Mine-Water Flow between Contiguous Flooded Underground Coal … · 2018-09-07 · ground coal mines...

Mine-Water Flow between Contiguous Flooded

Underground Coal Mines with Hydraulically

Compromised Barriers

DAVID D. M. LIGHT1

JOSEPH J. DONOVAN1

Department of Geology & Geography, West Virginia University, 98 BeechurstAvenue, 330 Brooks Hall, P.O. Box 6300, Morgantown, WV 26506-6300

Key Terms: Mining Hydrogeology, Mine Flooding,Recharge

ABSTRACT

Groundwater flow entering closed contiguous under-ground coal mines may be strongly influenced byleakage across inter-mine barriers. This study examinesa complex of multiple closed and flooded mines thatdeveloped into a nearly steady-state groundwater flowsystem within 10 to 50 years after closure. Field water-level observations, mine geometry, barrier hydraulicconductivity, recharge rates, and late-stage storagegains were parameterized to match known pumpingrates and develop a fluid mass balance. Verticalinfiltration (recharge and leakage) estimates weredeveloped using a depth-dependent model based on theassumption that most vertical infiltration is focused inareas with ,75 m of overburden. A MODFLOWsimulation of the nearly steady-state flow conditionswas calibrated to hydraulic heads in observation wellsand to known pumping rates by varying barrierhydraulic conductivity. The calibrated model suggestssignificant head-driven leakage between adjacentmines, both horizontally through coal barriers andvertically through inter-burden into a shallower mine inan overlying seam. Calibrated barrier hydraulic con-ductivities were significantly greater than literaturevalues for other mines at similar depths in the region.This suggests that some barriers may be hydraulicallycompromised by un-mapped entries, horizontal bore-holes, or similar features that act as drains betweenmines. These model results suggest that post-mininginter-annual equilibrium conditions are amenable toquantitative description using mine maps, sparseobservation-well data, accurately estimated pumpingrates, and depth-dependent vertical infiltration esti-mates. Results are applicable to planning for post-

flooding water-control schemes, although hydraulictesting may be required to verify model results.

INTRODUCTION

Underground mines can be classified into twogroups: above drainage and below drainage. Above-drainage mines can be further divided according tothe direction of mining: up-dip or down-dip. Up-dipmines are ‘‘free-draining.’’ Infiltration that reachesthese mines flows down-dip along the mine floor anddischarges at portals and other connections to thesurface, while infiltration that enters down-dip above-drainage mines, and all below-drainage mines, flowsto the lowest parts of the mine, resulting in mineflooding. Both groundwater inflow rates and accuratemine maps are essential for predicting the duration offlooding and subsequent mine-water discharge to thesurface. Groundwater-inflow estimation for closedunderground coal mines constrains recharge to areasof relatively shallow overburden and neglects leakageto deeper mined areas (Winters and Capo, 2004;McDonough et al., 2005; and McCoy et al., 2006).

Published recharge rates applied to mines withrelatively small areas of thin overburden cover,therefore, are generally minimum estimates of mineinflows. Mine maps and accurate groundwater-inflowrates (recharge and leakage) are essential to predictthe time required for a mine to flood (Younger andAdams, 1999; Whitworth, 2002). Inflow rates andmaps alone, however, often yield inaccurate estimatesof flooding times for individual mines that are directlyadjacent to, and therefore potentially connected to,other mines. In some cases, groundwater-elevationand mine-pool data for multiple mines show highlysimilar pool behavior between mines, suggestinginter-connection. As a result, an improved under-standing of the hydrogeological interactions betweenadjacent mines that stems from the development ofmore realistic mine-inflow models and groundwater-flow models depicting conditions in multiple adjacent

1Phone: 304-293-5603; Fax: 304-293-6522; emails: [email protected]; [email protected].

Environmental & Engineering Geoscience, Vol. XXI, No. 2, May 2015, pp. 147–164 147

mines will help clarify and improve predictions of themine-flooding process. Such information will benefitpost-closure operations by allowing more robustsizing, design, and location of mine-water extractionpumps and treatment plants, as well as the develop-ment of plans for mine-water control.

Purpose

The purposes of this research are to improve theunderstanding of post-flooding hydrogeological in-teractions between contiguous underground coalmines and to present a method for estimating mineinflow that includes vertical infiltration in areas withrelatively thick (.100 m) overburden. The improvedunderstanding stems from a steady-state groundwa-ter-flow model that was conceptualized using minedareas, inter-mine barrier thicknesses, and a waterbudget that is based on known pumping volumes andestimated mine-water inflows. Inter-mine coal-barrierhydraulic conductivities were calibrated using knowngroundwater elevations and used to calculate hori-zontal flow between mines. Mine inflows weredetermined using a depth-dependent vertical infiltra-tion model that is based on published recharge ratesand overburden thicknesses. The depth-dependentmodel offers improved vertical infiltration estimationover earlier methods, especially when the depth ofmining becomes relatively deep.

Background

Underground mining creates void space, removessupport for overburden, and changes stress fields,frequently resulting in subsidence of overlying strata(Singh and Kendorski, 1981; Booth, 1986). Subsi-dence features have been categorized into zones thatconsist primarily of collapsed and rubblized roofrock, vertical fractures, bedding-plane separations,and sagging yet otherwise constrained strata (Singhand Kendorski, 1981; Kendorski, 1993). After mineclosure, groundwater extraction ceases, and voidscreated by mining and subsidence begin to re-saturate, resulting in an anthropogenic aquifer(Adams and Younger, 2001). Flooding in thesecoal-mine aquifers is marked by the initial develop-ment of a phreatic surface or ‘‘pool’’ in the deepestportion of the mine (Donovan and Fletcher, 1999),which, with continued flooding, migrates up-diptoward shallower mined areas. Flooding ceases whenthe pool level reaches the elevation of a ‘‘spill point’’(Younger and Adams, 1999); alternately, mineinflows may be balanced by loses to barrier leakageor by groundwater-extraction pumping. Floodingprogress tends to follow a decaying exponential curve

over time, with flooding rates decreasing as the poollevel approaches the elevations of either groundwatersources or spill points (Whitworth, 2002). Theduration of flooding varies and is controlled byrecharge rates as well as the status of adjacent mines.Shallow mines tend to receive more recharge thandeeper ones (Winters and Capo, 2004) and thereforetend to flood more rapidly.

Considerable research has been conducted on thehydrogeology of closed underground coal mines,including the chemistry (Banks et al., 1997), volume(Pigati and Lopez, 1999), and seasonality (Pigati andLopez, 1999; Light, 2001) of mine-water discharges.Others have examined mine aquifer properties such asporosity (Hawkins and Dunn, 2007), specific yield(McCoy, 2002), hydraulic conductivity (Aljoe andHawkins, 1992), and retention time (Winters andCapo, 2004; Sahu and Lopez, 2009). Floodinghistories have been utilized to develop models forprediction of mine flooding (Younger and Adams,1999; Whitworth, 2002). Recharge-rate estimates forflooding and flooded mines vary from ‘‘the miner’s-rule-of-thumb’’ (Stoertz et al., 2001) to calculationsthat are based on discharge volumes (Winters andCapo, 2004; McDonough et al., 2005), pumpingrecords (Hawkins and Dunn, 2007), and numericmodeling (Stoner et al., 1987; Williams et al., 1993).Recharge is commonly restricted to areas of relativelyshallow overburden (,18 m, McDonough et al.,2005; ,75 m Winters and Capo, 2004), while leakageis typically not considered a significant source ofgroundwater for mine aquifers, although it has beenshown to occur and even been quantified (McCoy etal., 2006; Leavitt, 1999). Neglecting leakage suggeststhat deep mines should be ‘‘dry’’ or have limitedgroundwater inflow, and it results in recharge ratesthat are significantly greater than published values.This would indicate that leakage should have beenincluded in estimations of inflows to deeper mines.For the purposes of this investigation, recharge andleakage will be un-differentiated and referred to asvertical infiltration.

