Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, TN 429, 1994 Feb; :1-2
Objective: Determine the effectiveness of remining operations in reducing contaminant load (acidity, iron, and sulfate) of discharges emanating from abandoned surface and underground coal mines. Background: Until the implementation of remining initiatives, most States had regulations that held the operator remining an abandoned site responsible for preexisting acid mine drainage (AMD) discharges. For example, if a mining company wanted to remine an area hydrologically connected to an existing AMD discharge, the company became responsible, as soon as the site was activated, for treating that discharge to meet effluent standards. If the mining operation improved the quality of the discharge, but the discharge failed to meet effluent standards, the company was held accountable for perpetual treatment. Because of this regulation, most mine operators avoided abandoned sites with minable coal reserves and AMD discharges. However, changes in remining legislation allow coal companies to be released from treatment liability as long as the post-remining pollution load does not exceed the pre-remining level. If remining can improve water quality through improved mining and abatement techniques, abandoned mine land (AML) areas that previously were liabilities could become assets. Abandoned mine sites eligible for remining are geographically widespread and areally extensive. For example, over 29,000 kilometers of abandoned highwalls are currently estimated to exist in the Appalachian region, and a significant portion of this land could be economically reclaimed through remining. If abandoned sites can be reclaimed by remining, without the use of AML funds, more AML funds would be available for reclaiming additional areas. In addition, coal reserves, which have not been economically minable because of the potential discharge treatment liability, would be available. Approach: U.S. Bureau of Mines researchers analyzed the quality and flow rates of discharge water before and after remining operations in Pennsylvania, using several statistical methods, including exploratory data analysis, nonparametric upper prediction limits, and the Mann-Whitney U test. They evaluated water quality characteristics before and after remining, pollution abatement techniques, methods of statistical analysis, and pre-remining sampling schemes. Results: Water Quality Analyses of the contaminant concentrations, loading rates, and flow rates of mine discharges indicated that remining is successful overall in preventing additional ground and surface water degradation. Most discharges had post-remining pollution loads equivalent to or less than the pre-remining levels. At some discharges, significant degradation appears to have occurred; however, short-term or transient changes (less than 1 year) in flow and/or concentration arc the primary reasons for the degradation. The most common reason for a significant change in pollution load (increase or decrease) was a change in the discharge flow rate. Contaminant concentration was a subordinate factor in some cases. However, concentration may play a stronger role when a significant increase rather than a decrease in pollution load is indicated. Pollution Abatement Techniques: Because the mine discharge flow rate exerts a strong control on the pollution load, reducing flow through mining and/or reclamation practices will improve the probability that the operation will not incur long-term treatment liability. With this knowledge, mine operators may be more willing to enter into remining permits and regulating agencies may be more willing to issue them. Discharge flow-reduction practices can be incorporated into the permit-application abatement plan. Abandoned surface mines, prior to remining, commonly have unreclaimed open pits and closed-contour depressions in poorly sorted spoil that can serve as ground water recharge zones. For many abandoned surface mines, regrading spoil will greatly reduce surface water infiltration and increase runoff by eliminating these recharge zones. Regrading spoil to eliminate closed-contour depressions may be the most viable option because it is the least expensive method of reducing surface recharge and it is necessary to satisfy the reclamation requirements. Flow can also be reduced by diversion of recharging ground and surface waters away from the reclaimed site. Methods that decrease recharging surface waters include installing diversion ditches, capping the site with a low-permeability material, regrading spoil, and revegetating. Methods for decreasing recharging ground waters to the spoil include installing drains and/or grout curtains at or near the final highwall, using horizontal free-draining dewatering wells, and sealing adjacent underground mine entryways exposed during mining. Where remining exposes underground mines, sealing entryways may be the least expensive and most viable option. When remining on abandoned surface mines, installing a highwall drain may be the most viable option, if sufficient grade can be achieved to allow for a free-draining, low-maintenance system. Applicability: The study sites encompassed 21 coal seams and an extensive portion of the Pennsylvania bituminous coal fields. The geologic and hydrologic conditions are similar to those in other Appalachian coal mining States. Therefore, although this study was conducted exclusively in Pennsylvania, similar remining programs in other Appalachian States should be at least as successful in terms of pollution load reduction.