California Department of Resources Recycling and Recovery (CalRecycle) 

Regulations: Title 14, Natural Resources Division 7

Chapter 9. Planning Guidelines and Procedures for Preparing and Revising Countywide and Regional Agency Integrated Waste Management Plans

Appendix 1. General Guidelines for Sampling When Performing a Quantitative Field Analysis for a Solid Waste Generation Study (CIWMB - November 1990).

1. Sampling Solid Waste Generation, Diversion and Disposal - Perform these tasks in the following order:

(a) Identify the Populations.
In each jurisdiction, identify: the populations of (1) residential units, commercial units, industrial sites, and other sites of solid waste generation; (2) facilities and programs which recycle, compost, or source reduce solid wastes; and (3) solid waste transfer stations, and permitted solid waste transformation facilities and solid waste disposal sites. For the purposes of these Guidelines, a population is the aggregate from which a sample is chosen, and refers to the aggregate number of solid waste generators, solid waste diversion facilities and programs, or solid waste transfer, transformation and disposal facilities identified by a jurisdiction.

(b) Stratify the Populations (Optional Step).
Stratify each identified population into distinct subpopulations. The jurisdiction shall select the subpopulations. For example, to stratify the population for a solid waste diversion characterization, the jurisdiction could stratify the population of recycling facilities into the following subpopulations: drop-off centers, buy-back centers, and thrift shops. If the number of units in the subpopulation(s) is small, the jurisdiction may choose not to stratify the population, and instead choose a sample from the population as a whole.

(c) Random Sampling.
Assign a unique number to each identified unit of a population or subpopulation. Using a random numbers table or any other unbiased sampling method, choose the units to be sampled in the population or subpopulation, for each season identified by a jurisdiction. State the type(s) of unbiased sampling methods used in the solid waste generation study, when the study is submitted to the Board as a part of the SRR Element.

2. Sampling and Variability Determination: In order to determine the minimum number of samples to be taken from a population or subpopulation, a jurisdiction may use one of the following two methods:

(a) Klee and Carruth Method. Perform these tasks as follows:

(i) Sample, according to the requirements of Sections 18722, 18724 and 18726 of this Article, all of the solid waste generated, all of the solid waste diverted from disposal by recycling, composting or source reduction activities, and all of the solid waste transformed and disposed, for each identified population or subpopulation.

(ii) To determine the number of samples required for a statistically representative sampling from each population or subpopulation, the jurisdiction shall use the formula for normal approximation which is found in: A.J. Klee and D. Carruth, "Sample Weights in Solid Waste Composition Studies," American Society of Civil Engineers Journal of the Sanitary Engineering Division, volume 96(SA4), pages 945-954, August 1970, which is incorporated by reference.

This formula is:

The formula is described in the text following the image.

A 90% confidence level shall be used in this formula. Thus at 90% confidence level, z = 1.645 and s = 0.1632, where z is the normal standard deviate (one-tailed) for the confidence level desired and s is the estimated standard deviation of the sample, transformed (arcsin) basis.

A jurisdiction shall use these values for z and s in computing the minimum number of samples. A jurisdiction shall select the confidence interval and confidence width to be used in computing the minimum number of samples, i.e., the jurisdiction shall determine the d (small delta) value to use in the formula.

In order to determine d, a jurisdiction shall estimate its percent waste composition (x) by use of existing published data (waste category, and waste type if available) about the jurisdiction, and/or published data on percent waste composition from other jurisdictions. The source of the value of X used in the solid waste generation study shall be stated in the solid waste generation study.

Next, a jurisdiction shall select a level of precision or sensitivity (^) (large delta) (e.g., 1%, 2%, 3%) concomitant with its need for a given level of precision, with its population, and with the funds it has available for the solid waste generation study, as determined by the jurisdiction.

The waste category occurring in the highest percent in the selected waste stream shall be selected as the waste category for determining x and computing d.

(iii) All solid waste generation studies prepared using the Klee and Carruth Method for the purposes of meeting the requirements of the Integrated Waste Management Act of 1989, as amended, and otherwise approved by the Board, shall be considered to meet the requirements of this Article.

(b) American Society of Testing Materials (ASTM) Method.

(i) Sample, according to the requirements of Sections 18722, 18724 and 18726 of this Article, all of the solid waste generated, all of the solid waste diverted from disposal by recycling, composting or source reduction activities, and all of the solid waste transformed and disposed, for each identified population or subpopulation in the jurisdiction.