Unconfined storage in coal mines occurs mainly inthe area near the ‘‘beach,’’ where the phreatic surfaceintersects the floor of the mine (Hawkins and Dunn,2007). Its value has been estimated for differentextraction methods based on surface subsidence, coalseam thickness, and the height of roof collapse(McCoy, 2002). It has also been estimated usingpumping rates and corresponding changes in hydrau-lic head (Hawkins and Dunn, 2007). Confinedstorage, similar to vertical infiltration in relativelydeep mined areas, is commonly neglected, although itcould represent a significant volume of water in areasof confined groundwater. Inter-mine coal barrier

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148 Environmental & Engineering Geoscience, Vol. XXI, No. 2, May 2015, pp. 147–164

leakage rates have also been estimated (McCoy et al.,2006; Hawkins and Dunn, 2007).

STUDY AREA

The study area for this research includes sevenPittsburgh coal mines located within the Pittsburghbasin, Greene County, PA (Figures 1 and 2). Themines were operated for various periods, but allclosed between 1964 and 2004 and as of spring 2013were in the final stages of flooding, fully flooded, ormanaged by pumping to control mine-pool levels.Both the fully flooded mines (Crucible and Nemaco-lin) and the late-stage flooding mines (Pitt Gas andGateway) contain pools with elevations above thesurface of the adjacent Monongahela River (Fig-ures 2 and 3). Mine water is pumped to treatmentplants from two locations in the study area (Dilworthand Robena), and also from adjacent mines (Shan-nopin and Warwick #2), in order to manage poollevels in those mines. The study area is bordered byother Pittsburgh bed mines (Clyde, Humphrey,Shannopin, and Warwick #2) and is partiallyoverlain by a mine in the Sewickley coal bed(Warwick #3) (Figure 2). There are no knownsurface discharges within the study area, althoughgroundwater began discharging from an adjacentmine (Clyde, Figure 2) during early 2013 aftertemporary cessation of pumping operations in thatmine. The water level in one mine (Mather) iscurrently unknown, but the mine is believed to befully flooded with a pool elevation midway betweenthose in adjacent mines (Gateway and Dilworth).

Geologic and Hydrogeologic Setting

The Pittsburgh coal basin, located within theAppalachian Plateau physiographic province (Fenne-man, 1938), is bounded by the outcrop of thePennsylvanian-age Pittsburgh coal bed in parts ofsouthwestern Pennsylvania, southeastern Ohio, andnorthern West Virginia (Figure 1). The Pittsburghcoal is the basal unit of the Monongahela Group(Figure 4), which also contains the UniontownFormation. The coal bed varies in thickness butaverages 2.0 m, with minor variance in the study area.The Pittsburgh Formation consists of alternatinglayers of sandstone, limestone, dolomitic limestone,calcareous mudstones, shale, siltstone, and coal(Edmunds et al., 1999). The Sewickley coal, whichlies stratigraphically above the Pittsburgh coal byapproximately 30 m, is also mined in the basin(Figures 1 and 4), but it is neither as thick nor asextensive as the Pittsburgh coal (Hennen and Reger,1913). The Dunkard Group overlies the Mononga-

hela Group and varies in thickness up to 365 m(Edmunds et al., 1999). Structural dip of all thesestrata is typically less than five degrees (Beardsley etal., 1999).

Rocks in the Appalachian Plateaus Province tendto have low primary porosity and permeability(Stoner, 1983). Groundwater flow is primarilythrough networks of stress-relief fractures and bed-ding-plane separations, which occur along valleywalls and parallel to valley bottoms (Wyrick andBorchers, 1981; Kipp and Dinger, 1987). Hydraulicconductivity and storativity tend to decrease withdepth (Stoner, 1983), and only a small portion ofnatural groundwater flow extends to depths greaterthan 50 m (Stoner et al., 1987). The removal of coalby underground mining and consequent subsidence-induced re-distribution of overburden have consider-able impacts on the un-disturbed groundwater flowregime (Stoner, 1983; Booth, 1986). Undergroundcoal mining can also impact surface water by reducingrunoff and increasing baseflow (Stoner, 1987). Min-ing-induced subsidence tends to create large voids andrubble zones with greatly increased hydraulic con-ductivity (Singh and Kendorski, 1981; Aljoe andHawkins, 1992; Kendorski, 1993) compared to nativecoal and overburden (Hobba, 1991). Above rubblizedareas, vertical hydraulic conductivity is similarlyincreased, but this effect decreases with increasingheight above the rubble (Palchik, 2003). Post-closureflooding yields coal-mine aquifers (Younger andAdams, 1999), which tend to be locally heterogeneous

Figure 1. Extent of the Pittsburgh coal seam (light shading) withareas of underground mining in the Pittsburgh (medium shading)and Sewickley (dark shading) seams, in addition to GreeneCounty, PA (dashed line).

Coal Mine Interaction


with preferential flow paths (Aljoe and Hawkins,1992), due to overburden subsidence, coal pillargeometry, and spatial distribution of highly transmis-sive main entries (Figure 5). Yet on a mine-wide scale,water levels in different locations within flooded un-pumped mines are often fairly uniform (Aljoe andHawkins, 1992; Figure 3).

Coal-mine aquifers and overlying units can behydrostratigraphically characterized using overbur-den subsidence zones (Kendorski, 1993; Figure 4).The caved zone contains jumbled overburden col-lapsed into the mine to heights of 6 to 10t, where t isthe thickness of the coal seam, while strata in theoverlying fractured zone contain vertical fractures andbedding-plane separations extending to heights of 24

to 30t above the mine floor. The dilated zone showsbedding-plane separations, increased porosity, andhorizontal transmissivity, yet due to the absence ofthrough-going fractures, it acts as the principalaquitard between overlying strata and the fracturedand caved zones below. If overburden is sufficientlythick, a constrained zone consisting of gently saggingstrata may also be present. The surface fracture zonecontains extended and enlarged pre-existing fracturesfrom the ground surface to 15 m depth. Thesesubsidence zones were developed to describe over-burden re-distribution over longwall panels, butsimilar re-distribution is likely to occur in areas ofroom-and-pillar mining, especially where pillars arefully extracted (Peng, 1986). The distribution of

Figure 2. Underground Pittsburgh seam mines in the study area with structure contours of coal bottom (5 m interval), locations ofmonitoring wells, inter-mine barriers, and mine-water treatment plants (CLY 5 Clyde; CRU 5 Crucible; DIL 5 Dilworth; GAT 5

Gateway; HUM 5 Humphrey; MAT 5 Mather; NEM 5 Nemacolin; PIT 5 Pitt Gas; ROB 5 Robena; SHA 5 Shannopin; and WAR 5

Warwick #2).

