SLR Consulting (Cape Town office) Unit 39, Roeland Square Cnr Roeland Street and Drury Lane, Cape Town, Western Cape, 8001 Version: v3.0
Page 2 PREPARED BY: ABN 29 001 584 612 589 Hay Street Jolimont 6014 Australia +61 8 9422 5900 +61 8 9422 5901 perth@slrconsulting.com www.slrconsulting.com This report has been prepared by with all reasonable skill, care and diligence, and taking account of the timescale and resources allocated to it by agreement with the Client. Information reported herein is based on the interpretation of data collected, which has been accepted in good faith as being accurate and valid. This report is for the exclusive use of SLR Consulting (Cape Town office). No warranties or guarantees are expressed or should be inferred by any third parties. This report may not be relied upon by other parties without written consent from SLR. SLR disclaims any responsibility to the Client and others in respect of any matters outside the agreed scope of the work. DOCUMENT CONTROL Reference Date Prepared Checked Authorised 675.11246-R01-v3.0 Briony Croft Binghui Li Mark Caslin 675.11246-R01-v2.0 27 June 2017 Briony Croft Binghui Li 675.11246-R01-v1.0 13 June 2017 Briony Croft Binghui Li
Page 3 Shell is proposing to undertake well drilling activities offshore in Namibia. This report reviews the potential for underwater noise from Shell s activities to impact on fish and the fishing industry. It has been prepared in response to the issues and concerns raised by fishing industry stakeholders during the Scoping Stage of the Environmental Impact Assessment (EIA) process on the proposed project. Project activities with the potential to generate underwater noise have been assessed. This report describes the underwater ambient noise environment; major noise sources; noise threshold levels for impacts to fish; and estimates the distances at which noise may propagate at levels above the thresholds. The noise thresholds that have been considered concentrate on behavioural disturbance and masking effects; the potential for injury to fish due to noise exposure is minimal due to the distance from the drilling site to the fishing area of interest. Existing overall underwater ambient noise levels in the region are likely to range from about 80 db re 1 µpa (effective level of sound at nominal distance of one meter. The unit micro Pascal refers to sound pressure is measured in Pascals symbol Pa) in calm conditions, up to about 120 db re 1 µpa during periods of higher winds and or heavy rainfall, or when ships are moving past the area of interest. It is estimated that the median ambient noise level is around 100 db re 1 µpa, on the basis of historical wind speed and sea state data. The potential noise generated by drilling operations and supporting vessels has been identified, with source levels at a 1 m reference distance expected to be around 184 db re 1 µpa during drilling, and up to 190 db re 1 µpa from the supporting tug vessels during drill ship maintenance activities (e.g. cleaning, sanitation, and decontamination etc.). Potential seismic airgun array source for the Vertical Seismic Profiling (VSP) activities with a source level of 190 db re 1 µpa (rms) at a 1 m reference has also been considered. It should be noted that the noise emissions from the drilling operations and supporting vessels are generally constant in their temporal characteristics, while the noise emissions associated with seismic airgun sources have pulsive characteristics. As such, guidelines for fish exposed to the two types of noise are somewhat different. For the drilling operation scenarios, the semi-submersible drill ship option would minimize noise from drilling vessels, since its requirements for dynamic positioning using thrusters would be less than for a regular drill ship. However, in the far field there would be very little difference between noise from a regular drill ship and a semi-submersible drill ship, since both would be supported by vessels which would dominate the overall noise levels. The figure below illustrates the reduction in noise level with distance for the identified assessment scenarios, including the drilling operation scenarios and the scenario for the Vertical Seismic Profiling (VSP) activities.
Page 4 The extent of potential noise impacts will vary considerably depending on the equipment used and also on normal variation in ambient noise levels. Since the minimum distance between the drilling area of interest and the Tripp Seamount fishing area is around 50 km, received noise levels from the drilling activities at the fishing area are predicted to be within the typical range of existing ambient noise levels less than 5 km from the drilling location. On this basis, adverse underwater noise impacts at the Tripp Seamount are unlikely.
