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I Sediments encountered in the Stockton area consist of recent fill mate-nal, which vanes according to construction activities, older Pleistocene, Holocene and Recent Quaternary sediments which are ' approximately 200 feet duck in this area, and deeper continental deposits of Pliocene and Pleistocene age Locally, the site is underlain by the Riverbank Formation which consists of a brown to red-gray locally pebbly sand with minor silt and clay Overlying the Riverbank Formation is a thin layer of recent alluvial deposits chiefly composed of tan to brown silty sand with local zones of gravel and ' clay .5 Hydrogeology_ Stockton is located in the San Joaquin Groundwater Basin as defined in Depdrtment of Water Resources Bulletin 118-80 (January, 1990) The upper 700 to 800 feet of the unconsolidated sediments in the San Joaquin Basin contains a number of water-beanng zones The distribution of water-bearing zones is directly related to the subsurface geology in any particular area. For the most part, groundwater occurs in unconfined conditions, however, due to distribution of clay lenses in the sediments, groundwater can occur in semi-confined conditions as well For the most part, groundwater movement is southwesterly toward the valley trough,in the case of unconfined aquifers Locally, surface drainage and irrigation pumping can affect both groundwater flow directions and water table elevations Groundwater at the site varies from 15 to 30 feet below surface (bs) Water was encountered at 18 feet bs during the overexcavation of the gasoline UST basin on the property .0 CURRENT INVESTIGATION ' 3.1 Probe Investigatign Apex personnel supervised the dulling of eleven probe holes (P-I through P-11) on December 12 and 13, 1994, at the locations indicated on Figure 2 The probe sampling was conducted by ' Environmental Control Associates of Aptos, California, to depths of up to 30 feet bs, using 3/4- inch 14inch I D galvanized steel probe pipe The probe work was conducted according to the Apex standard operating procedures (SOP) included as Attachment A The probe process does not produce any cuttings, so cuttings disposition was not a factor in this investigation ' .2 Soil Sampling & Anall5is Soil samples were collected from the probe holes for field screening, classification and selection for laboratory analysis of hydrocarbons Two soil samples were collected from probe holes P-6, P-7 and P-8 and one soil sample was collected from P-1 through P-5 and P-9 through P-11 The soil samples were submitted under chain-of-custody, to Excelchem Environmental Labs of Sacramento, Cahfornia, a state-certified analytical laboratory Soil samples from P-1 through P-5, ' P-9 and P-10 were analyzed for total petroleum hydrocarbons, as gasoline (TPHg), TPH, as diesel (TPHd), benzene, toluene, ethylbenzene, and total xylenes (BTEX) by modified EPA Method 8015 and 8020, respectively Soil samples from P-4, P-5, P-9, P-10 were also analyzed for TPH, Phase II Site Assessment Report COLOI 001 January 23, 1995 Page 3