It could take weeks before a British Columbia-based mining company can plug a tailings pond that broke apart and sent water and mine waste into nearby lakes and rivers, the provincial government said Friday.
A water ban affecting about 300 people remains in place even though a second round of test results came back within guidelines for human health.
A tailings dam at the Mount Polley gold and copper mine, about 600 kilometres northeast of Vancouver, failed on Monday, releasing 10 million cubic metres of water and 4.5 million cubic metres of silt.
The dam breach, which caused what could be the largest tailings spill in BC's history, has prompted fears about the potential long-term impact on drinking water, fish stocks and the region's ecosystem.
The provincial government released an update on Friday that said the flow out of the tailings pond has "decreased dramatically" but has not stopped. The mine's owner, Imperial Metals Crop. (TSX:III), is building a temporary berm to prevent water and tailings from leaking out.
"The construction of the berm to prevent further tailings from flowing into Hazeltine Creek began last night (Thursday) and the company estimates that it will take about three weeks to complete," said the government update.
The ministry also released the second round of water testing results on Friday, which again showed levels of contaminants within drinking water standards.
A day earlier, the province released test results from samples that were collected on Monday, all of which came back within guidelines.
The latest samples were taken on Tuesday at various spots along Quesnel River.
"Analysis of these samples indicate that none of the chemical and physical parameter concentrations exceeded BC or Health Canada drinking water guidelines," said a memo that was distributed with the results.
All five testing sites had zinc levels above chronic, or long-term, exposure limits for aquatic life, which an accompanying memo said could be a problem if it persists.
"Exceedance of the chronic zinc guideline by a single sample taken does not indicate an impact to aquatic life," the memo said. Further samples will be collected to identify whether this concentration remains at this level over a longer period, which would indicate a greater potential impact to the most sensitive aquatic life."
Three testing sites showed levels of cadmium above aquatic life guidelines, but an accompanying memo said those levels are still below an updated set of draft guidelines that are currently under review.
Another concern is Polley Lake, which flows into a creek that drains into Quesnel Lake. Polley Lake's outflow into the creek is currently plugged by tailings debris, which has raised the lake's water level. Officials are worried the debris could break apart and send a dangerous wave of water down the creek.
The company is building a pipe to manually divert the lake's water, which so far has not been tested, into the creek, the Environment Ministry said.
At a community meeting on Thursday night in Likely, B.C., which is the closest town to the mine, several residents objected to sending more contaminated water into Quesnel Lake.
Company vice-president Steve Robertson responded that the water in Polley Lake would be tested by the time the pipe is in place.
The Environment Ministry sent Imperial Metals a pollution abatement order on Tuesday, and the ministry said the company has so far complied with reporting and planning deadlines.
There have been questions about the stability and maintenance of the tailings pond, though the company insists the dam was properly built and maintained and that there were never any problems with the dam before.
A consultant who authored an environmental report in 2011 said this week that the tailings pond water was too high when he examined it, and a former worker has also come forward to say he warned his superiors that the dam wasn't safe.
Knight Piesold Ltd., an engineering firm that was previously the engineer of record for the tailings facility, issued a statement Friday that said when it ended its relationship with the mine, it sent the company a memo that noted "the embankments and the overall tailings impoundment are getting large and it is extremely important that they be monitored, constructed and operated properly to prevent problems in the future."
Knight Piesold's statement said that when it was involved with the mine, the tailings pond was "operated safely and as it was designed."
The provincial government's written update on Friday said the company submitted yearly dam inspection reports and that the mine had received 16 geotechnical inspections since 1995. Its most recent inspection last September did not result in any inspection orders.
The Environment Ministry sent the company an advisory in May of this year that the height of effluent in the tailings pond exceeded authorized levels. The problem was fixed by the end of June, the ministry said.