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Advanced Monitoring Approaches for Contaminant Behavior

Geophysical

Geophysical methods have been used in recent years to improve the characterization of near subsurface properties and processes. Because geophysical data can be collected from many different platforms (such as at the ground surface, between wellbores, and within wellbores), they can interrogate subsurface variability over a variety of spatial scales and resolutions. The main advantage of using geophysical data over conventional measurements is that geophysical methods can provide spatially extensive information about the subsurface in a minimally invasive manner at a comparatively high resolution.

The ability to meaningfully interpret the geophysical data in terms of flow and transport parameters requires an understanding of how geophysical signatures respond to a variety of subsurface alterations associated with the remedial treatment, such as the introduction of the remedial treatment into porous medium and the subsequent biogeochemical transformations that occur as a result of the treatment. The ability to geophysically distinguish processes associated with a remedial treatment is a function of many factors, including (1) the geophysical method and acquisition geometry that is employed; (2) the contrast in geophysical properties induced by different components of the treatment process; and (3) the scale of the region that is impacted relative to the footprint of the geophysical method.

Changes in Geophysical response

A particularly attractive feature of geophysical methods for subsurface process monitoring is the ability to collect a suite of continuous datasets at the same location as a function of time. Time-lapse geophysical imaging can be extremely useful for monitoring the temporal evolution of a process because it effectively "removes" the response of the geophysical signatures to the components of the system that are static (such as lithology) and illuminates the components of the system that change over time. These approaches have been effectively used for hydrological investigations to monitor vadose zone water infiltration and to track the spatiotemporal distribution of a polylactate amendment into Cr(VI)-contaminated groundwater and associated biogeochemical responses. Hubbard et al. (2008) also highlighted the significant control of heterogeneity on the location of amendment and biogeochemical transformations. Recent efforts have explored how geophysical methods can be used to track the evolution of pore structures and field-scale flowpaths associated with remediation-induced end-products, such as precipitates or gases and illustrated that strong feedbacks occur between remediation-induced biogeochemical transformations and flow characteristics at the field scale.

Application of complex resistivity and radar methods encompass three different geophysical attributes that are being developed for quantifying foam distribution and reactivity: radar velocity, complex resistivity phase response, and electrical conductivity.

Metals and Radionuclides in the Vadose Zone

Project Information

DOE Office of Groundwater and Soil Remediation

Technology Innovation & Development Areas

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