Disentangling natural and anthropogenic impacts on groundwater by hydrogeochemical, isotopic and microbiological data: Hints from a municipal solid waste landfill.

•Biogeochemical data offered converging interpretations on landfill groundwater impact.•High concentrations of As, Fe, and Mn can be of geogenic origin at industrial areas.•The local isotopic signature allowed identifying diverse groundwater processes.•Microbial data provided supportive results on the impact of groundwater alterations.•A multivariate approach can improve assessments of groundwater quality and processes.