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PROPOSED WORK PLAN FORETANK CLOSURE SITE ASSESSMENT Shell Service Station 5725 Tracy Boulevard,Tracy California Delta Project No. 40-89-012 L Page 4 2.4 Soill/Leak Histor According to Shell's records no leaks or spills have been.: reported at this site.. The source of petroleum constituents detected in earlier investigations is unknown. At this time, no estimate of the volume of petroleum constituents present in soils and/or ground water beneath the site has been made. In-line leak detectors are currently used to monitor the double-walled tank annulus and dispensing lines. The monitoring systems have been checked annually to verify proper function and operations since installation in 1985. All systems have passed each annual test (personal communication, Mr. Bert Russell, Shell Oil Company, 1989): 2.5 Well Inventor An inventory of existing water supply wells within a one-half mile radius of the site was conducted by reviewing California Department of Water Resources records. A total of 22 wells were identified. Table 1 indicates the owner, owner's address, well location, year drilled, and use of each of the respective wells identified. In general; the wells used for domestic water supply have an average depth of approximately 200 feet and are cased for the first 100 feet. In addition there is a water supply well located on site of unknown construction and depth. The well appears to have been installed approximately at the time of site construction and,was taken out of use during 1974 when public sewer and water service were connected to the facility. 2.6 Under round Utilities Public utilities are located below Tracy Boulevard and are illustrated in Figure 2. Approximate locations where utilities enter the site are also indicated. It is unknown at this time whether or not the facility utilized an on-site septic system prior to hookup to the public sewer in 1974. Further, it is unknown whether the system was removed or abandoned in place. 3.0 PROPOSED SOIL, BORINGS This section describes the proposed assessment, including the depth and distribution of exploratory soil borings. The methods used to drill and sample the ,borings, analytical procedures, quality assurance plan, and the site safety plan are contained in Appendix C. C