Hydrogeologic facies models to delineate large-scale spatial trends in glacial and glaciofluvial sediments

摘要

Recent interest in contaminant transport in ground water has led hydrogeologists to the conclusion that predicting the movement of solutes requires information on the distribution of spatial trends and heterogeneities in porous media. Description of spatial trends has long been of interest to sedimentologists who have produced a large body of geologic information on the subject. In this paper, facies models are used to construct conceptual models of hydrogeologic facies for glacialmeltwater-stream sediment and till. These hydrogeologic facies models, which delineate large-scale trends in heterogeneity, are appropriate for use in designing hydrogeologic field tests and for estimating input to regional ground-water flow and transport models. This paper treats each facies as a homogeneous, anisotropic hydrogeologic unit. The models presented herein conceptualize the hydrogeologic relationships among facies and illustrate one method of converting the apparent chaos in nature into an orderly system that can be tested scientifically and modeled mathematically. The principles used to create conceptual models of hydrogeologic facies for the types of sediment considered in this paper can be extended to other sedimentary environments. It should be recognized, however, that such models do not address the small-scale heterogeneity present within individual facies. Additional basic research is required to measure hydraulic conductivity variation within representative hydrogeologic facies and to develop statistical descriptions to represent the variations. Such detailed descriptions of hydraulic conductivity may be necessary to describe ground-water flow at a local scale for analysis of contaminant transport.