The Environment Agency has demanded that a foul-smelling building site must improve after complaints.
Locals say construction on the former gasworks site in Brent Road, Southall, is causing health problems and forcing them to stay indoors during a heatwave.
To make the site habitable potential contaminants such as benzine and asbestos are cleaned from the soil.
Berkeley Group, which is behind the project, said pollution levels were well below "unacceptable levels".
A spokeswoman said the odours were not harmful to health.
But residents told the Local Democracy Reporting Service the "noxious tarry, petrol-y smell" was making their lives a misery.
David Marsden and his wife, who live nearby, both use inhalers for chest complaints, and said their four-year-old son had ended up in hospital three times because of his asthma.
Mr Marsden said: "I've had to take loads of time off this year with chest infections which I don't normally get.
"Something like this also causes a lot of stress and anxiety and you don't always realise the impact that it is having until later."
Angela Fonso said the smell constituted an "unacceptable level of pollution".
Her children, aged nine and 10, have to cover their noses whenever they leave, and the family have to sit indoors with the windows shut, she said.
"It makes me realise what it must have been like for people living in the industrial revolution," Ms Fonso said.
The Environment Agency said: "Whilst it is not possible to prevent all smells, we required the site to improve their odour controls, and they have now implemented a more extensive odour control regime."
Work will be finished on the project by September and will provide 480 homes and 40 acres of public open space, the Berkeley Group said.
Berkeley Group said it had installed 10 sensors around the site, five of which monitor the level of odour at all times.