206 F.3d 1286 (D.C. Cir. 2000)
Chlorine Chemistry Council and Chemical Manufacturers Association, Petitionersv.Environmental Protection Agency, RespondentNatural Resources Defense Council, et al., Intervenors
Nos. 98-1627, 99-1053, 99-1056
United States Court of AppealsFOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued February 11, 2000Decided March 31, 2000

On Petitions for Review of an Order of the Environmental Protection Agency
Thomas Richichi argued the cause for petitioners Chlorine  Chemistry Council, et al. and supporting intervenor Society of the Plastics Industry, Inc.  With him on the briefs were  Kathryn Y. Aspegren, David F. Zoll, Katherine L. Rhyne,  Paul D. Clement, Richard S. Wasserstrom, Jerome H. Heckman, Peter L. de la Cruz and Komal J. Hershberg.
John F. Cooney and Brock Landry were on the brief for  amicus curiae Public Health Scientists.
Karen L. Egbert, Attorney, U.S. Department of Justice,  argued the cause for respondent. With her on the brief were  Lois J. Schiffer, Assistant Attorney General, and Karen H.  Clark, Attorney, U.S. Environmental Protection Agency.  Christopher S. Vaden, Attorney, U.S. Department of Justice,  entered an appearance.
Alan Charles Raul and David M. Levy were on the brief  for amici curiae Congressman Tom Bliley.
Erik D. Olson was on the brief for intervenors Natural  Resources Defense Council and Physicians for Social Responsibility.
Before:  Silberman, Williams and Ginsburg, Circuit  Judges.
Opinion for the Court filed by Circuit Judge Williams.
Williams, Circuit Judge:


1
The Safe Drinking Water Act  ("SDWA" or the "Act") directs the Environmental Protection  Agency to set standards for the regulation of covered drinking water contaminants.  For each EPA sets a "maximum  contaminant level goal" ("MCLG"), defined as "the level at  which no known or anticipated adverse effects on the health  of persons occur and which allows an adequate margin of  safety."  42 U.S.C. S 300g-1(b)(4)(A).  The MCLG is somewhat as pirational.  After having set it, EPA is to promulgate  an enforceable standard, known as a maximum contaminant  level ("MCL"), which takes practical considerations into account while remaining "as close to the [MCLG] as is feasible."Id. S 300g-1(b)(4)(B).


2
In March 1998 EPA concluded that chloroform, a drinking  water contaminant, exhibits a "nonlinear mode of carcinogenic  action."  Notice of Data Availability:  National Primary Drinking Water Regulations:  Disinfectants and Disinfection  Byproducts, 63 Fed. Reg. 15,674, 15,686/1 (1998).  In other  words, exposures to chloroform below some threshold level  pose no risk of cancer.  But in promulgating the MCLG it  retained the existing standard of zero, which was based on  the previously held assumption that there was no safe threshold.  Final Rule:  National Primary Drinking Water Regulations:  Disinfectants and Disinfection Byproducts, 63 Fed.  Reg. 69,390, 69,398/3 (1998) ("Final Rule").  EPA justified its  action on a variety of grounds, including an alleged need to  consult the report of its Science Advisory Board ("SAB"),  which would not be available until after the statutory deadline  for rulemaking had expired.  Petitioners, including the Chlorine Chemistry Council, a trade association comprised of  chlorine and chlorine product manufacturers, petitioned this  court for review, arguing that EPA violated its statutory  mandate to use the "best available" evidence when implementing the provisions of the Safe Drinking Water Act.  42  U.S.C. § 300g-1(b)(3)(A).  We agree.


3
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4
Chloroform, a "nonflammable, colorless liquid," Proposed  Rule:  National Primary Drinking Water Regulations:  Disinfectants and Disinfection Byproducts, 59 Fed. Reg. 38,668,  38,694/2 (1994), is one of four compounds that together are  classed as "Total Trihalomethanes" ("TTHMs").  These are  byproducts of chlorination, the most widely used technique  for ensuring the safety of drinking water.  Chlorination plays  a significant role in the control of microbial pathogens and in  turn in the protection of public health;  but on the basis of  rodent tumor data the Agency has concluded that chloroform,  a byproduct of this process, acts as a probable human carcinogen.  Id. at 38,697/2.


