Regional Commingled Chlorinated VOC Plume Delineation
Decades of manufacturing along an industrialized corridor of a Midwestern city resulted in the release of chlorinated volatile organic compounds (VOCs) to the ground which eventually affected the quality of groundwater within a sole source aquifer. All the facilities used or had used many of the common chlorinated VOCs including: tetrachloroethene (PCE), tricholoethene (TCE), and 1,1,1-trichloroethane (TCA). Most of the industrial facilities fell within a narrow band along a similar groundwater flow path. As a result, the chlorinated VOC plumes became commingled as they migrated down-gradient forming one of the largest groundwater plumes in the country. The resulting commingled plume extended a distance of nearly four miles before reaching the city’s primary well field. State regulators identified the problem through a review of the city’s water quality results and assembled a list of potentially responsible parties (PRPs). Cox-Colvin was retained by the largest PRP to work in cooperation with the state agency and the other PRPs to delineate the plumes. The commingled nature of the plume made it difficult to identify specific source areas, develop appropriate response actions, and allocate response costs.
To delineate the plumes, Cox-Colvin completed a regional groundwater study based on a detailed evaluation of stratigraphic relationships, groundwater flow patterns, and soil and groundwater quality data associated with a combination of nearly 200 monitor wells, domestic wells, temporary well points, and industrial wells, and over 100 soil samples. Cox-Colvin crews installed many of the wells and collected most of the analytical data. The data are housed in a Data Inspector™, Cox-Colvin’s Environmental Information Management software. Through a detailed review of these data, Cox-Colvin was able to delineate six distinct source areas and associated groundwater plumes using ratios plots of PCE, TCE, TCA, and specific VOC breakdown products. The delineation resulted in a better understanding of each PRP’s contribution to the plume and helped to focus source area remediation efforts.