An “ocean of rubbish” emerged last summer, and later a week-long fire saw tonnes of waste burned, emitting dangerous fumes and forcing nearby schools to close.
The Bolton House Road site is currently sealed off and subject to a closure notice.
The government said people should never enter due to the potential harm.
In March, the government said it would directly fund the clean-up, with the EA given more powers to enforce waste crime.
However, five months after it was announced, the dump is still there.
Following the publication of the test results, an EA spokesperson said: “Our scientists will carefully consider these findings alongside our own evidence.
“Illegal waste sites are created by criminals who dump untreated waste for profit with no regard for what they leave behind and how this may affect local communities or harm the environment.”
Giving a wider update on the Bickershaw site, the EA told the Local Democracy Reporting Service it had supported the local authority with the sampling of waste located on Bolton House Road as part of the wider response to the incident.
A spokesperson said the EA carried out regular odour monitoring at and around the site and have not detected any significant odour issues during inspections.
On the clean-up of the site, it said: “Defra officials are in regular contact with Wigan council and local residents to ensure the clean-up operation can move as quickly as possible with important steps to be taken before proceeding to clearing up the site.”
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