Laserfiche WebLink
conditions are encountered neaz the outcrops. The saturated aquifer thickness of these units ranges <br />between four and 200 feet. <br />The Wadge Coal aquifers appeazs to be largely confined, whereas the Wadge Underburden aquifer <br />occurs under both confined and unconfined conditions. The Wolf Creek Coal occurs under confined <br />conditions, however the Wolf Creek Underburden is both unsaturated and unconfined. <br />Movement of groundwater in bedrock aquifers is controlled by structural folding and faulting and <br />stratigraphy. Confined conditions occur at synclinal axes, and unconfined conditions occur near the <br />outcrops. No significant faulting is known to occur within the proposed permit area. <br />Two recharge boundazies are known to exist in the permit area. An erosional face along the <br />northerly-plunging axis of the Fish Creek anticline provides a localized recharge boundary for the <br />Wadge Coal and Wadge Overburden. Additionally, the Wolf Creek Coal outcrop, parallel to the axis <br />of the Fish Creek Anticline, is a recharge boundary For the Wolf Creek Coal. <br />In general, the Williams Fork Formation, which includes the Twentymile Sandstone and the Middle <br />Coal Group has yields of up to 100 gpm but the average yield is approximately 10 gpm. The <br />underlying Trout Creek Sandstone has a yield of approximately 5 gpm and occurs under confined <br />conditions with an artesian head of 30 feet abou•e the ground surface. <br />Alluvial aquifers in the proposed permit area include the Sage Creek alluvium, Annand Draw <br />alluvium and Grassy Creek alluvium. The Sage Creek Alluvium has a saturated thickness of <br />between 7.5 and 56 feet. Annand Draw alluvium and Grassy Creek alluvium have saturated <br />thicknesses of 12 and 11-28 feet, respectively. Groundwater occurs under unconfined conditions in <br />the alluvial aquifers. <br />Movement of groundwater in the alluvial aquifers is controlled by the characteristics of the stream <br />drainages within which they occur, including the stream gradient as well as the width, thickness and <br />hydraulic conductivity of the alluvial deposits. Recharge to alluvial aquifers occurs as infiltration <br />from snowmelt and precipitation and as seepage losses from streams. <br />Baseline groundwater quality studies for the Yoast mine included the alluvial aquifers, the Middle <br />Coal Group, and the Trout Creek Sandstone. The following table summarizes baseline data for pH, <br />SOa, and total dissolved solids (TDS) for the units mentioned above. <br />Yoyi~ Minz ] ~ March 6.?001 <br />