11.
FUEL SPILL RISK ASSESSMENT
11.1.1 The proposed fuel reception facility at Tuen Mun Area 38 is intended as a permanent replacement for the existing temporary facility at Sha Chau. At present, aviation fuel is imported to Hong Kong in ocean going tankers and stored at a depot in Tsing Yi. The fuel is subsequently reloaded into 5,000 dwt tankers for transport to Sha Chau. The consumption of aviation fuel at the airport will reach an estimated 3,680,000 tonnes by 2004 representing approximately two trips a day to the AFRF at Sha Chau. The fuel is transferred from the AFRF to the airport by twin submarine pipelines. Aviation fuel has been transported to the airport by this combined method since 1995 and no spill incident has occurred in that time.
11.1.2 Construction of the PAFF will allow imported fuel to be stored directly for supply to the airport by pipeline eliminating the present double handling at Tsing Yi. In addition, the need for routine barge access to the AFRF in the sensitive waters of the Sha Chau and Lung Kwu Chau Marine Park will be eliminated.
11.1.3 Pollution of the sea by fuel spills is a concern due to the potentially deleterious consequences on a local scale. However, it is important to recognise that major spillages resulting from the tankering and transport of fuel are infrequent and by no means the principal cause of marine pollution from oils (Clark, 1992). A breakdown of the estimated 2 - 3x106 tonnes of oil entering the world’s oceans is presented below in Table 11.1.
Table 11.1 Breakdown
of Global Oil Losses to Marine Waters
|
Source |
% of total contribution |
|
Industrial and
urban run-off |
37 |
|
Marine shipping |
33 |
|
Tanker
accidents |
12 |
|
Atmosphere |
9 |
|
Natural sources |
7 |
|
Exploration and
production |
2 |
Reference: IOTPF,
1987.
11.2.1 Aviation fuel is potentially highly damaging and toxic if released to the marine environment in large quantities. A major spillage of aviation fuel could be directly toxic to marine organisms, harmful to sensitive marine and coastline habitats, adversely affect fisheries catches or their quality, degrade recreational or amenity areas such as beaches and be detrimental to other legitimate uses of marine water including abstraction.
11.2.2
Possible sources of a spill from the
facility can be identified as losses from the tank farm (e.g. tank rupture,
tank overfilling, land pipe failure, coupled with a failure of the containment
systems), the jetty (e.g. rupture of the loading arm, damage to an approaching
or berthed tanker) and the pipeline (e.g. offshore rupture). All these facilities will be designed,
constructed and operated in such a way as to ensure that the likelihood of
failure is minimised as far as reasonably practicable. The likelihood of a major fuel spill
from any of these circumstances has been shown to be extremely small. As discussed in Section
10, the statistically predicted frequency of a spillage varies between 6.6 x 10-6
per tank year for the tank farm, 3.4 x 10-7 per km per year for a
pipeline leak, 2.6 x 10-5 per year for a loading arm rupture at the
jetty and 3.5 x 10-5 per encounter for a vessel collision. Other magnitudes of spills with other
frequencies could occur. For
example a smaller spill could occur with a shorter frequency. However the assessment has considered
the larger spill as a worse case.
11.2.3 Notwithstanding the low likelihood of any environmental incident arising from a major spillage of fuel, some statistically quantifiable risk of failure will always remain and, therefore, it is essential to derive emergency contingency plans to effectively contain and clean up all accidental spillages quickly at short notice and to minimise the quantities of fuel reaching environmentally sensitive receivers. As such, it is necessary to identify possible sources and characterise conjectured spill incident scenarios and to understand the likely movement and dispersion of spilled fuel in the environment. This understanding will provide a solid basis for identifying suitable mitigation to ensure that the risks of losses and subsequent hazards to the environment are kept to a practical minimum and that the emergency contingency plans have full regard for the likely fate of any lost fuel to provide for effective remedial action to minimise impacts on sensitive environmental receivers.
11.2.4 A fuel slick on the sea surface will be subject to a number of degradation processes (see Farmer, 1997). These can be broadly categorised as follows :
¨ Spreading – fuel will rapidly spread on the sea surface in the immediate aftermath of a spill. Initial spreading is gravity driven away from the point of spillage such that thickness tends to decrease towards the edges where the slick is held by surface tension.
¨ Evaporation - lighter fuel fractions will quickly evaporate to the atmosphere. This process is enhanced in warmer weather and by wave and wind action. Previous studies in Hong Kong have identified that evaporation of heavy marine diesel oil considerably less volatile than aviation fuel is likely to be substantial in prevailing water temperatures of 23-24°C (Spooner, 1977). In a typical temperate climate most hydrocarbons with a boiling point below about 200oC will evaporate in less than 24 hours. Similarly evaporation of aviation fuel (boiling point 200 – 260oC ) is likely to be fairly rapid.
