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+ a) of Cr contamination of groundwater and surface water. Here data are presented for Cr, major ion and trace element concentrations and Cr stable isotope measurements of groundwater in a heavily contaminated aquifer in Buenavista, where Cr ore processing residue piles (COPRPs) located in a chromate production factory are the main source of Cr. The aquifer directly beneath the factory still retains very high Cr(VI) concentrations (∼121 mg/L). Ongoing pump and treat remediation is keeping the high concentration plume confined to the factory area and immediate vicinity, though Cr is also detected at some distance away. Chromium isotope data of the aquifer directly under the factory show only a small increase in δ⁵³Cr (+0.33‰ to +0.81‰) and indicates minimal reduction of Cr(VI) to Cr(III). Very high Cr(VI) concentrations have possibly overwhelmed natural reductants and furthermore fresh Cr(VI) was being leached into the groundwater from the COPRP. From just one year of Cr isotope data it is clear that more aggressive remediation techniques will be necessary to reduce or eliminate the contamination. The fringes of the Cr plume have substantially lower concentrations and can be partially explained by transport of the main plume or mixing between waters from the nearby landfill and highly contaminated waters from QC. While the source of Cr at the fringes of the plume could be attributed to a source from the nearby landfill instead of the main plume from the factory, the Cr stable isotope data show enrichment in the heavier isotopes and point to varying amounts of reduction. Isotopic enrichment seen between 2007 and 2008 along the fringe may indicate either reduction or less unreacted Cr(VI) is being transported to the fringes. In either case some potential for natural attenuation of Cr(VI) exists at the western margin of the plume with the landfill playing a role.     

Improving the descendant relationship of cluster galaxies at z < 1

In this work, we study how to improve well-known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of $120$ clusters, with masses greater than ${10}^{13.25}{M}_{\odot }$, selected from the IllustrisTNG simulations (namely, the TNG100 runs). In $99\%$ of the cases (i.e., $119$ systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is $28\%$ in the identification of descendants for this sample of cluster galaxies.