Water quality issue halts $450M Diavik mine expansion project for 3 days

Rio Tinto halted construction of a dike around its new openpit at the Diavik diamond mine for three days this week, cutting down an already-constrictedoperating windowfor the project and once again raising the prospect of delaysfollowing a similar incident last fall.

The voluntary shutdown, which lasted from Sunday evening to Wednesday evening, happened after one of the water monitoring stations near the construction site registered a spike above the level of total suspended solids (TSS) allowed by the mine's water licence.

Rio Tinto's licence says the level of TSS inside Lac de Gras, where Diavik is located, about 300 kilometres northeast of Yellowknife,cannot exceed 25 milligrams per litre in any grab sample. Sunday saw the level at one area of the lake spike to 28.5 milligrams per litre.

A report filed by the company Monday said the spike was caused by the shifting of a siltcurtain meant to prevent the TSS from spreading from the A21 construction site, a $450-million project.

By stopping work, the company avoided having an inspector from the N.W.T.'s Department of Lands issue a legislatively-mandated stop-work order, though an inspector did independently state the company was out of compliance with its licence.

Last year, when a similar spike occurred, an inspector said a recurrence like Sunday's would trigger a shutdown.

Following Sunday's spike, Rio Tinto had to report daily to an inspector about TSS measurements at three water stations.

Levels on Wednesday ranged between 6.5 milligrams per litre and 15.5 milligrams per litre, allowing for in-lake construction to resume that evening.

Discussions on water quality chug along

The shutdown comes amidst ongoing discussions with the Wekeezhii Land and Water Board in which Rio Tinto is advocating for more "flexible" rules around TSS levels to avoid shutdowns like the one this week.

The company has the support of the N.W.T. and Nunavut Chamber of Mines.

The design of two existing in-water dikes at the mine"wonDiavikthe highest engineering accolade in Canada from the highest level, the Canadian Council of Professional Engineers," the chamber wrote in its June newsletter, underscoring the potential damage to he mine'sreputation as the problems at A21 recur.

"Since receiving that award for their first dike,Diavikhas successfully constructed a second dike using the same construction and environmental protection techniques as the first dike...From our perspective, Diavik is the expert at both dike design and dike construction in the N.W.T."

Keeping the mine open

Rio Tinto wants the dike to be enclosed this year, and for mining of the A21 pit to begin in 2018.

A report released by the company earlier this year said the project was thus far on time and on budget.

The pit could help the mine, which employs around 1,000 people, remain open until 2024.

According to a report recently filed in the United Kingdom, where Rio Tinto is based, the company paid the N.W.T. government around$30million in taxes and fees related to Diavik last year.