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The sandstone and coal hydrostratigraphic units are referred to in this discussion as bedrock units. Of <br /> the bedrock units, the Trout Creek and Twentymile Sandstone have the greatest potential for serving as <br /> regional aquifers because individual sandstone beds in these units are thicker and more homogenous <br /> over wider areas than individual sandstone or coal beds in the lower member of the Williams Fork <br /> Formation. All the bedrock units have low hydraulic conductivity values, resulting in initial well yields <br /> in the vicinity of the PSCM permit area of less than 20 gallons per minute. Alluvium in Grassy Creek <br /> and Fish Creek may yield water to wells in limited usable quantities. <br /> Backfilled surface mine pits on lands of the Seneca II Mine that were transfered 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 290 <br /> gallons per minute. Flows varied seasonally, peaking in the springtime and diminishing to a minimum <br /> by late summer. Spoil leachate also seeps to Pond 004 in the Fish Creek drainage. Coal spoil leachate <br /> flowing into Ponds 002, 004, and the PeCoCo pond in the PSCM permit area maintain permanent pools <br /> in the ponds and can cause the ponds to discharge. <br /> Groundwater in the non-coal bedrock units is characterized by total dissolved solids in the 500 to 2,400 <br /> mg/l range, pH between 7 and 9, and a naturally high magnesium content. Groundwater in coal has <br /> characteristics similar to the non-coal bedrock units, but TDS is as much as 3,670 mg/l. The <br /> groundwater in the bedrock units is primarily a sodium bicarbonate-type, with local gradation to calcium <br /> magnesium sulfate. Groundwater 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 range. Spoil leachate is an <br /> alkaline calcium-magnesium sulfate type water, with total dissolved solids in the 2,600 to 4,300 mg/I <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 rock <br /> through intergranular porosity and fractures. Immediately down dip from a recharge area, the bedrock is <br /> under water table conditions. From a recharge area, bedrock groundwater flows under the force of <br /> gravity generally down dip, toward the deeper part of the Sand Wash Basin (or Twentymile Park east of <br /> the permit area) where the ground water is under confined conditions. The head (hydraulic pressure) at a <br /> location in a basin is determined by the height of the recharge areas above that location and the <br /> proximity to discharge areas. Bedrock units discharge ground water at low elevations in a basin <br /> wherever the units crop out or have a subcrop underneath the younger colluvium and alluvium. The <br /> dissolved solids content of ground water in bedrock units generally increases basinward from the <br /> 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 lows of <br /> the land surface. The alluvium of Grassy Creek and Fish Creek, and their tributaries, is either directly <br /> Op CO10 <br /> e <br /> 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 I `�' O <br /> �`1876� <br />