R-3 Repository :: Browsing by Author "Ward, C. H."

Browsing by Author "Ward, C. H."

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A Study of Surface Treatments on Carbonate Core Material for Application to Mineral Precipitation and Dissolution during Geologic Carbon Storage
(2013-06-05) Work, Sarah; Tomson, Mason B.; Bedient, Philip B.; Ward, C. H.; Hirasaki, George J.
Underground injection of acid gas has been studied for several decades for oil field applications, such as enhanced oil recovery (EOR), but is now being studied as a solution to climate change. This research aims to simulate underground conditions at injection sites, such as the pilot scale injection site located near the site of a coal fired power facility in the Black Warrior Basin of Alabama. This proposed carbon capture and sequestration (CCS) location would involve injection of liquid CO2 into a carbonaceous saline aquifer. The objective of this study was to investigate carbonate surface treatments that alter the kinetics and mechanism of mineral dissolution resulting from the injection of an acid gas (CO2) into a geologic formation. A variety of mineral coatings were tested in an attempt to preserve mineral integrity under acidic conditions. Surface active chemicals were first tested, including scale inhibitors, followed by a novel acid induced surface treatment that precipitates an inorganic layer on the calcite to preserve the acid soluble mineral. These experiments are the first to investigate the use of scale inhibitors for mineral preservation, although were found ultimately to have little impact on dissolution kinetics. However, anions of moderate to strong acids induced surface coatings that were determined to effectively inhibit dissolution. Additionally, a novel, high pressure flow-through experimental apparatus was developed to simulate pressure and temperature conditions relevant to injection sites. Similar mineralogical studies in the literature have used pressurized, unstirred, batch systems to simulate mineral interactions. Solids with an acid induced surface coating were tested in the high pressure column and no calcium was found to leave the column.
Antibiotic resistance vector transport, reservoir amplification and attenuation
(2008) Rysz, Michal; Alvarez, Pedro J.; Ward, C. H.; Gonzalez, Ramon
Microbial antibiotic resistance is an emerging environmental pollution problem with deleterious effects on water supplies and human health. Currently, little is known about the role of environmental factors in the maintenance, propagation and attenuation of antibiotic resistance. This study investigated the effects of antibiotic exposure concentrations, nutrient availability, and microbial growth rate on resistance dynamics, as well as, the porous medium transport characteristics of antibiotic resistance vectors. Exposure to high antibiotic concentrations increased, (1) the percentage of resistant bacterial strains in soil, (2) the persistence of resistant strains in soil and (3) the relative abundance of resistance genes in bacteria; and decreased the Shannon Weaver diversity index. Rich growth medium enhanced resistance plasmid maintenance and stability even in the absence of selective pressure of the antibiotic possibly be alleviating the metabolic burden imparted on the carrier bacteria by the resistance plasmids. The growth rate exerted a strain-specific response on resistance dynamics, with higher plasmid instability (i.e., increased loss) observed at higher growth rates (Pseudomonas aeruginosa), but no such effect observed for an Eschericha coli strain. Resistance vector plumes may be enhanced by: (1) groundwater conditions conducive to plasmid coagulation and colloid formation of approximately 1 mum, and (2) high concentrations of resistant bacteria that exhibit fast initial deposition, and strong blocking behavior after matrix deposition. The results of this research suggest that decreasing environmental antimicrobial concentrations will be conducive to the attenuation of microbial antibiotic resistance, but may not be sufficient in completely eliminating the resistance reservoirs, thus additional control methods may be needed to minimize the impact of these pollutants. The results should also provide insight to improve regulatory and sustainability decision-making processes related to the use of antibiotic in animal agriculture.
Aquatic phytotransformation of trinitrotoluene in contaminated media
(1996) Vanderford, Mindy; Ward, C. H.
