The Environmental Defense Fund ("EDF") and the Environmental Technology Council ("ETC") petition for review of a final determination by the Environmental Protection Agency ("EPA") not to add fourteen solvent wastes to its list of hazardous wastes under Subtitle C of the Resource Conservation and Recovery Act of 1976 ("RCRA"), as amended, 42 U.S.C. S 6921-6939b. Petitioners challenge two aspects of EPA's decision. First, petitioners contend that EPA made the scope of its listing rulemaking narrower than is permissible under the plain language of EPA's regulation governing such listing determinations. EPA analyzed whether the wastes produced when each of the fourteen chemicals is used as a solvent is hazardous. Such wastes usually consist of a number of constituent substances, but EPA limited its inquiry to whether the presence of the chemical solvent in the resulting waste was by itself a sufficient reason to list the waste as hazardous. Petitioners contend that EPA's regulation, 40 C.F.R. S 261.11(a)(3), which refers to "any toxic constituent," imposed on EPA the heavier burden of surveying the range of constituent substances comprising the waste before deciding not to list such wastes. Second, under EPA's regulation, EPA is to gauge the risks posed by a waste in part by considering plausible mismanagement scenarios, and petitioners challenge EPA's decision that wastes produced when one chemical, isophorone, is used as a solvent could not plausibly be disposed of in a landfill, maintaining that EPA lacked sufficient data to make that decision, rendering it arbitrary.

We hold that because EPA's regulation is silent as to how EPA must conduct its listing inquiry and because EPA reasonably concluded that no wastes from the solvent use of isophorone were, or were likely to be, disposed of in landfills, EPA permissibly limited the scope of its rulemaking to the toxicity of the solvents and conducted a reasonable evaluation of plausible mismanagement scenarios for isophorone. Accordingly, we deny the petition for review.

Congress enacted Subtitle C of RCRA, 42 U.S.C. SS 69216939b, to establish a "cradle-to-grave" regulatory structure providing for the safe treatment, storage, and disposal of hazardous waste. Natural Resources Defense Council v. EPA, 25 F.3d 1063, 1065 (D.C. Cir. 1994). Congress defined "hazardous waste" broadly in RCRA,1 delegating to EPA the task ofpromulgating regulations identifying the characteristics of hazardous waste and listing specific wastes as hazardous. Id. Pursuant to this authority, EPA has promulgated listing criteria to determine whether solid wastes are hazardous. 40 C.F.R. S 261.11. Once listed as "hazardous," a waste is subject to significant regulation. See Columbia Falls Aluminum Co. v. EPA, 139 F.3d 914, 915 (D.C. Cir. 1998); American Petroleum Institute v. EPA, 906 F.2d 729, 733 (D.C. Cir. 1990) (citing 42 U.S.C. SS 6922-6925).

In 1984, Congress amended RCRA to require EPA to decide by February 1986 whether to list "solvents" as hazardous wastes. 42 U.S.C. SS 6921(e)(2). When EPA did not act promptly, EDF filed suit seeking an order directing EPA to make a listing determination as to the hazardous nature of certain solvents. The result was a consent decree requiring EPA to "promulgate a final listing determination for solvent wastes on or before May 31, 1997."2 The consent decree specified that the "listing determination [was to] include the following spent solvent wastes, still bottoms from the recovery of the following solvents, and spent solvent mixtures: cumene, phenol, isophorone, acetonitrile, furfural, epicholorohydrin, methyl chloride, ethylene dibromide, benzyl chloride, ... p-dichlorobenzene, ... 2-methoxyethanol, 2-methoxyethanol acetate, 2-ethoxyethanol acetate, and cyclohexanol."3

The rulemaking under review is one of a series in which EPA has considered whether wastes from the use of specified chemicals as solvents should be listed as hazardous. See 51 Fed. Reg. 6537 (1986); 45 Fed. Reg. 74,884 (1980). To date, EPA has listed wastes from solvent use of approximately 30 chemicals. See 40 C.F.R. § 261.31, waste codes F001-F005.EPA determined that it could rely on the methodology it had used in the prior solvent rulemakings consistent with its obligations under the consent decree. See 63 Fed. Reg. 64372, 64373 (1998).

