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the site,using the results of previous site investigations and the most recent groundwater monitoring results from January 2010. Historic groundwater analytical data is presented in Appendix B,Table B-4. Monitoring well MW-1 was installed in December 2000 and initially sampled on December 20,2000, at which time the groundwater-monitoring program was implemented. Additional groundwater monitoring wells MW-2,MW-3,MW-4,MW-5,and MW-6 were installed in June,2002. Monitoring well MW-4 serves as the upgradient monitoring well. Monitoring well MW-7, the furthest downgradient monitoring well,was installed in July 2006. Concentrations of TPHD have historically been detected in monitoring wells MW-1,MW-2,MW-3,MW-5,and MW-6. Based on site investigations and groundwater monitoring completed to date,it appears that the majority of material detected in groundwater is located in the northeast portion of the site. The low level groundwater concentrations are not migrating extensively,based on the absence of petroleum hydrocarbons concentrations observed in the furthest downgradient well MW-7 and hydropunch groundwater samples (designated HP-#). Groundwater samples from well MW-7 have only been reported with one detection of petroleum hydrocarbons in groundwater exceeding the laboratory detection limits (47 ug/L TPHD;March 30,2007). The TPHD detected in well MW-7 on March 30, 2007,was below the TPHD WQO of 100 ug/L(RWQCB,2004). No petroleum hydrocarbons have been detected in groundwater samples collected from well MW-7 since the March 30,2007, monitoring event. Although historic groundwater samples collected from borings and wells in the vicinity of the former USTs and ASTs indicated low level concentrations of petroleum hydrocarbons in this L vicinity of the site,recent groundwater monitoring results from groundwater samples collected in all site wells indicate concentrations of TPHD in groundwater at the site are below laboratory detection limits and the TPHD WQO of 100 ug/L(RWQCB,2004). LGroundwater samples have been subjected to a silica gel cleanup procedure when samples indicate detectable concentrations of TPHMO and/ or TPHD since the December 2008 monitoring event. L During the four quarters of groundwater monitoring performed since December 2008,all analytical results for TPHD in groundwater samples collected in wells MW-1,MW-2,and MW-6 have been reported below the laboratory detection limits (<50 ug/L)for samples subjected to silica gel cleanup. The groundwater sample collected from well MW-3 was reported below the laboratory detection L limit(50 ug/L) for the March 2009 monitoring event following silica gel cleanup. Groundwater samples from well MW-3 were reported below the laboratory detection limit(50 ug/L)for groundwater samples during the December 2008,June 2009,and January 2010,monitoring events and silica gel cleanup was not performed. Well MW-4 has only been reported with three detections of TPHD exceeding the laboratory detection limits during historic monitoring in this well,and all concentrations of TPHD were less than 100 ug/L. Well MW-4 has been below the laboratory detection limit for TPHD (<50 ug/L) since March 2008 and silica gel cleanup was not performed. Well MW-5 has been below the laboratory detection limit for TPHD(<50 ug/L) since December 2008 and silica gel cleanup was not performed. \\Eureka\Projects\2007\007152-WOS\PUBS\rpt\20100324-1stHalf2010GWMR&RFC.doc 4ML 9