Vapor intrusion investigation and mitigation in a residential neighborhood

To evaluate vapor intrusion near a site with groundwater impacted by chlorinated solvents, primarily trichloroethylene (TCE), our client hired Barr to assist with a large-scale vapor intrusion investigation in a residential area. Using a tiered approach following the Minnesota Pollution Control Agency’s (MPCA’s) risk-based guidance, we first performed a desktop screening-level vapor-intrusion study to determine that vapor intrusion represented a potential concern and required further investigation.

Barr then collected soil-gas and groundwater samples in public rights-of-way to further evaluate the potential vapor intrusion risk and define areas where building-specific data was needed. This information indicated that building-specific data was needed from approximately 300 properties.

As part of the building-specific sampling effort, Barr communicated with property owners and building occupants regarding sampling, obtained access agreements, and scheduled appointments. Each property was assigned a “property coordinator,” a Barr staff member who followed the property through the life cycle of the project, including communicating with property owners and building occupants, obtaining access agreements, scheduling sampling appointments, and communicating sampling results. Due to the large number of properties, communications with property owners and other property-specific data were documented in a database for frequent reporting to our client and regulatory agencies.

This personalized approach resulted in participation from 95 percent of property owners. Barr’s sampling technicians used manually operated drills, vapor-pin sample ports, leak-testing methods, and Summa canisters to collect sub-slab soil gas samples. Indoor air sampling was also completed at selected locations.

Based on the results, active sub-slab depressurization mitigation systems were installed at more than 185 properties. Barr observed the installations and also observed and documented post-installation diagnostic testing to confirm the effectiveness of each system.