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15 June 2009 <br /> \dWe AGE-NC Project No.05-1306 <br /> Page 18 of 33 <br /> • MW-7 (twenty one rounds from 03 June 2004 to 05 March 2009 with a range of nineteen <br /> TPH-d detections from 78 ptg/l to 520 µg11 with no test for TPH-g since all results indicated <br /> non-detect). <br /> 6.1.2. Results of the Mann-Kendall Test <br /> Test results from MW-3 for TPH-d indicate "no trend" at both the 80 percent and 90 percent <br /> confidence level when considering results from the last ten consecutive rounds (21 August 2006 <br /> through 05 March 2009). The data set results indicate an(S) of-6.0, an average contaminant level <br /> of 11,480 µg11, a(6) of 6016.237, and a(CV) of 0.524 indicating that the "no trend" translates to a <br /> stability test result of"stable".Historically,TPH-g was detected a total of 5 times,toluene has been <br /> detected 2 times,and xylenes have only been detected a single time dating back to 1998. Therefore, <br /> statistical tests were not run concerning these constituents and neither benzene nor ethylbenzene <br /> have been detected in this well historically. Monitoring well MW-3 is located approximately 20 ft <br /> east/southeast of the September,2005 excavation footprint,which explains the residual results that <br /> appear to have been elevated for a period after the excavation but are trending downward now. One <br /> of the remedial alternatives proposed included excavating to this location;however,due to the need <br /> for shoring to a depth of 45 ft bgs,additional excavation this far outside the former UST basin was <br /> not cost effective or generally feasible. <br /> Test results from MW-4 for TPH-d indicate "decreasing" at both the 80 percent and 90 percent <br /> confidence level when considering results from the last ten consecutive rounds (21 August 2006 <br /> t- through 05 March 2009). The data set results indicate an(S)of-25.0,an average contaminant level <br /> of 5,615.50 µg/l, a (a) of 6312.418, and a (CV) of 1.124. Test results for TPH-g indicate <br /> "decreasing" at the 80 percent confidence level and "no trend" at the 90 percent confidence level <br /> '•• when considering the same data set with an(S) of-11.0, an average contaminant level of 123.00, a <br /> (a)of 242.661,and a(CV)of 1.973.Historically,TPH-g was detected a total of 6 times dating back <br /> to 07 June 2000 with two of these detections within the data set covering the last ten rounds. It <br /> should be noted that TPH-g has not been detected in MW-4 in the last 7 rounds of samples.Benzene, <br /> toluene,and ethylbenzene have not been detected historically and xylenes have been detected 2 times <br /> (June and September 2000). Therefore, statistical tests were not run concerning these constituents. <br /> Monitoring well MW-4 is located approximately 5 ft east/southeast of the September 2005 <br /> excavation footprint, which explains the residual results that appear to have been elevated for a <br /> period after the excavation but are trending downward now. One of the remedial alternatives <br /> proposed included excavating beyond this location laterally to MW-3;however,due to the need for <br /> shoring to a depth of 45 ft bgs, additional excavation this far outside the former UST basin was not <br /> ` cost effective or feasible. <br /> v <br /> Advanced GeoEnvironmental,Inc. <br />