13. ACCOUNTING FOR ASSET RETIREMENT OBLIGATIONS
We recognize AROs in the period in which we have an existing legal obligation associated with the retirement of a tangible long-lived asset, and the amount of the liability can be reasonably estimated. The ARO is recognized at fair value when the liability is incurred with a corresponding increase in the carrying amount of the related long lived asset. We depreciate the tangible asset over its estimated useful life. The liability is adjusted in subsequent periods through accretion expense which represents the increase in the present value of the liability due to the passage of time. Such depreciation and accretion expenses are included in cost of goods sold for operating facilities and other operating expense for indefinitely closed facilities.
Our legal obligations related to asset retirement require us to: (i) reclaim lands disturbed by mining as a condition to receive permits to mine phosphate ore reserves; (ii) treat low pH process water in phosphogypsum management systems (the “Gypstacks”) to neutralize acidity; (iii) close and monitor Gypstacks at our Florida and Louisiana facilities at the end of their useful lives; (iv) remediate certain other conditional obligations; (v) remove all surface structures and equipment, plug and abandon mine shafts, contour and revegetate, as necessary, and monitor for five years after closing our Carlsbad, New Mexico facility and (vi) decommission facilities, manage tailings and execute site reclamation at our Saskatchewan potash mines at the end of their useful lives. The estimated liability for these legal obligations is based on the estimated cost to satisfy the above obligations which is discounted using a credit-adjusted risk-free rate.
A reconciliation of our AROs is as follows:
|December 31,||May 31,|
|AROs, beginning of year||$||658.5||$||600.3||$||573.1|
|Revisions in estimated cash flows||67.2||59.4||65.4|
|AROs, end of year||723.9||658.5||600.3|
|Less current portion||86.3||83.5||87.0|