Integration of 3-D Hydrogeophysical and Hydrogeochemical Data from Picos Area in Piaui State, Northeast Brazil: Progress Report

The groundwater resources of the semi-arid eastern margin of the basin are relatively poorly understood and a major international research program has been set up to shed some light on some of the current problematical observations using an integrated geophysical, hydrogeological and hydrogeochemical approach. There are important confined aquifers in the area of study (which is centred on Picos City) but a significant proportion of the groundwater resources is saline in nature. The boreholes tapping the regional aquifers at some locations provide inorganic hydrogeochemical and fluid resistivity data allowing partial mapping of saline plumes (of possibly hydrothermal nature) which pose a serious threat to major water supply schemes in the area. Joint transient electromagnetic and magnetotelluric 3-D surveys were conducted in the area in 1996 to provide constraints on the borehole data and to facilitate a better understanding of the hydrogeochemical anomalies in the area. Preliminary results from the geophysical surveys are discussed and compared with pre-existing hydrogeochemical data in this paper.