United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued October 15, 2004 Decided December 10, 2004

No. 96-1062

EDISON ELECTRIC INSTITUTE, ET AL.,

PETITIONERS

v.

ENVIRONMENTAL PROTECTION AGENCY, ET AL.,

RESPONDENTS

AMERICAN PETROLEUM INSTITUTE,

INTERVENOR

Consolidated with

Nos. 96-1124, 03-1087, 03-1091, 03-1094

On Petitions for Review of an Order of the

Environmental Protection Agency

John C. Hall argued the cause for petitioners. With him

on the briefs were James N. Christman, Andrea W. Wortzel,

Alexandra D. Dunn, David E. Evans, Stewart T. Leeth, and

Richard H. Sedgley. Kristy A.N. Bulleit entered an appearance.

Fredric P. Andes argued the cause and filed the briefs for

intervenor.
2

Christina B. Parascandola and David S. Gualtieri,

Attorneys, U.S. Department of Justice, argued the cause and

filed the brief for respondents. Daniel R. Dertke, Attorney, U.S.

Department of Justice, entered an appearance.

Before: EDWARDS and RANDOLPH, Circuit Judges, and

WILLIAMS, Senior Circuit Judge.

Opinion for the Court filed by Circuit Judge RANDOLPH.

RANDOLPH, Circuit Judge: 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,
3

1

 Petitioners object to four of the ten test procedures described in the

2002 Final Rule: the Fathead Minnow Larval Growth Test Method

1000.0, the Fathead Minnow Embryo-larval Teratogenicity Test

Method 1001.0, Ceriodaphnia dubia (water flea) Reproduction Test

Method 1002.0, and Green Alga Growth Test Method 1003.0. See 67

Fed. Reg. at 69,972. Each of these four tests measures chronic

toxicity, which is defined in relation to test organisms’ growth and

reproduction, as opposed to acute toxicity, which is based on mortality

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.

I.

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”).1 It is this most recent version of the
4

rates. Id. at 69,953.

2 Petitioners suggest, without supporting authority, that because the

test results will be used as evidence in enforcement proceedings,

EPA’s rulemaking had to comply with the standard for scientific

evidence articulated in FED. R. EVID. 702, as interpreted in Daubert v.

Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993). Evidentiary

rules govern the admissibility of evidence at trial, not the

establishment of the processes whereby such evidence will be created.

See FED. R. EVID. 101 (“These rules govern proceedings in the courts

of the United States . . . .”). Of course, insofar as some of EPA’s own

criteria mirror the Daubert standard, EPA may not ignore or contradict

them without explanation.

3 This Report was an internal study on various testing methods,

undertaken at Congress’s express behest. Pub. L. No. 100-4, § 518(a),

101 Stat. 7, 86-87 (1987). The Report itself nowhere contemplates

being anything but a “study.” It is not strictly binding upon EPA and

any deviation from the Report is not per se arbitrary and capricious.

Cf. Report to Congress at 3-2 (“In most cases, no single [test] method

will contain all of the desirable characteristics.”).

tests that we now review. 

A.

Petitioners’ primary concern is that EPA did not adhere

to its usual criteria and procedures for ensuring the scientific

validity of the test methods.2 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”).3 While EPA

concedes that its WET tests do not incorporate every one of
5

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
6

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
7

4 The preferred metric for assessing precision is the coefficient of

variation (CV), which measures the extent to which multiple

measurements tend to depart from their average value. The greater the

CV, the less precise the measurement. By computing the CV using

toxicity units (TUcs) rather than the percentages originally recorded by

EPA, petitioners arrive at a grossly inflated result. For example,

analyzing reference toxicant data, Interlaboratory Study at 81-82 tbl.

9.8, EPA’s approach yields a CV of approximately 0.43—well within

the range of EPA’s other approved tests, Memorandum from Marion

Kelly, EPA Engineering and Analysis Division 1 (Oct. 16, 2002) (CVs

of approved chemical methods range from 0.03 to 0.64, and CVs of

organic methods from 0.12 to 1.04). Petitioners’ approach, however,

using the distorting TUc scale, results in a CV of 1.47—more than

triple the correct value. 

