Concerns are being raised about the safety of mining tailing dams near Waihi following Kaikoura earthquake, and the recent collapse of a tailings dam in Brazil.

Thames lawyer Denis Tegg says the Waikato Regional Council is ignoring his questions, which have arisen following the discovery announced last year of a major earthquake fault in the Hauraki plain, and the November 2015 collapse of the Fundao tailings dam in Brazil.

They have been brought to the fore by the sight of Kaikoura earthquake landslides, where whole hillsides have flowed down mountain valleys.

The collapse of the Fundao dam in Brazil was about the same size as the Waihi dam, before it collapsed in November 2015, spilling 36 million cubic meters of toxic tailings down 600km of the Doce River.

'A report on the cause of that just come out,” says Denis.

'While there was some poor maintenance and poor management of the dam, the actual trigger mechanism that set off that collapse is a very small earthquake of only 2.6 magnitude.”

Waikato Regional Council staff disagree.

'Staff note that the Fundao expert panel states that the failure of the dam would have occurred irrespective of the small earthquakes that occurred. i.e. the dam was already in precarious state of instability due to a combination of poor design, construction defects and poor operation and monitoring of the tailings dam and therefore was going to fail at some point in time,” says the reply to a question from SunLive.

'Having reviewed the panel's report, staff are of the opinion the Fundao tailing dam situation cannot be compared with the tailings dams at either Waihi or the Golden Cross tailings dam. '

Denis says the council and engineers are ignoring new information about the Kerepehi fault across the Hauraki Plains, which is quite close to the tailings dams at both Waihi and Waitekauri.

The new GNS picture of the fault is that it is more active than previously thought. It's now believed to have bigger earthquakes and more often.

There was a landslip under the Waitekauri tailings dam in 1996. The Golden Cross mine was shut and about $30 million spent on stabilizing the slip. It is closer to the Kerepehi fault than Oceana Gold's dams near Waihi.

A civil defence emergency was declared at the time and the mining company – Coeur Gold – was forced to closed the mine permanently and to spend around $NZ30 million on stabilization work.

Denis' complaint about the design of the tailings dam at Waihi is that it is based on old information, a seismic hazard study undertaken in 2007 and updated in 2010 – all before the GNS report in 2016 that suggests the region has a significantly greater earthquake risk than previously assumed.

'I'm not saying the dam's going to collapse,” says Denis.

'I'm just asking a question whether it's safe. The report from GNS is saying the basis on which they designed the dam is now outdated as far as earthquake risk.”

Should either of the tailings dams fail in an earthquake, we could be facing potentially New Zealand's worst ever environmental disaster, and loss of life and livelihoods on a significant scale, says Denis.

The Waikato Regional Council says a Tailings Storage Facility Monitoring Report is produced by the mining company each year.

This year's report is the 28th report and is required to be supplied to address the safety and stability of the tailings embankment and associated works.

Each report provides a summary of the construction activities that have occurred on each of the tailings dams over the year and details the design criteria and seismic stability for the tailings dams.

The design criteria is based on NZSOLD Guidelines and staff note that GNS is currently undertaking updated estimates of seismic hazard which once completed, will be taken into account as part of the annual Tailings Storage Facility Monitoring Report.

The annual reports are peer reviewed by an independent engineer who reports back to the Waikato Regional Council.

'Based on the process involved to date on how the tailings were designed and constructed, the annual monitoring process of the structures by qualified experts, and the peer review process undertaken by an independent qualified expert that has occurred since they were first constructed, staff are of the opinion that a situation such as what happened at the Fundao tailings dam would not occur,” says the council.

'Staff are confident that the current annual peer review process is appropriate to address issues of the stability of the tailings dam at Waihi with respect to risks likely to be encountered at the site.”

Denis want the review to be independent by someone who hasn't been appointed by the company themselves.

'I've basically been told that's not going to happen, they are going to self-regulate, and I just think that given the seriousness of the potential problems there, we should be taking it a bit more seriously.”