Estudio de línea base geoambiental de las subcuencas Vilcabamba, Santo Tomás y Alto Apurímac (Cusco - Apurímac) - [Boletín N 1]

Abstract

The study area includes large-scale mining projects that generate a large investment in our country; Hence the importance of studying how the quality of the water resource varies from the upper part of the Vilcabamba, Santo Tomás and Alto Apurímac sub-basins to the confluence of their main courses. Hydrochemical analysis based on the predominant ion identified 4 main hydrotypes: calcium bicarbonate, sodium bicarbonate, calcium sulfate, and sodium chloride. According to the analysis and interpretation, most of the bicarbonate sources are linked to the water-rock interaction of different geological units such as: Arcurquina Formation (carbonate rocks made up of bioclastic aggregates such as micritic and sparitic oolites, Albian-Cenomanian, Albian-Cenomanian), Formation Hualhuani (fine to medium-grained whitish quartz sandstones, Lower Cretaceous-Neocomian), Murco Formation (sandstones, siltstones, silt-claystones, Barremian-Aptian), Labra Formation (whitish gray quartz sandstones interspersed with calcareous sandstones, Upper Jurassic), Tacaza Group tuffs, lavas, brechas, andesitic breccia, composed of plagioclase, amphiboles), Cotabambas Unit (granodiorites (plagioclase, quartz and feldspars), tonalites (plagioclase and quartz) and diorites (plagioclase, amphibole). On the other hand, sulphated waters are related to zones of mineralization and hydrothermal alteration; this hydrotype in the Vil cabamba (Ampacho stream) is mainly associated with mining liabilities from old extraction activities; the chlorinated waters are related to hot springs. The exploratory statistical analysis of the 16 potentially toxic elements in the water (As, B, Be, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, Se, Sn, Ti and Zn) identified arsenic, copper, iron and manganese with a higher presence in the sampling stations (greater than 50%) and quantifiable dissolved concentrations (greater than the detection limit). For undetected data, the Robust Regression on order statistics (ROS) method was used. These statistical analyzes identified that high arsenic concentrations are related to hot springs; In the Santo Tomás sub-basin, the high concentrations of copper (0.0025 ppm in low water and 0.00222 ppm in avenues) are related to zones of mineralization; Iron is related to intrusive rocks and towards the upper part of the Vilcabamba sub-basin it is related to alteration zones with concentrations greater than 0.01290 ppm in avenues, while manganese presents a temporary behavior, varying its concentration randomly according to the season. (low water and avenue). The analysis of chemical and physicochemical quality of the water was carried out based on the total concentrations as indicated by the Environmental Quality Standards (ECAs) of the Peruvian regulations. The National Water Authority classifies these sub-basins for the use of vegetable irrigation and animal drinking (Category 3). The comparative analysis shows that around 95% of the sampling stations comply with the established standards, with the exception of some located in the Santo Tomás (Yavina and Cocha micro-basins) and Vilcabamba (Oropesa micro-basins) sub-basins that exceed the established limits, mainly of pH. , CE, Al, As, B, Li, Fe, Cu, Mn. From the joint analyzes, it was determined that the factors that alter the chemical quality of the water are mainly associated with natural agents (geological) and old extraction activities (environmental liabilities); The main natural agents are the zones of alteration, mineralization and thermal sources (modifiers of the chemical quality of surface waters according to their flow and concentration).