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USGS2016

Impact of formation water geochemistry and crude oil biodegradation on microbial methanogenesis

Converting non-producible crude oil to CH 4 via methanogenic crude oil biodegradation in oil reservoirs could serve as one way to increase our energy profile. Yet, field data supporting the direct relationship between methanogenesis and crude oil biodegradation are sparse. Indicators of methanogenesis, based on the formation water and gas geochemistry (e.g. alkalinity, δ 13 C–CO 2 ) were compared with indicators of crude oil biodegradation (e.g. pristane/phytane and n -alkane ratios) from wells in the Wilcox Group of Louisiana to determine if increases in extent of methanogenesis were related to increases in extent of crude oil biodegradation. Shallow wells (393–442 m depth) contained highly biodegraded oils associated with low extent of methanogenesis, while the deepest (> 1208 m) wells contained minimally degraded oils and produced fluids suggesting a low extent of methanogenesis. Mid-depth wells (666–857 m) in the central field had the highest indicators of methanogenesis and contained moderately biodegraded oils. Little correlation existed between extents of crude oil biodegradation and methanogenesis across the whole transect (avg. R 2 = 0.13). However, when wells with the greatest extent of crude oil biodegradation were eliminated (3 of 6 oilfields), better correlation between extent of methanogenesis and biodegradation (avg. R 2 = 0.53) was observed. The results suggest that oil quality and salinity impact methanogenic crude oil biodegradation. Reservoirs indicating moderate extent of crude oil biodegradation and high extent of methanogenesis, such as the central field, would be good candidates for attempting to enhance methanogenic crude oil biodegradation as a result of the observations from the study.

Organic Geochemistry↗

USGS1998

Biodegradation of the surfactant linear alkylbenzenesulfonate in sewage-contaminated groundwater: A comparison of column experiments and field tracer tests

Transport and biodegradation of linear alkylbenzenesulfonate (LAS) in sewage-contaminated groundwater were investigated for a range of dissolved oxygen concentrations. Both laboratory column and an 80-day continuous injection tracer test field experiments were conducted. The rates of LAS biodegradation increased with increasing dissolved oxygen concentrations and indicated the preferential biodegradation of the longer alkyl chain LAS homologues (i.e., C12 and C13) and external isomers (i.e., 2-and 3- phenyl). However, for similar dissolved oxygen concentrations, mass removal rates for LAS generally were 2-3 times greater in laboratory column experiments than in the field tracer test. Under low oxygen conditions (<1 mg/L) only a fraction of the LAS mixture biodegraded in both laboratory and field experiments. Biodegradation rate constants for the continuous injection field test (0.002-0.08 day-1) were comparable to those estimated for a 3-h injection (pulsed) tracer test conducted under similar biogeochemical conditions, indicating that increasing the exposure time of aquifer sediments to LAS did not increase biodegradation rates.Transport and biodegradation of linear alkylbenzenesulfonate (LAS) in sewage-contaminated groundwater were investigated for a range of dissolved oxygen concentrations. Both laboratory column and an 80-day continuous injection tracer test field experiments were conducted. The rates of LAS biodegradation increased with increasing dissolved oxygen concentrations and indicated the preferential biodegradation of the longer alkyl chain LAS homologues (i.e., C12 and C13) and external isomers (i.e., 2- and 3-phenyl). However, for similar dissolved oxygen concentrations, mass removal rates for LAS generally were 2-3 times greater in laboratory column experiments than in the field tracer test. Under low oxygen conditions (<1 mg/L) only a fraction of the LAS mixture biodegraded in both laboratory and field experiments. Biodegradation rate constants for the continuous injection field test (0.002-0.08 day-1) were comparable to those estimated for a 3-h injection (pulsed) tracer test conducted under similar biogeochemical conditions, indicating that increasing the exposure time of aquifer sediments to LAS did not increase biodegradation rates.

