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USGS2017

Hydrogeology, groundwater flow, and groundwater quality of an abandoned underground coal-mine aquifer, Elkhorn Area, West Virginia

The Pocahontas No. 3 coal seam in southern West Virginia has been extensively mined by underground methods since the 1880’s. An extensive network of abandoned mine entries in the Pocahontas No. 3 has since filled with good-quality water, which is pumped from wells or springs discharging from mine portals (adits), and used as a source of water for public supplies. This report presents results of a three-year investigation of the geology, hydrology, geochemistry, and groundwater flow processes within abandoned underground coal mines used as a source of water for public supply in the Elkhorn area, McDowell County, West Virginia. This study focused on large (> 500 gallon per minute) discharges from the abandoned mines used as public supplies near Elkhorn, West Virginia. Median recharge calculated from base-flow recession of streamflow at Johns Knob Branch and 12 other streamflow gaging stations in McDowell County was 9.1 inches per year. Using drainage area versus mean streamflow relationships from mined and unmined watersheds in McDowell County, the subsurface area along dip of the Pocahontas No. 3 coal-mine aquifer contributing flow to the Turkey Gap mine discharge was determined to be 7.62 square miles (mi2), almost 10 times larger than the 0.81 mi2 surface watershed. Results of this investigation indicate that groundwater flows down dip beneath surface drainage divides from areas up to six miles east in the adjacent Bluestone River watershed. A conceptual model was developed that consisted of a stacked sequence of perched aquifers, controlled by stress-relief and subsidence fractures, overlying a highly permeable abandoned underground coal-mine aquifer, capable of substantial interbasin transfer of water. Groundwater-flow directions are controlled by the dip of the Pocahontas No. 3 coal seam, the geometry of abandoned mine workings, and location of unmined barriers within that seam, rather than surface topography. Seven boreholes were drilled to intersect abandoned mine workings in the Pocahontas No. 3 coal seam and underlying strata in various structural settings of the Turkey Gap and adjacent down-dip mines. Geophysical logging and aquifer testing were conducted on the boreholes to locate the coal- mine aquifers, characterize fracture geometry, and define permeable zones within strata overlying and underlying the Pocahontas No. 3 coal-mine aquifer. Water levels were measured monthly in the wells and showed a relatively static phreatic zone within subsided strata a few feet above the top of or within the Pocahontas No. 3 coal-mine aquifer (PC3MA). A groundwater-flow model was developed to verify and refine the conceptual understanding of groundwater flow and to develop groundwater budgets for the study area. The model consisted of four layers to represent overburden strata, the Pocahontas No. 3 coal-mine aquifer, underlying fractured rock, and fractured rock below regional drainage. Simulation of flow in the flooded abandoned mine entries using highly conductive layers or zones within the model, was unable to realistically simulate interbasin transfer of water. Therefore it was necessary to represent the coal-mine aquifer as an internal boundary condition rather than a contrast in aquifer properties. By representing the coal-mine aquifer with a series of drain nodes and optimizing input parameters with parameter estimation software, model errors were reduced dramatically and discharges for Elkhorn Creek, Johns Knob Branch, and other tributaries were more accurately simulated. Flow in the Elkhorn Creek and Johns Knob Branch watersheds is dependent on interbasin transfer of water, primarily from up dip areas of abandoned mine workings in the Pocahontas No. 3 coal-mine aquifer within the Bluestone River watershed to the east. For the 38th, 70th, and 87th percentile flow duration of streams in the region, mean measured groundwater discharge was estimated to be 1.30, 0.47, and 0.39 cubic feet per square mile (ft3/s/mi2

West Virginia↗

USGS2014

Results of coalbed-methane drilling, Mylan Park, Monongalia County, West Virginia

The Department of Energy National Energy Technology Laboratory funded drilling of a borehole (39.64378°N., 80.04376°W.) to evaluate the potential for coalbed-methane and carbon-dioxide sequestration at Mylan Park, a public park in Monongalia County, W. Va. The total depth of the borehole was 2,525 feet (ft) and contained 1,483.41 ft of Pennsylvanian coal-bearing strata, 739.67 ft of Mississippian strata, and 301.93 ft of Devonian strata. The drill site was located directly over abandoned mines in the Pittsburgh and Sewickley coal beds. Coal cores from remaining Pittsburgh and Sewickley coal-bed-mine pillars were cut and retrieved for desorption from both mines. In addition, coals were cored and desorbed from the Redstone, Pittsburgh roof coal interval, Little Pittsburgh, Elk Lick, Brush Creek, Upper Kittanning, Middle Kittanning, Clarion, Upper Mercer, Lower Mercer, and Quakertown coal beds and coal zones. All coals are Pennsylvanian in age and are high-volatile A bituminous in rank. A total of 34.75 ft of coal was desorbed over a maximum period of 662 days, although most of the coal was desorbed for about 275 days. Measured raw-total-gas contents ranged from 0.43 standard cubic feet per ton (SCF/ton, an industry abbreviation) for the mined Sewickley coal bed to 130.98 SCF/ton for the Upper Kittanning coal bed. Volumes of residual gas were not measured; therefore, the gas volumes reported here should be regarded as minimum volumes. The amount of oxygen in the gas samples collected from the desorption canisters ranged from 2.55 to 20.13 percent. Methane contents ranged from 0 percent for one single canister from the Pittsburgh (WV–02–B3–4) and Little Pittsburgh (WV–02–CB3–2) coal beds to almost 81 percent for two canisters from the Clarion coal zone (WV–02–B3–16 and WV–02–B3–17), which suggests that all of the gas samples were contaminated to some degree by air. Therefore, all gas compositions reported have been normalized to remove the air. With a single exception (the Quakertown coal zone), the coals from the Mylan Park study area are thermogenic in origin with the isotopic composition of carbon (carbon 13, 13 C) in methane (expressed as δ 13 C in units of parts per thousand (per mil) relative to the Vienna Peedee belemnite (VPDB) standard) ranging from -32.39 to -50.66 per mil and ratios of methane to hydrocarbons of higher molecular weight ranging from 10 to 53. The Quakertown coal zone has a C 1 /C 2+ ratio of 913, suggesting that it contains some microbial gas. High-pressure carbon-dioxide adsorption isotherms were measured on composite coal samples of the Upper Kittanning coal bed and the Middle Kittanning and Clarion coal zones. Assuming that the reservoir pressure in the Mylan Park coals is equivalent to the normal hydrostatic pressure, the estimated maximum carbon-dioxide adsorption pressures range from a low of about 300 pounds per square inch (lb/in 2 ) in coals from the Clarion coal zone to 500 lb/in 2 for coals from the Upper Kittanning coal bed. The estimated maximum methane adsorption isotherms show that the coals from the Upper Kittanning coal bed and the Middle Kittanning coal zone are undersaturated in methane, but coals from the Clarion coal zone are close to saturation.

West Virginia↗