Questions are being asked after the discovery of asbestos-laden soil near Brisbane’s Leslie Harrison Dam.

Authorities investigating an unauthorised motocross track at the edge of the dam discovered it was made from illegally dumped soil, which later tests revealed contained asbestos.

A fleet of trucks turned up on Tuesday this week to remove a massive 606 tonnes of soil in a process that water authority Seqwater describes as “low risk”.

Even so, contractors will remove a further 100 millimetres of soil from beneath the surface to get rid of contamination that has been compacted into the ground.

Locals say they were left in the dark.

The local council informed Seqwater about the illegal dumping on August 12, but Seqwater says it took some time to confirm the ownership of the land in question.

It turned out that it belongs to the water authority.

“These dam lands and catchment were last surveyed back in the 1960s — there was certainly debate about that,” Seqwater spokesperson Mike Foster told the reporters.

“We got survey work completed in September that effectively advised us and confirmed for ourselves as well as the landowner that it was Seqwater [land].”

This meant that local residents were not warned about the asbestos-contaminated soil until trucks turned up to remove it.

Locals have accused the authority of allow the dam site to become degraded, and alleged that removal workers were not wearing hazardous protection equipment.

Seqwater says residents will receive more information in a letter to be delivered on Wednesday.