Hazardous Waste Treatment Council v. U.S. Environmental Protection Agency, Edison Electric Institute, Chemical Manufacturers Association, Intervenors

Angus Macbeth was on the brief for petitioner Chemical Waste Management, Inc., in No. 87-1459.

William R. Weissman and Douglas H. Green (for Edison Electric Institute, et al.) and G. William Frick and Thomas S. Llewellyn, Washington, D.C., (for American Petroleum Institute) were on the joint brief for intervenors.

Jacqueline M. Warren entered an appearance for petitioner Natural Resources Defense Council, Inc., in No. 86-1677.

Robert F. Van Voorhees and Mark B. Halverson, Washington, D.C., entered appearances for petitioner Chemetco, Inc., in No. 87-1057.

James K. Jackson, Washington, D.C., and Ralph J. Colleli, Jr., entered appearances for intervenor American Petroleum Institute in No. 86-1677. Arnold S. Block, Philadelphia, Pa., entered an appearance for intervenor American Petroleum Institute in Nos. 87-1016 and 87-1459.

Before WALD, Chief Judge, SILBERMAN and D.H. GINSBURG, Circuit Judges.

Opinion PER CURIAM.

Opinion concurring in part and concurring in the result filed by Circuit Judge SILBERMAN.

In 1984, Congress amended the Resource Conservation and Recovery Act ("RCRA"), 42 U.S.C. Sec. 6921-6991 (1982 & Supp. IV 1986), to prohibit land disposal of certain hazardous solvents and wastes containing dioxins except in narrow circumstances to be defined by Environmental Protection Agency ("EPA") regulations. See Hazardous and Solid Waste Amendments, Sec. 201(a), 42 U.S.C. Sec. 6924(e) (Supp. IV 1986). In these consolidated cases, petitioners seek review of EPA's final "solvents and dioxins" rule published pursuant to Congress' 1984 mandate. We conclude that the rule under review is consistent with RCRA, but remand one aspect of the rulemaking to the agency for further explanation.

A. Statutory Scheme.

The Hazardous and Solid Waste Amendments of 1984 ("HSWA"), Pub.L. No. 98-616, 98 Stat. 3221 (1984), inter alia, substantially strengthened EPA's control over the land disposal of hazardous wastes regulated under RCRA's "cradle to grave" statutory scheme. In preambular language to the HSWA, Congress, believing that "land disposal facilities were not capable of assuring long-term containment of certain hazardous wastes," expressed the policy that "reliance on land disposal should be minimized or eliminated." 42 U.S.C. Sec. 6901(b)(7). In order to effectuate this policy, HSWA amended section 3004 of RCRA to prohibit land disposal of hazardous waste unless the waste is "pretreated" in a manner that minimizes "short-term and long-term threats to human health and the environment," id. Sec. 6924(m), or unless EPA can determine that the waste is to be disposed of in such a fashion as to ensure that "there will be no migration of hazardous constituents from the disposal [facility]...." Id. Sec. 6924(d)(1), (e)(1), & (g)(5).

As amended, RCRA requires EPA to implement the land disposal prohibition in three phases, addressing the most hazardous "listed" wastes first. See id. Sec. 6924(g).1 In accordance with strict statutory deadlines, the Administrator is obligated to specify those methods of land disposal of each listed hazardous waste which "will be protective of human health and the environment." Id. In addition, "[s]imultaneously with the promulgation of regulations ... prohibiting ... land disposal of a particular hazardous waste, the Administrator" is required to

promulgate regulations specifying those levels or methods of treatment, if any, which substantially diminish the toxicity of the waste or substantially reduce the likelihood of migration of hazardous constitutents from the waste so that short-term and long-term threats to human health and the environment are minimized.

Id. Sec. 6924(m).

Respecting two categories of hazardous wastes, including the solvents and dioxins at issue here2 Congress, however, declined to wait for phased EPA implementation of the land disposal prohibition. For these wastes, Congress imposed earlier restrictions, prohibiting land disposal after dates specified in the HSWA except in accordance with pretreatment standards or pursuant to regulations specifying "protective" methods of disposal. Id. Sec. 6924(e)(1). These prohibitions, as applied to the solvents and dioxins listed in the HSWA, were to take effect November 8, 1986. Id.

