ORÍGENES DE CONTAMINACIÓN DE AGUAS SUBTERRÁNEAS EN UN SECTOR DE LA MARGEN IZQUIERDA DEL RÍO VIRILLA, SAN JOSÉ, COSTA RICA

Abstract

At least four wells located in Rohrmoser, San José had high concentrations of chloride (above500 ppm), which were over the drinking water limits set by Acueductos y Acantarillados (Water Supply and Sewage Service). The hydrogeochemical characteristics of groundwater in the urbanized area of the Central Valleywere analyzed, which was classified in general as a calcium magnesium-bicarbonate water which in the majo-rity of cases do not exceed the drinking water limits. Therefore, the anomolous concentrations found in thesewells, principally chloride, might be explained by a geothermal source. The hypothesis that the contaminationwas due to infiltration from the María Aguilar or Torres Rivers was also rejected, due to the fact that these surface waters had low concentrations in chloride. During long pumping tests, the concentrations of chloride andtotal hardness decreased almost 60%. This was due to the dilution by uncontaminated waters that were drawnto the well from outside of the plume of contamination.