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SolI 8onng and Momtortng Well Installation Report Page 7 Ranch Market,Riverbank,CA September 6 2000 summary of the wells located dunng the DWR records review and field search The locations of wells found dunng the records review and field search within a 2000-foot radius are shown on Figure 10 Copies of the DWR well logs are provided in Appendix F 6.3 Field Search A field check to identify sensitive receptors within a 2000-foot radius of the Site was conducted on August 11, 2000 A search was conducted for bodies of water which may provide ecological habitat, schools and residential areas, and industnal, municipal, or domestic wells In addition to the three domestic wells at the properties adjacent to Ranch Market, possible sensitive receptors were observed The field search confinned the presence of the Stanislaus River and Jacob Meyers Park approximately 700 to 1000 feet to the south A well is located on the Jacob Meyers Park property, which is approximately 700 feet from the Site Given the Stanisluas River and well at Jacob Meyers Park are less than 1000 feet from the Site, a release at the Site to groundwater could potentially have an impact on the well and the River However, all available evidence suggests no impact to the Park, River, and wells in that area from activities at Ranch Market There are several residences greater than 1700 feet to the north and up-gradient of Ranch Market These wells north of the Site are up- gradient and, therefore, have not been impacted by past activities at Ranch Market No wells were observed within the 2000 foot-radius, south of the Stanisluas River in Riverbank, California 7.0 SUMMARY AND CONCLUSIONS The depth to water was found at approximately 27 feet bgs and the groundwater gradient across the site is 0 0028 feet/foot toward the south Due to the proximity of the San Joaquin River, seasonal influences on gradient and flow direction are probable Based on analytical results and monitoring data collected at the Ranch Market Site, gasoline range petroleum hydrocarbons, mcluding BTEX,TPHg, MtBE, TBA, DIPE, 1,2-DCA, and EDB, were found adsorbed to soil and/or dissolved in groundwater Refer to Tables 2 and 3 for analytical results of groundwater and soil sampling at the site Referring to the Cross Sections A-A' and B-B'(Figures 5 and 6), the release of gasoline in the area of the former USTs appears to have migrated vertically downward to the groundwater, and then down gradient creating a 10 foot thick smear zone from 20 to 30 feet bgs (Table 2) The highest concentrations in soil of benzene, MtBE, and TPHg were found in the soil sample collected from MW-1 at 20 feet bgs, underlying the former UST pit The lateral and vertical extent of gasoline range petroleum hydrocarbons adsorbed to soil has not been completely defined in this area by the current data set (Table 2) The highest concentration of dissolved benzene, MtBE, and TPHg were found in the water sample collected from MW-1, located on the former UST pit (Table 3) MW-I was also the only well with samples that contained concentrations of DIPE and EDB Dissolved concentrations of 1,2-DCA and TBA were at their highest in samples from MW-1 Referring File R-Welllnstall&M&S rpt doe SECOR International incorporated