gabbards

Transcription

gabbards

DOCUMENT NO:
577000/403 – MGT100 – GGR – 107
DOCUMENT TITLE:
DECOMMISSIONING PROGRAMME
GREATER GABBARD OFFSHORE
WIND FARM PROJECT
Fluor Project No. 577000
Airtricity Project No. 403
CONTROLLED COPY NO: ______
1
31/08/07
0
REV
58
01/06/07 53
DATE
PAGES
Issued for
Secretary of
State Sign off
CJH CH
GM
JCH
Issued for
Approval
CJH CH
GM
JCH
APPR
APPR
FLUOR
AIRTRICITY
DESCRIPTION
BY
CHKD
Greater Gabbard Offshore Winds Limited
Greater Gabbard Offshore Wind Farm Project Fluor Project No. 66577000 Airtricity Project No. 403 Decommissioning Programme
Table of Contents
1.0
INTRODUCTION..............................................................................................................4
2.0
EXECUTIVE SUMMARY ...............................................................................................4
3.0
BACKGROUND INFORMATION .................................................................................7
3.1
Project Status ...........................................................................................................7
3.2
Project Overview .....................................................................................................7
3.3
Layout of Wind Farm and Ancillary Works ..........................................................10 3.4
Site Characteristics.................................................................................................11
3.4.1 Physical Characteristics .............................................................................11 3.5
Relevant Projects and Activities ............................................................................18 3.5.1 Offshore Wind Farms ................................................................................18
3.5.2 Marine Aggregate Extraction.....................................................................20 3.5.3 Disposal of Dredged Material....................................................................21 3.5.4 Subsea Cables ............................................................................................22
3.5.5 Oil and Gas ................................................................................................23 3.5.6 Fishing Activity .........................................................................................24
3.5.7 Shipping Activity .......................................................................................25
3.6
4.0
5.0
Nature Conservation ..............................................................................................26
DESCRIPTION OF ITEMS TO BE DECOMMISSIONED .......................................29
4.1
Guiding Principles .................................................................................................29
4.2
Proposed Decommissioning...................................................................................31
4.2.1 Offshore Wind Turbines ............................................................................32
4.2.2 Turbine Foundations & Transition Pieces .................................................35 4.2.3 Transformer Platforms ...............................................................................39
4.2.4 Anemometry Masts....................................................................................41
4.2.5 Cabling.......................................................................................................43
4.2.6 Scour Protection.........................................................................................46
DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES ..................48
5.1
Wind Turbines/Generating Equipment ..................................................................48 5.2
Foundations............................................................................................................49
Page 2 of 58
Greater Gabbard Offshore Wind Farm Project Fluor Project No. 66577000 Airtricity Project No. 403 Decommissioning Programme
5.3
T
ransformer Platforms ...........................................................................................50
5.4
Anemometry Masts................................................................................................50
5.5
Cables.....................................................................................................................50 5.6
S
cour Protection.....................................................................................................50
5.7
Waste Management................................................................................................50
5.8 Lighting and Marking ............................................................................................51 6.0
RE-POWERING ..............................................................................................................52
7.0
ENVIRONMENTAL IMPACT ASSESSMENT ..........................................................52
8.0
CONSULTATIONS WITH INTERESTED PARTIES ...............................................53
9.0
SCHEDULE AND THE REVIEW PROCESS .............................................................54
10.0
SEA-BED CLEARANCE................................................................................................55
11.0
RESTORATION OF THE SITE....................................................................................56
12.0
POST-DECOMMISSIONING MONITORING, MAINTENANCE AND MANAGEMENT OF THE SITE ...................................................................................56
13.0
SUPPORTING STUDIES ...............................................................................................57
14.0
ANNEX A: GREATER GABBARD ENVIRONMENTAL STATEMENT...............58
15.0
ANNEX B: GREATER GABBARD APPROPRIATE ASSESSMENT .....................58
16.0
ANNEX C: GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT ..............................................................58
Page 3 of 58
Greater Gabbard Offshore Wind Farm Project
1.0
Decommissioning Programme
INTRODUCTION
The Greater Gabbard Offshore Wind Farm will feature 140 turbines, generating a total
capacity of 500MW. Covering approximately 147km2, the project will be located some 26km
off the Suffolk coast, adjacent to sandbanks known as Inner Gabbard and The Galloper.
The wind farm is being developed by Greater Gabbard Offshore Winds Limited (GGOWL), a
company formed specifically to develop, finance, construct, operate and decommission the
project. The company is jointly owned by Airtricity Holdings (UK) Limited and Fluor
International Limited.
GGOWL obtained consent under Section 36 of the Electricity Act 1989 in February 2007 for
the Greater Gabbard Offshore Wind Farm. At this time the DTI also issued GGOWL a notice
under Section 105(2) of the Energy Act 2004 regarding the requirement to prepare and obtain
approval for the decommissioning programme for the project prior to construction
commencement.
This document presents the decommissioning programme for the Greater Gabbard Offshore
Wind Farm and is being submitted for approval in accordance with the Energy Act 2004
requirements. The decommissioning programme is informed and supported by the
Environmental Impact Assessment (EIA) for the Greater Gabbard Offshore Wind Farm
Project that was submitted to DTI in October 2005. The decommissioning programme
addresses all components of the wind farm below mean high water springs. The onshore
aspects of the project and the associated decommissioning requirements fall under the
planning permission granted under Section 57 Town and Country Planning Act 1990 by
Suffolk Coastal District Council.
Whilst the design life for the wind turbines is 25 years, the lease term for the project is 50
years. As such, GGOWL’s expectation is that the project will be ‘re-powered’ midway
through the lease term. Nonetheless, GGOWL acknowledges the UK’s international
obligations requiring installations to be decommissioned as soon as is reasonably practicable.
This programme therefore sets out the measures for decommissioning the project at the end
of the design life of the equipment during year 25. It is expected that as this time approaches,
GGOWL will seek approval from the Secretary of State to delay the decommissioning work
in favour of re-powering the project.
The programme is to be reviewed and revised as necessary throughout the lifecycle of the
project to reflect changing circumstances and regulatory requirements, and to incorporate
improvements in knowledge and understanding of the marine environment and advances in
technology and working practices.
2.0
EXECUTIVE SUMMARY
The Energy Act 2004 requires that GGOWL prepares and ultimately carries out a
decommissioning programme for the Greater Gabbard Offshore Wind Farm. This document
Page 4 of 58
constitutes the preliminary decommissioning programme for the project and is submitted for
approval prior to the construction of the wind farm.
The programme is informed and supported by the Environmental Impact Assessment (EIA)
carried out for the Greater Gabbard Offshore Wind Farm Project. The resulting
Environmental Statement was submitted as part of the project’s application for consent in
October 2005. The Environmental Statement provides detailed analysis of the baseline
physical, biological and human environment. The assessment of the impact of the project on
receptors and stakeholders takes into account decommissioning provisions that are consistent
with those presented in this document. A CD version of the Environmental Statement is
provided as Annex A to this document.
The programme is also informed by the outcome of the Appropriate Assessment undertaken
prior to the consent of the wind farm. This document is also provided as Annex B.
In considering appropriate decommissioning provisions, GGOWL have sought to adhere to
the following key principles:
• Safety for all at all times
• Consideration of the rights and needs of legitimate users of the sea
• Minimise environmental impact
• Promote sustainable development
• Adhere to the Polluter Pays Principle
• Maximise the reuse of materials
• Commercial viability
• Practical integrity
The following key documents have also informed the provisions presented:
• Decommissioning of Offshore Renewable Energy Installations under the Energy
Act 2004: Guidance notes for Industry, DTI, December 2006
• Guidelines and Standards for the Removal of Offshore Installations and Structures
on the Continental Shelf and in the Exclusive Economic Zone, International
Maritime Organisation (IMO), 19th October 1989
• Guidance Notes for Industry: Decommissioning of Offshore Installations and
Pipelines
under
the
Petroleum
Act
1998,
DTI,
http://www.og.dti.gov.uk/regulation/guidance/decommission.htm
Page 5 of 58
• Review of the Current State of Knowledge on the Environmental Impacts of the
Location, Operation and Removal/Disposal of Offshore Wind-Farms, OSPAR,
2006, ISBN 978-1-905859-15-3, www.ospar.org
• Guidelines for Environmental Risk Assessment and Management, Defra,
September 2002, http://www.defra.gov.uk/environment/risk/eramguide/08.htm
GGOWL’s starting assumption for establishing the extent of decommissioning is complete
removal. This assumption has been assessed against the guiding principles listed above and,
where appropriate, alternative solutions have been identified. A summary of the proposals for
decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are
outlined in the table below:
Component
Decommissioning Proposal
Wind Turbine/generating equipment
Complete removal from site
Foundations (wind turbine, met mast,
transformer platforms)
Cut off at or below seabed and removed
Cables (inter-array and export)
Left in situ
Anemometry masts
Complete removal of structure
Transformer platforms
Complete removal of topside
The measures proposed to decommission the installations as described above reflect the
strong emphasis GGOWL puts on minimising risks to safety and to the environment. As
such, GGOWL has sought practical solutions that involve minimal offshore operations.
In the absence of re-powering, GGOWL intends to begin decommissioning the project at year
25. It is intended that this process offshore be completed over a period of 300 days.
The decommissioning programme as currently proposed is to be reviewed and revised
throughout the lifecycle of the project to reflect changing circumstances and regulatory
requirements, and to incorporate improvements in knowledge and understanding of the
marine environment and advances in technology and working practices. A formal schedule
for review is proposed, where year 23 is identified as the final opportunity for a thorough
review and consultation process.
GGOWL’s approach to consultation about these works mirrors that undertaken during the
EIA process for the project, where importance is attached to early and open communication
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with all key stakeholders. Key stakeholders will have the opportunity to input into the draft
decommissioning programme, and to consider the final programme to be agreed prior to
decommissioning. Appropriate consultation and notification will be undertaken prior to the
works taking place.