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subsided materials and overburden thickness hasimplications for mine-aquifer water budgets includingrecharge and leakage. In relatively shallow areas(,75 m; e.g., Winters and Capo, 2004) where thesurface fracture and fractured zones intersect, re-charge rates will be highest , while in areas containingthicker overburden, aquifer inflow will occur asleakage through the dilated zone with relatively lowrates. Groundwater movement through overburden isinferred to be predominantly downward into minevoids and collapsed overburden in the caved zone,which are much higher in hydraulic conductivityrelative to un-mined coal and rocks. Inter-minegroundwater flow occurs horizontally through coalbarriers separating mines (e.g., McCoy et al., 2006;Hawkins and Dunn, 2007), although vertical flowbetween mines may occur where over- or underlyingseams have been mined (Miller, 2000). Flow betweenmines follows pressure gradients toward dischargelocations.

Hydraulic conductivity (K) within coal-mine aqui-fers is related to the degree of overburden alterationand subsidence and is significantly increased over Kwithin native coal (Harlow and Lecain, 1993). Withinthe caved zone, K in un-collapsed rooms and mains

can be very high, while in ‘‘gob’’ (collapsed) areas,collapsed overburden may reduce K values. Shale andother thinly layered rocks tend to collapse in smallpieces, resulting in poorly connected void space, whilesandstone and similarly massive rocks tend to collapsein large blocks, leaving significant void space (Palchik,2002). Strata in the fractured zone will have highvertical hydraulic conductivity (KV) relative to hori-zontal hydraulic conductivity (KH) (Palchik, 2002), yetthe number and size of vertical fractures decrease withincreasing distance above the mine void, resulting in asimilar reduction in KV (Palchik, 2003).

METHODOLOGY

Groundwater-Head Data

Groundwater elevations were calculated for sixmonitoring wells (Figure 2) using depth-to-watermeasurements and pressure transducers. BetweenSeptember 2000 and November 2005, pressuremeasurements were made using vented transducers,while after November 2005 measurements wererecorded primarily with sealed transducers andcorrected using barometric-pressure data collected

Figure 3. Groundwater elevations indicate fairly uniform pool levels in mines with multiple observation wells (CRU1 5 Crucible; DIL1 5

Dilworth; GAT1 and GAT2 5 Gateway; NEM1 5 Nemacolin; PIT1 5 Pitt Gas; and ROB1 5 Robena). The average surface elevation inthe Monongahela River (Maxwell pool) and mine-water treatment plant control levels are indicated by arrows.



within the study area. Pressures were recorded hourlyand then converted to average daily water levelsusing a database. Three of the monitoring wellsare previously existing rock-dust boreholes (GAT1,GAT2, and NEM1; Figure 2), while the other threewells (CRU1, PIT1, and MAT1; Figure 2) were alldrilled for the purpose of monitoring mine-poolelevations. Historical (pre-September 2000) ground-water-elevations for the pools within Gateway andRobena (GAT1 and ROB1, respectively; Figure 2) arefrom unpublished file data. While limited, recentgroundwater elevations for the pumped mines Dil-worth and Robena (DIL1 and ROB1, respectively;Figure 2) were provided by treatment-plant operators.

Geospatial Analysis

Mine outlines and areas, inter-mine coal-barrierdimensions, and overburden isopachs for the studyarea were mapped using a geographic informationsystem (GIS). Pittsburgh coal bed mine maps wereobtained from the Pennsylvania Department of

Environmental Protection (PADEP), digitized, andgeo-rectified using mining features depicted on themaps and located in the field using a globalpositioning system (GPS). Inter-mine barrier seg-ments were measured, and their areas and lengthswere used to estimate average width. All barriersin the study are assumed to be 2 m high, theapproximate thickness of the Pittsburgh coal in thisarea (Edmunds et al., 1999). The Pittsburgh coal bedstructure was developed using kriged base-of-coalelevations from mine maps to create a grid. This coal-bed structure grid was subtracted from the 10 mdigital elevation model (DEM) to create an overbur-den isopach. Because vertical infiltration rates aredependent upon overburden thickness, the latter is afactor in estimating the volume of groundwater thatreaches the mine aquifer.

Fluid Mass Balance

A water budget or fluid mass balance (FMB) formines i in the study area was developed to improveunderstanding of the flow regime. The FMB includesvertical infiltration (VI), extraction pumping (P),storage changes (DS), surface discharge (Q), andbarrier leakage (LB):

Xn

i~0

VIizLBizPizDSi{Qið Þ~0 ð1Þ

Vertical infiltration is the primary source of ground-water, while extraction pumping, surface discharge,

Figure 4. Generalized hydrostratigraphy of the Pittsburgh For-mation, Upper Pennsylvanian Monongahela Group (after Ed-munds et al., 1999). Scale is approximate.

Figure 5. Plan view of typical mine map showing variation inmining methods, main entries, and un-mined coal (pillars).

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and addition to storage are all sinks. Barrier leakagemay be a source or sink depending upon whether flowis into or out of the study area. In order to estimatemine inflow within the relatively deep mines of thestudy area, a depth-dependent vertical infiltrationmodel was developed using published recharge ratesfor mines in the Pittsburgh coal (Table 1). The modeluses a constant rate equal to the miner’s rule ofthumb (0.67 mm/d) of Stoertz et al. (2001) for depthsfrom 0 to 30 m and an exponentially declining rate fordepths below 30 m:

VI(d)~VI(0) dƒd1ð Þ ð2Þ

VI(d)~eVI(0)e{l(d) dwd1ð Þ ð3Þ

where VI(d) is the recharge rate at depth d below landsurface, VI(o) is the maximum vertical infiltration ratein shallow aquifers, d1 is the maximum depth at whichthe surface fracture and fracture zones intersect, l is alocation-specific vertical infiltration decline parame-ter, and e is a fit parameter. VI(o) (0.67 mm/d) issimilar to the vertical infiltration rate reported for un-mined areas in Greene County, PA (Stoner, 1983),and roughly 40 percent of the average vertical

infiltration rate for aquifers in the MonongahelaRiver basin of northern West Virginia (Kozar andMathes, 2001). The depth-dependent vertical infiltra-tion model was applied to the overburden isopach,yielding a vertical infiltration estimate for the studyarea.

Groundwater is extracted for treatment from twomines within the study area, and there are no knownsurface discharges. Increases in confined storagewithin fully flooded areas of Gateway and Pitt Gasmines were determined using the daily average changein water-level elevation during 2012 (Figure 3) and aconfined-storage coefficient estimate of 0.001. Specif-ic yield for the small unconfined area within Pitt Gaswas calculated (McCoy, 2002):

Sy~EmbCs

bð4Þ

where Sy is specific yield, Em is the coal extractionratio, Cs is the volume of void space remaining aftersurface subsidence, b is the height of the coal bed, andb is the height of caved overburden. Barrier leakageestimates (LBi) were calculated using head differencesbetween adjacent mines Dhj, with barrier heights b;barrier segments j; barrier segment widths wj and

Table 1. Vertical infiltration rates for regional coal mines.

