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HAR-01031-DEC-EN-REP-0001-ENV-A4
Harding Submerged Turret Loading (STL) System Decommissioning:
Environmental Report
Prepared for: TAQA Bratani Ltd
Aberdeen
Prepared by: Ramboll Environ
Edinburgh, UK
Date: August 2015
TAQA Document Number:
HAR-01031-DEC-EN-REP-0001-ENV – Rev A4
Project Number: UK12-20847
HAR-01031-DEC-EN-REP-0001-ENV – Rev A4
ENVIRON
Contract No: UK1220847 Issue: 7 Author Felicity Arthur (signature):
Project Manager/Director Nathan Swankie (signature):
Date: August 2015
This report has been prepared by ENVIRON with all reasonable skill, care
and diligence, and taking account of the Services and the Terms agreed
between ENVIRON and the Client. This report is confidential to the client,
and ENVIRON accepts no responsibility whatsoever to third parties to
whom this report, or any part thereof, is made known, unless formally
agreed by ENVIRON beforehand. Any such party relies upon the report at
their own risk.
ENVIRON disclaims any responsibility to the Client and others in respect of
any matters outside the agreed scope of the Services.
Version Control Record
Issue Description of Status Date Reviewer
Initials
Author
Initials
A First Draft 06/02/2015 NS FA/AB
1 First Issue to Client – Draft for comments 06/02/2015 NS FA
1A First review comments 18/02/2015 - FA
2 Second Issue 20/02/2015 NS FA
2A Second review comments 26/02/2015 FA
3 Final Issue 26/02/2015 FA FA
3A Third review incorporating DECC comments 22/06/2015 FA AB
4 Final Issue awaiting DP Appendix
amendments
30/06/2015 FA AB
5 Final Issue following on from DP Appendix
amendments
02/07/2015 FA AB
6 Final Issue incorporating additional client
comments
14/07/2015 FA AB
HAR-01031-DEC-EN-REP-0001-ENV-A4
Version Control Record
Issue Description of Status Date Reviewer
Initials
Author
Initials
6A Incorporation of client comments 06/08/2015 NS KB
7 Final issue incorporating additional comments 21/08/2015 NS KB
HAR-01031-DEC-EN-REP-0001-ENV-A4
ENVIRON
Contents
Page
Executive Summary i
1 Introduction 1
1.1 The Harding Field 1
1.2 Submerged Turret Loading System Decommissioning 1
1.3 Comparative Assessment for Suction Anchor Decommissioning 2
1.4 Relevant Legislation 4
1.5 Scope of the Environmental Report 4
2 Baseline Conditions 6
2.1 Physical Environment 6
2.1.1 Metocean Conditions 6
2.1.2 Seabed Sediments and Chemistry 7
2.2 Biological Environment 10
2.2.1 Designations 10
2.2.2 Plankton 14
2.2.3 Benthos 14
2.2.4 Seabirds 16
2.2.5 Fish 18
2.2.6 Marine Mammals 20
2.3 Human Environment 20
2.3.1 Commercial Fisheries 20
2.3.2 Shipping and Navigation 22
2.3.3 Marine Archaeology 24
2.3.4 Other Sea Users 24
3 Environmental Analysis 25
3.1 Methodology 25
3.1.1 Frequency/Likelihood 25
3.1.2 Severity (Magnitude) 26
3.1.3 Environmental Significance (risk) 26
3.2 Potential Effects 27
3.2.1 Designations 28
3.2.2 Seabed Disturbance 28
3.2.3 Underwater Noise 30
3.2.4 Socio-economic Effects 31
3.2.5 Accidental Events 31
3.2.6 Issues scoped out from potentially significant effect 32
4 Summary of Commitments 34
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List of Tables
Table 1.1: Duration of Each Component of the Decommissioning of the Suction Anchors by
RI 3
Table 1.2: Scoping Matrix 5
Table 2.1. Organisms recorded in TAQA video footage of STL system 16
Table 2.2: Seabirds for which there are known records in the area of the STL System 17
Table 2.3: Elasmobranch species identified as ‘Priority Marine Features’ for which there
are known records in the area of the STL System 19
Table 2.4. Landing of fish (demersal, shellfish and pelagic) in tonnes from 2009 to 2013 in
ICES square 47F1 21
Table 3.1. Frequency/Likelihood of an effect occurring 25
Table 3.2 Severity (Magnitude) of an effect 26
Table 3.3 Environmental Significance (Risk) 27
Table 3.4. Summary of activity/effect interactions for further consideration 27
Table 3.5: Vulnerability of seabirds to oil pollution throughout the year. 32
Table 4.1: Summary of Commitments 34
Table D.1: Species provided with designation and/or conservation status 44
List of Figures
Figure 1.1: Location of Harding Field and Submerged Turret Loading System infrastructure
Layout 1
Figure 2.1. Location of Harding Platform, Harding STL Buoy and suction anchors in
relation to the closest sediment samples 9
Figure 2.2A. Designations located within an approximate 150 km2 area from the Harding
STL System 12
Figure 2.2B. The closest designations within an approximate 300 km2 area from the
Harding STL System. 13
Figure 2.3: Fishing effort by ICES Rectangle Data. Rectangle 47F1. 21
Figure 2.3. Vessel density in the UK 2012. 23
HAR-01031-DEC-EN-REP-0001-ENV-A4
ENVIRON
Annex A: References
Annex B: Comparative Assessment and Environmental Scoping Matrices
Annex C: Concentration of contaminants in sediments measured in the Gardline
Environmental Ltd Study
Annex D: Designated Species
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Acronyms and Abbreviations
ABP: Associated British Ports
BAP: Biodiversity Action Plan
BCs: Background Concentrations
CA Comparative Assessment
CEFAS: Centre for Environment, Fisheries and Aquaculture Science
CITES: Convention on International Trade in Endangered Species
CPR: Continuous Plankton Recorder
DECC: Department of Energy and Climate Change
DP: Decommissioning Programme
DSV Diving Support Vehicle
ERRV Emergency Response and Rescue Vehicle
EU: European Union
GES: Good Environmental Status
ICES: International Council for the Exploration of the Seas
IUCN: International Union for Conservation of Nature
JNCC: Joint Nature Conservation Committee
LC: Low Concern
MOD: Ministry of Defence
MPA: Marine Protection Area
NMPi: National Marine Planning interactive
NT: Near Threatened
OPEP: Oil Pollution Emergency Plans
OSPAR: The Convention for the Protection of the Marine Environment of the North East
Atlantic
PAH: Polyaromatic Hydrocarbons
PLEM: Pipeline End Manifold
PMF: Priority Marine Feature
PSV Platform Supply Vessel
RCAHMS: Royal Commission on the Ancient and Historical Monuments of Scotland
RI: Reverse Installation
ROV: Remotely Operated Vehicle
ROVSV Remotely Operated Vehicle Support Vehicle
SAC: Special Area of Conservation
SNC: Scottish National Committee
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SPA: Special Protection Area
STL: Submerged Turret Loading
THC: Total Hydrocarbons
UK DMAP: United Kingdom Digital Marine Atlas
UK: United Kingdom
UKOOA: United Kingdom Offshore Operators Association
UNESCO: United National Education Scientific and Cultural Organisation
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Executive Summary
Ramboll Environ UK Ltd (Ramboll Environ) (formerly ENVIRON UK Limited) has undertaken
an environmental appraisal on behalf of TAQA Bratani Limited (TAQA) in support of
proposals to decommission the existing Submerged Turret Loading (STL) system from the
Harding field. The Harding field sits in a water depth of approximately 110m, approximately
320 km north of Aberdeen in the Central North Sea.
The STL system infrastructure to be removed comprises a mooring and interface buoy, eight
mooring lines and eight suction anchors. A pipeline from the Harding platform currently
connects through a Pipeline End Manifold (PLEM) on the seabed and riser into the mooring
and interface buoy, allowing stabilised hydrocarbons to be periodically loaded from the
Harding platform to shuttle tankers and transported to shore for processing. The pipeline and
PLEM will remain in place for reuse as part of the replacement loading system which will
subsequently be installed. The riser will be capped and removed along with the buoy. Works
associated with the pipeline, PLEM, riser and replacement loading system are not included
in this assessment.
A range of options were considered for decommissioning, particularly relating to the suction
anchors through a Comparative Assessment (CA). Complete removal of the suction anchors
by Reverse Installation (RI) was selected as the most suitable method.
In the event that removal by RI in relation to one or more of the suction anchors fails (i.e. one
or more of the suction anchors cannot be removed) for minor technical reasons, further
removal attempts shall be made as part of the planned 2016 works using contingency plans
identified by TAQA. Where removal is not possible for more substantive technical reasons
(e.g. due to structural failure or soil piping) rockdumping over the top of the anchor will be
carried out. Rock will be placed to ensure an overtrawlability ratio of maximum 1:3 and the
anchor will be left in situ to degrade naturally.
An initial environmental scoping workshop identified the potential for significant
environmental effects from these proposals on marine mammals; benthos and natural
seabed sediments and on commercial fisheries. Potential issues associated with human
health and safety were also identified at scoping stage and have been considered as part of
the CA.
