Hydrogeochemistry typology and quality of groundwater in the urban area of municipality of Lençóis, Bahia, Brazilian northeast

Abstract

The objective of this paper was to determine the types and quality of groundwater in fractured (metasedimentary) and granular aquifer in the urban area of the municipality of Lençóis, state of Bahia, Northeastern region of Brazil. For this, fifteen groundwater wells for sampling were analyzed in aquifers formed by quartzite rocks of the Chapada Diamantina Group, as well as, detrital cover. These parameters were analyzed: electrical conductivity, temperature, turbidity, total dissolved solids, pH, total hardness, HCO₃^-, Cl^-, NO₃^-, ^-, ^-, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺ e Fe³⁺. The results indicated that these waters are of good environmental quality for supply and potability, furthermore, they are freshwater, acid, soft and with low salinity. They waters are Na-Cl, and some points in a zone of the urban area indicate traces of nitrate, chloride, sulfate and calcium contamination, of anthropic source (wastewater). Based on the Gibbs diagrams, found that the groundwater in the urban area of Lençóis is of the rainfall dominance, evidencing a reduced water-rock interaction. The geogenic sources (natural) of the few dissolved ions in the waters can be attributed to hydrolysis process that occurs between the water and the quartz minerals constituent of rocks of the region.