Also, study area--elements over which the decisionmaker has no control. Overall probabilities, on the other hand, combine the probabilities that a spill will occur based on the volume estimates associated with the proposed lease area and the probabilities that the spill will then contact the various vulnerable resources, or targets. Thus, the overall probabilities represent the overall risks that the proposed leasing poses to the mid-Atlantic region's vulnerable In Appendix C, Tables 12 to 17 show these probabilities listed for the same time periods as the conditionals: 3, 10, and 30 days. resources. In Chapter IV, Sections E and M, the joint probabilities are used in such a manner as to give a general idea of the "true" overall risk to targets arising from OCS activities associated with the proposed action, independently of the conditional probabilities. On the other hand, Sections E.6 and E.7 incorporate the conditional and joint probabilities in the conclusions on the level of impacts projected for the fishery resources. IV.B.4. Effects of a Catastrophic Oil Spill This discussion of the effects of a catastrophic oil spill constitutes a worst case analysis of the possible effects of a spill of 100,000 barrels or more. Two major approaches were initially identified. The first would have involved an analysis targeted on the individual resource. This would have required potentially selecting a different set of factors for each resource and would not have yielded a meaningful overview of what a worst case scenario might actually entail. The second approach, the one used in this analysis, was to select a set of key circumstances which might in conjunction produce a truly worst case. This approach, it is believed, will permit a scientific investigation of the possible, though not necessarily probable consequences of a catastrophic oil spill. When essential information may be missing or uncertain, reasonable projections have been made with respect to the impacts on the species or resource in question. As a result, some secondary factors have been treated as variable, to permit a full discussion of ramifications for a particular resource. The following scenario has been adopted for the purpose of analyzing the environmental impacts of a hypothetical catastrophic oil spill of 100,000 barrels or greater in the mid-Atlantic. It is assumed that a well blowout occurs at the sea floor in the vicinity of Hudson Canyon in a water depth of about 60 m. The time of year is late spring. The spill rate is 15,000 barrels of crude oil per day for 10 days, releasing a total of 150,000 barrels of oil into the water. Within the first 24 hours during the actual blowout, the sea state is calm, causing the rising oil to form an unbroken slick. Thereafter, gale-force winds (50 kt) move the slick in a northerly direction. High winds and waves make cleanup and containment of oil impossible. partially weathered oil then contacts Long Island's southern coast. this scenario, it is assumed that the location, type, duration, and magnitude of the spill are such that, in conjunction with a combination of extreme meteorological, seasonal, and biological factors, severe damage to species and resources would result. Under It should be kept in mind that the simultaneous occurrence of these events is unlikely (e.g. the occurrence of gale-force winds in late spring coinciding with the greatest densities of fish eggs and larvae). Furthermore, the expected number of spills equal to or greater than 100,000 barrels associated with the proposed action is less than 1 (0.05); and the probability of 1 or more spills of this size occurring as a result of the proposed action is 5 percent. The likelihood of these events occurring under the conditions described in this scenario is thus remote. Effects on Water Quality: A catastrophic oil spill of over 100,000 barrels, although highly improbable in occurrence, would likely result in substantial, and possibly, major impacts on water quality. Occurrences of very large oil spills have been described in the representative cases of Ixtoc I (wellhead blowout releasing 3.1 million barrels), Bravo (surface platform blowout 175,000 barrels), Argo Merchant (tanker accident 180,000 barrels) and Amoco Cadiz (tanker accident 1.5 million barrels). Under the catastrophic oil spill scenario, the 150,000 barrels of oil rapidly released from a wellhead blowout would be widely dispersed by the action of wind and currents, resulting also in the transport of oil to shallow, coastal areas. Although some of the oil released would be distributed throughout the water column in the vicinity of the wellhead and probably a very large surface water area would be covered by floating oil, it is the oil reaching the relatively shallow (less than 60 meters depth) coastal areas and embayments that would cause the most severe water quality impacts. In these shallow areas, oil might be initially dispersed throughout the water column and might also become entrained in suspended particles and bottom sediments, subsequently being reintroduced into the water column as a result of tide, wind, or current action. Thus, elevated hydrocarbon levels may result in the water column for an extended period of time. Furthermore, although stormy conditions would likely enhance the break-up and dispersion of the spilled oil, they would also impede spill clean up procedures. Effects on Benthic Organisms and Plankton: During the first few hours of the spill, impacts would be limited to the immediate vicinity of the platform. Within 12 hours approximately 75 mi2 (approximately 8 blocks) of sea surface would be is expected to be covered by the slick. This slick would directly impact the phytoplankton, zooplankton, and ichthyoplankton found in the surface layers and would result in mortality. An indeterminate impact to organisms in the water column below the slick caused by the highly toxic soluble fraction of