Cengio and Saliceto (ACNA)

A dynamite factory was set up at Cengio in 1882. From 1908 it made sulphuric acid, oleum and TNT; in 1925 the works were converted to dye production and in 1929 ACNA was formed, passing to Montecatini (1931), Montedison (1964), Enimont (1988) and Enichem (1991). Production ended in January 1999.

Documented in the soil are heavy metals, aromatic amines, halogenated aromatics, chlorobenzenes, hexachlorobenzene, phenols, nitrobenzenes, PAHs, PCBs, dioxins and naphthalene- and anthraquinone-sulphonic compounds; in groundwater, aluminium, arsenic, iron, manganese, lead and naphthalene sulphonates. The 1999 perimeter distinguishes a high-risk zone A (the plant, the Pian Rocchetta landfill and the Bormida river bed to just above Saliceto) and zones B and C along the river.

Under the 2000 programme agreement between ACNA, ministries, Regions and the government commissioner the plant was split into four zones: A1 (material deposit), A2 (plant area), A3 (floodplain) and A4 (Pian Rocchetta). The A1 lagoons, basins for saline effluent, were emptied; about 1.5 million m³ of material removed from zones A2, A3 and A4 was placed in A1, which was then capped. Along the river runs a 2,500 m cement-bentonite cut-off wall keyed into the marl, topped by a concrete wall about 5 m high on average.

Zone A4 was certified in 2010–2012 and A2 in 2010; for the floodplain areas an addendum to the project was approved in 2023. The EU infringement procedure, linked to the missing environmental impact assessment, was closed in June 2020 after a retrospective assessment. Since 2017 a protocol between the Regions, the ARPA agencies and Eni Rewind has monitored the Bormida's water: ARPA Piemonte reports that the attention thresholds have never been exceeded. Eni Rewind states it had spent 497 million euro by the end of 2025.