Freasdail Wind Farm
RES
TECHNICAL APPENDIX A4.1 – DRAFT CONSTRUCTION METHOD STATEMENT (INCLUDING SUDS
DESIGN)
Technical Appendix A4.1 – Draft Construction Method Statement (including SUDS Design)
Construction and Decommissioning Method
Statement (Draft) Freasdail Wind Farm
CONTENTS
1.0
INTRODUCTION ................................................................................................................................ 1
2.0
REFERENCE DOCUMENTS ................................................................................................................ 1
3.0
CONSTRUCTION PHILOSOPHY ........................................................................................................ 1
3.1
Timescale
1
3.2
Archaeological Monitoring
1
3.3
Ecological Monitoring
2
4.0
DESIGN PHILOSOPHY ....................................................................................................................... 2
4.1
Public Highway Works Design Philosophy
2
4.2
Site Track Design Philosophy
2
4.3
Turbine Foundation Design Philosophy
3
4.4
Crane Pad Design Philosophy
3
4.5
Sub-Station Control Building Design Philosophy
4
5.0
CONSTRUCTION METHOD ................................................................................................................ 5
5.1
Access Roads
5
5.2
Site Entrance
5
5.3
Site Roads
6
5.4
Management of Surface Water
7
5.5
Temporary Site Compound
8
5.6
Turbine Foundations
8
5.7
Substation Control Building and Compound
9
5.8
Turbine Erection
10
5.9
Site Electrical Works
11
5.10 Grid Connection
12
5.11 Environmental & Waste Management
12
5.12 Pollution Control
12
5.13 Transport Management
12
6.0
DECOMMISSIONING METHOD ......................................................................................................... 12
6.1
Site Access Roads
13
6.2
Wind turbines
13
6.3
Turbine Foundations
13
6.4
Site Electrical installation
14
7.0
RECORDS......................................................................................................................................... 14
8.0
APPENDICES.................................................................................................................................... 14
APPENDIX 1 – ENVIRONMENTAL REQUIREMENTS FOR CONTRACTORS .................................................. 15
APPENDIX 2 – DRAFT SUDS DESIGN............................................................................................................ 19
APPENDIX 3 – WATER QUALITY MONITORING PROCEDURE ..................................................................... 20
APPENDIX 4 - PROCEDURE IN THE EVENT OF A CONTAMINANT SPILL
22
APPENDIX 5 – WASTE MANAGEMENT ......................................................................................................... 23
1.0
INTRODUCTION
This document outlines the methodology for the construction and decommissioning
of the proposed Freasdail Wind Farm development (hereafter referred to as ‘the
Development’).
RES Construction acknowledges, that unless otherwise agreed with the planning
authority, the development shall be carried out strictly in accordance with the
approved plans and conditions.
2.0
REFERENCE DOCUMENTS
Freasdail Wind Farm Environmental Statement (ES)
Chapter 8 of the Traffic Signs Manual
3.0
CONSTRUCTION PHILOSOPHY
The Development shall be constructed in accordance with the Environmental
Statement, prepared during the development stage of the project.
Where available the quietest plant and/or machinery will be employed and
maintained in good working order with appropriate silencers, mufflers or acoustic
covers fitted where applicable. Stationary noise sources will be sited as far away as
reasonably practicable from sensitive developments and, if necessary, shielded by
acoustic barriers.
Where appropriate and practicable, RES will use local contractors, plant and
materials in order to maximise the benefit of the Development to the local
community. Throughout the construction period of the project RES will maintain an
open dialogue with local residents and all other interested parties.
3.1
Timescale
The development will be commenced no later than the expiration of five years
beginning on the date on which the permission was granted.
Typically all work prior to the commissioning, including access to the site by lorries
except for the delivery of turbine parts and the erection of the turbines themselves,
shall be restricted to the hours of 07.00 – 19.00 on Mondays to Saturdays with no
activities on Sundays except other than to prevent or remedy any environmental
pollution or health and safety risks or where the quality of the project or
construction element could be compromised.
If any works are required outside these times or circumstances, written details will
be provided and agreed with the planning authority prior to commencing.
3.2
Archaeological Monitoring
Several sites of archaeological sensitivity are within the site boundary (Figure 9.2 in
Volume I of this ES). A written Scheme of Works will be prepared prior to
commencement of works and agreed with the planning authority. Where necessary,
1
sensitive areas will be fenced off prior to works commencing under the supervision of
an archaeological clerk of works and toolbox talks discussing site specific
archaeological sensitivities will be provided to subcontractors. If archaeological
features are discovered, then the RES Site Manager shall be notified immediately.
Written guidelines will be issued for use by all construction contractors containing
arrangements for calling upon retained professional support in the event that buried
remains of potential archaeological interest are discovered.
3.3
Ecological Monitoring
An Ecological Clerk of Works (ECoW) will be appointed to conduct pre-construction
protected species surveys and also regular monitoring during construction. Toolbox
talks discussing site specific ecological sensitivities will be provided to
subcontractors. Written guidelines will be issued for use by all construction
contractors containing the procotol and contact details for calling upon retained
professional support in the event that protected species are found.
4.0
DESIGN PHILOSOPHY
4.1
Public Highway Works Design Philosophy
All works to be carried out within the public highway shall be designed in accordance
with appropriate standards. All traffic management associated with the road
network improvements shall be in accordance with Chapter 8 of the Traffic Signs
Manual.
AutoTrack analysis has been carried out by RES from the A83(T) turning right onto
the site entrance (refer to Figure 4.12 of Volume I this ES).
A single option or combination of options for the delivery of both normal
construction traffic and abnormals loads will be used for the construction of the
Development.
4.2
Site Track Design Philosophy
All site tracks will be designed taking account of the loadings provided by the turbine
manufacturer following a site investigation. This will be carried out post-consent.
Peat probing across the site indicates a traditional track design will be utilised on
most of the site, however floating track methodology has also been described should
unexpected ground conditions be encountered during detailed post-consent
investigations.
Floating track construction will be adopted where ground conditions are poor or the
depth of peat exceeds 1.5 m. This system involves: installing a layer of geo-grid
directly onto the existing organic layer; placement of a layer of well graded coarse
stone; application of a further layer of geo grid; and laying the final layer of a finer
well graded stone for the running surface.
Traditional track construction will be used in areas identified within the Site
Investigation Report where the depth of the peat layer does not exceed 1.5 m, and
the underlying layer has adequate load bearing properties. This system will consist
2
of either 1 or 2 layers of stone depending on the load bearing capacity of base layer.
Where the underlying layer is clay, 2 layers of stone are used; the 6F2 stone capping
layer and the Type 1 running layer. In areas where the load bearing layer is rock,
the capping layer is omitted, and the Type 1 running layer is installed directly onto
the rock surface.
Straight sections of the track have a running width of 5 m (running track) with
additional shoulders and temporary working areas on each side of up to 1m wide to
give a total width of 7m (overall width). All bends have been designed using
AutoTrack and the effective width at these locations has been widened to suit.
Under-track drainage will be incorporated within the SuDS design as set out in
Appendix 2 of this document. Existing watercourses / drainage ditches will be
culverted using an adequately sized pipe at locations where the proposed access
track crosses, following the Controlled Activities Regulations (CAR).
4.3
Turbine Foundation Design Philosophy
Wind turbine foundations will be designed in accordance with relevant standards.
The turbine will be anchored to the foundation using a bolt assembly or insert which
shall be cast into the concrete.
The foundation geotechnical design will be based on the information contained in
the site investigation report which will be carried out post consent and factors of
safety will be incorporated in accordance with European design standards. The
foundation design will be within the limits of the typical dimensions detailed on
Figure 4.3 - Turbine Foundation General Arrangement (GA) drawing of Volume I of
this ES.
Depending on the wind turbine supplier the transformer and HV equipment could be
housed either adjacent to the turbine on a reinforced concrete plinth or within the
turbine tower or the nacelle. Power cables will be buried in HV compatible ducts
between the turbine and transformer.
An earth mat will be buried around the turbine and transformer to provide
protection to personnel in the event of an electrical fault.
The foundations will be designed in accordance with relevant UK safety legislation
and design regulations. A design risk assessment will be carried out and risk
mitigation measures will be incorporated into the design.
4.4
Crane Pad Design Philosophy
All crane pads have been designed taking account of the loadings provided by the
turbine manufacturer, and will consist of a compacted stone structure.
All crane pads will be formed from a suitably stiff layer and provide a minimum
bearing capacity of 200kN/m2 at finished level. Typically crane pad formation will
consist of either 1 or 2 layers of stone depending on the properties of the underlying
load bearing layer. Where the underlying layer is clay, 2 layers of stone formation
are used, the 6F2 stone capping layer and the Type 1 running layer. In areas where
the load bearing layer is rock, the capping layer is omitted, and the type 1 running
layer is installed directly onto the rock surface. The permanent crane pads shall be
3
up to 1200m2 as shown in Figure 4.4 of the ES and have a maximum cross and
longitudinal fall tolerance of 1% (1:100). Depending on the final choice of turbine
supplier there will be associated temporary areas for the storage of components and
a standing area for the tailing crane.
4.5
Sub-Station Control Building Design Philosophy
The substation and adjoining compound has been designed, sized and positioned to
be sympathetic with the surroundings and to comply with the requirements set out in
the approved layout. The building contains five rooms; Control Room, Switch Room,
Grid Room, Rest Room and Store Room. A WC with an external entrance is also
incorporated into the Control Room building. This detail is shown on Figure 4.8 of
the ES.
The foundations for the building will be designed based on the site investigation
report.
The substructure typically consists of in situ reinforced concrete raft foundation and
in situ concrete strip footings to supports all the solid block work internal and
external walls. Cable trenches will be formed with block work or concrete side
walls, and are positioned in accordance with the M&E requirements. Cable ducts
will be cast within the slab and/or buried within the soil, and are positioned in
accordance with M&E requirements. The ground floor consists of an in-situ
reinforced concrete ground bearing slab which is supported by well compacted
hardcore depending on soil conditions. The substructure is made water tight by the
installation of an approved Damp Proof Membrane which ties in with the Damp Proof
Course at ground floor level.
The superstructure consists of a traditional cavity wall construction with an overall
typical wall thickness of approximately 300 mm. This may include the use of wind
posts or provision of bedded masonry reinforecement. All door openings have been
sized to comply with the current M&E and Health and Safety requirements.
The ceiling for the switch room consists of pre-stressed pre-cast hollow core
concrete units or anti-intruder plaster board. All other ceilings are foil backed
plaster board.
The roof is a traditional pitch roof construction consisting of prefabricated timber
trusses, 12 mm plywood sheeting, sarking felt, timber battens, and roof tiles.
All doors will be made of steel or timber with steel sheeting for security
prefabricated to fit structural openings.
Foul drainage will discharge to the system or treatment plant which will be designed
in liaison with SEPA and by adhering to the Controlled Activities Regualtions (CAR).
Surface water will be taken away by a perimeter drain which will discharge to a
soakaway located at a lower level than the lowest point of the perimeter drain.
4
5.0
CONSTRUCTION METHOD
5.1
Access Roads
Prior to public road works, an agreement will be sought from Argyll and Bute
Council. All works to public roads, including formation of the new site entrance, will
be carried out under the appropriate Road Opening Permits in accordance with New
Roads and Street Works Act 1991. A detailed programme of all works and any
required traffic management proposals shall be submitted to and agreed by Argyll
and Bute Roads Department before commencement of works.
