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8 i $ V�K A S s d C I A T E S I ISI C Based on groundwater elevations measured on December 14, 1999, the direction of groundwater flow is generally toward the east-northeast at an approximate gradient of 0 002 ft/ft The direction of groundwater flow has ranged from southeast to northeast since groundwater monitoring was initiated in December 1988 ' 3.0 PREVIOUS ENVIRONMENTAL WORK ' Previous subsurface investigations performed included drilling seventeen soil borings, installing five groundwater monitoring wells (MW-1 through MW-5), seven vapor extraction wells (VW-1, VW-2s, VW-2d, VW-3, VW-4, VW-5s, and VW-5d), one piezometer (PZ-1), and one recovery ' well (RW-1), collecting and analyzing soil and groundwater samples, and monitoring fluid levels in the wells Quarterly groundwater monitoring was initiated at the site in December 1988 The locations of monitoring wells and pertinent site features are shown on Figure 2 A summary of ' well construction details is included in Table 1, a summary of monitoring data is included m Table 2, and a summary of laboratory analytical results is included in Table 3 ' In 1992, RESNA Industries Inc performed a groundwater aquifer test and performed a soil vapor extraction test (VET) A second VET was performed in January 1994 A complete summary of the pilot testing results and previous environmental work performed on site is contained in 4 RESNA Industries Inc 's Final Remediation Plan for Soil and Groundwater Remediation, dated November 17, 1994 RESNA recommended groundwater extraction and vapor extraction as a ' final remediation plan for impacted soil and groundwater at the site Copies of vapor extraction test monitoring data are included in Appendix B ' In January 1996, at the request of the City of Stockton, the site was reevaluated based on the release of a Lawrence Livermore report which recommended natural attenuation as a remedial alternative at petroleum hydrocarbon sites and the Final Remediation Plan was never ' implemented In May 1998, PHS/EHD requested that an air sparge/vapor extraction pilot test be performed at the site to evaluate the feasibility of using these methods to remove dissolved gasoline hydrocarbons from groundwater beneath the site In October 1998, ATC submitted a ' workplan to PHS/EHD which was subsequently approved with minor modifications On November 23, 1998, a vapor extraction test was performed by ATC using vapor well VW-1 ' as the vapor extraction point while monitoring vacuum response in the surrounding wells The test was approximately 15 hours in length Flowrates, applied vacuums, influent and effluent ' volatile organic compound (VOC) concentrations, and temperatures were also monitored during the test Vapors were extracted using an internal combustion (IC) engine equipped with a 5-hp blower and a moisture knockout chamber Two influent vapor samples and one effluent vapor ' sample were collected during the test Results and field readings from the short-term vapor extraction are included in Appendix B During the Lvapor extraction test, extraction flowrates ranging from,47 to 57 cubic feet per minute (cfm) resulted in vacuums of up to 0 8 inches of water to vadose wells VW-5s and VW-2d located W 162574 011CAP report doe 3