The former senior City of Montreal engineer who admits he took $600,000 in bribes over the years says corruption and collusion on public construction contracts was well known in his department, but it wasn't his job to report it.

Gilles Surprenant took the witness stand for the fourth day Wednesday at Quebec's corruption inquiry, where he has already testified to accepting lavish kickbacks from construction bosses who rigged the bids on city contracts, in exchange for his help in seeing the contracts through.

Surprenant's testimony on Wednesday described, for the first time, exactly how he helped funnel city money to construction companies.

Suprenant testified that he didn't think it was his role to contact police about the bid-rigging. (Charbonneau commission)

Standing in front of an engineering plan of Montreal's Queen Mary Road, the former bureaucrat explained a 2006 construction project he had designed. He had calculated workers would need to remove a layer of rock located five metres below street level, but he said the construction company, the on-site public works engineer and the head of the on-site engineering department had a different view. They claimed the rock started at street level and went down a full five metres, which would make the project more expensive.

Surprenant said he re-did his calculations, only to conclude the fix was in.

"So they excavated air? And billed for it?" inquiry lawyer Denis Gallant asked.

"Yes. As I told you, it was worth about $175,000," Surprenant replied.

Spoke openly about it

The former city engineer, who was at one time in charge of planning and budgeting for public works projects, said he took bribes on city contracts whether he went in to inflate prices or not.

Surprenant has testified he received about $600,000 in kickbacks from construction bosses over a 20-year period. While going through individual contracts at the inquiry over the last two days, tallying up the amounts he got for each of the 90 or so projects, the amount appears to be higher than that.

In most of those cases, the bribes ranged from a few thousand dollars to as much as $22,000. The engineer, who worked for the city from 1976 until his retirement in 2009, was also showered with gifts such as tropical golfing holidays, hockey tickets, wine and fancy holiday dinners.

Surprenant told the commission on Wednesday that he acted as an insurance policy for the construction entrepreneurs.

He said the inflated prices were well known in his office — and everyone knew, from his own bosses right down to low-level administrative assistants.

"I spoke openly about it to my supervisors. [But] I don't think it was my role, as a simple functionary, to call the police about it," Surprenant said.

30% cost inflation

The ex-bureaucrat already testified that his role was to manipulate a computer system that evaluated the cost of projects to ensure the price of contracts met what entrepreneurs wanted to pay.

Then, by about 2004, price estimates for city contracts were being automatically inflated because they were based on the cost of previous work.

Because the higher prices had become the norm, Surprenant said he stayed on top of it to ensure tenders weren't reverted to what the real value of the contracts should have been, but he rarely had to act to tack on the typical 30 per cent inflation.

He still took a cut from those contracts however, he said.

Surprenant insists he wasn't the mastermind of the alleged scheme, but merely a participant. Earlier in his testimony, the retired engineer said he felt pressured by the construction bosses to take part.

The amounts he received on each project weren't fixed, Surprenant told the commission, and ranged from between 0.5 and 1 per cent.

Surprenant has testified that a handful of city employees partook in the scheme, and they got money and gifts in exchange for helping fixed contracts go through.

With files from The Canadian Press