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

GROUNDWATER FLUX
groundwater is a significant contributor. The values for Zn and Ni are in a similar range to
those derived from the baseflow and riverbed piezometer data (Table 8.1) but the mass flux of
Cr is considerably higher than the 0.03-0.1 kgd -1 calculated from the riverbed data. This
suggests either a significant groundwater source not detected in the riverbed sampling or that
Cr enters as a surface water or pipe end discharge either in dissolved or particulate form.
As discussed in the previous chapter, the possibility exists that acidic groundwater discharge
may mobilise contaminants from within the metal rich riverbed sediments. The mass loading
appears to be low enough not to have a significant adverse impact on the overall surface water
quality under current conditions. For example, the maximum mass flux for zinc of 5 kgd -1 , if
added to a typical dry weather flow of 166 Mld -1 at Perry Barr would produce a rise in
concentration of only 0.03 mgl -1 . The study of mass flux has so far focussed on a general
contaminant contribution across the study reach. It would be beneficial to consider the
possible contributions from some of the individual contaminant plumes identified and to
assess whether any remediation is worth attempting on an individual plume basis.
8.4 Mass flux from individual contaminant plumes.
The calculation of mass flux from a discharging groundwater plume requires specific
information on:
• the spatial extent of the plume discharge area;
• the distribution of contaminant concentration values within the plume;
• the spatial distribution of groundwater discharge rates to the surface water mixing zone
across the plume;
• the impact of retardation processes such as sorption on the mass flux;
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