Geological Society of America
Release No. 06-22
Contact: Ann Cairns
For Immediate Release
June GEOSPHERE Media Highlights
Boulder, Colo. - The June issue of GEOSPHERE, published in electronic format only by the Geological Society of America, is now available online. Research published in GEOSPHERE spans all geology disciplines. Topics in this issue include: modeling nitrate transport in the Llagas sub-basin, California; new developments in modeling the movements of metals and radionuclides in groundwater; and use of GIS in detection and exploration of mineral deposits.
Access the issue at http://www.gsajournals.org/gsaonline/?request=get-current-toc&issn=1553-040X
High-resolution simulation of basin-scale nitrate transport considering aquifer system heterogeneity
Steven F. Carle, Atmospheric, Earth, and Energy Department, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA; et al. Page 195.
Prediction of future impacts from nitrate contamination in groundwater basins remains uncertain because nitrate sources are diverse, basin scale groundwater flow paths are lengthy, hydrostratigraphy is difficult to characterize, and hydraulic properties are heterogeneous. This study combines geostatistical techniques, parallel computing of flow simulation, and particle tracking to construct realistic scenarios of nitrate transport in the Llagas subbasin, California. A new geostatistical technique is used to incorporate well driller logs with uncertainty to constrain realizations of hydrofacies architecture. Nitrate transport simulation results spanning the 1940s to the future are consistent with observed nitrate contamination patterns, depth distribution and groundwater age trends. Comparison of results to a simplified homogeneous model with dispersivity coefficients indicates the heterogeneous model predicts much greater dispersion and the potential for future impacts to deeper wells, which is possible because geochemical data indicate dentrification is not likely to occur.
Identifying geochemical processes by inverse modeling of multicomponent reactive transport in the Aquia aquifer
Zhenxue Dai, Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA; et al. Page 210
The authors present a stepwise inverse modeling methodology that can include any number of conceptual models and thus consider alternate combinations of geochemical processes. Inverse modeling of reactive transport with multiple conceptual models helps to identify the most likely physical and chemical processes in the paleohydrology and paleogeochemistry of the Aquia aquifer. Identification criteria derived from information theory provide a quantitative basis for selecting the best among the candidate conceptual models.
Transport and biogeochemical reaction of metals in a physically and chemically heterogeneous aquifer
Timothy D. Scheibe, Pacific Northwest National Laboratory, Richland, WA 99352, USA; et al. Page 220.
Metals and radionuclides are important environmental contaminants of particular concern at legacy sites managed by the U.S. Department of Energy (DOE). Understanding and predicting their movement in the natural environment, including the subsurface (such as in groundwater), is an important goal of DOE-sponsored research. Predictions are needed for assessment of risks, design of engineered remediation strategies, and evaluation of long-term stewardship strategies. This research study demonstrates an approach for integrating different types of information from a real research site (including geophysical, microbiological, geochemical, and hydrologic data) into a highly resolved simulation model. The model is then applied to a hypothetical problem of uranium transport and bioremediation. Bioremediation is a potential strategy for improving groundwater quality by promoting the activity of naturally occurring bacteria that treat the contaminants directly in the subsurface and avoids the costs and risks of extracting contaminants from the subsurface and applying engineered treatments above ground. The results of the example problem illustrate the importance of properly characterizing spatially variable subsurface properties and demonstrate an advanced approach for integrating field data to accomplish this goal.
GIS analyses and favorability mapping of optimized satellite data in northern Chile to improve exploration for copper mineral deposits
Norbert Ott, Freie Universitšt Berlin, Berlin 12249, Germany; et al. Page 236.
Data integration and analyses within a geographic information system (GIS) can improve exploration and detection of mineral deposits. Ott et al. applied a GIS-based analysis and classification strategy of satellite data to the rich and well-explored porphyry copper province of northern Chile, attempting to recognize the distinctive signature of such giant ore deposits. Image-based favorability mapping is a supplementary exploration tool and can be used in conjunction with geophysical and geochemical data. To the already known geological and structural setting, optimized satellite data, transformed by various processing techniques, show typical rock alterations for selected training sites at La Escondida mining district and Quebrada Blanca mining district. These optimized data provide important surface indicators for detection and visualization of altered rocks and mineralization. This approach, in combination with geological field work, provides new impetus for exploration strategies and localization of hydrothermally altered rocks in less examined copper provinces of similar arid-semiarid climatic conditions throughout the world.
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