A cost estimate for the programme has been derived based on the equipment and personnel
requirements and the duration of the works. Financial security provisions have been carefully
considered to ensure that this liability will be met. Details of the cost and financial aspects of
the proposals are provided as Annex C to this programme.
3.0
BACKGROUND INFORMATION
3.1
Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site
allocation process in December 2003.
An Environmental Impact Assessment was carried out and an application for consent for the
project submitted in October 2005. The project was awarded the following consents in
February 2007:
• Section 36 Electricity Act 1989 (construction and operation of the wind turbines,
offshore transformer stations and met masts; granted by DTI)
• Section 5 Food and Environment Protection Act 1985 (installation of foundations
of offshore structures, rock armouring, scour protection etc; granted by DEFRA)
• Section 34 Coast Protection Act 1949 (obstruction to navigation works; granted by
DEFRA)
• Section 36A Electricity Act 1989 (navigation extinguishment declaration; granted
by DTI).
Planning permission has also been received under Section 57 of the Town and Country
Planning Act 1990 for the onshore works at Sizewell.
The project is scheduled to commence construction offshore in late 2008.
3.2
Project Overview
The wind farm is to be located 26km off the Suffolk coast, adjacent to two sand banks known
as Inner Gabbard and The Galloper. The project comprises 140 wind turbines which will be
installed over a total area of 147km2 and will generate a maximum capacity of 500MW. The
power will be brought to shore at Sizewell where an onshore sub-station will be located to
connect the wind farm to the National Grid. Figure 1 below shows the site’s location,
boundaries and the cable route to shore.
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Figure 1: Greater Gabbard Site Boundaries
The site coordinates are as follows:
Page 8 of 58
Offshore transformer platforms will transform the turbine interconnection voltage from 33kV
to 132kV for transmission ashore by up to four export cables. These offshore sub-stations will
have typical dimensions in the order of 20m length x 20m width x 15m height.
Up to six permanent meteorological masts of a nominal height of up to 105m will also be
constructed.
The foundations for the wind turbines will be steel monopiles of up to 6.5m diameter, driven
into the seabed using a hydraulic hammer from a jack-up barge/drilling rig or purpose built
installation vessel. Scour protection in the form of rock, gravel or frond mats may be used.
Transition sections will be used to connect the wind turbine tower to the foundation by means
of a grouted joint or a flanged connection.
The foundations for the meteorological masts will consist of a steel monopile with a diameter
of approximately 2.5m. Scour protection may be required and would be similar to that used
for wind turbine monopiles.
The foundations for the offshore substations will be based on a jacket structure which will be
secured to the seabed with piles.
If required, the use of scour protection around the foundations may consist of loose rock or
rough gravel, to be installed by means of grab and drop or bulldozed over the side of a vessel.
The use of mattresses for protection may also be used and installed by means of lowering
from a vessel to the base of the foundation.
The turbines will be connected to the offshore sub-stations via a network of 33kV cables
(inter-array cables) that are laid between the wind turbines and the offshore sub-stations. Up
to four subsea 132kV cables (export cables) will connect the wind farm to the shore.
The inter-array and export cables are likely to be buried using an underwater cable plough
that executes a simultaneous lay and burial technique by lifting a wedge of sediment,
allowing the cable to fall into this trench and then folding the sediment back on top of the
cable. In exceptional circumstances, and only following written authorisation from DEFRA,
cable burial Remote Operated Vehicle (ROV) may be used. This utilises high-pressure water
jets to fluidise a narrow trench into which the cable is located. The jetted sediments settle
back into the trench.
The inter-tidal cables may be installed from a barge or jack-up, which is either beached or
moored near Sizewell beach. The cable will be pulled beneath the inter-tidal zone using a
directional drilling technique, either beginning at the start of the run out to sea or at the end of
the run from sea. Near shore and deep water lay may be separate operations.
Page 9 of 58
3.3
Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm. The final layout will be determined in
agreement with DTI prior to construction.
Page 10 of 58
Figure 2: Indicative Wind Farm Layout
3.4
3.4.1
Site Characteristics
Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at
the Greater Gabbard site. These studies informed the Environmental Impact Assessment for
the project and included:
•
two geophysical surveys
•
a shallow geotechnical campaign (maximum penetration 25m)
•
a deeper geotechnical campaign (maximum penetration 50m)
•
a metocean campaign
•
benthic grab campaign
Additional information has also been obtained from other sources to complement that
obtained from the above surveys described above. The additional data acquisition includes:
Page 11 of 58
• SeaZone sea bed bathymetry data: to inform the far-field model domain and to
provide base mapping
• UK Hydrographic Office (UKHO) historical charts: to inform the study of
historical changes in the Inner Gabbard and The Galloper banks shape and form.
• Wavenet Data: a strategic wave monitoring network that provides a single source
of real time wave data from a network of wave buoys located offshore from areas
at risk from flooding.
• TotalTide tidal level data: to synthetically generate astronomical tidal level data
and current speed so that measured data from the metocean surveys can be
compared against the model data for an assessment of consistency
• British Geological Survey (BGS) surface sediment information: to provide a more
regional indication of the sea bed material
• Met Office data: wind and wave time series to provide details on the longer-term
offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and
analysis of the physical characteristics of the Greater Gabbard site. Following the submission
of the ES in October 2005, further detailed site investigation works have been carried out to
further GGOWLs understanding of the site.
The following sections provide summary information sufficient to inform consideration of
the decommissioning provisions.
A. Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the
following metocean characteristics:
Estimated Average Mean Wind
Speed (predicted)
Water Depth Range
Mean Surface Temperature
Salinity
8.5-9.5 m/s at 80m AMSL
-3.6m to – 8m CD (Inner Gabbard)
-2.4m to – 10m CD (The Galloper)
-20m to – 50m (off the sandbanks)
16.5°C (summer)
6°C (winter)
<34.75g/kg (summer)
>34.75g/kg (winter)
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B. Topography& Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central
part of the Southern North Sea and shows a relatively flat surface predominantly between 20
and 40 metres water depth. The area is characterised by large areas of low gradient upon
which 5 linear “open-shelf” sandbanks are formed. These sandbanks include the Inner
Gabbard and the Galloper. Inner Gabbard and Galloper sandbanks are similar in shape and
proportion:
•
A width of 1 to 1.2km in the middle and shallowest section
•
A width of 1.4km to 1.5km at the northern and southern ends
•
A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 3.8m and 2.5m CD respectively,
as surveyed in 2004. Both banks are thought to be relatively stable, and are not expected to
move significantly during the lifetime of the wind farm project.
C. Currents, Tidal Streams, and Rise and Fall of Tide
Tidal range varies across the area, with a spring/neap range at Harwich of 3.6/2.3 metres.
Storm surges due to abnormal weather conditions can cause significant changes to predicted
heights with the sea rising up to 3 metres above these heights in extreme NW and N
conditions, or falling up to 2 metres below these heights in Southerly gales.
General tidal flows are determined from the admiralty tidal stream atlas, tide tables and the
tidal diamonds on the chart. At the Greater Gabbard site, these tidal streams run at
approximately 200 degrees from about 5 hours before HW Dover turning to approximately
020 degrees by 2 hours after HW Dover. Tidal streams at the proposed site are noted as a
maximum of 2.2 knots at spring tides.
Astronomical tidal levels relevant to the Greater Gabbard site, determined from the
Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are
summarised below.
Tidal
Level
(mCD)
Walton-on-theNaze
Harwich
Inner GabbardA
GalloperB
LAT
MLWS
MLWN
MHWN
MHWS
HAT
0
+0.40
+1.10
+3.40
+4.20
+4.60
0
+0.6
+0.2
+0.40
+0.9
+1.0
+1.10
+1.4
+1.3
+3.40
+3.1
+3.2
+4.00
+3.7
+3.8
+4.40
+4.0
+4.2
Page 13 of 58
(A) Posn: 51’ 56” N 01’ 55” E
(B) Posn: 51’ 48” N 01’ 58” E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness)
are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction. Elsewhere
tidal streams generally run in the direction of the coast.
The tidal streams at The Galloper (51°44.3’ N 1°48.3’E) are presented below:
Time from High
Water at Sheerness
(hrs)
-6
-5
-4
-3
-2
-1
High Water
+1
+2
+3
+4
+5
+6
Current Direction
Spring Tide
320
215
209
211
216
221
275
029
037
039
038
036
020
0.1
0.4
0.7
0.9
0.8
0.5
0.1
0.4
0.7
0.9
0.7
0.5
0.2
Velocity (m/s)
Neap Tide
0.1
0.3
0.5
0.6
0.5
0.3
0.1
0.3
0.5
0.6
0.5
0.3
0.1
D. Sea and Swell
From metocean surveys undertaken at the site, the waves in the vicinity of the Inner Gabbard
and The Galloper banks are all relatively small, short period wind swells. The local wind
conditions appear to play an important role in determining the height and period of the waves
in the region. The area is also well known for storm surges, and the extreme water levels in
the area are caused by such surges acting over large tidal ranges.
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient
measures of waves, water levels, currents and suspended sediment concentrations within
wind farm area. The data provided was used to demonstrate an understanding of the waves
and tides in the area, and to allow a consideration of these processes in conjunction with
sediment transport. Understanding was also required for the occurrence and effects of major
events, in particular high frequency low energy events (tidally dominated events) and low
frequency high energy events (wave dominated events). In general, the surveys show that:
•
Maximum tidal range is of the order of 4m
Page 14 of 58
• surface currents peaked at approximately 1.8m/s
• bed currents were of the order of 0.7 to 1.7m/s
• the currents were aligned with the local sea bed topography
• typical significant wave heights were of the order of 3.6m
• maximum wave heights of the order of 6.2m were recorded
• the larger waves tended to originate from the north-east
E. Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of
Eocene age, comprising firm to stiff marine silty clay, clayey and sandy silts and subordinate
sands. This formation is evident underneath the site and surrounding area to a depth of over
100m (this being the penetration of the geophysical survey), with outcrops at the seabed
throughout the area. Older Palaeocene strata (Lambeth Group and Thanet Formation) lie
below the London Clay and above the surface of the Upper Chalk. Neither these formations,
nor the chalk, outcrop at the seabed within the site.
