rd v. McLucas, 782 F.2d 956, 959-61 (1 I th Cir. 1986); National Resources Defense Council v. Costle, 561 F.2d 904, 907-08 (D.C.Cir. 1977); see also Catmint) v. Berry, 922 F.2d 37 (1st Cir. 1990)(district court denied intervention at liability stage but indicated that it would consider a motion to inter