vertebrate groups from adjacent water systems will invade the new habitat. 

 Waterfowl, alligator, and wading and shore bird use will increase if and 

 when human activity becomes minimal. At the ecosystem level of organiza- 

 tion, these changes are of little consequence. 



During this phase of operations (one to three months), the new water 

 environment is exposed to a wide variety of pollutants from drilling mud, 

 sump discharge, and vehicle and equipment waste (exhausts, oil, grease, 

 gasoline). The adjacent levee/spoil-bank system, however, is isolated 

 from these substances. The kinds and amounts of these materials, and 

 hence their effects on adjacent systems, are site specific. These consi- 

 derations are treated in the appropriate ecosystems of this report. 



Unlike the previous phases of activity, the preparation and operation of 

 a wellsite involves continuous, noisy, and long-term disruption of sensi- 

 tive wildlife species. However, it is not possible to predict or quantify 

 the degree and/or significance of this displacement. The amount of noise 

 and human activity necessary to permanently displace wildlife is unknown, 

 but this factor should be seriously considered during this phase of oil 

 and gas operations since it extends the effects of the project beyond the 

 boundaries of the immediate site. 



4. Key attribute alterations 



The key attribute alterations include direct removal of vegetation and 

 consumers and localized changes in land elevation. Since the area 

 affected by excavation is usually small (relative to the undisturbed 

 region), the loss of food and cover for supported consumers is insignifi- 

 cant. The changes in land elevation can influence waterflow regimes, but 

 the total area affected is usually minor in comparison to the undisturbed 

 land. 



Installation and maintenance of lines . 



1. Activity sequence 



This section describes events primarily associated with pipeline activi- 

 ties but also addresses other types of lines such as surface supply and 

 flowlines and, at times, overhead electrical lines. The activity sequence 

 associated with line installation and maintenance is a function of the 

 line type, line alignment with respect to the levee, and basic physical 

 levee characteristics with respect to the adjacent marsh systems. 



Line installation in the levee system consists of one of two primary 

 types: (1) surface lines oriented along the levee and (2) pipelines that 

 penetrate or breach levees. Surface lines include small supply lines or 



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