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Forrner 76 Station 4409 S E [ ® 1R October 27, 2005 Page 5 were less than the concentrations reported during second quarter 2005 Fuel oxygenates ,N have not been detected in groundwater at MW-17 ; Review of the A monitoring zone isoconcentration maps indicates that ConocoPhillips has performed adequate delineation within the A monitoring zone for TPHg However, the Y MtBE concentration at downgradient well MW-2 increased to 53 pglL during third 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 5 station onto the former 76 site B monitoring zone isoconcentration maps indicate the k following TPHg is delineated to less than 50 pg/L with the exception of the 61 pg/L ' reported in MW-13, benzene is delineated to below its MCL of 1 0 pg/L, MtBE is delineated to below 13 pglL with the exception of the 32 pg/L reported in MW-14, and 1,2-DCA is not currently delineated Reported concentrations of TPHg, benzene, and 1,2-DCA at 13,000 pg/L, 700 pg/L and 0 50 pg/L respectively are not delineated in the C monitoring zone MtBE is delineated to less than the reporting limit in the C monitoring zone A, B, and C monitoring zone isoconcentration maps are included as Figures 4 through 15 CHARACTERIZATION STATUS Soil contamination delineated? Yes Dissolved groundwater delineated? No Free product delineated? NIA Current phase of protect? Assessment/Monitoring Frequency of sampling? Quarterly Soil remediation in progress? No , Anticipated start date? NIA Anticipated completion date? NIA d,w A monitoring zone groundwater gradient? 0 018 ft/ft northeast <� B monitoring zone groundwater gradient? 0 003 to 0 005 fUft northeast "4 C monitoring zone groundwater gradient? 0 003 ft/ft southeast 1 NEIGHBORING SITE ACTIVITIES The upgradient ARCO Service Station, located at 16 East Harding Way, appears to be affecting groundwater concentrations within A monitoring zone wells at the ConocoPhillips r, site Remediation technology at the ARCO site includes soil vapor extraction, groundwater ; k extraction, and ozone sparging An off-site ozone sparge system was installed during the second quarter of 2005 and became operational during third quarter 2005 Certified z�" laboratory analytical reports, chain-of-custody documentation, and field data sheets for the > ARCO station are included as Attachment D RECENT SUBMITTALS/CORRESPONDENCE Am 45 Submitted — Quarterly Summary and Monitoring Report— Second Quarter 2005, dated July 28, 2005 Submitted —Results of Vertical Assessment and Updated Site Conceptual Model, dated July 28, 2005 4409 3Q2005 QSR doc SECOR International incorporated