Chemical and physical controls on waters discharged from abandoned underground coal mines

Abstract

Abandoned up-dip drift mines in high-sulphur coal are a major source of acid mine drainage (AMD) in Appalachia. Studies of mines in the Monday Creek watershed of southeastern Ohio show that mines are recharged by surface runoff into subsidence features that dilate the natural stress-relief fracture system. The direct connection between the ground surface and the mines leads to a rapid response in the hydrograph, with a one- to four-day lag between precipitation and corresponding peak mine discharge. Subsidence occurs in topographic depressions where overburden is presumably relatively thin. Subsidence features drain 20–36% of the surface area. Unsaturated storage appears to be volumetrically insignificant, so that far more recharge occurs than the 5% often assumed for this region. Mine storage can change rapidly due to subsidence recharge. Hydrologically, mines with subsidence features behave like karst systems, with meteoric ‘quickflow’ representing more than 50% of the total flow. Mine discharge concentrations are relatively uniform through time, suggesting either equilibrium controls on chemistry or drainage of a well-mixed pool, or both. Evidence of dilution by high flows is slight. The first high flows after a baseflow period show only a slight increase in concentrations, attributed to flushing of stored reaction products. Loadings (concentrations x flow) depend on volumetric discharge and as a consequence are highly variable. The Eh/pH environment in up-dip drift mines indicates that mine waters are in contact with the atmosphere at least part of the time, unlike a true groundwater. Iron buffering partly controls pH, which clusters around values of 3.6–5.0.

Hydrology of the Abandoned Underground Corning Coal Mine, Perry County, Ohio

“…Comparing mine areas with loads, the acidity load from the eastern complex is proportional to area: The load is 33% of the total and the area is 35% of the total, even though flows are not proportional to area. If this finding is not simply fortuitous, it suggests that chemical equilibrium is not the dominant mechanism as observed in other mines (López and Stoertz, 2001).…”

“…Mines without known direct surface capture are recharged mainly by slow groundwater seepage, and discharge responds much more slowly to precipitation events (Shimala, 2000;López and Stoertz, 2001). Surface runoff and recharge are seasonal even with uniform rainfall, because of seasonal soil moisture storage and evapotranspirative demands.…”

“…Most mines show seasonal variations in discharge, with the highest discharge occurring in the spring months and the lowest during summer when evapotranspiration is highest. Concentrations of acidity and metals vary in response to recharge, and tend to be highest in the spring when stored reaction products are flushed from the mine during high flows (López and Stoertz, 2001).…”

“…Dilution is consistent with preferential flow paths and shorter residence times. In contrast, other mines in the region (López and Stoertz, 2001) exhibit relatively uniform discharge water quality, suggesting that the mine water equilibrates rapidly or that the pool is well mixed:…”

Use of Modflow Drain Package for Simulating Inter-Basin Transfer of Groundwater in Abandoned Coal Mines

“…al., 1998) by modifying boundary conditions and aquifer hydraulic properties. Hydrologic interconnection between highly permeable above-drainage underground mines promotes a shift from a classic topographically-dominated groundwater flow regime (Ferguson, 1967;Wyrick and Borchers, 1981;Harlow and LeCain, 1993;Sheets and Kozar, 2000) to one that is dip-dominated, with groundwater capture areas that greatly exceed the boundaries of individual mines (Lopez and Stoertz, 2001). Previous researchers have used MODFLOW in mined settings (Toran and Bradbury, 1988;Goode et.…”