Environmental Statement - Maersk Oil

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5‐ 18 Balloch Field Development Environmental Statement Section 5 Assessment of Potential Impacts and Controls For marine mammals, hearing impairment can occur when sound levels are high and, in the case of transient noise sources such as pile driving, when they are exposed to repeated sounds. The hearing loss can occur in two forms: Temporary Threshold Shift (TTS): On exposure to noise, the ear’s sensitivity level will decrease as a measure to protect against damage. This process is referred to as a temporary shift in the threshold of hearing, and generally returns to normal in 24 hours; Permanent Threshold Shift (PTS): A permanent change in the threshold of hearing caused by a sound level or cumulative exposure of a sound level that is capable of causing irreversible damage to the ear. On the basis of observed cetacean physiological and behavioural responses to anthropogenic sound, Southall et al., (2007) proposed precautionary noise exposure criteria for injury and behavioural responses (Table 5‐13). These criteria are currently considered the best available and are based on quantitative sound levels and exposure thresholds over which PTS‐onset could occur for different groups of species. By comparing the modelled sound pressure outputs against the Southall thresholds, the peak sound levels are not considered capable of causing a PTS to cetaceans, while a PTS may be caused to pinnipeds out to a short distance of 5 m. The range at which TTS extends to cetaceans and pinnipeds is approximately 1 m and 6 m respectively from the pile driver (Table 5‐13). Table 5‐13 Impact criteria for cetaceans and pinnipeds and the estimated ranges at which the auditory effects occur from the piling associated with the proposed Balloch development. Criteria Sound threshold level Range from pile driving (m) Injury to Cetaceans ‐ Permanent Threshold Shift 230 dB re 1 µPa Is not exceeded Injury to Cetaceans ‐ Temporary Threshold Shift 224 dB re 1 µPa 1 Injury to Pinnipeds (seals)‐ Permanent Threshold Shift 218 dB re 1 µPa 5 Injury to Pinnipeds (seals)‐ Temporary Threshold Shift 212 dB re 1 µPa 6 The diameter of the pile has been found to be the biggest influence on sound pressure levels generated from piling. The larger the pile to be installed, the larger the sound pressure levels which will be generated (Nedwell et al., 2007). The piles to be used for the Balloch subsea cooling spool are relatively small in diameter and are not expected to generate the high sound levels used for installing the larger diameter (>4 m) wind turbines. The only marine mammals that are considered to be at risk of PTS from pile driving activities are seals, but given the location of the Balloch development in the CNS the presence of any seals in the area is unlikely. It is also unlikely that any marine mammal species would be present in such close proximity to the pile driver (
Balloch Field Development Environmental Statement Section 5 Assessment of Potential Impacts and Controls Proposed control measures for impacts associated with underwater noise during the proposed Balloch development The following control measures are proposed to minimise the impact associated with underwater noise sources during all phases of the proposed development. The risk of noise associated with the vessels and drilling rig causing any significant impacts is low. Piling of the subsea cooling spool during the installation phase could cause relatively high sound levels. Providing the mitigation measures outlined above are followed, the impacts from underwater noise are assessed to be low. 5.5. ACCIDENTAL EVENTS Uncontrolled hydrocarbon spills following an uncontrolled blowout at the proposed Balloch development location are modelled and discussed in Section 6. This section also models the fate of the loss of the diesel inventory from the drilling rig and discusses Maersk Oil’s tiered response to respond to and mitigate such spills. 5.6. WIDER DEVELOPMENT CONCERNS The potential of the proposed development to: Cause an offence to European Protected Species; Impact on protected areas; Impact on other sea users; Have a transboundary impact is discussed in this section. 5.6.1. EUROPEAN PROTECTED SPECIES Proposed Control Measures Both the number of vessels required and the length of time the vessels are on site will be minimised; The JNCC piling protocol will be followed including: Piling will commence using soft start; Piling will commence in hours of daylight and good visibility; A trained marine mammal observer (MMO) will be present during piling operations Following JNCC guidance, no pile driving will commence if a marine mammal has been recorded within 500 m of the exclusion zone during the previous 20 minutes. This section assesses the impacts of noise on Marine European Protected Species (EPS) likely to be encountered in the area of the proposed development. EPS include all cetaceans, marine turtles and the Atlantic sturgeon. However, it is unlikely that marine turtles or Atlantic sturgeon will be found in the development area, therefore the assessment focuses on the cetaceans species likely to occur. As detailed in Section 3, there are several cetacean species distributed through the CNS that the EPS assessment should consider including harbour porpoise, minke whale, white‐beaked dolphin and white‐sided dolphin. The Offshore Marine Regulations 2007 (as amended 2010) contain a revised definition of ‘disturbance’ to European Protected Species. The Offshore Marine Regulations extended the offence to areas of UK jurisdiction beyond 12 nautical miles (nm). It is now an offence under UK Regulations to deliberately disturb wild animals of a EPS in such a way as to be likely to: 5 ‐ 19
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Environmental Statement - Maersk Oil

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