Numbat conservationists in Western Australia are appealing against an Environmental Protection Authority decision not to assess a proposal to build a large rubbish tip just 6km from the Dryandra woodlands.

The area is home to one of only two populations of the endangered marsupial to have survived colonisation.

The proposed 65-hectare waste disposal site is a consolidation of 11 rubbish tips from seven local government areas and is expected to bring in 5,000 tonnes of rubbish a year.

But conservationists say the feral animals attracted by the tip – namely cats and foxes – would have a devastating impact on native animals in nearby Dryandra, especially the West Australian state emblem, the numbat.

That’s of particular concern to a group of four men who call themselves the Numbat Task Force.

Once a fortnight, the men pile into two cars, reset their odometers and head into Dryandra woodland, 170km south east of Perth, driving at what the group’s unofficial founder, Sean van Alphen, described as “numbat speed” – about 10km an hour.

Talking over CB radios, the convoy slows down when they reach a likely patch of vegetation and scan for the tiny marsupials. Spotting a numbat is always worth the hours in the car.

“Your next numbat is always the best,” the Task Force’s newest member, Robert MacLean, told Guardian Australia.

MacLean and van Alphen give the same answer when asked why they devote hours of their spare time to searching for numbats, carefully cataloguing and photographing every one they find and posting the results on their Facebook page.

“Have you seen a numbat in the wild?” MacLean asks. “As soon as you do you will be doing the same thing. It’s a bit of an addiction.”

For the uninitiated, he explains that, “Numbats are like meerkats but better.”

“You get runners and sitters. Runners just keep on running and that’s all you see, then you get a little sitter and it’s always special because you get to spend a bit of time with them. It’s the sitters that make you the addict.”

The task force know the area so well that they have named popular numbat hangouts, as well as most of the numbats themselves.

“We have got the Sheriff, because there’s a little place in Dryandra that we call log city so we have got the Sheriff of Log City, and we can recognise her by sight,” MacLean said.

None of the men are conservationists by trade. MacLean drives a meat truck. Van Alphen works for an airline. John Lawson, the only one of the four to live locally, is caretaker of the Dryandra Woodland Village accommodation site.

But they have kept detailed records since 1999, and what those records show isn’t good.

A sharp decline in the numbat population last decade means days spent driving without success far outweigh the good days. In 2010 they didn’t see a single numbat. So far this year they have had six sightings, but MacLean says four of those were of the same numbat.

When Van Alphen started visiting Dryandra in 1992, there were 11.3 numbats per 100km. Last year, the Department of Parks and Wildlife survey found just 0.27 numbats per 100km – or one every 400km. The population has shrunk from 800 to just 50.

Van Alphen said feral cats caused the population crash. With the numbers at such a critical level, anything that attracts more cats to the area – like the proposed rubbish tip – could have a devastating effect.

“You could lose 10 of these animals on a bad day,” Van Alphen said. “I think that if something is not down very quickly we are not going to have any numbats left in Dryandra.”

Numbats once existed across Australia but were wiped out everywhere bar Dryandra and Perup, which lies 260km south. They are slowly being reintroduced to other areas but Dryandra, as a remnant population, is as valuable as it is vulnerable.

Van Alphen said the risk of increased cat predation from the proposed waste disposal centre, which is just 6km from the woodland, was too high.

Rubbish tips are known attractors of feral cats, who feed on rodents in the rubbish as well as the rubbish itself. A 2005 University of Sydney study described them as “biological attraction points around which free-living cats congregate in high densities.”

The study said the abundance of food made it difficult to conduct population control as cats, fussy about poison at the best of times, passed up baits for other options.

Van Alphen said he was concerned that even the much-touted new Eradicat baits, which have had success in sparser areas of the Wheatbelt during the hungry dry months, would not be as effective in an area so rich in live food.

And cats aren’t the only problem. Black rats, previously unrecorded in Dryandra woodland, could be brought in along with rubbish from other tips. Ravens, which mob native animals, are also expected to come.

The impact on native animals like numbats and woolies, which have recently been re-listed as endangered, was the key concern raised in public submissions to the development proposal. The Shire of Cuballing has jurisdiction over the proposal. In a meeting on 19 March, it said 56 of the 70 submissions it received raised concerns or objections to the proposal. Just five showed support.

Cuballing’s shire president, Mark Conley, said the council has requested further information from the Great Southern Regional Waste Group about how it proposes to manage environmental risks like feral animals and is yet to vote on the proposal.

Conley said they were unlikely to receive that information until May.

“We are very concerned about the numbat habitat; we have got to get more information about what the impact will be,” he said. “However something that’s overlooked by some people concerned about this is we will be closing two tips that are closer to Dryandra than the proposed waste site.”

An EPA notice published last week said the environmental impact of the proposed tip was “not so significant as to require assessment”. The Numbat Task Force and Greens MP Lynn MacLaren are both appealing against that decision.

“It is very surprising that the Environmental Protection Authority did not reject, or at least properly assess this tip proposal, which will increase rodent numbers and thus the number of feral predators, especially cats, in Dryandra, and Australian ravens, which prey on numbats,” MacLaren said.

MacLean urged the council to consider moving the waste centre, even if the EPA rejects the appeals.

“If we’re wrong about the impact of the tip, there’s no harm done,” he said. But if they are wrong, and the numbats go, it’s a massive price to pay.”