populations is an impact because people desire to shoot and eat mallards, 

 Similarly, coliform pollution of shellfish is an impact because people 

 need to eat clean shellfish. But neither pesticide pollution of the 

 water nor loss of submerged grass beds is an impact because they do not 

 usually directly impact human needs and desires. Instead, they are eco- 

 logical effects which lead to impacts but are not themselves impacts. 



One often encounters lists of items called impacts that read like 

 this: dredging, suspended solids, siltation, oxygen depletion, bottom 

 disruption, loss of oysters, and boat channels. Little can be done to 

 analyze such a list of "apples and oranges" until the items are related 

 to recognized elements of the impact cycle. For example, these items 

 can be related to the impact cycle as follows: 



Item 



Element 



dredging 



suspended solids 

 siltation 

 oxygen depletion 

 bottom disruption 

 loss of oysters 

 boat channels 



activity 



effect 



effect 



effect 



disturbance 



impact 



subproject 



With the items appropriately identified, analysis will show the 

 cause and effect sequence as follows: 



Element 



Item 



subproject 

 activity 

 disturbance 

 effects 



impact 



boat channel 



dredging 



bottom disruption 



suspended solids 



increase siltation 



oxygen depletion 



loss of oysters 



In this example, the major activity causing problems is dredging a 

 channel to a marina. To prevent the disturbance leading to loss of oysters 

 by siltation, the proposed work might be modified in one of three ways: no 

 dredging permitted, dredge only after oyster spawning is finished so that 

 the settling of floating oyster larvae on firm underwater substrates will 

 not be disturbed, or use a "turbidity screen" to confine the plume of sus- 

 pended particles. 



2.3 THE PROCESS OF IMPACT ASSESSMENT 



An assessment system is outlined below which harmonizes with the sys- 

 tem of information presented in this and other volumes of the "Environmental 

 Planning for Offshore Oil and Gas" series. It is also compatible with the 

 system of assessment that has been in use by the FWS for many years in 

 reviewing permits under the FWS Coordination Act and for several years 

 in reviewing EIS's under NEPA. Table 5 presents the bare framework 



8 



