portional to the speed and aniount of boat traffic. Erosion of fresh 

 spoil deposits will proceed until they become vegetated by pioneer- 

 ing plant groups. The ecesis will usually occur within two yr or 

 less, depending upon the edaphic conditions and sources of seed stock. 

 Increases in turbidity associated with vehicle traffic also have 

 short-term and long-term components; effects of both components are 

 usually minor. 



Fresh spoil lining the canal passage may interrupt existing small 

 drainage channels. This results in localized changes in runoff pat- 

 terns and amounts. The total area affected is site specific, but is 

 usually insignificant when compared to the remaining area of unal- 

 tered levee. 



Disturbances associated with dredging activities typically cause 

 short-term displacement of sensitive wildlife species from the 

 immediate area. Following the completion of the well (a matter of 

 several months), these species may reenter nearby sites if suitable 

 habitat conditions remain. Further short-term displacement may occur 

 during maintenance or repair sessions. 



4. Key attribute alterations 



Key attribute alterations induced by this phase of oil and gas oper- 

 ations involve changes in land elevations. First-order effects in- 

 clude complete removal or burial of vegetation and the creation of a 

 standing-water habitat in its place. Assuming adequate measures are 

 taken to prevent erosion/turbidity problems, the remainder of the 

 levee system is only slightly affected. In most cases the minor 

 alteration of water flows on the levee system (due to ruts or fresh 

 spoil placement) will not result in significant changes in vegetative 

 composition. The ecosystems adjacent to the levee may be more 

 severely altered (due to complete breaching) than the levee itself. 



Wellsite preparation and operation. 



1. Activity sequence 



This phase of oil and gas operations is applicable only in those cases 

 where wellsites per se (rather than access routes) are located within a 

 given landform. This typically occurs only on wide spoil deposits. The 

 equipment and techniques utilized during canal construction are also 

 employed during preparation of the keyway, or wellsite. Typical dimen- 

 sions approach 47 by 133 m (140 by 400 ft). Drilling and auxiliary equip- 

 ment and supplies are transported and stored on barges. A specialized 

 barge is employed for drilling. Its ballast tanks are flooded, it settles 

 to the bottom, and piles are driven to anchor it firmly in place. Impacts 



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