South Carolina Code of Regulations › Chapter 61 - DEPARTMENT OF HEALTH AND ENVIRONMENTAL CONTROL › Subchapter 61-79 - Hazardous Waste Management Regulations › Part 61-79.266 - STANDARDS FOR THE MANAGEMENT OF SPECIFIC HAZARDOUS WASTES AND SPECIFIC TYPES OF HAZARDOUS WASTE MANAGEMENT FACILITIES › Appendix 61-79.266.IX - Methods Manual for Compliance With the BIF Regulations Burning Hazardous Waste in Boilers and Industrial Furnaces › Section 61-79.266.7.0 - STATISTICAL METHODOLOGY FOR BEVILL RESIDUE DETERMINATIONS

Current through Register Vol. 48, No. 6, June 28, 2024
This section describes the statistical comparison of
					 waste-derived residue to normal residue for use in determining eligibility for
					 the Bevill exemption under
					 40 CFR
					 266.112.
7.1 Comparison of Waste-derived Residue with
				  Normal Residue
To meet the special criteria under 266.112(b)(1),
					 waste-derived residue must not contain appendix VIII, Part 261, constituents
					 (toxic constituents) at concentrations significantly higher than in residue
					 generated without burning or processing hazardous waste. Concentrations of
					 toxic constituents in normal residue are determined based on analysis of a
					 minimum of 10 composite samples. (Note that "normal" residue refers to residue
					 generated by a facility when operating without burning hazardous waste.) The
					 95th percent confidence interval about the mean of the normal residue
					 concentrations must be used in the comparison of waste-derived residue with
					 normal residue; the confidence interval is determined as described in
					 section7.2 below. The concentration of a toxic constituent in the waste-derived
					 residue is not considered to be significantly higher than in the normal residue
					 if the concentration in the waste-derived residue does not exceed the upper
					 95th percent confidence interval about the mean that was established for the
					 normal residue. Concentrations of toxic constituents in waste-derived residue
					 are determined based on analysis of samples taken over a compositing period of
					 not more than 24 hours.
7.2
				  Calculation of the 95th Percent Confidence Interval About the Mean for Toxic
				  Constituents in Normal Residue
The 95th percent confidence interval about the mean is
					 calculated for a set of values using a "t" distribution. In use of the "t"
					 distribution, it is assumed that the values are normally distributed; the "t"
					 distribution is applicable for use with small sample sets (i.e. approximately
					 10-30 samples). The 95th percent confidence interval about the mean is
					 determined using the following equation:
See
					 Image
The mean and standard deviation of these measurements,
					 calculated using equations above, are 11.5 and 2.9 respectively. Assuming that
					 the values are normally distributed, the upper 95th percent confidence interval
					 value about the mean is given by:
Table 7.0-1.- T Distribution
					 Values
Degrees of freedom
(n-1)
Percentage point of t distribution
(</2=0.025)
1
12.706
2
4.303
3
3.182
4
2.776
5
2.571
6
2.447
7
2.365
8
2.306
9
2.262
10
2.228
11
2.201
12
2.179
13
2.160
14
2.145
15
2.131
16
2.120
17
2.110
18
2.101
19
2.093
20
2.086
21
2.080
22
2.074
23
2.069
24
2.064
25
2.060
26
2.056
27
2.052
28
2.048
29
2.045
95th percent confidence interval value=11.5+2.2
								  62x(2.9/10)=13.6 ppm.
Thus, if the concentration of compound A in the
								  waste-derived residue is below 13.6 ppm, then the waste-derived residue is
								  eligible for the Bevill exemption for toxic compound A.
7.3 Normal Distribution Assumption
As noted in section7.2 above, this statistical approach
					 (use of the 95th percent confidence interval about the mean) for calculation of
					 the concentration in normal residue is based on the assumption that the
					 concentration data are distributed normally. The Department is aware that
					 concentration data of this type may not be distributed normally, particularly
					 when concentrations are near the detection limits. There are a number of
					 procedures that can be used to test the distribution of a data set. For
					 example, the Shapiro-Wilk test, examination of a histogram or plot of the data
					 on normal probability paper, and examination of the coefficient of skewness are
					 methods that may be applicable, depending on the nature of the data (Reference
					 1 and 2).
If the concentration data are not adequately represented by
					 a normal distribution, the data may be transformed to attain a near normal
					 distribution. The Department has found that concentration data, especially when
					 near detection levels, often exhibit a lognormal distribution. The assumption
					 of a lognormal distribution has been used in various programs at EPA, such as
					 in the Office of Solid Waste Land Disposal Restrictions program for
					 determination of BDAT treatment standards. The transformed data may be tested
					 for normality using the procedures identified above. If the transformed data
					 are better represented by a normal distribution than the untransformed data,
					 the transformed data should be used in determining the 95th percent confidence
					 interval using the procedures in section7.2 above.
In all cases where the applicant for the Bevill exemption
					 wishes to use other than an assumption of normally distributed data, or
					 believes that use of an alternate statistical approach is appropriate to the
					 specific data set, the applicant must provide supporting rationale and
					 demonstrate to the Department or permitting authority that the data treatment
					 is based upon sound statistical practice.
7.4 Nondetect Values
The Department is developing guidance regarding the
					 treatment of nondetect values (data where the concentration of the constituent
					 being measured is below the lowest concentration for which the analytical
					 method is valid) in carrying out the statistical determinations described
					 above. Until the guidance information is available, facilities may present
					 their own approach to the handling of nondetect data points, but must provide
					 supporting rationale in the operating record for consideration by the
					 Department or permitting authority.
7.5
1.
				  Shapiro, S.S. and Wilk, M.B. (1965), "An Analysis of Variance Test for
				  Normality (complete samples)," Biometrika, 591-611.
2. Bhattacharyya, G.K. and R.A. Johnson
				  (1977), Statistical Concepts and Methods, John Wiley and Sons, New
				  York.