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

WATER QUALITY INTERACTIONS
cation that approaches the drinking water PCV of 12 mgl -1 which it regularly exceeds in the
shallow (mean 11.6 mgl -1 ) and riverbed piezometers (mean 14.5 mgl -1 ) and surface water
(mean 19.8 mgl -1 ).
Calcium is the dominant ion in the groundwater system, increasing from a mean of 79 mgl -1
in the abstraction wells to 137 mgl -1 in shallow groundwater and 147 mgl -1 in the river bed.
This is a result of increased calcite dissolution and contaminant inputs, most likely from
CaSO4 that is found extensively in building waste and made ground. The calcium
concentration in the riverbed piezometers generally increases downstream across the aquifer
from levels of ~ 60 mgl -1 in the parkland (0 km) to ~150 mgl -1 immediately downstream from
industrialised areas (Figure 7.11a). It is difficult to say whether this change is simply related
to changing land use and increasing anthropogenic sources or whether changes in the
underlying hydrogeology along the reach are also having an impact. Progressing downstream
the river first flows over the Upper Coal Measures and then across the Kidderminster
Formation, which increases in thickness downstream to the contact with the Wildmoor
Formation and then the Bromsgrove Formation. In addition, the bedrock is overlain by an
extensive alluvial aquifer that covers much of the flood plain to depths of 5 m . Due to a
limited sample distribution, previous work on abstraction well data was unable to conclude
that there was any distinctive hydrochemistry characterising the sandstone aquifer sub-units.
However, the alluvium is expected to have a distinctive hydrochemistry with a lower calcite
content than the sandstone. The low calcium waters observed at the upstream end of the
aquifer are under-saturated with respect to calcite, and may represent a local fast-flow system
through the thin sandstone and overlying alluvial gravel. Increasing calcium content may
indicate a rising proportion of discharge from the underlying sandstone in addition to the
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