Leading American health experts say they do not believe the Nantygwyddon tip in south Wales is to blame for cancer and birth defects.
Nantygwyddon was closed after years of complaints
In their final report, the scientists conclude that short-term health problems such as breathing and skin and eye irritation were probably caused by gases released from the Rhondda landfill site.
But they say evidence does not support a link with more serious complaints, although they have asked for continued monitoring of three medical conditions.
Local protestors, who staged a long and ultimately successful campaign to close Nantygwyddon, are unhappy with the findings, and want a more thorough investigation.
The team from the Atlanta-based Agency For Toxic Substances And Disease Registry (ATSDR) visited the area last November.
ATSDR is widely regarded as the world's leading agency on public health and the environment, and it was called in by Welsh assembly members.
People living near the tip, above the village of Gelli, had complained for years about its impact on the environment and on their health.
It became a major political issue, and was believed to have contributed to shock defeats for the Labour Party in assembly and local council elections four years ago.
AM Leighton Andrews wants the recommendations accepted
Rhondda Cynon Taff Council agreed to stop dumping household waste at Nantygwyddon in December 2001, shortly after an assembly-commissioned report criticised the site and recommended its closure.
The Americans' report calls for monitoring of non-hodgkins lymphoma, sarcoidosis and gastoschsis.
Non-hodgkins lymphoma is a blood disease similar to cancer, sarcoidosis causes growths to occur on body organs, and gastroschisis is a birth defect involving the stomach.
The report also wants an all-Wales team to investigate a possible link between illness and the release of poisonous fumes.
Local Plaid Cymru councillor Syd Morgan, who is also the authority's cabinet member for waste management said: "It's no surprise that the report doesn't make a conclusive link between the tip and serious illnesses.
"This is because ATSDR was only commissioned by the assembly government to review previously published reports. Some of these reports are five years old and much of the relevant data was not available at the time to the scientists.
"What is welcome, is the recommendation to the local health board to carry out further tests on human health. The council itself will assist in that.
"We're sampling the tip material, which has never been done before, and we will be delighted to pass that information on to the local health board and residents."
Mr Morgan said the council was also in consultation with 12,000 local people on a remediation scheme for the site.
Rhondda Labour assembly member Leighton Andrews said he would urge ministers to implement its recommendations quickly.
"There are important lessons to be learned from this experience," he said.
"The assembly will need to share the experiences with other agencies around the UK. There should be no more Nantygwyddons."
Environment Minister Carwyn Jones and Health Minister Jane Hutt both said the report had some important recommendations which needed to be discussed.
The findings will be debated by the assembly's health committee this autumn.