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Former Discovery Chevrolet June 5, 1998 Tracy,California Corrective Action Plan monitoring wells MW-3 and MW-5. The laboratory analytical results indicated MTBE concentrations ranging between 5 ppb (MW-1) and 10 ppb (MW-2). 5.0 CORRECTIVE ACTION OPTIONS 5.1 Alternative No. 1: Remediation to Nondetectable Concentrations in Both Soil and Groundwater The fine-grained soil types that are present beneath the site (silty clay to clayey sand) suggest that remediation of soil to nondetectable levels would likely entail extensive excavation for the most timely nondetectable results, or a more cost-effective but less immediate procedure, such as passive remediation. Furthermore, the fine-grained soils suggest that the potential future beneficial uses for the shallow water-bearing zone beneath the site would be very limited, at best. Therefore, it is Horizon's professional opinion that further reducing petroleum hydrocarbon concentrations in soil or g g p y groundwater to background or nondetectable concentrations beneath the site is not economically or technically feasible. 5.2 Alternative No. 2: Remediation to Concentrations Which Do Not Affect Potential Beneficial Uses of Groundwater 5.2.1 Alternative No. 2: (Soil) As previously presented in the Remediation Alternatives section of the PAR, four remediation alternatives for soil and groundwater were briefly discussed as likely remedial alternatives for the site. These four remediation alternatives previously discussed for soils beneath the site were: 1) Passive Remediation, 2) In-Situ Vapor Extraction, 3) Excavation and Disposal, and 4) Excavation and Aboveground Treatment. Because of the fine-grained soil types that are present beneath the site, the first two soil remediation alternatives discussed for the site appear to be unlikely candidates for cost-effective and timely soil remediation at the site. The latter two soil remediation alternatives discussed for the site are more likely to be cost-effective and accomplished within a relatively limited amount of time. 3001-21.cap 9 HORIZON ENVIRONMENTAL INC.