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Non-Water Release Corrective Action Plan Corral Hollow Sanitary Landfill • 1.2 SHELL OIL PIPELINE EASEMENT In 1967, Shell Oil installed a high pressure oil pipeline within a 20-foot easement adjacent to Highway 580 that was granted to them by the County. Based on limit of waste investigations near the pipeline, refuse was discovered beyond the easement and into Caltrans property. As such, the closure cap was extended over this easement as part of the amended Final Closure Plan prepared by the County (October 2012). 2.0 GEOLOGIC AND HYDROGEOLOGIC OVERVIEW 2.1 SITE GEOLOGY AND HYDROGEOLOGY The geology and hydrogeology of the CHSL has been summarized from the report prepared by the County of San Joaquin, Department of Public Works, (SJDPW 2013). Surface soils at the site are typically sands and gravels to a depth of about 70 feet with Standard Penetration Test (SPT) blow counts ranging from 30 to 50 blows per foot (dense to very dense) for the sandy gravels and 20 to 30 blows per foot (medium dense to very stiff) for the sands, sandy silts, and sandy clays. The upper gravels, sands, and silts, are underlain by low permeability silts and clays to a depth of approximately 150 feet. Sands and gravels • predominate to a depth of approximately 430 feet. Highly impermeable sandy clays are present at 430 feet. The hydrogeology at the site is complex. A shallow perched aquifer is found beneath the northeast and east side of the landfill property. This aquifer is not found in the central and western portion of the landfill. This shallow aquifer is perched on the Corcoran Formation, which rises from the northeast, apparently intercepting the landfill base. The elevation of this shallow aquifer is approximately 230 feet (MSL). Depth to this shallow aquifer is approximately 25 feet (at its shallowest location) and gradually deeper at other portions of the landfill, these variations being the result of variations in the surface elevations and apparent recharge from off the property to the northeast. This perched aquifer is unconfined and pinches out in the proximity of the landfill, with groundwater at its highest elevation near the northeast corner of the landfill. The Corcoran Formation and the associated shallow aquifer are not found beneath the southwest side of the landfill. Attempts to locate and monitor the shallow aquifer south and east of the landfill footprint in 2003 and 2007 indicated an inconsistent aquifer elevation and aquifer discontinuity within the landfill property. Groundwater flows in the shallow aquifer to • the southwest, which is an opposite direction to the flow in the deep aquifer. 2 Geo-Logic Assoc I A T E S