What should be the valid basis for the contractor's claim of underpayment for imported borrow?

The valid basis for the contractor's claim of underpayment for imported borrow is proof of improper measurement by the engineer. This is fundamental because measurements taken by the engineer determine how much material is recorded and subsequently compensated for. If the contractor can demonstrate that the measurements were inaccurate or improperly calculated, it establishes a legitimate ground for claiming underpayment. This ensures that the contractor is fairly compensated for the actual amount of borrow provided, aligning the payment with the services rendered.

In construction projects, accurate measurement is vital for financial accounting; discrepancies due to inaccurate measurements can directly affect the contractor's revenue. Therefore, unless there is proof that the engineer made a mistake in measurement, the contractor may not have a strong argument for adjustment of the payment.

The other options do not provide a direct basis for a legitimate claim of underpayment. A claim alone, without substantiated evidence, lacks the necessary backing to warrant adjustment. Notarized load counts may offer some confirmation, but they do not directly address the issue of measurement accuracy itself. Proof of vehicle capacity could potentially provide context regarding the amount transported, but it also doesn't directly challenge the measurements made by the engineer. Thus, the strongest and most valid basis remains the evidence of improper measurement by the engineer.