Suitable notification shall be given to local residents detailing the full sequence of
work and contact details of key site personnel.
A Traffic Management Scheme proposal for abnormal loads will be provided to Argyll
and Bute Council and Transport Scotland post consent.
5.2
Site Entrance
For the avoidance of doubt, all construction traffic will be required to access the site
via the site entrance once it has been constructed with appropriate traffic
management at this point which will be agreed in liaison with Argyll and Bute
Council.
Prior to the commencement of any other works (save those required for site
investigation or surveys), the site entrance layout will be constructed as detailed on
Figure 4.12.
The site entrance will be constructed as follows: Obtain necessary permits and approvals from Argyll and Bute Council.
Inform statutory services & identify any assets to be protected or diverted.
Works will include re-grading / improve visibility and supplementing other signs
with additional warnings.
The visibility works at the site entrance will be checked and approved by Argyll
and Bute Roads Department prior to the use of the improved entrance.
Existing drainage will be incorporated into the design of the new site entrance to
the satisfaction of Argyll and Bute Roads Department.
Surfacing works at the site entrance will all be to the standard required by the
Specification for Highway Works.
Great care will be taken to ensure mud from the site roads does not become a
hazard on the route. Dry wheel washing facilities will be set up at the main
entrance to remove mud from the wheel of vehicles leaving the site. A monthly
monitoring regime will be set up and the weekly site safety checklist will be
amended to include a visual check once per week (minimum). The area will be
visually inspected daily but recorded weekly.
5
A full condition survey will be carried out in conjunction with the Local Authority
to determine the condition of the route adjacent to the site prior to works
commencing. This will involve a video survey of the proposed route and will
identify any existing defects. This report will be used later to agree if the works
have contributed to deterioration above and beyond normal wear and tear.
5.3
Site Roads
The layout and typical construction details of the site roads are detailed on Figure
4.1 and Figure 4.6 of the ES and will be constructed as follows: Establish alignment of the site roads from the construction drawings and mark
out the centrelines with ranging rods or timber posts.
Where the road alignment crosses existing drainage channels, pipe bridges will
be used. The pipes will be sized according to the width of the crossing and
installed in such a manner that will not interrupt the flow of the water course or
artificially raise or lower the invert of the bed.
The access tracks will be of single track design with a typical straight running
width of 5m. There will also be some local widening on the bends, junctions and
around turbine bases for the safe passage of large vehicles and working area.
The site access tracks will be a combination of excavated and, if necessary,
floated construction in accordance with the contract drawings. Typically floated
construction will be utilised between turbines where the peat depth is greater
than 1.5m. Specific sections of floated track will be designed following the postconsent site investigation campaign, if necessary.
The excavated section will, where practicable, have turf stripped over the area
of the excavation and stored adjacent to the tracks growing side up for reuse.
These areas will be oversized to facilitate the excavated subsoil material. The
subsoil material will subsequently be capped with topsoil to form an earth bund.
All excavation works will be carried out in accordance with the Excavated
Material Management Plan following detailed site investigation post-consent.
All Machinery shall work within the construction corridors as indicated on
contract drawings. Vehicle movement will be restricted to site tracks except
during track and base construction.
Generally, excavated material will be used as backfill around building elements.
However where this is not possible, re-profiling of the spoil and capping with a
layer of topsoil will be undertaken to form areas of permanent landscaping.
The subsoil will be excavated down to a suitable formation layer of either firm
clay or rock and the spoil deposited on either side of the track to form screening
bunds.
The floated sections of track will be constructed by laying Geogrid over the
existing surface, Type 1 will be placed by excavator and compacted in
accordance with the specification / design.
6
Well-graded granular fill will be spread and compacted in layers to provide a
homogeneous running surface. The thickness of layers and amount of compaction
required will be decided by the Site Manager based on the design which will take
account of the characteristics of the material and the compaction plant to be
used.
Drainage ditches will be excavated adjacent to the tracks. Where access roads
run parallel to contours regular cross drains will be placed below the road
surface to prevent excessive volumes of water collecting in the drainage ditches.
The running surfaces of the site roads will be finished to a cross fall of no less
than 1% to reduce ponding. Surface water runoff will not be allowed to discharge
directly into existing watercourses and will be routed through the SuDS system.
Batters will have a slope of between 1:1 to 1:2 (depending on depth and type of
material) and will be left as cut to re-vegetate naturally with local species.
Screening bunds will be formed along the edge of the site roads. The bunds will
be formed using the excavated subsoil and reinstated with the top vegetative
layer set aside during the excavation. No planting or seeding will be undertaken,
unless the bunds do not vegetate naturally. If seed is planted it will be an
appropiate seed mix, suitable to the local area.
The wind farm owner shall take responsibility for the upkeep of the on site
access tracks to the standard required for the operation of the wind farm during
the operational life of the wind farm. Monitoring of the condition of the tracks
will be carried out by the wind farm owner by visual inspection when using the
tracks on site and any repairs required would be carried out by a qualified
contractor.
5.4
Management of Surface Water
Detailed measures to address surface water management, including methodology for
dealing with water pumped from excavations, are based upon drainage design
criteria and philosophy to be prepared post consent.
The detailed drainage design and philosophy to be prepared will adopt a Sustainable
Drainage Systems (SuDS) approach as detailed in Appendix 2 of this document.
5.4.1 Complementary Sections
Refer to Appendix 1 – Environmental Requirements for Contractors
Refer to Appendix 2 – SUDS draft design statement
Refer to Appendix 3 – Water Quality Monitoring Procedure
Refer to Appendix 4 – Emergency Procedure in the Event of a Contaminant Spill for
the pollution contingency plans.
7
5.5
Temporary Site Compound and Parking
The temporary contractor’s compounds will be constructed at the locations indicated
on Figure 4.1 of the ES. The compound is designed to take account of Health and
Safety Executive (HSE) “good practice” requirements to avoid the need for large
articulated vehicles reversing inside the compound and increased stand-off between
pedestrians and vehicles.
The area to be used as the compound will be marked out at the corners using
ranging rods or timber posts
The compound will be established using a similar technique as the construction
of the site tracks.
Granular material will be spread and lightly compacted to provide a hard area to
site offices and storage containers.
Areas within the compound will be constructed as site roads and used as vehicle
hard-standings during deliveries and for parking of site vehicles. The size and
location of the hard-standings will be at the discretion of the site manager and
the requirements of the contractors.
A roofed, impermeable bunded area will be provided within the compound for
the storage of fuel oils.
The compound will require to be fenced all round and secured with lockable
gates.
Upon completion of the project the compound will be decommissioned by
backfilling the area with the material arising during excavation, landscaping with
topsoil and seeding with native species as required.
5.6
Turbine Foundations
The turbine foundations will be constructed in line with Figure 4.3; however, turbine
specific foundations will be designed to reflect the underlaying ground conditions
found during detailed site investigation works.
The extent of the excavation will be marked out and will include an allowance for
trimming the sides of the excavation to provide a safe working area.
Where practicable the turf will be stripped over the area of the excavation and
stored growing side up for reuse. The remaining soil will be excavated as
required and stored to one side for reuse during the landscaping around the
finished turbine.
Permanent storage areas will be identified as part of the Exacavated Material
Management Plan. These storage areas will typically be located adjacent to the
respective foundations to avoid unnecessary moving of material around site and
limit disruption to the development area as a whole.
8
The subsoil will be excavated to a typical formation depth of 3.0 m Below
Existing Ground Level (BEGL) to extract maximum benefit from the encountered
ground conditions. This material will be stored in an appropriate location
adjacent to the excavation. Structural backfill depth of 1.5 m is typically
maintained using the excavated material, pending confirmation it is suitable
following detailed site investigation.
No material will be removed from site and storage areas will be covered in
geotextile prior to stockpiling, in line with best working practice.
A layer of concrete blinding will be laid approximately 75 mm thick directly on
top of the newly exposed formation or structural fill, depending on specific
turbine ground conditions, tamped and finished with a screed board to leave a
flat level surface. The concrete should be protected from rainfall during curing
and all surface water runoff from the curing concrete should be prevented from
entering surface water drainage directly, in accordance with RES document
‘Environmental Requirements for Contractors’ found in Appendix 1.
High tensile steel reinforcement will be fixed in accordance with the designer’s
drawings & schedules. The foundation anchorage system will be installed,
levelled and secured to the blinding.
Ductwork will be installed as required, and formwork erected around the steel
cage and propped from the backside as required.
Concrete will be placed using a crane, pump or other suitable lifting device and
compacted when in the forms using vibrating pokers to the levels and profile
indicated on the drawings, in accordance with good working practises.
Any residue from empty concrete delivery trucks will be washed out into a
designated lagoon, which shall be fitted with an impermeable liner, and removed
from site in accordance with the Site Waste Management Plan.
Upon completion of the concreting works the foundation base will be covered
and allowed to cure.
Following the curing period any formwork around the foundation will be stripped
and stored for reuse. The foundation will be backfilled with a cohesive material,
where possible using the material arising during the excavation, and landscaped
using the turf set-aside during the excavation. A gravel footpath will be formed
from the cranepad to the turbine door and around the Turbine for maintenance.
5.7
Substation Control Building and Compound
The control building will be constructed in accordance with the following:
The area of the Control Building and Compound will be marked out using ranging
rods or wooden posts and the topsoil stripped and removed to a temporary
stockpile adjacent to the work site for use in landscaping. No material will be
removed from site and storage areas will be stripped of vegetation prior to
stockpiling in line with best working practises.
9
The dimensions of the Control Building and Compound area will be set to meet
the requirements of Grid Operator and the necessary equipment to safely and
efficiently operate the wind farm.
The foundations will be excavated down to the levels indicated by the designer,
shuttering installed and concrete placed.
The walls will be built up from the footings to DPC level and the floor slab
constructed, having first located any ducts or trenches required by the follow on
contractors.
The blockwork walls will then be raised to wall plate level and the gables and
internal partition walls formed.
The hollowcore ceiling slabs and roof trusses will be lifted into position using an
adequately sized mobile crane and the roof battened, tiled and sealed against
the weather.
Control Building finishes to be in keeping with the local area: o
Walls to be rough cast
o
Roof to be slate effect tiles
o
Doors to be made of steel or timber with steel sheeting for security.
The doors will be fitted and the external & internal finishings applied including
any fitted furniture.
The compound area will be re-graded, the electrical equipment plinths
constructed and an over site carpet of single size clean granular material will be
laid.
A palisade fence will be erected around the compound and the area surrounding
the building landscaped as required, returning it as far as practicable to near
original condition.
PIR operated external lighting will be installed on the building to allow safe
access during period of reduced light.
5.8
Turbine Erection
The turbine will be supplied with a light grey semi-matt finish and installed with a
tip-height not exceeding 100 m measured from existing ground levels to the blade tip
in the vertical position. The rotors of the turbines shall all rotate in the same
direction.
Turbines are delivered in sections to the site.
The sections are lifted by adequately sized mobile cranes (1 main crane and a
smaller tail crane to assist with the initial lift free of the transport) and
10
positioned on the foundations / other turbine sections until the entire turbine is
erected.
Upon completion of the erection all fasteners will be tightened to the correct
torque and the internal fit out of the turbine undertaken, and finally the mains
power will be connected to the turbine controller.
