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t 26 April 2011 AGE-NC Project No. 95-0104 Page 10 of 12 Overtime 1,2-DCA-impacted ground water migrated northeast,the consistent ground water flow direction at the site, from the UST area toward and beyond MW-8, and then off-site in the area of wells MW-13 and MW-14. However,as stated above 1,2-DCA concentrations detected in wells MW-13 and MW-14 have been low (6.1 pg/I and 34 pg/1) and were non- detect during the August 2010 sampling event. Currently, the lateral and vertical extent of 1,2-DCA-impacted ground water at the site is defined. The dissolved plume appears to be undergoing natural attenuation. 6.0. RISK ASSESSMENT - SOIL VAPOR INTRUSION EVALUATION A soil vapor intrusion investigation has not been performed at the site. AGE believes that residual soil contamination left in place will not pose a significant threat to human health or to the environment based on the following: • Petroleum hydrocarbon-impacted soil was encountered only belowthe former USTs at a depth of 17 feet bsg. • Impacted soil was mitigated in the former UST area by SVE remediation performed at the site in 1999. Remediation well VW-1 is screened between 22 feet and 72 feet bsg in the former UST area. • TPH-g, BTEX, and 1,2-DCA, were not detected above laboratory reporting limits in confirmation soil samples (P-1) collected from the site in July 2000. TPH-d concentrations detected in soil samples from P-1 were below the San Francisco Bay Regional Water Quality Control Board's Environmental Screening Levels(ESLs)for gross contamination and direct exposure in deep soils. 7.0. DISCUSSION AND CONCLUSIONS Based on data collected during site assessment and ground water monitoring events at the site, AGE concludes: • Since initiation of the ground water monitoring program, ground water elevations have ranged from approximately 22 to 62 feet below NAVD88 and depths to ground water have ranged from approximately 52 to 92 feet btoc. Ground water flow has been consistently towards the northeast at low hydraulic gradients. Ground water elevation data is summarized in Table 1. • AGE estimated that operation of the SVE system removed approximately 160 gallons of gasoline, or approximately 77 percent of petroleum hydrocarbons formerly impacting soil at the site. Advanced CcoEnvironmen tal,Inc.