Page 5 Table of Contents 1 INTRODUCTION 1 1.1 Issues of Concern 1 1.2 Project Area 1 1.3 Noise Assessment Objectives 2 1.4 Introduction to Underwater Noise Concepts 3 1.5 Introduction to Underwater Noise Propagation 4 1.6 Existing Underwater Noise Environment 4 1.7 Potential Impacts of Noise on Fish 7 1.8 Fish Noise Impact Thresholds 8 2 NOISE SOURCES AND ASSESSMENT SCENARIOS 10 2.1 Description of Project Activities 11 2.1.1 Equipment and Personnel Mobilisation 11 2.1.2 Exploration Well Drilling Operations 11 2.1.3 Vertical seismic profiling 11 2.1.4 Decommissioning 11 2.2 Underwater Noise Sources and Scenarios 12 3 THRESHOLD DISTANCE ESTIMATION 14 3.1 Distance Estimation Method 14 3.2 Distance to Noise Thresholds 15 4 DISCUSSION 16 5 REFERENCES 16 TABLES Table 1 Annual exceedance percentile table of wind speed 6 Table 2 Approximate coordinates for the first well for purposes of this assessment 10 Table 3 Scenarios and noise sources 12 Table 4 Equipment details, example vessels and speeds / airgun array specifications 12 Table 5 Potential source noise levels 13 Table 6 Distances to noise thresholds by scenario and source (distance from source to Tripp Seamount as 50-80 km) 15
Page 6 Table of Contents FIGURES Figure 1 Project area and seafloor types 2 Figure 2 Typical noise levels in air and underwater 3 Figure 3 Levels and frequencies of anthropogenic and naturally occurring sound sources in the marine environment (from www.ospar.org/work-areas/eiha/noise). Natural physical noise sources represented in blue; marine fauna noise sources in green; human noise sources in orange. 5 Figure 4 Wenz curves describing pressure spectral density levels of marine ambient noise from weather, wind, geologic activity, and commercial shipping. (Adapted from Wenz, 1962) 6 Figure 5 Major shipping routes around southern Africa. The approximate location of the licence area is also shown (red outline). Data from the South African Data Centre for Oceanography (image source: CSIR) 7 Figure 6 Scale of effects on marine life with increasing distance from noise source 8 Figure 7 Reproduced from ASA (2014). Guidelines for fish exposed to shipping noise or noise from other continuous sources, such as oil exploration drilling. 9 Figure 8 Reproduced from ASA (2014). Guidelines for fish exposed to seismic airgun noise sources. 10 Figure 9 Overall noise level attenuation with distance (with an attenuation factor of 20) to typical background level 15
Page 1 1 INTRODUCTION 1.1 Issues of Concern As part of the Scoping Phase in the EIA, stakeholder meetings were held with representatives from the fishing sector and officials from the Ministry of Fisheries and Marine Resources. At these meetings, the stakeholders raised their concern about the exploration drilling noise and its effect on the behaviour of fish, the potential movement of fish away from the area and the consequential impact on the livelihoods of the fishermen. The specific questions and issues of concern raised by the stakeholders in relation to noise are listed below: The last 5 years has seen a decline in tuna catch. Noise from the drilling operations may influence Tuna migration. (Ricky de Castro, Large Pelagic Association) We would like the noise levels information shared with the Large Pelagic Association. (James Van Zyl, Large Pelagic Rights Holder) TERMS OF REFERENCE Using relevant source materials provide a short description of likely noise levels that would be generated by a drilling unit. This should include confirming the origin of the noise (vessel and/or actual rock drilling operation at seafloor) and whether the sound source varies between the two proposed drilling unit alternatives; Provide typical sound levels generated by; other users of the sea, wind, waves, animals, etc.; Describe the likely baseline noise environment at the well site and Tripp Seamount or what they are likely to be in a far offshore environment; Describe noise sensitivities (assessment criteria) for relevant fish species; Indicate factors that may affect noise transmission loss (such as current, wind and water temperature); Determine the noise transmission loss between the noise source (two alternative locations) and Tripp Seamount and determine if there would be any noise difference between the surface and seafloor as the transmission decays; and Provide a graphical representation of noise decay with distance and depth. 1.2 Project Area Shell Namibia Upstream BV (Shell) is the operator and licence holder of Petroleum Exploration Licence PEL 39, covering the area indicated in Figure 1. Based on the analysis of seismic data, Shell is proposing to undertake well drilling in the northern portion of the licence area. The area of interest for drilling is located in the Orange Basin off the coast of southern Namibia. It is approximately 300 km south-south-west of the town of Lüderitz; 250 km west-south-west of the town of Oranjemund; and approximately 50 km from the Tripp Seamount (see Figure 1). Water depths in the area of interest range from approximately 1,500 m to 2,000 m. The seafloor in the area is predominantly mud or sandy mud, with areas of muddy sand around the Tripp Seamount and sand in some shallower areas closer to shore.
Page 2 Figure 1 Project area and seafloor types Offshore activity associated with the project would occur in the area of interest for drilling and along vessel support routes. The onshore logistics base would most likely be located at Lüderitz. If Walvis Bay (not shown in Figure 1) is used instead the noise impacts of support vessel movements would be similar, but would extend northward to Walvis Bay. 1.3 Noise Assessment Objectives This assessment aims to identify the potential for underwater noise from project activities to impact the fishing industry. A number of issues and concerns relating to fish and shellfish were raised by fishing industry stakeholders during the initial public participation process on the proposed project. The majority of the concerns raised relate to the potential underwater noise impacts on tuna. Other concerns raised related to large pelagic fishing in general, lobster catchments and abalone ranching. Fishing vessels of various types operate along the entire coast along the shelf-break and into deeper waters. While some fishing areas coincide with the area of interest for drilling, the primary area of concern for tuna and pelagic fish in general is understood to be the Tripp Seamount around 50 km - 80 km from the proposed drill location. Lobster catchments and abalone ranching occur in shallower water closer to shore, approximately 200 km or more from the area of interest for drilling.
