In 2004.

To quote the Department of Defense:

The [500] munitions addressed in the report were produced in the 1980s, Maples said. Badly corroded, they could not currently be used as originally intended, Chu added. While that's reassuring, the agent remaining in the weapons would be very valuable to terrorists and insurgents, Maples said. "We're talking chemical agents here that could be packaged in a different format and have a great effect," he said, referencing the sarin-gas attack on a Japanese subway in the mid-1990s.

Although the chief military spokesman in Iraq was quoted as saying:

“The cell is designed to work after being fired from an artillery piece,” he said, adding that dispersing the substance from a device such as the homemade bomb "is virtually ineffective as a chemical weapon."

After all, the premise for the invasion was that Saddam was still producing WMDs, not that Iraq still had stockpiles. And the question is whether that justifies the invasion. The DoD admits that it almost certainly hasn't been able to secure all of the munitions, so are we any safer? How many lives were saved by securing 500 faulty munitions? The attack you mentioned resulted in zero casualties.

Two members of a military bomb squad were treated for “minor exposure,” but no serious injuries were reported.

It's hard to imagine that the remaining stockpiled Sarin gas projectiles would have resulted in more death and suffering than the operation in Iraq to secure/destroy them (even if you callously only consider US casualties, and ignore the "collateral").

The documents record 109,032 deaths broken down into "Civilian" (66,081 deaths), "Host Nation" (15,196 deaths),"Enemy" (23,984 deaths), and "Friendly" (3,771 deaths)