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6 4 1 • 19 June 2000 AGE-NC Project No 96-0232 Page 34 of 35 10 2 REMEDIATION OF HYDROCARBON-IMPACTED GROUND WATER As the feasibility for in-situ air sparging, bioremediation and natural attenuation to effectively address the contaminants in ground water is low, and because hydraulic controls are necessary to prevent additional spreading of the dissolved MTBE-impacted plume,an ex-situ remediation method (i e pump and treat) will be the most effective method to remediate the site Petroleum hydrocarbon- and/or MTBE-impacted ground water associated with the Flag City Chevron unauthorized release appears to be limited to the area containing wells MW-1, MW-2, MW-4, MW-6, MW-7, MW-9A and MW-11 (A, B, C and D) Figures 8, 21, 22 and 23 depict general lithology and the approximate honzontal and vertical extent of the petroleum hydrocarbon- and/or MTBE-impacted ground water beneath the site in cross sectional view, Figures 27, 37 and 38 depict the estimated extent of dissolved MTBE in plan view The plume of impacted ground water at the site has an estimated north-south diameter of approximately 180 feet, an east-west diameter of 380 feet and appears to extend downward to a depth of approximately 55 bsg on-site, thickening to 65 feet off-site near on the Rocky's Restaurant property near P16 Vertical migration of MTBE has occurred in the Rocky's Restaurant domestic well to as much as 150 feet bsg, the greater vertical migration of MTBE in this area has apparently been facilitated by the design and construction of the domestic well The volume of MTBE-impacted ground water can be approximated by utilizing an equation for an ellipsoid,the dimensions of the ellipsoid was estimated at a short radius of 90 feet, a long radius of 190 feet and an average thickness of 50 feet When the data is calculated, the volume of impacted ground water associated with Flag City Chevron is an estimated 7,433,944 gallons Ground water extraction is recommended in conjunction with on-site treatment, the permitting process should be initiated to discharge treated water into the San Joaquin County storm drain system Use of air stripping technology in conjunction with specific MTBE-activated carbon technology is the recommended treatment for the extracted, impacted ground water AGE believes that utilization of an air stripping technology will reduce the cost of MTBE-activated carbon replacement and will help to ensure non-detect levels of contaminants pnor to discharge A Regional Water Quality Control Board NPDES permit and a San Joaquin County Public Works discharge permit will be required to discharge into the municipal storm drain system Obtaining the necessary discharge and NPDES permits will require between 6 and 10 weeks, AGE is in the process of procuring these permits If a discharge permit for the municipal storm drain system is denied, AGE recommends on-site treatment of impacted ground utilizing an air stripping technology and an MTBE-activated carbon technology and pursuing an RWQCB-CVR permit for a deep water injection well The well could be screened into non-beneficial usage water at depths in excess of 300 feet bsg, deep ground water Adtianced GeoEmlronmcntal,Inc