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T PROBLEM ASSESSMENT REPORT Moore Petrateum, Inc. 1399 E. Yosemite Avenue, Manteca, CA NOA Project No. 10-90.480 Prge 12 4.2 Extent of Petrol®urn Constituents in around Water Results of recent ground-water sampling at the site indicates that petroleum constituents are present at concentrations exceeding california mcls only at monitoring well 14W-1A. The highest benzene concentration which has been detected in monitoring wells at the site is 72 ppb which was detected at monitoring well MW-1A during the July, 1990, sampling event. Benzene concentrations in rom below or monitoring wells MW-2 and s in have decreased events to non— slightly above California mels in previous sampling 9 90�nsampling :vent. detectible concentrations during the July, There is inadequate data presently available to determine the significance (if any) of the minor fluctuations in benzene concentrations at 14W-2 and 14W-3. The moderate concentration of benzene detected at MW-IA is not unexpected due to the high TFH concentrations detected in soil samples from this well. It is important to note however, that the concentration of berzene seen in this well may be somewhat anomalous due to the possible of petroleum constituents. to the water table during transport drilling of this well. Shouldin icatee athd cline) in subsequent sampling evsnts will probably concentrations at this well. Figure 7 presents the interpreted extent of petroleum constituents in ground water at the site. 5.0 REMEDIATION ALTS NATIVES 5.S soil possible remediation alternatives for gasoline contaminated soils include in-situ biological treatment, soil excavation, and soil venting (in-situ volatilization) . Suil venting is typically utilized to volatilize gasoline constituents in sails that are moderately to highly permeable to air flow. Examination of the geologic cross-sections presented in Figures 4 indicates that Lhe bulk of petroleum constituents occur within permeable or tasilty airfsands. These lithologies should be sufficiently p to allow soil venting to be a viable remedial alternative. At this site, soil venting appears to offer a number of advantages over either in-situ biological treatment or excavation. Some of these _ advantages are: o soil venting will not affect continued site: operations. • Soil venting activities will not adversely affect -------------.._..-------------..-.-- ---------_-._ .-------_ground.--water_ beneath the site, and can be undertaken independently 0f gr ound=water--remediation-activities.