Each bin is emptied into a bag which is then weighed - keen third-form volunteer Samuel Newland solemnly intones the numbers for Yates to record - before being packed into a van and sent to the Waitakere Transfer Station for sorting.
The college has been funded by the Ministry for the Environment to set up what Yates calls "a state-of-the-art recycling system" and as part of the job, she is conducting an end-of-year audit of a week's waste.
Yates is co-director (with Bruce Middleton) of Waste Not Consulting, an organisation that describes waste reduction as "our core business, our speciality and our passion". Its clients include more than two dozen large corporates from Air New Zealand to Watercare, twice that many local authorities and a handful of government departments as well.
At Western Springs, part of the project involves setting up attractive bin stations with colourful, clean and bright signage.
"We decided to go all out on having it look good," explains Yates, "because if it looks good, the students will be more likely to work with it."
The food scraps are consigned to an industrial-size worm farm called a Tat-G, which produces rich vermicast for the college gardens that are also part of the project.
"The whole point of the process," Yates explains, "is to see what proportion of the waste being sent to landfill could actually have been composted or recycled and to develop strategies to make sure it is.
" Otherwise nobody actually knows what's in a bin."
Two days later, Yates and a trio of contract co-workers - Lynn Green, David Kannu and Robert Kornfeld - know precisely what is in those bags they weighed. They're picking through it, item by item, and sorting it according to material type.
For those of us who regard something chucked in the bin as both out of sight and out of mind, it might seem like a pretty unsavoury task. Certainly the Herald photographer turns a bit pale when the bottom of one bin turns out to be home to a large population of plump maggots. But to judge by the expressions on their faces, Yates and her co-workers might as well be picking strawberries.
But it is not a straightforward job. Sometimes they find themselves staring at an item, trying to determine what it's made of - few end up in the too-hard basket - and judgment calls have to be made for objects made of multiple materials. Once the task is complete, the reweighed bags will tell them precisely how accurate the sorting at source has been.
Yates seems the ideal person to answer my perennial question about the way I manage my domestic waste: doesn't it need to be done on an industrial scale to be effective? As individuals, we are encouraged to be terrified about putting the right piece of rubbish in the right bin, but it seems little more than a symbolic gesture when compared to the contribution of heavy industry and rampant consumerism to rendering the planet uninhabitable.
Her answer is a challenge to everyone to create a working composting system or worm farm.
"Over half of domestic rubbish is green waste and food waste," she says, explaining that the putrescible waste - the stuff that rots - is the source of the "very potent" methane emissions from landfills.
"So if you process your own food waste, you don't only reduce your rubbish by half, you reduce the harm caused by your rubbish - and you create a product that you can put on your garden."
For more information go to
www.wastenot.co.nz
