Presidio Square Apartment Complex
brown deer, wisconsin
In the early 1990s, chlorinated solvent contamination from dry cleaning and metal finishing industries was detected in the southern portion of a 20-acre apartment complex property. Concentrations of tetrachloroethylene (PCE), trichloroethylene (TCE), and their associated degradation products, as well as petroleum-based solvents such as toluene and xylene were observed in both soil and groundwater samples collected at the site. Multi-phase subsurface investigations involving soil and groundwater sampling and vapor intrusion assessments were performed at both on- and off-site locations under the direction of the WDNR, Department of Health and Human Services, and the City of Milwaukee Health Department, including the following:
Following extensive investigation and source area delineation efforts Sigma prepared a conceptual remedial action plan. The conceptual plan included a field pilot study to evaluate the in situ source treatment strategy. Based on the field pilot study performed by Sigma, enhanced anaerobic bioremediation was identified as the most cost-effective and applicable remediation technology to address volatile organic compounds present at the site. The in situ enhancement plan consists of providing appropriate substrate and nutrients to the subsurface to promote microbial population growth and accelerate bio-degradation of the toxic constituents to their less toxic degradation compounds. Considering the residential use of the property and limited access to the on-site source areas a network of shallow infiltration galleries were proposed for subsurface delivery of the substrate and nutrients.
Remediation System Design and Installation
The remedial system design plan was prepared and submitted to WDNR for review and approval. Following receipt of the WDNR approval and underground injection permit, the remedial system was installed in early 2008 and the program of periodic addition of bio-enhancing materials was implemented.
Soil vapor venting systems were installed beneath apartment buildings to prevent the accumulation and migration of volatile vapors from the impacted soil and groundwater. Within three months of system operation significant reductions in concentration of parent compounds were observed. In situ treatment will continue for the next two years (2009-2010) followed by natural attenuation monitoring.