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Former 76 Station 4409 S E C ® 1R January 27, 2006 Page 4 During the fourth quarter 2005 monitoring and sampling event October 6, 2005, the maximum TPHg, benzene, MtBE, and 1,2-DCA concentrations were 3,400 pg/L (MW-17), 190 pg/L (MW-17), 4,500 pg/L (MW-1), and 23 pg/L (MW-12), respectively (Table 1) A, B, and C monitoring zone isoconcentration maps are included as Figures 4 through 15 Review of the A monitoring zone isoconcentration maps indicates that ConocoPhdlips has performed adequate delineation within the A monitoring zone for TPHg However, the r MtBE concentration at downgradient well MW-2 increased to 130 pg/L during fourth quarter 2005 The current TPHg and MtBE concentrations in the A monitoring zone on the former 76 Station No 4409 are likely due to migration of dissolved contamination from the ARCO 4, station onto the former 76 site TPHg and MtBE concentrations in groundwater in the A monitoring zone have exhibited an increasing trend in wells MW-1, MW-3 and MW-4, which is likely due to migration of dissolved concentrations of TPHg and MtBE from the upgradient ' ARCO gasoline service station site However, the fourth quarter 2005 TPHg concentrations for MW-4 were less than reported concentrations during the third quarter 2005 a Review of the B monitoring zone isoconcentration maps indicate the following TPHg is delineated to less than 50 pg/L with the exception of MW-5 (980 pg/L), MW-8 (180 pg/L), MW-9 (910 pg/L), MW-10 (6800 pg/L), MW-12 (62 pg/L), MW-13 (260 pg/L), and MW-14 (56 pg/L), benzene is delineated to below laboratory detection with the exception of MW-6 (58 pg/L), MW-8 (1 7 pg/L), and MW-9 (2 2 pg/L), MtBE is delineated to below 18 pg/L with the exception of MW-5 (210 pg/L), MW-8 (75 pg/L), MW-9 (76 pg/L), and MW-10 (3,300 pg/L), and 1,2-DCA is not currently delineated Concentrations of benzene in on-site B ¢{` monitoring zone wells MW-5, MW-6, MW-8, MW-9 and MW-10 are decreasing Concentrations of TPHg in on-site B monitoring zone wells MW-5, MW-6, and MW-9 are decreasing Concentrations of TPHg in on-site B monitoring zone wells MW-8, and MW-10 k, are increasing Concentrations of MtBE in the last year in on-site B monitoring zone wells MW-6, MW-7, and MW-8 ranged from ¢ 0 50 pg/L to 5 1 pg/L Concentrations of MtBE are increasing in groundwater at MW-6, MW-7, MW-8, MW-9, MW-10, MW-12, and MW-13 Concentrations of MtBE are decreasing in groundwater at MW-5 Concentrations of 1,2- DCA in groundwater at MW-7 were consistent (2 2 to 2 4 pg/L) for the first four quarters of 1,2-DCA analysis but have generally increased during the past year Concentrations of 1,2- DCA are fluctuating but generally increasing in groundwater at MW-8, and MW-14 Concentrations of TPHg in off-site wells MW-11, MW-12, and MW-14 have ranged from <0 50 to 63 pg/L TPHg has been reported in groundwater at MW-13 since first quarter 2004 when the historical maximum concentration was reported at 110 pg/L The fourth w quarter results have shown a increase in MW-13 to a record high of 260 pg/L Benzene was reported in off-site wells MW-11 and MW-14 during one sampling event but is currently less than the reporting limit for both wells Benzene has not been detected in groundwater at MW-12 or MW-13 MtBE concentrations have been fluctuating in off-site well MW-12 between 0 57 pg/L and 7 3 pg/L but have decreased over the last two quarters The S concentrations of MtBE have also fluctuated in MW-14 from <0 50 to 56 pg/L MtBE has been detected for the first time the fourth quarter 2005 at 1 1 pg/L MtBE has not been 4 detected in groundwater at MWA 1 1,2-DCA has been reported in each of the off-site B monitoring zone wells 1,2-DCA concentrations within well MW-11, MW-12, and MW-13 , have consistently ranged between 7 3 and 35 pg/L The 1,2-DCA concentrations in well Frypl r kr1FT 4409 4Q2005 QSR(CR)doc SECOR lntemaUona!lncorporated rF � F xq � X,