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Ground Water

Shuangpo Ren, Andrew D Parsekian, Ye Zhang, Bradley J Carr
In granite aquifers, fractures can provide both storage volume and conduits for groundwater. Characterization of fracture hydraulic conductivity (K) in such aquifers is important for predicting flow rate and calibrating models. Nuclear magnetic resonance (NMR) well logging is a method to quickly obtain near-borehole hydraulic conductivity (i.e., KNMR ) at high vertical resolution. On the other hand, FLUTe flexible liner technology can produce a K profile at comparable resolution but requires a fluid driving force between borehole and formation...
May 15, 2018: Ground Water
David L Poulsen, Peter G Cook, Craig T Simmons, James L McCallum, Shawan Dogramaci
Hydraulic head differences across the screened or open interval of a well significantly influence the sampled water mixture. Sample bias can occur due to an insufficient pumping rate and/or, due to native groundwater displacement by intraborehole flow (IBF). Proper understanding of the sampled water mixture is crucial for accurate interpretation of environmental tracers and groundwater chemistry data, and hence groundwater characterisation. This paper uses numerical modelling to quantify sample bias caused by IBF in an un-pumped high-yield well, and the influence of pumping rate and heterogeneity on the volume of pumpage required to purge an IBF plume...
May 12, 2018: Ground Water
Robert J Agnew, Todd Halihan
The mechanisms leading to the formation of bubbles in springs and wells have received minimal attention beyond causation. Free phase gas quantification provides insight into a range of topics, from hazards that need to be managed to the economic value of soda waters. The presence of free-phase gas or vapor bubbles in groundwater may provide valuable information about the subsurface flow system. Additionally, free-phase gas or vapor bubbles may strip dissolved gasses from solution and introduce error into the assessment of gasses in springs, affecting analyses such as groundwater dating techniques...
May 8, 2018: Ground Water
R Chesnaux, S Santoni, E Garel, F Huneau
An analytical solution to calculate the recharge of unconfined aquifers with Dupuit-Forchheimer type flow conditions is proposed. This solution is derived from an existing closed-form analytical solution initially developed to determine groundwater travel time when the recharge of the aquifer is known. This existing solution has been modified to determine recharge when groundwater travel time is known. An illustration is given with a field case example for the Bonifacio aquifer of the island of Corsica (France), in the Mediterranean...
May 7, 2018: Ground Water
Aybulat Fatkhutdinov, Catalin Stefan
This study demonstrates the utilization of a multi-objective hybrid global/local optimization algorithm for solving managed aquifer recharge (MAR) design problems, in which the decision variables included spatial arrangement of water injection and abstraction wells and time-variant rates of pumping and injection. The objective of the optimization was to maximize the efficiency of the MAR scheme, which includes both quantitative and qualitative aspects. The case study used to demonstrate the capabilities of the proposed approach is based on a published report on designing a real MAR site with defined aquifer properties, chemical groundwater characteristics as well as quality and volumes of injected water...
April 27, 2018: Ground Water
Behzad Ataie-Ashtiani, Craig T Simmons, Dylan J Irvine
The term "convection" is commonplace in groundwater science. The transport equation that we routinely use is sometimes called the "Convection-Dispersion Equation". The term convection also often arises in connection with variable density groundwater flow processes, where groundwater flow is driven by buoyancy differences in fluid, created by differences in temperature and/or concentration. In this variable density groundwater flow context, convection is actually shorthand for free (or natural) convection...
April 25, 2018: Ground Water
Rui-Xuan Tang, Jing-Sen Cai, Tian-Chyi Jim Yeh
A first-order moment analysis method is introduced to evaluate the pore-water pressure variability within a hillslope due to spatial variability in saturated hydraulic conductivity (Ks ) during rainfall. The influences of the variance of the natural logarithm of Ks(lnKs ), spatial structure anisotropy of lnKs , and normalized vertical infiltration flux (q) on the evaluations of the pore-water pressure uncertainty are investigated. Results indicate different responses of pressure head variability in the unsaturated region and the saturated region...
April 25, 2018: Ground Water
Daniel Abrams, Henk Haitjema
Transit time distributions (TTDs) have a number of applications in the hydrologic sciences. Our work aligns with the group of researchers who use groundwater flow models to assess the transit time distribution of groundwater, not considering the other components of flow that comprise stream water (Kauffman et al., 2008; Sanford et al., 2012; Engdahl, 2017). If the input of a solute is ubiquitous over the watershed and known through time, then a convolution of the TTD and solute input yields the output concentration of groundwater discharging to a well or stream in the watershed over time (Małoszewski and Zuber, 1982)...
April 24, 2018: Ground Water
Peter F Andersen, James L Ross, Jon P Fenske
Groundwater models developed for specific sites generally become obsolete within a few years due to changes in: 1) modeling technology, 2) site/project personnel, 3) project funding, and 4) modeling objectives. Consequently, new models are sometimes developed for the same sites using the latest technology and data, but without potential knowledge gained from the prior models. When it occurs, this practice is particularly problematic because, although technology, data, and observed conditions change, development of the new numerical model may not consider the conceptual model's underpinnings...
April 17, 2018: Ground Water
James L Ross, Peter F Andersen
The Kalman filter is an efficient data assimilation tool to refine an estimate of a state variable using measured data and the variable's correlations in space and/or time. The ensemble Kalman filter (EnKF) (Evensen, 2004, 2009) is a Kalman filter variant that employs Monte Carlo analysis to define the correlations that help to refine the updated state. While use of EnKF in hydrology is somewhat limited, it has been successfully applied in other fields of engineering (e.g. oil reservoir modeling, weather forecasting)...
