NEWARK, NJ — For the fourth time in five months, strangely colored smoke has been spotted rising from a stack at a trash incinerator in Newark.

On Wednesday, purple smoke wafted above the Covanta incinerator on Raymond Boulevard, an incident spotted by a Patch reader (see below photo). The facility burns 2,800 tons of municipal garbage per day from New York City and all 22 municipalities in Essex County.

Covanta spokesperson James Regan confirmed there was a "purple plume" incident on Oct. 9, but said it was "very short in duration." It took place from 5:06 p.m. to 6:06 p.m. and didn't exceed the opacity limit on any of the incinerator's boilers, he said. It hasn't been the first time in recent history that a colorful cloud has floated above the incinerator. Previous incidents involving pink and purple smoke were reported on Sept. 20 and June 19.

The source for all three incidents was the same, Covanta has stated: iodine being burned as part of a regular trash delivery. While iodine isn't illegal to throw away with regular trash, the company continues to inspect waste deliveries and is working with generators to find the sources of iodine in the waste stream, Regan told Patch on Thursday.

"We've also implemented a number of operational protocols that reduce and minimize purple plumes when they are detected," he added.

Covanta has claimed that the colorful smoke isn't a public hazard to the nearby community, a stance that many local activists and residents have challenged.