Page 327 - Soil and water contamination, 2nd edition

314 Soil and Water Contamination

Figure 17.5 Conceptual diagram of the chalk aquifer of Dorset, highlighting the main geochemical processes
controlling groundwater composition. Adapted from Edmunds and Shand (2008a).
of bedrock geology on groundwater composition. The ‘hot spots’ of high K concentrations
in northern Portugal, the eastern Pyrenees and the Massif Central in France are related to
Hercynian granite intrusions. Enhanced K concentrations are also found in the young
alkaline volcanic rocks in Italy. Furthermore, many wells in the Carpathian Mountains
and Dinaric Alps also exhibit elevated K concentrations. The high K concentrations in
northeastern Europe are probably related to the deep sedimentary basins from which the
mineral water is extracted. However, the higher concentrations in bottled mineral water
could also be explained by a cultural bias in taste, with a tendency for Eastern Europeans to
prefer stronger-tasting, more mineralised water (Reimann and Birke, 2010).
In addition to bedrock geology, the origin of groundwater (rainwater or infiltrated
surface water or relict sea water) may also an important factor that determines the variation
in groundwater composition, especially in coastal areas. Van den Brink et al. (2007) showed
that bedrock geology and groundwater provenance are the two major factors accounting for
the vast majority of the variation in chemical composition of shallow groundwater at the
supra-regional scale (> 100 km) in the Netherlands. Land use appeared less important and
emerged as a significant factor only for the chemical composition of recently (post-1950;
see Section 17.5) infiltrated groundwater at regional and local scales. This insight led to the
development of a European aquifer typology intended to facilitate the assessment of the
major groundwater composition at the continental scale (Wendland et al., 2008; Pauwels
et al., 2009). This typology subdivides the European aquifers into eight major types, based
on aquifer rock. Each of these aquifer types has its typical range with respect to porosity,
permeability, and hydrochemistry. Some primary aquifer types are further subdivided
according to secondary criteria that address geochemical and hydrological factors in
particular, which are partly controlled by bedrock geology. For example, the sands and gravels
aquifer type is further subdivided to account for variation in salinity, redox conditions, and
carbonate content. The latter two factors are mainly controlled by the groundwater residence
time, which appears to be related to the depositional environment. In general, due to their
long groundwater residence times and sufficient reduction capacity, glacial sands and gravel
deposits exhibit the typical behaviour of anoxic, reduced aquifers. By contrast, fluvial sand
and gravel deposits generally exhibit oxidised conditions, although exceptions occur, such
as the fine and organic-rich deposits in the Rhine-Meuse delta, which favour reduced
conditions.

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