April 17, 2018: Ground Water
Mustafa Goodarzi, Jahangir Abedi-Koupai, Manouchehr Heidarpour
In this study, the impacts of climate change on crop water requirements and irrigation water requirements on the regional cropping pattern were evaluated using two climate change scenarios and combinations of 20 GCM models. Different models including CROPWAT, MODFLOW and statistical models were used to evaluate the climate change impacts. The results showed that in the future period (2017-2046) the temperature in all months of the year will increase at all stations. The average annual precipitation decline in Isfahan, Tiran, Flavarjan and Lenj stations for RCP 4...
April 15, 2018: Ground Water
Charles J Paradis, Emma R Dixon, Lauren M Lui, Adam P Arkin, Jack C Parker, Jonathan D Istok, Edmund Perfect, Larry D McKay, Terry C Hazen
The breakthrough curve obtained from a single-well push-pull test can be adjusted to account for dilution of the injection fluid in the aquifer fluid. The dilution-adjusted breakthrough curve can be analyzed to estimate the reaction rate of a solute. The conventional dilution-adjusted method assumes that the ratio of the concentrations of the non-reactive and reactive solutes in the injection fluid versus the aquifer fluid are equal. If this assumption is invalid, the conventional method will generate inaccurate breakthrough curves and may lead to erroneous conclusions regarding the reactivity of a solute...
April 15, 2018: Ground Water
Martinus Brouwers, Paul J Martin, Daron G Abbey, Jeremy White
Soil and groundwater contamination are often managed by establishing on-site clean-up targets within the context of risk assessment or risk management measures. Decision-makers rely on modelling tools to provide insight; however, it is recognized that all models are subject to uncertainty. This case study compares suggested remediation requirements using a site-specific numerical model and a standardized analytical tool to evaluate risk to a down-gradient wetland receptor posed by on-site chloride impacts. The base case model, calibrated to observed non-pumping and pumping conditions, predicts a peak concentration well above regulatory criteria...
April 6, 2018: Ground Water
Judith Schenk, Eileen Poeter, William Navidi
Information theory is the basis for understanding how information is transmitted as observations. Observation data can be used to compare uncertainty on parameter estimates and predictions between models. Jacobian Information (JI) is quantified as the determinant of the weighted Jacobian (sensitivity) matrix. Fisher Information (FI) is quantified as the determinant of the weighted Fisher Information matrix. FI measures the relative disorder of a model (entropy) in a set of models. One-dimensional models are used to demonstrate the relationship between JI and FI, and the resulting uncertainty on estimated parameter values and model predictions for increasing model complexity, different model structures, different boundary conditions, and over-fitted models...
March 31, 2018: Ground Water
Laura Foglia, Iacopo Borsi, Steffen Mehl, Giovanna De Filippis, Massimiliano Cannata, Enric Vasquez-Suñe, Rotman Criollo, Rudy Rossetto
No abstract text is available yet for this article.
March 31, 2018: Ground Water
Todd W Rayne, Kenneth R Bradbury, Jacob J Krause
A rural subdivision in south central Wisconsin was instrumented with monitoring wells and lysimeters before, during, and after its construction to examine the impacts of the unsewered subdivision on groundwater quality and quantity. Prior to construction, the 78-acre (32 hectare) site was farmland. Sixteen homes were constructed beginning in 2003. Initial monitoring from 2002-2005 showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate-N values as high as 30 mg/l and some detections of the herbicide atrazine...
March 30, 2018: Ground Water
W J de Lange, J P M Vink
We present a method to create a horizontal resistance layer at desired depth below soil surface to decrease seepage over a relatively large area. The layer is produced in a continuous process by means of numerous temporary screens of wells. Between each pair of screens groundwater flow is forced in horizontal direction. In the center of such flow, along virtual parallel flow lines, a chemical, viscous and dense fluid is injected that produces a clogging substance within several hours. The impact of density is overcome by the forced flow between screens...
March 30, 2018: Ground Water
Sergio Martos-Rosillo, Carolina Guardiola-Albert, Alberto Padilla Benítez, Joaquín Delgado Pastor, Antonio Azcón González, Juan José Durán Valsero
The correct characterization of aquifer parameters is essential for water-supply and water-quality investigations. Slug tests are widely used for these purposes. While free software is available to interpret slug tests, some codes are not user-friendly, or do not include a wide range of methods to interpret the results, or do not include automatic, inverse solutions to the test data. The private sector has also generated several good programs to interpret slug test data, but they are not free of charge. The computer program SlugIn 1...
March 26, 2018: Ground Water
A Scott Andres, Thomas P Ballestero, Mary L Musick
No abstract text is available yet for this article.
March 26, 2018: Ground Water
Stanley D Smith, Emeline Mathouchanh, Dirk Mallants
The hydraulic integrity of aquitards is generally assumed and relies on a few core-scale permeability measurements, drill-stem tests or textbook values. This approach is because hydraulic data across the full aquitard thickness is generally lacking. Proper assessment of aquitard integrity should be studied at the formation (spanning its entire thickness at a single point) or regional (formation properties at multiple locations throughout the basin) scale. One formation-scale approach uses environmental tracers and advection-dispersion modeling to constrain fluid flow rates...
March 24, 2018: Ground Water
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