A POWER station to be built on top of Town Hall to reduce the building’s greenhouse emissions could increase dangerous pollutants, a secret feasibility study has revealed.

The leaked confidential ­report by consultants AECOM outlined five possible designs for a trigeneration power plant using renewable gas-fired ­engines to generate electricity and supply hot and chilled water to Town Hall and the adjoining Town Hall House.

The scheme, costing up to $22 million, will decrease the City of Sydney’s reliance on coal-fired electricity and ­reduce the council’s carbon emissions, which equal 1500 cars driving for a year.

But air modelling carried out by AECOM on three of the options found they all ­increased the concentration of airborne nitrogen dioxide, carbon dioxide, sulphur dioxide and particulates present around Town Hall’s precinct.

Nitrogen dioxide can ­increase the likelihood of ­respiratory problems, inflame the lungs and reduce immunity to lung infections.

The design selected by the City of Sydney, a two-stage ­option labelled 5a and 5b, would increase pollution levels, but would fall within NSW Environmental Protection Authority guidelines.

The AECOM report states: “All maximum one-hour pollutant concentrations were predicted to be higher for ­design Option 5.”

media_camera Sydney’s Town Hall is a popular tourist destination during Christmas

The council has issued a tender to build and maintain the plant, weighing up to 251 tonnes and including two 650kw gas turbines, on Town Hall’s roof. Construction is due to begin in February.

Dr John Collier, principal of St Andrew’s School, which has children aged from kindergarten to Year 12, said he was not aware of the plans when contacted. “I will have my people look at it,” he said.

The AECOM report said the “air quality impacts” from the project could be mitigated by using selective catalytic ­reduction, a method that converts nitrogen dioxide into safer substances.

City of Sydney’s expression of interest documents demand that the plant comply with EPA standards.

“Trigeneration is a well-­established technology already operating in many properties across Sydney,” a spokesman said, adding Qantas, Google, 1 Blight St, Stockland’s headquarters at 133 Castlereagh St, Origin Energy’s headquarters at 20 Bond St, the Rooty Hill RSL and other local governments all use trigeneration.

Waverley Council is investigating the installation of the system at Bondi Junction.

Despite the assurances, there are still concerns about the health impact of raised pollution from the Town Hall plant, which the council plans to have operating in 2016.

Councillor Edward Mandla refused to comment on any of the AECOM report’s details, citing its confidential status. But he is among those who have demanded council CEO Monica Barone release the document so the potential risks can be made public.

A review is under way that could lead to parts of it being published.

“We’re right next door to a school, and during business hours we are proposing to ­release nitrogen dioxide, carbon monoxide and sulphur ­dioxide at levels that may ­exceed EPA requirements,” Cr Mandla said.

He added that “to suggest that is nobody’s business but our own is bizarre”.