Seabed sediments in the area of the STL system and specifically the suction anchors
comprises mud and sandy mud. The localised area would be disturbed during suction
anchor removal, however review of seabed monitoring data associated with the nearby
Harding platform indicates that the sediments are unlikely to contain contaminants above
background levels, therefore no significant effects from the mobilisation of historic
contaminants in the seabed are anticipated. Mobilised sediment will settle out quickly or be
dispersed by localised bottom currents. In the event of rockdumping to leave a suction
anchor in situ, localised effects on soft sediment benthic communities may be expected
however this is unlikely to be significant.
Activities particularly associated with the cutting of the mooring lines and removal of the
suction anchors and also associated with all decommissioning vessel activities will generate
underwater noise. Receptors identified within the vicinity of the STL system comprise a
number of species of marine mammals including low numbers of minke whale; white-beaked
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dolphin; and Atlantic white-sided dolphin. Harbour porpoise are also known to be present in
the area in higher numbers. Best practice mitigation measures will be employed during
decommissioning activities, and vessels will avoid concentrations of marine mammals where
they are observed.
Commercial fishery activities in the area are dominated by the use of demersal trawl gear.
The removal of the suction anchors will remove a potential snagging hazard from the
seabed. In the event of rock dumping where an anchor is required to be left in situ it will be
left in a condition so as not to present a snagging hazard in addition to which its location will
be recorded on fishSAFE to assist fishermen to avoid the structure(s) during fishing
operations.
Standard operating procedures according to the relevant Oil Pollution and Emergency Plan
(OPEP) will be in place at all times to control the potential for and mitigate any consequence
from accidental hydrocarbon releases during decommissioning operations. Flushing
activities performed from the Harding platform to a tanker moored to the STL system will
take place prior to removal of the buoy, which will ensure hydrocarbons are cleared from the
pipeline, riser and buoy therefore minimising the risk of accidental hydrocarbon
contaminated discharges to seawater during decommissioning.
Based on the assessment set out within this report and on the assumption that the
environmental commitments set out within this report are implemented throughout all
decommissioning activities, it is not anticipated that the activities as set out within the DP will
have significant residual effect on the receiving environment.
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1 Introduction
Ramboll Environ has undertaken the following environmental appraisal on behalf of TAQA
Bratani Ltd (TAQA) in support of proposals to decommission the existing Submerged Turret
Loading (STL) System. The STL system is currently providing facilities for stabilised
hydrocarbons produced from the Harding Field to be loaded into shuttle tankers for
transportation onshore for processing.
1.1 The Harding Field
The Harding field is located approximately 320 km north east of Aberdeen in block 9/23b in
the Central North Sea. Water depth is approximately 110 m.
The Harding platform is a jack-up platform producing stabilised hydrocarbons which are
stored in integrated storage cells located on the seabed beneath the platform and
periodically emptied via a 24” subsea flowline which runs for approximately 2 km east from
the platform to a STL System through which hydrocarbons are loaded to shuttle tankers for
transport to shore.
Figure 1.1: Location of Harding Field and Submerged Turret Loading System infrastructure Layout
1.2 Submerged Turret Loading System Decommissioning
As part of the operational requirements for the Harding Field, replacement of the current
loading system is scheduled between May and July 2016.
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In order to complete the replacement, the existing structures require decommissioning in
accordance with DECC guidance1. This Environmental Report (ER) covers the
decommissioning of the following components of the loading system:
STL mooring and interface buoy;
Eight Mooring lines each 675m length (225 m of wire, 450m of anchor chain) and
associated infrastructure; leading to
Eight suction anchors:
– 5 suction anchors measuring 8 m height, 5 m diameter and 41 tonnes; and
– 3 suction anchors measuring 10 m height, 5m diameter and 45 tonnes.
This ER assumes the mooring and interface buoy will be recovered and returned to its owner
for reuse/decommissioning by separate process. The eight mooring lines and the suction
anchors will be removed by the reversal of the installation method used when the items were
first installed (see section 1.3 for further detail). The riser will be capped and recovered to
the decommissioning vessel. The Pipeline End Manifold (PLEM) will remain in place for
reuse during the subsequent installation of the replacement STL system.
Once removed from the sea, the suction anchors and mooring lines will be disposed of via
an onshore accredited recycling/waste management facility.
Note: Decommissioning of the Dynamic Riser installed on the present system and
installation of the replacement loading system do not form part of this ER.
1.3 Comparative Assessment for Suction Anchor Decommissioning
The STL buoy and mooring lines are required to be removed prior to removal of the suction
anchors. A length of approximately 10-15 m of chain associated with the mooring lines will
remain in place and be removed with the suction anchors.
A range of options were considered for decommissioning of the suction anchors and a
Comparative Assessment (CA) was completed in order to identify the most appropriate
option for removal. The CA took account of safety; technical feasibility; environment and
social factors; and project costs. For further detail on the CA process see section 3.3.2 of
the Decommissioning Programme (DP) and also the Suction Anchor Decommissioning
Comparative Assessment Report (PDi, 2015). Environmental scoping matrices covering the
options which were considered within the CA and which were used to inform the CA process
are included in Annex B of this report.
Complete removal by Reverse Installation (RI) was selected as the most suitable method. RI
is carried out by attaching a pumping interface to the suction anchor and flushing water from
the vessel into the suction anchor in an attempt to reverse the suction pressure within the
anchor. Once the reverse installation method has raised the pile as far as possible,
completion of the removal of the suction anchor will be carried out using the vessel
1 DECC (2011): Guidance Notes: Decommissioning of Offshore Oil and Gas Installations and pipelines under the Petroleum Act 1008. Version 6. March 2011. UEN 09D/734
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crane/deck winch. Following the removal, an ‘overtrawlability assessment’ will be carried out
to ensure the seabed is left in a safe state.
Successful removal of the suction anchors using RI is not expected to result in any residual
depressions in the seabed. However, in the unexpected event that the overtrawlability test
identifies the seabed is not compliant2, review of the available remedial actions will be
undertaken, including appropriate consultations, to identify the preferred action.
The DP also identifies a worst case scenario whereby the differential pressure cannot be
raised to sufficient levels to overcome the soil friction resulting in the failure to remove either
a single or multiple suction anchors by RI. At the time of removal, reasonable endeavours
will be made to remove each of the eight suction anchors in turn, irrespective of the success
or failure of the RI methodology with the other anchors.
Failure to remove the suction anchors may be caused by soil failure and/or a range of
mechanical failures. The technical reasons associated with failure to remove suction
anchors have been considered in the Technical Note on Suction Anchor Removal Failure
Modes (TAQA, 2015). For each different reason for failure, contingency removal methods
have been identified and the complexity, time and cost implications and the likelihood of
success been assessed.
For technical failures, where the contingency repair options are identified to be complex
(requiring further engineering, potentially bespoke fabrication and/or novel solutions, and
with no guarantee of success), no further attempts will be made to remove the particular
suction anchor. In these circumstances a rock dump over the top of the anchor will be
carried out to ensure an ‘overtrawlable’ slope, which does not pose a hazard to other users
of the sea and will be left in situ.
Where contingency repair options are identified as straightforward, the repair will be made
and further attempts made to remove the suction anchor in 2016 as part of the planned
works. Should the additional attempt to remove the suction anchor be unsuccessful, rock
dumping will be carried out as detailed above.
In the event that failure to remove the suction anchor occurs part way through the recovery
process (i.e. the pile protrudes significantly further out of the seabed that initially found),
specific assessment of the situation will be carried out and the appropriate course of action
will be determined.
Table 1.1 details the anticipated duration of each component of the decommissioning of the
suction anchors by RI.
Table 1.1: Duration of Each Component of the Decommissioning of the Suction Anchors by RI
Activity Duration (days)
Vessel mobilisation and transit 1
2 Compliance is based on the NORSOK U-001 and/or ISO 13628 assessment for overtrawlability,
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Perform pre-survey of 8 suction anchors(3 hours/anchor) 1
Removal by RI and recovery of suction anchors (36 hours/anchor) 12
Remedial backfill operations, including an ‘overtrawlability’
assessment
2
Vessel transit and demobilisation 1
Total 17
Source: TAQA Bratani Limited. Environmental workshop, 10 November 2014
Additional details of each activity which were used to inform discussion within the
environmental scoping workshop (see section 1.5 below) are included in Annex B2.
1.4 Relevant Legislation
The primary legislation governing the decommissioning of The Harding STL system is the
Petroleum Act 1998 (as amended by the Energy Act 2008). Whilst the case for
Environmental Impact Assessment (EIA) is not prescriptive within statute, a clear reference
to the requirement for EIA under the terms of the Offshore Production and Pipelines
(Assessment of Environmental Effects) Regulations 1999 as amended (the EIA Regulations)
is set out within DECC guidance.
1.5 Scope of the Environmental Report
An environmental scoping workshop attended by representatives from both TAQA and
Ramboll Environ was held on 10th November 2014.
Preliminary environmental risk matrices were completed which documented high level
consideration of potential activity/receptor interactions based on the professional judgment of
environmental specialists and drawing, where appropriate, on previous experience and
lessons learned from previous decommissioning projects.
Potentially significant effects associated with the range of options for decommissioning the
DP activities described above were identified as part of the CA process (described above
and in Annex B). In addition, those effects specifically associated with the activities as set
out within the DP are summarised in Table 1.2 below and these form the basis of the
environmental considerations set out within the remainder of this ER3.
3 Note potential for effect at scoping stage was considered without mitigation.
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Table 1.2: Scoping Matrix
Notes: Refer to Tables 3.1, 3.2 and 3.3 which summarises the environmental risk methodology which has been applied.
