Solid Waste Data Analysis

Quantity

Solid waste data analysis begins with data that is either directly measured or estimated using proxy variables. The most basic and reliable measure of quantity is collected tonnage. Most municipal solid waste and much hazardous industrial solid waste are weighed as a routine step in transportation through intermediate to final destinations. Because economic transactions between waste generators and waste handlers are commonly assessed by weight or volume, such information is widely maintained by private and public entities. The reporting of waste quantities aggregated over time and geographic jurisdiction, as part of state or local waste management planning efforts, is common. In cases where volume, as opposed to weight, is the metric reported, standard weight-to-volume ratios for different materials or products can be used to calculate an estimated weight for a volume of transacted waste.

In other cases, waste quantity may be estimated using variables that measure consumption of products that end in waste. Information on domestic production, imports, and exports of materials and products is used in conjunction with information on product life spans to estimate waste quantities that consumers will generate after using up goods. In many cases, production and marketing data kept by private industries can be used to estimate numbers of units bought and sold. In such cases, standard unit weights are used to convert information [Page 838]into tonnages. This approach is basic methodology used by the Environmental Protection Agency's (EPA) long-standing national municipal solid waste report, “Municipal Solid Waste Generation, Recycling, and Disposal in the United States,” which is issued biennially. This report supplements its indirect quantity estimates with directly measured data provided by landfill operators, recycling processors, and municipalities.

Composition

Measuring waste composition is a quite different endeavor than measuring waste quantity. Direct measurement of composition does not take place routinely like waste quantity measurement does. Composition measurement begins by intercepting waste from generators or after collection, or in some cases by extracting waste from industrial properties, landfills, or incinerator inputs.

Multiple random samples are then broken down into constituent materials. This can be done at various levels of detail. State or local waste characterization studies, for example, assign workers to take samples of mixed garbage from collection trucks and to hand-sort contents into a range of categories that correspond to products or materials that are relevant to waste policy. By recording the total sample weight and the weight of each sorted category of material or product, such studies enable the calculation of a percent composition that can be averaged over many samples to develop an estimate that is statistically significant. Waste characterization studies use different category definitions and numbers of categories, but generally estimate the composition of paper, metal, plastic, glass, wood, organic, and inert inorganic materials in solid waste. Results of waste characterization studies are useful for understanding how much disposed of waste might be routed to recycling, reuse, or composting under different policies. Depending on level of detail, such studies also provide insight into the quantities of acutely hazardous categories of waste, such as batteries or electronics, that may be kept out of disposal through other policy interventions, such as disposal bans or extended producer responsibility programs.

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