A ten-year kerbside audit plan for twelve Victorian councils
Prepared by Rawtec for the Grampians Central West Waste Resource Recovery Group. Written by Jarvis Webb and Mark Rawson. Final version 18 December 2018.
Summary published
Twelve councils, all auditing their bins differently, at different times, to different sample sizes. The results could not be compared with each other or with the previous round.
Rawtec was asked to design one approach they could all use: what to sample, how often, at what confidence level, and what it would cost.
The answer is a ten-year schedule of 2,150 bin audits across 900 properties, with the bigger councils audited more often than the small ones.
Councils covered
Bin audits over the ten-year schedule
Confidence level the sample sizes are built to
Estimated cost of year one, all twelve councils
What the plan sets out
Audit frequency scaled to size
Ballarat City is audited every year, at 125 properties across five localities. Golden Plains and Moorabool every two years, at 100 properties across three localities. The remaining nine councils every four years, at 50 to 75 properties across two localities.
Sample size tied to population, with the uncertainty stated
Under 10,000 people: 50 properties, giving 10% to 12.5% uncertainty at 90% confidence. 10,000 to 20,000: 75 properties, 7.5% to 10%. 20,000 to 50,000: 100 properties. Over 50,000: 125 properties, 5% to 7.5%. The report puts the uncertainty in the table rather than leaving it implied.
What the region actually services
110,536 properties on general waste collection, 106,793 on recycling and 37,535 on organics. Across the region there are 48 localities with more than 200 people, from 36 small towns to three larger cities.
Transfer stations sorted by throughput
39 facilities handle under 100 tonnes a year, eight handle 200 to 500, four handle 500 to 1,000, seven handle 1,000 to 5,000 and one handles 5,000 to 10,000. The seven largest get audited every five years, the mid-sized ones once and then as needed, and the smallest only when there is a reason.
Costed, with the uncertainty declared
Year one covers all twelve councils, six weeks of physical audit time, $103,000 excluding GST. Year two covers three councils at $41,500. Year three covers one at $21,500. All to plus or minus 20%.
Timing standardised on purpose
September to November every year, so seasonality is consistent even though Sustainability Victoria recommends autumn. The plan says to account for the timing in the analysis rather than pretending it does not matter.
The awkward bits the plan names
The Sustainability Victoria guidelines dated from 2009 and gave no guidance on regional factors, alternative service models or the sorting technology in modern recovery facilities.
Sample sizes were chosen to balance 90% confidence against what a regional council can practically afford. The report states the trade-off instead of burying it.
Councils where organics is opt-in need a reliable subscriber list to sample representatively, and splitting the audit pushes the cost up.
Facilities under 500 tonnes a year may not see enough loads across a two-day audit window for the result to be useful.
Related reports
Audit methodology and regional strategy work.
The full study includes the year-by-year schedule, the locality selection and the 20 material categories.
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