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Geosynte& consultanls 2. BACKGROUND Background information for the Site is summarized in this section as it applies to the pre-design data collection objectives and sampling plan. 2.1 Project Background The Site is currently owned and operated by J.R. Simplot(Simplot).The Site is approximately 341 acres and is located at 16777 Howland Road in Lathrop,California(Figure 1). Previous assessment work identified fumigants as constituents of concern (COCs) for the former OCC Facility. A groundwater extraction and treatment system (G WETS or Treatment Plant) was installed at the Site in 1982 to address the CDCs. Additional environmental investigations identified sulfolane as a COC from the former OCC operations, and in 1992 the GWETS was modified to include the treatment of sulfolane (Ying, 1994). 2.2 Project Description GSH is currently expanding the groundwater extraction system to include new groundwater extraction wells to extract sulfolane-impacted groundwater on the eastern portion of the Site(EW- 18A, -1813, -19; Figure 2). Based on favorable evidence of biodegradation in samples collected during laboratory microcosm studies and from ongoing field pilot testing, GSH is evaluating the use of an aeration system to treat extracted sulfolane-impacted groundwater from the eastern portion of the Site. The aeration system will be located on the western portion of the Simplot property near the existing Treatment Plant, as shown on Figure 3. Based on the most recent pilot testing data, the conceptual design for the aeration system includes three (3) 120,000-gallon aboveground tanks', each with diameter of about 34 feet and a height of 25 feet. The tanks will be surrounded by a one-to two-foot-high berm for secondary containment. Additional equipment on the pad will include a series of sand filters, transfer pumps, and other miscellaneous piping and control equipment. Geosyntec will obtain the design criteria(e.g., acceptable settlement criteria) for the tanks and the foundations from the tank designer. The topography of the area where the proposed aeration system is anticipated to be installed is generally flat and largely unvegetated. The surficial soils generally consist of loose well-draining silts and sands and some fill material. The geotechnical subsurface conditions will be used to design the aeration system. Design for the aeration system will include such items as bearing capacity and static and seismic settlement estimates. Seismic design will be performed for the design earthquake at the aeration system location. Because the aeration system is underlain by sandy soils and the groundwater is relatively shallow, the potential for liquefaction under the design earthquake needs to be assessed. If the soils are liquefiable,the potential for sand boils, seismic settlement, and post-liquefaction seismic stability will be assessed. ' Steel-bolted. Other tanks may be considered based on other design considerations. Pre-Design Data Collection Work Plan 2 July 22,2019