Water (Post-operational Phase)
Good Practice
A wide range of methods can be used to prevent, mitigate and/or remediate the adverse effects of surface mineral workings upon groundwater and surface water, and these are described in detail in the Guide to Good Practice L0017. However, final decisions regarding which issues need to be addressed for any given site, and how these should be dealt with, have to be made by the MPA concerned. Ideally, these decisions should be made in consultation with the mineral operator, and with advice from appropriate statutory consultees, including the Environment Agency or SEPA (as appropriate).
Reclamation
There is a requirement to consider the environment for the whole life of a site, from excavation to reclamation. The effects of reclamation on surface and groundwater are therefore considered here. It includes both restoration (any work undertaken on completion of, or in parallel with, quarrying operations) and aftercare (any subsequent operations that involve bringing the land to the required standard for the intended use), although aftercare will be dealt with separately because it is not a direct effect of the operation.
Reclamation to open water
There is potential for contamination of both the open water body itself, and groundwater, which can be prevented using the measures in Table 2.
Table 2. Prevention of contamination connected with open water.
| If the open water is designated as a local nature reserve, it will usually receive a degree of management. |
| Ban or restrict motorised sports. |
| Restrict adjacent land uses to those with little or no pollution risk. |
| Control or prevent run-off from adjacent land. |
| Ensure backfill and landscaping material is free of contamination. |
| Avoid stagnation by ensuring sufficient through-flow. |
Restoring to open water can be part of creating a wetland habitat (Photograph 1), or it can be for recreational purposes such as a watersports centre (such as Pugneys Country Park in Photograph 2) or diving centre 328. In line with the guidelines above, the only powered craft allowed on the lake is the rescue boat, and an electric powered launch.
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Photograph 1. Restoration to open water as part of a flood relief scheme. |
Photograph 2. Pugneys Country Park: Watersports centre and wildlife lake. |
Additional measures to prevent contamination of the groundwater would be to line the excavation with low permeability material. Care must also be taken where open water reclamation schemes are sited in floodplains.
Backfilling with overburden or imported fill: effects on site drainage and surface run-off
This will depend on the nature of the backfill material, but suitable topography should be created to provide efficient and controlled run-off. Land drains can be installed to compensate for low permeability material.
Backfilling with overburden or imported fill: effects on groundwater levels and flow paths
Low permeability fills can distort patterns of groundwater flow, so there should be good monitoring and modelling to predict whether the following measures might be needed. The installation of channels of higher permeability material, and the installation of land drains discharging into surface watercourses can both be considered.
If the hydrogeology is clearly understood then it is often possible to take very simple measures to ensure that there are no negative impacts 329.
Backfilling with overburden or imported fill: effects on water quality
Wherever possible, only inert backfill and landscaping materials should be used. If potentially contaminating material is involved then the amount of time it is exposed to oxidation should be minimised. Low-permeability liners, grout curtains or cut-off barriers can be used to isolate contaminated material. Contaminated backfill should be restricted to areas above the predicted rebound groundwater levels.
Reclamation to Engineered Landfill
Landfill and waste management sites within disused quarries represent a major potential threat to the water environment unless they are designed and operated strictly in accordance with current best practice. Detailed guidance on such practice is given in the former DoE's Waste Management Paper 26B, "Landfill Design, Construction and Operational Practice". A simple list of measures is given in Table 3.
Table 3. Controlling groundwater pollution from landfill leachate.
| Restrict landfill and/or waste processing operations to inert materials. If not, follow best practice! |
| Retain an adequate thickness of unsaturated strata beneath the excavation to help attenuate any contaminated leachate. |
| For deeper excavations, backfill with inert material to re-establish an adequate unsaturated thickness before final reclamation. |
| Line excavation with synthetic liner before landfilling. |
| Use small, clay-lined cells to reduce the risk of large scale pollutant events. |
| Provide an adequate system for the collection and treatment of leachate. |
| Cap site to prevent leaching of contaminants by falling rainfall. |
| Create topography to provide adequate surface run-off throughout the site. |
| Provide and adequate drainage system to collect surface run-off and isolate it from waste material. |
Low level restoration
On-going pumping is usually required in this situation, although the pumping requirements can be reduced by partial exclusion of groundwater by means of bunds or liners. The requirement for long-term pumping to keep the site drained would normally be covered through planning obligations (Section 106). Consideration should be given to the potential effects of stopping the pumping and also to the effects of long-term pumping on other water users or wetland areas which
After Use
Agricultural after-use
Agricultural practices which could be harmful to groundwater and/or surface water, such as the intensive use of nitrate fertilisers, cannot easily be controlled through the planning system, once the land has been reclaimed for agricultural purposes. However, to minimise the risks, the measures in Table 4 may be considered as part of the reclamation design.
Table 4. Measures to minimise risks from agricultural afteruse.
| Control and minimise the use of fertilisers as much as possible. |
| Retain an adequate thickness of unsaturated material beneath the excavation to help attenuate contaminants. |
| Backfill with inert, preferably low-permeability material after excavation, to restore or increase the thickness of the unsaturated zone. |
| Avoid prolonged delays in the re-use of stripped topsoils which contain chemical residues. |
Studies and modelling may need to be carried out to assess the potential impact of schemes on the water environment, and appropriate measures taken to avoid or compensate for these.
Forestry and habitat regeneration
Mitigation work, where necessary, will depend on the specific nature of the problem. Drainage schemes on sloping sites, for example, will need to be designed in such a way that they do not exacerbate flooding and erosion. On floodplain sites, the establishment of a dense scrub or woodland could hinder the flow of floodwaters and may not, therefore, be appropriate.
In one situation 329 where restoration to agriculture may have resulted in a local aquifer being affected by nitrates, the site was restored as an ecologically important heathland project.
Industrial, commercial and residential after-use
The main risk from these forms of after-use is pollution from industrial processes, waste and contaminated run-off. While pollution from these sources is controlled, to some extent, by existing regulations and good practice techniques, the level of potential risk can be greater in reclaimed mineral workings, because of the increased vulnerability of underlying aquifers. Appropriate mitigation measures for industrial developments in disused quarries are given in Table 5.
Table 5. Mitigation measures for industrial developments.
| Restrict industrial after-uses to those with little or no risk of pollution. |
| Limitation and control of potential pollutants as much as possible. |
| Retention of an adequate thickness of unsaturated material above the water table to help the attenuation of contaminants. |
| Where this is not possible, backfill with inert materials to re-establish an adequate thickness of unsaturated material before redevelopment. |
| Use of low-permeability capping material to restrict the infiltration of contaminants. |
| Control of run-off from the site to limit impact on surface water. Treat before discharge if appropriate. |
Where reclaimed sites are to be used for housing, attention would need to be given to the control of surface run-off that may be contaminated with vehicle fuels, oils and de-icing agents, particularly from busier roads and car parking areas. Special attention may also need to be given to the prevention of accidental leakage from sewers and domestic waste connections.
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