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel
feature, considered to be the Paleo-Stour, which is interpreted as being filled with clayey,
sandy gravels and sandy, gravelly clays.
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that
also includes the Outer Gabbard, the North Falls and the South Falls. These banks are of the
open shelf linear type but they are particularly straight and narrow examples compared to
other banks of this type.
F. Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide
detailed information on the bathymetry, sea bed morphology, obstructions and shallow
geology.
The first campaign showed that:
• The shallow geology is dominated by Holocene Sands overlying London Clay
• The London Clay formation represents a sub-sea bed depth of between 60 and
100m
• Water depths to either side of the banks reach 50m (CD)
Page 15 of 58
• Sand waves occur on the sea bed to the south east of The Galloper
• The remainder of the sea bed surrounding the banks is generally flat and
featureless
• Asymmetric sand waves occur on the flanks of both banks, with the steeper sides
in opposing directions on either side of the banks
• Large sand wave covered by smaller sand waves and megaripples are shown on
the southern end of Inner Gabbard
• A pronounced paleo channel can be seen to the north of Inner Gabbard running
east-west reaching depths of 37m (CD), and passes beneath the overlying
sandbank
• The minimum depths on the Inner Gabbard and The Galloper are 3.80m and
2.48m (CD), respectively
The second survey included areas that were added to the wind farm site following an agreed
boundary change prior to the consent application. This second survey campaign showed that
within the main survey area:
• there are large areas of flat featureless seabed
• zones of sand waves and mega ripples exist to the south and north
• Holocene sediment (sands and gravels) overlay London Clay
• the thickness of the Holocene material ranges from centimetres to 5m
• the London Clay extends more than 100m below the sea bed
• there is evidence of extensive faulting in sections of the London Clay
• a paleo-channel exists to the north, running east-west and is approximately 400 to
900m wide, and up to 8m deep
In general, the survey shows that along the cable route:
• the formations are generally the same as the main wind farm site
• in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to
coarse grained sands
• in the last 5km to the shore, soft clays exist
Page 16 of 58
G. Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the
proposed Greater Gabbard Offshore Wind Farm site. Two of the locations were on the Inner
Gabbard and The Galloper sandbanks and two in the surrounding area. The purpose of the
survey was to acquire data relating to the underlying geology of the wind farm sites. This was
undertaken using a combination of sample boreholes, Standard Penetration Tests (SPT) and
Cone Penetrometer Test (CPT) at each location.
In general, the survey shows that:
• The sand layer is deeper on the banks than in the surrounding area. The sandbanks
have sediment depths of 13.75m and 21.65m on The Galloper and the Inner
Gabbard, respectively.
• In the surrounding area to The Galloper and the Inner Gabbard the depths of sand
are 0.4m and 0.1m, respectively
• Sand found on the banks is essentially homogenous, as slightly silty, fine to
medium sands. Sand generally contains less than 2% of gravel size particles
• Sand found in the surrounding areas has generally the same composition as on the
banks, but with a greater gravel size content (approximately 10%) including shell
fragments
• The clay layer ranges from 14.40m to 35.65m deep
• The clay is part of the lower London tertiary deposits, known as London Clay
• The clay is generally firm, becoming stiff to very stiff with depth
• Proportions of silt and clay are consistent, typically about 45% and 55%
respectively
A thorough geotechnical campaign was undertaken in 2006.
existing geotechnical knowledge.
This work confirmed the
H. Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005. The surveys
covered the proposed wind farm site and cable route. The purpose was to acquire data
relating to sediment characteristics and benthic communities, particularly Sabellaria
spinulosa. In general, the survey shows that:
• the Inner Gabbard and The Galloper sandbanks are composed of medium sands
with some gravel content
Page 17 of 58
• the surrounding deeper sea bed is composed of differing sediment types,
characterised by mud/clay, sand and gravels in differing proportions
• the cable route is characterised by a mix of sediments running through sands and
gravels to muds and then sands from the Inner Gabbard to the shore, respectively
3.5
Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the
vicinity of the Greater Gabbard Offshore Wind Farm. GGOWL has undertaken extensive
consultation with key stakeholders to inform the project’s EIA. A full analysis of the projects
relevant to the Greater Gabbard project is contained in Section 8 of the Environmental
Statement.
It is proposed that the register of key consultees identified during the EIA process is reviewed
and amended throughout the lifetime of the project and during the formal review
opportunities identified in section 9 of this document. Similarly, a register of relevant
activities and developments will be reviewed and maintained.
A consultation strategy and schedule will be devised prior to decommissioning. The nature
of this strategy will reflect the activities underway at the time; the interaction between these
activities and the decommissioning works; the relationships that have been built up with
stakeholders; and appropriate guidance and requirements that exist at the time. In any event,
the strategy will be based on the principles of clear, timely and open communication.
The starting point for the development of this strategy is the identification of existing and
reasonably foreseeable proposed developments in the region surrounding the Greater
Gabbard offshore wind farm. The following key activities currently take place in the area
and a brief review is presented here:
• Other offshore wind farms;
• Marine aggregate extraction;
• Disposal of dredged material;
• Subsea cables;
• Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area.
3.5.1
Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in
the vicinity of the Greater Gabbard site:
Page 18 of 58
Site
Kentish
Flats
Gunfleet
Sands
Gunfleet
Sands II
London
Array
Thanet
Developer
Round
of
Award
Capacity
Status
Vattenfall
One
90MW
DONG Energy
One
DONG Energy
Two
Up
to Consented,
108MW
construction
due 2009
64MW
Pre-consent
DONG
Energy/Shell/EON
Warwick Energy
Two
Two
Generating
Up
to Consented
1000MW
300MW
Consented
Page 19 of 58
Location
Distance
from
GGOW
F
8.5km off 55km
Whitstable
8km
off 40km
Clacton
10km
off 40km
Clacton
20km
off 15km
Essex
13km
off 35km
Margate
Figure 3: Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities
at the various sites. GGOWL will promote formal industry collaboration on this issue and, as
a minimum, will approach other developers to consider potential opportunities as part of the
ongoing review process for the Greater Gabbard decommissioning programme. However,
GGOWL’s starting assumption is that decommissioning will be undertaken in isolation at
Greater Gabbard in order that the provisions can be fully costed and sufficient financial
security provided. The status and requirements of surrounding projects will be carefully
considered in the planning and execution of the decommissioning process.
3.5.2
Marine Aggregate Extraction
The following areas are licensed, or are to be licensed (subject to consent) for the extraction
of marine aggregate within 10 km of the wind farm site:
Company
RMC marine (SCS)
RMC marine (SCS)
Extraction Area
Reference
239/1
452
Status
Licence
Application pending
Page 20 of 58
Distance from
Greater Gabbard
2.2km to NW
0.5km to W
Company
Extraction Area
Status
Distance from
Reference
Greater Gabbard
Hanson
119/3
Licence
4.1km to W
Figure 4: Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
3.5.3
Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries, and
are primarily sized for the quantities of material excavated from rivers and ports. The
Thames Estuary has several established disposal areas:
Name
Status
Inner Gabbard
Area 108/3
Inner Gabbard (east)
North West
Wash (HU199)
Open
Open
Submitted
Consent
Ship Open
Page 21 of 58
Distance
from
Greater Gabbard
5.2km
17.3km
for 1km
19.2km
The proposed extension to the southern dock space in the Port of Felixstowe is currently
under consideration. The material extracted during the construction process (up to 3.86 Mm3)
is proposed to be disposed at the existing Inner Gabbard dispersive disposal site, and the site
known as Inner Gabbard (east) disposal site.
Figure 5: Marine Disposal Sites in the Vicinity of Greater Gabbard
3.5.4
Subsea Cables
There are eight known subsea cables in the vicinity of the project. These are summarised in
the following table (source: The Crown Estate):
Company
National Grid
Transco
Hermes
GT UK
BT
Reference
UK-Netherlands
Interconnector
(BritNed)
Hermes
Atlantic Crossing
Seg B1
Farlands
Status
Consented
Telecoms cable not in
operation
Telecoms cable, in
operation
Telecoms cable, in
operation
Page 22 of 58
Distance from
Greater Gabbard
South of turbine
array
Intersects export
cable route
3km to east of
turbine array
Intersects export
cable route
Company
Reference
BT
BT
UK Netherlands 4
UK Netherlands 12
Flute (interoute)
Concerto North
Flute (interoute)
Concerto South
Status
Decommissioned
Scheduled to be
decommissioned
Telecoms cable, in
operation
Telecoms cable, in
operation
Distance from
Greater Gabbard
N/A
Intersects export
cable route
Intersects export
cable route
Intersects export
cable route
Figure 6: Subsea Cables in the vicinity of Greater Gabbard
3.5.5
Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact
Assessment, there were no known offshore oil and gas activities within 10km of the proposed
Greater Gabbard Offshore Wind Farm.
During 2007 the 24th licensing round for oil and gas was announced. A selection of the
blocks awarded were within the Thames Estuary, albeit some distance from the Greater
Gabbard wind farm. Figure 7 provides the details of those awards
Page 23 of 58
Figure 7: Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
3.5.6
Fishing Activity
Section 9.5.2 of the Environmental Statement provides a thorough analysis of the fishing
activity on site and was informed by site surveys; a review of existing data; and consultation
with industry.
