Department of Geology |
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Project Summary
The focus of this study will be to determine the cause of abrupt changes in flow volumes in a carbonate aquifer. Two locations, one in Scott Hollow Cave and the other in Organ Cave, West Virginia have been identified, each of which experienced a major, abrupt, long-term change in hydrology, possibly as the result of nearby drilling. The conduit flows in this study, have been named "spigots." The water associated with both flows deposits a red iron oxy-hydroxide precipitate. Evidence determining the source of the spigot flow will include: the spatial relation of the spigot flows to known wells, the timing of drilling and flow formation, the chemistry of spigot water compared to other local groundwaters, and the depression of the water table near deepened wells. This study will evaluate the source of both spigot flows and their influence on their associated karst systems.
Location and Overview of the Study Area
The study area is a region of rolling hills lying between the Allegheny Plateau and the western margin of the Valley and Ridge province. The area includes portions of Greenbrier County and Monroe County, West Virginia near the juncture of the Central and Southern Appalachians (Ogden, 1976; Dasher, 2000). It is comprised of numerous synclines and anticlines, with minor open folds with gently inclined limbs and many sinkholes (Davis, 1999). There are a number of rivers and tributaries dissecting and bounding the study area, but overall, it visibly lacks surface drainage between the boundaries. Dry valleys and sinkholes shape the plateau surface, resulting in a gently rolling landscape (Stevens, 1988). Along the edge of the plateau the relief varies from 100-600 feet. Notably, to the north, the plateau edge plunges 400-600 feet towards the Greenbrier River (Stevens, 1988). Much of the study area is agricultural land, bounded by hardwood forests along the margins (Stevens, 1988). The primary aquifers in this region are the Sinks Grove Limestone and the Hillsdale Limestone (comprising the Greenbrier Group), underlain by the semi-calcareous Maccrady Shale (Davis, 1999). Both Scott Hollow and Organ Cave, which are the focus of this study, are in vadose conditions.
Both caves are developed in the Middle-Late Mississippian Greenbrier Group, within the Hillsdale and Sinks Grove Limestones. Heller (1980) describes the Maccrady Shale, which is at the base of the Greenbrier Group, as a reddish-purple shale/mudstone containing thin layers of green shales and tan to gray siltstones (Fig. 1). The Maccrady Shale also contains discontinuous units of limestones and calcareous shales, interbedded near the upper portion of the Maccrady with the basal Hillsdale (Heller, 1980). The Hillsdale Limestone is primarily blue-gray in color, and contains interbedded shale near the base (Ogden, 1976). Grain size is characterized as fine-coarse upwards, and hosts an abundance of gray to black colored chert nodules (Ogden, 1976). The uppermost portion of the unit is recognized by 10-15 feet of shaly limestone (Ogden, 1976). Ogden (1976) describes the Sinks Grove (overlying the Hillsdale) as a massive, hard, fossiliferous limestone, containing small amounts of sand or shale near the upper portion of the bed. Weathered surfaces are blue-gray to yellow in color.
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Organ Cave is bounded by several surface drainage systems (Fig. 2). To the northwest are the Greenbrier River and Howard Creek, and to the south and southwest, Second Creek and Carpenter Creek. To the east, the basin is confined by the White Rock Mountains, which flank the Brown's Mountain Anticline (Stevens, 1988). Most of the recharge in the basin is through sinkholes and blind valleys. Lower Lipps and the Big Canyon stream passages are the primary drainage conduits within the Organ Cave system (Stevens, 1988).
Organ Cave formed along a syncline within the Organ Cave Plateau. Forty-six known caves have developed within the Plateau, Organ Cave being the second longest within the state of West Virginia at 37.6 surveyed miles (Stevens, 1988). The primary karst units associated within this study are the Hillsdale Limestone and the Maccrady Shale (Stevens, 1988).
The Scott Hollow drainage basin is to the southwest of Organ Cave. It is bounded to the north and northwest by the Greenbrier River, to the northeast by Second Creek and to the west by Flat Top Mountain. The two caves are separated by ~5 miles, with Second Creek running between the two basins.
The Scott Hollow drainage basin contains only one surface stream, Second Creek, and funnels other drainage from sinkholes. Allogenic runoff from Flat Top Mountain recharges Scott Hollow Cave and, the primary conduit (Mystic River) runs northward parallel to Flat Top Mountain (Dore, 1995). The Mystic River eventually flows into the Greenbrier River. Scott Hollow is formed within both the Sinks Grove and Hillsdale Limestones (Davis, 1999).
