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Geosyntec consultants 1. INTRODUCTION On behalf of Sims-Grupe Management Corporation,Inc. (SGM),Geosyntec Consultants,Inc. (Geosyntec) has prepared this Off-Site Source and On-Site Vapor Intrusion Investigation Work Plan (Work Plan) to identify potential off-site pathways and source(s)for the tetrachloroethylene(PCE)concentrations reported in domestic supply wells and to evaluate the potential for vapor intrusion(VI)to indoor air from subsurface soil impacted by chlorinated solvents from former dry-cleaning operations at the Park Woods Shopping Center in Stockton, California(Park Woods, or the Site; Figure 1). SGM refers to the center and cleaners as"Park Woods"though the spelling"Parkwoods"has been used in other documents,and both spellings have been identified in historical records.For consistency,"Park Woods"is used in this Work Plan. Since 2017, numerous soil, soil vapor, and groundwater investigations have been conducted to determine if releases from former dry-cleaner operations at the Site may be responsible for elevated PCE concentrations in the domestic supply wells located north of West Hammer Lane. In comparison to the supply wells, low concentrations of PCE in soil vapor and groundwater have been reported on Site, indicating that the downgradient impacts are likely caused by another PCE source(s). This Work Plan scope includes collection of off-Site soil vapor and groundwater samples near the sewer mains to evaluate releases from the sewer as a source of the domestic well impacts. The scope of work also includes collection of sub-slab and indoor air samples to evaluate the potential for vapor intrusion in select on Site buildings. 1.1 Regulatory Setting The Central Valley Regional Water Quality Control Board (CVRWQCB) issued a Water Code Section 13267 order (MRP R5-2017-0835)to the Site in 2017 based on the detections of PCE reported in off-site domestic and municipal supply wells located north of the Site. The order required the submittal of available documentation of current and past PCE use and disposal at the Site, sanitary sewer maps, and historical investigation and remediation information. Additionally, an investigation of soil vapor and groundwater was required. Indoor air samples, soil vapor samples and groundwater samples were collected at the Site. PCE was reported in some on-Site soil vapor samples at concentrations above commercial screening levels.PCE was not reported in indoor air samples and relatively low concentrations of volatile organic compounds(VOCs) were reported in Site groundwater monitoring well samples.No further action was recommended in 2018; however,the CVRWQCB did not concur with the conclusions and recommendation. An additional investigation of potential sources of PCE near the Site was requested by CVRWQCB in 2018 as part of a larger scale regional investigation of PCE in shallow groundwater along West Hammer Lane (CVRWQCB 2018a).MRP Order R5-2019-0806 was issued in 2019 which required quarterly groundwater monitoring and reporting of Site monitoring wells and a video survey of the PCE-impacted domestic supply wells. Additional groundwater monitoring wells were installed in 2020, and groundwater monitoring occurred between 2020 and 2024. MRP Order R5-2024-0813 was issued in 2024 and requires semi-annual groundwater monitoring and reporting. Three notices of violation (NOVs) have been issued to SGM for failure to comply with the MRPs between February 2020 and January 2025. This Work Plan has been 1 September 2025