The 672-foot east span of the former bridge, which is closest to the Westchester side, will be demolished using explosives at 9:30 a.m. on Jan. 12.
The original plan was to dismantle the whole bridge piece by piece rather than to use explosives, which officials worried might adversely affect Hudson River fish and wildlife.
But in September, workers dismantling the east span heard a loud popping sound and soon discovered that the structure was unstable. Taking that part of the bridge apart piece by piece could lead to collapse, Tappan Zee Constructors, the company responsible for the demolition, determined.
After the demolition, only a portion of the west span, nearer Rockland County, will remain; it will continue to be dismantled piece by piece, according to Tappan Zee Constructors.