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it <br /> Table 2-3 data indicate that gasoline constituent concentrations increase with depth. More <br /> data are required to statistically evaluate contaminant removal with respect to groundwater <br /> depth or with respect to time. The 3/12195 non-detect values for.NP-I-90' are suspect and <br /> may not be representative. <br /> Table 2-3 <br /> Gasoline Constituent Concentration in Nested Piezometer NP-I <br /> Ethyl _ Total <br /> TPH(g) Benzene Toluene Benzene Xylenes <br /> Piezometer Date { ) ORP (In9p Aln ) (m ) <br /> NP-1-70' 3/12195 96.9 14.6 26.9 0.22 14.6 <br /> NP-1780' 12/29/94 180 29 51 4.8 24 <br /> NP-1-80 3112/95 127 31.2 47.2 2.54 16.6 <br /> NP-1-90' 12/29/94 200 29 53 5.3 30 <br /> NP-1-90' 3/12/95 ND ND ND ND -ND <br /> 7 <br /> Additional gasoline is being removed by biodegradation. in the vadose zone. Future <br /> respiration rate tests should include the measurement of soil vapor oxygen depletion rate after <br /> AS/SVE system shut down. <br /> AS/SVE Progress Summary and Conclusions <br /> The AS/SVE system is achieving gasoline removal in three ways. Through SVE gasoline-is <br /> Y gg Y g , g <br /> removed at an estimated rate of 20 to 50 pounds per day. This rate is expected to decline <br /> rapidly and to approach an asymptotic rate of 2 to 4 pounds per day after 6 months or so. <br /> Gasoline is being removed at approximately 1 pound per month by biodegradation in the <br /> groundwater. Gasoline is also being degraded in the vadose zone. <br /> The SVE system has a radius of influence of greater than 20 to 25 feet, or enough coverage <br /> area to effect remediation of all known NAPL gasoline in the vadose zone. As soil vapor <br /> concentration declines, exchange of the engine for vapor phase GAC treatment and blower <br /> cycling should be considered to improve groundwater mixing and reduce operating cost. <br /> 1 <br /> f SFO10030981.doc 2-8 <br />