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Explosives contamination in vadose zone soil presents difficulties in remediation . Because vadose zone contamination can extend deep into the subsurface and underneath existing buildings and utilities , excavation is often infeasible . In response , this dissertation focuses on the development and testing of a practical system to enhance the remediation of vadose zone explosives contamination .
Soil at the DOE Idaho National Engineering and Environmental Laboratory field area was characterized for explosives contamination . Of the soil tested , the particulate TNT retained on a 3 mm screen contributed approximately 2000 ppm (96 .4 % ) of the overall soil contamination , compared to the soil that passed through the sieve , which averaged 75 ppm TNT . Contributing significantly to the contamination profile , heterogeneously dispersed , and likely point sources of contamination , the particulates thereby present difficulties in estimating the extent , risk , and treatability of explosives contamination in the soil .
For monitoring soil gases , a method was developed and validated using solid phase microextraction coupled with gas chromatography and mass selective detection (SPME -GCMS ) . The within -run precision (repeatability ) was 3 .5X tighter than the between -run precision (reproducibility ) in the 4 days . The esters gave the best repeatability from 50 to 80 ppmv while the corresponding alcohols gave the best results at 10 to 20 ppmv . The method was applied to monitor gases in laboratory and field studies testing explosives remediation in vadose zone soil .
Anaerobic and microaerobic batch and column studies using soil from the DOE Pantex Facility contaminated with hexahydro -1 ,3 ,5 -trinitro -1 ,3 ,5 -triazine (RDX ) , octahydro -1 ,3 ,5 ,7 -tetranitro -1 ,3 ,5 ,7 -tetrazocine (HMX ) , and 1 ,3 ,5 -trinitrobenzene (TNB ) were performed using gaseous carbon source additions . In the anaerobic batch study , over 99 days , flasks periodically receiving headspace pulses of 330 to 570 ppmv n -propyl acetate yielded 97 .5±0 .3 % TNB and 66 .7±43 .2 % RDX removal . Using ethanol in place of n -propyl acetate yielded similar results . Two column studies were performed using throughputs of oxygen , nitrogen gas , and organic carbon combinations . The columns supported less robust HE degradation than the batch systems . This difference in HE degradation between batch and column work may indicate that a key factor accumulated in the headspace of batch flasks , but was continually removed in the columns . |
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