4. Key attribute alterations 



The key attribute alterations involve primary and secondary effects. The 

 prir.ary effect is the direct long-term removal of plant assemblages and 

 directly dependent consumer groups within the production site. The 

 secondary effect is the associated long-term gradual changes in nearby 

 biota that result from subtle microenvironmental alterations of soil 

 structure, surface-water hydrology, soil toxicity, partial 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 composi- 

 tion and population levels 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 consumers' resource base, and 

 sensitivity of the consumer to altered habitat conditions. Sensitive 

 wildlife species may abandon otherwise favorable habitats because of 

 operational and vehicle-associated disturbances. 



Spills and cleanup . 



1. Activity sequence 



Accidental discharge of oil, gas, field brine, or other substances occurs 

 as a result of equipment failure, improper equipment operation, or human 

 error. Built-in safety mechanisms, if present, are activated automati- 

 cally to limit the quantity of discharge. Field personnel, once aware of 

 the spill or leak, immediately initiate procedures to confine discharges 

 to the smallest possible area. Containment berms or levees are erected, 

 if the site is large enough, to prevent further liquid expansion, or 

 shallow ditches may be excavated to intercept, channel, and concentrate 

 the effluent into collection sites. Draglines and marsh buggies are 

 utilized for such earthwork. Staw or hay is used to adsorb smaller, less 

 accessible quantities that vacuum units cannot remove. Vegetation coated 

 with oil or its derivates is either cut or burned. If burning is planned, 

 the contaminated areas are enclosed by fire lanes. Contaminated soils may 

 be excavated, removed, and replaced with other fill materials. Soil 

 replacement signals completion of the cleanup phase and the beginning of 

 site restoration. 



2. Primary ecological alterations 



Alterations will vary according to levee size, cleanup method, toxicity 

 of the chemical substances released, and spill size. 



2.1 Partial or complete removal of vegetation within the spill and 

 cleanup site; magnitude varies according to spill size 



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