Opinion for the Court filed by Circuit Judge ROGERS.
Thе Rogers Corporation (“the company”) petitions for review of the decision of the Environmental Appeals Board assessing a penalty of $281,400 for violation of section 15 of the Toxic Substances Control Act, 15 U.S.C. § 2614 (1994). The company challenges the decision on a variety of grounds. Suffice it to say, the company contends that the Board’s affirmance of the grant of the agency’s motion for partial accelerated decision, which requires a finding that “no genuine issue of material fact exists,” 40 C.F.R. § 22.20(a), was arbitrary and capricious. We agree, and, accordingly, we grant the petition and remand the case to the Board for further proceedings.
I.
The parties stipulated to the following facts: The company, a Massachusetts corporation that has its principal place of business in Connecticut, owns and operates a manufacturing facility that produces polyurethane elastomers and foams. During the relevant time period, the company used a heat transfer system known as “HTS 975,” which was located in a basement room. The HTS 975 used oil as a *1098 heat transfer medium, and oil occasionally dripped or wept from the pump bearings and then collected on the concrete floor beneath the HTS 975 in a shallow conсrete berm. From time to time, the company pumped the oil from the berm under the HTS 975 into drums, sampled the contents of the drums for hazardous waste constituents, and shipped the drums off-site for disposal. From at least 1988 to at least March 1992, analysis of the samples of residual heat transfer fluid taken from the berm did not reveal concentrations of poly-chlorinated biphenyls (“PCBs”) equal to or greater than 50 parts per million (“ppm”). In April 1993, however, sampling of 16 drums of waste oil revealed PCBs in excess of 50 ppm in nine drums. The company was notified of the excessive PCBs in June 1993, and the sixteen drums were shipped off-site for disposal in September 1993. In December 1993, the Connecticut Department of Environmental Protection inspected the company, found PCBs in excess of 50 ppm in two of five samples of oil taken from the HTS 975 room, and cited the company. Four months later, the Department ordered the company to conduct certain studies and to take remedial actions. In response, the company continued to investigate the source of the excessive PCBs and undertook remedial actions.
In September 1994, the Environmental Protection Agency (“the agency”) charged the company with improper disposal of PCBs from June 16, 1993, until on or around December 1, 1993 in viоlation of 40 C.F.R. § 761.60 and § 15 of the Toxic Substance Control Act, 15 U.S.C. § 2614, and proposed a civil penalty of $226,750. The company filed an answer in October 1994, and, pursuant to 40 C.F.R. § 22.15(c), requested a hearing. In its prehearing memorandum, the company stated that it would offer evidence that it had not used any PCB containing heat transfer fluids since 1972, and that the only logical source of the PCBs in the residual heat transfer fluid was the concrete floor and soil underneath the HTS 975. In a supplemental prehearing memorandum, the company proffered Robert S. Potterton as an expert witness who would “provide an opinion as to the physical/chemical basis for the unexpected appearance, in or about 1993, of PCB concentrations equal to or greater than 50 ppm in the fluid that was pumped from the bermed containment area in the vicinity of HTS 975.... ” Mr. Potterton would also testify about remediation efforts by the company.
Just short of three years after the agency filed its charge, on September 12, 1997, the company filed a motion for an accelerated decision, pursuant to 40 C.F.R. § 22.20(a). The company sought application of the agency’s historic waste exemption for PCB-containing fluids placed in a disposal site prior to February 17, 1978. Anticipating that the agency would rely on
In the Matter of Standard Scrap Metal Company,
TSCA Appeal No. 87-4, 1990 E.P.A.App. LEXIS 8,
The agency filed an opposition to the company’s motion for accelerated decision, a motion to file an amended complaint to increase the duration of the charged violation and the proposed penalty to $300,300 (based on evidence that the spill remained from June 16, 1993, until March 29, 1994, or later), as well as its own motion for a partial accelerated decision on liability. The company opposed the agency’s motion for a partial accelerated decision, renewed its argument based on the agency’s interpretation of its regulations as reflеcted in the proposed regulations, and also argued that the agency’s inference that a disposal took place in 1993 was unwarranted in light of the undisputed fact that there was no ongoing source of PCBs in the HTS 975. Asserting that the question of why PCBs suddenly showed up in 1993 berm samples was a matter of speculation, the company stated that question was irrelevant because there was no evidence of any spill or leak at the company in 1993. An attached affidavit from its engineer stated that no piping containing PCB had been connected to the HTS 975 after the system was drained of PCB oils in 1972 and that, upon cleaning the HTS 975 room floor and the disсovery of cracks in the sump area, the company discovered PCB contaminated soil underneath the floor.
