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SEC ® R SIEVOR 3 concentration of 0.88 ug/L in boring location GP-12, and ethanol was reported at a concentration of 610 ug/L in boring location GP-13 (SECOR, 2004). ' In September 2003, groundwater monitoring well MW-16 was installed. MW-16 was installed to a depth of 25 feet bgs, and screened from 5 to 25 feet bgs. MtBE was reported in one soil sample from well MW-16 (MW-16@25') at a concentration of 0.011ppm- Groundwater monitoring has been performed at the site since August 1998. Groundwater flow has generally been to the east-northeast with a gradient of 0.001 ft/ft. Y ! Historical soil analytical data isresented in Table u p e 1, and soil boring and well construction details are included in Table 2. Historical groundwater data is included in ' Appendix B, historical figures are included as Appendix C, and historical boring logs and well completion details are included in Appendix E. ' 2.3 Supply Well Survey In March 1999, IT performed a Sensitive Receptor Survey and reported 12 wells within ' a '/-mile radius of the site. The closest wells to the site were located approximately 0.15 miles west/southwest (upgradient) of the site and 0.13 miles east (crossgradient) of the site. The nearest downgradient wells were located approximately 0.3 miles . northeast of the site (IT, 2001). Water well location data is included in Table 3. On January 13, 2002, SECOR conducted a 500-foot door-to-door reconnaissance water well survey (SECOR, 2003). Department of Water Resources (DWR) records were reviewed to verify identified water well locations. Water well location data is included in Table 3. ' Additional irrigation well sampling and an influence study were conducted to verify that Lathrop Grammar School's irrigation well had not been impacted b p y petroleum hydrocarbons, particularly MtBE, and to determine if any pumping wells in the area may ' have been affecting groundwater flow at the site. The Lathrop Grammar School -f irrigation well was located approximately 1,600 feet northeast of the site. On October 6, 2003, pressure transducers with built in data-loggers were installed in five groundwater monitoring wells (MW-11, MW-12, MW-13, MW-14 and MW-16). On October 10, 2003, w. the pressure transducers/data loggers were removed from the wells. Based on the results from the transducers/data logger it was concluded that the Lathrop Grammar School well had not been influencing groundwater-elevation and flow at the site (SECOR, 2003). 2.4 Summary of Remedial Action SECOR conducted a five-day dual-phase extraction (DPE) event at the site on March f 25 through March 29, 2002. The objectives of the interim remediation/DPE feasibility f testing were to reduce the amount of hydrocarbons in soil and groundwater beneath the site; and to determine the feasibility of DPE as an applicable technology for remediation M l d 1205 SCM.doc 4 _.