The Avoca Mines
Historically, mining was centred at Avoca in the lower catchment and at Glendalough, Glendasan and Glenmalure in the upper catchment. Mining took place in an era when there were few environmental controls in place; as a result, significant environmental degradation occurred, none greater than at Avoca mines. Avoca has the longest production record of any mine in Ireland.
Avoca mines occupy a narrow 4-km long strip of land between Avoca village and the Meeting of the Waters, running north-west to south-east, and divided into two mining areas, Avoca East and Avoca West, straddling the Avoca River.
Avoca mines were an important source of employment in the past and have left a rich social and physical heritage of mining. Avoca also has the richest heritage of mining archaeology in Ireland that is an important part of Ireland’s industrial heritage - the remains of 19th century mine building, Cornish engine houses, cable systems and mine adits.
Avoca mine area. Image courtesy of CDM Smith Ireland Ltd
Open-cast mining in the 1970s and ‘80s transformed the landscape of the mines. The two pits in East Avoca produced large amounts of waste rock (spoil) which now forms a landmark 240 m-tall hill, Mount Platt (named after a former manager of the mines), containing 700,000 m3 of spoil today; it continues to be almost devoid of vegetation.
Between 1989 and 2002, the Pond Lode Pit was used by Wicklow County Council as a domestic refuse landfill. This was later found not have complied with the EU groundwater directive because the base of the landfill was not sealed and ‘pollutants were allowed to leach into the Avoca River’. Wicklow County Council monitors the landfill site under the terms of an EPA Waste Licence.
As a consequence of copper and pyrite extraction during the last phase of mining, rock waste and spoil containing levels of copper, lead and zinc that are toxic to most plants are abundant in the area, and consequently vegetation is sparse to non-existent on much of the mine surface. In other less inhospitable areas, heathers and trees such as Scots pine, birch and oak have established.
The 12-km stretch of the Avoca River from Avoca mines to the sea at Arklow is one of Ireland’s most polluted rivers, principally because of acid mine drainage (AMD) from the mines.
AMD is not unique to Avoca, but is a problem associated with metal and coal mines around the world, caused by the presence of sulphide minerals in the mine rocks. The principal culprit, Pyrite, is common in different rock types, but is particularly abundant in volcanically-altered metasedimentary rocks of marine origin, such as those found at Avoca. When it oxidises, it releases iron and sulphuric acid causing the release of other metals which accelerate the process.
Drainage streams carrying AMD often have conspicuous yellow or orange deposits of ferric hydroxide (‘yellow boy’) on the stream bed. The impact of AMD can depend a lot on the chemistry and other features of the water body that it contaminates but AMD can have a catastrophic impact on aquatic life.
Iron-rich effluent from East Avoca at Tigroney. Photo courtesy of Tom Harrington
AMD can cause a large increase in the acidity of the receiving water (i.e. a drop in pH), so that organisms that are sensitive to changes in pH, including trout, salmon and invertebrates, such as mayflies, may be killed. Many aquatic animals and plants have a low threshold of tolerance to these metals, and long-term exposure to high levels will be lethal.
Through biomagnification (the magnification of contaminant concentrations), predators at the apex of food chains, such as raptors, may accumulate lethal doses of contaminants from eating prey with high concentrations of metals in their tissues.
The end result for the ecology of a contaminated river is that species will be eliminated and food chains will be disrupted and may collapse. Even when the sources of AMD have been removed, toxic levels of metals may remain in sediments in the river bed for a long time and will continue to destabilise the river’s ecology.
The Avoca River is a spate river that can experience big fluctuations in water level over a short period of time. High water can temporarily dilute the impact of the AMD, but the river level can drop rapidly particularly in dry weather, amplifying the impact of the AMD discharges. Additionally, the Avoca River is a soft-water river that has limited capacity to resist pH changes and a constant influx of AMD can lower the pH. These features of the Avoca River and the nature of the AMD mean that the river’s capacity to assimilate the pollution and reduce the impact on its ecology is extremely limited.
As well as having a very bad impact on the Avoca River, AMD and metals in surface water drainage are damaging the surrounding land. The spoil heaps have no vegetation cover and are being eroded by wind and rain. Surface water run-off is not controlled or intercepted and run-off from Mount Platt has contaminated surrounding forestry, causing significant dieback of trees. Other areas of surrounding land have also been contaminated.
