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

WATER QUALITY INTERACTIONS
vary over time. High levels of temporal variability were also observed in the contaminant
concentrations within the discharging groundwater, perhaps associated with changes in the
source, levels of natural attenuation, recharge and groundwater flow, and interaction with the
surface water.
It is difficult to say how representative the riverbed piezometer sampling results are to the
overall level of contaminant discharge to the Tame. The large heterogeneity of the system
means that small variations in the position of the piezometer are likely to produce significant
variations in concentration. Sample spacing, both along and across the river channel, needs to
be closer to characterise the system fully. Significant changes in contaminant concentrations
may also occur in the vertical plane including the upper 30 cm of the riverbed which is
difficult to sample. It is also very likely that some contaminant plumes were not detected and
that, even within the plumes that were, localised zones of high concentration were missed.
Nevertheless, despite these limitations, the riverbed data yield a valuable insight into the
processes and contaminant concentrations occurring across the riverbed and on the larger
scale of the study reach.
The results of the surface water sampling under dry weather baseflow conditions were
complex and difficult to interpret as the river displays considerable temporal variation in
terms of both flow and mass flux. There are several time scales apparent in these variations:
on a seasonal basis with changes in baseflow, and over a daily cycle determined by pipe
discharges primarily from the sewage treatment works. In addition to this temporal variation
there is the spatial variation of discharge accretion that occurs progressively downstream. All
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