Good condition of Lake Nuasjärvi is important to Terrafame

The condition of Lake Nuasjärvi in Sotkamo and the contributing factors are continuously monitored. Terrafame monitors the quality of purified mine water that is led to the discharge pipe both at the mining site and in Lake Nuasjärvi, and publishes the results on its website in Finnish. Furthermore, the Kainuu Centre for Economic Development, Transport and the Environment monitors water quality in the lake and in deeper areas close to the discharge pipe and publishes the results on a regular basis.

Terrafame has been discharging purified water through Lake Nuasjärvi into the Oulujoki watercourse area since November 2015. During this winter, sulphate and metal concentrations in the purified water flowing through the discharge pipe have continued to remain below the estimated maximum limits specified at the environmental permit application.

There is natural seasonal variation in lake water quality in Finland. During the spring and autumn overturns, lake water quality tends to be homogeneous between the surface and the bottom. However, during the winter and summer, water in the deeper areas is thermally stratified and substance concentrations are higher than in the surface layer (epilimnion). Winter stratification is a normal phenomenon in Lake Nuasjärvi and is strengthened by emissions through the discharge pipe.

During this winter, the even spread of water containing sulphates in the deeper areas close to the discharge pipe has been as expected; concentrations have remained clearly below the maximum levels estimated at the environmental permit application. The autumn overturn of 2016 was normal and oxygen levels in the deep areas are good. In the bottom layer (hypolimnion) of Lake Nuasjärvi, levels of sulphate and metal concentrations and electrical conductivity are at their highest towards the end of the winter stratification period, in March–April, and at the end of the summer stratification in August.

Terrafame ensures the quality of water discharged via pipeline in accordance with its environmental permit, by taking samples twice a day and partly through continuous measurements. Terrafame has also commissioned water quality monitoring at Lake Nuasjärvi, through three continuously-operating measurement stations. Samples are also taken as part of Terrafame’s mandatory monitoring obligation, in order to collect data on factors such as sulphate concentrations in various parts of the lake.