Source Year Coal State OutcropsAverage

Depth (m) VI (mm/d) Method

Hawkins and Dunn 2007 LK; LF PA Yes 0.36 Pumping recordsMcDonough et al. 2005 P PA Yes ,18 4.65 Measured dischargeStoertz et al. 2001 MK OH Yes 15 0.67 Miner’s rule-of-thumbStoner et al. 1987 P PA 0.45 Numeric modelWilliams et al. 1993 P PA 0.25 Numeric modelWinters and Capo 2004

Delmont P PA Yes 31 0.72 Measured dischargeExport P PA Yes 37 0.59 Measured dischargeCoal Run P PA Yes 37 0.46 Measured dischargeIrwin P PA Yes 69 0.43 Measured dischargeGuffey P PA Yes 85 0.76 Measured dischargeMarchand P PA Yes 94 0.30 Measured dischargeBanning P PA Yes 96 0.32 Measured discharge

McCoy 2002Barrackville P WV No 149 0.05 Fluid mass balanceClyde P PA No 136 0.19 Fluid mass balanceJamison #9 P WV No 207 0.03 Fluid mass balanceJoanne P WV No 169 0.03 Fluid mass balanceJordan P WV Yes 130 0.11 Fluid mass balanceRobena P PA No 174 0.04 Fluid mass balanceShannopin P PA Yes 139 0.06 Fluid mass balanceWyatt P WV Yes 101 0.21 Fluid mass balance

Overburden , 18 m* P PA No 166 725 DDVIMOverburden , 75 m* P PA No 166 3.3 DDVIM

P 5 Pittsburgh; LK 5 Lower Kittaning; LF 5 Lower Freeport; MK 5 Middle Kittanning; DDVIM 5 depth-dependent vertical infiltrationmodel.*VI applied only to areas with overburden less than these thicknesses.



lengths Xj; and barrier hydraulic conductivity KB

(similar to McCoy et al., 2006):

LBi~Xn

j~0

KBbXj

Dhj

wj

ð5Þ

Groundwater-Flow Model Development

Groundwater-flow modeling was applied to betterunderstand the interactions between adjacent flood-ing and flooded coal mines. The goal of the model isto use groundwater-elevation heads for calibrationand pumping rates at treatment plants to define thewater budget. The numeric model depicts near-steady-state conditions in 2012, during which allmines in the study area except two flooding mineshad attained post-flooding hydraulic equilibrium.Groundwater elevations within the two exceptions(Gateway and Pitt Gas) were within 10 m ofanticipated equilibrium elevation. The pumping andwater-level data available for Dilworth and Robenaare from 2011, yet they are thought to be represen-tative of average conditions in those mines, as theirpool levels are maintained below control elevationsand do not vary significantly from year to year, nordo the average annual pumping volumes. The flowmodel thus depicts average post-flooding groundwa-ter control conditions, but it does not account forseasonal or inter-annual variability.

RESULTS

Groundwater Hydrographs

Groundwater-elevation hydrographs for the studyarea are shown in Figure 3. The hydrographs forCrucible and Nemacolin indicate approximate equi-librium with intra-annual fluctuations attributed toseasonal variations in vertical infiltration, precipita-tion, and evapotranspiration rates (Pigati and Lopez,1999; Light, 2001), as well as barrier leakage toadjacent mines. The fact that water levels haveequilibrated without surface discharge or pumpingcontrol indicates that these mines must lose waterentirely to barrier leakage. Their relative increases ingroundwater elevations between 2007 and 2009 areattributed to the effects of post-closure flooding inadjacent Dilworth mine, decreasing inter-mine headdifferences and barrier leakage from these two minesinto Dilworth. Dilworth mine-pool-level controlpumping began during 2008 and resulted in stabili-zation of the pools in Crucible and Nemacolin. TheRobena hydrograph indicates that extraction pump-ing for managing its pool level have made it a

groundwater sink for Nemacolin (Figures 2 and 3).The stable pool elevation within Mather in 2001–2002shows the mine was only partially flooded during thatperiod, and that any inflow from infiltration waslost by barrier leakage to adjacent Gateway and/orDilworth (Figures 2 and 3). While water-level dataare unavailable, the pool level in Mather is believed tohave begun rising when the pool in Gateway reachedthe elevation of the barrier separating those mines.The flooding rate in Mather most likely increasedfollowing the 2004 closure of Dilworth. The pool inDilworth is currently (2013) maintained by pumpingbelow 225.5 m (Figure 3). A stable pool elevationprevailed in Pitt Gas prior to 2007 and wasmaintained by cross-barrier horizontal boreholes thatwere installed to drain Pitt Gas mine water intoGateway. In early 2007, the groundwater level inGateway reached the elevation of those drains,initiating flooding within Pitt Gas. After 2007, PittGas and Gateway flooded in tandem, with fluctua-tions in the flooding rate attributed to variation inseasonally affected vertical infiltration as well asgroundwater heads in adjacent mines (Figure 3). Latein 2011, the pool elevation in Pitt Gas reached theelevation of its roof, resulting in accelerated floodingas water filled all mine voids and moved upward intolow-porosity overburden fractures. In early 2013, theflooding rate continued to increase, and water levelsin both mines were above the surface elevation of theMonongahela River (Figures 2 and 3). The potentialfor surface discharge from either Gateway or Pitt Gasat elevations above 233 m exists, as does thepossibility that vertical infiltration to these mines willbe entirely offset by barrier leakage to adjacent mines(similar to the case in Crucible and Nemacolin).

Geospatial Analysis

Mines in the study range from 2.3 to 80 km2 inarea, while overburden thickness varies from less than10 m to more than 300 m, averaging 166 m (Table 2).The mines contain relatively little area with thinoverburden. Less than 0.01 percent of the total areacontains overburden under 18 m thick, and overbur-den is less than 75 m thick in only 1.5 percent of thestudy area (Figure 6). Pitt Gas, the smallest andshallowest mine, accounts for roughly 1 percent of thetotal mined area and is the only mine with overburdenless than 18 m thick. Inter-mine coal barriers vary inaverage width from 22 to 80 m and in length from1600 to 7600 m (Figure 2 and Table 3). The barriersseparating Gateway from Mather and Nemacolinfrom Robena are the longest and narrowest, whilethe barriers separating Mather from Dilworth and

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Nemacolin from Dilworth are relatively short andwide (Table 3).

Fluid Mass Balance

Initial vertical infiltration estimates were made byapplying average daily extraction volumes for thepumps in Dilworth and Robena (Table 4 andFigure 2) first to mined areas with overburden lessthan 18 m thick (i.e., McDonough et al., 2005) andthen to mined areas with overburden less than 75 mthick (i.e., Winters and Capo, 2004). Both estimatesresulted in vertical infiltration rates that wereconsiderably greater than those reported in similarstudies (Table 1), indicating that vertical infiltrationto deeper mined areas is a significant portion of theFMB. Published recharge rates for mines in thePittsburgh coal (Table 1) were used to determine theform of the depth-dependent vertical infiltration modelfor depths below d1 (Eq. 3; Table 5 and Figure 7).Applying the depth-dependent vertical infiltrationmodel to the overburden isopach produced a vertical

infiltration estimate that exceeds total pumping byapproximately 60 percent (Table 4). This discrepancysuggests that barrier leakage to adjacent mines outsidethe study area may also occur. The pool level in Clydemine (Figure 2) was approximately 10 m above thegroundwater elevation in Gateway in fall 2012, whichindicates that Clyde could only act as a source, not as asink, of barrier leakage for Gateway. Similarly, thepool in Warwick #2 is maintained by pumping at anelevation of ,230 m, well above the mine-watercontrol elevation in Robena mine (215 m). However,both Humphrey and Shannopin mines (Figure 2)contain pools at lower elevations (157 and 190 m,respectively) than the control elevation in Robena, yetthey are also separated from Robena by relatively widebarriers of limited length, and likely neither minereceives significant leakage from Robena.