In order to further RCRA's basic purpose of mandating treatment of hazardous wastes in lieu of land disposal, Congress further provided that storage of wastes falling within the land disposal prohibition would be "prohibited unless such storage is solely for the purpose of the accumulation of such quantities of hazardous waste as are necessary to facilitate proper recovery, treatment or disposal." Id. Sec. 6924(j). Congress believed that permitting storage of large quantities of waste as a means of forestalling required treatment would involve health threats equally serious to those posed by land disposal, and therefore opted in large part for a "treat as you go" regulatory regime.

B. The Rulemaking Under Review.

In January 1986, EPA issued a notice of proposed rule-making announcing its draft implementation of the land disposal prohibition for solvents and dioxins. See 51 Fed.Reg. 1602 (1986) (hereinafter "Proposed Rule"). Approximately ten months later, after receiving extensive public commentary on the draft blueprint, EPA published a final solvents and dioxins rule differing in some respects from its draft approach. See 51 Fed.Reg. 40,572 (1986) (hereinafter "Final Rule"). These differences were especially striking in EPA's implementation of section 3004(j) and section 3004(m) of RCRA, governing the storage prohibition and treatment standards, respectively, for solvents and dioxins. These portions of the rule, together with other discrete portions of the rulemaking faulted by petitioners, are summarized below.

1. Section 3004(m) Treatment Standards.

In the Proposed Rule, EPA announced its tentative support for a treatment regime embodying both risk-based and technology-based standards. The technology-based standards would be founded upon what EPA determined to be the Best Demonstrated Available Technology ("BDAT"); parallel risk-based or "screening" levels were to reflect "the maximum concentration [of a hazardous constituent] below which the Agency believes there is no regulatory concern for the land disposal program and which is protective of human health and the environment." Proposed Rule at 1611. The Proposed Rule provided that these two sets of standards would be melded in the following manner:

First, if BDAT standards were more rigorous than the relevant health-screening levels, the latter would be used to "cap the reductions in toxicity and/or mobility that otherwise would result from the application of BDAT treatment[.]" Id. Thus, "treatment for treatment's sake" would be avoided. Second, if BDAT standards were less rigorous than health-screening levels, BDAT standards would govern and the screening level would be used as "a goal for future changes to the treatment standards as new and more efficient treatment technologies become available." Id. at 1612. Finally, when EPA determined that the use of BDAT would pose a greater risk to human health and the environment than land disposal, or would provide insufficient safeguards against the threats produced by land disposal, the screening level would actually become the 3004(m) treatment standard. Id.

EPA invited public comment on alternative approaches as well. The first alternative identified in the Proposed Rule (and the one ultimately selected by EPA) was based purely on the capabilities of the "best demonstrated available technology." Id. at 1613. Capping treatment levels to avoid treatment for treatment's sake, according to EPA, could be accomplished under this technology-based scheme by "the petition process":

Under this approach, if a prescribed level or method of treatment under section 3004(m) resulted in concentration levels that an owner/operator believed to be overly protective, the owner/operator could petition the Agency to allow the use of an alternative treatment level or method or no treatment at all by demonstrating that less treatment would still meet the petition standard of protecting human health and environment.

Id. at 1613. And the function served by health-screening levels of providing a default standard when the application of BDAT technology would itself pose a threat to human health and the environment could likewise be fulfilled by the petition process: "an owner operator could [ ] petition the Agency ... to allow continued land disposal of the waste upon a demonstration that land disposal of the waste would not result in harm to human health and the environment." Id.

The Agency received comments supporting both approaches, but ultimately settled on the pure-technology alternative. Of particular importance to EPA's decision were the comments filed by eleven members of Congress, all of whom served as conferees on the 1984 RCRA amendments. As EPA recorded in the preamble to the Final Rule:

[these] members of Congress argued strongly that [the health screening] approach did not fulfill the intent of the law. They asserted that because of the scientific uncertainty inherent in risk-based decisions, Congress expressly directed the Agency to set treatment standards based on the capabilities of existing technology.

The Agency believes that the technology-based approach adopted in [the] final rule, although not the only approach allowable under the law, best responds to the above stated comments.

Final Rule at 40,578.

