K.U. Weyer Ph.D., P.Geol., P.HG.
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada

© 2006 K. U. Weyer


Introduction

Groundwater flow is an effective agent for the transport of contamination in the subsurface. Groundwater flow systems can transport pollutants for short distances of 100 meter or less, or it can transport contaminations for distances exceeding several kilometers or 10th of kilometers.

Groundwater flows through pores in unconsolidated deposits (sand, silt, clay) and through joints and fractures in consolidated bedrock (shale, sandstone, limestone, dolomite). The openings in deposits and rock are called porosity and may reach from close to zero to more than 50 % of total rock volume. These pores may be more or less connected and thereby will be more of less permeable for water.

The topography of the groundwater surface is the determining boundary condition for groundwater flow. Groundwater flows always from highlands to lowlands, usually along curved flowlines such that water movement is downwards into the groundwater body in highlands (recharge areas) and upwards towards the groundwater table under lowlands (discharge areas). The driving force for groundwater flow is the gravitational force field. Modern gravitational groundwater dynamics revised a number of traditional concepts. In nature

(1) groundwater generally does not flow in the direction of the pressure gradient,
(2) groundwater generally does not flow parallel to the groundwater table, and
(3) groundwater flows in significant amounts through low permeability clay and mudstone layers.

The physics of groundwater flow, flow through low permeable layers, and regional groundwater flow is described in the following sections. Our goal is to show that groundwater, and thereby contamination, may seep vertically downwards from polluted areas and may not be monitored by routine installation of piezometers. The understanding of groundwater flow systems is a necessary condition for the design of effective monitoring systems, and thereby for any field investigation of subsurface contamination.

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