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are locally present in stream valleys. Recent colluvial slides and slumps may also be present in <br /> canyons and gulches throughout the area. <br /> The Seneca II Mine extracted coal on approximately 1,800 acres of land that was transferred to <br /> the PSCM. Coal seams were surface mined at the Seneca II Mine from the lower member of the <br /> Williams Fork Formation. The lower member of the Williams Fork Formation is approximately <br /> 300 feet thick in the permit area. Approximate thicknesses of the coal seams, in ascending <br /> stratigraphic order are: the Wolf Creek seam, 15 ft; the Wadge seam, 10 ft; and the Lennox seam, <br /> 4 ft. Shale, siltstone, and sandstone separate the coal seams. The Wadge seam is approximately <br /> 150 above the Wolf Creek seam and approximately 40 feet below the Lennox seam. The PSCM <br /> will mine coal from the Wadge seam in the Hayden syncline. <br /> Groundwater <br /> Groundwater hydrology information can be found in section 2.04.5 of the permit application. A <br /> "hydrostatigraphic unit" is a group of stata which has hydraulic continuity. Hydrostatigraphic <br /> units in and adjacent to the permit area that may serve as aquifers are (in ascending stratigraphic <br /> order): the Trout Creek Sandstone member of the Iles Formation, coal and sandstone beds in the <br /> lower member of the William Fork Formation, the Twentymile Sandstone member of the <br /> Williams Fork Formation, alluvial bodies in local drainages, and coal spoil backfill in reclaimed <br /> surface mine pits from the Seneca II Mine. <br /> The sandstone and coal hydrostratigraphic units are referred to in this discussion as bedrock <br /> units. Of the bedrock units, the Trout Creek and Twentymile Sandstone have the greatest <br /> potential for serving as regional aquifers because individual sandstone beds in these units are <br /> thicker and more homogenous over wider areas than individual sandstone or coal beds in the <br /> lower member of the Williams Fork Formation. All the bedrock units have low hydraulic <br /> conductivity values, resulting in initial well yields in the vicinity of the PSCM permit area of less <br /> than 20 gallons per minute. Alluvium in Grassy Creek and Fish Creek may yield water to wells <br /> in limited usable quantities. <br /> Backfilled surface mine pits on lands of the Seneca II Mine that were transferred to the <br /> PSCM discharge coal spoil leachate to the land surface at five locations in the Little Grassy <br /> Creek drainage. Sample data from the springs from 2005 through 2008 showed flows in the <br /> range of 0.4 to 290 gallons per minute. Flows varied seasonally,peaking in the spring and <br /> diminishing to a minimum by late summer. Spoil leachate also seeps to the Phase III released, <br /> Pond 004 in the Fish Creek drainage. Coal spoil leachate flowing into Ponds 002, 004, and the <br /> PeCoCo pond in the PSCM permit area maintain permanent pools in the ponds and can cause the <br /> ponds to discharge. <br /> Groundwater in the non-coal bedrock units is characterized by total dissolved solids in the 500 to <br /> 2,400 mg/l range,pH between 7 and 9, and a naturally high magnesium content. Groundwater in <br /> coal has characteristics similar to the non-coal bedrock units, but TDS is as much as 3,670 mg/l. <br /> The groundwater in the bedrock units is primarily a sodium bicarbonate-type, with local <br /> gradation to calcium magnesium sulfate. Groundwater in Grassy Creek and Fish Creek alluvium <br /> is an alkaline calcium magnesium sulfate water with TDS that ranges between 300 and 4,000 <br /> 5 <br />