Superfund Research Program
Transport, Transformation, and Remediation of Contaminants in the Environment
Project Leader: Kate M. Scow
Grant Number: P42ES004699
Funding Period: 1995-2015
Final Progress Reports
In research on fate of perchlorate in the environment and consideration of remediation technologies, the investigators found high concentrations of nitrate, a common co-pollutant, may delay reduction of perchlorate by soil microbial communities but may be important in maintaining high populations of perchlorate-degrading bacteria. Thus the interactions between perchlorate and nitrate must be considered in design of remediation practices. DNA fingerprinting of soils exposed to perchlorate revealed the presence of several bacterial strains identified as perchlorate degraders in other systems. Microbial perchlorate reduction was stimulated in soils amended with activated carbon or peat. This research may lead to identification of new solid matrices useful for treatment of perchlorate. The team’s research generated contacts between PIs and institutions (CA Water Resources Control Board office, engineering firms) interested in perchlorate contamination and remediation.
The researchers have demonstrated the potential for MTBE biodegradation by native microbial communities in groundwater, as well as continued research on a novel MTBE-biodegrading bacterium (Strain PM1). They demonstrated substantial potential for MTBE bioremediation via addition of oxygen to groundwater in samples from ten California shallow coastal aquifers. They have also demonstrated oxygen-stimulated MTBE biodegradation by native microbial communities at two field sites. Naturally occurring organisms genetically identical to Strain PM1 have also been detected at those sites in which MTBE biodegradation potential is present. These results are significant because they indicate potential in situ remediation of MTBE-contaminated groundwater may be achieved at numerous sites if oxygen is supplied.
The researchers demonstrated that chlorinated benzene compounds in solution can displace soil bound chlorinated benzenes of different chemical structures; in many cases this process proceeds many times faster than it does by flushing with clean water. This is important because contaminants at Superfund Sites invariably occur as mixtures and some contaminants may be significantly more mobile than estimated by most current site models, which assume that uptake and release of organic chemicals occurs independently. The team’s contributions include improved understanding of the mechanisms governing competitive interactions between contaminants in soils and better methods to predict these interactions in soils with different characteristics.
The researchers developed a model estimating human exposure to perchlorate released into groundwater used by the City of Rancho Cordova, CA as a drinking water source. The model accounts for transport of contaminated and uncontaminated water via the municipal water distribution network to specific locations, includes realistic complexity of the subsurface, and demonstrates limitations of conventional groundwater models for exposure analysis. Results include development of better ways of integrating groundwater exposure estimates with epidemiological analyses of human health effects. The researchers also completed analysis of efficiency of pump-and-treat groundwater remediation and found even modest amounts of groundwater heterogeneity can seriously exacerbate groundwater cleanup. Improved characterization and modeling tools for groundwater contamination were developed in the software packages RWHET and TproGS created as part of this project. Available free of charge, these tools help fill major gaps in characterization and transport modeling methods.