Remediation Technology Demonstration Project Profiles
In Situ Biogeochemical Reductive Dechlorination (BiRD) at Altus Air Force Base, Oklahoma
Last Updated: September 7, 2004 |
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| Site Identifying Information | ||
| Site Name, Location: | Altus Air Force Base, Altus, Oklahoma, United States
(EPA Region 6) |
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| Cleanup Program: | Not Specified | |
| Entity Responsible for Cleanup: | Air Force | |
| Site Type: | Aircraft Degreasing Operations | |
| Government Affiliation: | Federal | |
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| Project Information | ||||||||||
| Project Name: | In Situ Biogeochemical Reductive Dechlorination (BiRD) at Altus Air Force Base, Oklahoma | |||||||||
| Project Status: | Complete | |||||||||
| Contaminants Treated: |
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| Media Treated: |
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| Demonstration Technology and Type: | Monitored Natural Attenuation (In Situ Biological) |
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| Geology and Hydrogeology: | Three important geologic layers were identified and included a red clay alluvium, red shale, and blue green to redsiltstone, which extend from approximately 0 to 15 ft, 15 to 39 ft, 39 ft to bit refusal (39 to 47 ft) respectively. Layers of sulfate-rich mineral gypsum (Ca(SO4) 2H20)) were often found in the shale and siltstone layers. The aquifer is in the clay and shale layers beginning about 12 ft bgs. Ground water flow is towards the south-southwest. Iron concentrations, found in all the stratigraphic layers but especially in the upper clay zone, exceed concentrations of 2,000 mg/kg. The ratio of Fe2+/Fe total shows Fe2+ is <10% in background clays but approaches 100% in the hydrocarbon impacted clay zone due to direct or indirect microbial reduction. Elevated Fe2+ in the siltstone layer is not biological in origin but instead is caused by concentrations of chlorite rich clays giving it a blue green color. Sulfate concentrations are significantly depleted in the fuel impacted clay zone and there are correspondingly high concentrations of mineral FeS and FeS2. | |||||||||
| Demonstration Year: | 2003 | |||||||||
| Year of Publication: | 2003 | |||||||||
| Goal of the Demonstration: | To describe a method for assessing biogeochemical treatment for natural attenuation and engineered in situ bioremediation (Biogeochemical Reductive Dechlorination [BiRD]) in the treatment of TCE-contaminated site. | |||||||||
| Design and Operations: | This project involved evaluation of natural attenuation processes for TCE in a sulfate-rich environment, referred to by the vendor as BiRD. Eighteen soil borings (A-1 through A-18) were cored using a hollow stem auger rig to depths to 40 feet. Sediment samples were collected approximately every 2.5 feet and evaluated for mineral Fe and S species and for chlorinated solvents and fuel compounds using EPA Method 8260. Bore hole geophysics were run in each boring. Geostatistical modeling was performed in 3D using GridStat (2000). The attribute profiles shown on successive figures are vertical slices through their respective three-dimensional models developed by interpolating the spatial data for all borings simultaneously. All attribute profiles are taken along line of section crosses the ground water flow gradient and includes both the TCE and fuel source areas. A batch study, using live and killed microcosms, was also performed to determine if ERD or BiRD was occurring at this site. | |||||||||
| Performance Data Relevant to Demonstration Goals: | At the Altus AFB, high concentrations of both iron and SO4-2 are naturally present. Supplied organic(released fuel) stimulated SO4-2 reducing bacteria to produce iron sulfides and reduced iron minerals. Technically, the observed mass of FeS from the small fuel release site is sufficient to dechlorinate all of the TCE found in the clay aquifer but the mineral is not uniformly distributed. In the vertical profile, TCE was found to be predominantly in the clay/shale interface and in the high porosity shale layer at 23 feet. TCE was removed from the iron sulfide release area and no significant daughter products were produced. In map plan, TCE is almost completely removed in the clay layer in the fuel-impacted area but was present everywhere in the underlying shale. | |||||||||
| Interesting Aspects or Significance of the Demonstration: | Treatment of Recalcitrant Compounds | |||||||||
| Other Interesting Aspects or Significance of the Demonstration: | Abiotic biogeochemical treatment of chlorinated solvents | |||||||||
