Tracer testing to determine the groundwater transport parameters at the proposed waste facility at Kirwan Road has commenced, with dye released into bores at the site on Friday morning, July 19.
Shire of Esperance chief executive officer Matthew Scott and councillors Lara McIntyre, Basil Parker and John Parsons visited the proposed landfill site with Rockwater principal hydrogeologist Dr Peter de Broekert.
Esperance Merivale Tip Action Group members were also invited to attend, with Dr de Broekert providing a breakdown of the tracer test and recent core samples taken from the site.
The testing is part of a 41-step process to satisfy the elements of the Environment Protection Authority's Public Environmental Review of the proposal.
Attendees were taken to view the recent core samples retrieved from the location of the 'possible paleochannel', as identified in the latest geophysical assessment by consultants ASST.
The tests sought to identify the presence of karst-like landscape features that could form channels for landfill leachate.
Dr de Broekert said that, based on the core sample, which was 100 metres deep, he did not not see any evidence of a paleochannel in the area.
"These are not paleochannel materials," he said.
"I cannot see evidence of any paleochannel here."
While discussing the movement of groundwater at the site, EMTAG member David Johnson discussed the group's own dye test from February 2018, which saw the group release 20 litres of red vegetable dye into a sinkhole on the property adjacent to the tip site.
After 24 hours and 18 millimetres worth of rainfall, the dye was discovered in a spring 1.84 kilometres from the original test site.
Dr de Broekert confirmed he had not seen any features on the tip site that indicated that a tracer test at the proposed tip site would yield the same results.
"I haven't seen any features like that here," he said.
"In all of the cores we have drilled here, upwards of 40, I haven't found anything like what you're talking about here.
"We've done a lot of work on this site now.
"If a void of that nature is there, it's not in the body of work that has been done.
"It's about the balance of probability, you can never be sure of anything in the geological environment."
From 28 metres, Dr de Broekert said there was more than 40 metres of clay with very low permeability and weathered bedrock from about 70 metres.
In talks with EMTAG members, Shire of Esperance chief executive officer Matthew Scott said the council was committed to fulfilling the requirements of the Public Environmental Review.
"With our licenses, we need to show [the EPA] how we would mitigate an escape, what sort of methods and strategies we would have in place.
"The EPA require evidence that we can mitigate a potential escape.
"Council advocated for the PER [Public Environmental Review] because it is adamant that they don't want an environmental issue either.
"That's why we're undertaking multiple tests, so that we have multiple lines of evidence."
Later, attendees were taken to one of the two nests, each of which have three monitoring bores, to begin the tracer testing.
The testing used non-toxic dye to determine the amount of time it would take for water to travel at the site and leachate if a liner failure were to occur.
The test is also designed to prove, disprove or calibrate the theory that it would take more than 41 years for a contaminant to travel the 1.6 kilometres to the site's southern boundary, as calculated by the pump testing at the site in September 2018.
Based on the evidence gathered to date, Dr de Broekert said the data indicated that it would take at least several months for the dye to be picked up in one of the monitoring bores.
"This site was chosen because it is where the potential paleochannel was said to be," he said.
"The other is adjacent to the proposed landfill site, in the footprint.
"This will give us a good indication of how connected those underground pores are over this distance."
Following the tests, EMTAG chair Mark Biven extended thanks to the Shire of Esperance for inviting members to the site.
"On behalf of EMTAG, I would like to thank the shire and Peter [Dr de Broekert] for inviting us and allowing an open and transparent process," Mr Biven said.
"This is a long and costly process but our aim is to protect the land of local residents, the RAMSAR wetlands and this environment for the sake of future generations.
"That's at the forefront of our push."
It is understood the monitoring bores will be checked for the first time on Tuesday, July 23.