The Wheal Jane Incident and water quality

The Wheal Jane incident was a very visual mine water pollution event which affected the Fal Estuary in January 1992 and resulted in the establishment of an ongoing water treatment system. Previously published accounts of the Wheal Jane incident include Somerfield et al. (1994a), Banks et al. (1997) and Younger (2002).

Aerial photograph of the mouth of Restronguet Creek and Carrick Roads taken during the Wheal Jane incident. The orange plume entering Carrick Roads was made up of Fe hydroxides being carried in suspension out into the estuary. This very visual pollution incident caused widespread concern but had no significant biological impact. Photograph courtesy of the Environment Agency.

Wheal Jane was an important mine within the Carnon Valley; the modern workings intersected a large area of older workings within the area. The mine principally produced cassiterite, the main ore mineral for tin, but older interconnecting workings also produced pyrite and arsenopyrite. The modern workings within the mine extend to a depth of about 450 m and were extremely wet, probably due to mine water drainage entering the mine from the older surrounding workings. When the mine was operational water levels were managed by pumping, with the discharge of this water into the Carnon River after partial treatment. In 1991, a government grant which supported the dewatering of the mine was withdrawn, resulting in the closure of the mine and the cessation of pumping. Both the rise in the water levels and the water quality were monitored, and on the 17th November 1991 the mine water discharged into the River Carnon via an adit draining the mine. The initial water had a very acidic pH (2.8) and had a high metal loading. To control this discharge it was treated with lime, the adit was plugged and the water was pumped from the mine into the existing Wheal Jane tailings dam. However pumping was stopped on the 4th of January 1992 for technical reasons and whilst an alternative treatment method was being investigated on January 13th there was the accidental release of approximately 50 million litres of acidic (pH 3.1) metal laden water (Younger, 2002). Fe hydroxides carried in suspension in the mine water formed a very visual orange plume which flowed out via Restronguet Creek into Carrick Roads. The water was also contaminated with some metals in solution, the most significant of which was the presence of >600 parts per billion (ppb) of cadmium. This mine water was less dense than the saline waters in the estuary and formed a buoyant plume flowing out to sea. The impact was extremely visual and public concerns relating to health effects and the impact of the mine waste discharge on tourism in the area caused significant public pressure for both an immediate and a long term solution to the incident. Initially pumping recommenced with the treated mine water discharge being allowed to settle in the tailings dam. Hunt and Howard (1994) examined the speciation of arsenic within the waters in the Carnon River and in Restronguet Creek following the Wheal Jane event and found that arsenite concentrations in the Carnon River below the tailings dam decreased significantly with time after the event, whilst the levels within the estuary remained relatively constant. In contrast the concentration of arsenate was low in both the river and the estuary following the initial discharge but increased significantly in the estuary in the following July. The implication of these observations are that the concentrations of arsenate and arsenite within the estuarine area is probably unrelated to the mine water discharge. The discharge of mine water from Wheal Jane resulted in the establishment of a long term management system involving a passive reed bed storage system developed to treat the mine water discharge (Hamilton et al., 1999).  This has now been replaced with an active treatment plant, comprising a high-density sludge alkali dosing plant, which during its first full winter of operation treated  a total of 4,400 million litres of water (Younger, 2002).  To date the engineering treatment of the mine waster discharge from Wheal Jane has cost in excess of 20 million (Younger, 2002).

The Wheal Jane passive water treatment system during its construction. Photograph courtesy of Melanie Brown, CSM.

The Wheal Jane pilot passive treatment plant consists of three treatment schemes. All three include: 

Aerial photograph showing extent of the Wheal Jane water treatment system.

When mine drainage mixes with fresh river water ochres of iron oxides and hydroxides are commonly precipitated; these ochres formed the visible plume of contamination during the Wheal Jane Incident. Mineralogical studies on ochres in Cornwall (Singh et al., 1999) have shown that fresh sediments contain the minerals ferrihydrite and goethite which are commonly poorly crystalline. However, in older sediments the only mineral present is goethite, which appears to have precipitated around filamentous algae, which may be important factors in the precipitation of the ochres.

Additional Information

Wheal Jane Project website  Information on the bioremediation of acid mine drainage.