As part of the Québec regional groundwater characterization program (PACES), a detailed groundwater quality survey
was undertaken in the Outaouais Region (Québec, Canada). During the summers of 2011 and 2012, 139 samples were
taken from municipal and private wells which were analysed for major ions, nutrients, metals and sulphides. About 70%
of the samples were obtained from bedrock wells, mainly in the Canadian Shield and the remainder from wells screened
in Quaternary deposit aquifers. Analysis quality was evaluated by calculating the anion-cation balance. As a result, 127
samples with anion-cation charge balance errors within ±10 % were used for the determination of hydrogeochemical
facies. The classification by facies is also supported by multivariate statistical analysis, namely Principal Component
Analysis (PCA) and Hierarchical Clustering Analysis (HCA). The study has identified Champlain Sea invasion, cation
exchange and freshwater recharge as the main geochemical processes affecting groundwater chemistry in this region
