Stagnant water is unlikely to cause the foul “rotten eggs” smell that has assailed LRT riders at Rideau Station for more than a week, says an environmental engineer and groundwater expert.

The City of Ottawa and RTG have identified stagnant water as a suspected cause of the sulphur smell. LRT passengers say it is different from the well-known sewage smell centred at Parliament station.

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But a prominent hydrology expert from Western University isn’t buying that theory.

“Water at that depth cannot be stagnant. It’s obviously some kind of mix of polluted water or something else coming into this area” and entering the groundwater, said Slobodan Simonovic.

“At that depth the water is mixed with the soil and soil is providing usually positive effects (by) cleaning the water.

“I do not recall reading, hearing, or talking to anyone who would mention something like that (stagnant water deep underground).”

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The platform of Rideau is 26.5 metres deep — the deepest of any on the Confederation line.

Deep wells are usually the best sources for clean drinking water, he noted, “because the water in the well is the water that comes through the soil either from precipitation or from a nearby river or stream. Going through the soil, if the path is longer, the water gets cleaner.”

Soil “is basically functioning as a natural filter,” he said.

There are places where natural minerals in the ground mix with water and create the type of water used in spas, Simonovic said. Banff has hot springs with natural sulphur, for instance. But he said he would be “highly suspicious” about the chance that this could happen at Rideau.

“I think that in the urban area there must be some kind of connection with a drainage system” or buried waste.

The normal construction protocol would call for a waterproof exterior on the tunnel “and pretty good drainage around the tunnel is also done to divert water.”

A rotten egg smell is sometimes caused by hydrogen sulphide gas, though this has not been confirmed here by the city. This can come from a natural gas field, where it is called sour gas, and also from rotting organic material. Hydrogen sulphide is heavier than air and tends to collect in underground spaces.

Allan Hubley, who chairs the transit commission, announced Thursday afternoon that tests showed there is no danger from the air quality.

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However, riders are still unhappy with what some call an overpowering stench.

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This week a local historian has raised another possibility: What if an ancient drainage ditch — which ran very close to the modern Rideau station — is releasing the smell of ancient waste?

Andrew King traced the course of the ByWash — a ditch, and later an official sewer, winding generally north through the ByWard Market area. An old Ottawa Citizen story called it a “fetid, beer-coloured ditch” that was suspected of spreading cholera. It was covered over to form a sewer in 1872, King said.

“It had dead animals and sewage and swamp water,” King said. Local meat packers threw carcasses into it.

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King is the author of “So maybe there’s a leftover 1870s sewer that’s full of crap and… it’s leaching” and contaminating the ground near the station.King is the author of Ottawa Rewind: A Book of Curios and Mysteries

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