'We're good at this'

The successful closure of a tailings pond is a matter of professional pride to Swedish mining giant Boliden's international experts.

The steps the mining company is taking to 'return to nature' its 150hectare tailings pond in Navan, which holds the waste from Tara Mines, after mining ceases, were outlined by two specialists from Sweden, when the mine was the location this month for the annual meeting of all the group's environmental sections.

Catharina Nordeman, Boliden's Environmental, Health, Safety and Quality group manager stated: "Our basic philosophy is to minimise our footprint, the core value is responsibility."

Boliden does not walk away from closed tailings ponds, she said.

Boliden has 30 mine sites, including Tara Mines, some with multiple tailings ponds.

"Our track record is unique because we have done so many decommissionings," said Catharina.

The most common problem encountered by Boliden at its tailings ponds is ARD, acid rock drainage.

Fortunately, this issue does not arise in Navan. Because the host rock of Tara's lead and zinc deposits is limestone, acid generation potential is eliminated. As a result, it is relatively easy to re-vegetate the pond site.

As Brendan O'Reilly of Tara Mines' environmental section explained, back in 1986, the Navan company experimented successfully with re-vegetating a section of the tailings pond site.

Seven or eight research programmes were undertaken. "As well as showing we could grass the pond, we carried out extensive research, the main part of which was to have sheep grazing on the pond," he said.

The research was conducted in conjunction with Teagasc. "Even after a number of years, the meat from the sheep was fit for human consumption," he revealed, showing that no contamination had been picked up by the sheep.

The research involved use of compost for tailings cover. At other ponds, where the rock composition is different, such materials as sewage sludge can be used. This type of dry fill approach is by far the most expensive technique, costing about €10 per square metre.

Other Boliden ponds are far from this straightforward, frequently due to ARD issues.

Pia Lindstrom, from Boliden's Focus Area Responsible Environment, instances the Kristineberg mine, which has five tailings pond sites on about 300 hectares of land, with each presenting different decommissioning problems.

Boliden has used three different techniques, including flooding one pond to create a lake.

Two of the mines at this sites were opencast and the main one was underground.

Another site that posed a unique challenge was Stekenjokk in far northern Sweden. There are only about four weeks of summer there and no till or organic materials were available for decommissioning.

A lead mine with three tailings pond that presented special difficulties was Laisvall, which closed down in 2001.

Problems there were that in the mountain there is limited till (clayey material) for use in covering the pond and stabilising it to withstand the windy and frosty climate.

The company used sewage sludge and other organic materials at that site. Now, in one section, they find reindeer are frequenting the site, grazing on vegetation on one of the old ponds.

Internationally, one difficult decommissioning project is the Premier Gold site in British Columbia, an area with four metres of rain per year. In acid rock land, run-off of acid during rainfall is a factor the experts must contend with.

How it's done

What is decommissioning and how is it done were two questions addressed by Pia.

She stated that decommissioning (of tailings ponds) is removal of safety risks (hazardous materials) and structures, remediation of contaminated soil, contouring (landscaping) and reclamation such as re-vegetation.

As regard contaminated soil, Brendan O'Reilly said:" If you have enough control when you are open, you will have very little contamination."

Tara Mines was lucky in that even back when the mine only had two departments, one of them was environment (the other was exploration).

How does a mining company decommission ponds? Obviously, methods vary. One is dry cover, then there is groundwater saturation to obtain wetlands and the other is flooding the dam to obtain a lake.

The flooding technique is not going to be used in Navan.

One zinc mine already decommissioned is Saxberget, which unlike Tara, had ARD issues.

What Boliden did there was to use dry cover, initially placing sealing cover on top of the tailings or waste to prevent oxygen penetrating down to the tailings.

Then clayey till was used to compact it twice and on top of that, 1.5m of protective cover was used.

On the surface, there is vegetation. Interestingly, trees are never planted on pond sites.

Reports of a Spanish mine disaster some years ago when watercourses were contaminated raised concerns at Meath Co. Council level last year.

Brendan O'Reilly said that Tara Mines used the legacy of older mines that had disasters when it first set to work to open in Navan.

Back in 1972, he said, when an EIS had not been heard tell of, baseline studies were done by the original Canadian operators focusing on the pond.

Mining was new to Navan then and the site was very close to the town.

During the planning permission stage, Tara Mines had to have a 'closure plan'. As part of planning permission, the company also had to lodge funds with the County Council to facilitate closure should something go wrong.

The Navan tailings pond has been expanded since then, each expansion requiring a new planning application and permission.

Brendan stated that currently, about €7.5m has been advanced and is being managed for the closure of the operation.

One of the key aspects of the EU's Directive on mining waste and closure is that companies pay financial guarantees.

Monitoring goes on all year. Firstly, there is the weekly and monthly monitoring by the company itself. Tara Mines had two audits by the EPA last year when its experts arrived unannounced, said Brendan.

One of these focused exclusively on the tailings pond, and Tara had no non-compliances. "We take pride in being very good at this," commented Catharina Nordeman. Tara obtained ISO status last year.

The EPA arrives a few times yearly to take its own samples.

Pia stated that reviewing of pond decommissioning techniques and work to find better ones within the Euromines group never stops. Sustainability and self-maintaining solutions are the key aims.

Boliden focuses on site-specific criteria, alternative land use and always use the "best available techniques," added Pia.

Pia stressed that Boliden never walks away from a closed mine and keeps its decommissioned ponds under review.

However, no two mining experts would agree on how long this reviewing should go on for. Internationally, one current estimate is 100 years.