Sewer connection on Bornholmstraat replaced successfully

There is a large main pressure pipe between the sewage pumping station on Damsterdiep and the Garmerwolde wastewater treatment plant. The connection between the municipal sewer system and this main pressure pipe at Bornholmstraat was replaced last week.

Main sewer temporarily out of service

Around 80% of the city's wastewater ends up in this pressure pipe from the municipal sewer system. This pipe cannot simply be taken out of service. Nevertheless, this is what happened last week in order to replace the connection. The operation was successful due to careful preparation, precise timing, and excellent cooperation with Groningen Council, Hunze en Aa’s water authority, and the GMB Heijmans Infra consortium of contractors. 

Dry weather, buffering, and hard work

In dry weather, the main sewer pressure pipe can be shut down for a maximum of 8-10 hours. The sewage is then retained (buffered) in the downstream sewer system. Within this time slot, the old connection had to be dismantled and the pipe itself had to be closed off with a so-called blind flange, a metal plate. That meant hard work according to a precise schedule. In the construction pit, the contractor then made preparations for the installation of the new connection piece. We then shut down the pressure pipe again so that the connection could actually be installed. 

Install permanent connection to main pressure pipe in Bornholm Street
The replacement of the connection between the municipal sewer system and the main pressure pipe of the ewer water authority in Bornholmstraat was completed successfully in a short period of time.

Practice round

Over the past six months, we conducted various studies together with the contractor, finalised the design, drew up an action plan, and tested the 'emptying' of the pressure pipe. By practising buffering and 'emptying' the pipe at Bornholmstraat, we knew exactly what we had to do and what we had to coordinate with the three owners of the complex underlying pressure sewer system: Groningen Council, the Hunze & Aa's Water Authority, and our own water authority. We also worked closely with them on this. 

Reason

The new connection replaces a temporary solution from 2019. At that time, we discovered that the connection between the municipal pressure pipe and the main pressure pipe was leaking. The connection was sealed with a repair clamp at the time. This allowed us to quickly stop the leak. With a lifespan of approximately 10 years, this was only a temporary repair. That is why the clamp has now been replaced with a robust and durable solution. We will complete the work in the coming weeks and the contractor will restore the site to its original condition.