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15 June 2009 AGE-NC Project No.05-1306 Page 23 of 33 "increasing trend" at the 90 percent confidence level relative to TPH-d with a U statistic of 16.0. It should be noted that prior to the last three rounds of results, this well was indicating a "no trend" result with the three most recent rounds detecting TPH-d at only 320,260,and 290 gg/l,respectively. Constituents that have never been detected historically include TPH-g,benzene, and ethylbenzene. '' Toluene was detected one time dating back to June 2004. ` 6.3. SUMMARY OF STATISTICAL TEST RESULTS Results of the statistical tests including both Mann-Kendall and Mann-Whitney U Test support that this site should be evaluated for closure. Results generally indicate that the residual impacts to the local watertable post-remediation activities are within a small area immediately surrounding the former UST basin location and that the plume is overall stable and/or decreasing over time. The remedial activities no doubt had an impact on the residual levels that are remaining,primarily in the area of MW-3 and MW-4 which are showing a stable and/or downward/decreasing trend with respect .. to residual petroleum impacts in the area immediately adjacent to the former UST basin. These results lend support to the site specific low velocity flow characteristics,possibly influenced by tidal effects, such that residual levels of heavy hydrocarbons are not spreading laterally to a significant +- degree. In addition, all of the wells could not be analyzed statistically since tests are limited to wells that contained measurable contaminant levels and therefore not conducted on wells indicating historical non-detect levels or gaps in data sets that do not fit the minimum test requirements. Tests could only be completed for five of the ten on and off-site monitoring wells due to the overall lack of impacts to five wells.Further,tests were primarily relegated to assessment of residual TPH-d because of the lack of other constituents including TPH-g and BTEX providing additional evidence that the residual levels of petroleum have been adequately addressed through extensive investigative,remedial,and continued monitoring efforts. 7.0. POTENTIAL RECEPTORS The nearest surface water is the Stockton deepwater channel, located approximately 650 feet north of the site (Figure 1). Potable (drinking) water for the site and associated community of approximately 290,000 people is provided by the City of Stockton and the California Water Service. Some private wells are located in the vicinity of the site as discussed in Section 2.3,with the nearest well potentially used for drinking water is a domestic water well located approximately 1,300 feet to the southwest of the site. rr rr Advanced GeoEnvironmental,Inc.