Whittle Mine Water Treatment Scheme

• Information Sheet

Site History - Since the 1980s, when major closures and abandonment took place in the North East of England, there was an increase in mine water recovery in the area.

In 1997 when Whittle Colliery ceased mining and pumping operations it was estimated that mine water recovery was occurring at 5cm/day. As the area in the mine became flooded, ferruginous outbreaks were predicted. Such outbreaks at Whittle would have placed the local Hazon Burn in danger of pollution from the rising mine water. The Hazon Burn is a tributary of the River Coquet, any pollution in the River Coquet would have had an adverse effect on the river as an important local amenity, as the river contains salmon and is also one of the 27 river SSSIs in Britain.

It was decided that a preventative scheme should be used. A pump test was commissioned by UK Coal and construction started in late 1999.

Water Chemistry - The mine water at Whittle is net alkaline and is pumped from underground via a purpose drilled borehole. The water running underground was initially sampled at 4mg/l Fe concentration. But a sample from another borehole gave a reading of 900mg/l Fe. The water quality has now stabilised and is 42mg/l Fe. The flow rates during the pump test were between 10 and 40 l/sec. But in recent times the rising water underground has slowed to only 3cm/day and therefore it was felt that the underground water level could be controlled with a pumping rate of 15 l/sec.

Site Design - The scheme at Whittle is a preventative scheme and therefore the water was prevented from reaching the surface naturally. The water is pumped via a purpose drilled borehole that stretches 70m into the Whittle Colliery drift, with the water initially entering into the aeration cascade at the head of the treatment scheme. After aeration, the water simultaneously flows through two parallel settling ponds. These have an area of 800m² where the ochre precipitation takes place. The water then enters into three surface flow aerobic wetlands in series. The wetlands each have an area of 3000m². Wetlands 1 and 3 are planted with Typha Latifolia, with wetland 2 planted with Phragmites. The purpose of the planting was to distribute the flow of the water and polish the final discharge into the Hazon Burn.