EPA also relied on passages in the legislative history supporting an approach under which owners and operator of hazardous waste facilities would be required to use " 'the best [technology] that has been demonstrated to be achievable.' " Id. (quoting 103 CONG.REC. S9178 (daily ed. July 25, 1984) (statement of Senator Chaffee). And the agency reiterated that the chief advantage offered by the health-screening approach--avoiding "treatment for treatment's sake"--could "be better addressed through changes in other aspects of its regulatory program." Id. As an example of what parts of the program might be altered, EPA announced that it was "considering the use of its risk-based methodologies to characterize wastes as hazardous pursuant to section 3001 [of RCRA]." Id.; see 42 U.S.C. Sec. 6921 (1982 & Supp. IV 1986).3

Petitioner CMA challenges this aspect of the rule as an unreasonable construction of section 3004(m)'s mandate to ensure that "short-term and long-term threats to human health and the environment are minimized." 42 U.S.C. Sec. 6924(m) (1982 & Supp. IV 1986). In the alternative, CMA argues that EPA has failed to explain the basis--in terms of relevant human health and environmental considerations--for its BDAT regime, which allegedly requires treatment in some circumstances to levels far below the standards for human exposure under other statutes administered by EPA. Thus, CMA claims that EPA's action in promulgating a technology-based rule is arbitrary and capricious.

2. Section 3004(j) Storage Prohibition.

Section 3004(j) of RCRA, as noted above, prohibits the storage of wastes falling within a land disposal prohibition "unless such storage is solely for the purpose of the accumulation of such quantities of hazardous waste as are necessary to facilitate proper recovery, treatment, or disposal," 42 U.S.C. Sec. 6924(j) (1982 & Supp. IV 1986). In the Proposed Rule, EPA tentatively implemented this provision to allow generators to accumulate hazardous wastes on-site for up to 90 days, no questions asked. EPA selected this period in the belief "that it would allow a reasonable period for accumulation prior to further management without interfering with a generator's production process[.]" Proposed Rule at 1709. It observed that as a matter of prevailing industrial practice "most wastes were removed from the site of generation within 90 days." Id. Nevertheless, out of concern that "a longer time may, in some cases, be necessary to accumulate sufficient quantities to facilitate proper recovery, treatment, or disposal," id., the agency solicited comments on alternative storage periods that might be appropriate.

The comments received by the Agency ranged far and wide, but all found the 90-day period inadequate. A majority of the commentors favored a one-year storage period in order to accommodate small-quantity generators and others whose waste streams "accumulate[ ] more slowly than others." Final Rule at 40,582. On the basis of these remarks, EPA agreed that 90 days was an insufficient period for the adequate accumulation of wastes to facilitate recovery, treatment or disposal.

EPA ultimately settled on a one-year storage period, but the implementing regulation differed significantly in character from the 90-day proposal. The Final Rule provides:

An owner/operator of a treatment facility may store [ ] wastes for up to one year unless the Agency can demonstrate that such storage was not solely for the purpose of accumulation of such quantities of hazardous waste as are necessary to facilitate proper recovery, treatment, or disposal.

Id. at 40,643 (emphasis added) (codified at 40 C.F.R. Sec. 268.50(b) (1988)). A companion provision requires owners and operators to bear the burden of proving that storage for over a one-year period was for proper purposes under RCRA. See id. (codified at 40 C.F.R. Sec. 268.50(c) (1988)).

Characterizing the final storage rule, in effect, as a "shifting of the statutory burden of proof" which "effectively allows a one year override of the statutory prohibition" against storage, petitioners Hazardous Waste Treatment Council ("HWTC") and the Natural Resources Defense Council ("NRDC") challenge the rule as inconsistent with section 3004(j) of RCRA.

3. Responsibility for Testing Wastes Prior to Disposal.

A determination as to whether and to what degree treatment of a waste is required prior to land disposal depends upon the concentration of hazardous constituents in the waste. To facilitate these determinations and to ensure compliance with the land disposal prohibitions and applicable treatment standards, EPA proposed to implement requirements for mandatory testing in some circumstances. Proposed Rule at 1691.

The Agency was immediately confronted with the question of who, among generators, treatment facilities and land disposal facilities, should shoulder the responsibility of testing the waste prior to disposal. While several alternatives were available, EPA initially proposed that the land disposal facility alone be responsible for such testing. Proposed Rule at 1692.

