Accounting rules also require that an impairment charge or expense be recognized if the value of assets declines unexpectedly.
BarCap analyst estimates further impairment charges on top of £100bn taken over past four years Continue reading...
The company also warned it faced further impairment charges this year.
"But the restructuring charges and the impairment charges keep coming, and that's disturbing," Mr. Russell said.
On February 29, 2012, Edison took a $1 billion impairment charge related to the Homer City plant and several other coal-fired power plants.
In 2010, the tribe had a $58.1 million impairment charge which halted any work on the project.
Still, the potential impairment charge is unlikely to surpass $100 million.
That will be the decisive factor whether a company takes an impairment charge.
In the financial year 2010-11, Vodafone took a £6bn impairment charge linked to the declining value of southern European operations.
Return on average assets excluding the $3.4 million impairment charge was 0.86% for the quarter ended June 30, 2008.