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3.2.2.2 Bedrock Aquifers <br />• Ground water in the Mesaverde Formation occurs in sandstone <br />strata and coal seams. Because of the lenticular character of <br />the sandstone strata and low hydraulic conductivity of the coal <br />seams, there is not a significant aquifer within or above the <br />coal member of the Mesaverde Formation. <br />The presence of ground water in the "D" coal seam was <br />verified in three out of four piezometers installed in the study <br />area. The coal seam was not saturated in only one piezometer (DH <br />63 C). Two falling head permeability tests in piezometers DH 82 <br />C and DH 83 C, installed in the "D" coa~ seam, indicted a range <br />of hydraulic conductivity of 1.1 x 10 0 1 6 x 10 ft/day and <br />transmissivity of 1.7 x 10-1 to 3.0 x 10-1 ft~/day. <br />Recharge to the bedrock aquifers is provided by a.direct <br />infiltration of precipitation and runoff at outcrops and subcrops <br />underneath the colluvial sediments where saturated. Ground water <br />flow follows the dip of the bedrock strata, however, the flow is <br />very slow due to the low transmissivity. <br />Ground water in the coal and sandstone is of unconfined <br />character in a narrow zone near the outcrops and then of confined <br />character in the deeper portions of the basin. The <br />potentiometric surface in the "D" coal seam is slightly above the <br />• top of the coal. The highest head (~3 feet) was encountered in <br />piezometer DH 87. <br />Ground water in the bedrock aquifer is of bicarbonate, <br />sodium, sulfate type with a range of total dissolved solids from <br />375 to 5,540 mg/1. Concentration of total dissolved solids <br />increases with depth. Ground water samples from bedrock aquifers <br />were obtained from wells GR-77-7 (monitored since 1982), DH 60 <br />and DH 65. The range of pH is between 7.4 and 8.6. <br />3.3 Impacts of the Proposed Construction on Ground Water <br />Colorado Westmoreland, Inc, proposes to open new entries <br />into the Orchard Valley mine from a bench located in the central <br />part of the East Roatcap Creek drainage. The area of the bench <br />will be approximately 4.8 acres. The bench will be constructed <br />cross-valley with a cut approximately equal to the fill. Most of <br />the excavation will be in the colluvial sediment (808) and only a <br />small portion (209) in the bedrock. <br />Results of drilling investigation, boreholes DH 83 S, DH 84 <br />C and DH 88 S in particular, indicated that the thickness and <br />saturation of the colluvial sediments in the area of the proposed <br />construction are reduced. <br />. It seems that most of the cut area in both colluvium and <br />bedrock will be dry during excavation, assuming that the <br />construction will be completed during the dry season of the year. <br />Only a limited period of ground water level monitoring is <br />15 <br />