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GeoWorld July 2011

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subject to different constraints and have different costs. In addition, the method of financing is different for each. As the structure of solid waste changes, so does the optimal allocation of waste streams to sites. At the same time, the capacity limits that constitute “bottle- necks” for a particular waste stream may change. There are some paradoxes, however, in increased diversion. Because disposal rates often are contracted for years and frequently are based on charging only for garbage disposal, increasing diversion may worsen a municipality’s financial situation. Furthermore, due to the complex structure of fees and charges imposed by landfill operators and local jurisdictions, the most cost-effective allocation of waste streams to disposal sites doesn’t necessarily optimize carbon emissions associated with transportation. Economists view these paradoxes as pricing problems. Basing rates on a “snapshot” of the waste streams at one point in time guarantees a fiscal imbalance if the composition of the waste streams changes. Using an incorrect price for carbon emissions means there won’t be sufficient incentives to economize on waste hauling. The solutions, however, are straightforward (if politi- cally difficult). Alternative rate-setting practices would reduce the fiscal imbalance. Raising prices of carbon- emitting activities through corrective taxes would lead municipalities and disposal-site operators to appropri- ately account for the effects of carbon emissions in their waste-generating, hauling and disposal practices. A Linear Programming Approach To examine the sustainability of waste disposal, two highly stylized Linear Programming (LP) models were developed for a municipality’s disposal problem. The MIN-EXP model assumes that municipalities minimize total expenditure of waste-stream disposal. An alternative MIN-HAUL model assumes that municipalities minimize transporta- tion emissions (by minimizing ton-miles hauled). Geospatial methods are essential to such analysis, because they can model the transportation network capacity from origin to alternative destinations, which is reflected in transportation costs. In the MIN-EXP LP problem, transportation is one of the largest costs. In the MIN-HAUL LP problem, the vehicle ton-miles solution is determined by the locations of the various disposal sites and the transportation network that connects these sites with the origin. A hypothetical base case (corresponding to zero-percent diversion) is roughly calibrated to the experience of the city of San Jose, Calif., in 2004. This base case assumes that all shipments originate from a central collection facility. The amount of solid waste disposed in that year was about 6,800 tons per day, with approximately 24 percent of that total being garbage, 44 percent recycling and 32 percent composting. Calculations based on the model should be viewed as approximations for illustrative purposes only. In the MIN-EXP LP model, expenditures depend on the size of each waste stream, the “tipping fee” (per ton disposal fee) at a particular disposal site, the surcharge of the local jurisdiction, and the cost of transporting waste to the facility. Landfills are the second-most-significant source of methane emissions, according to the Environmental Protection Agency. An LP problem consists of three parts: the objective (goal) function, the inequality constraints and the non- negativity constraints on choice variables. The objective function and inequality constraints must be linear. Linearity of the objective function in the case of the MIN-EXP model means that municipalities take the tip- ping fees and surcharges as given, which is a reason- able assumption during the contract period with the landfill operator. A constant cost of transportation per ton-mile (which may differ by facility depending on the terrain or mode of transportation) also is assumed. lFigure 2. “Tipping fees” are a large part of waste-stream disposal costs. JUL Y 2O11 / WWW . GEOPLA CE . COM 19

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