It happened off East Gannon Avenue near U.S. 264 around 5 p.m. Tuesday.
The Raleigh employees were cutting grass when they located the substance near a drainage ditch. When they got close to it, they all started to feel ill.
They were all checked out by medical experts and cleared.
As a precaution, businesses near the area were evacuated. That includes East Wake Academy, Braven Environmental and Eastern Wake Education Center.
The substance was later identified as a cleaning agent. Crews put down absorbent mats and cleaned up the substance.
Investigators said the substance turned out to not be widespread or hazardous.