This study will focus on the southern portion of Scott Hollow Cave, along the North-South Passage. For Organ Cave, focus will be on the northeastern section of the cave in the Upper Stream Passage just upstream from the Waterfall Room. At these locations, new flows (spigots) have occurred and have been sustained from 4-10 years. Ten years ago, at the time of occurrence in Organ Cave, cavers witnessed the initial water flow blasting out of the conduit wall. In Scott Hollow Cave, four years ago, cavers noticed the flow one day, but the first breakthrough flow was not witnessed. The purpose of this thesis is to identify the cause of the new spigot flows and their relation to overlying aquifer changes.
It appears that the spigot flows are related to surface drilling in both Organ Cave and Scott Hollow. In 1991 in Greenbrier County, on a turkey farm near Organ Cave there was drilling for a water well. Soon after drilling, the spigot flow developed in Organ Cave. Similarly in Scott Hollow, in 1997, an active water well drill location was stationed near the cave and soon after spigot flow developed. What appears to be shale drill cuttings, due to the sediments' angular shape and uniqueness to surrounding sediments, were found dispersed a few feet around the spigot in Scott Hollow Cave
(Fig. 3). Following the initiation of spigot flow, a number of local wells went dry. This sequence of events suggests a direct relation between well drilling, spigot formation, and aquifer depressurization.
Procedures
Local water well drilling records from the Monroe County Health Department and the Greenbrier County Health Department will be used in identifying the relationships between local aquifers/wells, drilling, and the formation of the spigots. An evaluation will be made of the three primary aquifers associated with the Greenbrier Group: Maccrady-Hillsdale, Taggard, Pickaway-Union aquifers (Heller, 1980), and the number of wells that experienced a decline in water level at about the same time the suspected wells were being drilled.
Maps and cross sections will be constructed to analyze the relationships between the drainage basins, the overlying strata, associated aquifers, drill locations, and the orientation of the Scott Hollow drainage basin in relation to the Organ Cave drainage basin. Maps will also feature overall water gradients and paths of conduit flow when known. Also, bedding, jointing, fractures, and/or fissures will be included.
A discharge log will be kept recording spigot flow at seasonal intervals. Precipitation records will be obtained from the National Oceanic and Atmospheric Administration - National Climate Data Center (NOAA-NCDC) for correlation to discharge measurements. This data may reflect the potential source for the spigot flows. Constant rate discharge even with increased rainfall may indicate a diffuse source for recharge.
Chemical analyses of water samples from Scott Hollow and Organ Cave will aid in determining the groundwater source of the spigot waters. Both spigot flows produce a similar iron rich precipitate, which will be analyzed by measuring iron concentrations in water and mineralogy of the precipitate. Water samples will be taken at the mouth of the spigots, and also upstream in the main channel. The analysis will evaluate spigot flow influences on the overall water chemistry of the stream channels. Samples will be taken according to standard procedure (Davis, 1999). pH, temperature, and conductivity will be measured in the field. Laboratory analyses of the geochemistry may be indicative of the sources of flows and the effects they have on the study area.
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Inductively Coupled Plasma Spectrometer (ICP) and Atomic Absorption (AA) will be used to measure the concentration of cations in the water. Ion chromatography will be used to measure anion concentrations. Ion speciation will be used to identify the form of existing elements, and saturation indices (SI) will be calculated to identify minerals being dissolved and/or precipitated. These calculations will be made using WATEQ4F (Ball and Nordstrom, 1987).
Sediment samples will be collected at both caves, upstream and downstream of the spigot, and at the spigot. A laboratory analysis on the roundness of the grains will be made, identifying drill cutting from other cave sediment. A mineralogical analysis will be made of the drill cuttings and iron precipitate. This analysis will be made using X-ray powder diffraction (XRD) and thin section techniques.
Expected Results
Evidence used to determine the source of the spigot flow will include: the spatial relation of the spigot flows to known wells, the timing of drilling and spigot flow formation, the chemistry of spigot water compared to other local groundwater values, and the depression pattern of the water table. A correlative relationship will be formulated; revealing that surface drilling has caused spigot flow, which in turn is causing some previously producing wells to go dry. Field studies and laboratory geochemical studies will show the spigot flows create a change in water quality at the contact interface and downstream from the flow. This study will make hydrologists aware of the consequences of drilling in karst regions.
List of Figures
1: Generalized stratigraphic section of the Greenbrier Group near Scott Hollow and Organ Caves.
2: Map showing location of proposed study area.
3: Photo of spigot in Scott Hollow Cave.
References Cited
Reference Supplements
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Last Updated: 6/29/01
