Denis Tegg: How earthquake safe are the mine tailings dams at Waihi?

18 comments on “Denis Tegg: How earthquake safe are the mine tailings dams at Waihi? ”

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1. John up North 1

   10 December 2016 at 1:26 pm

   So what is the final plan for these poisonous mining by products? Or is that it, put it in a hole/dam and walk/slink away leaving nothing but mega tons of toxic sludge and no financial commitment when (not if) it turns to custard.

   Sounds like farming and the waterways but a much more concentrated toxic mixture……….. just spray and walk away!
   • rob 1.1

     10 December 2016 at 7:52 pm

     Probably glossed over with trees?transplanted! not germination or growth but a false look, until it’s damage becomes aware and then yrs of bullshit until nothing is done!
     Does that sound about right?
     They do as they always have done and most people will no what’s next. SADLY.
2. Draco T Bastard 2

   10 December 2016 at 1:52 pm

   Therefore it is perfectly reasonable to ask the question – would these structures withstand a large earthquake?

   Although a good question in context the real question that needs to be asked is:

   Why are we still allowing tailings dams?

   Having huge, man-made, poisonous lakes that will cause untold damage to the environment is obviously not the best solution. These tailings need to be treated and not just left.
   • dukeofurl 2.1

     10 December 2016 at 3:26 pm

     They say the tailings dams now support aquatic life such as ducks etc.
     Cynanide is of course found in the stones of pip fruit and in such things as almonds along side cigarette smoke.
     I think the gold mining process recovers the cyanide but the mine rocks become acid forming when exposed to air and water due to the sulphur content.
     • Draco T Bastard 2.1.1

       10 December 2016 at 3:51 pm

       [citation needed]

       Really, ‘I think’ isn’t good enough for such a critical discussion.
       • dukeofurl 2.1.1.1

         11 December 2016 at 7:24 am

         http://www.waihigold.co.nz/sustainability/environment/rehabilitation/rehabilitation-from-tailings-to-pasture-plantings-and-ponds/

         On the surface it seems the long term plan is Ok, but I dont think we have enough independent information to see if it really is that good.

         Of course the area was a virtual wasteland at the height of the mining in the 1920s, but the the regeneration since then has been mostly natural and not man made.

         There is a high level of knowledge put into these regeneration processes now, but of course that costs serious money.
         eg
         “Four types of water are expected to mix in the tailings ponds at closure:
         an initial pond of decant water
         annual precipitation (total rainfall minus total evaporation)
         overland flow of surface water into the pond
         upward directed flow of pore water which occurs as the tailings consolidate.”

         and
         “In the longer term the pond outlet structures will allow fish passage between the ponds and the Ohinemuri River. The ponds will be able to support a range of aquatic organisms, including submerged and emergent plants, insect larvae, eels and waterfowl, typically found in such pond-like environments and wetlands.”
         However there could be a strong chance some of these outcomes are not going to occur as hoped for. Its just the way of the world and engineering design doesnt have all the answers.
     • RedLogix 2.1.2

       10 December 2016 at 5:31 pm

       Old tailings dams are indeed the worst legacy of the mining industry. Especially ones that pre-date current standards which mandate very low cyanide levels. But even then, rock which has been in contact with cyanide … even when the ‘weakly available’ cyanide levels are very low, also has other heavy metals such as arsenic, mercury, lead and zinc liberated into environmentally unstable forms.

       It is now entirely possible to design the process so that ONLY clean tailings (waste rock) that has never been in contact with cyanide is stored on the surface; and for very small amounts that are potentially toxic to be stored safely back underground. The industry should be required to move quickly to this standard.

       Even so … vast amounts of liquefiable rock that has been crushed down to a micron level (chemically clean or not) is a long-term hazard. More work is needed to find effective ways to stabilise these dams. Left as they are, in the long-term disaster of some kind is almost inevitable.
       • dukeofurl 2.1.2.1

         11 December 2016 at 3:21 pm

         the Waihi basin is one of only two smaller areas in the North Island that match some parts of the West Coast for rainfall intensity.
         I imagine that means the peak rainfall rather than the annual rainfall. Very heavy rain and tailings dams dont mix- well they do in the worst way.

         From Branz Maps
         http://branz.maps.arcgis.com/apps/webappviewer/index.html?id=1bade5ce36a9459aa0de4bd5cecd6e36
3. Lloyd 3

   10 December 2016 at 4:11 pm

   Drowning in acidic mud is so much less fatal than cyanide poisoning.
   (Irony).
   • joe90 3.1

     11 December 2016 at 3:12 pm

     Landing in acidic water ain’t too flash, either.

