ARCHIVED REPORTS_2019 SOIL MGMT PLAN (JULY-REVISED)

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EKI B90047.00 Page 2 Former Pilkington North America Site Lathrop, California 1.2 Site Setting A summary of the geology and hydrogeology of the Site is provided below based on information provided in the WU1 Clean Closure and Work Plan Addendum (the “WU1 Plan”, AGE, 2019 – Appendix B). Geology The regional geologic setting is situated within the Great Valley Geomorphic Province of California, an elongated, northwest-trending structural trough running 400 miles through Central California. The Great Valley is bound to the north by the Klamath Mountains, the south by the Tehachapi Mountains, the east by the Sierra Nevada Mountains, and the west by the Coast Ranges. Approximately 32,000 feet of marine and continental sediment have been deposited almost continuously since the Jurassic Period. The northern and southern regions of the Great Valley are designated the Sacramento and San Joaquin Valleys, respectively. The Site is located within the San Joaquin Valley. Hydrogeology The Site and surrounding area lie within the San Joaquin Valley Groundwater Basin, Eastern San Joaquin Subbasin (5-22.01). This subbasin is bound on the south, southwest, and west by the Modesto, Delta-Mendota, and Tracy Subbasins, respectively, and on the northwest and north by the Solano, South American, and Consumnes Subbasins. The Eastern San Joaquin Subbasin is drained by the San Joaquin River and several of its major tributaries namely, the Stanislaus, Calaveras, and Mokelumne Rivers. The San Joaquin River flows northward into the Sacramento and San Joaquin Delta and is discharged into the San Francisco Bay. Annual precipitation within the subbasin ranges from about 11 inches in the southwest to about 25 inches in the northeast. Generally, the subsurface of the Site consists of silts and silty sands from the surface to 10 feet below ground surface (“bgs”), then grades into fine to medium sands at approximately 10 feet bgs and extending to 20 feet bgs. Groundwater at the Site is encountered in the fine to medium sands. Between May 2015 and November 2018, groundwater was encountered between approximately 12 and 16 feet bgs at on-Site wells. The groundwater gradient direction has varied toward the northeast to the south at low (0.0004 ft/ft) to moderate (0.02 ft/ft) hydraulic gradients. During 2017 and 2018, groundwater gradient direction has been consistently towards the south and southwest. Locally, the groundwater gradient direction in the southeasterly portion of the Site may be affected by the current groundwater extraction remediation being performed at the adjacent JR Simplot property. The Site is located at an elevation of approximately 15 feet above mean sea level (“MSL”), in an area of low topographic relief. Regional groundwater flow and slope of the area is toward the general southwest, which is consistent with the overall groundwater flow direction inferred at the Site and in the area. There are no surface water features on the Site. The nearest surface