After conducting its preliminary analysis, EPA issued a proposed rule on August 14, 1996, not to amend the solvent waste listing in 40 C.F.R. S 261.31 to include the fourteen solvent wastes. 61 Fed. Reg. 42,318, 42,138 (1996). Relying on its longstanding methodology, EPA stated that it was examining the toxicity of the spent solvents only, as opposed to any additional chemicals that might mix with the solvent to form a larger waste stream. See id. at 42,319-20. EPA explained that many of these solvent wastes are already regulated as hazardous waste because they either exhibit a hazardous waste characteristic or are mixed with other solvent wastes that are listed as hazardous. Id. at 42,319. EPA further explained that in limiting the scope of its proposed rule to "a determination only regarding the need for adding these specific wastes to the RCRA hazardous waste listings based on the specific criteria in the listing regulations," id. (emphasis added), it was exercising its broad discretion under RCRA and the consent decree "to reasonably define the scope of the listing determination." Id. at 42,320. This approach also was necessary as a practical matter, in EPA's view, because of the ubiquity of "solvents" in general. Id. 03 The proposed rule also identified the research and data gathered by EPA to determine "plausible mismanagement scenarios" for the solvents. Id. at 42,320-49.

Petitioners filed comments objecting to the limited scope of the proposed rule in view of the regulatory requirement to consider "any" hazardous constituents listed in Appendix VIII to 40 C.F.R. Part 2614.Petitioners also argued that EPA had failed to consider all plausible mismanagement scenarios. Petitioners contended that because the universe of possible solvent uses is too large to capture all mismanagement scenarios through empirical study, EPA should have relied upon such "standard" mismanagement scenarios as those involving land disposal even if EPA's particular research did not suggest the presence of such disposal methods.

In the final rule, EPA concluded that the solvents should not be listed as hazardous wastes. 63 Fed. Reg. at 64,372.EPA reiterated that it defined "spent solvent wastes" solely in terms of the solvent constituents, and that in view of the large number of potential solvent waste combinations, practical necessity dictated this manner of proceeding. Id. at 64,373-74, 64,383. EPA defended its methodology for determining plausible waste mismanagement scenarios, and deemed implausible those management scenarios EDF asserted to be "plausible." Id. at 64,377-82, 64,383-85. EDF and ETC petition for review.

Petitioners contend that EPA acted inconsistently with its regulation by limiting the scope of its rulemaking to solvents only, and that EPA acted arbitrarily and capriciously by relying on an industry-wide survey to identify plausible mismanagement scenarios for solvent wastes.5 The first contention turns on petitioners' interpretation of EPA's listing regulation; the second is limited by petitioners' focus on mismanagement scenarios for the solvent isophorone.

EPA's listing regulation provides in pertinent part:

(a) The Administrator shall list a solid waste as a hazardous waste only upon determining that the solid waste meets one of the following criteria:

(1) It exhibits any of the characteristics of hazardous waste identified in subpart C.

(2) It has been found to be fatal to humans in low doses or.... [has been shown through laboratory studies or otherwise to be capable of causing severe illness or death].

(3) It contains any of the toxic constituents listed in appendix VIII and, after considering [certain enumerated] factors, the Administrator concludes that the waste is capable of posing a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported or disposed of, or other-wise managed....

