Site History -The discharge at Blaenavon issues from an adit known as River Arch. The discharge joins with a major run off flow 30m downstream of the adit, with the culverted River Lwyd a further 400m downstream. Mining ceased at Big Pit in 1980. Water Chemistry -The minewater at Blaenavon is from deep coal mine workings. It issues from adit, which is also used as an escape route from the Big Pit mining museum. The mine water has a neutral pH but does not appear to have excess alkalinity. Iron concentration in the mine water is low (generally less than 7mg/l) with historic data showing intermittent flushing events of high concentration. Approximately 1km of the receiving stream is affected by the ferruginous water and discoloured by the discharge. Site Design -The treatment scheme required at Blaenavon due to the flow rates and topography of the area comprised a surface flow constructed wetland. The scheme, constructed during 2001, comprises three reed bed cells, gravity fed by a pipe that runs from approximately 100m inside the adit. The stream was diverted to enable the reed beds to be accommodated in the narrow valley. Minimal concrete was used on the scheme and this should give a natural, visually pleasing scheme. The construction costs for the scheme at Blaenavon were in the region of £300,000. |
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