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 yield valid conclusions about the

distribution of the original data.4 This error lies at the heart of

petitioners’ claims of extreme variability in the results of WET

testing. EPA, on the other hand, finds that the data support the

conclusion that these WET test methods exhibit a degree of

precision compatible with numerous chemical-specific tests

already in use. We credit EPA’s conclusions on this point.

Another of petitioners’ central contentions is that the

WET test methods produce an unacceptably high number of

false positives. EPA’s test design had contemplated a positive

error rate of no more than five percent, and as low as one

percent in certain instances; this understanding was reflected in
8

the 1998 Settlement Agreement. Petitioners allege false positive

rates between 12.5% and 56%, Reply Brief at 27, while EPA,

again analyzing the same data, finds an overall false positive

rate of 1.3%, with no individual test’s rate exceeding 5%. See

Final Rule, 67 Fed. Reg. at 69,968. The discrepancy stems from

the parties’ differing definitions of the term “false positive.”

EPA defines a false positive result as one indicating toxicity in

a blank sample. Interlaboratory Study at 66. Such results occur

quite infrequently. Petitioners’ definition, however, is far more

expansive, encompassing all results that exhibit toxicity greater

than the median toxicity for a given sample. Reply Brief at 25

n.29. Their concern is that some discharge permits may specify

an acceptable nonzero level of toxicity, which the effluent may

not exceed, and that the WET tests have the potential to produce

arbitrary permit violations. For example, if a permittee were

subject to a toxicity limit of 3 TUc, and a WET test of its

effluent would yield a 2 TUcresult most of the time, but up to 4

TUc some of the time, the latter outcome would constitute a

permit violation and potentially trigger an EPA enforcement

action.

This is certainly a problem for which EPA’s system must

account. It is not, however, a problem of false positives. What

petitioners describe relates to precision, which we already have

discussed. Multiple measurements will exhibit some degree of

variation, yielding an error band that extends above and below

some intermediate value. This is the case with chemical-specific

instrumental tests and, indeed, with virtually every water quality

test EPA uses. See 40 C.F.R. pt. 136. Furthermore, petitioners

neglect to mention that just as some permittees who “should be”

in compliance may be deemed violators, other permittees who

“should be” violators may be deemed in compliance. That is the

nature of any distribution: No matter how narrow the error

band, or how precise the test, there always will be some

measurements on the high end of the range, and some on the
9

5 One page of petitioners’ opening brief contains what purports to be

a constitutional argument—that if a particular WET test indicates

toxicity, this will constitute an irrebuttable presumption of petitioners’

guilt in violation of the Due Process Clause. As we stated in the text,

we are concerned here only with test methodology, not results of

particular tests in the field. Our decision does not endorse the validity

of any test result in the future, nor does it foreclose a defense that the

result is wrong. Those issues are simply not presented in this judicial

review of rulemaking. Furthermore, when the Supreme Court has

recognized the constitutional dimensions of presumptions, it has done

so solely with regard to statutory classifications, which tended to have

strong equal protection components as well. See, e.g., Weinberger v.

Salfi, 422 U.S. 749 (1975) (Social Security eligibility classifications

low. The real question is whether this variation is excessive,

and EPA has demonstrated that it is not. EPA also offered an

additional safeguard by designing the tests to give permittees the

benefit of the doubt, limiting false positive rates to at most 5%,

while allowing false negative rates up to 20%. EPA,

Understanding and Accounting forMethod Variability in Whole

Effluent Toxicity Applications Under the National Pollutant

Discharge Elimination System 5-6 to 5-7 (June 2000).

It is worth pausing here before we examine petitioners’

other attacks on the WET test methods. There is an important

distinction between the validity of a test method and the validity

of a particular result from the test when it is used to determine

compliance with permit conditions. Even by EPA’s

calculations, WET tests will be wrong some of the time, which

is why EPA warned against using a single test result to institute

an action for a civil penalty. See 67 Fed. Reg. at 69,968.