The type and volume of fishing activity currently taking place in the vicinity of Greater
Gabbard offshore wind farm is relatively low. Whilst the ground conditions at the site are
reasonable for most types of fishing, there are key constraints limiting activity including:
Page 24 of 58
• Lack of shelter: The Inner Gabbard and The Galloper sandbanks provide little or
no shelter to small vessels in any prevailing wind direction. The sea becomes
choppy above the sand banks, making crossing and working the banks
uncomfortable, difficult and at times dangerous. The sand banks themselves are,
generally described as “uncomfortable’ by local fishermen.
• Weather conditions: a major factor for many smaller vessels, given the large
distance between the site and shore.
• Wrecks: there are a number of wrecks in the area of the sandbanks that are
avoided by the drifters and trawlers
3.5.7
Shipping Activity
Section 9.5.3 of the Environmental Statement provides a thorough analysis of navigation
activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by
surveys; a review of existing data; and consultation with industry. A review of this activity is
presented below.
Shipping using the area includes commercial shipping, fishing, recreational yachting and
dredging. The various sand banks in the area modulate the main routes for commercial traffic
in the area, with the ‘gaps’ between them being well marked east-west navigable channels
that are used by vessels making their way into the main ship channels of the Thames and
Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in
August 2005 by the ‘Sunk User Group’. A submission to United Kingdom Safety of
Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for
adoption in 2007. This scheme has been approved and will be in place before the project is
constructed.
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in
the area with an average number of 115 vessel tracks seen by radar per day. Analysis shows
that over 90% of these tracks were made by commercial shipping (cargo, passenger, tanker
and dredger) with only 8% made by fishing vessels and 1% by recreational craft. Most of the
vessels were small with only 12% of the commercial vessels being over 40,000 DWT. The
predominant flags of registry were UK and Dutch.
The following Figure 8 shows information gathered on the busiest survey day, 31st August
2004.
Page 25 of 58
Figure 8: Shipping Traffic within the vicinity of Greater Gabbard Wind Farm, 31/08/04
3.6
Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore, although
many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall
have some form of conservation status. It is possible that the decommissioning process may
impact the integrity of these sites. The relevant and important designations along the coastline
of Suffolk are as follows:
Figure 9: Nature Conservation Designations in the Vicinity of Greater Gabbard
Page 26 of 58
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter
governmental treaty for their waterfowl populations, their important plants and animal
assemblages, their wetland interest or a combination of these. The convention allows for
such sites to extend to 6m below mean low water. The relevant sites are:
Site Name
Grid ref
Area
(ha)
TM465662 2004
Date
Designated
Minsmere1976,
Walberswick
extended
(UK11044)
1992
Alde-Ore
TM432487 2,437 1996
Estuary
(UK11002)
Qualifying Interest
Representative Wetland, rare species
Rare Species; substantial numbers of
individual waterfowl indicative of
wetlands; 1% of waterfowl species
population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 92/43/EEC on the
Conservation of Natural habitats and of Wild Fauna and Flora) which requires European
member states to establish sites for the purpose of contributing to the maintenance/restoration
of habitants and species of favourable conservation status listed in Annexes I and II of the
Directive. SACs relevant to the Greater Gabbard project are presented below.
Site Name
Grid Ref
Area
(ha)
Date
Designated
Qualifying Interest
Page 27 of 58
Minsmere to
Walberswick
Heaths and
Marshes
(UK0012809)
Alde, Ore and
Butley Estuaries
SAC
(UK0030076)
Orfordness –
shingle Street
SAC
(UK0014780)
TM468682 1265 2001
Annex I qualifying habitats are:
• Annual vegetation of drift line
• European Dry Heaths
TM444509 1562 2001
• Mudflats and sandflats not
covered by seawater at low tide
• Atlantic salt meadows
• Coastal lagoons
• Annual vegetation of drift lines
• Perennial vegetation of stony
banks
TM440486 901
2001
SPAs are designated under the Birds Directive (Council Directive 79/409/EEC on the
Conservation of wild birds) which requires member states to conserve habitats for rare or
vulnerable species in addition to regularly occurring species of migratory birds. In the UK,
all SPAs are first notified as SSSIs. Relevant SPAs are detailed below
Site Name
Grid Ref
Area
(ha)
Date
Designated
Minsmere Walberswick
(UK9009101)
TM465662 2000 1992
Sandlings
(UK9020286)
Alde Ore
Estuary
(UK9009112)
TM403602 1562 2001
TM432487 2437 1996
Qualifying Interest
Nationally important numbers of six
breeding species (Bittern, Marsh
Harrier, Avocet, Little Tern, European
Nightjar, Wood Larks) and three
wintering species (Bittern, Hen Harrier,
Avocet)
Nationally important numbers of
European Nightjar and Wood Larks
Nationally important numbers of
breeding Marsh Harrier, Avocet,
Sandwich Tern and Little Tern and
wintering Avocet; internationally
important numbers of wintering
Redshank and breeding Lesser Black
Backed Gull; also important
assemblages of breeding seabirds and
wintering waterbirds.
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the
presence of bird species including Red Throated Diver.
Page 28 of 58
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind
Farm receiving consent in order to satisfy the requirements of the Habitats Directive
(EC/92/42/EEC) and the Wild Birds Directive (EC/79/409/EEC), known together as the
Habitats Directive. The Appropriate Assessment is provided as Annex B.
This Assessment was considered necessary because of concerns raised about the potential
impacts of the Greater Gabbard Offshore Wind Farm development on the breeding
population of lesser black-backed gulls at the Alde–Ore SPA; and the potential cumulative
impacts from the wind farm and other developments (proposed and extant) in the Thames
Estuary on the integrity of the potential Greater Thames Estuary pSPA. The Assessment
addressed both these issues and, taking into account impact predictions, evidence from other
sites, uncertainties and whether there was reasonable cause for concern, it found that the
Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of
the Alde-Ore SPA. It was also found that, at the present state of knowledge, the wind farm
would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA, either
alone or in combination with other projects. The Assessment took a lifecycle approach to the
project, with the conclusions applying to all phases of the works, beyond construction and
operation through to decommissioning.
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and
Countryside Act 1981 (Section 28) as being of national nature conservation interest. They are
intended to provide the best examples of wildlife habitats, geological features and landforms
and receive greater protection through the Countryside and Rights of Way Act 2000. There
are a number of SSSI’s and an Area of Outstanding Natural Beauty (AONB) situated close to
the export cable landfall and associated onshore works. These are presented below
Site Name
Minsmere-Walberswick Heaths and Marshes
Sizewell Marshes
Leiston-Aldeburgh
Grid Ref
TM465662
TM466638
TM461595
Area (ha)
2326
104
534
Date Designated
1987
1992
1986
Areas of Outstanding Natural Beauty:
Site Name
Suffolk Coasts and Heaths
4.0
Area (ha)
40,400
Date Designated
1970
DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
4.1
Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore
Wind Farm, GGOWL has sought solutions that adhere to the following principles:
Page 29 of 58
Guiding Principle
Comments
Safety for all at all times
GGOWL is committed to adhering to the highest standards
for health and safety throughout the lifecycle of the Greater
Gabbard project. GGOWL seek to promote safe practices
and minimise risk in the development and implementation
of decommissioning solutions.
Consideration of the rights GGOWL respects the rights and needs of other users of the
and needs legitimate users seabed. Decommissioning activities will seek to minimise
of the sea
the impact on stakeholders and emphasis will be placed on
clear, open communication.
Minimise environmental
In considering decommissioning measures, the Best
impact
Practicable Environmental Option (BPEO), will be chosen
in order to minimise impact on the environment at an
acceptable cost.
Promote sustainable
In decommissioning the Greater Gabbard project, GGOWL
development
will seek to ensure that, as far as is reasonably practicable,
future generations do not suffer from a diminished
environment or from a compromised ability to make use of
marine resources.
Adhere to the Polluter Pays GGOWL’s decommissioning and waste management
Principle
provisions acknowledge our responsibility to incur the costs
associated with our impact on the environment.
Maximise the reuse of
GGOWL is committed to maximising the reuse of waste
materials
materials and pays full regard to the ‘waste hierarchy’.
Commercial Viability
Practical Integrity
In order that commercial viability is maintained, the
BATNEEC (Best Available Technique not Entailing
Excessive Cost) decommissioning solutions will be sought.
Solutions that are necessary to achieve one or more of the
above objectives must be practicable.
It is possible that not all of these objectives will be consistent with each other. In such
circumstances, solutions will be optimised subject to the necessary constraints. For example,
with respect to minimising the impact on the environment, the Best Practicable
Environmental Option (BPEO) will be sought where the option will be chosen that provides
the most benefit or least damage to the environment as a whole, at an acceptable cost, in both
the long and short term. Similarly, BATNEEC solutions ensure that the reduction in risk is
balanced with the practicability and cost of doing so.
In seeking to achieve these objectives, GGOWL is also committed to adhering to UK
legislation and international obligations. As such, GGOWL has drawn upon the following
documents to ensure the decommissioning programme meets those requirements:
• Decommissioning of Offshore Renewable Energy Installations under the Energy Act
2004: Guidance notes for Industry, DTI, December 2006
Page 30 of 58
• Guidelines and Standards for the Removal of Offshore Installations and Structures on
the Continental Shelf and in the Exclusive Economic Zone, International Maritime
Organisation (IMO), 19th October 1989
• Guidance Notes for Industry: Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998, DTI, http://www.og.dti.gov.uk/regulation/guidance/decommission.htm
• OSPAR guidance documents on offshore wind farms;
• Guidelines for Environmental Risk Assessment and Management, Defra, September
2002, http://www.defra.gov.uk/environment/risk/eramguide/08.htm
• United Nations Convention on the Law of the Sea (UNCLOS), 1982.
