INADVERTENT REROUTING OF GROUNDWATER FLOW IN CARBONATE AQUIFERS OF THE GREENBRIER VALLEY, WEST VIRGINIA

The Greenbrier Valley of West Virginia, on the eastern edge of the Appalachian Plateaus physiographic province, is a broad limestone terrane that is heavily karstified. Low-order surface drainage is nearly absent, and the groundwater system is a complex mix of confined and unconfined aquifers, fractures, and conduits (caves). Many of the caves are extensive. Water supply for homes and farms is primarily from wells, up to several 100 meters in depth. In two of the major cave systems, water well drilling appears to have introduced ongoing flows of water from other hydrostratigraphic units. These flows were investigated in an attempt to understand their origin and impact on the aquifers.

Scott Hollow Cave is a 40 km long conduit with 1 known entrance located in northern Monroe County. In 1997 a flow of water burst forth from a conduit wall along the North-South passage. Rock fragments found in the vicinity of this flow appeared to be shale drill cuttings. A red precipitate began to form on the streambed. Discharge was found to be 11 cubic meters per hour, and has continued to the present day. The water is high in sulfate, and very low in nitrate as compared to most other waters in the cave. In spring of 2001 large fragments of PVC well screen were found in this vicinity, along with electrical wire.

Organ Cave is a 64 km long cave system with several entrances located in Greenbrier County. In 1991 a new flow, termed the Red River, burst forth from the base of a wall in the Upper Stream Passage. It was noted that drilling of an agricultural well was being conducted in the vicinity of the cave that day. Discharge was found to be 6 cubic meters per hour, and has continued to the present day. A red precipitate is also present at this site, and the water chemistry is similar to that at Scott Hollow Cave.

In both of these instances the new water flows appear to be following bedding plane channels that were active in a previous (phreatic?) stage of cave growth. Drilling of uncased holes in such terrane can breach confining units, some of which are quite thin. This may then allow downward or upward leakage in to conduits that are under vadose conditions. This is reflected in the nitrate values of the new flow water, which are 2 orders of magnitude less than the usual cave conduit water. Negative impacts can include changes of water quality and aquifer decline.