Along Strike Migration and Degradation of Halogenated Hydrocarbons at Depth through Fractured Limestone

Since 1975, site operators have manufactured specialized equipment and assembled utility trucks at the now closed site. Several Environmental Site Assessments (ESAs) were completed from 1990 to 2004. A fuel underground storage tank was removed, shallow wells were installed, and halogenated hydrocarbon-contaminated soil was removed. The hydrogeologic setting has been interpreted from subsurface data from prior investigations and data from corehole drilling and drilling and construction of 24 wells (monitoring wells, hereafter referred to as MW-11 through MW-25 including designations of shallow [S], intermediate [I], and deep [D]). Double cased monitoring wells were constructed to prevent interconnection of the water-bearing zones and downward migration of contaminants. The site is underlain by a Cambrian age formation, the Conasauga Formation, consisting predominantly of interbedded limestone and calcareous shale with an approximate thickness of 1,100 to 1,900 feet. Ground-water movement occurs along solutionally enlarged fractures of limited size and bedding planes. Interpretation of ground-water elevations indicate the direction of ground-water movement is generally toward the southeast, similar to the dip of the formation. Ground-water analyses indicate that many wells have concentrations of halogenated hydrocarbons above Maximum Contaminant Levels. The distribution of the organic constituents in nested wells illustrates the source area in the vicinity of the site operational area in shallow wells and migration and degradation by-products (chemical and biological transformation) in deeper wells, along strike. The contaminated ground water encompasses most of the site and has also migrated to at least 225 feet below land surface.