Conceptual Model

Abstract

On the basis of the above-mentioned data, a conceptual model of the geohydrological system is proposed. First, the physical boundaries are defined: the upper one is the topography (permeable ; positive sign ); the lower one, the volcano-sedimentary complex (impermeable); the western, the Andes (permeable; positive); the eastern, the Ocean (permeable; negative ); and the northern and southern ones, the respective watersheds , assumed to be permeable and positive. The input are the net vertical input (59–76 mm/year), entering by special mechanisms; groundwater inflow ; and the contribution of losing streams , e.g. the Senguerr River. The main output is the ocean, followed by the domestic supply and the oil industry, though currently production water is re-injected . Intra-system transport is not very significant and occurs in the SGS, due to the occurrence of semi-confined aquifers . In this chapter, aquifer vulnerability is discussed; in order to assess it with the available data, the GOD method —developed by Foster and Hirata (1991)—was applied. It uses the indicators groundwater occurrence, overall lithology of aquiperm or aquitard and depth to groundwater table , with values ranging from 0 (negligible) to 1 (extreme). In this book, the vulnerability of the phreatic, semi-confined and confined aquifers of the SGS is assessed. In the phreatic aquifers, the values obtained are 0.52–0.7 (high); in the semi-confined, 0.273–0.343 (low to moderate); and in the confined, 0.065–0.084 (negligible). As the method considers an exogenous contaminant burden , reference is made to possible endogenous impact sources.