Jolley points out that the largest desirable source of biomass is sawmill waste and unwanted forest products. White fir is very high in BTU's, as is the bark of Doug fir, if it is not excessively high in moisture. Obviously the timber industry is very important, but the plants need more, so they have been forced to seek elsewhere. These deviations do not come without a cost. All metal must be removed from the pallets, so they have to go through a magnet and a sensoring device.
Stumps bring in a lot of unwanted soil and gravel.
Contaminants from dirt and grease have to be monitored. Often fresh prunings hold an excessively high moisture percentage. And some of the logical alternatives did not pan out at all. When trucks arrive, they are weighed inbound and a sample of the load is taken in a ziplock bag and delivered to the outbound scales. A typical 25ton load could well be 50 percent moisture, so Wheelabrator would consider this as 12.5 tons of fuel.