Caphouse Minewater Treatment Scheme

The minewater treatment facility constructed at the National Coal Mining Museum for England (NCMME) has been built to provide treatment and control of minewater at the museum. The system will enable the minewater levels to be maintained below the level of the underground exhibition gallery whilst providing a standard of treatment of the minewater to meet the discharge standards required by the Environment Agency.

Caphouse Colliery shaft first appeared on plans in 1791. When the colliery closed in 1985, it was part of the British Coal Corporation Barnsley Area – West Side complex with coal being transported to the surface at Woolley colliery, 7 miles to the south. Subsequent to its closure, Caphouse Colliery was established as the site for the Yorkshire Mining Museum (now NCMME), offering guided underground tours of the exhibition gallery in the mineworkings of the New Hards Seam.

A significant rise in minewater levels at the museum occurred in 1997 raising concern about the effectiveness of control of minewater from Woolley. As a precautionary measure the underground tour was temporarily closed to the public due to the risk of flooding of the exhibition galleries.It was decided to reinstate the old pumping station at Hope Shaft, together with the adjacent settlement ponds, to enable water to be pumped and treated locally to the museum. It was necessary to add lime to the minewater in order to provide adequate treatment before the water could be discharged to the local watercourse.

Following a scoping study carried out in 2000 which was commissioned by the NCMME and The Coal Authority to evaluate what actions could be taken to maintain the museum and secure its future. It was highlighted that the pumping and dosing arrangement at Hope Shaft should be upgraded and improved.

The minewater pumped by the hope shaft contains between 45 - 52 mg/l of iron, this level of iron is far too high to put straight into reedbeds and therefore required sufficient settlement to reduce the iron concentrations to nearer 10mg/l.

The existing facilities at Hope Shaft consisted of a lime dosing silo, an aeration cascade and two 1040m3 settlement ponds. These facilities had a historical discharge consent of 10mg/l iron, 3mg/l was strived for and achieved, but due to their small size and the increased loadings of iron ochre they had a very high maintenance requirement. The lagoons needing to be emptied every 4-6 weeks.

Once it became evident that this small treatment facility could not cope with the rise in minewater levels in the area Wardell Armstrong were appointed to design the enhanced treatment facilities. The site for construction of the treatment facility was steeply sloping, and the area available limited. This presented the designers with a challenge to engineer the tanks and reed beds onto the available site. The use of concrete tanks was unavoidable, these act as retaining walls in addition to their role as settlement lagoons. Innovative geotechnical engineering techniques have been used to construct the areas for the reed beds, including reinforced earth and soil nailing.

The final treatment scheme opened in October 2003 by Sir John Harmon, Chairman  of the Environment Agency, comprises of the original Hope Shaft treatment scheme and added to that were a flow balancing tank (1500m3), two 2000m3 settlement tanks, and two reedbeds in series measuring 4300m2 area in total. The enhancements now control the water and keep it at a steady level below the underground museum.

At present the reedbeds are in their infancy but when they become more established which will be next summer (2005) they will provide an important habitat for birds and insects. Once the wetlands are established the Authority expect the final discharge to be less than 1mg/l this is a reduction of approximately 50mg/l iron over the length of the scheme.

The scheme also incorporates an artificial badger sett.