As part of our application for development consent, we 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. 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 includes surveys to help us better understand existing underground utilities and archaeological features in the area we are looking to install the pipeline.
We’ll let people know when we are carrying out surveys near them and what they can expect from that work.
Before we can start with our installation works, we will need to prepare each working zone along the route. These works include activities such as vegetation clearance and environmental mitigation. Just like with installation, we will keep you informed before any works are due to take place.
Open cut trenching is the most common technique for installation of the pipeline. The animation below shows an example of how this technique is used.
At times, we will need to use trenchless techniques to install the pipeline, for example, under railway lines, major roads and river beds.
There are several trenchless techniques we’ll be using dependent on the obstacle.
Auger bore / Micro tunnel
Auger boring is best suited to relatively short crossings where we need to be careful about any impacts on the surface, for example crossing under railway lines. A drill head is attached to a length of pipe and this is used to bore to the other side of an obstacle.
Micro tunnelling is a similar technique. In this scenario, a tunnel is created under an obstacle and the pipe is placed within this tunnel.
The animation below shows an example of how this technique is used.
Horizontal directional drilling (HDD) / e-power
We’re using HDD in a number of places as it’s ideal for crossing large constraints, for example wide rivers. A drill bit is remotely guided by an engineer, travelling from a launch area to a reception area. The pipeline is then connected to the drill bit and pulled back through the pilot hole.
E-power is a similar technique. In this scenario, the borehole is permanently supported by either the drill head or the replacement pipe.
The animation below shows an example of how this technique is used.
Pipe pushing
Pipe pushing is used over short distances and has a smaller footprint than other drilling techniques. We’ll use it when we need to cross things like minor roads.
The animation below shows an example of how this technique is used.
Any major construction project comes with impacts and we’re working hard to ensure these are kept to a minimum. You may see a change in traffic patterns in your area during installation, particularly in areas where we’ll need to work in, or alongside, roads.
We are working with the county highways authorities in Hampshire and Surrey to review traffic diversion plans. On a temporary basis, we may need to use diversions and access roads, move pedestrian walkways and bus stops and, in some cases, close sections of road. Where we do need to close a road, this will be done for as short a time as possible to reduce impacts on local communities.
You can visit our interactive map here to see what to expect in your area.
We’ll be using two temporary logistics hubs as areas to store materials and equipment, and to provide staff facilities at key locations along the pipeline route.
A number of work compounds will also be established along the new pipeline route during construction. We use these to store the equipment we need for our work.
Hours of construction are governed under the terms of the DCO and will typically be between 08:00 and 18:00 on weekdays (except Public and Bank Holidays) and Saturdays. There are some exceptions where additional weekend or night-time work is permitted under the DCO (such as when we are using a trenchless technique that requires a period of continuous working as it cannot be interrupted).
Where we do need to work outside of our typical working hours, we’ll make sure local people are informed ahead of work starting.
We have looked carefully at potential noise impacts and how to manage them throughout construction. We have submitted a Noise and Vibration Management Plan to each relevant planning authority, in accordance with the outline certified in our DCO.
We are adopting a number of tried and tested measures to manage noise:
- Before works commence, the site workforce will be fully briefed on the need to keep all noise generated to a low level.
- Shouting and raised voices will not be permitted other than in cases where warnings of danger must be given.
- No personal radios will be allowed on site.
- All plant and vehicles will be required to switch off their engines when not in use and when it is safe to do so.
- In the absence of a mains electricity supply, super silent pack generators will be used as an alternative power supply.
- Construction compound layouts will be designed to ensure that the nosiest operations are located as far as possible from residential properties.
- Where possible, audible vehicle reversing sirens will be set to as low a setting as is compatible with safety requirements.
- Noise implications will be considered when planning activities such as deliveries of pipe and bulk materials.
In areas where higher levels of noise may occur, temporary noise screening will be installed to screen residential properties from the installation activity. The screening will comprise acoustic barrier material fitted to site fencing.
In developing the pipeline route, we have worked hard to keep environmental impacts as low as possible. For example, early in the development of the project we committed to avoiding all ancient woodland along the route. We feel, with the information that was made available to us, we have balanced environmental, engineering, planning and social/community concerns in our selection of the final route.
As we install the pipeline, we will implement the environmental commitments we have made to mitigate and reduce the impacts from construction. The principles and measures we are using to do this are contained in our Code of Construction Practice (CoCP) and Construction Environmental Management Plans (CEMP).
Once the pipeline is installed, we’ll reinstate the area. How we do this will depend on the area we are working in and will be in accordance with the approved relevant Landscape Environmental Management Plan (LEMP).
Where practicable, reinstatement of vegetation would generally involve the same or similar species to those removed (subject to restrictions for planting over and around pipeline easements).
Once buried, the pipeline is a quiet neighbour.