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A Mr.M. Scott Mansholt—CEMC Site Investigation Work Plan March 29,2006 Banta Road—UPRR Page 2 of 5 bore beneath the ROW. On December 11,2003,Ranger Pipeline encountered petroleum-affected soil at approximately 11 feet below ground surface(bgs). Excavation activities ceased until the affected soil could be properly evaluated. Ranger Pipeline stockpiled the affected soil adjacent to Banta Road pending waste characterization and eventual disposal. REGIONAL/LOCAL HYDROGEOLOGY Regionally,the site is located within the Tracy sub-basin(Groundwater Basin Number 5-22.15), which is defined by the areal extent of unconsolidated to semi-consolidated sedimentary deposits that are bounded by the Diablo Range to the west,the Mokelumne and San Joaquin rivers to the north,the San Joaquin River to the east,and the San Joaquin-Stanislaus county line to the south.' The Tracy sub-basin is located adjacent to the eastern San Joaquin Sub-basin to the east and the Delta-Mendota Sub-basin to the south. The above-mentioned sub-basins are located within the larger San Joaquin Valley groundwater basin. The Tracy sub-basin is comprised of continental deposits of late Tertiary to Quaternary age, which includes the Tulare Formation, Older Alluvium,Flood Basin Deposits,and Younger Alluvium.2 The thickness of these formations ranges from a few hundred feet in the western foothills to about 3,000 feet near the eastern margin of the basin. The Tulare Formation consists of semi-consolidated,poorly sorted,discontinuous deposits of clay, silt,and gravel. The Corcoran Clay is situated near the top of the Tulare Formation, separating groundwater in the basin in what has been reported as two primary aquifers. The upper aquifer is reported at 15 to 250 feet bgs and the lower aquifer is reported at 600 feet bgs. Depth to groundwater in the region varies from 5 to 15 feet bgs. Based on previous investigations, soils encountered near the site appear to be a mixture of fine- grained unconsolidated sediments, consisting mainly of clay(CL)and clayey sands (SC)with minor amounts of poorly graded sand(SP)and poorly graded gravel(GP). Shallow groundwater near the site has been encountered between 13 and 17 feet bgs. Regionally,groundwater flows toward the northeast. PREVIOUS ENVIRONMENTAL ACTIVITIES December 2003.3 In December 2003,the SSJID began construction of a 30-inch water pipeline beneath Banta Road. As part of the SSJID pipeline construction,Kleinfelder, Inc. advanced three soil borings to depths ranging from 14 to 19 feet bgs. One soil sample was collected from each boring,and an additional soil sample was collected from stockpiled soil excavated at approximately 12 feet bgs from the southern sidewall of the bore-and-jack pit. The four soil samples collected were submitted to Sequoia Analytical Laboratories in Sacramento,California, for total extractable petroleum hydrocarbons(TEPH),total purgeable petroleum hydrocarbons (TPPH),and benzene,toluene,ethylbenzene,and total xylenes(BTEX)analyses. BTEX concentrations were not detected in three of the four soil samples analyzed. Ethylbenzene and total xylenes were detected in the soil sample collected from the stockpiled soil. Concentrations of TPPH were detected in all four samples analyzed at concentrations ranging from 190 to 2,400 milligrams per kilogram(mg/kg). The highest TPPH concentration was detected in the soil sample collected from the north end of the bore-and-jack pit at approximately 14.5 feet bgs. The highest TEPH concentration was detected in the soil sample collected form the southern end of the bore pit at approximately 12 feet bgs. 1. Department of Water Resources,California's Groundwater,Bulletin 118,2003 Update. 2. Department of Water Resources,California's Groundwater,Bulletin 118,2003 Update. 3. Kleinfelder,2004. Limited Soil Sampling and Analysis,SSJID C451/UPRR Bore Pit,Banta Road and UPRR Crossing,Tracy,California. January.