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IC. (i A 4 �,J6 STANK CLOSURE SITE ASSESSMENT REPORT SW4 Ou Company 3725 Tracy Boulevard,Tracy,California Delta Project No.40-89-012 Page 15 1 to A topographic map was used to infer the regional direction of ground water flow. Due to the orientation and elevations of the valley and drainage network,the regional direction of ground water 1 flow is expected to be to the northwest and north. The slight change observed in the local ground water flow direction between the two dates may be slue to the flat gradient of the water table and I` the numerous surface water bodies in the area. 4.2.1 Hydraulic Co ductMty. Slug test and grain size analysis indicate that hydraulic conductivity values for a sandy silt to silty sand range between 1.0 and 34 feet per day with an average value of 15 feet per day. The values 1' obtained from the slug and grain size analysis correlate with expected hydraulic conductivity values for shmilar soils. 1, 4.3 Petrofeum Hydrocarbons in Soils 4.3.1 Proposed Location-fox_New Underc_i:ound Storage Tanks t Results of the chemical analysis for BTEX and TPH for soil samples collected at a depth of l 1 feet _ below the ground surface from soil borings Sly-7,SB-g,and SB-4 were below detection limits. The soil sample collected at a depth of 11 feet from SB-10 contained a concentration of TPH at 140.0 ppm. T. 4.5.2 Soils Near the Existing Underground-Storat<e Tanks Results of the chemical analysis for BTEX and TPH for soil samples collected at a depth of 1 I feet t. from soils borings(SB-2 and SB-3)were below detection limits. The soil samples collected at 7,depth of 11 feet from soil borings SB-I and SB-4 contained concentrations of TPH at 77.0 and 11.0 which were identified as Stoddard solvent. The source of the Stoddard solvent is unknown at this time. i. 4.4 P„glroleum Hydrocarbons-Un-Around Water Chemical analysis of the ground water samples collected from the on-site monitoring wells indicate concentrations of BTEX and TPH were below detection limits. Additional analyses were performed on the ground water from monitoring well MW-1 in order to receive a discharge permit from the City of Tracy for the discharge of water from the dewatering of the new underground storage tank location. i.