Under this approach, the disposal facility must either conduct an analysis of the waste or obtain an analysis of the waste from the generator or treater. Similarly, the owner or operator of a land disposal facility could arrange for the generator or treatment facility to supply all or part of the required testing data. However, if the generator or treater did not supply the testing data and the land disposal facility owner or operator chose to accept the waste, the owner or operator would be responsible for conducting the required testing.

Id. at 1691. The agency cautioned that this approach did not leave the generator without responsibility altogether. The generator was still obliged to determine "whether he must treat his waste prior to disposal." Id. "[R]ather than specifically requiring the generator to conduct testing, [however], the Agency [proposed to] allow determination of whether wastes meet the regulatory thresholds to be based on either testing or knowledge of the characteristics of the waste." Id. The Agency found this proposal desirable because "[i]t is flexible, does not require redundant testing, fits into the current regulatory scheme for the waste analysis plan and requires the testing to take place where the liability for disposal exists--at the land disposal facility." Id. at 1691.

The Final Rule bears substantial resemblance to that initially proposed by EPA, with one principal exception. As the agency explained, "[b]ecause the [treatment] approach promulgated [in the Final Rule] does not cap BDAT with screening levels, more wastes will require treatment to meet the specified treatment standards." Final Rule at 40,597. Given this expanded role for the treatment industry, EPA decided in the Final Rule to impose testing requirements on both treatment facilities and land disposal facilities. But, the agency followed the proposed rule insofar as it did not require testing by generators. See id. Thus, when sending waste to either a treatment facility for pretreatment or directly to a land disposal facility, the Final Rule permits generators to base their determinations as to the concentration of hazardous constituents in the waste on "waste analysis data, knowledge of the waste, or both." Id. No matter what the basis for their determinations, generators forwarding wastes directly to land disposal facilities must certify their conclusions to the facilities' operators. False certifications, under the Final Rule, may result in criminal penalties. See 40 C.F.R. Sec. 268.7 (1988); see also 42 U.S.C. Sec. 6928(d)(3) (Supp. IV 1986).

Petitioners HWTC and NRDC contend that it is arbitrary and capricious for EPA to require operators of treatment and land disposal facilities, but not generators, to test wastes within the land disposal prohibition.

CMA challenges EPA's adoption of BDAT treatment standards in preference to the approach it proposed initially primarily on the ground that the regulation is not a reasonable interpretation of the statute. CMA obliquely, and Intervenors Edison Electric and the American Petroleum Institute explicitly, argues in the alternative that the agency did not adequately explain its decision to take the course that it did. We conclude, as to CMA's primary challenge, that EPA's decision to reject the use of screening levels is a reasonable interpretation of the statute. We also find, however, that EPA's justification of its choice is so fatally flawed that we cannot, in conscience, affirm it. We therefore grant the petitions for review to the extent of remanding this issue to the agency for a fuller explanation.

A. The Consistency of EPA's Interpretation with RCRA.

Our role in evaluating an agency's interpretation of its enabling statute is as strictly circumscribed as it is simply stated: We first examine the statute to ascertain whether it clearly forecloses the course that the agency has taken; if it is ambiguous with respect to that question, we go on to determine whether the agency's interpretation is a reasonable resolution of the ambiguity. Chevron v. Natural Resources Defense Council, 467 U.S. 837, 842-45, 104 S.Ct. 2778, 2781-83, 81 L.Ed.2d 694 (1984).

1. Chevron Step I: Is the Statute Clear?

We repeat the mandate of Sec. 3004(m)(1): the Administrator is required to promulgate "regulations specifying those levels or methods of treatment, if any, which substantially diminish the toxicity of the waste or substantially reduce the likelihood of migration of hazardous constitutents from the waste so that short-term and long-term threats to human health and the environment are minimized." 42 U.S.C. Sec. 6924(m)(1).

CMA reads the statute as requiring EPA to determine the levels of concentration in waste at which the various solvents here at issue are "safe" and to use those "screening levels" as floors below which treatment would not be required. CMA supports its interpretation with the observation that the statute directs EPA to set standards only to the extent that "threats to human health and the environment are minimized." We are unpersuaded, however, that Congress intended to compel EPA to rely upon screening levels in preference to the levels achievable by BDAT.

