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i i18 February 2003 i AGE-NC Project No 96-0229 Page 8 of 9 i • TPH-g, BTEX and MTBE were reported for the sixth consecutive quarter in water samples collected from MW-9, suggesting that the plume of petroleum-impacted ground water may have shifted towards MW-9 (Table 3) i • The highest concentrations of off-site dissolved MTBE were detected in down-gradient well MW-6, elevated off-site MTBE concentrations has generally been observed at MW-6 since iMarch 2001 (Figure 9) Generally,increasing MTBE concentrations have been reported from MW-l OA since at least i March 2001, suggesting that the plume of MTBE-impacted ground water is migrating towards the northeast and beyond well MW-l0A (Table 3) • Since monitoring wells MWA and MW-1013 are "drowned", these wells should yield isamples representative of deeper ground water conditions Deeper ground water in the area of MW-1 (48 to 53 feet bsg)is impacted by significant TPH-g,BTEX, 1,2-DCA.and MTBE, ideeper ground water in the area of downgradient well MW-1 OB is impacted by MTBE e Although significant MTBE concentrations were detected in the sample collected from well MW-1 (screened 48 to 53 feet bsg)in deeper ground water,onlyminor MTBE concentrations i . were detected in the samples collected from thc, shallow water on-site well MW-2 (located 5 feet from MW-1), implying that a deeper vertically undelineated MTBE-impact may be present cross-gradient to down-gradient of the site (Figure 9) i i5 0. RECOMMENDATIONS Based upon data collected during September and November 2002, AGE recommends i0 Continued utilization of wells MW-1 through MW-12 for quarterly groundwater monitoring and sampling i • Continued ground water monitoring of the subject site concurrently with the Pacific Mini Mart (4511 Pacific Avenue) C Performance of a receptor survey to locate potential receptors within 2,000 feet of the site Due to 1) high concentrations of contaminants (i e MTBE, BTEX, 1,2-DCA) encountered at the isite that are significantly above the DHS's MCLs,2)the high mobility of MTBE dissolved in ground water and 3) a recent trend of increasing MTBE concentrations northeastward towards wells MW-9 and MW-10, AGE reconu-nended during a meeting with Mi Michael Infurna of the EHD that a ground water interim remediation(i e ground water pump-and-treat) work plan be implemented at the site to inhibit further off-site migration of the fue f-impacted ground water plume until a full scale iremediation system can be installed(Summary of 17 December 2002 Meeting, dated 18 December Advanced Geol,nvkronmental,Inc i