CONCORD -- Longtime Mt. Diablo school board trustee Gary Eberhart has announced he won't seek re-election in November.

Elected in 1995, Eberhart is the longest-serving trustee on the current board. His decision to step down leaves his seat open to four challengers who have taken out election papers, along with new candidates who may emerge before the filing deadline, which will be extended to Aug. 15 for non-incumbents.

Board President Sherry Whitmarsh, who ran on a slate with Eberhart four years ago, has not yet announced whether she will run again. The intended challengers for the two open seats are Attila Gabor, Brian Lawrence, Debra Mason and Ernesto DeTrinidad,

Eberhart's decision not to run for re-election was reported Wednesday on Claycord.com. Eberhart did not return phone calls Wednesday morning for comment.