Plan
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Fish an
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Seabird
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Marin
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Design
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Geo
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Natu
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Sedim
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Cu
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Bath
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Energy U
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Air Q
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deco
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Energy U
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Air Q
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ngo
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Waste
Man
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Wate
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Fisheries
Econ
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Recreatio
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Hu
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Marin
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Activities
Decommissioning of the STL Buoy itself
Sever and recover 8 mooring lines
Suction Anchor removal option 3. Rockdump, leave in place to
degrade naturally (only in event that Option 4 RI fails)
Suction Anchor removal option 4. Full Removal by Reverse
Installation
ENVIRONMENTAL ISSUES
Biological Environment Physical Environment Human Environment
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2 Baseline Conditions
The following section summarises known data relating to the current baseline conditions in
and around the STL System. The baseline assessment characterises the environmental
conditions within an area covered by a 5km radius from the location of the STL buoy.
However where data are available at different reference scales, the scale most relevant to
the project has been used4.
The baseline assessment includes the biological environment, the physical-chemical
environment (including the waves, winds and sediments) and also relevant aspects of the
human environment.
Baseline data sources have included project specific information and survey data provided
by TAQA. Baseline information on the benthos and fauna has been drawn from Remote
Operated Vehicle (ROV) surveys of the STL system completed in 2014. Whilst this 2014
survey was carried out primarily to assess potential damage to the structures, it also
provides imagery which has been used to assist in the characterisation of the current
benthos and fauna on these structures. Additional data has been drawn from sediment and
invertebrate sampling carried out around the main Harding Platform as applicable (ERT
(Scotland) Ltd, 2000; and Gardline Environmental Limited, 2013). This area is located
between 1.5 and 2.7 km from the structures of the STL system to be decommissioned.
This information has been supplemented with published and accredited literature and online
data resources including significant usage of the Scottish Government National Marine Plan
interactive (NMPi) tool.
A full list of references used is included in Annex A.
2.1 Physical Environment
2.1.1 Metocean Conditions
Metocean conditions in the North Sea vary throughout the year. A review of available data
relevant to the Harding Field indicates the dominant wind direction throughout the year
ranges from North West (NNW) to East South East (ESE) dependent on the season5. Wind
speeds also vary throughout the year. In the summer months wind speeds are at their
lowest with an average of 8.1 to 8.5 m/s. During the autumn and winter winds speeds are
greater at between 12.1 and 13.0 m/s on average.
Water circulation in the North Sea is affected by water depths, wind, tides, currents and
oceanic circulation within the North Atlantic. ROV surveys (TAQA, 2014) demonstrated a
water depth of up to approximately 115 metres in the region of the STL system, confirmed by
previous seabed environmental surveys (ERT, 2000). The general circulation pattern in the
North Sea is mainly cyclonic (Winther et al, 2006), with the Fair Isle leading into the Dooley
currents bringing North Atlantic water into the area of the Harding Field. In addition data
from Marine Scotland (2011) indicates waters circulation in the vicinity of the STL system are
4 For example where data is available based on regional or ICES administrative areas these have been specifically reference. 5 Based on observations from September 2011 to November 2014, taken from the Sleipner A Platform at 58°22’0”N (58.3667), 1°54’25”E (1.9069). Data obtained from Windfinder, available at: http://www.windfinder.com/weather-maps/report/norway#8/58.301/0.818.
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also influenced by more localised coastal currents. Water circulation varies over the course
of the year responding mainly to variations in wind direction and speed (Marine Scotland,
2011). Winds drive the waves which also therefore vary seasonally. Wave heights are
recorded as slightly smaller during spring and summer and higher during autumn and winter.
Winter wave heights are recorded at up to 3.26-3.50 m (ABP Marine Environmental
Research, 2014).
The effects of tides in this area are minimal, with some of the lowest tidal ranges and flows
recorded in the North Sea. The spring tide range is 1.76-1.79m (Marine Scotland, NMPi,
accessed Dec 20146), the tidal peak flow is <0.11 m/s and tidal powers of at most 0.06-0.10
kW/ m2 measured at approximately 50% from the surface, e.g. 50 to 60 metres depth (ABP
Marine Environmental Research, 2014).
Annual mean salinity at the surface and near the seabed is approximately 35.11 and
35.15 ‰ respectively and mean temperature at the surface and seabed are 9.45 and 8.43°C
respectively (Marine Scotland, NMPi, accessed Dec 20147).
2.1.2 Seabed Sediments and Chemistry
Sampling was carried out in the wider area of the Harding Platform (ERT (Scotland) Ltd,
2000; and Gardline Environmental Limited, 2013) for particle size, organic content and
sediment contamination in these areas (ERT (Scotland) Ltd, 2000; Gardline, 2006).
Closest seabed sampling locations were approximately 2 km west from the STL system itself
and between 1,475 and 2,672 m from the location of the closest suction anchors. See
Figure 2.1.
Particle size of substrates have strong associations with the hydrodynamic energy of the
area, the retention of chemicals pollutants and the type of organisms able to reside in the
habitat. Some of these factors are also affected by the organic content of sediments. In
both the 2000 and 2006 surveys the substrates were classified as fine to very fine sands,
considered representative of the wider area. The British Geological Survey data, classified
the seabed type around the STL system as mud and sandy mud based on (Marine Scotland,
2014).
Total organic matter was relatively uniform across the area surveyed in 2006, with no
discernible geographical pattern identified reflecting proximity to the Platform. Overall,
sediment organic matter concentrations appeared to have fallen since 2000, which may be
an indication of the potential for natural recovery of the seabed from historic incidents of
contamination.
Sediment samples from the 2006 survey (Gardline, 2006) were also assessed for Total
Hydrocarbons (THC), n-alkanes and isoprenoids (useful as an indicator of synthetic based
drilling fluids), a suite of polyaromatic hydrocarbons (PAHs) and a range of heavy metals.
Results from the closest sampling location8 to the STL system are presented in Annex C.
OSPAR Background Concentrations (BCs) from remote/pristine areas are also presented in
6 http://www.scotland.gov.uk/Topics/marine/seamanagement/nmpihome/nmpi, accessed 11.12.2014 7 http://www.scotland.gov.uk/Topics/marine/seamanagement/nmpihome/nmpi, (accessed 11/12/2014) 8 500m South East of the Harding Platform and approximately 1 km from the STL
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Annex C. Comparison of the samples with BCs enables an indication of the extent of
contamination to be drawn.
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Figure 2.1. Location of Harding Platform, Harding STL Buoy and suction anchors in relation to the closest sediment samples
Harding Platform location - Longitude, Latitude: 59°16’46.159 N, 01°30’58.594 E; Ordnance Survey (OS) Easting, Northing: 600424, 1048952; International Spheroid ED50 UTM projection Easting,
Northing: 6572267.2N, 415448.8E. Harding STL Buoy location - Longitude, Latitude: 59°16’37.230 N, 01°33’07.430 E; Ordnance Survey (OS) Easting, Northing: 602477, 1048785; International
Spheroid ED50 UTM projection Easting, Northing: 6571946.2N, 417482.0E
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The samples demonstrate concentrations of THC and PAH at or below the OSPAR BC
(where available) for all parameters other than Napthalene at the majority of stations greater
than 500m from the Harding platform in the 2000 survey. Background levels of
hydrocarbons were found at six of the eleven locations (including closest to the STL system)
in the 2006 survey.
Total n-Alkanes and Isoprenoids are useful indicators of drilling fluids. Although measurable
in the sample closest to the STL system, the concentrations were low compared to sampling
locations in closer proximity to the Harding Platform. No OSPAR BC are available for these
chemicals.
Concentrations of various heavy metals were assessed and were all less than BC (where
available), other than for iron. Concentrations of heavy metals were also less than BC at
many of the other sampling sites in the 2006 study. Barium can be a useful as an indicator
of drilling fluids. No BC is available for barium, however it was concluded in the Gardline
Environmental Ltd study that the barium concentrations in the sediments were indicative of
drill cuttings likely present in sediments up to 1km from the Harding platform and that these
were most concentrated in sediments close to the platform. Analysis of surficial sediments
extracts for drilling fluids, suggested the presence of at least two different types of drilling
fluid, both of which were found in differing states of degradation.
Overall, the sampling indicated little evidence of pronounced cuttings piles, which may
indicate erosion and transport of contaminated cuttings away from the site or deposition of
non-contaminated sediments over the piles. The survey report concluded that ‘based on
previously published information, ecological impacts of hydrocarbons in the concentrations
found at all bar one of the stations are likely to fall somewhere between negligible and
intermediate.’ Areas furthest away from the Harding Platform demonstrated the lowest
contamination levels and likely indicate a low level of contamination in the vicinity of the STL
system.
2.2 Biological Environment
The marine ecosystem is a complex assemblage from plankton at the base of the food
chain, through to cetaceans and elasmobranchs at the top. Species composition varies
seasonally, dependent upon factors such as breeding, feeding and migration.
2.2.1 Designations
The position of designations relative to the Harding STL system are shown in Figure 2.2 (A
and B).
A number of species which are accorded protection under a range of potentially relevant
legislation have recorded distributions in the area of the STL system. Those species with
designations and conservation status are summarised in Annex D and considered further in
the remainder of this section, as appropriate.
No records exist for International or European designated habitats within 5 km of the STL
system.
