Two construction workers were sent to hospital on Thursday with symptoms of nausea after yet another two metal drums - one crushed into pieces and another intact - were removed from a Guelph construction site where a total of 44 similar containers have been unearthed since September 2014.

On the outside of the intact drum, a gel-like substance was emitting an "unpleasant" odour, according the city.

"[The workers] were very close to the source of the odours, so they experienced some nausea," said Stacey Hare, communications officer with the city of Guelph.

"Work has resumed on the site and those two gentleman are back at work. The odours were strong at the very source, but even just a few metres away from the site they were less strong and they have since dissipated."

The site is located east of the Hanlon Expressway and north of Wellington Street, near Howitt Creek and a number of family residences. Hare said some residents in a nearby apartment building did complain about the smell on Thursday.

The gel substance was treated as non-hazardous waste and has been disposed of.

"Because we already had some experience with the previous drums we found in September, we're treating them similarly," said Hare. "There's no way to know for certain that it's exactly the same."

Eight metal drums were first unearthed last September, prompting the city to hire a third party investigator to examine its contents.

According to the report by MMM Group Limited, the drums held a mix of benzene, toluene, ethylbenzene, xylene and styrene in the drums.

A section of the construction site was shut down for several months, during which time it was examined for more drums. It was re-opened in June. These new drums were found outside the area that was cleared.

"Yes it was a surprise," said Hare.

"These two last metal objects, these two drums, were found outside the remediation area and outside the project route. The wall of the excavated area, the soil fell away, that's when we found one drum, contained it, removed it. And then in removing the surrounding soil, we found more crumpled metal that we eventually could confirm that yes, that was another drum."

Construction to install the water main has resumed, as the route itself is thought to be clear. According to the city, the construction site was a former landfill in the 1950s.

"Outside of the project route we recognize on either side we've got some historic landfill or historic industrial activity and we're continuing to monitor those sites, along with other brownfield sites across the city," said Hare.