Abstract
<jats:p>In the locality of San Pedro (department of Colonia, Uruguay), dairy production and agriculture are the main activities, which require considerable volumes of good-quality groundwater. The aquifers used to meet these demands are a fractured aquifer composed of Paleoproterozoic granites, and a sedimentary aquifer composed of the Raigón Formation. To assess the quality and hydrodynamic behavior of both aquifers, a survey of water points, measurements of physicochemical parameters, groundwater sampling, and generation of piezometric maps were carried out. Major-ion analyses were conducted at the Laboratorio de Agua y Suelos of the Centro Universitario Regional Litoral Norte (CENUR-LN), and arsenic analyses were carried out at the Centro Especializado en Química Toxicológica (CEQUIMTOX) of the Facultad de Química, Universidad de la República. According to the chemical analysis results, groundwater from both aquifers is classified as sodium-calcium bicarbonate type, showing high arsenic concentrations and contamination by nitrates and by total and fecal coliforms, which is primarily associated with inadequate water and soil management in dairy farming. Groundwater from the fractured and sedimentary aquifers showed an average arsenic concentration of 0.017 mg/L, with maximum concentrations of 0.034 mg/L and 0.03 mg/L, respectively. Considering both aquifers, it was found that 27% of the wells exceed the standard set by the Instituto Uruguayo de Normas Técnicas (UNIT 833:2008), and 91% of the wells exceed the concentration recommended by the World Health Organization (WHO).</jats:p>