Recent investigations indicate that 2,4,6-trinitrotoluene (TNT) is rapidly transformed in an aquatic environment by the action of photosynthetic organisms. Several plant species from a variety of culture conditions were examined that displayed the capacity to transform TNT. The kinetics of transformation and the fate of transformation products were monitored by MECE and HPLC analysis in both the aquatic media and within the plant tissues. (U)$\sp{14}$C-TNT was introduced into the plant systems in order to monitor the fate of the aromatic ring. In order to assess the action of plant biochemistry in isolation from ordinary periphyton, axenic plants were examined for their metabolic capacity. Experiments showed that the majority of TNT is rapidly transformed into an unidentified soluble product in the medium and plant tissues with small quantities of reduction products appeared transiently. Over time, an increasing amount of $\sp{14}$C was irreversibly associated with the plant tissue.
Bacterial attachment and transport through porous media: The effects of bacterial cell characteristics
(1995) Duston, Karen Lansford; Ward, C. H.
The effects of several microbial, chemical and physical parameters on bacterial attachment was studied in batch adsorption and column transport studies. Specifically, the role of bacterial characteristics, ionic strength of solution, roughness of solid surfaces, and hydraulic conductivity were tested. Using particle removal theory, the collision efficiency factor ($\alpha$) was calculated from the breakthrough of the cells (C/Co) in the columns. The values of $\alpha$ varied over three orders of magnitude. The distance that the cells were predicted to travel through the porous medium was calculated assuming C/Co = 0.05 (95% retention). Predicted travel ranged from less than 5 cm to almost 10 km. Bacterial surface characteristics that apparently affected attachment were electrophoretic mobility, hydrophobicity, and biopolymer production. Electrostatic interactions, described by DLVO theory, governed attachment of hydrophilic cells to hydrophilic surfaces. Hydrophobic interactions dominated attachment of hydrophobic cells. Steric hindrance may have resulted from the adsorption of extracellular biosurfactant onto cell and solid surfaces. Size also influenced retention of the cells in the porous medium. Cells less than 0.1 $\mu$m and greater than 3.0 $\mu$m in diameter were retained to a greater extent than cells with diameters within this range. Increased ionic strength resulted in increased attachment of cells. Attachment to sand grains was greater than attachment to glass beads, possibly because of the rougher surfaces. Lower hydraulic conductivity resulted in greater retention of cells.
Biosurfactant production by gasoline-degrading bacteria from a contaminated aquifer
(1992) Allen, Phillip Glenn; Ward, C. H.
Biosurfactants produced by subsurface bacteria may potentially enhance in situ bioremediation. A study was performed to characterize the production and enhancement of production of biosurfactants by 37 gasoline-degrading bacteria isolated from a gasoline-contaminated aquifer. Surface tension and emulsification capacity of the bacterial cultures growing on unleaded gasoline vapors were determined and mean surface tension and emulsification capacity values calculated. When liquid gasoline was added to the cultures, the mean surface tension reduction of the sample population was nearly doubled, compared to the cultures using only gasoline vapors. Many of the bacterial isolates were able to grow without significant surface tension reductions or emulsification. For two select isolates, optimum ammonium sulfate concentrations for growth and biosurfactant production were determined. Addition of yeast extract enhanced biosurfactant production by the two isolates. Both isolates were shown to initiate production of biosurfactants during the stationary phase of cell growth.
Biosurfactant production by organisms from an ecology study of a JP-4 jet contaminated site
(1996) Bruce, Cristin Lee; Ward, C. H.
The ability of subsurface microbial populations to degrade organic contaminants is affected by nutrient availability. A study was performed to measure the change in microbial ecology of a weathered JP-4 jet fuel contaminated site (Eglin Air Force Base, Florida) over the course of a nitrate-based treatment in terms of heterotrophs, JP-4 degraders, oligotrophs, biosurfactant producers, bioemulsifier producers, and predators. Microbial numbers increased and species diversity decreased in the nitrate-amended site significantly more than in background areas. The surfactant producing potential of native microbial communities decreased significantly with nitrate addition. Bioemulsification capacity of these communities was slightly lowered with addition of nitrate. Aerobic predators decreased over the course of the experiment, while microaerophilic predators increased significantly. Due to fluctuations in measured JP-4, no conclusions could be drawn about the success of nitrate addition as a remedial enhancement technique at this site.
