Gwynfi Mine Water Treatment Scheme

Site History - The Gwynfi Minewater discharge is associated with the former Glyncorrwg and Corrwg Rhondda Colliery at Blaengwynfi. The discharge affected a 2km length of the Nant Gwynfi, which is a tributary of the River Afan.

The topography of the site at Gwynfi is steep and hilly therefore there was limited land available for Reed bed creation. The land on which the treatment scheme is situated is on long term lease from the forestry commission and is maintained by the Coal Authority. The treatment system was designed by Ove Arup, and was completed in August 1998.

Water Chemistry - The minewater of the Gwynfi discharge is net alkaline, with a flow of up to 18 l/sec, pH of 6-7 and an Iron Concentration of approximately 8 mg/l.

The treatment required is to simply aerate the minewater to facilitate the oxidisation and precipitation of Iron.

Site Design - The treatment system was designed to reduce the loading of Iron into the river, whilst causing minimal disturbance to the surrounding environment.

Flows are diverted from the discharge to flow through the three reed bed cells. Discharge from the final reed bed rejoins the untreated, by-pass flow before entering the realigned river.

Limited land suitability meant that the system is unable to treat the highest peak flows but nevertheless provides substantial improvements most of the time. The times of very high flow are usually co-incident with high rainfall leading to increased dilution in the river to minimise impact.

The scheme included the use of Gabion baskets with local rock is aesthetically pleasing, as are the informal shapes of the reed beds.

The use of terracing aids with the aeration of the water whilst helping the aesthetic properties of the scheme. The construction costs for the scheme were £235,000.