Parsons Corp., Pasadena, Calif., has announced new roles for two top executives, following a corporate restructuring announced on Nov. 30. Virginia L. Grebbien is named president of the firm's new global environment and infrastructure group, which combines its former commercial technology and water infrastructure groups. Formerly president of the latter, she joined Parsons in 2008 from a previous role as western division manager for MWH Americas Inc. Parsons also named Michael M. "Mike" Walsh as president of its new Parsons Australasia group. His base location is still being determined, says the firm. Walsh was president of the commercial technology group. Both changes take effect on Jan. 1.