Page 3 1.4 Introduction to Underwater Noise Concepts There are similarities between noise underwater and noise in air but there are also differences. Noise propagation through both water and air represents energy travelling as a wave or a pressure pulse through a fluid (gas or liquid). The noise level or magnitude of noise is described in decibels (db) for both noise underwater and in air. However, the decibel unit describes noise levels relative to a reference value; it is not an absolute unit. The decibel reference values used to describe underwater noise and noise in air are different. Also, when describing noise levels experienced by people it is normal to adjust the reported level with a weighting factor (A-weighting) that accounts for the specific frequency-dependent hearing sensitivities of people. Other species of animals have different hearing sensitivities (e.g. dolphins can hear higher frequencies than people). This means that the A-weighting factor used to describe noise impacts to people in air should not be used when describing noise impacts to other species either in air or underwater. In addition to differences in the units used to describe noise in air and underwater, there are physical differences between air and water including differences in density and the speed of sound. These various factors mean that it is not possible to directly compare decibel noise levels perceived by people in air with noise levels underwater. Figure 2 provides an overview of the magnitude of typical noise levels occurring both in air and in water. Figure 2 Typical noise levels in air and underwater The highest noise levels occurring in air are typically of the order of 140 dba (A-weighted), a noise level that would be perceived as intolerable by people. In contrast, an underwater noise level of 140 db represents a moderate noise level, with noise elevated above the typical background level for example by vessel traffic passing several hundred meters away. Underwater noise levels up to 230 db or higher can occur in close proximity to some sources of noise, such as driving piles using an impact hammer (Hildebrande, 2009). For more information on underwater noise concepts, see www.dosits.org.
Page 4 1.5 Introduction to Underwater Noise Propagation The magnitude of the noise level at a particular location depends strongly on the distance from the noise source. Underwater noise propagation models predict the sound transmission loss between the noise source and the receiver. When the source level (SL) of the noise source is known, the predicted transmission loss (TL) is then used to predict the received level (RL) at the receiver location as: RL = SL TL The transmission loss between two distances D1 and D2 may be described by a logarithmic relationship with an attenuation factor F: TL= log If all losses due to factors other than geometric spreading are neglected, then the transmission loss would be predominantly due to spherical spreading (in deep water) or cylindrical spreading (in shallow water, bounded above and below). Spherical spreading means underwater noise would attenuate by 6 db with each doubling of distance, or F = 20. Cylindrical spreading means an attenuation of 3 db with each doubling of distance, or F = 10. In shallow water (less than about 300 m deep) noise propagation is highly dependent on the properties of the bottom and the surface as well as the properties of the fluid. Parameters such as depth and the bottom properties can vary with distance from the source. Sound energy at low frequencies may be transferred directly into the sea floor, rather than propagating through the water. Overall, the transmission loss in shallow water is a combination of cylindrical spreading effects, bottom interaction effects (absorption) at lower frequencies and scattering losses at high frequencies. In deep water offshore, such as that in the area of interest for drilling for this project, bottom interaction effects are less significant. In deep water, the transmission loss is primarily due to spherical spreading, with absorption and scattering losses at high frequencies. High frequency noise does not propagate as far as low frequency noise, as absorption effects are more significant for high frequencies than for low frequencies. Differences in water temperature and salinity throughout the water column also have an effect on noise propagation, since these can result in different sound speeds at different depths. The worst case for noise propagation typically occurs when the sound speed profile with depth results in bending of sound upwards in the water layers near the surface (an upwardly refracting surface duct ). In this situation, noise from sources at or close to the surface will propagate over longer distances. In practical cases the attenuation factor F can range from as low as 5 to as high as 30. A practical spreading loss model based on an attenuation factor of 15 for sound transmission is commonly assumed for projects near shore (NMFS, 2012). In deep water offshore, such as that in the area of interest for drilling for this project, spherical spreading (F=20) is commonly assumed (NMFS, 2016). 1.6 Existing Underwater Noise Environment Background or ambient noise in the ocean is variable, caused by a number of sources which fluctuate over time. These existing underwater noise sources include shipping noise or other anthropogenic noise sources, noise generated by waves and weather, and noise from biological sources. Figure 3 provides an overview of the noise levels produced by various natural and anthropogenic sources, relative to typical background or ambient noise levels in the ocean. Human contributions to ambient noise are often significant at low frequencies, between about 20 Hz and 500 Hz, with ambient noise in this frequency range typically dominated by noise from distant shipping (Hildebrand, 2009). In areas located away from anthropogenic sources, background noise at higher frequencies tends to be dominated by natural sources such as rainfall, surface waves and spray, fish choruses and snapping shrimp.
