Abstract

A case study was conducted on the application of modeling in site assessment. We determined the potential for migration of 3 heavy metals and several organic compounds from a site 300 yards north of a swimming area. The site has a history of environmental issues and incidents dating back to 1985. In 2010 the Minnesota Pollution Control Agency (MPCA) measure levels from 638 to 6847 mg kg^-1 of ethyl benzene, toluene and xylenes (BTEX) compounds in manholes, tanks, and soil on the site. Previously, lead (Pb), cadmium (Cd) and chromium (Cr) concentrations in soil ranged from 210 to 18,000 ug kg^-1. Using reactive transport models with MODFLOW, plumes were developed for metals and BTEX compounds based on data from sediment testing, geological features, and site data from MPCA. Our plume models predict that heavy metals would enter of the swimming lake through surface water runoff and a BTEX plume would enter the swimming lake and the Minnesota River through groundwater. Sediment samples from a drainage ditch adjacent to the site contained concentrations of Cd and Cr 10 times higher than a nearby reference site supporting our plume results. Sediment samples also indicated that Cd and Cr concentrations decreased down gradient, further supporting model predictions. BTEX compounds were not detected in sediment or water samples during the study. We find that incorporating three-dimensional groundwater modeling into a site assessment can provide a useful estimate of a plume’s direction and concentration and aid in determining future sampling locations.

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