Warwick #3 mine is in the Sewickley seam, about30 m above the Pittsburgh bed, and its locationstraddles the barrier pillar between Robena andShannopin mines (Figures 2 and 4). It was closeddue to significant groundwater inflow throughvertical fractures connecting it to the underlyingShannopin mine (Miller, 2000). The pool in Shanno-

Figure 6. Cumulative distribution of mine area versus overburden thickness. See Table 2 for overburden statistics.

Table 2. Mine area and overburden distribution statistics.

Mine Area (106 m2)

Overburden Thickness (m)

Min. Max. Avg.

Pitt Gas 2.3 8.30 153 85Crucible 22.6 35.5 222 133Nemacolin 39.6 49.8 240 142Mather 19.9 77.5 265 144Robena 79.0 31.4 328 175Dilworth 34.1 36.4 283 177Gateway 41.0 31.0 309 192All mines 238 8.30 328 166

Table 3. Measured barrier dimensions (refer to Figure 2 forbarrier locations).

BarrierID Mines

Total Length(m)

Average Width(m)

C1 Crucible-Dilworth 4,395 60C2 Crucible-Nemacolin 5,920 67G Gateway-Mather 6,290 22M Mather-Dilworth 1,600 80N1 Nemacolin-Dilworth 2,000 61N2 Nemacolin-Robena 7,570 36



pin has since been lowered by pumping to anelevation below 190 m (2012) to allow new miningin the Sewickley seam, making it a potential sink forleakage from Robena. It is interpreted that fracturesbetween both Robena and Shannopin and theoverlying Warwick #3 mine provide pathways forvertical leakage between Robena and Shannopin viathe Sewickley seam workings. Any groundwaterleaked into Shannopin is removed by pumping.Leakage from Robena to Shannopin via Warwick#3 is estimated thus:

LW~Xn

i~0

VIizPizDSið Þ ð6Þ

where LW is vertical leakage from Robena toWarwick #3 (Table 4). Estimated additions toconfined storage amounted to 471 m3/d withinGateway and 27 m3/d in Pitt Gas, while a rate of175 m3/d was added to storage within the approxi-mately 50,000 m2 unconfined area of Pitt Gas(Tables 4 and 6). Daily pumping volumes for Dil-worth and Robena were estimated by averagingannual total volumes (Table 7). Barrier leakageestimates were made for the two mines with multipleadjacent mines, Crucible and Nemacolin, assumingthat the barriers are intact, homogeneous, andwithout hydraulically compromised areas (Table 8).

These leakage estimates suggest that groundwater inNemacolin should leak primarily to Robena, while asmall portion leaks to Dilworth. Similarly, Crucible isexpected to leak most of its groundwater to Dilworth,with some going to Nemacolin.

Groundwater Flow Modeling

Data regarding coal-mine aquifers are often limitedto the spatial extent of mining, sparse groundwater-head measurements, and discharge volumes, whileconditions within mines and of inter-mine barrierpillars are unknown. This lack of informationrequires a number of assumptions in order toconceptualize groundwater flow within and betweenmines that comprise coal-mine aquifers. Generally, allgroundwater originates as vertical infiltration down-ward into the mines and flows toward groundwaterextraction pumps in Dilworth and Robena. Verticalinfiltration is inferred to be dependent upon overbur-den thickness, with the highest vertical infiltrationrates occurring in Pitt Gas and Robena below streamvalleys, while the lowest rates occur under hills andridges (Figure 8). Relatively small volumes of thegroundwater infiltrating Pitt Gas and Gateway areassumed to be retained as storage within these mines,

Figure 7. Estimates of groundwater vertical infiltration to un-derground mines, fitted using Eq. 2 and Eq. 3: VI(d) 5 VI(0) (d #

d1), VI(d) 5 VI(0) e2l(d) (d . d1) (l solid line and lmin dashed). Thedensity function (dotted line) describes overburden thickness formines within the study area.

Table 4. Vertical infiltration, pumping, storage, and leakage rates.

Mine DS VI BL

Crucible 2,981C1 1,774C2 1,207

Dilworth 29,240 2,468Gateway 2471 2,284

G 2,420CL 0

Mather 2,247M 4,668

Nemacolin 4,464N1 416N2 5,242

Pitt Gas 2202 725Robena 22,700 5,387

R 27,943

Total 211,940 2673 20,556 27,943

All values are m3/d; negatives offset VI.

Table 5. Parameters for Equations 2 and 3.

VI(o) (mm/d) d1 (m) l e lmin

0.67 33 0.021 2 0.023

Table 6. Parameters for Sy calculations.

b (m) b (m) Em Cs

20 2.0 0.80 0.80

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while the remainder leaks through the barrier betweenGateway and Mather, joining vertical infiltrationreceived by the latter mine before leaking intoDilworth through barrier segment M (Figure 9).Vertical infiltration entering Crucible leaks to bothDilworth and Nemacolin; similarly, vertical infiltra-tion that enters Nemacolin leaks to Dilworth andRobena (Figure 8). Based on anecdotal reports byminers (Miller, 2000) and on mass balance discrep-ancy, some additional flow is suspected to occurupward through vertical fractures from Robena toWarwick #3 in the Sewickley seam (Figure 9). It isassumed that the Gateway/Clyde barrier (north), theeast barriers of Crucible and Nemacolin (east), andthe deep mining faces of Gateway and Robena (west)all are effectively no-flow boundaries. Groundwatermovement to and/or from surrounding un-mined coalis assumed to be insignificant relative to otherportions of the FMB. Similarly, barrier leakagebetween the study area and surrounding mines(Clyde, Warwick #2, Humphrey, and Shannopin) isthought to be small and have no effect on overall flowdirections.

Modeling Approach

The U.S. Geological Survey (USGS) ModularFinite-Difference Flow Model (MODFLOW-2000)(Harbaugh et al., 2000) was employed to create asteady-state model of post-flooding groundwaterconditions under pumping control in the year 2012.Pre- and post-processing were conducted utilizingGroundwater Vistas version 6.22. At this time, allmines in the study area except Pitt Gas and Gatewayare thought to have been fully flooded and atseasonally fluctuating, but inter-annual steady state.

The goal of the model was to determine groundwater-flow paths and rates within and between mines in thestudy area.

The model employs a 100 3 100 m three-layer gridrotated 16 degrees to align with most inter-minebarriers (Figure 10). Internal coal pillars .10,000 m2

area were also considered no-flow regions. Flow is,however, known to occur across narrow inter-minebarriers separating the mines; the magnitude anddirection of this leakage were obtained by calibrationusing horizontal flow barrier (HFB) cells. HFB cellsallow modeling of barrier thicknesses greater or lessthan grid spacing and variation of local barrierhydraulic conductivities KB (Figure 10). Initial KB

values were 0.078 m/d, a value based on fieldcalculations of McCoy et al. (2006).

