Historical dry cleaning solvent spills from an active dry cleaners contaminated soil and ground water under a shopping center. The migration of contaminants in shallow ground water spread contamination from under the building into a residential subdivision. The resulting plume of contaminated ground water was more than 1,000 feet long.
Geology and Hydrogeology
The geology of the site was a complex of interbedded marine sediments. The surface material was interbedded silt and sand lenses. The water table was approximately 20 feet deep. The affected aquifer was an unconfined silty sand zone approximately 16 feet thick. The underlying formation was a dense clay aquitard.
Ground Water Contamination
The size of ground water plume that resulted from leaching soil contaminants was estimated to be 150,000 square feet. The contamination was tetrachloroethene (PCE) and its breakdown products trichloroethene (TCE), cis 1,2-dichloroethene (cis 1,2-DCE), and vinyl chloride. The following table shows the pre-treatment concentrations at the source area, mid-plume and at the front of the ground water plume.
With the high concentrations in the source area, a chemical oxidation treatment was implemented. For the downgradient plume, CL-Out bioremediation was selected and injected at key locations to effectively treat the plume. Ten units of CL-Out (5,500 gallons) were injected into the contaminated ground water through vertical injection wells scattered throughout the centerline of the ground water plume.
Within one year of the application of CL-Out, the contaminant concentrations were significantly reduced throughout the plume. The following table shows the contaminant reductions in the source area, mid-plume and down gradient plume front.
Please refer to the able below for the pre- and post-treatment sampling results. The contaminant concentrations were reduced by 97% in the source area, 86% at the leading edge of the plume, and 65% mid-plume. This effectiveness was the result of the concentration of effort in the source area and the front of the plume, where most of the injection took place and the greatest benefits were to be gained.