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104 results on '"Werkema, Dale"'

11. GW/SW‐MST: A Groundwater/Surface‐Water Method Selection Tool

Author

Hammett, Steven, primary, Day‐Lewis, Frederick D., additional, Trottier, Brett, additional, Barlow, Paul M., additional, Briggs, Martin A., additional, Delin, Geoffrey, additional, Harvey, Judson W., additional, Johnson, Carole D., additional, Lane, John W., additional, Rosenberry, Donald O., additional, and Werkema, Dale D., additional

Published
2022
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14. The microbial community structure in petroleum-contaminated sediments corresponds to geophysical signatures

Author

Allen, Jonathan P., Atekwana, Estella A., Atekwana, Eliot A., Duris, Joseph W., Werkema, Dale D., and Rossbach, Silvia

Subjects
Microbial colonies -- Research, Soil microbiology -- Research, Microbial populations -- Research, Biological sciences
Abstract

The investigation of the interdependence between geoelectrical signatures at underground petroleum plumes and the structures of subsurface microbial communities revealed that through their growth and metabolic activities, microbial populations adapt to the use of petroleum as a carbon source and could strongly influence their geophysical surroundings.

Published
2007

17. MoisturEC: A New R Program for Moisture Content Estimation from Electrical Conductivity Data

Author

Terry, Neil, Day-Lewis, Frederick D., Werkema, Dale, and Lane, John W.

Subjects
Soil, Waste Disposal Facilities, Electric Conductivity, Electromagnetic Phenomena, Groundwater, Article
Abstract

Noninvasive geophysical estimation of soil moisture has potential to improve understanding of flow in the unsaturated zone for problems involving agricultural management, aquifer recharge, and optimization of landfill design and operations. In principle, several geophysical techniques (e.g., electrical resistivity, electromagnetic induction, and nuclear magnetic resonance) offer insight into soil moisture, but data-analysis tools are needed to "translate" geophysical results into estimates of soil moisture, consistent with (1) the uncertainty of this translation and (2) direct measurements of moisture. Although geostatistical frameworks exist for this purpose, straightforward and user-friendly tools are required to fully capitalize on the potential of geophysical information for soil-moisture estimation. Here, we present MoisturEC, a simple R program with a graphical user interface to convert measurements or images of electrical conductivity (EC) to soil moisture. Input includes EC values, point moisture estimates, and definition of either Archie parameters (based on experimental or literature values) or empirical data of moisture vs. EC. The program produces two- and three-dimensional images of moisture based on available EC and direct measurements of moisture, interpolating between measurement locations using a Tikhonov regularization approach.

Published
2018

25. Scenario Evaluator for Electrical Resistivity Survey Pre-modeling Tool

Author

Terry, Neil, Day-Lewis, Frederick, Robinson, Judith, Slater, Lee, Halford, Keith, Binley, Andrew Mark, Lane Jr, John, Werkema, Dale, Terry, Neil, Day-Lewis, Frederick, Robinson, Judith, Slater, Lee, Halford, Keith, Binley, Andrew Mark, Lane Jr, John, and Werkema, Dale

Abstract

Geophysical tools have much to offer users in environmental, water resource, and geotechnical fields; however, techniques such as electrical resistivity imaging (ERI) are often oversold and/or overinterpreted due to a lack of understanding of the limitations of the techniques, such as the appropriate depth intervals or resolution of the methods. The relationship between ERI data and resistivity is nonlinear; therefore, these limitations depend on site conditions and survey design and are best assessed through forward and inverse modeling exercises prior to field investigations. In this approach, proposed field surveys are first numerically simulated given the expected electrical properties of the site, and the resulting hypothetical data are then analyzed using inverse models. Performing ERI forward/inverse modeling, however, requires substantial expertise and can take many hours to implement. We present a new spreadsheet-based tool, the Scenario Evaluator for Electrical Resistivity (SEER), which features a graphical user interface that allows users to manipulate a resistivity model and instantly view how that model would likely be interpreted by an ERI survey. The SEER tool is intended for use by those who wish to determine the value of including ERI to achieve project goals, and is designed to have broad utility in industry, teaching, and research.

Published
2017

29. The Dual‐Domain Porosity Apparatus: Characterizing Dual Porosity at the Sediment/Water Interface.

Author

Scruggs, Courtney R., Briggs, Martin, Day‐Lewis, Frederick D., Werkema, Dale, and Lane, John W.