All three layers are confined (LAYCON 5 3) andrepresent groundwater flow within the mined area, aswell as in overlying collapse and fracture zones, e.g.,well beneath the shallow groundwater-flow system.The un-flooded portion of Robena up-dip of itswater-table surface was not modeled. Vertical infil-tration and barrier leakage occurring in this regionwere added to adjacent active cells in order tomaintain the FMB.

Boundaries and Parameterization

Boundaries for the model include a recharge(vertical infiltration) boundary at the top of modellayer 1, no-flow cells at the bottom of layer 3, and no-flow cells representing un-mined coal at the perimeterof the model. A single constant-head cell was locatedin reasonable proximity to the pumps in bothDilworth and Robena, at the elevation of the averagepool control elevation maintained in these minesduring 2011 (Table 9), as an aid in calibration. Theconstant-head cells were removed once calibrationwas achieved.

MODFLOW WEL-package (specified-flux) cellswere utilized to simulate pumping from Dilworth andRobena; movement of groundwater into storagewithin nearly flooded Gateway and Pitt Gas; andupward leakage from Robena into the overlyingWarwick #3 mine and, ultimately, into Shannopin tothe south (Figure 10). Average daily pumping ratesfor Dilworth and Robena were estimated using

Table 7. Monthly (2011) extraction volumes for pumps in the study area (1,000 m3).

Mine Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

Robena 260 40.9 0.68 0 175 295 216 0 0 0 0 0 988Dilworth 250 368 303 344 300 344 407 231 0 323 249 251 3,372Total 4,360

Table 8. Barrier leakage estimates for mines with multiple adjacentmines (refer to Figure 2 for barrier locations).

Barrier ID Mines Dh (m) LB (m3/d)

C1 Crucible-Dilworth 19 223.8C2 Crucible-Nemacolin 2.7 40.8

Crucible total 264.5N1 Nemacolin-Dilworth 16.3 83.4N2 Nemacolin-Robena 24.3 801.5

Nemacolin total 884.9



operator-supplied values for 2011 (Table 7). Thecalculated daily increase in storage within Pitt Gasand Gateway was distributed across 3,951 WEL cells(Table 4 and Figure 10). Barrier leakage into Robenafrom Nemacolin and vertical infiltration to Robena inexcess of pumping from Robena were distributedamong 233 WEL cells in Robena to simulate leakageto Warwick #3 (Table 4).

Layers 2 and 3 were assigned isotropic K values of1000 m/d to simulate large conduits associated withmain entries and highly conductive gob zones. Inlayer 1, KH was assigned a value of 1.0 m/d, while KV

was assigned a value of 100 m/d, reflecting the factthat layer 1 is thought to contain significant verticalfracturing.

The top of layer 1 is where groundwater entersactive cells in the model by vertical infiltration. Theper-cell infiltration rate was calculated at 100 3

100 m2 grid scale using local overburden thicknessand the depth-dependent vertical infiltration relation-ship (Figures 7 and 8).

Calibration

Although groundwater elevations vary seasonallyin all these mines, average annual elevations withinmonitoring wells during 2012 (Table 9 and Figure 3)were used for calibration. Calibration was accom-plished by iteratively adjusting KB of individual inter-mine barriers until modeled heads were within 1.0 mof target values (Table 9). The calibration processalso required a reduction in the volume of ground-water extracted by WEL cells for DS within Gatewayand Pitt Gas (Table 4). A head change criterion of1025 m and mass balance error of 0.007 percent wereconsidered sufficient for convergence.

Figure 8. Vertical infiltration rates applied to the groundwater-flow model. This and later maps have been rotated from geographic northto align with the model grid.

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Model Results

Calibration required increasing KB values forbarrier sections by one to three orders of magnitudeover initial estimates (Table 10). The calibratedpotentiometric contours indicate flow within individ-ual mines from relatively high vertical infiltrationareas towards leaky barriers, pumps, and the WELcells, which simulate leakage into the overlyingWarwick #3 mine (Figure 11). These contours deflect

at leaky inter-mine barriers as a result of differencesin conductivity between mines and barriers. In short,the barriers tend to maintain individual pools withineach mine that may receive leakage or leak into one ormore adjacent mines. The potentiometric contoursmay be analyzed to show the locations of flow dividesthat partition the study area into a number ofcatchments, while particle traces indicate that ground-water may move through multiple mines beforedischarging (Figure 11).

Figure 9. Conceptual model of groundwater flow across leaky barriers.



DISCUSSION

Results indicate that post-mining hydrogeologywithin flooded and flooding underground minecomplexes is amenable to numerical modeling.

Known data, including groundwater elevations, minemaps, and pumping volumes, can be combined withvertical infiltration estimates to allow calculation ofbarrier leakage rates and flow patterns within andbetween adjacent mines. Results also indicate the

Figure 10. Boundary condition types and locations within the groundwater-flow model. WEL cells for storage and leakage are located inlayer 1; extraction wells, constant heads, and targets are all in layer 3.

Table 9. Observed and modeled groundwater-elevation heads in meters.

Target Min. Max. Avg.* s Modeled

CRU 236.3 237.5 237.0 0.35 237.0GAT1 228.0 233.4 230.5 1.46 230.6GAT2 227.5 233.0 230.1 1.62 230.6NEM 233.6 234.9 234.3 0.33 234.4PIT 229.4 235.0 231.8 1.42 230.9DIL 213.6 219.9 217.4 1.5 217.0**ROB 209.0 213.1 211.3 1.1 211.0**

*Year 2011 for DIL and ROB, 2012 for all others.**Values assigned to constant-head cells during initial calibration.

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potential for compromised barriers with leakage ratessignificantly greater than would be observed due tohomogeneous barrier leakage alone.

Calibrated KB values suggest that coal barrierswithin the study area are more conductive than thosein the Pittsburgh seam studied by McCoy et al.

(2006). It is likely that these barriers are hydraulicallycompromised by un-mapped entries between mines,boreholes, or subsidence. The actual KB values forintact coal barriers may well be similar to thosedetermined by McCoy et al. (2006), but the signifi-cantly greater calibrated KB values are the result ofaveraging relatively low-KB barrier segments withrelatively highly conductive compromised barriersections. The distribution of barrier leakage out ofNemacolin and Crucible into adjacent mines indicatesvariation in barrier hydraulic properties and geome-try. The calibrated KB values for barriers N1 and N2are similar (Table 10), which suggests that thesignificantly greater barrier leakage from Nemacolinto Robena than from Nemacolin to Dilworth(Table 4) results from the greater length and narrowerwidth of N2 relative to N1 (Table 3), as well as thesteeper head gradient between Nemacolin and Ro-

Table 10. Calibrated KB values.

Inter-Mine Barrier K (m/d) % McCoy*

C1 0.53 700C2 2.00 2,600G 0.55 700M 25.00 32,000N1 0.30 400N2 0.49 600

*Average K for intact coal barriers: 0.078 m/d (McCoy et al.,2006).