When the controller is ‘booted up’ the turbine commissioning will commence,
and following the successful execution of the ‘tests on completion’ the turbines
will be handed over as complete.
5.9
Site Electrical Works
Substation and switchgear: - The substation will have a domestic electrical
system including lights, sockets, fire alarm and intruder alarm. This would be
designed, installed and commissioned by registered electrical contractors. The
high voltage switchgear is installed using a truck mounted hydraulic crane, the
indoor equipment is then connected, wired, tested and commissioned, typically
by engineers supplied by the switchgear manufacturer. The operation of this
equipment is by suitably authorised operators who have undergone extensive
training. The equipment will be decommissioned in the reverse of the above,
removed from site, dismantled and disposed of in an approved manner.
Underground Distribution: - All electricity and other service cables between the
turbines and the sub-station / control building shall be placed underground. The
ground is trenched typically using a mechanical digging machine. These machines
will be regularly inspected for safety and condition and will be well maintained.
All operators will have the required certification. The top layer of soil is removed
and saved so that it is replaced on completion. The cables are bedded with
suitable material unless the ground conditions are such that no bedding is
required. The depth of the cables is to meet all national and international
requirements; a suitable marking tape is installed between the cables and the
surface. On completion the ground will be reinstated as previously described
above. The cables are terminated on the transformers at each turbine location.
The terminations are of an outdoor watertight design. On decommissioning the
cables will be cut away below ground level and sealed.
Transformers: - The transformers are delivered by the manufacturer. Dependant
on the turbine model selected, the units will either be placed directly onto a
reinforced concrete plinth alongside the turbine foundation within an enclosure
or installed within the turbine tower. The Transformers will be of the sealed type
and supplied full of oil so will not require topping up or filtering on site. They will
be inspected for any damage prior to offloading. The units will be installed using
a small mobile all terrain crane and will be tested, commissioned and energised
by suitably trained and authorised persons. The accessible MV & LV sections of
the transformer will be protected within an enclosure which shall be locked at all
times displaying appropriate warning signs. The units will be decommissioned in
the same manner, removed from site and disposed of by a company certified to
handle such materials. This specialist company will also dispose of any oil or
residual waste products.
11
5.10
Grid Connection
Connection to the utility's system shall be by overhead line or underground cable
to a point determined by the utility in accordance with their recognised
standards, planning conditions and any landowner agreements.
All work associated with the grid connection will be undertaken to the utility
company’s specifications and requirements.
5.11
Environmental & Waste Management
For details of environmental management measures to be adopted during the
construction phase, including details of wheel washing facilities, concrete washout
facility and of the designated refuelling area, refer to Appendix 1 – Environmental
Requirements for Contractors and Appendix 5 - Waste Management.
The following will be key undertakings of the Environmental and Waste Management
on site.
Wheel washing facilities will be provided at the site entrance. These are likely to
be the waterless drive through type. These will be regularly maintained and road
conditions monitored to ensure public roads are not contaminated with mud or
dust.
Fuel on site will be controlled in accordance with the RES Environmental
Requirements for Contractors (Appendix 1).
All works will be carried out in accordance with the relevant noise legislation and
good working practise.
A Habitat Management Plan is provided in the Environmental Statement and
details measures required to enhance ecology at the site.
5.12
Pollution Control
Refer to Emergency Procedure in the Event of a Contaminant Spill, Appendix 4 for
details of the emergency procedure to be followed and actions to be taken in the
event of a hazardous waste spillage such as oil, fuel and chemicals, occurring on a
wind farm construction site or an operational wind farm site in order that the
environmental impacts that may be associated with a hazardous waste spillage may
be mitigated.
5.13
Transport Management
A Transport Management Plan will be developed in liaison with Argyll and Bute
Council and Transport Scotland.
6.0
DECOMMISSIONING METHOD
The permission is for a period of 25 years from the date that the electricity from the
development is first connected to the grid, such date to be notified to the planning
authority within 1 month of such connection. Within 12 months of the end of the 25
year period all wind turbines, ancillary equipment and buildings shall be dismantled
to ground level and removed from the site, and the land shall be restored in
12
accordance with a restoration and after-care scheme to be submitted for the
approval of the planning authority.
On reasonable request of the planning authority, the developer will provide
appropriate information concerning the supply of electricity to the grid from any
turbine. If any turbine fails to supply electricity to the grid for a continuous period of
9 months, then, unless otherwise agreed in writing with the planning authority, a
scheme for the decommissioning of the turbine and any other ancillary equipment
above ground level relating solely to that turbine, and including the restoration of
the site involved, shall be submitted to the planning authority within 3 months of the
end of the 9 months period of non-supply and carried out in accordance with the
scheme approved.
6.1
Site Access Roads
At the request of the landowner or other empowered body, the site tracks will be
reinstated to the approximate pre-wind farm condition, otherwise the tracks may
remain as an access route for other activities. Should the tracks be reinstated the
following shall take place:
The granular material that forms the roads will remain in place
The screening bunds along the sides of the tracks will be stripped of topsoil and
used as backfill for the tracks
Upon completion of the backfilling the topsoil stripped from the bunds will be
used to landscape the backfilled track and reseeded as necessary, and
Backfilling of tracks will be carefully planned to avoid having to travel plant and
equipment on freshly reinstated land.
6.2
Wind turbines
The decommissioning of the wind turbines will be the reverse of the erection
process involving the same lifting plant and equipment.
It is anticipated that the turbines will be taken down and loaded straight onto
the back of transport and removed from site for reconditioning or breaking.
The turbines may be broken down into smaller component parts than during
erection, in particular the rotor blades may be cut up into more manageable
sections prior to removal from site.
6.3
Turbine Foundations
Following the removal of the wind turbine the concrete foundation will be
chopped back to 1,000 mm below existing ground level.
The steel foundation insert or bolt ring and any reinforcement exposed will also
be cut back and treated with a proprietary corrosion protection system.
13
Upon completion of the corrosion protection the foundation will be backfilled
with material generated local to the foundation, covered with topsoil and
reseeded as required.
There is no appreciable effect on the local environment from buried reinforced
concrete structures left in-situ over many decades past the 20-25 year working life of
the wind farm.
6.4
Site Electrical installation
The electrical equipment will be decommissioned in the reverse of the installation
method described in 5.11 above, removed from site, dismantled and disposed of in
an approved manner. Cables may be left in the ground if recovery is not reasonably
practicable.
7.0
RECORDS
Records, as-built drawings, specifications, operational maintenance manuals and
residual risks will be collated and filed in the Project Health & Safety file based upon
the requirements Construction (Design & Management) 2007.
Unless otherwise agreed in writing the wind farm operator shall log wind speed and
wind direction data continually and shall retain data which has been obtained for a
period of no less than the previous 12 months. The data shall include the average
wind speed in metres per second for each 10-minute period.
8.0
APPENDICES
14
APPENDIX 1 – ENVIRONMENTAL REQUIREMENTS FOR CONTRACTORS
The followingidentifies environmentally safe working practices and standards for particular
operations that must be implemented by all subcontractors when working on a site managed
by RES. The procedures have been developed to ensure that RES and all its subcontractors
comply with SEPA Pollution Prevention Guidelines, and additional planning requirements set
out by the Local Planning Authority and other enforcing bodies. As part of the procedure an
environmental checklist would been created, which would be completed on site every 2-3
weeks by the site manager. Detailed below is the scope of the procedures contained within
the document, and a brief summary of what is required of the subcontractors on-site.
Existing Features
Contaminated land
Any remediation or disposal of contaminated land will only be carried out following
consultation with the local environmental authority, if no work is required on the
contaminated land it will be fenced off to prevent disturbance.
Underground services
Assessment of the hazards for underground services where present shall include an
assessment of the environmental impact of damage during construction.
Existing storage tanks
Any old containers found on site would be checked and emptied by a Licensed Waste Carrier
before removal. Copies of licence certificate would be obtained and handed to RES site
manager for inclusion in Project Health and Safety File.
Protection from vandalism
Vandalism, theft and tipping are common causes of pollution and the compound area should
be adequately protected by fencing and locked to discourage unauthorised access. Any
occurrence of tipping on the site would be reported to site management who would inform
the local environmental authority and the police, if necessary.
Site Drainage
Surface and foul water drains
Surface water drains should carry uncontaminated rainwater only and shall be protected
from ingress of silt, or any other contaminants. Wet cement and raw concrete would not be
allowed to enter any watercourse.
Deliveries
Fuels and oils
Fuel and oil deliveries shall take place within the designated refuelling area only; a
responsible person would supervise site deliveries to ensure that the correct amount of
material is delivered to the correct tank and that the level is checked prior to refilling to
avoid spillage.
Storage of Fuels, Oils and Chemicals
All fuels and oils will be stored in a designated area only, including mobile bowsers when not
in use. Generators permanently stationed in site compound (used for powering site cabins)
15
would be kept in the designated refuelling area, or be bunded (the bund shall be capable of
containing 110% of the fuel tank’s capacity) or shall have a double skinned fuel tank.
Chemicals on site will be stored in accordance with their COSHH assessment and appropriate
spill kit kept by subcontractor.
Security
All bowsers would be stored so as to minimise the risk of collision, run-away and vandalism.
They will not be stored adjacent to watercourses. When not in use, bowsers would be
securely stored in the designated refuelling area.
Marking
The contents of any tanks on site will be clearly marked. Warning notices including “No
smoking” and “Close valves when not in use” shall also be displayed.
Removal
No tanks or containers may be perforated or dismantled on site. A competent operator will
empty all contents and residues for safe disposal elsewhere.
Waste management
Treatment and storage
All waste would be stored in designated areas that are isolated from surface drains, prior to
removal from site.
Skips would be covered to prevent refuse blowing away and rainwater accumulating. They
would be replaced when full and the contents disposed of in accordance with statutory
requirements
Disposal
Chemical containers, used oil and filters, solvents, paints, electrical items, contaminated
materials and hazardous refuse are all classified as “special waste” and, as such, would be
stored in a bunded area away from watercourses and disposed of by licensed contractors in
a controlled manner.
Earthworks
Dealing with silty water
Silty water can arise from excavations, exposed ground, stockpiles, wheel-washing and site
roads and water containing silt would not be discharged directly into rivers, streams or
surface water drains. Where silty water does occur, it is vital that the silt that is held in
suspension is allowed to settle out before the water reaches a watercourse. Draft SuDs
arrangements are detailed in Appendix 2.
Excavations
Where possible, water will be prevented from entering excavations. Use of cut-off ditches
and well point de-watering may be necessary. Water discharged by any pumping
arrangement will be dealt with according to the site drainage plan.
Topsoil Stripping and Reinstatement
It is of paramount importance to minimise disturbance to flora and fauna whilst carrying out
the construction works, and to ensure that disturbed habitats regenerate quickly after
completion of the works. Topsoil and vegetation (stored separately from subsoil) would be
16
retained and reinstated over the track shoulders where reasonablly practicable and all other
areas of stripped ground, as soon as possible to prevent erosion and leaching.
On wet and marshy ground it may be necessary to store excavated materials on a geotextile
in order to minimise disturbance to the vegetation below.
Exposed ground and stockpiles
The total quantity of exposed ground and stockpiles and storage duration would be
minimised in order to minimise generation of silt and dust. If long-term storage is required
then stockpiles can be seeded or covered and silt fences constructed from a suitable
geotextile. In dry weather dust suppression measures may be required.
