Is an activity within an exempt class still subject to CEQA review?

An activity within an exempt class nonetheless is subject to CEQA review if "unusual circumstances" exist which would create a "reasonable possibility" that the activity would have a significant impact on the environment. (Guidelines, 15300.2, subd. (c).) The party challenging the exemption finding has the burden to establish such exception. (Fairbank v. City of Mill Valley (1999) 75 Cal.App.4th 1243, 1259.) Petitioners have failed to carry their burden to establish, by substantial evidence or a fair argument,¹⁹ such an exception to such exemption exists.