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Ground Water

Paul M Barlow, Stanley A Leake, Michael N Fienen
The term capture, related to the source of water derived from wells, has been used in two distinct yet related contexts by the hydrologic community. The first is a water-budget context, in which capture refers to decreases in the rates of groundwater outflow and (or) increases in the rates of recharge along head-dependent boundaries of an aquifer in response to pumping. The second is a transport context, in which capture zone refers to the specific flowpaths that define the three-dimensional, volumetric portion of a groundwater flow field that discharges to a well...
March 15, 2018: Ground Water
Caitlin Barnes, Todd Halihan
A systematic review across USGS identified potentially induced seismic locations was conducted to discover seismic distance patterns and trends over time away from injection disposal wells. Previous research indicates a 10 km (6 miles) average where the majority of induced seismicity is expected to occur within individual locations, with some areas reporting a larger radius of 35 km (22 miles) to over 70 km (43 miles). This research analyzed earthquake occurrences within nine USGS locations where specified wells were identified as contributors to induced seismicity to determine distance patterns from disposal wells or outward seismic migration over time using established principles of hydrogeology...
March 13, 2018: Ground Water
Daniel K Burnell, Jie Xu, Scott K Hansen, Lawrence S Sims, Charles R Faust
Many studies indicate that small-scale heterogeneity and/or mobile-immobile mass exchange produce transient non-Fickian plume behavior that is not well captured by the use of the standard, deterministic advection-dispersion equation (ADE). An extended ADE modeling framework is presented here that is based on continuous time random walk (CTRW) theory. It can be used to characterize non-Fickian transport coupled with simultaneous sequential first-order reactions (e.g. biodegradation or radioactive decay) for multiple degrading contaminants such as chlorinated solvents, RDX, pesticides, and radionuclides...
March 13, 2018: Ground Water
Greg Keir, Nevenka Bulovic, Neil McIntyre
Setting limits on groundwater extractions is important to ensure sustainable groundwater management. Lack of extraction data can affect interpretations of historical pressure changes, predictions of future impacts, accuracy of groundwater model calibration, and identification of sustainable management options. Yet, many groundwater extractions are unmetered. Therefore, there is a need for models that estimate extraction rates and quantify model outputs uncertainties arising due to a lack of data. This paper develops such a model within the Generalised Linear Modelling (GLM) framework, using a case study of stock and domestic extractions in the Surat Cumulative Management Area, a predominantly cattle farming region in eastern Australia...
March 13, 2018: Ground Water
Zargham Mohammadi, Mohammad Javad Gharaat, Malcolm Field
Tracer breakthrough curves provide valuable information about the traced media, especially in inherently heterogeneous karst aquifers. In order to study the effect of variations in hydraulic gradient and conduit systems on breakthrough curves, a bench scale karst model was constructed. The bench scale karst model contains both matrix and a conduit. Eight tracing tests were conducted under a wide range of hydraulic gradients from 1 to greater than 5 for branchwork and network-conduit systems. Sampling points at varying distances from the injection point were utilized...
March 13, 2018: Ground Water
Rosemary Knight, Ryan Smith, Ted Asch, Jared Abraham, Jim Cannia, Andrea Viezzoli, Graham Fogg
The passage of the Sustainable Groundwater Management Act in California has highlighted a need for cost-effective ways to acquire the data used in building conceptual models of the aquifer systems in the Central Valley of California. One approach would be the regional implementation of the airborne electromagnetic (AEM) method. We acquired 104 line-kilometers of data in the Tulare Irrigation District, in the Central Valley, to determine the depth of investigation of the AEM method, given the abundance of electrically conductive clays, and to assess the usefulness of the method for mapping the hydrostratigraphy...
March 9, 2018: Ground Water
Julien Farlin, Piotr Małoszewski
The use of the annual cycles of stable isotopes to estimate the parameters of transit time distribution functions has been recently criticised by Kirchner who showed that if the catchment is heterogeneous the mean residence time calculated from the damping of the amplitude of the input signal is often underestimated by large factors. We modify Kirchner's initial analysis and show that the estimation bias is a function of the degree of heterogeneity. In low heterogeneity cases corresponding to permeable aquifers, the transit time distribution of a simple exponential model developed assuming a homogeneous medium deviates only slightly from the true transit time distribution, and thus estimated and true mean transit times are close...
March 6, 2018: Ground Water
Neil Terry, Frederick D Day-Lewis, Dale Werkema, John W Lane
Non-invasive 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, 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...
March 6, 2018: Ground Water
Tracie R Jackson, Keith J Halford, Philip M Gardner
Groundwater availability studies in the arid southwestern United States traditionally have assumed that groundwater discharge by evapotranspiration (ETg ) from desert playas is a significant component of the groundwater budget. However, desert playa ETg rates are poorly constrained by Bowen Ratio energy budget (BREB) and eddy-covariance (EC) micrometeorological measurement approaches. Best attempts by previous studies to constrain ETg from desert playas have resulted in ETg rates that are within the measurement error of micrometeorological approaches...
March 6, 2018: Ground Water
Mark Ranjram, James R Craig
A simple and fast treatment of hydrogeologic features with irregularly shaped boundaries in two-dimensional analytic element groundwater flow models is presented. The star domain shapes of the features are restricted to closed shapes represented as smooth and continuous single-valued functions of distance from a focus point, r̂θ. The element can be used to treat a variety of boundary and continuity conditions, including those of irregularly-shaped lakes or heterogeneities in hydraulic conductivity. The new element is demonstrated via some simple illustrative test cases and shown to be efficient, accurate, and much simpler to implement than existing solutions for irregular shapes...