5
On July 29, 1994 EPA issued a proposed rule on disinfectants and disinfection byproducts in water.  This included a  zero MCLG for chloroform, based on EPA's finding of an  absence of data to suggest a threshold level below which there  would be no potential carcinogenic effects.  Id.  The Agency's default method of inferring risk at exposure levels for which  it has no adequate data is linear extrapolation from cancer  incidence inferred at exposures for which it does have data.See EPA's Proposed Guidelines for Carcinogen Risk Assessment, 61 Fed. Reg. 17,960, 17,968/3 (1996).  Thus, either if  the evidence supports linearity, or if there is "insufficient"  evidence of nonlinearity, EPA assumes that if a substance  causes cancer at any exposure it will do so at every non-zero  exposure (though with cancer incidence declining with exposure).  But EPA acknowledges its authority "to establish nonzero MCLGs for carcinogens if the scientificevidence"  indicates that a "safe threshold" exists.  See Final Rule, 63  Fed. Reg. at 69,401/2.  And petitioners here assume the  validity of the linear default assumption.


6
In 1996 Congress amended the SDWA, enshrining in the  statute a timetable previously set by EPA for rules relating  to disinfectants and disinfection byproducts associated with  water treatment.  42 U.S.C. § 300g-1(b)(2)(C);  Proposed  Rule:  National Primary Drinking Water Regulations:  Monitoring Requirements for Public Drinking Water Supplies, 59  Fed. Reg. 6332, 6361 (1994).  The relevant deadline here was  November 1998.  In preparation for the necessary rulemaking EPA formed an advisory group in 1997 whose purpose  was "to collect, share, and analyze new information and data,  as well as to build consensus on the regulatory implications of  this new information."  Notice of Data Availability:  National  Primary Drinking Water Regulations:  Interim Enhanced  Surface Water Treatment Rule, 62 Fed. Reg. 59,486, 59,491/1  (1997).


7
On the basis of the committee's findings and recommendations, EPA in November 1997 published a Notice of Data  Availability ("NODA"), 62 Fed. Reg. 59,388 (1997), and in  1998 it published a second NODA specific to chloroform, 63  Fed. Reg. 15,674 (1998).  Among the findings it discussed  were those arrived at by a panel of experts organized by the  International Life Sciences Institute.  The panel, whose work  was subject to independent peer review and was convened  under the auspices of the EPA, concluded on the basis of  chloroform's mode of action that although it was "a likely carcinogen to humans above a certain dose range, [it was]  unlikely to be carcinogenic below a certain dose range."  Id.  at 15,685/1.  The panel recommended "the nonlinear [ ] or  margin of exposure approach [as] the preferred approach to  quantifying the cancer risk associated with chloroform exposure."  Id. at 15,686/1.


8
EPA agreed.  It said that "[a]lthough the precise mechanism of chloroform carcinogenicity is not established," nevertheless "the chloroform dose-response should be considered  nonlinear."  Id. at 15,685/3.  Rather than operating through  effects on DNA, which is consistent with linearity, chloroform  evidently works through "cytotoxicity" (i.e., damage to the  cells) followed by regenerative cell proliferation.  Id.  Employing the threshold approach that it found was entailed by  chloroform's mode of action, EPA then calculated an MCLG  of 600 parts per billion ("ppb"), based solely on carcinogenicity.  Id. at 15,686/2.  This level built in a 1000-fold margin of  error in relation to the maximum safe dosage implied from  the animal studies used by EPA.  Id.  But because even  lower chlorine doses cause liver toxicity (a non-cancer effect),  EPA proposed an MCLG of 300 ppb.  Id.


