In assessing best performing sources' level of performance, we quantified certain types of variability, notably analytic measurement variability that is an inherent component of performance tests, and run-to-run variability (variability in source's performance in the multiple runs that are averaged to yield the results of a combustion performance test). We also expressed sources' performance in terms of a parameter (a "normalizing parameter") relating to a source's function (either volumetric gas flow rate or, for energy recovery units, heating value of hazardous waste fuel) so that performance of sources of different size could be directly and meaningfully compared. Failure to account for quantifiable variability would have lead to standards unachievable by the best performing sources. Failure to normalize test results would have precluded meaningful comparison among sources of different size and would have lead to multiple subcategories based on unit size, a needlessly ungainly approach.
For more information, see the hazardous waste combustion web page.