Simplified modelling of pollutant transport in naturally-layered aquifers : a thesis submitted for the degree of Philosophiæ Doctor (PhD), 2015 February, Institute of Natural & Mathematical Sciences, Massey University

Abstract

Chemical species such as tracers or dissolved pollutants fl ow along with the slow-moving water as it makes its way through the complex porous structure of the aquifer; during this process they are dispersed in different directions. The rate of dispersion depends on the geometric characteristics of the porous structure and speed of the fl uid. Generally, groundwater systems have layered structures determined by different events in the geological processes that formed them. The layers in a system have di erent physical properties, and their thicknesses are not uniform. This naturally layered structure is used here to advantage by discretizing them into almost horizontal layers, where each may have different geometrical characteristics such as thickness permeability, dispersivitiy, porosity, etc. The system of advection-dispersion equations that model the

uid and species transport then have coeffcients that depend mainly on depth, but with a layer composition that may change with horizontal distance. The mean dynamic pressure (or mean hydraulic head) may be assumed constant vertically at each horizontal point if it is not in the vicinity of a well or where there is very small vertical ow. In the vicinity of recharge or pumping wells, the mean dynamic pressures or hydraulic heads for each sub-layer of the aquifer may be allowed to have different values for each different sub-layer. Steady-state fl uid fl ow is considered in this thesis in both confined and phreatic (unconfined) aquifers.