9
When EPA came to promulgate its final rule in December  1998, however, its MCLG was again zero.  Final Rule, 63  Fed. Reg. at 69,398/3.  It stuck with 1994's zero level despite  its explicit statement that it now "believe[d] that the underlying science for using a nonlinear extrapolation approach to  evaluate the carcinogenic risk from chloroform is well founded."  Id. at 69,401/1.  It justified the action on the basis that  "additional deliberations with the Agency's SAB on the analytical approach used" and on the underlying scientific evidence were needed "prior to departing from a long-held EPA  policy."  Id. at 69,399-69,401.  It could not complete such  additional deliberations by the November 1998 statutory  deadline, and, moreover, the rulemaking would not affect the  enforceable MCL for TTHMs.


10
After briefing on the petition for review at issue here, but  before oral argument, EPA moved for a voluntary remand to  consider the SAB report on chloroform that would soon be available.  But EPA made no offer to vacate the rule;  thus  EPA's proposal would have left petitioners subject to a rule  they claimed was invalid.  We denied the motion.


11
On February 11, 2000, the day of oral argument, EPA  released a draft report by the SAB on chloroform.  See Draft, ChloroformRisk Assessment Review, February 10,  2000 (visited March 27, 2000) <http:  //www.epa.gov/  science1/chlod00x.pdf>.  The report concluded that chloroform exhibits a "cytotoxic" mode of action.  Such a mode of  action (unlike a "genotoxic" mechanism, which acts directly on  a cell's DNA) involves no carcinogenic effects at low doses; thus a nonlinear approach is "scientifically reasonable."  Id.  at 17.  After consideration of the draft SAB report, EPA  stated that it "no longer believes that it should continue to  defend its original decision," and moved that this court vacate  the MCLG.  Motion for Vacatur, at 2 (February 24, 2000).


12
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13
EPA in its motion to vacate concedes that "the discussion  on standing at oral argument indicates that petitioners may  indeed meet minimum requirements for standing," a necessary precursor to our providing any relief beyond the vacatur  proposed by EPA.  Given our independent duty to be sure of  our jurisdiction, Floyd v. District of Columbia, 129 F.3d 152,  155 (D.C. Cir. 1997), we address EPA's now evidently abandoned jurisdictional arguments.


14
EPA's brief contends that petitioners lack Article III  standing because they have not demonstrated injury-in-fact  from the MCLG.  Lujan v. Defenders of Wildlife, 504 U.S.  555, 560-61 (1992).  We have already held, in International  Fabricare Inst. v. EPA, 972 F.2d 384, 390 (D.C. Cir. 1992),  that an association of dry cleaning businesses had standing to  attack EPA's setting of a zero MCLG for a contaminant used  in their business.  There we pointed to the MCLG's link to  risks of "greater liability under the Comprehensive Environmental Response, Compensation and Liability Act ('CERCLA'), 42 U.S.C. SS 9601-9675," id., which under some circumstances may entail remedial action achieving "a level or standard of control which at least attains Maximum Contaminant Level Goals established under the Safe Drinking Water  Act," 42 U.S.C. § 9621(d)(2)(A).


15
EPA challenges petitioners' theory on several grounds. First, it says, its regulations provide that when a zero MCLG  is set, it is the MCL, not the MCLG, that is used to set  cleanup standards.  40 CFR § 300.430(e)(2)(i)(C).  In this  case, says EPA, the MCL set for TTHMs would control. Since there is no suggestion that the effective MCL will  imminently be affected by the zero MCLG, and petitioners  have not challenged the MCL for TTHMs, EPA argues that  they have failed to demonstrate an injury.


