The impact of urban groundwater upon surface water - eTheses ...

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provide refuge to benthic invertebrates that are the base of the aquatic food web (Battin, 1999,
Barnard et al.,1994). Hyporheic organisms are likely to show the effects of pollution from
discharging groundwater before organisms within the water column and so provide an
indicator of the impact of contaminated groundwater (Environmental Protection Agency (US),
1998).
Surface water exchange and storage within the hyporheic zone influences downstream
nutrient and contaminant transport, and may be associated with enhanced biogeochemical
transformation of these compounds in the surface water. Hyporheic flow paths are typically
small but if rates of chemical reactions are rapid enough and the volume of exchange great
enough then substantial modifications of surface water quality may occur (Choi et al., 2000,
Packman et al., 2000, Harvey et al., 1993).
2.1.3 Groundwater contamination
The natural background chemistry of groundwater resulting from recharge composition and
mineral dissolution can be substantially modified by a wide range of contaminants that may
be present as different phases within the subsurface environment. These include; synthetic
organic compounds, hydrocarbons, metals and other inorganics, and pathogens such as
viruses and bacteria. Conant (2000) summarised the factors that may help to determine the
impact of a contaminant present in the subsurface on a surface water body. They include:
1. physical and chemical characteristics of the contaminants;
2. geometry and temporal variations in the contaminant source;
3. transport mechanisms (advection and dispersion);
4. reactions (reversible and non-reversible).
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