A B-Double, carrying the herbicide glyphosate, left the Hume Highway about 10 kilometres south of Tarcutta and hit a tree on January 29.

The crash sadly killed the driver, despite the efforts of passersby and first responders, and spilled up to 4000 litres of glyphosate, some of which spread into Keajura Creek.

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The NSW Environment Protection Authority has been assisting Fire and Rescue NSW crews in their hazmat operation salvaging the herbicide, which spilled from four split 1000 litre drums.

FRNSW crews installed containment booms in the creek on Friday night to control the glyphosate but some of the chemical had already spread into the small waterway.

EPA director regulatory operations regional west Gary Whytcross said the fast response by emergency services meant most of the spill was contained.

"This is a serious event, just given the volumes of the herbicide that were involved," he said.

"Because the emergency services really quickly put [containment] booms in the creek we're confident that we've contained most of the herbicide that spilled behind those booms."

Mr Whytcross said tanker trucks had pumped 96,000 litres of potentially polluted water from the creek, which will be treated and disposed of.

"We're pretty confident that that volume of water has got most of any contaminated water that was in the creek," he said.

"But some of it could have got past the booms, or [spread] before the booms got put in. And that's why we've asked landholders to take a cautious approach."

As a precaution, landholders south of the crash site have been warned not to pump any water from the creek until the results of an EPA testing operation come back.

"The landholders have been fantastic in that respect, they've responded really well to that," Mr Whytcross said.

He said EPA staff were still working at the site of the crash to take water samples that he hopes can be tested by the start of next week.

Glyphosate is a common but controversial weed killer used in agriculture that Mr Whytcross said would be toxic to small organisms living in the creek and some vegetation at the crash site.

"The advice is that people would be needing to consuming concentrated [amounts] to be harmed by it, but our view is that we don't want to be taking any risks for any of the landholders," he said.