Strategies for In-Situ Bioremediation of Chlorinated Solvent Contamination of Groundwater
The main recommendations to emerge from the conference are: (1) In situ bioremediation is constrained by our limited understanding of subsurface microbiology. Uncertainty in the delivery of treatment chemicals in complex hydrogeological environments presents significant challenges to scientists and engineers alike. The addition of treatment chemicals to aquifers to enhance bioremediation needs the acceptance of regulatory authorities before these emerging technologies progress from pilot scale to full-scale established technologies. One of the major unknowns is the fate of biodegradable pollutants in dual porosity aquifers, in particular the location of biological activity (matrix or fracture). Mass transfer mechanisms and rates need to be elucidated for complex component, multi-phase contaminants in the soil, vadose and saturated zones in these complex subsurface environments. (2) Reactive barriers are now recognized as a valid alternative to pump -and-treat where the operation time scale is believed to be long. However, experience to date has focused on relatively shallow plumes in poorly consolidated geologies. Future research efforts should include the application of the barrier approach to contaminated groundwaters in deep consolidated aquifers where groundwater supplies are often impacted by long-lived contamination sources. (3) Source zone treatment has focused mainly on the non-aqueous phase liquids (NAPLs). These pollutants, in particular the DNAPLs, result in long-lived sources of contamination that are typically not suited to treatment by conventional remedial treatment technologies such as pump -and-treat. Treatment approaches may be highly site specific and further work needs to be undertaken to identify plume time scale (100s to 1000s of years) benefits of partial mass removal from NAPL source zones. Research efforts need to identify technologies to deal with NAPLs in deep consolidated, and often dual-porosity, aquifers. Research must also consider coupling combined source zone and plume treatment technologies and the development of predictive tools to assess the performance of these enhanced treatment approaches. (4) Flow and transport modeling is used extensively in the design and performance evaluation of pilot scale tests conducted to remediate contaminated sites. The development of predictive models to represent the long-term behavior of pollutants in groundwater and assess the performance of remediation technologies requires essential underpinning from a range of disciplines. Research efforts should focus on incorporating heterogeneity, inherent in complex sedimentary architecture and fractured dual porosity domains, in multi-process models. (5) Site characterization to identify the location and mass distribution of pollutants in heterogeneous environments is essential in identifying the risk to potential receptors, for focusing remediation technologies and in providing ''base-line'' data for performance assessment. Our understanding of pollutant distribution is seriously limited by the ability to measure and represent both geological features and contaminant distribution at appropriate scales. The amount of uncertainty determines how effectively we deliver, treat and assess the performance of remediation technologies. The characterization of DNAPL source zones for delineating the distribution of DNAPL and in focusing remediation technologies remains a significant challenge--at present there are no DNAPL sites in deep consolidated aquifers where full site characterization has been validated. The prevalence of contaminants at hazardous waste sites is well documented; if they are not removed or sequestered, they can contaminate millions of litres of groundwater over time scales of decades and even centuries. The remediation of polluted groundwater is driven by the need to reduce risks by achieving regulatory compliance, or in reducing liabilities, at the least cost. Variability in the nature of the pollutant source, the uncertainty in the pathways for plume migration and the wide scope of potential remediation scenarios due to site specific constraints suggest that integrated remediation technologies offer the greatest hope for the cost-effective remediation of polluted groundwater. Prior to investing in remedial technologies, decision makers want to know the benefits, both short term and long term, that will be derived from a proposed remedial activity. However, we are faced with a legacy of pollutant source zones that will generate plumes for many centuries, and perhaps longer. A significant paradigm shift is therefore required to manage groundwater pollution on appropriate time scales, a long-term strategy is required that challenges current approaches that are constrained by 30-40 year fiscal cycles.
- Research Organization:
- Stanford University, Stanford, CA (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM) (US)
- OSTI ID:
- 827617
- Resource Relation:
- Conference: Groundwater Quality 2001: 3rd International Conference, Sheffield (GB), 06/18/2001--06/21/2001; Other Information: PBD: 18 Jun 2001
- Country of Publication:
- United States
- Language:
- English
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