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Well Decommissioning Work Plan JACOBS 1 . Introduction and Background Jacobs Engineering Group Inc. (Jacobs), on behalf of Pacific Gas and Electric Company (PG&E), has prepared this Well Decommissioning Work Plan (Work Plan)for the Former Stockton Manufactured Gas Plant (MGP) Site located at 535 South Center Street in Stockton, California (the Site) (Figure 1; figures and tables are presented at the end of this document). This Work Plan proposes the decommissioning of two wells. The wells have been installed for groundwater monitoring as described further below. 1.1 Objective The objective of the proposed work is to permanently decommission two monitoring wells in accordance with the applicable State of California, San Joaquin County, and City of Stockton requirements. 1.2 Site Description and Background The Former Stockton MGP is located at 535 Center Street in Stockton, California. The Site produced gas from coal and/or crude oil between 1860 and 1930. The Site consists of three areas: • Area I —Historical site of gasification plant (3 acres). • Area II -Available historical documents indicate that Area 11 was not used for manufacturing operations. • Area III — Historically used for gas storage (1 acre). Areas I and II are owned by PG&E and currently used for gas transmission and an electrical substation, respectively. Area III is no longer owned by PG&E and is currently used by Snow Cleaners, Inc., a leather cleaning company. A small strip of land south of Areas I and II between the PG&E fence line and the Hazelton Avenue sidewalk is currently owned by the City of Stockton. This area is referred to as the "Hazelton Avenue strip."Areas I, II, and III are presented in Figure 2. One monitoring well proposed for destruction is located in the sidewalk of the Hazelton Avenue strip (MW-21). The other monitoring well (MW-23R) is located in Area II, which is an active electrical substation. Environmental activities have been conducted at the Site since 1986. Wells have been installed at the Site during multiple investigations dating back to 1987. From 1999 to 2000, approximately 24,000 tons of soil was removed along with several underground storage tanks and structures containing oil. In 1991 a surface cap was installed over portions of the Site. Residual concentrations of polycyclic aromatic hydrocarbons (PAHs); benzene, toluene, ethylbenzene, and total xylenes (BTEX); and total petroleum hydrocarbons (TPH)were detected in groundwater and soil gas. 1.3 Well Details Two wells related to groundwater monitoring activities are proposed to be decommissioned based on low concentrations of constituents of concern (COCs)that are below remedial action objectives (RAOs). The monitoring wells are identified as MW-21 and MW-23R and are part of the post-remediation monitoring and reporting program (MRP) (ETIC, 2020). The California Department of Toxic Substances Control (DTSC) has concurred with decommissioning well MW-23R (Zone B). Analytical results for TPH in the diesel range (TPH-d) conducted without silica gel cleanup (SGCU) (95 micrograms per liter[pg/L])are below the RAO (100 pg/L). DTSC also agreed that MW-21 (Zone A)should be decommissioned because it has shown non-detect for TPH-d for more than four consecutive rounds of sampling. Even though MW-21 has been analyzed for TPH-d with SGCU, another well, (MW-20) is downgradient and near the contamination plume and will continue to be monitored for TPH-d in the next sampling event. The Central Valley Regional Water Quality Control Board (CV-RWQCB) agreed with the proposal to decommission both wells MW-21 and MW-23R because the analytical data for TPH-d conducted without SGCU (95 pg/L) is below the RAO of 100 pg/L and no COCs have been detected above RAOs for several years in MW-21 (DTSC, 2021). FES0817211625BAO