4. Key attribute alterations 



The key attribute alterations are disturbance factors associated with 

 concentrated activities and potential pollutants associated with drilling. 

 These attribute alterations are largely unpredictable, especially the 

 effects of pollutants since the persistence and potency of spilled com- 

 ponents are highly variable. Furthermore, the certainty of a particular 

 sort and size of accident is unknown. 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 number of indi- 

 viduals and species before damage is noticed. By this time, affected 

 organisms and waterflows 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. Since much of the gas and oil activities in the delta 

 marsh are water-oriented and self-contained, facilities requiring external 

 electrical utilities are infrequent and often impractical. Most facili- 

 ties have electrical generating capabilities at the site. Overhead 

 electrical lines are limited to only the most stable sites and subse- 

 quently this category will henceforth receive only minor consideration in 

 this discussion. 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 leveed roads, spoil 

 banks, or other elevated ridges. Flowlines carrying crude to the pro- 

 cessing center or brine to disposal wells also follow similar routes. 

 Lines are small and usually connected and placed by hand. Equipment 

 supply is provided by barges or small boats that use existing canals or 

 waterways. 



Where surface lines cross unmodified marsh, a survey crew enters on foot, 

 by boat, or by marsh buggy, depending upon the length of the lines, 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 flow- 

 lines are either buried in the bottom or elevated atop support pilings. 

 Barge-mounted draglines or jetting barges may be necessary for the 



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