Plant
Refuelling
Where possible, mobile plant will be refuelled in the designated area. Where plant is to be
refuelled outside this area a double skinned bowser must be used and re-fuelling would take
place over a drip tray. Refuelling shall always take place away from watercourses or surface
drains
Maintenance
Plant and site vehicles are to be well maintained and any vehicles leaking fluids must be
repaired or removed from site immediately. Any servicing operations would take place over
drip trays.
Road Cleanliness
Site roads
Site Roads would be brushed or scraped as required to minimise dust and mud deposits,
especially at site entrances and any watercourse crossings. If necessary during dry weather,
dust suppression may be achieved by spraying water onto the site tracks to dampen down
the airborne dust particulate.
Public Highways
Measures would be undertaken throughout the construction phase of the wind farm to
ensure that dust and mud does not migrate onto the adjacent public highways, private roads
or accesses. This may require the establishment of a wheel washing station comprising an
apron onto which vehicles would drive in order to clear the wheels and undersides using a
power washer. Any water used during the wheel washing process would be collected and
passed through a silt trap before discharging into a soakaway. Run off water would be
channelled via a silt trap into a purpose made soakaway and not discharged directly into
watercourses.
Drip Trays
After use the drip tray will be cleaned using an appropriate absorbent material which would
be disposed of in accordance with COSHH regulations. Drip trays would be regularly checked
and cleaned.
Concrete
17
Concrete is highly alkaline and corrosive and can have a detrimental impact on
watercourses. Washing-out of concrete wagons on site would not be permitted, unless in a
designated sealed wash-out pit. No tools, equipment or materials would be washed in
watercourses. Mortar mixing and material storage areas must be away from watercourses.
Sulphate resistant concrete shall be used where geological conditions dictate, to prevent
long term corrosion of concrete (local release of alkaline compounds) due to sulphate
attack.
Wildlife
Wildlife shall be protected from entering and becoming trapped in any part of the works on
the site as far as reasonably practicable. For excavations this may mean that fences,
crossings or escape routes are necessary.
18
APPENDIX 2 – DRAFT SUDS DESIGN
19
Drainage Management (SuDS) Design Statement
For Planning
Proposed Freasdail Wind Farm, Kintyre
Client:
RES UK & Ireland Ltd
Prepared by:
McCloy Consulting Ltd.
August 2012
52 Mallusk Enterprise Park, Newtownabbey, Northern Ireland BT36 4GN
T: +44 28 9084 8694 E: info@mccloyconsulting.com W: www.mccloyconsulting.com
MCL115-48
REVISION HISTORY
Document Reference:
Revision
Reference
Revision
Status
MCL115-48_DG01
Date of
Issue
Reason for Issue / Amendments
Issued to
1
DRAFT
03/07/2012
Working Draft Issued for Comment / Original
RES UK & Ireland
2
FINAL
08/08/2012
Issued Final / Minor Amendments
RES UK & Ireland
CONTRACT
This report describes work commissioned by RES UK & Ireland Ltd following written instruction by their representative. The
RES UK & Ireland Ltd representative for the contract was Scott Manning.
Prepared by:
Paul Singleton
Graduate Engineer
Reviewed by:
Anthony McCloy
Director
Approved by:
Anthony McCloy
Director
Date:
08 August 2012
DISCLAIMER
This document has been prepared solely as a Drainage Management (SuDS) Design Statement for RES UK & Ireland Ltd.
McCloy Consulting Ltd accepts no responsibility or liability for any use that is made of this document other than by RES UK &
Ireland Ltd for the purposes for which it was originally commissioned and prepared.
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
August 2012
MCL115-48
CONTENTS
1
INTRODUCTION ...................................................................................................................................................................1
1.1
1.2
1.3
2
TERMS OF REFERENCE .......................................................................................................................................................1
STATEMENT OF AUTHORITY .................................................................................................................................................1
INTRODUCTION ...................................................................................................................................................................1
SITE DETAILS & HYDROLOGY...........................................................................................................................................2
2.1
2.2
3
SITE DETAILS .....................................................................................................................................................................2
SITE HYDROLOGY ...............................................................................................................................................................2
RELEVANT GUIDANCE AND LEGISLATIVE REQUIREMENTS ........................................................................................3
3.1
RELEVANT GUIDANCE AND LEGISLATIVE REQUIREMENTS ......................................................................................................3
3.1.1
UK / Scotland Legislation and Planning Policy ......................................................................................................3
3.1.2
SEPA Guidance Notes and Selected Industry Guidance ......................................................................................3
3.1.3
Construction Industry Research and Information Association (CIRIA) – Guidance Manuals ................................4
4
DESIGN CRITERIA ...............................................................................................................................................................5
5
SUDS DESIGN PHILOSOPHY .............................................................................................................................................6
5.1
5.2
5.3
5.4
6
CONTROLLING RUNOFF .......................................................................................................................................................6
WATER QUALITY & TREATMENT...........................................................................................................................................6
PRESERVING SITE HYDROLOGY & GROUNDWATER RECHARGE .............................................................................................6
SUMMARY ..........................................................................................................................................................................7
DRAINAGE DESIGN PHASE - DETAILED CONSIDERATIONS.........................................................................................8
6.1
6.2
PREAMBLE .........................................................................................................................................................................8
WATERCOURSES & WATERCOURSE CROSSINGS ..................................................................................................................8
6.2.1
Identification of Watercourse Crossings ................................................................................................................8
6.2.2
Design of Watercourse Crossings .........................................................................................................................8
6.2.3
Preservation of Overland Flow Routes ..................................................................................................................9
6.3 HYDROLOGICAL BUFFER ZONES ..........................................................................................................................................9
6.3.1
Watercourse Buffer Zones .....................................................................................................................................9
6.4 DRAINAGE DESIGN..............................................................................................................................................................9
6.4.1
Natural / Construction Runoff Separation ..............................................................................................................9
6.4.2
Trackside Drainage ..............................................................................................................................................10
6.4.3
Check Dams ........................................................................................................................................................10
6.4.4
Drainage Grips .....................................................................................................................................................10
6.4.5
Runoff Attenuation ...............................................................................................................................................11
6.5 FORESTRY CLEARANCE WORKS ........................................................................................................................................11
6.6 TEMPORARY SPOIL MANAGEMENT .....................................................................................................................................11
7
CONSTRUCTION PHASE – DETAILED CONSIDERATIONS ...........................................................................................12
7.1
PLANNING AND PHASING OF DRAINAGE WORKS..................................................................................................................12
7.1.1
Site-wide Requirements .......................................................................................................................................12
7.1.2
Timing of Works ...................................................................................................................................................12
7.2 SPECIFIC CONSTRUCTION PHASE MEASURES.....................................................................................................................13
7.2.1
Working in the Vicinity of Water / Buffer Zones ...................................................................................................13
7.2.2
Watercourse Crossings........................................................................................................................................13
7.2.3
Working in the Vicinity of Groundwater Dependent Terrestrial Ecosystems........................................................13
7.2.4
Mini-Settlement Ponds / Lagoons ........................................................................................................................14
7.2.5
Turbine Bases and Crane Pads ...........................................................................................................................14
7.2.6
Substation and Temporary Compounds ..............................................................................................................14
7.2.7
Cable Trenches....................................................................................................................................................14
7.2.8
Dewatering ...........................................................................................................................................................15
7.2.9
Excavated-type Track Makeup ............................................................................................................................15
7.2.10 Floated-type Track Makeup .................................................................................................................................15
8
SUDS MAINTENANCE MANUAL.......................................................................................................................................16
8.1
RECOMMENDATIONS FOR CONSTRUCTION PHASE...............................................................................................................16
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
August 2012
MCL115-48
APPENDICES
APPENDIX A
General Arrangement and Typical Detail Drawings
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
August 2012
MCL115-48
1
INTRODUCTION
1.1
Terms of Reference
RES UK & Ireland Ltd has appointed McCloy Consulting Ltd to undertake preliminary sustainable storm water drainage
(SuDS) design in order to demonstrate surface water management measures for the proposed Freasdail Wind Farm,
Kintyre (hereafter referred to as ‘the Development’).
This design statement explains the concepts and rationale adopted in preparing the drainage management (SuDS)
proposals that have been prepared for the development.
1.2
Statement of Authority
McCloy Consulting is an independent environmental consultancy specialising in SuDS, drainage, hydrological and
hydrology assessments, river modelling and flood risk assessment. McCloy Consulting has ongoing involvement in
numerous SuDS projects across the UK and has developed a particular expertise in hydrological assessment and
sustainable drainage design for wind farm sites.
McCloy Consulting has had successful involvement in the design of innovative SuDS solutions for 50+ onshore wind
farms in accordance with current best practice guidance in the United Kingdom, Republic of Ireland and Europe.
1.3
Introduction
The construction phase of all projects is a period within which there is an increased potential for pollution, in particular
silt pollution to local watercourses due to unearthed clay surfaces causing release of fine grained soils (silt and clay).
The focus of this document is to provide sufficient detail to ensure that pollution of watercourses will not occur as a
result of construction, operation and maintenance activities at the site, and to minimise the risk of any such occurrence.
The main objectives of the project in terms of drainage have been identified and defined as follows:
•
To propose appropriate, robust and buildable SuDS techniques for the prevention of erosion and the
removal of silts and pollutants from construction runoff.
•
To provide guidance on suitable silt settlement and pollution prevention measures for the deforestation
process.
•
To ensure that permanent drainage at the development is designed to a sufficient hydraulic capacity to
contain a pre-determined return period rainfall event.
•
To give consideration of the control and monitoring proposals for the dewatering of excavations.
•
To make provision for the GWDTEs identified at the site.
The drainage design adopts a SuDS approach, using temporary SuDS for the drainage of the temporary works during
the construction phase. The use of swales, check dams and settlement ponds in series provides a sequence of surface
water management measures that will mitigate any adverse impact on the hydrology of the site and surrounding areas
during the construction phase of the project. These techniques will be supported by the use of other pollution
preventative measures such as silt fences and silt mats where necessary.
Where construction activities near watercourses and water bodies are essential, steps have been undertaken to identify
sufficient mitigation measures for the protection of the watercourses against pollution and have been presented on
drawings accompanying this report. Construction activities in the vicinity of watercourses within the site include
construction of site tracks; wind turbine infrastructure including turbine hard standings, access track, meteorological
mast, construction compound, electrical substation, cabling and associated activities. Silt management and pollution
prevention during all elements of construction has been given due consideration within the design statement and within
the scope of the full SuDS design.
This report gives both specific and general details on the drainage method for temporary works, permanent site
drainage and pollution prevention measures for silt management.
Drainage Management (SuDS) Design Statement
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August 2012
MCL115-48
2
SITE DETAILS & HYDROLOGY
2.1
Site Details
The proposed development site is located in Argyll and Bute. The development site boundary covers approximately 511
hectares.
From the centre of the site lies Whitehouse, approximately 2.5 km north, and Clachan approximately 7 km southwest.
Further afield, Tarbert is located approximately 10.3 km to the north northeast. The centre point of the Site has
Ordnance Survey grid reference 182440 659197.
The site spans approximately 3km from west to east and 2.5km from north to south. Loch Freasdail is situated to the
north-west of the site and Loch Cruinn is located along the southern boundary of the site.
The wind farm comprises of 11 turbines and associated infrastructure including 5.5km of new access track, upgrade to
approximately 2.9km of existing track, temporary compounds, substation and permanent met mast.
