2010-11-16_PERMIT FILE - C1996083A (22)

Home Browse Search

2.04.7 Hydrology Description Ll The areas of the colluvial- alluvial sediments in Hubbard Creek and Terror Creek lie below the coal seam to be mined. Protection of these sediments is provided by limited extraction zones under the Creeks and assuring the projected extent of subsidence is 100 -feet from the centerline of the Creeks. Mesaverde Formation - Perched Groundwater All of the mines in the region report a similar experience as that observed at the Bowie No. 2 Mine. The Mesaverde formation does not contain extensive aquifers. Typically, the formation is dry or the rock units are of such low permeability they yield insufficient water for sustained use. Even the extensive Rollins Sandstone, the recognized aquifer in the region, is highly cemented and a low producer. Groundwater occurrences within the Mesaverde Formation have been interpreted from monitoring holes and logs run during the exploration drilling process (refer to Geology Map 07). From the monitoring holes, water quality samples were obtained and static water levels or potentiometric elevation data were noted. The data shows there is also groundwater in the coal seams. In addition, file research was done on the logs of the exploration drill holes to detect static water levels noted during drilling or logging. From the available information east of Terror Creek, two saturated horizons within the Mesaverde Formation, above the Rollins Sandstone, were interpreted. Both are characterized as locally discontinuous saturated strata occurring as perched horizons. One is stratigraphically between the Rollins Sandstone member and the "C" coal seam, typically 200 ft. below the "D" coal seam (refer to the potentiometric surface presented on Map 11, Lower Perched Water Zone). The other, is located above the "D" coal seam (refer to the potentiometric surface presented on Map 10 Upper Perched Water Zone). The "D" coal seam is located 400 feet above the Rollins Sandstone and is separated from the Rollins Sandstone by sandstones, siltstones, clays, and coal seams. A potentiometric surface map of the D -Seam is presented on Map 10B. Maps 10 and 11 were prepared utilizing exploration data obtained from static water measurements from monitoring wells and, geophysical logging and drill logs. A table entitled "Static Water Levels in Exploration Drill Holes" located in Volume III, Exhibit 3, was compiled primarily from geophysical logs run during the exploration process. In some older drill holes on the site, few field records of the type and amount of drilling fluid, casing (if any), and logging activities are available. Although, the drill medium is usually noted on the electric logs (if available). More documentation exists for the more recently drilled holes. Many of the deeper PR -12 2.04-34- 07/10 A PfR6v6D '