REV105747 - Laserfiche WebLink

Home Browse Search

" Dudaslt Page 2 January 19, 1999 On page 2.0~-72 and 2.05-74, BRL very brietly addresses the potential for off-site migration of groundwaterfrom the abandoned worki ngs. BRL states that the only potential impact the mine will have on groundwater is to intercept it in the underground workings, and the abandoned mine workings would not be expected to transmit water to the surrounding strata. BRL further indicatesthat there are no data for pemieabilityor transmissivityof the saturated portions of the coal bearing member of the Mesaverde Formation available within the permit area. No monitoring has been provided in the "D" seam down gradient of the mine workings to verify these conclusions or assess potential impacts. An additional downgradient monitoringwell is recommended. The well should be constructed such that the perforated interval of the casing is installed across the entire thickness of the "D" seam strata. 2. An Upper Perched Water Zone is discussed on page 2.04-25 of the revised permit text and Map 10 shows a potentiometric surface for this water bearing zone. Based on the information presented, it appears that this perched water zone may be a major source for water flowing into the mine workings below. Based on a predicted mine discharge rate of 175 gallons per minute, this inflow may be substantial. With the exception of DH-39 and DH-49, all of the "D" ,seam overburden wells have been destroyed or removed by construction. DH-39 and DH-49 are located up gradient of the mine workings and possibly outside of the area that may be influenced by mining. It appears likely that the Upper Perched Water Zone may be dewatered due to mining operations. Are there existing wells that will provide adequate and continued monitoring of the Upper Perched Water Zone? If adequate monitoring of this water zone is not provided, an alternativemay be to include mine inflow monitoring and reporting to the approved water quality monitoring program. It is recommended that for flows of sufficient discernable volume (>Sgpnr), an initial sample should be obtained for laboratory analyses and then sampled annually thereafrer. The pazameterlist should be the same for the groundwater list currently used. Field parameters (pH, conductivity, and temperature) and inflow rates should be measured quarterly and reported in the AHR. The mine inflow monitoring should include all significant sources of inflow. As indicated on page 2.05-67, in addition to water moving from formations above the coal seam, some water may occasionally seep into the mine from the coal seam and surrounding strata. 3. The Probable Hydrologic Consequences and the Hydrologic Reclamation Plan presented with the revised text do not adequately address the potential for perpetual discharge from the