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r .. .................. J-3 ERE—TANK QLAWMAITFs 68SESSMENTPO Shell Oil Company 5735 Tracy Boulevard,Tracy,Calitarnin Delta Project No,40-69-013 Page 4 i In-line leak detectors are currently used to monitor the double-walled tank annulus and dispensing i lines. The monitoring systems have been checked annually to verify proper function and operations r.o since installation in 1985. All systems have passed each annual test (personal communication, Mr. Bert Russell, Shell Oil Company, 1989). 2.5 Well Inn-ertory An inventory of existing water supply wells within a ane-half mile radius of the site was conducted by reviewing California Department of Water Resources records. A to.al of 22 wells were identified. Table 1 indicates the owner, owner's address, well location, year drilled, and use of each of the I respective wells identified. In gensral, the wells used for domestic water supply have an average depth of approximately 200 feet alt:+ 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 Underground U1111I1e 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 sysrem prior to hookup to the public sewer in 1974. Further, h it is unknown whether the system was removed or abandoned in place. 330 RESULTS 3.1 Site GealoQv Subsurface geology at the site has been inferred from drilling and sampling 12 soil borings in which 3 were converted to monitoring wells (MW-1, MW-2, and MW-3). Soil boring and monitoring well locations are shown in Figure 2. Soil borings SB-1, SB-2, SB-3, and SB-4 were drilled near the i existing underground storage tanks to depths of 21, 16, 16,and 16 feet, respectively. Soil borings SB-7,SB-8,SB-9,and SB-10 were drilled within the area of the proposed new underground storage tanks to depths of 20, 16, 16,and 16 feet,respectively. Monitoring wells MW-1, MW-2,and MW-3 i were drilled and installed around the perimeter of the site to depths of 22 feet. Soil boring SB-I 1 was drilled in front of the service station to a depth of 10 feet. Soil samples were collected at 5- foot-intervals-for - foot-intervals-for class ification-by_-the--Unified Soil_Classification System_(USCS). Selected soil samples were submitted to a California-certified Iaboratory for chemical analyses. Soil boring logs - are presented in Appendix C.