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SAP/QAPP Addendum Lodi-125 N Stockton Final March 24,2025 TPH exceedances in the former UST area and inform soil handling and disposal procedures during redevelopment. Subsurface soil samples will be collected at the following intervals: 5 to 8 feet bgs, 8 to 10 feet, 10 to 13 feet bgs,and 13 to 15 feet bgs. Soil samples will be analyzed for arsenic and lead (EPA Method 6010),and TPH (EPA Method 8015M [TPH-g,TPH-d,and TPH-mo]).Analytical results will be compared to the EPA RSLs for industrial and residential soil(EPA 2024),the DTSC SLs for commercial and residential receptors (DTSC 2022),and the RWQCB Tier 1 ESLs (RWQCB 2019). 3.1.4 Soil Crds Sampling Twenty soil gas sampling locations will be finished as permanent soil gas wells for future soil gas sampling events (Figure 4). Soil gas samples will be collected at 5 feet bgs and 15 feet bgs. Soil gas sampling will not occur within 48 hours of installing the wells or within 24 hours after a precipitation event. Soil gas samples will be analyzed for VOCs (EPA Method Toxic Organics [TO]-15) and helium(as a leak tracer gas) (ASTM D1946). Analytical results of soil gas samples will be compared to RWQCB Tier 1 ESLs (RWQCB 2019).If ESLs for given analytes are not available from RWQCB,EPA vapor intrusion screening levels (VISLs) for commercial and residential receptors will be used (EPA 2024).Helium is measured for informational purposes and will not have screening criteria. 3.1.5 Ambient Air Sampling Five indoor air samples will be collected,one from each room in the unoccupied office building(Figure 4). Indoor air samples will be collected over an 8-hour period. One outdoor air sample will also be collected over an 8-hour period to determine background concentrations of AOCs.The outdoor air sample will be in a well- ventilated area (away from areas of exhaust) and placed at breathing height.The indoor and outdoor air samples will be analyzed for VOCs (EPA Method TO-15 SIM).Analytical results will be compared to DTSC ambient air SLs for commercial and residential receptors (DTSC 2022) and RWQCB Tier 1 ESLs for indoor air (RWQCB 2019).If SLs for given analytes are not available from either DTSC or RWQCB,EPA ambient air RSLs for industrial and residential receptors will be used (EPA 2024). 3.2 Data Quality Objectives The Toeroek Team applied the DQO process for this project to: (1) clarify study objectives and decisions to be made based on data collected; (2) define the most appropriate types of data to collect; (3) determine the 11