Ground for concern
STEPHEN FOSTER
argues that groundwater is undervalued
and urgently
needs protection
Groundwater is a vast, mystical - and threatened -
resource. Simply defined, it is water that accumulates under ground,
stored in the pores that exist in sediments like sand and gravel and in
the fractures in rocks such as sandstone and limestone. It amounts to 97
per cent of all the planet's fresh water, excluding what is locked in
polar ice caps, and at least 1,500 million people worldwide depend on it
for drinking water. It is thus of fundamental significance to human life
and economic development.
Groundwater can be neither readily observed nor directly measured, and so
remains something mythical or mystical to many people. It is in continuous
slow motion. In areas of permeable subsoil, excess rainwater infiltrates
the soil and the unsaturated layer below. When it reaches the water-table
and joins a so-called aquifer, it begins a long slow, underground journey,
typically at rates ranging from a few millimetres to a few metres per day.
Eventually it finds outlets, such as riverbeds, wetland seepages, natural
springs, man-made wells or even the sea. The discharge of groundwater
systems is the normal source of dry-weather flow in lowland rivers.
The rainwater often takes years or even decades to find its way down from
the soil to the water-table and most groundwater has long flow-residence
times under the
surface because aquifers have a very large storage volume, far greater
even than the largest of surface impounding reservoirs. Some groundwater
can be extremely old, partly derived from rain that fell hundreds or even
thousands of years ago.
People have exploited groundwater for millennia. The spring, where it
emerges from the earth, is synonymous with the beginning, the source of
life and the season of new growth. Ready access to perennial springs or
shallow wells has often been the single most important factor in locating
permanent human settlements.
Groundwater has many advantages over surface water for water supply:
- It is reliable in dry seasons or droughts because of the large storage.
- It is cheaper to develop, since, unpolluted, it requires little
treatment.
- It can often be tapped where it is needed, on a stage-by-stage basis.
- It is less affected by catastrophic events.
As a result groundwater has become immensely important for human water
supply in urban and rural areas in developed and developing nations alike.
Countless large towns and many cities derive much of their domestic and
industrial water-supply from aquifers, both through municipal wellfields
and through very many private boreholes.
More and more farmers all over the world are using groundwater to irrigate
their crops during the dry season. In the more arid areas, where rainfall
is low and less predictable, groundwater may be the only source of supply
for all types of agricultural activity, including watering livestock.
Resources under pressure
Yet groundwater resources are coming under increasing pressure from a
rapidly growing human population - both through an ever-increasing demand
and through a contaminant load on the land surface which is steadily
growing in volume and chemical complexity, especially in Southeast Asia
and Latin America.
Despite their importance, there is still not enough concern about
protecting groundwater resources. The fact that they are 'out of the
public sight' has caused them also to be 'out of the political mind' and
they are too often abandoned to chance.
Groundwater is now being abstracted at unsustainable rates in many areas,
seriously depleting reserves. This happens when uncontrolled drilling of
wells causes the overall rates of withdrawal from aquifers greatly to
exceed their replenishment from rainfall and other sources over decades or
more. This 'overabstraction' causes many serious problems. Often the yield
of wells is reduced and the cost of pumping increased. In extreme cases,
this may lead to the wells being abandoned, with premature loss of
infrastructure investment.
Deterioration and pollution
In some geological conditions, the falling groundwater level induces
compaction of underground strata and serious subsidence of the land
surface, causing costly damage to urban infrastructure and increasing the
risk of flooding. On many coasts and small islands, overabstraction is
leading to the intrusion of saline water inland, causing effectively
irreversible deterioration of groundwater resources.
Evidence is also accumulating that groundwater is becoming increasingly
polluted. The most common contaminants are nitrate, salinity, soluble
organic compounds (including synthetic toxic species) and, in certain
conditions, some fecal pathogens. The subsoil and the underlying soil and
rock formations can eliminate or attenuate many water pollutants by
natural physical, chemical and biological processes. But this natural
capacity does not extend to all types of water pollutants and varies
widely in effectiveness under different hydrogeological conditions, being
rather limited in the more vulnerable areas.
Serious pollution of groundwater occurs when contaminants are discharged
to, deposited on, or leached from the land surface, at rates significantly
exceeding the natural attenuation capacity. This is occurring widely as a
result of both the indiscriminate disposal of liquid effluents and solid
wastes from urban development with inadequate sanitation arrangements, and
of uncontrolled effluent disposal and leakage of stored chemicals into the
ground from industrial activity.
Intensification of agricultural cultivation can also lead - and has led -
to significant and widespread deterioration in groundwater quality in some
conditions. The principal problems are the leaching of nutrients and
pesticides, and increasing salinity in the more arid environments.
Groundwater pollution is insidious and expensive; insidious because it
takes many years to show its full effect in the quality of water pumped
from deep wells; expensive because, by this time, the cost of remediating
polluted aquifers will be extremely high. Indeed, restoration to drinking
water standards is often practically impossible.
Groundwater is one of the most valuable natural resources possessed by
many developing nations. Without proactive management and protection there
is a serious risk of irreversible deterioration on an increasingly
widespread basis. Under the pressure of the need to rapidly develop new
water supplies, there is rarely adequate attention to, and investment in,
the maintenance, protection and longer-term sustainability of
groundwater.
Action needed for maintenance and
protection
Rapid surveys of the state of groundwater exploitation, aquifer pollution
vulnerability and subsurface contaminant load are urgently needed. The
risk of pollution and the susceptibility of aquifers to the effects of
overabstraction can then be assessed and protection measures can be
prioritized and initiated. In some cases abstraction must be better
controlled, through a combination of regulation, pricing and incentives.
Similarly the risk of pollution must be reduced by incorporating groundwater
vulnerability as a factor in land-use planning and environmental controls.
Many countries need better focused monitoring of groundwater levels and
quality so that a clearer picture can be painted of the actual state of
resources and of what must be done to use them more effectively - and to
preserve them for future generations.
Professor Stephen Foster, who has worked on groundwater in 30 countries
and holds many awards, is Director of Groundwater and Geotechnical Surveys
at the British Geological Survey, and Chairman of the International
Association of Hydrogeologists' Burdon Commission on Hydrogeology for
Developing Nations.