Environmental Science & Technology↗

USGS2001

Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes

Diffusion, sorption and biodegradation are key processes impacting the efficiency of natural attenuation. While each process has been studied individually, limited information exists on the kinetic coupling of these processes. In this paper, a model is presented that couples nonlinear and nonequilibrium sorption (intraparticle diffusion) with biodegradation kinetics. Initially, these processes are studied independently (i.e., intraparticle diffusion, nonlinear sorption and biodegradation), with appropriate parameters determined from these independent studies. Then, the coupled processes are studied, with an initial data set used to determine biodegradation constants that were subsequently used to successfully predict the behavior of a second data set. The validated model is then used to conduct a sensitivity analysis, which reveals conditions where biodegradation becomes desorption rate-limited. If the chemical is not pre-equilibrated with the soil prior to the onset of biodegradation, then fast sorption will reduce aqueous concentrations and thus biodegradation rates. Another sensitivity analysis demonstrates the importance of including nonlinear sorption in a coupled diffusion/sorption and biodegradation model. While predictions based on linear sorption isotherms agree well with solution concentrations, for the conditions evaluated this approach overestimates the percentage of contaminant biodegraded by as much as 50%. This research demonstrates that nonlinear sorption should be coupled with diffusion/sorption and biodegradation models in order to accurately predict bioremediation and natural attenuation processes. To our knowledge this study is unique in studying nonlinear sorption coupled with intraparticle diffusion and biodegradation kinetics with natural media.

Journal of Contaminant Hydrology↗

USGS2012

Biodegradation of chloroethene compounds in groundwater at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, 1999-2010

The U.S. Geological Survey evaluated the biodegradation of chloroethene compounds in groundwater beneath the former landfill at Operable Unit 1 (OU 1) of the U.S. Naval Undersea Warfare Center (NUWC), Division Keyport. The predominant contaminants in groundwater are the chloroethene compounds trichloroethene, cis -1,2-dichloroethene, and vinyl chloride. The remedy selected for groundwater contamination at OU 1 includes phytoremediation and natural attenuation. In 1999, the U.S. Navy planted two hybrid poplar plantations, referred to as the northern and southern plantations, over the most contaminated parts of the landfill. The U.S. Navy monitors tree health, groundwater levels, and contaminant concentrations to assess the effectiveness of phytoremediation. The U.S. Geological Survey began a cooperative effort with the U.S. Navy in 1995 to monitor the effectiveness of natural attenuation processes for removing and controlling the migration of chloroethenes and chloroethanes. Field and laboratory studies from 1996 through 2000 demonstrated that biodegradation of chloroethenes and chloroethanes in shallow groundwater at OU 1 was substantial. The U.S. Geological Survey monitored geochemical and contaminant concentrations in groundwater annually from 2001 through 2010. This report presents groundwater geochemical and contaminant data collected by the U.S. Geological Survey during June 2010 and evaluates evidence for continued biodegradation of chloroethenes in groundwater. Geochemical and contaminant concentration data through 2010 indicate that biodegradation of chloroethenes in groundwater continued beneath the landfill at OU 1. Contaminant concentrations in groundwater decreased beneath most of the 9-acre landfill between 1999 and 2010. The evidence indicating that biodegradation was a primary cause for the decreased concentrations included decreasing ratios of more highly chlorinated compounds to less chlorinated compounds over time, and widespread detections of non-chlorinated biodegradation end-products ethane and ethene. No widespread changes in groundwater reduction-oxidation (redox) conditions were observed that could result in either more or less efficient biodegradation. Even with continued biodegradation, dissolved-phase contaminant concentrations in the tens of milligrams per liter have persisted beneath part of the 0.7-acre southern plantation. The magnitude and persistence of those concentrations indicate that non-aqueous phase liquid chloroethenes likely are present beneath the southern plantation and are not substantially affected by biodegradation. During 2010, chloroethenes continued to be measured in shallow groundwater samples from the southern part of the adjacent marsh, although at the lowest concentrations ever measured. Flux calculations based on 2010 data indicate that 95 percent of dissolved-phase chloroethenes in the upper aquifer beneath the southern landfill were degraded before discharging to surface water. Overall, biodegradation of chloroethenes in groundwater throughout OU 1 continued through 2010, and it prevented most of the mass of dissolved-phase chloroethenes in the upper aquifer beneath the landfill from discharging to surface water.

