Northern Ireland: Kilkeel Sewage Treatment Works

Brief Description:

The construction of a major extension to an existing sewage treatment works at Rooney Road, Kilkeel, Co.Down, to give a works capable of providing EC compliant treatment for an inlet capacity of 12.5 Ml/day.

The existing works are situated in a very restricted site bounded by commercial premises and adjacent to the major fishery harbour of Kilkeel.

The Works included:-

The construction in reinforced concrete of the following structures:-

A new inlet works, including screening and degritting facilities and anoxic tanks;

2 No. oxidation ditches approx. 41m x 18m x 4.5m deep;

2No. hopper bottomed final settlement tanks, 20m diameter x 3.7 m deep;

2 No. Storm tanks 12.5m diameter x 4.5m deep;

A sludge thickening tank, 9.25m diameter x 4.8m deep;

A sludge holding tank, 11m diameter x 3m deep.

An Outfall Pumping Station.

The contract also included the construction of new access roads, an air blower house, a new control building and various retaining walls.

The laying of a 150m long new 600mm dia. storm overflow pipe to the Kilkeel River, together with the demolition of various redundant structures and the laying of a substantial length of interconnecting pipework and some 2,300 m of ducting.

Excavation for most of the main structures, at depths of up to 7.5 metres, was intended to be carried out within sheet piled cofferdams,due to due to the nature of the ground, the relatively high standing water level and the restricted nature of the site.

However, as a result of vibration caused by some sections of the sheet piling encountering an unexpectedly dense layer of gravel, it was deemed necessary to complete the remaining cofferdams using secant piling in order to minimise the effect on neighbouring properties.

Construction of the works involved the provision and placing of a total of over 3000 cu.metres of concrete and some 300 tonnes of reinforcement.

The construction programme was greatly restricted by having to maintain the existing over- worked treatment works in a fully operational state throughout the contract period and also having to contend with some of the wettest weather on record adding substantially to the stormwater intake.