A review of Priority Marine Features in the vicinity of the STL system identified the presence
of the Ocean Quahog (Arctica Islandica) (discussed in Section 2.2.3 below) within 1 km of
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the STL system. Although evidence of burrows was observed in the ROV footage, there are
no records of burrowing mud amphipods (Maera loveni) - a component species of burrowed
mud, designated as a Scottish Priority Marine Feature (PMF) - within 15 km of the STL
system (Marine Scotland Web Map Service – designations). No other Priority Marine
Features (habitats or species) have been identified within 15 km radius of the STL system.
The Braemar Pockmarks are an Annex I Habitats Directive habitat and are recorded as the
closest Special Area of Conservation (SAC) to the Harding STL system, at approximately
30 km south. The Marine Protected Areas (MPAs) illustrated in 2.2B are, in order of
approximate distance from the STL system: Central Fladen (approximately 90 km west), The
Norwegian Boundary Sediment Plain (approximately 121 km south) and Mousa to Boddam
(approximately 170 km North West).
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Figure 2.2A. Designations located within an approximate 150 km2 area from the Harding STL System
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Figure 2.2B. The closest designations within an approximate 300 km2 area from the Harding STL System.
The map is biased towards the west North Sea to the west of the System due to higher number of significant designations in this region.
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2.2.2 Plankton
Plankton are microscopic plants and animals that inhabit the pelagic zone and are typically
free floating. Phytoplankton are plants and zooplankton are animal species. Both
phytoplankton and zooplankton form the basis of the food chain and constitute a vital food
source for many higher level organisms.
In the Northern North Sea long term data (SAHFOS, 2014) indicates the dinoflagellate genus
Ceratium dominates the phytoplankton community and copepods dominate the zooplankton.
Blooms of phytoplankton occur in the spring, followed by a smaller peak in the autumn. The
last publicly available dataset from 2001 demonstrated population peaks of various Ceratium
species in February, June to August and October to November in the area of the STL
system (SAHFOS Win CPR). The blooms occur mainly as a result of lower water mixing,
stratification and longer daylight hours. The greatest concentrations are in the top 30-50m of
the water column (Johns and Reid, 2001). Zooplankon populations peak approximately two
months following the increase in phytoplankton populations. Johns and Reid (2001) indicate
North Sea plankton is dominated by the copepods Calanus spp and Pseudocalanus spp.
The long term data set indicates increasing phytoplankton concentrations in recent years,
considered likely to be associated with observed increases sea surface temperatures (Johns
and Reid, 2001).
2.2.3 Benthos
Benthic organisms are those that live in and on the bottom of the ocean floor. Some benthic
organisms feed by filtering particles from the water and others by collecting deposits from on
or within the substrate. Records of designated benthic organisms exist in the vicinity of the
STL system. These include the Ocean Quahog (Arctica Islandica) designated as a Scottish
Priority Marine Features (PMF) and included on OSPAR list of threatened and/or declining
species. The closest recorded observation is 1km from the STL system.
2.2.3.1 Benthic Community Surveys
Benthic community surveys at 11 sites around the Harding Platform (between 1.5 and 2.7
km from the STL system) were conducted in 2006 and found a total of 168 adult and 31
juvenile taxa. Recorded taxa from all the sites consisted on average of 42% polychaete
annelids, 23% crustaceans, 26% molluscs, 6% echinoderm and 4% minor phyla. The data
from the sampling point closest to the STL system (Figure 2.1), indicated some of the
highest scores for number of individuals, number of adult taxa, Shannon-Wiener Diversity
Index, Margalef’s Richness and Pielou’s Evenness, number of individual polychaetes,
crustaceans, molluscs, echinoderms and minor phyla. This is indicative of a more
ecologically diverse and less impacted benthos than other sampling locations. Statistical
analyses also showed a correlation between the variations in the concentrations of a suite of
hydrocarbon measurements and the overall faunal multivariate pattern. This suggests that
of the variables measured, hydrocarbon contamination of the sediments is the factor most
likely to be influencing the community around the Harding platform.
Historical benthic community survey data also exists from 2000. Sampling locations varied
between the surveys in 2000 and 2006. Comparisons were made between the community
composition from the two sampling sites in closest proximity to the Harding STL System in
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2006 and 2000 (See Figure 2.1). In 2000 high numbers of Capitella spp and Ophryotrocha
spp polychaetes were recorded. These species are pollution tolerant, opportunistic species
that may dominate in contaminated environments, such as one impacted by hydrocarbons
and metals associated with oil and gas drilling. In the 2006 samples only small numbers of
these species were recorded.
2.2.3.2 ROV Footage
Most recent ROV footage from 2014 (TAQA, 2014) was viewed to give a high level indication
of the habitat and organisms on and in the immediate surroundings of the suction anchors.
The dominant organisms observed on the suction anchors and in the immediate vicinity are
recorded in Table 2.1 and include cnidarian (in particular anemones and dead man’s
fingers), tube worms, echinoderms (in particular starfish), sponges, cod and encrusting
algae.
The footage also indicated a muddy/sandy benthic environment with evidence of burrows,
and areas littered with bivalve shells. This further validates the 2000 and 2006 sampling
results and the benthic records data held by Maine Scotland (Marine Scotland) which
indicate fine sands and mud/sandy mud environment respectively.
Data on the benthic species recorded in the ROV footage from 2014 and the benthic
community survey data from 2000 and 2006 offers limited opportunity for comparison as the
survey techniques employed in each survey are not comparable. The benthic community
surveys used grab samples to collect macrofaunal species primarily residing in the sediment
(a quantitative analysis). The ROV footage was undertaken primarily to survey the integrity
of the structures, but has also been used here to provide a valuable resource for observing
species either attached to the structures or those living in close proximity to the structures (a
qualitative analysis). Although some of the same species may be present on the sediment
surface and in the sediment, it is not possible to confirm this from the video footage, which is
not focused on the sediment itself.
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Table 2.1. Organisms recorded in TAQA video footage of STL system
Common
Group name Phylum (class) Observations
Invertebrates
Anemones Cnidaria Widespread distribution over all structures. Limited
occurrence on the surface of the sediment. Highly abundant.
Tube worms Annelida
(polychaete) Widespread distribution over all structures. Highly abundant.
Dead man’s
fingers Cnidaria Widespread distribution over all structures. Highly abundant.
Hermit crabs Crustaceans Low abundance observed
Starfish Echinodermata Widespread distribution over all structures. Highly abundant.
Sponges Porifera Abundance and distribution difficult to determine from footage
Brittlestars Echinodermata
Low abundance. Observed most frequently on the mooring
chain connectors.
Urchins Echinodermata Low abundance observed
Barnacles Crustaceans Low abundance observed
Hydroids Cnidaria Low abundance observed
Crabs Crustaceans Low abundance observed
Bryozoans Bryozoa Low abundance observed
Chordata
Cod (Gadus
spp.) Teleosts
Frequent observations around mooring chains and suction
anchors.
Flat fish Teleosts Occasional observations around mooring chains and suction
anchors.
Monkfish Teleosts One observation in the vicinity of a mooring chain
Plants
Encrusting
algae
Rhodophyta and
Ochrophyta
Extensive coverage of a thin layer of algal growth. Due to the
quality of the footage no further details are possible.
Notes: Each video was played. The proportion of each video watched varied dependent upon the quality of the footage, the area of the structure being assessed, and the duration of the video. In general, approximately 8 sub-sections of each video was watched. Particular attention was given to the potential occurrence of designated species. Habitats and features were also noted where indicative of organisms such as, burrows and bivalve shells.
2.2.4 Seabirds
A number of seabirds use the offshore waters in the region of the STL system. Of those
birds frequently occurring in the area 11 have been observed years round although their
abundance varies seasonally, including Fulmars, Gannets, Gulls and Puffins. Another seven
types of birds use the region during the summer including Shearwaters, Storm petrels and
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Skuas. A limited number of seabirds over winter in the area. Table 2.2 summarises known
seabirds in the area of the STL system.
Table 2.2: Seabirds for which there are known records in the area of the STL System
Common
name
(Latin
name)
Timing frequency (based on UKDAMP1) Notes
J F M A M J J A S O N D
Fulmar
(Fulmarus
glacialis)2
Sooty
shearwater
(Puffinus
griseus)2
Low numbers observed
Manx
shearwater
(Puffinus
puffinus)2
Low numbers observed.
High contact time with
water
European
storm-petrel
(Hydrobates
pelagicus)2
Low numbers observed.
Low contact time with
water
Gannet
(Morus
bassanus)2
High time utilisation of the
sea. Large foraging range
Pomerain
skua
(Stercorarius
pomarinus)2
Widely dispersed, mobile
and highly aerial
Arctic skua
(Stercorarius
parasiticus)2
Highly aerial
Great skua
(Sterorarius
skua)2
Medium contact time with
water
Common gull
(Larus
canus)
Low number observed.
Herring gull
(Larus
argentatus)
Lesser black
backed gull
(Larus
fuscus)
Relatively aerial species
Great black
backed gull
(Larus
marinus)
Aerial lifestyle and widely
distrubuted
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Table 2.2: Seabirds for which there are known records in the area of the STL System
Common
name
(Latin
name)
Timing frequency (based on UKDAMP1) Notes
J F M A M J J A S O N D
Kittiwake
(Rissa
tridactyla)
Abundant species. Aerial
lifestyle and widely
distrubuted
Arctic tern
(Sterna
paradisaea)
Low numbers observed.
Highly aerial
Guillemot
(Uria aalge)
Widely distributed. High
abundance. High contact
time with water. Autumn
moult.
