Mont. Code Ann. § 76-7-206

For the purpose of this chapter, an environmental control easement is assignable unless the instrument of conveyance or ownership expressly provides otherwise. An assignee must be qualified under the terms of this chapter to hold an environmental control easement. If an assignment is made in violation of the provisions of this section or in violation of the express terms of the instrument creating the easement, the assignment is void and the environmental control easement interests and obligations remain with the assignor.