The evidence behind a defensible closure estimate

1. Start with the decision and the boundary

An estimate prepared to compare removal methods answers a different question from an estimate supporting a financial provision. State the purpose, asset boundary, end state, pricing date, execution window and exclusions before presenting the total. Otherwise, two apparently conflicting numbers may simply describe different work.

Begin with a physical inventory that can be reconciled to the scope. A platform, pipeline, well and onshore receiving facility can each introduce separate work packages. Include the interfaces: isolation, cleaning, temporary support, transport, waste acceptance, surveys and evidence required after execution. An exclusion needs both a reason and an identified destination; “by others” is incomplete unless someone owns that work in another package.

2. Connect quantities to a practicable method

A quantity multiplied by a rate is only useful when the method behind the rate remains feasible. Explain what must be true for the selected vessel, lifting sequence, cutting approach or waste route to work. Record whether quantities come from reconciled drawings, survey, inspection, contractor information or an assumption. Keep the source revision beside the input rather than in an unstructured attachment folder.

Consider a module with an uncertain weight. The important question is not merely how much steel to add to the quantity. It is whether the uncertainty could change the lifting arrangement, crane selection, offshore sequence or transport configuration. That is a method uncertainty with several cost consequences. Treating it as a small quantity allowance can hide the actual decision.

3. Make uncertainty reviewable

Separate missing scope, variable quantities, uncertain productivity, market rates and discrete events. Record how each has been treated so that the same exposure is not counted in a duration allowance, a rate premium and contingency. A range should have an explanation of what changes across it. A confidence label unsupported by a defined method does not make the estimate more reliable.

For financial reporting, AASB 137 addresses recognition and measurement of provisions, including the best estimate, uncertainty and discounting where material. Those are accounting judgments. Engineering should supply the scope, methods, timing and evidence needed to inform them, with a clear reconciliation to the finance team's calculation. AASB 137, paragraphs 14 and 36 to 47 ↗ (opens in a new tab).

4. Build the review file alongside the estimate

ASA 540 focuses the auditor's work on matters including methods, assumptions, data and estimation uncertainty. ASA 500 addresses the sufficiency and appropriateness of audit evidence. Neither standard provides a label that an engineering consultant can award to an estimate in advance. ASA 540 ↗ (opens in a new tab), ASA 500 ↗ (opens in a new tab).

A practical review file contains a scope-to-cost map, an assumption register, source records, method narrative, sensitivity results and changes since the preceding estimate. Record unresolved contradictions explicitly. The key test is whether a reviewer can select a material cost line and trace it back to an identifiable obligation, asset, quantity and execution assumption without relying on the estimator's memory.