PROJECT OBJECTIVES
During the shutdown phase, dewatering operations will cease, allowing the mined shafts and layers to refill with ground water. Surface-water discharge should significantly decrease during this phase with the cessation of dewatering operations, but may gradually resume once the pre-mining ground-water levels are neared. The monitoring of the rate and extent of recovery of ground water within and near the mine, and the impact of the water-quality changes on surface water are of a regulatory and scientific interest.
The USGS will monitor the recovery of ground water outside of the mine, and within the mine itself. The recovery of the ground-water levels and changes in ground-water quality will provide the Maryland Department of the Environment, Bureau of Mines (MDE-BOM) information as to when steady-state recovery will be reached, and provide additional information on the long-term impacts the mine has in the area. In addition, the recovery of the ground-water-flow system in the areas impacted by the longwall mining method has not been monitored extensively in the U.S. The more than 25 years of monitoring during operation by the MGS and the USGS provides a unique opportunity to study the changes on a large-scale coal-mined, ground-water system. The hydrologic significance is to monitor the changes to surface and ground water as a mine-stressed system recovers to a post-mined stressed system with the corresponding hydraulic changes.
One of the three streams that have been the primary discharge point for the dewatering operations will continue to be monitored for stage.
STATEMENT OF PROBLEM
To monitor ground- and surface-water impacts through the closure for the Mettiki Coal Corporation mine in Garrett County, Maryland. The intention of this project is to continue the long-term monitoring program to monitor the effects of continued mining and to begin collecting the data necessary to assess the hydrologic effects of a coal mine as operations cease
STRATEGY AND APPROACH
The approach for the USGS is to (1) conduct water-quality sampling and testing of ten wells that overlie or penetrate below the piezometric level of the mine pool, (2) conduct periodic groundwater-level monitoring at seventeen USGS wells in the project area, (3) continue operation of the surface-water discharge station in McMillan Fork, and (4) obtain eight surface water quality grab samples from the North Branch Potomac River watershed for water quality testing that includes most of the same parameters being tested in the ground-water samples.
| Groundwater-Quality Profiling |
| Water-quality samples will be collected at selected wells where water level is currently monitored. Samples will be collected from 10 existing wells using passive diffusion. Samples will be analyzed for pH, specific conductance, and concentrations of trace metals and major ions. Trace metals will be determined using inductively coupled plasma- mass spectrometry. Water extracted during testing will be monitored for ambient pH and specific conductance. Data collected by the USGS will be used by MDE to determine the relationship between chemistry of the mine pool and water in overlying strata, and to provide a vertical profile of ambient water-quality characteristics that may reveal spatial patterns and subsurface hydraulic connections in the study area. |
| Surface Water Sampling |
| Water-quality samples and discharge measurements will be collected at 7 selected locations in the North Branch Potomac River watershed during the same period samples for the groundwater Water-Quality Profiling are being collected. 3 of the 7 sites sampled (main stem points of the Potomac) will have unfiltered iron added to existing lab schedules. Samples will be analyzed for pH, specific conductance, and concentrations of the same trace metals and major ions as thegroundwater samples. The data will be used by MDE to compare surface water chemistry in the watershed to the ground water chemistry of the mine pool and overlying strata to provide a more detailed profile of ambient water-quality in the study area. |
| Ground-Water Level Monitoring |
| Current mine pumping is maintaining the pool elevation at a relatively constant elevation, therefore it is anticipated that ground water levels should be somewhat stabilized. Water levels in 17 existing wells will be measured 4 times during the study year. Sample dates will be selected to reflect anticipated highest, lowest and intermediate levels. Field measurements and data quality-assurance checks will be used by USGS to prepare the hydrologic records for publication. |
| Surface-Water Monitoring |
| The surface-water monitoring program will allow MDE to document the changes to surface-water flow based on the cessation of pumping from within the mines. These changes may result from changes in direct discharge from mine pumping and baseflow from ground-water-level recovery. One existing surface-water gage, at McMillan Fork will be used to determine discharge from continuous (15 minute intervals) measurements of stage. Ratings of stage and discharge are to be maintained through routine servicing (usually every six weeks), discharge measurements at a range of stage conditions, quality assurance checks of data, and preparing hydrologic records for publication. |
