Mettiki Mine Post-Operation Monitoring

Objectives

The Mettiki mine is entering the last phase of operation, and will soon be shutting down. 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.

Two 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 work consists of three components, the first being the evaluation of existing monitoring wells, and the other two components consisting of surface-water monitoring for stage and discharge, and ground-water-level monitoring.

Evaluation of Existing Monitoring Wells
A network of wells has been used to monitor the ground-water levels in the area of the Mettiki mine for 25 years. Many of these wells have been directly or indirectly impacted by mining operations. Some may no longer be effective or representative of true ground-water levels, or may intercept mine shafts or tunnels. Therefore, before recovery monitoring begins, an evaluation of existing wells would be completed to determine the status of each of these wells. The first step to be completed will be geophysical logging by 3-arm caliper for each of the wells. In the next couple of years, those wells that would appear to be useful for monitoring, borehole video imaging and single-well aquifer testing will be completed for further evaluation and to determine if any well development will be necessary.

Five days for logging rig, operator, travel, etc. is planned in the field for three-arm caliper logging, with two additional days planned for office work for field preparation, generation of final logs, etc. Paper copies of the logs will be provided. This assumes all existing wells could be logged.

Surface-Water Monitoring
The surface-water monitoring program would document the changes to surface-water flow based on the cessation of pumping from within the mines (i.e. changes in direct discharge into the streams) and ground-water-level recovery (i.e. changes to baseflow to the streams) by measuring stage and calculating discharge. Two existing surface-water gages, at Laurel Run at Dobbin Road and McMillan Fork, will require routine maintenance runs, usually every six weeks, quality assurance/quality control check of data, and publishing the data in the USGS MD/DE/DC District Annual Data Report.

Ground-Water Monitoring
The wells that for the monitoring program will be selected based on criteria to be developed in conjunction with the MDE, the MGS and the USGS. These costs assume field measurements, QA/QC check of data, and publishing the data in the USGS MD/DE/DC District Annual Data Report. Since the mine is still actively pumping, the currently measured schedule of once every three months will be adequate. If pumping ceases, a more intensive measuring of water levels with one continuous recorder and more frequent hand-held measurements for the other monitoring wells is recommended. For this year, measurements in only ten wells once every three months are assumed to be needed after the evaluation of the existing network is completed.