In line with industry best practice, a series of studies has been commissioned into the environmental aspects of the proposed quarry extension.
The findings have informed and shaped the proposals to ensure they minimise the impact on people, wildlife, the landscape and other environmental factors such as surface and ground water during the preparatory works and for the operation and future management of the extended quarry.
Glendinning is very mindful that this is particularly important as the site is inside the boundary of the Dartmoor National Park.
Therefore all aspects of the environment have been carefully addressed through both desk studies and site surveys before being further discussed during our extensive consultations with the local community and statutory authorities following the initial announcement of our proposals.
The following is a summary of the main effects of the proposals. Further information is available in the Environmental Statement and its Non-Technical Summary available on the Planning Documents tab, or via the Dartmoor National Park Authority website.
Significant consideration has been given to the possible effects of the proposals on ecology, particularly considering the size and location of the site. Wildlife and protected species surveys have been undertaken over a two-year period to determine features of ecological value within and immediately adjacent to the site. These include:
- Extended Phase 1 Habitat Surveys including Hedgerow Surveys;
- Great Crested Newt Survey;
- Reptile Survey;
- Bat Roost Survey;
- Bat Activity Survey;
- Dormice Survey;
- Badger Survey;
- Breeding Birds Survey;
- Invertebrates Survey: and
- An Arboricultural Tree survey to BS5837.
Drawing on the results of these surveys, an Ecological Mitigation and Enhancement Strategy has been prepared which seeks to avoid or reduce impacts on wildlife and maintain habitat connectivity around the quarry extension and the surrounding landscape. This will include the progressive relocation of hedgerows from the extension area, new hedgerow and broadleaved woodland creation, and enhancement of retained habitats. A landscape and ecology management plan would be implemented to ensure the biodiversity value of created and retained habitats is maintained in the long-term.
The site falls within the Dartmoor National Park, which is principally designated because of the outstanding quality of the landscape. Therefore the visual effects and effect on the landscape character have been assessed and carefully considered. Information of the existing landscape, both in the immediate site and the wider landscape surrounding the site which may be affected, was gathered through both desk based study and site survey work as part of a Landscape and Visual Impact Assessment. The purpose of the assessment is to describe and evaluate the likely significant landscape and visual effects arising from the proposed quarry extension.
The future Landscape Strategy has been informed by the results of the Landscape and Visual Impact Assessment and the Ecological Mitigation and Enhancement Strategy.
Some advance tree planting has already taken place along the A38 frontage, and further advance planting was done in spring 2016. The planting will help to screen views of the initial phases of the extension site from surrounding areas and reinforce the vegetation pattern of the local landscape. Hedgerows from within the extension site will be progressively removed and translocated to suitable areas. As they are completed, the overburden bunds surrounding the extraction area will be seeded and progressively planted with native woodland planting. The replacement route for Alston Lane and access to Alston Farm and Cottage will be designed to be like traditional Devon lanes, single track with passing places and lined with Devon hedgebanks.
This is summarised in the Landscape Strategy drawing shown below.
Traffic and Roads
There will be no increase in quarry traffic if the proposed extension is granted permission. Vehicles travelling to and from the quarry will continue to use the accesses already in place which connect with the B3352 and a four way junction onto the A38.
Part of the existing Alston Lane between Linhay Hill Quarry and the proposed extension needs to be removed in preparation for the start of quarrying. The existing junction onto the A38 at Alston Cross will be closed.
An alternative route along the approximate line of the public footpath behind the existing quarry will be provided to join Balland Lane a short distance beyond the school.
In addition a replacement route for access to Alston Farm and Alston Cottage will be provided. Traffic counts have been undertaken to help assess the impact of these changes to the road network. Local residents who are likely to be affected have been consulted.
A signage strategy will be implemented to discourage through traffic from further afield diverting to Caton Lane in order to reach the A38, and proposals for improving the Caton slip road off the A38 are the subject of a separate application submitted to Teignbridge District Council in March 2018.
Scenario 1 – Local traffic to Exeter
Following closure of Alston Lane, the route to Exeter will be longer, but the access to the A38 will be via a safer junction.
Scenario 2 – Through traffic to Exeter
Current preferred route to Exeter is via Alston Lane. If this is closed, traffic will need to follow alternative route via Goodstone Cross and Drumbridges. Signing and ‘Sat Nav’ updates at Hooks Cross will discourage traffic using Caton Lane to reach the A38 via Caton Cross.
Scenario 3 – Local traffic to Plymouth and Ashburton
Following closure of Alston Lane, the route to Plymouth and Ashburton will be shorter, and the access to the A38 will be via a safer junction.
Scenario 4 – Through traffic to Plymouth
Closure of Alston Lane will not change the route used by through traffic to travel towards Plymouth.