By Order of November 13, 1997, an administrative law judge (“ALJ”) granted the agency’s motions to amend the complaint and for partial accelerated decision on liability. The ALJ denied the company’s motion for accelerated decision, and the company’s request for oral argument, inasmuch as the company had not set forth a basis for the request “other than its generalized assertion that it is entitled to judgment as a matter of law in this matter.” 1997 Order on Liability at 2. The ALJ summarized the stipulated facts and observed that the partiеs disagreed as to the legal inferences to be drawn therefrom. Noting that the company had offered “no direct evidence showing when the uncontrolled discharges at issue took place or how these discharges were caused,” the ALJ concluded that “the only plausible explanation for the presence of PCBs at regulated levels in 1993 after years of lower levels ... is that there was an uncontrolled discharge in 1993.” Id. at 23. Because the company failed to dispose of the PCB-contaminated oil in the prescribed manner, the ALJ found that there was an ongoing violation of the disposal requirements of § 761.60(a). The ALJ rejеcted the company’s attempt to invoke the historic waste exemption because (1) the berm under the HTS 975 was not a disposal site within the meaning of the exemption; and (2) the company had failed to carry its burden of showing that the PCB spill occurred prior to February 17, 1978. Of the two causation theories suggested to the ALJ upon review of the evidence, the ALJ concluded that the company’s leaching-up theory, whereby PCBs had leached up from the concrete floor and soil into the oil in the berm, “strains the imagination to envision,” while the agency’s theory that *1100 increased production had dislodged residual PCBs remaining inside the HTS 975 “appears far more likely.” Id. at 24-25. The ALJ accordingly found that there were no genuine issues of material fact, and, upon rejecting the company’s statute of limitations and due process arguments, concluded that the agency was entitled to judgment as a matter of law on liability.
During the penalty phase of the proceedings in April 1998, the company attempted to introduce new, exculpatory evidence that would show that the excessive PCBs in 1993 resulted from contamination of the samples by pre-1978 PCBs that had collected in the concrete and soil beneath the berm. The company proffered, consistent with the ALJ’s ruling that the new еvidence would be considered only with regard to the penalty, expert evidence relevant to the duration of the violation. The proffered evidence was twofold: (1) that, contrary to the agency’s theory that oil continued to drip and come into contact with PCB-contaminated oil in the berm, which under the anti-dilution provision results in a 286-day violation, the State’s sampling method in December 1993 entrained into the sample PCB-contaminated concrete, resulting from the previous use of PCBs at the facility and their release into the berm; and (2) that, to a reasonable degree of scientific certainty, Mr. Potterton opined thаt the company’s change in its method of collection of oil, from one type of pump to a more efficient wet/dry vacuum system, which was a more aggressive collection procedure, directly resulted in PCB levels over 50 ppm by entraining concrete particles and dust and introducing oils from cracks in the immediate surface of the slightly porous, PCB-contaminated concrete. The ALJ imposed a penalty of $281,400.
The Environmental Appeals Board (“Board”), upon de novo review, affirmed the 1997 Order on liability and the $281,400 penalty. The Board rejected the company’s contention that the Board should consider all the evidence in the administrative record including its new evidence explaining the source of the PCB concentrations in excess of 50 ppm, ruling that its review of an accelerated decision will “generally” be limited to the evidence and arguments in the administrative record at the time the accelerated decision was made. The Board also rejected the company’s contention that the ALJ had erred in refusing to consider relative to liability the new evidence proffered at the penalty hearing, ruling that the law of the case doctrine permitted the ALJ to reject the company’s new exculpatory evidence once liability had been determined. The Board further ruled thаt the company had failed to meet its burden of production and persuasion to show as an affirmative defense that the historic waste exemption applied. Based on the evidence that PCB contamination had been found in the waste oil in previous years and that production had increased significantly in 1993, and in view of the company’s failure to carry its burden of showing that the PCBs were released prior to February 17, 1978, the Board concluded that the ALJ had reasonably inferred that the excessive PCBs came from oil weeping from the HTS 975 rather than PCBs leaching up from the concrete and soil beneath the floor. Finally, the Boаrd declined to apply the regulations effective August 28, 1998, because the complaint had been filed and liability determined before the new regulations became effective. The Board did not rule on the ALJ’s alternative holding that the company was not entitled to the historic waste exemption because the berm was not a proper disposal site.
II.
