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gradients in the central area range from 0.09 to 0.12 ft/f t. Flow gradients in the • <br />southern area range from 0.10 to 0.12 ft/ft. The overall flow gradients for th e Wadge <br />overburden and Wadge coal aquifers are very siini lar; however, the potentiometric surface <br />for the Wadge coal in the southern area is approximately 100 feet higher than the surface <br />for the Wadge overburden. Both the Wadge overburden and the Wadge coal potentiometric <br />surfaces are influenced at the locations where the aquifers outcrop along the 006 <br />tributary and the aquifers appear to contribute to the local spring and alluvial flow at <br />these points. <br />The potentiometric surface for the Wolf Creek coal aquifer is shown on Exhibit 7-4. The <br />Wolf Creek coal potentiometric surface was constructed using the arithmetic mean of the <br />values for the period of record that are believed valid. Water in the Wolf Creek coal <br />aquifer is under confined conditions. Artesian heads rapidly increase in the direction of <br />dip with the smaller heads occurring near the crop. The direction of flow is principally <br />to the west. Flow gradients overall are less steep than those for the shallower aquifers. <br />This is because the deeper aquifers do not crop downg ra dient and are less influenced by <br />drainage erosion and channel incision. Flaw gradients range from 0.10 ft/ft in the • <br />northern area to 0.115 and 0.116 ft/ft in the southern and central areas, respectively. <br />The potentiometric surface for the Wolf Creek coal aquifer is approximately 100 feet <br />higher than the surface for the Wadge coal as one moves away from the crop and then they <br />become comparable further down dip. <br />Recharge. The primary sources of recharge to the alluvial aquifers at the Seneca II-W <br />Mine area are discharge from underlying bedrock aquifers and infiltration of <br />precipitation. Studies of the nearby Piceance Basin (which is climatically similar to the <br />Yampa River Basin) predicted an average recharge of 0.66 inches per year. (Weeks et. al., <br />1974), Based on this similarity, Warner and Dale (1982) used 0.5 inches as an annual <br />recharge rate for their groundwater simulation model of the Yampa River Basin. The <br />streams within Hubberson Gulch and Watering Trough Culch also may contribute to the <br />alluvial aquifer, although this contribution is thought to be small since these streams <br />are ephemeral. <br />Recharge to the hed rock aquifers primarily occurs as infiltration of rainfall and snowmelt <br />at outcrop areas which parallel the axis of the Sage Creek Anticline. Each of the bedrock <br />aquifers are separated by relatively impermeable confining layers which, in general, • <br />prevent inter-aquifer movement of gr•ou ndwate r. However, analysis of pumping test data for <br />20 <br />