40 C.F.R. S 261.11 (emphasis added).6 Petitioners focus on the italicized languageof subsection (3) as requiring EPA to consider the presence of "any" hazardous constituents listed in Appendix VIII to 40 CFR Part 261, not just the solvent itself. Petitioners also maintain that to conclude otherwise would render meaningless the distinction between the routes to listing provided in subsections (1) and (2), which focus on the toxicity of the waste to be listed, and subsection (3), which focuses on the existence of toxic constituents in the waste and the potential for the waste to pose a health or environmental hazard when improperly managed. Further, because most of the solvents at issue are not listed in Appendix VIII of Part 261, petitioners maintain that EPA cannot construe S 261.11(a)(3), which refers to the presence of "toxic constituents listed in appendix VIII", to mean that the chemical solvent is the toxic constituent to be examined. In addition, petitioners contest EPA's view of the impracticality of examining other toxic constituents potentially present in the solvent wastes.

The court is bound to accept " '[a]n agency's interpretation of its own regulations ... unless it is plainly wrong.' " Chemical Waste Management, Inc. v. EPA, 869 F.2d 1526, 1538-39 (D.C. Cir. 1989) (quoting General Carbon Co. v. Occupational Safety and Health Review Comm'n, 860 F.2d 479, 483 (D.C. Cir. 1988)). See also, e.g., Natural Resources Defense Council v. EPA, 25 F.3d 1063, 1068-69 (D.C. Cir. 1994); Hazardous Waste Treatment Council v. Reilly, 938 F.2d 1390, 1395 (D.C. Cir. 1991). Especially "on 'a highly technical question ... courts necessarily must show considerable deference to an agency's expertise.' " Chemical Waste Management, 869 F.2d at 1539 (quoting MCI Cellular Tel. Co. v. FCC, 738 F.2d 1322, 1333 (D.C. Cir. 1984)). We hold that EPA did not clearly err in interpreting its listing regulation to require only that it analyze the toxicity of the solvents, rather than other constituents with which the solvents might be combined.

Petitioners' "plain language" and supporting contentions are unpersuasive. Subsection (3), on which petitioners rely, merely provides a threshold that must be met before a listing determination may be made on the basis of constituent content: that is, that "any" Appendix VIII constituent be present in the waste. 40 C.F.R. S 261.11(a)(3). And the distinction relied on by petitioners between the three major listing criteria in S 261(a) demonstrates only that EPA has given itself the option of evaluating either toxic characteristics of the waste as a whole, § 261(a)(1) and (2), or of specific constituents within the waste, § 261(a)(3), and does not preclude the possibility that a waste may consist of one constituent, much less that in a particular rulemaking EPA will focus, pursuant to S 261(a)(3), on one constituent.7 That all of the solvents are not listed in AppendixVIII does not demonstrate error; EPA points out that it is routine to add a waste to Appendix VIII and simultaneously to list a waste as hazardous based on that constituent. See Dithiocarbamate Task Force v. EPA, 98 F.3d 1394, 1398 (D.C. Cir. 1996).8

It is also significant that EPA does not purport to have made a non-listing determination for specific solvent waste combinations without having evaluated the toxicity of those combinations; to the contrary, EPA made clear that its rulemaking concerns only the toxicity of the solvents. See, e.g., 63 Fed. Reg. at 64,383. There is nothing to suggest that EPA could not in the future examine specific solvent waste combinations on the basis that the specific waste combinations as a whole are toxic; many such wastes already are listed due to the existence of toxic constituents other than the solvent itself. 61 Fed. Reg. 42,319. EPA thus not only did not misinterpret its regulation, but did not abuse its discretion under its regulation.9

To the extent that petitioners contend that EPA's risk analysis was flawed insofar as its study of "plausible mismanagement" scenarios was inadequate, petitioners focus only on the solvent isophorone. EPA's approach, as illustrated by its examination of isophorone, involved gathering data on those industry categories (known as "standard industry classifications", or "SIC"s) that might include facilities that use isophorone as a solvent, mailing preliminary questionnaires to facilities within those SICs, and then mailing more detailed, "Section 3007"10 questionnaires to those facilities for whom follow-up was warranted. Contending that EPA's initial literature search was insufficiently thorough to target all relevant SICs, petitioners argue first, that a number of isophorone users were discovered through "pure serendipity" when they were mailed surveys for other reasons, and that there thus is no way of knowing how many remaining isophorone users exist, and second, that EPA has not accounted for all known domestic and imported quantities of isophorone in the United States. More fundamentally, petitioners assert that the attempt to conduct a comprehensive industry survey was flawed from the beginning, and that a "random sampling" would have been a preferred approach, because the solvents are potentially used by so many facilities in so many different industries. As a result, petitioners conclude, EPA mistakenly assumed that it had isolated all potential isophorone mismanagement scenarios and improperly disregarded the "presumptive" mismanagement scenario of landfill disposal on thebasis that this scenario did not match EPA's empirical data.

