Compare waste quantities only after matching the reporting boundaries

Anil Khatwani

Oct 13

3 min read

Fictional waste-generated comparison, in metric tonnes. Year 1: sites A and B total 160. Year 2: the same sites total 156, plus 44 from newly opened Site C, giving a full total of 200. The full reported total increases 25%; the same two sites decrease 2.5%. The difference in site coverage is explicit; the figures alone do not establish performance or cause.

Before describing a change in waste as better or worse performance, check what each number includes. A new site, a shorter period or a different moisture content can change the reported weight. The percentage calculation may be correct while the explanation overstates what the data shows.

For sustainability and finance teams, a useful comparison starts with a written specification of the two quantities. Keep the full reported totals visible, then explain any additional like-for-like analysis.

Write the comparison specification

Record these seven attributes for each period before calculating a change:

Sites and entities: which operations are included, newly added, closed or missing.
Time covered: start and end dates, missing months and any partial-year operation.
Activity covered: the processes included and whether the figure concerns own operations or another part of the value chain.
Waste scope: which streams are included and whether their definitions have changed.
Quantity being compared: waste generated, sent for recovery or sent for disposal; keep the chosen quantity consistent.
Measurement basis: units, wet or dry basis, weighing or estimation method, and any conversion assumptions.
Data version: the approved dataset, corrections, unresolved gaps and source references.

These are practical review fields, not a prescribed GRI template. GRI 306-3 addresses waste-generation totals and the context needed to understand their compilation. Its guidance distinguishes direct measurements from modelling. GRI 306: Waste 2020, Disclosure 306-3

Separate a new site from the matched-site change

Consider a fictional business with complete twelve-month records. In Year 1, its only operating sites are A and B. Site C opens at the start of Year 2. Assume the same waste scope and measurement method throughout; all quantities below are metric tonnes of waste generated.

Site A: 100 tonnes in Year 1; 96 in Year 2.
Site B: 60 tonnes in Year 1; 60 in Year 2.
Site C: not operating in Year 1; 44 tonnes in Year 2.

The full reported total rises from 160 to 200 tonnes. The change is (200 − 160) ÷ 160 × 100 = 25%.

For sites A and B together, the total falls from 160 to 156 tonnes. Their change is (156 − 160) ÷ 160 × 100 = −2.5%. The bridge between the reported totals is 160 − 4 + 44 = 200 tonnes.

A clear description is: “Total waste generated increased by 40 tonnes, including 44 tonnes from newly opened Site C. The two continuing sites generated 4 tonnes less than in Year 1.” Both views matter. Reporting only the matched-site decrease would hide the larger total.

The 4-tonne decrease does not establish its cause. Check production, product mix, downtime and process changes before attributing it to a waste-reduction initiative. Keep any evidence for that explanation separate from the arithmetic.

If C had operated in Year 1 but its records were missing, the comparison would have a data-coverage gap. Do not label that situation as a newly opened site or silently treat its missing quantity as zero.

Check what the weight includes

In a separate fictional example, comparable measurements of a sludge stream show 10 tonnes wet weight at 30% dry solids in Year 1, and 8 tonnes at 40% dry solids in Year 2. Assume the percentages are representative mass fractions measured consistently.

Year 1 dry solids: 10 × 0.30 = 3 tonnes.
Year 2 dry solids: 8 × 0.40 = 3.2 tonnes.
Wet weight decreases by 20%; dry-solids mass increases by approximately 6.7%.

The lower wet weight alone cannot establish a reduction in dry-solids mass. Record the sampling basis and uncertainty before drawing an operational conclusion. This calculation is supplementary analysis, not a direction to replace the measurement basis required for the applicable disclosure.

Explain changes that cannot be matched

Where the method or coverage has changed, assess whether a supported restatement is appropriate. Keep the original figure, revised figure, reason and calculation trail identifiable. GRI 2-4 requires reporting restatements and explaining their reasons and effects; its guidance addresses criteria for significant changes. GRI 2: General Disclosures 2021, Disclosure 2-4

If historical data cannot be reconstructed, explain the break and limit the conclusion. GRI 1’s Comparability guidance addresses consistent methods, historical restatements and explanations where restatements are absent. A matched-site calculation does not remove the need to explain the full reporting scope. GRI 1: Foundation 2021, Comparability principle

Prepare the reporting explanation

Nitium’s sustainability and GRI reporting support helps organise disclosure mapping, draft content and information gaps within an agreed scope. Discuss your reporting needs with the intended disclosure, reporting periods and a non-confidential description of the comparison issue.

Sources checked 13 October 2026. The examples are fictional. This guide supports reporting preparation; it is not a complete GRI disclosure, legal opinion, certification or independent assurance conclusion.