This excerpt taken from the WLK 8-K filed Feb 14, 2007.
Property and Equipment
The Business records properties at cost. Maintenance and repairs are charged to earnings; replacements and betterments are capitalized. When the Business retires or otherwise disposes of assets, it removes the cost of such assets and related accumulated depreciation from the accounts. The Business records any profit or loss on retirement or other disposition in earnings. Asset impairments are reflected as increases in accumulated depreciation.