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Contamination of groundwater by naturally occurring arsenic has recently become a disturbing environmental problem in Viterbo area, Central Italy. Arsenic concentrations in most of the public supply networks exceed the maximum allowable limit of 10 μg/l (WHO) for drinking water. The primary purpose of this paper is to obtain a better understanding of the factors contributing to the high levels of As in water supply networks. This study focuses on (a) the determination of basic hydrochemical characteristics of groundwater, (b) the identification of the major sources and processes controlling the As contamination in public supply networks, (c) to find out possible relationships among the As and other trace elements through principal component analysis (PCA). Groundwater samples from public water supply wells and springs were collected and analysed for physico-chemical parameters and trace elements. Springs and well water samples are predominantly of the Na–HCO3, Na –Ca–HCO3 and Ca–HCO3 types and the highest arsenic concentrations were observed in Na–HCO3 type water. Eh-pH diagrams reveal that H2AsO4− and HAsO42−, As(V) arsenate, are the dominating As species highlighting slightly to moderately oxidizing conditions. Geochemical modeling indicates that arsenic-bearing phases were undersaturated in the groundwater, however most of the samples were saturated with respect to Fe (i.e. magnetite, hematite and goethite) and Al (diaspore and boehmite) oxide and hydroxide minerals. Concentrations of As, Li, B, Co, Sr, Mo, U and Se are highly correlated (r > 0.7) with each other, however in some groundwater samples As show also good correlations (r > 0.5) with Fe and Mn elements reflecting the relationships among the trace elements result from different geochemical processes. Evaluation of the principal component (PCA) analysis and geochemical modeling suggest that the occurrence of As and other trace element concentrations in groundwater are probably derived from (i) weathering and/or dissolution of volcanic source aquifer materials and (ii) adsorption/desorption processes on the Fe and Al oxide and hydroxide minerals.

The present work provides hydrochemical and stable isotope data and their interpretations for 54 springs and 20 wells, monitored from 2002 to 2006, in the Southern Latium region of Central Italy to identify flow paths, recharge areas and hydrochemical processes governing the evolution of groundwater in this region. The hydrogeological conceptual model of the carbonate aquifers of southern Latium was based on environmental isotopic and hydrochemical investigation techniques to characterize and model these aquifer systems with the aim of achieving proper management and protection of these important resources. Most of the spring samples, issuing from Lepini, Ausoni and Aurunci Mts., are characterized as Ca-Mg-HCO 3 water type, however, some samples show a composition of Na-Cl and mixed Ca-Na-HCO 3 -Cl waters. Groundwater samples from Pontina Plain are mostly characterized by Na-Cl and Ca-Cl type waters. Geochemical modeling and saturation index computation of the Lepini, Ausoni Aurunci springs and Pontina Plain wells shows an interaction with carbonate rocks. Most of the spring and well water samples were saturated with respect to calcite and dolomite, however all sampled waters were undersaturated with respect to gypsum and halite. The relationship between δ 18 O and δ 2 H, for spring and well water samples, shows shifts of both the slope and the deuterium excess when compared to the world meteoric (WMWL) and central Italy meteoric (CIMWL) water lines. The deviation of data points from the meteoric lines can be attributed to evaporation both during the falling of the rain and by run-off on the ground surface before infiltration. Most springs and wells have a deuterium excess above 10‰ suggesting the precipitation in the groundwater comes from the Mediterranean sector. On the basis of local isotopic gradients, in combination with topographic and geologic criteria, four recharge areas were identified in the Aurunci Mountains. In Pontina Plain, the elevations of the recharging areas suggest that the Lepini carbonate aquifers are feeding them.

In southern Latium region, Central Italy, groundwater and spring water resources in the carbonate aquifers are the major contributors of drinking and irrigation water supply. The aim of this study was to review hydrochemical processes that control the groundwater chemistry and to determine the suitability of springs and groundwater for irrigation and drinking purposes on the basis of the water quality indices. Physical (pH, electrical conductivity, total dissolved solids) and hydrochemical characteristics (Na ? , K ? , Ca 2? , Mg 2? , HCO 3 -, Cl -, and SO 4 -) of springs and groundwater were determined. To assess the water quality, chemical parameters like sodium adsorption ratio (SAR), total hardness, Mg-hazard (MH), sodium percentage (Na %), salinity hazard, permeability index, and Kelly's ratio were calculated based on the analytical results. A Durov diagram plot revealed that the groundwater has been evolved from Ca to HCO 3 recharge water, followed by mixing and reverse ion exchange processes, due to the respective dominance of Na-Cl and CaCl water types. According to Gibbs's diagram plots, chemical weathering of rock forming minerals is the major driving force controlling water chemistry in this area. Groundwater and spring samples were grouped into six categories according to irrigation water quality assessment diagram of US Salinity Laboratory classification and most of the water samples distributed in category C2-S1 and C3-S1 highlighting medium to high salinity hazard and low sodium content class. The results of hydrochemical analyses and the calculated water quality parameters suggest that most of the water samples are suitable for irrigation and drinking purposes, except for the samples influenced by seawater and enhanced water-rock interaction. High values of salinity, Na %, SAR, and MH at certain sites, restrict the suitability for agricultural uses.