tanker can remain moored and continue loading in 15 to 20 foot waves [2]. 

 The frequency of oil spills from SPM's and shoreside marine terminals is 

 reported to be about the same [5], In both, oil is transferred through 

 flexible hoses or fixed couplings. Hoses wear out quickly in rough seas, 

 and couplings break. The same likelihood for human and mechanical failures 

 exists. Both harbors and SPM's average one oil spill for every 50 ship 

 calls [5]. However, SPM's extend the range of tanker operations, increase 

 the use of tanker volume, eliminate lightering, and minimize dredging 

 requirements. 



Subproject: Submerged Transmission Systems (SP-20) 



Disturbing Activities: Pipeline installation; oil and gas transport 



Construction disturbance associated with pipeline installation begins 

 with trenching of bottom sediments by jet sleds during pipe burial. This 

 causes an increase in turbidity and displaces benthic organisms or dis- 

 rupts their habitat. Some bottom sediments are too hard to be jetted, 

 so explosives must be used. Nearshore corridors are most likely to tra- 

 verse environmentally sensitive areas, particularly in the estuaries 

 behind barrier islands. The pipeline landfall is also an environmentally 

 critical point. Special protective and restorative measures must be taken 

 when pipelines cross beaches, wetlands, heavy surf zones, or sea cliffs. 



Turbidity and its impacts on benthic organisms have been reported 

 to occur 200 plus feet from the pipeline construction site. Shrimp have 

 also been recorded to be attracted to the new bottom sediments after pipe- 

 line burial. If benthic organisms are displaced they will usually reestab- 

 lish within 18 months after construction. The onshore and nearshore impacts 

 of pipeline construction are the most damaging and lasting. 



Currently, all the oil produced off California and 97 to 98 percent 

 of Gulf of Mexico oil is piped ashore. Moreover, all present U.S. gas 

 production is piped ashore because of the proximity to shore. Gasifica- 

 tion plants have not been constructed in the U.S. because of the immediate 

 access to market areas or economical quantities of gas are too scarce to 

 justify construction. When small quantities of gas are available three 

 options are available: (1) run the gas with the oil in a pipeline, (2) 

 reinject the gas to maintain formation pressure and (3) flare the gas at 

 the platform. 



Because most of the known potentially hydrocarbon-bearing formations 

 lie within 200 miles of shore and are in water of suitable depths, pipelines 

 will probably continue as the preferred OCS transportation mode for the 

 United States [5]. However, gasification plants may become economical in 

 Alaska as large finds are occurring and a market is not immediately 

 available. Table 8 shows that the expected number and total volumes of oil 

 spills are greater for tankers than for pipelines, regardless of the size 

 of the hydrocarbon find. At present, therefore, pipelines also appear to 

 be environmentally safer than tankers. 



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