A team of "external technical experts" has determined that the cause of this summer's massive sinkhole on Rideau Street was not caused by a failure of municipal infrastructure, according to the City of Ottawa's solicitor.

According to a Thursday memo from Rick O'Connor, the team is "confident" that problems with city infrastructure had nothing to do with the emergence of the June 8 sinkhole — which caused a stretch of the busy downtown street to collapse, initiated a gas leak, and forced businesses to temporarily evacuate.

"The city's external technical experts were unable to pinpoint a singular cause of the event, but are confident, based on their analysis of all the available evidence, that the sinkhole was not precipitated by a failure of city infrastructure," wrote O'Connor in his memo.

O'Connor said the report those experts compiled "cannot be made public at this time" but that city councillors could see him to view their findings.

Both the city and the Rideau Transit Group, which is overseeing construction of Ottawa's forthcoming light rail line, had been endeavouring to find out how the collapse happened.

RTG has hired an independent company to conduct its own investigation into the cause of the sinkhole.

The consortium refused to comment Thursday on the findings of the city's report.

A drone captured the scope of the sinkhole that swallowed three lanes of Rideau Street on June 8, 2016.

'A good outcome'

Earlier this month, Steve Cripps, the city's director of O-Train construction, said the two separate investigations would be made public within a few weeks.

On Thursday, Cripps called the still-private findings of the technical experts "a good outcome for us."

"At this point it's really become an insurance matter," said Cripps. "There's project insurance that cover both the city and the consortium ... so really it's now down to a matter of the insurers taking all of this information."

"Mr. O'Connor, as he's noted in his memo, doesn't want to be releasing information that may prejudice the city's position in any claims or potential future litigation — if something comes to that."

According to the memo, there have been 31 "claims for compensation" submitted by affected businesses and property owners since the June 8 sinkhole, in addition to the city's own claim for $1.5 million in repair costs.

Cripps said he expected the insurers would also be carrying out their own investigation.

"At this point I can't say we're confident we're off the hook, but again, it will be up to the insurer as to how they will react."

Rideau-Vanier Coun. Mathieu Fleury said encroachment fees are designed to protect precious sidewalk space in the ByWard Market. (CBC News)

City in 'strong position'

One of the major questions has been whether a broken watermain that flooded Rideau Street was the cause of the sinkhole — or simply an unhelpful element street's collapse.

Rideau-Vanier Coun. Mathieu Fleury told CBC News Thursday that the findings of the engineering team's findings suggest it's the latter, and that light rail excavation work is to blame.

"We believe we have the information that provides that the watermain did not collapse before the soil collapsed," Fleury said.

"We believe we're in a strong position, that the excavation was the cause of the sinkhole."

While the two sides could go to court over sinkhole-associated costs, Fleury said he doubted the dispute would spoil the city's relationship with RTG, calling it a "disagreement."

The insurance claims submitted by both the city and RTG total about $10 million — a small portion of the $2.1-billion overall cost of the light rail project, Fleury added.