IDENTIFICAÇÃO DA ZONA DE DISPERSÃO SALINA COM APLICAÇÃO DOS MÉTODOS ELÉTRICO E ELETROMAGNÉTICO NO DOMÍNIO DA FREQÜÊNCIA NO AQÜÍFERO COSTEIRO DE PLAYA PANAMÁ, COSTA RICA

Abstract

In Costa Rica, only a few coastal aquifers have been studied with the employment of geophysical methods. No scientific investigation which uses simultaneously two different methods to analyze the hydrogeologic properties of coastal aquifers, particularly to define salt intrusion has been done before in the area of study.The aquifer of Playa Panama, localized on the Pacific Coast, in the northwest part of the country (picture 1), has a moderate hydric potential, to be used for tourist purposes. The Average monthly rainfall in the region is 1944 mm/year, the potencial evapotranpiration is of 1930 mm/year (table 1). The aquifer is composed of basaltic angular conglomerates, mainly eroded from the Nicoya Complex. The aquifer geometry was analyzed through the application of Vertical Electrical Soundings (VESs) using a Schlumberger array, and conductivity measurement in the frequency domain. The results were complemented with stratigraphic, hydrogeological and hydrochemical data and suggest a decreasing of the aquifer’s thickness towards the sea, and a non polluted condition. The saline dispersion zone was also studied with both techniques, together with an electric section obtained with Wenner array. Both methods showed a high sensitivity in the area corresponding to the salt intrusion (pictures 8,9), which occurs at a depth of 15 m in the sediments and at a distance not exceeding 65 m landward from the high tide line.