Collecting Your Own Solid Waste Characterization Data: CalRecycle Uniform Waste Disposal Characterization Method

The California Department of Resources Recycling and Recovery (CalRecycle) developed a uniform waste disposal characterization method for collecting data on the waste stream. The method was developed for local governments in California to use in meeting regulatory requirements for solid waste planning; however, anyone interested in collecting information on the types and amounts of materials in the waste stream may find it useful. The method was designed to collect information only on the disposed waste stream, not on materials that have been diverted through recycling, composting or source reduction. California has no requirement for collecting detailed diversion data.

Note: This method allows the use of CalRecycle’s waste characterization database (default data) to meet regulatory requirements for waste disposal characterization studies. The database was designed to provide information for planning solid waste programs in the absence of local solid waste studies, not for measuring the local waste stream. Jurisdictions must carefully evaluate whether the database provides the information needed, and at the level of accuracy needed, for the intended use. Many factors determine the accuracy and effectiveness of the default data when applied to local conditions (see data limitations).

A brief word about "generation" versus "generator." The term "generation" means all waste created within a jurisdiction, both that which is disposed and that which is diverted. "Generator" means a person or business that creates the waste.

A detailed outline of the method follows:

This method is required to be used by jurisdictions conducting waste disposal characterization studies under the following two circumstances [ see Public Resources Code (PRC) Section 41770(b) ]:

a) If a jurisdiction does not meet the 25 percent or 50 percent diversion goal, CalRecycle may direct it to conduct a waste characterization study, and if so, the jurisdiction must use this method.

b) If a jurisdiction revises its source reduction and recycling element (SRRE), and includes new waste characterization data in the revision, it must use this method to collect data to be included in the revision.

Jurisdictions may not need to conduct comprehensive studies to characterize the entire waste stream, but may do studies targeted on a particular sector of the waste stream (such as the residential or nonresidential sector), or on specific groups of generators such as groups of businesses (termed "subpopulations"). Jurisdictions shall use this method to characterize waste disposed, and need not collect information on waste diverted for the purposes of this method.

Step 1. The jurisdiction will select a characterization approach (i.e., how data will be collected) from the following:

  • Landfill sampling.
  • Waste generator sampling.
  • Use of default data from CalRecycle's Waste Characterization Database.
  • Use of existing data.
  • Combination of approaches where appropriate.

A jurisdiction conducting a new waste characterization study for the purposes of submitting information to CalRecycle as specified above shall consider the following factors in determining how data will be collected for the study:

  1. Direction from CalRecycle if required to conduct a waste characterization study because diversion goals have not been met [PRC section 41770(b) and 14CCR 18726(b)].
  2. New information the jurisdiction intends to include in a revised SRRE.
  3. Intended use of waste characterization data and purpose for data collection, such as targeting diversion programs, facility design, monitoring diversion program success, determining changes in waste stream characteristics, etc.
  4. Resources available for collection of waste characterization data, such as funding, staff time and expertise, etc.
  5. Degree of accuracy and reliability of the data needed to satisfy the intended uses.
  6. The extent of the data collection needed to satisfy the intended uses (i.e., comprehensive v. targeted studies).
  7. Any other factors the jurisdiction deems important.

After considering these factors, the jurisdiction will determine which of the five data collection approaches is most suitable. If factors indicate one particular approach, but the jurisdiction wishes to use another, it must explain in the SRRE how the chosen approach meets the needs of the data collection effort and/or specific direction given by CalRecycle if goals have not been met.

The jurisdiction may also use a mass balance/materials flow data collection approach for a targeted part of the waste stream, such as household hazardous waste. With a mass balance method, information on a jurisdiction's waste stream is developed by using data on quantities of commodities sold in the jurisdiction's marketplace to estimate solid wastes generated as a result of the sale of these commodities. The jurisdiction must explain how use of this method is the most appropriate approach to collect the specific data needed.

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Step 2. The jurisdiction will collect data that is statistically representative of the waste stream being characterized.

a. Selecting Samples for Field Studies

For landfill studies, samples shall be chosen randomly. Vehicles from which samples are taken shall be chosen randomly, and the sampled portion of the vehicle load shall also be chosen randomly by the grid method or by the cone and quarter method as described in the ASTM "Standard Test Method for Determination of the Composition of Unprocessed Municipal Solid Waste." The minimum sample weight shall be 200 lb. for each sample, and only one sample will be taken from each truck.

For generator studies, the sector or subpopulation being sampled should be subdivided into sampling groups ("stratified"). Groups (strata) should be based on criteria affecting waste patterns such as size of business (based on number of employees) or type of residence (multifamily or single family). Samples should be allocated to each group according to its proportion of the waste stream.