Washington↗

USGS2004

Chloroethene biodegradation potential, ADOT/PF Peger Road Maintenance Facility, Fairbanks, Alaska

A series of 14C-radiotracer-based microcosm experiments were conducted to assess: 1) the extent, rate and products of microbial dechlorination of trichloroethene (TCE), cis-dichloroethene (cis-DCE) and vinyl chloride (VC) in sediments at the Peger Road site; 2) the effect of three electron donor amendments (molasses, shrimp and crab chitin, and 'Hydrogen Release Compound' (HRC)) on microbial degradation of TCE in three Peger Road sediments; and 3) the potential significance at the site of chloroethene biodegradation processes other than reductive dechlorination. In these experiments, TCE biodegradation yielded the reduced products, DCE and VC, and the oxidation product CO 2. Biodegradation of DCE and VC involved stoichiometric oxidation to CO 2. Both laboratory microcosm study and field redox assessment results indicated that the predominant terminal electron accepting process in Peger Road plume sediments under anoxic conditions was Mn/Fe-reduction. The rates of chloroethene biodegradation observed in Peger Road sediment microcosms under low temperature conditions (4?C) were within the range of those observed in sediments from temperate (20?C) aquifer systems. This result confirmed that biodegradation can be a significant mechanism for in situ contaminant remediation even in cold temperature aquifers. The fact that CO2 was the sole product of cis-DCE and VC biodegradation detected in Peger Road sediments indicated that a natural attenuation assessment based on reduced daughter product accumulation may significantly underestimate the potential for DCE and VC biodegradation at the Peger Road. Neither HRC nor molasses addition stimulated TCE reductive dechlorination. The fact that molasses and HRC amendment did stimulate Mn/Fe-reduction suggests that addition of these electron donors favored microbial Mn/Fe-reduction to the detriment of microbial TCE dechlorinating activity. In contrast, amendment of sediment microcosms with shrimp and crab chitin resulted in the establishment of mixed Mn/Fe-reducing, SO42--reducing and methanogenic conditions and enhanced TCE biodegradation in two of three Peger Road sediment treatments.

Alaska↗

USGS1996

Distribution of petroleum hydrocarbons and toluene biodegradation, Knox Street fire pits, Fort Bragg, North Carolina

An investigation was conducted at the Knox Street fire pits, Fort Bragg, North Carolina, to monitor the distribution of toluene, ethylbenzene, and xylene (TEX) in soil vapor, ground water, and ground-water/vapor to evaluate if total concentrations of TEX at the site are decreasing with time, and to quantify biodegradation rates of toluene in the unsaturated and saturated zones. Soil-vapor and ground-water samples were collected around the fire pits and ground-water/vapor samples were collected along the ground-water discharge zone, Beaver Creek, on a monthly basis from June 1994 through June 1995. Concentrations of TEX compounds in these samples were determined with a field gas chro- matograph. Laboratory experiments were performed on aquifer sediment samples to measure rates of toluene biodegradation by in situ micro- organisms. Based on field gas chromatographic analytical results, contamination levels of TEX compounds in both soil vapor and ground water appear to decrease downgradient of the fire-pit source area. During the 1-year study period, the observed temporal and spatial trends in soil vapor TEX concentrations appear to reflect differences in the distribution of TEX among solid, aqueous, and gaseous phases within fuel-contaminated soils in the unsaturated zone. Soil temperature and soil moisture are two important factors which influence the distribution of TEX com- pounds among the different phases. Because of the short period of data collection, it was not possible to distinguish between seasonal fluc- tuations in soil vapor TEX concentrations and an overall net decrease in TEX concentrations at the study site. No seasonal trend was observed in total TEX concentrations for ground- water samples collected at the study site. Although the analytical results could not be used to determine if ground-water TEX concen- trations decreased during the study at a specific location, the data were used to examine rate constants of toluene biodegradation. Based on ground-water toluene concentration data, a maximum rate constant for anaerobic biodegradation of toluene in the saturated zone was estimated to be as low as 0.002 d-1 or as high as 0.026 d-1. Based on analyses of ground-water/vapor samples, toluene was the prin- cipal TEX compound identified in ground water discharging to Beaver Creek. Observed decreases in ground-water/vapor toluene concentrations during the study period may reflect a decrease in source inputs, an increase in dilution caused by higher ground-water flow, and(or) removal by biological or other physical processes. Rate constants of toluene anaerobic biodegradation determined by laboratory measurements illustrate a typical acclimation response of micro-organisms to hydrocarbon contamination in sediments collected from the site. Toluene biodegradation rate constants derived from laboratory microcosm studies ranged from 0.001 to 0.027 d-1, which is similar to the range of 0.002 to 0.026 d-1 for toluene biodegradation rate constants derived from ground-water analytical data. The close agreement of toluene biodegradation rate constants reported using both approaches offer strong evidence that toluene can be degraded at environmentally significant rates at the study site.

