For the purpose of government-wide financial statements, the cost of cleaning up a government-owned landfill and closing the landfill is "is accrued on a pro-rated basis each period based on how full the landfill is."
This approach reflects the matching principle in accounting, which states that expenses should be recognized in the period in which they are incurred or when they contribute to revenue generation, rather than when they are paid. In the case of a landfill, the cost of cleanup and closure is gradually incurred as the landfill is filled up.
Therefore, governments typically accrue these costs proportionally over the period during which the landfill is in use, based on its capacity and usage rate. This method ensures that the financial statements accurately reflect the liability as it grows, rather than waiting until the costs are actually incurred or when they become estimable in full.