Other legislation of relevance includes:
• Hazardous Waste Regulations 2005; and
• London Convention 1972 and the 1996 Protocol, relating to the prevention of marine
pollution by dumping of wastes.
• Construction (Design and Management) Regulations 2007
• Appropriate H&S Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard
project. Necessary measures will be put in place during the decommissioning of the project
to ensure that these areas, or other such areas that may be identified during the operation of
the project, are not compromised during decommissioning activities.
4.2
Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the
project. The overriding aim is to develop a project that is safe, durable and cost-efficient
throughout its lifetime. Taking a lifecycle approach to the design and development work
ensures that decommissioning considerations are incorporated into decision-making and,
where possible, means that the principles identified above are being incorporated into early
decision-making.
Taking into account the UK’s commitments under UNCLOS; IMO standards and the work of
OSPAR, GGOWL’s starting assumption in establishing the decommissioning requirements
has been complete removal of all offshore components to shore for reuse, recycling or
incineration with energy recovery or disposal at a licensed site. This assumption has been
assessed for all components against the key criteria presented above. In some instances this
option has not been considered to be appropriate and alternative options have been
Page 31 of 58
considered. These alternatives have also been assessed according to the above criteria and
the optimum solution selected.
A further prerequisite for not fully removing a component is consistency with at least one of
the circumstances set out on page 25 of DTI guidance as situations where such a solution may
be considered. These circumstances set out in the DTI guidance are listed below (it is noted
that there is some duplication with the guiding principles described above).
• “the installation or structure will serve a new use, whether for renewable energy
generation or for another purpose, such as enhancement of a living resource
(provided it would not be detrimental to other aims, such as conservation). In
these situations, we would normally expect the decommissioning programme to set
out the eventual decommissioning measures envisaged should the installation or
structure finally become ‘disused’ and a point reached when extending its life or
finding a beneficial reuse is no longer possible;
• entire removal would involve extreme cost. It is considered that design decisions
should, as far as possible, result in installations which are affordable to remove,
but it is recognised that some elements, such as deep foundations, may
nonetheless be costly to remove;
• entire removal would involve an unacceptable risk to personnel;
• entire removal would involve an unacceptable risk to the marine environment;
• the installation or structure weighs more than 4000 tonnes in air (excluding any
deck and superstructure) or is standing in more than 100 m of water and could be
left wholly or partially in place without causing unjustifiable interference with
other uses of the sea.”
To facilitate assessment of the decommissioning proposals, the analysis is preceded by a
description of each of the components of the project to be decommissioned.
4.2.1
Offshore Wind Turbines
Component Description
At the time of writing, the make, model and capacity of wind turbine to be installed at
Greater Gabbard offshore wind farm has yet to be finalised. These details will be confirmed
prior to sign-off of the GGOWL decommissioning programme and the following provisions
are based on the maximum dimensions and weights associated with a 3.6MW turbine and are
consistent with the dimensions and weights used in GGOWL’s Environmental Statement.
Consistent with the conditions of consent for the works, the following decommissioning
provisions assume a maximum tip height of 170m above Mean Sea Level (MSL), with a
Page 32 of 58
nominal 105m hub height and a maximum rotor diameter of 130m. The towers will be
tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator, gearbox and other
operating equipment. The unit transformer will be located in the tower base (above the high
tide level).
The transformer will either be oil-filled (surrounded by a bund conforming to the required
standards) or cast-resin.
Figure 10: An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes
and will be made up of:
• Hub casting: nodular cast iron
• Blades: three blades, each up to 52m long and made from carbon fibre
Figures 11-13: Construction of an Offshore Wind Turbine
Page 33 of 58
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh
approximately 125 tonnes. Components will include:
•
•
•
•
•
Gear box: 50 tonnes
Generator: 50 tonnes
Main Shaft and bearings: 5 tonnes
Transformer/power inverter: 1 tonne
Housing: 19 tonnes
Key components of the tower section will include:
• Ladders
• Lift
• Power inverter
• Power cable
• Control equipment
• Bolts
• Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete
weight.
Figure 14: Tower Section
A. Decommissioning Proposal
It is intended that all the above components are fully removed from site, before being
disassembled onshore. This reduces offshore risk, for example in relation to spillage, and
facilitates safe deconstruction onshore.
In terms of the key criteria, this approach has been assessed as follows:
Page 34 of 58
OFFSHORE WIND TURBINES
Criterion
Complete Removal
Safest option, involving standard procedures and minimal
work offshore.
Consideration of the rights Complete removal of structure best long-term solution.
and needs legitimate users of Appropriate notification and consultation would precede
the sea
temporary works/disturbance
Risk of spillage slight as all pollutants are fully contained
Minimise
environmental inside the nacelle and removed in single lift.
All
impact
dismantling takes place onshore therefore minimizing the
risk of spillage.
Materials completely removed from site, ensures future
Promote
sustainable generations do not suffer from a diminished environment or
from a compromised ability to make use of marine
development
resources.
Adhere to the Polluter Pays Entirely consistent: owner pays full cost of removal and
Principle
disposal
Maximise the reuse of All deconstruction to take place onshore, maximum
materials.
potential for reuse of materials.
Most commercially viable solution:, minimal works
offshore, maximum re-sale/reuse value from materials,
minimum residual risk
Known/tried procedures reduced risk due to minimal
Practical Integrity
offshore works
4.2.2
Turbine Foundations & Transition Pieces
A. Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard
offshore wind farm project. This solution comprises driving a hollow steel pile into the
seabed sub-strata, relying on the frictional properties of the seabed sediments for support.
These structures will extend up to 65m in length, 6.5m in diameter and 700 tonnes in weight.
Foundations will require ancillary equipment including:
• Cable entry and protection features: The cables are to be installed in a “J-tube”
arrangement, a steel tube of approximately 250mm diameter located internally within
the monopile. Each structure will have between two and five J-tubes. At the end of
each J-tube, cable entry will be facilitated by a bell-mouth shaped opening.
Page 35 of 58
• Corrosion protection: a combination of a protective paint coating and installation of
sacrificial anodes on the subsea structure. The anodes are standard products for
offshore structures and are welded onto the steel structures. The anodes typically
consist of zinc and aluminium, and are connected to the structure via doubler plates to
ensure the integrity of the primary structure is maintained in the unlikely failure of an
anode connection. Cadmium will not be used. The number and size of anodes will be
confirmed during detailed design.
• Transition pieces making the connection between the foundation and the tower will
weigh up to 300 tonnes and will include the following components:
• Boat fenders
• Access ladders
• Transformer (oil filled)
• Switchgear (gas filled breakers)
• Control equipment
• Cables
• Access deck
• Handrail sections
• Grating
• Marine access door
An access platform comprising two access ladders (with integral personnel safety protection)
will enable access to the wind turbine at any state of the tide. The access ladders and platform
will be constructed from steel. The structures will have provisions for personnel safety, e.g.
life-rings. The total weight of these arrangements is typically 10 tonnes per installation,
therefore 1400 tonnes of steel will be required for the 140 wind turbines.
Figure 15: Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
B. Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to
remove. However, design codes and standards limit the ability to reduce steel thicknesses
and to lighten the structures to ease future removal. The result is that the monopiles are of a
size that means they will not be able to be removed from the seabed once piled to the design
penetration depth of approximately 35m below seabed. Consequently it is proposed that the
foundations are cut at or below seabed. In the first instance a general target of cutting one
metre below seabed is proposed, though it may be necessary to vary the target depth for
individual turbines subject to site specific factors such as the specific ground conditions at
each turbine location. It is noted that in order to overcome vast frictional forces, considerable
excavation will be needed. In order to be able to undertake the cutting procedure, the
diameter of the excavation hole will increase by at least two metres for every additional metre
in depth below seabed. As such, it may be considered too intrusive and damaging to consider
cutting below one metre depth.
It is proposed that, following the cutting operation, the foundations and transition pieces be
removed as a single structure. The total lift weight of this structure will be in the order of 660
tonnes.
The following table compares and contrasts the options of complete removal of foundations
with the alternative of cutting below seabed as described above. The same considerations
apply to the foundations used for transformer platforms and met masts.
FOUNDATIONS
Criterion
Complete Removal
Cutting Below Seabed
High risk to personnel Fewer activities to be undertaken over
Safety for all at all
associated with lifting extreme a shorter time period offshore,
times
weights. Risk compounded by minimising risk to personnel.
significant length of time
Page 37 of 58
Criterion
FOUNDATIONS
Complete Removal
needed to undertake works Post decommissioning site monitoring
offshore.
Diver operations will identify any unlikely exposure
would be required
with the result that safety risk is
insignificant.
Disadvantages to other users
of the marine environment
Consideration
of include disruption over a
the rights and needs longer time period whilst the
legitimate users of works are undertaken and
the sea
remaining
scour
holes
associated with excavation
Minimise
environmental
impact
Promote
sustainable
development
Adhere
to
Polluter
Principle
Maximise the
of materials.
Commercial
Viability
No risk presented providing cutting is
to sufficient depth, site is monitored
post decommissioning; any unlikely
exposure identified.
Excavation pits over a wide
area causing significant impact
to
marine
environment.
Associated
dumping
of
excessive volume of waste
material
also
required.
Disturbance would take place
over long time period.
Some artificial reef habitat
may be lost, but long term risk
of decay and pollution will be
eliminated.
Considerably reduced works footprint
relative to complete removal. Works
would take place over reduced time
period and involve less equipment.
Seabed recovery time shorter than
complete removal scenario.
Some artificial reef habitat may be
lost, but long term risk of decay and
pollution will be eliminated.
In the long term complete
removal affords maximum
flexibility over use of seabed,
though
considerable
destruction over the whole site
in short-medium term
Some activities may be limited at
turbine locations: eg extraction (given
incidence of london clay on site
demand for extraction unlikely).
Providing remaining structures do not
become exposed most future activities
will not be affected. Seabed recovery
is highly likely.
