Raised to the ground

STEPHEN Forster, director of groundwater and geotechnical surveys at the British Geological Survey, who has conducted studies of groundwater in 30 countries, reports that the resource is becoming increasingly polluted. He also points out that it is being abstracted at unsustainable rates in many areas, seriously depleting reserves. "An uncontrolled drilling of wells causes the overall rates of withdrawal from acquifers to greatly exceed their replenishment from rainfall and other sources, over decades or more," informs Forster. Groundwater amounts to 97 per cent of the earth's freshwater resources -- excluding what is locked in polar ice caps -- and at least 1,500 million people worldwide depend on it for drinking water. A rapidly growing population has placed such water under increasing pressure in recent decades (Our Planet, Vol 8, No 3).

Derived mainly from rainwater, groundwater can be neither readily observed nor directly measured. However, in areas with a permeable subsoil, excess rainwater seeps into the soil and joins the water-table below. It takes years or even decades for rainwater to reach an acquifer, a water-bearing stratum of permeable rock. On joining the aquifer it begins a long and slow journey further underground. The rates at which it travels could range from a few millimetres to a few metres per day. Eventually, it finds other outlets such as riverbeds, wetlands, natural springs, human-made wells and even the sea. Interestingly, some samples of groundwater could be extremely old, derived from rain that fell hundreds or even thousands of years ago.

Overabstraction can cause serious problems. It often leads to a reduced yield of wells, which hikes the cost of pumping. In extreme cases, wells could even be abandoned, causing the premature loss of infrastructural investment. Moreover, the falling groundwater level can induce compaction of underground strata, leading to serious geological disturbances and subsidence of the land surface. This could produce costly damages to urban infrastructure and an increased risk of flooding. Besides, in coastal areas and islands, the overexploitation of groundwater results in the intrusion of saline water inland, causing the deterioration of groundwater resources.

Above all, pollution is playing havoc with the quality of groundwater. There is growing evidence that groundwater is being polluted by industrial and agricultural practices. The most common contaminants are nitrates, salinity, soluble organic compounds and under certain conditions, faecal pathogens (disease-causing microbes in human or animal stool).

Forster believes that there are two reasons for the pollution of urban groundwater. The first is the indiscriminate disposal of liquid effluents and solid wastes, coupled with inadequate sanitation arrangements. The second is the leakage of stored chemicals into the ground from industrial units. In rural areas, the use of harmful pesticides and fertilisers does the damage.

Underlying soil and rock formations could eliminate many water pollutants by natural, physical, chemical and biological processes. But under the present circumstances, Forster feels that the task is unmanageable because firstly, the capacity to do so does not extend to all water pollutants. And secondly, the effectiveness of the process varies, depending on the hydrogeological conditions of the area. This leaves an insidious and expensive problem at hand. "Clever, because it takes many years to show its full effect on the quality of water pumped from deep wells and expensive because, by this time, the cost of remedying the polluted acquifers will be too high," he reasons.

Being one of the most valuable natural resources possessed by many developing nations, immediate action is demanded for the maintenance and protection of groundwater. Surveys of the state of groundwater exploitation, acquifer pollution vulnerability and contaminant load under soil are required. But such concern is yet to be generated. "The fact that it is out of public sight has caused it to be out of the political mind," laments Forster.

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