Environmental Statement - Maersk Oil

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3 ‐ 6 Balloch Field Development Environmental Statement Table 3‐4 Average water temperature for the Balloch development (BODC, 1998). Section 3 Baseline Environment Location Mean temperature in winter ( o C) Mean temperature in summer ( o C) Sea surface 2.5 19.9 Sea bottom 4.5 11 During late spring, the water column begins to stratify due to increased solar radiation and calmer conditions. This results in the formation of a thermocline in the water column, separating a warm less dense surface layer from the rest of the water column, where winter temperatures remain. The thermocline increases in depth between May and September and is typically between 20 m to 50 m during summer (OSPAR Commission, 2000). In late August/early September, stratification begins to break down due to decreased solar heating and increased wind and wave action. Water temperature remains relatively uniform through the water column during the winter months (Doody et al., 1993). 3.3.6. SALINITY Like temperature, salinity affects the properties of seawater and the marine organisms inhabiting it. Fluctuations in salinity are largely caused by the addition or removal of freshwater from seawater through natural processes such as rainfall and evaporation. The salinity of seawater around an installation has a direct influence on the initial dilution of aqueous effluents, such that the solubility of effluents increases as salinity decreases. Salinity in the development area shows little seasonal variation, with water salinities of approximately 35 throughout the year (BODC, 1998). 3.3.7. AMBIENT AIR QUALITY Air quality measurements are not measured on offshore sites; however, regular monitoring of onshore sites is carried out by local authorities in many rural areas. Air quality from rural locations can be used as an approximation of the air quality that is likely to apply in a nearby offshore location. As such, information for a rural Scotland location (Strath Vaich) has been used as a proxy for the Balloch location and is presented in Table 3‐5. Table 3‐5 Ambient concentration of NO 2 for Strath Vaich (AEA Energy and Environment, 2008). 3.3.8. WATER QUALITY Averaging time µg/m 3 Average 1.0 1 98 th Percentile 7.5 99.9 th Percentile 16.0 100 th Percentile 16.8 1 Converted assuming an ambient air temperature of 10 o C Regional inputs from coastal discharges and localised inputs from existing oil and gas developments may affect water quality in different areas of the North Sea. Water samples with the highest levels of chemical contamination within the North Sea are generally found at inshore estuary and coastal sites that are subject to high industrial usage. Where concentrations of total hydrocarbons are found to be high offshore, this is normally in the immediate vicinity of installations. Concentrations generally fall to background levels within a very short distance of the point of discharge (CEFAS, 2001). The North Sea Quality Status Reports (North Sea Task Force, 1993) state that, although the waters of the NNS as a whole do not contain contamination above normal background levels, slightly higher levels of some contaminants (e.g. copper, iron and vanadium) are typically found in the shallower SNS. Lead is an exception as dissolved lead is quickly removed onto the surfaces of suspended particulate matter (SPM) which is relatively high in the coastal SNS area (apart from in the Dogger Bank region). It therefore does not get transported in the dissolved phase to the SNS by coastal
Balloch Field Development Environmental Statement Section 3 Baseline Environment circulation patterns (CEFAS, 1998). Since lead from estuarine sources tends to be trapped in near‐ shore areas, atmospheric inputs of lead become increasingly important away from the coast. Similar to lead, Polycyclic Aromatic Hydrocarbons (PAHs) generally absorb to particulate matter/suspended solids as they have low water solubility and are hydrophobic. Background water concentrations of PAHs are therefore often below the limit of detection. Similarly, due to their low solubility, polychlorinated biphenyl (PCB) concentrations in water are usually extremely low (< 1 ng/l) and difficult to detect. Typical concentrations of THCs (total hydrocarbons), PAHs, PCBs and heavy metals in the surface waters of the North Sea are shown in Table 3‐6. There was no monitoring of water contaminants and heavy metals as part of the Balloch environmental studies; only contaminants associated with the sediments were analysed and these are presented in Section 3.5.3. Table 3‐6 Summary of typical contaminant levels found in North Sea surface water (Sheahan et al., 2001). Location Oil and Gas Installations THC (µg/l) PAH (µg/l) PCB (µg/l) Nickel (µg/l) Copper (µg/l) Zinc (µg/l) Cadmium (ng/l) Mercury (ng/l) 1‐30 ‐ ‐ ‐ ‐ ‐ ‐ ‐ Estuaries 12‐15 >1 30 ‐ ‐ ‐ ‐ ‐ Coast 2 0.02‐0.1 1‐10 0.2‐0.9 0.3‐0.7 0.5 10‐32 0.25‐41 Offshore 0.5‐0.7
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B ‐ 2 Halocarbon release during e
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B ‐ 4 Lube and hydraulic oil spil
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Discharges to Sea Discharge from pi
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Production Phase Environmental Aspe
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B ‐ 10 Drainage water Discharge o
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Physical presence Oil and gas infra
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Major accidental events Other envir
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Environmental Statement - Maersk Oil

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