March 6, 2018: Ground Water
M Adil Sbai
Advective particle tracking is a conventional groundwater modeling technique that is widely used as a screening tool but lacks robustness as a reliable method for general applications. In this work, we investigate the suitability of industry-standard, finite-difference, grid-based methods as an alternative to the conventional particle-tracking approach. The presented method is classified as a particular case of the more general forward- or backward-in-time advective-dispersive probabilistic transport approaches...
February 22, 2018: Ground Water
Charles Fitts
This proposed technique allows sensible and numerically stable behavior in multi-layer analytic element models when layers dewater. When saturated thickness approaches zero in an unconfined or fresh/salt interface domain, the domain transitions to a very thin confined domain with a minimum saturated thickness M. M is an adjustable input parameter, so you can make the horizontal flow in dewatered domains negligibly small by making the minimum saturated thickness very small. Vertical flows can pass through a dewatered domain, whether it is near the surface or at depth...
February 12, 2018: Ground Water
Emil O Frind, John W Molson
The delineation of wellhead protection areas (WHPAs) under uncertainty is still a challenge for heterogeneous porous media. For granular media, one option is to combine particle tracking (PT) with the Monte Carlo approach (PT-MC) to account for geologic uncertainties. Fractured porous media, however, require certain restrictive assumptions under this approach. An alternative for all types of media is the Capture Probability (CP) approach, which is based on the solution of the standard advection-dispersion equation in a backward mode, making use of the analogy between forward and backward transport processes...
February 8, 2018: Ground Water
Melinda L Erickson, Helen F Malenda, Emily C Berquist
Naturally occurring arsenic can adversely affect water quality in geologically diverse aquifers throughout the world. Chronic exposure to arsenic via drinking water is a human health concern due to risks for certain cancers, skin abnormalities, peripheral neuropathy, and other negative health effects. Statewide in Minnesota, USA, 11% of samples from new drinking water wells have arsenic concentrations exceeding 10 μg/L; in certain counties more than 35% of tested samples exceed 10 μg/L arsenic. Since 2008 Minnesota well code has required testing water from new wells for arsenic...
February 8, 2018: Ground Water
Liang Xiao, Ming Ye, Yongxin Xu
Transient confined-unconfined flow conversion caused by pumping in a confined aquifer (i.e., piezometric head drops below the top confined layer) is complicated, partly due to different hydraulic properties between confined and unconfined regions. For understanding mechanism of the transient confined-unconfined conversion, this paper develops a new analytical solution for the transient confined-unconfined flow towards a fully penetrating well in a confined aquifer. The analytical solution is used to investigate the impacts on drawdown simulation by differences of hydraulic properties, including transmissivity, storativity and diffusivity defined as a ratio of transmissivity and storativity, between the confined and unconfined regions...
February 8, 2018: Ground Water
William K Eymold, Kelley Swana, Myles T Moore, Colin J Whyte, Jennifer S Harkness, Siep Talma, Ricky Murray, Joachim B Moortgat, Jodie Miller, Avner Vengosh, Thomas H Darrah
Horizontal drilling and hydraulic fracturing have enhanced unconventional hydrocarbon recovery but raised environmental concerns related to water quality. Because most basins targeted for shale-gas development in the USA have histories of both active and legacy petroleum extraction, confusion about the hydrogeological context of naturally occurring methane in shallow aquifers overlying shales remains. The Karoo Basin, located in South Africa, provides a near-pristine setting to evaluate these processes, without a history of conventional or unconventional energy extraction...
February 6, 2018: Ground Water
Rebecca L Kreuzer, Thomas H Darrah, Benjamin S Grove, Myles T Moore, Nathaniel R Warner, William K Eymold, Colin J Whyte, Gautam Mitra, Robert B Jackson, Avner Vengosh, Robert J Poreda
Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south-central New York...
February 6, 2018: Ground Water
Peng Huang, Ting Fong May Chui
The hyporheic zone is the saturated interstitial space surrounding a stream. Water actively moves into, through, and out of the hyporheic zone, resulting in hyporheic exchange (HE), which is crucial to the physicochemical and biological processes in these systems. The HE in pool-riffle sequences is one of the most common forms of HE and has received a vast amount of attention. This study aimed to derive empirical equations to predict the scale, residence time and flux of HE in a single pool-riffle sequence by considering stream discharge, bedform geometry, streambed hydraulic conductivity, and groundwater flow...
February 1, 2018: Ground Water
Jennifer S Harkness, Kelley Swana, William K Eymold, Jodie Miller, Ricky Murray, Siep Talma, Colin J Whyte, Myles T Moore, Erica L Maletic, Avner Vengosh, Thomas H Darrah
Enhanced production of unconventional hydrocarbons in the United States has driven interest in natural gas development globally, but simultaneously raised concerns regarding water quantity and quality impacts associated with hydrocarbon extraction. We conducted a pre-development assessment of groundwater geochemistry in the critically water-restricted Karoo Basin, South Africa. Twenty-two springs and groundwater samples were analyzed for major dissolved ions, trace elements, water stable isotopes, strontium and boron isotopes, hydrocarbons and helium composition...
January 30, 2018: Ground Water
Richard W Healy, Sosina S Haile, David L Parkhurst, Scott R Charlton
Variably saturated groundwater flow, heat transport, and solute transport are important processes in environmental phenomena such as the natural evolution of water chemistry of aquifers and streams, the storage of radioactive waste in a geologic repository, the contamination of water resources from acid-rock drainage, and the geologic sequestration of carbon dioxide. Up to now our ability to simulate these processes simultaneously with fully coupled reactive transport models has been limited to complex and often difficult-to-use models...
January 29, 2018: Ground Water
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