The recommended rule of stratification and sample allocation is the "80/20 rule." This rule states that generally, the largest generators that make up 20 percent of the entities (businesses or types of residences) to be sampled will generate 80 percent of the waste. When using this rule, the sector or subpopulation should be stratified into the 80/20 grouping. The total number of generators to be sampled should be allocated so that 80 percent of the samples are randomly assigned to entities in the large generator group, and the remaining 20 percent of the samples are randomly assigned to the remaining entities (which generate 20 percent of the waste). This rule can be used for sampling at the sector level or subpopulation level.

Other methods of grouping generators may be used which the jurisdiction determines to be most appropriate for its intended use of the waste characterization data.

If data needed for stratification is not available (such as number of employees in each business), random selection of generators may be used rather than stratification. Jurisdictions may use random sampling based on other reasons also, but the jurisdiction must explain how the selected approach is most appropriate for the particular data use.

Other methods of sample selection and sample allocation may be used if first submitted to CalRecycle staff for approval prior to the beginning of the study on a case-by-case basis. CalRecycle staff shall review each case within a reasonable period of time, usually not to exceed 30 days.

b. Determining Number of Samples Needed for Field Studies

The minimum number of samples, and minimum weights of samples to be characterized shall be selected from the following table, based on the waste stream to be sampled and type of study. Studies conducted according to these guidelines shall be considered to be statistically representative.

Sample Numbers for Waste Characterization Studies for Planning Use
Type of Study Minimum Number of Samples per Year Minimum Sample Weight
Disposal Facility (Landfill) Based Sampling  for the Residential Sector 30, distributed over a minimum of 2 seasons 200 pounds
Disposal Facility (Landfill) Based Sampling for the Nonresidential Sector 40, distributed over a minimum of 2 seasons 200 pounds
Generator Based Sampling for the Residential Sector 40, distributed over a minimum of 2 seasons 125 lbs. or 1.5 CY or Whole Sample
Generator Based Sampling, Nonresidential Sector-Level Study 50, distributed suitably to reflect seasons 125 lbs. or 1.5 CY or Whole Sample
Generator Based Sampling--Subpopulation Level with Similar Businesses in Subpopulation 25, distributed suitably to reflect seasons 125 lbs. or 1.5 CY or Whole Sample
Generator Based Sampling--Subpopulation Level with Different Businesses in Subpopulation 40, distributed suitably to reflect seasons 125 lbs. or 1.5 CY or Whole Sample

Seasonal sampling: The composition of the waste stream may vary during the calendar year due to cyclical patterns of local climate, demography, trade or commerce. In order for waste characterization data to reflect these seasonal variations, sampling should occur during a minimum of two seasons for landfill studies and for generator based residential studies. The minimum number of samples may be split between sampling periods, i.e. for residential landfill studies 15 samples may be taken in each of two seasons, so that the minimum number of samples for the year (30) will be statistically representative of the waste stream for the year and reflect seasonal variation. If the jurisdiction wishes data to be statistically representative for each season, then the minimum number of samples should be characterized for each season.

For generator based sampling in the nonresidential waste stream at the sector or subpopulation level, the jurisdiction should assess possible affects of seasonality on the generators to be sampled. If seasons are identified (for example due to tourism cycles or other commercial cycles), sampling according to the above requirements should occur in the season most important for planning diversion program and/or other data needs.

A jurisdiction may conduct sampling in only one season if:

  1. It has evaluated whether the waste stream being characterized is affected by seasonal factors.
  2. It has determined that sampling during only one period during the year will provide data that is statistically representative and reflects seasonal variation in the waste stream being characterized.
  3. It receives approval from CalRecycle staff for the alternative sampling plan prior to the beginning of the study (usually within 30 days of submittal to CalRecycle staff) and
  4. It characterizes the minimum number of samples as specified in the table above.

A jurisdiction may use minimum sample numbers lower than those in the above table if:

  1. It demonstrates that the proposed alternative sampling plan will provide data that is statistically representative for the purpose of the study (for example, a study focused on 20 specific businesses), and/or
  2. It demonstrates only limited sampling is possible due to financial or other resources constraints, and
  3. It receives approval by CalRecycle staff for the alternative sampling plan prior to the beginning of the study (usually within 30 days of submittal to CalRecycle staff).

c. Use of Default Data or Existing Data to Be Statistically Representative

Jurisdictions may use default data to meet the requirements for statistically representative data, however they must evaluate the applicability of default data to their local conditions, such as local diversion programs, climate, economic factors, demographic factors, and other factors. In using default data, jurisdictions must recognize that the data represents the disposed waste stream, and may reflect diversion programs that were in place at the time and location the default data was collected. These evaluations should be discussed in the SRRE.

Studies based on use of existing data will be considered to be statistically representative of the jurisdiction using the data if: (1) the existing data comes from studies which meet the criteria outlined in the table above, and (2) if the data comes from the jurisdiction itself or from a jurisdiction that is comparable in the numbers and types of generators, and in other aspects, to the target jurisdiction.

