Removal of petrochemical and other waste products from storage pit areas, 

 from impregnated substrates around production facilities, and from spill 

 areas prevents potential long-term input and bioaccumulation of heavy 

 metals, petrochemical hydrocarbons, brine, and other noxious substances 

 in the marsh food chain. Removal of soil toxins speeds natural recovery 

 processes by improving growth conditions. 



Land management objectives regulate which specific consumer groups or 

 plant assemblages are encouraged by planting techniques, filling and 

 removal processes, and other restoration procedures. These objectives 

 determine, to a large extent, how extensive the efforts will be or in what 

 direction restoration will proceed. 



Restoration typically occurs on sites which previously supported various 

 types of displacement-producing activities or on sites which have just 

 recently been disturbed. Displacement, if it were to occur, has already 

 been effected by such prior processes. Additional effects are probably 

 minor and temporary in nature. Site shutdown and restoration should, if 

 successful, encourage the return of sensitive wildlife species. 



4. Key attribute alterations 



Restoration of the hydrologic regime is the pivotal aspect of site reha- 

 bilitation; it controls or combines with other less critical regulatory 

 parameters, and ultimately determines the health and productivity of the 

 delta marsh environment. The hydroperiod determines how mcuh water covers 

 the marsh, its depth, what the salinity regime may be, and to what extent 

 sediment accretion occurs. Standing water provides cover for numerous 

 aquatic and semiaquatic consumer species and provides a mechanism for tran- 

 sporting detritus and dissolved nutrients. Second-order effects include 

 the regulation of sunlight available to submergent vegetation. Hydrologic 

 restoration is accomplished by reestablishing prior drainage pathways and 

 surface contours. This may include unblocking former sources of water 

 inflow, filling in or plugging canals, removing or breaching continuous 

 elevated levees and spoil banks, and revegetating barren sites. 



Levees and Spoil Banks 



Seismic preexploration . 



1. Activity sequence 



The techniques utilized for seismic preexploration activities when 

 they take place on levees is the same as when they occur on rela- 

 tively dry marsh surfaces. However, an entire shot line is rarely 

 conducted on a levee/spoil-bank system. Typically, the shot line is 



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