A release of chlorinated solvents led to impacts to the shallow aquifer underlying an active manufacturing facility with a residential neighborhood located immediately downgradient.
Geosyntec completed a groundwater investigation that identified impacts to shallow groundwater by chlorinated solvents underlying the neighborhood, which required further investigation to identify if the vapor intrusion to indoor air pathway was complete in any of the nearby residences.
Geosyntec's Scope of Services
Geosyntec was retained to complete vapor intrusion investigations at both the manufacturing facility and the downgradient residential neighborhood. We used high volume sampling (HVS) to complete a cost-effective evaluation of sub-slab soil gas chlorinated solvent concentrations beneath the existing manufacturing building. Based on the observed sub-slab concentrations, we installed a sub-slab depressurization (SSD) system to mitigate vapor intrusion to indoor air at the 60,000-square-foot facility.
We also installed 25 soil gas probes to guide the residential vapor intrusion investigation in shallow and deep pairs to evaluate attenuation within the unsaturated zone. Concentrations of site constituents exceeded the residential shallow soil gas screening level at multiple locations, suggesting the vapor intrusion to indoor air pathway was likely complete at several properties. We expanded the study area step-wise based on soil gas results to include over 150 residential properties, completing and documenting community outreach efforts to gain access which included letters, phone calls, and door-to-door knocking. When access was granted, we met with the residents in their homes to describe the sampling protocol.
Getting access to over 90 properties allowed us to complete sub-slab, basement, and indoor air sampling at all properties with a full basement. At homes with crawlspaces, we collected crawlspace and indoor air samples. Based on the observed results, we offered SSD or sub-membrane depressurization (SMD) systems to basement or crawlspace properties, respectively, that showed indoor air concentrations above the relevant residential indoor air screening level. Over 30 residential mitigation systems have been installed thus far.
Geosyntec successfullly identified and mitigated the vapor intrusion exposure pathway at both commercial and residential locations. Throughout the process, we have maintained excellent relations with state regulators and affected homeowners, allowing the project to progress quickly. In addition, we took a proactive and transparent stance with our community involvement and outreach program, developing and maintaining collegial relationships with the local news media, the County Health Commissioner, and the City Manager's office. This allowed to get out ahead of public opinion, potentially saving our client from significant and costly litgation.
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- Location: Southwestern Ohio
- Client: Confidential
- Project Practice Areas: Contaminated Sites, Air Quality
- Type of Facility: Residential area
- Services Provided: Commercial vapor intrusion mitigation, Residential vapor intrusion investigation and mitigation, Community relations, Regulatory negotiation
- Type of Work: Vapor intrusion mitigation
- Governing Regulation: Federal and state regulations