Assessment of NO3−, As, and F− background levels in groundwater bodies: A methodological review and case study utilizing sequential Gaussian simulation (SGS)

The aim of this study is to systematically review prior research on methodologies employed for assessing the NBLs in groundwater. These methods include statistical and probability, pre-selection, integrated pre-selection and statistical, and soft clustering methods. These methods are categorized into subgroups, each briefly explained along with its respective advantages and disadvantages. Investigation underscores the influence of geogenic processes on determining the natural background level. The secondary objective is to illustrate which elements are subject to the most thorough evaluation within the NBL. A majority of conducted studies have concentrated on the analysis of chloride (Cl), arsenic (As), sulphate (SO42-), and sodium (Na), given their substantial importance in discussions related to natural background levels. Notably, nitrate (NO3-) has garnered specific focus in research exploring anthropogenic processes. Finally, this study investigated three potentially harmful pollutants for human health include NO3-, fluoride (F-), and As in various groundwater samples of the Campania region in southern Italy. Therefore, the sequential Gaussian simulation (SGS) algorithm, as a state-of-the-art method, was proposed to process a total of 600 water samples. Results showed that the concentration of NO3- seems to be restricted in the plain, possibly due to the presence of peat lenses and clay materials that act as a buffering mechanism. Regarding Fluoride, elevated levels were observed in areas characterized by outcrops of volcanic lithologies, the presence of reworked volcanic materials, or areas marked by lateral recharges from volcanic aquifers. The concentration of As partially aligns with that of Fluoride, although the presence of peat lenses and clay materials appears to play a significant role in releasing Arsenic. The results of this work could represent an efficient tool in management of local groundwater resources establishing guidelines for water abstraction, land use planning and to mitigate further phenomenon of groundwater pollution. The identification of chemical background level of potentially toxic elements is mandatory to ensure a sustainable management of water resources allowing the targeting of specific action of remediation or safeguarding.