Water-Resources Investigations Report↗

USGS2007

Dissolved organic carbon in Alaskan boreal forest: Sources, chemical characteristics, and biodegradability

The fate of terrestrially-derived dissolved organic carbon (DOC) is important to carbon (C) cycling in both terrestrial and aquatic environments, and recent evidence suggests that climate warming is influencing DOC dynamics in northern ecosystems. To understand what determines the fate of terrestrial DOC, it is essential to quantify the chemical nature and potential biodegradability of this DOC. We examined DOC chemical characteristics and biodegradability collected from soil pore waters and dominant vegetation species in four boreal black spruce forest sites in Alaska spanning a range of hydrologic regimes and permafrost extents (Well Drained, Moderately Well Drained, Poorly Drained, and Thermokarst Wetlands). DOC chemistry was characterized using fractionation, UV-Vis absorbance, and fluorescence measurements. Potential biodegradability was assessed by incubating the samples and measuring CO2 production over 1 month. Soil pore water DOC from all sites was dominated by hydrophobic acids and was highly aromatic, whereas the chemical composition of vegetation leachate DOC varied significantly with species. There was no seasonal variability in soil pore water DOC chemical characteristics or biodegradability; however, DOC collected from the Poorly Drained site was significantly less biodegradable than DOC from the other three sites (6% loss vs. 13-15% loss). The biodegradability of vegetation-derived DOC ranged from 10 to 90% loss, and was strongly correlated with hydrophilic DOC content. Vegetation such as Sphagnum moss and feathermosses yielded DOC that was quickly metabolized and respired. In contrast, the DOC leached from vegetation such as black spruce was moderately recalcitrant. Changes in DOC chemical characteristics that occurred during microbial metabolism of DOC were quantified using fractionation and fluorescence. The chemical characteristics and biodegradability of DOC in soil pore waters were most similar to the moderately recalcitrant vegetation leachates, and to the microbially altered DOC from all vegetation leachates.

Alaska↗

USGS2007

Biodegradation of PAHs and PCBs in soils and sludges

Results from a multi-year, pilot-scale land treatment project for PAHs and PCBs biodegradation were evaluated. A mathematical model, capable of describing sorption, sequestration, and biodegradation in soil/water systems, is applied to interpret the efficacy of a sequential active-passive biotreatment process of organic chemicals on remediation sites. To account for the recalcitrance of PAHs and PCBs in soils and sludges during long-term biotreatment, this model comprises a kinetic equation for organic chemical intraparticle sequestration process. Model responses were verified by comparison to measurements of biodegradation of PAHs and PCBs in land treatment units; a favorable match was found between them. Model simulations were performed to predict on-going biodegradation behavior of PAHs and PCBs in land treatment units. Simulation results indicate that complete biostabilization will be achieved when the concentration of reversibly sorbed chemical (S RA) reduces to undetectable levels, with a certain amount of irreversibly sequestrated residual chemical (S IA) remaining within the soil particle solid phase. The residual fraction (S IA) tends to lose its original chemical and biological activity, and hence, is much less available, toxic, and mobile than the "free" compounds. Therefore, little or no PAHs and PCBs will leach from the treatment site and constitutes no threat to human health or the environment. Biotreatment of PAHs and PCBs can be terminated accordingly. Results from the pilot-scale testing data and model calculations also suggest that a significant fraction (10-30%) of high-molecular-weight PAHs and PCBs could be sequestrated and become unavailable for biodegradation. Bioavailability (large K d , i.e., slow desorption rate) is the key factor limiting the PAHs degradation. However, both bioavailability and bioactivity (K in Monod kinetics, i.e., number of microbes, nutrients, and electron acceptor, etc.) regulate PCBs biodegradation. The sequential active-passive biotreatment can be a cost-effective approach for remediation of highly hydrophobic organic contaminants. The mathematical model proposed here would be useful in the design and operation of such organic chemical biodegradation processes on remediation sites. ?? 2007 Springer Science+Business Media B.V.

