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ENVIRONMENTAL RESEARCH BRIEF: SPATIAL HETEROGENEITY OF GEOCHEMICAL AND HYDROLOGIC PARAMETERS AFFECTING METAL TRANSPORT IN GROUND WATER
Citation:
Davis, J. A., J. A. Coston, C. C. Fuller, E. Dixon, AND K. M. Hess. ENVIRONMENTAL RESEARCH BRIEF: SPATIAL HETEROGENEITY OF GEOCHEMICAL AND HYDROLOGIC PARAMETERS AFFECTING METAL TRANSPORT IN GROUND WATER. U.S. Environmental Protection Agency, Washington, DC, EPA/600/S-93/006 (NTIS 94-114774), 1993.
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Description:
Reliable assessment of the hazards or risks arising from groundwater contamination and the design of effective means of rehabilitation of contaminated sites requires the capability to predict the movement and fate of dissolved solutes in groundwater. The modeling of metal transport in groundwater requires adsorption coefficients to describe ion adsorption to soils, sediments, and rock surfaces. Metal-ion sorption in natural systems is usually thought to be controlled by surface reactions with Fe and Al oxyhydroxides and organic coatings on particles. he importance of surface coatings makes it difficult to relate the bulk mineralogical comp6sdion of a sample to its adsorptive reactivity. Determining the predominant adsorbing surface in a mineral assemblage can be a useful approach to modeling adsorption with a surface complexation model. ne objective of this study was to search for a geochemical "indicator" of the mineral surface(s) controlling lead (Pb) and zinc (Zn) sorption on the aquifer sand. The spatial variability of parameters used in models for solute transport in groundwater are of significance in the simulations of solute movement. ariability of hydraulic conductivity has been shown to be a key cause of observations of macroscale dispersion in sand and gravel aquifers. Like hydraulic conductivity, adsorption coefficients and other geochemical properties of the porous medium are expected to be spatially variable. In this study, 14 continuous cores of subsurface material (approximately 4 meters in length and 5 cm in diameter) were collected from a shallow sand and gravel aquifer near Falmouth, Massachusetts where the spatial variability of hydraulic conductivity has been previously studied. Each core was sectioned into subsamples 10 cm in length, yielding approximately 500 subsamples in total. For about 400 of these subsamples, measurements were made of : 1) grain size distribution to estimate hydraulic conductivity and 2) lead (Pb2+) and zinc (Zn2+) adsorption for a constant set of experimental conditions (in an artificial groundwater solution at pH 5.3).