Definition. A waste sort is a process to estimate the proportion
of different discards in an area's waste stream by taking a small number
of samples that are randomly selected and also are representative and unbiased.
Purpose. A waste sort provides information to determine, for
example, the size a materials recovery facility or an incinerator, changes
in composition over time, the response to policy initiatives intended to
divert material from the waste stream.
Statistics' Role. If random selection rules and other good practices
are followed, statistics helps to: (1) improve the chance
that the percentage estimates from your sampling are correct and (2)
quantify the uncertainty band that surrounds any estimate for a sampling.
Elements. A waste sort consists of [a] development of
a study design, [b] selection of a random sample,
[c] implementation of field work and [d] analysis
of the results.
[a] Study Design. This structures how the waste sort will be conducted and is critical to producing solid results. It consists of eight steps: (1) stating the question, (2) defining the waste stream, (3) drawing the waste shed, (4) stratifying the population, (5) planning sampling strategies to minimize biases, (6) listing the materials to be sorted, (7) fixing the time periods to be studied, and (8) determining the desired level of reliability.
[b] Selecting Samples. This involves selecting the samples to produce the best results. It consists of five steps: (1) estimating how many samples needed to achieve the desired level of reliability, (2) allocating those samples to any strata, (3) randomly selecting trucks from which to pull samples, (4) selecting samples from within those trucks, and (5) insuring that each sample weighs enough to produce reliable results.
[c] Sorting Samples. This brings the process into the field to sort the samples. It consists of: (1) assembling a crews to pull samples from the trucks, to supervise sorting crews and to sort, (2) acquiring equipment to pull and sort, including use of an end-loader, and a digital scale, shovels, tarps, work gloves, first aid kits, recording sheets and clip board, etc. (3) sorting the samples by the materials on the list, and (4) weighing and recording the materials sorted from each sample.
[d] Analyzing Samples. This is where the results from the sort are compiled. It consists of: (1) converting the weights of each material in each sample into percentages, (2) calculating the average percent that each material is in the samples, and (3) calculating the confidence intervals around those averages.
More Help Aids
Statfacts Primer an essential foundation in the basic statistics needed to do good waste sorts included in the appendix
Examples an illustrative demonstration of each of the procedures and equations used included as part of the text
A Glossary an explanation of statistical terms also included in the appendix to help understand the meaning of the technical words
WasteSort™ a software program to facilitate data collection and perform all of the statistical calculations purchased separately. To order or for more information call toll free 800-449-1010