Over the past 25 years work has been progressing on upgrading and refurbishing the old drainage system and providing new trunk sewers to open up additional land for development, in Sligo city and its environs. To date the Main Drainage Scheme has been constructed in three stages.
Stage I of the scheme was completed between May 1975 and May 1977. The work completed under this stage consisted of the construction of the new Riverside Interceptor from Doorly Park to the tank sewer at Custom House Quay. It also included the construction of new sewers in the Cornageeha and Tonaphubble areas. These works increased the capacity of existing sewers within the city and eliminated a number of private discharges to the Garavogue River. It also made redundant the old Doorly Park Treatment Works and opened up the Cornageeha and Tonaphubble areas for development. The sewers were designed to serve a total of 1,300 houses along with the Industrial Estate at Cleveragh.
This stage, completed between September 1975 and September 1978, provided for the construction of a new trunk sewer to serve some 38,000m2 of industrial buildings in Finisklin. Also included in this stage was the extension of a existing 300 dia. Sewer in Finisklin Road and the provision of an ejector station to pump foul flow into this extended sewer from houses in Alma Terrace. These houses were originally sewered individually to the estuary and were too low to be serviced by gravity into the drainage network. The present outfall to the estuary at the east end of the Deepwater Berths Road was also constructed under Stage 2.
This stage was subdivided into 2 phases as follows.
Phase I included for the construction of a new trunk sewer to open up areas for development in Caltragh, Maugheraboy and Cornageeha. It was in effect a continuation of the Stage 2 sewer serving Finisklin. Completed between February 1980 and April 1981, this stage also included for the construction of a new sewer along Lord Edward Street.
Phase II of Stage III consisted of the construction of a new gravity sewer from the old tidal storage tank at Cartron to a point approximately 200m downstream, the abandonment of this old tank and the diversion of the north side flow westwards through this new sewer before being brought across the estuary through a new inverted syphon to the existing outfall point on the south side.
It also included for the construction of the Mall Interceptor which picked up isolated discharges to the Garavogue River on the North side of the Mall, discharging into the Riverside Interceptor on the south side of the river through an inverted syphon.
Phase II also included for the construction of the Tank Sewer Duplicator from the Customs House along Ballast Quay to the outfall location together with new sewers to serve existing ribbon development and to open up new areas for housing developments in Kevinsfort and Ballydoogan/Woodville areas to the west of the town.
In May - September 2000 a significant extension to the network was provided under a Service Land Initiative Scheme to provide for development of the Caltragh area opening large areas on the south of the city for imminent development.
Network modelling of the sewer systems was carried out and a hydroworks model was prepared. A Polluters Pays Principle Report was prepared in order to establish the likely percentage demand from the industrial sector. A foreshore lease was obtained from the Department of Marine. Maritime Archaeological assessment and a monitoring programme of the Garavogue River and estuary have been reported in accordance E. I. S. Certification.
The new secondary treatment plant and associated outfall pipeline will be constructed under Stage IV of the scheme. Jennings O’Donovan & Partners, in association with J B Barry & Partners Limited, Consulting Engineers, have been appointed as client representatives and pre-qualification process is complete.
The plant will be constructed in a bunded area in the estuary, which was developed during dredging works, which took place in the Harbour area in the 1980’s. The plant will be designed for a population equivalent of 50,000 and the tendering process is expected to be completed by the end of 2004.
Also to be included in this stage are storm overflow facilities and associated pumping plant adjacent to the existing outfall, a pumping main from the existing outfall to the treatment plant and a further sewer line running eastwards from the end of the Deepwater Berths Road to the main pumping station will be provided. Two isolated discharges to the river estuary near Hyde Bridge are also to be connected to the drainage system.
An Advanced Civil Works Contract for the provision of the new Waste Water Treatment Works was awarded to Ascon Ltd, Civil Engineering and Building Contractors, which included provision for the Civil Engineering Works required for the construction of Accommodation Works in advance of the proposed treatment works. The works completed in December 2002 included repairs to and raising of the bund wall at the proposed Waste Water Treatment Works site, provision of 130,000m3 stone fill, removal of an existing pumping station, upgrading of the substandard Finisklin Road to the county boundary, 800mm pipeline rising main and service pipe work and the provision of an access road to the bund site.
The Advanced Civil Works Contract has cleared the way for the Design, Build and Operate Contract proposed for the treatment process. The DBO Contract will be designed for a population equivalent (p.e.) of 50,000 at 60g B.O.D. h/day with facility to upgrade to 80,000 p.e. Sligo County Council is looking forward to the Public Private Partnership approach being adopted to deliver and operate this treatment plant. Under the Government’s ‘Polluter Pays’ policy framework, all non-domestic users of this new facility will be expected to contribute to the cost of construction and to the ongoing management of the facility.
In 1993 the Department of the Environment, Heritage and Local Government engaged the consultants Weston-FTA Ltd to identify appropriate solutions for the treatment and disposal of sewage sludge in Ireland, taking into consideration legislative, technical and environmental requirements. The completed Sludge Strategy Study divided the country into 48 separate regions for the purposes of sludge management. Sligo is located in Region Five - Sligo/Leitrim - which includes much of south Sligo, the northern half of County Leitrim and part of County Cavan. Region Five has Sligo as the hub centre for the treatment of sewage sludge throughout this area. Thus the new works, in addition to catering for primary and surplus activated sludge generated on site, will also cater for imported sludge from other Local Authorities wastewater treatment plants throughout Region Five.