(a) An EIS is required if the proposal is determined to have a significant impact on the human environment pursuant to subpart E.

(b) An EIS will normally be required if the proposal:

(1) Would provide a site or sites for hospitals or nursing homes containing a total of 2,500 or more beds; or

(2) Would remove, demolish, convert, or substantially rehabilitate 2,500 or more existing housing units (but not including rehabilitation projects categorically excluded under § 50.20), or which would result in the construction or installation of 2,500 or more housing units, or which would provide sites for 2,500 or more housing units.

(c) When the environmental concerns of one or more Federal authorities cited in § 50.4 will be affected by the proposal, the cumulative impact of all such effects should be assessed to determine whether an EIS is required. Where all of the affected authorities provide alternative procedures for resolution, those procedures should be used in lieu of an EIS.