Terra-Petra Environmental Engineering is pleased to provide environmental engineering services for the design of the vapor intrusion mitigation system (VIMS) being proposed for a new affordable housing development in the Diridon Station Area in San Jose, CA.

The project consists of a multi-family residential building having 130 units with 5 stories above grade (no below grade elements). The lowest level will consist of parking with lobby, offices and a community room. The building footprint is approximately 23,400 SF on 1.02 acres.

The site where the proposed building is to be constructed did contain an Underground Storage Tank (UST) potentially containing PCE which was considered to be a Recognized Environmental Condition (REC). As such, soil vapor data was collected from the site during both wet and dry seasons approximately 9 months apart. The data showed that no on-Site sources of PCE have been identified at the Site. Further, no VOCs were detected at concentrations above residential DTSC-AF SLs for future buildings, and no further investigation, evaluation or consideration of exposures associated with VOCs in soil vapor is proposed. Additionally, no residential units were being proposed on the ground floor of the new development. However, the regulatory oversight agency for this site is still requiring that passive Vapor Intrusion Mitigation System (VIMS) be designed and installed at this building.

Terra-Petra was engaged to design a pragmatic code compliant VIMS system that would take into consideration the lack of site-specific risk. As such, we were able to design a creative membrane system that limited the more protective mitigation measures to areas of higher residential occupancy/risk of exposure. These areas included the community room and elevator lobby. While areas of lower risk such as the trash enclosure rooms and parking garage we were able to design a system that would be protective of VI, but also reduce overall cost impacts on the project’s budget.

Terra-Petra will also be providing Construction Administration services and Construction Quality Assurance/Quality Control Services.

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