SITE INFORMATION AND CORRESPONDENCE

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27 October 2010 AGE-NC Project No. 05-1256 Page 9 of 19 ground water, with an isolated distribution beneath the dispensers. Ground water depths have remained stable between approximately 18 feet and 22 feet bsg across the monitoring well network (Table 2; Appendix D). As a result, a minimal smear zone of soil contamination above and below the current water table has developed. Fluctuations in ground water depths across the site appear to be correlated to seasonal or annual ground water recharge (Appendix D). Fuel oxygenates and petroleum hydrocarbons within the saturated zone, in contact with ground water, includes a large area of minor MTBE and TPH-g concentrations providing for estimates of 43 pounds MTBE and 101 pounds TPH-g (Figures 5 and 6; Appendix C). The soil plumes appear to be narrow in shape, extending southeast, typical ground water flow direction, of the dispenser/source area. Ground water is likely moving through this mass,desorbing contaminants. Significant masses of dissolved MTBE and TPH-g, ranging between 75 to 266 pounds and 152 to 524 pounds, respectively,were calculated to remain within the water table (Figures 8 and 9; Appendix E). As discussed in Section 5.2., the magnitude ground water plumes shifted/migrated from wells MW-1, MW-2 and MW-6 to wells MW-3, MW-7 and MW-8 between March 2008 and October 2008, and back to wells MW-1 , MW-2 and MW-6 in February 2009 (Table 3; Appendix D). The overall migration of the plumes appears to be east-southeast, down-gradient of the dispenser/source areas, beneath Interstate Highway 5 southbound on-ramp (Figures 8 and 9). 9.0. SOIL REMEDIATION ALTERNATIVES A significant mass of contamination remains in soil beneath the dispenser area.To mitigate remaining contamination, AGE has evaluated two remedial technologies to treat contaminated vadose zone soil— ex-situ treatment (excavation) and soil vapor extraction (SVE). The feasibility, duration, and costs of each remedial method are discussed below. 9.1. EX-SITU TREATMENT OF IMPACTED SOIL Hydrocarbon-impacted soil can be minimally excavated and treated on-site or transported off-site for recycling/disposal. On-site treatment alternatives (ex-situ) include aeration, bioremediation, vapor extraction, and thermal destruction. All are feasible methods for above-ground remediation of soil contaminated with petroleum hydrocarbons. Off-site disposal generally involves transportation of impacted soil to a licensed treatment/disposal facility. Advanced GeoEnvironmental,Inc.