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 Teignbridge District Council have approved a planning application for improvements to the Caton slip road off the A38.
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.
The Water environment
Extensive investigations and analysis have been undertaken to record the existing situation in the water environment surrounding the quarry and to consider how this may be affected by the quarry extension proposals. This has been reported in a Hydrogeological Impact Assessment dated 2020. The following describes the findings and how the likely effects have been assessed.
A Monitoring Strategy is proposed to track changes to the existing situation and provide early warning of unexpected changes as a result of the proposals. The findings will be recorded in regular summary reports, and reassessments will be made in advance of each stage of the proposed extension, and also if triggered by a potential ‘early warning’ from one or more of the ‘sentinel’ boreholes.
Proactive water management is highly important to ensure operation of the quarry and protection of existing water features.
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 north west of the quarry at Lower Brownswell and north of the quarry from Waye Plantation and the west side of Alston Wood. The spring flows join to flow via a culvert under the quarry’s existing spoil tip and then in open channel around the west side of the quarry.
Inflows of water into the quarry, including groundwater, are stored in the quarry and pumped to the Balland 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 construction of Waye Lane 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 also from groundwater inflow from further afield. However 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 associated environmental permit for the water discharge activity.
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 unnamed watercourse, referred to as the Alston stream, mainly infiltrates to ground, but can also drain under the A38 via a culvert near Alston Cross to flow into the catchment of the Kester Brook.
The quarry extension and overburden bunds will intercept this watercourse, so new drainage channels will be formed around the extended quarry and overburden bunds to convey the flow to the A38 culvert near Alston Cross. Separate drainage channels will be provided to manage surface water runoff from the bunds. This will also connect with the drain to the A38 culvert.
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 cattle creep underpass east of Caton Cross to eventually join the Kester Brook.
Monitoring is proposed to provide early warning of unexpected effects as a result of the proposals. In the event that flows to the Kester Brook are reduced, a contingency of pumping water from the quarry to the Kester Brook catchment via the watercourse adjacent to Caton Lane can be introduced if the monitoring shows that to be prudent.
The quarry is working an outcrop of the Chercombe Bridge Limestone Formation (CBLF), within the catchment of the River Ashburn, part of the much larger River Dart catchment. The limestone has been subject to weathering (dissolution) processes over geological time, forming a variety of karst features – cavities and conduits - within the rock. The CBLF is ‘buried karst’ which means that the conduits which would normally allow rapid transmission of groundwater are filled with low permeability clay material, reducing their importance for groundwater flow within the deposit.
As with many quarries that work below the level of the water table, the quarry has intersected some features from which water flows into the void, though the major component of groundwater inflow is at the level of the quarry’s sump. This water is pumped from the base of the void and discharged to the Balland Stream following settlement in the Balland Pit under the terms of the water discharge activity permit regulated by the Environment Agency. The dewatering from the quarry has resulted in drawdown of the groundwater, which forms a deep cone of depression of currently up to 60m within the quarry footprint, with drawdown of less than 10m at the edges of the quarry, reducing to 0m at the edges of the drawdown area.
The drawdown area will expand as the quarry is deepened to 0m AOD and extended to the north east, so a projection of the maximum extent of the quarry’s drawdown has been made based on measured inflows of groundwater within the quarry and recharge to the groundwater from rainfall. The projected maximum extent of drawdown is a conservative calculation because it does not take account of the contribution to recharge from sinking streams, which are characteristic of karst limestone and are present over the CBLF. Nevertheless, the proposed extension is considered likely to extend the quarry’s drawdown area north eastwards across the groundwater divide into the catchment of the Kester Brook.
The proposals are not anticipated to extend the drawdown area to the south west because of recharge to the CBLF by the water pumped from the quarry void into the Balland Stream, and also infiltration from the Balland Pit. To the north and south the extent of the drawdown area is constrained by the nature of the adjoining geological formations.
Measurements in boreholes in the area surrounding the quarry and the extension area show that there are large seasonal variations in groundwater levels in the CBLF, together with rapid response to rainfall and declines thereafter. This occurs both within the current drawdown area and outside it, with some of the largest variations (approx. 22m) being in one of the boreholes furthest from the quarry, indicating that these variations are not likely to have been caused by the quarry.
Monitoring the quantity of groundwater inflows to the quarry and rainfall together with associated pumping levels has highlighted that the quarry’s dewatering regime is highly seasonal, with 79% of all inflows in October to March and only 8% of groundwater inflows between June and September.
Therefore the drawdown within the projected maximum drawdown area is anticipated to occur mainly in winter when groundwater levels are notably higher than in summer. The dramatic reduction in dewatering rates during summer, when groundwater levels are at their lowest means the amount of drawdown apparent in summer near the maximum projected extent of drawdown is likely be negligible.
Nevertheless to reduce the potential for effects on the catchment of the Kester Brook, two recharge features are proposed to the north east of the bunds: a balancing pond for water pumped from the quarry, and an unlined section of ditch for controlled flow from the Alston stream to infiltrate to ground. Additionally a contingency to supplement the stream flow towards the Kester Brook is planned to be introduced if the monitoring shows that to be prudent.
The ongoing discharge of pumped water to the Balland stream and infiltration from the Balland Pit will continue to limit drawdown to the south west.
Summary of effects on the water environment
The effects from the quarry extension and deepening proposals are not anticipated to be significant because:
- Local springs and abstractions to the north and south are recharged from higher land to the north or south.
- The water which flows into the quarry will continue to be pumped to the Balland Stream.
- 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.
- A balancing pond for water pumped from the quarry and unlined section of ditch for controlled flow from the Alston stream are proposed to maintain the existing water divide in the northeastern part of the extension area and mitigate the effect on the Kester Brook, with a contingency to supplement stream flows in that direction if the monitoring shows that to be prudent.
- The changes to the water environment will be closely monitored and regularly reported. Reassessments will be made in advance of each stage of the extension and also if triggered by the ongoing data collection.
- 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 2020 and discussed in the section on the Water Environment.
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 changes to drainage by human intervention, and with extreme rainfall events or prolonged wet weather.
Against this background, potential causes of land instability associated with the proposals for the deepening and extension of the quarry have been considered: namely changes to the surface water management, and ground loading associated with the proposed overburden bunds, and dewatering of the quarry. 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. With regard to effects of dewatering: the investigations for the water environment show that large seasonal variations in groundwater levels already occur naturally throughout the limestone outcrop. This is reflected in substantially higher inflows of water into the quarry void and associated higher rates of dewatering in the winter and dramatically lower inflows and lower rates of dewatering in the summer.
This means that the resulting amount of drawdown beyond the deepened quarry and extension boundary will be significantly less than the 10m or more natural variation in the groundwater level that already occurs annually. This leads to the conclusion that the effect of the proposals on groundwater levels and therefore the land stability implications in the limestone areas surrounding the existing quarry and extension area is likely to be negligible.
The Land Stability Assessment takes account of proposed risk management and mitigation measures, such as hydrogeological and land stability monitoring and regular reporting, maintenance of the groundwater divide in the north east of the extension area by the proposed balancing pond for pumped water from the quarry and the unlined ditch for controlled flow from the Alston stream, the proposed reassessments before each stage progresses, and further reassessments if triggered by a potential ‘early warning’ from the ongoing data collection. In addition an approach to sinkhole investigation and repair is put forward and confirmation that the quarry holds appropriate public liability insurance so that in the event of a new sinkhole occurring as a result of the quarry operations, the damage would be repaired or otherwise remedied as deemed appropriate by the insurers.
The conclusion of the Land Stability Assessment 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.