Woolley Minewater Treatment Scheme

As the coal mines in the area closed and pumping from them and their associated Pumping Mines ceased, until finally in 1991 all pumping in the "West Yorkshire Coalfield" stopped. Woolley Mine was developed by British Coal as the central mine water pumping station to control the level of water in underground workings including the area between Barnsley and Huddersfield.

The Coal Authority took over the Woolley site in November 1994 and inherited a requirement to deal with significantly increasing volumes of minewater to be controlled to contain rising umderground water levels. Volumes in excess of 200 l /sec (2650 gallons per minute) were being dealt with 24 hours per day. In addition, the National Rivers Authority (NRA) (now the Environment Agency) was also seeking improvements in the minewater discharge quality into the River Dearne and affected this by tightening of the discharge consent parameters.

During its passage through underground workings, the minewater becomes contaminated  with iron dissolved from the pyritic minerals exposed in the coal measures strata. The discharge when raised to the surface at Woolley initially had total iron concentrations in excess of 100mg / l. As this minewater is a typical bicarbonate minewater (i.e. contains temporary acidity), when exposed to air (or receives sufficient dilution in a watercourse), it produces the typical ochreous colouration due to the presence of hydolysed iron-oxyhydroxide particles, which in turn results in the discoloration and blanketing of the bed of the receiving watercourse if allowed to discharged untreated.

A minewater treatment plant was in place at Woolley when the transfer from British Coal to the Coal Authority was completed. However, the quality of the discharge of up to 15mg/l total iron was not acceptable. In view of the Environment Agency consent which required a maximum of 5mg/l from May 1995 and 3mg/l from May 1996 urgent improvements were therefore necessary to allow the Coal Authority to comply with the quality requirements of the consent and necessary to protect the quality of the River Dearne.

In the longer term, removal of the fine iron particles was achieved by the introduction of a ´wetland´ which provided a low cost, low maintenance passive method of tertiary remediation of the minewater.

The wetland at Woolley is 1.4 Ha in area and was at the time of construction the largest man made wetland in the UK specifically designed to improve the quality of a minewater discharge.

It was planted in June 1995 and consists of about 40,000 Wetland plants. A variety of species were selected based upon their tolerance to minewaters. Bull rushes and reeds provide the bulk of the species, and were supplied and planted by Yarningdale Nurseries Ltd of Warwick, altjough other aquatic types were also incorporaed to provide variety and colour to the bed. The wetland has now developed and can be seen to be contributing to the Coal Authority´s conservation responsibilities. It provides a wildlife habitat on the River Dearne migratory route and attracts over 20 species of birds including a number of species of wildfowl.

Planting was directly into soil and allied with a simple inlet flow control system, a cost effective design was achieved. The wetland has now matured; it has resulted in a significant improvement in discharge quality with iron concentrations consistently below as 1mg/l total iron.