Page 5 Figure 3 Levels and frequencies of anthropogenic and naturally occurring sound sources in the marine environment (from www.ospar.org/work-areas/eiha/noise). Natural physical noise sources represented in blue; marine fauna noise sources in green; human noise sources in orange. Figure 4 shows the Wenz curves describing pressure spectral density levels of marine ambient noise from weather, wind, geologic activity, and commercial shipping. As can be seen from the figure, ambient noise can vary considerably with weather and sea state (Wenz, 1962). Around the well drilling location, wind speeds exceed Beaufort Scale 3 for over 90% of the year, and are at or above Beaufort Scale 5 for 50 % of the year (see ). The area of interest for drilling is also located in the vicinity of the main shipping route around southern Africa (Hildebrand, 2009) (see Figure 5). In correlation with the relations between the pressure spectral density levels and the wind force in Beaufort Scale as shown in Figure 4, the overall underwater ambient noise levels in the project area are estimated to range from about 80 db re 1 µpa in calm conditions (including possible low frequency noise component), up to about 120 db re 1 µpa during periods of higher winds and or heavy rainfall, or when ships are moving past the area of interest. In summary, ambient or background underwater noise levels in the study area would be expected to typically be above about 80 db re 1 µpa. Ambient or background underwater noise levels of the order of 100 db re 1 µpa would not be unusual in periods of moderate to high winds or when shipping movements are occurring in the area. Based on the wind speed data it is estimated that ambient noise levels at or above 100 db re 1 µpa may occur around 50% of the time. It also should be noted that the noise emissions from different sources have differences in both spectral (i.e. in relation to frequency) and temporal characteristics. For example, noise emissions associated with drilling operations are generally broadband and constant in nature, while noise emissions from airgun array sources used either for Vertical Seismic Profiling (VSP) activities or seismic surveys present temporally as repetitive pulses.
Page 6 Figure 4 Wenz curves describing pressure spectral density levels of marine ambient noise from weather, wind, geologic activity, and commercial shipping. (Adapted from Wenz, 1962) Table 1 Annual exceedance percentile table of wind speed
Page 7 Figure 5 Major shipping routes around southern Africa. The approximate location of the licence area is also shown (red outline). Data from the South African Data Centre for Oceanography (image source: CSIR) Walvis Lüderit Oranje 1.7 Potential Impacts of Noise on Fish The potential impact of man-made noise on a marine animal depends on the level of noise exposure. At low to moderate exposure levels, underwater noise may cause an overt change in the behaviour of a marine animal. At high exposure levels, underwater noise can induce a reduction in hearing sensitivity or even physical injury. The impact of noise exposure depends on a number of factors related to the physical and spectral characteristics of the sound (e.g., the intensity, peak pressure, frequency, duration, duty cycle), and to the animal under consideration (e.g., hearing sensitivity, age, gender, behavioural status, prior exposures). The type and level of impact also depends on whether the noise is impulsive, repeated or continuous in character. Generally speaking, marine animals are more sensitive to noise events with impulsive characteristics in comparison with continuous noise events (NMFS, 2016). A scale of effects of underwater noise on marine life is presented in Figure 6. The following four effect groups are of major significance: Mortality or lethal effects: life threatening physical injuries, including death and severe physical injury. Fish mortality is associated with very high source noise levels, with fish in close proximity to the noise source (for example, underwater explosions). Susceptibility to mortality at a particular sound level can vary between fish species, for example shellfish and fish without swim bladders can typically survive higher noise levels. Physiological effects: non-life threatening physical injuries, such as temporary or permanent auditory damage. The type and severity of physiological effects at different noise levels can also differ between species. Some fish detect and respond to sound predominantly by detecting particle motion in the surrounding fluid; others are capable of detecting sound pressure via the gas bladder. Masking effects: the reduction in the detectability of a sound as a result of the simultaneous occurrence of another noise. Masking noise interferes with the ability of the animal to detect and respond to biologically relevant sounds.