Water, Air, & Soil Pollution↗

USGS2011

Biodegradation and attenuation of steroidal hormones and alkylphenols by stream biofilms and sediments

Biodegradation of select endocrine-disrupting compounds (17β-estradiol, estrone, 17α-ethynylestradiol, 4-nonylphenol, 4-nonylphenolmonoexthoylate, and 4-nonylphenoldiethoxylate) was evaluated in stream biofilm, sediment, and water matrices collected from locations upstream and downstream from a wastewater treatment plant effluent discharge. Both biologically mediated transformation to intermediate metabolites and biologically mediated mineralization were evaluated in separate time interval experiments. Initial time intervals (0–7 d) evaluated biodegradation by the microbial community dominant at the time of sampling. Later time intervals (70 and 185 d) evaluated the biodegradation potential as the microbial community adapted to the absence of outside energy sources. The sediment matrix was more effective than the biofilm and water matrices at biodegrading 4-nonylphenol and 17β-estradiol. Biodegradation by the sediment matrix of 17α-ethynylestradiol occurred at later time intervals (70 and 185 d) and was not observed in the biofilm or water matrices. Stream biofilms play an important role in the attenuation of endocrine-disrupting compounds in surface waters due to both biodegradation and sorption processes. Because sorption to stream biofilms and bed sediments occurs on a faster temporal scale (<1 h) than the potential to biodegrade the target compounds (50% mineralization at >185 d), these compounds can accumulate in stream biofilms and sediments.

Environmental Science & Technology↗

USGS2003

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

The U.S. Geological Survey (USGS) solute transport and biodegradation code BIOMOC was used in conjunction with the USGS universal inverse modeling code UCODE to quantify field-scale hydrocarbon dissolution and biodegradation at the USGS Toxic Substances Hydrology Program crude-oil spill research site located near Bemidji, MN. This inverse modeling effort used the extensive historical data compiled at the Bemidji site from 1986 to 1997 and incorporated a multicomponent transport and biodegradation model. Inverse modeling was successful when coupled transport and degradation processes were incorporated into the model and a single dissolution rate coefficient was used for all BTEX components. Assuming a stationary oil body, we simulated benzene, toluene, ethylbenzene, m , p -xylene, and o -xylene (BTEX) concentrations in the oil and ground water, respectively, as well as dissolved oxygen. Dissolution from the oil phase and aerobic and anaerobic degradation processes were represented. The parameters estimated were the recharge rate, hydraulic conductivity, dissolution rate coefficient, individual first-order BTEX anaerobic degradation rates, and transverse dispersivity. Results were similar for simulations obtained using several alternative conceptual models of the hydrologic system and biodegradation processes. The dissolved BTEX concentration data were not sufficient to discriminate between these conceptual models. The calibrated simulations reproduced the general large-scale evolution of the plume, but did not reproduce the observed small-scale spatial and temporal variability in concentrations. The estimated anaerobic biodegradation rates for toluene and o -xylene were greater than the dissolution rate coefficient. However, the estimated anaerobic biodegradation rates for benzene, ethylbenzene, and m , p -xylene were less than the dissolution rate coefficient. The calibrated model was used to determine the BTEX mass balance in the oil body and groundwater plume. Dissolution from the oil body was greatest for compounds with large effective solubilities (benzene) and with large degradation rates (toluene and o -xylene). Anaerobic degradation removed 77% of the BTEX that dissolved into the water phase and aerobic degradation removed 17%. Although goodness-of-fit measures for the alternative conceptual models were not significantly different, predictions made with the models were quite variable.