     Several thousand snow geese may have died after landing in a former open-pit copper mine in Montana that is now filled with highly acidic water.

     A Nov. 28 snowstorm forced the migrating geese to take refuge in the Berkeley Pit, a 900-foot-deep pit lake of heavy metals and other dangerous chemicals that is now a federal cleanup site in Butte, Mont.

     The site has seen a horror like this before: In 1995, 342 geese landed on the pit, drank its water, and suffered fatal burns to their tracheae and other internal organs.

     http://www.latimes.com/nation/la-na-montana-toxic-geese-20161207-story.html
4. Robert Glennie 4

   10 December 2016 at 9:43 pm

   Coromandel is fortunately not that seismically active. It is not to say there is no seismic activity because nowhere is entirely immune to seismic activity, BUT, if there is a large quake that causes damage to the tailings dams it will probably come from a fault in the Taupo Volcanic Zone where you can expect up to a magnitude 7.0 on some of the larger faults.

   Once you get into Waikato, the seismic hazard diminishes significantly as you are well away from the tectonic belt parallel to the tectonic plate boundary off the Hawkes Bay coast.

   Here are two maps from G.N.S. One shows deep quakes and the other shows shallow quakes. The big gap in deep quakes in the South Island is the Alpine Fault.

   http://info.geonet.org.nz/display/quake/Earthquake?preview=/950275/1278078/Deep_Seismicity.png

   http://info.geonet.org.nz/display/quake/Earthquake?preview=/950275/1278077/Shallow_Seismicity.png
   • Robert Glennie 4.1

     10 December 2016 at 10:08 pm

     If people are really concerned, they should contact Environment Bay of Plenty (assume Waihi falls in their boundaries)and ask if there are significant fault lines nearby and what they are capable of doing. The Regional Council will have that information on file.
     • Denis Tegg 4.1.1

       11 December 2016 at 10:44 am

       Robert
       You clearly haven’t read the article or the latest report from GNS Science on the Kerepehi Fault which is less than 20 km away from these tailings dams. This 2016 report says the rupture interval is 1000 years, rather than 6 to 8000 years, as previously thought, and that a magnitude 7.4 earthquake is possible if multiple segments of the fault ruptured together. The report says that towns close to the fault could experience MM8 MM9 or even MM10 (very destructive) intensity damage.

       Which is the whole point as to why the seismic safety of the dams needs to be re-examined.
     • Macro 4.1.2

       11 December 2016 at 1:15 pm

       Waihi does not form part of Environment Bay of Plenty – it is part of Waikato Regional Council. See the article above!
       The Kerepehi Fault is an active fault line – it is unusual in being a rift valley – the Coromandel Penisula is moving away from Auckland (who wants to be part of them anyway/ sarc) at around 10cm /century. The Firth of Thames forms part of that rift valley. And yes the geological activity in the Taupo area will have and has had significant impact on the Hauraki plains – The Waikato river for instance used to flow into the Firth until the massive eruption from Taupo closed that and forced the river to flow out to the Tasman rather than the Pacific.
       As Dennis outlines in the article above, the current GNS report of 2016 raises considerably the risk of significant earthquake on the Kerepehi fault. Previous assesments were not so alarming.
       It should also be noted that while those of us in Thames did not feel the Kaikoura quake (and my home is situated directly on top of the Thames fault line), the people on the plains around the Kerepehi fault certainly did.
   • Jenny Kirk 4.2

     11 December 2016 at 8:45 am

     Many people once thought Christchurch wasn’t seismically active, as well. How wrong they turned out to be !
     And as the Kaikoura earthquakes indicate, seismic activity goes a long way into areas other than the nearby centre.
     What is more, seemingly long dead volcanoes can also stir awake .
     I don’t think anyone can say there is no place in NZ that is immune from earthquake or volcano activity ……. and the hazard of tailings dams has not been diminished in any way by the fact that birds might visit them, nor by what geotech experts suggest might happen in the future.
     • dukeofurl 4.2.1

       11 December 2016 at 3:03 pm

       Christchurch has all ways been seen as close to the highest siesmically active zones, obviously they have now moved the boundary to include the city area. But it was only say from about the Waimakariri River moved to south to about lake Ellesmere/Te waihora.
       I imagine the extreme zone will be adjusted south a bit too to now include Kaikoura
5. Jenny Kirk 5

   10 December 2016 at 9:50 pm

   This is useful information. Thanks for posting it.
6. saveNZ 6

   11 December 2016 at 6:45 am

   Shocking!

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