Environmental Engineering Reference
In-Depth Information
4.3
Groundwater
Groundwater pollution is usually associated with diffuse sources and because of that, it
has been omitted from monitoring and control under the effluent discharge approach to
water quality management applied in the past. Chapters 6,7, 9 and 10 present different
case studies related to the pollution of ground water resources in the Lake Chivero
catchment. The diffuse pollution sources investigated are related to municipal wastewater
and sludge reuse for the irrigation of pastures, and with specific urban sources - semi-
formal settlements, cemeteries and a solid waste disposal site. At all studied locations,
elevated levels of dissolved solids, nitrate, metals (Fe, Pb, Cd) and fecal coliforms were
found. All examined boreholes at the solid waste site show that the pH levels were lower
than normal within a range of 4 to 6. The highest concentrations with respect to coliforms
were found at several locations in the cemetery and at all studied locations in Epworth.
The results obtained in Chapter 6 show that the case, needing the most urgent and
immediate action, is related to the semi-formal settlement in Epworth, where the polluted
shallow aquifer serves as a water supply source for the population, which generates the
pollution. As a short-term measure, the people living in this area should be advised to
boil the water used for direct consumption or direct body contact. The longer-term
abatement measures have been discussed in more detail in the following section. The
groundwater pollution with respect to metals is also of concern as it prohibits the direct
consumption of groundwater for drinking or bathing purpose.
The spatial integration of the results with respect to groundwater quality and the
assessment of the extent of transport of pollutants along the aquifer require the mapping
of the available data with respect to the aquifer structure and its water quality. Localized
studies, as the ones presented in this topic, could serve as warning signals and should
point out the need to take urgent or long-term measures. However, the successful solution
of the problem and the process of recovery of the aquifer quality, as a result of
implemented abatement measures, could only be achieved if such spatial integration is
implemented in practice. The most appropriate tool for such an integration would be the
implementation of a GIS, which could provide the spatial data integration with respect to
rainfall, land use patterns, urban infrastructure, geological and climatic conditions in
addition to surface and ground water resources in terms of quantity, levels and quality.
The availability of information databases and their spatial reference could be used to
analyze links and interrelations between the different components, surface-ground water
interactions and the process of pollutants' transport. Such databases, if compatible, could
be extracted for incorporation into higher hierarchy models, as explained earlier in this
chapter.
5 TYPICAL POLLUTION SOURCES AND ABATEMENT
MEASURES
Diffuse pollution is difficult to identify and assess. Its remediation could be extremely
complex and costly, as it concerns the whole extent of natural water bodies. The recent
practice of diffuse pollution abatement measures is related to the preliminary retention
and partial treatment of storm water from densely populated urban developments and
highway runoff, before it reaches natural water bodies (Debo & Reese 2003). In many
