5.3 - national infrastructure planning · figure 3.13: portishead 132/33kv substation figure 3.14:...

May 2014Application Reference EN020001

5.3.1Do

cum

ent

Hinkley Point C Connection Project

Environmental StatementProject Description

Regulation 5(2)(a) of the Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009

Hinkley Point C Connection Project

ENVIRONMENTAL STATEMENT – MAY 2014

VOLUME 5.3.1, CHAPTER 3 – PROJECT DESCRIPTION

Hinkley Point C Connection Project – Volume 5.3.1

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Document Control

Document Properties

Organisation National Grid

Author Bobby Clayton, TEP

Approved By Ian Grimshaw, TEP

Title Environmental Statement Chapter 3 – Project Description

Document Reference Volume 5.3.1

Date Version Status Description/Changes

09/05/14 A Live Final version for DCO submission

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Table of Contents

3 Project Description ................................................................................................................ 9 3.1 Introduction .............................................................................................................................. 9 3.2 Location of the Proposed Development .................................................................................... 9 3.3 Summary of the Proposed Development ................................................................................ 12 3.4 Pylon Details .......................................................................................................................... 23 3.5 Materials and Waste ............................................................................................................... 28 3.6 Order Limits ............................................................................................................................ 31 3.7 Detailed Description of the Proposed Development ................................................................ 31

INSETS (VOLUME 5.3.1)

Inset 3.1: Location of the Proposed Development

Inset 3.2: Pylon Profiles

Inset 3.3: Proposed Construction Compound at Bath Road

Inset 3.4: Typical Construction Compound Area

Inset 3.5: Typical Bellmouth

Inset 3.6: Photograph of Typical Scaffolding Area (Road Protection)

Inset 3.7: Typical Pylon Working Area

Inset 3.8: Proposed Pylon Working Area at Pylon LD4

Inset 3.9: River Axe Cable Bridge Crossing Option

Inset 3.10: Towerhead Brook Cable Crossing

Inset 3.11: Typical 400kV Underground Cable Construction Swathe

Inset 3.12: Location of the Bridgwater Tee Cable Sealing End (CSE) Compound

Inset 3.13: Plan of the Bridgwater Tee Cable Sealing End (CSE) Compound

Inset 3.14: Location of the South of the Mendip Hills CSE Compound

Inset 3.15: Plan of the South of the Mendip Hills CSE Compound

Inset 3.16: Location of Sandford Substation

Inset 3.17: Plan of Sandford Substation

Inset 3.18: The AT Route

Inset 3.19: The N Route

Inset 3.20: The W and Y Routes at Churchill Substation

Inset 3.21: Location of Churchill Substation Modifications


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Inset 3.22: Plan of Churchill Substation Modifications

Inset 3.23: W Route Undergrounding from Pylon W36R

Inset 3.24: The G Route

Inset 3.25: The G, DA and BW Routes into Seabank Substation


Inset 3.27: Portishead Substation Plan

Inset 3.28: Avonmouth Substation Plan

Inset 3.29: Seabank Substation Plan

APPENDICES (VOLUME 5.3.2)

Appendix 3A: Pylon Staking Tables

Appendix 3B: Preliminary Construction Programmes

Appendix 3C: Crossings Schedule

Appendix 3D: Utilities Schedule

Appendix 3E: Bellmouth Schedule

Appendix 3F: 400kV and 132kV Cable Crossing Schedule

Appendix 3G: Construction Risk Assessments and Method Statements

Appendix 3H: T-pylon Construction Information

FIGURES (VOLUME 5.3.3)

VOLUME 5.3.3.1

Figure 3.1: The Proposed Development

Figure 3.2: The Proposed Development - Preferred Route Option A and Alternative Route Option B

VOLUME 5.3.3.2

Figure 3.3: Construction Plans

VOLUME 5.3.3.3

Figure 3.4: Construction Plans – Preferred Route Option A and Alternative Route Option B

Figure 3.5: Indicative Access for Future Maintenance

Figure 3.6: Indicative Access for Future Maintenance – Preferred Route Option A and Alternative Route Option B

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VOLUME 5.3.3.4

Figure 3.7: Environmental Constraints

Figure 3.8: Pylon Profiles

Figure 3.9: Sandford 400/132kV Substation

Figure 3.10: Seabank 400/132kV Substation

Figure 3.11: Churchill 132/33kV Substation

Figure 3.12: Avonmouth 132/33kV Substation

Figure 3.13: Portishead 132/33kV Substation

Figure 3.14: Bridgwater Tee Cable Sealing End Compounds

VOLUME 5.3.3.5

Figure 3.15: South of the Mendip Hills Cable Sealing End Compound

Figure 3.16: Typical Site Laydown Areas

Figure 3.17: Typical Underground Cable Technical Arrangements

Figure 3.18: River Axe and Towerhead Brook Crossing Options

Figure 3.19: Temporary Construction Road and Bridge Details

Figure 3.20: Culvert Construction Details

Figure 3.21: Typical 400/132kV Horizontal Directional Drilling Reception and Drive Site

Figure 3.22: Typical Bellmouth Arrangements

Figure 3.23: Typical Pylon Working Area

Figure 3.24: Pylon Foundations

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3 PROJECT DESCRIPTION

3.1 Introduction

3.1.1 In accordance with the Schedule 4, Part 1 of the Infrastructure Planning (Environmental Impact Assessment Regulations) 2009 (the 2009 Regulations), this chapter provides a description of the physical characteristics of the Proposed Development and the land use requirements during the construction and operational phases.

3.1.2 This chapter provides both an overview of the project description and further detail of each component part of the Proposed Development (see section 3.7 below). The Proposed Development can be viewed on the following plans:

Proposed Development Plans (Volume 5.3.3, Figure 3.1);

Proposed Development Plans - Preferred Option A and Alternative Option B (Volume 5.3.3, Figure 3.2);

Construction Plans (Volume 5.3.3, Figure 3.3);

Construction Plans – Preferred Option A and Alternative Option B (Volume 5.3.3, Figure 3.4);

Indicative Access for Future Maintenance (Volume 5.3.3, Figure 3.5);

Indicative Access for Future Maintenance – Preferred Option A and Alternative Option B (Volume 5.3.3, Figure 3.6)

Technical Drawings of Individual Proposed Development Components (Volume 5.3.3, Figures 3.8 – 3.24).

3.1.3 The structure of this chapter is as follows:

3.2 - Location of the Proposed Development.

3.3 - Summary of the Proposed Development.

3.4 - Pylon Details.

3.5 - Materials and Waste.

3.6 - Order Limits.

3.7 - Detailed Description of the Proposed Development.

3.2 Location of the Proposed Development

Introduction

3.2.1 The Proposed Development is in south west England and crosses the administrative boundaries of the following district and county authorities (see Volume 5.1.2, Figure 1.1 and Inset 3.1 below):

Somerset County Council;

West Somerset District Council;

Sedgemoor District Council;

North Somerset Council;

Bristol City Council; and

South Gloucestershire Council.

3.2.2 ‘Sections’ have been identified along the route of the 400kV connection from Bridgwater to Seabank based on areas of similar landscape character (Sections A-G inclusive). An additional Section has been defined based on the area of works


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for the Hinkley Line Entries (Section H). The Sections are illustrated at Volume 5.1.2, Figure 1.1.

Section A – Puriton Ridge;

Section B – Somerset Levels and Moors South;

Section C – Mendip Hills;

Section D – Somerset Levels and Moors North;

Section E – Tickenham Ridge;

Section F – Portishead;

Section G – Avonmouth; and

Section H – Hinkley Line Entries.

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Inset 3.1: Location of the Proposed Development

Summary of Environmental Characteristics

3.2.3 The area is predominantly rural, with much of the land comprising pastoral fields. Built development is largely focused along the Severn Estuary to the west of the Proposed Development and includes settlements at Bridgwater, Burnham-on-Sea, Weston-super-Mare, Clevedon, Portishead and Avonmouth. Smaller towns and villages are dispersed widely throughout the area. There are hamlets and individual residential properties within or adjacent to the Proposed Development areas.


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3.2.4 The area is characterised by a series of prominent ridges which run east to west and include: the Puriton Ridge, north of Bridgwater; the Mendip Hills east of Weston-super-Mare and Tickenham Ridge north of Nailsea. There are expanses of low open ground between the ridges.

3.2.5 The main roads in the wider area include the M5 and M49 motorways and the A370, A38, A39 and the A368 which provide links to Bristol. The local road network comprises minor roads which connect to the main roads.

3.2.6 Environmental designations are illustrated at Volume 5.3.3, Figure 3.7. The Mendip Hills Area of Outstanding Natural Beauty (AONB) extends across the route of the proposed connection approximately in the middle of the route between Bridgwater and Seabank; part of the Mendip Hills AONB can be seen at Inset 3 below. The AONB is designated for its landscape and scenic importance although the Mendip Hills are also valued for the many industrial archaeological sites, reflecting the lead, coal and cloth industries. Sites of Special Scientific Interest (SSSI) crossed by or close to the route of the connection are Biddle Street, Yatton SSSI, Tickenham Nailsea and Kenn Moors SSSI, Bridgwater Bay SSSI and the River Avon SSSI (both of which form part of the Severn Estuary Special Protection Area (SPA) and Ramsar site). There are many listed buildings in the vicinity of the Proposed Development.

3.2.7 The internationally designated sites of the Severn Estuary (SPA, Special Area of Conservation (SAC) and Ramsar), Somerset Levels and Moors (SPA and Ramsar), the North Somerset and Mendip Bats SAC and the Mendip Limestone Grasslands SAC lie to the east and west of the Proposed Development. Part of the proposed modifications to the Hinkley line entries are within the Bridgwater Bay SSSI and the Severn Estuary SPA and Ramsar site.

3.2.8 The design for the 400kV overhead line, underground cables, CSE compounds, substations and 132kV connections is based on environmental, technical and economic studies as well as consideration of consultation responses in respect of the proposed Development.

3.2.9 Volumes 5.6.1 – 5.16.1 (‘Baseline Environment’ section) provide full details of the baseline environment in which the Proposed Development would be constructed.

3.3 Summary of the Proposed Development

3.3.1 The proposed Hinkley Point C Connection project includes the following principal elements:

construction of a 57km 400kV electricity transmission connection (see Volume 5.3.3, Figure 3.1 and Figure 3.2) between Bridgwater in Somerset and Seabank, near Avonmouth, comprising:

- installation of a 400kV overhead line; and - installation of 400kV underground cables.

modifications to existing overhead lines at Hinkley Point, Somerset (see Volume 5.3.3, Figure 3.1.20);

construction of three 400kV cable sealing end (CSE) compounds along the route of the connection (see Volume 5.3.3, Figure 3.1.2 and Figure 3.1.6);

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construction of a 400/132kV substation at Sandford, North Somerset (see Volume 5.3.3, Figure 3.1.9);

extension of the existing 400kV substation at Seabank (see Volume 5.3.3, Figure 3.1.19);

the removal of existing 132kV overhead lines and the construction of replacement 132kV overhead lines and 132kV underground cables (see Volume 5.3.3, Figure 3.1);

extensions/modifications to existing 132kV substations at Churchill, Portishead, Avonmouth and Seabank (see Volume 5.3.3, Figures 3.1.10, 3.1.16, 3.1.18 and 3.1.19); and

associated works, for example, temporary access roads, highway works, temporary construction compounds, scaffolding, work sites and ancillary works (see Volume 5.3.3, Figure 3.1).

400kV Transmission Connection

3.3.2 The main component of the Hinkley Point C Connection project is the construction of a new 400kV electricity connection of approximately 57km between Bridgwater, Somerset and Seabank Substation, near Avonmouth. The connection would comprise new overhead lines and new underground cables as described below:

400kV Overhead Line

3.3.3 The new 400kV overhead line between Bridgwater, Somerset and Seabank Substation, near Avonmouth, would comprise three parts:

1) Construction of a new 400kV overhead line of approximately 4.5km from the existing Hinkley to Bridgwater 275kV overhead line on Horsey Level (which would be uprated to 400kV operation) to the existing Hinkley to Melksham 400kV overhead line north of Woolavington.

2) Construction of a new 400kV overhead line of approximately 12.75km from the existing Hinkley to Melksham 400kV overhead line north of Woolavington to a proposed CSE compound south of the Mendip Hills and the River Axe.

3) Construction of a 400kV overhead line from the proposed Sandford Substation to Seabank Substation. In the Portishead/Portbury area two options are included within the Development Consent Order (DCO) application: National Grid’s preferred route (Option A); and an alternative route (Option B). The total length of the preferred route is approximately 29.8km (Option A) and the alternative route is 31.2km (Option B). Volume 5.2.1 provides further detail regarding the consideration of alternatives.

3.3.4 The 400kV overhead line would comprise conductors supported by steel lattice pylons and T-pylons. It is proposed that Sections A (Puriton Ridge), B (Somerset Levels and Moors South), D (Somerset Levels and Moors North), E (Tickenham Ridge) and F (Portishead) would utilise the T-pylon and that Section G (Avonmouth) would utilise steel lattice pylons.

Installation of 400kV Underground Cables

3.3.5 As part of the connection between Bridgwater and Seabank, National Grid is proposing to install 400kV underground cables in two locations. These comprise:


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approximately 300m of underground cables between two single circuit CSE compounds on Horsey Level, north of Bridgwater (see Volume 5.3.3, Figure 3.1.2) where two trenches each with up to three cables could be installed; and

approximately 8.5km of underground cables between a CSE compound south of the Mendip Hills and the proposed Sandford Substation within which the cable sealing ends for the underground cables would be sited. The cables would be installed in four trenches approximately 1.8m deep and 2m wide each containing up to three cables (see Volume 5.3.3, Figure 3.1.6 – 3.1.9).

Modifications to the Overhead Lines at Hinkley Point

3.3.6 To connect the proposed Hinkley Point C Power Station to the high voltage transmission network National Grid is proposing to construct a 400kV substation (Shurton Substation) within the boundary of the power station complex. This substation formed part of EDF Energy’s proposals, which were granted Development Consent in March 2013 and therefore does not form part of this Proposed Development. To connect the proposed Shurton Substation to the transmission network, two of the existing overhead lines which currently connect into Hinkley B Power Station will need to be diverted into the new Shurton Substation and a new overhead line interconnector constructed between the proposed Shurton Substation and the existing Hinkley B Substation (see Volume 5.3.3, Figure 3.1.20).

3.3.7 These works would include the construction of approximately 4.5km of new 400kV overhead lines and the removal of approximately 2.3km of existing overhead lines. It is proposed that the new overhead lines would utilise steel lattice pylons.

Construction of CSE Compounds

3.3.8 CSE compounds are required where overhead lines and underground cables connect to each other and typically include switchgear, support structures and perimeter security fencing.

3.3.9 Two single circuit CSE compounds of approximately 34m by 30m are proposed on Horsey Level, north of Bridgwater to achieve a crossing of electrical circuits where the new overhead line interfaces with the existing Hinkley to Bridgwater overhead line (see Volume 5.3.3, Figure 3.1.2).

3.3.10 A double circuit CSE compound of approximately 65m by 40m is proposed adjacent and east of the M5 motorway to the south of the Mendip Hills and the River Axe (see Volume 5.3.3, Figure 3.1.6). This compound provides the interface point between the overhead line proposed through the Somerset Levels and Moors and the underground cables proposed through the Mendip Hills which connect directly to Sandford Substation.

Construction of a 400/132kV Substation at Sandford

3.3.11 To maintain supplies on the 132kV distribution network following the removal of the existing 132kV overhead line, a new 400/132kV substation is proposed adjacent to Nye Road in Sandford, North Somerset (see Volume 5.3.3, Figure 3.1.9). The substation would be sited within a compound of approximately 143m by 217m and would include 400kV and 132kV electrical plant and equipment, super grid transformers (SGTs) and shunt reactors, electrical switchgear, perimeter fencing,

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access roads, landscaping and the cable sealing ends onto which the underground cables through the Mendip Hills would connect.

Extension of the Existing 400kV Substation at Seabank

3.3.12 To facilitate connection of the proposed 400kV overhead line onto Seabank Substation an extension to the existing substation building of approximately 24m and a minor extension to the substation perimeter fence are required together with the installation of electrical plant, equipment and switchgear (see Volume 5.3.3, Figure 3.1.19).

The Removal of Existing 132kV Overhead Lines

3.3.13 As part of the Proposed Development, over 65km of existing 132kV overhead lines would be removed. The overhead lines proposed for removal are as follows:

Approximately 53.2km of the existing overhead line (F and G Route) between Bridgwater and Avonmouth substations (see Volume 5.3.3, Figure 3.1).

Approximately 9km of the existing overhead line (W Route) between Nailsea and Portishead Substation (to be replaced with underground cables) (see Volume 5.3.3, Figure 3.1.14 – 3.1.16).

Approximately 1.5km of the existing overhead line (AT Route) to the south of Puxton (see Volume 5.3.3, Figure 3.1.9).