¨ Dispersion - wave action will break up a slick and eventually cause it to form droplets. These may remain in suspension or fall to the sea floor. Fuel spills would be expected to remain cohesive until spreading depletes thickness to less than about 0.1 mm.
¨ Emulsification – fuel in the sea will gradually physically absorb water to form emulsions. The process is enhanced by the mixing action of wind at the fuel / water interface. As emulsification continues the fuel density will increase until it approaches that of the surrounding water.
¨ Dissolution - lighter fuel fractions may dissolve in water. However, in subtropical climes such as in Hong Kong the process of evaporation would dominate and dissolution is unlikely to be significant. Dissolved components of the spilled fuel will ultimately be absorbed in sediments or released to air by evaporation.
¨ Sedimentation – emulsified fuel will have an increasing tendency to sink to the seabed. Fuel in contact with particulate matter e.g., sand entrained by nearshore wave action, will also deposit on the sea floor.
11.2.5 The physical form of aviation fuel spilled to sea will obviously be transformed through the processes outlined above and it will ultimately be lost to the atmosphere or deposited to sinks on shore or on the seabed. A spillage of aviation fuel is likely to dissipate through the primary driving forces of evaporation, emulsification, sedimentation and biodegradation within a period of about 3 days (ERM, 1995).
11.2.6 By far the most serious environmental consequences of a major fuel spill would occur in the early stages when the fuel may form extensive slicks on the sea surface. Direct contact with the fuel may be fatal for many types of marine organisms.
11.2.7 Dissolved fuel components may be toxic to marine life especially sensitive life stages such as fish larvae, which could be affected by concentrations of the order of 50ug/l. However, widespread fish kills are not usually observed following oil spills. Fish would normally be expected to leave the affected area and return once the fuel has dissipated. Petroleum hydrocarbons either ingested and/or adsorbed from the water column will be fairly rapidly detoxified by fish (Whipple et al., 1981) and crustaceans (Capuzzo and Lancaster, 1981) to non-toxic metabolites but low residual concentrations of hydrocarbons in the water or within the food chain can cause serious tainting of fish and shellfish flesh rendering them inedible or unfit for sale. Although it should be noted that slight tainting does not appear to be a problem to local consumers.
11.2.8 Sessile and immobile fauna such as bivalve molluscs are more susceptible to direct contact than free swimming species. Exposure to aviation fuel could potentially cause smothering and clogging of gill filaments. Molluscs are able to avoid polluted ambient conditions for long periods through closure of the shell. Nevertheless these species remain vulnerable on account of their limited ability to metabolise and excrete fuel compounds (owing to relatively inefficient enzyme systems involved in petroleum hydrocarbon metabolism; Moore et al., 1987) and thus they may accumulate toxic hydrocarbons from the water column to high concentrations (e.g., Goldberg et al., 1978).
11.2.9 Marine mammals have the ability to detect hydrocarbon spills and take evasive action. This has been observed previously following incidents involving large crude oil tankers. Comparable studies following losses of aviation fuel to the sea are not available but a similar behaviour pattern would be expected. Ritchie and O’Sullivan (1994) reported negligible effects on otters, seals and dolphins following the wreck of the crude oil tanker the Braer off the Shetland Isles, UK. A review of another incident involving a major crude oil spill from the Sea Empress off the coast of Wales, UK found that whilst some seals caught up in the spill were oiled there were no mammal deaths caused by the spill (SEEC 1996). Of more direct relevance to the PAFF study area, previous reviewers have concluded that it is unlikely that a population of dolphins would be disabled by a spill at sea. Dolphins directly observed from reconnaissance aircraft and surface vessels following two oil spills in Texas, USA were seen to move under or around thick oil slicks (from review of ERM, 1995).
11.2.10 Biomagnification of spilled hydrocarbons through the marine food chain is unlikely to be a particular concern for dolphins. The principal food species of Indo-Pacific Humpback dolphins are estuarine fish although squid and crustaceans (shrimp) may be occasionally preyed upon (Jefferson, 1998; 2000). Both fish and crustaceans are able to metabolise petroleum hydrocarbons relatively efficiently although there may be some risk from species including molluscs (e.g. squid that may form part of the dolphins’ diet) which may store hydrocarbon pollutants. However, dolphins themselves are able to metabolise and excrete hydrocarbons and thus elevated accumulation within dolphin tissue is most unlikely.
11.2.11 Surface slicks resulting from a major spillage may seriously affect avian fauna. Contacted fuel oil could cover and destroy the protective insulation and buoyancy function of bird feathers as well the ability of an affected bird to fly. Attempts to self clean by preening may result in direct ingestion of the fuel and its toxic constituents. As a consequence of these processes, bird fatality has repeatedly been seen to be rapid and widespread in the aftermath of major crude oil spillages. For the purposes of this assessment it is assumed that spilled aviation fuel would be similarly damaging.