Upon considering petitioners' challenge to EPA's methodology, we hold that petitioners fail to show that EPA's action was "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law." 5 U.S.C. S 706(2)(A).Rather, EPA's "reasons and policy choices ... conform to 'certain minimal standards of rationality'...." Small Refiner Lead Phase-Down Task Force v. EPA, 705 F.2d 506, 52021 (D.C. Cir. 1983) (citation omitted). See also, e.g., Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 402, 416 (1971). EPA has demonstrated that a landfilling "presumption" did not necessarily apply in the case of isophorone. Rather, EPA concluded that the high organic content of isophorone found in EPA's survey called for a presumption of thermal treatment, such as incineration, combustion in a boiler, or fuel blending, given the fuel value of organic waste and the potential for liability arising from landfilling organic matter.11 See 61 Fed. Reg. at 42,345; 63 Fed. Reg. at 64,38485; 59 Fed. Reg. 66,072, 66,074 (1994). EPA employed a reasonable methodology in reaching this conclusion, both in analyzing isophorone data to determine the high organic content of the solvent, and in analyzing isophorone treatment to compare the presumptive thermal treatment of organic waste with the empirical reality of isophorone's disposal. While petitioners maintain that EPA's literature search was incomplete, EPA's decision to review the relevant literature to identify uses of isophorone by SIC code, and to limit its review of the publication Chemical Abstracts to a four-year period, was well within its discretion. As EPA pointed out, isophorone solvent use is extremely limited, and it is highly unlikely that a process that is still in use today would not be reported in recent publications. A four-year research limitation thus was a reasonable choice for EPA to make. Similarly, petitioners fail to show that EPA's methodology for compiling a facilities mailing list, which involved cross-referencing the SIC codes relevant to isophorone with other EPA data sources, was not reasonably designed to identify and contact those facilities utilizing isophorone as a solvent. Such cross referencing between the relevant SIC codes and EPA's Toxic Release Inventory ("TRI") for all facilities reporting the use of other TRI chemicals marks a thorough approach to scanning across facilities to determine possible isophorone users that would not otherwise be located. While there may be other ways to approach the task that EPA identified, EPA's approach was not arbitrary.

Furthermore, regarding petitioners' contention that EPA overlooked many isophorone-using facilities that were later identified through "pure serendipity", EPA points out that all of the facilities responding to its initial survey that claimed to use isophorone as a solvent were either included in the targeted SIC codes or mistakenly responded where their use of isophorone did not meet the definition of solvent use.12 Similarly, a number of responses to the final survey mistakenly claimed non-solvent uses of isophorone, and hence the final number of reported responses differs from the number originally identified as potential survey recipients. More fundamentally, petitioners have provided no basis on which the court can conclude that "random sampling" would have produced more accurate data. So far as we can tell from petitioners' succinct statement, theadvantage of random sampling arises from the fact that it purports to do no more than to gather representative facts from which to draw logical presumptions as to management scenarios, whereas EPA's "industry survey" risks analytical rigidity where the survey falls short of its task. However, EPA did no more than draw the logical conclusion of presumptive thermal treatment from the high organic content of the isophorone wastes surveyed, a conclusion confirmed by empirical waste treatment data and thus supporting the reasonableness of EPA's methodology.13

Accordingly, we deny the petition for review.