reenter nearby sites if the areas remain essentially unaltered. Human 

 activity and associated noises extend project effects beyond the boun- 

 daries of the immediate site. 



4. Key attribute alterations 



Alterations associated with line installation are functions of line size, 

 site location, and placement methodology. Surface flowlines and supply 

 lines and permanent overhead lines within road and access canal easements 

 typically generate short-term impacts of limited areal extent. Impacts 

 are quickly reclaimed by the system and generate little, if any, 

 noticeable subsequent effects on consumer components. Gas and oil tran- 

 sportation pipelines, on the other hand, can modify important ecosystem 

 attributes. Key alterations involve: (1) changes in land elevations, 

 either through canal dredging and/or spoil deposition, both of which may 

 lead to fundamental alterations of the existing marsh hydrologic regime, 

 and (2) direct removal of productive fresh marsh vegetation and dependent 

 consumer groups as a result of dredging and spoiling activities. Resul- 

 ting productivity losses may be either temporary or long term, depending 

 upon the installation technique used and the extent of site restoration. 

 Major alterations of intramarsh circulation patterns and standing water 

 characteristics resulting from open, unplugged pipeline ditches and 

 associated spoil levees are capable of generating changes in plant 

 distribution and composition. Desirable wildlife species may be either 

 favored or discouraged by such readjustments. 



Placement and operation of production facilities . 

 1. Activity sequence 



Production aspects occur both at the wellsite and at a central treatment 

 complex. Normally at a wellsite only slight structural modifications of 

 the existing pad or drilling barge site are necessary to convert the well 

 to production status. Placement of gathering flowlines from the well to 

 the treatment facilities requires activities as described for the instal- 

 lation and maintenance of lines; these include line survey, limited 

 vegetation clearing, line installation, and necessary site restoration. 

 If exploratory drilling was conducted from a floating barge, the barge is 

 removed and replaced by a small elevated platform supporting the wellhead. 

 Small-scale digging and pile driving are required. 



Centralizes treatment facilities are typically located on firm, upland 

 sites if they are available nearby. Otherwise, the complex is construc- 

 ted in the marsh using the same construction techniques and processes 

 employed in preparing a wellsite. Treatment and processing equipment may 

 be supported on (1) a leveed pad, (2) a platform complex elevated on 

 pilings and supplemented by stationary barges, or (3) a combination of 

 the above. Brine-disposal lines are installed to transport brine to 



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