Douglas Gunnison

Attenuation mechanisms of N-nitrosodimethylamine at an operating intercept and treat groundwater remediation system

The North Boundary Containment System (NBCS), an intercept-and-treat system, was established at Rocky Mountain Arsenal (RMA), Commerce City, CO, to remove low-level organic contaminants from a groundwater plume exiting RMA to the north and northwest. N-nitrosodimethylamine (NDMA) was detected in groundwater collected from the dewatering and recharge zones of the NBCS system. Concern over the fate of NDMA, in terms of potentially exiting the boundaries of the arsenal, prompted an investigation to evaluate potential attenuation mechanisms for NDMA within the alluvial aquifer system and within the NBCS itself. Groundwater, soil, and granular activated carbon (GAC) samples were taken from key locations in the NBCS system. Soil and GAC samples were assayed for sorption kinetics and for adsorption and desorption properties using 14C-labeled NDMA. NDMA biodegradation experiments were conducted by following 14CO(2) evolution from 14C-labeled NDMA in soils and GAC samples under aerobic and anaerobic conditions. The sorptive capacity of the site soils for NDMA was insignificant. Furthermore, the adsorption of the NDMA by the soil was almost completely reversible. Evaluation of the degradation potential of the native microbial consortia indicated a high level of NDMA mineralization when measured using bench-scale microcosms. The native consortia had capability to mineralize the NDMA under both aerobic and anaerobic incubations, indicating facultative characteristics. Testing of the local groundwater chemistry revealed that the area of the aquifer of interest was microaerobic and neutral in pH. These conditions were optimal for NDMA removal. While sorption was insignificant, degradation was a significant attenuation mechanism, which may be the reason that no NDMA has migrated off-site. This gives rise to the potential of a long-term sink for attenuating NDMA within the recharge zone of the treatment system.

Fate of 2,4,6-Trinitrotoluene in a Simulated Compost System

Abstract Composting of 2,4,6-trinitrotoluene (TNT) contaminated soils is a potentially economical remediation alternative. To determine whether environmentally undesirable emissions or residuals are produced, an explosives contaminated soil was amended with radiolabelled TNT before composting in a small-scale compost simulation system. Mass balance results indicated that TNT was not mineralized to volatile organic compounds and almost no radiolabelled CO 2 was produced. Only transformation to the solvent extractable products, 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene, and conjugation to cellulosic, humin, humic acid and fulvic acid occurred. More than half of the added radioactivity was recovered in the cellulose plus humin fractions.

Bioslurry treatment of a soil contaminated with low concentrations of total petroleum hydrocarbons

The objective of this study was to investigate the degradation patterns of petroleum hydrocarbons during bioremediation of soils containing low levels of contaminants. The study was conducted in pilot-scale bioslurry reactors (70 l) under aerobic conditions. The reactors were equipped with a process-gas-recirculation system to ensure complete containment and eventually complete degradation of all contaminants. The concentrations of benzene, toluene, ethyl benzene, and xylenes (BTEX-compounds) and of naphthalene, anthracene, and phenanthrene were found to decrease rapidly. But, polyaromatic hydrocarbons (PAHs) containing >3 aromatic rings did not show significant biodegradation. Addition of rapidly metabolizing substrates such as sodium acetate and/or phenanthrene did not enhance the degradation of PAHs containing >3 aromatic rings. However, the augmented phenanthrene was rapidly metabolized.

Monitored Natural Attenuation of Explosives

Explosives are subject to several attenuation processes that potentially reduce concentrations in groundwater over time. Some of these processes are well defined, while others are poorly understood. The objective of the project was to optimize data collection and processing procedures for evaluation and implementation of monitored natural attenuation of explosives. After conducting experiments to optimize data quality, a protocol was established for quarterly monitoring of thirty wells over a 2-year period at a former waste disposal site. Microbial biomarkers and stable isotopes of nitrogen and carbon were explored as additional approaches to tracking attenuation processes. The project included a cone penetrometry sampling event to characterize site lithology and to obtain sample material for biomarker studies. A three-dimensional groundwater model was applied to conceptualize and predict future behavior of the contaminant plume. The groundwater monitoring data demonstrated declining concentrations of explosives over the 2 years. Biomarker data showed the potential for microbial degradation and provided an estimate of the degradation rate. Measuring stable isotopic fractions of nitrogen in TNT was a promising method of monitoring TNT attenuation. Overall, results of the demonstration suggest that monitored natural attenuation is a viable option that should be among the options considered for remediation of explosives-contaminated sites.

Capping Contaminated Dredged Material

Abstract The ability of various uncontaminated cap materials of varying thicknesses to isolate contaminated dredged material from the water column was assessed in large (250 l.) reactor units using chemical and microbial tracers. Heavy metals, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and bacterial spores contained in the underlying contaminated dredged material were monitored in the overlying water column, clams ( Rangia cuneata ) suspended in the water, and burrowing polychaetes ( Nereis virens ). Tissue analysis of Rangia indicated that none of the 5 cm cap thicknesses tested was totally effective in preventing contaminant transfer to biota. However, cap materials consisting predominantly of clay and silt appeared more effective than sand in preventing contaminant transfer to biota. Rangia did not show elevated tissue concentrations of chemicals when contaminated sediment was covered with a 50 cm cap. However, chemical and microbial results indicated that Nereis breached both the 5 cm and 50 cm thicknesses of all cap materials tested.

Application of Continuous Culture Technology for the Development of Explosives‐degrading Microorganismsa

Microorganisms exposed to anthropogenic substances have sometimes responded by acquiring new genes for degradation of these compounds, either for detoxification or to enable the microbe to use the contaminant as a source of energy to meet metabolic needs.’ However, even in these microorganisms, the pathways necessary for degradation may lack sufficient genetic control to obtain maximum biological destruction. As Chakrabarty’ has indicated, community catabolism of the contaminant may decrease effectiveness in catabolism by individual microorganisms as a result of self-imposed constraints on rapid degradation of common metabolites by natural communities participating jointly in the degradation of the compound. Previously, application of continuous culture technology as a process termed “plasmid-assisted molecular breeding” was used to facilitate development of bacterial strains capable of complete degradation of anthropogenic compounds, such as the xcnobiotic pesticidc 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).* More rccently, it has been suggested that application of continuous culture technology, coupled with more intensive selective pressures may accelerate development of new metabolic capabilities in a microorganism or enhance acquisition of such capabilities from other bacteria having the requisite biodegradative genes.’ We report here the application of continuous culture tcchnology utilizing chemical gradients coupled with other environmental selective pressures, based on the anticipated physiological capabilities required for a single specics of microorganism

Sediment-water interactions and mineral cycling in reservoirs

This study was conducted to examine the influences of sediment-water interactions on releases of iron (Fe), manganese (Mn), and nutrients to the overlying water in established reservoirs. Emphasis was placed on sediment-water interactions under anaerobic conditions, and on sediment-water interactions with and without an externally supplied source of biologically available organic carbon. These studies were conducted in large, 2501 reactor chambers containing 20 cm of sediment and 2101 of water. Results showed that at the end of an anaerobic incubation, the overlying water more closely resembles the composition of sediment interstitial water rather than aerobic surface waters. Dissolved oxygen depletion was shown to result in remobilization of metals and nutrients from sediment into the overlying water. Addition of organic matter to the overlying water resulted in enhanced release rates of Fe and Mn. It is postulated that Fe and Mn trapped in the sediment surface layer under aerobic conditions were reduced and released to the water column under anaerobic conditions.