Consistent
in
principle,
assuming a suitable disposal
the
solution can be found for the
Pays
excavated waste material and
that the seabed can be
restored.
reuse Maximum material potentially
available for reuse
Not commercially viable –
excavation and extreme lifting
Page 38 of 58
Consistent as far as is reasonably
practicable – all remains to be
suitably buried.
Less material available for reuse
relative to complete removal.
Less
expensive
alternative
to
complete removal, involving minimal
FOUNDATIONS
Complete Removal
involves major equipment excavation
requirements over longer
periods of time
Not a practical solution:
Extreme risk associated with
heavy
lift,
considerable
Standard procedures and equipment
excavation
needed
with
associated storage or disposal
of large volume of waste.
Criterion
Practical Integrity
This analysis shows that cutting below seabed is preferable to complete removal on the
grounds of safety, practical integrity and commercial viability.
GGOWL consider that there to be consistency between this proposal and the relevant
circumstances set out in DTI guidance:
•
entire removal would involve extreme cost.
•
entire removal would involve an unacceptable risk to personnel;
It is also noted that this approach is standard practice within the oil and gas industry for
similar structures.
Although GGOWL is committed to cutting foundations below seabed, contingency plans will
be put in place to ensure appropriate actions are carried out in the unlikely event that
remaining structure(s) become exposed. Please see Section 12 for details.
4.2.3
Transformer Platforms
The purpose of an offshore sub-station platform is to transform the voltage of the electricity
generated at the wind turbine to a higher voltage suitable for transmission of power to shore.
Up to four offshore sub-stations will be required and located at strategic points within the
turbine array. The substations will have typical dimensions of 20m length x 20m width x
15m height. The total height of the sub-station including the foundation will be up to 40m
above LAT.
The components within the sub-station offshore platforms will include:
•
Medium to high voltage transformers
•
High voltage GIS (gas insulated switchgear)
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•
Back-up diesel generator and tank
•
Accommodation facilities
•
J-tubes
•
Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles.
The jacket structure will weigh approximately 450 tonnes, with the piles each weighing
approximately 200 tonnes and the topsides weighing 500 tonnes. Figure 16 gives an
indicative representation of an offshore transformer support structure.
Figure 16: Indicative Transformer Support Structure
It is proposed that all topside structures and ancillary equipment be removed. In particular, as
the transformers may be oil or resin filled they will be taken to shore complete, reducing the
potential for offshore spillage risk and facilitating safe deconstruction. The complete lift
weight will be in the region of 500 tonnes. The justification for complete removal of the
topsides is outlined below
PLATFORM TOPSIDES
Criterion
Complete Removal
Safest option, involving standard procedures and minimal work offshore.
Consideration of the rights Complete removal of structure best long-term solution. Appropriate
and needs legitimate users notification and consultation would precede temporary works/disturbance
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PLATFORM TOPSIDES
Criterion
Complete Removal
of the sea
Minimise
impact
environmental Risk of spillage slight as all pollutants are fully contained and removed in
single lift. All dismantling takes place onshore
Materials completely removed from site, ensures future generations do
Promote
sustainable
not suffer from a diminished environment or from a compromised ability
development
to make use of marine resources.
Adhere to the Polluter Pays
Entirely consistent: owner pays full cost of removal and disposal
Principle
Maximise the reuse of All deconstruction to take place onshore, maximum potential for reuse of
materials.
materials.
Most commercially viable solution:, minimal works offshore, maximum
re-sale/reuse value from materials, minimum residual risk
Main risk is heavy lift and this can be mitigated by use of correct
Practical Integrity
procedures and capable vessels and equipment. Most practical method
It is proposed that the four legged jacket, including leg piles, are cut to 1m below seabed.
This will involve a total lift of approximately 850 tonnes. The justification for cutting
foundations below seabed provided in section 4.2.2.B above also applies to this proposal.
4.2.4
Anemometry Masts
Permanent anemometry masts will be required for the operations phase. Such masts will be
the same height as the wind turbine hub, ie up to 105m above mean sea level, and will feature
a foundation installed in a similar manner to the foundations for the wind turbines, described
above. The anemometry masts will be connected to the wind turbine array using buried
subsea cables.
A anemometry mast consists of the following parts:
•
Monopile foundation
•
Platform including boat landing
•
Met mast including instrumentation (above and possibly below water)
•
Control cabinet, solar panels and batteries
•
Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of
approximately 2.5m and a length of approximately 70m, of which up to 30m will be driven
into the seabed. The monopile will be made of approximately 400 tonnes of steel. Scour
protection is not envisaged to be necessary.
Figure 17: Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
It is proposed that all anemometry equipment and supporting towers are completely removed
and deconstructed onshore.
The monopile foundation will be removed in accordance with the provisions made in Section
4.2.2 B. It is estimated that approximately 29m would remain below the seabed. The total
lift weight of the removed section, including the weight of the deck, is approximately 200
tonnes.
ANEMOMETRY MASTS
Criterion
Complete Removal
Safest option, involving standard procedures and minimal work offshore.
Consideration of the rights
Complete removal of structure best long-term solution. Appropriate
and needs legitimate users
notification and consultation would precede temporary works/disturbance
of the sea
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ANEMOMETRY MASTS
Criterion
Complete Removal
Minimise
impact
environmental Risk of spillage slight as all pollutants are fully contained and removed in
single lift. All dismantling takes place onshore
Materials completely removed from site, ensures future generations do
Promote
sustainable
not suffer from a diminished environment or from a compromised ability
development
to make use of marine resources.
Adhere to the Polluter Pays
Entirely consistent: owner pays full cost of removal and disposal
Principle
Maximise the reuse of All deconstruction to take place onshore, maximum potential for reuse of
materials.
materials.
Most commercially viable solution:, minimal works offshore, maximum
re-sale/reuse value from materials, minimum residual risk
Main risk is heavy lift and this can be mitigated by use of correct
Practical Integrity
procedures and capable vessels and equipment. Most practical method
4.2.5
Cabling
Export Cables: Subsea power cables are required to connect the wind farm to the electricity
transmission system. These cables will also comprise internal fibre optics for wind farm
control purposes. The 3-core cables will consist of copper conductors with integral insulation,
core screening, and steel armour (for stiffness and impact resistance).
The export cables will be buried to a depth ranging between at least 1.0m and 1.5m below
seabed. It is considered that the proposed burial depths for export cables are sufficient to
ensure that the cables do not become exposed by the removal of overburden material. Burial
within clay, as opposed to within mobile sediment, ensures that cables remain buried
indefinitely. At the beach end of the cable route, the export cables will be uncovered for a
length below LAT.
Inter-Array Cables: The inter-array cables will be relatively short in length (typically 650 to
1200m) and will interconnect the wind turbines within the arrays to each other and to the
offshore sub-station platforms. The cables are expected to be standard 3-core, copper
conductor, XLPE (or equivalent) insulated and armoured submarine cable, rated at 33kV. The
cables have an external diameter of approximately 150mm.
All cables are to be buried in the seabed to a nominal depth of 1–1.5m. Where the inter array
cables cross sandbanks, burial shall be at 1.5m depth. It is proposed that cables will be set
into the London clay underlying the sand waves to ensure that they stay buried throughout the
lifetime of the project, and beyond.
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a
point below the surface of the seabed to allow the cable to remain buried. The cut sections
would be removed with minimal disruption of the seabed. For any inter array cable crossing
sand banks, it would be proposed to leave in situ as the disruption caused by jetting and or
excavating the sand bank to remove the cable is regarded as being detrimental to the seabed.
It is considered that these proposed burial depths are sufficient to ensure that the inter-array
cables do not become exposed by the removal of overburden material. Burial within clay, as
opposed to within mobile sediment, ensures that cables remain buried indefinitely.
The estimated total cable length, for both export and inter-array cables is approximately 320
km. Note that cables are not oil/fluid filled.
Figure 18: Typical cross section of 3 core copper XLPE armoured 33kv subsea cable,
representative of inter-array cables (courtesy Nexans)
Figure 19: Typical cross section of 13 core copper XLPE armoured 132kV subsea
cable, representative of export cables (courtesy Nexans)
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At the time of writing GGOWL intends to follow the current industry standard by leaving
both inter-array and export cables in-situ. As such, life-cycle costs and environmental impact
will be considered in the design of the inter-array and export cables.
Whilst it is considered that cables are buried at a safe depth, contingency plans will be put in
place to ensure appropriate actions are carried out if the cables do become exposed. Please
see Section 12 for details.
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would
be to cut and pull through the cables to the onshore jointing pit. This operation would not
impact the seabed.
CABLES
Criterion
Complete Removal
Safety for all at all Risk to personnel not excessive
times
Leaving in situ
Burial within stable clay seabed
does not pose safety risks to
marine users
No risk presented from leaving
Consideration
of
affords
maximum buried cables in situ. Potential for
the rights and needs Removal
extraction
activities
limited
legitimate users of flexibility over use of seabed
the sea
(though unlikely in London Clay)
Given the considerable length of
cable and the need for jetting
techniques, removal would cause Benign - no environmental impact
Minimise
considerable damage and disruption associated
with
long
term
environmental
to the seabed and established disintegration of buried cables.
impact
communities.
These impacts
could be considered large relative to
the environmental gains from
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CABLES
Criterion
Complete Removal
removal.
Though considerable ‘troughs’
would remain on the seabed in the
Promote
short-medium
term,
complete
sustainable
removal
affords
maximum
development
flexibility over use of seabed in the
long term.
Adhere
to
the Consistent,
assuming
suitable
Polluter
Pays disposal option is found for surplus
Principle
cable components
Maximise the reuse Maximum material, eg copper,
of materials.
potentially available for reuse
Commercial
Expensive operation, offset to an
Viability
extent by copper re-sale value
Possible to undertake. Likely to
Practical Integrity
cause
damage
to
marine
environment.
