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Sigma soil and groundwater investigation and remediation for Harley-Davidson

Wauwatosa, Wisconsin

Harley-Davidson Motor Company retained Sigma in 2000 to continue subsurface soil and groundwater investigation activities associated with chlorinated solvents Trichloroethylene (TCE) and daughter products Dichloroethylene (DCE) and Xylenes (VC) previously discovered at the site.

Sigma’s additional investigation work included installation of shallow monitoring wells, intermediate-depth piezometers (approximately 35 feet below grade), and deep piezometers (up to 96 feet below grade); advancement of Geoprobe soil borings and test pits in source areas to better characterize chlorinated solvent impacts to soil; completion of groundwater sampling events; and performance of bench-scale testing evaluating potential in situ remediation technologies. Sigma reviewed remedial options with Harley-Davidson to derive the best solution to satisfy Wisconsin Department of Natural Resources (WDNR) regulations and minimize potential liabilities.

In 2004, Sigma began implementing the WDNR-approved remedial action plan, which consisted of 1) source area soil treatment via chemical oxidation with potassium permanganate; 2) down- gradient groundwater control with a low-permeability slurry wall and bentonite plugs around underground utility lines; 3) site grading, construction of improved stormwater controls, and placement of low permeability engineered barriers to reduce surface water infiltration; and 4) remediation by natural attenuation groundwater monitoring to address residual subsurface impacts.

The first three remediation components were successfully completed in the summer of 2004. Highlights include a 95% reduction in TCE mass in approximately 1,250 cubic yards of source-area soil and the installation of 415 feet long by 45 feet deep soil-bentonite slurry wall. The natural attenuation groundwater monitoring component of the remediation strategy was completed between August 2004 and July 2009 and demonstrated that the initial remediation work was effective and that residual chlorinated solvent impacts were degrading over time. WDNR issued final case closure in February 2010 with land use restrictions and WDNR GIS Registry listing for residual soil and groundwater impacts present at the site at the time of closure.