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

WATER QUALITY INTERACTIONS
(the furthest upstream of the riverbed profiles). The riverbed piezometers and the shallow
piezometers located on the river banks display a considerable contrast with the EC measured
in the surface water at the same location.
A general upward trend in EC values is observed in the riverbed piezometers downstream
across the aquifer which coincides with a change in land use, from parkland and residential
areas (first 4 riverbed profiles) to more industrial areas. Adjacent samples in the surface water
profile for the Tame taken on consecutive days 19-20/7/00 show two large step changes in the
EC of 30% (796 to 1035 μScm -1 ) and 47% (815 to 1200 μScm -1 ). These are associated with
temporal changes in the sewage treatment works (STW) discharges and different sampling
times. By comparison, hourly sampling at Profile 8 over an eight hour period on 26/7/00
showed an increase through the day in surface water EC of only 14% (825 to 941 μScm -1 ).
This daily variation makes it difficult to interpret the surface water profiles and relate them to
the discharge of contaminated groundwater. There is no conclusive evidence in the surface
water profile of any impact from the high EC plume located in the riverbed (Figure 7.1).
Data on EC and flow in the River Tame for 1998 from the gauging station at Water Orton
(Figure 7.2 a and b) show considerable (50-200 μScm -1 ) daily and weekly fluctuations in EC.
These are only partly explained by variations in STW discharge and probably indicate
multiple sources of flux to the river. Rainfall events are sometimes seen to produce a rapid
initial peak in EC reaching values of over 1,500 μScm -1 associated with the first flush of
urban run-off and overflow discharges from combined sewer overflows (CSOs). Levels of EC
then fall due to dilution by the subsequent drainage of less contaminated run-off.
243