11.2.12 Fuel spills would also be a major concern where they could potentially impact on slow growing coral species. The destruction of coral stands could take years to recover.
11.2.13 Impacts on mangroves could also persist for many years if spilled fuel became entrained within the complex ecosystems in which any attempts at clean up are likely to be very problematic. Mangrove trees could defoliate on contact with fuel. Direct contact with an influx of fuel could be devastating for juvenile fish, molluscs and crustaceans and other fauna inhabiting the diverse mangrove habitat.
11.2.14 Aside from the direct environmental impacts discussed in the preceding section, major fuel spills could impact on beaches forcing their closure for expensive clean-up.
11.3
Prediction and Evaluation of Impacts
11.3.1.1 The likelihood and severity of potential impacts has been assessed by means of a conventional environmental risk analysis involving :
¨ identification of fuel spillage scenarios;
¨ impact assessment; and
¨ identification of mitigation measures.
Fuel Spillage Scenarios
11.3.1.2 Fuel spill scenarios have been identified in the Hazard to Life assessment (Section 10 refers) and as mentioned above, these comprise spills from four main elements of the PAFF system, namely, from marine transport, the jetty, submarine pipeline and the tank farm. The causes of the spills considered include failure of the system and accident incidents. A summary of the spill scenarios considered in this assessment is provided in Table 10.8.
11.3.1.3 In terms of likely movement, spilled fuel reaching the sea surface from either an incident at the seawall adjacent to the tank farm or in the vicinity of the jetty will behave in an approximately similar manner under any given set of tidal conditions and any given spill quantity. The dominant parameter will be the spill quantity and the key driving force will be the hydrodynamic currents, which will increase away from the shoreline towards the main Urmston Road channel. For conservative assessment purposes, a greater understanding of the likely area of spill spread can be gained by simulating an incident located on the seaward approach to the jetty. Thus, for the purposes of this assessment, this scenario with an incident point 500m from the jetty as the centre point of the release has been modelled.
11.3.1.4 The worst credible scenario that would result in the largest pool of oil at sea has been determined to be the rupture of an 80,000dwt tanker. The actual risk of such an incident is very low as discussed in Section 10. An assumed loss of 7% of the dwt would lead to a maximum instantaneous release of 5600 tonnes of fuel. For conservative assessment purposes the thickness of the pool formed is assumed to be small, in the region of 10mm in the first instance, and based upon this, the resultant size of pool from the worst case spill would be in the region of 945m in diameter.
11.3.1.5 Notwithstanding the above worst case scenario, the proposed pipeline from the PAFF tank farm to the coupling point at the existing AFRF will stretch undersea for approximately 4.8km and a failure could be conjectured for any point along this length. Spills arising from pipeline failure and surfacing offshore may behave differently from spill sources on land or close to the PAFF jetty. In order to cover the range of impacts that could possibly arise should this very unlikely circumstance ever arise, two pipeline spill scenarios have also been modelled. These are leakage from a pipeline rupture approximately 1000m from the tank farm shoreline in the middle of the Urmston Road channel where the hydrodynamic currents are relatively strong and the strongest advection would be expected. Additionally, in view of the particular concerns relating to impacts near the existing AFRF within the Sha Chau and Lung Kwu Chau Marine Park, an additional simulation has been conducted at a release point at the marine park boundary approximately 400m from the existing AFRF.
11.3.1.6 The worst credible case pipeline spill would result from a full bore rupture of one of the pipelines. Aviation fuel from the submarine pipeline will initially be driven out of the release outlet opening by momentum as the fuel is pumped through. On detection of the leak, pressure sensors will automatically trigger closure of valves at the tank farm end of the pipeline. This will be effected within a few minutes of a catastrophic pipeline failure. Subsequently, following relaxation of the pressure differential, fuel will escape more slowly through a buoyancy driven process as it is gradually displaced by seawater. This release will be resisted by the 2 bar head of pressure experienced at the seabed and thus release will be very gradual in comparison to the initial momentum driven release. In practice this latter phase of the release could be effectively mitigated through implementation of an emergency contingency action plan to externally plug the point of rupture.
11.3.1.7 Similarly, vertical movement of the emergent fuel plume will initially be momentum driven close to the release outlet. This momentum will however be diminished by the pressure head experienced at the pipeline depth and the physical obstruction of rock armour protection such that the fuel is likely to seep through the seabed and percolate through the rock armour losing much of its momentum in the process. Thereafter, the plume rise will be mostly buoyancy driven. As the fuel rises it is likely to entrain water creating a water fuel emulsion, which will eventually reach the sea surface. This process coupled with weathering and tidal motions of the sea will mean that by the time the fuel reaches the sea surface, it will not remain as one large pool. Rather, the fuel would have broken up into a number of small emulsified pools thus facilitating its degradation. However, for the purposes of undertaking a conservative assessment, it has been assumed that a coherent surface patch will form.
