DELINEATING THE SUBSURFACE – APPLYING SURFACE GEOPHYSICS TO LOCATE GROUNDWATER FLOW IN A KARST AQUIFER

Pollution and alteration of surface and subsurface hydrology increasingly threaten karst areas. In order to protect these fragile and dynamic areas, efficient diagnostic methods must be adapted for use in complex karst settings. While application of surface geophysical techniques to karst problems is not new, its use to delineate possible flow paths of clean water is. This study examines stream loss in a small tributary of the Youghiogheny River known as Hoyes Run in Garrett County, Maryland. The stream bounds the pit of the Deep Creek limestone quarry, operated by Keystone Lime Company. During low flow, the stream abruptly terminates in a swallet, leaving approximately 300 m of dry bed. Two other zones of loss were located during periods of higher flow. Multiple resistivity profiles using the SuperSting™ Resistivity System were generated along the zone of stream loss. A 3-D model of possible void space corresponding to resistivity response was generated using EMIGMA™ geophysical interpretation software. The resulting polygon suggests that a sizable void exists between the stream loss zone and the quarry pit. Dye trace using fluorescein™ confirmed the flow path of water from the stream into the quarry. Geologic examination of the area reveals several sizable known caves developed in the same limestone sequence {Greenbrier Formation, Loyalhanna Member (Ml)}; however, there are no known cave entrances in the immediate vicinity. Borehole confirmation is slated before remediation measures are executed. A possible repeat of the resistivity profiles utilizing attenuation enhancing salts injected into the groundwater is being considered to improve signal density. The study suggests that surface geophysics coupled with computer-based modeling can locate possible flow paths for groundwater in a karst aquifer, even in the absence of obvious karst surface expression.