Drogheda Wastewater Treatment Plant

Project Summary

Coffey Construction completed this £4.4m contract for Louth County Council to upgrade an existing wastewater treatment works from a capacity of PE 68,000 to a capacity of 101,000 in April 2007.

Project Description

CCL was main contractor and economic operator for all civil engineering works relating to the upgrade of the existing plant and was Principle Contractor for the site.The works included the construction of a primary settlement tank, 2 aeration tanks (1,500m3), a final settlement tank, pumping station, interconnecting pipework and associated site works.  The project design was provided by the client.

Project Delivery

The site had three levels, each supported by large retaining walls, and the tanks were built in excavations up to 8 metres deep.  Several of the tanks were constructed fully underground. The works were undertaken within a constrained site and the site was also live, as the existing plant remained fully operational throughout the works.  Three contractors were working on the site: CCL, the M&E contractor and the plant operator.  As Principle Contractor, we organised fortnightly contractor coordination meetings which were attended by the Client and Client’s Representative to ensure that the works of each contractor were properly planned and the potential for disruptive conflicts minimised.  Disruption was minimal, and a potential area for additional contractor costs was removed.

The construction of several of the new tanks was complicated by their proximity to existing tanks and buildings.  In one instance, the position of a new tank in the design required excavation to be carried out which would undermine a retaining wall.  We proposed that the tank had to be moved a few metres to avoid additional client costs to support the wall.  In a number of instances throughout the project, we encountered services which were not as identified on the contract drawings, and where practical, we proposed that the works to be constructed be moved to avoid diverting the services and to mitigate against delays.  As a result, we started to undertake trial trenching in advance of all excavation works.

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