Lahti Aqua admits monitoring failures after Hollola sewage spill

Lahti Aqua has confirmed that a blockage caused 60 million litres of sewage to spill into waterways in Hollola, while admitting that its monitoring systems failed to detect the incident. The environmental impact appears to have been less severe than expected, Yle reports.

The spill occurred at the former Salpakangas wastewater treatment plant and lasted from 20 May to 19 July. Sewage flowed into the Vähäjoki watercourse and from there into the Porvoonjoki River.

Lahti Aqua said no direct signs of the spill were detected in the Porvoonjoki’s water quality by mid-August. Bacteria levels were elevated in some parts of the waterways, but experts assessed that they were more likely linked to other sources. Otherwise, water quality was largely normal for the area and time of year, and nutrient levels were typical for the rivers.

Preliminary studies of fish in the Porvoonjoki found no significant effects from the spill. Additional monitoring of bottom-dwelling organisms will be carried out during the autumn.

The blockage was found in a sewage transfer line between Herrala and Ali-Juhakkala. The unusually large spill was discovered in early August.

Lahti Aqua said the automatic overflow monitoring system at the disused treatment plant had not worked as intended, and no alarm was triggered. The company said it considers the incident serious despite the limited environmental effects.

“We do not consider what happened acceptable,” Lahti Aqua chief executive Jouni Lillman said in a statement. He said the prolonged overflow had exposed shortcomings in the company’s monitoring that needed to be addressed.

The faulty overflow monitor has been replaced, and Lahti Aqua has begun assessing the root causes of the incident and its monitoring procedures.