Minnesota↗

USGS2000

Biodegradation of chlorinated ethenes at a karst site in middle Tennessee

This report presents results of field and laboratory investigations examining the biodegradation of chlorinated ethenes in a karst aquifer contaminated with trichloroethylene (TCE). The study site, located in Middle Tennessee, was selected because of the presence of TCE degradation byproducts in the karst aquifer and available site hydrologic and chlorinated-ethene information. Additional chemical, biological, and hydrologic data were gathered to evaluate whether the occurrence of TCE degradation byproducts in the karst aquifer was the result of biodegradation within the aquifer or simply transport into the aquifer. Geochemical analysis established that sulfate-reducing conditions, essential for reductive dechlorination of chlorinated solvents, existed in parts of the contaminated karst aquifer. Other areas of the aquifer fluctuated between anaerobic and aerobic conditions and contained compounds associated with cometabolism, such as ethane, methane, ammonia, and dissolved oxygen. A large, diverse bacteria population inhabits the contaminated aquifer. Bacteria known to biodegrade TCE and other chlorinated solvents, such as sulfate-reducers, methanotrophs, and ammonia-oxidizers, were identified from karst-aquifer water using the RNA-hybridization technique. Results from microcosms using raw karst-aquifer water found that aerobic cometabolism and anaerobic reductive-dechlorination degradation processes were possible when appropriate conditions were established in the microcosms. These chemical and biological results provide circumstantial evidence that several biodegradation processes are active in the aquifer. Additional site hydrologic information was developed to determine if appropriate conditions persist long enough in the karst aquifer for these biodegradation processes to be significant. Continuous monitoring devices placed in four wells during the spring of 1998 indicated that pH, specific conductance, dissolved oxygen, and oxidation-reduction potentials changed very little in areas isolated from active ground-water flow paths. These stable areas in the karst aquifer had geochemical conditions and bacteria conducive to reductive dechlorination of chlorinated ethenes. Other areas of the karst aquifer were associated with active ground-water flow paths and fluctuated between anaerobic and aerobic conditions in response to rain events. Associated with this dynamic environment were bacteria and geochemical conditions conducive to cometabolism. In summary, multiple lines of evidence developed from chemical, biological, and hydrologic data demonstrate that a variety of biodegradation processes are active in this karst aquifer.

Tennessee↗

USGS2000

Redox conditions and the efficiency of chlorinated ethene biodegradation: Field studies

The effect of redox conditions on the efficiency of chlorinated ethene biodegradation was investigated at two field sites. One site (NAS Cecil Field, FL) is characterized by predominantly Fe(III)-reducing conditions in the contaminant source area, grading to predominantly sulfate- reducing conditions downgradient. This sequence of redox conditions led to relatively inefficient biodegradation of chlorinated ethenes, with high concentrations of trichloroethene extending more than 400 meters downgradient of the source area. In contrast, a second site (NBS Kings Bay, GA) characterized by predominantly sulfate-reducing conditions in the source area followed by Fe(III)-reducing conditions downgradient. In this system perchloroethene (PCE) and TCE were rapidly biodegraded and extended less than 100 meters downgradient. Rates of ground- water transport are similar at the two sites (???0.2 m/d) indicating that the succession of redox processes, rather than other hydrologic factors, is the principal control on biodegradation. In particular, redox conditions that favor the initial reduction of highly chlorinated ethenes (methanogenic or sulfate-reducing conditions) followed by more oxidizing conditions (Fe(III)- reducing or oxic conditions) favors efficient biodegradation. Thus, documenting the succession of redox processes is an important step in understanding the efficiency of chlorinated ethene biodegradation in ground-water systems.

Conference Paper↗

USGS2006

Research approach to teaching groundwater biodegradation in karst aquifers

TSU in partnership with the USGS has conducted extensive research regarding biode??gradation of contaminants in karst aquifers. This research resulted in the development of a numerical approach to modeling biodegradation of contaminants in karst aquifers that is taught to environmental engineering students in several steps. First, environmental engineering students are taught chemical-reaction engineering principles relating to a wide variety of environmental fate and transport issues. Second, as part of TSU's engineering course curriculum, students use a non-ideal flow laboratory reactor system and run a tracer study to establish residence time distribution (RTD). Next, the students couple that formula to a first-order biodegradation rate and predict the removal of a biodegradable contaminant as a function of residence time. Following this, students are shown data collected from karst bedrock wells that suggest that karst aquifers are analogous to non-ideal flow reactors. The students are challenged to develop rates of biodegradation through lab studies and use their results to predict biodegradaton at an actual contaminated karst site. Field studies are also conducted to determine the accuracy of the students' predictions. This academic approach teaches biodegradation processes, rate-kinetic processes, hydraulic processes and numerical principles. The students are able to experience how chemical engineering principles can be applied to other situations, such as, modeling biodegradation of contaminants in karst aquifers. This paper provides background on the chemical engineering principles and karst issues used in the research-enhanced curriculum. ?? American Society for Engineering Education, 2006.