Approximately 550m of the existing overhead line (N Route) near Mead Lane, Sandford (see Volume 5.3.3, Figure 3.1.9).

A short section of the existing overhead line (BW Route) between Portishead and Avonmouth to achieve a crossing of electrical circuits (to be replaced with underground cables) (see Volume 5.3.3, Figure 3.1.16 – 3.1.17 and Figure 3.2).

Approximately 2.1km of existing overhead line (G Route) from the existing Avonmouth substation northwards (to be replaced with underground cables) (see Volume 5.3.3, Figure 3.1.18).

A short section of three existing 132kV overhead lines (G, DA and BW Routes) in the vicinity of Seabank Substation to achieve a crossing of electrical circuits (to be replaced with underground cables) (see Volume 5.3.3, Figure 3.1.19).

Construction of 132kV Overhead Lines

3.3.14 To maintain connections with the existing 132kV distribution network in North Somerset 132kV overhead line connections are required between the proposed Sandford Substation and the existing overhead lines feeding Weston-super-Mare (AT Route) (2.3km) and Churchill (N Route) (285m) and between Churchill Substation and an existing overhead line that currently bypasses the substation (264m) (see Volume 5.3.3, Figure 3.1.9).

Construction of 132kV Underground Cables

3.3.15 To facilitate construction of the proposed 400kV overhead line and to maintain connections with the existing 132kV distribution network a number of sections of 132kV underground cables are required. The underground cables proposed are as follows:


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A short section of approximately 220m of underground cable (Y Route) to connect Churchill Substation with an existing overhead line that currently passes by the substation (see Volume 5.3.3, Figure 3.1.10).

Approximately 600m of underground cables (AT Route) in the vicinity of the proposed Sandford substation (see Volume 5.3.3, Figure 3.1.9).

Approximately 10km of underground cables (W Route) between Nailsea and Portishead Substation (see Volume 5.3.3, Figures 3.1.14 – 3.1.16).

Approximately 2.3km of underground cables (G Route) between the existing Avonmouth substation and just south of the Bristol to Avonmouth railway line (see Volume 5.3.3, Figure 3.1.18).

A short section of approximately 170m for Option A (see Volume 5.3.3, Figure 3.1.17 and Figure 3.2) and 620m for Option B (see Volume 5.3.3, Figure 3.1.16 and Figure 3.2) of underground cable (BW Route) to allow the 400kV overhead line to cross an existing 132kV overhead line to the north east of Portishead.

Three short sections of underground cable (G, DA and BW Routes) of between 150m and 300m to allow the 400kV overhead line to cross three existing 132kV overhead lines in the vicinity of Seabank Substation (see Volume 5.3.3, Figure 3.1.19).

Extensions/Modifications to Existing 132kV Substations

3.3.16 As a result of changes to the 132kV distribution network, modifications are required to existing 132kV substations at Churchill, Portishead, Avonmouth and Seabank (see Volume 5.3.3, Figures 3.1.10, 3.1.16, 3.1.18 and 3.1.19). These works involve the installation of electrical plant, equipment and switchgear and are largely confined to within the existing substation compounds. In the case of Churchill and Seabank Substations, small substation extensions are also required to accommodate the electrical connections.

Associated works, for example, temporary access roads, highway works, temporary construction compounds, work sites and ancillary works

3.3.17 In addition to the above, a number of other works would be required during construction and operation of the Proposed Development. These include temporary masts and supports for overhead line construction, temporary and permanent access roads, modifications to the highway network and construction storage and working areas (see Volume 5.3.3, Figure 3.1).

3.3.18 The Proposed Development is summarised in Table 3.1 below stating the Sections in which each component of the Proposed Development occurs.

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Table 3.1 Proposed Development Components

Proposed Development Component Section(s)

400kV Overhead Line

Construction of a new 400kV overhead line of approximately 4.5km

from the existing Hinkley to Bridgwater 275kV overhead line on

Horsey Level (which would be uprated to 400kV operation) to the

existing Hinkley to Melksham 400kV overhead line north of

Woolavington.

Construction of a new 400kV overhead line of approximately

12.75km from the existing Hinkley to Melksham 400kV overhead

line north of Woolavington to a proposed CSE compound south of

the Mendip Hills and the River Axe.

A and B

400kV Overhead Line

Construction of a 400kV overhead line from the proposed Sandford Substation to Seabank Substation. In the Portishead/Portbury area two options are included within the DCO application: National Grid’s preferred route (Option A); and an alternative route (Option B). The total length of Option A is approximately 29.8km and 31.2km for Option B.

D, E, F and G

Modifications to the Overhead Lines at Hinkley Point

H

CSE Compounds

Two single circuit CSE compounds of approximately 34m by 30m are proposed on Horsey Level, north of Bridgwater. A double circuit CSE compound of approximately 65m by 40m is proposed adjacent and east of the M5 motorway to the south of the Mendip Hills and the River Axe.

A (Bridgwater Tee)

B (South of Mendip Hills)

400kV Underground Cables

These comprise approximately 300m of underground cables between two single circuit CSE compounds on Horsey Level, north of Bridgwater and approximately 8.5km of underground cables between a CSE compound south of the Mendip Hills and the proposed Sandford Substation.

A (Bridgwater Tee)

B, C and D (between CSE compound and Sandford Substation


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Removal of Existing 132kV Overhead Lines

Approximately 53.2km of the existing overhead line (F and G

Route) between Bridgwater and Avonmouth substations.

Approximately 9km of the existing overhead line (W Route)

between Nailsea and Portishead Substation (to be replaced

with 132kV underground cables).

Approximately 1.5km of the existing overhead line (AT Route)

to the south of Puxton.

Approximately 550m of the existing overhead line (N Route)

near Mead Lane, Sandford.

A short section of the existing overhead line (BW Route)

between Portishead and Avonmouth to achieve a crossing of

electrical circuits (to be replaced with 132kV underground

cables).

Approximately 2.1km of existing overhead line (G Route) from

the existing Avonmouth Substation northwards (to be replaced

with 132kV underground cables).

A short section of three existing 132kV overhead lines (G, DA

and BW Routes) in the vicinity of Seabank Substation to

achieve a crossing of electrical circuits (to be replaced with

132kV underground cables).

A, B, C, D, E, F and G (F and G Route)

D, E and F (W Route)

D (AT and N Route)

F and G (BW Routes)

G (G Route)

G (G, DA and BW Routes at Seabank)

Sandford Substation D

Construction of 132kV Overhead Lines

132kV overhead line connections are required between the proposed Sandford Substation and the existing overhead lines feeding Weston-super-Mare (AT Route) (2.3km) and Churchill (N Route) (285m) and between Churchill Substation and an existing overhead line that currently passes by the substation (264m).

D

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Construction of 132kV Underground Cables

A short section of approximately 220m of underground cable (Y

Route) to connect Churchill Substation with an existing

overhead line that currently passes by the substation.

Approximately 600m of underground cables (AT Route) in the

vicinity of the proposed Sandford substation.

Approximately 10km of underground cables (W Route)

between Nailsea and Portishead Substation.

Approximately 2.3km of underground cables (G Route)

between the existing Avonmouth substation and just south of

the Bristol to Avonmouth railway line.

A short section of approximately 170m for Option A and 620m

for Option B of underground cable (BW Route) to allow the

400kV overhead line to cross an existing 132kV overhead line

to the north east of Portishead.

Three short sections of underground cable (G, DA and BW

Routes) of between 150m and 300m to allow the 400kV

overhead line to cross three existing 132kV overhead lines in

the vicinity of Seabank Substation.

D (Y and AT Routes)

D, E and F (W Route)

F and G (BW Routes)

G (G Route)

G (G, DA and BW Routes at Seabank)

Seabank 400kV Substation Extension G

Extensions/Modifications to Existing 132kV Substations

Modifications are required to existing 132kV substations at Churchill, Portishead, Avonmouth and Seabank.

D (Churchill)

F (Portishead)

G (Avonmouth and Seabank)

Associated Works

These include temporary masts and supports for overhead line construction, temporary and permanent access roads, modifications to the highway network and construction storage and working areas.

A, B ,C, D, E, F, G and H

Construction of the Proposed Development

3.3.19 Construction of all components of the Proposed Development would commence with the preparation and installation of temporary access roads and working areas, where necessary improvements to the existing highway network would be undertaken to facilitate construction access and activities. Temporary contractor’s compounds, offices and welfare facilities would also be established along the proposed route to house the staff, equipment and materials for the works. Any topsoil and subsoil excavated would be stored separately along the working area in accordance with the Draft Construction Environmental Management Plan (CEMP) (see Volume 5.26.1) so that it can be put back once construction activities are complete. The construction compounds would take approximately four weeks to establish and would be in use for the same duration as the construction of the


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associated proposed Development component set out in Table 3.2. The following temporary construction compounds are proposed:

Table 3.2 Temporary Construction Compounds

Compound Name Local Authority Proposed Development Component

Anticipated Start Date

1: Bridgwater Tee (Bath Road)

Sedgemoor District Council Bridgwater Tee March 2016

2: A38 Bristol Road (underground cables)

Sedgemoor District Council 400kV underground cables

November 2015

3: A38 Bristol Road (overhead lines)

Sedgemoor District Council 400kV overhead lines January 2016

4: South of the Mendip Hills (Hams Lane)

Sedgemoor District Council 400kV underground cables

November 2015

5: Barton Road Sedgemoor District Council 400kV underground cables

December 2015

6: Castle Hill North Somerset Council 400kV underground cables

January 2016

7: Towerhead Road North Somerset Council 400kV underground cables

February 2016

8: Sandford Substation

North Somerset Council Sandford September 2016

9: AT Route North Somerset Council AT Route October 2017

10: Churchill North Somerset Council Churchill October 2016

11: Engine Lane North Somerset Council W Route underground cables

November 2015

12: Nailsea North Somerset Council W Route November 2015

13: Church lane North Somerset Council W Route November 2015

14: Clevedon Road North Somerset Council W Route underground cables

November 2015

15: Whitehouse Lane

North Somerset Council W Route underground cables

November 2015

16:Caswell Hill North Somerset Council W Route November 2015

17: Sheepway North Somerset Council W Route November 2015

18: BW Route (west) North Somerset Council BW Route November 2015

19: BW Route (east) North Somerset Council BW Route November 2015

20: St Andrews Road

Bristol City Council 400kV overhead lines March 2017

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Compound Name Local Authority Proposed Development Component

Anticipated Start Date

21: Kings Weston Lane

Bristol City Council G Route June 2017

22: G Route (east of M49)

Bristol City Council G Route underground cables

June 2017

23: Seabank (Severn Road)

Bristol City Council Seabank July 2017

3.3.20 For the 400kV overhead line, foundations would be installed and the pylon components delivered to site. The lattice pylon would be erected in sections, with a mobile crane used to lift the assembled sections into position. The T-pylon consists of approximately ten sections and would either be constructed on the ground and lifted by a crane in to position or by lifting each individual section in to place. The insulators would be fastened to the pylons in preparation for the installation of the conductors (wires). The conductors would be delivered to site on drums using HGVs and would be installed in sections between tension pylons using tensioning and pulling machines. Once the overhead line is constructed, the temporary access tracks and working areas at the pylon sites would be removed and the ground reinstated by removing stone and trackways.

3.3.21 For the 400kV underground cables, a working area approximately 100m wide would be created along the length of the underground cables and protected by post and wire fencing. Vegetation would be cleared and topsoil would be stripped from the areas of ground to be disturbed in the working area. Where required, drainage improvement works would be implemented to ensure the site of the cables installation is free from risk of flooding. Cable drums would be delivered to working areas using HGVs, with smaller vehicles such as tractors used to transport the drums and other materials along a temporary haul road. Up to three cables would be installed into four trenches approximately 1.8m deep and 2m wide. The required separation between each cable trench will vary depending on ground conditions, cable depth and cable manufacturer, but a typical cable easement once installed would be approximately 40m, apart from horizontal directional drilling (HDD) sites where it would be wider. Fibre optic cables would also be installed to ensure the connection could be periodically monitored. Above ground link boxes/ link box pillars would be required where individual cable sections are jointed. The joints between lengths of underground cables installed from the drums would be made on-site in controlled and clean conditions. Once the cables have been laid and the trenches backfilled, the temporary haul road and access tracks would be removed and soil replaced. Wherever possible hedgerows would be planted or replaced although trees cannot be planted on top of the cables.

3.3.22 For the substations and CSE compounds, topsoil would be removed and a clean and stable working platform established for the development. Construction of concrete foundations for some of the electrical equipment would be undertaken including installing troughs for the underground cables connections. A series of earth tapes or an earth grid would be installed below the ground to create an ‘earth mat’ to make the compound electrically safe. The substation support structures and electrical equipment and the CSE structures would then be erected. Prior to


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the substation or CSE compounds being brought into service, commissioning tests would be undertaken. Upon completion of the works, temporary site installation facilities and working areas would be removed and the soil replaced. For works at existing substations construction activities would be similar to those outlined above but on a smaller scale.

3.3.23 The construction process for 132kV steel lattice pylons would be similar to that outlined above for 400kV overhead lines. The 132kV wood pole overhead lines would not require cranes or stone pads for installation and the poles would be installed in a single operation and secured at the end of each activity avoiding the need for the working area to be fenced. The conductors would be delivered to site on drums using HGVs and would be installed in sections between tension poles using tensioning and pulling machines. Once the overhead line is constructed, the temporary access tracks and working areas would be removed and the ground reinstated by removing stone and trackways.

3.3.24 To facilitate the removal of the existing 132kV overhead lines, the area around each pylon would be cleared and where appropriate fenced. Fittings such as dampers and spacers would be removed from the conductors and the conductors would be cut into manageable lengths or winched on to drums in a reverse process to that used during installation. The pylons would either be dismantled by crane, with sections cut and lowered to the ground, or the legs of the pylon would be cut and it would be pulled to the ground using a tractor before being dismantled. Foundations would be removed to a depth of approximately 1m and subsoil and topsoil reinstated. In exceptional circumstances the entire foundation may be removed.

3.3.25 For the 132kV underground cables, a working area approximately 60m wide would be created along the length of the underground cables and protected by post and wire fencing. As with the 400kV underground cables vegetation would be cleared, topsoil would be stripped from the areas of ground to be disturbed and where required, drainage improvement works would be implemented to ensure the site of the cables installation is free from risk of flooding. Cable drums would be delivered to working areas using HGVs, with smaller vehicles such as tractors used to transport the drums and other materials along a temporary haul road. Up to tree cables would be installed into two trenches approximately 1.2m deep and 1m wide. The required separation between each cable trench will vary depending upon ground conditions, cable depth and cable manufacturer, but a typical cable easement once installed would be approximately 20m, apart from HDD sites where it would be wider. Fibre optic cables would also be installed to ensure the connection could be periodically monitored. Below ground link pits would also be required where individual sections of cable are jointed. The joints between lengths of underground cables installed from the drums would be made on-site in controlled and clean conditions. Once the cables have been laid and the trenches backfilled, the temporary haul road and access tracks would be removed and soil replaced. Wherever possible hedgerows would be planted or replaced although trees cannot be planted on top of the cables.

3.3.26 Should development consent be granted, National Grid intends to start construction in autumn 2015 and the construction should be complete by approximately autumn 2019. A preliminary construction programme is provided below and also at Volume 5.3.2, Appendix 3B.

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Table 3.3 Preliminary Construction Programme

Proposed Development Component Proposed Start Date

Proposed Finish Date

400kV Overhead Line 400kV Route Q1 2016 Q3 2019

400kV Cable Mendip Hills Route Q4 2015 Q3 2019

Bridgwater Tee 400kV Cable Route Q1 2016 Q4 2016

AT Route Underground and Overhead Line

Q4 2017 Q2 2018

W Route Q4 2015 Q3 2017

BW Route Avonmouth Option A Q4 2015 Q2 2017

BW Route Portishead Option B Q4 2015 Q2 2017

G Route 26/06/2017 Q2 2018

Seabank BW, G, DA Routes Q1 2016 Q2 2018

N Route Overhead Line Q4 2017 Q2 2018

Hinkley Line Entries Q1 2016 Q4 2018

Y Route Churchill Q4 2016 Q3 2017

W Route Churchill Q4 2016 Q3 2017

Sandford 400/132kV Substation Q3 2016 Q3 2018

Seabank 400/132kV Substation Q3 2017 Q3 2019

Churchill 132/33kV WPD Substation Q4 2015 Q3 2017

Portishead 132/33kV WPD Substation Q2 2017 Q3 2017

Avonmouth132/33kV WPD Substation Q4 2017 Q2 2018

Removal of Southern Half F Route Q3 2017 Q3 2018

Removal of Northern Half F Route Q3 2018 Q4 2019

Removal of 132kV G Route Q2 2018 Q4 2019

3.4 Pylon Details

Pylon Size

3.4.1 Details of the standard dimensions of 400kV and 132kV pylons are set out in Table 3.4 below. The heights stated are standard heights and widths; specific details of the size of individual pylons proposed are contained within the staking tables (see Volume 5.3.2, Appendix 3A) and the pylon profile drawings (see Volume 5.3.3, Figure 3.8). The staking tables provide information about the proposed pylons including pylon specification, type, geographical coordinates, height and pylon


24

number. The pylon number is shown on the Proposed Development Plans (Volume 5.3.3, Figure 3.1 and Figure 3.2).