Razorbill
(Alca torda)
High contact time with
water.
Little auk
(Alle alle)
High contact time with
water.
Puffin
(Fratercula
arctica)
High contact time with
water. Late winter moult.
Notes:
1 UKDMAP (based on information for the general surrounding area, Information collated from between 1980
and 1997.)
2 Additional data on population data taken from Stone et al, 1995. An atlas of seabird distribution in north west
European waters
Presence noted Particularly high densities of birds noted at these timings (resident
birds)
2.2.5 Fish
The North Sea is an important area for commercial and non-commercial fish species.
Important commercial fish species include Sprat (Sprattus sprattus), Sandeel (Ammodytes
marinus), Herring (Clupea harengus), Haddock (Melanogrammus aeglefinus), Saithe
(Pollachius virens), Whiting (Merlangius merlangus), Mackerel (Scomber scombrus), Cod
(Gadus morhua), and Norway pout (Trisopterus esmarkii). Blue whiting (Micromesistius
poutassou) also use the area as juvenile fish. High level review of the video footage (2014)
also noted individuals from various groups of fish including, Monkfish, flatfish and cod.
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2.2.5.1 Elasmobranchs
A number of elasmobranch species are known to be present in the Central North Sea. Many
elasmobranch species are particularly vulnerable to the effects of human activities as late
reproductive age and resultant slow reproductive rate. Basking sharks have been observed
in this region during April to October, when they come to feed on the plankton blooms.
Table 2.3 details species of elasmobranchs recorded in the area of the STL system and any
times of peak observations.
2.2.5.2 Cephalopods
Cephalopods include squid, octopus and cuttlefish. Cephalopods are important elements
food webs, providing an important food source to many species of whales, dolphins, seals,
birds and large fish. Squid are also commercially important in the North Sea. The most
abundant species in the area are Loligo forbesi and Loligo vulgaris with a peak breeding
season from December to March in Scottish waters and a one year life cycle. Catch of squid
in the region of the STL system are relatively low in comparison to elsewhere in the North
Sea (Young, 2001).
Table 2.3: Elasmobranch species identified as ‘Priority Marine Features’ for which there are known records in the area of the STL System
Peak recordings Designations
Common
name
J F M A M J J A S O N D Priority
Marine
Feature
(PMF)
OSPAR
threatened/
declining
species
IUCN
Red
List
Basking shark
(Cetorhinus
maximus)
Y Y EN
Blue shark
(Prionace
glauca)
Y Y NT
Common skate
(Dipturus batis)
Y Y CR
Porbeagle
shark (Lamna
nasus)
Y Y CR
Sandy ray
(Leucoraja
circularis)
Y VU
Spiny dogfish Y Y CR
Peak observations Recorded observations
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2.2.6 Marine Mammals
The most commonly occurring cetaceans recorded seasonally in the area of the STL system
are Minke whale (Balaenoptera spp.) (May to September), White-beaked dolphin
(Lagenorhynchus albirostris) (June to November), Harbour porpoise (Phococena
phococena) (April to September), and Atlantic white-sided dolphin (Lagenorhynchus acutus)
(June to September) (UKDMAP, 1998; JNCC 2003). All sightings for cetaceans, with the
exception of harbour porpoise are recorded at a frequency of 0.01 – 0.09/km (UKDMAP,
1998). The harbour porpoise has a widespread distribution and is the most frequently
sighted cetacean in the North Sea, with many records in the vicinity of the STL system
(UKDMAP). The UK total population is estimated at 328200 individuals (JNCC, 2008a).
There is some evidence that distinct populations of porpoises exists in the central and
northern North Sea.
Other cetaceans recorded as rare in the region include; Common bottlenose dolphin
(Tursiops truncatas), Short beaked common dolphin (Delphinius delphis), Risso’s dolphin
(Grampus griseus), most commonly sighted between July and August; the Killer whale
(Orcinus orca) known to occur all year round, Pygmy sperm whale (Kogia breviceps) and the
Humpback whale (Megaptera novaeangliae) (JNCC (2003)). All species other than the
Humpback whale and the Pygmy sperm whale are listed are on the PMF list for Scotland.
Most cetaceans are most commonly recorded in the area during summer and autumn
months.
The harbour porpoise is listed as Annex II species in the Habitats Directive, providing special
conservation status to this species. All cetaceans are listed in Annex VI which make it an
offence to kill, injure, capture or disturb these animals.
Records show the occurrence of harbour seals (Phoca vitulina) and grey seals (Halichoerus
grypus) in the vicinity of the STL system. (Hammond et al., 2001). The population of grey
seals is estimated at 97,000 to 159,000. Research carried out recently using tracking
methods indicates minimal usage of the area and immediate vicinity, with animals spending
far greater time in areas to the north and south (Sea Mammal Research Unit (SMRU), 2014).
2.3 Human Environment
2.3.1 Commercial Fisheries
The North Sea commercial fishing industry is operated by fishing fleets from the UK (in
particular Shetland, Fraserburgh and Peterhead) and Norway. The closest important fishing
grounds to the STL system are ‘Fladen Ground’, ‘The Patch’, and ‘40 Mile Ground’. All
landings are reported according to the regions in which they were caught. Harding Field is
located within International Council for the Exploration of the Sea (ICES) square 47F1.
Fishing activity includes demersal, pelagic and shellfish fisheries, although is dominated by
demersal fisheries targeting cod, haddock and whiting, using demersal trawl and Scottish
Seine methods9. Fishing effort10 in the study area varies over the course of the year with
9 Information sourced from Scottish Government website - http://www.scotland.gov.uk/Topics/marine/marine-environment/species/fish/demersal (accessed on 28/11/2014) 10 Fishing effort is an indicator of the amount of time spent fishing at a particular area. This data is automatically collected in large vessels. UK fishermen are required to report the catch information, e.g. species and landing
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higher effort in the months January to April, however this varied year upon year. Fishing
effort for ICES 47F1 is shown in Figure 2.2. Landings for the same area are summarised in
Table 2.4.
Landings within ICES 47F1 are lower than other ICES squares in close proximity.
Figure 2.3: Fishing effort by ICES Rectangle Data. Rectangle 47F111.
Table 2.4. Landing of fish (demersal, shellfish and pelagic) in tonnes from 2009 to 2013 in ICES square 47F1
Year Total Landings Demersal Shellfish Pelagic
2013 1,728 906 5 817
2012 880.16 542.11 12.08 325.97
2011 872.28 577.15 81.37 213.76
2010 1,097.3 906.8 36.8 153.8
2009 1,804 816 70 918
Source: http://www.scotland.gov.uk/Topics/Statistics/Browse/Agriculture-Fisheries/RectangleData
amounts, when landing their catches. It is useful to consider both the fishing effort and the tonnage of fish landed, as these may vary year upon year. Landing amounts are limited by quotas set by the EU for each country. 11 Data accessed from the Scottish Government (available at): http://www.scotland.gov.uk/Topics/Statistics/Browse/Agriculture-Fisheries/RectangleData
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2.3.2 Shipping and Navigation
No commercial ferry routes are located in the area. Fishing vessels will occur regularly in
the vicinity. Vessel activity associated with activity at the Harding platform, Harding field and
adjacent production facilities also occurs regularly.
Data on vessel density in the North Sea has been investigated in a report from the Marine
Management Organisation (2014). See Figure 2.4. The figure is based on data collected
using Automatic Identification System (AIS)12. AIS signals are classified as ‘Class A’ and
‘Class B’. AIS Class A is a standard requirement for international voyaging ships with a
gross tonnage of 300 plus tonnes and all passenger ships, regardless of size. AIS B is a
non-mandatory form of AIS often used by smaller commercial craft, fishing vessels and
recreational vessels.
Figure 2.4 indicates a density of vessels in the vicinity of the STL System, in the region of
0.1 to 5 vessels per week. Based on the fishing effort data presented in Figure 2.3, during
the months from January to April, three to five fishing vessels would be expected to occur
per day over the entire ICES 47F1 square, where the STL system is located. During the
other months of the year, fewer fishing vessels (one to three) would be expected to occur
per day13.
Vessel traffic associated with supporting operations at the Harding Oil and Gas field include
offloading tankers, Platform Support Vessels (PSV), Emergency Response and Rescue
Vessels (ERRV), Diving Support Vessels (DSV) and Remotely Operated Vehicle Support
Vessels (ROVSV). The total number of annual vessels supporting the field is expected to be
approximately 75. Assuming these vessels are not included in the vessel density records,
as per Figure 2.3, the occurrence of these additional vessels would not be considered to
significantly increase the density of marine traffic in the area.
12 Use of AIS data for assessing vessel density is limited in that AIS is not a mandatory requirement for all vessels and also by the effectiveness of signal transmission with distance away from land. A short term sample at the Port of Southampton showed 16% of commercial vessels were not identified in the Maritime and Coastguard Agency (MCAs) AIS dataset (Marine Management Organisation, 2014). 13 For the months from January to April, the minimum and maximum recorded fishing effort days recorded between 2013 and 2010, was approximately 90 to 135 respectively. The number of fishing effort days was divided by 30 days (representative of a typical month), equivalent after rounding to 3-5 vessels per day. The same approach was used for the remainder of the months where fishing effort was generally been recorded as lower. Fishing effort was approximated at between 40 and 75 days per month, equivalent after rounding to 1 – 3 vessels per day.