Subjects
POROSITY, POROUS materials, SEDIMENTS, GROUNDWATER tracers, ELECTRIC conductivity, FOREIGN exchange rates
Abstract

The characterization of pore‐space connectivity in porous media at the sediment/water interface is critical in understanding contaminant transport and reactive biogeochemical processes in zones of groundwater and surface‐water exchange. Previous in situ studies of dual‐domain (i.e., mobile/less‐mobile porosity) systems have been limited to solute tracer injections at scales of meters to hundreds of meters and subsequent numerical model parameterization using fluid concentration histories. Pairing fine‐scale (e.g., sub‐meter) geoelectrical measurements with fluid tracer data over time alleviates dependence on flowpath‐scale experiments, enabling spatially targeted characterization of shallow sediment/water interface media where biogeochemical reactivity is often high. The Dual‐Domain Porosity Apparatus is a field‐tested device capable of variable rate‐controlled downward flow experiments. The Dual‐Domain Porosity Apparatus facilitates inference of dual‐domain parameters, i.e., mobile/less‐mobile exchange rate coefficient and the ratio of less mobile to mobile porosity. The Dual‐Domain Porosity Apparatus experimental procedure uses water electrical conductivity as a conservative tracer of differential loading and flushing of pore spaces within the region of measurement. Variable injection rates permit the direct quantification of the flow‐dependence of dual‐domain parameters, which has been theorized for decades but remains challenging to assess using existing experimental methodologies. Article impact statement: Introducing a novel instrument designed to study the exchange of solute between mobile and less‐mobile porosity (i.e., dual‐domain behavior) near the sediment/water interface. [ABSTRACT FROM AUTHOR]

Published
2019
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33. Geophysics for Contaminant and Site Remediation

Author

AKINYEMI, Lukman, primary, Alausa, Shamsudeen Kunle, additional, Soule, Ralph Pollister, additional, Franklin, Ryan, additional, Bartruff, Anthony, additional, Bridge, Cas F., additional, Bizzell, Karson R., additional, Ramachandran, Kumar, additional, Buckman, Christopher, additional, Calkin, Scott, additional, Wehnert, Amy, additional, Mundell, John, additional, Brumbaugh, Ryan, additional, Gildea, Kevin, additional, Funk, Pilar Cuadra, additional, Phillips, Charles, additional, Werkema, Dale, additional, Atekwana, Estella E, additional, Aal, Gamal Z Abdel, additional, Hodges, Greg, additional, Veloski, Garret, additional, and Hammack, Richard, additional

Published
2015
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38. 4D TIME-LAPSE GRAVITY INVERSION

Author

Karaoulis, Marios, primary, Revil, Andre, additional, Minsley, Burke, additional, Todesco, Micol, additional, Zhang, Junwei, additional, and Werkema, Dale, additional

Published
2013
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40. 1DTempPro V2: New Features for Inferring Groundwater/Surface-Water Exchange.

Author

Koch, Franklin W., Voytek, Emily B., Day‐Lewis, Frederick D., Healy, Richard, Briggs, Martin A., Lane, John W., and Werkema, Dale

Subjects
GROUNDWATER monitoring, WATER temperature, GROUNDWATER flow, COMPUTER software, PARAMETER estimation, TIME-varying systems, HYDRAULIC conductivity
Abstract

A new version of the computer program 1DTempPro extends the original code to include new capabilities for (1) automated parameter estimation, (2) layer heterogeneity, and (3) time-varying specific discharge. The code serves as an interface to the U.S. Geological Survey model VS2DH and supports analysis of vertical one-dimensional temperature profiles under saturated flow conditions to assess groundwater/surface-water exchange and estimate hydraulic conductivity for cases where hydraulic head is known. [ABSTRACT FROM AUTHOR]

Published
2016
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50. 1DTempPro: Analyzing Temperature Profiles for Groundwater/Surface-water Exchange.

Author

Voytek, Emily B., Drenkelfuss, Anja, Day ‐ Lewis, Frederick D., Healy, Richard, Lane, John W., and Werkema, Dale

Subjects
GROUNDWATER temperature, COMPUTER software, USER interfaces, HYDROLOGY
Abstract

A new computer program, 1DTempPro, is presented for the analysis of vertical one-dimensional ( 1D) temperature profiles under saturated flow conditions. 1DTempPro is a graphical user interface to the U.S. Geological Survey code Variably Saturated 2-Dimensional Heat Transport ( VS2DH), which numerically solves the flow and heat-transport equations. Pre- and postprocessor features allow the user to calibrate VS2DH models to estimate vertical groundwater/surface-water exchange and also hydraulic conductivity for cases where hydraulic head is known. [ABSTRACT FROM AUTHOR]

Published
2014
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