Table 3.4 Standard Pylon Dimensions

Pylon Type Height Width

Steel Lattice 400kV 46.5m 18.2m

T-pylon (400kV) 35m 31m

PL 1 Lattice 132kV 24.2m 9.5m

PL 16 Lattice 132kV 26.4m 9.4m

Wood Pole (H Pole) 12.4m 3m between poles or 5.7m across steel frame

132kV Pylons to be Removed

3.4.2 A number of existing 132kV pylons are proposed to be removed as part of the Proposed Development. Details of the number of 132kV pylons proposed for removal are set out below.

Table 3.5 Pylons to be Removed

Route Number of Pylons Overhead Line Distance

Bridgwater to Portishead (F Route)

177 47.8km

Portishead to Avonmouth (G Route)

21 5.4km

Avonmouth to Pylon G32 (G Route)

7 2.1km

Pylon G42 to Seabank (G Route) 1 231m

Nailsea to Portishead (W Route) 34 9km

Weston Tee (AT Route) 3 1.5km

Pylon BW2 to Seabank (BW Route)

1 249m

Option B BW Route removal to Portishead Substation

3 620m

N Route Removal 1 550m

Pylon DA2 to Seabank 1 183m

TOTAL OPTION A 246 67km

TOTAL OPTION B 249 67.6km

*The figures specified only include the main areas of 132kV removal/undergrounding

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Pylons Proposed

3.4.3 A number of 400kV pylons are proposed to be installed as part of the Proposed Development. Details of the number of 400kV pylons proposed are set out below.

Table 3.6 Proposed 400kV Pylons

New Pylons (Excluding Replacements)

Overhead Line Distance

Bridgwater Tee to Huntspill 12 4.5km

Huntspill to CSE compound 36 (plus 2 gantries within the CSE compound)*

12.75km

Sandford Substation to Seabank Substation (Option A)

93 (plus 2 gantries within Sandford Substation)*

29.8km

Sandford Substation to Seabank Substation (Option B)

95 (plus 2 gantries within Sandford Substation)*

31.2km

Option A Total 141 47.1km

Option B Total 143 48.5km

*Gantries within the CSE compound and Sandford Substation are excluded from the total pylon numbers

3.4.4 A number of different 400kV and 132kV pylon types are proposed as part of the Proposed Development. They are set out in the staking tables described above (see also Volume 5.3.2, Appendix 3A); pylon profiles are also illustrated at Volume 5.3.3, Figure 3.8 and at Inset 3.2 below.


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Inset 3.2: Pylon Profiles (not to scale)


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Pylon Colour and Material

3.4.5 The colour and material of the proposed pylons would be as follows:

light grey composite frame with circular shape and light grey/light blue composite material insulators for a T-pylon; and

grey steel frame and light grey/light blue composite material insulators for lattice pylons.

3.5 Materials and Waste

3.5.1 This section provides an estimation of the materials and waste likely to be used for the Proposed Development and the procedures that would be put in place to manage and reduce waste.

3.5.2 National Grid has produced an Outline Waste Management Plan (WMP) (Volume 5.26.2). The Outline WMP presents a strategy and action plan for the management of waste which is likely to arise during the construction phase of the Proposed Development.

3.5.3 The objectives of the Outline WMP are:

minimise the volume of waste produced;

re-use any waste produced, where practicable;

recycle (recover) the waste, where reuse is not practicable; and

dispose of any remaining waste streams in accordance with legislative requirements.

3.5.4 Table 3.7 below describes the likely waste types and arisings of the Proposed Development.

Table 3.7 Forecast of Likely Waste Types and Arisings (see Table 4.1 of Volume 5.26.2)

Proposed Development Component

Waste Type Base Case Project (Tonnes)

Multiplier for HPCC (As per National Grid)

Estimated Volume (Tonnes)

400kV Underground Cables - Base Case Used: Ross Cables Project SWMP

Construction Metals

360 4 1440.00

Packaging

60.5 4 242.00

Concrete

100 4 400.00

Tiles and Ceramics

12 4 48.00

Timbers

150 4 600.00

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Soils and other Excavated Materials

46200 4 184800.00

Plastics 5 4 20.00

Oils 11 4 44.00

Other 305 4 1220.00

Subtotal

188814.00

400kV Overhead Lines - Base Case Used: Norton-Spennymoor Overhead Line Project SWMP

Construction Aluminium 750.00 3 2250.00

Glass 45.00 3 135.00

Iron and Steel 950.00 3 2850.00

Concrete 600.00 3 1800.00

Paper and Cardboard Packaging 7.50 3 22.50

Wood 25.00 3 75.00

Biodegradable Waste 250.00 3 750.00

Plastic 1.00 3 3.00

Concrete, Bricks Tiles and Ceramics Contaminated

340.00 3 1020.00

Soil and other Excavated Materials 500.00 3 1500.00

Absorbents Filter Materials - Spill Kits

0.70 3 2.10

Mixed Construction and Demolition Waste

200.00 3 600.00

Mixed Packaging 30.00 3 90.00

Portable Toilets 80.00 3 240.00

Tiles and Ceramics 300.00 3 900.00

Road Sweeper 20.00 3 60.00

Mixed Metals 100.00 3 300.00

Subtotal

12597.60

Removal of Overhead Line

Pylons

No. Pylons Pylon Weight (Tonnes)

Totals

F, W and G Route (132kV)

Steel (Pylons) 246* 6.276 1525

Conductors

km Conductor (12 per span)

Conductor Weight (Tonnes/km)

Totals

F and G Route Aluminium Alloy (AAC) 696 1.04 723.84

W Route Aluminium Alloy (AAC) 96 1.04 108.58


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Subtotal 832.42

*Based on preferred route Option A. Total would be 249 should alternative route Option B be selected.

Earthworks

3.5.5 As is shown in Table 3.7, the largest proportion of material/waste produced during the construction phase of the Proposed Development would be as a result of earthworks for the undergrounding of the 400kV underground cable route through the Mendip Hills and foundations of permanent structures such as pylons, CSE compounds and substations, and temporary structures such as access roads. Waste material from these excavations would include:

surface vegetation;

topsoil, subsoil and substrate materials such as sand, depending on local geology, and stones; and

made ground.

3.5.6 The majority of excavated material would be retained on-site for re-use as backfill and landscaping during the construction and operational phases. This material would not then be classified as ‘waste’.

3.5.7 Where any of this material is to be ‘discarded’, and therefore come under the definition of waste, it would largely be non-hazardous, inert waste. Any incompatible or hazardous wastes will be stored and handled in accordance with the Hazardous Waste Regulations 2005.

Removal of Existing 132kV Overhead lines

3.5.8 The second most significant proportion of the waste arisings would be as a result of the removal of existing 132kV overhead lines as follows:

the F Route between Bridgwater Substation and Portishead Substation;

the W Route between Nailsea and Portishead Substation; and

the G Route from Portishead Substation to Avonmouth.

3.5.9 Altogether, 246 (Option A at Section F and G) or 249 (Option B at Section F and G) 132kV steel lattice pylons, of the type PL16 would be removed. Constructed from steel, the pylons are 26m high and their cross arms 9.4m across, at the widest point.

3.5.10 Between each of the pylons are conductors made of all aluminium alloy (AAAC). The PL16 has three cross arms; double rows of conductors extend from the end of each cross arm. This means that each span (distance between pylons) consists of

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12 conductors. The approximate length of the F (and G) Routes to be removed is 57km; in the case of the W Route, a total of approximately 9km of conductors will be removed. The total length of conductor to be removed will be twelve times these distances.

3.5.11 In addition, six 400kV pylons would be removed in Section H.

3.5.12 Steelwork would be cut-up or dismantled on site and then removed to a facility for recycling.

General Waste

3.5.13 Waste produced by welfare facilities associated with the construction of the Proposed Development would be classified as municipal waste.

3.5.14 Other general wastes likely to be produced during the construction phase include:

aggregate; cement; concrete; cardboard; packaging waste; timber; and

scrap metal

3.5.15 The management of waste is described in the Outline Waste Management Plan (Volume 5.26.2). Waste would be managed using the principles of:

reduce;

re-use; recycle; recover; and

disposal.

3.6 Order Limits

3.6.1 The Order Limits, identified in the Proposed Development Plans (see Volume 5.3.3, Figure 3.1) as a red outline, are fixed and detail the anticipated maximum extent of land in which the Proposed Development may take place (if approved and subject to Development Consent Order Requirements and any other associated commitments). Further details regarding the Order Limits are provided in Volume 5.5.1, section 5.6.

3.7 Detailed Description of the Proposed Development

3.7.1 This section provides a detailed description of the Proposed Development building upon the summary provided at section 3.3 above.


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400kV Overhead Line

Description

3.7.2 The 400kV overhead line would comprise conductors supported by steel lattice pylons and T-pylons (see Volume 5.3.3, Figure 3.8). Two pylon designs are proposed for the 400kV overhead line as follows:

Sections A, B, D, E and F: T-pylon; and

Sections G and H: Lattice pylon.

3.7.3 The proposed transition point from the T-pylon to the lattice pylon in Section G would occur at a point south of the River Avon and north of the M5 and Easton-in-Gordano. The exact point of transition would depend on which of the two 400kV overhead line options were selected.

3.7.4 There are three variants of each pylon design (see Volume 5.3.3, Figure 3.8), to allow for different requirements along the route:

suspension pylons (which support the overhead line in a straight line);

tension pylons (which support the overhead line where it changes direction by up to 30 degrees); and

terminal pylons (which support the overhead line when it connects to substations or to underground cables via a CSE compound).

3.7.5 In addition, the flying angle structure is proposed for the T-pylon which would accommodate a change in direction up to ten degrees.

3.7.6 The typical height for a tension, terminal and suspension pylon is approximately 46.5m for a steel lattice pylon and approximately 35m for a T-pylon. Pylon heights can vary according to environmental and topographical conditions.

3.7.7 The typical base footprint of a steel lattice pylon is approximately 7m x 7m comprising the area enclosed by the pylon base consisting of steel work rising from four stub foundations. The base footprint of a T-pylon is approximately 2-2.3m in diameter and represents the area taken by the solid support of the pylon fixed to its foundation.

3.7.8 The typical span or interval between lattice or T-pylons is approximately 360m (the length of spans would vary depending on ground level, heights of pylons and angles).

3.7.9 The following parts of this chapter describe the proposed 400kV overhead line connection in each of the Sections together with a high level description of the key environmental features.

Section A: Puriton Ridge

3.7.10 Proposed overhead line works in Section A would consist of:

the removal of 24 existing 132kV lattice pylons;

the installation of eight 400kV T-pylons; and

the installation of two replacement lattice 400kV pylons.

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3.7.11 Section A extends approximately 2.8km from the Bridgwater 275/132kV substation to the east of Bridgwater near Dunwear in the south to Woolavington Road in the north. The landscape is a combination of flat open landscape of wet grassland, arable and wetland divided up by wet ditches or wide, deep ‘rhynes’, typical of the Somerset Levels and Moors Character Area. Puriton Ridge is part of the Polden Hills, contains numerous woodlands and forms a characteristic feature in views in this Section. The nearest villages are Knowle, Woolavington and Puriton. This Section is predominantly rural with Bridgwater, Puriton and Woolavington providing the closest concentrations of economic activity and tourism resources.

3.7.12 The proposed 400kV overhead line would commence at the existing Hinkley to Bridgwater 275kVi overhead line (VQ Route) at Horsey Level.

3.7.13 North of the 400kV connection point to the existing VQ line, there would be two CSE compounds each with a footprint of approximately 34m x 30m These would be single circuit compounds and are required to achieve a crossing of electrical circuits on the existing Hinkley to Bridgwater 275kV VQ overhead line. This would be achieved by undergrounding approximately 300m of 400kV underground cable between the two CSE compounds

3.7.14 To facilitate the construction of the CSE compounds and the crossing of the electrical circuits a temporary overhead line would be installed south of the existing Hinkley to Bridgwater 275kV VQ Route overhead line. A construction compound area (Bridgwater Tee/Bath Road Compound) would be constructed immediately east of the VQ Route (see Inset 3.3 below).

Inset 3.3: Proposed Construction Compound at Bath Road


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3.7.15 A typical construction compound area is shown at Inset 3.4 below and would typically be required to accommodate a laydown area for the temporary storage of plant

and materials, a number of welfare cabins and in some instances a small number of car

parking spaces. The temporary construction compounds would be constructed within the blue hatched area (the proposed construction compound at Barton Road is provided in Inset 3.3 above as an example); all typical construction compounds are shown at Volume 5.3.3, Figure 3.16 and are listed at Volume 5.3.2, Appendix 3B.

Inset 3.4: Typical Construction Compound Area

3.7.16 Access to the proposed construction compound, CSE compounds and pylons would be via a proposed bellmouth west of the A39 Bath Road and south of Crandon Bridge. The temporary construction haul road from the construction compound would run across the fields in a westerly direction and to serve the CSE compound working areas before turning north to access the proposed locations of pylons ZGA1 and ZGA2. A typical bellmouth arrangement (Type 1 – bio-directional

35

access and egress) is shown at Inset 3.5 below; all typical bellmouth arrangements (Type 1, Type 2 - uni-directional access and egress and Type 3 - crossovers) are shown at Volume 5.3.3, Figure 3.22; the Bellmouth Schedule is provided at Volume 5.3.2, Appendix 3E.

Inset 3.5: Typical Bellmouth Arrangement (Type 1)

3.7.17 Visibility splays would be required for proposed bellmouths to maintain highway safety. Visibility splays are shown on the Construction Plans (see Volume 5.3.3, Figure 5.3).

3.7.18 To the immediate south of the proposed CSE compounds there is a Grade II listed building, Horsey Manor Farm, the setting of which includes the Scheduled Monument (SM), Horsey Deserted Medieval Village (DMV).

3.7.19 The 400kV overhead line would run north, crossing the King’s Sedgemoor Drain close to the A39 Puriton Hill. King's Sedgemoor Drain is an artificial drainage channel which diverts the River Cary, west of Somerton, along the southern slopes of the Polden Hills, to discharge into the River Parrett at Dunball near Bridgwater. The channel, which was constructed between 1791 and 1795, is used to help drain the peat moors of King's Sedgemoor. A temporary construction haul road would be constructed alongside the channel to the south of the A39 accessed via the proposed bellmouth from the A39 Bath Road and providing access to proposed pylon ZGA3.

3.7.20 The 400kV overhead line would then traverse Puriton Ridge; this is the western most extent of the Polden Hills (part of the Mid Somerset Hills). On the ridge, there are a number of small settlements and woodlands. The overhead line would pass between gaps in woodlands and residential areas on the ridge, travelling northeast, passing approximately 150m to the east of the larger settlement of Puriton at its closest point.

3.7.21 Construction access to pylons ZGA4 – ZGA8 would be from Woolavington Road to the north and would comprise a temporary haul road.


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Section B: Somerset Levels and Moors South

3.7.22 Proposed overhead line works in Section B would consist of:


the installation of 40 proposed 400kV T-pylons;

the installation of two replacement 400kV lattice pylons; and

the installation of two 400kV pylons (a ‘goal post’) at the transition point from overhead line to underground cable at the proposed CSE compound south of the Mendip Hills.

3.7.23 Section B extends approximately 16km from Woolavington Road in the south to Webbington Road in the north, which forms the southern boundary of the Mendip Hills AONB. The Section comprises the Somerset Levels and Moors, surrounded by low hills and ridges characterised as the Mid Somerset Hills.

3.7.24 The 400kV Hinkley to Melksham overhead line (ZG Route) passes west to east through the southern part of the Section, north of the former Royal Ordnance Factory at Puriton (ROF Bridgwater) (the proposed site of the Puriton Energy Park). The 132kV F Route runs south to north across the Section passing through Mark, to the east of East Huntspill and west of the settlements of Tarnock and Biddisham. This 132kV overhead line would be removed as part of the proposal.

3.7.25 In this Section, the proposed 400kV overhead line would run north from Woolavington Road and cross Woolavington Level, passing to the east of the former ROF Bridgwater before connecting to the existing 400kV ZG Route. The 400kV ZG overhead line would be dismantled between this connection point and a point approximately 0.7km to the west where the proposed 400kV connection would continue in a northerly direction. The existing 132kV F Route, to be removed, passes between these two points.

