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Vapor Intrusion Assessment Work Plan Project number:60653972 Pursuant to Monitoring and Reporting Program(MRP)Number(No.)R5-2003-0703 (dated March 27, 2003)and MRP No.R5-2010-0818(dated August 10,2010)issued by the CVRWQCB, groundwater monitoring and reporting was performed from October 1996 to September 2019. Starting in the 3rd Quarter 2019,MNA monitoring and reporting has been ongoing at the Site pursuant to MRP No.R5- 2019-0906(dated November 6,2019). 1.4 Remedial Action Summary In July 1995,Pilko conducted the Phase 2 Site Investigation of BP Chemicals'Applied Aerospace Composites Facility at the Site following the February 1995 sale of the property.The investigation was authorized by BP to identify the areas on site impacted by previous operations. Groundwater and soil vapor samples were collected from 65 locations at the Site by Transglobal Environmental Geochemistry, Inc. (TEG). Soil vapor samples were collected at 6 and 12 feet below ground surface(bgs)and analyzed from VOCs. This investigation detected the highest VOC concentrations near the Former Hazardous Material and Waste Storage Area with concentrations of 1,1-dichloroethylene(1,1-DCE)between 10 and 80 microgram per liter(µg/L)and 1,1,1-trichloroethane(1,1,1-TCA)between 1 and 26 µg/L. Small concentrations of these same VOCs were detected near the Sewer Line and Lift Station at 1 (1,1,1-TCA) and 3 (1,1-DCE) µg/L.Additional detections occurred in the,at the time,undeveloped area in the western portion of the Site,with the highest concentrations of 1,1,1-TCA and 1,1-DCE at 11 and 54 µg/L,, respectively(Pilko 1995). Following the Pilko investigation,Parsons installed soil vapor extraction(SVE)well VEW 1 for pilot testing in 1997(Parsons 1997). Based on the effectiveness of the pilot study test,Parsons submitted the August 1998 Remedial Action Work Plan(Parsons 1998b),recommending SVE and groundwater extraction and treatment system(GWETS)as viable technologies for soil and groundwater remediation in the source area.An SVE treatment system and GWETS were installed and began operation in May 1999 and focused on source area treatment. The Remedial Alternatives Evaluation(Parsons 1999a)was then submitted to evaluate remediating the entire Site,and the following alternatives were evaluated: • Alternative A: Source Area Remediation and MNA • Alternative B: Expansion of Existing Groundwater Extraction System • Alternative C:Air Sparging with SVE Alternative A,which included soil(via SVE)and groundwater(via GWETS)treatment in the source area with MNA for the rest of the Site,was recommended as the most favorable remedial alternative. However, CVRWQCB's February 11, 1999,response to the 1998 Fourth Quarter Monitoring Report indicated that the MNA parameters yielded limited evidence to support natural attenuation and recommended other remedial alternatives besides natural attenuation be utilized to enhance GWETS.In addition, CVRWQCB's September 16, 1999,response to the Remedial Alternative Evaluation(Parsons 1999a)stated that Alternative A would not meet the project water quality objectives(WQOs) specified in the response, and BP needed to implement Alternative B or some other alternative to capture the entire plume and meet the project WQOs. Subsequently,the GWETS was expanded in 2000 to control plume migration outside the source area(Parsons 1999b). The SVE system was continuously operated from May 25 to August 17, 1999 and was monitored for effectiveness by 17 nested vapor monitoring points installed across six locations.Adjusted operations to modify vacuum field and change vapor flow paths were conducted from September to March 2000. The system was given a 7-month rest period then operated continuously from September to December 2000, where it was terminated due to a declining mass removal rate. Confirmation sampling was conducted in January 2001 at six locations to confirm low VOC concentrations found in the vapor extraction wells and monitoring points. Of the 24 samples, 18 returned non-detect for the contaminants of concern and only four samples contained detectable concentrations of the principal VOCs of concern(1,1-DCE, trichloroethene(TCE),toluene, and tetrachloroethene(PCE)). Concentrations detected were 0.03 to 0.92 Prepared for: California Regional Water Quality Control Board,Central Valley Region AECOM