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FINAL CAPPING, CLOSURE AND POST-CLOSURE COSTS | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract] |
FINAL CAPPING, CLOSURE AND POST-CLOSURE COSTS | FINAL CAPPING, CLOSURE AND POST-CLOSURE COSTS Accrued final capping, closure and post-closure costs include the current and non-current portion of costs associated with obligations for final capping closure and post-closure of our landfills. We estimate our future final capping, closure and post-closure costs in order to determine the final capping, closure and post-closure expense per ton of waste placed into each landfill as further described in Note 3, Summary of Significant Accounting Policies. The anticipated time frame for paying these costs varies based on the remaining useful life of each landfill, as well as the duration of the post-closure monitoring period. The changes to accrued final capping, closure and post-closure liabilities are as follows:
| Fiscal Year Ended December 31,
| 2017 |  | 2016
Beginning balance | $ | 44,207 |  |  | $ | 41,041 |
Obligations incurred | 3,022 |  |  | 2,441 |
Revisions in estimates (1) | 11,498 |  |  | (2,052 | )
Accretion expense | 4,401 |  |  | 3,606 |
Obligations settled (2) | (838 | ) |  | (829 | )
Ending balance | $ | 62,290 |  |  | $ | 44,207 |
(1) | Relates to changes in estimates and assumptions concerning anticipated waste flow, cost and timing of future final capping, closure and post-closure activities at certain landfills, including the Subtitle D landfill in Southbridge, Massachusetts ("Southbridge Landfill"), as well as changes to expansion airspace. See Note 10, Commitments and Contingencies and Note 15, Other Items and Charges for disclosure regarding Southbridge Landfill.
(2) | Includes amounts paid and amounts that are being processed through accounts payable as a part of our disbursement cycle.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -URI http://asc.fasb.org/subtopic&trid=2175671 + Details
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