Opinion ID: 519994
Heading Depth: 2
Heading Rank: 1

Heading: The EPA's Statistical Method of Developing the BAT Limitations

Text: 256
Long-Term Averages 257 To derive the BAT limitations the EPA averaged over a long term the amount of the toxic discharged by what it considered to be the best plant or plants in the data base using BAT technology. It then multiplied this long-term average by a variability factor, a number always greater than one, to account for its estimate of the reasonable variation from the average that could be expected by the several best-performing plants in the data base. The product was the BAT limitation for that toxic. 258 A toxic may be present in a discharge in such a small amount that it cannot be detected by state-of-the-art analytical methods, that is, the amount of a toxic may be less than the analytical minimum. Generally, the analytical minimum for the detection of a toxic is 10 parts per billion (ppb), a proportion that, following an analogy employed by CMA at oral argument, is comparable to one minute in two thousand years. For the purpose of calculating long-term averages the EPA assumed that the amount of an undetected substance contained in a discharge (the non-detect value) equalled the analytical minimum; in other words, if the toxic might be present, but only in such a small concentration that it could not be detected by currently-used analytical methods, the EPA assumed the toxic was present at the analytical minimum, generally 10 ppb. None of the petitioners objects to the EPA's use of non-detect values in the calculation of long-term averages, presumably because assigning the analytical minimum to a reading in which a specific toxic could not be detected had the effect of raising the long-term average and thus raising the effluent limits. CMA objected to weighted averaging of such values, however, because this lowered the limitations. 259 The long-term averages were calculated by averaging detectable values and non-detect values. The EPA calculated the average of the assigned non-detect values and the average of detectable values for the data base and then weighted the averages according to the proportions of all non-detect and detectable values reported for plants in the data base for a given pollutant. The long-term average for a particular plant was calculated as the weighted sum of the averages of detect and non-detect values reported for plants in the data base. 198 260 CMA contends that the EPA's weighted averaging of non-detect values significantly lowered the long-term averages it calculated from measured effluent concentrations, and thus lowered the OCPSF effluent limits for at least 27 pollutants. CMA concludes that this was without justification or support, hence arbitrary. 261 The choice of statistical methods is committed to the sound discretion of the Administrator. 199 Weighted averaging is a recognized statistical method for adjusting a data set when the data for particular units, plants in this case, are not represented by a comparable number of readings or samples. When some units in a data set are represented by fewer readings than other units in the set, the units represented by fewer readings should be given less weight in the average, i.e., discounted through weighted averaging. Conversely, those units in a data set based on a larger number of readings should be given greater weight in the average. Including a unit for which there is a smaller number of readings in a calculation, without discounting it by weighted averaging, would distort the average. 200 262 CMA correctly contends that use of a different averaging method would yield different results. Indeed, several different methods might have been used, each producing a different result. As the First Circuit has noted, however, [t]he choice of any given method may mean that an alternative method would yield different results. The necessary corollary ... is that any other system chosen would be open to the same criticism. We will not leave the Agency so vulnerable. 201 We agree, provided, of course, that there is no demonstration that the Agency's method was chosen arbitrarily or merely for the purpose of achieving a predetermined prejudicial effect. The EPA's use of weighted averaging to determine the long-term averages was not an abuse of discretion.
263 The same plant using the same treatment method to remove the same toxic does not always achieve the same result. Tests conducted one day may show a different concentration of the same toxic than are shown by the same test the next day. This variability may be due to the inherent inaccuracy of analytical testing, i.e., analytical variability, or to routine fluctuations in a plant's treatment performance. 264 The EPA attempted to take this variability into account. To do so, it calculated the BAT limitations by multiplying the long-term average concentration of each pollutant by a variability factor that reflected observed variations in treatment performance experienced by plants that had attempted to remove that pollutant. The EPA computed the variability factor for each plant in the BAT data base for that pollutant or, if there were two or more plants with a significant number of data points in the detectable range, it averaged the variability factors for all the plants. 265 CMA asserts that averaging variability factors from different plants assumes that the plants are similar, an assumption that is not supported by the record, and that the EPA has failed to show that the different plants can reduce the amount of variability to the factor computed by the EPA. CMA further contends that the EPA should have created separate subcategories to account for the different variability experienced by the various types of plants using BAT. 266 As the EPA notes, averaging variability factors inures to the benefit of the industrial petitioners because it yields a greater variability factor than the factor that would have resulted from using data from the single plant that experienced the least variability. The EPA decided not to subcategorize BAT plants on the basis of variability because the EPA determined that OCPSF plants utilizing BAT could achieve uniformly high levels of removal of toxics. 202 267 The reasonableness of the variability factors used by the EPA is supported by the record. 203 Moreover, CMA has failed to demonstrate that the greater variability measured at some plants is due to uncontrollable factors rather than plant inefficiencies or that the fact of such greater variability shows that the limitations are not achievable.