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WORK PLAN FOR ADDITIONAL SOIL VAPOR SURVEY Introduction May 30, 2014 1.0 Introduction On behalf of Chevron Environmental Management Company (CEMC) and Phillips 66 (P66), Stantec Consulting Services Inc. (Stantec) has prepared this technical work plan to conduct assessment of hydrocarbons in shallow soil vapor for the L&M Operable Unit (OU) which overlaps with and is adjacent to the eastern boundary of the Delta View Apartments (802 West Weber Avenue) and west of the North Lincoln Street and West Weber Avenue cross road in San Joaquin County, California (the "Site"; Figure 1). The work plan was prepared in response to a correspondence from the Regional Water Quality Control Board-Central Valley Region (RWQCB-CVR) dated April 7, 2014 (Affachment 1) and previous meetings with the RWQCB-CVR on March 7, 2014. 1.1 PURPOSE AND SCOPE OF WORK Previous site assessment activities and quarterly groundwater and soil gas sampling have identified hydrocarbon impacts to shallow soil vapor and groundwater,which historically has occurred at depths less than 11 feet below ground surface (bgs) at the site and site vicinity. Hydrocarbons in soil vapor potentially associated with shallow soil and groundwater impacts have been evaluated ongoing since 2005 for both areas on- Site in the potential source area as well as off-Site in the adjacent Delta View Apartment Buildings. However, several soil vapor points originally installed have since been compromised, either due to additional assessment work or water infiltration into capillary fringe pore space preventing the collection of accurate shallow soil gas samples within these areas. Several of these soil vapor sampling compliance locations have since become data gaps for continuance of insuring human health protection of volatile organic carbons (VOCs) via the indoor air intrusion pathway to apartment residents. To address these identified data gaps, soil vapor assessment activities will include the installation of single-depth soil vapor sampling probes at seven (7) off-Site Delta View Apartment complex locations (APSV-1 1 through APSV-17) and two (2) on- Site locations (UPSV-7 and UPSV-8) across the L&M OU.The primary objective of the assessment work is to obtain soil vapor data from both the previously compromised locations (APSV-2 and APSV-4) and any additional data gaps that may be warranted to comply with the Stantec's Vapor Intrusion Contingency Plan, submitted January 17, 2014 (Affachment 1) which also complies with the shut down and rebound study of the soil vapor extraction (SVE) remedial system. The soil vapor analytical results will be used to evaluate current subsurface soil vapor hydrocarbon concentrations and the vapor intrusion exposure pathway as well as to remain in compliance with the contingency plan that expresses vapor intrusion screening level bench marks for VOCs that are assumed to remain protective of human health while the SVE system is shut down for rebound studies. The generalized scope of work proposed by Stantec includes the following: 1.1