2.2
Site Hydrology
The following is based on a combination of desktop study, information provided by the peat stability assessment and
walkover survey observations from a walkover carried out by McCloy Consulting staff on 5-6 June 2012:
•
Drainage at the site is generally to the north. The eleven turbines are located around a hill in the south of the
site. Local topography in the areas surrounding T2, T3 and T4 fall south towards Loch Cruinn; land gradients
around the remainder of the turbines fall to the north.
•
The majority of the site lies within the catchment of the Claonaig Water which discharges to Claonaig Bay,
7km east of the site; areas to the west of the site drain to the Grassfield Burn and Whitehouse Burn. The
Grassfield Burn meets the Whitehouse Burn 1km north of the site in the village of Whitehouse and the
watercourse enters West Loch Tarbert 1km downstream of the confluence point.
•
Watercourses contained within the Claonaig Water catchment include the Allt an Cille and Allt Mhic an t-Saoil.
The tributary network for the Claonaig Water, Grassfield Burn and Whitehouse Burn is extensive and ranges
from well defined and modified streams to man-made ‘grips’ and forest drains.
•
Rainfall records indicate that the Freasdail site is relatively wet with a high annual rainfall (SAAR) in the region
of approximately 1500 mm (data sourced from FEH CD-ROM).
•
The underlying metamorphic rocks are generally impermeable with ground water present at shallow depths.
The overlying till is highly variable with a low groundwater potential, but with the possibility of granular lenses
containing groundwater.
Drainage Management (SuDS) Design Statement
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MCL115-48
3
RELEVANT GUIDANCE AND LEGISLATIVE REQUIREMENTS
3.1
Relevant Guidance and Legislative Requirements
It is proposed that all drainage relating to the Development will be constructed using best practice and in conformance
with the requirements of the relevant regulatory authorities. The key legislation and guidance which will be adhered to
are defined as follows.
3.1.1 UK / Scotland Legislation and Planning Policy
•
Water Framework Directive (2000/60/EC)
•
Planning and Flooding Scottish Planning Policy 7 (2010)
•
Water Environment and Water Services (Scotland) Act 2003
•
UK Water Quality (Water Supply) Regulations 2000
•
EC Fisheries Directive (78/659/EEC)
•
Land Drainage Act 1991
•
Scottish Executive Environment Group - Water Environment (Controlled Activities) (Scotland) Regulations
2005 (revised July 2008)
•
SEPA Guidelines for Water Pollution Prevention from Civil Engineering Contracts and Special Requirements
•
PAN (Online): Renewable Energy Technologies
•
SPP Scottish Planning Policy
3.1.2 SEPA Guidance Notes and Selected Industry Guidance
•
SEPA Pollution Prevention Guidance Notes (PPGs):
o PPG01 General Guide to the Prevention of Water Pollution
o PPG02 Above Ground Oil Storage Tanks
o PPG03 Use and Design of Oil Separators in Surface Water Drainage Systems
o PPG04 Disposal of Sewage where no Mains Drainage is available
o PPG05 Works in, near or liable to affect Watercourses
o PPG06 Working at Construction and Demolition Sites
o PPG07 Refueling Facilities
o PPG08 Safe Storage and Disposal of Used Oils
o PPG18 Managing Fire Water and Major Spillages
o PPG20 Dewatering Underground Ducts and Chambers
o PPG21 Pollution Incident Response Planning
o PPG22 Incident response – Dealing with spills
o PPG26 Pollution Prevention Storage and Handling of Drums & Intermediate Bulk Containers
•
Scottish Executive (2002) River Crossings and Migratory Fish: Design Guidance
•
SEPA Regulatory Position Statement, Developments on Peat, National Waste Policy Unit, 9 February 2010
•
Engineering in the Water Environment, Good Practice Guide, Construction of River Crossings, First Edition,
SEPA, April 2008
•
Engineering in the Water Environment, Good Practice Guide, Temporary Construction Methods, First Edition,
SEPA, March 2009
•
Good Practice During Windfarm Construction, A joint publication by Scottish Renewables, Scottish Natural
Heritage, Scottish Environment Protection Agency, Forestry Commission Scotland, Version 1, October 2010
•
Floating Roads on Peat, Scottish Natural Heritage/Forestry Commission Scotland, August 2010
•
Forest and Water Guidelines 5th Edition (Forestry Commission 2011)
•
BS6031: 2009 Code of Practice for Earthworks
•
DEFRA Good Practice Guide for Handling Soils (MAFF 2000)
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MCL115-48
3.1.3 Construction Industry Research and Information Association (CIRIA) – Guidance Manuals
•
CIRIA Report C502 Environmental Good Practice on Site
•
CIRIA Report C532 Control of Water Pollution from Construction Sites
•
CIRIA Report C648 Control of Pollution from Linear Construction Project. Technical Guidance
•
CIRIA Handbook C692 Environmental Good Practice on Site
•
CIRIA Handbook C651 Environmental Good Practice on Site Checklist
•
CIRIA Report C689 Culvert Design and Operation Guide
•
CIRIA Report C697 The SUDS Manual
Drainage Management (SuDS) Design Statement
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4
DESIGN CRITERIA
Surface water management on the site will use the principles of Sustainable Drainage Systems (SuDS). The design
criteria and objectives of SuDS applicable to the wind farm development site are:
•
to maintain existing runoff volumes and frequencies that tend to be increased as a result of the development,
thus having a neutral impact on the risk of downstream flooding;
•
encouraging natural groundwater recharge (where appropriate) to minimise the impacts on aquifers and river
base flows in the receiving catchment;
•
to minimise sediment loads in the runoff with particular attention being given to the construction phase of the
project;
•
remove pollutant concentrations in storm water, thus protecting the quality of the receiving water body;
•
avoidance of high surface water runoff velocities, particularly at the entry point to settlement features. Energy
dissipation devices of multiple outflow structures will help to restrict re-suspension of sediment;
•
to act as a buffer for accidental spills by preventing direct discharge of high concentrations of contaminants to
the receiving water body; and
•
to contribute, where practicable, to the enhanced amenity value; providing habitats for wildlife and
opportunities for biodiversity enhancement.
Specifically, surface water management at the site will aim to:
•
provide permanent silt / pollutant removal within the drainage system for the site protection standard event
(i.e. 1-in-1year storm);
•
provide hydraulic drainage capacity for a 1-in-30 year storm, with additional site protection up to a 1-in-200
year event (including factors of safety for the effect of climate change);
•
ensure that all structures crossing watercourses provide a sufficient conveyance capacity, i.e. 1-in-200 year
for areas where access is required at all times during a flood event, and 1-in-30 year event where flooding of
tracks is deemed acceptable. Structure designs will ensure a level of freeboard is provided to the design
event and include factors of safety for the effect of climate change;
•
maintain hydrological characteristics of the site with respect to runoff rates, volumes and flow routes.
•
manage hydraulic erosion on site and provide for reinstatement of vegetation along the access track; and
•
ensure that the runoff discharged from the site does not cause deterioration in the receiving watershed when
compared to existing baseline conditions.
These design criteria have been translated into an outline design philosophy to steer drainage design and surface water
management at the site.
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
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August 2012
MCL115-48
5
SUDS DESIGN PHILOSOPHY
In order to meet the design criteria and objectives detailed in Section 4 of this report, the following design philosophy
has been developed.
5.1
5.2
5.3
Controlling Runoff
•
Track and hard standing runoff will be handled by sheet flow to trackside ditches or swales.
•
On floated sections of track where the road surface is proud of surrounding ground, runoff will be handled by
sheet flow to undisturbed vegetation in riparian zones along the track edge.
•
Tracks and hard standing areas are to be constructed from unbound aggregate and are not surfaced, thus
helping to reduce runoff rate and volume. This has been allowed for within the design philosophy through the
utilisation of a reduced runoff coefficient of 70%, and a heavy silt loading assumed as defined by D'Arcy et al
(2000)1, for light industrial and engineering land uses.
•
Piped under track drainage will be provided with associated sumps, check dams and erosion protection. The
under track drainage will provide a means for flows to pass from a swale on the uphill side of the track to the
downhill side of the track.
•
In cases where the tracks must follow a significant longitudinal gradient, transverse drains (‘grips’) will be
constructed where appropriate in the surface of the tracks to divert any runoff flowing down the track into the
adjacent drainage ditch / across open ground.
•
Rate and volume of runoff will be attenuated using check dams located in trackside swales and ponds located
at significant new hard standing areas. Attenuation features will reduce flow velocities preventing scour and
allow settlement of silts prior to discharge.
Water Quality & Treatment
•
Natural / construction runoff separation will be maintained on site in all practicable instances. Natural run-off
will be prevented from entering excavations and track water drainage swales through the use of natural water
diversion / cut-off ditches installed as enabling works (prior to main earthworks).
•
A treatment train will be designed with a minimum of two stages of treatment for polluted runoff from the site
during the construction phase.
•
All treatment settlement features (check dam backwaters, sumps and ponds) are to be designed to offer
sufficient retention time to settle out the silt grain sizes anticipated.
•
Silt laden runoff within trackside swales will be treated through the provision of small check dams at specified
centres along the swales (to be specified as part of detailed design). Note that steeper swale sections will
require a greater frequency of check dams.
•
Appropriate site management measures will be taken to ensure that runoff from the construction site is not
contaminated by fuel or lubricant spillages. Earth spillages into any existing streams will also be avoided.
There will be no discharge of trade effluent, sewage effluent or contaminated drainage into any watercourse
system or ditch. Any dewatering from excavations will be via surface silt traps, check dams and settlement
ponds to ensure sediment does not enter surrounding watercourses.
•
Small balancing ponds may be required at each turbine location.
•
Areas stripped of vegetation should be kept to a minimum. Stripped vegetation should be reinstated as early
as possible.
Preserving Site Hydrology & Groundwater Recharge
•
Where floated-type tracks are required:
o trackside drainage shall generally be excluded in order to preserve the structural integrity of the subsurface and to avoid creating preferential flow routes;
o under-track drainage shall be provided at close regular frequencies in order to allow balancing of
shallow ground water levels; and
1
D’Arcy B J, Ellis J B, Ferrier R C, Jenkins A and Dils R (Eds.) (2000). Diffuse pollution impacts. The environmental and economic impacts of diffuse pollution in
the UK. Terence Dalton Publishers, Suffolk, UK.
1
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
6
August 2012
MCL115-48
o
5.4
specific under track drainage crossings shall be provided at all watercourses, drains, and existing
drainage / cuttings in order to preserve existing hydrology.
•
Where excavated-type tracks are proposed, including and around turbine bases (with associated crane hard
standing areas):
o ditches (swales) will be used to hold water temporarily for settlement of silts and conveyance to
regular outflow points (“breakouts”);and
o discharging and dispersal of flows from swale overland via riparian zones at regular frequencies will
assist in maintaining the hydrological characteristics of the site. There will be no direct discharge of
untreated water from swales to watercourses. Provision of regular outflows will avoid concentrating
large volumes of runoff into point discharges.
•
Field drains/streams will be piped directly under the track through appropriately sized drainage pipes.
•
Where appropriate a lateral drainage ditch (cut-off drainage ditch) will be cut along the uphill side of the track
to intercept the natural runoff. This lateral drain will be directed under the track at regular intervals through
adequately sized cross drains. The purpose of the cut-off ditch is to prevent natural runoff water entering
excavations and to provide natural / construction run-off separation.
