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Rosemary Knight - One of the best experts on this subject based on the ideXlab platform.

  • the inversion of surface nmr t1 data for improved Aquifer Characterization
    Geophysics, 2013
    Co-Authors: Mike Mullerpetke, Jan O. Walbrecker, Rosemary Knight
    Abstract:

    ABSTRACTA crucial component in sustainable freshwater management is the reliable and cost-effective Characterization of groundwater Aquifers. A technique that allows noninvasive Characterization of shallow (<100  m) Aquifers is surface nuclear magnetic resonance (surface NMR). The measured parameter longitudinal relaxation time T1 provides a link to pore-scale properties and can be used to estimate the hydraulic conductivity of the sampled region. The recent development of an optimized acquisition scheme, phase-cycled pseudosaturation recovery (pcPSR), has significantly advanced our ability to acquire surface-NMR T1 data. Building on these findings, we developed an inversion scheme that can reconstruct the depth-distribution of T1 from pcPSR data. To stabilize the inversion, we took a staggered approach: We first determined the distribution of water content and effective transverse relaxation time T2*, and then we resolved the T1 structure. We tested the capability of the inversion in a synthetic study us...

  • The inversion of surface-NMR T1 data for improved Aquifer Characterization
    GEOPHYSICS, 2013
    Co-Authors: Mike Müller-petke, Jan O. Walbrecker, Rosemary Knight
    Abstract:

    ABSTRACTA crucial component in sustainable freshwater management is the reliable and cost-effective Characterization of groundwater Aquifers. A technique that allows noninvasive Characterization of shallow (

  • The Use Of Ground Penetrating Radar For Aquifer Characterization: An Example From Southwestern British Columbia
    8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, 1995
    Co-Authors: Jane Rea, Rosemary Knight
    Abstract:

    Twelve kilometers of ground penetrating radar (GPR) data have been collected over the Brookswood Aquifer in southwestern British Columbia. The data have been analyzed to assess how GPR can be used to characterize the distribution and connectivity of hydraulic units. We have used GPR to locate the Aquifer/aquitard boundary at several locations in the study area. The electrical contrast between these two materials makes the Aquifer/aquitard boundary an excellent target for GPR surveys. GPR was also used to reconstruct the paleo-environment of one area of the Brookswood Aquifer. This was accomplished by using a modification of the concept of architectural element analysis. Radar elements were identified in the survey and were assigned sedimentary parameters using data from trenching and drilling in the area. These elements were used to develop an interpretation of the paleo-environment that provides information about the spatial distribution of hydraulic units. INTRODUCTION Hydrogeologists require quantitative data to produce a realistic model of the spatial variabilities in hydraulic properties of an Aquifer. Such data can be difficult and expensive to obtain. A possible solution is to develop geophysical techniques as a means of Aquifer Characterization. Ground penetrating radar (GPR), a shallow geophysical technique, is well suited for this purpose as it can be used to image to a depth of up to 30m in sand and gravel environments. However, the image produced by a GPR survey does not supply hydrogeologic parameters directly. The focus of this paper is to investigate how GPR can be used for Aquifer Characterization. At an Aquifer scale of lo’s to 100’s of meters, the most fundamental aspect of Aquifer Characterization is the determination of the Aquifer’s hydraulic connectivity through mapping of Aquifer/aquitard interfaces. GPR can be used for this purpose due to the large contrast in electrical conductivity between the sand and gravel material of an Aquifer, and the clay rich material of an aquitard. The electrical conductivity of a material affects the penetration depth of radar waves, such that radar waves penetrate well through resistive material, but poorly through conductive material. Aquifers, composed of sands and gravels, are resistive, while aquitards, composed of clay rich materials, are electrically conductive. Therefore a radar survey will show good penetration in Aquifer materials and very poor penetration in aquitards. By exploiting this difference in radar response, the Aquifer boundaries can be mapped. At a smaller scale of centimeters to meters, the determination of the internal structure of an Aquifer is also important for Aquifer Characterization. For example, anisotropy within the Aquifer can cause significant differences in hydraulic properties and so must be identified where present. In addition, identification of sedimentary features aids in the determination of the paleo-environment that can provide important insight into the probable arcal extent and orientation of geological units. GPR can be used to image these features because of changes in their electrical properties. GPR and Sedimentology GPR has received considerable attention as a means of imaging sedimentary stratigraphy (Jo1 and Smith, 1992; Smith and Jol, 1992; Pratt and Miall, 1993; Greenhouse et al, 1987; Rea et al, 1991; Huggenberger et al, 1994). The key question that needs addressing is exactly which sedimentary aspects of the subsurface are imaged with GPR. A GPR survey, conducted by transmitting radar waves into the subsurface and recording the reflected energy, will image changes in the subsurface dielectric constant and conductivity. If these electrical properties correspond to changes in sedimentary parameters, then a GPR survey can be said to image sedimentary features. The dielectric constant and conductivity of earth materials are dependent upon composition and geometry of the solid and liquid components. Sedimentological classification is based upon five fundamental properties from which all others can be derived: grain composition, size, shapes, orientation and packing (Blatt et al, 1980). These five properties clearly are related to the composition and geometry of the solid component of a system. It is therefore reasonable to assume that a change in sedimentological properties at some boundary will cause a change in electrical properties. If the resulting change in electrical properties is large enough, then the sedimentary boundary will be imaged in a radar survey. The complicating issue is the liquid, usually water, component which does not play a role in sedimentary

