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St Sampson Wastewater Catchment Improvements
Guernsey Water is currently carrying out works to improve the wastewater catchment around St Sampson Harbour, the project is the biggest in the company's current 10 year business plan (launched April 2016) with an investment of £3 million.
The Reasons For This Major Investment
The water quality on both the north and south sides of St Sampson Harbour is sometimes an issue after very heavy rainfall when the combined sewer overflows (CSOs) activate. This can have an impact on the quality of the nearby bathing waters.
The area around Summerfield Road and La Hure Mare is prone to flooding during heavy rainfall which needs to be resolved.
The pumping station is very deep and prone to failure making access difficult so maintenance work needs to be done to upgrade this.
The proposed plans to develop Leales Yard and other sites in and around St Sampson and the Vale are likely to present an even greater demand on the existing sewer and foul water system so this needs to be addressed.
Phase one of the project, the extension and upgrade of a pumped rising main was completed in May 2017, this enables the pumping station to handle greater flows, reducing the reliance on combined sewer outfalls (CSOs) to the north & south of the harbour entrance and therefore greatly reducing the risk of pollution in the area.
"In this area the geography of the island dictates the need to pump foul water to our BGWwC (Belle Greve Wastewater centre). On occasions, particularly during heavy rainfall, the sewers become overloaded resulting in the need for the various CSOs to come into operation. This is by no means ideal. The investment we have made here reinforces the importance we place on our environment as well as our focus on longer term strategic improvements to the island's wastewater infrastructure," Mr Walker said.
Part of this first phase also included the installation of a HDPE (5m x 3m x 2.5m) tank under the Bulwer Avenue car park (opposite the Les Grandes Maisons Road junction) this will act as a storage tank during periods of heavy rainfall and is connected to the gravity sewer which flows to the BGWwC.
Phase two will involve replacing a 235m length of the Vale Road sewer (diameter 900mm) to increase its size and storage capacity in order to prevent flooding in the area as a result of the greater flows that will be passed forward from the HSS pumping station. This phase will run sequentially with phase three
Phase three will involve the build of new and upgraded gravity sewers (length 475m, diameter 225mm-450mm) around Summerfield Road and La Hure Mare. This will divert flows from a very overloaded part of the network which will reduce the risk of foul water flooding and also the frequency and volume of spills at the CSO's.
It should be noted this work is not targeted at resolving the surface water flooding that occurs around the Vale Avenue and La Route du Braye junction
The fourth phase will be upgrading the pumping station at St Sampson Harbour, This will include:
- Replacement of electrical components which are badly corroded and at the end of their design life.
- Changes to the access arrangements to make the working area more safe and secure
- Improvements to the pumps to enable a greater range of flows to be pumped to BGWwC, up to a maximum of 150 L/s