Footpaths and Rights of Way
Alternative routing will be provided for the route of the footpath from Balland Lane to Alston Lane, to ensure that at least equivalent provision is achieved when the existing route is upgraded to a highway (Waye Lane). Permissive footpaths will be created alongside the northern end of Waye Lane (Stage 0), linking Alston Lane with Caton Lane (Stage 1) and then southwards along the far edge of the quarry extension area (Stage 3). A circular path will be created around the quarry edge as part of the final restoration of the site once all extraction has finished.
Proactive water management is highly important to ensure operation of the quarry and protection of existing water features.
The quarry extension will intercept more drainage routes, so new drainage features will need to be formed around the altered terrain to manage surface water runoff around the extended quarry and bunds and along Waye Lane. The current situation sees water flowing both south west to the Balland Stream and south east to the Kester Brook.
Water Flow to the Balland Stream
The Balland Stream source flows from hillsides west of the quarry, whereas watercourses north of the quarry and from Waye Plantation and the west side of Alston Wood drain through the quarry.
Inflow including groundwater is stored in the quarry and pumped to the Ballard Stream. This is authorised by the Environment Agency under a permit which limits the rate at which water can be discharged. The water storage helps to reduce flood risk in Ashburton.
With the upgrade to the Waye Lane route in stage 0, there will be drainage improvements in the upper catchment of the Balland Stream which will provide increased attenuation and further reduce flood risk for Ashburton.
As the quarry area increases to the east there will be more water to manage within the quarry, primarily due to rain falling on the enlarged quarry area, but the capacity for water storage will also increase and the rate at which water is discharged will remain carefully controlled by the pumping regime and environmental permit to discharge.
Water Flow to Kester Brook
Springs north of Alston Farm and rainfall run-off from Alston Wood and Alston Farm flow south east across the farm fields. This water mainly infiltrates to ground, but can also drain under the A38 via a culvert near Alston Cross to flow into the Kester Brook.
Springs and run-off east of the quarry extension at Alston Farm, from Hooks Cross and Little Barton Farm, flow south adjacent to Caton Lane, and then north of Caton Farm to pass under the A38 via a large culvert east of Caton Cross to join Kester Brook.
New drainage formed around the overburden bunds will allow convey and attenuate the flow to existing drainage north of the A38 and the culvert near Alston Cross.
Groundwater, Springs and Abstractions
Groundwater is pumped from the existing quarry and the volume to be abstracted will increase as the quarry extends. The existing quarry already intercepts ground water inflow at mid-height in the quarry’s north east face, though the major component of groundwater inflow is at the quarry’s sump.
The impact of that abstraction is not anticipated to be significant because:
- Local springs and abstractions to the north are recharged from higher land to the north.
- The water which flows into the quarry will continue to be pumped to the Balland Stream, but a proportion could be pumped towards the Kestor Brook if deemed prudent.
- The water from north east of Alston Farm will flow around the east side of the extension area and so continue to flow towards the Kester Brook.
- Watercourse / drainage channel
- Underground drainage
- Indicative overland run-off flow route
The key features of heritage interest within the extension area are:
- The group of listed buildings at Alston Farm, comprising Alston farmhouse, courtyard, adjoining barn and stables and mill, with its waterwheel remaining and associated features, together with the threshing barn adjacent to Alston Cottage
- The field system defined by the hedgerows which is little changed from the Tythe Map; The fields have been extensively cultivated, and are not considered likely to contain any remaining in situ archaeology.
- Listed buildings at Waye House and Place House
- There are also records of two old quarries along the southern boundary of the extension area although no physical evidence is apparent now.
Specialist consultants AC archaeology were appointed to assess the impacts of the proposals on these features. This was done by research into old maps and historical records and by site visits.
The main effect will be on the settings of the listed buildings at Alston Farm. Following the relevant guidance (The Setting of Heritage Assets, Historic Environment Good Practice Advice in Planning: 3) the conclusions are:
the proposed quarry extension will affect the landscape setting of Alston Farmstead and the separate barn by removing the farmland field pattern in front of it, but this will not affect the appreciation of their architectural and historical value.
The settings of Waye House and Place House will not be significantly changed.
Much of the field pattern in the extension area will be lost. A record will be made of each hedgerow as it is removed and some of the hedgerow relocations will be used to recreate the former field pattern on the existing tip and on the new bunding.
Noise, Dust and Vibration
Noise, dust and vibration have to be actively managed when quarrying to minimise their impact and will continue to be managed in line with good practice.
During the quarry expansion the noisiest periods will be:
- during construction of the upgrade to the Waye Lane route, and
- during construction of bunds and the northern overburden tip.
It is envisaged that the construction of the upgrade to the Waye Lane route will take about one to two years, with work progressing from the south to the north, so construction work could be audible by nearby residents for about 3 to 4 months.
