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AARCADIS <br /> Ms. Marilyn Petruescu Arcadis U.S., Inc. <br /> Central Valley Regional Water Quality Control Board 400 Capitol Mall <br /> 11020 Sun Center Drive, Suite 200 9th Floor <br /> Rancho Cordova, California 95670 Sacramento, CA 95814 <br /> United States <br /> Date: September 30, 2024 Phone: 916-786-0320 <br /> Our Ref: 30208418 www.arcadis.com <br /> Subject: Site Investigation and Well Installation Workplan <br /> Leaking Underground Storage Tank (T0607700166) <br /> 16777 Howland Road <br /> Lathrop, California <br /> Dear Ms. Petruescu: <br /> Arcadis U.S., Inc. (Arcadis), on behalf of Glenn Springs Holdings, Inc. (GSH), has prepared this Site Investigation <br /> and Well Installation Work Plan (Work Plan)for the Leaking Underground Storage Tank(LUST) Case at 16777 <br /> Howland Road in Lathrop, California (the Site; Figures 1 and 2). This Work Plan was prepared in response the <br /> Central Valley Regional Water Quality Control Board's (CVRWQCB) LUST Case— Site Investigation Status letter <br /> dated June 11, 2024 (Letter; Attachment 1). In their letter, the CVRWQCB directed GSH to submit a work plan to <br /> assess petroleum hydrocarbons in soil and groundwater near the former underground storage tanks (UST), and <br /> to assess the nature and extent of petroleum hydrocarbon impacts to groundwater. <br /> This Work Plan presents the methods and procedures for the proposed installation of groundwater monitoring <br /> wells, advancement of soil borings, and other activities to evaluate the current concentrations of petroleum <br /> hydrocarbons in soil and groundwater at the Site. <br /> BACKGROUND <br /> Occidental Chemical Corporation (OCC)operated an agricultural chemical production facility at the Site from <br /> 1964 to 1982. In 1982, the facility was sold to J.R. Simplot (Simplot)which has since operated an agricultural <br /> fertilizer manufacturing facility from 1982 to 2024. OCC has assigned GSH the responsibility of managing the <br /> groundwater remedial program related to OCC's obligations (Remedial Program) at the Site. This Remedial <br /> Program, which primarily involves groundwater extraction and treatment, has been ongoing since 1982. In June of <br /> 2024, GSH additionally took over the LUST cleanup case from Simplot, per a previous agreement between the <br /> two parties. <br /> The LUST case is associated with gasoline and diesel USTs that were located in the central portion of the Site <br /> (Figure 2). The history of USTs on the Site, previous environmental investigation, and regulatory involvement are <br /> described in the sections below. Historical reports associated with the USTs are located on the Regional Water <br /> Quality Control Board's GeoTracker website. <br /> UST History and Removal <br /> Two 5,000-gallon gasoline and one 10,000-gallon diesel UST were on the Site in 1982. In 1982, the two 5,000- <br /> gallon gasoline USTs were replaced by one 10,000-gallon gasoline UST. <br /> 1/7 <br />