Superfund Research Program

Transport, Transformation, and Remediation of Contaminants in the Environment

Project Leader: Kate M. Scow
Grant Number: P42ES004699
Funding Period: 1995-2015

Project-Specific Links

Final Progress Reports

Year:   2014  2009  2004  1999 

Preliminary batch studies of the interaction of perchlorate with soil have been undertaken. Results suggest that little adsorption of perchlorate occurs under conditions where large amounts of an aqueous perchlorate solution are contacted with small amounts of soil. However, as solution/soil ratios approach 2 g/g, nearly complete removal of perchlorate is observed. Results are similar for solutions with pH ranging from 1 to 7. A few experiments in which activated carbon was contacted with perchlorate solutions revealed very strong uptake by activated carbon.

At Port Hueneme Naval Base in Oxnard, California, an MTBE-contaminated groundwater plume has been inoculated with an MTBE-degrading bacterium (strain PM1) and also sparged with oxygen. Laboratory tests showed that adding the organism to groundwater samples in microcosms led to rapid and substantial MTBE degradation. After six months in the field, not only is there significant reduction of MTBE downstream of the inoculated plots but also in the uninoculated control plots, suggesting that native MTBE-degrading organisms have been stimulated by oxygen. Molecular biology tools are being developed and used to complement information on MTBE biodegradation potential and rates by Strain PM1 and native degraders. Primers specific to the 16S rDNA region of PM1 have been developed and amplification of groundwater samples indicate that strain PM1 is still surviving in the field at Port Hueneme 2 months after inoculation. The comparison of intertranscribed spacer region analysis (ITS), a DNA fingerprinting method, of microbial communities exposed or not exposed to MTBE was used to screen for native MTBE-degrading strains of bacteria at both sites. Classical enrichment and isolation techniques, combined with sequencing of the 16S rDNA, were simultaneously used to identify MTBE-degrading strains in the groundwater samples and compare them to the community patterns.

New experiments employing geostatistical and transport modeling tools developed previously in this project show that molecular diffusion, which is in effect neglected in most transport models, tends to dominate plume behavior and is a much stronger influence on transport than local scale mechanical dispersion. This work also elucidates causes of the observed scale dependence of dispersivity.

Biodegradation simulation experiments show that spatial heterogeneity of biodegradation rate constants can have a dramatic effect on plume characteristics such as center of mass, total contaminant mass, and maximum concentrations. Further, we showed that biodegradation processes in "slow" zones (e.g., clays, silts) are more important close to the source while biodegradation processes in aquifer zones (e.g., sands and gravels) are more important at distal locations.