The continuation of hydrogeological investigations in the north and east of the Valle Central, Costa Rica : final report 1984-87

This report is the conclusion of a three year investigation of the groundwater resources of the Valle Central in Costa Rica carried out jointly by BGS (British Geological Survey) and SENARA (Servicio Nacional de Aguas, Riego y Avenamiento) on behalf of ICAyA (Instituto Costarricence de Acueductos y Alcantarrillados) under the terms of their loan agreement with the World Bank. The objective of the investigation is to obtain a better understanding of the complex groundwater regime, principally of the Colima aquifers, and on this basis to make recommendations for a rational policy of further groundwater exploitation and the prevention of groundwater pollution. The study has been based on new hydrogeological information gained from the drilling of cored investigation boreholes and trial production boreholes and re-evaluation of existing data. A variety of hydrogeological techniques have been employed, including borehole flow logging and laboratory testing of rock hydraulic properties, and numerous water samples have been analysed for a wide range of chemical parameters. The laboratory tests of rock properties have been particularly important in providing new scientific data about the movement and storage of water in the lavas and pyroclastics. It is concluded that development of an additional 1000-1500 1/s of groundwater from the Colima aquifers is possible. The most effective strategy for development is the construction of new wellfields. Recommended areas for new groundwater abstraction include an extension of the Valencia Wellfield, a new wellfield within the area between Pitahaya and Barreal and a possible well field south of the Aeropuerto Juan Santamaria. The groundwater quality is generally excellent but there are indications of deterioration and, in some areas, aquifers are at risk of becoming seriously contaminated in the future. As groundwater development expands it will be increasingly important to monitor both groundwater levels and groundwater quality in order to maintain borehole yields and the potability of groundwater supplies.