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1 , <br /> 1 12 February 2002 <br /> • AGE-NC Project 99-0570 <br />' Page 3 of 4 <br />' Benzene was detected in sample MW-2 at a concentration of 0 53 µg/I Other BTEX compounds <br /> were detected in sample MW-2 at concentrations as high as 7 1 µg/1 (ethylbenzene) <br />' MTBE was detected in samples MW-1, MW-2 and MW-3 at 4 5 µg/I, 4 0 µg/1 and 500 µg/l, <br /> respectively by EPA Method 8260 No other fuel oxygenates were detected in any of the samples <br /> Laboratory results of water samples analyzed for petroleum hydrocarbons are summarized in <br />' Table 2 The laboratory reports for the quarterly monitoring event (MAI Laboratory ID No 82234 <br /> to 82238) QA/QC reports and chain-of-custody form are Included in Appendix B <br />' 4.0. SUMMARY AND CONCLUSIONS <br />' Based on the findings from this Investigation, AGE draws the following conclusions <br /> • Ground water on the site was flowing toward the north from the former dispenser area at a <br /> hydraulic gradient of 0 02 feet/feet <br /> • MTBE was detected in three ground water samples,with the highest dissolved concentration <br /> • occumng southeast of the dispenser area and the former UST excavation, at 500 µg/i <br /> • TPH and BTEX compounds were detected in two ground water samples <br /> • The up gradient well, MW-3, has had Increasing contaminant concentrations over the last <br /> four quarters and has the highest MTBE concentration <br /> I <br /> 5.0. RECOMMENDATIONS <br /> Based upon the investigation results during the 4th quarter 2001, AGE recommends <br /> • Continued quarterly ground water monitoring, the next quarterly ground water monitoring <br /> event is tentatively scheduled for late February 2002 <br /> • Installation of additional shallow and deep-screened ground water monitoring wells based <br /> on the findings of the existing shallow ground water monitoring wells and soil borings, the <br /> screen intervals for the deep-screened monitoring wells should be placed to define and <br /> monitor the vertical extent of the ground water plume <br /> • Conduct a ground water extraction test to obtain general aquifer characteristics such as <br /> I hydraulic conductivity, transmissivity, storativity and drawdown at various pumping rates <br /> Results of the ground water extraction test would be utilized to estimate a radius of influence <br /> Advanced GeoEnvironmental,Inc <br />