2010-12-09_GENERAL DOCUMENTS - C1982057

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4) the possible increase in water quantity and decrease in quality of alluvial water in Hubberson Gulch and its unnamed tributary along the access road, due to infiltration of spoils discharge; 5) the establishment of a relatively unconfined aquifer of poor quality in the backfilled pits. A discussion of the potential impacts follows. During mining, inflows may be expected to develop from perched aquifers within the Williams Fork overburden, from a limited Williams Fork overburden aquifer, and from the Wadge coal aquifer. Coal removal is by an updip strip method. As a general rule, more water will be encountered at the first cut than when the operation proceeds updip. Inflows from units underlying the Wadge are not expected, as mining methods should not cause fracturing of the relatively impermeable underlying materials. Regional aquifers located in or near the permit area include the Tow Creek Sandstone, Trout Creek Sandstone and Twenty Mile Sandstone. The Twenty Mile Sandstone lies stratigraphically above the Wadge coal (the seam being mined) by about 525 feet. The Twenty Mile Sandstone which has been eroded over much of the Seneca II-W Mine area will not be disturbed by mining operations, so its water quality and quantity will not be affected. The Tow Creek Sandstone lies more than 1300 feet below the Wadge coal. Due to the thickness of the interburden between the Tow Creek and Wadge, it is not likely that hydraulic pressures capable of affecting this aquifer will develop. Therefore, mining activities are not expected to disturb this regional aquifer. About 200 feet below the Wadge coal lies the Trout Creek Sandstone. The Trout Creek is thought to be an aquifer of regional significance, but is not monitored at this site. The applicant completed a water supply well in the Trout Creek from which they sustain an average pumping rate of 35 gallons per minute. The relatively impermeable interburden between the Wadge coal and the Trout Creek Sandstone (which includes the Wolf Creek coal) and the stratigraphic distance between them will preclude impacts to the Trout Creek sandstone from mining. The Wolf Creek coal seam, which lies 150 to 170 feet below the Wadge coal seam, is the first significant aquifer below the mined seam. This seam, which is up to 12 feet thick, appears to be saturated in this area. Due to the dip of the unit and the confining nature of the over and underburden, the Wolf Creek has as much as 770 feet of artesian head in a well. It should be noted that the amount of head is aerially variable as the aquifer conditions change from water table (unconfined) near outcrops to confined conditions at depth. Due to mining methods and the thickness and type of interburden between the Wolf Creek and Wadge, pit inflows from upward movement of the Wolf Creek are not Seneca II-W Findings Document 37 C1982057 Permit Renewal No. 5 December 9, 2010