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Guernsey Water has a responsibility to remove wastewater from all properties on the island and treat it appropriately for return into the environment. We are also responsible for the surface water infrastructure on the island, which transports run-off from streams, properties and roads safely out to sea.
Beneath the island's roads is a network of foul water sewer pipes totaling approximately 167km that collect sewage from around 80% of domestic households. These sewer pipes, collectively referred to as the sewerage system, are cleaned, maintained and inspected on a regular basis so as to ensure satisfactory performance throughout the life of the asset.
There are 56 pumping stations which transport wastewater to the Belle Greve Wastewater Centre, where non-biodegradable matter over 6mm in diameter is removed from the flow by mechanical screens. Grit, which would otherwise damage pipelines and pumps, is also removed. The resulting wastewater is then discharged through a long sea outfall pipe which extends more than 2km out into the fast flowing waters of the Little Russel.
Ultra-Violet (UV) rays of the sun and the natural wave action together with massive dilution provide the current bacteriological breakdown, such that any effects from the outfall are virtually eliminated once more than 20 to 30 metres away. This was backed up by scientific evidence provided by global water quality experts Intertek, who carried out an in-depth study of our bathing waters back in 2011, which can be viewed by clicking the button below.
The surface water drainage system is a combination of douits, ditches, channels, culverts, pipes and 9 pumping stations that take rainwater and any other liquid run-off from the land (a surface water outfall is shown in the image below). Many landowners throughout the Island share the responsibility for ensuring that these are kept clear from debris that would otherwise block the flow of water and cause flooding.
In times of exceptionally heavy rainfall and when the main sewerage system cannot cope with the flows from combined systems then 'stormwater' (a mixture of rainwater and diluted sewage) overflows into the surface water drainage system. Such occurrences are carefully monitored as the frequency of these 'spills' is an indication as to the operational efficiency of the foul water network.
Most modern properties (built after 1970) have separate foul-water and surface-water pipes. Properties built prior to this, or in areas where there is not a dual pipe system, have what is termed 'combined drainage'. This means that rainfall significantly increases flows into the foul water system. As part of Guernsey Water's Surface Water Management Policy, we are encouraging separation and attenuation of surface water into the foul network. This will also mean reduced costs to transport flows to our Belle Greve Wastewater Centre.
There are in the region of 4,000 properties that are not presently connected directly onto the public sewer network and these have storage tanks, known as cesspits, which have a legal obligation to be watertight and which are emptied regularly by road tankers. The sewage is taken by road to locally convenient points on the sewerage system where it is discharged.
Previous business plans have prioritised sewer network extensions to provide connections to those properties not currently served by our 'main drain'; however the cost of this is high when compared with the limited environmental and public health benefits. Therefore a detailed review of this strategy was undertaken and a report submitted to the States assembly. As a result, our previous target of a 95% customer connection rate has been rescinded in favour of including this activity in our investment plans as other priorities allow. This means that we have not planned to carry out any further sewer extensions before 2022, which will allow us to focus our resources on tackling the higher priorities of flooding and pollution from sewer overflows.
The Cesspit Emptying Service operates from Griffiths Yard with a fleet of 36 tankers, collecting approximately 650 loads of sewage every day! This service is operated by States Works through a contract with Guernsey Water.
The service is for customers whose property is not connected to the sewer network. At these properties wastewater is held in a cesspit until it is collected by a cesspit tanker. The tanker then travels to an emptying point, where it discharges the sewage it has collected into the island's sewer network. Our pumping stations then transfer it through our network to Belle Greve Wastewater Centre.