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Geosyntec(> consultants 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 (CRWQCB). Remediation at the Site has included excavation of soil containing elevated levels of COCs, phytoremediation to address nitrogen and potential other residual COCs in soil and groundwater, and injection of carbon substrate into the subsurface to enhance the remediation occurring through bioremediation. The phytoremediation system is presently composed of approximately 1,300 red gum eucalyptus trees (Eucalyptus camuldulensis) planted on a 5- to 10-ft grid pattern that covers about 2.3 acres of the Site. The system was initially installed in 2003 and additional plantings were added in 2013. 3. OBJECTIVES AND SCOPE OF WORK While performing the 2024 groundwater monitoring events, Geosyntec identified two damaged Site monitoring wells,MW-5B and MW-7B (both shallow groundwater zone wells), due to anomalous groundwater elevations and concentrations of COCs. The damaged wells were noted in the 2024 Annual Groundwater Monitoring Report,I which was submitted to the CRWQCB on November 1, 2024. Subsequent downhole camera inspections confirmed that both wells have a cracked joint in their casing, which may be attributable to the presence of tree roots in the immediate vicinity of these wells. Based on these findings, Geosyntec proposes to destroy monitoring wells MW-5B and MW-7B by over-drilling to remove the well construction materials within the original borehole, after which the created hole will be filled completely with appropriate sealing material,consistent with standards presented in the San Joaquin County Well Standards.z Geosyntec proposes to install two new monitoring wells, hereafter referred to as MW-5C and MW-7C, as replacements for wells MW-5B and MW-7B, respectively, within 15 feet of the original well that will be destroyed. Each of the two new monitoring wells will be constructed in the same general configuration as the well it is intended to replace (i.e., approximately the same terminal depths, construction materials, casing, and screened intervals, etc.); however, exact terminal depths and screen elevations ' Geosyntec Consultants, Inc., 2024. 2024 Annual Groundwater Monitoring Report, November 2024. 2 San Joaquin County Environmental Health Department,2005.San Joaquin County Well Standards (San Joaquin County Ordinance Code Section 9-1115.6),February 2005. OxyChem-Stockton MW Replacement Work Plan 7.18.25 2 2025.07.18