Peabody Energy announced Tuesday that it will permanently shut down the Willow Lake mine in Southern Illinois due to unacceptable safety standards, compliance and overall operating performance.

According to a press release issued by the company on Tuesday, “these ongoing issues make the operations unsustainable.” Closure of the Willow Lake Mine will put some 400 employees out of work.

Willow Lake sold 2.2 million tons in 2011. Peabody Energy says they do not expect the closing to have an impact on their ongoing earnings.