WASTE

Big pipes cross playground

Tuesday 27 July 2010, 7:54AM
By Gisborne District Council
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GISBORNE

Gisborne’s Adventure Playground has become a big-boys’ playground over the past few weeks as Connell Contractors’ workers lay pipes to take screened and treated wastewater to the existing Stanley Road treatment site.

Connells are subcontracted to HEB Structures, lead contractor for the $39.5 million Gisborne Wastewater Project. 

HEB Structures project engineer Simon Davies says that with initial works around the existing milliscreening plant completed on Saturday, works have now switched to the outfall line.

“Pipes will be laid down the side of the Stanley Street plant to the existing outfall, ready for connection later in the year. We will soon start pressure testing the pipes and also building major pump stations at Lytton Road, and Innes, Parkinson and Banks streets.

“We expect to see the pipework across the Adventure Playground completed this week.”

The 700mm diameter pipes have already been laid from outside the outfall pump station in Banks Street – the new site of the wastewater treatment plant --down Banks Street and under Awapuni Road to the Adventure Playground.

Before the Connells’ team digs trenches and places pipes, ground water is pumped out of the area by “wellpoint dewatering”. A series of pipes is thrust vertically several metres into the ground, connected to another horizontal pipe and then to a pump.

Meanwhile, work on the Banks Street site is moving ahead at pace with three main buildings being erected and three pump stations in progress.

About two thirds of the 40 pre-cast concrete panels – each of them 8.8m tall and 8.5 tonnes -- have been erected to form the external wall of the biological trickling filter tank. A bed of concrete columns have been poured in situ to form the foundations for the tank floor. These will support the 11,000 haybale-like black plastic blocks (called structured plastic media) with which the tank will be filled. Pre-treated wastewater will be pumped up through the tank’s central column to a height of 8m from where it will be distributed via rotating arms to trickle slowly through the plastic media. The resulting biotransformation process will see human waste transformed into plant-like matter before it is discharged through the existing outfall pipe 1.8km into the sea.

Work is also progressing on the western industrial separation scheme where a 200mm rising main has been installed to cross the railway, next to where it crosses SH35 near McDonalds Road. In the Aerodrome Road area, pipes are being laid towards the airport runway and eventually to town.