GASOLINE AND GROUNDWATER: EMERGENCY MANAGEMENT AND REMEDIATION OF AN URBAN KARST CONTAMINATION EVENT

Since the 1980’s, the City of Bowling Green, Kentucky, has dealt with numerous gasoline leaks in the underground rivers that comprise its urban karst landscape. After extensive work to conduct dye traces, geophysical investigations, and mapping of the cave passages and groundwater system, many of the issues caused by leaking underground storage tanks (USTs) and other surface spills were eradicated as sources were identified. Regulations of UST installation and monitoring practices evolved to reduce the threat of leakage. In March 2019, gasoline vapors were detected within Lost River Cave at the tourist entrance and throughout other parts of the system at actionable concentrations that persisted for several weeks on and off. Following storm event activity, the vapor concentrations increased and persisted at levels that initiated a response by the Kentucky Division of Waste, EPA, City of Bowling Green Environmental Compliance Division, and WKU CHNGES to locate and resolve the source of the leak, which had spread throughout the underground passages of Lost River. After an initial investigation of the area for obvious leaks or sources from local gas stations and bulk facilities, additional work was conducted to locate sinkholes, vapors, and other potential sources. A sinkhole was opened after finding high concentrations of vapors using a PID, which led to the discovery of an extensive epikarst cave system with a running stream in which product was discovered and sampled. Analysis indicated weathered gasoline and a dye trace study was conducted using three dyes from a nearby bulk facility with aged storage tanks and to connect the newly discovered stream to Lost River and surface water bodies, from which all traces were successful. After identifying the bulk plant at the potential source, UST removal occurred and additional monitoring of downstream sample sites occurred to measure the attenuation of the gasoline as the system responded to storm events and the remediation process. Upon removal of the tanks and after multiple storm flushes, the vapors decreased and the detection of gasoline in the new cave fell below actionable levels. The outcomes led to the discovery of a new tributary to the system and the need for improved mapping, GIS database construction, dye tracing, facility monitoring, and emergency response planning for urban karst groundwater contamination events, which are currently underway for the City of Bowling Green and being developed for application across urban karst areas.