3.7.26 To achieve the connections between the ZG and LD routes, two temporary 400kV overhead lines would be installed. The first due south of the existing ZG Route connection running east to west; the second would be installed via pylon ZGA13 running in a north westerly direction to a temporary pylon immediately south of proposed pylon LD2. Once the second temporary line is installed, the first would be removed to enable the completion of the connection activities between the LD and ZG routes. The second temporary line would then be removed.

3.7.27 Construction access for the works in the Woolavington area would be from three proposed bellmouths along the west of the B3141 Causeway and one bellmouth on Middle Moor Drove which connects to the B3141 Causeway from the east. The proposed 400kV overhead line (LD Route) north of the 400kV ZG Route would cross the Huntspill River, which is a National Nature Reserve (NNR) and Local Wildlife Site (LWS); it is an artificial river, built in 1940 to supply process water to ROF Bridgwater. The NNR is owned and managed by the Environment Agency.

3.7.28 The 400kV overhead line would continue in a northeasterly direction, across the B3139 towards and across Huntspill Moor, to the east of East Huntspill. The proposed 400kV connection would be further east at this point than the existing 132kV overhead line. It would continue travelling northeast, crossing the River Brue and then turn north passing the settlement of Mark through a gap in properties on

37

the Causeway between Wainbridge Farm and Court Farm. This is east of the existing 132kV overhead line (to be removed).

3.7.29 The proposed 400kV overhead line would oversail Ash Trees Farm House at Butt Lake Road south of Mark Causeway. National Grid has purchased this property and proposes to demolish it to enable the construction and operation of the Proposed Development. One of the existing outbuildings would be retained for the purpose of ecological mitigation (see Volume 5.8.1, section 8.7).

3.7.30 Construction access along this part of the route would be north and south of Merry Lane at Huntspill Moor. Construction access to pylons (LD4 – LD9) south of Merry Lane would be via the proposed bellmouth on the east of the B3141 Causeway and north of Woolavington Bridge. Access to pylons LD10 – LD31 north of Merry Lane would be from the Church Road via Factory Lane and an access south off the A38 at Rooks Bridge located further north in Section B. The pylon locations would be served through internal construction haul roads running along the proposed alignment through the fields, crossing a number of public highways by proposed bellmouths as detailed at Volume 5.3.3, Figure 3.22. The Bellmouth Schedule is provided at Volume 5.3.2, Appendix 3E.

3.7.31 There are a number of Grade II listed buildings in the village of Mark including, Wainbridge Farmhouse, Orchard Cottage, Wayside & Willow Dean, the Methodist Chapel and Vole House which is situated north of the village. This comprises the listed buildings in Section B that are close to the Proposed Development.

3.7.32 North of Mark, the 400kV overhead line would closely follow the line of the existing 132kV overhead line which would be removed, travelling further north, towards the Mendip Hills AONB. The 400kV connection would cross the A38 at Tarnock; construction access to the south of Rooks Bridge would be via the A38 as described above. Construction access to the north would be via an access off the A38 east of Tarnock Farm. This would provide access to the two construction compounds (A38 Bristol Road Compounds) proposed east and west of pylon LD33 and an internal construction haul road running north through the fields providing access to the pylons, CSE compound south of the Mendip Hills and the 400kV underground cable construction area.

3.7.33 Immediately north of Rooks Bridge, the 400kV overhead line would begin to run west of the F Route, taking it further away from the settlement at Biddisham. A CSE compound (the transition point between overhead line and underground cables) would be constructed immediately east of the M5 south of the Mendip Hills. The footprint of the proposed CSE compound is approximately 65m x 40m. A construction compound (South of the Mendip Hills/Hams Lane Compound) would be constructed immediately west of the proposed CSE compound; this would be used for the construction of the CSE compound and the 400kV underground cables.

3.7.34 From the CSE compound, the 400kV underground cables route would run northeast and would be routed under (or over via a bridge – see Volume 5.3.3, Figure 3.18 for further details) the River Axe and follows to the east of the M5, before entering the Mendip Hills AONB.

3.7.35 The 400kV connection route deviates from the F Route at East Huntspill and, for a stretch north to Mark, separate construction access points are proposed for the 132kV overhead line removal. These accesses would run from the B3139 (Church Road) in East Huntspill and Southwick road, Southwick.


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Section D: Somerset Levels and Moors North

3.7.36 Proposed overhead line works in Section D would consist of:



the installation of two 400kV pylons (a ‘goal post’) at the transition point from underground cable to overhead line at the proposed Sandford Substation;

the installation of seven 132kV lattice pylons, ten 132kV wood ‘H’ pole pylons;

the installation of one 132kV lattice cable sealing end platform pylon (CSEPP); and

the installation of two replacement 132kV lattice CSEPPs.

3.7.37 Section D extends for approximately 15km from the AONB boundary on the A368 to Clevedon Road (near Stone-Edge Batch). The landscape in this area is flat and open and divided by ditches and rhynes, many of which are designated as SSSIs. The nearest towns and villages to the 400kV connection in Section D are Congresbury, Yatton, Kingston Seymour, Nailsea and Tickenham. The whole of Section D is also in the area of the Forest of Avon Community Forest.

3.7.38 In this Section, the proposed 400kV underground cable connection would continue north from the Mendip Hills for approximately 1km before connecting directly into the proposed 400/132kV substation north of Sandford.

3.7.39 A construction compound (Towerhead Road Compound) would be constructed west of the underground cable crossing of the A368 at the beginning of Section D (Towerhead) and would be accessed via the bellmouth created at Towerhead Road.

3.7.40 Two construction compounds (Sandford Substation Compound and the AT Route Overhead Line Compound) would be constructed at Sandford substation both accessed via the A368 following the construction haul route as detailed on the Construction Plans (Volume 5.3.3, Figure 3.3 and Figure 3.4).

3.7.41 North of Sandford substation the proposed 400kV overhead line would follow the alignment of the existing 132kV F Route passing across Drove Way immediately west of the apple orchard at Droveway Bridge and then north, to the east of Nye Farm at which there is a possible medieval moated site (SM). Grade II Listed Buildings in this Section include: Hope Farmhouse, North End; Manor Farmhouse, Kennmoor Road; Stone-Edge Farmhouse, Clevedon Road and Wellhouse Farmhouse, Stone-edge Batch.

3.7.42 The route would continue directly north, to the east of Puxton Moor SSSI and the settlement of Puxton, across the Congresbury Yeo River and the westernmost section of Biddle Street SSSI at Yatton. Both SSSIs are designated for their rhynes and ditches. Construction access would be via two temporary haulage roads off the A370 Weston Road approximately 2km west of Congresbury, one travelling south accessing pylons LD51 and beyond, the other travelling north accessing pylons LD52 - LD54 crossing the Congresbury Yeo via a temporary bridge.

3.7.43 The route would continue north, crossing the Bristol to Weston rail line to the west of Yatton, following the existing 132kV F Route as it turns sharply to the east, north of Lampley Road between Kingston Seymour and North End. The proposed route

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deviates slightly from the 132kV F Route at this point, turning east closer to Lampley Road, at a less acute angle and then turning slightly east again prior to crossing Rush lane, north of North End, to return to following the existing F Route. Construction access would be from a proposed bellmouth on Kenn Road providing access to proposed pylons LD62 – LD55 running south through internal haul roads with crossings of the public highway at Lampley road and Weberham Lane via bellmouth crossings.

3.7.44 From Kenn Road, the 400kV route continues in a northeasterly direction towards Nailsea, crossing the Tickenham, Nailsea and Kenn Moor SSSI. As it passes to the west of Nailsea, the route deviates slightly from that of the existing F Route, travelling further to the west and more distant from the edge of the settlement.

3.7.45 Construction access would be from Kennmoor Road in the south of this part of the connection (pylons LD63 – LD71) and from Nailsea Wall (pylons LD72 - LD75) for part to the north. Access to pylons LD76 – LD78 located to the west of Nailsea would be from North Drove with access to the remaining pylons in Section D; and LD79 – LD81 accessed from Hanham Way which would also provide access for the undergrounding works of the 132kV W Route.

3.7.46 The proposed 400kV overhead line route would turn to the north as it passes the north of Nailsea and continues into Section E, at Stone-edge Batch, Tickenham.

Section E: Tickenham Ridge

3.7.47 Proposed overhead line works in Section E would consist of:

the removal of 27 existing 132kV lattice pylons; and

the installation of 12 proposed 400kV T-pylons.

3.7.48 Section E extends for approximately 4km from Clevedon Road (near Stone-edge Batch) in the south across the ridge to the M5 motorway. The Section is defined by the elevated wooded landform of Tickenham ridge. Its landscape is mainly woodlands (many of which are SNCIs and contain ancient woodland) and is higher than the surrounding countryside. It is characterised by limestone ridges and escarpments contrasting with low-lying shallow valleys. The nearest towns and villages to the connection are Clapton-in-Gordano and Portbury.

3.7.49 In this Section, the 400kV overhead line route keeps to the south of the existing F Route, continuing to run northeast. Prior to crossing Cadbury Camp Lane, the route turns to the north to pass between the woodlands of Chummock Wood (an SNCI) and Mogg’s Wood. At this point, the route deviates from the existing F Route, and continues northeast, crossing the ridge obliquely on Caswell Hill, with Priors Wood SNCI to its west. The route turns and heads north at Prior’s Wood where it then crosses the M5 motorway.

3.7.50 To facilitate construction of the 400kV overhead line in Section E (Tickenham Ridge), 9km of the W Route 132kV overhead line owned and operated by WPD would be removed from a point southwest of Nailsea (Section D) to Portishead substation.

3.7.51 Section E comprises a complex and varied historic landscape. In contrast to the Somerset Levels and Moors, the fields in this Section are not bordered by ditches. Aquatic habitats in the vicinity of the connection are limited to the watercourse that runs through the valley of Priors Wood and a few scattered ponds and ditches


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around the visitor attraction of Noah’s Ark Zoo Farm. Small areas of pre-18th century woodland are present in the centre and the north of the Section.

3.7.52 Batch Farm is the only Grade II listed building present in this Section and there are a number of non-designated heritage assets in the area including the site of a deserted medieval village east of Whitehouse Lane.

3.7.53 Construction access in this Section would comprise temporary construction haul roads accessed via bellmouths off the B3138 Clevedon Road. This would provide access to pylons LD81 – LD87, the 132kV W Route underground cable working corridor and the removal of the existing 132kV overhead lines of the F Route and W Routes. The works associated with the removal of the 132kV overhead lines would be largely confined in the works area for the proposed 400kV route and would use the same construction access routes.

3.7.54 Construction access to the remaining proposed 400kV pylons (LD88 – LD93) would be from a bellmouth constructed on the junction of Whitehouse Lane, Cadbury Camp Lane and Cuckoo Lane which would also provide access for the 132kV W Route removal and undergrounding.

3.7.55 Two construction compounds (Caswell Hill Compound and Caswell Hill Compound) are proposed immediately adjacent the proposed 400kV overhead line in the central and northern extents of Section E; these compounds would enable the construction of the W Route underground cable.

Section F: Portishead

3.7.56 For preferred route Option A, proposed overhead line works in Section F would consist of:

the removal of 25 existing 132kV lattice pylons; and

the installation of seven proposed 400kV T-pylons.

3.7.57 For alternative route Option B, proposed overhead line works in Section F would consist of:

the removal of 28 existing 132kV lattice pylons (F Route, the G Route and the W Route);

the installation of nine proposed 400kV T-pylons; and

the installation of one replacement 132kV lattice CSEPP.

3.7.58 Section F extends for approximately 2km north from the M5 motorway to the existing Portishead 132kV electricity substation and east to the Portbury Docks complex. It has a flat open estuarine and riverside landscape which has little woodland, although it is within the Forest of Avon Community Forest. The landscape is characterised by Clapton Moor and the Gordano Valley, which together present long distance views as far as Avonmouth. There are no designated or important undesignated historic buildings or structures in the Section. There are a number of designated wildlife sites, including the Severn Estuary SPA, SAC, SSSI and Ramsar site.

3.7.59 The town of Portishead lies to the west of the proposed connection and Sheepway and Portbury lie to the east. Other urban influences within and adjacent to this

41

Section include Portbury Wharf, and industry at The Royal Portbury Dock and Avonmouth Docks. The M5 motorway runs southwest-northeast along the southern boundary of this Section.

3.7.60 There are two potential routes for the proposed 400kV connection in this Section. These are described as the ‘preferred route (Option A)’ and the ‘alternative route (Option B)’.

3.7.61 From its crossing of the M5, Option A would run broadly parallel and to the north of the motorway, crossing the A369. The Portbury Hundred and following adjacent and parallel to the route of a disused railway before entering the Portbury Docks complex. It would pass through part of Portbury SNCI, remaining close to the motorway, and would cross the A369 at the cross roads with Station Road/Sheepway where there is a gap in the roadside woodland. A short traverse across fields to the east of Sheepway would bring the overhead line to the disused railway which forms the southern boundary of the Portbury Docks.

3.7.62 Construction access for the proposed works would be via two bellmouths which would access temporary haul roads off the A369 Portbury Hundred immediately north of the M5.

3.7.63 Option B would largely follow the alignment for the existing W Route 132kV overhead line (which would be removed from the south western extent of Nailsea to Portishead Substation and replaced by 132kV underground cables). The 400kV overhead line would run to the east of the present alignment of the W Route, crossing Sheepway at a point west of Sheepway Gate farm and continue north until it reaches the southernmost extent of the drain ‘Old Sea Bank’, which forms the western boundary of Portbury Wharf residential area. Here it would turn to the northeast and would be at its closest to Portbury Wharf approximately 250m to the east, before turning slightly east. The route continues northeast, passing to the southeast of Portishead substation, turns slightly east again and then sharply southeast to run parallel and to the north of the alignment of the existing G Route, crossing The Drove Rhyne (SNCI) into the Portbury Docks complex.

3.7.64 Construction access for Option B would be via temporary haulage roads from Caswell Lane in the south, Sheepway in the central area and The Drove to the east.

Section G: Avonmouth

3.7.65 For preferred route Option A, proposed overhead line works in Section G would consist of:


the installation of 30 proposed 400kV lattice pylons;

the installation of two ‘special’ lattice 400kV pylons (one on each bank of the River Avon);

the installation of one 132kV lattice CSEPP; and

the installation of five replacement 132kV CSEPPs.

3.7.66 For alternative route Option B, proposed overhead line works in Section G would consist of:


the installation of 25 proposed 400kV lattice pylons;


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the installation of two ‘special’ lattice 400kV pylons (one on each bank of the River Avon); and

the installation of four replacement 132kV CSEPPs.

3.7.67 Section G extends northeast from the Portbury Docks complex to Seabank substation. The landscape is flat, developed and includes Portbury and Avonmouth Docks, Avonmouth village, offices, and storage and distribution developments in the Severnside area. It lies in the Forest of Avon Community Forest, although there is little woodland in this Section. The M5 motorway runs along the eastern edge of this area, crossing the river Avon in the south of the Section. To the north, the M49 motorway runs through the area and connects the M5 to the Severn Bridge.

3.7.68 There are open long distance views across Avonmouth and Portbury Docks to the Severn Estuary, Severn Bridge and Welsh Hills beyond from the surrounding elevated landforms at Kings Weston Hill, Spaniorum Hill, Portishead and Tickenham Ridge. In Avonmouth, the landscape is flat with views limited by industrial buildings and dock structures. The village of Avonmouth lies immediately north of the River Avon in the centre of this Section, with the Bristol suburbs of Shirehampton and Lawrence Weston to the east of the proposed connection beyond the M5 and M49 motorways.

3.7.69 There are two Scheduled Monuments in Section G: a World War Two anti-aircraft battery beside Smoke Lane approximately 2km north of the proposed 400kV overhead line and Mere Bank, near Avonmouth Waste Water Treatment Works (WWTW), believed to be a medieval flood defence and directly crossed by the Proposed Development. The route crosses the Severn Estuary SPA, SAC, SSSI and Ramsar site at the River Avon and runs alongside the designation on the northwest shore of Avonmouth.

3.7.70 In this Section, the two possible routes described in Section F meet at a common point south of the Portbury coal stock yards. At this point the Proposed Route would deviate from the alignment of the existing G Route 132kV overhead line and run in a north easterly direction, crossing the River Avon before turning northwest and running to the north of Avonmouth Dock, passing the western edge of Avonmouth residential area. It would then turn north and pass across the Dock estate to the east of Royal Edward Dock. At the northern end of the Easter Arm of the docks, the Proposed Route would turn east, running parallel and to the north of Avonmouth Way. As it passes to the north of Avonmouth 132/33kV substation it would turn to the northeast, crossing Kings Weston Lane to follow to the north of the M49. It would continue to run alongside the M49, crossing Lawrence Weston Road Rhynes SNCI, and to the south east of Avonmouth waste water treatment works before it crosses the railway line at Moorhouse Lane. It would then turn to the north and northwest to connect into Seabank substation. North of the railway, the Proposed Route would cross Hallen Marsh Junction SNCI.

