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F.. FiV 6.0 CONCLUSIONS/RECOMMENDATIONS The test data ::..eve demonstrated that vapor extraction is an effective approach to the remediation of gasoline hydrocarbon contaminated soils at the subject site. The current placement of vadose wells VP1, VP2 and VP3 are adequate to affect the area of impacted soils in the tank pit area, as identified by soil sam- pling. Because boring ASBI identified an area of elevated soil hydrocarbons beneath the island along the east side of the property, a single vadose well will be placed in that area. Each well will operate at vapor extraction rates of approximately 30 to 70 cfm Four alternatives for control of extraction system off-gas emis- sions were evaluated. These are thermal oxidation, catalytic oxidation, carbon adsorption and destruction by an internal — combustion (IC) engine. Based on the relatively low levels of hydrocarbons in the vapor samples and the relatively high perme- abilities a combination of vapor phase carbon and an IC engine are recommended. The IC engine will be utilized for the initial extraction period (anticipated 30 to 60 days) during which vapor concentrations drop rapidly. After the extraction stream drops below approximately 10 lbs/day of hydrocarbons, the IC engine will be removed and replaced with activated carbon canisters, - Each wellhead will be equipped with vacuum gauges, sample port and control valve so that the flow rate can be adjusted to maxi- mize recovery rate. The IC engine is capable of drawing up to - approximately 150 cfm depending upon soil conditions. It is estimated that the TPH as gasoline concentrations in vapor re- moved from the wells will be reduced below 558 ug/l (125 ppmv) within 60 days of operation. The system would then be converted i to use activated carbon and a vacuum blower to complete the remediation. It is estimated that the blower/carbon adsorption - unit will operate for approximately 150 to 220 days. { 7.0 REFERENCES ~ Bear, J., 1979, Groundwater Kdra.ulics, McGraw Hill, N.X. Johnson, P.C., Kemblowski, M.W., Colthart, J.D., 1990, Quantita- tive Analysis for the Cleanup of Hydrocarbon Contaminated Soils by In-Situ Soil Venting, Groundwater, V.28, 11o.3, r, pp.413-429. 4