Statistical Analysis of the Hydrogeochemical Evolution of Groundwater in Alluvial Aquifer of Arak Mighan Playa, Markazi Province, Iran

Abstract

This paper presents results of hydro-chemical processes controlling groundwater chemical composition, using an integrated application of hierarchical cluster analysis and factor analysis of a major ion data set of groundwater from Mighan playa aquifer. Cluster analysis classified samples into four clusters(A, B, C and D) according to their dominant chemical composition: cluster A (dominant composition: Ca-HCO3; mean TDS: 267 mg/l), cluster B (dominant composition: Ca-Mg-SO4-Cl; mean TDS: 1029 mg/l), cluster C (dominant composition: Na-Mg-SO4; mean TDS 667 mg/l) and cluster D (dominant composition Na-Mg-SO4¬-Cl; mean TDS 2998 mg/l), which were described by the first factor of factor analysis. Results of the factor analysis suggested that the spatial variation of groundwater quality is influenced by processes of carbonate minerals dissolution and mixing of saline water (Mighan playa). The calculated playawater fractions (ƒplaya) of the groundwater shows that cluster D water is almost four times more saline than cluster B water and twice and a half more saline than cluster C water, where the difference between salinities can be explained by proximity of cluster D water to the playa. In the present study, 23.8 % of the playawater samples were found to contain chloride concentrations above 250 mg/l suggesting that playawater intrusion has reached alarming levels yet. The saline/brackish groundwater is the result of the processes of evaporation (for samples close to the Mighan playa) and dissolution of SO4 and Cl evaporative salts (such as thenardite, gypsum and halite).