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Limited Phase II Environmental Site Assessment Report April 2, 2007 Page 2 bay that extends to an approximate depth of 8 feet below ground surface (bgs). The facility was formerly equipped with four 350-gallon above-ground storage tanks (ASTs) containing motor oil and one 500-gallon use oil AST. These tanks have been removed, and were formerly located within the oil change pit. A sump and associated submersible pump is located within the floor of the oil change pit, in the northwest corner of the oil change facility. The sump collected oil and rinse water from floor washing (AEI, 2006). The location of the sump is shown on Figure 2. GEOLOGY AND HYDROGEOLOGY The site is located at an approximate elevation of 26 feet above mean sea level, with the local topography sloping gently towards the southwest. The United States Geological Survey (USGS) has identified the area surrounding the site to be underlain by the Stockton Clay, a poorly drained soil with moderate water holding capacity. These soils were formed in alluvial deposits derived from a mix source of parent rocks. The nearest natural surface water is the Calaveras Rivers, located approximately 0.95 miles to the south-southeast of the property. The Mokelumne Aqueduct is located approximately 900 feet northwest of the site. AEI reports that groundwater is anticipated to be approximately 63 feet bgs. Based on regional topography, the direction of groundwater flow beneath the site has been inferred to be towards the southwest. SCOPE OF WORK To evaluate the subsurface conditions adjacent to the sump, SECOR supervised the drilling of one soil boring (GP1) to a maximum depth of 25 feet bgs. The soil boring was drilled using direct push drilling equipment. The soil boring location is shown on Figure 2. Pre-Field Activities Prior to drilling, SECOR prepared a site-specific health and safety plan (HASP) in accordance with OSHA 29 CFR 1910.120(e) and SARA 126 to address potential hazards at the site during the proposed field activities. The HASP was reviewed, signed, and adhered to by all on-site personnel. Additionally, SECOR obtained an approved SJCEHD boring permit (Attachment A). An important safety consideration in situating the proposed soil boring is the proximity to utilities. Prior to drilling, SECOR contacted Underground Service Alert (USA). USA notified local utilities of the planned work. SECOR also contacted with Cruz Brothers Locators, a private utility locator company, to search for other utilities that may or may not be marked. Prior to drilling with mechanized equipment, SECOR personnel performed a health and safety tail-gate meeting and discussed safety issues related to potential subsurface utilities that may exist at the site. P:/CEC/Stockton/Stockton Limited Phase II ESA Report FINAL 04.02.07 SECOR