Nothing we have written thus far, and nothing we write in the

balance of this opinion forecloses consideration of the validity

of a particular test result in an enforcement action. See 33

U.S.C. § 1369(b)(2). That issue is not before us. The case

involves only the validity of the WET test methods.5
10

for spouses and stepchildren); Vlandis v. Kline, 412 U.S. 441 (1973)

(state residency classifications for college tuition); see also JOHN E.

NOWAK & RONALD D. ROTUNDA, CONSTITUTIONAL LAW § 13.6 (5th

ed. 1995). There is no such classification here. To the extent

petitioners’ complaint is that in some future enforcement proceeding,

they will not be able to attack the WET test methodology (if we rule

in EPA’s favor in this case), they are not speaking of an irrebuttable

presumption at all. This case is their chance to rebut the so-called

“presumption.” Their inability to do so in some future proceeding is

simply a consequence of the judicial review provision in 33 U.S.C. §

1369(b)(2).

Petitioners’ next objection is to EPA’s failure to establish

detection limits for WET test methods. The public commenters

raised this point and EPA explicitly addressed it in promulgating

its Final Rule. 67 Fed. Reg. at 69,968. Detection limits are

applicable only to tests that rely on instrumental measurements;

they represent the sensitivity thresholds of the technology,

below which measurements become unreliable or impossible.

Because WET testing is a biological and experimental, rather

than an instrumental, method, “detection limit concepts are not

applicable.” Id.; see also Report to Congress at 3-11. The

ratified test methods, however, entail a built-in mechanism that

serves the same basic purpose as detection limits in instrumental

tests—to reduce the likelihood that random “noise” will result

in a false positive result. A single WET test involves exposing

multiple batches of organisms to the effluent at various

concentrations, as well as to a “control” sample of pure water,

and then aggregating the effects on each batch. Statistical

analysis then is used to ensure that any observed differences

between the organisms exposed to a given effluent concentration

and those exposed to the control blanks most likely are not

attributable to randomness—that they are statistically

significant. See Final Rule, 67 Fed. Reg. at 69,957-58. This

safeguard addresses petitioners’ concerns. EPA, in short, has

offered a reasoned and thorough explanation of its decision on
11

this subject. The law requires no more. See, e.g., Int’l

Fabricare Inst. v. EPA, 972 F.2d 384, 389 (D.C. Cir. 1992).

Petitioners also assert that EPA failed to demonstrate the

availability and applicability of WET testing—that is, the ability

of laboratories across the nation to conduct WET testing

properly and consistently. One of the main purposes of the

Interlaboratory Study was to ensure that a wide range of

laboratories could implement the prescribed test methods

without introducing an undue degree of variability or error.

More than 90% of laboratories were able to complete the ratified

tests in accordance with all mandatory procedures, with success

rates reaching 100% for several tests. Final Rule, 67 Fed. Reg.

at 69,955. When EPA was unable to find enough available

laboratories for a trial of certain WET test methods, it withdrew

those methods from 40 C.F.R. pt. 136. Id. Although the

Interlaboratory Study clearly supports the availability and

applicability of the challenged tests, petitioners think that

procedural defects invalidate it. The claim is that because

laboratories chosen for the test knew in advance that they would

be participating, EPA violated its own guidelines, which

required the study to be “blind.” Interlaboratory Study at A-21.

This misapprehends the nature of blind testing. EPA called for

“blind samples,” id. (emphasis added), and that is what the

laboratories received—samples with no indication about which

were the control “blanks” and which were the reference

toxicants, Proposed Rule, 66 Fed. Reg. 49,794, 49,806 (Sept. 28,

2001). Petitioners also allege that EPA improperly ignored the

results of the peer review process. But EPA published an

extensive point-by-point response to peer comments and

acknowledged the peer-review process in its revisions to the

Final Rule, 67 Fed. Reg. at 69,954. The Interlaboratory Study

thus complied with the appropriate procedures and established

the ratified tests’ availability and applicability.
12

Another important test characteristic is

“representativeness,” that is, the ability of test results to predict

instream effects accurately. Petitioners claim that EPA failed to

establish the presence of such correlations for several of the

WET tests, particularly with regard to Western state waters,

which differ chemically from their Eastern counterparts. EPA

responds by pointing to the results of numerous studies on this

subject conducted throughout the 1990s. These studies support

the representativeness of the WET test methods in general, and

several demonstrate representativeness with regard to particular

Western waters. See, e.g., EPA, A Review of Single Species

Toxicity Tests: Are the Tests Reliable Predictors of Aquatic

Ecosystem Community Responses? 47-50 (July 1999). It is

unrealistic in the extreme to require correlation studies on every

stream in the nation. EPA took the sensible approach of relying

on sampling techniques to draw general conclusions, while

leaving some implementation details to local entities. See Am.