11.3.1.8 Any rupture in the pipeline would cause a pressure drop and the integrated detection system would instigate an automatic shutdown of the fuel pumps. The pumping rate of the fuel within the pipeline is 1,500m3/hour and, assuming a shut down response time of 180 seconds, a spill volume of 75m3 or 60 tonnes would occur. For the conservative purposes of this assessment it is assumed that this volume will be released instantaneously and spread on the surface as a single coherent patch with a thickness of 10mm. This corresponds to an initial patch diameter of 98m.
11.3.1.9 The three scenarios identified above thus represent conjectured events likely to result in :
¨ the largest credible spill to sea;
¨ a spill into the main Urmston Road marine channel where the hydrodynamic currents and thus spill spread is expected to be greatest; and
¨ a spill immediately on the boundary of the Marine Park.
11.3.1.10 These three scenarios are considered adequate to characterise the full range of spill impacts that may arise in the operational phase of the facility.
Computer Models
11.3.1.11 The worst case scenarios identified above have been simulated using hydrodynamic and particle tracking models to gain an understanding of the movement and range of conjectured fuel spills from the operation of the fuel receiving facility and the supply pipeline to the airport. It is important to bear in mind that the modelling assessment is based on a multiplicity of conservative parameter inputs to identify the extreme range of plume movement that might be credibly predicted. The output is intended to facilitate implementation of an effective emergency contingency plan to ensure best practical protection of any sensitive receivers that might be considered at risk, notwithstanding the very low likelihood of such an event ever occurring in practice.
11.3.1.12 Delft Hydraulics have established well calibrated three-dimensional hydrodynamic and water quality models of the Pearl Estuary and the whole of Hong Kong Territorial waters. These models have been calibrated and validated using a number of historic data sets. The latest model is referred to as the Update model and it could be applied directly in the present assessment of the fuel pipeline. However, the model grid resolution in the area of interest is considered to be too coarse and therefore another existing higher resolution model of tidal flows covering the Western Harbour and North West New Territories, referred to as the Western Harbour Model, has been applied. The Western Harbour Model of tidal flows extracts boundary conditions from the Update model and has also been fully validated by Delft Hydraulics for EPD. The areas covered by both the Update Model and the Western Harbour Model are shown in Figure 6.8. Details of the Western Harbour Model’s mesh is presented in Figure 6.9.
11.3.1.13 As in previous studies of potential aviation fuel spills in Hong Kong e.g. the EIA for the existing AFRF at Sha Chau (ERM, 1995), a random walk particle tracking model has been used to simulate the fuel release. The three-dimensional particle tracking model, PART, forms part of the Delft3D suite of models and it takes hydrodynamic input from the Delft3D Western Harbour model of tidal flows which has already been calibrated.
Key Modelling Assumptions
11.3.1.14 The fuel spill is simulated as buoyant particles. Based on the volume of fuel spilled, the extent of the initial patch has been calculated on the basis of an assumption that the fuel will spread under hydrostatic forces until it reaches a thickness of 10mm. It is also assumed that this spreading occurs over a timescale, which is short compared, to any significant transport by tidal currents.
11.3.1.15 As a result of evaporation and emulsification, it is assumed, as in earlier studies, to have a decay linearly to disappearance after 4 days (ERM, 1995). This decay rate is selected to be lower than might actually be found in practice and so does not overestimate fuel losses.
Scenarios Simulated
Offloading
Jetty
11.3.1.16 A major spill from a ruptured tanker has been simulated at a point 500m seaward from the offloading jetty within the main approach channel (see Figure 11.1). The initial diameter of the patch is taken to be 945m based on an assumed loss of 5600 tonnes of fuel.
Pipe
Route
11.3.1.17 Leakages at two points along the pipe route have also been simulated. The centre point of the surface patches was simulated to in the middle of the Urmston Road Channel approximately 1000m from the Tuen Mun area coastline and at the point where the pipeline crosses the marine park boundary approximately 400m from the existing AFRF at Sha Chau (see Figure 11.1). In each case, it is assumed that 75m3 or 60 tonnes of fuel are lost forming a patch of 98m initial diameter.
Tidal
Conditions Simulated
11.3.1.18 Based on the previous studies, it is not expected that any significant coherent fuel patch will survive for longer than 60 to 72 hours. Nevertheless the simulations were run for periods of 4 days with surface fuel assumed to persist over this period. In order to cover the possible range of tidal conditions under which a fuel spill might occur, in each of the wet and dry seasons, the same fuel spills were simulated over a 4-day period of large amplitude tides and again over a 4-day period of small amplitude tides. The same releases were also simulated to begin at high water and at low water to cover the possible range of transport routes which might occur.