the crude oil would occur; however. Such impacts would range from modified behavior (which may be long-term and ultimately result in mortality) to death. The degree and extent of this impact from the soluble fraction is difficult to determine because it is dependent on a number of variables such as: advective sub-surface currents, relative toxicity of the crude oil, solubility of the more toxic fraction, and the dynamics of the slick (how much oil comes in contact with water). The benthic organisms at this time would be expected to experience a minimal, but indeterminate, amount of impact. Near the wellhead blowout some direct oiling of the benthos would probably occur; however, the extent of the oiling would be determined by the relative oil/water densities and bottom current regime. Oil from the slick could be transported to the bottom by oil adsorbed onto suspended sediment or detrital particles or incorporated into zooplankton fecal pellets. This oil would most likely impact filter feeding organisms; however because of the large dispersion of oiled particles, the impacts would be expected to be limited to sublethal effects, which would vary depending upon concentration of oiled particles. The assumptions for this analysis are that a storm with gale-force winds. (32 to 63 mi/h) moves into the area and moves the slick northward at a rate of between 1 and 2 mi/h. In addition to aiding the transport of the oil, a large amount of oil could be advected through the water column because of the wave action caused by the storm and contact the bottom. After 3 days, 45,000 bbl of oil would have been spilled. This could result in a slick of approximately 450 mi2 (50 blocks), but the slick should be greatly fractionated because of the storm. At this time, if it is assumed that the storm has accelerated dissolution of the soluble fraction of the oil (the soluble fraction representing 20 to 30 percent of the total crude), up to 13,000 bbl of the lighter hydrocarbons would be dissolved throughout the water column. would form concentration gradients of the more toxic soluble fraction. resulting from the soluble hydrocarbons would vary from death through reduced growth or reproductive capacity to no detectable effect depending on the specific organism and where in the gradient it is found. At the end of the 10 day period, approximately 150,000 bbl of oil would have been released, which could cover up to 1,500 mi2 (167 blocks) of sea surface. It is assumed that part of the slick would have contacted Long Island and ultimately would impinge on approximately 120 miles of coastline, Thirty to 40,000 bbl of the lighter hydrocarbons would have dissolved into the water masses (or evaporated). Advection of the oil to the substrate under the slick could impact up to 960,000 acres of bottom. Oil which contacted the shore would be worked into the sediments in the intertidal and subtidal zones and would be released back to the water column at a rate dictated by the physical regime of the area. Benthos which is directly contacted by the oil would probably be smothered and not survive. Generally, the persistence of oil in the substrate is negatively correlated with the dynamics of the area. Impacts Because the area involved is not one of high energy input, it is expected that the oil contamination would be evident and impact the benthos for more than one year. Considering the potential areal extent of the spill and the persistence of hydrocarbons within the affected area, a major impact on the benthos is expected. The phytoplankton, because of high turnover rate, inoculation from adjacent unpolluted water masses, and areawide and patchy dispersion, will be expected to suffer only moderate impacts. The zooplankton should also receive only moderate impacts, because of circumstances similar to those indicated for phytoplankton. Effects on Marine and Coastal Birds: It is likely that large numbers of birds would be fouled by the oil and die, because many species migrate through the mid-Atlantic during the late spring. The breeding effort for the year could be a failure because the birds in the region would be adults that had begun nesting or were on their way to the breeding grounds. Breeding and nesting adults that might not contact the spill at sea could still suffer when the spill reached the Long Island shore, which is a major breeding area (see Table III.B.4-2). Nesting areas are generally located above the high tide line but feeding occurs in tidally influenced areas and in shallow nearshore waters. These feeding areas could become contaminated for many years if the spilled oil entered the bottom sediments. As a result, prime feeding and breeding areas would become useless; and bird populations could be depressed for many years if a catastrophic event actually occurred (Samuels and Ladino, 1984). Effects on Sensitive Coastal Habitats: When the spill reached nearshore coastal waters, it could contaminate bottom sediments. This contamination could be periodically disturbed and foul beach areas long after the spill has occurred and been dissipated. Under the operations assumptions, the spill would reach shore (assumed to be Long Island). In this case, it could foul beaches, wetlands, and inland waters. Water quality would be degraded, vegetation would die back, and large numbers of birds and fish could also perish. Sensitive coastal areas could suffer further damage from large-scale clean up efforts that might involve the use of chemical dispersants or mechanical removal of oiled sand, sediments, or vegetation. Although water quality could improve relatively quickly, it might take several seasons or even years for plant and animal populations to return to their former numbers. Effects on Endangered and Threatened Species and Species of Concern: Long Island is an important stop-over point for migrating peregrine falcons and possibly for bald eagles. In the spring, adult birds migrating