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i 15 lune 2009 --� AGE-NC Project No.05-1306 Page 31 of 33 10.0. RECOMMENDATIONS AGE recommends discontinuing ground water monitoring.Based on the results of site investigation and remediation activities to date,the site should be evaluated for closure based on: • Completion of site investigation. • Free product is no longer present. • Successful source removal/remedial activities exceeding the proposed volume of impacted soils. • Off-site down-gradient wells MW-5 and MW-6 indicate plume has not traveled significantly. • Lack of constituents other than TPH-d; and dissolved TPH-d is defined below CRWQCB water quality objectives. • Lack of receptors (potable water supplies, surface waters). • Off-site impacted ground water at the McCormick and Baxter NPL site, the land use �} restriction on the NPL site not to use water for human consumption or agriculture; local ground water has a background chemical impact, degrading the beneficial uses of the local aquifer. • Residual levels remaining should not pose a threat to human health, as construction cannot occur over the former UST area. • 36 groundwater monitoring events were considered for statistical analysis via Mann-Kendall and Mann-Whitney U Test. Only four of the existing wells had the required number of detections for petroleum constituents with results indicating stable and/or declining trends in three of the four wells including MW-3, MW-4, and MW-5 (Mann-Whitney indicated increasing trend,however the highest level was 100 µg11 TPH-d which meets the objective). { Lack of receptors for the ground water pathway relative to the dimensions of the stable and/or receding residual plume. • Vapor survey information indicates that the vapor pressure of the remaining low levels of weathered petroleum are too low to pose a threat to human health. f Advanced GeoEnvironmental,Inc.