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L GEOMATRIX w Mr. Don Culbertson Chevron Pipe Line Company 12 January 1995 Page 3 w temporarily contained on-site in D.O.T.-approved 55-gallon drums, pending analysis and disposal by CPL. The monitoring wells will be surveyed for vertical and horizontal control J" by licensed surveyors for use in evaluating groundwater flow direction. The survey will be tied to an existing well; if a discrepancy is noted, all the existing wells will be resurveyed. The new monitoring wells will be included in the quarterly groundwater monitoring program. ar EVALUATION OF SITE CHARACTERIZATION The lateral and vertical distribution of petroleum-affected soil has been adequately characterized along the southwestern property boundary of the site via a series of borings, trenches, and monitoring wells. As discussed with the RWQCB, lateral definition of affected soil to the south of West Byron Road (if any) is not addressed in this project. Locations of soil borings, monitoring wells, and trenches and their corresponding analytical results were compiled from earlier work by Toxic Technology, Inc. (TTI) and Erler and Kalinowski, Inc. (EKI) and are presented on the site plan (Figure 1, Appendix B; revised December 1994). Analytical data in areas of particularly dense data control (areas around MW-23 and around MW-13) indicate that the presence of either residual separate-phase product or elevated concentrations of total petroleum hydrocarbons (TPH) in soil is quite limited in lateral extent. This finding is consistent with the general poor mobility of the product at the site, which is a result of the degraded, heavy (long-chain) nature of the petroleum and the fine-grained sediments beneath the site. � Previous workers (TTI,EKI) have stated that the vertical extent of petroleum-impacted soil was limited primarily to depths between 5 and 16 feet (the current water table is at a depth of 7 feet). Analytical data shown on the site plan support these conclusions, with several ,i. borings indicating non-detect TPH results at depths greater than 16 feet. Visual observations from the trenching also support this conclusion (TTI). The vertical distribution of petroleum in soil is probably due to historical fluctuations in the water table. Piezometric data from site wells indicates that groundwater flows in a northerly direction. Monitoring wells are distributed within affected soil areas and immediately downgradient of such areas. TPH in groundwater samples is very limited in lateral extent and has been consistently detected only in samples collected from monitoring wells screened across TPH- affected soil (MW-2, MW-23, MW-24, and MW-13). Other petroleum constituents, such as L- BTEX or PNAs, do not appear to measurably affect site groundwater. Hydrogeologic cross-sections A-A' and B-B' (Figures 2 and 3) have been developed across j"' areas of dense data control to illustrate the limited nature of the lateral and vertical extent of