16
But the MCL for TTHMs is in fact not dispositive in  setting the cleanup standard for chloroform.  EPA has in the  past rejected use of the TTHM MCL for that purpose, saying  that that MCL is "based on an analysis evaluating the health  benefits of chlorinating public drinking water supplies against  the detrimental effects of the production of trihalomethanes  as a result of chlorinating those supplies."  U.S. EPA, Superfund Record of Decision, String fellow Hazardous Waste Site,  at 25 (Sept. 30, 1990).  Instead, EPA has set chloroform  cleanup goals as low as 6 ppb (far below the 100 ppb MCL for  TTHMs), based on an assumption that chloroform poses a  risk of cancer at any dose, but that 6 ppb would yield an  acceptable cancer risk of one-in-a-million.  Id.  Thus EPA's  actual practice belies its claims here as to the inconsequentiality of the chloroform MCLG.


17
EPA also argues that unlike the petitioners in International Fabricare, neither petitioners nor their members here have  yet been subjected to cleanup costs for chloroform contamination, and thus have not demonstrated a "genuine threat" of  CERCLA liability.  EPA's Br. at 21.  But in a forwardlooking suit the petitioners' subjection to past injury is relevant primarily as it may shed light on whether the challenged  action has a "substantial probability" of causing injury.  Florida Audubon Soc'y v. Bentsen, 94 F.3d 658, 666(D.C. Cir.  1996) (en banc).  CERCLA imposes joint and several liability  on "any person who by contract, agreement, or otherwise arranged for disposal or treatment ... of hazardous substances owned or possessed by such person."  42 U.S.C.  § 9607(a)(3).  In light of petitioners' contention that they face  liability "for the cleanup of chloroform at Superfund sites  across the country," Petitioners' Reply Br. at 16, we find it at  least substantially probable that a zero MCLG, as compared  with a nonzero one, will expose them to higher cleanup costs.


18
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19
Before turning to the merits of petitioners' claim, we note  EPA's contention that its motion to vacate obviates the "need  for the Court to issue an opinion."  Motion for Vacatur, at 3.But we have no reason to believe that mere vacatur provides  an adequate remedy if, as we ultimately conclude, EPA's  action was unlawful.  Petitioners request that we instruct  EPA to "promulgate a non-zero MCLG using the best available peer-reviewed science."  Petitioners' Initial Br. at 34.But EPA has not indicated an intention to take such action  upon vacatur.  Moreover, EPA makes no claim that the 1994  zero MCLG would not be automatically revived by vacatur of  the 1998 rule.  Our agreement with the petitioners on the  rule's lawfulness will thus bring issues of remedy into play.


20
On the merits petitioners argue that EPA's decision to  adopt a zero MCLG in the face of scientific evidence establishing that chloroform is a threshold carcinogen was inconsistent with the Safe Drinking Water Act.  Section  300g-1(b)(3)(A) of the Act states unequivocally that "to the  degree that an Agency action is based on science, the Administrator shall use ... the best available, peer-reviewed science  and supporting studies conducted in accordance with sound  and objective scientific practices."  In promulgating a zero  MCLG for chloroform EPA openly overrode the "best available" scientific evidence, which suggested that chloroform is a  threshold carcinogen.


21
EPA provides several arguments in defense of its action. First, it argues that to establish a non-zero MCLG would be a  "precedential step," that represents "a major change in the  substance of regulatory decisions related to chloroform."


22
EPA's Br. at 28-29.  We do not doubt that adopting a  nonzero MCLG is a significant step, one which departs from  previous practice.  But this is a change in result, not in  policy.  The change in outcome occurs simply as a result of  steadfast application of the relevant rules:  first, the statutory  mandate to set MCLGs at "the level at which no known or  anticipated adverse effect on the health of persons occur," 42  U.S.C. § 300g-1(b)(4)(A), as determined on the basis of the  "best available" evidence;  and second, EPA's Carcinogen  Risk Assessment guidelines, stating that when "adequate data  on mode of action show that linearity is not the most reasonable working judgment and provide sufficient evidence to  support a nonlinear mode of action," the default assumption  of linearity drops out.  Proposed Guidelines for Carcinogen  Risk Assessment, 61 Fed. Reg. at 17,969/1.  The fact that  EPA has arrived at a novel, even politically charged, outcome  is of no significance either for its statutory obligation or for  fulfillment of its adopted policy.


