Geography Reference
In-Depth Information
Box 4.3 The groundwater quality time bomb
There have been many instances where groundwater contamination
has been related to damage to human health (e.g. too much fluoride
causing debilitating bone diseases, or too much nitrate causing lack of
oxygen in the blood; arsenic poisoning which seems to be an acute
problem in Bangladesh and West Bengal, India). Often it is long-term
exposure that is the problem rather than a one-off drink. This is because
groundwaters, unlike surface waters, are often fairly clean from sources
of infectious disease. However, this is not always the case, especially if
there is poor waste water management on the surface. It also depends
on how good a filter the soil and rock are within the aquifer. Indeed this
filtering property means that supplies from local wells are often not
chlorinated to remove the infectious carriers such as
E. coli
bacteria.
Human health problems have led to legal standards for the concen-
trations of many solutes in drinking water within most countries. Con-
tamination can take place quite some distance from the abstraction
point if the aquifers are well connected. Surface landfills, chemical
spills, leaking underground tanks at fuel stations and many other
surface management strategies lead to contamination of groundwater
from point sources. Diffuse sources such as fertilisers and pesticides
from farming may also be important contaminants in some areas. In
many places there is only a slow percolation of contaminants into some
aquifers. For some deep aquifers the water may take 50 years or more
to percolate down. In some developed countries the peak use of fertilis-
ers that were applied at rates that were too great for plant uptake
occurred in the 1970s or 1980s. Here, despite good environmental pro-
tection measures since then, and careful controls over the use of fert-
ilisers in groundwater source zones, the levels of solutes such as nitrate
may be continuing to increase in groundwater. There is therefore a long
time lag between surface management and groundwater quality
changes in some locations so that the groundwater problem only
emerges several decades after good management has been imple-
mented. One solution to this is to mix the contaminated groundwater
with water that has relatively low concentrations of solutes to enable
all of the water resource to be used. However, this would require mul-
tiple water sources for a supply area, which is not always possible.
Instead, very costly removal techniques have to be applied to strip out
the contaminants from the water.
