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Edison Electric Institute v. Environmental Protection Agency

December 10, 2004


On Petitions for Review of an Order of the Environmental Protection Agency

Before: Edwards and Randolph, Circuit Judges, and Williams, Senior Circuit Judge.

The opinion of the court was delivered by: Randolph, Circuit Judge

Argued October 15, 2004

Edison Electric Institute and organizations representing corporate and municipal dischargers brought these consolidated petitions for review, claiming that certain of EPA's "whole effluent toxicity" or "WET" test methods were invalid. The tests are set forth in rules promulgated pursuant to the Clean Water Act, 33 U.S.C. § 1251 et seq. (the "Act"). The Act prohibits the discharge of pollutants except in compliance with individual permits issued by EPA or the states. States prescribe their own water quality criteria, which EPA reviews for conformity with the Act. Water quality standards typically consist of two complementary parts: numerical limits on the allowable concentration of particular pollutants in ambient water ( e.g., "no more mercury than 5 parts per billion"), and a descriptive, "narrative" criterion regarding the entire effluent ( e.g., "no toxic pollutants in toxic amounts"). See 33 U.S.C. § 1251(a)(3). WET tests are used to measure compliance with standards of the latter type.

While the numerical restrictions comprise the backbone of the permitting system, EPA has found that, standing alone, these limits are not sufficient. Effluents may contain many different pollutants. Even if no single pollutant were present in a harmful amount, the mix of different pollutants still might have negative effects upon aquatic organisms. In light of the myriad potential interactions among various pollutants, traditional instrumental tests are ill-suited to making the determination. Instead, laboratories expose aquatic organisms to samples of the effluent, at various concentrations, and measure the extent to which the organisms are adversely affected. If, in the laboratory, the effluent is harmful to the test organisms at a certain concentration, then it is presumed also to be harmful to aquatic life in the stream -- i.e., to be toxic -- at that concentration.

This approach has an appealing simplicity, but the use of living specimens introduces a significant potential for variability between and within tests. In designing and refining the WET test methods, EPA sought to minimize the effect of organic idiosyncracy by taking experimental and statistical precautions. The crux of petitioners' complaint is that EPA has not gone far enough. We disagree, and therefore deny the petitions for review.


These WET test methods were first implemented in 1995. 60 Fed. Reg. 53,529 (Oct. 16, 1995). Petitioners brought an action challenging them, as a result of which the WET tests were modified pursuant to a settlement of the action, after which EPA repromulgated them in 2002. 67 Fed. Reg. 69,952 (Nov. 19, 2002) ("Final Rule").*fn1 It is this most recent version of the tests that we now review.


Petitioners' primary concern is that EPA did not adhere to its usual criteria and procedures for ensuring the scientific validity of the test methods.*fn2 These criteria include accuracy, precision, practical applicability, establishment of detection limits, and the minimization of external interference. See EPA, Availability, Adequacy, and Comparability of Testing Procedures for the Analysis of Pollutants Established Under Section 304(h) of the Federal Water Pollution Control Act 3-2 to 3-5 (Sept. 1988) (" Report to Congress ").*fn3 While EPA concedes that its WET tests do not incorporate every one of these factors, the real question is whether EPA adequately accounted for any departures. We find that it did.

EPA explained at length, both in its response to public comments and in the Final Rule, that there are two major distinctions between WET tests and most other test methods approved for assessing permit compliance under the Act. First, while most tests rely on instrumentation to conduct chemicalspecific numerical measurements, WET testing is biological, using live organisms that cannot be, for example, calibrated. Second, unlike properties such as chemical concentration, toxicity is both measured and defined by the WET tests ( i.e., it is a "method-defined analyte"). These are meaningful differences, which serve to limit the usefulness of petitioners' analogies between WET testing and chemical-specific instrumental methods.

EPA admits that accuracy, in its technical rather than colloquial sense, is inapplicable to WET testing, but it does not follow that the tests are therefore "inaccurate." Accuracy is a composite of two distinct characteristics: "precision" and "bias." The former measures the variation among the results of multiple tests of the same sample; the latter describes any systemic and persistent deviation of the average value of a test method from an accepted "true value." Final Rule, 67 Fed. Reg. at 69,965. While precision can be, and has been, evaluated for WET methods, "bias" cannot be because it relies on comparisons with an independent, objective, "true value." When measuring chemical concentration, for example, it is a simple matter for a laboratory to combine pure water with a given toxicant in a certain ratio, and then assess the ability of instruments correctly to ascertain this known concentration. For a method-defined analyte such as toxicity, however, there is no such thing as a "true value" independent of the WET tests themselves. This does not mean that the tests are inherently unreliable, but rather that their scientific validity must be assessed through other means. This is consistent with EPA's treatment of other method-definite analytes. See generally 40 C.F.R. pt. 136.

While conceding the inapplicability of bias, EPA stated in the rulemaking that its WET test methods satisfy precision. 67 Fed. Reg. at 69,965. Petitioners argue that this conclusion is unsupported. The record contains extensive raw data, from the main EPA Interlaboratory Study and other privately commissioned studies, regarding the variability of WET toxicity measurements. See, e.g., EPA, Final Report: Interlaboratory Variability Study of EPA Short-term Chronic and Acute Whole Effluent Toxicity Test Methods (Sept. 2001) (" Interlaboratory Study "). From essentially the same data, petitioners draw quite different statistical conclusions than EPA.

Petitioners' analysis of this data does not convince us that EPA's action was "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law." 5 U.S.C. § 706(2)(A). And this is not just because of the deference we give to EPA when it evaluates "scientific data within its technical expertise." City of Waukesha v. EPA, 320 F.3d 228, 247 (D.C. Cir. 2003) (quoting Huls Am., Inc. v. Browner, 83 F.3d 445, 452 (D.C. Cir. 1996)); Appalachian Power Co. v. EPA, 135 F.3d 791, 801-02 (D.C. Cir. 1998). It is also because there are several errors in petitioners' methodology. One is petitioners' choice of units of measurement. According to EPA procedure, WET test results are recorded as percentages, representing how much dilution, if any, of an effluent sample is required for a certain effect to occur ( e.g., for the "No Observable Effect Concentration" datapoints, the percentage represents the level of dilution at which the mixture ceases to affect the organisms). Effluent that must be diluted to a 25% concentration before it ceases to cause demonstrable harm is more toxic than effluent that need only be diluted to 50%. In order to simplify the expression and application of these test results, EPA devised a scale of chronic toxicity units ("TUc"), equal to 100 divided by the measured percentage value, such that the 25% sample above would translate to 4 TUc, while the 50% sample would be 2 TUc. Thus, the higher an effluent's TUc rating, the more toxic the effluent. Petitioners make the mistake of assuming that relying on this invented scale in performing statistical analysis will ...

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