Blominmäki sewer excavations

The excavation work on sewer tunnels began in December 2014 in the area of Mikkelänkallio and Blominmäki, and continued the next year as part of the preparatory excavation work on the West Metro’s station in Finnoo. Since then, the work has continued first as part of the excavation work concentrating on those areas. Since 2018, four different contracting projects have been in progress to complete the tunnel system: Mikkelä II, Malminmäki, Eestinkallio and Finnoo II. The excavation work from the Mikkelä direction was finished in August 2019. In the northern branches of Malmimäki, the excavation work will last longer, approximately until the summer of 2020. After the excavation, reinforcement and technical construction work continues for a longer time. All contracting works will be completed in the summer of 2021, at the latest.

Look map at zoomable version (pdf, 15Mb)

The sewer tunnels will be excavated deep in the bedrock

The main contractor for the excavation and construction of inlet and discharge tunnels of the wastewater treatment plant is Kalliorakennus-Yhtiöt Oy in the Mikkelä, Eestinkallio and Malminmäki contracts. In the Finnoo II contract, the principal contractor is TYL FMS, a joint venture of SRV Infra Oy and Pohjolan Kalliotyö Oy.

The inlet tunnel collects wastewater between the present Suomenoja plant and the Blominmäki wastewater treatment plant. The discharge tunnel leads purified water from the Blominmäki plant to the present Suomenoja discharge tunnel ending up in the open sea. The bottom of the inlet tunnel descends evenly from Finnoo to Blominmäki from a level of −12 m to −20 m in relation to the sea level. Starting from the Blominmäki wastewater treatment plant, the bottom of the discharge tunnel descends from the level of +1 m to +0 m when entering the vertical shaft on the north side of the Espoo River, and underneath it from the level of −19 m, it descends down to −26 m underneath the present Suomenoja wastewater treatment plant in respect of the sea level. Before the connection to the present sea discharge tunnel, water will be led or pumped above the sea level. The width of the tunnels is ca. 4.5 metres and their height is 5.5 metres. Altogether there will be approximately 20.4 kilometres of excavated sewer and access tunnels leading to the sewer tunnels in conjunction with the Blominmäki wastewater treatment plant project. The excavation work progresses at ca. 100 metres per month in good bedrock and an unbuilt environment. Vibrations caused by blasting and also the conditions set by the Espoo Environment Centre delay the progress of excavation work in many locations.

Working hours

Above-ground work:

  • on weekdays 7:00-18:00, and if necessary, also 18:00 to 21:00 (after 18:00 below 35dB)
  • on Saturdays 9:00 to 18:00 (under 35dB)

Underground work:

  • on weekdays 7:00-18:00, and if necessary, also from 18:00 to 22:00 (after 18:00 below 40dB)
  • weekends and midweek holidays from 9:00 to 22:00 (under 35dB)
  • if necessary on weekdays from 22:00 to 7:00 or on weekends and midweek holidays from 22:00 to 9:00 (less than 30dB)

Tunnel blasting:

  • Monday to Friday from 7:00 to 22:00
  • Saturdays from 9:00 to 18:00

The loading and transport of blasted rock from the tunnel:

  • weekdays from 7:00 to 22:00, weekends and midweek holidays from 9:00 to 22:00
  • if necessary on weekdays from Monday to Friday from 22:00 to 7:00, as well as weekends and midweek holidays from 22:00 to 9:00

The exact dB level refers to the indoor noise level of a residential building, which is measured when necessary.

Before the blasting work begins and also after it has finished, a blast vibration consultant carries out a building inspection of the properties in the nearby area and damping measures for vibration sensitive equipment. The concerned properties are informed separately in due course. Throughout the blasting period, the blast vibration consultant of the ordering party performs observational measurements for excavation vibrations using a continuous vibrometer in the nearest properties. The allowable vibration levels are based on the Ministry of Economic Affairs and Employment’s regulations for the excavation and blasting field. 

Possible changes in the progress of excavation and blasting work can be made due to the measurement results gained so that no damage occurs. The entire excavation work is carried out in compliance with safety regulations and official instructions. We are sorry for any inconvenience that may occur.

Mikkelä ll, Eestinkallio and Malminmäki

In Mikkelä, the tunnels have already been excavated in conjunction with the wastewater treatment plant’s excavation phase so that the work can be started from completed tunnel ends. In Eestinkallio and Malminmäki, the construction and excavation work on tunnels’ maintenance connections, used as access tunnels during the excavation phase, are already in progress. Work on these sites began with aboveground construction and opencast blasting. Only after that, could excavation of the tunnels themselves into the rock get started.

Contact details of the main contractor for residents if required:

  • project manager Mikko Piirainen, 044 551 55 31
  • responsible site manager Paavo Kolehmainen, 040 716 56 79
  • blasting expert Raimo Kastikainen, 040 564 53 52

email address format: first name.last name(at)

Finnoo II excavation works

In Finnoo, the tunnels have been already excavated in conjunction with the excavation phase of the West Metro’s Finnoo station so that the work can be started from completed tunnel ends. The most critical point for the schedule was to get the maintenance/pipe tunnel excavated under the West Metro’s station by October 2019. This goal was achieved. Besides the tunnels, the contract comprises in-rock pumping station construction in the current area of the Suomenoja wastewater treatment plant. This includes several channels and other structures and also aboveground buildings. The new discharge tunnel is connected to the Suomenoja wastewater treatment plant’s sea discharge tunnel which leads water to the south side of Gåsgrund, 7.5 km away and 15 m deep by the open sea.
Main contractor contact information for residents: TYL FMS, tel. 040 631 8700, finnoo2(a)

3D-models of the sewage tunnels

RockPlan has made videos about the sewage tunnels and the pumping station to be built.