Ground for concern



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.

farmingEvidence 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.


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