Hydrogeochemistry and behavior of groundwater in the Río Claro basin, Biobío Region.

Abstract

 A hydrogeochemical study of the groundwater and surface water of the Río Claro hydrographic basin of the Yumbel quadrangle (VIII Region, Biobío), including their classification and behaviour is presented. 24 groundwater samples and 3 surface water samples from the río Claro system were chemically analysed. The grain size distribution of 4 soil samples was determined. Based on these results, the waters belong to the calcium bicarbonate and magnesium bicarbonate genetic types. The calcium and magnesium water types are in direct relation to the areas crossed, weathered granite and black basaltic sands, respectively. Mixed calcium-magnesium and magnesium-calcium waters, with high contents of total dissolved solids, were found at the igneous rock-sediment boundary, thus indicating the direction of subterraneous flow. Soil granulometry indicates that the area consists of residual material, product of the weathering of granitic rocks and accumulations of basaltic sands from the Antuco Volcano. This results in strong variations of effective porosity and permeability, which are specific characteristics for infiltration, movement and formation of aquifers controlled by lithology. Chemical analyses of subterranean waters demonstrate them to be apt for consumption, and irrigation without risk of soil alkalinisation and salinification.