The principal focus in this subproject is upon oil and gas pipe- 

 lines which are a direct result of the siting of oil and gas transmission 

 facilities and processing. The disturbances caused by other types of 

 transmission lines are similar to those caused by oil and gas pipelines, 

 but are often smaller in scale. 



Construction activities may disrupt soil, vegetation, ecologically 

 vital areas, and fish and wildlife habitats. The greatest ecological 

 damage may occur from excavation. 



The pipelaying method used for oil and gas lines depends upon the 

 type of terrain to be crossed. If a pipeline crosses wetlands in which 

 there is no firm ground to support equipment, a canal 40 to 50 feet wide 

 may be needed. Lay barges are usually utilized in such areas. The 

 dredged material will be placed alongside the canal and form a low, flat 

 levee, punctuated periodically by openings to allow drainage. With 

 required openings and bulkheading (plugging the ends), erosion, salt- 

 water intrusion and disruption of drainage patterns are reduced. In 

 firmer wetland areas, a smaller canal about 10 feet wide will be dredged 

 and backfilled using equipment on working mats or pads. On firm land, 

 the routine trench and backfill method is used, which is the same 

 technique by which water and sewer lines, cables, and so forth are buried. 



The severity of the impact depends greatly on the characteristics 

 of the site. On flat upland sites the impact may be temporary, since 

 severe erosion of disturbed soils should not occur and vegetation and 

 habitat effects would be localized, providing that the site is restored 

 to pre-construction conditions. However, where pipelines cross rivers 

 and wetlands, the impact potential is much larger as disruption of soils 

 could cause greater erosion and downstream sedimentation affecting both 

 aquatic and terrestrial habitats. Long-term modifications in water 

 quality, water table levels, and vegetation could result if water-holding 

 properties of soil layers in wetlands were not restored to pre-construction 

 conditions [7]. 



In developing overland transmission systems, then, provisions should 

 be made for: (1) maintaining the natural shoreline; (2) minimizing 

 dredging; (3) arranging proper disposal of spoil; (4) avoiding wetlands; 

 (5) eliminating runoff erosion, (6) backfilling; (7) maintaining tidal 

 exchange; (8) restoring vegetation; and (9) construction and maintenance 

 of bulkheads or pilings at all crossing of natural tidal creeks and rivers 

 throughout the project life. 



4.11 .2 Location 



Location of transmission corridors is a key factor in reducing 

 potential ecological disturbances. Corridors should be sited as much as 

 possible on firm, dry ground. Wherever possible, pipeline routes should 

 follow existing transportation and utility routes and corridors to 



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