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i INTRODUCTION • The second phase of a drilling investigation that began in the fourth quarter of 2004 was conducted during March 2005 at 3931 Newton Road The first phase had confirmed that diesel fuel is locally present in three semi-confined aquifers of the late Pleistocene Riverbank Formation beneath the main zone of contamination in the overlying Modesto Formation The purpose of the second phase was to locate the limit of contamination in these aquifers by installing additional wells farther from the contaminant source Water samples that were collected in March after the wells were dulled ' indicated that some but not all of the wells succeeded in outlining the limit of contamination A second set of samples was collected in July 2005 to confirm the March results, and the results are reported here The project site is located in an industrial area on the northeast outskirts of Stockton near U S Highway 99 (Figure 1) Originally agricultural propertY, the site was developed as a commercial truck terminal in 1973 A diesel and gasoline fueling facility, consisting of two underground storage tanks (UST's), was formerly present on the south side of the storage yard (Figure 2) This facility was removed in 1989, and evidence of soil contamination was discovered Several thousand cubic yards of contaminated soil were removed from the UST excavation in 1990 and treated using above-ground enhanced bioremediation methods, and several phases of drilling have been completed since then to investigate the extent of groundwater contamination and residual soil contamination • 2.0 PROCEDURES Groundwater monitoring took place on July 12 The wells were opened and allowed to equalize with atmospheric pressure, and then the depth to groundwater was measured with a water level meter In nested wells, the depth was measured in both casings The measurements were recorded on the Well Monitor Report (Appendix A) before the wells were purged Depth data are given in Table 1 A Grundfos purge pump was used to pump between 9 and 20 gallons of water from each well before sampling The water was disposed of on site Samples were collected in disposable plastic bailers and preserved in I-liter amber bottles The samples were labeled and placed into a cooled ice chest for later shipment to the laboratory The laboratory report is contained in Appendix B and the data are summarized in Table 2 3.0 RESULTS 3.1 Depth to Groundwater and Groundwater Flow Directions As shown in Table 1, the depth to groundwater on July 12 ranged from 615 to almost 63 feet This is similar to but slightly more than in March The few inches of decline in the water table is probably due to the start of seasonal agricultural pumping 2