PAN 64: Reclamation of Surface Mineral Workings
ANNEX A - MINERAL WORKINGS IN SCOTLAND
1. The following section summarises the characteristics of the main mineral types worked in Scotland, and provides guidance on their reclamation. It should be read in conjunction with the more general advice contained in this PAN.
2. The relatively high economic value of coal makes it cost effective to work seams overlain by thick layers of overburden. During the life of the site there is therefore a need for the storage of topsoil, subsoil and large volumes of overburden. The volumes involved can be minimised by progressive working and reclamation of the site. In many cases the high ratio of overburden allows the site to be infilled to pre-working levels without the need for importation of additional fill materials.
3. Soil wetness at opencast coal sites can cause difficulties when handling soils, as there may be limited opportunities during the year when the soils are in a suitable dry condition. Because of the heavy texture of soils often associated with opencast sites, reclamation schemes need to aim to install a drainage system as soon as possible following soil reinstatement.
SAND AND GRAVEL WORKINGS
6. Sand and gravel workings are a common form of mineral extraction in Scotland. Most production exploits drift deposits in river valleys or glacial and fluvio-glacial gravel deposits. The ratio of mineral to overburden is usually high, which means that the importation of fill is necessary if the land is to be returned to its original levels. In some cases this may not be appropriate or necessary.
7. Much of the sand and gravel resource is overlain by relatively thick and high quality soils, which enables high standards of reclamation to be achieved. At some sites very stony soils can be a limiting factor, which can be addressed through aftercare stone picking. Sites with a high water table can be allowed to fill with water following extraction and are often used for the creation of habitats for wildlife.
HARD ROCK QUARRIES
8. Hard rock quarries in Scotland include igneous rock, limestone/dolomite and sandstone. Many of these quarries where granted planning consent following the second world war when environmental considerations were not given the weight they are today. Consequently many were worked with little regard to reclamation. There are specific challenges associated with the reclamation of these older permissions including:
- inadequate supplies of fill material;
- shortage of soil resources;
- the water table level; and
- sidewall stability.
9. The ability to integrate older quarries with the surrounding landscape can be compounded by the regularity of the quarry landscape, consisting of production benches and faces, and the quarry margin which can often finish abruptly at the boundary of the planning consent. Planning authorities therefore need to be flexible in reviewing old permission and may need to permit some variations in quarry boundaries to enable satisfactory reclamation to take place.
10. Reclamation of new quarries or quarry extensions should be considered from the start of the planning process and integrated with the working methods. There needs to be a clear set of landscape objectives and a reclamation strategy that details the final landform, methods of working, progressive reclamation and integration into the adjacent landscape and land uses. This must be flexible since working objectives, priorities, opportunities and techniques will change over the long timescale. It is likely that most reclamation strategies for hard rock quarries will require updating during the life of the working.
11. A number of techniques are available for reducing the visual impact of hard rock quarries. Production benches and quarry faces can be designed to create a landform in keeping with the surrounding landscape. Alternatives to final face treatment, such as restoration blasting and rollover, can create a more natural appearance by reducing the face angle and creating buttresses and scree slopes. Where fill materials are available, it may be possible to fill all or part of a site, including total or partial masking of the quarry margins. Consideration can be given to developing a reclamation margin ( see paragraph 43 of the main text).
12. The success of vegetation establishment is largely dependent on the soil resources available. In new quarries or extensions soils can be stripped and used in restoration. In older quarries where soil resources are limited use of soil-forming materials and amendments is usually required. Vegetation can be established directly onto the rock faces using techniques such as hydroseeding, pouring or spot seeding. Measures will be required to prevent damaged to vegetation from rabbits and other wild animals.
13. It is essential that the long term safety of hard rock quarries is considered. The stability of quarry faces is the principal safety issue although deep water and steep banks resulting from sub-water level working and land instability are also important. Rock-fall can be a hazard to people and livestock and can destroy or disturb revegetated areas lower down the face. Stabilisation measures such as scaling can be undertaken on excavated quarry faces and slopes to ensure they are safe, particularly where members of the public have access. It is good practice that scaling is carried out before vegetation is planted. Careful recording and monitoring can be undertaken on a regular basis and ongoing scaling carried out where necessary.
