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Groundforce has supplied pumps and settlement tanks for a unique river diversion contract in County Mayo.


Civil and environmental contractor MEIC of Ballinasloe, County Galway, on behalf of Mayo County Council, is using two 4” Super-silent pumps and three water settlement tanks to divert the Bundorragha River at Delphi while essential repairs are made to an old stone bridge further downstream.


The contractor was required to lower the water level so that shuttering for two concrete wing walls could be fixed beneath the nine-metre span two-lane road bridge. The walls will strengthen the old bridge, which has suffered from extensive scour, and prevent further erosion by the water.


“Our biggest challenge here was the environment,” says Ronan Butler, project manager with MEIC. “It's a really beautiful landscape and the river is an important salmon fishery - you can have salmon swimming right past your legs when you're wading in the river!”


The river also contains rare pearl-mussels which are highly sensitive to alkalinity - a major risk where concrete is being poured.


Having temporarily dammed the river upstream from the bridge, MEIC used 4” Super-silent pumps from Groundforce's Portlaoise depot to pump the water at the rate of 100 litres/sec through the three settlement tanks.

The Groundforce range of pumps is fully bunded to ensure no fuel or oil spillage can contaminate the environment. The settlement tanks each measure approximately 4m x 2.5m x 1.5m and contain a series of weirs to separate sediment from the water.


In this instance, MEIC added an additional “silt fence” comprising shallow trenches dug in the boggy ground and lined with a filter membrane. Water pumped through the settlement tanks was allowed to flow into these trenches and soak through to find its own way back into the river below the bridge.


“We've never employed this method before but the results are excellent,” says Mr Butler. “We start pumping two hours before we start pouring concrete and continue pumping for two hours afterwards until the concrete has started to cure.


“The water we return to the river is cleaner than when it was extracted - it's near drinking water quality,” he says.


“We chose to use the Groundforce pumps on this project because we have had good service from the company in the past and because we needed bunded pumps for the sensitive location,” explains Mr Butler.


“And because there are houses quite near the site, we wanted the quietest pumps we could find,” he adds.


The pumps were delivered on 23 August and off-hired after the concreting was completed in mid-September.


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