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Figure 2.4. Vessel density in the UK 201214.
14 Vessel density data taken from the Marine Management Organisation assessment on UK shipping and density using Automatic Identification System (AIS) data (MMO, 2014).
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2.3.3 Marine Archaeology
No records of marine designated areas, wrecks or archaeological remains in the vicinity of
the STL system were identified15. Whilst there remains the possibility of previously
unrecorded archaeological sites in the vicinity of the STL system, no evidence has been
observed to date during previous survey.
2.3.4 Other Sea Users
No leisure or recreational users were identified in the vicinity of the Harding STL system16.
There are no designated offshore areas in the vicinity of the STL system used by the
Ministry of Defence (MOD).
The closest recorded active cable is a telecommunications cable approximately 18.5 km to
the north east (Kingfisher charts, 201417).
15 (NMPi, accessed Dec 2014; www.Finstrokes.com) 16 (NMPi, accessed Dec 2014; www.Finstrokes.com) 17 Kingfisher charts available at: http://www.kis-orca.eu/map (accessed on 20/11/2014)
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3 Environmental Analysis
The following section considers the potential for significant environmental effects on the
marine environment as a result of the implementation of the preferred option for
decommissioning the STL system.
3.1 Methodology
The evaluation of the potential for significant effect utilises a standard structured
methodology based on established best practice guidance18 and has been based on the
professional judgment of environmental specialists. The application of the methodology also
draws, where appropriate, on previous experience and lessons learned from previous
decommissioning projects.
Potential activity/effects interactions were identified as part of the Comparative Assessment
(see Section 1.4 for further details). Each potential activity/effect interaction was then
evaluated based on the following criteria.
3.1.1 Frequency/Likelihood
The frequency (for planned events) or likelihood (for unplanned events) of the identified
activity/effect interaction occurring was considered based on the criteria set out in Table 3.1.
Table 3.1. Frequency/Likelihood of an effect occurring
Likelihood Score
Planned Activities Duration Accidental Events (Likelihood)
1 Less than a day
Extremely remote - less than once every
1000 years and more than once every
10,000 years
2 Day to week Remote - less than once every 100 years
and more than once per 1,000 years
3 Week to month Unlikely - less than once every 10 years
and more than once per 100 years
4 Month to year Possible - less than once per year and
more than once per 10 years
5 Year to many years Likely - more than once a year
18 Oil and Gas UK (2014): HSO88 Guidance on Risk Related Decision Making Issue 2 July 2014; UKOOA (1999): A framework for risk related decision support – industry guidelines, UK Offshore Operators Association
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3.1.2 Severity (Magnitude)
The severity of the identified activity/effect interaction if it were to occur was then considered
based on the guidelines as set out in Table 3.2 below.
Table 3.2 Severity (Magnitude) of an effect
Effects level Guidelines
0 None No interaction and hence no change expected.
0 Beneficial
Likely to cause some enhancement to the ecosystem or
activity within the existing structure. May help local
population
1 Negligible
Change which is unlikely to be noticed or measurable
against background activities. Negligible effects in terms of
health and standard of living.
2 Slight
Change which is within the scope of existing variability, but
can be monitored and/or noticed. May affect behaviours,
but not a nuisance to users or public.
3 Moderate
Change in the ecosystem or activity in a localised area for a
short time (<2 years), with a good recovery potential.
Similar scale of effect to existing variability but may have
cumulative implications. Potential effect on health, but
unlikely. May cause nuisance to some users.
4 High
Change in the ecosystem or activity over a wider area
leading to medium-term (>2 years) damage, but with a
likelihood of recovery within 10 years. Possible effect on
human health. Financial loss to users or public
5 Very High
Change in the ecosystem leading to long term (>10 years)
damage and poor potential for recovery to a normal state.
Likely to affect human health. Long term loss or change to
users or public finance.
3.1.3 Environmental Significance (risk)
The potential environmental significance posed by each activity/effect interaction considered
was then evaluated based on combining likelihood of the effect occurring with the magnitude
of that effect if it were to occur. This evaluation was completed based on the matrix set out
within Table 3.3.
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Table 3.3 Environmental Significance (Risk)
Likelihood/probability
5 4 3 2 1
Sev
eri
ty
5 High High High High High
4 High High High High Moderate
3 Moderate Moderate Moderate Moderate Low
2 Moderate Moderate Low Low Low
1 Low Low Low Low Low
0 No impact
OR positive effect
No impact OR positive
effect
No impact OR positive
effect
No impact OR positive
effect
No impact OR positive
effect
3.2 Potential Effects
Those activity/effect interactions identified through the high level scoping evaluation (see
section 1.5) as having ‘Moderate’ or ‘High’ potential for effect (without mitigation) (are
summarised in Table 3.4 below and are further discussed and evaluated within the
remainder of this section.
Table 3.4. Summary of activity/effect interactions for further consideration
Activity Potential Effects Location where considered
within this ER
Sever and recovering
mooring lines
Effects on marine mammals Section 3.2.3: Underwater
Noise
Leave in situ until Field
decommissioning.
Effects on benthos Section 3.2.1 Designations; and
Section 3.2.2 Seabed
Disturbance
Effects on marine mammals Section 3.2.3 Underwater Noise
Effects on fish and shellfish Section 3.2.4 Socio-economic
effects
Effects on commercial fisheries
(damage or loss of fishing gear)
Accidental events Section 3.2.5 Accidental events
Full removal by reverse
installation
Effects on natural seabed sediments Section 3.2.1 Designations; and
Section 3.2.2 Seabed
Disturbance Effects on benthic community
Effects on marine mammals Section 3.2.3 Underwater Noise
Effects on fish and shellfish Section 3.2.4 Socio-economic
effects
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Table 3.4. Summary of activity/effect interactions for further consideration
Activity Potential Effects Location where considered
within this ER
Accidental events Section 3.2.5 Accidental events
3.2.1 Designations
3.2.1.1 Cetaceans
The location of the Harding STL system lies within the know distribution or range of a
number of cetacean species. Harbour porpoise are widely distributed in the area of the STL
system and are protected under Annex I of the Habitats Directive. All cetaceans are
protected under Annex IV of the Habitats Directive making it an offence to kill, injure, capture
or disturb these animals. Potential effects on cetaceans are considered within section 3.2.3:
Underwater noise.
3.2.1.2 Offshore Deep Sea Muds and Protected Benthic Species
There are no confirmed records of offshore deep sea muds as defined under Annex I of the
Habitats Directive within 5 km of the STL buoy location. There are records of the ocean
quahog listed within 1km of the site. See section 3.2 below for further consideration of
potential effects from seabed disturbance.
3.2.2 Seabed Disturbance
3.2.2.1 Disturbance to Natural Seabed Sediments
The DP proposes removal of the suction anchors by reverse installation. This will involve
pumping water (assumed untreated seawater), into the suction piles to raise the internal
pressure and allow them to be pulled from the seabed. At least one attempt shall be made
to remove each of the eight suction anchors, independent of the success or failure to remove
the other anchors (as outlined in Section 1.3 of this report).
Disturbance to local mud and sandy mud sediments immediately surrounding the suction
anchors will occur during removal of the suction anchors. This could be expected to lead to
the suspension of fine sediments into the water column and a resultant temporary
deterioration of water quality in the immediate area and down-current of each of the suction
anchors.
Seabed conditions in the area surrounding the suction anchors have been characterised as
mud and sandy mud. The localised area which would be disturbed during suction anchor
removal is unlikely to contain levels of contaminants significantly elevated above background
levels. In addition TAQA have confirmed that no hydrocarbon or chemical components
either currently or historically have been directly associated with the suction anchors. No
effect is therefore anticipated as a result of mobilisation of historically contaminated
sediments.
All efforts will be made to reduce seabed disturbance to an absolute minimum. Where there
are areas affected, they will be left in a condition fit for other users. Disturbed seabed
sediments will settle out or be dispersed by localised bottom currents.
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The DP also identifies possible scenarios that may occur during removal of the suction
anchors that would result in disturbance of the sediment, considered in TAQA (2015). -
These include:
Removal of the suction anchors from the ground may be unsuccessful;
A highly unlikely scenario in which the suction anchor may be required to be temporarily
placed on the seabed following removal to enable alteration of the lift rigging.
A highly unlikely scenario in which removal of the suction anchor results in a significant
depression in the seabed.
Under the circumstances that removal of a suction anchor is unsuccessful (including
additional attempts in 2016 should contingency repair options be undertaken) it is proposed
to rock dump a protective cap over the suction anchor to reduce the risk to other sea-users
and leave in situ. Localised seabed disturbance may occur, limited to the area immediately
surrounding each suction anchor during rock dumping. For the purposes of this scenario it
has been assumed that a maximum safe overtrawlable slope ratio of 1:3 will be achieved
projecting up to approximately 3m from the natural seabed level19. As a result an additional
total area of up to approximately 500m2 (0.05ha) immediately surrounding an individual
suction anchor could be expected to be directly impacted by rock dumping. For each suction
anchor an estimated 284 to 667m3 of rock would be dumped to provide adequate coverage
at a 3 to1 slope.
In the event that failure to remove the suction anchor occurs part way through the recovery
process (i.e. the pile protrudes significantly further out of the seabed than initially found),
specific assessment of situation will be carried out and the appropriate course of action will
be determined.
Placement of a suction anchor temporarily on the seabed is considered a highly unlikely
scenario that will be avoided where ever possible. In the event a suction anchor is required
to temporarily placed on the seabed during the removal process, additional seabed
disturbance may be occur.
