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Laboratory analysis determined that no TPHd, TPHg or BTEX constituents were detected in any of the monitoring wells Analytical results are summarized in Table 2 Copies of field notes and ' well purge logs are included in Appendix A and copies of laboratory reports and chain-of-custody documentation are included in Appendix B 3.0 HYDROGEOLOGIC SETTING The subject site is located at 601 South Ventura in Stockton California (Figure 1) The site is ' situated at an approximate elevation of 5 mean feet above sea level, in the San Joaquin Valley geologic province Local surface sediments consist of Quaternary to Recent alluvial sediments as flood basin deposits In general, these sediments are comprised of silts and clays, with minor sands The regional groundwater gradient is approximately 12 feet per mile to the northeast In the San Joaquin Valley, the Flood Basin Deposits have been estimated to be as much as 100 feet thick Because of their fine-grained nature, the flood basin deposits in general do not yield much water to wells and impede the vertical movement of water The majority of groundwater used for irrigation and drinking water supplies is extracted from more permeable zones beneath the flood basin deposits The uppermost water bearing zone beneath the site flows toward the southeast During the period of investigation, the depth to groundwater at the site has ranged from 19 14 feet (MW-4, December 8, 1992) to 5 19 feet (MW-3, February 23, 1996) below grade When groundwater levels were last measured on February 23, 1996, the depth to water ranged from 5 19 feet (MW-3) to 6 47 feet (MW-4) below grade The direction of groundwater flow has been generally east to southeast, with a gradient magnitude of approximately 0 01 feet per feet 4.0 SITE BACKGROUND 4_1 Tank Removal and Excavation On March 9, 1989, one 6,000-gallon under underground gasoline tank and one 8 000- gi' g gallon underground diesel tank were removed from the site Hydrocarbon contamination was noted in soil samples ' collected from the east side of the tank pit excavation, however, a water sample collected from the southwest comer of the pit did not record any fuel constituents above method detection limits ' Laboratory results are summarized in Table 3 Due to the elevated concentrations of petroleum hydrocarbons in the soils, further investigation was required 4.1.1 Overexcavation of Tank Locations On October 25, 1989, the floor of the former tank pit was deepened from 10 to 18 feet below grade ' using a tracked excavator Subsequent to excavation, 12 soil samples were collected from the floor and sidewalls of the pit at the locations shown on Figure 4 The samples were placed on ice, secured, and transported under chain-of-custody protocol to Argon Laboratories The samples were analyzed for BTEX, TPHg, ethylene dibromide (EDB), 1,2-dichloroethane (EDC), and organic w 1943311A,..re dor 2 S � I