Robert G. Maliva - One of the best experts on this subject based on the ideXlab platform.

  • Siliciclastic Aquifers Facies Models
    Springer Hydrogeology, 2016
    Co-Authors: Robert G. Maliva
    Abstract:

    Siliciclastic Aquifers are composed of sediment and rock that are dominated by silicate minerals, particularly quartz, feldspar, and clays. Siliciclastic Aquifer properties are controlled by the grain size, sorting, and diagenesis of the sediments. Well-sorted sand and gravel facies deposited by flowing water and air tend to have the highest hydraulic conductivities and form Aquifers, whereas low-energy clay-rich facies form confining and semiconfining strata. Facies models are provided for fluvial, alluvial fan, delta, eolian, glacial, and linear terrigenous shoreline (beach and barrier) depositional systems. Very large (multiple orders of magnitude) variations in hydraulic conductivity occur on multiple scales. A key issue for Aquifer Characterization is the connectivity and orientation of both clean sandy Aquifer strata and clay-rich confining strata, which varies between depositional facies.

  • Aquifer Characterization and Properties
    Springer Hydrogeology, 2016
    Co-Authors: Robert G. Maliva
    Abstract:

    Aquifer Characterization is broadly defined as processes by which the three-dimensional structure, hydraulic and transport properties, and chemistry of Aquifers are evaluated. Aquifer Characterization provides the foundation for groundwater modeling, which is ubiquitously used to evaluate sedimentary Aquifers. Detailed Aquifer Characterization is particularly important where solute transport is a concern, as Aquifer heterogeneity has a much greater impact on groundwater flow direction and rates than it does on Aquifer heads. An introduction to Aquifer hydraulic and transport parameters and basic Aquifer heterogeneity concepts is provided. Aquifer heterogeneity includes layered, lateral, and multiple-porosity systems. Aquifer Characterization starts with an initial conceptual geological model development, followed by evaluations of the type and scale of Aquifer heterogeneity and the values of petrophysical and hydraulic parameters, and finally, data analysis and synthesis, and groundwater flow and solute-transport modeling.

  • Evaluation of Aquifer Storage and Aquitard Properties
    Springer Hydrogeology, 2016
    Co-Authors: Robert G. Maliva
    Abstract:

    Data on Aquifer storage properties (storativity and specific yield) are required for transient groundwater models. Storativity is usually determined from Aquifer pumping tests using the Theis method or variations thereof. Quantification of specific yield is much more challenging because of the long time required (especially in fine-grained sediments) for gravity drainage to occur to completion. Evaluation of the properties of aquitards (semi-confining units) may also be a key element of Aquifer Characterization and modeling investigations. Heterogeneity, particularly a strong scale effect, and very slow groundwater flow rates are the main challenges associated with aquitard Characterization. Multiple methods should be employed to evaluate Aquifer storage and aquitard properties with the values subject to adjustment during the model calibration process.