The statute directs EPA to set treatment standards based upon either "levels or methods" of treatment. Such a mandate makes clear that the choice whether to use "levels" (screening levels) or "methods" (BDAT) lies within the informed discretion of the agency, as long as the result is "that short-term and long-term threats to human health and the environment are minimized." To "minimize" something is, to quote the Oxford English Dictionary, to "reduce [it] to the smallest possible amount, extent, or degree." But Congress recognized, in the very amendments here at issue, that there are "long-term uncertainties associated with land disposal," 42 U.S.C. Sec. 6924(d)(1)(A). In the face of such uncertainties, it cannot be said that a statute that requires that threats be minimized unambigously requires EPA to set levels at which it is conclusively presumed that no threat to health or the environment exists.

Nor are we at all persuaded by CMA's interpretation of NRDC v. EPA, 824 F.2d 1146, 1163 (D.C.Cir.1987) (en banc ), in which we held that EPA was not permitted to "substitute[ ] technological feasibility for health as the primary consideration under Section 112 [of the Clean Air Act]." That provision requires the Administrator to set air pollution standards "at the level which in his judgment provides an ample margin of safety to protect the public health." 42 U.S.C. Sec. 7412(b)(1)(B). EPA had set emission standards for vinyl chloride, however, "based solely on the level attainable by the best available control technology," 824 F.2d at 1149, despite its finding that such levels would create health risks. It had neither stated that the risks it found were insignificant, nor explained how the risks it accepted were consistent with its statutory duty to provide "an ample margin of safety." Id. This court held that EPA had erred in failing to consider whether the best available technology was sufficient to provide the statutorily mandated margin of safety. Id. at 1164-66.

Contrary to CMA's implication, however, the court did not hold, or even imply, the converse--that EPA could not require generators to use technologies that would reduce emissions to a point below that which would provide an "ample margin of safety." Indeed, the court noted that "Congress ... recognized in section 112 that the determination of what is 'safe' will always be marked by scientific uncertainty and thus exhorted the Administration to set ... standards that will provide an 'ample margin' of safety," id. at 1165; we then concluded that "[o]nce 'safety' is assured, the Administrator should be free to diminish as much of the statistically determined risk as possible by setting the standard at the lowest feasible level." Id.

This is not to say that EPA is free, under Sec. 3004(m), to require generators to treat their waste beyond the point at which there is no "threat" to human health or to the environment. That Congress's concern in adopting Sec. 3004(m) was with health and the environment would necessarily make it unreasonable for EPA to promulgate treatment standards wholly without regard to whether there might be a threat to man or nature. That concern is better dealt with, however, at Chevron 's second step; for, having concluded that the statute does not unambiguously and in all circumstances foreclose EPA from adopting treatment levels based upon the levels achievable by BDAT, we must now explore whether the particular levels established by the regulations supply a reasonable resolution of the statutory ambiguity.

2. Chevron Step II: Is EPA's Interpretation Reasonable?

The screening levels that EPA initially proposed were not those at which the wastes were thought to be entirely safe. Rather, EPA set the levels to reduce risks from the solvents to an "acceptable" level, and it explored, at great length, the manifest (and manifold) uncertainties inherent in any attempt to specify "safe" concentration levels. The agency discussed, for example, the lack of any safe level of exposure to carcinogenic solvents, 51 Fed.Reg. at 1,628; the extent to which reference dose levels (from which it derived its screening levels) understate the dangers that hazardous solvents pose to particularly sensitive members of the population, id. at 1,627; the necessarily artificial assumptions that accompany any attempt to model the migration of hazardous wastes from a disposal site, id. at 1,642-53; and the lack of dependable data on the effects that solvents have on the liners that bound disposal facilities for the purpose of ensuring that the wastes disposed in a facility stay there, id. at 1,714-15. Indeed, several parties made voluminous comments on the Proposed Rule to the effect that EPA's estimates of the various probabilities were far more problematic than even EPA recognized. See, e.g., Comments of Natural Resources Defense Council, Record at 29,000-62.

CMA suggests, despite these uncertainties, that the adoption of a BDAT treatment regime would result in treatment to "below established levels of hazard." It relies for this proposition almost entirely upon a chart in which it contrasts the BDAT levels with (1) levels EPA has defined as "Maximum Contaminant Levels" (MCLs) under the Safe Drinking Water Act; (2) EPA's proposed "Organic Toxicity Characteristics," threshold levels below which EPA will not list a waste as hazardous by reason of its having in it a particular toxin; and (3) levels at which EPA has recently granted petitions by waste generators to "delist" a particular waste, that is, to remove it from the list of wastes that are deemed hazardous. CMA points out that the BDAT standards would require treatment to levels that are, in many cases, significantly below these "established levels of hazard."

