Giant sewage spill exposes Finland’s reporting gaps

A sewage spill of 60,000 cubic metres in Hollola has highlighted how little authorities know about sewage discharges into the environment, Yle reports. Environmental permits require treatment plants to report spills, but some go unreported.

The spill, discovered in August, released 60 million litres of sewage over two months at a disused wastewater treatment plant. Some of the sewage entered the Vähäjoki, which flows into the Porvoonjoki.

Marja-Leena Skinnari, group manager responsible for supervising wastewater treatment plants at Finland’s Permits and Supervision Agency, said official reports did not show a clear trend in the number of spills.

She said operators generally followed the regulations and that information about particularly large spills was likely to reach the authorities. However, she said it was impossible to estimate how many overflows went unreported.

One possible reason is that sewer systems are managed in very different ways. In larger municipalities, the work may be handled by a company owned by the municipality, while in sparsely populated areas responsibility may lie with a cooperative that operates less professionally. Responsibility for the sewer network may also rest with a different organisation from the treatment plant, while reporting obligations apply only to treatment plants.

Skinnari said this layered system could prevent information from moving as effectively as it should.

Based on the available information, experts consider the Hollola spill exceptionally large. The agency said it knew of no other sewage spill of comparable size and duration.

Hannu Mustonen, chief executive of Aqua Palvelu, which is responsible for maintaining the sewer systems in the area, said the spill could have caused more serious environmental damage. Most of the solid material, including faeces, ended up in the basins of the old treatment plant, limiting the harm.

Mustonen described the incident as exceptional in scale. Aqua Palvelu is responsible for the condition of Lahti Aqua’s water and sewer network. The surrounding environment is being monitored closely after the spill.

The spill resulted from several coinciding factors. Changes in the flow of sewage through the network were not detected because of human error, and a faulty sensor failed to trigger an alarm.

Under the Environmental Act, the Permits and Supervision Agency cannot punish those responsible for a spill. It can require them to investigate the environmental effects and carry out any necessary follow-up measures, such as clean-up work.

If the authorities clearly determine that a spill was deliberate and repeated, or resulted from negligence, they can ask the police to investigate. Such cases are considered individually, Skinnari said.

The Finnish Environment Institute published a study on the environmental significance of sewage spills in 2022, focusing mainly on the bodies of water into which they flow. Data collected by the institute indicate that spills account for about 0.2 percent of all wastewater treated.

Wastewater overflows are most commonly caused by heavy rainfall, when more water reaches a treatment plant than it can process. Climate change and deteriorating sewer networks are increasing the risk of spills.