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,. r I WE 1 { PRELIMINARY HYDROGEOLOGISI'ASSESSMENT REPORT 148W West Frontage Road Manteca, California Delta Project No. 40-88479 Page 11 TABLE 8 Ground Water Analytical Results F� Sample Date Benzene Toluene Eth lbenzene Xylenes EDC EDB TPPH J,4 MW-1 05-11-89 0.0021 NF NF 0.005 NF NF X0.1 MW-2 05-11-89 0.0017 0.007 NF 0.005 NF NF 0.10 MW-3 05-11-89 0.088 0.037 0.003 0.032 0.017 NF 0.017 MW4 05-11-89 1.40 0.34 0.007 0.55 0.018 NF 0.018 i NOTES. _. All results are Iisted in parts per million (ppm). NF = Not Found. 4.0 D1sCUs5ION 4.1 Extent of Petroleum Hvd�rbon Constituents in soil r' BTEX and TPPH were detected in each boring in relatively low concentrations(c 0.7 ppm). The highest concentrations in each boring occurs at depths of 15 to 25 feet below grade. Borings MW-1,MW-2,MW- 3, and MW4 are situated peripherally to the tank duster and pumping island (Figure 2). The lateral extent of the BTEX.const:,senis and TPPH in the soil at.the site is undetermined. 4.2 Extent of Dissolved Hydrocarbon Constituents in the Ground Water i� Low dissolved BTEX and TPPH concentrations were detected in ground water samples from monitoring '. wells MW-1 and MW-2. Higher dissolved BTEX and TPPH concentrations were found in monitoring i . wells MW-3 and MW-4. Monitoring well MW-4 located downgradient from the pump island, contains higher benzene concentrations (1,400 ppb) than MW-1, MW-2, and MW-3. The lateral extent of the' �*■ dissolved hydrocarbon plume has not yet been determined, but appears to extend in a downgradient direction east of monitoring well MW-4. iw. 5.0 RECQMME"ATIONS - --Based-on the results of the Preliminary Hydrogeologic Assessment, Delta recommends the following: t Installation of four additional ground water monitoring wells to further define the lateral and vertical extent of petroleum constituents in soil and ground water. Proposed monitoring well € �; locations are shown in Figure 8