April GEOSPHERE media highlights

Boulder, Colo. - The April issue of GEOSPHERE, published in electronic format only by the Geological Society of America, is now available online. This is a special issue on modeling groundwater flow and reactive transport in physically and chemically heterogeneous media. More papers on this topic will follow in the June issue.

Access the issue at http://www.gsajournals.org/gsaonline/?request=get-current-toc&issn=1553-040X

Modeling dense nonaqueous phase liquid mass removal in nonuniform formations: Linking source zone architecture and system response

Lawrence D. Lemke, Wayne State University, Detroit, MI 48202, USA; and Linda M. Abriola, Department of Civil and Environmental Engineering, Tufts University, Medford, MA 02155, USA. Page 74.

Dense nonaqueous phase liquids (DNAPLs) such as chlorinated solvents like tetrachloroethene (PCE) represent one of the most intractable sources of groundwater pollution. Following their accidental release, DNAPLs migrate into the subsurface in a complex fashion, invading pore spaces normally filled with water to varying degrees. They then dissolve very slowly under natural conditions, often over the course of many decades, forming a persistent source of contamination. This paper uses numerical simulations to study the distribution of PCE entrapped in high saturation pools and low saturation ganglia within a sandy aquifer with spatially varying hydraulic properties. Specifically, the study examines changes in the distribution of PCE in ganglia and pools and relates the reduction in dissolved contaminant concentration to changes in the ganglia-to-pool mass ratio of the contaminant throughout a simulated cleanup project. The results suggest that characterization of DNAPL contaminated sites in terms of their ganglia-to-pool mass ratio may be a useful tool to help predict the effectiveness of certain engineered remediation processes.

A chloride transport model for identifying sequential bioreactive systems of chlorinated solvents

Yunwei Sun, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA; and Xinjian Lu, Department of Management, California State University, East Bay, CA 94542, USA. Page 83.

A handy model is presented in this paper to evaluate biodegradation of chlorinated solvents. During biodegradation of chlorinated solvents dissolved in groundwater, chloride concentration is elevated relative to background conditions. Using the developed model, records of chloride concentrations can be used as supplemental information to estimate reaction rates and to interpret the bioreactive system of chlorinated solvents.

Geochemical interpretation of groundwater flow in the southern Great Basin

J.E. Koonce, Department of Geoscience, University of Nevada-Las Vegas, Las Vegas, NV 89154; Z. Yu (corresponding author), State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China; et al. Page 88.

This paper reports on a statistical method used to interpret the hydrogeochemical data in groundwater. The analysis results help identify groundwater sources and predict the contaminant transport.

Stochastic analysis of transport and multicomponent competitive monovalent cation exchange in aquifers

Javier Samper and Changbing Yang, Universidad de La Coruņa, ETS Ingenieros de Caminos, Campus de Elviņa s/n, 15192 La Coruņa, Spain. Page 102

The study of contaminant migration in physically and geochemically heterogeneous aquifers has been traditionally described in terms of random processes and has focused on the analysis of a single contaminant. This paper addresses for the first time the statistical analysis of a set of interacting and competing contaminants which undergo chemical reactions in heterogeneous aquifers. A novel method is presented which simplifies the complex equations describing the migration and chemical interactions of contaminants to the point that analytical expressions for large-scale effective migration parameters can be derived. These results will be relevant for groundwater contaminant studies and safety assessment of waste disposal.

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