THE area's three biggest odour emitters are under scrutiny to ensure smells don't linger into nearby neighbourhoods.
At a community forum last week odour expert Terry Schultz unveiled recent findings.
Eastern Creek Landfill, the nearby Global Renewables UR3R facility and SITA at Kemps Creek will have their licences varied after they were identified as the main contributors.
Mr Schultz and the odour unit team conducted 30,000 "sniffs" between September 3 and 11 in the morning, afternoon and evenings at nine waste and recycling facilities.
They cleared six facilities.
The other three sites must start odour reduction programs, engage an expert to review their operations, conduct surveys on and off their premises from October and take part in an odour unit study in six months.
"We are in the early phases of fixing the problem," EPA chairman Barry Buffier said. "There's not one site that's sole cause but we have a better handle on the situation."
The EPA will investigate further after residents expressed concern about Enviroguard Erskine Park.
"While the odour expert company did not detect noticeable smells, the EPA will work with residents to resolve noise and out-of-hour truck movements," a spokeswoman said.
St Clair resident Phil Vella believes the smell is coming mainly from Enviroguard.
"The smell is so bad you can't open the windows or front door," he said.
Penrith councillor Greg Davies congratulated the EPA and the waste companies on their efforts since August.
"What I'm annoyed about is that I wrote to you (the EPA) about this as mayor in 2003 and nothing was done," he said at the forum.
"What has been done in the last eight weeks should have been done back then."