what actually happened

I have completed a huge research effort to ascertain the probable cause of the tailings dam wall subsidence based on numerous articles from the available literature and reports from RED.

The literature suggests that design and construct problems leading to failure are becoming the least likely cause and lapses in operating and maintenance procedures are the preponderance of the current issue. Where design issues may effect the stability of the dams “the prominent causes are earthquakes, landslides, extreme storms, massive snowmelt, equipment malfunction” and are required to be accounted for in the design criteria.

From an extreme weather (rain fall) perspective, the mine site experienced a relatively dry period during April to the day of the subsidence and beyond (there was a day of 35mm of modest rainfall 5 days earlier on 20/4). This compares with much higher rainfall events of up to 431mm in 40 hours as reported by RED for January which was the excuse for lower material movement in that month. IMO the extreme weather events and their effect on any stability issues have been engineered in to the design by GHD since RED should have had problems earlier if this was the case. I’m sure the Insurers have concluded this.

The other major issue that the engineers seemed to have attended to in the stability of dams worldwide is with respect to earthquakes. Since my last post on this subject I have rechecked the earthquake databases for the area. Except for a relatively small earthquake of 4.5 Richter on 13/04/13 within 250km of the site there was nothing else closer to the date of the subsidence of 25/04/13. This compares with the 192 earthquakes of the same magnitude or greater (up to 7.6 Richter) in the same region within the 9 months prior to the incident. A 7.6 Richter is 1,100 times more powerful than a 4.5 so things would be really rocking! Again, IMO the extreme earthquake events and their effect on any stability issues have been engineered in to the design by GHD since RED should have had catastrophic problems earlier if this was the case. And again, I’m sure the Insurers have concluded this as well.

Now we have a real dilemma. If major natural events and a combination of them have not effected the tailings dam up until the day the “minor soil disturbance at the crest of the operating tailings dam wall was noted during the normal daily inspection routine on 25 April 2013” (as reported by RED in the Prospectus on 19/07/13), then what did? Since the inspections are NORMAL, DAILY and ROUTINE what was different in the proceeding DAY or TWO to cause the problem since presumably there had been no problem reported from the “normal daily inspections” earlier. And I am certain the Insurers have asked this one!

Directly from the literature, the only probable way a tailings dam can have this kind of failure, when it has previously withstood the equivalent of a rollicking, roller coaster ride in a cyclone, is some form of human operating error within days of the incident. And I’m sure the Insurers know this is the case. I have my theories about exactly what happened in the preceding days but would like the company to report what the error was so we can be assured it won’t happen again.