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Final Capping, Closure and Post-Closure Costs (Tables)
12 Months Ended
Apr. 30, 2014
Asset Retirement Obligation Disclosure [Abstract]  
Changes to Accrued Capping, Closure and Post-Closure Liabilities
The changes to accrued final capping, closure and post-closure liabilities for fiscal years 2014 and 2013 are as follows:

 

     Fiscal Year Ended April 30,  
     2014     2013  

Beginning balance

   $ 43,170      $ 39,629   

Obligations incurred

     3,621        3,188   

Revisions in estimates (1)

     (3,728     (694

Accretion expense

     3,967        3,538   

Payments

     (2,376     (2,491
  

 

 

   

 

 

 

Ending balance

   $ 44,654      $ 43,170   
  

 

 

   

 

 

 

 

(1) The revisions in estimates for final capping, closure and post-closure for fiscal years 2014 and 2013 consist of changes in cost estimates and the timing of final capping and closure events, as well as changes to expansion airspace and tonnage placement assumptions.