Taff minewater given clear bill of health

The Taff Merthyr Minewater Treatment Scheme in South Wales, developed and operated by Parsons Brinkerhoff, has seen levels of iron in the Taff Bargoed Valley, South Wales, fall by 97 per cent - clear proof of the scheme's success.

The Taff Merthyr Minewater Treatment Scheme is one of the largest examples of environmentally sustainable remediation of polluted minewater. The project is located on the site of the former colliery, where minewater was discharging directly into the local river. The scheme now needs a minimum of operation and maintenance. It has improved the overall water quality standard of the waterway and promotes the growth of local wildlife within and around the river. Downstream, a separate project has also been completed to provide canoe and sport facilities. This scheme is such a success largely because of the improvement in river water quality, resulting from the minewater treatment scheme.

The minewater emanating from the disused coalmine contains the characteristic red iron ochre. Treatment comprises five streams of tiered reedbeds, each preceded by a settlement lagoon. Minewater is collected and directed via a pumping station to the settlement lagoons, that retain the minewater for a minimum of 24 hours. At this stage a large amount of the iron ochre drops out of solution and settles. The subsequent reedbeds then act as a final polishing system to further reduce the iron ochre content.

The reedbeds were created on the cleared site and are earth-bottomed ponds with earth bunds at the edges. A concrete wier controls the minewater entry and exit to the reedbed and evenly diverts the water from the previous reedbed/settlement lagoons, and then into the next bed. This prevents short-circuiting of the system, maximising the settlement, retention time and efficiency of the reeds. The concrete weirs incorporate a cascade to aerate the minewater. This action encourages the iron to fall out of solution.

As the reeds become established, the quality of the resultant river water will improve still further. At the maximum expected deposition rates of the iron ochre within the reedbed, the settlement lagoons will need to be cleaned every five years. While
each reed bed is expected to continue to function well for up to 25 years, before it is replaced.



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