Areas of comparability for the residential waste stream to be considered include urban and rural characteristics, climate, geography, population and housing patterns, other sociodemographic factors, and local diversion programs. Areas of comparability for the nonresidential waste stream to be considered include types of commercial and industrial businesses, relative proportions of business types, sizes of businesses, and existing diversion programs. The jurisdiction should consider and discuss each area in the SRRE, and include relevant numerical information that is commonly available.

Existing and comparable data to be used for a new waste characterization study should not be older than five years, should be compatible with the intended purpose of the new study, and should be specific enough to meet the needs of the new study.

Studies based on existing data that was collected using the uniform waste characterization method will be considered to be statistically representative.

Studies conducted using a combination of data collection approaches will be considered statistically representative if data collected from each approach is shown to be statistically representative according to the above requirements.

Other data that does not meet the criteria outlined above may be acceptable if the jurisdiction can show that it is statistically representative based on other criteria, and approved by CalRecycle staff prior to use on a case-by-case basis.

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Step 3. Use of Standard Characterization Protocols

a. Use of Uniform Field Sorting Protocols

Field studies shall be conducted using appropriate field sorting protocols. A model protocol is available from CalRecycle that can be used as a guideline. Other information on field procedures can be found in Appendix A of the 2004 Statewide Waste Characterization Study.

b. Use of Standard Material Type Definitions

Field studies shall be conducted using standard material type definitions. At a minimum, data will be collected at the material type level. If more detailed data is collected for submission to CalRecycle, the jurisdiction may design specific subtypes according to the protocols described below.

c. Use of Standard Protocol for Lumping/Splitting Material Categories

If a jurisdiction develops a new material classification, it should be composed of material subtypes that can be separated and added back into standard material types. Also, more detailed subtypes should be able to be combined into an existing standard type. If a detailed material is a significant part of the waste stream being sampled, a separate type should be developed for it that can later be included under a standard type.

d. Use of Standard Protocol for Classifying Composites/Problem Items

For objects made of more than one material type (composite items), the predominate material type by weight determines the material classification of the object. Items that have the potential to be diverted through waste prevention or recycling should be classified into higher value material types. Materials that have little potential for diversion programs should be classified in lower value material types.

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Step 4. Use of Minimum Health and Safety Standards

Jurisdictions should consider health and safety protocols before conducting field studies. CalRecycle has a sample protocol that can be used as a guideline. Every waste characterization study is different, not only are there different kinds of risks associated with the kinds of waste materials encountered, but different risks from location, weather, traffic, site security, and other issues. The local waste characterization project manager should assess the health and safety issues associated with each individual sort and establish the appropriate training, procedures, and safeguards.

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Step 5. Use of Standard Data Analysis Methods

Data analysis and extrapolation procedures depend on the type of study conducted and the level of detail of the data. In general, the following procedures will be used for the corresponding study type:

a. Landfill (Disposal Facility) Sampling

For randomly selected samples from a sector (e.g., residential, commercial, industrial, etc.) taken at a disposal facility, the overall sector composition is calculated simply by adding each of the individual material type percentages and dividing by the number of samples.

The overall composition for a jurisdiction should be calculated by weighting the overall sector composition of each material type by the relative contribution of each sector tonnage and then summing the weighted composition.

b. Generator Sampling

Generator studies require subdividing of the sector or subpopulation into strata (groups), according to criteria which affect waste patterns such as business size (for the nonresidential sector) or number of residents in residential strata (for example multifamily and single family generators). Individual sample data is extrapolated to represent the entire waste stream being characterized. This extrapolation is done by weighting the individual data according to how important it is in the overall waste stream. Data from an individual generator (such as a business) is weighted according to the size of the business (number of employees). Data from each strata is weighted according to the size of the strata. This method improves overall accuracy by taking the size of the generator and strata into account, rather than by treating all generators equally.

The extrapolation technique uses a correlative factor of tons disposed per employee (or resident) for each generator sampled, average correlative factors for each stratum, and weighting by number of employees or residents in each strata to develop the overall composition for the waste stream being characterized. The same basic technique can be used to develop the composition for a whole sector (residential or nonresidential), or for a subpopulation (smaller group of businesses or residences) for a generator study.

The mathematical formula for calculating the percent of a component for a subpopulation is shown below.

Composition Percent for Subpopulation = 

The mathematical formula for calculating the percent of a component for a subpopulation.


pij = composition percent for ith company in the jth stratum
nj = number of samples in the jth stratum
tij = tonnage at ith company in the jth stratum
eij = employment at ith company in the jth stratum
ej = employment in the jth stratum of the subpopulation

The jurisdiction may use another data analysis procedure if it demonstrates that it is a more appropriate method for analyzing the specific data collected, and if approved by CalRecycle staff on a case-by-case basis.


Comments, suggestions, questions? Contact CalRecycle waste characterization staff at