Figure 11. Calibrated steady-state hydraulic heads for layer 3. Symbology as for Figure 9.



bena (the N2 barrier) compared to Nemacolin andDilworth (the N1 barrier; Table 9 and Figure 11).The C1 and C2 barriers are of similar width, but C2 islonger and more conductive; nevertheless, Crucibleleaks more water into Dilworth than it does toNemacolin, which suggests that the higher headgradient between Crucible and Dilworth is theprimary control on barrier leakage out of Crucible(Tables 3, 4, 9, and 10). The calibrated KB for barrierM is an order of magnitude higher than all other KB

values calculated in the model (Table 10), yet M isalso the widest and shortest barrier (Table 3). Theseand other observations are interpreted as strongevidence that many barrier sections in this study areaare hydraulically compromised and not exhibitingsimple matrix or fracture flow.

Calibrated groundwater-elevation contours indicateflow toward the pumps in Dilworth and Robena andtoward WEL cells in Robena, which simulate leakageto Warwick #3, and also locate several flow divideswithin the study area (Figure 11). The locations of theflow divides reflect variation in barrier hydrauliccharacteristics and geometry and outline catchmentsthat illustrate the partitioning of groundwater betweenthe different sinks. The catchments show that ground-water infiltrating any individual mine may flowthrough multiple adjacent mines before reaching asink (Figure 11). For example, vertical infiltrationentering Pitt Gas flows though Gateway, Mather, andmost of Dilworth before being extracted from Dil-worth, while vertical infiltration that enters Cruciblemay leak directly to Dilworth, leak to Nemacolin, andthen to Dilworth, or leak to Nemacolin, flow throughRobena, and then pass through Warwick #3 in routeto pumps in Shannopin. The calibrated groundwater-elevation contours also depict relatively low headgradients within individual mines as well as significantdifferences between KB and K in the collapsed zone,indicated by the deflection of contour lines nearbarriers. Both mimic shallow hydraulic gradientsobserved in underground mine pools (Aljoe andHawkins, 1992).

The model indicates that groundwater elevations insome contiguous flooded mines may achieve season-ally varying, inter-annual equilibrium when barrierleakage from these mines to adjacent mines issufficient to offset vertical infiltration. Crucible andNemacolin maintain relatively constant groundwaterelevations by discharging to adjacent mines. Thecurrent conditions in Mather are unknown, butgroundwater elevations in that mine are similarlythought to at equilibrium as inflowing water leaks toDilworth. During this study, Pitt Gas and Gatewaywere still flooding yet leaking considerable volumes ofwater to Mather. At present, it is uncertain whether

these mines will achieve steady state by barrierleakage or ultimately discharge to the surface.

The depth-dependent vertical infiltration modelyields infiltration rates that decrease exponentiallywith increasing depth, whereas earlier methods tendedto apply uniform recharge rates to shallow areas whileassuming vertical infiltration is negligible in relativelydeep (.75 m) mined areas. Applying recharge only tothin overburden areas (,75 m) resulted in rates thatwere orders of magnitude greater than values reportedfor relatively shallow mines. The vertical infiltrationmodel therefore offers an improved method when deepmining becomes a significant portion of the totalmined area. Yet, there is some uncertainty in thevertical infiltration model. Within the study area,modeled vertical infiltration exceeds extraction pump-ing by roughly 40 percent (Table 4). The model can beadjusted to site-specific information by changing the lvalue (Eq. 3). A minimum l (lmin) value was attainedby setting vertical infiltration equal to pumping andadditions to storage within Gateway and Pitt Gas andignoring barrier leakage into or out of the study area,yet calibrating the groundwater-flow model to lmin

requires groundwater flow from Robena to Nemacolinagainst the head gradient. It is likely that the actual lvalue is between 0.021 and 0.023 within the study area,yet further refinement of l is considered unwarrantedgiven uncertainties in barrier leakage rates, verticalleakage from Robena to Warwick #3, and thepotential for barrier leakage between the study areaand surrounding mines.

CONCLUSIONS

N Post-closure mine flooding often results in complexhydrogeological conditions among groups of adjacentmines. These conditions are influenced by verticalinfiltration, barrier leakage, and pumping rates.

N The post-mining hydrogeology of mine complexesis amenable to numerical modeling given knowndata, including groundwater-elevation heads,pumping rates, and the geospatial extent of mining.

N Current recharge estimation for undergroundmines assumes that recharge only occurs in areaswith relatively thin (,75 m) overburden andneglects leakage to deeper mined areas. Thisrestriction results in increasingly high rechargerates as the depth of mining increases.

N The depth-dependent vertical infiltration modeloffers an improved method for estimating rechargeto underground mines, especially as the area ofrelatively deep mined area (.75 m) increases. Themodel is amenable to modification for site-specificconditions in other mine complexes.

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N Calibrated coal-barrier hydraulic conductivity val-ues are greater than those reported by McCoy et al.(2006) by 33 to 253. The causes for these increasesare unknown, but it is speculated that un-mappedentries between mines, boreholes, or other condi-tions have resulted in hydraulic compromise ofbarrier integrity.

N The calibrated groundwater-flow model indicatesthat barrier leakage is sufficient to offset verticalinfiltration within individual mines, making itpossible for groundwater extraction pumps in oneor more mines to control pool elevations inmultiple adjacent mines. The model further indi-cates that vertical leakage may play a role in theFMB of mines that are overlying or underlyingother mined coal seams. Vertical leakage isespecially likely when the inter-burden separatingmined seams lies within the fractured zone.

N The results of this study have implications for otherflooding and flooded underground mines, includingthe post-closure treatment of mine water. Failure toconsider post-flooding hydrogeological conditionssuch as potential inter-mine connections amongadjacent mines may result in poorly sited pumps,undersized wastewater treatment plants, and un-derestimation of water-treatment budgets.

ACKNOWLEDGMENTS

The authors would like to thank T. D. Light, J.Hawkins, and two anonymous reviewers for com-ments that improved the manuscript.

REFERENCES

ADAMS, R. AND YOUNGER, P. L., 2001, A strategy for modelingground water rebound in abandoned deep mine systems:Groundwater, Vol. 39, No. 2, pp. 249–261.

ALJOE, W. W. AND HAWKINS, J. W., 1992, Application of aquifertesting in surface and underground mines: Groundwater

Management, Vol. 13, pp. 541–555.

BANKS, D.; YOUNGER, P. L.; ARNESEN, R.; IVERSEN, E. R.; AND BANKS,S. B., 1997, Mine-water chemistry: The good, the bad and theugly: Environmental Geology, Vol. 32, No. 3, pp. 157–174.

BEARDSLEY, R. W.; CAMPBELL, R. C.; AND SHAW, M. A., 1999,Chapter 20. Appalachian Plateaus. In Shultz, C. H. (Editor),The Geology of Pennsylvania: Pennsylvania GeologicalSurvey, Harrisburg, PA, and Pittsburgh Geological Survey,Pittsburgh, PA, pp. 286–297.

BOOTH, C. J., 1986, Strata-movement concepts and the hydro-geological impact of underground coal mining: Groundwater,Vol. 24, No. 4, pp. 507–515.

DONOVAN, J. J. AND FLETCHER, J., 1999, Hydrogeological and

Geochemical Response to Mine Flooding in the Pittsburgh Coal

Basin, Southern Monongahela River Basin: Project WV-132,Final Report to the U.S. Environmental Protection Agency,Morgantown, WV, p. 47.

