(a) Actions undertaken or approved prior to the effective date of this article, except:

(i) In the case of an action where it is still practicable either to modify the action in such a way as to mitigate potentially adverse environmental effects or to choose a feasible and less environmentally damaging alternative, in which case the commissioner may, at the request of any person or on his own motion, in a particular case, or generally in one or more classes of cases specified in rules and regulations, require the preparation of an environmental impact statement pursuant to this article; or

(ii) In the case of an action where the responsible agency proposes a modification of the action and the modification may result in a significant adverse effect on the environment, in which case an environmental impact statement shall be prepared with respect to such modification.

(b) Actions subject to the provisions requiring a certificate of environmental compatibility and public need in articles seven, ten and the former article eight of the public service law; or

(c) Actions subject to the class A or class B regional project jurisdiction of the Adirondack park agency or a local government pursuant to section eight hundred seven, eight hundred eight or eight hundred nine of the executive law, except class B regional projects subject to review by local government pursuant to section eight hundred seven of the executive law located within the Lake George park as defined by subdivision one of section 43-0103 of this chapter. 6. Lead Agency. When an action is to be carried out or approved by two or more agencies, the determination of whether the action may have a significant effect on the environment shall be made by the lead agency having principal responsibility for carrying out or approving such action and such agency shall prepare, or cause to be prepared by contract or otherwise, the environmental impact statement for the action if such a statement is required by this article. In the event that there is a question as to which is the lead agency, any agency may submit the question to the commissioner and the commissioner shall designate the lead agency, giving due consideration to the capacity of such agency to fulfill adequately the requirements of this article.