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months of the study as162,600 kg (138: "��lb) of TPH were of simple field dataL.�ese methods allow the quantitation }
<br /> e;tracted from the site due to volatilizvm and in situ bio- of air permeability\—A its variability under actual field
<br /> t 'degradation.An additional 33,200 kg(73,100 lb)of JP-4 were conditions, and are recommended for SVE and bioventing
<br /> removed during bioventing between September 16, 1989, and field system design. S
<br /> November 14, 1990, resulting in a total mass removal from 6. .: Conclusive evidence was provided to indicate signif-
<br /> the site of 95,800 kg (211,100 lb) of JP-4 over the 23 month icant biological activity at the Hill AFB, Utah, field site.
<br /> operating period. Of this total, 53,650 kg (118,200 Ib) of JP- Without enhancement, a total of 15 to 20 percent of the
<br /> 4 was attributed to volatilization as indicated by vent gas hy- recovered JP-4 could be attributed to biodegradation.With g
<br /> drocarbon concentrations, while the recovery of 42,150 kg enhancement this proportion increased to greater than 80
<br /> f, (92,900 1b) of JP-4 was to biodegradation as meas- percent, resulting in 33,200 kg (73,100 lb) of TPH being ;w
<br /> ured from vent gas oxygen deficit determinations. This car- biodegraded during the 14 month bioventing portion of the
<br /> responds to a 56 to 44% volatilization to degradation ratio study.
<br /> l during the entire operating period. q7.9 Nutrient addition at field JP-4 bioventing sites has
<br /> Final soil TPH concenuadons were measured in more then consistently been shown to be ineffective in stimulating ;.
<br /> 200 soil cores collected from within the area of contamination microbial respiration rates, suggesting that nutrient avail-
<br /> to confirm the hydrocarbon recovery data determined from ability is not rate limiting under field conditions at these
<br /> vent gas measurements. These vent gas results were substan- sites. However, moisture addition to the 30 to 50076 field
<br /> tiated as the average residual TPH soil concentration was less capacity level appears to be essential in order to optimize
<br /> than 5 mg/kg dry wt. soil at the end of the bioventing period. microbial activity within a bioventing treatment system. '
<br /> This soil hydrocarbon level represents greater than 99.5%over- S. Operation of bioventing systems for the remediation
<br /> all contaminant removal and a residual TPH concentration of JP-4 jet fuel contaminated sites appears to be optimal
<br /> ! below those required for closure of the site. for biodegradation, i.e., maximum biodegradation/mini-
<br /> mum volatilization, at 0.25 to 0.5 pore volume/d. At this
<br /> ;I- operating flow rate, soil gas retention time is sufficient to
<br /> SUMMARY AND CONCLUSIONS yield 80 to 85076 hydrocarbon recovery as respiration prod-
<br /> uct gas(COJ, while minimizing TPH recovery in the form
<br /> I� of VOC emissions.
<br /> The application of bioventing to vadose zone bioremediation 9, In situ field respiration studies indicated that 02 up-
<br /> has been reviewed, and its advantages over aqueous based take rate measurements were better indicators of biological
<br /> bioremediation systems4in terms of its superior oxygen transfer activity at the site than were CO2 production rate deter-
<br /> ability has been highlighted. Bioventing system applications minatians. G02 measurement sensitivity was susceptible to,
<br /> and design were contrasted to those of conventional SVE sys- varying soil environmental conditions, notably soil water
<br /> tems, and the two key.�elements of bioventing system design content. Soil gas CO2 measurements did not consistently
<br /> evaluation, i.e., in situ"microbial activity and air permeability detect respiration changes during the study.
