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r <br />' INTERIM REMEDIAL ACTION PLAN <br /> 4491 West Durham Ferry Road <br /> Tracy, Caldomia <br /> Delta Project No 40-91-732 <br /> Page 7 <br /> depth of 5 feet below the ground surface indicated the chemicals analyzed were below the laboratory's <br /> limit of detection <br /> r <br /> 3.6 Ground Water Chemistry <br /> Chemical analyses of the ground water from monitoring wells MW-1 and MW-2 indicated the presence <br /> of TPH as gasoline at concentrations ranging from 140 to 48,000 ppb Concentrations of benzene were <br />' detected In monitoring wells MW-1 and MW-2 ranging from 2 3 to 3,300 ppb (Table 4) Petroleum <br /> hydrocarbons have generally been below the method detection limits in monitoring well MW-3 <br /> 4.0 PHASE I INVESTIGATIVE SUMMARY <br /> Based on the soil samples collected at 5-foot intervals at the three monitoring well locations, the site <br />' appears to be underlain by sandy silt with a 2-foot-thick lens of sand at approximately 3 feet below the <br /> ground surface The water table was observed to be approximately 10 feet below the ground surface <br /> The direction of ground water flaw was calculated to be toward the northeast at a gradient of <br /> approximately 0 005 <br /> TABLE 3 <br /> CHEMICAL ANALYSES OF SOIL SAMPLES <br /> Concentrations in Milligrams per Kilogram mg/kg (ppm) <br /> ' Sample Date Sample Depth <br /> Location Sampled eet Benzene Toluene Ethylbenzene Xylenes EDCa ED13 1PHc <br /> MW-2 08/28/91 S 0 013 0 018 <0 005 002 <0 005 <0 005 <05 <br /> MW-3 08/28/91 10 <0 005 <0 005 <0 005 <0 005 <0 005 <0 005 <05 <br /> ' a 1,2 Dichloroethane <br /> b Ethylene dibromide <br /> c Total petroleum hydrocarbons <br /> ' RPTo45 TA <br />