values) indicate that very little water is available for upward <br />movement. Due to mining methods and the thickness and type of interburden <br />between the Wol# Creek and Wadge, pit inflows at Seneca II-W, from upward <br />movement of the Wolf Creek, are not expected. <br />About 200 feet below the Wadge coal lies the Trout Creek Sandstone. The <br />relatively impermeable interburden between the Wadge coal and the Trout Creek <br />Sandstone (which includes the Wolf Creek coal) and the stratigraphic distance <br />between them will preclude impacts to the Trout Creek Sandstone from mining. <br />The Tow Creek Sandstone lies more than 1300 feet below the tJadge coal. Due to <br />the thickness of the interburden between the Tow Creek and lJadge, it is not <br />likely that hydraulic pressures capable of affecting this aquifer will develop. <br />On summary, there is little likelihood of cumulative impacts to bedrock <br />aquifers from mining by the Hayden Gulch Mine and Seneca II-W Nine for several <br />reasons. The transmissivity and storativity values of the ididdle and upper <br />tdesaverde formations are low. There are only three regional aquifers, and <br />they are hydrologically separated from mining impacts by sediments of <br />considerable thickness and low permeability. There are few reported faults in <br />the region and low vertical permeabilities. <br />-22- <br />b - . <br />