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Additional Soil and Groun&0�*r Investigation Work Plan -� CCT Stockton Rail Yard, 1645 Cherokee Lane, Stockton,CA October 4, 2007 Page 2 2.0 SITE DESCRIPTION The subject property is located in a commercially zoned area at 1645 Cherokee Road, Stockton, California (Figure 1 and 2). The site, currently owned by CCT, is a non-paved triangular lot operated as a rail yard and maintenance facility by the CCT. The site is bounded to the north by a commercial facility, to the southwest by Sanguinetti Lane, and to the southeast by Cherokee Road. 2.1 Regional Geologic Setting The subject property is situated at an elevation of 21 feet mean sea level (MSL) and lies within the Great Valley Province, which is dominated by the alluvial basin of the Sacramento Valley. This region is composed primarily of Quaternary aged alluvium, mainly in the form of unconsolidated flood plain deposits. The main soil types that exist in this type of deposit are sand, silt, gravel and clay that are irregularly interstratified. The primary mechanism for sedimentation in this area has been fluvial. 2.2 Site Geologic Subsurface Conditions The subject property is underlain by layers of silt, sandy silt, and silty sand(URS Greiner Woodward Clyde (URSGWC) 1999)• Depth to groundwater in onsite wells was approximately 45 to 50 feet below grade (fbg) during 2001 and 2002. During the excavation activities performed in 2005, groundwater was encountered in the excavation at approximately 75 fbg. The groundwater flow direction has been estimated to be toward the northeast. 2.3 Sensitive Receptors URSGWC published a survey of wells located within a 2,000 foot radius of the site as performed by Vista Information Solutions, Inc. The survey identified five wells,three of which are public supply wells within a 2,000 foot radius of the site. The nearest of these wells is located approximately 1/4 mile southwest of the site (URSGWC 1999)• 3.0 SITE BACKGROUND January 26, 1999: One 1,000-gallon diesel and one 6,000-gallon gasoline underground storage tank(UST) were previously maintained on site for an unknown period of time and were removed from the site by Thorpe Oil Company in January 1999. One soil sample, collected from the diesel tank excavation at 9 feet below grade (fbg) contained 8,000 milligrams per kilogram (mg/kg)total petroleum hydrocarbons as diesel (TPH-d) (Hydro-Environmental Technologies, Inc. (HETI) 2004). August 2-3, 1999: Five soil borings (B-1 through B-5) were drilled to a maximum depth of 56.5 fbg. TPH-d was detected in 14 of the 28 soil samples collected at depths ranging from 10 to 55.5 fbg. The maximum TPH-d concentration was detected in the sample collected from B-1 at 10 fbg at a concentration of 22,000 mg/kg. TPH-d was detected at 94,000 micrograms per liter(lig/1) in the grab groundwater sample collected from B-1, which was the only groundwater sample collected during this investigation (URSGWC 1999). These analytical results are included in tabular form in Appendix Al. The locations of these borings are show on Figure 3.