Pinyon Plain Mine (formerly Canyon Mine) | Permit of Interest | FAQs: Page 4 of 7

How will groundwater be protected?

Through the General APPs, the facility has in place several engineering controls at the facility including:

  • The lined impoundment,
  • Drainage design, grading and berming,
  • Monitoring of the water in the mine shaft, and
  • Pumping water out of the shaft.

These existing engineering controls will carry forward into the Individual APP. These controls protect the two potential aquifers in this area -- Coconino groundwater and the Redwall-Muav Aquifer. Out of an abundance of caution, these controls will be augmented with additional groundwater quality monitoring as part of the Individual APP.

Coconino Groundwater:

  • Groundwater in the Coconino Formation is about 940 feet below the surface. The mine shaft was drilled below the Coconino Formation to a depth of about 1,470 feet, and an impermeable liner was installed at the bottom of the shaft. Groundwater from the Coconino Formation seeps into the shaft and accumulates. Once the water reaches a certain level in the shaft, a sensor turns on a pump to move the water to the surface and direct it into the lined impoundment or storage tanks for evaporation. Because water in the shaft is pumped out, it cannot enter the Coconino Formation. As a result, groundwater cannot be impacted by mining operations.
  • In addition, the U.S. Geological Survey (USGS) conducts regular monitoring of Coconino groundwater quality from an observation well located at the facility property boundary. Water quality monitoring results from this well are all below Arizona’s Aquifer Water Quality Standards. These water quality monitoring data are found here | View USGS Data >
  • ADEQ is requiring the mine owner (EFRI) through the individual permitting process to establish groundwater monitoring wells in the Coconino groundwater. With these wells, ADEQ will be able to validate what we can already infer from the geologic record: all water on site is being captured by the mine shaft. The groundwater monitoring wells also will be used to determine the groundwater flow direction for the facility and to monitor downgradient groundwater.

Redwall-Muav Aquifer:

  • The Redwall-Muav Aquifer is about 2,525 feet below the surface. In addition to the impermeable liner and pumping out water from the shaft previously described, over 500 feet of impermeable rock layers between the bottom of the mine shaft and the Redwall-Muav Aquifer serve as a natural protective barrier that prevents water in the shaft from reaching the Redwall-Muav Aquifer.
  • In addition, because of the liner at the bottom of the shaft and the impermeability of the rock layers below the mine, this water cannot enter the Redwall-Muav Aquifer during mining operations.
  • The mine has a groundwater monitoring well in the Redwall-Muav Aquifer that was required under the USFS ROD and USFS-approved facility Plan of Operations is being used to confirm lack of adverse impacts to groundwater as well as to ensure proper reclamation after mine closure. Water quality monitoring results from this well are all below Arizona’s Aquifer Water Quality Standards. USGS water quality monitoring data for this well are found here | View USGS Data >

Finally, as part of the Clean Closure Plan required under the USFS-approved facility Plan of Operations, after operations have ceased, the owner will seal off the saturated portion of the Coconino groundwater from the mine shaft, thereby preventing any potential groundwater contamination after final reclamation of the mine. Relevant provisions of the Clean Closure Plan will be reviewed and included in the Individual APP.

Will the mine shaft flood?

Water within the mine shaft is being maintained at the bottom of the lined portion of the shaft, which is about 12 feet high. Per the requirements of the General APP, the permittee must intermittently pump all of this water out of the lined mine shaft and properly manage that water.

Before drilling the mine shaft, EFRI estimated that the mine shaft would generate approximately 10 gallons per minute (gpm). Currently, the mine shaft generates about 19-20 gpm, about twice the original estimate. As a result, EFRI has made the necessary adjustments to their water management practices to accommodate the additional flow in the existing lined impoundment and storage tanks.

The Individual APP application will include a water balance calculation to demonstrate the lined impoundment and storage tanks provide adequate storage capacity for water pumped out of the mine shaft.