Mineral County Miner | Nelson Tunnel work continues
MINERAL COUNTY – Work continues on the Nelson Tunnel project north of Creede as spring makes its way to the high country. Dania Zinner, US EPA Region 8 Remediation Project Manager with the Environmental Protection Agency, said in an interview on Tuesday, April 5 that the project is on schedule and progressing well.
“The Nelson Tunnel is the lowest level of a mining complex including, but not limited to, the Nelson Tunnel, Commodore Mine, Amethyst Mine, Happy Thought Mine and Last Chance Mine,” Zinner said. . “The Nelson Tunnel was dug to serve as a drainage and conveyance tunnel for the complex in the 1890s. Shortly thereafter, the owner of the Commodore Mine drove the Commodore Tunnel Level 5 to serve as a conveyance tunnel for the Commodore ore and to compete with the Nelson tunnel.
As work was being completed on Level 5 of the Commodore mine, the EPA noticed large rockslides which signaled the need to work on releasing the pressure built up by the water flowing through the Nelson Tunnel which is located under the Commodore mine.
“The Level 5 Commodore Tunnel sits above the Nelson Tunnel and is connected by vertical mine workings,” Zinner said. “While water levels fluctuate periodically in the larger Nelson Tunnel mining pond, water flows into the Level 5 Commodore Tunnel, allowing pressure relief on the larger holding pond before the water does not return to the lower Nelson. In this way, the stability of the Level 5 Commodore Tunnel is critical to the stability of the larger Nelson Tunnel Retention Basin. The Nelson Tunnel mine basins are highly mineralized with high levels of zinc and cadmium.
It is further explained by Zinner that throughout the process, “DRMS monitored water levels and working conditions in 2016, 2017 and early 2018 and reported that conditions in the level 5 Commodore tunnel were deteriorating at an increasing rate.As the works continue to deteriorate without intervention, further rockfall could completely block the water flow path between the two tunnels, hampering the decompression that the The Commodore Level 5 tunnel currently provides.Such a blockage would also prevent any inspection of water levels beyond, eliminating any knowledge of the amount of water retained in the system.
According to Zinner, the project is in the final phase of the removal process which included stabilization areas of the Level 5 Commodore Tunnel to prevent further deterioration. Clearing a lot of debris such as rockfall from the tunnel roof or tunnel floor walls to prevent water from pooling. Maintain and maintain vertical connections between Commodore Level 5 and the Nelson Tunnel Maintain physical access between the Commodore Level 5 Tunnel and the Nelson Tunnel. Rehabilitate the portal door structure and maintain the Level 5 Commodore Tunnel; walls and roof for worker access.
“This removal effort will aid any future repair efforts at the Superfund site by ensuring continued access to key portions of the Nelson Tunnel for corrective design and water level monitoring. There are also plans to keep the Level 5 Commodore Tunnel open so that it can relieve pressure on the Nelson Tunnel impoundments and thereby reduce the likelihood of a large, sudden and uncontrolled release of the Nelson Tunnel,” Zinner said.
The next steps for the Nelson Tunnel site are the remedial design of the planned bulkhead in the Nelson Tunnel to reduce the likelihood of a sudden large release of mining-influenced water.