Summary
The proposed SuDS design provides a surface water management train that will mitigate any adverse impact on the
hydrology of the site.
Application of the above design philosophy in the detailed design and construction of site specific elements is
considered in the following sections of this report.
Drainage Management (SuDS) Design Statement
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August 2012
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6
DRAINAGE DESIGN PHASE - DETAILED CONSIDERATIONS
6.1
Preamble
The following key considerations have been identified in the preliminary design of hydrology and drainage for the site.
These issues and development of suitable mitigating measures will be given further consideration during the detailed
design stage of the project.
•
Identification of watercourse crossings and drainage paths across the site;
•
Sizing and definition of hydraulic capacity requirements for watercourse crossings;
•
Detailed design of track drainage & silt management;
•
Detailed design of turbine and compound drainage & silt management;
•
Separation of natural and construction runoff;
•
Forestry clearance works;
•
Spoil storage;
•
Requirement for attenuation storage;
•
Definition of buffer-zones.
Note that the infrastructure layout and associated SUDS design prepared for purposes of Planning is preliminary only.
Post consent, track layout design and associated SuDS design will be further developed to minimise and mitigate for
the effects of pollution to all local watercourses.
6.2
Watercourses & Watercourse Crossings
6.2.1 Identification of Watercourse Crossings
A number of watercourses have been identified on the site during preliminary design of drainage that will be affected by
the construction of a new or upgraded watercourse crossing (culvert, bridge or similar) in order to allow the proposed
development on the site.
Works required by the wind farm development will cross several types of water conveying features. Thus in the context
of the SuDS drainage proposals, a “watercourse” will encompass the following:
•
Significant natural rivers and streams as normally perceived and charted by OS 1:50,000 series mapping.
Chapter 10 of the ES states that “three new watercourse crossings are proposed, of unnamed tributaries of Grassfield
Burn and Claonaig Water and only four upgrades of existing crossings are proposed.”
Additional consideration will be given to design of other drainage crossings at detailed (post-planning) design stage,
where other drainage crossings of ditches and drains alongside existing roads; tracks and field boundaries; moorland /
peatland drainage; and incised channels in peat (e.g. hags or gullies) may be required.
It should be noted that a number of the smaller uncharted watercourses are normally dry and are effectively natural
drainage paths in periods of wet weather only. Works to watercourse crossings will be subject to authorisation by SEPA
as per the Water Environment (Controlled Activities) Regulations 2011.
6.2.2 Design of Watercourse Crossings
Design of watercourse crossings will be undertaken at detailed design stage. As part of the drainage design, detailed
mapping of drainage paths across the site has been undertaken; utilising topographical surveys, contour mapping and
aerial photography. Detailed mapping aided the accurate definition of catchment extents for each of the water crossing
locations.
In Scotland, engineering works in or near water bodies must have prior consent from the SEPA in the form of a CAR
license under the terms of the Water Environment (Controlled Activities) Regulations 2011.
It should be noted that all watercourse crossings will be designed on a bespoke basis. The following guidance will be
used in the sizing of watercourse crossings;
•
Hydrological assessments made using a number of methods including Flood Estimation Handbook (Statistical
Analysis) and Flood Studies Report (FSR) where appropriate to determine the design flow
•
CIRIA Culvert design and operation guide (C689)
Design of water crossing structures will comply with the provisions made in the Construction Method Statement for the
site, as well as additional considerations in this report.
Additional factors used in the determination of design and orientation of watercourse crossings include:
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Provision of clear span where required under CAR or where provision is required to protect sensitive aquatic
habitats; provision of clear span crossing to be agreed with appointed suitably qualified ecologist;
•
Crossing direction to generally be perpendicular to access track direction, therefore minimising the length of
stream affected;
•
Provision through design for the passage of out-of-bank flood flows;
•
Crossings are generally located in an area where bank slopes are the shallowest available, thus reducing the
potential for runoff to carry sediment into the watercourse.
Additional mitigation will be designed to prevent pollution of the watercourse during the construction of the watercourse
crossing to reduce residual risk (for example the temporary installation of silt fences in the stream channel
downstream).
6.2.3 Preservation of Overland Flow Routes
Overland flow across the ground will be preserved by the provision of cross-track drainage (cross drains) at regular
intervals and at all natural depressions and flow collection points.
Upslope “cut-off drains” will also be employed to intercept overland flows and shall be installed in areas where:
•
significant overland flow is anticipated to cross the proposed excavated track alignment, and;
•
other areas such as borrowpits and construction compounds where excavations occur into a slope, in order to
prevent surface water flowing across an area of construction works.
All cut-off drains are to drain to an area downslope of the works, with piped under-track cross drains provided where
required. Cut-off drains should have regular discharges and be installed with attention to natural catchments, cut-offs
should not alter the overall hydrology and serve only to allow natural water to bypass the works area while following
roughly main natural flow routes.
Cross drains will be minimum 450mm in diameter; all piped drainage will be sized in accordance with the guidance
provided in Section 6.2.2 Design of Watercourse Crossings.
Water intercepted in cut-off drains is considered clean or natural (i.e. uncontaminated by clays or silts from excavations
or track aggregate).
Natural water intercepted in cut-off drains shall be retained separate from trackside drainage (construction runoff)
wherever practicable. This shall be achieved by ensuring natural drainage is piped under trackside drainage swales,
and discharged overland separately.
Frequency and location of specific cross drains will be specified following inspection of contour and detailed
topographical data, with cross drain frequency dictated by:
6.3
•
Upslope catchment draining to any cut-off drain;
•
Terrain gradients lateral to the proposed access track;
•
Terrain gradients longitudinal to the proposed track;
•
Location of natural depressions and points of flow collection.
Hydrological Buffer Zones
6.3.1 Watercourse Buffer Zones
Buffer (exclusion) zones will be maintained around all identified watercourses as per EIS requirements. Where the local
site environment requires additional protection (e.g. steep slopes or lack of vegetation between construction corridor
and watercourse) the buffer zone will be increased or stringent mitigation measures introduced.
Watercourses have been identified from 1:50,000 OS mapping and 50m buffer zones are indicated on the SuDS
General Arrangement Drawing. Buffers will act as filters minimising sediment transport, attenuating flows and
maximising infiltration as per requirements of the ES.
6.4
Drainage Design
6.4.1 Natural / Construction Runoff Separation
Drainage management will ensure that clean water is not permitted to mix with contaminated water from sources such
as excavation dewatering or track runoff, where “clean water” should be interpreted as natural surface runoff unaffected
by construction / earthworks runoff.
Design will ensure that upslope cut off ditches are to be installed in order to intercept and divert natural upslope surface
water runoff prior to it coming in contact with areas of excavation. The construction will be phased to ensure that
natural runoff cut off ditches are installed ahead of main earthworks wherever practical. This is intended to reduce the
Drainage Management (SuDS) Design Statement
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flow of natural water runoff onto any exposed areas of rock and soil, thereby reducing the amount of potential silt laden
runoff requiring treatment.
Installed drainage will allow provision for natural runoff intercepted in cut-off ditches to pass through and under track
structures separate to drainage provided for track runoff.
Temporary silt / pollution prevention and scour protection measures will be provided in artificial clean water drainage
installed in order to mitigate potential for scouring and transport of sediment from newly excavated channels.
Diversion drainage is to discharge either to existing watercourse channels (via silt removal features) or be dispersed
over vegetated ground. Diversions are to be designed to avoid collection and interception of large catchments creating
significant point flows, with associated risks due to scour and hydraulic capacity.
6.4.2 Trackside Drainage
The cross fall on the track will be aligned to divert contaminated surface water from track surface or excavations into
trackside swales by overland sheet flow or via track surface grips.
The swale and track shoulder will be vegetated as soon as possible after construction, in order to reduce potential for
runoff from exposed aggregates and clays, and promote removal of suspended solids within runoff by filtration in
vegetation. Any vegetation used will be appropriate to the local area. Temporary erosion protection may be required
until the vegetation becomes established (coir matting or similar).
All swales will be kept as shallow as possible so that they pose no health and safety risk to plant or personnel.
Maximum depth of standing water will be limited to 0.5m within the ponds and 0.3m within the swales.
Drainage swales shall be designed to satisfy the following conveyance and water quality criteria:
•
Hydraulic conveyance of 30-yr runoff with consideration to effect of 200-yr (flood protection) event;
•
Store treatment volume “Vt” (15mm rainfall on drained area);
•
Demonstrate adequate settlement of solids for the anticipated residence time in the swale.
Under-track piped drainage crossings will be provided to allow up-slope swales to drain to the down slope side.
Crossings will be provided at regular intervals (to be determined at detailed design stage) and at all localised low points.
Outlets from crossing pipes shall generally coincide with swale breakouts.
Note that construction water under track crossings and breakouts are to be maintained separate from natural water
crossings (see Section 6.4.1).
There will be regular outflow points (”breakouts”) from the swales throughout the SuDS system to eliminate the potential
for the generation of large flows at single outflow points. This will assist the drainage network in maintaining the natural
hydrological response displayed by the natural catchment. Outflows will be directed away from watercourses and
across open vegetation to increase the drainage path and buffer zone between the point of discharge and the
watercourse.
6.4.3 Check Dams
It is proposed that rock check dams will be installed within trackside swales at regular frequencies, in order to reduce
flow velocities and improve conditions for the settlement of solids in transit. It is intended that these dams will be
relatively simple to construct but provide treatment of construction runoff at source.
The stone used for the construction of the check dams will be a small ‘clean’ graded stone. On steeper slopes the check
dams will be anchored using larger stone placed on the downhill side of the check dam to prevent washing away of the
smaller graded stone. The frequency of the check dams will be determined at detailed design stage.
The check dams will serve dual functions, by both removing and settling out silts and reducing flow velocities, therefore
mitigating against the effects of erosion within the swale.
Where feasible and where observed site conditions allow, the frequency of installed check dams may be reduced postconstruction phase, due to reduced silt loading anticipated following completion of construction activities and reduced
site traffic.
6.4.4 Drainage Grips
Drainage grips will be installed on the track surface in order to direct runoff into trackside drainage or to downslope
settlement / filtration features. Positioning of grips will be determined at detailed design stage and on an observational
basis during construction, however in general the need for grips will be greatest in areas on steep longitudinal track
gradient.
Installation of grips will prevent extensive rutting of the track structure and aids drainage of the track surface, which in
turn reduces potential for trafficking of the surface to cut the track and generate silt.
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Drainage grips will generally be designed and installed at the required locations to suit traffic volumes, and will comprise
a steel channel section or similar installed flush to the track surface.
6.4.5 Runoff Attenuation
Runoff from large hard standing areas such as the site compound, turbine hard standings, and substation will be
attenuated to mimic natural runoff patterns.
Flow rates from tracks will be reduced through use of attenuating check dams “at source”, with pass-forward flow rate
reduced by filtration and temporary detention.
Attenuation will utilise shallow ponds to aid removal of suspended solids. Calculations for the determination of storage
requirements will be undertaken at detailed design stage.
Consideration will be given to the potential for further storage features across the site. The use of large impounded
storage features (using earth embankments etc.) will be discouraged, due to long term maintenance requirements and
risk of embankment failure.
The general location of the small balancing ponds should ensure that they pose minimal health and safety risk to site
personnel, particularly whilst constructing the wind turbine rotor blades during the installation process (as this process
takes place adjacent to the crane hard standing). Warning signage is to be provided to all ponds during the construction
phase.
