CARACTERIZAÇÃO HIDROGEOQUÍMICA DOS AQUÍFEROS DA REGIÃO DA APA CARSTE DE LAGOA SANTA, MG

Hydrogeochemical characterization of aquifers in the region of EPA Lagoa Santa Karst, MG

Abstract

This hydrogeochemical study involves the Environmental Protection Area of Lagoa Santa Karst, 504km², north of Belo Horizonte. The aquifer lithologies concerned were the pelito-carbonate sequence of Sete Lagoas Formation, metapelites of Serra de Santa Helena Formation and granite-gneisses of Belo Horizonte Complex. The first one divides into Pedro Leopoldo Member, lower, composed by impure limestones, with pelitic intercalations, and Lagoa Santa Member, upper, containing pure limestones. The waters are calcium bicarbonated, secondarily mixed to sodium bicarbonated, when associated to basement and coverings. The concentrations of Ca²⁺ and Si⁴⁺ were fundamental for distinction between carbonate and noncarbonate aquifer units, also allowing the identification of mixed waters, elucidation of the recharge mean and horizontal and vertical compartmentalization of aquifer system. The lithological heterogeneity conferred on the lower Member led to its subdivision into four water types, while the waters of the Lagoa Santa Member are homogeneous, reflecting its lithological homogeneity. The high productivity of the deep wells is due to the dissolution of purest rock portions and to this location near faults and of lithological contact between the members, whereas in springs the intensity of karstification processes in purer limestones of Lagoa Santa Member controls the flow rate.