Case Study PDF

"Stockton performed in an exemplary manner. They understood and acknowledged the potential for environmental pollution and worked with our site team to minimise such hazards. Their work completed on-time to accuracy and quality."

Gerry Somers
Construction Services Director
Trant Construction Ltd.



Push-reamed HDD Outfall with major environmental factors

The Project

This was a very demanding project, with no drilling access to the exit side of the crossing. There was restricted access both in Poole Harbour for the welding and string working and at the designated SSSI area and golf course, for the construction works. The close working partnership between Southern Water, Stockton and Trant Construction ensured safe delivery of a difficult project. The major constraint was the need to prevent the drilling tool from emerging from the seafloor until the final ream was completed - preventing the escape of drilling fluid into the sea.

Impact Assessment

SDL carried out an in-depth impact assessment and produced working procedures that successfully prevented significant breakout and controlled the risks inherent in the drill as the bore increased and the fluid pressure grew.


As well as major physical constrainsat the drilling site, the coastline is a Site of Special Scientific Interest(SSSI). A detailed environmentalassessment and effective operational controls ensured minimal impact on the environment throughout the project. With only 2 months to complete the project and restrictions imposed by Poole Harbour on marine operations the project required the use of divers and various seabased activities. SDL's previous marine projects experience proved invaluable in developing effective health and safety plans and in managing the project safely yet completing to time and cost.

Project Management

One of the key factors in the project was the involvement of SDL in the early design and planning. This resulted in the prefabrication of the HDPE string and pre-testing along the Poole Harbour sea defence wall before being floated out in one continuous length to the exit point where connection to the drill string was completed and the pipe installed.

Project Summary

  • Barton-on-Sea Outfall Poole Harbour welding and towing of pipe - 560m, HDPE outfall line.
  • 609m, 610mm horizontal directional drill Push-ream directional drill SSSI and restricted access.
  • Marine operations including use of divers Impact and environmental assessments Involvement.

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