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HYDC07 12/5/05 5:32 PM Page 263

Groundwater pollution remediation and protection 263

Fig. 7.7 Conceptual model of a
wellhead protection area and associated
terminology. As shown, the zone of
contribution (ZOC) and the zone of
influence (ZOI) do not coincide. For the
ZOC, groundwater is removed from the
pumping well from only a relatively small
portion of the downstream area of the
well, but it may extend as far as the
groundwater divide on the upgradient side
of the well. By contrast, the downgradient
portion of the groundwater within the
ZOI is not drawn towards the pumping
well but continues downgradient, while
the ZOI does not extend to the upgradient
limit of the ZOC. However, experience
shows that if the ZOC is small, then the
ZOC and ZOI will generally overlap
(Livingstone et al. 1995).

zone, an attenuation zone and a management and drink production. As illustrated schematically
zone. Specific guidance is available in more complex in Fig. 7.9, the orientation, shape and size of the
hydrogeologic settings such as in confined aquifers SPZs are determined by the hydrogeological char-
(United States Environmental Protection Agency acteristics and the direction of groundwater flow
1991a) and fractured rocks (United States Environ- around each source. Steady-state groundwater flow
mental Protection Agency 1991b). modelling is used to define three zones (Zones I, II
In England and Wales, the Environment Agency and III) in each SPZ and a set of groundwater pro-
(1998) has established source protection zones (SPZs) tection policy statements set out the acceptability
that are applied to public water supplies (there are of various polluting activities in each zone, for ex-
nearly 2000 major sources) and private water sup- ample landfill operations and the application of liquid
plies, including bottled water, and commercial food effluents to land.