The Nottinghamshire Derbyshire coalfield is a major area for water pollution concern and hydrogeological interest. The area is set in a reasonably simple geological setting with the dip of the strata going from outcrops in the west and successive strata layering one on top of the other to the east. The region has had a mining history going back in time to at least the Middle Ages though some evidence shows roman use of coal from the outcrop in the Amber and Erewash valleys. Apart from the initial taking of coal from the outcrop of seams where they were easy to exploit the first coal seam deeper access was by bell pits that today can still be seen as small collapse hollows across the area.
The mines developed in the 16th and 17th Centuries following coal seams from the outcrop and interconnecting with deeper seams via shafts: when drainage became an issue, interfering with the winning of the coal due to groundwater flooding the working faces. Before the advent of mine water pumping engines this problem was, where possible, managed by the digging of drainage tunnels often known as soughs or adits. These non-productive sough workings led water to drain out of the mines at lower levels from those of the working faces, into valleys: much evidence of such works has been found in the Erewash Valley and several others are recorded in ancient estate maps of the Wollaton mine workings just to the west of Nottingham draining to the River Leen.
At the end of the 19th Century there were around 400 working collieries operating in the region, removing vast tonnages of coal destined not just for the home market but for export around the world due to the remarkable variety of qualities and calorific values of the coals mined, from bright house coals to steam generating. Much of the production being exported via Goole and Hull to countries including Australia, Aden, South America, Russia and Europe. In Britain in 1905 over 236 million tonnes of coal (an unimaginable but correct figure) were mined from beneath the landscape. When considered that not just coal was being extracted at these collieries but iron stone, fire clays and much else leaving large voids from near outcrop to some considerable depths below the region.
Now that deep mining has ceased the issues of minewater, the water that flows from both the outcrop towards the deeper workings and from the strata including the aquifer rocks; both limestone and sandstone that overlay the coal bearing strata. In the past such water was controlled below ground by pumping and stoppings, water control dams. Such headings were set in the worked out areas of workings to exclude the water from working areas, many such stoppings had valves set into their masonry construction so as to allow water pressure to be managed to disallow stopping bursts and uncontrolled inundation. The worked out collieries at strategic locations were maintained as drainage pumping stations where such water as was able to be captured at these locations could help lessen the pumping liability at deeper working levels.
The use of some outlier minewater pumping sites are still maintained so as to avoid the too swift accumulation of water at deep mine facilities and at the same time avoiding the discharge of minewater by overtopping to local streams close to the outcrops or via long forgotten soughs.
The National Rivers Authority simplified overview of the coalfield and the direction of water flow within the still operational minewater pumping regime 1995.
The following sketch plans (Awbery HG, The Protection of the Nottinghamshire Coalfield by the Bentinck Minewater Concentration Scheme. IMWA 1988) outlines the minewater management at the working collieries and pumping shafts.
The Bentinck pumping scheme took water from the pump lodge at Bentinck Drift and piped through to Annesley where the water is raised to the surface passing through settlement lagoons before entering a pipeline to the River Trent 17.5 kilometres to the south Closed in 1999).
The pumping shafts on the left side of the plans and the working shafts are to the right or western part. The interlinking of underground workings is emphasised and demonstrate the free flow of water from one set of mine workings to another.
Today the main pumping stations operated by the Coal Authority are Woodside, A Winning, Silkston, Penistone, Fender and Wooley.
There are several other planned sites for pumping along the coal outcrops including Dukes Level, Summerley and Unstone. The likely reopening of other minewater pumping schemes such as that at Langton (always considered key to the minewater gravitational flow beneath ground) may delay the need to pup at Calverton in Nottinghamshire by up to 5 years but environmental issues will need to be overcome regarding consents from the Environment Agency.
The Annesley Bentinck Colliery minewater pumping scheme was turned off on Christmas Eve 1999. Prior to that the pumps removed 1.2 million gallons of high chloride water per day. This discharge was routed by a 17.5 kilometre pipeline from Annesley to the River Trent close to the confluence of the River Leen. The best guess or educated estimate of the Coal Authority, British Geological Survey and Environment Agency was that water from this area of the coalfield would arrive at Calverton within 20 years. That being the deepest area of workings within this section of the coalfield. The expected water quality was that there would be high iron levels and especially high chloride levels that will require either treatment using reverse osmosis (RO) or dilution. The economic implications of such RO water treatment ensures that the minewater pumped from the Calverton minewater treatment scheme will need a pipeline to take the discharge to the River Trent close to the major discharge of the Stoke Bardolph Sewage Treatment Works to allow dilution of the chloride rich discharge.
The complexity of minewater treatment in the Derbyshire Nottinghamshire borders and the links into south west Yorkshire have been simplified in the above paper as the intention to is to demonstrate the present basic knowledge of the area.