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AMD and Extreme Weather (9 replies)

9 months ago
Obersturmbann 9 months ago

Does anyone have experience on how flood and / or drought affect the water quality of pit lakes? I appreciate any bibliographical reference with this acid mine drainage ARD topic.

Ace Levy
9 months ago
Ace Levy 9 months ago

I would think the pit lakes chemical response to storms and drought would be a function of the size of lake itself whose chemistry will be an accumulation of all the reactions in the pit walls as the pit filled. The contribution from one or more storms or droughts may be insignificant in comparison to the mass/reservoir of metals, acidity, and anions already present in the lake. It sounds like an interesting mass-balance problem; each site will be different. I hope that others weigh in on this with real experience.

Victor Bergman
9 months ago
Victor Bergman 9 months ago

There are a number of pit-lake water quality studies published in Mine Water and the Environment, the journal for the International Mine Water Association. Clint McCullough edited a collection entitled, "Mine Pit Lakes: Closure and Management" that was published by the Australian Centre for Geomechanics and the Mine Water and Environment Research Centre in 2011. That volume gives some good background on pit lakes including a chapter discussing how rapid filling of lakes with diverted river or mine water affects water quality, which may be conceptually similar to the flooding situation depending on the relative volumes of pit lake and flood waters.

9 months ago
Obergruppenfuhrer 9 months ago

Great question, but it may be harder to find answers based on actual data than you might think.

Some years ago (1999) Lisa Shevenell and two colleagues published a very interesting study, Controls on pit lake water quality at 16 open-pit mine sites in Nevada. Applied Geochemistry v. 14 (July 1999), p, 669-687. It may be that Lisa followed up on those studies over time, and so could perhaps speak empirically, at least on the low-ppt side, if not also for flooding. I believe it is probably best to try to reach her through her company,www.atlasgeoinc.com, though she remains (I think) adjunct at UNR and might respond there, too.

Mining of course happens in many places, and you might want to look also in some of the European literature, for example around the re-flooding of lignite mines in central Europe. There was a review article about this, specifically the Lusatian Lignite District near Cottbus, in a volume edited by Geller, Klapper and Salomons1998, Acidic Mining Lakes: Acid Mine Drainage, Limnology and Reclamation. Berlin: Springer. The Lusatian article is Fries et alp. 25-45; much of the biblio is in German, which would be a big problem for me, but perhaps not you. The advantage to looking there may be that there is a longer period of record and it is toward the wet side.

An interesting lake to look at these questions would be the pit lake at the McLaughlin Mine in Lake County, California. There was a preliminary paper (Rytuba et al, 2000) on this in the ICARD 2000 proceedings, but the lake was just beginning to rebound at that point. It is interesting to your question because the Coast Ranges are subject to extremely high rainfalls during El Nino cycles, and of course the area is now in a major long-term drought. There may be publically-available information through the Regional water Quality Control Board.

9 months ago
Obersturmbann 9 months ago

Thanks a lot. I very appreciate all your helpful thoughts and I am thankful for the references you provided to me. Indeed there are several, well documented studies about the controlled flooding process of mining sites in Central and East Germany. The same area was also affected by the European Floods in 2002 that caused the water level in the lignite mining pit Goitsche to rise to 7m within two days, 3m above the targeted level. Another extreme flood in 2013 lead to a levee breach and induced an even higher water level than 11 years prior to that.

Through research I observed natural floods affect mining areas more often than I realized. Since flooding with river water in general has a kind of a positive effect on the pit lake water quality (even if there is still an influx of acidity from surrounding rock), I am interested in vice versa effect of a drought. Does evaporation significantly increase the risk for the formation of pit lakes containing increased acidic water, higher content of dissolved metals and other chemical constituents? Can a drought refresh the iron sulfide oxidation in the sediments? Do groundwater resurgence and the wash out of the weathering products lead to an even higher acidic lake?

Carmen Ibanz
9 months ago
Carmen Ibanz 9 months ago

While not specific to Pit Lakes I’ve done several presentations on extreme weather events/climate change and mining. 

I think the other commenter’s have covered Pit Lakes, but you might find other possible implications for mining operations interesting. I have several PowerPoint’s covering this in the event you’re interested in more info.

9 months ago
Sudhirkumar 9 months ago

I'm a newbie to mining drainage, but in the hydrology literature extreme events have the impact of increasing mass flow by dislodging deeper more evolved ground waters into the active surface regime. Although dilution prevails, the net flux of solutes rises. There are a number of experimental watersheds where this has been demonstrated - in China or Korea as I recall. Apologies if this are implicitly understood by the group.

9 months ago
Unterstarm 9 months ago

You cites some good examples in Australia though published data may be hard to find. You may want to investigate Nordstrom, D.K., 2009, Acid rock drainage and climate change: Journal of Geochemical Exploration. v. 100, p. 97-104.

John Koenig
9 months ago
John Koenig 9 months ago

There was some work done here in New Zealand that showed during El Nino (causing higher air surface pressures) that metal loads were much higher than previously recorded. It was thought that air was being pushed further into underground working and waste rock dumps enabling greater oxidation of pyrite than previously.

Carl Jenkins
9 months ago
Carl Jenkins 9 months ago

On the surface aspects of AMD, I was able to monitor the effects of monsoon at a copper mine in India.

The first one is a quick flush of surface waterways and exposed AMD-affected rocks and waste. It results in an immediate and intense peak in pollutants transfer (metals, sulphate, particles) washed towards drainage, along with no appreciable acid release - thanks to dilution.
Following this short episode comes a long period of cleaner water release, with AMD contaminants hardly detectable due to heavy dilution. Exposed surfaces are washed further, releasing clays and other particles.
AMD surface oxidation, sulphate build up and available metals start again to build on exposed surfaces when the weather returns to dry.

If one pays attention to pollutant concentrations only, it is easy to overlook the massive pollutant transfer. This must be determined as pollutant flow, by integrating concentrations and water flow data. Actual pollutant flow determination during floods may be challenging, due to extremely low concentrations through dilution, and due to the uncertainties on measuring water flow in such conditions.

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