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r R i t Fourth Quarter 2005, Quarterly Progress Report January 12, 2006 Page 2 3.0 SUMMARY AND CONCLUSIONS • Groundwater in the A -zone flows radially inward towards a northwest to southeast trending trough. The hydraulic gradient is variable; • Groundwater flow direction in the B -zone is towards the east at a hydraulic gradient of 0.009 ft/ft and to the southwest at a hydraulic gradient of 0.01 ft/ft, and; • No rebound of chemical concentrations has been observed in any monitoring or F extraction wells after cessation of groundwater extraction and treatment activities in April 2005. 4.o RECOMMENDATIONS Based on the data presented above and the historical data, SECOR recommends the GWET # system remain offline. Significant rebound has not been observed since the shutdown of the GWET system on April 18, 2005. SECOR will prepare no further action (NFA) required status report during the first quarter 2006. As required by the RWQCB and pursuant to the CAO, Fl�monitoring and sampling will continue until NFA status concurrence is obtained. Z:IChevron1957751Periodic Monitoring\Q P R1200514th Quarter -2005 QPR.doc Mazimum'Constituent Concentrations in;:µglL (Welt !D.) ZOne Toluene Total Xylenes MBE TAME EtBE.: 160 1 15 A -zone <0.5 <0.5 (EX -1) (EX -1) (EX -1) B -zone 3 (MW -1813) 2 (MW -18B) 3 (MW -5B) <0,5 <0.5 C -zone <0.5 ' <0.5 <0.5 <0.5 <0.5 Explanations: µg/L = Microgram per liter < Indicates the constituent was not present at or above the method detection limit shown. TPHg, benzene, ethylbenzene, TBA, DIPE, methanol, ethanol, 1,2 -DCA, and EDB were not detected at or above the laboratory method detection limits in samples collected. 3.0 SUMMARY AND CONCLUSIONS • Groundwater in the A -zone flows radially inward towards a northwest to southeast trending trough. The hydraulic gradient is variable; • Groundwater flow direction in the B -zone is towards the east at a hydraulic gradient of 0.009 ft/ft and to the southwest at a hydraulic gradient of 0.01 ft/ft, and; • No rebound of chemical concentrations has been observed in any monitoring or F extraction wells after cessation of groundwater extraction and treatment activities in April 2005. 4.o RECOMMENDATIONS Based on the data presented above and the historical data, SECOR recommends the GWET # system remain offline. Significant rebound has not been observed since the shutdown of the GWET system on April 18, 2005. SECOR will prepare no further action (NFA) required status report during the first quarter 2006. As required by the RWQCB and pursuant to the CAO, Fl�monitoring and sampling will continue until NFA status concurrence is obtained. Z:IChevron1957751Periodic Monitoring\Q P R1200514th Quarter -2005 QPR.doc