Careful consideration went into deciding the exact location of the caverns and the layout of the plant. The geology of the underground salt layer in the area was a key factor in determining the suitability of the site, along with the extent of the existing natural screening. The caverns will be located within a previously unexploited part of the extensive salt layer under the area which has been used to supply brine and salt for hundreds of years.

In deciding the project location we also took into account the distance between local buildings and the plant, and connection to water, brine, electricity and gas networks.

Construction

Construction of the eight well heads started in Autumn 2005. It involves drilling over 700m underground and putting in steel casings that will maintain the shape of the well in preparation for the cavern creation.

The salt caverns are created by a process called solution mining. Water is pumped down a pipe inside pre-drilled wells into the salt. It dissolves the salt and is removed as brine. This will be used by chemical industries including a local manufacturer of soda ash at Northwich, which is supplied with heat and power by our Winnington CHP plant.      

The cavern shape can be controlled by adjusting the position of the pipes.      

The salt layer is extensively tested during construction by sonar-logging and extraction of samples for laboratory analysis to ensure its suitability. We also carry out pressure tests of the completed wells and caverns to ensure the completed scheme is safe.

Operation

A processing plant is needed to control the flow and quality of gas going into and out of the National Transmission System (NTS). Electrically-driven compressors are used to pump gas in and out of the caverns, and dryers are used to remove moisture from the gas which is absorbed while in the caverns before it is returned to the NTS. The plant also controls the temperature of the gas.

This will be the most visible part of the plant when completed but additional landscaping will minimise visibility and enhance the existing natural screening.