11.3.2.1 The above scenarios have been modelled and the relevant plots provided in Appendix F, together with a summary of the findings below. Surface flow velocity vector plots are also provided in Appendix F.
Spill at Offloading Jetty
11.3.2.2 The worst case fuel spill scenarios is the tanker rupture at the jetty spilling some 5600 tonnes of fuel instantaneously (Scenario 1). The spill from this scenario spreads to the mouth of Deep Bay and in a south easterly direction towards Green Island, depending upon the season, tidal range and time of spill within the tidal cycle. In all cases the spill dissipates rapidly and disappears within 2 days.
Dry
Season
11.3.2.3 During the dry season, releases at high water flow towards Ma Wan and Tsing Yi, reaching the west coast of Ma Wan, and the Ma Wan Fish Culture Zone, after some 7 hours. The coastline of the north eastern tip of Lantau Island and Rambler Channel would also be affected in the short term. Ma Wan and the coastline along Castle Peak Road is also affected during mid-ebb releases.
11.3.2.4 For a small amplitude tide with spills at high water and mid-flood, the spill is not caught by the strong Urmston Road currents and instead moves southwards towards the airport platform and the North Lantau coast between Tung Chung and reaching partially as far as Yam O Wan. The key sensitive receivers in this case include the seagrasses and mangroves at Tai Ho Wan. However, seagrasses and mangroves in Tung Chung Bay should not be affected and the cooling water intakes at the airport and Tung Chung should be submerged below the level of the spill.
11.3.2.5 Low water and mid-flood (large amplitude tide) releases oscillate between the Brothers, Neilingding Island and the west side of Sha Chau. Initially the plume is swept up the coastline between Castle Peak and Black Point towards Deep Bay but does not affect the coast at Lung Kwu Tan where horseshoe crab are known to breed, nor does the plume appreciably enter into Deep Bay. However, after some 10 or 11 hours after the spill, the Lung Kwu Chau and Sha Chau area is affected in the short term. This area is frequently used by the Indo-Pacific Humpback Dolphin and the dispersion of the plume could result in dolphins leaving the area until the spill has dissipated. Ma Wan is also affected by the release at mid-flood, as is some of the coastline and beaches along Castle Peak Road.
11.3.2.6 A low water small amplitude tide release, however, does affect the coast at Lung Kwu Tan but the spill disappears from the area within a few hours. At this tide the spill ultimately ends up along the North Lantau coast but dissipates with about 12 hours. Ma Wan and the fish culture zone are not affected.
Wet
Season
11.3.2.7 During the wet season, the spills show similar patterns flowing eastwards along the coastline and towards Ma Wa and Tsing Yi. Releases at high and low water during the wet season spread out thinly along the coastline on the east side of Castle Peak Bay and will potentially affect the gazetted beaches in this area. However, the effects are short lived with the spill virtually disappeared after 24 hours. The release at mid-flood spreads out rapidly to affect large areas between the Tuen Mun coast and the Brothers. The spill affects the North Lantau coast and Ma Wan in the short term. Low amplitude tides during mid-flood and low water also effect Lung Kwu Tan briefly (2-3 hours).
11.3.2.8 During a mid-ebb release, the spill follows the pattern of the high and low water spills and hugs the coastline from Castle Peak Bay to the Rambler Channel. However, part of the spill breaks off and a pool of fuel moves past Ma Wan and through the Kap Shui Mun channel, with the Ma Wan Fish Culture Zone being affected for only between 1-2 hours. Again the spill disappears within about a day.
11.3.2.9 In summary, the worst case fuel spill has the potential to effect the coastline at Lung Kwu Tan which is a nursery for horseshoe crabs, the Ma Wan fish culture zone, the beaches along the Tuen Mun to Sham Tseng coastline, the mangroves and seagrasses at Tai Ho Wan on the north Lantau coastline and Lung Kwu Chau. As the spill is large and divides up into numerous patches as it disperses, there may be disturbance to fish and dolphins in the short term. Notwithstanding, overall, these fauna are likely avoid the spill and the spill will disappear in a very short period of time.
Spill from Pipeline in Urmston Road
11.3.2.10 The second scenario considered comprises the release of fuel as a result of the pipeline rupture in the Urmston Road. Due to the smaller amount of inventory and the use of automatic pumping shutdown facilities, the potential release is significantly smaller than the tanker rupture with only 60 tonnes predicted to be released. Thus, the size of the resultant pool is notably smaller.
Dry
Season
11.3.2.11 The releases during the dry season oscillate between Deep Bay and the tip of north east Lantau and the pool generally stays as one mass. The spill disappears within about 12 hours and, generally, does not affect any coastal areas with the exception of Lung Kwu Chau for a period of 1-2 hours during mid-flood releases and the north eastern tip of Lantau and Ma Wan during mid-ebb tides.
