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i Soil vapor gasoline-constituents, documented in the RI/FS, were not detectable in shallow soil near the footprint of the former service station. Soil vapor contamination is detectable in the -piezometer NP-2-45' at a depth of 45 feet near the NAPL source. Contact with contaminated soil vapor also is not likely because of the depth at which it is first encountered and the distance between the NAPL source and the nearest receptor off site. Treatment Options The present AS/SVE system is rapidly removing gasoline from the smear .zone that is considered the source of contamination. Treatment options discussed in this section are intended to remove dissolved-phase gasoline in the groundwater plume. Source removal is well underway. The two options described and evaluated herein are (A) intrinsic bioremediation demonstration and (B) pumping with aboveground treatment. Option A: Intrinsic Bioremediation Demonstration i . Intrinsic bioremediation refers to naturally occurring processes that reduce the concentration of subsurface contaminants without mechanical intervention. It may be possible to completely remediate the plume with intrinsic bioremediation alone. Recent interest in intrinsic remediation has been spurred by greater awareness of the significant rate and,extent at which groundwater contaminants are biodegraded under naturat conditions coupled with -increased recognition of the'limitations of conventional groundwater remediation approaches (' (i.e., pump and treat). An intrinsic remediation demonstration refers to the collection and,evaluation of site-specific data that allow quantification of the extent and rate of intrinsic remediation, to support the assessment of potential risks posed by site contamination and the selection of an appropriate site remedy. An intrinsic remediation demonstration is a valuable tool for improving the cost- effectiveness of groundwater remediation. At applicable sites, the demonstration may be used (C6 to establish that groundwater plumes wiL not reachpotential_mgrs or other points of compliance, in which case active demonstration may also be used,to.help focus remedial actio on n source control, which is typically more cost-effective than plume remediation. Even if active plume remediation is required, an intrinsic remediation demonstration will often provide information that may be used to reduce the scope, duration, and cost of such remediation. Option A includes the following components: l 4 • Continued operation of the AS/SVE system for source removal I • Demonstration of intrinsic remediation + Groundwater monitoring y • Contingency plan for evaluating monitoring data and determining the need for { intervention I 5P010030983.DOC 4-3