If indeed EPA had determined that wastes at any of the three levels pointed to by CMA posed no threat to human health or the environment, we would have little hesitation in concluding that it was unreasonable for EPA to mandate treatment to substantially lower levels. In fact, however, none of the levels to which CMA compares the BDAT standards purports to establish a level at which safety is assured or "threats to human health and the environment are minimized." Each is a level established for a different purpose and under a different set of statutory criteria than concern us here; each is therefore irrelevant to the inquiry we undertake today.

The drinking water levels, for example, are established under a scheme requiring EPA to set "goals" at a level at which "no known or anticipated adverse effects on the health of persons occur." 42 U.S.C. Sec. 300g-1(b)(4). EPA is then to set MCLs as close to its goals as "feasible," taking into account, among other things, treatment costs. 42 U.S.C. Secs. 300g-1(b)(4), (5). Since SDWA goals are set only to deal with "known or anticipated" adverse health effects, a mere "threat" to human health is not enough in that context. Moreover, SDWA levels are set without reference to threats to the environment. Finally, EPA must consider costs in setting its MCLs; there is no similar limitation in Sec. 3004 of RCRA.

Similarly, in promulgating the OTC levels, EPA made clear that, "[i]n establishing a scientifically justifiable approach for arriving at [OTC levels], EPA wanted to assure a high degree of confidence that a waste which releases toxicants at concentrations above the [OTC level] would pose a hazard to human health." EPA Hazardous Waste Management System; Identification and Listing of Hazardous Waste ..., Proposed Rule, 51 Fed.Reg. 21,648, 21,649 (1986) (emphases added). Thus it is clear that wastes with toxicant levels below the OTC thresholds may still pose "threats to human health [or] the environment." Id. at 21,648 (emphases added).

Finally, CMA points to the "delisting levels" as appropriate points of comparison. The term is a bit misleading, however. EPA delists particular wastes in response to individual petitions, see, e.g., 42 U.S.C. Sec. 6921(f)(1), and it has not adopted formal, or even de facto, levels below which any waste will be delisted. That EPA has delisted, in particular circumstances, wastes containing concentrations of solvents higher than those called for by the BDAT standards adds nothing to CMA's argument. The treatment standards establish a generic approach, requiring that all wastes deemed to be hazardous be treated to a set level in order to minimize threats to health and to the environment. If a waste is listed as hazardous, and an individual generator wants to dispose of it without meeting the BDAT standards, it may petition to have its particular waste delisted. If the agency grants the delisting petition, only the petitioner is affected; the generally required level of treatment remains the same. Hence, there is no inconsistency between a "delisting level," accepted in particular circumstances, that permits a higher level of a particular contaminant then the BDAT level otherwise generally applicable.

In sum, EPA's catalog of the uncertainties inherent in the alternative approach using screening levels supports the reasonableness of its reliance upon BDAT instead. Accordingly, finding no merit in CMA's contention that EPA has required treatment to "below established levels of hazard," we find that EPA's interpretation of Sec. 3004(m) is reasonable.

Our concurring colleague suggests that our discussion of the reasonableness of the BDAT standard is unnecessary, if not "perhaps analytically impossible." Con.Op. at 371. Contrary to the impression given in his separate opinion, however, the basis upon which we find EPA's interpretation reasonable here is not one that we have supplied, but the one EPA itself put forth. In its Initial Rule document discussing BDAT as well as screening levels, and in its briefs to this court, EPA has presented precisely the arguments we find persuasive here. While, as we shall see, those arguments are inadequate to justify the choice made, in the Final Rule, in favor of BDAT as against screening levels--which also seem to present a reasonable approach--they do demonstrate that the BDAT approach is reasonable.