Wet
Season
11.3.2.12 Wet season releases tend to stay closer to the Tuen Mun coastline but do drift up into Lung Kwu Tan on occasions. At high water, the spill will reach the Castle Peak Bay and the beaches in this area and at mid-ebb, releases would migrate as far as the Rambler Channel and the beaches at Sham Tseng. As for the dry season the spill is short lived, dissipating in about 12 hours.
Spill from Pipeline at Marine Park
Boundary
11.3.2.13 Fuel spill Scenario 3 considers the effects of a fuel spill from the pipeline close to Sha Chau on the Marine Park boundary, 400m from the existing AFRF at Sha Chau. As with Scenario 2, the pipeline release is small comprising some 60 tonnes of fuel and a small consolidated pool results.
Dry
Season
11.3.2.14 A spill at this location during the dry season has the potential to affect three main areas, namely the north and western side of Lung Kwu Chau, Sha Chau and the natural coastline of north western Lantau, including Sham Wat and Kau San Tei. In all of these cases, the spill dissipates within a matter of hours.
Wet
Season
11.3.2.15 The wet season spill disperses in different directions depending upon the tides. High water releases moving towards the Brothers and then on to the eastern tip of Lantau, accumulating briefly in Tso Wan. Low water spills do not reach the coast but oscillate between the airport platform and the Tuen Mun coastline. Mid-flood spill will affect Lung Kwu Tan for a period of 1-2 hours and releases at mid-ebb ultimately accumulate in Tai O where mangroves are present. The spill in this area is shown to disappear after about 12 hours.
11.3.3
Predicted Ecological
Impacts from an Aviation Fuel Spill
11.3.3.1 There have been few studies into the ecological impacts from aviation fuel spills in Southeast Asian seas and available information is usually only available for crude oil spills. Ecological impacts are particularly evident in low-energy shallow coastal waters (i.e., those characterised by seagrass and mangrove habitats) that are known to require decades to return to their pre-spill condition whereas exposed hard substratum rocky-shores tend to recover from spills relatively quickly (months to a few years). An oil spill in Indonesian waters mostly affected mangroves in sheltered bays where recovery times were greater than 2.5 years and chronic discharges from a petrochemical plant led to reductions in intertidal invertebrates and tainting of fish in Jakarta Bay (GESAMP, 1993). The modelling has shown that the duration of impacts attributable to an aviation fuel spill are not expected to be persistent, however, soluble fuel fractions could induce toxicity to marine organisms and deplete the oxygen content of seawater.
11.3.3.2 Diving and surface-dwelling seabirds and certain marine mammals (such as sea otters) are the most obvious victims of oil spills (GESAMP, 1993) although such incidents generally have negligible impacts on both fish and dolphin populations as these two groups are known to avoid direct contact (Clark, 1992). For the purposes of this assessment it is assumed that a surface slick of aviation fuel would impact similarly.
11.3.3.3 The Indo-Pacific Humpback dolphins in the study area comprise the Hong Kong/Pearl River Estuary population that are distributed over a wide spatial area (mostly comprising the area around the mouth of the Pearl River and Hong Kong’s North-western waters). The dolphin population are known to show marked shifts in the distribution in these waters (Jefferson, 2000) and it is most likely any inhabiting areas directly affected by an aviation fuel spill will disperse to areas away form the spill. Even considering the worst-case scenario 1 that led to wide spatial distribution of fuel, owing to the high mobility and wide range of the dolphin, significant impacts are therefore not anticipated. The highest potential for any impact to dolphins attributable to a fuel spill is most likely to be sub-lethal. Ingestion of heavily fuel-tainted fish may pose some risk (chronic exposure of certain PAHs can be carcinogenic in higher mammals) although as described above, these concentrations would likely be low and fuel components such as PAHs can be metabolised fairly rapidly by fish and also subsequently when tainted fish are ingested by dolphin. It is also noted that owing to the ephemeral nature of any spill and consequent short-term bioavailability of fuel for uptake by fish, any risks associated with ingestion of prey items tainted by toxic fuel components are small and highly short-term (acute). Chronic exposures of fuel-tainted prey items are not anticipated and the sublethal risks attributable to consumption of oiled food items are, therefore, also insignificant.
