The Combe Down area is:
- Within the World Heritage Site of the City of Bath;
- Adjacent to the Cotswold Area of Outstanding Natural Beauty (AONB);
- Within a conservation area, containing a number of Listed buildings;
- Above a Grade 1 aquifer;
- A Site of Special Scientific Interest;
- A Special Area of Conservation;
- Of international importance for Greater and Lesser Horseshoe bats;
- Of international geological importance partly due to the work of William Smith.
An Environmental Statement was carried out for the stabilisation scheme and was submitted to the Local Planning Authority in December 2002. The Planning Application and Environmental Statement can be seen at the Combe Down Stone Mines Information Centre in Combe Down.
Due to the multitude of environmental issues, environmental management was an essential part of the Project. The Project Team, contractors and consultants operated environmental management plans to all site works. Audits of the plans were regularly undertaken.
Combe Down forms a plateau capped by Great Oolite limestones between the valley of the River Avon and Horsecombe Vale. The geology of the region is dominated by rocks of Middle and Lower Jurassic age. The Great Oolite is the uppermost lithology. This is underlain by the clays of the Fuller’s Earth Formation, which in turn is underlain by limestones of the Inferior Oolite and the Midford Sands of the Lias. The Great and Inferior Oolite formations provide effective aquifers (rock in which water can be stored and pass through) for public and private water supplies.
The Great Oolite stone, used for building purposes, formed over 146 million years ago when the area was underneath a deep tropical sea on which the shells of ooliths were deposited. The ooliths bonded together to form the distinctive rock known as oolitic limestone or locally as ‘Bath Stone’. The Romans found that it was easily worked and used it for important fortifications. During the 17th Century, small quarries were opened on the edge of the Combe Down plateau, with major quarries being developed in the 18th Century.
The British Geological Survey (BGS) worked with the Bath & North East Somerset Council to ensure no adverse impact is associated with the Project.
The slopes of the Combe Down plateau are over-steepened as a result of erosion by the River Avon and its tributaries. This has led to land slippage on many of the slopes. Furthermore, softening of the Fuller’s Earth clays has led to cambering of the overlying strata, especially near the edge of the plateau. This has resulted in stress fractures in the form of gulls, being a feature across the plateau. Some of these features remain empty (or void), others are filled with clay or rock fragments. Examples can be seen in Springfield Quarry, off Entry Hill Rise, Bath.
The Combe Down Mines lie above a Grade 1 aquifer (rock in which water can be stored and pass through, and which is then suitable for use as drinking water) and a source protection zone on account of the potable water supply.
Water movements on Combe Down are largely controlled by the geology. Water percolates the permeable surface rocks of the Combe Down plateau and emerges as springs on the valley sides above the impermeable Fullers Earth.
The aquifer underneath Combe Down is split into 2 main parts. The top part is made up of Great Oolite limestones with Fullers Earth underneath. The lower part is made up of Inferior Oolite limestones with Midford Sands. Water for public and private use is extracted from the springs that issue at the base of these units, in particular at the Prior Park, Whittaker and Tucking Mill springs.
It is important that the stabilisation project does not affect the quality or quantity of water emerging at these springs, and that any changes in groundwater flow do not cause instability in the slopes of the plateau.
Combe Down and its surrounding area is of great value for nature conservation with a wide variety of flora and fauna, including wild populations of bats, deer and badgers. A significant amount of land in Combe Down is designated as sites of special nature conservation interest.
The stone mines are of particular significance comprising part of the Combe Down and Bathampton Down Site of Special Scientific Interest (SSSI) and forming part of the Bath and Bradford on Avon Bats Special Area of Conservation (SAC).
The high conservation value of the nature conservation designations makes ecology and the natural environment a key issue which will be regarded throughout the project.
In May 2006, the Combe Down Stone Mines project team began work relating to the protection of bat species within the historic abandoned mine workings at Combe Down.
The Combe Down Stone Mines are of significance for a variety of bat species, particularly greater and lesser horseshoe bats and vespertilionid bats. The bat species that inhabit the mines are protected under UK and European legislation and as such it is illegal to kill, injure or disturb bats, obstruct access to bat roosts or damage or disturb bat roosts. In 1994 the Combe Down Mine complex was documented as being in the top 10 sites in Britain, and the top 20 sites in Europe, for hibernating bats. In order to comply with UK and European legislation an essential element of the Combe Down Stone Mines project is the protection of the bat species that inhabit the mine complex. The engineering methods for the stabilisation of the mines have been influenced by the bat habitat and the works currently underway at Grey Gables, Monkton Combe have been planned under the guidance of English Nature and the project’s bat specialist who is the Department of Environment and Rural Affairs (DEFRA) bat licence holder.
The works incorporated engineering methods that allowed part of the mine to retain the conditions required by the bats whilst at the same time providing stabilisation to the land above. The works involved creating chambers and passages and utilising existing and new underground roadways to provide areas which were both safe for the bats and also the properties above ground. These chambers, passages and underground roadways were constructed from a combination of steel and concrete. All internal surfaces were shotcreted to provide areas suitable for the habitation of bats. In addition a chimney and a tunnel have been constructed to improve the ventilation from the Grey Gables mine to the Mount Pleasant mine and a bat sump for the long term monitoring of bats has also been constructed.