Susan Sharpless Hubbard

Stochastic Forward and Inverse Modeling: The “Hydrogeophysical” Challenge

Successful integration of geophysical and hydrogeological datasets represents a recent and major breakthrough in hydrogeological site characterization. As discussed in Chapter 1 of this volume, the value of integrating these datasets for characterization lies in the extensive spatial coverage offered by geophysical techniques and in their ability to sample the subsurface in a minimally invasive manner. However, this breakthrough is associated with a few difficulties. One difficulty resides in the non-unique relationships that sometimes exist between hydrogeological and geophysical attributes; integration of hydrogeological and geophysical data under non-unique conditions has been investigated by Rubin et al. (1992), Copty et al. (1993), Hubbard et al. (1997) and Hubbard and Rubin (2000). This non-uniqueness can exist even under idealized conditions of error-free measurements in natural systems comprised of multiple hydrogeologically significant units (i.e., Prasad, 2003), and it is only exacerbated by measurement errors. In applications, the situation becomes even more difficult because the rock type at the location associated with the geophysical attribute is almost always unknown, and thus the applicable petrophysical model is also almost always unknown. Another difficulty stems from the disparity between the spatial resolution of the geophysical attributes and the scale that characterizes the hydrogeological attributes, collected for example, through boreholes (c.f., Ezzedine et al., 1999). This scale disparity hinders efforts to develop unique and accurate relations between the two types of measurements, and introduces another source of uncertainty.

Hierarchical Bayesian method for mapping biogeochemical hot spots using induced polarization imaging

Author(s): Wainwright, HM; Flores Orozco, A; Bucker, M; Dafflon, B; Chen, J; Hubbard, SS; Williams, KH | Abstract:

Treatability Test Plan for an In Situ Biostimulation Reducing Barrier

This treatability test plan supports a new, integrated strategy to accelerate cleanup of chromium in the Hanford 100 Areas. This plan includes performing a field-scale treatability test for bioreduction of chromate, nitrate, and dissolved oxygen. In addition to remediating a portion of the plume and demonstrating reduction of electron acceptors in the plume, the data from this test will be valuable for designing a full-scale bioremediation system to apply at this and other chromium plumes at Hanford.

Hanford 100-D Area Biostimulation Treatability Test Results

Pacific Northwest National Laboratory conducted a treatability test designed to demonstrate that in situ biostimulation can be applied to help meet cleanup goals in the Hanford Site 100-D Area. In situ biostimulation has been extensively researched and applied for aquifer remediation over the last 20 years for various contaminants. In situ biostimulation, in the context of this project, is the process of amending an aquifer with a substrate that induces growth and/or activity of indigenous bacteria for the purpose of inducing a desired reaction. For application at the 100-D Area, the purpose of biostimulation is to induce reduction of chromate, nitrate, and oxygen to remove these compounds from the groundwater. The in situ biostimulation technology is intended to provide supplemental treatment upgradient of the In Situ Redox Manipulation (ISRM) barrier previously installed in the Hanford 100-D Area and thereby increase the longevity of the ISRM barrier. Substrates for the treatability test were selected to provide information about two general approaches for establishing and maintaining an in situ permeable reactive barrier based on biological reactions, i.e., a biobarrier. These approaches included 1) use of a soluble (miscible) substrate that is relatively easy to distribute over a large areal extent, is inexpensive, and is expected to have moderate longevity; and 2) use of an immiscible substrate that can be distributed over a reasonable areal extent at a moderate cost and is expected to have increased longevity.

Development of HydroImage, A User Friendly Hydrogeophysical Characterization Software

HydroImage, user friendly software that utilizes high-resolution geophysical data for estimating hydrogeological parameters in subsurface strate, was developed under this grant. HydroImage runs on a personal computer platform to promote broad use by hydrogeologists to further understanding of subsurface processes that govern contaminant fate, transport, and remediation. The unique software provides estimates of hydrogeological properties over continuous volumes of the subsurface, whereas previous approaches only allow estimation of point locations. thus, this unique tool can be used to significantly enhance site conceptual models and improve design and operation of remediation systems. The HydroImage technical approach uses statistical models to integrate geophysical data with borehole geological data and hydrological measurements to produce hydrogeological parameter estimates as 2-D or 3-D images.

Multi-scale Characterization and Prediction of Coupled Subsurface Biogeochemical-Hydrological Processes

To advance solutions needed for remediation of DOE contaminated sites, approaches are needed that can elucidate and predict reactions associated with coupled biological, geochemical, and hydrological processes over a variety of spatial scales and in heterogeneous environments. Our previous laboratory experimental experiments, which were conducted under controlled and homogeneous conditions, suggest that geophysical methods have the potential for elucidating system transformations that often occur during remediation. Examples include tracking the onset and aggregation of precipitates associated with sulfate reduction using seismic and complex resistivity methods (Williams et al., 2005; Ntarlagiannis et al., 2005) as well as estimating the volume of evolved gas associated with denitrification using radar velocity. These exciting studies illustrated that geophysical responses correlated with biogeochemical changes, but also that multiple factors could impact the geophysical signature and thus a better understanding as well as integration tools were needed to advance the techniques to the point where they can be used to provide quantitative estimates of system transformations.

Integrated Hydrogeophysical and Hydrogeologic Driven Parameter Upscaling for Dual-Domain Transport Modeling

Our research project is motivated by the observations that conventional characterization approaches capture only a fraction of heterogeneity affecting field-scale transport, and that conventional modeling approaches, which use this sparse data, typically do not successfully predict long term plume behavior with sufficient accuracy to guide remedial strategies. Our working hypotheses are that improved prediction of contaminant transport can be achieved using a dual-domain transport approach and field-scale characterization approaches.

Subsurface Biogeochemical Heterogeneity (Field-scale removal of U(VI) from groundwater in an alluvial aquifer by electron donor amendment)

Determine if biostimulation of alluvial aquifers by electron donor amendment can effectively remove U(VI) from groundwater at the field scale. Uranium contamination in groundwater is a significant problem at several DOE sites. In this project, the possibility of accelerating bioreduction of U(VI) to U(IV) as a means of decreasing U(VI) concentrations in groundwater is directly addressed by conducting a series of field-scale experiments. Scientific goals include demonstrating the quantitative linkage between microbial activity and U loss from groundwater and relating the dominant terminal electron accepting processes to the rate of U loss. The project is currently focused on understanding the mechanisms for unexpected long-term ({approx}2 years) removal of U after stopping electron donor amendment. Results obtained in the project successfully position DOE and others to apply biostimulation broadly to U contamination in alluvial aquifers.