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Oil in the Sea III: Inputs, Fates, and Effects
TABLE D-2 Summary of Oil and Gas Facilities Spill Data for the East Coast of Canada, 1990-1999
(8,200 gallons). The number of platforms existing in offshore Mexican waters is relatively small, but in U.S. coastal waters, there are a significant number of shallow-water platforms, especially in the northern Gulf of Mexico. Approximately 877 petroleum facilities were located in U.S. coastal waters in 1992 (Federal Register, December 16, 1996, p.66089). Using scattered data bases from the U.S. Coast Guard, several state reports, and estimating the number of offshore platforms in Mexican waters (130 platforms), a calculated volume of 61.0 tonnes (18,000 gallons) appear to be a reasonable estimate of discharge from these facilities. Thus, in North American coastal waters, a total annual load discharged is calculated at 89.0 tonnes per year (28.0 tonnes in Canadian waters plus 61.0 tonnes in other coastal waters).
Thus, an estimated total of 146.0 tonnes have been discharged annually into North American waters by accidental spills and blowouts from offshore oil and gas facilities in U.S.offshore., U.S. coastal waters, Canadian and Mexican waters. Tables 2-2 through 2-6 includes annual average petroleum hydrocarbon load from accidental discharges, reported between 1990 and 1999, from offshore oil and gas facilities in the four zones where reliable data was available. These average annual loads were calculated from accidental discharges reported in a known latitude and longitude (and thus represent a subset of the numbers reported in Table D-3). Note that in Tables 2-2 through 2-6, that approximately 90% of the total discharges from production facilities occurred in Zone G (central and western Gulf of Mexico) and of that amount, nearly 50% was within coastal waters.
SPILLS FROM OFFSHORE PIPELINES
Pipeline spill data for North American waters were obtained from two data sets: U.S. Coast Guard and the Minerals Management Service. Table D-4 shows the total and average pipeline spills from 1990 through 1999 in offshore North American waters (MMS data base). Additional spills, as determined from the U.S. Coast Guard data base, resulted in a calculated annual volume of discharged petroleum hydrocarbons in offshore waters to be 59.0 tonnes. In coastal waters, the only reliable data was from the U.S. Coat Guard data base (Table D-5). The data base, however, included spills from facilities and contained non-crude spills. These were removed, and a calculated volume of 1,100 tonnes per year was calculated. It is estimated that there are 23,236 miles of pipelines in offshore North American waters (DeLuca and Leblanc, 1997), thus the average accidental discharge per mile of pipeline would be 0.074 tonnes per pipeline mile. These calculations do not include spills from pipelines in Mexico as the data was not available. The number and length of pipelines in Mexico are relatively small when compared to those in the United States and it is though that the volume spilled is proportionate. Canadian data was available, but no discharges were reported. Using these scattered data bases, an annual total discharge into Norh American waters by accidental spills from pipelines is calculated to be 1,690 tonnes per year.
Offshore Oil and Gas Production and Pipeline Spill Summary
Thus, the total documented average volume of petroleum hydrocarbons accidentally discharged from offshore facilities (platforms and pipelines) per year into North American waters during the past decade is 1,836 tonnes (Tables D-3 and Tables 2-2 through 2-6).
INTERNATIONAL SPILLS FROM PLATFORMS AND PIPELINES
Internationally, the amount of petroleum introduced to the sea from oil/gas production and pipeline spills and blow
TABLE D-3 Summary of Calculated Inputs from Offshore Oil and Gas Facilities for North American and Worldwide Waters