TIMELINE

1950s-2002: 3M makes several perfluorinated chemicals (PFCs) at its Cottage Grove plant that are used in Scotchgard, non-stick cookware, fire retardants and other products.

2004-05: State health officials detect PFCs in Oakdale city wells and more than 200 Lake Elmo private wells.

January 2007: Health authorities report 3M chemicals in the groundwater of six more east-metro communities.

May 2007: 3M signs an agreement to clean up dumps where PFC wastes were buried between 1956 and 1974.

2009: 3M chemicals are found in the blood of 100 east-metro residents in volunteer study. Cleanup begins at sites where 3M chemicals were dumped.

December 2009: The federal Environmental Protection Agency singles out PFCs and expresses "strong concern about the risks" of exposure.

2012: EPA intends to propose action to address potential risks from PFCs.