23
Second, and similarly, EPA supports its action on the basis  that "it could not complete the deliberations with the SAB"  before the November 1998 deadline.  EPA's Br. at 29;  Final  Rule, 63 Fed. Reg. at 69,399/1.  But however desirable it may  be for EPA to consult an SAB and even to revise its conclusion in the future, that is no reason for acting against its own  science findings in the meantime.  The statute requires the  agency to take into account the "best available" evidence.  42  U.S.C. § 300g-1(b)(3)(A) (emphasis added).  EPA cannot reject the "best available" evidence simply because of the  possibility of contradiction in the future byevidence unavailable at the time of action--a possibility that will always be  present.


24
Third, EPA justifies its decision not to adopt a nonzero  MCLG on the basis that it had to reevaluate one of its  underlying technical assumptions--that ingestion of chloroform in drinking water accounts for 80% of total exposure to  chloroform.  As it stated in its final rule, EPA is currently  considering use of a 20% relative source contribution for  drinking water, which would lower the MCLG to 70 ppb.Final Rule, 63 Fed. Reg. at 69,399/3.  Along these lines, EPA's counsel conceded at oral argument that a science based MCLG would fall into the interval between 70 and 300  ppb.  The uncertainty on this issue may have provided support for choosing the lowest nonzero MCLG from within that  interval, but none for choosing an MCLG outside the range of  uncertainty.


25
Fourth, EPA argues that since the final MCL for TTHMs  is unaffected, the MCLG has no actual effect, and thus EPA's  decision to publish an MCLG of zero pending further review  of the scientific evidence was entirely reasonable.  In light of  our analysis of the standing issue, the no-effect premise is  plainly incorrect.  Even if it were correct, we fail to see why  it would justify EPA's disregard of its own scientific findings.


26
Finally, EPA argues that its statements in the 1998 Notice  of Data Availability do not represent its "ultimate conclusions" with respect to chloroform, and thus in adopting a zero  MCLG it did not reject what it considered to be the "best  available" evidence.  In fact, the zero MCLG merely represented an "interim risk management decision" pending the  final SAB report.  EPA's Br. at 35.  We find these semantic  somersaults pointless.  First, whether EPA has adopted its  1998 NODA as its "ultimate conclusion" is irrelevant to  whether it represented the "best available" evidence.  All  scientific conclusions are subject to some doubt;  future, hypothetical findings always have the potential to resolve the  doubt (the new resolution itself being subject, of course, to  falsification by later findings).  What is significant is Congress's requirement that the action be taken on the basis of  the best available evidence at the time of the rulemaking. The word "available" would be senseless if construed to mean  "expected to be available at some future date."  Second, EPA  cannot avoid this result by dubbing its action "interim."  The  statute applies broadly to any "[a]gency action";  whether the  action is interim is irrelevant.


27
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28
Although we agree with petitioners that the zero MCLG for  chloroform is inconsistent with the Safe Drinking Water Act and that it should be vacated, we are unclear as to what  further remedy petitioners seek.  In their opening brief  petitioners requested that this Court instruct EPA to "promulgate a non-zero MCLG using the best available peer reviewed science as identified in the March 31, 1998 NODA  and the December 16, 1998 Final Rule on an expeditious  timetable to be specified by the Court."  Petitioners' Initial  Br. at 34.  At oral argument, however, counsel for petitioners  conceded that this request was a misstatement, and that EPA  should be allowed, and required, to consider the new SAB  report as well.  Further, the consequences of simple vacatur  are themselves unclear.  Accordingly, we will schedule briefing on the parties' positions as to remedy.


29
Finding the Agency's December 1998 rule adopting a zero  MCLG for chloroform to be arbitrary and capricious and in  excess of statutory authority, see 5 U.S.C. § 706(2)(A) & (C),  we vacate the rule.  A separate order on briefing additional  remedies will issue shortly.


30
So ordered.

