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Challenge
Groundwater beneath an automobile dealership in Elkhart, Indiana was contaminated with volatile organic chemicals. These chemicals in the groundwater appeared to be migrating downgradient and off-site, and had the potential to impact adjacent residential areas and the St. Joseph River.
Action
To quantify potential chemical exposure concentrations due to off-site transport to receptor locations, Mundell personnel used the two-dimensional analytic element code GFLOW to generate a composite regional and site-specific groundwater flow model. This model was used to determine the pathway of groundwater moving downgradient of the site and to identify potential receptors along this migratory pathway. Using the results of the flow modeling as a basis, chemical transport modeling using the computer code MT3D was performed to evaluate the effects of dispersion, contaminant retardation and decay on the potential downgradient chemical concentrations resulting from on-site releases.
Results
The modeling analysis predicted no measurable impact to St. Joseph River water quality from the site due to the limited contribution of groundwater flow relative to the discharge rates in the St. Joseph River near Elkhart. An analysis of the impact of on-site pumping for direct consumption of groundwater indicated the impacts to human-health should be less than a cancer risk level of 4.3 x 10-6. Based on this risk assessment, the State of Indiana did not require active groundwater remediation at this site. This site has subsequently been closed and received a Covenant-Not-To-Sue under the State’s Voluntary Remediation Program.
