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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 30 (1992), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A three-dimensional (3-D), advection-based numerical model has been developed for simulating two-well injection withdrawal tracer tests in heterogeneous granular aquifers, and the model has been applied to perform various simulations of an actual two-well tracer test conducted previously in a confined aquifer at a field site near Mobile, Alabama. Information obtained from a series of independent field tests is used as input in the model to account for the 3-D spatial distribution of the hydraulic conductivity (K) at the test site.The numerical model is based on a simplified, Lagrangian approach in which the transport of the tracer between the injection and withdrawal wells is modeled taking into account advection only. Processes such as dispersion, sorption, and chemical or biological reactions are neglected. Despite field data limitations and various simplifying assumptions, the model predictions of the withdrawal-well concentration breakthrough and of the mean tracer arrival times at various levels of two multilevel observation wells are in good overall agreement with the corresponding field observations.The results of this study indicate that it will be possible to construct realistic, predictive models of contaminant transport in heterogeneous granular aquifers if the necessary effort is made to obtain field measurements of the 3-D spatial distribution of hydraulic conductivity. The extent and feasibility of such an effort are expected to depend on the particular contamination problem at hand. Future research should be directed toward the problems of field measurement scale selection and the development of K distributions for models from sparse data sets.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 24 (1986), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper illustrates several interesting effects of aquifer stratification on the results of two-well tracer tests by means of a simplified computer model. In the model, it is assumed that the aquifer is horizontal, confined, of constant thickness and porosity, and perfectly stratified in the vicinity of the test wells. The nonuniform advection pattern is taken into account in detail by the model, but the local hydrodynamic dispersion is completely neglected. This simplified model has been verified in part by comparisons with available analytical solutions valid for homogeneous aquifers and in part by comparisons with the results of a two-well field experiment of Pickens and Grisak (1981a) which was performed in a locally stratified aquifer. The applications of the model to several field situations with assumed values of the relevant parameters show that the concentration versus time breakthrough curve measured at the withdrawal well during a standard two-well test would be very sensitive to variations of the hydraulic conductivity in the vertical. Without the use of supplementary observation wells with isolated multilevel sampling points, the standard test would give little useful information about the hydraulic and dispersive characteristics of an aquifer. Factors such as the length of the tracer injection period, the use of recirculation and the physical size of the experiment all have a strong effect on the breakthrough curve measured at the withdrawal well, making the interpretation of field results difficult unless aquifer stratification is measured and properly taken into account.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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