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a. - 15 June 2009 AGE-NC ProjectNo.05-1306 Page 15 of 33 water table. Mass and volume calculations are presented in Appendix G. 5.4.2. Mass of Petroleum Hydrocarbons Remaining Based on the estimated lateral and vertical extent of adsorbed TPH-d,which currently impacts soil and a review of soil analysis results (Figures 6 through 8, Table 1), an updated mass of TPH-d was prepared.Based on soil sample analysis performed prior to(excluding samples collected from within the excavation area)and following site remediation,AGE estimates approximately 2,725 pounds of �. TPH-d remain present in soil on the site.Mass and volume calculations are presented in Appendix G. As discussed in Section 3.0,prior to remediation is was estimated that approximately 75 percent of the mass was located in the proposed excavation area. Updated calculations post-remediation �• indicate that approximately 78 percent to 84 percent of the mass of TPH-d has been removed from the site.This re-calculated estimate is consistent with expectations and results of the excavation and subsequent statistical analysis of ground water trends indicating a stable and/or decreasing plume Lo as presented in Section 6.0. Additional evidence supporting these calculations is included in the estimated time to compliance trend discussion presented in Section 9.0. The preliminary mass and volume calculations presented in the CAP-A,which were higher did not account for the plume shape and extrapolated areas that provided a conservative estimate;based on the reduced concentrations detected during the excavation sampling(presuming natural attenuation over the soil sampling-monitoring events);thus less contamination may be residual in the deep soil on the site. 1.. G.O. STATISTICAL ANALYSIS OF RESIDUAL TPH-GID IN GROUND WATER The Mann-Kendall and Mann-Whitney statistical tests were performed to evaluate the trend of residual TPH-d and TPH-g concentrations at various monitoring wells. These tests can be used to show whether ground water contaminant concentrations in a monitoring well are increasing,stable, or decreasing. However, neither test is able to determine the rate at which the concentrations are changing over time.The statistical test results can be used to demonstrate whether natural attenuation .- is effective by showing decreasing contaminant concentrations at an appropriate confidence level. Both tests were selected for inclusion in this discussion because each test has limitations. Specifically,the Mann-Kendall test is not appropriate for data sets showing seasonal influences,but �. can be used with as little as four consecutive rounds of sampling. Overall the results from this site indicate some seasonal trends on certain wells over certain periods of time,but it does not seem to be a consistent seasonal trend or influence.The Mann-Whitney test allows for evaluation of seasonal influences but requires a minimum of 8 consecutive sampling rounds.Therefore,since both tests are generally acceptable for use with the data sets, both analyses are provided to support the Advanced GeoEnvironmental,Inc.