Kaymac Marine & Civil Engineering were commissioned by Morgan Sindall Plc to assist with Early Contractor Involvement to aid in the design and installation of a new 642m long outfall pipe in the Village of Parrog, Pembrokeshire.
The original outfall pipe installed in 1964 had fractured in 2008, which caused treated effluent to enter the sea below the Mean Low Water Springs level, at a point inshore of the consented discharge point.
The quality of the water had been continuously monitored since the fracture and the Environment Agency had stated that unless the test results improved, this popular Newport Sands beach would lose its Eco-Label 'Blue Flag' status, which in turn, will result in the small village becoming less popular with tourists who are so vital to the local economy.
Kaymac's experience in the marine environment allowed the design to be reviewed with regard to its 'buildability' and being able to source and transport the required materials to the site. The design was altered so that the original scope of importing thousands of Tonnes of rock as backfill material could be replaced with the use of pre-cast concrete weight collars and mattresses that would be fitted to and around the pipeline, with the pipe being laid in a deeper excavation as to what was originally proposed- Thus providing a more cost effective and environmentally friendly solution.
Kaymac planned to undertake the project via both land based and marine based operations. The land based plant included 2 No. 70T telescopic piling rigs, which were required to install over 530 No. Larssen sheet piles over the course of the project. A temporary stone access ramp was installed from the land to the beach to allow the plant access to conduct the works. The ramp lay adjacent to an original 130 year old Grade Listed lifeboat slipway- access on the slip was impossible on the slipway as any tracked plant could cause significant damage to the structure.
Access for the land based plant and materials became an issue as the works location was approximately 1 mile away from the nearest usable beach access slipway. Due to a tidal range in the region of 3.8m and with relatively little storage space on the beach, it was decided that the best option would be to import the pipeline, rather than attempt to weld smaller sections of pipe together on the beach. This would also be in the favour of the local residents, as to weld the pipe on site, would mean that the few access roads would not be kept busy with deliveries during the busy Summer months.
With careful planning and internet consultations with a Norwegian supplier, the pipeline was sourced, fabricated to the required design and delivered via a tug boat from Norway to Fishguard Harbour (over 960 nautical miles), to await the necessary preparatory works required by the design. Once delivered, the pipe was split into 3 lengths- 550.0m, 53.0m and 27.0m. Over 200 No. Pre-cast concrete collars each weighing 320 kg, were individually attached to the pipe by Kaymac operatives and steel sinking lids were fixed to the open pipe ends. These sinking lids included fixed valves, which allowed Kaymac to control the influx of water and air into the pipe during the sinking procedure.