Harding Submerged Turret Loading (STL) System … · 2015. 9. 18. · Loading (STL) System. The STL...

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


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


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


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


UK1220847 Issue: 7 ENVIRON

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


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



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



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


UK1220847 Issue: 7 i ENVIRON

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


UK1220847 Issue: 7 ii ENVIRON

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.


UK1220847 Issue: 7 1 ENVIRON

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.



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



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,



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.



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.

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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



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.

http://www.windfinder.com/weather-maps/report/norway#8/58.301/0.818



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

http://www.scotland.gov.uk/Topics/marine/seamanagement/nmpihome/nmpi

http://www.scotland.gov.uk/Topics/marine/seamanagement/nmpihome/nmpi



Annex C. Comparison of the samples with BCs enables an indication of the extent of

contamination to be drawn.



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



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



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).



Figure 2.2A. Designations located within an approximate 150 km2 area from the Harding STL System



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.



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



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.



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



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 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



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)


Highly aerial

Guillemot

(Uria aalge)

Widely distributed. High

abundance. High contact

time with water. Autumn

moult.

Razorbill

(Alca torda)


water.

Little auk

(Alle alle)


water.

Puffin

(Fratercula

arctica)


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.



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



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

http://www.scotland.gov.uk/Topics/marine/marine-environment/species/fish/demersal

http://www.scotland.gov.uk/Topics/marine/marine-environment/species/fish/demersal



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

http://www.scotland.gov.uk/Topics/Statistics/Browse/Agriculture-Fisheries/RectangleData

http://www.scotland.gov.uk/Topics/Statistics/Browse/Agriculture-Fisheries/RectangleData



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.



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).



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)

http://www.kis-orca.eu/map



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



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.



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


effect


effect


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



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.



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



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.



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

http://www.fishsafe.eu/



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.



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.



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



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.



Annex A

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Annex B: Comparative Assessment and Environmental Scoping Matrices



Annex C

Concentration of contaminants in sediments measured in the Gardline Environmental Ltd Study



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



Annex D: Designated Species



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




Species Habitats


IUCN Red

List


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




Species Habitats


IUCN Red

List


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.


http://www.ospar.org/content/content.asp?menu=00730302240000_000000_000000

http://www.bto.org/volunteer-surveys/birdtrack/bird-recording/birds-conservation-concern

http://www.snh.gov.uk/protecting-scotlands-nature/priority-marine-features/priority-marine-features/

http://www.snh.gov.uk/protecting-scotlands-nature/priority-marine-features/priority-marine-features/

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