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Figure 1. Wood harvested within each colored band can be transported to the center of <br />each county in 15- minute increments. <br />most- to least- expensive woody biomass <br />resources. For example, if urban waste wood <br />were delivered within the one -hour limit, the <br />total delivered cost would be $19.46 per dry <br />ton, or $1.25 per million British thermal <br />units (MMBtu). However, if pulpwood were <br />delivered from the same distance, the <br />delivered cost would increase to $49.14 per <br />dry ton, or $3.04 per MMBtu, primarily <br />because pulpwood is more expensive than <br />urban wood waste. <br />Physical Availability <br />In addition to the delivered cost of wood, <br />knowing how much of each type of woody <br />biomass is available is necessary to <br />construct supply curves. Annually harvested <br />pulpwood and annually available urban <br />wood waste and logging residues within the <br />two NC counties are shown in Table 2. <br />For urban wood waste, it is assumed that <br />0.203 green tons (40% moisture content) of <br />urban wood waste is generated per person <br />per year (Wiltsee 1998). Urban wood waste <br />includes municipal solid waste wood from <br />yard <br />waste and tree trimming but excludes <br />industrial wood (e.g., cabinet and pallet <br />production) and construction and demolition <br />debris. This average yield was multiplied by <br />county population estimates and reduced by <br />40% to estimate total annual county yield of <br />urban wood waste. For example, in <br />Buncombe County, this results in 26,700 <br />green tons of urban wood waste per year. <br />The amount of logging residue and <br />pulpwood for all counties in North Carolina <br />was obtained from the USDA Forest Service <br />(2003) Timber Product Output Reports. <br />This database provides forest inventory and <br />harvest information, including annual yields <br />of forest residues and pulpwood. We <br />reduced the figure for logging residues by <br />30% to exclude stumps. For example, in <br />Orange County, there are 22,700 green tons <br />(37% moisture) of logging residues <br />available annually from existing forestry <br />operations. There are also 6,400 green tons <br />(50% moisture) of pulpwood harvested <br />annually. <br />Moisture content refers to the amount of moisture remaining in wood and is an important consideration in the <br />quality of biomass resources. Moisture content is 0% in oven -dried biomass, about 20% for air -dried biomass, and <br />about 50% for fresh or "green" biomass. As the moisture content of wood increases, the energy content per unit <br />mass of wood will decreases. Thus, wood with low moisture content will combust more efficiently than wood with <br />high moisture content. Moisture content referred to in this document is reported on a green- weight basis. <br />3 <br />