6.5
Forestry Clearance Works
It is anticipated that the area of forestry present across parts of the site would be felled either during the enabling works
phase or prior to commissioning of the Development.
Felling will be undertaken in accordance with a separately produced Forestry Management Plan. It is anticipated that
felling will be undertaken using specialist machinery, with merchantable timber transported off site.
Where branch wood and unmerchantable timber is left on site, residue has potential to wash into surface water
channels and enter downstream watercourses. Additionally, there is potential for rutting from vehicle movement within
the forested area (and consequently generation of silts).
In order to mitigate potential for entry of silts and biodegrading material entering downstream watercourses, the
following will be implemented:
•
Clean stone check dams will be installed within existing forestry main collector drains in advance of
commencement of forestry clearance works, trapping silt in runoff.
•
Silt traps / mini settlement ponds will be installed on forestry main collector drains prior to final discharge to
downstream watercourses. The settlement ponds trap any floating debris being washed off site, and will be
installed on the downstream ends of the interceptor grips to ensure that all drainage from the forested area
can be treated.
•
The lower end of the site will be cordoned off with silt fences. This will allow sheet flow through the system,
but will prevent floating debris from entering the river system.
Water quality monitoring will be undertaken during the deforestation process, with a particular emphasis on reviewing
parameters likely to be affected by forestry works, i.e. total suspended solids, biological and chemical oxygen demand,
ammonia, nitrates and phosphates, turbidity and presence of oils.
6.6
Temporary Spoil Management
Management of spoil, including temporary and permanent spoil generated from excavations, would be detailed as part
of a Construction Method Statement to be approved by SEPA / SNH prior to construction. Site and drainage design
would ensure the following in terms of drainage for temporary spoil management areas:
•
There will be no depositing of material within the 50m watercourse buffer zones.
•
Spoil shall be placed in such a manner so as to ensure no ponding of surface water on top of spoil heaps.
•
Temporary spoil should be graded to ensure that all direct precipitation will run directly off the surface.
•
Temporary spoil deposition areas will be designed to ensure that natural flow paths (drainage channels) are
not be altered or blocked by deposited spoil.
•
Permanent spoil heaps or berms would be covered with biodegradable matting in order to expedite
establishment of vegetation in areas where significant erosion is observed. Spoil heaps in the vicinity of
watercourses would be provided with silt fences on the downhill slope in order to trap fine sediment in runoff.
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7
CONSTRUCTION PHASE – DETAILED CONSIDERATIONS
Specific requirements to be imposed on any Contractor involved in the construction of the scheme will be further
detailed in a Construction Method Statement to be approved by SEPA / SNH prior to construction.
All site personnel should be made aware of their environmental responsibilities at the site induction prior to being
allowed to work on site, and through the production of a Method statement, outlining Environmental Requirements for
Sub-contractors, which will include environmental emergency response procedures to deal with spillages, should they
occur.
This section of the report outlines the steps which should be undertaken during the construction phase of the project to
ensure compliance with the relevant guidance and legislation outlined in Section 3 of this report. Site visits by the SuDS
Designer will be agreed in advance and will be undertaken at various stages of the construction process to ensure that
the proposed SuDS scheme is being constructed in line with the design.
In accordance with BS6031: 1981 Code of Practice for Earth Works, land disturbance will be kept to a minimum and
disturbed areas will be stabilised as soon as possible. Soil handling will be undertaken with reference to best practice
guidelines available from DEFRA in the form of the Good Practice Guide for Handling Soils (MAFF 2000). In principle,
soil excavation should be undertaken during dry periods whenever possible. However, it is noted that other factors such
as bird nesting season and other ecological constraints may affect working timeframes. Therefore working only during
dry weather may not always be practicable or feasible.
A Spoil Management Plan should be developed for the site which will detail the placement of excess spoil across the
site and will be based upon the recommendations from the site Peat Slide Risk Assessment. All drainage
recommendations from the peat stability report will be incorporated into the detailed SuDS design.
Essential mitigation measures relevant to controlling erosion and runoff from construction of the SuDS are described in
SEPA’s pollution prevention guidance notes.
7.1
Planning and Phasing of Drainage Works
7.1.1 Site-wide Requirements
Unless proven technically infeasible, temporary or permanent drainage & silt management features (SuDS) will be
constructed prior to earthworks (including preliminary or enabling works) proceeding to construct any linear works
(tracks / hard standing areas / cable routes), turbine bases, and other infrastructure, including:
•
Temporary silt fences should be erected in areas where risk of pollution to watercourses has been identified
e.g. watercourse crossing locations and areas where tracks or other infrastructure lie within watercourse buffer
zones.
•
Upslope cut-off drainage channels approximately parallel to the proposed excavated track alignment should
be installed in advance of any excavated cuttings for the track or turbine hard standing areas. This will
prevent washout by surface flows of exposed clays in excavations and fine sediments in track makeup, and
increase efficiency of silt removal in future trackside drainage swales.
•
Watercourses, drains, natural flow paths and cut-off drain outlet locations should be identified and charted, in
order to ensure that piped crossings can be installed in advance of or adjacent to the track construction.
•
Settlement ponds should be constructed in advance of commencing excavations for WTG foundations and at
any other locations identified as required at detailed design stage.
•
Trackside drainage swales should be installed in parallel with track construction. Note that this may require
that drainage swales are reformed on an ongoing basis as temporary track alignments are modified to their
eventual finished design level.
In addition, spoil management is to be planned in advance of earthworks and on an ongoing basis, in order to allow
planning of drainage required in advance of spoil being deposited.
Suitable prevention measures should be in place at all times to prevent the conveyance of silts to receiving water
courses.
7.1.2 Timing of Works
Works on the site likely to cause a high risk to surface water would be programmed so as to avoid unfavourable
prevailing ground conditions and seasonal rainfall.
Site clearance should take place in advance of construction works.
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7.2
Specific Construction Phase Measures
7.2.1 Working in the Vicinity of Water / Buffer Zones
The following procedures apply to the general construction activities either within watercourses or in the vicinity of
watercourses.
•
Ensure tracks would be built in strict accordance with the approved designed layout and therefore remain
outside the relevant buffer zones to rivers and watercourses.
•
Due cognisance would be given to the prevailing ground conditions and season when programming the
execution of the works in order to minimise generation of silt laden runoff.
•
Works would plan so that trackside drains do not discharge directly into watercourses, but rather through a
buffer area of adequate width (see below) or via a constructed settlement feature such as pond or
sequence of silt fences.
•
Cement and concrete would be kept outwith buffer zone to avoid contamination of watercourses.
•
Runoff from excavations would NOT be pumped directly to watercourses. Where dewatering of excavations
is required, water shall be pumped to the head of a treatment train (swale, basin, or detention pond) in order
to receive treatment and removal of silts prior to re-entry to the natural drainage system.
Construction buffer zones to drainage features will be set as stated in Section 6.3.1.
Buffer zones are shown on the SuDS general arrangement overview drawings included with this report. It is noted that
SuDS treatment techniques would be utilised to remove silts from runoff prior to the discharge of flows over open
vegetated areas.
In the event that a specific short term risk to water quality is identified on site, specific localised measures will be
implemented including:
•
Placing temporary filtration silt fences within drainage channels where siltation is observed
•
Installing temporary constructed settlement features such as sumps or settlement ponds / lagoons where
required.
•
Imposing methods of work designed to limit areas of exposed excavations, e.g. in areas where existing
track upgrade works lie in close proximity to watercourses.
7.2.2 Watercourse Crossings
It is noted that watercourse crossings have been avoided wherever possible as part of the design evolution of the site.
Where crossings are unavoidable, initial design undertaken to date and all future detailed design will ensure that risk to
the receiving environment is reduced at design stage.
Residual risk to watercourses specific to the construction stage will be fully addressed in the Contractor’s construction
method statement and in addition to those points outlined in Section 6.2.2 will include:
•
Erection of silt fences along watercourse banks adjacent to, upstream and downstream of crossing
locations in order to intercept polluted runoff;
•
Due cognisance would be given to the prevailing ground conditions and season when programming the
execution of the works in order to allow works to be undertaken during periods of low river flows.
•
Utilise construction methods that avoid or minimise use of cementitious materials in the vicinity of the
watercourse;
•
Avoid disturbance to the river bed where practical or specifically denoted.
Crossings of a number of cut drains and minor drainage path crossings will be required, whose exact locations will be
determined at detailed design stage.
7.2.3 Working in the vicinity of Groundwater Dependent Terrestrial Ecosystems
Three GWDTEs have been designated on site, as outlined in Section 10.5.2.7 of the ES. Locations of GWDTEs on site
are shown in Figure 7.4.
As noted on the SuDS layout drawings, particular measures should be applied in the vicinity of GWDTEs to ensure
minimal disturbance of the local natural hydrological conditions. Following guidelines outlined in the Hydrology Chapter
of the ES, prior to track construction, site operatives should:
•
identify flush areas / natural depressions
•
provide pipes and / or drainage matting to ensure hydraulic conductivity is maintained within the GWDTE
•
provide site fences and ensure suitable measures are in place to avoid pollution of the GWDTE
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avoid diverting flows away from the GWDTE’s through the introduction of drainage channels
•
7.2.4 Mini-Settlement Ponds / Lagoons
The following shall apply to the construction of settlement ponds at the site:
•
All flow depths to be kept to a normal depth of 0.3m with a maximum depth of 0.5m maximum.
•
Side slopes to be shallow, nominally at a 1 in 3 side slope (maximum).
•
Install cut-off drains around the working areas to intercept natural surface runoff and divert it around and
away from the works; surface water runoff may also be diverted around the excavation using heavy timbers
or similar laid on the surface of the ground. Post completion of the scheme the cut-off drains can be infilled
and any timbers removed.
•
Material excavated from the settlement pond should be compacted around the edge of the pond, which will
provide a natural barrier to prevent site personnel from falling into the pond.
•
Consideration will be given to retention of the settlement ponds as permanent ponds in post construction
phase, should they be deemed to provide ecological and habitat benefit for the site (feeding ground for
snipe for example). All construction waste materials such as generated silts and gabion baskets should be
removed and disposed of in an appropriate manner before a pond is left as permanent.
•
Inspect mini-settlement ponds for damage after intense storms in particular at the entry point and around
the forebay area. The mini-settlement ponds will also be inspected at each site visit (conducted by the
SuDS Engineer) and in line with the construction period maintenance schedule.
7.2.5 Turbine Bases and Crane Pads
Excavated turbine foundations are likely to result in large volumes of displaced excavated material as spoil, as well as
concrete operations. Specific measures are therefore required to manage potential for silt laden runoff from spoil, silt
laden runoff from pumped dewatering, and cementitious contamination in pumped dewatering from turbine bases.
Therefore, the following drainage measures will apply:
•
Concrete will not be allowed to enter watercourses under any circumstances, and drainage from excavations
in which concrete is being poured will not be discharged directly into existing watercourses without appropriate
treatment. Delivery trucks, tools and equipment will be cleaned at designated washout areas located
conveniently and within a controlled area of the site. In addition the following drainage measures will apply;
•
Installation of cut-off drains around the working areas to intercept natural surface runoff and divert it around
and away from the works;
•
Minimise the stockpiling of materials and locating essential stockpiles as far away from watercourses as
practical (outwith buffer zones). Excavated clays are to be battered back and covered by topsoil in order to
minimise potential for runoff from exposed clays;
•
Polluted (silt laden) water collected in the base of the excavation gathered in a sump, and pumped at a low
flow rate into either the mini-settlement pond or track swale for treatment. Dewatering of excavations direct to
watercourses will not be permitted;
•
The foundation working areas should be re-vegetated as soon as possible after construction.
