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Geosyntec O consultants 1. INTRODUCTION Geosyntec Consultants Inc. (Geosyntec) has prepared this Work Plan for Collection of Soil Samples (Work Plan) on behalf of Glenn Springs Holdings, Inc. (GSH) and J.R. Simplot Company for the former agricultural chemical distribution facility located at 1904 Charter Way, Stockton, California (the site). The Work Plan was prepared to meet the requirements for obtaining a Site Mitigation Boring Permit, as stipulated by the San Joaquin County Environmental Health Department's (SJCEHD) Site Mitigation Program Guidance document, which indicates requirement for submittal of a work plan describing "the site history and the purpose and scope of the proposed investigation. The work plan must include drilling procedures, well and/or boring construction/destruction methods, disposal methods for soil and/or wastewater generated, a site map and a safety plan." 2. SITE BACKGROUND The site was used from 1955 to 1993 for storage and distribution of agricultural chemicals. The site occupies approximately 4.2 acres in a predominantly industrial area west of the City of Stockton, California. A residential neighborhood borders the site to the east. A map of the site is presented on Figure 1. Previous investigations indicate that the site is underlain by relatively continuous thin layers of sand, silt and clay to a depth of about 150 feet below ground surface (ft bgs). The upper 16 to 20 feet are fine-grained materials with a relatively continuous fine- to medium-grained sand interval occurring between about 20 and 40 ft bgs. Sand intervals were also identified at 60, 80 and 100 ft bgs. Groundwater monitoring wells have been installed on-site and in the adjacent residential area to monitor the shallow(20 to 40 ft bgs) and intermediate (70 to 90 ft bgs) groundwater zones. Groundwater levels vary seasonally at the site with levels declining during the summer months and recovering during the winter months. Groundwater level data for the past 10 years of monitoring show that the water level in the shallow zone varied seasonally between depths of about 5 and 12 ft bgs. The direction of horizontal groundwater flow in the shallow zone is easterly. Previous investigations have reported that site constituents of concern (COCs) include (i) nitrate in site soils at concentrations above regulatory criteria, and(ii) 1,2,3-trichloropropane, 1,2-dichloropropane, and nitrate in the groundwater underlying the site at concentrations above regulatory criteria. At this time,the site is regulated by the Central Valley Regional Water Quality Control Board (RWQCB). Remediation activities conducted at the site include excavation of soil containing elevated levels of COCs, injection of carbon substrate into the subsurface to enhance the remediation occurring through bioremediation, on-site phytoremediation to address nitrogen 2024 TR0712 Stockton Soil Sampling Work Plan 1 2024.08.2