4.2.6
Leaving in situ
Some future activities may be
limited, eg extraction (unlikely on
London clay).
Benign, no pollution risk
No reuse possible if left in situ
Limited cost involved with re
burial of cable ‘ends’
N/A
Scour Protection
Scour is the term used for the localised removal of sediment from the area around the base of
support structures located in moving water. When a structure is placed in a current, the flow
is accelerated around the structure. If the bed is erodable (and the shear stresses are of
sufficient magnitude), a scour hole forms around the structure. This phenomenon is known as
local or structure-induced sediment scour.
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given
the underlying London Clay formation either exposed or with veneers of sand and gravel on
top. As such, there is little perceived need for scour protection materials. Nonetheless, for the
purposes of the EIA and this decommissioning programme, it has been assumed that some
scouring of the upper softer clay and/or sand and gravel material may occur and, as such,
scour protection measures around the structures, such as rock dumping or fronded mattresses,
may be needed.
For monopile foundations, the procedure involves establishment of a thin rock layer installed
prior to pile driving, with a mean rock size (D50) of 100-300 mm. This layer will typically be
24 m in diameter with a height of 0.5 m (i.e. a total volume of 226 m). After driving of the
pile, cover stones with D50 of between 400-750 mm are placed around the foundation. The
total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D), i.e. the total volume of cover stones will be 1,432 m³ per foundation, and up to
200,480 m3 for 140 foundations.
It is possible that cable protection measures will be required at the sandbank margins. At the
time of writing GGOWL do not have details of these measures but will revert to JNCC, MFA
and DBERR about all scour protection requirements once this information is available.
In the unlikely event that scour material is required, it is proposed that this is left in situ
following decommissioning.
Scour Material
Criterion
Complete Removal
Other
Safety for all at all Removal is a labour intensive activity, Reduced risk for contractors.
times
involving divers and posing an Marginal, increase in risk to
marine users: some additional rock
unacceptable risk to personnel.
over small areas at specific
locations
Consideration
of Removal affords maximum flexibility over May limit uses of seabed. May
generate positive habitat benefits.
the rights and needs use of seabed
legitimate users of
the sea
Minimise
Removal will cause considerable damage Habitat
for
established
environmental
and disruption to the seabed and communities retained, no short or
impact
established communities.
Associated long term detrimental effects on
equipment and vessels will generate marine environment anticipated.
disturbance and additional noise over wide
area. These impacts could be considered
large relative to the environmental gains
from removal. Materials gathered would
need to be dumped elsewhere.
Promote sustainable Consistent in principle, assuming suitable Prevents some future activities on
development
disposal solution found
the seabed.
Total area of
sterilisation is small
Adhere
to
the Consistent in principle
Inferior option to complete
Polluter
Pays
removal in this regard
Principle
Maximise the reuse Opportunities for reuse of materials N/A
of materials.
gathered are limited. Materials would
need to be disposed of elsewhere.
Commercial
Expensive, labour intensive, high volume Costs
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limited
to
ongoing
Scour Material
Criterion
Complete Removal
Other
Viability
operation
monitoring
Practical Integrity
High reliance on manual work, labour N/A
intensive. Possible but not practical
In relation to the circumstances set out in the DTI guidance where non-removal may be
considered acceptable, it is considered that in this instance “the installation or structure will
serve a new use … through the enhancement of a living resource”. It is also considered that
entire removal would involve an unacceptable risk to personnel.
5.0
DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors, by final design
choices (for example in relation to foundation type) and by the equipment and vessels
available at the time. The measures described in this section are based on current technology
and information, but it should be recognised that the methods may evolve over time.
Periodic review of the Decommissioning Programme and the measures proposed within it
will take place throughout the lifetime of the wind farm to accommodate new information.
For example, new offshore technologies are continually being evaluated, tested and
developed. GGOWL expects considerable advances over the lifetime of the project with new
techniques evolving as experience and knowledge in the sector grows. In particular, it is
acknowledged that lessons may be learned through the construction and operation of the
project and through industry experience in decommissioning renewable energy and other
offshore installations. Sufficient time must be given to researching the different available
technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best
practice guidelines and future legislation.
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the
Greater Gabbard offshore wind farm project in order to ensure that the best technology is
selected and efficient and safe procedures are followed.
5.1
Wind Turbines/Generating Equipment
The decommissioning of the superstructure (i.e. removal of turbine components including
blades, nacelle, and tower) is likely to be a reversal of the installation process.
Opportunities to re-use the generating equipment will be maximised. Health and Safety will
be of paramount importance during decommissioning.
All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and
standards at the time the work starts).
The general methodology for carrying this out is as follows:
• De-energize and isolate from Grid (may be undertaken in phases)
• Mobilise suitable heavy lift vessel(s) to the wind farm location
• Remove rotor component parts
• Cut turbine interconnecting cables adjacent to the substructures
• Remove nacelle including gearbox and generator
• Remove turbine tower
• Transport all components to an onshore site at which they will be processed for
reuse, recycling or disposal.
Once onshore, the structures and substructures will be reduced to sizes suitable for disposal
as follows:
• Removal of all hazardous substances and fluids from the turbines (such as oil
reservoirs and any hazardous materials and components). All components to be
disposed of in accordance with relevant regulations
• All steel components sold for scrap to be recycled. This forms the bulk of the
structures and substructures
• The turbine blades (fibreglass) will be disposed of in accordance with the relevant
regulations in force at the time of decommissioning. One potential disposal
method identified is to break down the fibreglass into a pulp for use as cavity
insulation in buildings
5.2
Foundations
On current knowledge, abrasive diamond wire cutting is likely to be the preferred method for
cutting all the foundation structures at or below seabed. The final method chosen shall be the
least damaging to the surrounding seabed and most environmentally acceptable means
available.
The use of divers for any of the removal works will be minimised and if possible removed
completely.
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The general methodology for decommissioning of the wind turbine monopiles is likely to be
as follows:
• Operate cutting procedure at or below seabed
• Remove transition piece and upper part of monopile as a single object using
suitable lifting vessel
• Transport to onshore location for offloading/disposal.
• Remove internal equipment, disassemble onshore.
5.3
Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described
for the turbines and turbine foundations. The complete ‘topside’ structure will be removed in
a single lift, taken by suitable vessel to an onshore facility where the equipment and structure
will be dismantled and the constituent parts processed for reuse, recycling and or disposal.
5.4
Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation
procedure, with the mast being removed with a relatively small crane barge. The monopile
will be cut-off below sea-bed level using similar technology to the large foundation
monopiles.
5.5
Cables
In light of the proposal to leave cables buried under the seabed, the cable will be cut at a
suitable point as close to the foundation as possible, with the ends buried to a proposed depth
of 1 metre below seabed level. This will minimise the further disruption to the seabed and
any established marine life in the area.
5.6
Scour Protection
If required, it has been proposed that any scour protection will be left in situ.
5.7
Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the
‘waste hierarchy’ which suggests that reuse should be considered first, followed by recycling,
incineration with energy recovery and, lastly, disposal. In any event, waste management will
be carried out in accordance with all relevant legislation and it would be intended that any
disposal took place on land.
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In following the waste hierarchy and subject to evolution of technology, change in
regulations and demand for materials over the lifetime of the project, the waste management
of the main project components might involve:
Waste Type
Pre-treatment
Wind turbine foundations
Steel from wind turbine
foundations, tower and
nacelle removed to shore
Copper from power cables
and transformers
Glass-fibre Reinforced
Epoxy (GRE) from the
blades
Used lubricants from wind
turbine
Non-recyclable materials and
fluids
Disposal / Recycle / Reuse
Establish available design
life at end of 25 years.
Reuse by repowering with
new/superior wind turbines
or other renewable
generation technology.
Break down into
transportable size
Recycle
Strip cable from power
cables and transformers
Recycle
Break down into
transportable size
Recycle
Filter
Recycle
Landfill
As a part of the review process, all appropriate regulations and guidelines will be reviewed.
A waste management plan will be drawn up well in advance of the commencement of
decommissioning to ensure that adequate time remains for the proper provisions to be made.
5.8
Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the
Electricity Act 1989, GGOWL is committed to exhibiting the appropriate marks and lights
during the decommissioning of the wind farm.
In relation to aviation safety, the shape, colour and character of the lighting will be compliant
with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation
Authority).
In relation to navigational safety, lights and marks will be agreed with Trinity House, in
consultation with the Maritime and Coastguard Agency. In particular, Trinity House will be
consulted prior to decommissioning to specify any obstruction marking that may be required
during the removal operations. In the event that any obstruction is left on site that may be
considered to present a hazard to navigation GGOWL will provide the necessary marking
specified.
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6.0
RE-POWERING
Whilst the design life for the project is 25 years, the lease term for is 50 years. As such,
GGOWL’s expectation is that the project will be ‘re-powered’ midway through the lease
term. In comparison to full decommissioning as described above, this is only likely to
involve removing and replacing the turbine topsides and possibly some additional equipment,
such as that on the transformer platforms.
Nonetheless, GGOWL acknowledges the UK’s international obligations that require that
installations are decommissioned as soon as is reasonably practicable. As such, adequate
provisions must be in place to ensure that the project can be fully decommissioned at year 25
in order that Government is not exposed to unacceptable risk. This programme therefore sets
out the measures for decommissioning the project at year 25.
At this point, GGOWL will present the case that re-powering is appropriate and achievable
and seek approval from the Secretary of State that the agreed decommissioning programme
be deferred in accordance with the remaining lease term for the project.
7.0
ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard
project between 2004 and 2005. The resulting Environmental Statement was submitted as
part of the project’s successful application for consent in October 2005. A lifecycle approach
was taken in considering and assessing the impacts of the project and in seeking to mitigate
and minimise the effect of the works. In all instances a ‘worst case’ approach was taken to
the assessment. As such, the assessment of the impact of the project on receptors and
stakeholders takes into account decommissioning provisions that are either consistent or more
onerous than those presented in this document.
