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beds in these units are thicker and are more homogeneous over wider areas than individual sandstone <br />or coal beds in the lower member of the Williams Fork Formation. All of the bedrock units have low <br />hydraulic conductivity values, resulting in initial well yields in the vicinity of the PSCM permit area <br />of less than 20 gallons per minute. The presence of natural fractures in the bedrock at a well location <br />can enhance yield. Actual hydraulic conductivity values and ground water flow velocities may be <br />significantly greater than shown in Table 1 (perhaps by an order of magnitude) because the data are <br />from slug and production tests of wells that probably had significant formation damage caused by <br />plugging of porosity with drilling mud and/or migration of fine-grained pore-fill (e.g., kaolinite). <br />Alluvium in Grassy Creek and Fish Creek may yield water to wells in limited usable quantities <br />where alluvium is sufficiently thick. <br />Backfilled surface mine pits on lands of the Seneca II Mine that are proposed for transfer to the <br />PSCM discharge coal spoil leachate to the land surface at five locations in the Little Grassy Creek <br />drainage. Sample data from the springs from 2005 through 2008 showed flows in the range of 0.4 to <br />290 gallons per minute. Flows varied seasonally, peaking in the springtime and diminishing to a <br />minimum by late summer. Spoil leachate also seeps to pond 004 in the Fish Creek drainage. Coal <br />spoil leachate flowing into Ponds 002, 004, and the PeCoCo pond in the PSCM permit area maintain <br />permanent pools in the ponds and can cause the ponds to discharge. <br />Ground water 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. Ground watger in <br />coal has characteristics similar to the non-coal bedrock units, but TDS is as much 3,670. The ground <br />water in the bedrock units is primarily a sodium bicarbonate-type, with local gradation to calcium <br />magnesium sulfate. Ground water in Grassy Creek and Fish Creek alluvium is an alkaline calcium <br />magnesium sulfate water with TDS that ranges between 300 and 4,000 mg/l. Spoil leachate is an <br />alkaline calcium-magnesium sulfate type water, with total dissolved solids in the 2,600 to 4,300 mg/1 <br />range. <br />Bedrock hydrostratigraphic units in the vicinity of the PSCM permit area are likely recharged by <br />meteoric waters wherever a significant quantity of snowmelt or rainfall accumulates on bedrock <br />outcrops at high elevations around the perimeter of the Hayden Syncline. The water seeps into the <br />rock through intergranular porosity and fractures. Immediately downdiip from a recharge area, the <br />bedrock is under water table conditions. From a recharge area, bedrock ground water flows under <br />the force of gravity generally downdip, toward the deeper part of the Sand Wash Basin (or <br />Twentymile Park east of the permit area) where the ground water is under confined conditions. The <br />head (hydraulic pressure) at a location in a basin is determined by the height of the recharge areas <br />above that location and the proximity to discharge areas. Bedrock units discharge ground water at <br />low elevations in a basin wherever the units crop out or have a subcrop underneath the younger <br />colluvium and alluvium. The dissolved solids content of ground water in bedrock units generally <br />increases basinward from the recharge areas. <br />The potentiometric surface of ground water in the confined portions of the bedrock units slopes <br />generally basinward. Local relief on the potentiometric surface probably mimics the overlying <br />topography, with potentiometric highs and lows roughly coinciding with the overlying highs and <br />lows of the land surface. Ground water flow velocity in bedrock units probably is on the order of a <br />Peabody Sage Creek Mine 6 May 7, 2010