Planning chiefs unanimously backed a massive expansion of a 4,447-acre brine field in Northwich, but officers were quizzed about provision of warning signs so local walkers do not have accidents.

Cheshire West and Chester’s planning committee rubber-stamped an application by Inovyn Enterprises for four new wells at its Holford brine fields site in Lostock Gralam. It will see an extra 10 million tonnes of brine extracted from the site, with planning permission now granted up until 2042

The existing site has been in operation since the 1930s and produces three million tonnes of salt a year. It currently supplies an Inovyn site in Runcorn, where the brine is used as one of the key raw materials for the production of chlorine, caustic soda, chlorinated derivatives and food grade salt. Brine is also supplied to the Tata Ash Plant in Northwich.

The salt beds are 120m below the surface, are around 240m thick and represent what planners called 'a significant mineral reserve' of salt.

The approved plans will also involve the creation of a 35m-wide construction corridor where soil would be stripped and temporarily stored.

Speaking at the committee meeting, planning chair Cllr Gina Lewis questioned officers on safety around public footpaths in the area.

She said: “Will there be suitable signage for anybody who does use those footpaths, about what's going on so that they don't end up perhaps having an accident?”

Officers said there would be an informative attacked to the permission. Informatives are notes for the applicant that are included in the decision letter which provide guidance on issues such as statutory requirements.

Now that permission is granted, extraction of the brine will be undertaken via a process known as solution mining, which involves the drilling of a borehole into an underlying saltbed.

Water is then pumped into the well dissolving the salt, forming brine, which can then be pumped out - thereby creating a cavity.

When depleted - usually after 25 years - the cavity is then left filled with brine and capped with the well head remaining at the surface.