Lithgow's hazardous materials team was called to a chemical spill at Wallerawang Sewerage Plant on Thursday, October 17.
Wallerawang Fire and Rescue NSW was alerted to the spill at about 9.30am on Thursday morning as part of a general emergency response.
Deputy captain Luke Curran said patches of dead grass and puddles of chemicals were found in a dirt drain at the site.
Lithgow's HAZMAT unit was called to address the spill, which was believed to be caustic soda.
The Environmental Protection Authority (EPA) was also believed to have been at the site, along with Lithgow City Council staff.
Deputy Captain Curran said absorbents were used to mop up the spill, which had pooled in the drain. It was then covered in sand.
Four Wallerawang Fire and Rescue crew members were at the site, along with two HAZMAT responders, and representatives from Katoomba.
Fire and Rescue crews remained at the site for eight hours.
Lithgow City Council and the EPA have been approached for comment.
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