EDMUNDS, W. E.; SKEMA, V. W.; AND FLINT, N. K., 1999, Chapter 10.Pennsylvanian. In Shultz, C. H. (Editor), The Geology ofPennsylvania: Pennsylvania Geological Survey, Harrisburg, PA,and Pittsburgh Geological Survey, Pittsburgh, PA, pp. 148–169.

FENNEMAN, N. M., 1938, Physiography of Eastern United States:McGraw-Hill, New York, 714 p.

HARBAUGH, A. W.; BANTA, E. R.; HILL, M. C.; AND MCDONALD,M. G., 2000, The U.S. Geological Survey Modular Ground-Water Model—User Guide to Modularization Concepts andthe Ground-Water Flow Process: U.S. Geological SurveyOpen-File Report 00-92, p. 121.

HARLOW, G. E., JR. AND LECAIN, G. D., 1993, HydraulicCharacteristics of, and Groundwater Flow in, Coal BearingRocks of Southwestern Virginia: U.S. Geological SurveyWater-Supply Report 2388, 36 p.

HAWKINS, J. W. AND DUNN, M., 2007, Hydrologic characteristicsof a 35-year-old underground mine pool: Mine Water and theEnvironment, Vol. 26, No. 3, pp. 150–159.

HENNEN, R. V. AND REGER, D. B., 1913, Marion, Monongalia, andTaylor Counties: West Virginia Geological and EconomicSurvey, Morgantown, WV, 844 p.

HOBBA, W. A., 1991, Relation of Fracture Systems to Transmis-sivity of Coal and Overburden Aquifers in Preston County,West Virginia: U.S. Geological Survey Water-ResourcesInvestigations Report 89-4137, 24 p.

KENDORSKI, F. S., 1993, Effect of high-extraction coal mining onsurface and ground waters. In Peng, S. S. (ed.), Proceedings,12th International Conference on Ground Control in Mining:West Virginia University, Morgantown, WV, pp. 412–425.

KIPP, J. A. AND DINGER, J. S., 1987, Stress-relief facture control ofground-water movements in the Appalachian Plateaus. InNWWA Focus Conference on Eastern Regional Ground-WaterIssues, July 1987: Burlington, VT, 6 p.

KOZAR, M. D. AND MATHES, M. V., 2001, Aquifer-CharacteristicsData for West Virginia: U.S. Geological Survey Water-Resources Investigations Report 01-4036, 74 p.

LEAVITT, B. R., 1999, Mine flooding and barrier pillar hydrologyin the Pittsburgh basin. In Proceedings 16th Annual Interna-tional Pittsburgh Coal Conference. Pittsburgh, PA, Paper 6-4.

LIGHT, D. D. M., 2001, A Hydrogeological and HydrogeochemicalCharacterization of the Truetown Mine Discharge: Unpub-lished M.S. Thesis, Department of Geological Sciences, OhioUniversity, Athens, OH, 271 p.

MCCOY, K. J., 2002, Estimation of Vertical Infiltration into DeepPittsburgh Coal Mines of WV-PA: A Fluid Mass BalanceApproach: Unpublished M.S. Thesis, Department of Geologyand Geography, West Virginia University, Morgantown,WV, 151 p.

MCCOY, K. J.; DONOVAN, J. J.; AND LEAVITT, B. R., 2006,Horizontal hydraulic conductivity estimates for intact coalbarriers between closed underground mines: Environmental &Engineering Geoscience, Vol. 12, No. 3, pp. 273–282.

MCDONOUGH, K. M.; LAMBERT, D. C.; MUGUNTHAN, P.; AND

DZOMBAK, D. A., 2005, Hydrologic and geochemical factorsgoverning chemical evolution of discharges from an aban-doned, flooded, underground coal mine network: Journal ofEnvironmental Engineering, Vol. 131, No. 4, pp. 643–650.

MILLER, L., 2000, Warwick Coal Mines: Greene County, Pennsyl-vania: Rita Miller Publishing, 256 p.

PALCHIK, V., 2002, Influence of physical characteristics of weakrock mass on height of caved zone over abandonedsubsurface coal mines: Environmental Geology, Vol. 42,No. 1, pp. 92–101.

PALCHIK, V., 2003, Formation of fractured zones in overburdendue to longwall mining: Environmental Geology, Vol. 44,No. 1, pp. 28–38.



PENG, S. S., 1986, Coal Mine Ground Control, 2nd Ed.: John Wiley& Sons, New York, 491 p.

PIGATI, E. AND LOPEZ, D. L., 1999, Effect of subsidence onrecharge at abandoned mines generating acidic drainage: TheMajestic Mine, Athens County, OH: Mine Water and theEnvironment, Vol. 18, No. 1, pp. 45–66.

SAHU, P. AND LOPEZ, D. L., 2009, Using time series analysis of coalmine hydrographs to estimate storage, retention time, andmine-pool interconnection: Mine Water and the Environment,Vol. 28, No. 3, pp. 194–205.

SINGH, M. M. AND KENDORSKI, F. S., 1981, Strata disturbanceprediction for mining beneath surface water and wasteimpoundments. In Peng, S. S. (ed.), Proceedings of the 1stConference on Ground Control in Mining: West VirginiaUniversity, Morgantown, WV, pp. 76–89.

STOERTZ, M. W.; HUGHES, M. L.; WANNER, N. S.; AND FARLEY, M.E., 2001, Long-term water quality trends at a sealed, partiallyflooded underground mine: Environmental & EngineeringGeoscience, Vol. 12, No. 1, pp. 51–65.

STONER, J. D., 1983, Probable hydrologic effects of subsurfacemining: Groundwater Monitoring Review, Vol. 3, No. 1,pp. 128–137.

STONER, J. D.; WILLIAMS, D. R.; BUCKWALTER, T. K.; FELBINGER, J.K.; AND PATTISON, K. L., 1987, Water Resources and the Effectsof Coal Mining, Greene County, Pennsylvania: PennsylvanianGeological Survey Water Resource Report 63, 4th Series, 166 p.

WHITWORTH, K. R., 2002, The monitoring and modelling of minewater recovery in UK coalfields. In Younger, P. L. andRobins, N. S. (Editors), Mine Water Hydrogeology andGeochemistry: Geological Society of London Special Publi-cation 198, pp. 61–73.

WILLIAMS, D. R.; FELBINGER, J. K.; AND SQUILLACE, P. J., 1993,Water Resources and the Hydrologic Effects of Coal Mining inWashington County, Pennsylvania: U.S. Geological SurveyOpen-File Report 89-620.

WINTERS, R. W. AND CAPO, R. C., 2004, Ground water flowparameterization of an Appalachian coal mine complex:Groundwater, Vol. 42, No. 5, pp. 700–710.

WYRICK, G. G. AND BORCHERS, J. W., 1981, Hydrologic Effects ofStress-Relief Fracturing in an Appalachian Valley: U.S.Geological Survey Water-Supply Paper 2177, 51 p.

YOUNGER, P. L. AND ADAMS, R., 1999, Predicting Mine WaterRebound: Environment Agency R & D Technical ReportW179, Bristol, UK, 109 p.

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