B2/2007Y Entry of treated wastewater into the drinking water network in Nokia on 28–30 November 2007

Between Wednesday, 28 November 2007, at about 12.00 and Friday, 30 November 2007, at about 12.00, treated wastewater (technical water) from the wastewater treatment plant of Kullaanvuori was accidentally allowed to enter the drinking water network, causing illness to more than 8,000 people in the town of Nokia and the surrounding area. The entry of the technical water into the drinking water network was possible because a valve had been built, in breach of regulations, between the sewage network and the drinking water network. The entry of the wastewater into the drinking water network exposed people to a large number of illness-causing contaminants.

The wastewater treatment plant of Kullaanvuori was completing installation and maintenance work on Wednesday, 28 November 2007. The installation work required that the plant’s drinking water network was closed for a period of time. At the same time, polymer containers used in the sludge treatment process were being drained and washed. These containers did not start filling with clean water automatically; as a result, the operator in charge opened a technical water valve (for treated wastewater), with the intention of filling the polymer containers. Because of the open valve, about 400 m3 of treated wastewater flowed into the municipal drinking water network.

At the same time, on 28 November, the waterworks of Maatiala, in the town of Nokia, was completing information-technology-related installation work requiring the shutting down of automatic functions. Unable to restart automatic functions after the installation procedures, a decision was made in the waterworks to acquire additional water from the city of Tampere. Later that day, the waterworks received several notifications from consumers concerning ill-smelling and ill-tasting water. The waterworks personnel concluded that this was caused by the opening of the water line to Tampere, and also by water pipe repair work completed earlier on the street Ristiveräjänkatu. The waterworks personnel reacted to the complaints by initiating rinsing actions in the water network. In response to the complaints that were accumulating, the health inspector issued a recommendation on Friday, 30 November 2007, that drinking water has to be boiled before using. Soon thereafter, the reason for the water’s contamination became apparent.

The first announcements were made to the media at around 1 p.m. on Friday, 30 November 2007, in Tampere’s radio news programmes, on the town of Nokia’s Web site, and via other media channels.

The direct cause of the accident was that an inappropriate connection had been built between the wastewater and drinking water networks, and valves in both networks were simultaneously open.

The Accident Investigation Board recommends the development of well-functioning operating models and practices that enable the organisation of continuous risk assessment in wastewater treatment plants. The board also recommends the completion of a study that would ensure the generation of up-to-date information on the state of wastewater treatment and on any possible shortcomings in this, and also that environmental health plans concerning preparedness and readiness be drawn up in the proper way, with these specifically addressing leadership and communications responsibilities during waterborne epidemics. Furthermore, the board recommends that the Ministry of the Interior co-operate with other parties to ensure that relevant decrees and regulations are brought up to date in such a way that preparedness seamlessly covers all situations from disturbances to emergency conditions.

B2/2007Y Report (pdf, 3.64 Mt)

B2/2007Y Report (pdf, 1.2 Mt)

Animation of distribution of treated waste water (wmv, 4.52 Mt)