The New South Wales Government has plans to build pollution ventilation shafts in Sydney's north shore and northern beaches areas, as part of the multi-billion-dollar Western Harbour Tunnel and Beaches Link project.

Shafts between 20 and 35 metres high will be constructed near schools and homes, to disperse the fumes from thousands of trucks and cars expected to access the new underground toll-road.

A planning document marked "cabinet-in-confidence", seen by ABC News and Fairfax, pinpoints the locations of the shafts and maps the air quality impact zones surrounding them.

It also red-flags political issues that could anger local residents and "impose significant project risk".

Map showing area a pollution stack may be built in Seaforth, based on 'cabinet-in-confidence' documents. ( ABC News )

Seaforth Oval stack KU Bligh Park Preschool

Where are the stacks going?

Engineering maps show a 500-metre radius around homes, schools, and parklands where dispersed pollution mixes with air, all marked as "sensitive receptors".

The review also warns Cabinet members that "a major risk to the project is perceived air quality impacts".

In Balgowlah, where the shaft is located at the bottom of a valley, the document identifies a risk of "plume downwash" — where pollution is drawn close to the ground, potentially entering houses and buildings.

Map showing area a pollution stack may be built in Balgowlah, based on 'cabinet-in-confidence' documents. ( ABC News )

Balgowlah Golf Course stack Seaforth Childcare

Seaforth Childcare Seaforth Public School

Seaforth Public School Northern Beaches Secondary college

Northern Beaches Secondary college Northside Preschool

Northside Preschool Balgolwlah Kinder Haven

In North Sydney, "existing residential buildings" are identified as a "potentially significant constraint" around shafts. At other locations on the route the document recommends further air-quality modelling to identify pollution concentrations in neighbourhoods.

Risks revealed in report

The risks of breaching air safety is also explored in a chapter of the report.

The southern shaft location — near Wenona School — is identified as problematic. Dispersal of pollution is hindered by tall apartment buildings less than 20 metres away.

Background pollution in North Sydney is also elevated by nearby freeways, and the report says the project may cause "cumulative air quality impacts".

Map showing area three pollution stacks may be built in North Sydney, based on 'cabinet-in-confidence' documents. ( ABC News )

North Sydney stacks Wenona School

Wenona School North Sydney Boys High School

North Sydney Boys High School Marist College North Shore

Marist College North Shore St Mary's Primary School

St Mary's Primary School Cammeraygal High Senior Campus*

Cammeraygal High Senior Campus* Crows Nest Kindergarten

Crows Nest Kindergarten Anzac Park Public School

Anzac Park Public School Monte Sant Angelo Mercy College

Monte Sant Angelo Mercy College Cammeray Public School

Cammeray Public School KU Cammeray Preschool

KU Cammeray Preschool Ku Grandstand Preschool *Originally published as Crows Nest School

A data set shows unsafe levels of PM2.5 and PM10 recorded in nearby monitoring stations.

The microscopic particles are found in exhaust fumes, and were declared carcinogen by the World Health Organisation in 2013.

The report says authorities should consider alternative location for the southern stack, away from residents and schools.

Map showing area a pollution stack may be built in Gore Hill, based on 'cabinet-in-confidence' documents. ( ABC News )

Gore Hill stack Butterflies Early Learning Childcare Centre

Butterflies Early Learning Childcare Centre Puddleducks Early Learning Centre

Additional wind modelling is also recommended. But major changes to the route and scope of works are unlikely.

A final business case — the "Base Plan" and strategy for final approval is also contained in the report.

The key recommendation is that the Planning Minister could declare the Base Plan as "critical state significant infrastructure", limiting objectors who oppose the project, and fast-tracking environmental approvals.

Melinda Pavey, the NSW Roads Minister, was approached for comment.

A spokesperson declined to answer specific questions, but said exhaust outlet locations were not finalised, as "geotechnical work is ongoing to determine the preferred route".