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FINAL CAPPING, CLOSURE AND POST-CLOSURE COSTS
 12 Months Ended
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.