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06 August 1999 • AGE-NC Project No 98-0450 Page 2 of 3 impacted soil This excavation would remove approximately 60% to 70% of the total mass of hydrocarbons Shonng would be necessary if excavating to a depth of 35 feet and, because of space limitations at the site, the excavated soil would have to be hauled off-site for treatment and/or disposal The relative duration of the excavation project would be dust a few weeks, however, the remaining impacted soil at the site would have to be monitored or"modeled" in order to obtain site closure, which could extend the entire "treatment" period to 12 months or longer 11 As stated in the CAP, the cost for excavation of impacted soil in the core portion, off-site treatment of the impacted soil and the importation of clean fill material would range between $185,000 and $230,000 Additional costs, up to $50,000, could be incurred due to special shoring, piling and/or monitoring and sampling requirements Excavation would be an effective remediation method for hydrocarbon-impacted soil at the site However, based upon overall cost,duration and feasibility, soil vapor extraction (combined with m- situ air sparging) is still the preferred remedial option . IN-SITU BIOREMEDIATION In-situ bioremediation is a viable remediation alternative for ground water at the site Although specific physicochemical or biological analysis of ground water have not been performed at the site, it is likely that the addition of either nutrients or bacteria and nutrients would effectively remediate contaminated ground water The duration of a ground water bioremediation system at the site is estimated between 24 and 36 months Prior to the initiation of a bioremediation system, additional feasibility studies would be necessary to determine the presen, microbe activities and nutrient concentrations in various wells at the site Costs for implementation and monitoring of a full-scale bioremediation system are estimated between $60,000 and S120,000 Special regulatory requirements for monitoring and/or permitting could increase the cost and project duration substantially The Central Valley Regional Water Quality Control Board (CVRWQCB) has been reluctant to issue discharge permits to inject bacteria and nutrients into the subsurface Although bioremediation is certainly a viable remediation alternative for the treatment of hydrocarbon-impacted ground water at the site, in-situ air sparging combined with soil vapor extraction offers a more reliable, proven and cost-effective treatment system for the site Advanced GeoEnwonmentaI,Inc