Abstract
Abstract: More than two hundred homes in Hazleton, Pa. were found to have benzene vapors (a known carcinogen) from one of the largest underground gasoline storage tank spills in PA history. Remediating this site became the number one priority of USEPA Region III (EPA). A relic underground coal mine situated along a 3000 ft long plunging syncline beneath the Laurel Gardens neighborhood complicated site geology. The U.S. Army Corps of Engineers (USACE) determined if air filled mine voids existed and contained gasoline and gasoline vapors. The plan called for four study phases: Determining the mine location, Visualizing the geology and water table, Modeling mine pool effects on plume behaviors, and Field sampling to verify study results. Mine Location: GIS was used to georeference and compare a 19th century mine map of unknown datum and coordinate system with old aerial photos, boreholes data and microgravity survey results. Extremely accurate location of the mine was critical for locating potential gas filled voids. Visualization: A three dimensional geologic model was constructed from the GIS data and available site data depicting the relationship between site geology, the mine void, the mine pool elevation and the surrounding groundwater table. This predicted air filled mine voids in the upper areas of the syncline. Modeling: A finite element groundwater model (FEMWATER) was developed to study mine pool effects on gasoline plume movements. Two different approaches were compared for modeling the mine pool. In one approach the mine void was modeled as high conductivity aquifer. In the adopted approach, it was modeled as an interior boundary with assigned heads. The model showed dissolved gasoline contaminants migrating to the mine. Field Sampling: Using the gravity data and 3 dimensional mine model, several target areas for drilling were identified. Gas vapor explosion was a concern during drilling. The drilling plan incorporating the use of on-demand nitrogen gas connected to a drill rig. A gas filled mine void was encountered and an aqueous sample confirmed gasoline contamination in the mine.
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