REP50182 - Laserfiche WebLink

Home Browse Search

Ground Weter Flow The direction of regional ground water flow in the permit area is eastward away from the center of the Raton Basin. Recharge is believed to take place largely in the western uplift area where the west limb of the syncline dips upward at close to 90°. The ground water flow systems within the permit area generally conform to this regional scheme although historic mining and local geology in the area have distorted the flow directions. The underground mines now act as large storage reservoirs and provide some degree o[ interconnection between various goal zones. Futhermore, the dikes and faults in the permit area, acting as low permeability barriers, tend to align the direction of ground water flow. Thus, bedrock ground water flows from the center of the Raton Basin, discharging along the subcrop limits o[ the water-bearing strata of the Vermejo Formation. Based on water inflows from drilling response tests and pump testing, the coal scams have been identified as the most permeable water-bearing strata. Other significant water-bearing strata include the Lennon sandstone which overlies the Lennon Coal Seam, and, at shallow depths, the Trinidad Sandstone which underlies the Vermejo Formation. Toble 1 is a compilation of the piezometers installed in this study, their locations, depths, strata and calculated values for hydraulic conductivity. Flow through sandstone units is primarily intergranular, following bedding plants. The shale beds of the Vermejo Formation in the permit area are generally discontinuous and interbedded with sandstone units having occasional sandstone layers that are quite massive. These shale beds are considered to be several orders of magnitude less permeable than coal or sandstone units and, hence, tend to act as aquitards. Although surface water flow is seldom recorded in Maitland and Gordon Arroyos, subsurface flow in the alluvium has been documented. The alluvium is generally unconfined and mostly unsaturated, therefore, no specific data exists on the range of hydraulic conductivities for these materials. The eastward gradient indicates ground water flow occurs along the base of the alluvial valleys. Seasonal water levels indicate that the water table fluctuates, corresponding to the rate of recharge from upstream. In the spring, the alluvium is more saturated than during the fall (see alluvial well data in Appendix 1). I The major features which influence ground water Clow in bedrock, and hence, affect piezometric elevations in the permit area are the dikes and faults that have intruded the local strata, Maitland and Gordon Arroyos that have eroded channels into the bedrock formations, and the underground mine workings that cross geologic units and boundaries. The dikes and faults are geologic barriers confining the local movement of ground water. The arroyos are in hydrologic communication with bedrock and coal bearing strata. Thus, to avoid substantial inflow, the arroyos were not historically undermined. These historic mine workings are now considered major hydrologic conduits. J To Cacilitate discussions, the mine area has bcen divided into three hydrogeologic sectors. These sectors are shown on Figure 1 and discussed below. Sector I ' Sector f is bounded by the dike along the southern boundary of the permit area and on the north by Maitland Arroyo. Three historic mines exist in this sector and are located in the Lower Robinson, Lennox and Cameron coal seams. The mines in the Lennox and Cameron seams are considered to be hydrostatically ' connected by either mine audits or numerous drillholes in the aria. Observation wells in the various strata throughout the sector all have similar static water levels indicating hydraulic interconnection (see water Icvel information for the 10 and 12 series wells, Appendix 1). it is significant to note that the static water level ' elevations Cor these coal seams are roughly at the same elevation at which each of the coal seams subcrop in the alluvium bentath Maitland Arroyo.