assemblages and directly dependent consumer groups within the well- 

 pad site. The secondary effect is the associated long-term gradual 

 changes of biota in nearby areas that result from subtle, microenvi- 

 ronmental alterations of soil structure, surface water hydrology, 

 soil toxicity, selective vegetation removal, and disturbance 

 factors. Community response to such secondary alterations is 

 expressed by the different plant assemblages which develop through 

 competition under new abiotic conditions. The species composition 

 and population level of the consumer groups may or may not respond 

 to secondary habitat alterations. Response is a function of the 

 areal extent of the change, the size of the consumer's resource 

 base, and the sensitivity of the consumer to altered habitat condi- 

 tions. Sensitive wildlife species may abandon otherwise favorable 

 habitats because of drilling, operational, and vehicle-associated 

 disturbances. 



Installation and maintenance of lines. 



1. Activity sequence 



This section describes events associated with the following types of 

 lines: pipelines, flowlines, utility lines, and overhead electrical 

 lines. The activity sequence associated with all types is basically 

 similar, except that some require less extensive environmental 

 alterations than others. 



The survey crew enters and stakes the route and alignments. The 

 clearing crew may follow to remove larger trees and other dense 

 vegetation. Vegetation clearing may be partial or complete depend- 

 ing on line size and whether or not the line is to be buried. Large 

 underground lines require total vegetation removal, usually com- 

 pleted with bulldozers. Construction equipment enters to prepare 

 the site for access by trenching and line-installing equipment. 

 Preparation involves grading, filling, and leveling procedures for 

 larger pipelines, but for the installation of surface lines, utility 

 lines following existing roadways, and small underground lines 

 crossing level terrain, site preparation is minimal. For buried 

 lines, a trench is dug and the spoil is piled continuously along one 

 side. Holes are dug for pole placement to support elevated lines. 

 Surface lines require no additional site alterations. Buried lines 

 are laid, and trenches are covered by backfilling. The site is 

 graded to flatten residual fill, reseeded, and abandoned. In the 

 case of large pipelines and overhead electrical lines, the rights-of- 

 way are periodically maintained either by mowing or with herbicide 

 treatment. Emergency repairs or testing may occasionally require 

 reentry of excavation and repair equipment to stop line leakage. 



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