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Accounting for Asset Retirement Obligations (Tables)
12 Months Ended
Dec. 31, 2019
Accounting for Asset Retirement Obligations  
Schedule of Change in Accounting Estimate The assumptions used to calculate the increases to the Palo Verde ARO liability are as follows: 
 
Escalation
Rate
 
Credit-Risk
Adjusted
Discount Rate
Original ARO liability
3.60
%
 
9.50
%
Incremental ARO liability (2010)
3.60
%
 
6.20
%
Incremental ARO liability (2016)
3.25
%
 
4.34
%

Schedule of Asset Retirement Obligations
 
2019
 
2018
ARO liability at beginning of year
$
101,108

 
$
93,029

Liabilities settled
(118
)
 
(272
)
Accretion expense
9,115

 
8,351

ARO liability at end of year
$
110,105

 
$
101,108