Box 4

TAPPING GROUNDWATER RESOURCES IN THE CARACAS VALLEY

The city of Caracas relies on treated surface water derived from a number of reservoirs for its water supply. Increased demand as a result of rapid growth in the city s population (now exceeding 5 million inhabitants), the poor condition of the water distribution system and adverse climatic conditions have led to a serious deficit in the drinking water supply. Additionally, water losses from the distribution system have led to a rise in the water level, making it necessary to pump groundwater to prevent flooding of the underground transportation system. Exploitation of the Caracas aquifer has long been considered as the best approach to reducing the water deficit (currently 260 000 m3 per day) and avoiding engineering problems in the underground transport system and geotechnical problems in the basements of many buildings.

In 1994, the Agency launched a special technical co-operation project to provide key information on the potential and properties of the Caracas aquifer as an additional source of water. During the past year, hydrological, geophysical, chemical and isotopic data were collected to characterize and identify the sources of recharge to the aquifer, to study the dynamics of the groundwater, and to evaluate the vulnerability to pollution of different sectors of this aquifer located in an urban environment. The information indicated the existence of two groundwater subsystems: the shallow part of the aquifer, characterized by groundwater with fast circulation and highly vulnerable to pollution, and the deep part (below 50 m) with older groundwater, better protected from pollution and with good quality water for drinking purposes.

On the basis of the information obtained through this study, the location and design of new wells was proposed. Fifty new wells will be drilled during 1996 and it is expected that they will contribute to reducing the present water restrictions (up to 12 hours a day in some districts), providing more than 112 000 m3 per day (around 43% of the existing water deficit). These wells, together with other measures to reduce wastage and leakage to groundwater, will improve the availability of water to the population, especially in some outlying areas of the city where water is still distributed by trucks. Monitoring of the quality of the water pumped from the Caracas aquifer will be carried out by a laboratory being upgraded with Agency assistance.