Water Quality Control In Public Supply Springs And Wells Of Viterbo Area, Central Italy

Most people in Viterbo area, Central Italy, meet their domestic needs from groundwater resources. This paper assesses the geochemical characteristics of most part of public water supply network in Viterbo area and their suitability for drinking and agricultural purposes. More than two hundred water samples were collected from springs and wells for the evaluation of water quality parameters and the results were compared to the World Health Organization (WHO) standards. Principal component analysis (PCA) was applied to water hydrochemical data in the aim of understanding main processes controlling water chemistry. The first two PCs (PC1 and PC2) explain 73.1 % of the total variance within all the measured parameters. Based on the loading plot between the first two components three different groups were identified (Group A: EC, Na, Ca, NO3, Cl and SO4 and T; Group B: Mg, TDS, K, F and HCO3 and Group C: pH) reflecting the main rock types in the area investigated, where the volcanic materials are the most dominant formations. Water samples are characterized by three hydrochemical types: (A) Na-HCO3, (B) Na-Ca HCO3 and (C) Ca -HCO3. The results show that most of the waters within the study area are slightly acidic to slightly alkaline nature with TDS values below 500 mg/l, however some samples from Facies C show higher TDS values (up to 1480 mg/l) and classified as brackish water. The total hardness of water samples from Facies A and B range from 32.3 to 186.3 mg/l and fall between soft and hard water category, while the samples from Facies C classified as soft to very hard water with the highest value of 716.5 mg/l. US Salinity diagram (USDA) was used to evaluate the water quality for irrigation and most water samples distributed in category C1-S1, C2-S1 and C3-S1 highlighting low to high salinity hazard and low sodium content class. According to calculated values of percentage sodium (Na %), magnesium hazard (MH), Kellys ratio (KR) and permeability index (PI), the springs and groundwater are suitable for irrigation. The chemical constituents, such as Ca, Mg, Na, K, Cl, HCO3, SO4 etc., in most of the water samples are within the permissible limits of the World Health Organization (WHO) drinking water quality guidelines. However, the presence of high fluoride (max: 3.23 mg/l), nitrate (max: 100 mg/l), and arsenic (max: 57 mu g/l) concentrations, exceeding the permitted limits in some springs and wells, threat human health in the area.