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.