Biosurfactant production by subsurface microorganisms
(1991) Francy, Donna S.; Ward, C. H.
Biosurfactants have potential for enhancement of in situ biorestoration. A study was performed to characterize biosurfactant production by microbes from several subsurface environments contaminated with petroleum hydrocarbons. Emulsification of hydrocarbons was used to identify microorganisms with the greatest potential to produce biosurfactants. Biostimulated zone microbes contained the greatest proportion of emulsifiers as compared to contaminated and pristine zone microbes. Biostimulation was the dominant factor which selected for and encouraged growth of microbial emulsifiers; exposure to hydrocarbon was also important. The degree of emulsification by biostimulated microbes was greater for the contaminant hydrocarbon than for heavier fuels. Emulsification of hydrocarbons may be an important mechanism in biorestoration by increasing the bioavailability of the contaminant; however, no attempt was made to assess this possibility or relationship. Since biosurfactants are emulsion stabilizers, they merit further attention for enhancement of in situ aquifer restoration.
Buffalo Bayou oxygen balance and stream protection analysis
(1984) Todd, David Anderson; Bedient, Philip B.; Adams, John A. S.; Ward, C. H.
Buffalo Bayou suffers from low dissolved oxygen/ levels and so cannot support a wide variety or large population of fish and aquatic vegetation. The low oxygen concentrations are largely due to the in-stream degradation of sewage discharged into the Bayou. This study seeks to assess the current water quality of the Bayou, and to determine the impact of point discharges, non-point discharges, and other factors on stream quality. From data on the stream's water quality and its response to various factors, computer models have been calibrated, verified, and used to predict future and hypothetical stream quality. Consideration is given to the effect of increased sewage discharges, varied levels of in-plant treatment, and alternative options of direct treatment of the stream through flow augmentation and stream aeration. Conclusions are drawn as to the effectiveness of the various schemes for protecting the Bayou's water.
Chronic and acute toxicity testing in fish
(1974) Ellis, Randy Sue; Ward, C. H.
Both chronic and acute toxicity tests were performed using several species of fish. Chronic toxicity tests concerning lead were performed using mudfish (Fundulus heteroclitus). These experiments ran for 3 days. Results indicate that threshold concentration of lead for this species approaches .75 mg/1. Even at this concentration, there is definite uptake of lead at a rate greater than that exhibited in the control fish, but less than that exhibited by fish at higher concentrations. Acute toxicity tests were run using pure oxygen in an effort to determine this gas' role in the production of gas bubble disease in fish. Three fresh-water species, including the fathead minnow (Pimephales promelas), golden shiner (Notemigonus crypoleucas), and rainbow perch (Tilapea mozambique), and one salt-water species, Atlantic croaker (Micropogon undulatus), were tested. All efforts to produce gas bubble disease were futile. However, the experiments did produce serious doubt as to the role of oxygen in the production of gas bubble disease. Also, the extreme subjectiveness of the symptoms of gas bubble disease and the lack of any definitive studies of natural situations in which gas bubble disease develops (such as phytoplankton blooms) indicate that this disease and its causes are ill-defined and are in further need of clarification.
Dispersion and retardation of contaminants in a high pressure liquid chromatography soil column system
(1984) Waggett, Gordon Gray; Tomson, Mason B.; Bedient, Philip B.; Ward, C. H.
The development of a high-pressure/high-flow rate soil chromatography system as a protocol method for the rapid screening of chemicals in natural, undisturbed aquifer samples is proposed. A mathematical advective-dispersive transport model was applied which evaluated the soil column and apparatus as a two-layered system. Results pertaining to the dispersion and retardation of six neutral-organic contaminants in one aquifer sample indicated that useful information could be obtained for other soil samples and transport processes as well. Close agreement was reached between experimental and theoretical breakthrough curves. Correlations between dispersion, seepage velocity and retardation were addressed. The transport model assumed equilibrium adsorption mechanisms. Kinetic- equilibrium adsorption terms may be necessary to model the retardation mechanisms at high flow rates.