to summer breeding grounds could become fouled with oil when preying on crippled or oil fouled seabirds. The adult falcons or eagles could die shortly after being oiled or could reach the breeding ground, but fail to rear their young sucessfully because the adult could transfer the oil to its eggs or young. Therefore, under a catastrophic oil spill scenario, peregrine falcon and bald eagle populations could suffer declines. A catastrophic spill could result in a major impact on endangered or threatened sea turtles inhabiting the mid-Atlantic region. While the spill was at sea, it could come in contact with adult leatherback, loggerhead, and green sea turtles migrating into the region or into more northern waters. The large spill could disorient or disrupt the migrational patterns of the sea turtles. The spill could also affect feeding activity by dispersing preferred food sources or the oil could be ingested accidentally. Ingestion of oil or oil fouling of turtles at sea could result in the death of some individuals. This large spill would not affect nesting beaches, because sea turtle nesting areas occur south of Cape Hatteras, primarily. Therefore, under this catastrophic oil spill scenario, mortalities to sea turtles and possible population declines could occur. If a catastrophic spill should occur in the mid-Atlantic OCS region, it could also result in a major impact on endangered or threatened marine mammals. If such a spill occurred during the spring, it could interfere with the migration of sperm, fin, humpback, and right whales and their calves into and through the region. Adult whales are believed to feed very little or not at all when migrating. However, some oil or petroleum vapors could be ingested and have a negative effect on the animals. This could disrupt normal behavior, reduce the animals fitness or ability to survive, and possibly lead to death. The loss of an adult female could also result in the loss of an unborn calf or juvenile. A large oil spill could disorient a calf or juvenile and cause it to become separated from the adult and possibly die. The juveniles could ingest the oil and suffer lethal effects. Because of their very small population, right whales could suffer the most from a major oil spill. Therefore, a catastrophic oil spill, a hypothetical but unlikely event, could result in the loss of some adult or juvenile whales. This would be especially damaging to the right whale, while the other species should recover quickly. Effects on Fish Resources: The most obvious effect of such a large spill, hypothesized to occur during the late spring, would be to produce large scale mortalities of eggs and larvae distributed within the areal extent of the spill. Figure 41 (Appendix G) shows concentrations off Long Island in late spring to be in the range between 10 to 10,000 eggs per square meter, and approximately the same for larvae. For the area of the spill (1.8 million square meters), egg and larvae mortalities could be expected to be in the range between 18 million and 1,800 million each. In addition to the lethal effects within the spill area, reduced oil concentrations around the fringes of the spill could be expected to produce sublethal effects, much the same as described by Tilseth et al. (1984). A spill of this size would pose a serious threat to pelagic finfish migrating northward during spring and summer. While actively swimming fish might avoid oil spills (Nelson-Smith, 1972), a spill of this size could be expected to alter migration patterns of such mid-Atlantic species as cod, mackerel, bluefish, striped bass, bluefin tuna, ocean pout, and spiny dogfish. Given the scenario of spill occurrence at a water depth of 60 m, with gale-force winds driving the oil toward the south shore of Long Island, serious impacts on such shellfish as blue crab, surf clam, hard clam, soft clam, bay scallop, ocean quahog, and sea scallop would be expected. Under these conditions, oil would be driven into bottom sediments resulting in irritation, coating, or direct mortality of these species. Bays and coastal regions of the south shore of Long Island are valuable nursery regions for many mid-Atlantic species. Juveniles in the path of this extensive spill could be expected to exhibit radically altered behavioral patterns or be killed directly. In addition, zooplankton and phytoplankton utilized as food sources by early life stages of many fish are known to be sensitive to oil. A decline in this food source would translate into reduced growth rates for nearshore fish resources. Extensive egg and larva mortalities would be expected with resultant population decreases for many mid-Atlantic fish resources, a wide range sublethal effects for many species not within the center of the spill, alteration of migrational pathways for several pelagic species, direct mortality and/or reduced growth for nearshore juvenile finfish, and an alteration of the trophic level interactions of many mid-Atlantic species. Effects on Commercial and Sport Fisheries: The rate of spill from the well blowout is projected to be 15,000 barrels per day. Using this figure, after 3 days, an area of approximately 450 square miles could be expected to be covered by an oil slick between Hudson Canyon and the south shore of Long Island. Because the spill could be so extensive and would coincide with the time of peak spawning, initial egg and larvae mortalities could be high. URI and ASA, Inc. (1982) modelled an assumed spill on Georges Bank which was designed to occur at a rate of approximately 50,000 barrels per day for 30 days. This spill rate is over 3 times greater than the scenario described in this section. However, in the URI and ASA, Inc. simulation, it was calculated that cumulative losses to the cod fishery peaked at 23.9 percent in the seventh year after the spill. For the spill rate of 15,000 barrels over 10 days, cumulative losses could be expected to be less. |