(Note: At the present time MMS is studying proposed rules which would consolidate into one document the currently multi-tiered rules of MMS's offshore programs that govern oil and gas operations on the OCS. The proposed rules would merge the various operating requirements now found in the regulations, OCS Operating Orders, and other documents into a single set of requirements to be codified at 30 CFR Part 250. An explanation of the proposed rulemaking changes may be found at the end of Section IV.A.2.)

IV.B. Oil Spills in the Mid-Atlantic Marine Environment

Oil spills are one of the major concerns of exploration, development, and production of offshore hydrocarbon resources. Their potential harm to the physical environment, and thus to economic and biological resources, cannot be readily assessed. Some spills, depending on the conditions, can be harmful while others do not seem to significantly affect vulnerable resources.

Oil spills vary both in size and in the damage they effect on the environment. Some spills are almost unavoidable; this type is usually small in volume and may go undetected for long periods of time. An example of this type of spill can be found associated with any type of vessel using hydrocarbons as a source of energy. Other spills can be massive. The Ixtoc I well blowout in the Gulf of Mexico's Bay of Campeche spilled an estimated 3.1 million barrels of oil in approximately 10 months, thus becoming the largest spill ever in the history of exploration for hydrocarbon resources. Assuming a constant rate of discharge, the Ixtoc I spill amounted to approximately 310,000 barrels of oil per month. On a weekly basis, this was about twice the amount of oil spilled by the Argo Merchant in 1976 in the Nantucket Shoals area off the eastern United States--the largest tanker spill in U.S. waters.

Not all large spills are caused by well blowouts. Over a 2-week period the Amoco Cadiz spilled 20 to 25 times the amount of oil off the coast of Brittany, France, than did the 1969 well blowout in the Santa Barbara Channel, California in 1 month. In other words, amount of spillage cannot be associated with a particular type of accident. Because of the conditions at the time these two spills occurred, they both resulted in substantial damage to biological and economic resources.

The time of the spill is of the utmost importance in determining the extent of impacts (URI and ASA, 1982), as are location, existing weather conditions at the time of the spill, and characteristics of the spilled substance. Oil spilled from the barge Florida in September, 1969 off Fassett's Point, West Falmouth, Massachusetts released approximately 4,100 barrels of No. 2 fuel oil into Buzzards Bay. The prevailing south to southwesterly winds in this region created an oil-in-water emulsion which spread over more than 1,000 acres of Wild Harbor River, causing immediate large scale mortality of marine animals in the intertidal and subtidal zones of the river (Sanders et al., 1980). This is an example of a relatively small spill (compared with those mentioned above) that, because of its location, the prevailing weather conditions, and the type of substance involved, resulted in massive adverse impacts on some local resources.

OCS oil exploration and production activities contribute only 2 percent or less of the total petroleum entering U.S. navigable waters (USCG, 1983), and less than 1 percent of that entering the highly utilized Gulf of Mexico OCS (Regional FEIS, Gulf of Mexico, 1983). However, oil spills are still considered to be the most common source of marine pollution resulting from OCS oil and gas exploration and production. Causes of major OCS oil spills include pipeline accidents, well blowouts, and tanker and barge operations and accidents. In addition to accidental oil spillage primarily during production and transportation, chronic, low-level petroleum inputs to the marine environment can occur during routine discharges from exploratory rigs, platforms, and OCS support vessel activity.

With respect to all phases of OCS oil field development in the United States, Gulf of Mexico records represent the most extensive data base for petroleum inputs into the marine environment. This information may be used as an indi

cation of the factors which may be responsible for oil spills in the midAtlantic should oil development occur as a result of proposed Sale No. 111. One important factor which is different, however, is that most oil produced from OCS leasing in the Gulf is transported to shore by pipeline rather than by tanker--as proposed for Sale No. 111.

Most spills from OCS activities are small. Seventy-six of the 7,107 oil spills on the Gulf of Mexico OCS between 1964 and 1981 were greater than 50 barrels. The largest number of oil spills (greater than 50 barrels), as well as the largest volume of oil spilled (62 percent of total) in the Gulf has been the result of pipeline failures, usually the result of anchor dragging (Regional FEIS, Gulf of Mexico, 1983). Since pipeline transport of oil for Sale No. 111 will be limited to only gathering lines, rather than transport to shore, this type of accidental oil spillage is not likely to be a major factor here.

Production well blowouts (most blowout spillage usually results from producing wells, not from wells being drilled) have been the result of equipment malfunction, workover procedures, human errors, storms, and collisions. Northern Gulf of Mexico OCS statistics (1964 to 1981) show that there were 100 blowouts during this period, of which 9 resulted in loss of oil and/or condensate. In all, 63,582 barrels of oil were spilled from these 9 incidents (Regional FEIS, Gulf of Mexico, 1983). The Ixtoc I well blowout on June 3, 1979, in the Bay of Campeche, although not a U.S. operation, also bears consideration as it became the largest oil spill (approximately 3.1 million barrels) in history. This exploratory well blew out as a result of uncontrolled drill hole pressure and ineffectiveness of the blowout preventer device (O'Brien, 1981), and was not capped until March 23, 1980--10 months later.

