The dry-cleaning businesses have operated at the site since the 1960s and the facility has been vacant since 2006. Between 1999 and 2005, sampling and chemical analysis by others, of soil, soil gas, groundwater and surface water revealed the presence of VOCs, primarily PCE and its breakdown products, in the soil, soil gas and groundwater at the site. A Corrective Action Plan (CAP) was prepared to remediate the identified contamination. The CAP included excavation of VOC impacted soil, the installation of an extensive ozone groundwater treatment system, and the installation of additional groundwater monitoring wells. Stratus personnel was contracted to implement the CAP and continue the site groundwater monitoring program.
During 2007 and 2008 Stratus personnel implemented the soil excavation component of the CAP and removed and disposed of approximately 150 cubic yards of PCE impacted soil and weathered rock from within the building and from an area immediately outside the facility’s back door. Following the cleanup actions, Stratus personnel designed and installed a sub-slab depressurization system to protect future occupants from potential vapor intrusion to indoor air from residual contamination within the underlying fractured bedrock. During the preparation for the soil removal activity, Stratus personnel identified asbestos containing materials inside the structure that were appropriately monitored, removed, and disposed. In addition, during soil removal inside the building two unexpected items were discovered, a vertical shaft that appeared to be an abandoned hand-dug well from a former residence at the site, and piping that led to an unreported abandoned 500-gallon diesel UST located in the site parking lot. Stratus personnel worked with the client and the RWQCB to close the former well, and to remove the UST and remediate contaminated soil and weathered rock surrounding the UST (it had leaked diesel into the adjoining soil and impacted groundwater). A separate CAP was prepared by Stratus personnel, approved by the RWQCB, and implemented for the diesel impacted soil and groundwater. Based upon the results from the PCE and UST remedial actions, and the continuation of the groundwater monitoring program, Stratus personnel recommended modifying the original CAP to eliminate both the ozone groundwater treatment system and the installation of additional groundwater monitoring wells. These recommendations were accepted by the RWQCB and resulted in an approximate $200,000 cost savings for the client. Stratus personnel submitted a Rationale for Considering No Further Action for Chlorinated Volatile Organic Compounds in Groundwater and was successful in eliminating groundwater monitoring (destroying all groundwater monitoring wells), resulting in an annual cost savings of $25,000.
Stratus recently installed and sampled 3 soil gas probes in the former dry-cleaning building in accordance with the DTSC Advisory for Active Soil Gas Investigations, and Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (Vapor Intrusion Guidance). We are in the process of preparing a human-health risk assessment using site-specific data, in accordance with the California version of the USEPA Vapor Intrusion Model. The USEPA model has been modified by the DTSC Human and Ecological Risk Office (HERO) to include Cal/EPA toxicity criteria values for the risk calculation component. The site has subsequently been redeveloped as a leased commercial space.
