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

WATER QUALITY INTERACTIONS
mgl -1 in the riverbed), but with generally low 10-20 mgl -1 background levels. These
background levels are lower than might be expected given the high level of local contaminant
sources and may reflect microbial reduction. Evidence for reduction has been found in the
multilevel riverbed piezometers (Figure 7.8b). Profile 2 displays a rapid decline in nitrate
levels to below detection limits within 30cm of the riverbed, coincident with anaerobic
conditions and an Eh of 100 mv. A small subset of samples from the three multi-level
riverbed piezometers at profile 8 were analysed for nitrite which was detected in all the
samples with maximum values of 0.33 mgl -1 recorded.
Chloride concentration shows higher mean values than medians throughout the system
reflecting locally high levels of contamination with maximum values of 1,873 mgl -1 measured
in the riverbed piezometers. Median values varied from 46 mgl -1 in the abstraction wells to 41
mgl -1 in the shallow groundwater and 63 mgl -1 in the riverbed piezometers. Four of the deep
abstraction wells displayed low chloride values of between 10 to 26 mgl -1 , implying an older
uncontaminated source of groundwater, and current background levels from all waters in
Sutton Park averaged 25 mgl -1 . The widespread more elevated levels of chloride found
generally in the groundwater are a result of anthropogenic contamination from industry and
urban sources including a high loading from winter road salting, leaking mains and sewers,
and the degradation of chlorinated organic compounds. The surface water shows significantly
higher levels of chloride (median 162 mgl -1 ) than the groundwater as a result of sewage
inputs and the subsequent discharge to the river (>30% of DWF). Previous workers (Jackson,
1981, Ford, 1990) have indicated that high chloride concentrations in ground waters
abstracted from the Tame Valley may have resulted from the inflow of surface water into the
aquifer during periods of peak historical abstraction. The three abstraction wells sampled
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