The Oregonian's Julie Sullivan has been following the story of the National Guard troops who were exposed to the carcinogen hexavalent chromium at the Qarmat Ali water plant in Iraq - which contracting giant KBR was tasked with rebuilding. (Oregonian stories are here; also see our past posts on the subject here, here, and here.) Now, Sullivan reports, US Representative Earl Blumenauer of Oregon has sent a "sharply worded" letter to Secretary of Defense Robert Gates asking for details about an immunity deal that KBR reportedly struck with the Department of Defense. Twenty-six Oregon Army…