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AGS <br /> constituents, will be evaluated to ensure stoppage of any releases. The potential future <br /> impact of mobile constituents on groundwater will be evaluated with respect to the rate <br /> of pollutant migration and take into accoun: fluctuating groundwater levels and the depth <br /> of pollutants in the vadose zone. Specifically; contaminant fate and transport models <br /> adopted by the American Society of Testing and Materials (ASTM. 1995) will be used to <br /> evaluate the potential for contaminant migration from soils to the water table. Fate and <br /> transport model results; standard exposure factors adopted by the U.S. Environmental <br /> Protection Agency (USEPA, 1989b) and ASTM (1995), and current and future land use <br /> designation will be used to quantitatively evaluate potential health risks associated with <br /> exposure to soil contaminants at each OVVS site. <br /> Based on evaluation of these criteria; the need, if any, for active remediation will be <br /> determined. Per Tri-Regional guidelines (RWQCB, 1990: 1991 : 1996). an NFAR letter <br /> will be requested for sites successfully meeting the above requirements. <br /> 4.2 LOW RISK GROUNDWATER DESIGNATION <br /> In accordance with Tri-Regional guidelines (RWQCB, 1990; 1991 ; 1996), the following <br /> criteria must be met in order for a site to be designated as a low risk groundwater case: <br /> 1 . Contaminants remaining in the vadose zone must not reverse or threaten to <br /> reverse the mass reduction rate of groundwater pollutants (see No. 4 below); <br /> 2. Separate-phase product has been removed to the extent practicable, <br /> 3. No existing water supply wells, deeper aquifers, surface waters, or other <br /> receptors are threatened by pollutants remaining in the aquifer; and <br /> 4. The total pollutant mass remaining in the groundwater is decreasing at predicted <br /> rates and neither creates. nor threatens to create; a risk to human health and <br /> safety or future beneficial use(s) of the aquifer. <br /> 18 <br /> L.1Wpwin6D\WPDOCS195-CLTS11995195D3D4p1WorK Ran\Work Pian aoc 03/10/99 <br />