Tools of groundwater protection below the city of Caracas, Venezuela.

Caracas city obtains drinking water from neighbouring catchment areas. Since these water resources are limited in quantity, groundwaters under the city are also considered for drinking water supply. Hydrochemical and isotope investigations show that the active recharge zone which may readily be contaminated reaches to about 50 m below floor. At greater depths the passive recharge zone extends to a maximum of 300 m and is by far less susceptible to groundwater pollution than the active recharge zone. The water balance indicates recharge to the Caracas aquifer of 2.1 m3/s from losses of the distribution and collector systems of waters as well as from subsurface lateral groundwater inflow into the Caracas valley. The active recharge zone of the aquifer beneath Caracas actually acts as an important microbiological reactor. It was proposed that exploitation of 20% of the total amount of groundwater re-charge from depths below 100 m would be sustainable and provide unpolluted water. Abstraction from the active recharge zone would require protection measures in the city area, which are not feasible.