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e <br /> PRELMNARY MROGEOLOGIC ASSESSMENT REPORT <br /> 5491 'F Strset,Banta,California <br /> Delta Project No.40-"l <br /> - Page 12 <br /> 4.0 DISCUSSIONf <br /> 4.1 Extent of Petroleum Hydrocarbon Constituents In Soil <br /> - Reltively low concentrations of BTEX (<0.3 ppm) were found in MW-1 soils at 10 and 20 feet below <br /> -- grade. The MW-1 10 feet below grade sample had the highest TPPH concentration of 450 ppm. Boring <br /> r MW-2 and MW-3 samples did not contain detectable benzene or TPPH, but -BTEXcomponwtsjwwp <br /> pXesent isrkwe,66cinitiatiotllit <br /> Boring MW-3 did not contain detectable BTEX or TPPH Boring MW-3 is spatially separated from <br /> MW-1 and MNV-2, both of which are located at the west end of the !ark cluster near the dispensing <br /> facility. The absence of BTEX and TPPH in boring MW-3 suggests the lateral distributionofof the <br /> hydrocarbon constituents in the soil is peripheral to borings MW-1 and MW-2. The vertical extent of <br /> - BTEX and TPPH concentrations in the soil exceeds 20 feet below grade in boring MW-1. The highest <br /> concentrations are noted near the surface in MW-1 (10 feet below grade) and MW-2-B (5 feet below <br /> grade). <br /> 4.2 Extent of Dissolved Hydrocarbon Constituents in Ground Water <br /> Sample MW-1 contained relatively low concentrations of BTEX and TPPH in the most recent(June 27, <br /> 1989)sampling event. The benzene and TPPH concentrations were 0.15 ppm,and 01.80 ppm,respectively. <br /> Monitoring wells MW-2 and MW-3 both contained benzene (0.0005 ppm and 0.0003 ppm, respectively) <br /> and xylene(0.002 ppm)in concentrations below the California MCUs. TPPH was below detectable levels <br /> t" in MW-2 and MW-3. <br /> l 5.0 RECOMMENDATIONS <br /> 1 <br /> Based on the results of the Preliminary Hydrogeologic Assessment, Delta recommends the following: <br /> • Installation of three additional ground water monitoring wells to further define the lateral and <br /> I vertical extent;of petroleum constituents in soil and ground water. PropD;,ed monitoring wells <br /> 1� E <br /> locations are shown in Figure 8. <br /> t� Collection of soil samples at 5-foot intervals during drilling of all additional monitoring wells. <br /> 3i <br />