Page 8 Behavioural effects: include perceptual, stress and indirect effects of which the most common are startle responses or avoidance of an area. Behavioural responses can vary with species and sometimes extend over large distances (tens to hundreds of kilometres), until the noise decreases below the background sound level. Figure 6 Scale of effects on marine life with increasing distance from noise source 1.8 Fish Noise Impact Thresholds Threshold levels for underwater noise impacts on fish have been the subject of research over many years, however the majority of that research has focused on the potential for physiological effects (injury or mortality) rather than on quantifying noise levels with behavioural effects. A review of the literature and guidance on appropriate thresholds for assessment of underwater noise impacts are provided in the 2014 Acoustical Society of America (ASA) Technical Report Sound Exposure Guidelines for Fishes and Sea Turtles (ASA, 2014). The ASA Technical Report includes thresholds for mortality (or potentially mortal injury) as well as degrees of impairment such as temporary or permanent threshold shifts (TTS or PTS, indicators of hearing damage). Separate thresholds are defined for peak noise and cumulative impacts (due to continuous or repeated noise events) and for different noise sources (eg explosives, pile driving, and continuous vessel noise, drilling or dredging). In relation to fish behavioural impacts, the ASA Technical Report includes a largely qualitative discussion, focussing on long term changes in behaviour and distribution rather than startle responses or minor movements. For this exploratory drilling project, the potential types of noise sources are drilling noise and vessel noise, as well as a small airgun array used for the Vertical Seismic Profiling (VSP) activities. The relevant ASA guidance on noise thresholds for continuous noise sources is reproduced in Figure 7, and for seismic airgun noise sources is reproduced in Figure 8. The ASA qualitative approach to various types of noise includes definitions of effects at three distances from the source defined in relative terms: Near (N): this distance typically refers to fish within tens of meters from the noise source; Intermediate (I): distances within hundreds of meters from the noise source; and Far (F): fish within thousands of meters (kilometres) from the noise source. The ASA does provide numeric noise thresholds for physiological effects for some fish (those where the swim bladder is involved in hearing). However, for most effects and categories of fish the risk of effect is described qualitatively as low, moderate or high risk. Most tuna do not have a swim bladder.
Page 9 As can be seen in Figure 7 and Figure 8, for both continuous noise sources and pulsive seismic airgun sources at distances far from the source location, there is a low risk of adverse behavioural responses for any fish types. A moderate risk of masking effects is identified in the far range of distances for fish without a swim bladder, i.e. of the order of kilometres from the noise source. For the purpose of this impact assessment, the objective is to determine a range of distances at which noise from project activities has the potential to exceed ambient or background sound levels. Adverse masking noise and other behavioural effects are not expected in locations where noise from the project is below the background level, i.e. below 80 to 120 db re 1 µpa. Figure 7 Reproduced from ASA (2014). Guidelines for fish exposed to shipping noise or noise from other continuous sources, such as oil exploration drilling. Note: Most tuna do not have swim bladders, relying on continual swimming to maintain position in the water.
Page 10 Figure 8 Reproduced from ASA (2014). Guidelines for fish exposed to seismic airgun noise sources. Note: Most tuna do not have swim bladders, relying on continual swimming to maintain position in the water. 2 NOISE SOURCES AND ASSESSMENT SCENARIOS Shell is proposing to drill either one or two exploration wells. Only one well would be drilled at any one time (i.e., the second well would follow the first, and noise would not be generated from two drilling sites at the same time). The proposed location of drilling the first well (within the area of interest for drilling) is shown in Table 2. This location is approximately 50-80 km from the Tripp Seamount. Table 2 Approximate coordinates for the first well for purposes of this assessment Latitude S Longitude E 29 4 9 13 41 31
Page 11 2.1 Description of Project Activities 2.1.1 Equipment and Personnel Mobilisation The drilling unit could sail directly to site either from outside Namibian waters or via a Namibian port. Support vessels would mobilise from Lüderitz or Walvis Bay. Drilling materials, such as casings, mud components and cement would be imported using a container vessel directly to the onshore logistics base from where the support vessels would transfer it to the drilling unit. Transportation of personnel to and from the drilling unit for crew transfers would be provided by helicopter from Lüderitz. Helicopter operations are expected to occur almost daily. 2.1.2 Exploration Well Drilling Operations Various types of drilling platform can be used to drill an exploration well, depending on the water depth and marine operating conditions experienced at the well site. Shell is considering two alternative drilling unit options, a drill ship or a semi-submersible drilling vessel (rig). A drill ship is a purpose-built drilling vessel designed to operate in remote and often deep water conditions. This ship would be held in position during drilling by dynamic positioning thrusters. A semi-submersible drilling vessel is essentially a drilling rig located on a floating structure of pontoons. Such rigs typically require a tow vessel or barge to transport the vessel to its drilling location. When at the well location, the pontoons are partially flooded (or ballasted), to submerge the pontoons to a pre-determined depth below the sea level where wave motion is minimised. This gives stability to the drilling vessel thereby facilitating drilling operations. Dynamic positioning thrusters would also be used; but the load on dynamic thrusters would be less than for a drill ship. The drilling unit would be supported / serviced by at least three specialist support vessels, which would facilitate equipment, material and waste transfer between the drilling unit and onshore logistics base. 2.1.3 Vertical seismic profiling Vertical Seismic Profiling (VSP) is maintained as an optional evaluation tool that is undertaken as part of the conventional wireline logging program when the well reaches target depth to generate a highresolution seismic image of the geology in the well s immediate vicinity. The VSP images are used for correlation with surface seismic images and for planning ahead of the drill bit during drilling. VSP uses a small airgun array, typically comprising either a system of three 250 inch airguns with a total volume of 750 inch of compressed nitrogen at about 1800 psi (12,410 kpa) or two 250 inch airguns with a total volume of 500 inches. These volumes and the energy they release into the marine environment are significantly smaller than what is required or generated during exploration seismic surveys. The VSP airgun array is operated from the drilling unit. During VSP operations, four to five receivers are positioned in a section of the borehole (station) and the airgun array is discharged approximately five times at 20 second intervals. The generated sound pulses are reflected through the seabed and are recorded by the receivers to generate a profile along 60 to 75 m section of the well. This process is repeated as required for different stations in the well and it may take up to 8 to 10 hours to complete, depending on the well s depth and number of stations being profiled. 2.1.4 Decommissioning Once drilling and logging have been completed, the exploration well(s) would be plugged, tested for integrity and abandoned. On completion of decommissioning, the drill unit and support vessels would leave the licence area.
