GENERAL30618 - Laserfiche WebLink

Home Browse Search

-23- Overlying the Upper Coal Member is the Barren Member of the Mesa Verde Group. This unit consists of interbedded sandstones, siltstones, shales, and coals. The unit is not thought to be of marine origin and, as a result, the sandstones and the coals are highly lenticular, discontinuous, and of limited lateral extent in outcrop. This unit ranges up to 1,500 feet thick and outcrops throughout most of the five year permit area. Ground water occurs in both the sandstones and the coal seams of the Mesa Verde Formation. Regional ground water movement is northeasterly, down the dip of continuous stratigraphic units. Local ground water movement is controlled by topography, faults, fractures, and discontinuous lenticular sandstones. The most continuous sandstone aquifers of any significance in the region are the Rollins Sandstone and the massive sandstone separating the Upper and Lower Coal Members of the Mesa Verde Formation. However, the latter massive sandstone produces very little water, as evidenced by the dryness of the Bear Mine and the lack of springs associated with this unit. Coal seams within the Mesa Verde Formation also act as continuous aquifers. The Barren Member of the Mesa Verde Formation contains lenticular channel sandstones, some.of which may have sufficient length and thickness to transmit ground water flows regionally. Regional ground water aquifers are recharged along outcrops and subcrops beneath the alluvium of streams to the southwest of the permit area within the Minnesota Creek Basin. However, due to the steepness of topography in the outcrop areas, (i.e. sandstones are ledge formers), and narrowness of the stream valleys, these regional aquifers receive little recharge. Some recharge to the continuous units and much of the recharge to the more discontinuous, lenticular units will come directly from the percolation of snowmelt and precipitation downward through sands and along fractures. Preliminary pump tests conducted by WECC indicate the transmissivity of the F-seam to be 16.68 g/d/ft and that of the Barren Member to be 2.46 9/d/ft. A piezometric surface map for the combined F seam and Barren was submitted by WECC. Movement is likely to be very slow on a regional basis and to the north east along dip. Locally, water flow through fractures probably occurs more rapidly, as suggested by the seasonal fluctuation in discharge rates of some springs in the mine plan area. The direction of migration of water in the coal seams and larger sands will probably be northeasterly in the direction of dip. However, based on hydrologic monitoring data, in the Barren Member there appears to be a ground water divide approximately following the topographic divide separating the North Fork from Minnesota Creek. South of this divide, ground water in the Barren Member flows toward Minnesota Creek. All Bear Coal Company mining operations are north of the Minnesota Creek divide. Discharge of ground water occurs through numerous seeps and springs. Additional springs are identified on Table 2.8.1.0. Flows from these springs range up to 60 gpm during spring runoff, however, most observed flows are significantly less.