CALL FOR PROPOSALS:

ORGANIZERS

  • Harvey Thorleifson, Chair
    Minnesota Geological Survey
  • Carrie Jennings, Vice Chair
    Minnesota Geological Survey
  • David Bush, Technical Program Chair
    University of West Georgia
  • Jim Miller, Field Trip Chair
    University of Minnesota Duluth
  • Curtis M. Hudak, Sponsorship Chair
    Foth Infrastructure & Environment, LLC

 

Paper No. 3
Presentation Time: 2:15 PM

A NEW METHOD FOR RAPID SOURCE ZONE DELINEATION AND DETERMINATION OF VADOSE ZONE CONTAMINANT BIODEGRADATATION RATES USING SURFICIAL GAS EFFLUXES


SIHOTA, Natasha and MAYER, K. Ulrich, Earth and Ocean Sciences, University of British Columbia, 6339 Stores Rd, Vancouver, BC V6T 1Z4, Canada, nsihota@eos.ubc.ca

Natural attenuation of organic contaminants (e.g. hydrocarbons) has become a widely accepted sustainable management option under a range of hydrogeologic conditions. In order to guide remedial action there is a need to develop approaches to rapidly delineate contaminated source zones in the field. In addition, demonstration that contaminant mass losses are occurring and estimation of mass loss rates can serve to inform choices on the type and extent of corrective action required, while also enabling more accurate estimation of source zone longevity.

One approach to achieve these objectives is to measure the carbon effluxes (CO2 and CH4) at the ground surface above the contaminated region. This method is suitable for identifying regions of active biodegradation and for quantifying depth and terminal electron acceptor-integrated biodegradation rates. In ecosystem sciences a common technology for this kind of measurement is a dynamic closed chamber system; however, this technique has not previously been applied at contaminated sites. Preliminary work in a crude oil-contaminated aquifer near Bemidji, MN demonstrated that measurements of surficial CO2 effluxes using the chamber methods are useful to delineate petroleum hydrocarbon containing source zones and to provide estimates of depth-integrated vadose zone hydrocarbon degradation rates.

In order to further test the capabilities of the method under different hydrogeologic conditions and to determine its sensitivity to a variety of contaminant classes, follow-up studies were conducted at several field sites, including a pipeline leak, former refinery sites, and biofuel releases. Results of these trials indicate that the method provides a robust tool for evaluating vadose zone biodegradation rates under a wide range of environmental conditions.

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