40 CFR 1504.2 - Criteria for referral.
Environmental referrals should be made to the Council only after concerted, timely (as early as possible in the process), but unsuccessful attempts to resolve differences with the lead agency. In determining what environmental objections to the matter are appropriate to refer to the Council, an agency should weigh potential adverse environmental impacts, considering:
(a) Possible violation of national environmental standards or policies.
(c) Geographical scope.
(e) Importance as precedents.
(f) Availability of environmentally preferable alternatives.