Pieve Vergonte

The plant was built around 1915 and made chlorine, caustic soda, sulphuric acid, fertilisers and chlorinated insecticides, DDT among them; it passed through several owners, the last being Enichem. DDT production ended in 1996; the mercury-cell chlor-alkali unit ran until the end of 2017. Part of the area still hosts an operating chemical plant.

Process residues seeped into the soil and groundwater and reached the Marmazza stream, which ran through the plant, then the Toce and Lake Maggiore. In soils inside the plant, DDT and its derivatives exceed the legal limit by up to 100,000 times; dioxins, metals, hydrocarbons, chlorobenzenes and PCBs are also present. In 1996 the Swiss authorities found DDT above their limits in fish from the lake.

In 2003 the Ministry of the Environment sued Syndial (Eni group): in 2008 the Turin court set the damage at about 1.9 billion euro; in 2017 the Court of Appeal replaced compensation with an obligation to remediate and repair, a ruling upheld by the Court of Cassation in 2021 (Il Post).

The remediation project, approved on 21 October 2013 at an expected cost of 159.3 million euro, provides for diverting the Marmazza upstream of the site, excavating the contaminated soil with screening and washing, a 680,000 m³ confinement facility, a stronger hydraulic barrier downstream, and air sparging and soil vapour extraction. Works started in 2016; a variant was needed because the volume of contaminated soil turned out to be larger. In Toce sediments downstream of the plant, sampled in 2014 and 2019, DDT, mercury and arsenic reach levels potentially toxic to benthic invertebrates.