Page 12 2.2 Underwater Noise Sources and Scenarios The project description has been used to develop a list of scenarios and equipment that generate underwater noise with the potential to affect fish. These scenarios and sources are summarised in Table 3. Further details of the vessels and other equipment types expected to be comparable to those likely selected by Shell are provided in Table 4. Table 3 Scenarios and noise sources Drilling Operations Activity / Scenario Drill Ship Option Equipment / Noise Source Semi-Submersible Drill Rig Option 1. Mobilisation Drill ship in transit Tow vessel or heavy lift vessel Support vessels (x 3) Support vessels (x 3) Helicopter Helicopter 2. Well Drilling Drill rig Semi-submersible drill rig Operations Support vessels (x 3) Support vessels (x 3) Helicopter Helicopter 3. Decommissioning Drill ship in transit Tow vessel or heavy lift vessel Support vessels (x 3) Support vessels (x 3) Helicopter Helicopter 4. VSP VSP airgun array Table 4 Equipment details, example vessels and speeds / airgun array specifications Noise Source Description Drill ship E.g. Noble Globetrotter II, length 189 m, 8 x 4790 kw main engines, transit speed estimated 10 knots Semi-submersible drill rig E.g. Deepwater Nautilus, length 114 m Heavy lift vessel Use of a heavy lift vessel to transport a semi-submersible drill rig is likely to be the worst case situation for noise. E.g. MV Blue Marlin, length 217 m, 12,640 kw main engine, cruise speed 14.5 knots Support vessels (each) Offshore Services Vessel. E.g. Far Sitella, length 82 m, 3 x 2,450 kw main engines, 9,996 BHP, service speed 12.5 knots Helicopter E.g. AgustaWestland AW139 VSP airgun array E.g. a small airgun array, typically comprising either a system of three 250 inch airguns with a total volume of 750 inch of compressed nitrogen at about 1800 psi or two 250 inch airguns with a total volume of 500 inches Overall broadband source noise levels shown in Table 5 have been identified for each potential noise source on the basis of a literature review. At this time, the specific drill rigs and support vessels to be used have not been confirmed. Therefore, this assessment identifies estimated source levels for representative equipment that may be used. In practice, noise can vary, in particular for vessels in transit depending on propulsion system loading and vessel speed. Source noise levels for drill ships and support various vessels in transit have been estimated by scaling from frequency dependent reference vessel measurements, using the formulation described in Ross (1976) to adjust source levels on the basis of estimated ship length, power and speed, as applied by Wales and Heitmeyer (2002). Source levels for the VSP airgun array are based on data provided by Shell.
Page 13 For the drill ship option during drilling (rather than transiting), noise levels can range from 145 to 190 db re 1 µpa (OSPAR, 2009). The noise at the higher end of the range is due to drill ships using thrusters for dynamic positioning; cavitation around propellers and thrusters is the most significant source of drill ship noise. Noise is also generated by machinery such as power generation units and pumps, and transmitted into the water via the hull. The noise generated by equipment such as the drill string in the water is relatively low. Table 5 Noise Source Heavy lift vessel Potential source noise levels Notes Transporting semi-submersible drill rig, estimated as typical max commercial vessel noise db re. 1µPa @ 1 m (rms) Reference 188 McKenna et al (2012) Drill ship in transit Estimated from size, speed and power 186 Ross (1976) ; Wales Support vessels Source level per support vessel, 183 and Heitmeyer (2002); (each) estimated from size, speed and power Warner et al (2014) Support vessels Logarithmic sum of source levels for 188 - (three) three support vessels Helicopter 150 m elevation 109 Richardson et al (1995) Drilling (drill ship) Noble Discoverer, no support vessels 175 Provided by Shell (unpublished) Drilling (drill ship) Kulluk, no support vessels 169 Provided by Shell (unpublished) Drilling (drill ship) Drilling (semisubmersible drill rig) Drilling and support vessels Drill ship maintenance Stena Forth operating with one support vessel 184 Kyhn et al (2011) Polar Pioneer, no support vessels 170 Provided by Shell (unpublished) Stena IceMAX operating with four 188 MacDonnell (2016) support vessels, to stern Stena Forth during maintenance 190 Kyhn et al (2011) VSP A small airgun array 190 Data provided by Shell Kyhn et al (2011) report source noise levels for the drill ship Stena Forth of 184 db re 1 µpa during drilling, and 190 db re 1 µpa during maintenance work on the drill ship. Efforts were made to restrict the influence of support vessel noise on these measurements, but at least one support vessel was always on standby near the Stena Forth during the measurements, and the measured sound at distances of more than 1 km from the rig are a composite of drill ship noise and support vessel noise. Shell provided additional measured noise data from 3 individual drill ships, the Noble Discoverer; the Kulluk; and the Stena IceMAX. The Stena IceMAX measurements are reported in MacDonnell (2016), measurements of the other vessels have yet to be published.
