TRANSPORT AND TECHNICAL SERVICES
VAL PLAISANT FOUL and SURFACE WATER SEWER UPGRADE
Contract 10203
Purpose of the Report
To seek approval to issue Tenders for the construction of the above scheme.
Background
This scheme is a combination of the Capital programme for upgrading the existing foul sewer network, and for separating existing combined sewers into individual Foul and Surface Water Sewers within St Helier.
The existing foul and combined sewers in Val Plaisant, between Clarendon Road and Victoria Street, are served by an existing Combined Sewer Overflow (CSO) at the junction of Val Plaisant and Victoria Street. This CSO has an outlet to the surface water tunnel that runs from Grands Vaux down to the West of Albert Pumping Station and thence to sea.
The Island Sewer Model has shown that the CSO operates, i.e., discharges storm sewage to the surface water system, on as little as a 1 in 1 year storm. The report entitled THE FINAL ANALYSIS OF THE OPERATION OF THE COMBINED-SEWER OVERFLOWS WITHIN ST. HELIER dated July 2000, recommends a number of solutions to improve this situation.
The solutions proposed are that the forward flow at the CSO be limited to reduce loading on under capacity lengths of sewer downstream, that the upstream foul sewer be increased in size to provide storage, and that the weir wall in the CSO chamber be raised to reduce the incidence of spills to the SW system. When these measures are implemented, it is predicted that virtually all spills at the CSO will be eliminated up to a 30 year event.
Furthermore, in recent years there have been sewer separation schemes to serve Clarendon Road and Midvale Road, and these at present are connected to the combined sewer in Val Plaisant that is linked to the Sewage Treatment Works.
Therefore, at the same time it is intended to install a separate surface water sewer to pick up these areas, together with existing Val Plaisant road drainage and the separated sewers in Convent Court, and discharge them to the surface water tunnel in Val Plaisant. This will not only reduce the loading on the Sewage Treatment Works, but will also reduce the likelihood of overflows at the CSO.
In order to facilitate the laying of the required sewer pipework, it is necessary for Jersey Gas, Jersey Water and the JEC to divert some of their existing services. The majority of the work undertaken by Jersey Gas shall be undertaken as part of their main upgrading programme; however the department will be liable for the work at the junction of Val Plaisant and Victoria Street. The cost of the work by Jersey Water and the JEC shall be borne by the Department. All works associated with the service companies will be carried out independently by the relevant service company prior to commencement of the sewer scheme.
Discussion
The existing sewers in Val Plaisant are very deep, in excess of 5 metres to Invert Level, so an alternate solution to the pipe upsizing was sought. The Island sewer model showed that similar results could be achieved by laying a piggy back sewer above the existing sewer. It is therefore proposed to lay approximately 300 metres of 500mm diameter foul sewer in Val Plaisant between Victoria Street and Clarendon road. A surface water sewer, varying in diameter between 400mm and 700mm shall be laid in the same trench above the new foul sewer.
It is proposed to seek tenders for the foul and surface water sewer upgrade contract from the following local contractors:
Geomarine Limited
P Trant (Jersey) Limited
Brenwal Limited
The estimated cost of the contract is £950,000.
Given the size and nature of the project, consideration has been given to inviting UK contractors to tender for the work. However, whilst this would have the benefit of marginally increasing competition at the tender stage, there are several significant risks and dis-benefits of so doing.
These include the fact that the UK Water industry is particularly buoyant at this time which is resulting in a skills shortage on the mainland. Given that there will be little opportunity for UK contractors to obtain repeat work from this Department, should a UK contractor succeed in winning this contract, numbers and quality of labour is likely to be patchy which will not assist in the construction of a scheme which has some difficult construction elements.
In addition, allowing UK contractors the chance of obtaining this work would undermine the good relationship that exists between this Department and local contractors, some of whom are currently short of work. Failure to win this contract by a local company could further deplete the Island’s skill base.
For these reasons, it is recommended that UK contractors are not asked to tender for this scheme.
However, whilst the local contractors listed above have the capability of carrying out the work proposed, in order to maximise the skills that the contractors have available, it is proposed that the tendering process for this scheme be a two part bid, based on a quality and price submission, rather than basing the award on price alone.
This form of tendering could result in the contract being awarded to the contractor who did not submit the lowest price but should ensure that the appointed contractor has fully understood all the requirements and whose overall submission was best in terms of quality.
This form of tendering has already been used successfully by the Department on behalf of the Education Committee for construction works at Le Rocquier School and also for major road resurfacing works carried out by the Department.
In addition to the estimated construction cost above, the service company diversion work is estimated at £100,000. It is anticipated that the service company works will commence in October 2007 for an approximate six week period. It is anticipated that the installation of the foul and surface water sewers will commence in January 2008 and take approximately sixty five weeks.
Sufficient funds are available in Vote C0418 – Sewer Reconstruction
Recommendation
The Minister is requested to approve the scheme so tenders can be issued to the above contractors on the basis of a two part submission.
Reason(s) for Decision
The scheme is both part of the continuing foul sewer and CSO upgrading programme as well as the ongoing programme of separating surface and foul water drainage in St Helier.
Sufficient funds are available in Vote No C0418 (Sewer Reconstruction)
Action Required
Tender documents to be issued to Contractors.
Written by: | G. Le Monnier - Assistant Engineer, Engineering Design and Technical Records Section |
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Approved by: | John Rogers – Director of Waste Management. |
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22nd June 2007