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,y 20 October 1998 <br /> �✓' AGE NC Project No. 98-0470 <br /> Page 6 of 7 <br /> 4.4. -HYDROCARBON-IMPACTED GROUND WATER <br /> The results of laboratory analysis of the ground water sample collected at the site are as follows: <br /> .� TPH-g was detected in the ground water sample at a concentration of 1,5 10 micrograms per <br /> liter(parts per billion: ppb). <br /> Benzene was detected in the same sample at a concentration of 205 ppb. <br /> • Toluene,ethyl benzene and xylenes were detected in ground water sample at concentrations <br /> of 132 ppb, 16 ppb and 253 ppb, respectively. <br /> • MTBE was detected in the water sample at a concentration of 43 ppb, as analyzed by EPA <br /> Method 8260m. <br /> Laboratory results of samples analyzed are summarized in Table 2 and Table 3. The laboratory <br /> reports (Sequoia.ID 5807334-01) QA/QC report and chain-of-custody form-are included in <br /> Appendix D. <br /> 5.0. SUMMARY AND CONCLUSIONS <br /> Based upon the results of the subsurface investigation.and historical research, AGE concludes: <br /> • Hydrocarbon-impacted soil in the area of the former UST was encountered from depths of <br /> approximately 20 to 50 feet bsg. <br /> • The detection of MTBE by EPA method 8260m in soil collected from beneath the dispenser <br /> area of the former UST suggests a release time within the last fifteen to twenty years, <br /> t,.. although portions of the hydrocarbon release may be older. <br /> • The concentration of dissolved benzene detected in well MW-1 exceeds the state maximum- <br /> contaminant level (MCL) of 1 ppb. <br /> • -MTBE was detected at concentrations greater than the'State of California Action Limit of <br /> 14 ppb in the ground water sample collected from the well. <br /> LW <br /> L-„ <br /> Advanced GeoEnvironmental,Inc. <br />