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' ARCO Products Company 5 ARCO 4932 16 E Harding Way Stockton,CA November 9 2001 -supply wells are located within -- - •- pp y t a 500-foot radius of the site Nearby wells were located ' approximately 1/2 mile east of the site at the Stockton State Hospital and approximately 2,000 feet northwest at the intersection of Wyandotte and Commerce (As indicated by SJCPHS in their letter dated Nov 21, 2000 Historical wells survey data is included in ' Table 6 Conduit Study ' SECOR evaluated the potential for migration of petroleum hydrocarbons through utility corridors or underground improvements near the site Depth to water at the site is ' approximately 27 feet bgs and no underground improvements or utilities were identified near this depth Since underground improvements and utilities do not intersect the water table, low migration potential for contaminants in groundwater exists through ' these areas Higher potential exists for vapor phase contaminant migration through these areas i ' Stockpiled Soil Approximately 13 cubic yards of soil generated during the drilling of the two borings and installation of the five wells was stockpiled onsite One composite sample (4 parts ' to 1 sample) was collected from the stockpiled soil and analyzed for TPHg, BTEX, MtBE, and total lead Soil was disposed of at Forward Landfill in Manteca, California '• Stockpiled soil analytical data is presented in Table 7 SUMMARY OF FINDINGS • Five monitoring wells and two soil borings were dnIled in at the site to depths up to 80 feet bgs Generalized geologic cross sections ' (Figures 3 and 4) depict a sequence of interbedded sands and clay/silt mixtures Table 1 recaps well construction details for all site wells • Low levels of petroleum hydrocarbons were found in soils during this investigation Table 2 summarizes soil test results TPHg and benzene were detected in one of the 36 samples analyzed at concentrations of 6 9 mg/kg and 0 12 mg/kg, respectively (SB-2, 26 5') Toluene was detected in two samples at concentrations of 0 0056 mg/kg (MW-6, 15') and 0 0051 mg/kg (MW-6, 29') Xylenes were detected at a maximum concentration of 0 15 mg/kg (SB-2, 26 5') EPA Method 8260 results reported MtBE up to S 2 mg/kg (MW-6, 40') No ethylbenzene TAME, TBA, DIPE, EtBE, EDB, ' and 1,2-DCA were detected in soil samples analyzed • Groundwater contains dissolved TPHg, benzene and MtBE Figure 5 ' provides a map view of the distribution of hydrocarbons in groundwater TPHg and benzene were reported in water samples ' from well MW-9 at concentrations of 200 ug/l and 12 ug/l, ' 077 43826 330/AddAssess doc