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=--"SOMA <br /> OMA <br /> Working To Restore Nature <br /> } <br /> 4.0 SUBSURFACE CONDITIONS <br /> Soils encountered beneath the site consist primarily of elastic silt (MH), lean clay (CL), and <br /> ' fat clay (CH) to a depth of approximately 29 feet below grade, the maximum depth explored. <br /> Apparent discontinuous sand lenses were noted at varying depths. <br /> ' Groundwater beneath the Site was first encountered at approximately 13 feet below grade. <br /> P Y <br /> ' After well completion, the piezometnc surface stabilized to approximately 12 to 13 feet below <br /> grade. Based on July 15 and 22, 1994 monitoring data (Table 2), static groundwater fluctuates <br /> between approximately 12.34 and 15.28 feet below grade and flows to the northwest under a <br /> gradient of approximately 0.0015 ft/ft or 8 feet per mile. Groundwater gradient maps for July <br /> 15 and 22, 1994 are presented on Plates 3 and 4, respectively. <br /> 1 <br /> 5.0 CONCLUSIONS <br /> ' 5.1 Soil Contamination <br /> Gasoline hydrocarbons were detected in borings MW4 and MW6 (Table 1) at levels near or <br /> below laboratory detection limits Detected hydrocarbons, most notably TPHg (1 3 and 2 4 <br /> t parts per million) were detected near the groundwater interface at depths between 10 to 15 feet <br /> below grade. The low levels of gasoline hydrocarbons at this depth may be due to the past <br /> presence of dissolved contaminants in the capillary fringe. <br /> ' 5.2 Groundwater Contamination <br /> TPHg was detected in groundwater samples collected from MW 1 and MW2 at 8,200 ppb and <br /> 12,000 ppb, respectively. No petroleum hydrocarbon analytes were detected in the water <br /> samples collected from wells MW3 through MW7. The extent of groundwater contamination <br /> has been defined. Dissolved gasoline hydrocarbons in the groundwater beneath the are limited <br /> to a localized area in the vicinity of monitoring wells MW 1 and MW2. <br /> ' 6.0 REFERENCES <br /> ItESNA Industries Inc., Interim Proilem Assessment Report. Soil and Groundwater <br /> Contamination• 2403 West Navy Dnve, Stockton. California, June 18, 1992 <br /> United States Geological Survey; 75 Quadrangle; Stockton West, Calfornia, <br /> Photorevised 1976 <br /> r <br /> 1500911REPOMXSR-0844 FNL <br />