Monaghan subsidence: Safety reports provide a mine of information

For weeks before subsidence destroyed a GAA club in Co Monaghan, between five and 11 million litres of water per day flowed into the mine beneath, says Caroline O’Doherty.

Monaghan subsidence: Safety reports provide a mine of information

For weeks before subsidence destroyed a GAA club in Co Monaghan, between five and 11 million litres of water per day flowed into the mine beneath, says Caroline O’Doherty.

Between five and 11 million litres per day of water poured into an underground mine before a subsidence in Co Monaghan last year, and did so for weeks after the problem was discovered.

At its peak, 700,000 litres per hour of water flooded into the gypsum mine, near the village of Magheracloone, or enough to fill one and a half 25-metre swimming pools in a single hour.

Five weeks into the incident, the mine operator, Gyproc, was still struggling to stem the flow or even to quantify its source.

A health and safety officer who visited the scene wrote in his notes, afterwards: “Major problem for mine.”

Three weeks later, six million litres per day were still pouring in, Gyproc was running out of space in an adjacent disused mine to which it had been diverting the flood water through pumps and pipes, and a race against time was on to build underground bulkheads to stop it.

Four weeks after that, support pillars in the disused mine were dislodged by the flood waters and collapsed, causing the subsidence that destroyed a GAA grounds, clubhouse, and community centre, which, a day earlier, had hosted a blitz attended by hundreds of children and adults.

A primary school was also temporarily evacuated and several roads closed.

Eight months on from the start of the flooding, 100,000 litres per hour of water, or 2.4m litres a day, are still flowing into the mine, and Gyproc is continuing an intensive pumping operation.

The scale of the problem is clear from notes compiled by inspectors from the Health and Safety Authority (HSA) during three site visits, between the time the flooding began, last June, and the subsidence in September, and during two visits afterwards.

HSA inspectors only had powers to inspect the working conditions for mine staff dealing with the emergency, and not to investigate the incident as a whole, but their notes convey how serious it was.

Water started flooding into the Drummond mine on June 22 last year, after miners broke through rock into a previously undetected water source.

A HSA inspector who visited on June 26 noted: “The water is not at pressure, but the flow is extremely high, making 450-470 cubic metres (450,000-470,000 litres) per hour.

“The mine was set up with a pumping capacity of 120-160 cubic metres per hour and the normal make is 20 cubic metres per hour.

As the water rises, the lower part of the mine is filling up and even though additional pumps have been brought in and two tractors are being used as pumps, the flow is greater than the pumping capacity.

He noted that a large pump, capable of moving 800 cubic metres per hour, was due to arrive from the UK the next day and a group of miners were to follow the next week, to help build bulkheads [barriers] when the water receded.

In the meantime, tractors were being used to run pumps and there were concerns they would overheat.

“There are fire extinguishers close to the tractors, as they are working 10 hours continuously, before being stopped, refuelled, and lubricated,” he wrote.

The water was being pumped to an old, open-cast quarry, but it could only take seven days’ worth of water.

After that, the plan was to flood the old, adjacent Drumgossatt mine, which was expected to allow for 30 days worth of water.

The inspector advised mine management that they would need to carry out risk assessments as the waters receded and as the flooded tunnels became accessible, “as they may need scaling [removal of loose rock] and/or ground support”.

The next available note is of an inspection carried out on August 1.

A different inspector noted that water was still coming into Drummond at a rate of 400m3 per hour (400,000 litres), but it was now felt Drumgossatt had sufficient capacity for 70 days.

Preparations were being made for grouting — pumping in cement or other material — to try to seal the gap and at least reduce the intake of water.

This inspector wrote: “Appears water is coming from saturated dolomite sands above gypsum. Has to be confirmed size and range. Major problem for mine.”

When he visited again, on August 21, he noted that the water inflow had reduced to 250-300 cubic metres per hour, but Drumgossatt was now “half-full of water”.

“Will grout to reduce intake and gain timeline to build bulkhead,” he wrote.

The next note comes from an inspection on September 28, four days after the subsidence. The inspector, who had originally visited on June 26, was in no doubt what had happened.

His note began: “Inspection following on from surface-subsidence incident at Magheracloone GAA club caused as a result of pumping water from the mine into old mine workings at Drumgossatt mine, causing pillar [support] failure in the old mine.”

He said water flow into the mine had reduced to 235 cubic metres per hour, “from a peak of 700 cubic metres per hour”, but the old mine was almost full and negotiations were taking place with Monaghan County Council and the Environmental Protection Agency (EPA) to permit temporary pumping into the local Bursk river.

“The concern is the level of sulphides,” he wrote.

He had previously noted that the incoming water contained levels of sulphides “much higher than the mine water normally pumped”.

Gryproc could only discharge water into the Bursk if the river level was high enough to dilute the sulphide-rich mine water.

With last summer’s drought, the river levels were low, which was why the company diverted the water into Drumgossatt.

The inspector wrote: “There have also been road closures, as a result of the subsidence, and, initially, a school was evacuated, though this has been reopened.

The GAA clubhouse and community centre are damaged beyond repair and are unsafe and access is

prohibited. Contracts are being drawn up to construct the bulkheads.”

He returned again on October 15, the date of the last available note, and wrote: “Water is now down to 170 cubic metres per hour.”

He said a contractor had been appointed to construct bulkheads and, when construction began, it would take four to five weeks to complete.

An aerial image of the Gyproc open cast mine. Photo: Pat Byrne.

An aerial image of the Gyproc open cast mine. Photo: Pat Byrne.

In response to queries at the weekend, Gyproc said the company had begun working to resolve the water issue immediately that it was discovered.

“Gyproc activated a detailed, phased, and comprehensive engineering programme to manage the ingress of water and ensure the ongoing safety and integrity of the mine.

"This programme involved a number of activities and the water flow has now been reduced to approx. 100 m3/hour,” it said.

It explained why construction of the bulkheads only began in October. “Our own experts and independent experts evaluated a number of potential engineering interventions to manage the water ingress.

“Following the selection of the intervention deemed to have the best long-term outcome, work commenced on it in August, with physical construction of the bulkheads commencing in early October, and the bulkheads are being used as part of an ongoing water-management plan at Drummond mine.”

It said water was now being released to the Bursk, but that: “There is a regular and stringent monitoring programme in place and agreed with the EPA to ensure that there is no negative impact on the local environment.”

Water stored in Drumgossatt was being “slowly released into the river Bursk, in line with advice on dewatering from independent mine experts and established mining practice,” it said.

Asked why the surrounding communities of Magheracloone, Drumgossatt, and Knocknacran had not been formally notified, last June, that a major incident had taken place underground, the company said all employees and relevant public authorities had been informed.

“Given the widespread local awareness, and discussion of the water ingress, there was no formal public information campaign.

As the situation evolved, and particularly with the subsidence event in September, we initiated a public communication programme and this continues.”

The Irish Examiner revealed last month that subsidence checks on land above the old Drumgossatt mine only took place twice a year, as part of a management plan set out by the Department of Communications, Climate

Action and the Environment, and the internal structures of the mine had not been inspected for 13 years before last September’s collapse, because water prevented access.

A forum of local residents, mine company management, public representatives, and state agencies was set up, earlier this month, to deal with local concerns.

Gyproc is working to provide detailed underground maps for residents and investigations are continuing on the remaining closed road.

Negotiations are also taking place to try to resolve the loss of the GAA facilities and community centre.

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