Leadership in a northern Alberta hamlet will be evacuating about 150 people after a chemical mix-up at the community's water plant. Vern Janvier, chief of the Prairie Chipewyan First Nation, said the First Nation decided on Monday to offer residents who rely on piped water the option of leaving their homes.  There are 107 houses on the system, and Janvier said from one to six people live in each house. He anticipates there will be between 150 and 200 evacuees.