Abstract

MADRIGAL-SOLIS, Helga; FONSECA-SANCHEZ, Alicia  and  REYNOLDS-VARGAS, Jenny. Hydrogeochemical characterization of Barva and Colima aquifers in the Central Valley of Costa Rica. Tecnol. cienc. agua [online]. 2017, vol.8, n.1, pp.115-132. ISSN 2007-2422.  https://doi.org/10.24850/j-tyca-2017-01-09.

Anthropogenic processes and interactions with the geologic material in the aquifers determine the chemical composition of groundwater. This study describes the hydrogeochemical characterization of Barva and Colima volcanic aquifers in the Central Valley of Costa Rica, to contribute to the understanding of the interactions between the two aquifers and determine whether there is a chemical evolution from the upper to the lower sections of Barva aquifer. During 2002-2004, from one to 9 sampling campaigns were performed in 51 locations and, nitrates and major ions were analyzed. The waters of the Barva and Colima were of mixed Ca-Mg-Na-HCO3 type, except for one site. An increase in bicarbonates, chlorides, nitrates, calcium, magnesium, sodium and potassium was found from the highlands to the lowlands of Barva aquifer, probably due to natural dissolution of rocks and leaching of ions from anthropogenic activities. In terms of nitrates, the highlands showed a median of 0.2 mg/l of NO3-N, while in the midlands and lowlands the median concentrations increased to 3.6 and 5.3 mg/l, respectively. However, the southwestern region in the study area showed an increased in HCO3 - and Na+ ions solely and lower nitrates concentrations with respect to the lowlands of Barva aquifer, with a median of 1.1 mg/l of NO3-N. Compared to the Barva aquifer, the Colima presented lower concentrations of nitrates in locations overlain by Barva aquifer, since nitrates from anthropogenic sources are diluted in this aquifer before their possible percolation into Colima aquifer. It is recommended ongoing monitoring programs to assess potential increases in nitrate concentrations in both aquifers.

Keywords : Barva and Colima aquifers; groundwater hidrogeochemistry; nitrates; Piper; Stiff.