11.3.3.4 Research into the impact of a major oil spill on marine ecological receivers and fisheries following a spill of 4000 tonnes of heavy marine diesel in Hong Kong (Ap Lei Chau) in 1973 showed that local fish species were able to metabolise the oil (ambient aromatic fraction concentration calculated at 45-60 mg l-1; Spooner, 1977). Although mortality was evident in some fish held in cages (10% mortality was observed in the stock held in the fish cages at Sok Kwu Wan, Lamma Island within one month of the spill) that were unable to avoid the oil and highly territorial species (such as damsel fish and porcupine fish) were killed (Spooner, 1977), the catastrophic impacts recorded in the fish farming operation were short-lived and recovery was rapid (nine months), following dissipation of oil in the water column and restocking of fish in the cages (Spooner, 1977). Although short-term impacts to some fish have been reported in Hong Kong due to major spills of heavy oils, the lighter aviation fuel is predicted to dissipated very rapidly and disappear within 1-2 days (based upon the worst case Scenario 1) and hence impacts to free swimming fish from an aviation fuel spill are predicted to be insignificant. However, the modelling has also predicted that the Ma Wan fish culture zone could be affected in the short-term and while there will be rapid dissipation of the fuel, some mortality could occur and it will be necessary to protect this resource in the event of a spill, subject to the location and timing of the spill.
11.3.3.5 Filter-feeding invertebrates such as bivalves are known to accumulate high concentrations of petroleum hydrocarbons (Goldberg et al., 1978) owing to relatively inefficient enzyme (mixed function oxygenase) detoxification. There are numerous molluscs in the study area (Section 7) and significant mortality of bivalves has been recorded previously in Hong Kong following a spill of 4000 tonnes of heavy marine diesel (Spooner, 1977). As discussed above in Section 11.2.8 the direct contact with lighter aviation fuels is less likely to have an impact on filter-feeding fauna compared with heavy crude oils and molluscs can accumulate high concentrations of petroleum hydrocarbons without suffering mortality (although sublethal responses are still often evident). Owing to the transient nature of any fuel spill, impacts on molluscs are predicted to be insignificant in the longer-term.
11.3.3.6 It is noted that under certain circumstances, a spill may briefly reach Lung Kwu Tan. This area is also known as a nursery area for horseshoe crabs. Although it is difficult to predict the impacts of a fuel spill on horseshoe crabs as few data are available, as adult animals are highly mobile, a spill briefly (a matter of hours is predicted) reaching Lung Kwu Tan is not anticipated to represent a significant impact. A fuel spill may, however, impact less mobile juvenile stages that are unable to avoid spills effectively. Although impacts are predicted in the less mobile juvenile crabs, impacts to the overall population are not considered to be significant. Notwithstanding, it would be recommended to protect this area in the event of a spill.
11.3.3.7 Corals are not predicted to be greatly affected by a surface spill in the study area as the fuel would largely float and the depth of the water in the North-western waters is a sufficient buffer between the surface and sublittoral corals. A subsurface spill due to damage of the submarine pipeline could, however, lead to direct impacts on corals as oil spills are known induce both histopathological injury and mortality (Brown and Howard, 1985). Although major oil spills have been reported to cause substantial mortality in coral reef systems (GESAMP, 1993) it is notable that spill of 4000 tonnes of heavy marine diesel from Ap Lei Chau did not have any noticeable impacts on the coral reef fauna found subtidally at Lamma Island (Spooner, 1977). It would appear that intertidal corals are more vulnerable to oil than those found subtidally (GESAMP, 1993) presumably because oils are washed ashore and trapped in intertidal coral reefs. Oil pollution also appears to be most harmful to corals over prolonged (chronic) exposures (GESAMP, 1993). The few coral records from the study area indicate that the species present are mostly subtidal and a surface aviation fuel spill is not considered to pose a significant threat. Similarly, a subsurface spill through a burst pipe will be of short duration as the oil rises rapidly to the surface and the predicted impacts to corals are considered to be highly localised and overall impacts are insignificant.
11.3.3.8 Accidentally spilled fuels are known to be particularly damaging in low-energy shallow coastal waters that are often inhabited by important flora such as mangroves and seagrasses. There are no significant mangrove stands or seagrass communities in the immediate vicinity of the PAFF although important mangal is present at San Tau and Tai Ho Wan on the Northwest coast of Lantau (Tam and Wong, 2000). The modelling results indicate that the stand at San Tau would not be affected by any spills. However, the stand at Tai Ho Wan, together with the stand in Tai O could be affected in the short term (less than a day) if a spill was to occur. Accumulated heavy oils in low-energy habitats such as mangrove stands are known to be persistent and have the potential for long-term impacts. As discussed above in Section 11.3.3.1 the modelling has shown that the duration of impacts attributable to an aviation fuel spill is not expected to be persistent and chronic (long-term) exposures appear to be more damaging to biological communities. Although short-term impacts attributable to a fuel spill to seagrass beds and mangroves are predicted, it is likely that they will not be of the magnitude observed through heavy oil exposures. There is not, therefore, expected to be any significant long-term damage in the biological communities present at Tai Ho Wan and Tai O due to a short-exposure to fuel as both exposure time and persistence are predicted to be acute only.