  • Groundwater Model Development
    Springer Hydrogeology, 2016
    Co-Authors: Robert G. Maliva
    Abstract:

    Aquifer Characterization programs are usually performed with the objective of obtaining the data required to develop numerical groundwater models. Groundwater modeling starts with the development of a conceptual model, which is followed by the selection of a modeling code and model discretization. Initial values for the hydraulic and transport properties are then assigned to each model cell or element, which are subject to adjustment during the model calibration process. Predictive simulations are performed to evaluate the response of the Aquifer to various stresses (e.g., groundwater pumping scenarios). A deterministic approach has been taken for most groundwater models, in which the goal is to obtain a single solution that represents a ‘best’ estimate of future conditions. The alternative stochastic approach involves running a large number of simulations in a probabilistic framework to explore the range of possible future conditions. The basic premise of stochastic modeling is that due to an incomplete knowledge of the spatial variability of parameters, the decision is made to analyze all (or least numerous) plausible representations of the Aquifer. Stochastic modeling has high data requirements and is not a substitute for a robust Aquifer Characterization program.

  • Aquifer Characterization Program Development
    Springer Hydrogeology, 2016
    Co-Authors: Robert G. Maliva
    Abstract:

    Aquifer Characterization programs need to be designed to provide the specific data required for groundwater resources projects, which commonly involves the development of conceptual and numerical groundwater models. Available Characterization techniques are compiled in terms of the type of information provided and scale (investigated volume or radius of influence). Important considerations in the selection and implementation of Characterization techniques are the investigated volumes and resolution of the technique, scale of Aquifer heterogeneity, scale at which data will be used (e.g., model grid cell size), and whether or not solute transport is of concern. Selection of techniques should also consider the scale dependence of hydraulic conductivity values. Aquifer Characterization techniques have underlying assumptions and limitations, and field conditions requirements that constrain their successful implementation.

David O. Walsh - One of the best experts on this subject based on the ideXlab platform.

  • Multiecho scheme advances surface NMR for Aquifer Characterization
    Geophysical Research Letters, 2013
    Co-Authors: Elliot Grunewald, David O. Walsh
    Abstract:

    [1] Surface nuclear magnetic resonance (NMR) is increasingly used as a method to noninvasively characterize Aquifers. This technology follows a successful history of NMR logging, applied over decades to estimate hydrocarbon reservoir properties. In contrast to logging, however, surface methods have utilized relatively simple acquisition sequences, from which pore-scale properties may not be reliably and efficiently estimated. We demonstrate for the first time the capability of sophisticated multiecho measurements to rapidly record a surface NMR response that more directly reflects Aquifer characteristics. Specifically, we develop an adaptation of the multipulse Carr-Purcell-Meiboom-Gill (CPMG) sequence, widely used in logging, to measure the T2 relaxation response in a single scan. We validate this approach in a field surface NMR data set and by direct comparison with an NMR log. Adoption of the CPMG marked a landmark advancement in the history of logging NMR; we have now realized this same advancement in the surface NMR method.

Hugo A Loaiciga - One of the best experts on this subject based on the ideXlab platform.

Elliot Grunewald - One of the best experts on this subject based on the ideXlab platform.

  • Multiecho scheme advances surface NMR for Aquifer Characterization
    Geophysical Research Letters, 2013
    Co-Authors: Elliot Grunewald, David O. Walsh
    Abstract:

    [1] Surface nuclear magnetic resonance (NMR) is increasingly used as a method to noninvasively characterize Aquifers. This technology follows a successful history of NMR logging, applied over decades to estimate hydrocarbon reservoir properties. In contrast to logging, however, surface methods have utilized relatively simple acquisition sequences, from which pore-scale properties may not be reliably and efficiently estimated. We demonstrate for the first time the capability of sophisticated multiecho measurements to rapidly record a surface NMR response that more directly reflects Aquifer characteristics. Specifically, we develop an adaptation of the multipulse Carr-Purcell-Meiboom-Gill (CPMG) sequence, widely used in logging, to measure the T2 relaxation response in a single scan. We validate this approach in a field surface NMR data set and by direct comparison with an NMR log. Adoption of the CPMG marked a landmark advancement in the history of logging NMR; we have now realized this same advancement in the surface NMR method.