Edaphic and pyric influences on two contiguous savannas of East Texas
(1979) Streng, Donna Rae; Harcombe, P. A.; Fisher, Frank M.; Ward, C. H.
Vegetation, soil, history (land use and tree age), site favorability (tree growth rates), and flammability were examined in four contiguous East Texas communities, two of which are savannas. The data suggest that woody plant densities are edaphically limited on one of the savannas (sedge meadows), and fire limited on the other savanna (pine-bluestem savanna). The edaphic savanna (meadows) has acidic soil with a shallow claypan, and these features are apparently responsible for its distinctive vegetation, low sapling densities, and slow tree growth rates. The soil characteristics (profile, texture, pH) and the tree composition of the fire savanna are similar to a neighboring forested upland. It is inferred that fire has reduced tree density since tree growth rate and sapling densities are higher than in the forest, and it appears that logging was not responsible for low tree densities. Furthermore age histograms from this savanna reveal low hardwood recruitment from 1953-196. 1955-1956 was a period of drought in East Texas and age structures from all communities examined have a noticeable gap during this period with the savanna's being more extensive. This age gap suggests that drought reduces tree recruitment (increases mortality) and in some communities this reduction is further accentuated by fire. Also, since both savannas are more flammable than the wooded areas (as measured by Rothermel's (1972) model of fire spread) they probably bum more frequently. Thus, they are maintained by a positive feedback cycle -- i.e. burning increases flammability by favoring herbs which increases the probability of a recurring fire. On the other hand, one of the wooded communities (west side) was a former savanna (as revealed by aerial photographs), which through chance or the intervention of man has remained fire-free long enough to develop a densely packed, nonflammable fuel bed. The present nonflammability of this community suggests that it may have effectively escaped from the influence of fire.
Effect of surfactant addition on phenanthrene biodegradation in sediments
(1994) Tsomides, Harry James; Ward, C. H.
A literature search and laboratory treatability study were conducted to determine the potential of commercial surfactants to enhance the bioremediation of PAH-contaminated sediments. Phenanthrene was used as a model PAH and an inoculum of PAH-degrading microorganisms enriched from an aquatic sediment was used in sediment-water slurry microcosm biodegradation experiments. The abilities of nonionic surfactants to reduce surface tension and enhance phenanthrene solubility, the effect of sediment on the physical behavior of surfactants, and the effects of surfactants on phenanthrene biodegradation were examined. Of the surfactants tested, all except Triton X-100 severely inhibited phenanthrene mineralization. Adding Triton X-100 to microcosms with or without sediment significantly enhanced the extent of phenanthrene mineralization after 1 week. These experimental results suggest that this surfactant may be useful in the bioremediation of PAH-contaminated sediments and that further studies using pilot-scale systems or a field demonstration are warranted.
Effects of age on toxicity to freshwater algae of water soluble extracts of No. 2 fuel oil
(1979) Hsieh, Ying-Ping; Ward, C. H.; Fisher, Frank M.; Tomson, Mason B.
