ARCHIVED REPORTS_2003 FEASABILITY STUDY REPORT AND SITE ASSESSMENT WORK PLAN

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S E C O R • 2003 Feasibility Study Report and Site Assessment Work Plan July 18, 2003 Page 4 2.3 Surface Water The site is located approximately 2'/2 miles west of the San Joaquin River, within the San Joaquin River Basin (Figure 6). The CRWQCB-CVR defines the San Joaquin River basin as the area drained by the San Joaquin River, including all watershed tributaries to the San Joaquin River, and the Delta south of the Sacramento River and south of the American River Watershed. Tom Paine Slough and the Paradise Cut are located approximately one mile northeast of the site (USGS, 1998). Historical groundwater gradient data suggest that Tom Paine Slough and the Paradise Cut are gaining surface water bodies. Three unlined retention ponds are located onsite along the northeastern site boundary. These ponds are used to temporarily store surface water run-off prior to surface discharge. These ponds may also recharge shallow groundwater. 2.4 Hydraulic Connection with Aquifers The Upper Tulare Aquifer contains groundwater in unconfined conditions from approximately 5 feet bgs to approximately 200 feet bgs. Below this depth, groundwater is confined by the impermeable Corcoran Clay Layer. The unconfined Upper Tulare Aquifer is in hydraulic communication with surface water, reducing water quality in the Upper A and A zone of the Upper Tulare Aquifer(USGS, 1998). 2.5 Local Land Use Land use in the area is primarily agricultural with some industrial. The site is surrounded to the north, west and east by farmland. A card lock facility and an equipment maintenance shop, operated by Woolsey oil, are located just south east of the site. Interstate 5 is located approximately 400 feet east of the site. 2.6 Previous Investigations and Remedial Actions Between December 1983 and May 2003, 54 monitoring wells, 13 remediation wells and three piezometers were installed at the site. During this period of time, Wells T-2, MW-2, MW-10, MW-11, MW-14, MW-16, MW-20, and MW-21 have been destroyed; Well MW-9 cannot be located following demolition and rough grading of the former the Keylock facility. Fifty four of the existing wells are constructed to monitor the shallow water-bearing zones (Upper A-Zone and A-Zone) to depths of 15 to 30 feet bgs. The remaining six wells (MW-12B, MW-13B, MW-22B, MW-23B, MW-50B, and MW- 64B) are used to monitor the B-Zone, installed to depths ranging between 55 to 65 feet bgs. A profile of existing monitoring well screen intervals is included as Figure 7. Previous remedial actions have included dual extraction (DE), limited soil excavation, and ISO- GENT" pilot testing. Historical groundwater elevation and concentration summary tables are included as Attachment C. Historical soil concentration summary tables are included as Attachments D. Historical soil concentration maps and 1003 groundwater elevation and concentrations maps are provided as Attachments E and F, respectively. I:\Chevron\1001621\REPORTS\2003\2003FS\FS_2003_revD.doc