For more information on the DNAPL Website, please contact:
Linda FiedlerTechnology Assessment Branch
PH: (703) 603-7194 | Email: fiedler.linda@epa.gov
Dense Nonaqueous Phase Liquids (DNAPLs)
Detection and Site Characterization
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Geochemical Analysis for Evidence of Biodegradation
Abstracts of Journal Articles
Altered Geophysical Response Reflects Changes in Microbial Community Structure in Petroleum Contaminated Sediments
Allen, J.P. (Western Michigan Univ., Kalamazoo); E.A. Atekwana and E.A. Atekwana (Univ. of Missouri-Rolla); S. Rossbach (Western Michigan Univ.). Eos: Transactions of the AGU, Vol 87 No 36, Jt. Assem. Suppl., Abstract NS41A-01, 2006
In an investigation of the microbial diversity of a petroleum-contaminated site, the main objective was to characterize the microbial community structure in zones of higher and lower conductivity. Culture-independent 16S rRNA gene libraries were constructed using sediment samples collected from the contaminated and background sites. Diversity indices indicated that the microbial community at the contaminated site contained fewer, more dominant populations, whereas the microbial community at the background site was much more diverse. The microbial communities in and around the aged underground petroleum plume have adapted to the available carbon source (petroleum hydrocarbons) and influence the geophysical and geochemical surroundings through their catabolic activities. The information gained in this study suggests that changes in microbial community structures parallel changes in the geophysical properties of contaminated sediments, providing strong evidence of the feasibility of using geoelectrical measurements for the monitoring of natural or engineered bioremediation processes.
Bioavailable Ferric Iron (BAFeIII) Assay, ESTCP Project Number CU-0009: Cost and Performance Report
Lebron, C. (NFESC); P. Evans, M. Trute, R. Olsen, and R. Chappell (CDM); J. Wilson and C. Adair (EPA/Ada); E. Weber, J. Kenneke, and B.T. Thomas (EPA/Athens); T. DiChristina (GIT); J. Drexler (UC). Environmental Security Technology Certification Program (ESTCP), CR-05-005-ENV, 41 pp, 2005
A bioavailable ferric iron (BAFeIII) assay was invented and developed by CDM with funding from the U.S. Air Force. This report describes the demonstration and validation of this novel analytical technology at four DoD installations. The assay is a standardized bioassay that directly measures the concentration of BAFeIII in soil or sediment. A BAFeIII test kit based on the assay is manufactured by New Horizons Diagnostics Corporation (NHD) of Columbia, MD. BAFeIII is an important terminal electron acceptor with significant assimilative capacity in many natural environments. Dissolved ferrous iron (Fe II) in groundwater is typically measured to assess Fe III reduction and calculate assimilative capacity, but this measurement underestimates this terminal electron accepting process because most Fe II remains bound to the soil. Dissolved Fe II also gives no indication of the amount of Fe III present in aquifer soil that is bioavailable. BAFeIII in the soil must be measured to quantify the true assimilative capacity of an aquifer. Iron-reducing bacteria (FeRB) use and are dependent on BAFeIII. FeRB are known to oxidize or mineralize various organic compounds, such as benzene, toluene, vinyl chloride (VC), and methyl tertiary butyl ether (MTBE). Continued activity over a period of years is dependent on the presence of sufficient BAFeIII. BAFeIII can also affect reductive dechlorination in MNA and EAB applications. BAFeIII can result in TCE being reductively dechlorinated to cDCE only, and further reductive dechlorination can be inhibited. Thus, knowledge of the BAFeIII concentration can indicate the potential for incomplete reductive dechlorination of TCE. It can also be used for planning EAB remedies. If the BAFeIII concentration is sufficient to inhibit cDCE reductive dechlorination, reductive dechlorination of TCE to cDCE and VC followed by oxidative biodegradation of VC and possibly cDCE under iron-reducing conditions may be a better approach. The overall objective of this project was to demonstrate and validate the performance of the BAFeIII assay as an analytical technology for use in supporting bioremediation.
Case Studies
A Case Study of Indirect Geochemical Indicators
Jacobs, J.A. (Environmental Bio-Systems Inc.); D.G. McEdwards (The McEdwards Group). NGWA 2006 Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Assessment, and Remediation Conference, 6-7 November 2006
Although enhanced aerobic bioremediation is a slow process, it can reduce site closure schedules from decades for natural attenuation in an anaerobic environment to a few years with the addition of dissolved oxygen. The iSOC gas infusion system allows oxygen to dissolve slowly at about 15 cc/min or 0.77 cubic feet per day per monitoring well. For in situ enhanced bioremediation of petroleum hydrocarbons, direct contaminant concentrations are useful to monitor the success of the project; however, as water levels rise and fall over the complete hydrologic cycle, confirmatory data for microbial activity and changes in geochemical conditions can be provided by other indirect indicators, such as dissolved oxygen, heterotrophic plate count, specific aerobic degraders, macronutrients ammonia nitrogen and ortho-phosphate, total inorganic carbon, total organic carbon, total dissolved solids, speciated alkalinity, pH, oxygen reduction potential, chemical oxygen demand, biological oxygen demand, ferrous iron, sulfate, and nitrate. A gas infusion case study using the iSOC technology in Maple Shade, NJ, was evaluated for indirect indicators to verify that enhanced bioremediation was responsible for the hydrocarbon degradation of benzene (>96%), MTBE (89%), and TBA (54%) that occurred over a 6-month period. The data showed that the degradation was related to the iSOC treatment rather than to seasonal changes in the hydrologic contaminant cycle.
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