| Lessons Learned: | Significant benefits can be realized by engineered remediation by supplying a source of labile organic and/or sulfate (SO4-2). The process has a number of advantages over enzymatic reductive dechlorination including: (1) Reservoir permeability is not affected(2) Use of substrate for methanogenesis is inhibited by electron acceptor competition with SO4-2. High SO4-2 environments augment rather than impede the process (3) Sulfate reducing bacteria are ubiquitous and common, so bioaugmentation is not necessary(4) The rate of FeS production is rapid(5) The experimental rate of dechlorination is very quick(6) The requirement for subsurface mixing is minimized(7) Deleterious byproducts (such as vinyl chloride) are not produced | |||||||||
| Other Demonstration Information (such as cost data, if available): | At Altus Air Force Base, Building 506 was identified as the source for a chlorinated solvent release principally consisting of TCE. A fuel release is also located near Building 506 at an area known as OWS-506. The source of the fuel includes an oil water separator, underground storage tanks for fuel, and possibly associated fuel distribution lines. This fuel release site is located down and cross-gradient of the chlorinated solvents release area. From the outset the sediment was suspected to be high in mineral Fe3+ and it was known that ground water contained very high concentrations of naturally occurring SO4-2. Thus, the site "naturally" contained all the elements (organic, Fe+3, and SO4-2) in a TCE impacted area necessary to examine BiRD under field conditions. In vertical profile, TCE was predominantly found in the clay/shale interface and in the high porosity shale layer at 23 feet. TCE is absent in the iron sulfide-rich sediment zone. | |||||||||
| Other Comments about the Demonstration: | Abiotic processes may be important to dechlorination. Mineral iron sulfides can fully dechlorinate TCE and PCE without elevated vinyl chloride. Abiotic dechlorination is spontaneous and rapid. The biotic process occurs via reductive dechlorination, and involves direct enzymatic processes in heterotrophic bacteria that can use TCE and PCE as electron acceptors in the presence of an electron donor substrate. BiRD theory: This approach is biogeochemical because it is a sequential process beginning with a microbiological step followed by mineralogical/geochemical interactions resulting in reductive dechlorination. Of special interest to BiRD are sulfur/iron mineral complexes induced by microbial sulfate reduction. Oxidation of an organic by sulfate-reducing bacteria produces hydrogen sulfide (H2S) according to the general reaction: (1) CH2O + 0.5 SO4-2=>HCO3- + 0.5 H2S (g). Equation 1 is the biological step in BiRD. Sediments normally have available Fe+3 oxide/hydroxide minerals that provide a chemical sink for H2S, forming various iron sulfide minerals as: (2) 2FeOOH (s) + 3 H2S (aq) => 2FeS (s) + So + 4H2O. Equation 2 is abiotic, spontaneous, and almost instantaneous. One mole of sulfide in H2S is oxidized to elemental sulfur to facilitate the reduction of two moles of Fe+3 to Fe+2 resulting in the formation of two moles FeS. With time FeS is converted to more stable pyrite (FeS2) as: (3) FeS (s) + So => FeS2. Therefore, equations 1 and 2 show that 66% to 50% of the reduced SO4-2 should precipitate as FeS with the remaining 33% to 50% as either So or FeS2. The suggested chemical reaction for TCE dechlorination via FeS oxidation is:4/9 FeS + C2HCl3 + 28/9 H2O => 4/9 Fe(OH)3 + 4/9 SO4-2 + C2H2 + 3 Cl- + 35/9 H+ | |||||||||
| Vendor(s) or Consultant(s) Associated with the Demonstration: |
Earth Sciences Division, Oklahoma City, OK Rowan University, Glassboro, NJ Air Force Center for Environmental Excellence |
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| Information Source(s) for the Demonstration: |
Biogeochemical Treatment for the Engineered and Natural Attenuation of Chlorinated Solvents, Paper H-16, in: V.S. Magar and M.E.Kelley (Eds.), In Situ and On-Situ Bioremediation - 2003. Proceedings of the Seventh International In Situ and On-Site Bioremediation Symposium (Orlando, Florida, June 2003). ISBN 1-57477-139-6, published by Battelle Press, Columbus, Ohio. http://www.battelle.org/bookstore# |
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| Contact Information | ||||||||||
| Point(s) of Contact: |
Jess W. Everett Rowan University 201 Mullica Hill Road Glassboro, New Jersey 08028, United States |
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James Gonzales Air Force Center for Environmental Excellence Brooks AFB, Texas, United States |
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Lonnie G. Kennedy (Primary Contact) Earth Sciences Division 3233 NW 63, Suite 105 Oklahoma City, Oklahoma 73116, United States E-mail: lkennedy@telepath.com |
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