A severe boron pollution has been recognized in the shallow aquifer of Isola di Castelluccio (central-eastern Tuscany, Italy) since 2009. Previous investigations showed that the high boron concentrations (up to 57 mg L-1) were related to an anthropogenic source. It was likely due to current and/or past industrial and artisanal activities, which were using B-compounds during their productive cycles. However, a univocal source of boron has so far not been recognized. In this work, we present and discuss new geochemical and isotopic data related to an extensive campaign (June 2016) carried out in 33 domestic well and piezometer waters. In addition, the results from a three-weekly to monthly monitoring survey (from August 2014 to December 2019) on selected waters were used to recognize signals in response to dry and wet periods or related to the presence of the recently installed hydraulic barrier. To verify the efficiency of the hydraulic barrier a numerical model of the shallow aquifer was performed by using the MODFLOW computer program. This study has allowed to identify where the source of contamination is likely located. This implies that specific investigations can now be carried out to definitively remove the anthropogenic source of boron.