3.7.71 Construction access for the Proposed Route would be via local roads in the centre and east of the Avonmouth docks complex.

3.7.72 There are five construction compounds proposed in Section G, the first south of the River Avon is adjacent to proposed pylon LD105 and would be used for the BW

43

Route works (Option A). Moving north of the River Avon, the second compound (St Andrews Road) encompasses the area surrounding proposed pylon LD115 and would be used for the construction of the 400kV overhead line. The third and fourth compounds (Kings Weston Lane and East of the M49) would be used for the G Route works. The final compound would be east of Seabank Substation and would be used for the Seabank Substation line entries.

Section H: Hinkley Line Entries Modifications

3.7.73 ‘Line entries’ refer to how overhead lines approach and connect to substations on the high voltage transmission network. The landscape in this Section is generally flat, low-lying marshland and farmland and the built forms of the existing Hinkley Point A and B power stations are strong influences. The nearest villages to the proposed works are Wick, Stolford and Shurton.

3.7.74 The proposed 400kV substation called Shurton Substation would be constructed as part of the new Hinkley Point C Power Station. Existing overhead lines that currently connect to the existing Hinkley Point A and B power stations need to be moved to allow the new substation to be connected. It is also proposed to make a new, short connection from Shurton Substation to the existing Hinkley Point B 400kV substation.

3.7.75 To the south of the proposed Hinkley Point C Power Station the existing Hinkley to Bridgwater (VQ Route) and Hinkley to Taunton (ZZ Route) overhead lines would be diverted immediately to the northwest of Whitewick Lane approximately 500m east of Wick and travel in a north westerly direction for a short stretch before turning to the west, to cross Middle Moor Drove and then slightly north again, across Wick Moor Drove to connect with the proposed Shurton Substation.

3.7.76 These diversions would include the removal of six existing pylons and the construction of 13 new pylons. This overhead line would consist of three new pylons two of which would be within Wick Moor (part of the Bridgwater Bay SSSI and the Severn Estuary SPA and Ramsar site).

3.7.77 Construction access to the 400kV overhead line working areas would be from local roads. Access to the working area around Shurton substation would be via bellmouths situated on Wick Moor Drove which leads to Hinkley Point A and B Nuclear Power Stations. Access to the working area for the removal of the existing 400kV and 275kV overhead lines and new pylon working areas would be via an unnamed road opposite the properties of Sunshine Cottage and Zine Farm in Stolford. A number of the proposed access routes are those that will be in use for the construction of the Hinkley Point C Power Station. Further detail regarding shared access is provided in the Transport Assessment (Volume 5.22).

3.7.78 Within 250m of the proposed new overhead line between Hinkley Point B Substation and Shurton Substation, there is a Scheduled Monument ‘Pixies Mound’. It is a round cairn; a prehistoric funerary monument dating to the Bronze Age (c.2000-700 BC). The area around the Hinkley Point line entries section contains prehistoric, Roman and medieval settlements, as well as undated enclosures.

3.7.79 EDF Energy have made proposals for landscape restoration after construction of the Hinkley Point C Power Station which would likely include a Country Park and Nature Reserve south of the new power station site and west of proposed overhead line entries. Proposals comprise new broad-leaved woodland on the slopes of new


44

gently rolling hills. North of this woodland the character of the Holford valley and the prominence of Green Lane ridge in the north would be maintained.

Construction

3.7.80 Existing overhead line pylons will require permanent removal or replacement to facilitate the installation of the new overhead lines forming part of the Proposed Development. Upon removal much of the material would be taken for recycling.

3.7.81 Fittings, such as dampers and spacers, would be removed from the conductors. The conductors would be cut into manageable lengths or would be winched onto drums in a reverse process to that described for construction. Scaffolding would be used to protect areas of land as in construction. The fittings would be removed from the pylons and lowered to the ground.

3.7.82 Each pylon may be dismantled by crane, with sections cut and lowered to the ground for further dismantling and removal from site. Depending on the space available, it may be possible to cut the pylon at the base and then pull the pylon to the ground using a tractor. The pylon can then be cut into sections on the ground. Foundations would be removed to a depth of approximately 1m and subsoil and topsoil reinstated. In exceptional circumstances the entire foundation may be removed.

3.7.83 Construction activities would begin with the preparation and installation of temporary access roads to each pylon site some of which may require the culverting or bridging of watercourses. Details of crossings are provided on the Construction Plans (Volume 5.3.3, Figure 3.3 and Figure 3.4) which should be cross referenced to the Crossing Schedule provided at Volume 5.3.2, Appendix 3C. The types of crossing proposed are:

bridge;

box culvert;

circular culvert; and

porous fill.

3.7.84 Some temporary scaffolding would be installed during the works as a safety measure to protect roads, railways, Public Rights of Way (PRoWs) and distribution network overhead lines which would be crossed by the new 400kV overhead line. Some distribution network overhead lines which would be crossed by the new 400kV overhead line may be temporarily switched off or may be relocated or placed underground; scaffolding would not be needed in these cases. A photograph of a typical scaffolding area (road protection) is provided at Inset 3.6 below; scaffolding details are also provided on the Construction Plans (Volume 5.3.3, Figure 3.3).

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Inset 3.6: Photograph of Typical Scaffolding Area (Road Protection)

3.7.85 Existing field accesses from public highways may need to be widened to give access to construction vehicles, or temporary new accesses may be required. Temporary access tracks would be required to the site of each pylon and may be required to access possible scaffolding sites. For access on agricultural land, temporary tracks would be installed, using crushed stone (MOT Type 1 or similar) with a reinforcing geotextile membrane to protect soils. Temporary access roads would be approximately 4m wide and 300-500mm deep.

3.7.86 Temporary tracks would continue along the length of the overhead line as far as possible so that construction traffic can run on dedicated routes and avoid the public highway. Temporary stone pads would also be required adjacent to each new pylon location for plant such as cranes and piling rigs, which would be used to construct the pylons.

3.7.87 A typical pylon working area is shown at Volume 5.3.3, Figure 3.23, Figure 3.3 and Inset 3.7 below. An example of the proposed pylon working area is provided below for Pylon LD4 (see Inset 3.8) and is demarcated by the uniform green polygon surrounding the pylon. The size of the pad would depend on the size of the pylon base, and the type of foundation being installed but range from approximately 40m x 50m for a T-pylon, approximately 40m x 40m to 50m x 50m for a standard lattice pylon, approximately 70m x 70m for a 90 degree deviation steel lattice pylon, approximately 70m x 70m for the two special lattice pylons (one on each bank of the River Avon), and approximately 80 x 60m for the pylons at the entry point to the consented Shurton Substation.


46

Inset 3.7: Typical Pylon Working Area

Inset 3.8: Proposed Pylon Working Area at Pylon LD4

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3.7.88 The area around each pylon would be cleared and where appropriate fenced to keep the public and any livestock away from construction work. During the works gated entrances to the working areas would be installed to restrict access to construction vehicles and personnel only. Outside working hours the working areas would be locked and attended by a security guard.

3.7.89 The foundations of the lattice pylons would be piled or excavated. Pre-mixed concrete would be delivered to site in wagons along with steelwork for the foundation frames and bases. The foundation comprises steelwork encased in concrete with ‘stubs’ appearing through the concrete above ground to which the pylon legs are attached. For the T-pylon a mini-piled or tube-piled solution would be used depending on ground conditions. Details of pylon foundations are provided at Volume 5.3.3, Figure 3.24.

3.7.90 The steelwork for the pylons would be delivered to site in pre-constructed sections or in numbered parts and would be bolted together on the ground. The lattice pylon would be assembled in sections beginning with each leg being fastened to the stubs. The pylon would be erected using a mobile crane which would lift the assembled steelwork into position. Linesmen would bolt together the pylon, climbing to each part to help guide the next section into place and fasten the bolts. The number of pylon sections would vary according to the size of the pylon being built. The insulators would be fastened to the pylons in preparation for installing the conductors. Insulators are used to resist the flow of electricity. They prevent the electricity from the conductor reaching the pylon.

3.7.91 The T-pylon consists of approximately ten sections and could be completely constructed on the ground and lifted in one section, or could be constructed by adding individual sections working from the foundation flange. The main monopole sections can be connected via slip joint or internal bolted flanges. Linesmen would be required to install the bolts whether at ground level or height. Some pre-assembly can be achieved at the manufacturers.

3.7.92 The wires (conductors) of the overhead line would be delivered to site on drums using heavy goods vehicles (HGVs). Tractors and other smaller vehicles would be used to transport the drums and other materials along the temporary access roads. The conductors would be installed in sections between tension pylons where the line changes direction. A pulling site would be established at one end of the section with the conductors running out from a tensioning site at the other end of the section.

3.7.93 Pilot wires would be laid at ground level (and over temporary scaffolding protecting obstacles such as roads and railway lines) along the length of the section between the pulling site and the tension site. The pilot wires would be lifted and fed through running wheels on the cross arms of all the pylons in the middle of the section, and then fed around the pulling machine at the pulling site (referred to as Equipotential Zones (EPZ) as detailed on the Construction Plans (see Volume 5.3.3, Figure 3.3).

3.7.94 The tensioning machine would keep the wires off the ground and prevent the conductors running freely when the pulling machine pulls the pilot wire. In rare cases when it is not possible to run the pilot wires from ground level, helicopters may be used to pull them through. When the conductor is fully ‘run out’, it would be fastened at its finished tension and height above ground by linesmen working from platforms on the pylons and suspended from the conductors or in the case of T-


48

pylon from Mobile Elevated Work Platforms (MEWP). Additional fittings such as, spacers and dampers, would be fitted to the conductors. Spacers prevent the conductors from touching each other and dampers prevent oscillations in the overhead line.

3.7.95 Once the overhead line is constructed, the temporary access tracks and working areas at the pylon sites would be removed and the ground reinstated by removing stone and trackways. Soils would be restored to their previous condition. Other surfaces would be reinstated and bellmouths would be restored to their condition at the commencement of the works.

Maintenance

3.7.96 The overhead line would be subject to annual inspection from the ground or by helicopter. The inspection would identify if there are any visible faults or signs of wear and can also indicate if changes in plant or tree growth or development have occurred which may risk infringing safety clearances. Inspections would confirm when refurbishment is required.

3.7.97 The overhead line is made up of a variety of materials, from concrete, cast iron and steel for the foundations, steelwork for the pylon and aluminium alloys for the conductors. All these materials have an expected lifespan, which varies depending on how the overhead line is used and where it is located. Typically, pylons (T-pylon and lattice) have a life expectancy of approximately 80 years, the conductors have a life expectancy of 40 - 60 years and the insulators and fittings have a life span of approximately 25 years. The lifespan of a pylon may be longer than the anticipated 80 years, depending on its condition and refurbishments.

3.7.98 Refurbishment work would be undertaken typically on one side of the pylon and then the other, so that one side can be kept ‘live’ and in use.

3.7.99 Refurbishment can involve:

the replacement of all the conductors and earth wire;

the replacement of insulators and all the steelwork that holds the conductors and insulators in place; and

painting or replacing the pylon steelwork.

3.7.100 During refurbishment there would be activity along the overhead line, particularly at tension pylons where the new conductor is installed and the old conductor taken down.

3.7.101 Vans would be used to carry workers in and out of site and HGVs/trucks would be used to bring new materials and equipment to site and remove old equipment. Temporary works including access routes and scaffolding to protect roads would be required as for construction. For work to a T-pylon MEWPs would be also be required. The type i.e. tracked or normal would depend on the ground conditions, time of year and the nature of the works to be undertaken.

Decommissioning

3.7.102 If the connection is no longer required, the overhead line may be removed. Upon removal much of the material would be taken for recycling. Similar access would be required as outlined for construction.

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3.7.103 Fittings, such as dampers and spacers, would be removed from the conductors. The conductors would be cut into manageable lengths or would be winched onto drums in a reverse process to that described for construction. Scaffolding would be used to protect areas of land as in construction. The fittings would be removed from the pylons and lowered to the ground.

3.7.104 Each pylon may be dismantled by crane, with sections cut and lowered to the ground for further dismantling and removal from site. Depending on the space available, it may be possible to cut the pylon at the base and then pull the pylon to the ground using a tractor. The pylon can then be cut into sections on the ground. Foundations would be removed to a depth of approximately 1m and subsoil and topsoil reinstated. In exceptional circumstances the entire foundation may be removed.

400kV Underground Cables

Description

3.7.105 Proposed overhead line works in Section C would consist of the removal of 22 existing 132kV pylons (F Route). No new overhead line works are proposed in Section C.

3.7.106 The proposed 400kV underground cables would be installed via open trench unless alternative methods for crossings (horizontal directional drilling (HDD) or cable bridge) are stated in the 400kV and 132kV Cable Crossing Schedule (see Volume 5.3.2, Appendix 3F).

3.7.107 400kV underground cables are proposed to be installed between the two proposed CSE compounds (see Volume 5.3.3, Figure 3.17) in Section A near Bridgwater and through Section C (Mendip Hills) where they would commence at a CSE compound (Volume 5.3.3, Figure 3.15) to the south of the River Axe in the northern extent of Section B. From the CSE compound, the 400kV underground cables route would run northeast and be routed under or over the River Axe (HDD or cable bridge), follow to the east of the M5, HDD installation under the Old Lox Yeo before entering the Mendip Hills AONB.

3.7.108 Section C extends for approximately 6km from the southern boundary of the AONB on Webbington Road to the northern boundary of the AONB on the A368, west of Sandford. The existing 132kV F Route overhead line passes through the area on a south west to north east alignment (this line would be removed). The Section includes the western extent of the Mendip Hills AONB; a range of limestone hills which stretch eastwards from the Bristol Channel rising above the flat Somerset Levels and Moors.

3.7.109 In this Section, the 400kV underground cables would continue to travel for a short distance alongside the M5, and then enter the Mendip Hills AONB at Loxton Gap, at the foot of Crook Peak which is designated as a Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC). The cable crossing of Webbington Road is proposed by HDD or open cut. A cable construction compound is proposed to the east of the route at the foot of Crook Peak.

3.7.110 Construction access to the underground cable working area in the south of this Section would be via a bellmouth proposed to the east of Tarnock Farm on the A38 at Rooks Bridge (Section B). The temporary construction haul road for the underground cable construction would commence at the South of the Mendip Hills CSE compound.


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3.7.111 The cables would then extend through the low lying land in the valley of the Lox Yeo River, a LWS, broadly following the route of the existing 132kV overhead line but occasionally detouring to avoid woodland, development and environmental features. In this area the 400kV underground cables would travel in a north easterly direction, crossing the Lox Yeo River by HDD and the A371 Banwell Road (via HDD or open cut), to the north of the settlement of Winscombe. A cable route construction compound is proposed on an area of land west of Banwell Road, to the south of the cable route.

3.7.112 Southwest of Sandford, the cables would turn to the north, again following the route of the existing 132kV overhead line which would be removed. At this point, the cables would pass to the immediate east of Banwell Wood which is an SNCI and includes the Banwell Ochre Caves SSSI and Banwell Camp SM. The cables would be installed via HDD or open cut above or beneath the existing gas pipe east of Banwell Wood then cross the A368 Towerhead Road to the west of Mead Lane, Sandford, into the southern extent of Section D. The Towerhead Road cable crossing would be by open cut technique.

3.7.113 In Section D the proposed cables route continues north crossing Towerhead Brook and Mead Lane before connecting directly into the proposed 400/132kV substation north of Sandford.

3.7.114 The underground cables would be made of a copper core with cross linked polyethylene insulation. Two fibre optic cables would be laid with the electricity cables for monitoring and protection of system conditions

3.7.115 The cables would be laid in trenches. There would be up to 12 cables for the connection laid in four groups (four trenches) made up of three cables per group. There would be a gap of approximately 350mm between each of the three cables within the group, and a separation distance of approximately 3m between each of the groups. A typical cross section of an underground cable working area is shown at Volume 5.3.3, Figure 3.17. Depending on the cable manufacturer, joints in the cables would be required every 700m to 1km (a typical joint bay is illustrated at Volume 5.3.3, Figure 3.17.5). At each cable joint two above ground kiosks approximately 0.6m wide, 1m long and 1.5m high would be required, which would be used to monitor and occasionally test the underground cables.

Crossings

3.7.116 The construction of the underground cables and the associated haul/access roads (the latter for the entirety of the Proposed Development, not restricted to those associated with underground cables) would require the temporary and in some instances permanent crossings of various watercourses and utilities along the proposed route. Details of crossings are provided on the Construction Plans (Volume 5.3.3, Figure 3.3) which should be cross referenced to the Crossing Schedule provided at Volume 5.3.2, Appendix 3C, the Utilities Schedule provided at Volume 5.3.2, Appendix 3D and the 400kV and 132kV Cable Crossing Schedule provided at Volume 5.3.2, Appendix 3F. The types of crossing proposed are:

HDD;

bridge;

box culvert;

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circular culvert; and

porous fill.

