An EIS is required for proposals for legislation and other major actions significantly affecting the quality of the environment. The lead agency decides whether an EIS is required in the threshold determination process, as described below.

(1) In making a threshold determination, the responsible official shall:

(a) Review the environmental checklist, if used:

(i) Independently evaluating the responses of any applicant and indicating the result of its evaluation in the DS, in the DNS, or on the checklist; and

(ii) Conducting its initial review of the environmental checklist and any supporting documents without requiring additional information from the applicant.

(b) Determine if the proposal is likely to have a probable significant adverse environmental impact, based on the proposed action, the information in the checklist (WAC 197-11-960), and any additional information furnished under WAC 197-11-335 and 197-11-350; and

(c) Consider mitigation measures which an agency or the applicant will implement as part of the proposal, including any mitigation measures required by development regulations, comprehensive plans, or other existing environmental rules or laws.

(2) In making a threshold determination, the responsible official should determine whether:

(a) All or part of the proposal, alternatives, or impacts have been analyzed in a previously prepared environmental document, which can be adopted or incorporated by reference (see Part Six).

(b) Environmental analysis would be more useful or appropriate in the future in which case, the agency shall commit to timely, subsequent environmental review, consistent with WAC 197-11-055 through 197-11-070 and Part Six.

(3) In determining an impact's significance (WAC 197-11-794), the responsible official shall take into account the following, that:

(a) The same proposal may have a significant adverse impact in one location but not in another location;

(b) The absolute quantitative effects of a proposal are also important, and may result in a significant adverse impact regardless of the nature of the existing environment;

(c) Several marginal impacts when considered together may result in a significant adverse impact;

(d) For some proposals, it may be impossible to forecast the environmental impacts with precision, often because some variables cannot be predicted or values cannot be quantified.

(e) A proposal may to a significant degree:

(i) Adversely affect environmentally sensitive or special areas, such as loss or destruction of historic, scientific, and cultural resources, parks, prime farmlands, wetlands, wild and scenic rivers, or wilderness;

(ii) Adversely affect endangered or threatened species or their habitat;

(iii) Conflict with local, state, or federal laws or requirements for the protection of the environment; and

(iv) Establish a precedent for future actions with significant effects, involves unique and unknown risks to the environment, or may affect public health or safety.

(4) If after following WAC 197-11-080 and 197-11-335 the lead agency reasonably believes that a proposal may have a significant adverse impact, an EIS is required.

(5) A threshold determination shall not balance whether the beneficial aspects of a proposal outweigh its adverse impacts, but rather, shall consider whether a proposal has any probable significant adverse environmental impacts under the rules stated in this section. For example, proposals designed to improve the environment, such as sewage treatment plants or pollution control requirements, may also have significant adverse environmental impacts.