B. Was EPA's Explanation Adequate?

The Supreme Court has made it abundantly clear that a reviewing court is not to supplement an agency's reasons for proceeding as it did, nor to paper over its plainly defective rationale: "The reviewing court should not attempt itself to make up for such deficiencies [in the agency's explanation]; we may not supply a reasoned basis for the agency's action that the agency itself has not given." Motor Vehicles Manufacturers Ass'n v. State Farm Mut. Auto Ins. Co., 463 U.S. 29, 43, 103 S.Ct. 2856, 2866-67, 77 L.Ed.2d 443 (1983) (citing SEC v. Chenery Corp., 332 U.S. 194, 196, 67 S.Ct. 1575, 1577, 91 L.Ed. 1995 (1947)). "We will, however, 'uphold a decision of less than ideal clarity if the agency's path may reasonably be discerned.' " Id. (quoting Bowman Transportation, Inc. v. Arkansas-Best Freight System, Inc., 419 U.S. 281, 286, 95 S.Ct. 438, 442, 42 L.Ed.2d 447 (1974)). Accordingly, in order to determine whether we can affirm EPA's action here, we must parse the language of the Final Rule to see whether it can be interpreted to make a sensible argument for the approach EPA adopted. We find that it cannot.

As we have said, EPA, in its Proposed Rule, expressed a tentative preference for an approach that combined screening levels and BDAT. It indicated that it thought either that approach or BDAT alone was consistent with the statute, and recognized that there were myriad uncertainties inherent in any attempt to model the health and environmental effects of the land disposal of hazardous wastes. It initially concluded, however, that despite those uncertainties, the better approach was to adopt the combination of screening levels and BDAT. Nevertheless, in the Final Rule, it rejected its earlier approach, and adopted a regime of treatment levels defined by BDAT alone.

In order fully to convey the inadequacy of EPA's explanation, we quote the relevant portion of the Final Rule at length:

Although a number of comments on the proposed rule favored the first approach; that is, the use of screening levels to "cap" treatment that can be achieved under BDAT, several commenters, including eleven members of Congress, argued strongly that this approach did not fulfill the intent of the law. They asserted that because of the scientific uncertainty inherent in risk-based decisions, Congress expressly directed the Agency to set treatment standards based on the capabilities of existing technology.

The Agency believes that the technology-based approach adopted in today's final rule, although not the only approach allowable under the law, best responds to the above-stated comments. Accordingly, the final rule establishes treatment standards under RCRA section 3004(m) based exclusively on levels achievable by BDAT. The Agency believes that the treatment standards will generally be protective of human health and the environment. Levels less stringent than BDAT may also be protective.

The plain language of the statute does not compel the Agency to set treatment standards based exclusively on the capabilities of existing technology.... By calling for standards that minimize threats to human health and the environment, the statute clearly allows for the kind of risk-based standard originally proposed by the Agency. However, the plain language of the statute does not preclude a technology-based approach. This is made clear by the legislative history accompanying the introduction of the final section 3004(m) language. The legislative history provides that "[T]he requisite levels of [sic] methods of treatment established by the Agency should be the best that has been demonstrated to be achievable" and that "[T]he intent here is to require utilization of available technology in lieu of continued land disposal without prior treatment." (Vol. 130, Cong.Rec. 9178, (daily ed., July 25, 1984)). Thus, EPA is acting within the authority vested by the statute in selecting [sic] to promulgate a final regulation using its proposed alternative approach of setting treatment standards based on BDAT.

The Agency believes that its major purpose in adopting the risk-based approach of the proposal (i.e., to allow different standards for relatively low-risk, low-hazard wastes) may be better addressed through changes in other aspects of its regulatory program. For example, EPA is considering the use of its risk-based methodologies to characterize wastes as hazardous pursuant to section 3001.

51 Fed.Reg. at 40,578.

To summarize: after EPA issued the Proposed Rule, some commenters, including eleven members of Congress, chastised the agency on the ground that the use of screening levels was inconsistent with the intent of the statute. They stated that because of the uncertainties involved, Congress had mandated that BDAT alone be used to set treatment standards. EPA determined that the "best respon[se]" to those comments was to adopt a BDAT standard. It emphasized, however, that either course was consistent with the statute (and that it was therefore not required to use BDAT alone). Finally, it asserted, without explanation, that its major purpose in initially proposing screening levels "may be better addressed through changes in other aspects of its regulatory program," and gave an example of one such aspect that might be changed.

This explanation is inadequate. It should go without saying that members of Congress have no power, once a statute has been passed, to alter its interpretation by post-hoc "explanations" of what it means; there may be societies where "history" belongs to those in power, but ours is not among them. In our scheme of things, we consider legislative history because it is just that: history. It forms the background against which Congress adopted the relevant statute. Post-enactment statements are a different matter, and they are not