EPHRATA - REC Silicon is suing Grant County, claiming the county's appraisal was wrong by more than $600 million.

The company filed the civil suit in Grant County Superior Court requesting a refund of the alleged excess of property taxes it paid in 2010.

Attorneys for the company claim the county didn't appraise the property correctly.

REC Silicon was in the process of improving the 105 acre property it owns on Road N NE in Grant County during the assessment period ending in 2009, according to the complaint. The company was building plants to add to its production.

The county assessed the property's value at $1.26 billion for 2010 property taxes, more than twice the $590 million the company claims the land was worth, according to the complaint. REC Silicon paid the taxes under written protest.

For 2011 REC Silicon is paying $16 million in property taxes, according to Grant County Assessor's Office. This year the property was valued at $1.3 billion.

G. Kim Risenmay, a Seattle attorney representing REC, offered 10 possible mistakes the county made in assessing the property, including using, "a fundamentally wrong basis to calculate and assess the value of this property;" failing "to take into consideration and adjust the fair market value of the property in light of sales of comparable property;" and failing to take into account costs of production, equipment and materials.

The company also claims the county failed to assess the property at the same rate as other property in the county, according to the complaint.

The Washington state Department of Revenue reportedly determined the county assessed real property in the county at 85.4 percent of its market value and personal property at 95.6 percent of its true market value.

"Grant County's combined ratio of assessed value compared to true and fair market value was 86.3 percent," according to the complaint. "If REC Silicon's property had been assessed uniformly with other property in Grant County at 86.3 percent of it's true market value, this property, with a true market value of $590 million would have received an assessed value of $507 million."

Risenmay claims the error violated a state Constitution requirement stating all taxes, "shall be uniform upon the same class of property within the territorial limits of the authority levying tax," according to the complaint.

The company is requesting a refund of its property taxes for any amount above the $507 million it alleges it should have been assessed, according to the complaint. It also wants interest paid on the difference.

Commissioner Cindy Carter and Assessor Laure Grammer said they couldn't comment because of the pending litigation.