Residents in West Yorkshire have raised concerns about plans to build the HS2 rail line through a former mining area, after an eight-metre-long crack opened up in the ground along the proposed route.

Plans for the Yorkshire section of the high-speed train line were changed earlier this year, taking it to the east of Sheffield instead of through the Meadowhall shopping centre, on the city’s border with Rotherham.

But people living in Crofton, near Wakefield, have argued that the company has failed to consider the effect that the area’s coal mining legacy could have on costs.

Jonathan Pile, a health and safety consultant and anti-HS2 campaigner, discovered the crack while walking his dog in August. He contacted the Coal Authority when it became clear that the hole was getting bigger.

He said the government agency attended the following day, fenced off the area and posted danger signs. They then filled the hole with 15 tonnes of stone.

When will HS2 be built? Work on phase one, London to Birmingham, should start in summer 2017, although major work on clearing the route, bridges and tunnels will start mid-2018. The bill giving Phase One planning permission and powers became law in 2017, but a similar bill for the remaining northern route, with twin branches to Manchester and Leeds, is still to be drawn up. First trains are expected to run in 2026, with some services continuing from HS2 to existing railway tracks, allowing fast direct trains between London and stations across the north. The full network is expected to be completed in 2033.

In a letter to Pile, the Coal Authority stated: “Recorded deep mining has taken place within the zone of influence of the fissure and therefore the Coal Authority accepts liability in respect of this ground collapse.”

A timeline of the project, published by HS2 Ltd, shows that the company does not plan to conduct a detailed ground investigation until shortly before construction begins. A spokesperson for the company said it was confident “the historical mining features in Crofton pose no major risk to the construction programme”.

The area around Crofton, which was near the Nostell and Sharlston collieries, was heavily mined and includes many filled in open cast mines. As a result of subsidence, groups of houses were demolished in the 1980s and 1990s.

“As with any Yorkshire coal mining community, they dug under houses, they dug everywhere. But HS2 will just throw money at the problem,” said Pile, whose family home is 265 metres from the proposed high-speed train line.

The decision to scrap plans torun the HS2 line through the Meadowhall centre, and instead take it east of Sheffield, came after similar concerns were raised that the ground beneath the site was “mush” and riddled with old mine workings.

Risk documents published by HS2 Ltd state that there is a 68% likelihood of the cost of the project increasing as a result of new information coming to light about mining in the area.

An HS2 spokesperson said they were aware of “the rich history of coal mining in the area” and that they had conducted assessments on the suitability of the land.

“The findings from these studies were taken into account, alongside many other factors, during the route selection process,” they said. “We are confident that the historical mining features in Crofton pose no major risk to the construction programme.

“We continue to engage with the Coal Authority as we progress the more detailed design of the railway, and will carry out a programme of ground investigation works prior to construction. This will inform the engineering measures we will put in place to safely manage the presence of historical coal mining beneath the railway.”