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6 �® Unsaturated soil Remedial Description of the Preferred Extraction and Alternatives Treatment Technologies Current data indicate that two areas require unsaturated soil cleanup: (1)the Gasoline Spill Area where the contaminants are FHCs For Ground Water and VOCs,and(2)the Building 518 Area,where only VOCs are present. ■ Extraction A third area,the East Taxi Strip Area Pumping where VOCs and tritium are pre- This is the most common method of removing ground water for treatment sent,may also require cleanup.All three areas are in the southeastern above ground. Extraction wells are drilled at strategic locations throughout part of LLNL.Two remedial altema- the area of the ground water contamination. The locations of the wells,the fives were developed for the unsatu- pumping rates,and the amount of pumped water vary with the subsurface rated soil. characteristics. The extracted water is then piped to a treatment facility. Soil Alternative No.l(The Preferred ■ Treatment Alternative) Air Stripping(with granular activated carbon treatment of the vapors) Under this alternative,the unsatu- Air stripping is a commonly used process in which VOCs and FHCs are rated soil would be cleaned up using removed from water(Figure 3). Extracted ground water is transported via vacuum-induced venting to extract pipes to a tower,where it is sprayed into the top of the tower. As the water the FHC and VOC vapors. The cascades down through packing material within the tower,a high-powered vapors would then be treated at the blower forces air upward surface by catalytic oxidation to destroy t_.e contaminants. Any water through the water. This vapor cont-,ining tritium following causes the contaminants Treated air out the treatment process will be evaluat- to come out of the water t ed using the EPA AIRDOS Model to and into the air. Thus,the determine its health impact. If a sig- flow by air cleans or aeration filet air nificant health risk is established,fur- "strips" the water of tower =L? ther treatment of the tritium in the air volatile contaminants. rf stream will be done to assure that the The air containing the risk is reduced to an acceptable level. contaminants is then Packing Discharge Estimated Cleanup Time: It may passed through GAC fil- material pumps take up to 10 years to clean up the ters prior to release to the Air In unsaturated soil using this alternative. atmosphere. This virtual- r Cost: The present-worth cost of ly eliminates measurable this alternative is$1.1 million. air emissions of VOCs Clean water out and FHCs. Soil Alternative No.2 f. Extraction well Under this alternative,contami- GAC has a strong nants in the unsaturated soil would attraction for VOCs(such water level be left in place and allowed to as TCE)and FHCs. As air degrade,volatilize,or possibly flows through the filter, Contaminated ground water migrate to ground water under nat- the contaminants cling to ural conditions. If any contamina- the carbon,thereby tion of ground water above removing them. The Figure 3. Air Stripping. drinking water standards occurs,it GAC must be replaced would be detected by periodic periodically because the filter eventually reaches its maximum ability to monitoring and remedied by absorb the contaminants. The used filters are subsequently treated offsite to pumping the water to a surface destroy or recycle both the filters and the contaminants. treatment facility. Estimated Cleanup Time: It may take 90 years to clean up the contamination in the unsaturated soils using this alternative. Cost: The present-worth cost of this alternative is$0.9 million. Note: See sect ons 5.2.4 and 5.3.3 of the PRAP for a discussion of the relative ti costs of the treatment technologies.