3.7.117 Culvert construction details are provided at Volume 5.3.3, Figure 3.20.

3.7.118 Underground cables would have to be routed deeper and with greater separation between them when a trenchless technique is used for installation at a river crossing or other location. These crossings can be completed via HDD and would be used to avoid environmental constraints along the cables route. Volume 5.3.3, Figure 3.21.1 shows a typical 400kV HDD arrangement with reception and drive site.

3.7.119 Proposed HDD locations (and proposed alternative installation techniques) are shown on the Construction Plans (see Volume 5.3.3, Figure 3.3, in Table 3.8 below and at Volume 5.3.2, Appendix 3F.

Table 3.8 400kV Underground Cables - HDD and Other Installation Options

Reference Crossing Installation Option (bold indicates a preferred method)

400-HDD-01 River Axe HDD/Bridge

400-HDD-02 Old Lox Yeo HDD

400-HDD-03 Webbington Road HDD/Open Cut

400-HDD-04 Lox Yeo River HDD

400-HDD-05 Castle Hill HDD/Open Cut

400-HDD-06 Gas Pipe (south of Sandford) HDD/Open Cut

400-HDD-07 Towerhead Brook Bridge

3.7.120 If HDD is not practicable because of the depth required at a crossing then a cable bridge may be used (HDD or cable bridge is a proposed option at the River Axe) (see Inset 3.9 below).


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Inset 3.9: River Axe Cable Bridge Crossing Option

3.7.121 Construction access for the northern cables route into Sandford Substation would be from the proposed bellmouth at Towerhead Road. This road would be retained as a semi-permanent feature (to enable the delivery of the substation SGTs) and finished in grasscrete upon completion of the construction works. Subsequently, all crossings north of Towerhead Road would be permanent crossings including the Towerhead Brook crossing; the underground cables at Towerhead Brook would be installed in a cables bridge that would form part of the access road described above (see Volume 5.3.3, Figure 3.18). Inset 3.10 below shows the proposed cables bridge crossing at Towerhead Brook.

Inset 3.10: Towerhead Brook Cable Bridge Crossing

3.7.122 The temporary haul road as described runs along the length of the underground cables route with construction access provided at either end so that construction traffic can run on dedicated internal routes and avoid using multiple public highways. The Construction Plans detail the five public highway crossing points (via proposed bellmouths) required for the temporary construction haul road.

3.7.123 Temporary road bridges would be required at various points along the route of the Proposed Development. Their locations are provided on the Construction Plans (Volume 5.3.3, Figure 3.3) and the Crossings Schedule (Volume 5.3.2, Appendix 3C).

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3.7.124 The works associated with the removal of the 132kV overhead line would be confined within the works for the 400kV connection and would use the same construction access routes.

Construction

3.7.125 Similar to the construction of the overhead line, underground cables construction activities begin with the establishment and preparation of the working area and the installation of the temporary haul road adjacent the underground cable route and temporary access tracks to connect the haul road to the local road network. A temporary haul road would continue along the length of the underground cables so that construction traffic can run on dedicated routes and avoid public highways as far as possible.

3.7.126 Existing field accesses from public highways may need to be widened to accommodate construction vehicles or temporary new accesses may be required. For access on agricultural land temporary tracks of approximately 5m wide would be installed using crushed stone (MOT Type 1 or similar) and with a reinforcing geotextile membrane to protect soils.

3.7.127 Temporary contractor’s compounds and offices would be established at five locations (A38 Bristol Road; South of the Mendip Hills/Hams Lane; Barton Road, Castle Hill; and Towerhead Road) along the cables route to house the staff, equipment and materials for the works. The four locations proposed in the cable working areas as described above have been chosen due to their accessibility for HGVs, existing services and in some instances provide hard-standing to avoid or reduce the need to import material to set up the compound. Static and mobile security would be deployed to the work sites.

3.7.128 A working area approximately 100m wide would be created along the length of the underground cables route, protected by post and wire fencing. A typical 400kV underground cable construction swathe is presented at Volume 5.3.3, Figure 3.17 and Inset 3.11 below.


3.7.129 Constraints along the cables route may reduce the working width in places, for example where there are trees, important hedgerows or other features to be avoided. Vegetation would be cleared and topsoil would be stripped from the areas of ground to be disturbed in the working area. The excavated topsoil and subsoil would be stored separately along the working area in accordance with good practice so that it can be put back once the installation of the underground cables is complete. Drainage improvement works would be implemented to ensure the site of the cables installation is free from risk of flooding.

3.7.130 The underground cables trenches would be excavated up to approximately 1.8m deep and 2m wide. Timber panels would be used to reinforce the trench sides.


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3.7.131 The underground cables would be delivered to the working areas on drums using HGVs of approximately 38 tonnes capacity. Tractors and other smaller vehicles would be used to transport the cable drums and other materials along the temporary haul road. The underground cables would be pulled off the drums onto rollers in the trenches. Up to three cables would be laid in each of the trenches at a depth of approximately 1.1m on a bed of cement bound sand (CBS) and then surrounded by an additional layer of CBS, which would be delivered to site in concrete lorries. Fibre optic cables would be placed in the trenches with the cables to ensure the connection can be monitored from the above ground kiosks or link pits. Protective tiles would be laid above the CBS to protect the cables from future excavation works. Marker tape would be installed above the protective tiles in each trench as an additional warning that cables lie beneath.

3.7.132 The joints between lengths of underground cables installed from the drums would be made on-site in controlled and clean conditions. Underground cable jointing is labour intensive, very technically demanding and essential to the effective operation of the cables. The finished joints are protected by a glass fibre box filled with resin or bitumen which is buried in the cables trench.

3.7.133 Where trenchless techniques are used, the methods install ducts and the cables are pulled into the ducts. HDD would use a drilling machine which is placed in an excavated pit and has a drilling head which can be steered to control the depth and direction to emerge in a pit at the other end of the section to be drilled. The drill may undertake a number of passes to make the hole wider and would then pull ducts through. Thrust boring would use a hydraulic technique to push a pipe through the ground from an excavated pit to a receptor pit and then a duct would be installed through each hole created. A draw wire would be installed in each duct to be used to pull the cables through the ducts.

3.7.134 Once the cables have been laid and trenches backfilled, reinstatement work would begin. The temporary haul road and any temporary access tracks would be removed and the stored soil would be replaced, with any surplus soil (usually subsoil) taken off site. The post and wire fencing would be removed. Where possible, hedgerows would be replanted or replaced although trees cannot be planted on top of the cables. Where trees have been removed from the cables swathe and planting elsewhere has been agreed, this would be undertaken. Other surfaces would be reinstated and widened accesses would be restored to their condition at the commencement of the works. The land would be reinstated to its previous condition and uses wherever possible.

Maintenance

3.7.135 The underground cables have above ground kiosks at the joints to monitor the cables. Monitoring is carried out via fibre optic cables installed with the underground cables. If any cable repairs are required, the landowner and those with interest in the land would be contacted and National Grid would liaise regarding access routes and timing. The area where the fault has been identified would be accessed via temporary trackway or temporary access made up of crushed stone (MOT Type 1 or similar), a working area would be established and the ground would be excavated. If part of a cable needed to be replaced, the section of the cable (between two joints) would need to be removed and new joints constructed.

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3.7.136 Underground cables have a life expectancy of approximately 40-50 years. After 40-50 years the cables would require replacing, assuming the connection is still required. If there is space a new cable route would be constructed alongside the existing to avoid excavation and removal of the old cables. If the old cables need to be removed then a similar method would be followed as installation.

Decommissioning

3.7.137 If the connection is no longer required, the underground cables would be decommissioned. The cables would remain buried in the ground. In exceptional circumstances the cables may be removed.

3.7.138 If the underground cables were to be removed upon decommissioning, similar methods and access would be required as outlined for installation.

CSE Compounds

Description

3.7.139 A CSE compound provides the point of connection between overhead lines and underground cables. Three CSE compounds are required.

3.7.140 Proposed CSE compounds 1 and 2 (see Volume 5.3.3, Figure 3.14) are single circuit compounds in the vicinity of the Bridgwater Tee in Section A (Ordnance Survey Grid Reference 331940, 139657). These CSE compounds are required to allow a circuit of the Bridgewater – Hinkley 1 line to cross beneath the Bridgewater – Hinkley 2 overhead line by underground cables to create a future “Teed” circuit between Bridgewater – Melksham and Shurton.

3.7.141 The location of the proposed Bridgwater Tee CSE compound is shown at Inset 3.12 below.


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Inset 3.12: Location of the Proposed Bridgwater Tee CSE Compound

3.7.142 A plan of the proposed Bridgwater Tee CSE compound is shown at Inset 3.13 below.

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Inset 3.13: Plan of the Proposed Bridgwater Tee CSE Compound

3.7.143 Proposed CSE compound 3 (see Volume 5.3.3, Figure 3.15) is a double circuit compound south of the River Axe in Section B (OS Grid Reference 337306, 154519). It provides the interface point between the overhead line and proposed underground cables in Section C (Mendip Hills). North of Section C a separate CSE compound is not required at the transition between underground cables and overhead line as the cables would connect directly into the proposed 400/132kV substation north of Sandford.

3.7.144 The location of the proposed South of the Mendip Hills CSE compound is shown at Inset 3.14 below.


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Inset 3.14: Location of the Proposed South of the Mendip Hills CSE Compound

3.7.145 A plan of the proposed South of the Mendip Hills CSE compound is shown at Inset 3.15 below.

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Inset 3.15: Plan of the Proposed South of the Mendip Hills CSE Compound

3.7.146 The single circuit CSE compounds would each occupy a footprint of approximately 34m x 30m (see Volume 5.3.3, Figure 3.14); the double circuit CSE compound would occupy a footprint of approximately 65m x 40m (see Volume 5.3.3, Figure 3.15). Each CSE compound would comprise a terminal pylon with down-leads connecting to a gantry (approximately 13-14m high) which then connects to CSEs and other electrical equipment. Two gantries are proposed at the South of the Mendip Hills CSE compound. A small control room approximately 4m wide and 3m long may be required in each compound. The compound would be surrounded by a 2.4m high palisade fence to protect the equipment.

Construction

3.7.147 CSE compound construction activities would begin with the preparation and installation of the temporary access road to the CSE compound. A temporary construction compound of approximately 50m x 50m would be required adjacent to each site. A construction compound area (Bridgwater Tee/Bath Road Compound) would be constructed immediately east of the VQ Route to facilitate the construction of CSE compounds 1 and 2.

3.7.148 Construction access to CSE compounds 1 and 2 would be via a bellmouth entrance off the A39 Bath Road and from there along temporary haulage roads to be constructed across fields to the west. Construction access to CSE compound 3 would be via a temporary access route running north and west from a gap in properties on the A38 at Tarnock to the site of the new compound. The permanent


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access to CSE compound 3 for future maintenance would be via Hams Lane which runs south from the village of Loxton and over the M5 via a bridge.

3.7.149 The initial preparatory works would comprise stripping of topsoil and levelling each site to create a level platform for construction. Temporary perimeter fencing would be installed to secure the area. Construction of concrete or piled foundations for the terminal pylon and concrete foundations for some of the electrical equipment would be undertaken including installing troughs for cables. A stone pad for a mobile crane would be installed in the working area. A series of earth tapes would be installed below the ground to create an ‘earth mat’ to make the CSE compound electrically safe.

3.7.150 Once the troughs are completed the underground cables would be installed via the troughs onto the CSE structures. The CSE terminations, line gantries and other electrical equipment, such as earth switches, would be lowered onto their foundations and support structures by a mobile crane. A weather-proof cover would be fastened over a scaffold whilst the cables terminations are being installed. The electrical installation would be completed with connections of the overhead line to the underground electrical cables via down-leads. The permanent site boundary palisade fence would be completed.

3.7.151 The temporary site installation facilities would be removed and, where required, temporary working areas would be restored to their original condition. Soil stripped away for levelling may be used (where it is safe to re-use) to form bunds around the South of the Mendip Hills CSE compound where mitigation planting would be established. Security would be deployed to the CSE compound sites throughout the construction phase.

Maintenance

3.7.152 Infrequent visits would be made to the CSE compound to monitor the underground cables and carry out periodic maintenance and checks on the electrical equipment within the compound. When the CSE compound requires refurbishment or replacement works, vans would be used to carry workers in and out of site and trucks would be used to bring new materials and equipment to site and remove old equipment. Temporary scaffolding may be required to protect any infrastructure around the compound.

Decommissioning

3.7.153 The lifespan of a CSE compound is approximately 40 years. Relays used for protection and control housed in the control building typically would have a life of 15 years. When the CSE compound’s useful life has expired the materials would be removed and taken for recycling. Similar methods and equipment would be required for dismantling as outlined for construction. The cables would remain buried in the ground. In exceptional circumstances the cables may be removed.

400/132kV Sandford Substation

Description

3.7.154 The proposed substation is shown at Volume 5.3.3, Figure 3.1.19 and 3.9). A substation is the electrical interface point between the high voltage transmission

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network (owned and operated by National Grid) and the Distribution Network Operator (in this case WPD). Substations are a method of controlling power flows and voltages between the transmission system and distribution system. A transformer in a substation would change (or ‘transform’) voltage from one value to another value. Transformers generally reduce a voltage from a higher level to a lower level. The transformers in a 400/132kV substation are referred to as SGTs. Other components in the substation would include shunt reactors, switchgear, steel support structures, welfare accommodation, ancillary buildings, backup diesel generator, oily water interceptor and a low voltage electricity supply connection.

3.7.155 The proposed substation would contain two SGTs to reduce the voltage from the transmission system at 400kV to the 132kV required by WPD to allow onward distribution of the electricity to homes and businesses. The proposed substation would also contain two shunt reactors to stabilise the voltage on the connection.

3.7.156 The proposed substation would use 400kV Highly Integrated Switchgear (HIS) for outdoor use and 132kV air insulated switchgear (AIS). The 400kV equipment would be insulated by a gas called sulphur hexafluoride (SF6); the 132kV equipment would be insulated by the air. The maximum dimensions of the proposed substation would be 217m x 143m with a maximum height of electrical equipment of 13m.

3.7.157 The substation would comprise impermeable concrete surfaces, surrounded by areas of permeable stone chippings. It would be secured with a palisade fence approximately 2.4m high with an electrified fence approximately 4m high inside it. A permanent access road would be taken from Nye Road at the substation’s eastern boundary. A semi-permanent access road is proposed from Towerhead Road and would access the substation at the western boundary; the road would be finished in grasscrete and would enable the delivery of the SGTs. A permanent road and cables bridge crossing of Towerhead Brook would be required as part of this semi-permanent access road

3.7.158 The location of the proposed Sandford Substation is shown at Inset 3.16 below.


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Inset 3.16: Location of the Proposed Sandford Substation

3.7.159 A plan of the proposed Sandford Substation is shown at Inset 3.17 below.

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Inset 3.17: Plan of the Proposed Sandford Substation

Construction

3.7.160 A temporary construction compound would be established adjacent to the proposed substation to allow for the safe construction of the permanent operational substation high voltage compound. The area would be shared with the cables installation contractor to make best use of available land. The construction compound area generally would comprise temporary cabins for offices and for welfare facilities for construction site workers. There also would be allocated areas for receiving deliveries, for storage of materials and equipment and (where required) for storage of waste items to be removed.

3.7.161 The initial preparatory works would comprise the temporary removal and storage of topsoil and the installation of a temporary stone capping in the substation construction area to provide a clean and stable working platform. If possible, the permanent site boundary perimeter fencing would be completed early in the construction programme to secure the construction area. Electrification of the


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fence would take place as the substation is fitted out with lighting and power. Where required, excavations, piling and concrete foundations would be provided for the substation electrical equipment. An earth grid would be installed below the ground to create an ‘earth mat’ to make the compound electrically safe. The substation support structures and electrical equipment then would be erected.

3.7.162 Prior to the substation being brought into service, commissioning tests would be required, starting with testing the individual items of plant and culminating with testing the installed system as a whole. Following successful testing, the substation would be connected to the electricity transmission system.

Maintenance

3.7.163 The substation would be unmanned. Maintenance of the substation would be undertaken approximately every 3 years, involving electrical isolation of equipment before it is worked on. Visual checks would be undertaken on a monthly inspection visit to the site. If the substation requires refurbishment or replacement works, vehicles would be used to carry workers in and out of site and suitable vehicles would be used to bring new materials and equipment to site and remove old equipment.

Decommissioning

3.7.164 The lifespan of a substation is approximately 40 years. If its useful life has expired and it is to be removed, the equipment would be safely disconnected from the transmission system and carefully dismantled. Much of the material of the substation would be taken for recycling; the remainder would be disposed of in accordance with the WMP. Similar methods and equipment would be required for dismantling as for construction.

