A MINING geologist says Cheshire's underground salt deposits pose a serious risk to HS2's future safety.

Dr Rosalind Todhunter, a retired chartered geologist who worked in mining, quarrying, and mineral extraction, told members of the High Speed Rail (Crewe to Manchester) Bill Select Committee the proposed HS2 phase 2b route runs over the most hazardous part of the Cheshire salt district in terms of ground subsidence. 

Lostock Gralam resident Dr Todhunter also explained when both the M6 and M56 were built, planners deliberately sited the route to avoid this area as the risk of subsidence was too high.

The ground in question is where salt-rich rock is very near the surface, whereas in other areas, it is ‘capped’ or overlain by a layer of mudstone, a harder rock which protects the salt beneath from being dissolved by water from above.

In her professional opinion, she said, it means the tracks of the new HS2 line would face serious risk of subsidence.

In her evidence, Dr Todhunter said: “The Cheshire salt district is underlaid by potentially hazardous ground with shallow salt.

“The ground is made up of layers of mudstone, and sandwiched between it is about a 200-metre-thick layer of salt.

“Where the mudstone is sitting on top of the salt is known as dry rockhead.

“Wet rockhead is where the salt is near the ground’s surface and does not have a protective layer above it.  

“This is where there is a potential risk of salt forming a solution from contact with surface or groundwater, turning from a solid state to a liquid state, leaving voids, and leading to ground collapse.

“The HS2 2b route north of Crewe is to built over wet rockhead. This is known unstable ground where there is potential risk of salt dissolution and ground collapse.

“The route therefore does not avoid the area of known geohazard.”

Dr Todunter appeared before the select committee alongside Lostock Gralam parish councillor, Simon Hayes, on Monday, April 17.

The pair also addressed the committee on issues including the proposed route’s impacts on industry in the area, visual and noise disturbance, problems caused by construction, and the track blocking public rights of way between Lostock Green and Rudheath.

Dr Todhunter added: “I chose to buy a house in Lostock Green because it’s on the stable ground of the dry rockhead.

“I believed it wise to avoid the area of known geohazards.”

Salt extraction as brine and rock salt has been taking place in the Cheshire salt district since pre-Roman times.