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Harding Lawson Associates <br /> Ground water withdrawn under either type of horizontal <br /> system would be disposed of off-site or treated on-site and then <br /> II6 discharged. The treatment option used would depend upon the <br /> amount of water generated during an initial start-up period. <br /> Either system is wall suited to low-yielding, water- <br /> bearing formations. Ground water would be monitored upgradient <br /> and .downgradient of the. dra.in. to evaluate the effectiveness 'of:- <br /> the :remedial system. Horizontal drains have been used frequently <br /> and effectively to control and intercept subsurface flow. This <br /> o <br /> method of ground-water extraction is considered veryCot <br /> practical <br /> and will be given further consideration. <br /> r 2. Treatment Alternatives <br /> e <br /> Air itKinRing - Air stripping `transfers gasoline hydro- <br /> L <br /> carbons from an aqueous to a vapor phase'. Ground water .contain <br /> ing .hydrocarbons is broughtto the top of a tower filled with <br /> plastic packing medium that provides a high surface area. This <br /> water is sprayed downward over the packing medium while air is <br /> t f <br /> blown upward from -the bottom of. the tower. Aix, pollution control <br /> j <br /> k� devices :,(activated carbon canisters) may be required to remove . <br /> stripped hydrocarbonsbefore the air is discharged to the atmos- <br /> {at. phare. Spent carbon would have to be treated by eitheron-site <br /> or orf-site regeneration,` or' disposed of at a Class I landfill. <br /> Air stripping is .an established technology that has i. <br /> been used by industry for many years. ' This alternative has been <br /> F t <br /> used frequently at.sites where ground water contains detectable <br /> s concentrations of gasoline hydrocarbons; the technique is <br />