Guernsey Wastewater Introduction
Mandate
The mandate of Guernsey Wastewater is:
"To deliver to its customers a reliable wastewater collection service which conveys, treats and returns flow to the environment sustainably and efficiently.”
Beneath the Island’s roads is a network of foul water sewer pipes totalling approximately 150km that collect sewage from 74% 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.
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 discharge’. This means that rainfall significantly increases flows into the foul water system.
There are in the region of 5,000 properties that are not presently connected directly onto the public sewer network and these have storage tanks, known as cesspits, which are legally supposed 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.
Through careful analysis of the sewerage system engineers are able to determine the most cost effective way in which to maintain, operate and expand the network. It is believed possible to connect 95% of the properties onto the sewerage system at reasonably economical rates. The remaining 5% are more distant from the public sewers and could not, on their own, justify the connection costs.
There are 57 pumping stations which transport the wastewater to the centralised treatment facility at Belle Greve. Here, litter (in the form of non-biodegradable matter) is chopped up and grit is removed which would otherwise damage pipelines and pumps. The resulting wastewater is then discharged through a long sea outfall pipe which extends more than 1,600 metres out into the fast flowing waters of the Little Russel (at the present time consideration is being given to further waste water treatment before discharge into the sea).
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.
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. 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 thus cause flooding.
In times of exceptionally heavy rainfall and when the main sewerage system cannot cope with the flows from combined systems (as mentioned above) 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 state and adequacy of the foul water network.
Planning for the Future
In order to make sure that the wastewater infrastructure is maintained and improved and that customers get the best possible service, the wastewater section is in the process of putting together a number of key documents.
The first of these, the Drainage Area Plan, involves surveying the existing sewerage network through the use of CCTV cameras, and making recommendations to rehabilitate any structure, service or hydraulic problems that might exist. The second document, the Network Extension Plan, details the plans to get 95% of the Island's population connected to the public sewer system (the main drain). Both of these documents will feed into the Wastewater Business Plan, which will be released in 2012. All of these documents will be available to download from this website.
The Wastewater Business Plan will outline the strategic direction of the wastewater section, and list the capital projects and the corresponding expenditure required to carry out the improvements needed.
The main project at the moment involves installing treatment at the Belle Greve station, where all wastewater flows are now directed (with the exception of minor flows from Fort George, which will be redirected in the near future). A design consultant has been appointed to progress how the treatment will work. However, it is important for Guernsey Wastewater to assess the marine impact of wastewater outfalls before determining the design criteria for any sewage treatment solution.
Guernsey Wastewater will present a full report on sewage treatment to the States of Guernsey in January 2012.