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and V&W that railroad locomotives are washed and flushed on the engine tracks adjacent :o this boring, and that the wash water collects in this depression. in the boring. Upgradient directed V&W to move 10 feet to the west of B3 and drill a new boring(B4). After B4 w. s drilled, a water sample was collected from B3, although most of the water had drained fro a the borehole while B4 was being drilled. The samples were analyzed for Total Petroleum Hydrocarbons as diesel, benzene, toluene. ethylbenzene, and xylene (BTEX), and MTBE by EPA methods S015m and 8020(Appen lix B). The results are summarized in Table 1 and plotted on Figure 3. The soil results confirn the observations made in the field (i.e. hydrocarbons only at 15 and 20 feet in B 1). No MTBE was detected in either of these samples. Diesel-range hydrocarbons were detected in the water sample from B3 at a concentration of 1,700 ppm. The laboratory noted that oil-range compounds were a significant component of the hydrocarbons, as would be expected in locomotive-,vash/flush water. 5.0 CONCLUSIONS AND RECONINIENDATIONS We conclude that this site meets the criteria fora conditional site closure as outlined is c Appendix B (No Further Action Requests) of the Tri-Regional Board Staff Reconrnrendations for Preliminary Ir7vestigation and Evahiation of U70e1-ground Tar k Sites. We have therefore included the Appendix B Checklist of Required Data for X Further Action Requests as Appendix C. The criteria are discussed below. Criterion 1: Demonstrate that only the vadose zone :has been affected. Drilling in and around the UST excavation indicates that leakage from the fueling faci'ity was limited to the excavation. The boring through the excavation indicates that diesel penetrated less than 10 feet below the excavation, to a maximum depth of 20-25 feet. Borings within 5 feet of the lateral margins of the excavation encountered no contaminated soil whatsoever, indicating that lateral leakage from the UST or dispens ;r did not occur to any appreciable extent. The depth to groundwater in the Stockton arc a in general is presently near its historically highest level, and is reported to be between 40 and 45 feet at a site less than 2000 feet to the north. Based on ions-term groundwater measurements by the Flood Control Section of the San .loaquin County Public Works Department, it is unlikely that groundwater has been shallower than 35 feet at the site It is therefore not likely that the saturated zone has been impacted. Criterion 2: The release has been stopped and source(s) of hydrocarbons in the vadose zone have been removed or permanently contained. The UST and dispenser have been removed, and the residual hydrocarbons are restrict ed to the silt bed that underlies the site to a depth of more than 25 feet. Silt beds typicalir have fairly low permeability, and diesel has limited mobility in soil. Hence, the contaminants are effectively contained. 3