Consistent with the commitment to undertake reviews of the decommissioning provisions
contained within this document, it is proposed that the existing EIA is reviewed throughout
the lifetime of the project. A final review will be undertaken towards the end of the life of the
installation when the final details of the decommissioning measures are known in order to
address the impact of these has been appropriately assessed. At this point a decision will be
made as to whether a more detailed assessment is required. Key criteria that will inform this
decision include:
• Identification and assessment of potential impacts on the environment, including
exposure of biota to contaminants associated with the installation, other biological
impacts arising from physical effects, conflicts with the conservation of species,
with the protection of their habitats, or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could
include:
• Benthic: side scan sonar, imaging
• Ornithological: a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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• Marine Mammals: should decommissioning activity give rise to high
noise levels, it may be appropriate to survey marine mammal activity
• Review of Nature Designations
• Identification and assessment of potential impacts relating to interference with
other legitimate uses of the sea. It is possible that the nature and/or intensity of
human activities taking place on/around the Greater Gabbard site such as
commercial fishing may have changed over the lifetime of the project. A review
will be undertaken to identify those activities with potential to be affected by
decommissioning.
• Identification and assessment of potential impacts on amenities, the activities of
communities and on future uses of the environment
• Identification and assessment of potential impacts on historic environment
interests
If required, the final EIA will fill any ‘gaps’ in relation to the above. It will also describe the
measures envisaged to avoid, reduce and, if possible, remedy any significant adverse effects
indicated.
The use of explosives is not proposed, however should explosives be necessary during the
course of decommissioning, the potential impact of these on marine life, particularly marine
mammals, will be assessed. The use of explosives will be fully justified and a mitigation
strategy proposed. All appropriate guidelines and regulations such as those currently
available from JNCC will be followed.
8.0
CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to
the successful development of the Greater Gabbard offshore wind farm project. These
principles were adopted during the development of the project and will be applied during the
life of the offshore wind farm including the decommissioning phase of the project.
GGOWL proposes to seek the advice and opinions of the following parties in drafting and
reviewing the decommissioning programme for the project.
• Centre for Environment, Fisheries and Aquaculture Science
• Joint Nature Conservation Committee
• Natural England
• The Environment Agency
• English Heritage
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•
The Maritime and Coastguard Agency
•
Trinity House Lighthouse Service
•
National Federation of Fishermen’s Organisations
•
Kent and Essex Sea Fisheries Committee
•
Chamber of Shipping
•
Royal Yachting Association
•
Harwich Haven Harbour Authority
•
British Marine Aggregate Producers Association.
In order that the impact on legitimate marine users and stakeholders is minimised, early and
comprehensive consultation prior to decommissioning is required. This strategy will be
finalised and undertaken as part of the final review process undertaken prior to
decommissioning.
At the time of decommissioning, and in accordance with Clauses 5c and 5d of the Greater
Gabbard consent under Section 36 of the Electricity Act 1989, GGOWL will issue timely and
efficient Notices to Mariners and other navigational warnings of the position and nature of
the decommissioning activities that will be taking place. Efforts will be made to ensure that
this information reaches mariners in the shipping and fishing industry as well as recreational
mariners. The UK Hydrographic Office will be notified as appropriate on the progress and
completion of the works.
9.0
SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25, coinciding with the end of the
design life of the turbines and the mid-life of the Crown Estate lease for the project.
It is proposed that full decommissioning in accordance with the provisions described above
will take 260 days to undertake:
• Project management, planning and procurement – 90 days
• Offshore decommissioning – 140 days
• Onshore works (including dismantling and disposal) – 170 days
Note that offshore decommissioning and onshore works will run in parallel. A detailed
programme of the works will be provided towards the end of the life of the project.
GGOWL acknowledges that the most important steps in the decommissioning process are the
planning ahead and the selection of the best decommissioning options. As has been indicated
throughout this document, it is intended that the current decommissioning provisions are
rigorously reviewed and assessed over the lifetime of the project.
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GGOWL intends to undertake internal reviews of the decommissioning programme
throughout the life of the project and proposes that a formal review exercise is undertaken
with DTI at the following times:
• 2 years following commencement of generation;
• 10 years following commencement of generation (2 years prior to provision of
financial security);
• 18 years following commencement of generation (mid way through the period during
which financial security is provided).
It is proposed that a final review is undertaken in year 23. This will be the opportunity to
finalise the detail of the decommissioning provisions, schedule and costs. As indicated in
Section 7, this is also the opportunity to ensure that the impact of the works has been
appropriately assessed and to determine in consultation with DTI and key stakeholders,
whether a revised EIA or Appropriate Assessment is necessary. This will also be the final
opportunity to consult with the stakeholders identified in Section 8 above about the details of
the decommissioning provisions and the schedule of works.
10.0
SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle, GGOWL proposes to clear the seabed in
accordance with the provisions made in this decommissioning programme and to collect and
provide evidence to reflect this.
Following decommissioning, surveys will be carried out to show that the site has been
cleared. These surveys will enable identification and subsequent recovery of any debris
located on the sea-bed which may have arisen from activities related to the Greater Gabbard
offshore wind farm and which may pose a risk to navigation, other users of the sea or the
marine environment. It is currently intended that side scan sonar will be used to identify
debris, with an ROV deployed to investigate and recover any potential hazards identified.
The area to be covered will be determined prior to decommissioning but GGOWL is aware of
the guidance for oil and gas installations which specifies a 500m radius around any
installation.
Reference will also be made to the “Archaeological No Build Areas” in order that these are
not inadvertently cleared in the process of removing any debris. Analysis of the survey data
will also ensure that items for removal and disposal relate only to the wind farm. The
appropriate competent authority will be approached regarding the identification of other
anomalies that may be of archaeological interest.
It is important that this process of collecting and presenting evidence that the site is cleared is
independent. GGOWL propose that an independent survey company complete the surveys
and that they report in parallel to both GGOWL and DTI.
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11.0
RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site, as
far as is reasonably practicable, to the condition that it was in prior to construction.
Consistent with the decommissioning provisions detailed above, the key restoration work will
relate to:
• Ensuring that foundations cut below seabed (turbines, met mast, platforms) are
made safe and adequately covered
• Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered
that such works present unnecessary and unacceptable risk to personnel. Rather, it is
considered that allowing the seabed to ‘self-settle’ is sufficient and in proportion to the
limited environmental impact of the proposed decommissioning.
12.0
POST-DECOMMISSIONING MONITORING, MAINTENANCE AND
MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations, some post
decommissioning activities are proposed in order to identify and mitigate any unexpected
risks to navigation or other users of the sea which may be posed by the remaining materials
(for example, where cables or foundations may have become exposed due to natural sediment
dynamics).
The proposed post decommissioning activities are appropriate to:
• the scale and nature of the remaining infrastructure
• the degree of risk that any remains become exposed
• the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large, it is
considered that the risk of exposure is extremely low, primarily due to the depth at which
foundations will be cut and cables buried and the relative stability of the seabed in the area.
In comparison to the oil and gas industry where the likelihood of debris falling overboard
over the life of the installation is relatively high, such risks are low for the Greater Gabbard
project where offshore work associated with operations and maintenance is low and
contained within the turbine structure.
Given that the site is not heavily fished, and that the distance offshore deters recreational
users from the site, it is also considered that the degree of risk to legitimate marine users is
low.
On the basis of this low degree of risk, it is proposed that the following monitoring surveys
are undertaken for elements left in situ beneath the sea-bed:
Page 56 of 58
• Once at the time of completion of decommissioning
• Annually for the following two years
• Once after 5 years
• Once after 10 years
At each proposed time, GGOWL will perform a geophysical survey including a
magnetometer survey on the site. As indicated in section 10 above, GGOWL propose to use
an independent survey company to complete the surveys. The company will be requested to
report in parallel to both GGOWL and Government.
In the event of protrusion, or in the event that scour protection materials are left on site
following decommissioning (see section 4.2.6), GGOWL will ensure that notification is given
to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be
marked on relevant charts and mariners informed accordingly.
It is noted that, at the time of writing, a solution for addressing residual liability has not been
finalised. Until a solution has been agreed GGOWL do not consider it appropriate to detail
any specific management or maintenance procedures within this document.
13.0
SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in
the document:
• Greater Gabbard Environmental Statement, October 2005
• Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm,
December 2006
• Decommissioning of Offshore Renewable Energy Installations under the Energy
Act 2004: Guidance notes for Industry, DTI, December 2006
• Guidelines and Standards for the Removal of Offshore Installations and Structures
on the Continental Shelf and in the Exclusive Economic Zone, International
Maritime Organisation (IMO), 19th October 1989
• Guidance Notes for Industry: Decommissioning of Offshore Installations and
Pipelines
under
the
Petroleum
Act
1998,
DTI,
http://www.og.dti.gov.uk/regulation/guidance/decommission.htm
• Review of the Current State of Knowledge on the Environmental Impacts of the
Location, Operation and Removal/Disposal of Offshore Wind-Farms, OSPAR,
2006, ISBN 978-1-905859-15-3, www.ospar.org
Page 57 of 58
• Guidelines for Environmental Risk Assessment and Management, Defra,
September 2002, http://www.defra.gov.uk/environment/risk/eramguide/08.htm
• Guideline on Decommissioning Cost Estimation, Turner & Townsend Energy for
UKOOA, December 2006, www.oilandgas.org.uk/ukooa
14.0
ANNEX A: GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
15.0
ANNEX B: GREATER GABBARD APPROPRIATE ASSESSMENT
16.0
ANNEX C: GREATER GABBARD DECOMMISSIONING PROGRAMME
FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58

gabbards

Transcription

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