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

WATER QUALITY INTERACTIONS
general under-saturation with respect to calcite), rather than the larger, more complex and
perhaps slower systems operating in the Tame Valley. Acidic conditions were observed in the
peat bogs of Sutton Park and this has increased the mobility of the heavy metals such that
values of copper in the riverbed piezometers are comparable with those in the Tame Valley.
The results indicate a conceptual model for groundwater contamination in the Birmingham
Aquifer that incorporates both diffuse and multiple point sources that generate contaminant
plumes which, subject to natural attenuation, discharge to the river system or abstraction
wells. Diffuse pollution by low levels of many contaminants was observed in the shallow and
deep groundwater throughout the Tame Valley associated with mains and sewer leakage (Cl,
NO3), widespread usage (Cl as a road de-icer) and atmospheric fall-out (SO4). Other source
areas of more limited spatial extent are associated with current and historical land use. The
riverbed piezometer profiles showed a general increasing trend in some contaminant
concentrations across the aquifer associated with changes in land use from parkland and
residential to more industrialised areas. For example, the minimum concentrations of sulphate
in the riverbed profiles rises from 45 mgl -1 to 69 mgl -1 across the study reach (Figure 7.7a).
The contaminant point sources may have considerable variability in size ranging from large
areas (100’s m 2 ) of made ground to localised areas (10’s m 2 ) associated with spills and
leakage from industrial processes. The resultant plumes may follow a flow path up to several
kilometres in length with a considerable vertical component through both fractures and matrix
to the final discharge point. The final location and extent of the plume discharge area to the
river is dependent on the groundwater/surface water interactions and the degree of lateral
dispersion. The average spacing between the riverbed piezometer profiles was ~ 400m and so
it is likely that a number of plumes were not detected by this coarse sample spacing.
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