The effects of fresh-prepared, 4-day-aged and 8-dayaged Ho. 2 fuel oil water soluble fractions on the growth of Selenastrum capricornutum were investigated. The freshprepared water soluble fraction inhibits both the growth rate and cell yield of S. capricornutum. Its toxicity decreases after four days but there is still residual toxicity. This residual toxicity decreases very slowly; the effects of the 8day-aged water soluble fraction on S. capricornutum are comparable with those of the 4-day-aged one. The components of the water soluble fractions were identified by a mass spectrometer interfaced to a gas chromatograph. The major components are aromatic compounds, of which, the benzene and indene derivatives volatilize '.very quickly. Naphthalene and methyl naphthalenes volatilize in four days. However, the di-aromatic and tri-aromatic compounds, having boiling points higher than naphthalene,are still in the medium after 8 days. Sixteen component compounds were chosen for chemical analysis and toxicity testing. The concentrations of these compounds in the fresh-prepared , 4-day-aged and 8-day-aged water soluble fractions were determined, and their toxicities were investigated by "algal lavra" technique. The concentration distribution test on the agarized medium shows that the concentrations of naphthalene and phenanthrene are comparable at a selected distance after diffusing in the medium for four days. The results indicate that methyl, dimethyl and trimethyl naphthalenes are more toxic than naphthalene. The most toxic compounds are dibenzofuran, fluorene, phenanthrene and dibenzothiophene, v/hich have high boiling points.
Growth and root inhibition in Axenic hydrilla verticillata cultures
(1984) Cook, Rebecca Ann; Ward, C. H.; Tomson, Mason B.; Matthews, Kathleen S.
Hydrilla verticillata Royle is a submersed aquatic weed infesting waterways throughout the world. Hydrilla was introduced into the United States in 196 and has spread across the southern states. Hydrilla has extensive reproductive capacity, spreading by seeds, axillary and subterranean vegetative buds, fragmentation, and stolons. Subterranean buds, called tubers, are the predominant form of reproduction. This reproductive potential has made mechanical, chemical, and biological control largely ineffective. To study the life cycle of Hydrilla, Elaine and Ward (1981) developed a method for producing axenic cultures from tubers. The process by which axenic cultures were produced involves surface treatment of the tuber with sodium hypochlorite and removal of outer bud scales. Tubers were grown in a mineral salts media containing 15 ug/ml penicillin and 1 ug/ml streptomycin to prevent bacterial growth. Two percent glucose and .5 per cent casein were added to facilitate detection of bacterial contamination. Axenic cultures produced by this method have inhibited shoot and root growth. In the present study, different variables in the process were analyzed for inhibitory effects. Addition of yeast extract, IAA, IBA, GAg, and kinetin failed to overcome stem or root growth inhibition. Neither NaOCl treatment nor dissection as separate factors affected growth or root development. Sodium hypochlorite treatment followed by dissection resulted in retarded growth at times, although mature plants did develop. Addition of penicillin and streptomycin or penicillin, streptomycin, glucose, and casein resulted in inhibited growth and root production. Casein and streptomycin both inhibited stem and root growth in all cases. Glucose slightly enhanced growth. Penicillin had no significant effects on shoot growth or root formation and growth. Axenic cultures with penicillin and glucose exhibited no inhibitions. Streptomycin inhibits growth of roots at 15, 5, and 1 ug/ml. Penicillin did not affect growth of stems or roots at 25, 75, or 15 ug/ml but did not effectively control bacteria. Neomycin, ampicillin, tetracycline, and chloramphenicol were tested separately at 25, 75, and 15 ug/ml and in combinations at 75 ug/ml as possible alternatives to streptomycin. All were inhibitory to shoot growth. Root formation was significantly inhibited by all concentrations of chloramphenicol, and the higher concentrations of neomycin and tetracycline. Several of the antibiotic combinations, tested in conjunction with 25 ug/ml penicillin, were effective against bacteria but were inhibitory to hydrilla growth at tested concentrations.
Growth optimized algal cultures for hazard assessment
(1981) Klaine, Stephen James; Ward, C. H.; Bedient, Philip B.; Tomson, Mason B.
Static and dynamic cultures of Selenastrum capricornutum Printz were optimized and compared for evaluation of toxic chemicals. Pigment analysis, nucleic acid and protein concentrations, and productivity measurements indicated that once growth was optimized, the alga was physiologically similar in both systems. The toxicity of phenol and g-naphthol to S. capricornutum was tested using both static and dynamic systems and results did not differ significantly. Toxicant concentrations were monitored with time throughout the toxicity bioassays. Results demonstrate that growth optimized static algal cultures can be used for hazard assessment without loss of sensitivity.
