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 3 the B zone encountered as shallow as 50 feet bgs (SECOR, 2003b). The lower boundary of the B- zone has not been explored. 2.2.1 Groundwater Flow Rates, Directions, Recharge, and Discharge A 2003 Aquifer Testing Report, (SECOR, 2003d) suggests hydrogeologic communication exists between the Upper A zone and A zone onsite. However, locally, there is no distinction between the Upper A and A zones. Groundwater beneath the site generally flows to the north with gradients ranging from approximately 0.0008 feet per foot (ft/ft) to 0.06 ft/ft. A rose diagram showing the historical gradient and flow directions of shallow groundwater (i.e. Upper A and A zones) is provided as Figure 5 (SECOR, 2003c). Aquifer test results indicate an average transmissivity(T) and specific yield (Sy) of approximately 381 square feet per day (ft 2/day) and 0.41 cubic feet per cubic feet (ft3 per ft), respectively. Based on a saturated thickness of 20 feet in the A zone, the average conductivity (K) was approximately 19 feet per day (ft/day) or 0.0067 centimeters per second (cm/sec). The pumping well radius of influence (ROI) was calculated to be approximately 83 feet. Historical groundwater gradient data suggests that shallow groundwater flows toward and may discharge to Tom Paine Slough and the Paradise Cut. Groundwater in the area appears to recharge from rain fall. The average rain fall for the city of Tracy is 7.9 inches annually (hftp://www.worldclimate.com/cgi-bin/data.pl?ref=N37Wl 21+2200+048996C). • 2.2.2 Groundwater Use The San Joaquin groundwater basin underlies the site. Beneficial uses of groundwater in the area include municipal, irrigation, stock watering, process and service supply (SECOR. 4'h Quarter /Annual 2002 Quarterly Groundwater Monitoring Report). A summary of water wells within a one mile radius of the site and their approximate locations are provided as Table 1 and Figure 6, respectively. There are no county or city operated pumping wells in the general area. San Joaquin County municipal water supply wells are typically screened in the Lower Tulare Aquifer. Groundwater located in the Upper A, A and B zone beneath the site is not used for human consumption due to naturally poor water quality. In a conversation between SECOR and Lee Helms (Helms, Lee. Telephone Interview. 13 May 2003), Mr. Helms indicated a domestic well on his property produces water high in total dissolved solids (TDS), and this water is not used for human consumption . 2.2.3 Extraction Wells Affect on Groundwater Flow One onsite groundwater extraction well (WSW-1) and fourteen offsite groundwater extraction wells were identified within a one mile radius of the site (Table 1 and Figure 6). Based on historical groundwater monitoring data, pumping from these wells does not appear to impact groundwater flow. No groundwater injection wells were identified in the vicinity of the site. I:\Chevron\1001621\REPORTS\2003\2003FS\FS_.2003_revD.doc