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

WATER QUALITY INTERACTIONS
source for the surface water contamination. No information is available on pipe discharge
concentrations across the aquifer but it is thought that some discharges comprise
contaminated groundwater abstracted for use in industrial processes and eventually
discharged to the river.
The surface water concentration profile for TCE (Figure 7.21a) is complex and shows
considerable variation between different sampling periods. It is not possible to relate high
levels of TCE in the groundwater at a particular location directly with local increases in
surface water concentrations. However, levels of TCE are maintained or increased across the
aquifer despite volatilisation and this indicates continuing input from what are believed to be
groundwater sources. There is perhaps a general increase for all the sampling periods in the
TCE surface water concentrations from 4 km onwards which may correspond to the changes
in land use and hydrogeological factors discussed for the inorganic water quality. There is
evidence to suggest that some of the TCE is being derived from intermittent sources, probably
pipe discharges. An example of this was the large peak detected on 11/5/01 at 3 km which
was not detected in any of the previous sampling. A similar high degree of variability is seen
in both the PCE and TCM surface water profiles (Figure 7.21 b and c). Reasons for the
variability between and within sampling periods may be a combination of factors:
1. changes in pipe and groundwater plume discharge rates and concentrations;
2. variation in river flow;
3. different temperatures and surface water mixing will alter rates of volatilisation;
4. the quantities detected are low and may be subject to large percentage errors in the
analyses; and
5. variation in the type and quantity of suspended particulate matter may alter sorption rates.
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