Accidental oil spills from tankers and barges, as well as oil discharged during normal operations such as ballast discharge, tank washing, and bilge bunkering, are probably the largest source of oil entering U.S. waters. Twenty-two of the 76 oil spills greater than 50 barrels in the Gulf of Mexico between 1964 and 1981 were caused by vessel collisions or accidents during oil transfer or handling operations, resulting in a total spillage of 13,814 barrels of oil. The high oil spill hazard of transportation of oil by tankers is an important factor in assessing the relative oil spill risks of a particular OCS area, and consequently has been incorporated into the Oil Spill Risk Analysis Model (OSRAM) for the proposed action (see Section IV.B.3 and Appendix C). As already noted, the largest oil spill in U.S. history was that of the Argo Merchant tanker which ran aground southeast of Nantucket Island, Massachusetts in 1976, spilling a total of 7.7 million gallons (roughly equivalent to 180,000 bbls) of No. 6 fuel oil (see Grose and Mattson, 1977).

With the enactment of the 1978 Port and Tanker Safety Act (P.L. 95-474) and the 1980 Act to Prevent Pollution from Ships (P.L. 96-478), the latter becoming effective on October 2, 1983, stringent requirements have now been set directed at preventing marine pollution from both accidental and operational discharges by tank vessels carrying oil and hazardous materials in bulk. The implementing regulations (such as 33 CFR 151-157 and 46 CFR 30) for these two Acts are under the authority of the U.S. Coast Guard. These regulations require a variety of safeguards including such items as vessel construction standards, navigation procedures, and limitations on operational discharges (e.g. in reference to oil-tainted ballast water).

IV.B.2. Fate and Effects of Oil in the Offshore Marine Environment

The nature of impacts from oil spills in the marine environment depends largely on the nature and proportion of the oil's chemical components (e.g. hydrocarbons present) and the changes in this composition as the oil weathers (undergoes a number of physical and biochemical processes which reduce the concentration of the oil in the environment). Weathering ("aging") processes,

in turn, largely depend on oceanographic and meteorologic factors at the time of the spill.

Hydrocarbons in crude oil fall into four major categories: alkanes (paraffins, aliphatics), cycloalkanes (cycloparaffins, naphthenes), aromatics, and naphthenoaromatics. Crude oils from different sources can differ appreciably in percentage composition of the various hydrocarbon fractions. Consequently, the possibilities for combined chemical types are enormous, resulting in extremely complex mixtures of varying toxicity.

Non-hydrocarbon components in oil, which include compounds that contain sulfur, nitrogen, oxygen, and trace metals, generally range from 0 to 15 percent (concentrations in oil are in the ppm range). Trace metals are present in very small concentrations, with nickel and vanadium usually the largest proportion, and cobalt, mercury, iron, and manganese present in smaller amounts (Connell and Miller, 1980; Final EIS for OCS Sale No. 49).

Weathering involves a number of physical and biochemical processes which change the chemistry and reduce the concentration of oil in the environment. These processes include evaporation, dispersion, dissolution, emulsification, biodegradation, photo-oxidation, and sedimentation. Any or all of these processes can be expected to operate on any oil spilled within the proposed Eventually, a tar-like residue would be left which would break up into tar lumps or tar balls. Types of weathering processes and transport paths of spilled oil at sea are depicted in Figure IV.B.2-1 and their relative importance in Figure IV.B.2-2.

After the discharge of oil into water, a surface slick forms because of the low solubility of most oil components. Currents, waves, and winds then act to spread the oil slick into thin films (Lee, 1980). The extent of spreading is also very much dependent on the physical and chemical nature of the particular oil (NAS, 1975).

Evaporation of the more toxic and volatile, lower-molecular-weight hydrocarbons (e.g. benzene, toluene) from the water column would occur immediately after oil is spilled. The amount of oil that would evaporate depends on the extent of spreading, temperature, wind speed, solar radiation, and composition of the oil, but, within a few days, evaporation could remove up to about 50 percent of the oil depending on environmental conditions (e.g. rough seas would tend to increase evaporation rates) (NAS, 1975). For the Ixtoc I blowout in the Gulf of Mexico, evaporation was the predominant weathering mechanism. About 30 percent of the oil evaporated immediately after escaping from the well, resulting in a nearly equivalent loss of saturated and aromatic hydrocarbons (Boehm et al., 1981; Golob and McShea, 1981). After the North Sea Ekofisk Bravo blowout 35 to 40 percent of the oil, consisting of the lighter hydrocarbon components, evaporated immediately. After 12 hours, 50 percent had evaporated, and after 15, days 68 percent had evaporated (Haegh and Rossemyr, 1980). Similarly, after the Amoco Cadiz spill