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16 October 2006 AGE-NC Project No. 98-0520 Page 6 of 10 ' The RISC WorkBench modeling for volatilization from soil to indoor air(concentration in building) were steady-state models as follows: • Ethyl-benzene: 0.0106 µg/1 which is significantly lower than the residential ESL of ' 420,000 µg/i. • Toluene: 0.000999 µg/l which is significantly lower than the residential ESL of 63,000 µg/1. • TPH Aromatic C8-10: 0.418 µg/1 which is significantly lower than the residential ESL of ' 26,000 µg/l. • TPH Aromatic C10-C12: 0.0560 µg/1 which is significantly lower than the residential ESL of 26,000 µg/1. • Total'xylenes: 0.0176 µg11 which is significantly lower than the residential ESL of 150,000 µg/1. ' The complete results including graphs from the RISC WorkBench modeling for both volatilization from ground water to outdoor air and volatilization from soil to indoor air are included as Appendix F. Additionally, based upon the soil vapor extraction pilot test from September 2005 results with no ' reported detectable amounts of any constituent of concern,the probability of soil vapor diffusing to the surface is unlikely. ' Based upon these results, it is very unlikely ground water or other sensitive site receptors are impacted. 4.0. SUMMARY AND CONCLUSIONS The summary of the second quarter ground water monitoring is provided as follows: • Depths to ground water ranged from 16.42 feet to 17.54 feet below the tops of the well ' casings. Ground water elevation at the site averaged approximately 22.30 feet above MSL. • The net ground water flow was inferred to be generally flowing toward the west to southwest at a gradient between 0.0005 ft/ft and 0.001 ft/ft. • TPH-g was reported in the samples collected from wells MW-2, MW-3 and MW-5 at ' concentrations of 450 µg/1, 2,200 µg11 and 8,800 pg/i, respectively. Advanced GeoEnvironwental,Inc. 1