14. Progressive restoration of hard rock quarries assists in returning the landscape to a form more in keeping with its surroundings within a shorter timescale. For long-life quarries, where the upper faces will be visible for many years prior to completion of mineral working, it is best practice to require progressive reclamation of finished upper faces and benches at an early stage.
See Circular 34/1996 paragraphs 25 and 26.
15. Dormant quarries are those where planning permission is still extant but which are not being worked. Dormant sites are required to be registered but conditions only need to be submitted prior to the re-commencement of working. Operators may consider some form of interim or temporary reclamation on dormant sites using simple techniques of soil formation and revegetation to create some basic landscape improvements. Such reclamation could be reviewed if the quarry is re-activated. Planning authorities can attach a condition to new quarries or extensions requiring temporary landscaping or reclamation in the event that the quarry becomes dormant for more that say 5 or 10 years.
16. Abandoned or 'orphan' quarries are not controlled by the Review of Old Minerals Permissions regulations. Like other forms of derelict land they rely on other mechanisms for treatment. The landowner is responsible for dealing with significant hazards and public safety concerns, although funding for any work is usually limited. There are examples of funding from a variety of sources being co-ordinated to improve abandoned quarries, particularly near urban areas. Environmental improvements may be secured by allowing some reworking of abandoned quarries or quarries where reclamation has not been completed satisfactorily.
See Slate Waste Tips and Workings in Britain. Richards Moorhead & Laing Ltd, 1995.
17. Slate working was once large scale in several areas of Scotland but the few existing workings are relatively small. Slate production created vast quantities of waste material, which was usually tipped adjacent to the working area. It is generally impractical to backfill quarry holes, and in most cases it is therefore necessary to reclaim the spoil in situ. Soil is rarely available in sufficient quantities to cover the spoil, and where vegetation establishment is required it is usual to plant directly into the spoil material. The physical and chemical characteristic of the spoil limits its suitability as a growth medium. In the absence of soil, surface preparation techniques usually include the crushing of the surface slate waste to produce fine fragments and the use of amendments.
METALLIFEROUS MINING SITES
See The Reclamation and Management of Metalliferous Mining Sites. ECUS, 1994.
18. There is currently little metalliferous mining in Scotland although former spoil heaps do occur. Wastes from metal mines and those generated during the extraction and processing of materials such as gold and barytes, may contain concentrations of metals which present problems for the successful establishment of vegetation and hence for site reclamation.
See Non-ferrous Metalliferous Mineral Extraction in Scotland - Processes and Environmental Consequences. Wardell Armstrong, 1993.
19. Approaches to the reclamation of metalliferous mine sites vary from non-intervention to large scale earth moving and revegetation according to site characteristics. It is advised that expert advice is sought on a site specific basis to assess possible hazards in relation to planned usage.
20. The options for establishment of vegetation are generally to cover the wastes with soil and/or other soil-forming materials such as non-metalliferous overburden or to plant directly into the wastes using suitable species, including in appropriate cases metal tolerant plant varieties, with ground preparation treatments and amendments. In some instances barrier layers or membranes are required to prevent excessive percolation of water into the metal rich wastes.
See Restoration and Revegetation of Colliery Spoil Tips and Lagoons. Richards Moorhead & Laing Ltd, 1996.
21. The fine-particle residues from the processing of minerals are normally disposed of as high moisture slurries into lagoons impounded within purpose built dams. The reclamation of tailings lagoons can present major engineering problems since the deposited materials may remain unstable for many years. The principal sources of tailings in Scotland are the working of coal, and associated minerals. Large silt lagoons from washing of sand and gravel or crushed stone may also present similar physical characteristics. Chemically, there are wide variations between the different types of tailing.
See Report of the Working Group on Peat Extraction and Related Matters, 1999. www.planning.odpm.gov.uk/peatland
22. Reinstatement of sites to a condition suitable for an appropriate afteruse should be an integral part of the planning of peat extraction. Where peat bogs have been damaged by peat extraction they can be restored to a range of afteruses including agriculture, forestry or nature conservation. Restoration of Damaged Peatlands (Wheeler and Shaw, 1995) provides information on recreating raised bog habitats as well as alternative afteruses.