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The carrying values are based on external appraisals that are completed annually as of December 31. The appraisals utilize a combination of the discounted cash flow and sales comparison approaches to arrive at the estimated value. The significant unobservable inputs (level 3) included in the discounted cash flow models used when determining the fair value of standing timber and agricultural assets include: 

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Key valuation assumptions include a weighted average discount and terminal capitalization rate of 6.9% (2012 – 6.2%), and terminal valuation dates of 20 to 28 years (2012 – 20 to 90 years). Timber and agricultural asset prices were based on a combination of forward prices available in the market and price forecasts. 

## 13. INTANGIBLE ASSETS 

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Intangible assets are allocated to the following cash-generating units: 

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## a) Infrastructure – Utilities 

The company’s Australian regulated terminal operation has access agreements with the users of the terminal which entails 100% take or pay contracts at a designated tariff rate based on the asset value. The concession arrangement has an expiration date of 2051 and with an option to extend the arrangement an additional 50 years. The aggregate duration of the arrangement and the extension option represents the remaining useful life of the concession. 

## b) Infrastructure – Transport 

The company’s Chilean toll road concession provides the right to charge a tariff to users of the road over the term of the concession. The concession arrangement has an expiration date of 2033, which is the basis for the company’s determination of its remaining useful life. Also included within the company’s transport operations is $355 million (2012 – $348 million) of indefinite life intangible assets which represent perpetual conservancy rights associated with the company’s UK port operation. 

The following table presents the changes to the cost of the company’s intangible assets: 

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