Summary

Mine Type	Underground
Status	Active
Commodities	Coal (thermal)
Mining Method	Longwall Continuous
Production Start	...
Mine Life	...
Snapshot	Twentymile Mine is the most efficient underground coal mine in the world, producing the highest output per man-year. Twentymile Mine was the first to develop a scissorveyor that allows belt structure flexibility and eliminates production delays for structure removal as the longwall retreats. On March 10, 2023, a Florida-based company Twentymile Pumped Storage, LLC, submitted an application to the U.S. Federal Energy Regulatory Commission (FERC), proposing to study the feasibility of the Twentymile Pumped Storage Project to convert the underground Twentymile Mine into a 250 MW pumped storage facility. The project would use water already in the mine's tunnels to generate electricity during peak demand. As of February 2026, this project is still in the preliminary permitting process. At the time, Twentymile Mine was still producing coal, although production was expected to decline as regional power plants closed by the end of the decade.

Deposit type

• Sedimentary

Summary:

Coal is extracted from the Wadge seam, which averages 9-feet thick. Longwall mining in the Wolf Creek seam began in September 2016.

No significant groundwater flows have been encountered while mining in the Wolf Creek seam or in the interburden between the Wadge seam and the Wolf Creek seam.

Mining Methods

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Comminution

Crushers and Mills

Processing

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Commodity Production

Commodity	Units	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
Coal (thermal)	M tons	....	....	....	....	....	....	2.6	3.1	3.8	2	3.5
Heat Content	BTU/lb		11,200	11,200	11,200		11,200	11,200	11,200	11,200	11,200	11,200

Personnel

Job Title	Name	Profile	Ref. Date
.......................	.......................		Feb 27, 2026

Employees	Year
......	2025
......	2024
......	2023
......	2022
......	2021
......	2020
......	2019
......	2018
......	2017
......	2016