Iron & Steel Inst. v. EPA, 115 F.3d 979, 1005 (D.C. Cir. 1997).

Pursuant to the Clean Water Act’s National Pollutant Discharge

Elimination System, 33 U.S.C. § 1342(a), states retain

discretion, subject to EPA guidance and recommendations, to set

their toxicity thresholds in order to compensate for local

conditions at the permitting stage. See 40 C.F.R. §

122.44(d)(1)(iii). In light of this discretionary, rather than

mandatory, nature of state implementation of standards and

thresholds, we also are unpersuaded by petitioners’ assertion

that the WET program amounts to an illegal federal water

quality standard.

The role of state permitting authorities also should allay

the concern, which petitioners express, that the correlation

between laboratory toxicity and instream impacts grows weaker

at lower levels of toxicity. Before implementing a test method,

EPA must establish that the measured characteristic bears a

rational relationship to real-world conditions; the available
13

studies reasonably support such a conclusion with regard to

chronic toxicity. EPA, Technical Support Document for Water

Quality-Based Toxics Control 8 (Mar. 1991) (finding likelihood

that data may be explained by randomness, rather than actual

correlation, to be 0.1%). Petitioners are worried that they might

be subject to excessive restrictions; such limits, however, would

be imposed by local authorities, and are not part of the

rulemaking under review in this case. The WET test methods

offer only a means of measuring compliance with those

limits—individual dischargers remain free to challenge their

permits, on a case-by-case basis, if they believe that local

authorities are regulating at a level that poses only a minimal

risk to aquatic life. See 40 C.F.R. §§ 124.19, 124.21.

The ratified WET tests are not without their flaws. But

perfection is not the standard against which we judge agency

action. WorldCom, Inc. v. FCC, 238 F.3d 449, 461 (D.C. Cir.

2001); Northwest Airlines, Inc. v. U.S. Dep’t of Transp., 15F.3d

1112, 1119 (D.C. Cir. 1994). EPA’s decision was informed by

years of scientific studies, negotiation, and public notice-andcomment, and it represents the agency’s expert judgment

regarding the implementation of the aims of the Clean Water

Act. Petitioners have not demonstrated that EPA ignored

relevant record evidence, contradicted its own policies without

explanation, or otherwise acted arbitrarily and capriciously. See

Motor Vehicle Mfrs. Ass’n v. StateFarm Mut.AutoIns. Co., 463

U.S. 29, 41-42 (1983);Prof’lPilotsFed’n v. FAA, 118 F.3d 758,

771 (D.C. Cir. 1997); Natural Res. Def. Council, Inc. v. EPA,

822 F.2d 104, 111 (D.C. Cir. 1987).

II. 

American Petroleum Institute (“API”) seeks to intervene

for the purpose of challenging EPA’s failure to ratify for use in

the Pacific Ocean three WET test methods that measure acute
14

toxicity. “An intervening party may join issue only on a matter

that has been brought before the court by another party.” Ill.

Bell Tel. Co. v. FCC, 911 F.2d 776, 786 (D.C. Cir. 1990), citing

Vinson v. Wash. Gas Light Co., 321 U.S. 489, 498 (1944). The

issue presented by API overlaps with the issues petitioners raise

only insofar as both involve whole effluent toxicity. The bare

assertion that API “agree[s]” with petitioners’ claims, Reply

Brief at 37, does little to cure this defect. The procedural device

of intervention does not contemplate so broad a compass. We

will not consider API’s arguments.

III.

For the reasons set forth above, having considered and

rejected petitioners’ other arguments, we deny the petitions for

review.