Hydrogeochemistry and behavior of groundwater in the Rio Claro basin, Biobio Region

A hydrogeochemical study of the groundwater and surface water of the Rio Cl aro hydrographic basin of the Yumbel quadrangle (VIII Region, Biobio), incl uding their classification and behaviour is presented. 24 groundwater sampl es and 3 surface water samples from the rio Claro system were chemically an alysed. The grain size distribution of 4 soil samples was determined. Based on these results, the waters belong to the calcium bicarbonate acid magnes ium 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 ro ck-sediment boundary, thus indicating the direction of subterraneous flow. Soil granulometry indicates that the area consists of residual material, pr oduct of the weathering of granitic rocks and accumulations of basaltic san ds from the Antuco Volcano. This results in strong variations of effective porosity and permeability, which are specific characteristics for infiltrat ion, movement and formation of aquifers controlled by lithology. Chemical a nalyses of subterranean waters demonstrate them to be apt for consumption, and irrigation without risk of soil alkalinisation and salinification.