Imperial Minerals, the owners of the Mount Polley Mine in British Columbia, say a crack in their tailings dam found in 2010 was almost a kilometer away from the spot where the dam containing toxic waste failed this summer, and that the company “fully complied” with a series of recommendations to improve safety at the pond.

The dam failed on Aug. 4, releasing 24 million m³ of water and mine tailings into Quesnel Lake in central British Columbia.

But New Democratic Party leader John Horgan is calling for the release of technical documents to show just what the company and the province knew about the safety of the dam prior to the Aug. 4 breach, The Globe and Mail reported.

The last geotechnical inspection by the ministry of mines at Mount Polley took place in September of 2013 and resulted in no orders related to the tailings storage facility, according to ministry officials.

The government has not opened its inspection files, saying it must “protect the integrity and independence” of an independent engineering investigation and inquiry into the tailings pond breach that is expected to be completed in January.

Bill Bennett, Minister of Energy and Mines, said in an interview that his government’s engineers were aware of the 2010 fissure – the one far from the crack that caused the massive leak – and believed concerns had been properly addressed by the company.

“The advice from my staff is that the 2011 inspection by the ministry and by the engineers indicated the deficiencies found in 2010 had been dealt with,” he said. Bennett repeated that he cannot release the reports at this time, on the advice of the Ministry of Justice.

Imperial Metals Corp., the Vancouver-based company that operates the gold and copper mine, has mostly retreated from the public eye since the dam failure.

In a rare statement from the company dated Oct. 3, the company acknowledged that a crack at least 10 meters in length had been observed in the earthen dam while work was under way to raise the dam in 2010, and that a number of instruments required to measure water pressure behind the dam were in a state of disrepair.

Those details were cited by the company’s engineering firm of record at the time, Knight Piesold, in it final report before Imperial Metals switched to a new engineering firm, AMEC.

The company said it acted on a string of recommendations from AMEC. More sand was packed around the dam and a “significant instrument replacement program was carried out.” A stability assessment was then undertaken in 2011 that “confirmed that the factor of safety in the vicinity of the crack was more than adequate, exceeding the required safety standards.” The company “received no indication that there remained any issues of concern.”

This summer, crews were working to once again raise the tailings dam at the Mount Polley mine when the structure failed and sent a torrent of waste and debris into surrounding waterways, raising fears about drinking water and the long-term impact on wildlife.

Imperial Metals had asked the Ministry of Environment for a permit to release more treated effluent from its tailings pond. That permit was pending when the dam gave way.