May 1, 2013, 2:00 PM - 4:00 PM, EDT (18:00-20:00 GMT)

You may also be interested in the following archive of this seminar:

• May 1, 2013

Recently, "large-dilute plumes" of chlorinated solvents have emerged as a peculiar challenge in environmental clean-up. This class of plume has several defining characteristics. These characteristics include biogeochemical conditions that result in slow contaminant degradation and that allow plume expansion, as well as matrix diffusion that results in secondary sources and that extends remediation timeframe. Research at these sites has highlighted key challenges and potential opportunities. Complicated fine-scale heterogeneity resulting from the interaction of migrating contaminants with subsurface lithology and hydrology is a particularly significant and recurring challenge — resulting in concentrated plume cores and the need for innovative-focused characterization and monitoring. Understanding the subsurface distribution of contaminants and how the plume is changing in time and space are keys to successful environmental response actions. Research and data on attenuation of contaminants resulting from physical assimilation along the flow path (such as a plume interacting with inactive pore spaces) and from degradation by abiotic and microbial processes have extended our knowledge of natural attenuation rates in aerobic-oligotrophic aquifers. The research indicates that aerobic processes, particularly abiotic degradation due to magnetite/minerals and aerobic cometabolism, are occurring in many large-dilute plumes. The attenuation rates are correlated with measurable parameters such as magnetic susceptibility or various microbial population metrics, including oxygenase enzyme activity probes, DNA composition/quantity, and total microbial counts. Consistent with the observed plume scales, the data confirm that aerobic degradation processes are slower than anaerobic degradation processes. Nonetheless, incorporation of these natural rates into models and predictions provides an important tool to aid in developing a comprehensive strategy for large-dilute plumes — mitigating the requirement for complete removal during source treatment and encouraging combined remedies as well as the development of amendments to sustainably and cost-effectively enhance degradation rates.

• Kenda L Neil, CIV EXWC, EV32 (Kenda.Neil@navy.mil)
• Brian Looney, Savannah River National Laboratory (brian02.looney@srnl.doe.gov)
• Fred Payne, ARCADIS (Fred.Payne@arcadis-us.com)
• Karla J Harre, CIV EXWC, EV3 (karla.harre@navy.mil)

• Jean Balent, U.S. EPA Technology Innovation and Field Services Division (balent.jean@epa.gov)

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