Growth rate, tree form and bark texture of Quercus falcata Michx. and Q. falcata variety pagodaefolia E11. in four stands in Southern East Texas
(1979) Glitzenstein, Jeff Steven; Harcombe, P. A.; Ward, C. H.; Fisher, Frank M.
Quercus falcata Michx. growth rate, importance (basal area), tree form, and bark texture were examined over a local gradient in soil moisture (as inferred from site vegetation, slope position and soil texture) . At drier sites, growth rate was found to be slower, bark was found to be rougher, and the maximum tree height was found to be smaller. Quercus falcata basal area also differed greatly between study sites. However, contrary to expectation, changes in basal area did not parallel changes in diameter growth rate, suggesting the possible importance of historical factors in determining the distribution of this species. The frequency of occurrence of the two varieties of Quercus falcata, variety falcata and Q. falcata var. pagodaefblia Ell., was compared among the four study sites, and within one study site. As was found by Caplenor et al. (1968), variety falcata reaches its maximum abundance under drier conditions, while variety pagodaefolia is most abundant in moister environments.
Impacts of unsaturated zone reaeration on the bioattenuation of organic contaminants in groundwater systems
(2000) Neale, Charles Nelson; Hughes, Joseph B.; Ward, C. H.
Reaeration, or the diffusion of O2 through the unsaturated zone and into an aquifer system, is a mechanism that influences the extent of hydrocarbon contaminant bioattenuation in ground water. A series of laboratory and numerical modeling experiments were completed to determine the amount of O2 supplied to an anaerobic aquifer by reaeration under various unsaturated zone conditions and to quantify the impacts of reaeration on the migration of hydrocarbon plumes in ground water. Results from laboratory experiments indicated that reaeration flux rates exhibited a bimodal distribution and either approached 12,000 Mg/M2-day or were less than 2,000 Mg/M2-day. Soil water content significantly affected the reaeration flux rate while soil type, soil O2 utilization rate, and unsaturated zone thickness did not influence the reaeration rate. In some cases, the capillary rise impeded O2 transport into the bulk ground water due to high water content near the base of the capillary region. An unsaturated zone transport model was developed to predict reaeration flux based on the effective diffusion coefficient of soil (Ds), liquid-side mass transfer coefficient (KL), Soil O2 utilization rate (Rsoil), and unsaturated zone thickness (z). Good agreement was generally found between the predicted and experimental flux results. Results from numerical modeling experiments indicated that reaeration reduced the steady-state length of hydrocarbon plumes in ground water for aquifer hydraulic conductivities of K = 10--2 cm/s and K = 10--4cm/s. Important groundwater reaeration parameters having an influence on the steady-state hydrocarbon plume length included the concentration of O2 in the overlying soil gas (C O2(g)), the ground water mass transfer coefficient (KL,GW), the vertical dispersivity in the saturated zone (alphav), and the zone of reaeration or the thickness of the top model layer (ZR). The relative importance of each of these parameters was on the order of alphav > > KL,GW > CO2(g) > ZR.
Microbial degradation of selected aromatic compounds in a hazardous waste site
(1983) Lee, Michael Donald; Ward, C. H.; Tomson, Mason B.; Bedient, Philip B.
Microbial degradation of five aromatic compounds was followed in aseptically-taken subsurface soil samples and ground water samples from the vicinity of a pit used to dispose the waste from a wood creosoting plant. The five compounds--anthracene, dibenzofuran, fluorene, naphthalene, and pentachlorophenol--were contaminants found in the soil and ground water. There was degradation of the selected compounds in the subsurface soil, although the importance of biological activity was not conclusively shown. Microbes in the ground water were able to biodegrade all five of the compounds with naphthalene, dibenzofuran, and fluorene being degraded most rapidly. Faster rates of degradation were noted for the more contaminated wells which had microbial populations that were adapted to the compounds. The presence in both ground water and soil samples of microbes which could utilize the aromatic compounds (except pentachlorophenol) as sole carbon sources was also demonstrated. Their numbers decreased with depth in the soil and increased with levels of contamination in the ground water. Total microbial counts on soil samples from 15 and 24 ft (water table) below the surface were about the same, but lower than that in the surface samples.
