Prediction of Water Movement
Through Soils — A First Step in Waste
Transport Analysis
R. WILLIAM NELSON, Senior Research Scientist
JAY R. ELIASON, Research Scientist
Geochemical and Geophysical Research
Battelle Memorial Institute
Pacific Northwest Laboratory
Richland, Washington
INTRODUCTION
With the growth of modern society and technology to support urbanization,
the amount of wastes of all kinds have multiplied significantly. Progress in waste
treatment has provided, and the developing technology will continue to provide,
better and more economical treatment methods and facilities. Even so, flow sheets
for treatment processes and facilities often show the disposal of a waste stream to
ground. Such disposal imposed on the greater use of fertilizers, pesticides, and
herbicides in agriculture, the traditional septic tank disposals and the possible accidental leakage into the ground from storage tanks and pipelines, emphasize the
importance of having realistic methods for predicting the movement of contaminants through the ground. Certainly the balance between safety and economy of
disposal can only be realistically evaluated by knowing prior to disposal the effects
and hazards involved. Such evaluations should rest upon a sound knowledge of
basic scientific phenomena rather than intuitive and subjective observation and
estimates.
The purpose of this paper is to interrelate recent theoretical advances in describing the flow of fluids in porous media to problems involving the transport of
pollutants through soils. This work is directly related to that earlier described by
Cearlock (1), in that some of the needed methods of flow analysis he referred to
are provided. First a brief review is presented of the three broad phases of analysis
necessary to predict waste transport through porous material.
Three broad phases of analysis are involved in predicting contaminant transport through porous media. They are: the macroscopic fluid flow analysis, the
microscopic flow analysis for diffusion and hydrodynamic dispersion, and the reactions or interactions of contaminants with the porous material, organic material
or biological components of the soil. These latter considerations are discussed in
greater detail and appropriately interrelated by Cearlock (1), and are only generally considered here.
The macroscopic flow analysis considers the large effects of the flow system
such as paths of flow, rates of flow, velocity distribution, travel times and any
other physical aspect of interest in the macroscopic flow systems. It involves
describing or predicting the energy relationship to the geometry of the flow system. An example is the linear energy dissipation and flow patns in a laboratory
column; or as a second example, the multidimensional paths of flow from a surface pond toward a nearby stream. Other important considerations in macro-flow
include the effects of heterogeneous soils found under real field situations and the
conditions of multi- or single-phase fluid flow. All of these factors are interrelated through the equations of the macroscopic flow analysis.
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