Cameco Corp reports that remediation work at the No.1 Shaft at its Cigar Lake uranium project was temporarily suspended on August 12 after an increase in the rate of water inflow to the mine was observed. “Remediation and dewatering of the No. 1 Shaft had been progressing smoothly up to this point,” said Tim Gitzel, Cameco’s CEO. “An inflow at this rate is disappointing but our remediation plan, as approved by our joint venture partners, recognised the risk and included specific actions to be taken at various levels of inflow.”
No. 1 Shaft had been pumped down to 430 m below surface when the increase was reported early Tuesday morning. Work in the shaft was suspended a few hours later. During the day, the inflow rate increased steadily to approximately 600 m3/hr, which is beyond the range that can be managed while sustaining work in the shaft. The mine has a total depth of 500 m and the mine underground workings are at the 480-m level. Work in the shaft has been suspended while the situation is assessed to determine the source and characteristics of the inflow, implications for planned remediation work and the impact, if any, on the planned production date.
The current plan is to allow the water level in the shaft to rise to approximately 100 m below surface. This will allow additional data to be gathered from instruments used to monitor groundwater conditions. As the water level rises, the rate of inflow will naturally diminish. This information will be analysed to determine next steps. After this is complete, the water will be allowed to return to the natural equilibrium level. As previously disclosed, the remediation plan for Cigar Lake includes options to address excess inflows including additional grouting from surface and ground freezing if necessary.
Pumping capacity is 1,000 m3/hr from four dedicated dewatering pumps installed in wells down to the 500-m level. The water management system is limited by the treated water release limit of 550 m3/hr under the existing licence. There is a 74,000 m3 contingency storage pond at the surface that allows pumping at rates above the release limit for a limited period.