Page 14 For the Noble Discoverer and the Kulluk the data provided by Shell represents the noise from drilling operations in isolation (i.e. no support vessels were operating near the drill ships at the time of the measurements). For the Stena IceMAX, measurements included drilling noise in addition to the noise from four offshore support vessels broadband noise from drilling was not able to be isolated from the support vessel noise. Noise levels measured during drilling indicate a drilling source level (at 1 m reference distance) of 174.9 db re 1 µpa for the drillship Noble Discoverer, and 168.6 db re 1 µpa for the Kulluk drilling unit. For the Stena Icemax while anchored, the overall noise source level from drilling and support vessel operations at a 1m reference distance was 185.8 db re 1 µpa (measured at beam) and 187.7 db re 1 µpa (measured to stern). Shell also provided underwater noise measurement data for a semi-submersible drill rig, the Polar Pioneer. For this rig, noise levels measured during drilling indicate a drilling source level (at 1 m reference distance) of 170.1 db re 1 µpa. The source levels during drilling operations for all these drilling units are less than or similar to the noise generated by large vessels at normal operating speeds. For the two possible drilling options, i.e. with dynamically positioned drillship Stena IceMAX or the semi-submersible drill ship, the overall noise level produced by a drilling operation is expected to be dominated by the noise from supporting vessels. Therefore, the overall noise levels from the drilling operations with the two types of drill ship options would be similar. For the purpose of this analysis, the potential noise sources in Table 5 may be consolidated into four representative or worst case scenarios as follows: Drill ship and offshore support vessel 184 db re 1µPa (dominated by thrusters and OSV) Semi-submersible drill ship and offshore support vessel 183 db re 1µPa (dominated by OSV) Maintenance scenario - 190 db re 1µPa VSP airgun array scenario - 190 db re 1µPa In relation to the potential for underwater noise to be generated by helicopters, the broadband noise levels underwater due to helicopters flying at altitudes of 150 m or more are expected to be around 109 db re 1µPa (Richardson et al, 1995) at the most noise-affected point. This noise level is considerably less than the underwater noise generated by other support vessels, and can be considered as negligible in overall noise level. 3 THRESHOLD DISTANCE ESTIMATION The objective of this assessment is to estimate the distances at which noise from the drilling operations might be detectable above the estimated broadband ambient noise level in the project area which is estimated to range from 80 up to 120 db re 1µPa, with a median level around 100 db re 1µPa. At distances where the noise from drilling operations reduces to the background level or below it is assumed there is minimal potential for masking or behavioural response effects to adversely affect fish. 3.1 Distance Estimation Method The US National Marine Fisheries Service provides guidance on estimating the extent of underwater noise impacts (NMFS, 2016). Appendix D of this guidance provides a calculation method for determining the radius r from the noise source at which the sound level is equal to the acoustic threshold. For mobile noise sources such as transiting vessels the Appendix D method assumes a 20log(r) spreading loss. The distances to the identified median ambient level of 100 db re 1µPa threshold has been calculated for each scenario. In situations with drilling and several vessels operating simultaneously in an area, the loudest source (vessel noise) will dominate the overall noise level. Figure 9 shows the attenuation with distance of noise from each of the main noise sources, relative to the typical range of background sound levels.