East Avoca Pit from the summit of Mount Platt. Photo courtesy of Tom Harrington
Besides being dissolved in river water, metals may end up in sediments on the river bed and these can be a reservoir for long-term exposure. They can be re-dissolved in the water and be absorbed through the gills of fish and other aquatic animals or can be absorbed by algae and plants on the riverbed and be passed up and concentrated in food chains.
In 2003 the Eastern Regional Fisheries Board-University of Newcastle study ‘Restoring the Avoca’ examined a number of options for treatment of AMD from the mine. They concluded that revegetation of the spoils ‘…may be an appropriate means of changing the site appearance, but...it is highly unlikely to result in any great change in the amount of polluted water being generated on the site’. Active treatment of the mine drainage was identified as the only technically viable option.
In 2013 the Government provided funding, initially for a 3-year monitoring programme of discharges from the Avoca mining area and the river downstream from the mine. The monitoring period was subsequently extended and is currently ongoing. By 2020, over €5 million had been spent on monitoring and remediation works at the mines.
Despite the water quality challenges in the Avoca system, salmon and freshwater pearl mussel have managed to hang on. Some salmon still manage to get past the Avoca mines and spawn upstream. When it becomes operational, Arklow WWTP should produce a real improvement in water quality in the estuary, which will help the migration of salmon and sea trout.
The EPA includes five locations on the Avoca River from Avoca Bridge to Arklow Bridge as part of their national river quality monitoring network, using the diversity and structure of macroinvertebrate communities in rivers as indicators of water quality. The most recent assessment, in 2020 at Avoca Bridge, produced a Q-value score of 3 (moderate water quality), an apparent improvement compared to previous scores of 0 or 1 (Bad) in 2016.
So there are hopeful signs that water quality downstream of the mines may be slowly improving. Remediation of the more exposed spoils and pits, while not solving the problem, could produce improvements in water quality that could benefit downstream biodiversity and fish migration. Installation of the long-awaited wastewater treatment works at Arklow and Avoca, as well as improving water quality in the lower river, will refocus attention and ramp up efforts to address the pollution from Avoca mines.
References and Further Reading
CDM, Executive Summary: The Department of Communications, Energy and Natural Resources Feasibility Study for the Management and Remediation of the Avoca Mining Site. . 2008, CDM: Dublin.
Cowman, D., Ballymurtagh Mine, Avoca: a history. Journal of the Mining Heritage Trust of Ireland, 2011
Cowman, D., The mining community at Avoca 1780-1880. , in Wicklow History and Society., K. Hannigan and W. Nolan, Editors. 1994, Geography Press: Dublin
Coy, N., Avoca – The life and death of an Irish mine. Journal of the Mining Heritage Trust of Ireland, 2019
Doyle, A., Younger, P.L., Gandy, C.J. and Coulton, R., Restoring the Avoca River: an Integrated Social/Technical Scoping Study of Acid Mine Drainage Remediation Options. Report prepared for ERFB by University of Newcastle. 2003, Eastern Regional Fisheries Board: Dublin
Gallagher, V. and P. O'Connor, The Avoca mine site. Biology and Environment-Proceedings of the Royal Irish Academy, 1999. 99B (1)
Gray, N.F. and M. Sullivan, The Environmental Impact of Acid Mine Drainage. Technical Report 27. Water Technology Research, Trinity College, University of Dublin. 1995, Trinity College Dublin. (Tigroney Press Wicklow, Reissued). http://hdl.handle.net/2262/80221.
Oireachtas Reports, https://www.oireachtas.ie/en/debates/question/2020-09-15/167/#pq-answers-166_167_175. 2020, Department of Communications Climate Action and Environment: Dublin.
Smith, J., EU court rules Irish landfill broke directive., in The Irish Times. 2007: Dublin.
Sullivan, M., Gray, N.F. and O'Neill, C., A Synoptic Overview of the Avoca-Avonmore Catchment and the Mines in Technical Report 26, Water Technology Research, Trinity College, University of Dublin, Dublin 1995 (Tigroney Press Wicklow Reissued 2017).
Thomas, A. and P. McArdle, Avoca our Mining Heritage: A Brief History of Metal Mining in the Vale of Avoca 1998 Dublin.: Geological Survey of Ireland.