ONE of the Hunter’s most contaminated sites – the former Hamilton AGL Gasworks – is leaching carcinogenic and toxic materials, including cyanide, ammonia and lead, into groundwater and poses a risk to human health and the Hunter River, documents with the NSW Department of Planning show.

The Clyde Street site, which has been derelict for 30 years, was ‘‘a significant source of contamination that is migrating off site via groundwater towards residential areas and Styx Creek’’, reports say.

Even remediating the area poses environmental risks because of the extent and highly toxic nature of contaminated material, and the complex and highly technical nature of remediation processes.

NSW Planning Minister Rob Stokes is expected to take formal control of the assessment of planned remediation works more than four years after the NSW Environment Protection Authority declared it a significantly contaminated site with ‘‘highly toxic’’ materials that were ‘‘a risk to human health and the environment’’.

The 2011 declaration launched a process requiring Jemena to remediate the site or risk prosecution.

On September 15 the NSW Planning Assessment Commission recommended the 7 hectare former gasworks be declared a state significant area after Newcastle City Council expressed concerns about its capacity to assess the highly technical and complex remediation.

The former gasworks land was strategically significant because it was adjacent to the Woodville junction site which was the original Newcastle transport interchange site before the NSW Government settled on the Wickham interchange.

Remediation work, which Jemena hopes to start in late 2016 following assessment of the proposal, could include a process that has not been used in Australia before.

The Planning Assessment Commission found remediation ‘‘has the potential to be environmentally polluting given the highly toxic and carcinogenic contaminants on site’’.

‘‘The remediation project is highly complex and the location of the site in close proximity to residents adds to the complex nature of the project,’’ the commission found.

A report prepared for Jemena found the old gasworks site had a range of known carcinogens, potentially carcinogenic compounds and toxic compounds including benzene, polycyclic aromatic hydrocarbons (PAHs), total recoverable hydrocarbons (TRH), benzo(a)pyrene, cyanide, ammonia and lead.

More than 65,000 cubic metres of overburden to a depth of four metres below ground level was found to be contaminated.

‘‘The site is heavily contaminated and needs to be remediated to reduce the risk to human health and enable the site to be used for commercial and industrial purposes,’’ the report said.

A Jemena spokesperson said the company had been communicating with affected residents since June last year.

‘‘Remediation of contaminated sites is a highly regulated and independently monitored process, so Hamilton North residents can be assured the clean up of the Clyde Street site will proceed safely,’’ the spokesperson said.

‘‘We are fully committed to fully remediating the Clyde Street site to Environmental Protection Authority standards.’’