Page 15 Figure 9 Overall noise level attenuation with distance (with an attenuation factor of 20) to typical background level 3.2 Distance to Noise Thresholds The estimated distances from the various sources to the median 100 db re 1µPa background noise level are summarized in Table 6. Table 6 Distances to noise thresholds by scenario and source (distance from source to Tripp Seamount as 50-80 km) Scenario Mobilisation or demobilisation - drill ship Mobilisation or demobilisation semisubmersible drill rig Drilling operations - drill ship Drilling operations - semi-submersible rig Noise Sources Included Source Level db re 1µPa @ 1 m Distance to 100 db re 1µPa (km) Drill ship transiting 186 20 OSV x 3 188 25 Helicopter 109 n/a Heavy lift vessel 188 25 OSV x 3 188 25 Helicopter 109 n/a Drill ship + OSV 184 16 Maintenance 190 32 Helicopter 109 n/a Semi sub drill ship + 183 OSV 14 Maintenance 190 32 Helicopter 109 n/a VSP activities A small airgun array 190 32
Page 16 4 DISCUSSION In relation to the potential for behavioural disturbance or masking effects, the extent of noise impacts above the background noise level may vary considerably depending on the specific vessels used and the number of support vessels operating. It will also depend on the variation in the background noise level with weather and with the proximity of other vessel traffic (not associated with the project). Noise from project activities is expected to decrease to below the estimated median ambient background level of 100 db re 1µPa within a distance of around 32 km from the drill site in all cases, with maintenance and VSP activities representing the worst case scenario for noise. The worst case scenario for the maintenance activities and the VSP activities would be expected to occur only for relatively short periods of time. In addition, noise from project activities is expected to decrease to below the estimated upper boundary of ambient background level of 120 db within a distance of less than 5 km from the drill site in all cases. The noise levels from drilling would often be considerably below the noise levels from supporting vessel movements. If a drill ship is used, the dominant noise source is likely to be the dynamic positioning thrusters. Noise from machinery or the drill string in the water is considerably quieter. Noise from drill ship operation with a support vessel is expected to decrease to below 100 db re 1µPa within about 16 km of the drill site. The semi-submersible drill rig option would be expected to be marginally quieter. The nature of this drill rig requires less dynamic positioning effort, so the noise is minimized. With a semi-submersible rig, noise would be dominated by the support vessels and is expected to decrease to below 100 db re 1µPa within about 14 km of the drill site. In addition, when mobilising or demobilising, several vessels may operate in close proximity and vessel noise may extend over relatively large distances (out to about 25 km). In terms of constant noise sources for the drilling operations, vessel noise is expected to dominate the noise generated by the project as a whole. The types of vessels proposed for the work and their noise emissions are likely to be similar to existing vessels operating in the area. In particular, commercial shipping vessels transiting around southern Africa (see Figure 5) would be expected to have similar noise emissions and impacts on animals. Although fishing vessels are smaller and can be quieter than cargo ships, noise from fishing vessels can also be a significant contributor to the ambient noise environment. Since the minimum distance between the drilling area of interest and the Tripp Seamount fishing area is around 50 km, adverse underwater noise impacts to fish are unlikely. Noting the greater distances of around 200 km or more to the lobster catchments and abalone ranching areas near shore, underwater noise impacts to these industries are also expected to be negligible. 5 REFERENCES ASA (2014) Sound Exposure Guidelines for Fishes and Sea Turtles: A Technical Report prepared by ANSI-Accredited Standards Committee Se/SC1 and registered with ANSI. ASA S3/SC1.4 TR-2014 Hildebrand, A. (2009) Anthropogenic and natural sources of ambient noise in the ocean. Marine Ecology Progress Series Vol 395:5-20. Kyhn, L.A., Tougaard, J. and Sveegaard, S. (2011). Underwater noise from the drillship Stena Forth in Disko West, Baffin Bay, Greenland. National Environmental Research Institute, Aarhus University, Denmark. 30 pp. NERI Technical Report No. 838. http://www.dmu.dk/pub/fr838.pdf MacDonnell, J. (2016). Shelburne Basin Venture Exploration Drilling Project: Sound Source Characterization, 2016 Field Measurements of the Stena IceMAX. Document 01296, Version 3.0. Technical report by JASCO Applied Sciences for Shell Canada Limited.
Page 17 McKenna, M.F., D. Ross, S.M. Wiggins, and J.A. Hildebrand (2012). Underwater radiated noise from modern commercial ships. Journal of the Acoustical Society of America 131(1): 92-103. NMFS (2012). Guidance Document: Sound propagation modeling to characterize pile driving sounds relevant to marine mammals. U.S. Dept. of Commer., NOAA, NMFS Northwest Region and Northwest Fisheries Science Center. Memorandum. NMFS (2016). Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing: Underwater Acoustic Thresholds for Onset of Permanent and Temporary Threshold Shifts. U.S. Dept. of Commer., NOAA. NOAA Technical Memorandum NMFS-OPR- 55, 178 p. OSPAR (2009). Assessment of the environmental impact of underwater noise. OSPAR Commission, publication number: 436/2009. Richardson, W.J., C.R. Greene, C.I. Malme and D.H. Thomson [1995]. Marine mammals and noise. Academic Press. 576 pp. Ross, D. (1976) Mechanics of Underwater Noise, Pergamon, New York. Wales, S. C., and Heitmeyer, R. M. (2002) An ensemble source spectra model for merchant shipradiated noise. The Journal of the Acoustical Society of America 111(3), 1211-1231. Warner, A. C. et al (2014) Underwater Acoustic Measurements in Haro Strait and Strait of Georgia: Transmission Loss, Vessel Source Levels, and Ambient Measurements. JASCO Document 00659, Version 3.0. Technical report by JASCO Applied Sciences for Hemmera. Wenz GM (1962) Acoustic ambient noise in the ocean: spectra and sources. Journal of the Acoustical Society of America 34:1936 1956.