Trial trench surveys

As part of our application for development consent, we clearly identified the potential impacts of installing the replacement pipeline as part of the Environmental Impact Assessment process. This covered social, cultural and historical impacts, not only impact on the natural environment. We also conducted surveys to assess the engineering proposals for the pipeline, such as assessing potential access routes or ground conditions where trenchless installation techniques could be used.

Our final route for the replacement underground pipeline includes ‘Limits of Deviation’, which show the maximum area within which the pipeline could be installed, if we are granted development consent. While our application is being examined by the Planning Inspectorate, we are continuing to carry out surveys to help us determine the most suitable place to install the replacement pipeline within the Limits of Deviation. This will include surveys to help us better understand existing underground utilities and archaeological features in the area we are looking to install the pipeline.

When preparing our application, we collected information on underground services and carried out above ground scanning of roads to help determine location of these services. However, in congested areas there are challenges in accurately locating the position, and particularly depth, of services using this method.

We are now looking to establish the exact location of the existing utilities within roads by conducting utility trial trenching. This will help us to produce a more robust assessment of the position of existing utilities and determine the most suitable place to install the replacement pipeline within the Limits of Deviation. Safety is a key priority for the project and it’s vital that we understand what is already in the roads we intend to install along, if granted permission.

On behalf of Esso, O’Connor Utilities will be working in roads through Hampshire and Surrey including Cove Road, Balmoral Drive, Red Road, Canford Drive and Ashford Road. We will post a letter to addresses within 50 metres of the location of the trial trenches. The works will last for approximately five days in each location. The project will be working closely with local highway authorities to seek permits for the work and will provide notice with advance warning signs and letters to local residents. The works began on 18 November 2019.

 What can I expect to see?

  • Prior to works contractors may need to mark the footpaths and road surfaces with coloured spray paint. The paint is a water-based formula and should biodegrade in six to eight weeks.
  • The contractor would then use cable avoidance tools (CAT) to detect buried utilities prior to any ground excavation.
  • Excavation will either be done by hand or by using a vacuum excavator which can quickly create precise holes to aid in uncovering buried utilities. In some areas we may consider mechanised techniques.


Traffic management

Temporary traffic management (traffic lights) will be used and you may experience some disruption. We would like to apologise in advance for any inconvenience caused and will endeavour to keep the disruption to a minimum. There may also be a requirement to conduct ground investigation works across vehicle access points, but we will always maintain access by means of ramp boards and our Site Construction Manager will be on hand to discuss individual circumstances.

We are aware that some residents may have special requirements, in particular, mobility problems, or questions about the work. Please contact the project team.

Alongside the utility trial trenching program, the project is also carrying out further above-ground tracing surveys that will allow us to produce a more robust assessment of the placement of utilities. Utilities can cross over each other and do not necessarily stay in one position along the length of a road so we need to survey the length of some roads through Surrey and Hampshire. As with the utility trial trenching, the project will be working closely with local highway authorities to seek permits for the work and will provide notice with advance warning signs and letters to local residents. These surveys will take a one to two days in a single location. The contractor will need to mark pavements and road surfaces with coloured spray paint. The paint used is a water-based formula specifically designed for this purpose and should biodegrade in six to eight weeks. On-street parking may be suspended on some roads throughout the surveys.

Some of the above-ground tracing surveys will take place at night. This approach has been agreed with the local highway authority. The project does not anticipate much noise disturbance. The contractor is legally required to use vehicles with flashing amber warning lights to ensure their safety during the works and will use a temporary traffic management system to minimise disruption.

Contacting us

We are aware that some residents may have special requirements, in particular mobility problems, or questions about the work. Please contact the project team.

Before installing the replacement pipeline, we will be checking to see if there is any significant archaeology within the Order Limits of the pipeline to determine any mitigation required during construction. We will be carrying out archaeological trial trenching across the pipeline route and will begin this work in early 2020.

What is archaeological trial trenching?

Archaeological trial trenching helps determine the extent, complexity and state of preservation of archaeological remains, allowing for more detailed mitigation measures to be planned and reducing the risk of delays during construction if unknown archaeology was to be found.

Trial trenches are dug using mechanical excavators and typically a team of 4-5 personnel will be working on site including an archaeologist.  Several trenches are dug in each location to give a good indication of the archaeology in the area. The depth of the trial trenches will vary, however it is unlikely that any trench would be more than 1m in depth.

We will seek to to agree suitable and appropriate access with landowners in advance to minimise disruption and agree appropriate mitigation. The locations of trial trenches have been developed to provide further information on previously identified archaeological remains and to confirm the presence or absence of archaeological remains in areas of unknown potential.

What do we mean by mitigation?

If trial trenching identifies heritage assets of interest, then there will be a requirement to reduce the impacts on these during construction. There are several types of mitigation which range from watching brief (where an archaeologist monitors groundwork during installation of the pipeline), to full excavation of a site prior to installation of the replacement pipeline.

To provide more information about archaeological trial trenching, we have created an information sheet.