New 132kV Overhead Line and Underground Connections at Sandford and Churchill Substations

Description

The AT Route

3.7.165 The new 400/132kV Sandford Substation described above would supply the 132kV network in the vicinity after the removal of the F Route 132kV overhead line. To maintain supplies to the existing distribution network, a 132kV overhead line and 132kV underground cables would be required between the proposed substation and the existing 132kV overhead line (known as the ‘AT Route’) (see Volume 5.3.3, Figure 3.1.9). The connection would be installed in part by 132kV underground cables, approximately 700m, from Sandford substation to proposed pylon AT33 east of proposed pylon LD40. This would allow these 132kV circuits to cross underneath the northern section of the existing 132kV F Route overhead line as this could not be removed until the replacement connection and the proposed 400kV overhead line is in place. Approximately 1.5km of existing AT Route overhead line would be removed.

3.7.166 The overhead part of this connection would comprise approximately 2.3km of double circuit 132kV overhead line on steel lattice pylons approximately 26m high. Pylon heights would vary (depending on topography and degree of angle) with the

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maximum height not likely to exceed 29m. The typical span between these 132kV steel lattice pylons would be approximately 250m although the length of each span would vary depending on the route and the heights of each pylon.

3.7.167 The 132kV underground cables would commence at a 132kV CSEPP immediately east of proposed pylon LD40 and would head in a south easterly direction around the eastern boundaries of the proposed substation before entering the substation and connecting to equipment.

3.7.168 The proposed 132kV overhead line would start at the cable sealing end platform pylon (CSEPP) east of the proposed pylon LD40 would then continue in a westerly direction to a point northwest of Hardmead Rhyne. From this point the 132kV overhead line would run in a north westerly direction crossing Nye Drove (a small track and PROW), Rockers Rhyne and Havage Drove where it passes east of Box Bush Farm. The alignment finishes by turning west and connecting onto the existing AT Route overhead line via pylon AT25R.

3.7.169 Approximately 1.5km of the existing 132kV AT Route overhead line would be removed between the new AT connection point at pylon AT25R north of Box Bush Farm and the existing 132kV F Route overhead line to the east. The proposed AT Route is shown at Inset 3.18 below.


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Inset 3.18: The AT Route

The N Route

3.7.170 A 132kV connection approximately 285m long is also required between the proposed Sandford Substation and existing 132kV overhead lines (known as the ‘N Route’) (see Volume 5.3.3, Figure 3.1.19). This connection would be an overhead line using two lines of single circuit wood poles (ten in total) each comprising an H formation of two wood poles connected at the top with a steel lattice crossarm frame approximately 12.4m high. There would also be an underslung earthwire on each circuit. Approximately, 550m of the existing N Route 132kV overhead line would be removed between the new connection point at pylon N15R and the existing F Route connection currently north of Westleigh Farm; this would include the removal of 2 pylons. The proposed N Route is shown at Inset 3.19 below.

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Inset 3.19: The N Route

The W and Y Routes

3.7.171 A new single circuit connection would also be required between each of the existing W and Y Route 132kV overhead lines and the existing 132/33kV Churchill substation (see Volume 5.3.3, Figure 3.1.10). The connection to the W Route from Churchill Substation would comprise approximately 264m of new 132kV overhead line using existing steel lattice pylons. The connection to the Y Route would comprise approximately 220m of single circuit 132kV underground cables the transition between the existing Y Route overhead line and new underground cable would be made using a CSEPP at pylon Y1R. The proposed W and Y Routes at Churchill Substation are shown at Inset 3.20 below.


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Inset 3.20: The W and Y Routes at Churchill Substation

Construction

3.7.172 The H wood pole supports are likely to be installed using 4 wheel drive vehicles and plant such as tractors and trailers that do not need temporary access roads. However it has been assumed that these temporary tracks would be installed for all of the works. Construction activities would begin with the preparation and installation of temporary access roads to each pylon and pole site.

3.7.173 Construction access for the AT Route work would predominately be off Puxton Road; for the N Route work off Nye Road (major access point is A368 Towerhead Road); and for the W and Y Routes would be off the B3133 Stock Lane. Existing accesses from public highways may need to be widened to accommodate construction vehicles or temporary new accesses may be required. Temporary access tracks would be required to the site of each pylon and pole and may be required to possible scaffolding sites. For access on agricultural land temporary tracks would be installed, using crushed stone (MOT Type 1 or similar) with a reinforcing geotextile membrane to protect soils. Temporary access roads would

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be approximately 4m wide and 300mm-500mm deep. Temporary tracks would continue along the length of the overhead line as far as possible so that construction traffic can run on dedicated routes and avoid the public highway.

3.7.174 Temporary stone pads would also be required adjacent to each new pylon for the crane to lift the steelwork into place. The size of the pad would depend on the pylon design and the type of foundation being installed but would range from 20m x 10m to 25m x 15m. No cranes or stone pads are required for wood poles installation.

3.7.175 The area around each pylon would be cleared and where appropriate fenced to keep the public and any livestock away from construction work. During the works gated entrances would be installed to restrict access to construction vehicles and personnel only. Outside working hours the areas would be locked. Wood poles would be installed in a single operation and would be secure at the end of each activity avoiding the need for a working area to be fenced.

3.7.176 The pylons and wires (conductors) of the overhead line would be delivered to site using lorries with the conductors wrapped around the drums. Tractors and other smaller vehicles would be used to transport the drums and other materials along the temporary access roads. The conductors would be installed usually in sections between tension pylons and poles where the line changes direction. A pulling site would be established at one end of the section with the conductors running out from a tensioning site at the other end of the section.

3.7.177 Once the overhead line is constructed, the temporary access tracks and working areas would be removed and the ground reinstated by removing stone and trackways. Soils would be restored to their previous condition. Other surfaces would be reinstated and widened access would be restored to their condition at the commencement of the works.

3.7.178 A temporary construction compound would be constructed immediately east of proposed pylon AT33 to facilitate the AT Route installation works; the installation of the N Route would be undertaken using the Sandford Substation compound. A temporary construction compound east of Churchill Substation would be used during the W and Y Route installation works.

Maintenance

3.7.179 In general, distribution network overhead lines require very little maintenance. The overhead line would be subject to annual inspection from the ground. The overhead line would also be inspected from the air every 2 years. The inspection would identify if there are any visible faults or signs of wear and can also indicate if changes in plant or tree growth or development has occurred which may risk infringing safety clearances. Inspections would confirm when refurbishment is required.

3.7.180 The overhead line is made up of a variety of materials. Experience indicates that a new overhead line of this type would require refurbishment after 40 years.

3.7.181 Refurbishment can involve:

the replacement of all the conductors and earth wire;

the replacement of insulators and all the steelwork that holds the conductors and insulators in place; and

the replacement of pylon steel work or installing replacement wood poles.


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3.7.182 During refurbishment there would be activity along the overhead line, especially at tension pylons and poles where the conductor is installed and the old conductor taken down. Vans would be used to carry workers in and out of site and trucks would be used to bring new materials and equipment to site and remove old equipment. Temporary works including access routes and scaffolding to protect roads would be required as for construction.

3.7.183 The lifespan of the overhead line may be longer than the anticipated 80 years, depending on its condition, refurbishments and depending on the transmission network requirements.

Decommissioning

3.7.184 If the connection is no longer required, the overhead line and underground cable may be removed. Upon removal much of the material would be taken for recycling. Similar access would be required as outlined for construction.

3.7.185 Fittings, such as dampers and spacers, would be removed from the conductors. The conductors would be cut into manageable lengths or would be winched onto drums in a reverse process to that described for the stringing of conductors during the construction of pylons. The remaining fittings would be removed from the pylons and lowered to the ground.

3.7.186 The pylons may be dismantled by crane, with sections cut and lowered to the ground for further dismantling and removal. If there is space available, the legs of the pylons would be cut and the pylon pulled to the ground using a tractor before being dismantled. Foundations would be removed to a depth of approximately 1m and subsoil and topsoil reinstated. In exceptional circumstances the entire foundation may be removed.

3.7.187 The cables would remain buried in the ground. In exceptional circumstances the cables may be removed.

Modifications at Churchill 132/33kV Substation

Description

3.7.188 There is an existing 132/33kV substation at Churchill (OS Grid Reference 345170, 162225). The proposed modifications and extensions to the existing Churchill substation (see Volume 5.3.3, Figure 3.1.10 and Figure 3.11) are required to allow for the turn in of two circuits, one from the W Route which would consist of an overhead line and one from the Y Route which would consist of an underground cable. The boundary fence of the existing 132kV compound would be extended by approximately 12m to the north and 10m to the south to accommodate two new bays required to accommodate the W and Y circuits. A gantry is required for the W Route turn in (overhead line) and a CSE for the Y Route underground cable. There would be minor modifications to the busbar and protection equipment.

3.7.189 The location of the proposed modifications at Churchill Substation is shown at Inset 3.21 below.

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Inset 3.21: Location of Proposed Churchill Substation Modifications

3.7.190 A plan of the proposed modifications at Churchill Substation is shown at Inset 3.22 below.


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Inset 3.22: Plan of Proposed Churchill Substation Modifications

Construction

3.7.191 The modifications would be undertaken within the boundary (and extended boundary) of the existing compound which would allow safe access to the working areas. A temporary compound area (Churchill Compound) would be constructed adjacent to the existing substation that allows for the safe removal of the existing infrastructure and construction of the new electrical equipment. The compound area would comprise temporary cabins for offices and for welfare facilities for construction site workers. There would be parts of the compound allocated for receipt of deliveries, for storage of materials and equipment and for storage of waste to be removed.

3.7.192 The initial preparatory works would comprise the extension of the existing substation fence line and enabling works for the new equipment. Where required, excavations and concrete foundations would be provided for the substation

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electrical equipment. A below ground earth grid would be installed to ensure the compound is electrically safe.

3.7.193 Prior to bringing the new components of the substation into service, tests would be required. Following successful testing, the new components of the substation would be connected to the electricity distribution system.

Maintenance

3.7.194 The substation would remain unmanned. Maintenance of the new components in the substation would be undertaken approximately every 3 years as part of the regime of maintenance which is presently undertaken. Visual checks would be undertaken on a monthly inspection visit to the site. If the new components of the substation require refurbishment or replacement works, vehicles would be used to carry workers in and out of site and suitable vehicles would be used to bring new materials and equipment to site and remove old equipment as presently occurs at this substation.

Decommissioning

3.7.195 The lifespan of a substation is approximately 40 years. If the useful life of the new substation components has expired and they are to be removed, the equipment would be safely disconnected from the transmission system and carefully dismantled. Much of the material of the substation would be taken for recycling. Similar methods and equipment would be required for dismantling as for construction.

Removal of the Existing 132kV Overhead Line (F and G Routes and Sections of the AT, N, DA and BW Routes)

Description

3.7.196 The existing F Route 132kV overhead line runs in a broadly south to north direction between Bridgwater 275/132kV substation and Portishead 132/33kV substation (see Volume 5.3.3, Figure 3.1.1 – 3.1.16). It is supported by lattice steel pylons approximately 26m high. From Portishead Substation, the overhead line is called the G Route (see Volume 5.3.3, Figures 3.1.17 – 3.1.19) and then travels in an easterly direction through the Royal Portbury Docks before travelling north and crossing the River Avon supported on two pylons approximately 90m high. To the north of the River Avon the G Route oversails a number of residential properties and a school in Avonmouth Village before connecting into the existing 132/33kV Avonmouth substation.

3.7.197 The AT, N (see Volume 5.3.3, Figure 3.1.9), BW (see Volume 5.3.3, Figures 3.1.16, 3.1.17, 3.1.19 and 3.2), DA (see Volume 5.3.3, Figure 3.1.19), W (see Volume 5.3.3, Figure 3.1.14 – 3.1.16) and G Routes (see Volume 5.3.3, Figure 3.1.18 – 3.1.19) would also be removed in places. These existing overhead lines would be replaced with new overhead line and underground cable connections.

3.7.198 As part of the Proposed Development, the existing 132kV overhead lines (the F Route and the G Route) would be removed in their entirety (with the exception of the foundations which would be removed to a depth of approximately 1m). In exceptional circumstances the entire foundation may be removed.


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Removal

3.7.199 Removal activities would begin with the preparation and installation of temporary access roads to each existing pylon site. As detailed on the Construction Plans where possible and practicable, access to the F Route pylons would be from the construction accesses and haul roads used for the 400kV overhead line and underground cable development. Where this is not possible access locations have been detailed from the local highway network to facilitate the removal activities.

3.7.200 Existing accesses from public highways may need to be widened to accommodate construction vehicles or temporary new accesses may be required. Temporary access tracks would be required to the site of each existing pylon. For access on agricultural land temporary trackway may be laid or temporary tracks would be installed with a reinforcing semi-permeable membrane to protect soils.

3.7.201 A contractor’s compound and office would be shared with those established for the 400kV overhead line and underground cable works in the vicinity of the development to house the staff during the working day, as well as equipment and materials for the works. Where possible, sites have been chosen due to accessibility for HGVs, existing services and provision in some cases of hardstanding to avoid or reduce the need to create a level base for the compound. The import of material would be required to provide hardstanding if suitable material is not already there.

3.7.202 Scaffolding would be temporarily installed during the works as a safety measure to protect roads, railway, PRoW and other existing distribution network overhead lines which are crossed by the existing 132kV overhead lines.

3.7.203 The area around each pylon would be cleared and where appropriate fenced to keep the public and any livestock away from construction work. During the works gated entrances would be installed to restrict access to the working area to construction vehicles and personnel only. Outside working hours the working areas would be locked and attended by a security guard.

3.7.204 Fittings, such as dampers and spacers, would be removed from the conductors. The conductors would be cut into manageable lengths or would be winched onto drums in a reverse process to that described for the stringing of conductors during the construction of pylons. The remaining fittings would be removed from the pylons and lowered to the ground.

3.7.205 The pylons may be dismantled by crane, with sections cut and lowered to the ground for further dismantling and removal. If there is space available, the legs of the pylons would be cut and the pylon pulled to the ground using a tractor before being dismantled. Foundations would be removed to a depth of approximately 1m and subsoil and topsoil reinstated. In exceptional circumstances the entire foundation may be removed.

3.7.206 Once the overhead line is removed, the temporary access tracks and working areas at the pylon sites would be removed and ground reinstated by removing stone and trackways. Soils would be restored to their previous condition. Other surfaces would be reinstated and widened accesses would be restored to their condition at the commencement of the works.

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Maintenance and Decommissioning

3.7.207 As the 132kV overhead lines would be removed, no maintenance or decommissioning phases would be involved for this component of the Proposed Development.

Removal and Undergrounding of 132kV Overhead Lines

Description

The W Route

3.7.208 To facilitate construction of the 400kV overhead line in Section E (Tickenham Ridge), 9km of the W Route 132kV overhead line owned and operated by WPD would be removed (see Volume 5.3.3, Figures 3.1.14 – 3.1.16) from a point southwest of Nailsea to Portishead substation starting in Section D. These circuits are an essential part of the WPD distribution network in North Somerset and would be replaced by approximately 10km of 132kV underground cables. The 132kV underground cables would commence at a CSEPP (pylon W36R) to the southwest of the settlement of Nailsea in the northern extent of Section D (see Inset 3.23 below).

Inset 3.23: W Route Undergrounding from Pylon W36R


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3.7.209 The cables would be installed in an easterly direction from the CSEPP before heading north adjacent to Engine Lane, bordering the western extent of Nailsea. The 132kV underground cable circuits would then be split and installed in the road through the western extent of Nailsea. One circuit would continue north on Engine Lane prior to heading east on North Street. The other circuit would head east along Blackfriars Road before turning north on Hannah More Road and continuing north on Queens Road. The two circuits would meet at the junction of North Street and Queens Road then continue in a north westerly direction on Hanham Way. The cables then turn North off Hanham Way into fields prior to Parish Brook before continuing in a northerly direction climbing Tickenham Ridge. The cables head north easterly along Tickenham Ridge before descending the ridge, crossing the M5 motorway and continuing in a northerly direction to Portishead substation (in Section F). The 132kV underground cables would broadly follow the line of the existing 132kV W Route overhead line but deviate slightly east from it to avoid woodland, development and environmental features as far as possible, although the route does run through Portbury Nature Reserve and the SNCI. The route length would be approximately 10km.

3.7.210 There would be seven site compounds/construction laydown areas located along the proposed W Route. These would be located at:

Engine Lane;

Nailsea;

Church Lane;

Clevedon Road;

Whitehouse Lane;

Caswell Hill; and

Sheepway.

3.7.211 HDD is proposed as the only installation option for 5 crossing points for the W Route; HDD or open cut installation is proposed for a further four locations (see Table 3.9 below and Volume 5.3.2, Appendix 3F).

