Modelagem hidrogeoquímica do sistema aquífero pelito-carbonáticoexistente no CNPMS da Embrapa Sete Lagoas/MG Brasil

Abstract

This dissertation is one of the byproducts of the technical cooperation agreement signed in January 2008 between the CNPMS, the DESA and COPASA. Aimed at characterizing and modeling the behavior hydrogeochemical groundwater aquifer system pelitic-carbonateexisting in the area comprising the CNPMS, located in the city of Sete Lagoas, Minas Gerais - Brazil, seeking to understand the natural processes resulting from water-rock interaction. We collected 600 soil samples, of which 17 were mineralogically characterized by X-raydiffraction In addition, 359 was collected groundwater samples, between the months of November 2010 and October 2011, 30 monitoring points, including 26 of them drain water Porous Aquifer Coverage and 4 capture water in the fissure-Karstic Aquifer . From the results of physical-chemical analysis of groundwater samples, and median temporal behavior of the main parameters was analyzed. Furthermore, it was calculated, using theprogram PHREEQC, the saturation index of major minerals occurring in the aquifer system studied. At another point, these same samples were classified according to type hydrochemical through a cluster analysis, from which defined three hydrochemical zoning, which are directly associated with the movement and transit time of groundwater in theaquifer system. A conceptual hydrogeochemical model was developed in order to characterize the geochemical and hydrochemical environments and thus describe the process of evolution of groundwater in the aquifer system. This model were asked the following interpretations.In the vadose zone, the performance of the combined process of evaporation and dissolution of minerals iron and aluminium provides a "evapoconcentration" these elements in the water, making it saturated goethite, hematite and gibbsite. Upon reaching the water table, groundwater is supersaturated in goethite, hematite and gibbsite, with a potential to precipitation of these minerals, both in the dry and in the wetseason. Moreover, reaches the groundwater unsaturated quartz, throughout the year. Regarding the k-mica product and its modification, kaolinite, they become susceptible to dissolution when the aquifer is achieved by pulses significant recharge of rainwater. For calcite, the waters of the upper aquifer Coverage unsaturated always showed up, due to not being in direct contact with the limestone. At the base of Porous Aquifer Coverage, which is in contact with saprolite, it appears that after significant episodes of rain, groundwater becomes present with the potential for solubilization k-mica, kaolinite and silica available to groundwater which becomes supersaturated in quartz. The silica content found in them is the change of silicate minerals, including kaolinite is the most stable, according to the diagrams of stability of aluminosilicates. The basal contact of the Aquifer Overlay the top of the limestone reactionenhances the dissolution of calcite in the rainy season, which, however, come to be supersaturated with respect to this mineral in the dry season.Groundwater percolates to the aquifer karst-fissure reaches the state of supersaturation in calcite, due to the direct and prolonged contact (enough) with limestone (carbonate). It is observed also that almost always reaches the groundwater aquifer karst already saturated inquartz, mica and kaolinite, except when it receives a significant recharge, due to significant rainfall events, making it about unsatured these minerals. Moreover, we note that there is a fall in ISGibsite waters of karst aquifer, leading to a precipitation occurs suppose this mineral oroxide / hydroxide aluminum in contact with the carbonate bedrock.