What we learned weighing every trailer for a year

Finding one: piece counts lie in spring

Inbound weight per pallet is not constant. Across twelve months it varied by a substantial margin, peaking in April and bottoming in a dry September. The pallets were not different; the water in them was.

This matters for reporting. A diversion rate calculated from piece counts will look stable across the year while the actual tonnage moving through the building swings considerably. Worse, the material most likely to end up in the disposal stream — soaked, mould-bloomed, split — is also the heaviest, so piece counting systematically understates the disposal fraction. That is a flattering error, which is exactly the kind worth being suspicious of.

We report by weight for this reason, and we would encourage anybody reading a supplier's diversion report to ask which basis it uses before reading anything else in it.

Finding two: more steel than the textbooks say

We had been using a published average for steel content per pallet. Weighing our own magnetically separated bales against the pallets that produced them put the real figure above that average. The likely explanation is repair history: a pallet that has been through several repair cycles carries the original fasteners plus every subsequent one, and the recovered pool skews toward repaired units.

We revised the constant upward on our carbon methodology page. It is one of the few revisions that made a number look better, and it is also one of the smallest in overall significance — but it was measured, so it went in.

Finding three: covered storage shows up in the data

Cores collected from customers with covered storage weigh consistently less per unit and grade consistently better than cores from open piles. We suspected this; the weighbridge quantified it. The difference is large enough that it is now the first thing we raise with any customer selling cores regularly.

The practical advice that came out of it is unglamorous: move the pile under an existing overhang, shorten the collection interval, or take a drop trailer. All three are cheap, and all three show up in what we can pay.

Why we publish this

Sustainability claims are worth what the underlying data can survive. We publish our constants, our method and our exclusions so that a customer's auditor can disagree with us specifically rather than generally. Two of those constants have been revised since first publication after customers' consultants made persuasive cases, and both revisions made our headline numbers smaller.

A methodology that never changes is probably not being checked by anybody. That is not a comfortable thing to publish and it is the most useful signal we can give.

Appendix: the data behind this

Every piece on this site closes with the slice of our operating record that bears on what it argues. The full record is published at /resources/operating-record.

Related reading