EPA concerns over potential for recurrence of pipeline breaches and risk to surface water
The uncontrolled release of 250 to 300 tonnes of mine waste or tailings solids was reported to the Environmental Protection Agency (EPA) by Boliden Tara Mines on 12th November last year.
The spill was onto land within the Tara Mines site.
An alarm activated and an Emergency Response procedure was initiated. An immediate plant shutdown commenced and mill personnel were dispatched to walk the length of the pipeline. Members of the management team were notified.
Following the notification, the EPA conducted a site visit at the Knockumber mine site.
According to its website the agency “inspected the location of the incident and the area where the pipeline failure had occurred.
“Tailings was observed coating the drainage ditches on either side of the nearby access road. Tankers were present at the site of the incident pumping water from the drainage ditches for disposal in the Tailings Management Facility (TMF).”
According to the report, Boliden indicated that the differential pressure alarms had been activated at 05.30 on 12th November, and the AG mill went into shutdown at 05.36. The pipeline was then flushed out with water to prevent blockages.
Boliden then conducted a walkover of the pipeline, during which they discovered the location of the failure.
“At the time of the failure, the licensee (Boliden) was backfilling and the content of the pipeline consisted of fine tailings and water being pumped at a rate of approximately 2,000m3/hr. The licensee estimated that the fine tailings accounted for approximately five per cent of the contents of the tailing pipeline with the rest being water.”
The EPA report said it was later estimated that between 250 to 300 tonnes of tailings solids were released to the surrounding area due to the failure of the pipeline.
Boliden also informed the Agency that the drainage ditch beside the pipe was connected to a culvert that drained to the site surface water pond. To prevent further mobilisation of the tailings and water, they constructed two berms, one within the drainage ditch in front of the culvert and the other beside the road.
“The Agency inspected the site surface water pond and observed that the water was grey in colour and some of the vegetation was stained with a grey material. The licensee took a sample at a manhole upstream of the site surface water pond, which was observed to be clear in appearance.
“Prior to the Agency arriving onsite, the licensee took a number of samples from the surface water ponds onsite to determine if there was any evidence of contamination as a result of the incident.”
Subsequent results from these samples received by the Agency indicated that there was no evidence of contamination in the surface water ponds and the results were within the licence limits.
“The licensee explained that after passing through the site surface water ponds, the water would drain to the reclaim water ponds in the mine water pond system.
“The agency inspected the reclaim water ponds but could not identify any evidence to suggest that tailings had entered the system .
“The licensee also informed the Agency that the water in the reclaim pond was normally reused in the mining process or treated in the wastewater treatment plant before being discharged.”
While the EPA was onsite, an external contractor arrived to investigate the cause of failure and to repair the pipeline. Boliden explained that they intended to repair the pipeline in the following two days and restart the AG mill gradually.
Meanwhile, they would continue to tanker the pooled carrying water to the tailings facility and subsequently begin to excavate the affected soil over the following weeks, which would also be brought to the tailings facility for disposal.”
The EPA noted that Boliden had previously reported incidents in relation to the failure of the tailings pipeline over the last ten years, with failures and release of tailings occurring on 17/08/2016, 16/12/2020 and 17/12/2022.
A compliance investigation was opened to address these failures.
“To date, the licensee has replaced and integrity tested the tailings pipeline and reclaim pipeline from the TMF as far as the north bank of the River Blackwater. However, the licensee had failed to implement adequate preventative measures to prevent recurrence of this issue for the length of pipelines located within the mine site.” according to the report.
During the site visit, the Agency expressed their concerns regarding the potential for recurrence of pipeline breaches at the mine site and emphasised the risk to surface water. After the site visit, the licensee provided the Agency with details of short-term, medium term and long-term action plan to address the failures with the pipelines.
According to the Agency, since the site visit, the licensee replaced the failed pipeline section and resumed site operations; tankered all pooled carrying water away from the site of the incident; sent the failed pipeline section for integrity testing; and began works to remove and replace the affected soil at the site of the incident.
The Agency required Boliden to continue to carry out the corrective actions outlined under their short-term, medium-term and long-term plan.
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