1	Enhanced Bioremediation for Treatment of Chlorinated Solvent Residual Source Areas – Case Study and Implications Kent S. Sorenson, Jr. Ryan A. Wymore
2	Bioremediation Background In Situ Bioremediation of chlorinated solvents: Solvents utilized as electron acceptors by indigenous microorganisms Chlorine atoms sequentially replaced with hydrogen through “reductive dechlorination”
3	Microbial Metabolism
4	Bioremediation Metabolism
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6	A Paradigm Shift? Conventional applications for in situ bioremediation limited to dissolved phase for two primary reasons: Concerns about toxicity Impact on nonaqueous sources thought to be no better than pump and treat New research reveals that in situ bioremediation may be extremely effective for chlorinated solvent source areas
7	Enhanced Mass Transfer In situ bioremediation can enhance mass transfer, addressing the concerns previously thought to limit bioremediation applications: Many investigators have shown that dechlorinating bacteria actually have an ecological niche in high concentration areas Several studies have shown that in situ bioremediation enhances mass transfer of contaminants through at least three mechanisms
8	Mechanisms of Enhanced Mass Transfer Mechanisms for enhanced mass transfer Bioremediation removes contaminants from the aqueous phase, thereby increasing the driving force for mass transfer = k(C_s-C) Increasing solubility of reductive dechlorination degradation products greatly increases the maximum aqueous contaminant loading The electron donor solution can be used to decrease interfacial tension, thereby increasing the effective solubility
9	Enhanced Mass Transfer: Mechanisms 1 and 2 Enhanced mass transfer of chlorinated solvent NAPLs due to reductive dechlorination has been demonstrated in at least two laboratory batch studies: Yang and McCarty (2000) showed enhanced PCE dissolution up to a factor of 5 higher than without reductive dechlorination Carr et al. (2000) showed reductions in NAPL longevity of 83% due to reductive dechlorination in continuously stirred tank reactors
10	Enhanced Mass Transfer: Mechanisms 1 and 2 Enhanced mass transfer of chlorinated solvent NAPLs due to reductive dechlorination has been demonstrated in at least one laboratory column study: Cope and Hughes (2001) demonstrated total chlorinated ethene removal was 5 to 6 times higher with reductive dechlorination as compared to abiotic washout
11	Enhanced Mass Transfer: Mechanisms 1 and 2 Enhanced chlorinated ethene removal due to reductive dechlorination in columns with PCE DNAPL (Courtesy of Joe Hughes)
12	Enhanced Mass Transfer: Mechanism 3 The impact of sodium lactate and other electron donor solutions on water-TCE interfacial tension was investigated in unpublished laboratory studies The results supported a pending patent for the Idaho National Engineering and Environmental Laboratory The process is referred to as Bioavailability Enhancement Technology^TM (B.E.T.^TM)
13	Impact of Electron Donor Solutions on Interfacial Tension
14	Enhanced Mass Transfer: Mechanism 3 Enhanced mass transfer due to electron donor solution interaction with nonaqueous TCE, followed by complete reductive dechlorination has been observed in at least one field study: Sorenson (2000, in press) showed that TCE concentrations were greatly enhanced due to facilitated transport associated with the electron donor solution (high concentration sodium lactate) This work will serve as our case study
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16	Test Area North (TAN) Background Industrial wastewater (including solvents), low-level radioactive wastes, and sanitary sewage were injected directly to the Snake River Plain Aquifer from the late 1950s to 1972 TCE plume is nearly 2 miles long Residual source area is about 100 ft in diameter Contaminated aquifer is about 200-400 ft deep Aquifer is comprised of fractured basalt
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18	Record of Decision (1995) Pump and treat selected as default remedy Treatability studies established for alternative technologies: zero-valent iron monolithic confinement in situ chemical oxidation in situ bioremediation natural attenuation 100-year remedial time frame
19	Objectives for the 1-year In Situ Bioremediation Field Evaluation Primary Objective: Demonstrate that biodegradation of TCE can be significantly enhanced through electron donor addition Create hydraulic “treatment cell” to maintain hydraulic containment of the source area and control residence time Determine controls on process efficiency through extensive monitoring
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22	Electron Donor Distribution
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24	Redox Conditions
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33	Long-Term Dechlorination
34	Enhanced Mass Transfer from DNAPL Source Area
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37	Status of Enhanced In Situ Bioremediation at TAN Formal regulatory approval to implement bioremediation at the TAN DNAPL source area as a replacement for the default remedy has been granted. A ROD amendment was signed in 2001.
38	Ft. Lewis ESTCP Demonstration The project will use two in situ treatment cells to quantitatively demonstrate the enhanced mass transfer and degradation that occurs due to in situ bioremediation in a chlorinated solvent source area One cell will be operated to test the first two mass transfer mechanisms, while the other will add the third mechanism Project planning is underway; field work is scheduled to begin in January 2003