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

WATER QUALITY INTERACTIONS
parkland to > 500 m from the river and may be considered to give background urban metal
concentrations. Similar low levels of metal concentration across the aquifer in more
industrialised areas indicate that the impact of industry on the levels of heavy metals in the
groundwater is perhaps lower than expected. Taking into account both sides of the river nine
of the 18 profiles did not display concentrations above the background. Movement of heavy
metals across the groundwater-surface water interface was investigated at a particular site by
the use of multilevel sampling techniques. The results of this work will be discussed in the
next section in conjunction with other water quality data from the same plume.
7.6 Discharge across the groundwater-surface water interface of a multi-
component contaminant plume
Groundwater plumes located using the riverbed piezometers were sometimes found to contain
a cocktail of several different contaminant types, both inorganic and organic, that may be
associated with metals-related industry. Such was the case for Profile 8, where an acidic
plume was found discharging from one bank, with elevated levels of nickel, zinc, copper,
aluminium, fluoride, sulphate, nitrate, TCE and TCA. A combination of data is presented to
show on a local scale the processes occurring during the discharge of the contaminant plume
across the riverbed. The interpretation of the multilevel data is based on upward vertical flow
as indicated by the 2D flow modelling of Profile 8, and field measurements that indicate
heads of 1-4 cm in all the piezometers relative to DWF river levels. However, there is a
degree of uncertainty as heterogeneity within the sediments and the bed forms may lead to
some degree of lateral flow both inwards from the bank and down river.
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