Characterizing a VOC Plume Migrating From Fractured Shale into a Karst Limestone Aquifer

ABSTRACT: Delineation of the NAPL source zone in the vicinity of an oil burn pit (OBP) at Letterkenny Army Depot (LEAD) revealed the presence of source material on both sides of a nearby groundwater divide resulting in a bilobate plume. While the northern lobe of the plume migrating from the OBP had been well defined, the southern lobe of the plume had been previously undetected. An investigation was initiated to determine whether the southern lobe of the plume had reached the Pinola Fault (900 ft downgradient), the formation contact between the Martinsburg Shale and the St. Paul Limestone, and if so, what impacts the plume was having on groundwater/surface water quality in the limestone aquifer. Dye tracing and aquifer tests had shown significant differences in groundwater velocities between the two rock types (i.e.; ft/year in the shale versus >2,000 ft/day in the limestone).