Hydrogeologic investigations of contaminant movement in karst aquifers in the vicinity of a train derailment near Lewisburg, Tennessee

Abstract

A train derailment near Lewisburg, Tennessee, in October 1990 prompted two series of groundwater investigations. The first was to determine the subsurface flow route of chloroform and styrene that sank into the underlying karst aquifer. The second was to determine the source of contamination for two nearby residential wells which were found to be contaminated with trichloroethylene (TCE). Water-sample analysis and a dye trace performed at the time of the train derailment indicated groundwater flow to Wilson Spring. A dam was constructed to contain the entire discharge from the spring so that it could be treated before being discharged into Big Rock Creek. Three springs and three water wells were contaminated with chloroform and styrene. Dye traces were performed to determine groundwater flow directions in the vicinities of the TCE-contaminated wells and in the vicinities of potential sources. At the train derailment, the chloroform and styrene sank into the Upper Ridley Karst Aquifer and pooled on top of the Lower Ridley Confining Layer. An exploratory well revealed a layer of chloroform (a Dense Non-Aqueous Phase Liquid DNAPL) on the bottom, a layer of groundwater in the middle, and a layer of styrene (a Light Non-Aqueous Phase Liquid LNAPL) on top. Groundwater with relatively low levels of chloroform and styrene in solution was carried by a small cave stream southeast along the strike to Wilson Spring. Chloroform product moved by gravity southwest down-dip along weathered bedding planes. Treatment of contaminated groundwater from Wilson Spring and recovery wells at the spill site has occurred continuously since October, 1990.