pollutants. Since the area affected by excavation is small (relative to 

 the unmodified marsh), the loss of food and cover for dependent consumers 

 is less extensive than losses caused by the access route. The changes in 

 land elevations can influence water flow regimes, but the total area 

 affected by the pad site is usually minor in comparison to the undis- 

 turbed 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 waterflows will have 

 served as agents of dispersal, so 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 sur- 

 face 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 they range from simple to complex. 



Water, gas, and other lines brining 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 types of surface lines typically placed alongside leveed 

 roads and access canals. Lines are small and are usually connected and 

 placed by hand. Equipment is provided by trucks or barges that use ex- 

 isting access routes. 



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

 by boat, or by marsh buggy, depending upon the length of the line; the 

 crew clears and stakes the alignment. Equipment 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. 

 Draglines or jetting barges are required for the burying procedures. 

 Placement of supports for elevated flowlines is accomplished by marsh 

 buggy, boat, or hand operations. Site characteristics such as water 

 depth and area! expanse determine what field equipment is required. 



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