What are the elements of estoppel and what is the test for estopping the government?

The elements of estoppel are: (1) knowledge of the true facts by the party to be estopped; (2) intent to induce reliance or actions giving rise to a belief in that intent; (3) ignorance of the true facts by the relying party; and (4) detrimental reliance. Watkins v. United States Army, 875 F.2d 699, 709 (9th Cir.1989) (en banc), cert. denied, --- U.S. ----, 111 S.Ct. 384, 112 L.Ed.2d 395 (1990). Additionally, for the government to be estopped there must be affirmative misconduct (not mere negligence) and a serious injustice outweighing the damage to the public interest of estopping the government. See id. at 707-08.