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Fj - City of Stockton A68106.OIA May 29, 1996 Page 2 and Mesozoic metamorphic and igneous rocks. T1 e shallow subsurface geology in the site vicinity is a heterogeneous mix of gravel, sand, sil , and clay (Hackel, 1966). ' 2.2.2 Hydrology: First encountered groundwater in the site vicinity occurs under unconfined (water table) conditions at depths fluctuating between 5 and 15 feet below site rl grade (BSG) (San Joaquin County, Public Health Services, 1996). Sediments containing fresh groundwater are largely unconsolidated siltsnd sands which were derived from river channel, flood plain, and alluvial fan deposits of P 'ocene to Recent age (Davis and others, 1959). 2.3 Project History:.On December 3, 1992, one 550-gallon diesel fuel UST was removed from the site. An analysis of a soil sample coil cted at 9.5 feet BSG beneath the UST j detected total petroleum hydrocarbons - dies--I range constituents (TPH-D) at a _ concentration of 1,200 milligrams per kilogram (mg/kg), toluene at 0.0078 mg/kg, ethylbenzene at 0.0077 mg/kg and xylenes at 0.12 mg/kg. In a request for bid letter dated February 8, 1996the City of Stockton (City) requested a rwork plan for the project site to include four sc it borings advanced by the direct push technique (soil probe) to depths of 20 feet BSG. In a letter dated March 21, 1996 the San Joaquin County Public Health Services (SJCPHS) suggested that soil borings be advanced to determine the vertical and horizontal extent o soil contamination. In addition, if soil contamination appears to extend to groundwater, the SJCPHS suggested that a groundwater sample be collected. The following work plan provides an outline of actions to satisfy the request of the City and the suggestions of the SJCPHS. 3.0 PURPOSE AND SCOPE The purpose of this site characterization is to delirrit the lateral and horizontal extent of soil impacted with PPCs. Furthermore, the presence or absence of PPCs in groundwater will Y+ be assessed. The following scope of work is proposed to achieve the stated objective: f- • Obtain permits from the SJCPHS • Collect subsurface soil samples from selected locations at the project site; 0 Collect a grab groundwater sample; Chemically analyze soil and groundwater sarriples in the laboratory for selected PPCs. • Evaluate the field and analytical data and ssess the lateral extent of PPC migration in soil; C i -