Environmental impact studies typically address a minimum of two alternatives, and sometimes as many as ten, but usually three to five alternatives. The minimum number typically represents a choice between construction and operation of a project versus project nonapproval. The alternatives can encompass a range of considerations. Typical categories of alternatives, expressed generically, include:
1. Site location alternatives
2. Design alternatives for a site
3. Construction, operation, and decommissioning alternatives for a design
4. Project size alternatives
5. Phasing alternatives for size groupings
6. No-project or no-action alternatives
7. Timing alternatives relative to project construction, operation, and decommissioning
Decision-focused checklists are systematic methods for comparing and evaluating alternatives. Scaling, rating, or ranking-weighting checklists can be used in such comparisons and evaluations. In scaling checklists, an algebraic scale or letter scale is assigned to the impact of each alternative on each environmental factor. In ranking checklists, alternatives are ranked from best to worst in terms of their potential impacts on identified environmental factors, while rating uses a predefined rating approach. These checklists are useful for comparative evaluations of alternatives, thus they provide a basis for selecting the preferred alternative.
In weighting-scaling checklists, relative importance weights are assigned to environmental factors and impact scales are determined for each alternative relative to each factor. Weighting-ranking checklists involve importance weight assignments and the relative ranking of the alternatives from best to worst in terms of their impacts on each environmental factor. Numerous weighting-scaling and weighting-ranking checklists are available for environmental impact studies. These methods represent adaptations of routinely used multicriteria or multiattribute decision-making techniques; such techniques are also called decision-analysis techniques.
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