Cofferdam installation at Oldham WwTW

In 2015 United Utilities, the North West's regional water company, appointed main contractor Black and Veatch to deliver the Oldham and Royton Integrated Strategy (ORIS.)

SGC Civil Engineering were appointed as the large buried pipework sub-contractor, and were involved in the work to improve water quality standards in the River Irk by reducing the number of unsatisfactory intermittent discharges (UIDs) from the Oldham wastewater treatment works.

Part of this was achieved by installing a large 5 sided cofferdam, 6.5m deep, to enable the installation of a storm return collection chamber to feed the existing storm tanks. After collaboration with Black and Veatch, we suggested changes to the methodology of how the cofferdam should be installed, opening up the design to allow us to work more quickly and enhancing safety standards. This delivered a £50,000 saving.

The whole operation had to be completed whilst the wastewater treatment works remained live, which meant the installation of an overpumping system. Because we were working on an already established site, we had to take into consideration a multitude of existing services whilst the excavation took place.

Once we got the cofferdam to depth, we installed the triple line 1m diameter pipes adjoining the final settlement tanks. This required specialist cutting of the existing tanks and we then installed the formwork to hold the pipes in place.