Elmwood Avenue PCE Vapor Intrusion Mitigation

WHEM has been under the contract with the Vermont Department of Environmental Conservation (VT DEC) to sample soil vapor and indoor air of residential buildings along Elmwood Avenue, Spring Street, and LaFountain Street in Burlington. This neighborhood in the Old North End has been been affected by a release of tetrachloroethylene (PCE) from historical dry cleaning operations. By combining our data with data from the EPA and a consultant for the responsible party, we have identified 20+ homes to date that are impacted or at risk of being impacted by PCE by vapor intrusion (VI).

Once VI impact has been established at a home, WHEM then conducts a mitigation assessment. The assessment combines elements of an evaluation of corrective action alternatives and corrective action plan into a streamlined, actionable mitigation plan. WHEM has completed 14 VI assessments to date. The mitigation assessment work first involves characterizing building use and construction, utilities, and vapor intrusion pathways. We then conduct sub-slab communication testing using an innovative system we developed for this project. The results of this testing are then used to predict the estimated radius of influence that a sub-slab depressurization system (SSDS) would create. Based on the dimensions of the building, we are then able to determine if an SSDS is a suitable mitigation strategy. Concurrently, we also consider the following mitigation options: 1) no action, 2) vapor barrier installation, 3) concrete pouring and/or sealing, or 4) a combination of strategies.

To date, WHEM has then worked with VT DEC, the homeowner, a professional engineer, and a mitigation system installer to construct the SSDS at 10 homes. After completion of the system, we develop an Operations and Maintenance (O&M) manual for the homeowner and document construction details in an As-Built report. The final step is conducting ongoing performance monitoring of the systems on an annual basis to ensure continued operation of the SSDS.