7.2.6 Substation and Temporary Compounds
The following shall apply to the construction of the temporary compound at the site:
•
During construction of the substation and temporary compounds, similar measures to those implemented
during turbine/crane pad construction will be used to limit water ingress, sediment erosion and concrete
pollution.
•
‘French drains’ or similar will be constructed around the substation to ensure ground water levels around
the building can be managed and that internal sumps within the building do not become waterlogged.
7.2.7 Cable Trenches
It is noted that where feasible, the design of cable trench alignment will avoid the creation of preferential flow routes.
The following shall apply to the construction of all cable trenches at the site:
•
To minimise impacts from disturbance, cables would be laid in small trenches along the side of access
tracks as far as possible.
•
Due cognisance would be given to the prevailing ground conditions and season when programming the
execution of the works in order to reduce the likelihood of runoff entering the excavations.
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•
Excavation of cable trenches will be carried out over short distances, with frequent backfilling of trenches in
order to minimise opportunity for the ingress of water into open trenches.
•
Temporary silt traps would be provided in longer trench runs and on steeper slopes.
•
Where constructed trackside swales are disturbed by cable installation, swale slopes would be correctly
reinstated post infilling of the cable trench.
7.2.8 Dewatering
In order to control dewatering activities and to ensure that all dewatering, particularly pumped dewatering from
excavations, is controlled and allows for pollution prevention measures, a permit-to-work system will be imposed on the
Contractor
A permit would be required to be issued to a competent person prior to allowing any specific dewatering to commence.
7.2.9 Excavated-type Track Makeup
Where an excavated type track construction is specified, all potentially contaminated construction runoff would be
directed to flow to track-side drainage channels as per Section 6.4.2, to be installed as tracks are constructed. The
contractor should ensure that:
•
Upslope cut-off drainage is installed ahead of main earthworks as enabling works, and associated crossing
points through the proposed track alignment are identified and planned in advance;
•
Temporary swales are installed as may be necessary at the down slope extent of the working strip, with
associated settlement features;
•
Spoil arising from excavations for the track foundation should be placed on the upslope side or both sides of
any excavation. Care must be taken to ensure that temporary or permanent trackside spoil does not cause
infilling of any upslope cut-off drainage previously installed;
•
Permanent swales and under-track crossings are planned and installed to suit the design requirements. It is
recommended that swales are formed using a v-ditch type excavator bucket customised to suit the swale
profile determined at design stage, in order to provide a uniform swale section to suit hydraulic requirements;
•
Check dams are installed within swales as soon as possible after forming the swale channel; and
•
Placement of track-edge protection or side-cast spoil (where proposed) does not conflict with surface water
drainage by preventing water from flowing over the track edge onto adjacent vegetated ground.
Drainage swales and track shoulders would be top soiled and seeded out (using hydroseeding where feasible) in order
to accelerate the establishment of vegetation within drainage channels as soon as is feasible after completion of the
track and drainage across the site.
7.2.10 Floated-type Track Makeup
Where a floating type track construction is specified, all potentially contaminated construction runoff would be
encouraged to flow over the track edge as sheet flow onto adjacent undisturbed vegetation. The contractor should
ensure that:
•
Existing drainage paths and overland flow-routes are identified in advance of track construction, and culvert
pipes installed as the floating track advanced;
•
Placement of track-edge protection or side-cast spoil (where proposed) does not conflict with surface water
drainage by preventing water from flowing over the track edge onto adjacent vegetated ground. Where side
cast spoil causes impediment to over the edge drainage due to differential settlement during or post
construction, action will be taken to either re-grade spoil to suit, or install a track edge drainage swale within
the soft shoulder formed by side-cast spoil to a discharge point;
•
Side-cast spoil from elsewhere on the site does not conflict with under-track drainage installed, or that undertrack drainage pipes are extended sufficiently that side-cast spoil does not affect their operation.
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
15
August 2012
MCL115-48
8
SUDS MAINTENANCE MANUAL
8.1
Recommendations for Construction Phase
This report will serve as the primary SuDS System maintenance manual for the construction phase. It is envisaged that
regular site inspections are arranged during the construction phase of the wind farm, in order for the SuDS Engineer to
validate that the SuDS specification is being adhered to by the contractor and to make additional recommendations
where potential problems are identified.
The site would maintain a register of temporary pollution prevention measures installed in order to ensure regular
maintenance was undertaken.
In addition to the regular site inspections carried out by the SuDS Engineer, the following construction inspections will
be undertaken by the site engineer during the construction phase of the project.
•
All Check dams and mini-settlement ponds to be checked at least once fortnightly via a walkover survey
during the full period of construction. All excess silts to be removed and land applied in accordance with
relevant authority and landowner requirements. Land applied silts should not be located where wash off to
local watercourses may occur.
•
Where check dams have become fully blocked with silt, they should be replaced. Procedure for replacement
of the check dam is as follows:
o
o
o
o
o
Silt deposits to be removed from the upstream side of check dams.
Removed silt to be disposed of by spreading in an area of the site where surface runoff will not
convey silt deposits back to a water course.
The existing 20mm stone check dams are to be removed and disposed of appropriately. Stone
materials removed from the check dams should not be disposed of over vegetated areas of the site.
Replacement check dam to be installed using 20mm stone.
Where there are regular incidents of check dam blockage further check dams to be installed (every
15-20m intervals) within the swales.
•
Soil in the swales should not be smeared or compacted so that permeability is reduced.
•
All excavations are to the required size and gradient and located in correct position. Due to the size and
nature of the site, there will be scope for some latitude with this. However, variations to the original design
should be kept to a minimum and only implemented where necessary (i.e. due to localised site constraints).
•
Ensure side slopes of SuDS features are correct, where applicable.
•
Ensure depth of excavation of SuDS features is correct, where applicable.
•
Any temporarily stored or stockpiled material will be placed in a manner to ensure stability (i.e. level ground,
maximum height 1m etc.) and in the case of unforeseen collapse will not cause infilling of the swale.
•
Debris (e.g. loose roots) to be removed from the base of the swale.
•
Should there be noticeable effects of erosion along the swales or at discharge points, suitable erosion
protection measures such as placement of large stones or erosion protection mattresses should be installed at
the area affected.
The construction phase SUDS maintenance manual will be a live working document and will be used to inform and
develop the post construction maintenance manual.
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
16
August 2012
MCL115-48
APPENDIX A
General Arrangement
and Typical Detail Drawings
Drainage Management (SuDS) Design Statement
Freasdail Wind Farm, Kintyre
17
August 2012
N
T9
T 10
MAST 73
T 11
T7
T6
T8
T1
T5
T4
T3
T2
N
T9
T 10
MAST 73
T 11
T9
T 10
T7
T6
T8
T1
T5
T4
T3
T2
MAST 73
T 11
T7
T6
T8
T
T5
T4
T3
T2
APPENDIX 3 – WATER QUALITY MONITORING PROCEDURE
A suitably qualified consultant would be appointed to provide water quality monitoring
services for the Development. The following contains information regarding proposed
procedure, testing regime and legislation to be employed.
Legislation
The key primary legisaltion currently enforced by SEPA in Scotland is the Water Environment
and Water Services (Scotland) Act 2003 (WES Act). Any surface or groundwater (where
feasible) whose catchment lies wholly or partially within the Proposed Wind Farm site would
therefore be considered ‘controlled water’ with respect to this water quality monitoring
programme. Controlled water covers all tidal rivers, all freshwater rivers and watercourses,
all lakes and ponds and any water contained in underground strata.
Strategy
During construction works carried out at the Development site, there is a potential for
contamination, emanating from construction plant or materials to enter the controlled
surface and groundwaters either by direct runoff, leaching or infiltration. Consequently, it
would be necessary to monitor the concentrations of certain key contaminants at key
locations throughout the Proposed Wind Farm site. Due regard would be given to the
relevant ‘Pollution Prevention Guidelines’ prepared vt SEPA, EA and NIEA, specifically PPG5
(‘Works in, near or liable to affect watercourses) and PPG6 (‘Working at Construction and
Demolition Sites’). These sampling points would represent a selection of relevant
watercourses and available wells, where present.
The exact location of each sampling point and method would be determined during a
walkover survey to be conducted as part of a hydrological desk study. The location of the
sample points would reflect the point on all relevant controlled waters closest to the
proposed active construction areas. Sampling points up-stream and down-stream of the
construction activity area should also be selected to provide a full profile of the controlled
waters.
Sampling Interval
Site sensivity will be taken into account when deciding on the level and periodicity of
sampling. The proposed monitoring plan would be discussed and agreed with SEPA prior to
commencement.
Reporting
A baseline report would be prepared following the baseline water quality monitoring
programme. This report will provide details of any contamination concentrations recorded
and will be used to depict “uncontaminated background pollution levels” for the site.The
results will be compared to the most relevant Environmental Quality Standards appropiate.
Any environmental deterioration illustrated by the results would be highlighted.
In the event of a potential pollution incident, all relevant monitoring points would be visited
and re-sampled to determine any changes relative to baseline data. A report detailing the
findings would be prepared for each incident and recommendations provided for further
monitoring and / or requisite mitigation measures.
Following completion of the construction of the wind farm, all sample points would be
revisted, re-sampled and analysed for the full suite of analytical parameters and a further
20
report prepared, assessing and discussing any impacts upon water quality throughout the
construction process.
All information recovered during the monitoring process would be collated and an
assessment made regarding the impact on the surface and groundwater of the construction
activities.
Personnel
All personnel taking samples, analysing and reporting would be suitably qualified. The
contractor would be appointed based upon evidence of previous relevant experience within
the UK.
21
APPENDIX 4 - PROCEDURE IN THE EVENT OF A CONTAMINANT SPILL
The following details the emergency procedure to be followed and actions to be taken in the
event of an oil, fuel and chemical spill occurring on the Development.
Spill kits of appropriate form and size for the controlled substances will be supplied on site;
they are also present on any mobile refuelling bowsers on construction sites. In the event of
a spill occurring trained personnel shall:
Cease work in the vicinity immediately
Identify source of pollution
Immediately deploy the spill kit in accordance with the manufacturer’s instructions
Dispose of used spill kits and any other contaminated material e.g. rags used during
the incident in accordance with the environmental waste management regulations
and by a licensed disposal company. Waste transfer certificates will be retained.
In the event of a concrete spillage into a water channel or surface water, SEPA will be
informed of the incident and further advice sought if required. Every effort will be made to
contain the movement of the liquid cement.
Incident forms will be completed within 48 hours of the incident occurring.
22
APPENDIX 5 – WASTE MANAGEMENT
RES shall ensure waste is minimised on the construction site by reducing, re-using and
recycling waste. A Site Waste Management Plan (SWMP) will be created which identifies all
waste streams and responsibilities. The SWMP would also identify methods of managing the
wastes and act as a checklist to ensure each waste is disposed of correctly.
The SWMP will be periodically reviewed and amended as required. All waste disposal records
will be retained and copies provided, where necessary.
23