Category Archives: Vapor Intrustion Mitigation

Terra-Petra Environmental Engineering is providing environmental engineering services for the design of the vapor intrusion mitigation system (VIMS) for a development of affordable Senior Housing in downtown San Rafael, CA. The development consists of the construction of a new six-story building. The building footprint is approximately 14,000 SF.

The site served as a Manufactured Gas Plant prior to the proposed improvements. Site assessment work was completed at the site prior to Terra-Petra’s involvement. A Human Heath Risk Assessment (HHRA) and a Site Conceptual Model (SCM) were carried out to determine the potential risk exposure posed to future construction workers, future commercial occupants and future residential occupants of the building based on VOC’s at the site. It was determined that the calculated risks for all potential receptors were less than the bench marks set forth for the property. The bench marks for this site were HI = 1 and ILCR = 1E-6. Results of the evaluation suggest that soil vapor intrusion mitigation systems may not be required to protect future occupants on this parcel.

The Department of Toxic Substances Control (DTSC) was engaged to serve as the lead regulatory agency at the site. Terra-Petra was directed to design a VIMS system in compliance with DTSC’s published guidelines, which we are in the process of completing.

It will be up to the DTSC to determine if the submitted VIMS design package meets DTSC guidelines and the soil vapor mitigation system provides for adequate human health assurance per the terms of the Land Use Covenant (LUC). If so, the DTSC can formally approve this project. Terra-Petra is confident that our VIMS design will satisfy the mitigation requirements as we have a vast amount of experience designing such systems that have been reviewed/approved by the DTSC.

Aside from the design work, Terra-Petra will be assisting our client in soliciting bids form qualified and experienced vapor intrusion contractors in the Bay Area. We will also be reviewing submittal packages and providing support throughout the Construction Administration Phase of the project. Our inspection crew is slatted to inspect and document the installation of the system using our state of the art field reporting system.

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.