Evaluation of characteristics and hydrogeochemical evolution of Mashhad-Chenaran aquifer by inverse geochemical modeling in Phreeqc

Mashhad-Chenaran aquifer catchment covered by various geological formations (igneous, metamorphic, carbonate, non-carbonate and alluvium) which effects on the quality and the type of groundwater. Statistical analysis of water quality of more than 1000 samples of selected water resources (springs, qanats and wells) from 1987 to 2020 and the application of hydrogeochemical techniques shows that the dominant type of water discharge from igneous, metamorphic, carbonate, non-carbonate, non-carbonate and alluvial are CaNaHCO3, CaHCO3, CaMgCl and NaCl, respectively. In igneous and metamorphic rocksm the dissolution of silicate and plagioclase (albite and anorthite) minerals and feldspars increases the Ca+2 and Na+ in water. However, in carbonate and non-carbonate sedimentary formations, Ca+2, Mg+2 and Cl- ions are dominant in water due to the dissolution of calcite, dolomite and evaporation. Investigation of the average of long-term quality data and 14 piezometric in the plain shows that, although groundwater due to recharging from surrounding mountains has varius water types, but along the flow direction, except the northwest region which is affected by evaporation (Jks) and has sodium chloride, the dominant type of water is sodium sulfate. In the alluvial aquifer, the calcite, dolomite and aragonite minerals are supersaturated and the gypsum, anhydrite and halite minerals are saturated. The inverse hydrogeochemical model results in Phreeqc software, indicate that the dissolved materials in water in the second group results from the dissolution of calcite, dolomite and albite minerals in the first group.