Conference Paper↗

USGS2012

Estimated trichloroethene transformation rates due to naturally occurring biodegradation in a fractured-rock aquifer

Rates of trichloroethene (TCE) mass transformed by naturally occurring biodegradation processes in a fractured rock aquifer underlying a former Naval Air Warfare Center (NAWC) site in West Trenton, New Jersey, were estimated. The methodology included (1) dividing the site into eight elements of equal size and vertically integrating observed concentrations of two daughter products of TCE biodegradation– cis -dichloroethene ( cis -DCE) and chloride–using water chemistry data from a network of 88 observation wells; (2) summing the molar mass of cis -DCE, the first biodegradation product of TCE, to provide a probable underestimate of reductive biodegradation of TCE, (3) summing the molar mass of chloride, the final product of chlorinated ethene degradation, to provide a probable overestimate of overall biodegradation. Finally, lower and higher estimates of aquifer porosities and groundwater residence times were used to estimate a range of overall transformation rates. The highest TCE transformation rates estimated using this procedure for the combined overburden and bedrock aquifers was 945 kg/yr, and the lowest was 37 kg/yr. However, hydrologic considerations suggest that approximately 100 to 500 kg/yr is the probable range for overall TCE transformation rates in this system. Estimated rates of TCE transformation were much higher in shallow overburden sediments (approximately 100 to 500 kg/yr) than in the deeper bedrock aquifer (approximately 20 to 0.15 kg/yr), which reflects the higher porosity and higher contaminant mass present in the overburden. By way of comparison, pump-and-treat operations at the NAWC site are estimated to have removed between 1,073 and 1,565 kg/yr of TCE between 1996 and 2009.

New Jersey↗

USGS2009

Biodegradation of 17β-estradiol, estrone, and testosterone in stream sediments

The release of endocrine-disrupting chemicals (EDCs) in wastewater treatment plant (WWTP) effluent poses a significant threat to the ecology of surface water receptors, due to impacts on the hormonal control, sexual development, reproductive success and community structure of the indigenous aquatic organisms and associated wildlife. Among the EDCs commonly observed in WWTP effluent, the natural [e.g., 17??-estradiol (E2) and estrone (E1)] and synthetic [e.g., ethynylestradiol (EE2)] estrogens are particular concerns owing to their high endocrine reactivity in both in vitro and in vivo laboratory models. These reproductive hormones have been identified as the primary cause of estrogenic effects in wastewater effluent, with greater than 95% of the estrogen receptor agonist activity in effluent attributed to this contaminant group. The potentials for in situ biodegradation of 17??-estradiol (E2), estrone (E1), and testosterone (T) were investigated in three, hydrologically-distinct, WWTP-impacted streams in the United States. Relative differences in the mineralization of [4- 14 C] substrates were assessed in oxic microcosms containing sediment or water-only from locations upstream and downstream of the WWTP outfall in each system. Upstream samples provided insight into the biodegradative potential of sediment microbial communities that were not under the immediate impact of WWTP effluent. Upstream sediment from all three systems demonstrated significant mineralization of the "A" ring of E2, E1 and T, with the potential of T biodegradation consistently greater than of E2 and no systematic difference in the potentials of E2 and E1. Downstream samples provided insight into the impacts of effluent on reproductive hormone biodegradation. Significant "A" ring mineralization was also observed in downstream sediment, with the potentials for E1 and T mineralization being substantially depressed relative to upstream samples. In marked contrast, the potentials for E2 mineralization immediately downstream of the WWTP outfalls were more than double that of upstream samples. E2 mineralization was also observed in water, albeit at insufficient rate to prevent substantial downstream transport in the water column. The results of this study indicate that, in combination with sediment sorption processes which effectively scavenge hydrophobic contaminants from the water column and immobilize them in the vicinity of the WWTP outfall, aerobic biodegradation of reproductive hormones can be an environmentally important mechanism for nonconservative (destructive) attenuation of hormonal endocrine disruptors in effluent-impacted streams.

