Forensic officers are excavating wetlands north-west of Hobart in the hope of finding Miss Butterworth’s remains.

The 20-year-old typist and Miss Tasmania Quest entrant vanished from Claremont in August, 1969 and police believe  she was murdered.

Investigators say there is credible evidence Miss Butterworth’s killer dumped her body alongside the Lyell Highway, between Granton and New Norfolk.

Officers have levelled a disused, overgrown car park near where they believe her body lies, and have started clearing thick vegetation surrounding the area.

But investigators yesterday received information the area beyond the car park, towards the River Derwent, was once an illegal tip.

Detective Senior Constable Cary Millhouse said his immediate priority was now to get rid of all the landfill.

‘‘Once we dig all that up, we’ll find a whole heap of household rubbish,’’ he said.

‘‘It’s not complicated, but it just extends the time and cost.’’

Senior Constable Millhouse said a larger excavator had been brought on site to help clear away the trash, while a bigger digger had also joined the police fleet.

He could not say how long the extra work would take.

The excavation was originally expected to take at least two to three weeks.

Despite the complication, Senior Constable Millhouse is confident it will not stop police finding Miss Butterworth’s remains or personal effects.

‘‘We don’t believe she is anywhere near any of that rubbish,’’ he said.

‘‘If she’s in there, she’s going to be in a site that’s lower or deeper or wider.’’

He said Miss Butterworth’s family and loved ones were being kept informed of developments at the site.