An existing 112,637 square foot residential apartment complex was found to have been built over a former dry cleaner. Legacy contamination caused elevated concentrations of tetrachloroethene (PCE), creating an unacceptable vapor intrusion risk to the building. The complex “U-Shaped” foundation and finished interior spaces created numerous problems for the installation of any interior piping or pressure field extension (PFE) ports
To solve these problems, GZA excavated around the building, drilled through the foundation wall in several locations, and used air knife technology to carve out PFE trenches below the slab. All system piping was insulated, buried underground, and connected to blowers that were installed on the outside of the building. The system consists of a total of 27 PFE ports connected to 12 industrial blowers. Negative pressure testing showed adequate negative pressure throughout the entire building footprint. Paired 24-hour indoor air and sub-slab vapor confirmation samples confirmed that the system was working properly and protecting the residents from potential vapor intrusion from the dry cleaner release.
The project successfully retrofit an active Sub-Slab Depressurization (SSD) Vapor Mitigation System that provides adequate negative pressure throughout the entire building footprint of an existing 112,637 square foot residential apartment complex. The owner was able to keep the residents safe, obtain a Retroactive No Association Determination for the release, and secure financing for the property.