The reverse installation method, combined with the seabed sediment type, mean that it is
very unlikely that a depression in the seabed will be left following the removal of the suction
anchor. However, should a depression be identified during the overtrawlability test20, review
of the available remedial actions will be undertaken, including appropriate consultations, to
identify the preferred action.
3.2.2.2 Effects on Benthic Communities
Localised seabed disturbance is anticipated as a result of suction anchor removal and any
other possible scenarios that may occur during removal of the suction anchors, such as rock
placement (see above) which may result in some localised mortality to slow
moving/sedentary benthic organisms. Anchor removal will also result in the localised
suspension of fine sediments into the water column with subsequent settlement of sediment
in the immediately surrounding area and down-current from each suction anchor. Again
19 The suction anchors currently protrude above the seabed by between 1 and 1.8m (TAQA, 2015b). A minimum of 1m rock coverage above the highest point is assumed for each suction anchor. For this reason a max estimated height for rockdumping above seabed for the purposes of this evaluation has been assumed at 3m. Each suction anchor has an area of 20m2 representing a diameter of 5m. 20 Failure to comply with the requirements of overtrawlabilty as per NORSOK U-001 and ISO 13628
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sedentary and filter-feeding benthic organisms within the area of settlement would be
particularly susceptible to smothering. Settlement of sediment would also result in
temporary sedimentation of any burrows in the immediate vicinity of the STL system –
though it is anticipated that burrowing organisms would have a higher tolerance to turbid
conditions and smothering.
Review of recent ROV footage has identified an assemblage of hard substrate marine
organisms currently established on the suction anchors, including Cnidarians (Anemone and
dead man’s fingers); Polychaete tube worms; Echinoderms (Star fish and Brittle stars),
Porifera. Suction anchors removal could be expected to result in the total loss of this current
assemblage, although this is not considered likely to be of ecological significance.
3.2.3 Underwater Noise
Activities associated with cutting of mooring lines; and removal of the suction anchors or (if
necessary) rock dumping, will require the use of vessels. For the purposes of this
assessment it has been assumed that these vessels will likely make use of dynamic
positioning in order to maintain their position whilst completing proposed operations.
Cetaceans are particularly vulnerable to vessel activities that produce noise (frequency and
level dependent), due to their reliance on sounds for detecting their physical surrounding,
detecting prey, navigation, communication & group dynamics, mate selection, danger
avoidance and prey stunning. The impacts of anthropogenic noise on cetaceans has been
linked to disturbance and displacement behaviours, ranging from avoidance behaviours,
through to physiological impacts, with the potential to result in death of an animal (Simmonds
et al., 2004).
Cetacean species most commonly recorded in the area of the STL system comprise Minke
whale, White beaked dolphin, and Atlantic white-sided dolphin. Records indicate presence
in the summer months at a low frequency (0.01 – 0.09/km). Harbour porpoise have been
observed more frequently.
Noise associated with DP may occur from the types of vessels anticipated to be used and
also as a result of the cutting of the mooring lines using either a diamond wire or hydraulic
cutter. The use of diamond wire cutters or hydraulic cutters is expected to be of short
duration. Noise levels generated from these activities are anticipated within the known
range to cause disturbance to these species with resultant evidence of possible avoidance
behaviour.
Further noise from other equipment for example equipment used for pumping seawater as
part of reverse installation may also occur. Additional noise disturbance from rock dumping
(if required) may cause temporary disturbance, but is anticipated only to occur for a short
duration.
Noise levels anticipated will be similar to those currently experienced in the area from
commercial shipping and oil industry supply vessels, as detailed in Section 2.3.2. Removal
by RI will be short duration operations and all work programmes will be planned to optimise
vessel time in the field.
Offshore vessels will avoid concentrations or marine mammals.
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3.2.4 Socio-economic Effects
3.2.4.1 Commercial Fisheries
The area of the STL System is particularly used for demersal fishing using trawl gear. These
fishing methods are susceptible to snagging on any structures placed on the seabed as they
are dragged along the seabed purposefully to catch bottom dwelling species.
The suction anchors once removed will remove a potential snagging hazard and therefore
potentially offer a small positive effect on overtrawlability and commercial fishery activity in
the area. In the event of failure in removal of any anchor, resulting in coverage of the anchor
with rock dump, an overtrawlability test will be carried out once rock dumping is complete. In
the event suction anchors remain in place (even with a protective rock dump cover), they
represent a snagging hazard. The covering with the rock dump will reduce the risk of
snagging, however the risk may change over time if the anchors and/or cap start to break
down. The structures should be recorded on fishSAFE21 to assist fishermen to avoid these
structures during fishing operations.
During removal the potential exists for decommissioning activities to affect commercial
fishing activities due to the physical presence of vessels, ROVs and divers in the area which
may obstruct access to the fishing grounds. At present the STL system has a 500m safety
zone set around the structure to reduce the chance of fishing equipment snagging. Due to
the length of the mooring lines, each of the suction anchors is located outside of this safety
zone. In the long term, removal of the STL system will reduce the risk posed to the fishing
industry as the risk of snagging equipment will be reduced/removed.
No obvious economic benefits or losses have been identified. No economic losses are
anticipated to the fishing industry due to incorporation of a safety zone as efforts are simply
diverted elsewhere. Potentially these areas act as closed areas protecting stock (CEFAS,
2003).
3.2.5 Accidental Events
A risk of both water column and sediment contamination exists from oil spills from vessel
activity during decommissioning. Risks are posed to all organisms utilising the benthic and
water environments, including seabirds, mammals, fish, plankton, elasmobranchs and
benthic organisms.
The risk to seabirds is dependent upon a suite of factors including the amount of time spent
on the water, the bio-geographical population, the reliance of the species on the marine
environment and potential rate of population recovery. The Joint Nature Conservation
Committee (JNCC, 1998) combined these factors to produce an Oil Vulnerability Index for
seabirds in offshore environments (UKDMAP, 1998). The risk to seabirds in the area of the
STL system is presented in Table 3.5. The greatest risk to seabirds from any oil incident is
during January, February, July and November.
21 www.fishsafe.eu
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Table 3.5: Vulnerability of seabirds to oil pollution throughout the year.
Month J F M A M J J A S O N D
* * * * *
Few birds Moderate High Very high
Notes: * Vulnerability classification based on the classification from an area in close proximity as data did not exist for the
location of the STL system.
The plankton community is also vulnerable to water pollution, such as oil spills. Planktonic
larval stages and eggs are particularly susceptible to the effects of water contamination, with
associated increased mortality and premature hatching. Effects on plankton populations
may result in consequences for higher organisms due to diminished food sources and
changes in recruitment of larval planktonic species to habitats in other areas.
Fish are most vulnerable to the effects of oil spills during spawning when contaminants can
result in acute and chronic effects. Spawning of commercially important species in the
region including the STL system occurs mostly from January to June. These species also
spend much of their first few months of life in the upper water layers before moving to the
seabed (Barreto and Balley, 2013).
Standard operating procedures according to the relevant Oil Pollution Emergency Plan
(OPEP) will be in place at all times to control the potential for oil spills and also to mitigate
any consequences from such spills.
Flushing activities performed from the Harding platform (approximately 2km to east of STL
system) to a tanker moored to the STL system will take place, prior to removal of the STL
buoy which will ensure hydrocarbons are cleared from the pipeline, riser and buoy removing
risk of hydrocarbon contaminated discharges to seawater during decomissioning.
As no hydrocarbons or chemicals have been associated with the long term operation of the
suction anchors and mooring system it has been assumed no potential for large scale spills
of historic hydrocarbon contaminants from the operation of the suction anchors and mooring
exists.
3.2.6 Issues scoped out from potentially significant effect
Nineteen receptors and activities were initially consider for potential effect by the
decommissioning activities. These are detailed in the Scoping Matrix in Figure 1.2. Each
receptor was considered in the initial scoping stage for potential risks and effects. Any
receptor identified as having a Medium or greater potential effect is discussed above in
Section 3.2. Any receptor identified as having ‘Low or ‘No impact/positive effects’ were
omitted from any further analysis.
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Consideration of the potential for significant effect on ‘Energy Use and Air Quality’ resulting
from both the decommissioning activities and also any ongoing monitoring and survey work
was completed at this stage. The initial assessment considered factors including but not
limited to: the number of day’s vessels and other machinery would be in use, the potential for
dispersion of gases due to metrological conditions and the baseline volume of vessel traffic
present in the area.
Taking account of standard commitments including: the use of efficient, decommissioning
vessels suitable for the work tasks and which will be subject to an independent Vessel
Suitability Survey prior to charter; and optimisation of vessel time within the field, the initial
assessment classified the risks of significant environmental effect as ‘Low’ Consequently
potential effects on energy use and air quality were not considered further within this report.
The standard practice commitments have been however been included within the summary
of commitments as detailed in Table 4.1.
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4 Summary of Commitments
Table 4.1: Summary of Commitments
Effects Management
Seabed Disturbance All efforts will be made to reduce seabed disturbance to an absolute minimum, where there are areas effected,
they will be left in a condition fit for other users; and
Disturbed seabed sediments will rapidly settle out or be dispersed by localised bottom currents.