Table 3.9 W Route 132kV Underground Cables - HDD Installation Options


132-HDD-01 Multiple SSSI Ditches HDD

132-HDD-02 Land Yeo HDD

132-HDD-03 Clevedon Road HDD/Open Cut

132-HDD-04 Cadbury Camp Lane HDD

132-HDD-05 Whitehouse Lane HDD/Open Cut

132-HDD-06 M5 HDD/Open Cut

132-HDD-07 The Portbury Hundred HDD

132-HDD-08 Network Rail/Sheep Way HDD/Open Cut

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132-HDD-09 Portishead Substation HDD

The BW Route

3.7.212 To facilitate construction of the 400kV overhead line in Section F (Portishead), part of the BW 132kV overhead line owned and operated by WPD would be removed (see Volume 5.3.3, Figure 3.2). If the preferred route (Option A) was followed, approximately 580m of this line would be removed close to the River Avon; approximately 170m of this line would be installed underground. If the alternative route (Option B) was followed, approximately 600m of this line would be removed close to Portishead Substation; approximately 620m of this line would be installed underground. The BW Route circuits are an essential part of the WPD distribution network and would need to be replaced by 132kV underground cables. The 132kV underground cables would broadly follow the line of the existing 132kV BW Route overhead line in both cases.

3.7.213 A temporary construction compound would be constructed west of Sheepway Lane for the BW Route works (Option B only); the temporary compound for the Option A BW Route works would be constructed adjacent proposed pylon LD105.

The G Route

3.7.214 To facilitate construction of the 400kV overhead line in Section G (Avonmouth), approximately 2.1km of the G Route 132kV overhead line (see Volume 5.3.3, Figure 3.1.18) owned and operated by WPD would be removed between Avonmouth 132/33kV substation and the existing 132kV pylon G31 (on land immediately east of the M49 and south of the railway serving the Avonmouth industrial area). The G Route circuits are an essential part of the WPD distribution network and would need to be replaced by 132kV underground cables for approximately 2.3km. The 132kV underground cables although broadly following the direction of the existing 132kV G Route overhead line take a different route approximately 500m to the east and deviate from it to avoid, development and environmental features as far as possible. The cables would connect at a new CSEPP (G31R).

3.7.215 HDD or open cut is proposed at crossing 132-HDD-10; north of this crossing (between Kings Weston Lane and Lawrence Weston Road) there are three potential alignments proposed for the G Route due to constraints provided by existing infrastructure, namely the M49. These routes are as follows:

to the eastern extent of the Order Limits consisting of open cut installation beneath the M49;

east of centre of the Order Limits consisting of HDD or open cut installation (132-HDD-11) beneath the M49 and then open cut installation north of the M49; and

to the western extent of the Order Limits consisting of HDD installation beneath the M49 and then open cut installation north of the M49.


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3.7.216 Table 3.9 below and Volume 5.3.2, Appendix 3F provides details of the crossing options detailed above.

Table 3.10 G Route 132kV Underground Cables - HDD Installation Options


132-HDD-10 Kings Weston Lane HDD/Open Cut

132-HDD-11 M5/M49 Underpass HDD/Open Cut

132-HDD-12 M49 HDD

3.7.217 Two temporary construction compounds would be constructed to facilitate the G Route works; one at Kings Weston Lane and one east of the M49. Part of the proposed G Route undergrounding together with the two proposed compound areas is shown at Inset 3.24 below.

Inset 3.24: The G Route

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The G, DA and BW Routes

3.7.218 To facilitate construction of the 400kV overhead line in Section G (Avonmouth) at Seabank Substation, between approximately 150 and 300m of each of the G, DA and BW Routes 132kV overhead lines (see Volume 5.3.3, Figure 3.1.19) owned and operated by WPD would be removed west of Crook’s Marsh. Each of these circuits would need to be replaced by 132kV underground cables and a CSEPP. The 132kV underground cables would broadly follow the line of the respective existing overhead lines. Inset 3.25 below shows the proposed G, DA and BW Routes into Seabank Substation.

3.7.219 A temporary construction compound would be constructed at Seabank (Severn Road) to enable the G, DA and BW Route works at Seabank Substation.

Inset 3.25: The G, DA and BW Routes into Seabank Substation

General

3.7.220 The 132kV underground cables would be made of a copper core with cross linked polyethylene insulation.


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3.7.221 For a double circuit, the cables would be laid in two trenches. There would be up to 6 cables for the double circuit connection with three cables installed together in each trench. Depending on the cable manufacturer, joints in the cables would be required every 800m to 1.2km (W and G Route only). At each cable joint a surface accessible link pit would be required, which would be used to monitor and occasionally test the underground cables. A temporary access track would be required to access the link pit when maintenance and repairs are required.

3.7.222 Underground cables would have to be routed deeper and with greater separation where crossings are encountered which require a trenchless technique. These crossings can be completed by HDD. Volume 5.3.3, Figure 3.21.2 shows a typical 132kV HDD arrangement with reception and drive site.

3.7.223 This technique would be likely used to avoid environmental and other constraints along the cable route including: the Tickenham, Nailsea and Kenn Moors SSSI (number of ditches); the Land Yeo; Cadbury Camp Lane; and the Portbury Hundred (all W Route HDD). Other locations are proposed for either HDD or open cut; or HDD or bridge. All potential HDD locations are shown on the Construction Plans (see Volume 5.3.3, Figure 3.3 and Figure 3.4) and in the corresponding 400kV and 132kV Cable Crossing Schedule at Volume 5.3.2, Appendix 3F.

3.7.224 The transition between the existing overhead line and underground cable would be made using a CSEPP (see Volume 5.3.3, Figure 3.8).

Construction

3.7.225 Construction access for the W Route would for the most part be the same as for the 400kV connection; additional access points from Engine Lane, Hanham Way Clevedon Road Caswell Lane and Sheepway would be required.

3.7.226 Construction access for the BW Route close to Portishead Substation (Alternative Route Option B) would be taken from Sheepway; this is also the proposed access location for the laydown area for the W Route undergrounding where a compound would be established south of Sheepway between the disused railway lane and the Portbury Hundred. Construction accesses for the BW Route close to the River Avon (Proposed Route Option A) would be from an internal private road on the Portbury Dock accessed via Marsh lane. Construction accesses are the same as those used for the 400kV route in that area.

3.7.227 Construction access for the G Route would be taken from Avonmouth Way and Kings Weston Lane close to the M49 and also providing construction access for the 400kV route. Two laydown areas for the G Route works are proposed east of Kings Weston Lane and north of junction 18a of the M5. Construction access for the G, A and BW Route works close to Seabank Substation would be the same as those used for the 400kV route in that area (predominately via Ableton Lane and Severn Road).

3.7.228 Similar to the construction of the overhead line, underground cables construction activities begin with the establishment and preparation of the working area and the installation of the temporary haul road along the underground cable route and any temporary access tracks required to connect with the local road network. A temporary haul road would continue along the length of the underground cables as far as possible so that construction traffic can run on dedicated routes and avoid

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public highways. Post and wire fencing would be installed along both sides of the entire temporary haul road.

3.7.229 Existing accesses from public highways may need to be widened to accommodate construction vehicles or temporary new accesses may be required. For access on agricultural land temporary tracks of approximately 5m wide would be installed using crushed stone (MOT Type 1 or similar) and with a reinforcing geotextile membrane to protect soils.

3.7.230 Temporary contractor’s compounds and offices would be established to house the staff, equipment and materials for the works. Where possible, proposed compound sites have been chosen due to their accessibility for HGVs, existing services and where possible provide some hard-standing to avoid or reduce the need to import material to set up the compound. Both static and mobile security would be deployed to the work sites.

3.7.231 Where there are constraints such as woodland, groups of trees or built form along the route, the width of working area would be reduced. Within the working area vegetation would be cleared and topsoil would be stripped. The topsoil would be stored along the working area so that it can be put back once the installation of the underground cables is complete. Drainage improvement works would be implemented to ensure the site of the cables installation is free from risk of flooding.

3.7.232 The underground cables would be delivered to the working areas using lorries of approximately 38 tonnes with the cables wrapped around drums. Tractors and other smaller vehicles would be used to transport the cable drums and other materials along the temporary haul road. The underground cables would be pulled off the drums onto rollers within the trenches.

3.7.233 The underground cable trenches would be excavated up to approximately 1.2m deep and 1m wide. Timber panels would be used to reinforce the trench sides. Up to three cables would be laid in each of the trenches at a depth of approximately 1.1m on a bed of and surrounded by stone dust which would be delivered to site in lorries. Fibre optic cables would be placed in the trenches with the cables to ensure the connection can be monitored from the above ground kiosks. Above the cables, protective tiles would be laid to protect the cables from future excavation works. As an additional warning method, marker tape would be placed into each trench to warn that cables lay beneath.

3.7.234 A typical 132kV underground cable construction swathe is presented at Volume 5.3.3, Figure 3.17 and Inset 3.26 below.


3.7.235 The underground cable joints would be undertaken on-site in controlled and clean conditions. Underground cable jointing is labour intensive and very technically


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demanding but essential to the effective operation of the cables. The finished joints are protected by a glass fibre box filled with resin or bitumen.

3.7.236 At the sections where HDD would be undertaken, the cables would be pulled through ducts that have been installed. Cable pulling rigs would be required to pull the cables through ducts.

3.7.237 Once the cables have been laid, reinstatement work would begin. The temporary haul road and any temporary access tracks are removed and the stored soil is replaced, with any surplus soil taken off site. The post and wire fencing would then be removed. Where possible, hedgerows would be replanted or replaced although trees cannot be planted on top of the cables. Where trees have been removed from the cables swathe and planting elsewhere has been agreed, this would be undertaken. Other surfaces would be reinstated and widened accesses would be restored to their condition at the commencement of the works. The land would be reinstated to its previous condition and uses wherever possible.

Maintenance

3.7.238 The underground cables have above ground kiosks at the joints to monitor the cables. Monitoring is carried out via fibre optic cables installed with the underground cables. If any cable repairs are required, the area where the fault is would be accessed via temporary trackway or temporary access made up of crushed stone (MOT Type 1 or similar), a working area established and the ground excavated.

3.7.239 As with 400kV underground cables, 132kV underground cables have a life expectancy of approximately 40-50 years. After 40-50 years the cables may require replacing, assuming the connection is still required. If there is space a new cable route would be constructed alongside the existing to avoid excavation and removal of the old cables. If the old cables need to be removed then a similar method would be followed as installation.

Decommissioning

3.7.240 If the connection is no longer required, the underground cables would be decommissioned. The cables would remain buried in the ground. In exceptional circumstances the cables may be removed.

3.7.241 If the underground cables were to be removed upon decommissioning, similar methods and access would be required as outlined for installation.

Modifications at Portishead 132/33kV Substation

Description

3.7.242 There is an existing 132/33kV substation at Portishead (OS Grid Reference 348390, 176930.). The proposed modifications to the existing Portishead substation (see Volume 5.3.3, Figure 3.1.16 and Figure 3.13) would be required to allow for access to underground the W Route. A new CSE would be installed to terminate the new cable entry of the W Route and another CSE to terminate the undergrounding of the BW Route (Option B). These works would also require the removal of the existing W Route pylon located in the centre of the compound.

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3.7.243 A plan of the proposed modifications at Portishead Substation is shown at Inset 3.27 below.

Inset 3.27: Portishead Substation Plan

Construction

3.7.244 A temporary compound area would be constructed adjacent to or within the existing substation to allow for the safe removal of the existing infrastructure and installation of the proposed electrical components. The compound area would comprise temporary cabins for offices and for welfare facilities for construction site workers. There would be parts of the compound allocated for receipt of deliveries, for storage of materials and equipment and for storage of waste.

3.7.245 The initial preparatory works would comprise enabling works for the new equipment and safe removal of the existing tower and lines. Where required, excavations and concrete foundations would be provided for the substation electrical equipment.

3.7.246 Prior to bringing the new components of the substation into service, tests would be required. Following successful testing, the new components of the substation would be connected to the electricity transmission system.

Maintenance

3.7.247 The substation would remain unmanned. Maintenance of the new components in the substation would be undertaken approximately every 3 years as part of the regime of maintenance which is presently undertaken. Visual checks would be


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undertaken on a monthly inspection visit to the site. If the new components of the substation require refurbishment or replacement works, vehicles would be used to carry workers in and out of site and suitable vehicles would be used to bring new materials and equipment to site and remove old equipment as presently occurs at this substation.

Decommissioning


Modifications at Avonmouth 132/33kV Substation

Description

3.7.249 There is an existing 132/33kV substation at Avonmouth (OS Grid Reference 352860, 178370). The proposed modifications to the existing Avonmouth substation (see Volume 5.3.3, Figure 3.1.18 and Figure 3.12) are required to facilitate the removal and undergrounding of the G Route overhead line between the substation and existing pylon G31. This involves the removal of Towers G24 and G23A which are at the southern extent of the substation compound and the construction of a CSE for the termination of the G Route underground cable. The works also include the removal of additional electrical equipment including busbar. A plan of the proposed modifications at Avonmouth Substation is shown at Inset 3.28 below.

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Inset 3.28: Avonmouth Substation Plan

Construction

3.7.250 A temporary compound area would be constructed either immediately adjacent or within the existing substation to allow for the safe removal of the existing infrastructure and construction of the proposed components. The compound area would comprise temporary cabins for offices and for welfare facilities for construction site workers. There would be parts of the compound allocated for receipt of deliveries, for storage of materials and equipment and for storage of waste to be removed.


Maintenance



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Decommissioning


Extension of 400kV Seabank Substation and Modifications to 132kV Seabank Substation

Description

3.7.254 There is currently a 400kV Gas Insulated Switchgear (GIS) Substation at Seabank (OS Grid Reference 353640, 182233). The proposed extension to the existing 400kV Seabank Substation (see Volume 5.3.3, Figure 3.1.19 and Figure 3.10) would comprise extending the steel framed switchgear building and annex, electrical switchgear, Gas Insulated Busbar (GIB), steel support structures and ancillary buildings. A 400/132kV SGT would be removed to enable the works.

3.7.255 The proposed substation would use indoor and outdoor 400kV GIS and Air Insulated Switchgear (AIS). The GIS substation equipment would be insulated using sulphur hexafluoride (SF6). The building would be extended by approximately 24m. The operational compound boundary also would be extended on the eastern side by 10m x 20m (200m2) and in the south eastern corner by 15m x 20m (300m2). The maximum height of the outdoor electrical equipment would be 13m.

3.7.256 The majority of the substation would be surfaced with permeable stone chippings; impermeable concrete surfaces would be used for foundations and access. The extended parts of the substation compound would be secured with an electrified palisade fence approximately 4m high to match the existing fencing and the extended substation would continue to use the existing access road from the public highway through the Seabank Power Station.

3.7.257 At the southern extent of the 132kV substation compound, modifications in the form of new CSEs would be required to facilitate the underground connection of the G, BW and DA Routes into the 132kV Seabank Substation.

3.7.258 A perimeter flood defence wall with flood gates is proposed around the 400kV substation to mitigate tidal flood risk. The minimum proposed defence level of 8.05mAOD is 400mm above the 1 in 1000 (0.1%) annual probability event level of 7.65mAOD at the end of the design life, taking account of sea level rise associated with climate change.

3.7.259 A plan of the proposed modifications at Seabank Substation is shown at Inset 3.29 below.

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Inset 3.29: Seabank Substation Plan

Construction

3.7.260 A temporary construction compound area would be constructed adjacent to the existing substation that allows for the safe construction of the permanent operational substation high voltage compound. The construction compound area would comprise temporary cabins for offices and for welfare facilities for construction site workers. There would be parts of the compound allocated for receipt of deliveries, for storage of materials and equipment and for storage of waste to be removed.

3.7.261 The initial preparatory works would comprise the extension of the substation fence line and enabling works for the new equipment. Where required, excavations, piling and concrete foundations would be provided for the substation electrical equipment. A below ground earth grid would be extended from the existing


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compound to ensure the compound is electrically safe. The new substation support structures and electrical equipment then would be erected.


Maintenance


Decommissioning

3.7.264 The lifespan of a substation is approximately 40 years. If the useful life of the new substation components has expired and they are to be removed, the equipment would be safely disconnected from the transmission system and carefully dismantled. Much of the material of the substation would be taken for recycling. Similar methods and equipment would be required as for construction.

Indicative Access for Future Maintenance

3.7.265 National Grid would require infrequent access to ensure the Proposed Development could be appropriately maintained. The access would typically be made by foot, 4x4 or tractor and trailer and would not typically require any new temporary accesses; however access to tension pylons may require temporary stone roads or aluminium trackway to be laid. Upon completion of any maintenance works, surfaces would be restored to their previous condition. The indicative accesses for future maintenance are shown at Volume 5.3.3, Figure 3.5 – 3.6.

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i This connection is being uprated to 400kV. The line has consent to operate at this voltage. Existing pylons would remain in place.

5.3 - national infrastructure planning · figure 3.13: portishead 132/33kv substation figure 3.14:...

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