Conference Paper↗

USGS2013

Complex resistivity signatures of ethanol biodegradation in porous media

Numerous adverse effects are associated with the accidental release of ethanol (EtOH) and its persistence in the subsurface. Geophysical techniques may permit non-invasive, real time monitoring of microbial degradation of hydrocarbon. We performed complex resistivity (CR) measurements in conjunction with geochemical data analysis on three microbial-stimulated and two control columns to investigate changes in electrical properties during EtOH biodegradation processes in porous media. A Debye Decomposition approach was applied to determine the chargeability ( m ), normalized chargeability ( m n ) and time constant ( τ ) of the polarization magnitude and relaxation length scale as a function of time. The CR responses showed a clear distinction between the bioaugmented and control columns in terms of real ( σ′ ) and imaginary ( σ″ ) conductivity, phase ( ϕ ) and apparent formation factor ( F app ). Unlike the control columns, a substantial decrease in σ′ and increase in F app occurred at an early time (within 4 days) of the experiment for all three bioaugmented columns. The observed decrease in σ′ is opposite to previous studies on hydrocarbon biodegradation. These columns also exhibited increases in ϕ (up to ~ 9 mrad) and σ″ (up to two order of magnitude higher) 5 weeks after microbial inoculation. Variations in m and m n were consistent with temporal changes in ϕ and σ″ responses, respectively. Temporal geochemical changes and high resolution scanning electron microscopy imaging corroborated the CR findings, thus indicating the sensitivity of CR measurements to EtOH biodegradation processes. Our results offer insight into the potential application of CR measurements for long-term monitoring of biogeochemical and mineralogical changes during intrinsic and induced EtOH biodegradation in the subsurface.

Journal of Contaminant Hydrology↗

USGS2009

Biodegradation of 17β-estradiol, estrone and testosterone in stream sediments

Biodegradation of 17β-estradiol (E2), estrone (E1), and testosterone (T) was investigated in three wastewater treatment plant (WWTP) affected streams in the United States. Relative differences in the mineralization of [4- 14 C] substrates were assessed in oxic microcosms containing saturated sediment or water-only from locations upstream and downstream of the WWTP outfall in each system. Upstream sediment demonstrated significant mineralization of the “A” ring of E2, E1, and T, with biodegradation of T consistently greater than that of E2 and no systematic difference in E2 and E1 biodegradation. “A” ring mineralization also was observed in downstream sediment, with E1 and T mineralization being substantially depressed relative to upstream samples. In marked contrast, E2 mineralization in sediment immediately downstream from the WWTP outfalls was more than double that in upstream sediment. E2 mineralization was observed in water, albeit at insufficient rate to prevent substantial downstream transport. The results indicate that, in combination with sediment sorption processes which effectively scavenge hydrophobic contaminants from the water column and immobilize them in the vicinity of the WWTP outfall, aerobic biodegradation of reproductive hormones can be an environmentally important mechanism for nonconservative (destructive) attenuation of hormonal endocrine disruptors in effluent-affected streams.

Colorado, Iowa↗

USGS2011

Reinterpreting the importance of oxygen-based biodegradation in chloroethene-contaminated groundwater

Chlororespiration is common in shallow aquifer systems under conditions nominally identified as anoxic. Consequently, chlororespiration is a key component of remediation at many chloroethene-contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products is interpreted as evidence that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene-contaminated shallow aquifer systems, however, nonconservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms and is consistent with contaminant degradation to nondiagnostic mineralization products like CO 2 . While anoxic mineralization of chloroethene compounds has been proposed previously, recent results suggest that oxygen-based mineralization of chloroethenes also can be significant at dissolved oxygen concentrations below the currently accepted field standard for nominally anoxic conditions. Thus, reassessment of the role and potential importance of low concentrations of oxygen in chloroethene biodegradation are needed, because mischaracterization of operant biodegradation processes can lead to expensive and ineffective remedial actions. A modified interpretive framework is provided for assessing the potential for chloroethene biodegradation under different redox conditions and the probable role of oxygen in chloroethene biodegradation.

Ground Water Monitoring and Remediation↗