Underwater noise. Disturbance to
marine mammals
Offshore vessels will avoid concentrations of marine mammals;
Both mooring line cutting and removal of suction anchors by reverse installation will be a short duration of
operation and all work programmes will be planned to optimise vessel time in the field;
Similar noise levels are anticipated to those currently experienced in the area from commercial shipping and oil
industry supply vessels; and
Minke whale, White beaked dolphin and Atlantic white-sided dolphin are known to be present in the area in the
summer months at a low frequency (0.01 - 0.09/km) therefore there is unlikely to be significant disturbance.
Harbour porpoise have been observed in higher numbers.
Effects on Commercial Fisheries:
Damage or loss of fishing
gear/Dropped objectives
UK Hydrographical Office and Kingfisher along with the Scottish Fishermen’s Federation (SFF) and fishSAFE will
be informed of all activities and of any structures left in place;
Any structures left in place, will be left in such a way that they present no greater risk to other users than at
present;
TAQA Bratani Limited will establish lines of communication to inform other sea users, including fishermen, of
vessel operations during decommissioning activities; and
A post decommissioning ‘as-left’ survey will be conducted at the end of Field decommissioning, and any debris
discovered and found to be a part of the removal operation, or off the elements previously removed, shall be
recovered. This is in compliance with NORSOK U-001 and ISO 13628.
Accidental events oil/diesel spill A risk of both water column and sediment contamination does exist from oil spills from vessel activity during
decommissioning. Standard operating procedures according to the relevant OPEP will be in place at all times to
control this and mitigate any consequences from such spills;
Flushing activities performed from the Harding platform (approximately 2km to east of STL system) to a tanker
moored to the STL system will take place, prior to removal of the STL buoy which will ensure hydrocarbons are
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Table 4.1: Summary of Commitments
Effects Management
cleared from the pipeline, riser and buoy removing risk of hydrocarbon contaminated discharges to seawater
during decomissioning.
As no hydrocarbons or chemicals have been associated with the long term operation of the suction anchors and
mooring system it has been assumed no potential for large scale spills of historic hydrocarbon contaminants from
the suction anchors and mooring system; and
Continual monitoring of fuel status will be completed with regular visual inspections of sea surface throughout the
works.
Discharges Flushing activities performed from the Harding platform (approximately 2km to east of STL system) to a tanker
moored to the STL system will take place, prior to removal of the STL buoy which will ensure hydrocarbons are
cleared from the pipeline, riser and buoy removing risk of hydrocarbon contaminated discharges to seawater
during decomissioning. This will be covered by appropriate chemical permits outwith the scope of this ER.
As no hydrocarbons or chemicals have been associated with the long term operation of the suction anchors and
mooring system and no use of chemicals is anticipated, no resultant discharges to seawater are expected.
Energy Use and Emissions Efficient, decommissioning vessels suitable for the work tasks will be utilised and an independent Vessel
Suitability Survey will be completed prior to charter.
Work programmes will be planned to optimise vessel time in the field.
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Annex A
References
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Joint Nature Conservation Committee, (JNCC) (2007): Second Report by the UK under
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OSPAR Commission. (2010): Background Document for Common skate Dipturus batis.
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Annex B: Comparative Assessment and Environmental Scoping Matrices
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Annex C
Concentration of contaminants in sediments measured in the Gardline Environmental Ltd Study
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Table C.1: Concentration of potential contaminants at sampling location closest to STL system from the Gardline Environmental study conducted in 2006 (Gardline Environmental Ltd, 2013)
Parameter Concentration
(µg/g dry
sediment)
Background
concentrations3
Barium µg/g dry sediment 660
Mercury µg/g dry sediment 0.06
Arsenic µg/g dry sediment 2.0 15
Cadmium µg/g dry sediment 0.2 0.2
Chromium µg/g dry sediment 12 60
Copper µg/g dry sediment 4 20
Iron µg/g dry sediment 5660 0.6-6.3
Lead µg/g dry sediment 12 25
Manganese µg/g dry sediment 97 -
Nickel µg/g dry sediment 5 30
Strontium µg/g dry sediment 84 -
Vanadium µg/g dry sediment 13 60-110
Zinc µg/g dry sediment 20 90
Redox potential (Eh) (mV) (SHE)1 437
Total hydrocarbons µg/g dry sediment 3.7 Up to 55
Total n-Alkanes and Isoprenoids2 µg/g dry sediment 0.465
Naphthalene Total (C1-C4 128) ng/g dry sediment 22 5
Phenanthrene/Anthracene (sum of C1-C3 178) ng/g
dry sediment
7 204
Fluoranthene/Pyrene (sum of C1-C2 252) ng/g dry
sediment
5 334
Notes:
1 SHE – Standard hydrogen electrode. Samples corrected to SHE potential values. Samples taken from surface layer, top
1cm.
2 Comprised of n-alkanes nC12 to nC36 and can be a useful measure for the presence of synthetic based drilling fluids
3 Background Concentrations (BC) taken from the OSPAR ‘Agreement on background Concentrations for Contaminants in
Seawater, Biota and Sediment (OSPAR Agreement 2005-2006). The Background Concentrations represent the
concentrations of substances from remote/pristine sites based on historical data.
4 Background concentrations recorded for individually for Phenanthrene, Anthracene, Fluoranthene and Pyrene. The BCs
were summed to calculate the combined concentrations.
5 Background concentrations based on a study by the North Sea Task Force (1993) on the typical THC concentrations in
sediments remote from anthropogenic activity
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Annex D: Designated Species
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Table D.1: Species provided with designation and/or conservation status
Species Habitats
Directive UK BAP OSPAR
IUCN Red
List
Birds of Conservation
Concern
Priority
Marine
Feature
Seabirds
Sooty shearwater (Puffinus griseus) NT Amber listed
Manx shearwater (Puffinus
puffinus) S5 >25% decline LC Amber listed
European storm-petrel (Hydrobates
pelagicus)
International
obligation LC Amber listed
Gannet (Morus bassanus) LC Amber listed
Pomerain skua (Stercorarius
pomarinus) LC
Arctic skua (Stercorarius
parasiticus) S5 >25% decline LC Red listed
Great skua (Sterorarius skua) LC Amber listed
Common gull (Larus canus) LC
Herring gull (Larus argentatus) S5 >25% decline LC Red listed
Lesser black backed gull (Larus
fuscus) X LC Amber listed
Great black backed gull (Larus
marinus) LC Amber listed
Kittiwake (Rissa tridactyla) X LC Amber listed
Arctic tern (Sterna paradisaea)
International
obligation LC Amber listed
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Table D.1: Species provided with designation and/or conservation status
Species Habitats
Directive UK BAP OSPAR
IUCN Red
List
Birds of Conservation
Concern
Priority
Marine
Feature
Guillemot (Uria aalge) X LC Amber listed
Razorbill (Alca torda) LC Amber listed
Little auk (Alle alle) LC Amber listed
Puffin (Fratercula arctica) LC Amber listed
Commercial fish
Saithe (Pollachius virens) X
Norway pout (Trisopterus esmarkii) LC X
Whiting (Merlangius merlangus) LC X
Mackerel (Scomber scombrus) LC X
Elasmobranchs
Basking shark (Cetorhinus
maximus) X EN
X
Blue shark (Prionace glauca) X NT X
Common skate (Dipturus batis) X CR X
Porbeagle shark (Lamna nasus) X CR X
Sandy ray (Leucoraja circularis) X VU X
Spiny dogfish X CR X
Cetaceans
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Table D.1: Species provided with designation and/or conservation status
Species Habitats
Directive UK BAP OSPAR
IUCN Red
List
Birds of Conservation
Concern
Priority
Marine
Feature
Minke whale (Balaenoptera spp.) Annex IV X
White-beaked dolphin
(Lagenorhynchus albirostris) Annex IV X
Harbour porpoise (Phococena
phococena)
Annex II &
Annex IV X X
Atlantic white-sided dolphin
(Lagenorhynchus acutus) Annex IV X
Pinnipeds
Harbour seals (Phoca vitulina) X
Grey seals (Halichoerus grypus) Annex II X
Notes:
The Habitats Directive (1992) – Species and habitats designated under Annex I, II and/or IV
UK BAP – Biodiversity Action Plan Species for Scotland – available at: http://jncc.defra.gov.uk/page-5705 (accessed on 22/01/15)
OSPAR – List of threatened and/or declining species and habitats in the North East Atlantic - available at
http://www.ospar.org/content/content.asp?menu=00730302240000_000000_000000 (accessed on 22/01/15)
IUCN Red List – is a international recognized list of the global conservation status of plant and animal species and is based on an objective system of assessing the risk of
extinction of a species. Classification categories include: Extinct (Ex); Extinct in the Wild (EW); Critically Endangered (CR); Endangered (EN); Vulnerable (VU); Near
Threatened (NT) Least Concern (LC); Data Deficient (DD)
Birds of Conservation Concern – Review of the conservation status of birds regularly found in the UK, based on global conservation status, recent decline, historical decline,
European conservation status, rare breeders, localised species and international importance. It has been compiled for the UK by the leading bird conservation organisations
(Eaton et al., 2009). Available at: http://www.bto.org/volunteer-surveys/birdtrack/bird-recording/birds-conservation-concern (accessed on 22/01/2015)
Priority Marine Feature – Priority habitats and species as developed by Scottish Natural Heritage and JNCC available at http://www.snh.gov.uk/protecting-scotlands-
nature/priority-marine-features/priority-marine-features/ (accessed on 22/01/2015). Burrowing mud is also a priority marine feature.
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