Potentially toxic elements in waters from Los Humeros geothermal power plant: Natural or anthropogenic?

Abstract

Identifying sources of potentially toxic elements (PTE) in groundwater in Los Humeros geothermal power plant, Puebla, Mexico, a site with more than 20 years of electricity generation history through geothermal resources, is a great challenge; especially when human activities are taking place within the geothermal power plant. Through the analysis and differentiation of three types of water (domestic, natural, and hydrothermal), this study aimed to track potentially toxic elements in surface and groundwaters analyzed from statistical standpoints to understand their potential transportation processes and determine their natural or anthropogenic origin. As a result, the hydrothermal waters were the most enriched [As (23,112 μg L−1), Cu (737 μg L−1), S (571 mg L−1), Sb (117 μg L−1), and Se (47.8 μg L−1)] and therefore found to be the major influence of potentially toxic elements in the water chemistry of the region. In addition, the domestic waters were found to be transitional, having moderate concentrations [As (44.2 μg L−1), Cd (4.14 μg L−1), Cr (10.5 μg L−1), Na (71.4 mg L−1), K (15.2 mg L−1), and V (36.4 μg L−1)]. Finally, the natural waters had the lowest concentrations of most elements, except for Na [Cd (4.04 μg L−1), Na (76.5 mg L−1), Cr (2.29 μg L−1), K (12 mg L−1), and V (30.2 μg L−1)]. Furthermore, the sampling in two seasons and two years suggest that dynamic processes are taking place in the site, since no clear correlation was found between seasonal data. The main transport processes for the PTE might be the water-rock interaction, tectonic and structural geology, and the influence on the direct and indirect rainwater infiltration into the caldera.