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11 June 2002 AGE-NC Project No. 96-0229 Page 4 of 5 • Ground water flow direction in the area of wells MW-1 through MW-10 was inferred to be towards the northeast at an approximate gradient of 0.003 ft/ft. This appears to be the prevailing flow direction for the area. • Due to the low hydraulic gradient at the site, slight variations in ground water measurements or changes of recharge/discharge of the local ground water could greatly modify the inferred ground water flow direction. 16- • Monitoring wells MW-1 and MW-10B are "drowned", and yield samples representative of 4 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 and MTBE; deeper ground water in the area of &- downgradient well MW-10B is impacted by minor MTBE. • Significant MTBE concentrations were detected in the sample collected from well MW-1 (screened. 48 to 53 feet bsg) in deeper ground water, however only minor MTBE concentrations were detected in the samples collected from shallow water on-site wells MW-2 (located 5 feet from MW-1), implying that a deeper, vertically undelineated MTBE-impact may be present crossgradient to downgradient of the site (Figure 5). • The highest concentrations of off-site dissolved MTBE were detected in downgradient wells MW-6 and MW-7; low concentrations of dissolved MTBE were detected at wells MW-8, MW-9, MW-10A and MW-10B; a trend of increasing off-site MTBE concentrations has generally been noted since March 2001. • TPH-g, BTEX and MTBE were reported for the third consecutive quarter in water samples collected from MW-9; suggesting that the plume of petroleum-impacted ground water may have shifted towards the east. • The elevated concentrations of petroleum hydrocarbons detected in samples collected from wells MW-1, MW-2, MW-3, MW-6 and MW-7 indicate that these wells are within or near the dissolved petroleum hydrocarbon"core area" of the plume (Figure 4). 5.0. RECOMMENDATIONS LW Based upon data collected during February 2002, AGE recommends: • Continued utilization of wells MW-1 through MW-10 for quarterly ground water monitoring and sampling. • Continued ground water monitoring of the subject site concurrently with the Pacific Mini Mart (4511 Pacific Avenue). • Performance of a receptor survey to locate potential receptors within 2,000 feet of the site. Advanced GeoEnvironmental,Inc.