Construction of the bunds will take place in a series of ‘campaigns’ in years 2, 10, 13, 16, 31, 40, 43 and 46 from the start of operations. Each campaign will last about 4 months to condense activity thereby optimising plant and management time.
Measurements have been made of existing background noise levels, both around the existing quarry and around the extension area. Noise levels along the A38 are higher because of passing traffic. Calculations have been made of anticipated noise levels due to the extension proposals. Mitigation measures will include:
The quarry operating hours and the rate of tipping (plant movements) will be controlled to ensure noise levels are within noise control standards.
Construction work will be subject to limited working hours – 0800 to 1800 Mondays to Fridays; 0800 to 1300 on Saturdays, with no working allowed on Sundays and Bank Holidays.
In addition the outer faces of the spoil tips will be built first to help shield the nearest residents from subsequent construction work.
In the longer term, the bunds surrounding the extension will help reduce noise disturbance from ongoing quarrying, in the same way that the existing bunds and spoil tip help shield noise from working in the existing quarry.
The main sources of dust in the quarry are the processing plant in the southern part of the existing quarry and along haul routes used to transport stone to the processing plant, although dust monitoring in the last year has shown that levels of dust around the quarry are very low.
The new processing plant installed recently has much improved dust control compared with the older plant and is subject to Environmental Permit controls. It will continue to be used to process the stone extracted from the extension area.
Haul routes for the extension will be slightly longer than they are at present, but normal dust control techniques still apply e.g. speed limited and dampening with water.
These and other measures will be used to control dust associated with construction of the upgrade to the Waye Lane route and overburden bunds.
Typical dust control measures include:
- Only work whilst the soil is in a suitable condition i.e. damp, cohesive rather than dry and dusty.
- Minimise the extent of exposed areas.
- Finished spoil tip areas to be smooth and planted as soon as possible.
- Dampening areas with water spray.
- Erect temporary netting around exposed areas to reduce wind speeds.
- Reduce levels of work when the wind blows directly towards neighbouring houses.
Modern blasting is very sophisticated and levels of vibration are carefully controlled by modifying the following:
- Number of blast holes.
- Weight of explosive.
- Amount of stemming (inert backfill to a blast hole)
- The blast timing sequence.
This means that blasting in the existing part of the quarry is well within the limits set by the current planning permission.
The blasting in the extension area will similarly be controlled so the effects are at a practical minimum and within authorised levels.
Potential effects on land stability have been assessed because of the buried karst character of the Chercombe Bridge Limestone deposit that Linhay Hill Quarry is working.
Karst is “the term applied to topography formed by the dissolution of soluble rocks, such as limestone, as a consequence of fluids moving across and through them. … Areas of karst are usually characterised by the distribution of caves, sinkholes (dolines, or doline groups (ponors); points of surface water recharge), springs (points of resurgence of water passing through the rock) and dry valleys” (BGS website). Evidence of those type of features is observable in the Chercombe Bridge Limestone at Linhay Hill Quarry, and elsewhere between Ashburton and Bickington and further afield such as near Buckfast.
A Land Stability Risk Assessment has been prepared in accordance with Planning Policy Guidance. The Risk Assessment evaluates geological information and results of specific land stability surveys together with the hydrogeological interpretation presented in the Hydrogeological Impact Assessment 2018.
The Risk Assessment identifies that there are ongoing land stability risks which are inherent to all buried karst landscapes, with the trigger for subsidence such as sinkhole formation principally associated with extreme rainfall events or prolonged wet weather, and with changes to drainage by human intervention.
Against this background, potential causes of land instability associated with the proposals for the extension and deepening of the quarry have been considered, namely the quarry dewatering, changes to the surface water management, and ground loading associated with the proposed overburden bunds. The consideration appraises the site specific geological and hydrogeological factors which affect the likelihood of sinkhole occurrence in combination with the quarry extension proposals and specifically the drainage control measures which reduce the likelihood of a subsidence event. Other risk management and mitigation measures also apply such as hydrogeological and land stability monitoring, the phased way that the proposals are to be implemented and the timescale over which the quarry will develop, and an approach for sinkhole investigation and repair.
The finding is that the combination of site specific factors together with implementation of the drainage control and other risk management and mitigation measures mean that residual land stability effects of the quarry extension and deepening proposals are assessed to be of slight or neutral significance.
In buried karst terrain which exists in several areas within south Devon there will always be residual uncertainty regarding the precise location and timing and severity of individual sinkholes, if any were to occur, though for the Chercombe Bridge Limestone Formation around Linhay Hill Quarry that residual risk is minimised by avoiding concentrated infiltration drainage and monitoring for potential precursors of surface subsidence.
Furthermore it should be borne in mind that most other limestone quarries in the UK are also in karst limestone, many of them notably larger and deeper than Linhay Hill Quarry.