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2.04.7 Hydrology Description <br />probably a function of return irrigation flows and well completion depths near the <br />alluvium-Mancos shale contact. <br />Localized Alluvium-Colluvium <br />Localized deposits of alluvium-colluvial material reworked by fluvial processes <br />are present within the area, primarily within the Hubbard Creek, and Terror Creek <br />drainages. Hydrologic testing in similar material performed by Colorado <br />Westmoreland Inc. (CWI) during development of their Steven's Gulch well field <br />showed that yields from these sources are moderate (27 gpm at Steven's Gulch <br />well field), with transmissivity values ranging from 187 to 230 sq. ft. per day, and <br />storage coefficient of 0.0002. Water from wells penetrating this lithotype are <br />classified as sodium bicarbonate (Brooks, 1983). Recharge is accomplished <br />from precipitation and run-off, and water is discharged from seeps or springs. <br />Although similar in some respects, these areas do not fulfill the requirements of <br />being Alluvial Valley Floor areas. <br />Several years of water table monitoring in the CWI wells installed in the Steven's <br />Gulch indicated the water level in this aquifer is below the local streambed for <br />most of the year, and therefore the streams are recharging the aquifer. <br />The areas of the colluvial-alluvial sediments in Hubbard Creek and Terror Creek <br />lie below the coal seam to be mined. Protection of these sediments is provided <br />• by limited extraction zones under the Creeks and assuring the projected extent of <br />subsidence is 100-feet from the centerline of the Creeks. <br />Mesaverde Formation -Perched Groundwater <br />• <br />All of the mines in the region report a similar experience as that observed at the <br />Bowie No. 2 Mine. The Mesaverde formation does not contain extensive <br />aquifers. Typically, the formation is dry or the rock units are of such low <br />permeability they yield insufficient water for sustained use. Even the extensive <br />Rollins Sandstone, the recognized aquifer in the region, is highly cemented and a <br />low producer. <br />Groundwater occurrences within the Mesaverde Formation have been interpreted <br />from monitoring holes and logs run during the exploration drilling process (refer to <br />Geology Map 07). From the monitoring holes, water quality samples were <br />obtained and static water levels or potentiometric elevation data were noted. In <br />addition, file research was done on the logs of the exploration drill holes to detect <br />static water levels noted during drilling or logging. From the available <br />information, two saturated horizons within the Mesaverde Formation, above the <br />Rollins Sandstone, were interpreted. Both are characterized as locally <br />discontinuous saturated strata occurring as perched horizons. One is <br />stratigraphicallyhetween the Rollins Sandstone member and the "C" coal seam, <br />typically 200 ft. below the "D" coal seam (refer to the potentiometric surface <br />presented on Map 11, Lower Perched Water Zone). The other, is located above <br />the "D" coal seam (refer to the potentiometric surface presented on Map 10 <br />PR-10 2.04 - 26 - 09/26/08 <br />ft? FPRo v~l> <br />~l~-y~~s <br />