11.3.3.9 It should be noted that the risk from a fuel spill is low as accidents due to human error and pipeline failure at marine terminals represent one of the lowest sources of petroleum hydrocarbon inputs to the sea world-wide (see Table 11.1 above) and reflects the care taken to reduce accidents (Clark, 1992). However, notwithstanding the rapid disappearance of the fuel, contingencies to protect key coastline areas including the islands located within the Marine Park and marine resources will be needed to be included in the spill response plans.
11.4.1 The mitigation measures identified here are also summarised in the Environmental Mitigation Implementation Schedule in Appendix B. All elements of the fuel handling, storage and transportation system will be designed to minimise the risk of failure and resultant leaks and spills to the lowest practicable level. Tanks in the tank farms will be constructed in a bunded area surrounding the tanks which will have collection capacity greater than the maximum content of the largest tank to contain any fuel spills. Shut off valves shall be installed within the wider site storm drainage system to provide for further emergency retention of spillages. Protection against leaks from the bottom of the tanks is achieved by the installation of an impermeable membrane in the tank foundation beneath the tank bottom. In respect of the pipeline, besides protection of the pipeline being covered with a protective rock armour layer, integrated methods of control will also be built into the design of the pipeline. A leak detection system will be installed to provide early detection of any leak and at the first sign of a pressure drop, would instigate an automatic shut-off system. Contingency plan procedures will require investigation and immediate action to stem the release.
11.4.2 All tankers approach the berth using a pilot and tug system to minimise the risk of grounding or striking the jetty. In addition, a workboat will be on standby at the jetty during tanker berthing to pull the containment boom into place around the vessel as well as to contain the actual spills. Skimmers will also be available for quick deployment in case of a spill.
11.4.3 While these methods will minimise the risk of a spill, minimise the amount of a spill and contain the spill if it did occur, it will also be necessary to define an emergency response plan and implement an operator-training programme to assure the quick response needed to further minimise the impact of any fuel leak.
11.4.4 The results of the spill modelling have shown that some key sensitive marine ecological receivers could be affected in the short term by a spill associated with the PAFF. As such it will be necessary to include contingencies to protect these resources in the spill response plan. The locations which should be protected by the rapid use of booms are as follows:
¨ Ma Wan fish culture zone;
¨ Lung Kwu Tan beach and horseshoe crab nursery area;
¨ Tai Ho Wan mangroves and seagrass stands;
¨ Tai O mangrove stand;
¨ gazetted beaches in Castle Peak Bay and along the coast to Sham Tseng;
¨ coastline of Lung Kwu Tan, Sha Chau and Tree Island.
11.4.5 The rationale for any spill response plan should be based around prevention and early detection and will need to be in place before the commissioning of the PAFF. A further key element will be to define a comprehensive programme of visual inspections and checks. In developing any response plan, reference should be made to Marine Department’s Maritime Oil Spill Response Plan. The key features which should be included in the plan are summarised below:
¨ organisation of the spill response team and the responsibilities of each member. Suitable and regular spill response training should be provided to the operating personnel and regular spill response drills should be conducted to test and exercise the responses;
¨ response strategies/procedures to be adopted in the case of an spill, including:
- reporting to relevant Authorities;
- identification of the source of spill;
- containment of leaking fuel;
- recovery and processing of free fuel;
- clean up methodology; and
- handling and disposal protocols.
¨ establish an emergency control centre on the PAFF site;
¨ establish effective communication emergency mechanisms and a 24-hour emergency contact list;
¨ training and competence level requirement of PAFF staff;
¨ provision and maintenance of spill equipment at the PAFF land site, on the PAFF jetty at the Sha Chau reception point and at the HKIA site;
¨ sub-contracting services;
¨ drills and exercise requirements; and
¨ follow-up procedures and post spill recording.
11.5.1 With the above recommended mitigation measures in place to prevent, contain and clean-up spills and leaks of fuel stored or conveyed to and from the site, potential environmental impacts on the environment, particularly water quality and marine ecology can be minimised. While the risk of spills cannot be completely prevented, the risks can be minimised and are well within acceptable bounds. The proposed mitigation measures keep impacts to a practical minimum such that no adverse residual impacts are predicted from spilled fuel.
11.6
Environmental Monitoring and Audit
11.6.1 Based upon the integrated mitigation measures and procedures which will be put in place to prevent, contain, clean-up and dispose of any spillage, significant environmental effects are highly unlikely to arise. The regular programme of inspections of the system during the operational stage will be specified in the emergency response plan. However, it is recommended that a design phase audit of the spill response plan is undertaken to check that it includes the necessary elements and of the design of the pipelines, tanks and jetty to ensure key spill detection and control elements are included. Further details are provided in Section 15 of this report and in the EM&A Manual.
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