Multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system (original) (raw)

2008, Journal of Hydrology

The study of groundwater hydrogeochemistry of the Paleozoic Basses-Laurentides sedimentary rock aquifer system in Québec produced a large geochemical dataset. Groundwater samples were collected at 153 sites over a 1500 km 2 study area and analyzed for major and minor ions. The large number of data can lead to difficulties in the integration, interpretation and representation of the results. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples, and to identify geochemical processes controlling groundwater geochemistry. This subgroup consisted of 144 samples and 14 parameters (Ca 2+ , Mg 2+ , Na + , K + , HCO À 3 , Cl À , SO 2À 4 , Fe 2+ , Mn 2+ , Br À , Sr 2+ , F À , Ba 2+ , HS À ). Seven geochemically distinct clusters, C1-C7, resulted from the HCA. Samples from clusters C3, C4, C6 and C7 are mostly located in preferential recharge areas. The majority of these samples have Ca-Mg-HCO 3 recharge groundwater (C3, C6, C7) and Na-HCO 3 evolved groundwater (C4). Samples from the other three clusters (C1, C2, C5) are characteristic of an aquifer system under confined conditions. The majority of these samples have Na-HCO 3 evolved groundwater (C1, C5) and Na-Cl ancient groundwater that exhibits elevated concentrations in Br À (C2). In addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry, the distribution of clusters also showed the importance of the geological formations on minor and trace elements, such as Fe 2+ , Mn 2+ , Sr 2+ , F À and Ba 2+ . The first five components of the PCA account for 78.3% of the total variance in the 0022-1694/$ -see front matter ª (R. Therrien), msavard@nrcan.gc.ca (M.M. Savard). Journal of Hydrology (2008) 353, 294-313 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l