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10 May 1999 AGE-NC Project No. 95-0103 Page 5 of 6 3.5. MASS OF RECOVERED HYDROCARBONS — Due to no detection of hydrocarbons in the soil vapor extraction influent stream no mass removal calculation was preformed. Low concentrations of BTEX may have been in the influent stream, however, these concentration were below the detection limits for the chemical analysis for BTEX. _ 4.0. DISCUSSION/CONCLUSIONS Based on data collected at the site and monitoring during site remediation, AGE concludes: • The relative ground water elevations at the site increased 0.82 feet over the last quarter. The map of ground water contours indicates a depression in the area of well MW-1. _ • Monitoring wells MW-1, MW-2, MW-3, and MW-4 had ground water approximately four feet above the top of the screened interval, potentially reducing the effectiveness of these _ ground water monitoring wells to characterize the dissolved-phase hydrocarbon plume. • The greatest concentrations of petroleum hydrocarbons as gasolinewere detected in samples — collected from well MW-3 west of the site. Hydrocarbons were detected at lesser concentrations in wells MW-1, MW-4, MW-5 and VE-6. The highest concentration of benzene was detected in the sample collected from monitoring well MW-4. • Detectable concentrations of hydrocarbons were not present in the samples collected from the off-site wells MW-2, MW-6 and on-site vapor well VW-7. _ • A reduction of the dissolved-phase hydrocarbon plume concentrations on the site has occurred. A minor decrease of the dissolved TPH-g concentrations has occurred the samples from well MW-3. • The current concentrations of benzene in samples MW-I and MW-4 are less than 0.01 % of the initial and highest concentrations of benzene detected in samples from the monitoring — wells; however, some of the concentration decline may be due to ground water being more than four feet above the top of the well screens. • MTBE was detected in the ground water sample from well MW-I at a concentration of 2.3 kzg/l, and was detected in the sample from MW-4 at a concentration of 7.5 ug/l by EPA Method 8020, but the latter sample was not analyzed by EPA Method 8260. — • The concentrations of benzene exceed the state maximum contaminant level {MCL} for drinking water of I Mcg/l in four of the monitoring wells sampled. • Based on analytical data from the soil vapor samples, it is inferred that the SVE system has removed most of the hydrocarbons from the vadose soil zone in the SVE system's area of influence. Advanced GeoEnvironmentai,inc.