Abu Dhabi Sewerage Services Company (ADSSC) has awarded one construction contract and selected preferred bidders on a further two contracts on the project to build a AED5bn ($1.4bn) sewer beneath Abu Dhabi Island.

The Strategic Tunnels Enhancement Programme is the largest infrastructure project the Abu Dhabi authorities have tendered this year.

Italy’s Impregilo has won the AED891m contract to build the middle section of the 40-kilometre-long tunnel that will take sewage from Abu Dhabi Island to treatment plants at Al-Wathba, outside Abu Dhabi city.

“The 40-km-long tunnel will take sewage from Abu Dhabi Island to Al-Wathba”

The contractor will build 15 kilometres of the tunnel between Mussafah and Mafraq, with a diameter of 6.3 metres and six 40-50-metre-deep access shafts.

Impregilo will start work by the end of the year and should finish the job in the second half of 2013.

ADSSC has also picked Impregilo as the preferred bidder for a second package estimated at AED785m, which involves the construction of a 15.6km, 5-metre-diameter tunnel between Mafraq and Al-Wathba. The other bidders are France’s Bouygues, Lindenberg-Emirates, Germany’s Ed Zueblin, and Italy’s Astaldi. South Korea’s Samsung Corporation is the preferred bidder for the third package, estimated to be worth AED1.1bn, to dig the 16.1km, 4-metre-diameter tunnel from Abu Dhabi Island to the Mussafah area. The other bidders for the third package are Brazil’s Odebrecht and Australia’s McConnell Dowell.

ADSSC has also invited contractors to bid by mid October for an estimated AED2bn contract to build a pumping station at Al-Wathba that will pump sewage from the tunnels to the treatment plants. The prequalifiers for the pumping station include Bouygues; Vinci Construction Grand Projets, also French; Lindenberg-Emirates; Odebrecht; Samsung Corporation; and the local/Australian Al-Habtoor Leighton Group.

ADSSC, which was spun out of Abu Dhabi Water & Electricity Authority (Adwea) in July, is investing heavily in wastewater infrastructure.