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ASSET RETIREMENT OBLIGATIONS (Tables)
 3 Months Ended
Mar. 31, 2017
ASSET RETIREMENT OBLIGATION  
Schedule of Asset Retirement Obligations

Aggregate carrying amounts of asset retirement obligations are as follows (dollars in thousands):

 

 

 

 

 

 

 

 

 

 

March 31, 

 

December 31, 

 

 

    

2017

    

2016

 

Asset retirement obligation at beginning of period

 

$

58,583

 

$

55,215

 

Liabilities incurred

 

 

 —

 

 

5,844

 

Liabilities settled

 

 

(184)

 

 

(1,298)

 

Accretion expense

 

 

626

 

 

3,751

 

Change in cash flow estimate

 

 

(2,601)

 

 

(4,929)

 

Asset retirement obligation at end of period

 

$

56,424

 

$

58,583