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VV'Y' � M 1 �Tc A S S O C I A T E S I N C r- 1 3.4 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, VW4, 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 in 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 Mthe pilot testing results and previous environmental work performed on site is contained in 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 1 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 deation 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 feasibihty of using these methods to remove dissolved ' gasoline hydrocarbons from groundwater beneath the site In October 1998, ATC submitted a workplan to PHS/EHD wluch was subsequently approved with minor modifications 1 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 ' W 162574 GITAP report doc 4