<br /> determinations, were highlighted. Finally, the application of 10. Quantification of in situ respiration rates and ox-
<br /> bioventing and bioventing design concepts were illustrated ygen transfer potential indicated that daily oxygen demand
<br /> through a case study of JP-4 jet fuel contaminated soil re- was :being satisfied in slightly over 1 hr at the lowest rate
<br /> mediation at Hill AFB, Utah. Based on this review of bio- at which the Hill AF$bioventing system could be operated,
<br /> venting fundamentals, and of the performance of a field-scale i.e.,2I2 actual L/s(450 acfm).Oxygen demand could have
<br /> bioventing system, theafollowing conclusions can be made: been satisfied at flow rates much lower than this value,but
<br /> 1. SVE systems can be utilized as highly.efficient oxygen concerns over limited radii of influence at low extraction
<br /> transfer systems for;°vadose zone oxygenation_ Vent system rates suggest operating at higher flow rates for short time
<br /> oxygen transfer rates have been shown to be much higher
<br /> + periods during remediation. Optimal bioventing system de-
<br /> than in situ oxygeniuptake rates at a number of Feld JP- sign for the Hill AFB site was suggested to be two vent
<br /> 4 contaminated bioventing sites, providing an opportunity wells operating at 212 actual L/s (450 acfm) for 0.75 hr/d
<br /> for optimizing treatment through SVE system operational each: This results in sufficient oxygen transfer and ensures
<br /> modifications and vienting rate controls. coverage of the entire area of contamination, while signif-
<br /> 2. Conventional SVE systems do differ significantly icanily reducing the volume of extracted air that must be
<br /> from bioventing systems in their design orientation. Air handled prior to discharge.
<br /> extraction rates are maximized for contaminant recovery
<br /> in SVE systems, while bioventing systems attempt to max-
<br /> imize vapor retention within the soil to encourage microbial
<br /> degradation of contaminant vapors. LITERATURE CITED
<br /> 3. Methods toreduce vapor extraction rates to maxi-
<br /> mize vapor retention times in the soil are compatible with
<br /> enhancing biodegradation reactions. These procedures re- 1. Alexander, M., Introduction to Soil Microbiology, John
<br /> salt in minimizing volatilization, potentially eliminate the Wiley and Sons, Inc., New York, NY, pp- 467 (1977).
<br /> need for vent gas treatment, maximize the utilization of 2. Atlas, R. M_, "Microbial Degradation of Petroleum Hy-
<br /> oxygen in situ, and provide a framework for the develop drocarbons:an Environmental Perspective,"Micro.Rett.,
<br /> mens of truly optimized in situ biological treatment systems. 45(1): 185-209 (198I).
<br /> At the Hill AFB site, reduced flow rates and maximized 3. Dragun, J., "Microbial Degradation of Petroleum Prod-
<br /> flow path distances allowed the direct discharge of vent gas ucts'in Soils," in Soils Contaminated by Petroleum-En-
<br /> without off-gas treacincnt, while stili being below the reg- viroismenta! and Public Health Effects, E. 1. Calabrese
<br /> ulatory limit of 50 ppmv TPH. and;P. T. Kostecki, Ed. John Wiley and Sons,Inc., New 3
<br /> 4. For bioventing systems to be successful, contami- York, NY, pp. 289.-300(1988),
<br /> nants of interest must be biodegradable under field con- 4. Wetzel, R. S., C. M. Darst, et aI_, rn Situ Biological
<br /> ditions at rates that can be effectively exploited. Methods Treatment Test at Kelly Air Force base, Volume II—Field
<br /> described by Hinchee et al. [2p, 21] for in situ respiration Test Results and Cost Model, Final Report TR-85-52,
<br /> I rate determinations should be utilized to quantify the pres- Headquarters Air Force Engineering Services Center,Tyn-
<br /> ence and rate of bioactivity prior to field scale system design. dali Air Force Base, FL, 1987.
<br /> r 5. Methods presented by Johnson et al. [221 allow the 5. Downey, D. C., R. E. Hinchee, et al_, "Combined Bio.
<br /> determination of in situ air permeability from the collection logical and Physical Treatment ofa Jet Fuel-Contaminated
<br /> .s
<br /> 52 February, 1993' �i
<br /> Environmental Progress (Vol. 12, 130. 1)
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