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6
Groundwater quality and

contaminant hydrogeology

6.1 Introduction inants of groundwater include chemicals such as heavy
metals, organic solvents, mineral oils, pesticides and
The occurrence of groundwater contamination is a fertilizers, and microbiological contaminants such as
legacy of past and present land-use practices and poor faecal bacteria and viruses. Table 6.1 is a compilation
controls on waste disposal. Many raw materials and of the sources and potential characteristics of ground-
chemicals have had a long history of usage before water contaminants.
becoming recognized as hazardous. During this time, This chapter is first concerned with the quality of
handling and waste disposal practices have frequently water intended for drinking and irrigation purposes
been inadequate. Hence, it must be considered that as determined by international water quality stand-
any industrial site where hazardous materials have ards. Given the importance of water hardness to
been used is now a potential source of contamin- consumers and its apparent health benefits, a section
ated land. In the United States alone, the National provides background information on this water qual-
Academy of Science (1994) reported that there are an ity parameter. Following this introduction to water
estimated 300,000 to 400,000 hazardous waste sites quality, the principles of groundwater contaminant
in the United States and that, over the next three transport are then discussed in relation to non-
decades, 750 billion US dollars could be spent on reactive and reactive solutes and their behaviour in
groundwater remediation at these sites. In the United homogeneous and heterogeneous aquifer material.
Kingdom, with its long industrial history, there are The latter part of the chapter provides an overview of
estimated to be as many as 100,000 contaminated major polluting activities, including industrial, min-
land sites covering between 50,000 and 200,000 ha, ing, agricultural and municipal sources of contamin-
equivalent to an area larger than Greater London. ants, and concludes with a discussion of the causes
Added to this picture of industrial contamination, the and effects of saline intrusion in coastal regions.
drive towards self-sufficiency in agricultural produc-
tion and the increasing urbanization of the world’s
growing population directly threaten the quality of 6.2 Water quality standards
groundwater through the over-application of agri-
chemicals and the often uncontrolled disposal of The chemical composition of natural groundwaters
human and landfill wastes. is discussed in Section 3.3. In addition, groundwaters
As a definition, contaminated groundwater is may contain synthetic organic compounds and micro-
groundwater that has been polluted by human activ- biological organisms, for example organic solvents
ities to the extent that it has higher concentrations and pathogenic bacteria, introduced from sources of
of dissolved or suspended constituents than the surface contamination. To limit the possible harmful
maximum admissible concentrations formulated by effects of natural and introduced components of
national or international standards for drinking, groundwater, various measures have been developed
industrial or agricultural purposes. The main contam- to protect water users. Water quality criteria include