Project Summary
This project involved the installation of a foul sewer collection system within Achill town and outlying areas, in County Mayo, in Ireland.
Project Description
The works included 5 pumping stations, a wastewater treatment plant and a marine outfall. Approximately 6km of sewers were laid along busy narrow roads, the majority of which were rising mains. The sea outfall is a 300mm HDPE pipe which runs 190m out from the shore and has a branched diffuser protected with rock armour. The diffusers sit above low tide level (see photograph), and a tidal clock forms part of the SCADA system which discharges the treated waste only when the tide has risen above them.
Coffey Construction was responsible for the design and construction of the scheme and for a 6-month maintenance period. The design and installation of the Process and MEICA elements were undertaken by Coffey Construction’s subsidiary, Coffey Water. The civil engineering design was contracted to HGL O’Connor. The project value was £3.9m and the works were completed in 2010.
Project Delivery
Pipelines
Pipelines on this contract consist of gravity and rising mains. In total there is approximately 6000m of a trench. For the majority of the pipeline, there is a gravity main (dia 225mm and 300mm) in the trench, depending on the location you may have a combination of gravity, rising main (1km of size 160mm dia pipe), water (700m of 150 dia water main)and ducting. The pipeline was laid in through the middle of the town and the surround back roads in the village. A lot of rock was encountered while laying the pipes and gas blasting were used in certain sections to fracture the rock. The depth of the work was 6.0m in certain sections. The pipeline was excavated using 45-ton excavators with one excavator have a breaker and the other 30ton carrying out the backfilling and lifting of the pipe. The pipeline was reinstated every evening as the works were being carried out around the town and there was a lot of public interaction with the works. The works were fenced off at all times to prevent the public having access to the works.
An effluent outfall pipeline was laid out 190m into the harbour.The diffuser system will consist of a vertical 300mm pipeline with 300mm branches off the top, each ending with a check valve system. The diffuser system will be complete with a diffuser chamber finished with rock armour approximately 190m from the shore.The works and laying of the pipe were carried out on a low spring tide.
Pipelaying in the construction of the foul sewer involves 5564 metres of 225mm twin wall PVC-U sewer pipes with spigot and socket flexible joints.
Pipelaying in the construction of the foul sewer involves 378 metres of 300mm of concrete sewer pipes Class H with spigot and socket flexible joints
Pipe laying in Rising Mains
Pipelaying in the construction of rising mains from the various pumping stations involves 5564 metres of HPPE pipe Class SDR11 fusion jointed complete with sluice valves, scour valves and air valves.
Pumping Stations
- All Civil Works associated with Pumping Stations at:
- Sraheens Pumping Station No. 1
- Sraheens Pumping Station No. 2
- St. Finions Pumping Station
- Achill Sound Bridge Pumping Station
- Old Railway Pumping Station
- Waste Water Treatment Plant
New Treatment Plant
The project involves the construction of a Wastewater Treatment Plant and Ancillary Works. The Treatment Works has been designed to treat wastewater from an equivalent population of 1200. The works will include the construction of Inlet Works, Treatment Units, Control Building together with Rising Mains and interconnecting Pipework, outfall pipework to sea, associated with Site Works.
The works to be completed will also include Entrance and Accommodation Roads, and Site Development all as previously described in Section Five of this Specification.
Concrete Works
More specifically the works to be completed are as follows:
- Inlet Pumping Station – 1 no
- Inlet Works – 1 no
- Flow Splitting Chamber – 1 no
- SBR Unit – 1 no
- UV Sterilisation Chamber – 1 no
- Final Effluent Sampling & Measurement Chamber – 1 no
- Tidal Tank – 1 no
- Activated Sludge Pumping Station – 1 no
- Supernatant Pumping Station – 1 no
- Sludge Pumping Station
- Sludge Thickening/Storage Tank – 1 no
- Control Building – 1 no
- Control Building – 1 no
- Air Blower Slab– 1 no
Additional Works
In addition, the contract included for the construction of the following additional elements of work:
- Interconnecting Pipework including outfall pipework from Tidal Tank
- Landscaped Screening Mounds and Landscaping.
- Paved Areas and access Roadways, Turning Bays, and Skip Areas
- Flow Meter Chambers
- Site Drainage, cable ducts and water mains around the sites.
- Cattle Grid, Entrance Gates and Boundary Walls and Fencing.