Microbial transport through porous media: The effect of hydraulic conductivity and injection velocity
(1991) Marlow, Harold J.; Ward, C. H.
Microorganisms have been added to the subsurface in an attempt to enhance bioremediation. The transport, attachment and fate of these organisms as well as their possible contribution to remediation remain poorly understood. The effect of hydraulic conductivity and injection velocity on microbial transport through porous media was investigated. Glass chromatography columns were packed separately with clean quartz sand of two diameters (0.368 mm or 0.240 mm) and two hydraulic conductivities (1.37 $\times$ 10$\sp{-1}$ cm/sec and 3.65 $\times$ 10$\sp{-2}$ cm/sec respectively). Three injection velocities, 1.18 $\times$ 10$\sp{-3}$, 2.35 $\times$ 10$\sp{-3}$ and 4.73 $\times$ 10$\sp{-3}$ cm/sec were investigated. Microbial transport under the conditions tested was limited and could be predicted mathematically using a model based on filtration theory which incorporated particle trajectory analysis.
Microcosm Assessment of Aerobic Intrinsic Bioremediation and Mineralization Potential for three 1,4-Dioxane Impacted Sites
(2013-11-19) Van Orden, Elisa; Alvarez, Pedro J.; Ward, C. H.; Tomson, Mason B.
1,4-Dioxane (dioxane) is a potential carcinogen widely used as a stabilizer for chlorinated solvents, and it exhibits high mobility in groundwater. Dioxane is recalcitrant to biodegradation, and its physicochemical properties preclude effective removal by volatilization or adsorption. Through this long-term microcosm study, we have assessed the natural attenuation potential of dioxane for multiple sediment and groundwater samples collected from three sites located in Los Angeles, CA. Groundwater and sediment samples were taken from three locations at each plume, representing the source zone, middle and leading edge. A total of 13 monitoring wells were sampled to prepare the microcosms and subsequently assess the indigenous potential to biodegrade dioxane. The microcosms were spiked with 14C-labeed dioxane to assess mineralization potential (per 14CO2 recovery). No dioxane loss and less than 8% CO2 recovery was observed in the negative controls, indicating that dioxane removal (and mineralization) was due to biodegradation. Positive control microcosms amended with the dioxane degrader Pseudonocardia dioxivorans CB1190 exhibited dioxane degradation activity statistically indistinguishable from observed batch incubations prepared with mineral media, indicating an absence of inhibitory compounds in source zone samples. Complete dioxane removal, exhibiting linear (zero-order) kinetics (indicative of saturated enzymes), was observed during 24 weeks incubation in all biologically active, unaugmented microcosms. Up to 43% mineralization as CO2 and 5% to 7% biomass growth was observed in unaugmented microcosms experiencing rapid dioxane loss. Degradation activity decreased with increasing distance from the contaminant source zone, presumably due to less acclimation. Source-zone microcosms from Site 1 exhibited relatively high biodegradation activity (323.9 ± 7.6 µg/L/day) and were respiked with dioxane for confirmatory purposes. The respike (2 ppm dioxane) was degraded faster within four weeks, suggesting a higher level of acclimation (possibly due to the growth of indigenous dioxane degraders) after the initial 24 week study. Source-zone microcosms from Site 2 and 3 exhibited biodegradation activities of 1.4 ± 0.09 µg/L/day and 47.1 ± 1.8 µg/L/day, respectively. Overall, these results show that indigenous microorganisms capable of degrading dioxane are present at the three sites considered, and suggest that monitored natural attenuation should be considered as a remedial response.

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