Distribution of Ca and Mg in groundwater flow systems in carbonate aquifers in Southern Latium Region (Italy): Implications on drinking water quality

The investigation of hydrochemical properties of springs from the carbonate aquifers of the southern Latium region (Central Italy) aimed to: (i) identify different processes responsible for the hydrochemical evolution of groundwater; (ii) determine the levels of Ca and Mg in the drinking water networks and; (iii) determine the effect of hardness on water quality. Based on the dominance of major cations and anions three hydrochemical facies have been identified: (1) Ca-Mg-HCO3; (2) Mixed Ca-Na-HCO3-Cl; (3) Na-Cl. In all cases, Ca-Mg-HCO3 facies predominates reflecting the main rock types in the area, where limestone, dolomitic limestones and dolomites are common. The total dissolved solids (TDS) and electrical conductivity (EC) range from 101 to 1320 mg/l and 138 to 2310 µS/cm, respectively. Most of the springs are supersaturated with respect to carbonate minerals, however all sampled waters were undersaturated with respect to evaporite minerals. The compositional changes in Ca and Mg concentrations are controlled by distance from the recharge area (i.e. groundwater discharging from the lower elevations tends to have the highest concentrations of Mg). The classification of water based on total hardness (as CaCO3) shows that most of the spring water samples fall between hard (150-300 mg/l) and very hard (> 300 mg/l) water type.