4. Key attribute alterations 



ion 



The key attribute alterations include direct removal of vegetatit.. 

 and consumers, localized changes in land elevation, and introduction 

 of pollutants. Since the area affected by levees and pit excavation 

 is small for a single wellsite (relative to the unmodified marsh), 

 the loss of food and cover for supported consumers is limited. 

 However, changes in land elevations can influence waterflow regimes 

 over a significant area so that the area affected may range from the 

 wellsite alone to much larger portions of the marsh. 



Because the persistence and potency of spilled components is highly 

 variable, the extent of impacts from pollutants is not predictable. 

 Since the effects of sublethal levels of persistent pollutants are 

 not catastrophic (as is the case in a blowout or major spill), the 

 toxins may permeate large numbers of individuals and species before 

 damage is noticed. By this time, affected organisms and water flows 

 will have served as agents of dispersal, so that areas much larger 

 than the wellsite may be affected. 



Installation and maintenance of lines. 



1. Activity sequence 



Lines associated with oil and gas activity may be separated into 

 three categories based on similarities of characteristics: (1) 

 temporary surface lines to supply drilling sites with water and gas; 

 (2) permanent or temporary overhead electrical lines to supply 

 electrical and phone service to production, treatment, and pump 

 station facilities; and (3) permanently buried lines which transport 

 gas and oil to distribution or refining centers. The activity 

 levels required for each line type vary according to category and 

 range from simple to complex. 



Water, gas, and other lines bringing supplies to the wellsite are 

 usually laid on the surface, typically paralleling existing access 

 roads or canals. Flowlines, carrying crude to the processing center 

 or brine to disposal wells, are other surface lines typically placed 

 alongside leveed roads and access canals. Lines are small and 

 usually connected and placed by hand. Equipment supply is provided 

 by trucks or barges that use existing access routes. Where surface 

 lines cross unmodified marsh, a survey crew enters by foot or marsh 

 buggy, depending upon the length of the line, and clears and stakes 

 the alignment. Equipment supply is provided by marsh buggy. Lines 

 are usually connected and placed by hand. When crossing open water 

 areas (canals, bayous, ponds, etc.), supply lines and flowlines are 

 either buried in the bottom or elevated atop support pilings. 



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