(ii) A jurisdiction shall use Section 9 and Table D of Draft No. 4 of the proposed ASTM "Method for Determination of the Composition of Unprocessed Municipal Solid Waste", dated January 24, 1990, which is incorporated by reference. A jurisdiction may also use the values for s and x in Table C of this Method, or may use values for s and x found in published solid waste characterization studies which were conducted in California subsequent to 1984. Other sections of this Method may be used with Section 9 and Table D. Once a final version of this Method is adopted by ASTM, that Method shall become the approved method for compliance with this Article.

All solid waste generation studies prepared using the Draft ASTM Method for the purposes of meeting the requirements of the Integrated Waste Management Act of 1989, as amended, and otherwise approved by the Board, shall be considered to meet the requirements of this Article.

3. Sort and Identify. Sort and identify the solid wastes from each population and/or subpopulation, using the sources of waste generation listed in Section 18722(i) of this Article, and the waste categories and waste types listed in Section 18722(j) of this Article.

4. Assignment of Waste Category and Waste Type. Assign each identified solid waste material to one of the waste categories and waste types listed in Sections 18722 (j) of this Article, or to any additional waste types which a jurisdiction chooses to add to the list of waste types in section (j) of this Article.

5. Volume or Weight Measurement. Measure the volume or weight of each solid waste material that has been identified.

6. Tabulate and Analyze Data. Perform these tasks in the following order. Tabulate and analyze all data compiled about the waste categories and waste types. As a part of the analysis, a jurisdiction shall compute (a) and (b) as follows:

(a) Determination of Mean and Variability.
Compute the sample mean (x) for volume or weight for each waste category and waste type identified.

Note, x = Exi/n, where xiis a sample weight or volume and n is the total number of samples taken in the population or subpopulation sampled.

Next, compute the variance (s2; i.e.,where s2 = E(xi- x)2/n-1) and the standard deviation of the mean (s), for volume or weight measurement for each population and subpopulation, using the following formula:

(Graphic here, not reproduced in this format)

(b) Set Confidence Levels for Sample Mean.
Set a 90% confidence level around the sample mean (x), for each waste category and waste type identified.

Use the formula:

The formula is described in the text following the image.

where tn-1 is the t value taken from the Student's t test values in Table 1, and where (n-1) is the degrees of freedom for the Student's t test for a 90% confidence level.

Note: This formula is used to establish a confidence interval for a population mean when the population variance is unknown. This formula is found in: M. Woodward and L.M.A. Francis. 1988. Statistics for Health Management and Research, Section 7.4.3, pgs. 161-162. London: Edward Arnold Publishers, which is incorporated by reference.

7. Data Analysis Adjustment. The data analysis conducted in steps 1 through 6 may be adjusted to include waste categories and waste types which:

(a) are known, by current written records held by the solid waste recycling, composting, source reduction, transformation or disposal facilities, to be disposed or diverted in a jurisdiction or in permitted solid waste facilities used by a jurisdiction, and

(b) may otherwise have been overlooked in the random sampling procedure.

TABLE 1
Student's t Values*
Number of
Samples (n)
Degrees of
Freedom (n-1)
90% Confidence
Level
2 1 6.314
3 2 2.920
4 3 2.353
5 4 2.132
6 5 2.015
7 1.943
8 7 1.895
9 8 1.860
10 9 1.833
11 10 1.812
12 1 1.796
13 12 1.782
14 13 1.771
15 14 1.761
16 15 1.753
17 16 1.746
18 17 1.740
19 18 1.734
20 19 1.729
21 20 1.725
22 21 1.721
23 22 1.717
24 23 1.714
25 24 1.711
26 25 1.708
27 26 1.706
28 27 1.703
29 28 1.701
30 29 1.699
31 30 1.697
36 35 1.690
41 40 1.684
46 45 1.679
51 50 1.676
61 60 1.671
71 70 1.667
81 80 1.664
91 90 1.662
101 100 1.660
121 120 1.658
141 140 1.656
161 160 1.654
189 188 1.653
201 200 1.653
oo oo 1.645

*Source: George Savage, Draft ASTM Method, ASTM Designation DXXXX XX, Table D, January 1990, Philadelphia, PA: American Society of Testing Materials.

Note:

Authority cited: Sections 40502 and 41824, Public Resources Code.
Reference: Sections 41030, 41031, 41032, 41033, 41300, 41330, 41331, 41332, 41333, 41780 and 41781, Public Resources Code.

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