Borehole flowmeter based groundwater sampling and isotopic fingerprinting support source apportionment of a public water supply well field contaminated by chlorinated pitches: the case of Bussi sul Tirino (Abruzzo region, Central Italy

A public water supply well field, composed by 8 wells attaining a depth between 32 and 62 m b.g.s. and pumping out more than 400 L/s to about 300.000 inhabitants (Pescara province, Abruzzo region, Central Italy), has been involved for more than 20 years, from the opening in 1984 to the decomissioning in 2007, by a contamination of chlorinated aliphatics (PCE, TCE, TCM, CT). The well field is located in the narrow and long alluvial valley of the Pescara river surrounded by important limestone aquifers of Central Apennines. About 2 km upstream, at the confluence of the Tirino river with the Pescara river, is located one of the oldest chemical and petrochemical plant (Bussi sul Tirino plant) in Italy. It dates back to the end of the nineteenth century and with a production of chloromethanes active from the 60's to 2007. On 2005, a huge illegal dump of industrial wastes (more than 3 hectares in size) was discovered in the alluvial valley floor of the Pescara river during an investigation of the public prosecutor of the Pescara court. The valley of the Pescara river is filled with a complex assemblage of porous (alluvial gravels and sands, debris) and fractured (travertines) high permeability aquifers intermingled with silts and clays of lacustrine or alluvial origin. The lateral recharge from the Pescara river and/or surrounding limestones is such to induce a high dilution effect to the dissolved contaminants originated at the source. In order to apportion the source of contamination, in terms of location and of process of wastes generation, in range of the action at the Court of Assizes of Chieti, an hydrogeological investigation has been performed, supported by the Italian Attorney General. CSIA (Carbon Stable Isotope Analysis) of chlorinated compounds, integrated by chlorine fingerprinting on PCE, was adopted as a main tool of source apportionment of chlorinated pitches production process. In order to enhance the mass recovery of chlorinated compounds by low flow sampling on 25 boreholes between the source and the receptor, a preliminary flowmeter survey was performed. This allowed to identify the proper sampling location along the screen of the boreholes. The isotopic affinity of the compounds, detected at the well field, with the production process of chlorinated pitches has been clearly put in evidence as a consequence of the strong deplenishment of delta13C values.