HR: 0800h
AN: H21A-0990 INVITED     [Abstracts]
TI: Characterizing Spatial Variability of Microbial Processes: In-situ Determination of Biodegradation Activity
AU: * Brusseau, M L
EM: brusseau@ag.arizona.edu
AF: Department of Soil, Water, and Environmental Science, The University of Arizona 429 Shantz Building, Tucson, AZ 85721 United States
AU: * Brusseau, M L
EM: brusseau@ag.arizona.edu
AF: Department of Hydrology and Water Resources, The University of Arizona 429 Shantz Building, Tucson, AZ 85721 United States
AB: Characterizing the occurrence, magnitudes, and rates of biodegradation at the field scale has become of great interest, especially with respect to evaluating the feasibility of applying in-situ bioremediation and monitored natural attenuation for hazardous waste site remediation. Potential spatial variability of microbial activity, which may be influenced by a multitude of factors, complicates site characterization. Biotracer tests are one of several methods that have been used to characterize the biodegradation potential for field-scale systems. In this study, field experiments were conducted at two sites to evaluate the utility of the biotracer method for characterizing the spatial variability of biodegradation activity. The first site is a chlorinated-solvent contaminated regional aquifer in Arizona, and the second site is a mixed-waste contaminated surficial aquifer in Utah. Mass recovery of the biotracer decreased approximately linearly with increasing residence time for the chlorinated-solvent site. Similar behavior was observed at the mixed-waste site, except in the region adjacent to the injection zone, where percent recoveries were much lower. First-order biodegradation rate coefficients obtained from model calibration of the tracer data varied between 0.2 and 0.5 1/d for the chlorinated-solvent site. For the mixed-waste site, the values varied between 0.1 and 0.6 1/d down-gradient of the injection wells, and between 0.7 and 2.6 1/d near the injection wells. Considering the large range over which biodegradation rate coefficients can vary, the rate coefficient exhibited relatively minimal spatial variability (factor of 2.5) for the chlorinated-solvent site. Conversely, the spatial variability of the rate coefficient was an order of magnitude greater for the mixed-waste site. These differences in variability are consistent with conditions associated with the respective sites. For example, the greater microbial activity observed in the vicinity of the injection wells for the mixed-waste site is consistent with the biomass distribution determined from analysis of core samples, which shows larger bacterial cell densities for the region near the injection wells. These results illustrate the utility of biotracer tests for in-situ characterization of microbial activity (e.g., biodegradation potential), including evaluation of potential spatial variability.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting