Geochemistry and Cr stable isotopes of Cr-contaminated groundwater in León valley, Guanajuato, México

León valley, located in the Mexican state of Guanajuato, has a long history (35+ years) of Cr contamination of groundwater and surface water. This study aims to present data on chromium (Cr), major ion and trace element concentrations, and Cr stable isotope measurements from a heavily contaminated aquifer in Buenavista, where chromium ore processing residue piles (COPRPs) from a chromate production factory are the primary source of contamination. The aquifer directly beneath the factory is reported to have extremely high Cr(VI) concentrations, reaching up to 121 mg/L. Ongoing pump and treat remediation efforts are successfully confining the contamination plume, although chromium is also detected at distances away from the factory site. The chromium isotope data collected from the aquifer indicate only a minimal increase in d53Cr (+0.33‰ to +0.81‰), suggesting that there has been little reduction of Cr(VI) to less toxic Cr(III). The data may imply that the exceedingly high Cr(VI) concentrations have overwhelmed natural reductants within the environment.