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Tri Regional Recommendation Page 19 of 24 Appendix A 6.3 NFAR Criteria for Low Risk Vadose Zone required in all cases unless it can be shown Cases that the collection of such sampling) is unreasonable or unattainable, (e.g.,the Vadose zone cases are those sites for which estimated depth to water is greater than 100 documentation has been provided to demonstrate feet below the deepest soil impacts). that fuel hydrocarbons or additives have not reached and are not expected to reach 6.4 NFAR for Cases Above Background groundwater. If site conditions do not meet the Groundwater Conditions criteria below,then additional remediation may be required. All of the following must be Ideally,the goal of remediation is to ensure that demonstrated in order to designate a vadose zone contaminants are cleaned up to background water site as "low risk". quality. However, contaminants may be allowed to remain in the groundwater above background 1. The release has been stopped and the levels in certain cases.Any proposal to leave source of contamination has been removed contaminants in groundwater at levels above or remediated. Soil that contains mobile background must include justification for such constituents in concentrations that threaten degradation. Cleanup levels above background to degrade water quality or result in a must also conform to all applicable state policies, significant risk to human health and safety regulations and procedures. See Policy for or the environment(as determined by site Investigation and Cleanup of Contaminated Sites specific data, or as concluded using in Chapter IV of the Water Quality Control Plans appropriate mathematical models) should (Basin Plans)for the Central Valley Region. be considered a source. Central Valley Regional Water Quality Control 2. The site has been adequately characterized. Board staff have closed UST cases that do not The vertical and lateral extent of subsurface meet background water quality levels,but the impact must be defined to the degree that it water quality objectives at the site are met,or will is necessary to evaluate whether the site be met within a reasonable timeframe. In most of currently poses, or in the future may pose, a these instances, concentrations of pollutants were significant threat to human health and either below or close to applicable water quality safety,waters of the State,or other nearby objectives prior to closure. sensitive receptors. The level of detail required at a given site will depend on the Cases that have been closed above background contaminants of concern,the types of levels in groundwater were deemed to be low potential receptors and exposure pathways, risks to other receptors such as surface water and and the proximity of the potential receptors. drinking water wells. Regional Board staff Groundwater beneath a site and adjacent considers the following low risk factors when surface waters are to be considered as making this determination: receptors. 1. The source of the UST release has been 3. No waters of the State, or other sensitive identified and removed. receptors are likely to be impacted. Waters of the State include all groundwater and 2. Free-phase product in groundwater has surface water regardless of current use. been removed to the full extent practicable, Central Valley aquifers generally are not in accordance with the UST Regulations segregated into discrete units,but are (Title 23, CCR, Section 2655). subject to vertical and horizontal migration of water(either by natural or man-induced 3. Contaminants remaining in the vadose zone mechanisms)and any pollutants carried by cannot migrate in soil vapor or leach at or in the water may degrade the waters of concentrations that would cause the State. Groundwater sample(s) are