Sunday, September 19, 2010

Avoca mines: Sunday Times

Once again the problem of Avoca mines has hit the newspapers with renewed demands for immediate, yet conflicting, action to be taken.

In my opinion the problem of rehabilitating the abandoned Cu-Pb mining site at Avoca has become much more complex than when we first put forward our own rehabilitation plan in 1995 after our intensive five year study that has been the basis of all the subsequent work done on the site. My main concern is that the movement of water through the mine workings may significantly alter due to ochre deposition and lead to acid mine drainage (AMD) being discharged into surrounding sub-catchments. This has already been seen in the changing pattern of discharge rates from some of the minor adits. Also, that any physical work done on the site may also cause problems both in terms of AMD generation as well as altering the current flow pattern.

Our own studies have indicated that the river has shown significant recovery since closure, although the rate of recovery has flattened out since 2006. The closure of the fertilizer factory, which had been shown in our studies in the early 1990’s to be the major limiting factor for salmonid migration into the catchment due to ammonia toxicity, has meant that salmon have been present for many years. However, the damage to the habitat diversity of the river, mainly from ferric hydroxide precipitation, has left it relatively impoverished in terms of other species. So where do we go now? My firm belief is that we should largely wait and see. The action of surface water on Mount Platt has to be controlled, that has been obvious for two decades and is a relatively simple and cheap thing to do. But as the article in today’s Sunday Times points out a balance has to be struck between preserving the mining and environmental heritage of the site as well as reducing the impact on the river.

Theresa Hughes of the Water Technology Research Group has been looking at an alternative treatment for the acid mine drainage coming from the Avoca site that may provide a sustainable treatment solution. She has been working on the co-treatment of AMD with domestic wastewater which means that treatment is done at a central treatment facility that will be monitored and maintained 24/7, unlike many on-site systems used at abandoned mines. The problem is that the AMD has to be treated to a very high level forever, and this is best achieved using more conventional treatment technology. What is interesting is that neither Avoca nor Arklow have proper domestic wastewaetr treatment systems in place at this time offering the potential to invest both the capital and operating costs from the treatment of Avoca mines in a new permanent co-treatment facility. More details of Theresa’s work can be seen via the link.

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