On appeal, the company contends that the ALJ erred in granting the agency’s *1101 motion for accelerated decision on liability by making, with no supporting evidence, a self-described technical inference that PCBs must have spilled in 1993, and then blocking all contrary evidence that the company sought to put in the record. The company maintains that the ALJ’s reliance on the agency’s inference was not only contrary to the nature of accelerated decisions, which the agency acknowledges are like summary judgment, but also contrary to the agency’s own 1979 regulatory scheme, which presumed that PCB-containing oil would flush completely from the company’s heat transfer system within three months of the introduction of non-PCB oils. The company also contends that the agency could not shift its burden of proof as to its prima facie case, as was done in Standard Scrap, nor penalize the compаny for historic PCB contamination in the face of undisputed evidence that its source was pre-1978 PCB oil. The company further maintains that the agency’s clarification of its regulations on the historic waste exemption applies ab initio, citing Supreme Court and agency precedent. Finally, the company contends that the agency impermissibly blocked subsequent key evidence, and that it was a violation of the company’s due process right to fair notice to penalize the company for an historic spill.
A.
The Toxic Substances Control Act (“Act”), 15 U.S.C. §§ 2601-2692 (1994), provides for regulation of the use and disposal of. toxic substances priоr to their manufacture, processing, distribution, and use in order to protect human health and the environment. Section 5 goes so far as to bar, with only limited exceptions, the manufacture of a new chemical substance or new use prior to notice to the Administrator who, upon finding that there is a reasonable basis to conclude such action presents or may present an unreasonable risk of injury to health or the environment, may prohibit or place restrictions on its manufacture, processing, or distribution. 15 U.S.C. § 2604. The Act gives special attention, however, to PCBs in view of the seriousness of their threat to human health and the environmеnt.
See Envtl. Def. Fund, Inc. v. EPA,
In 1978, the agency promulgated the first of two sets of regulations to carry out § 6(e).
See Envtl. Def. Fund,
As amended, the regulations in effect in 1993-94 also contained a 50 ppm cutoff, and defined “disposal” to mean “intentionally or accidentally to discard, throw away, or otherwise complete or terminate the useful life of PCBs.” 40 C.F.R. § 761.3 (1993). Subpart D set forth the disposal requirements, defining “[s]pills and other uncontrolled discharges of PCBs at concentrations of 50 ppm or greater [to] constitute the disposal of PCBs.” Id. § 761.60(d)(1). A prefatory note to Sub-part D stated that PCB items that have been placed in a disposal site are considered to be “in service” for purposes of Subpart D, and that Subpart D does not require “remоval of PCBs and PCB items from service and disposal earlier than would normally be the case.” Id. pt. 761, Subpart D (prefatory note). Subpart G, regulating spill cleanup, requires the cleanup of PCBs within 48 hours of notice or awareness of a spill. Id. § 761.125(c).
The Board interpreted the prefatory note in Subpart D of the disposal regulations in
Standard Scrap,
1990 E.P.A.App. LEXIS 8,
Effective August 28, 1998, the agency amended the PCB regulations. See 63 Fed. Reg. 35,384 (1998) (codified in scattered sections of 40 C.F.R. Part 761). Comments on the regulations as proposed in December 1994 had urged clarification of the prefatory note in light of the Board’s decision in Standard Scrap. See 59 Fed. Reg. 62, 788, 62, 792. The 1998 regulations deleted the prefatory note and provided that sites where PCBs have been placed in a land disposal facility, spilled, or otherwise released to the environment pri- or to April 18, 1978, are presumed not to present an unreasonable risk of injury to health or the environment from exposure to PCBs at the site, and do not necessarily require further disposal action unless, on a ease-by-case basis, the Administrator makes a finding that spills, leaks, or other uncontrolled discharges, such as leaching from a pre-1978 disposal site, constitute ongoing disposal that may present an unreasonable risk of exposure to PCBs. 40 C.F.R. § 761.50(b)(3)(i)(A) (2000). The regulations further clarified the burden on the respondent, providing that “[t]he owner or operator of a site containing PCB remediation waste has the burden of proving the date that the waste was placed in a *1103 land disposal facility, spilled, or otherwise released into the environment!.]” Id. § 761.50(b)(3)(iii).
B.
Under the agency’s Consolidated Rules of Practice, an ALJ may issue an accelerated decision if there are no genuine issues of material fact and the movant is entitled to judgment as a matter of law.
See.
40 C.F.R. 22.20(a). The Board has construed an accelerated decision to be in the nature of summary judgment, and has adopted the formulation of the Supreme Court in
Anderson v. Liberty Lobby, Inc.,
To prevail, then, on a motion for accelerated decision on liability, the agency “must show that it has еstablished the critical elements of [statutory] liability and that [the respondent] has failed to raise a genuine issue of material fact on its affirmative defense....”
BWX,
2000 E.P.A.App. LEXIS 13, at *43. As to the affirmative defense, the Board has explained that “the [agency’s initial] task is to show that there is an absence of support in the record for the defense.”
Id.
at *44 (citing
Celotex,
The evidence before the ALJ on liability consisted of the pleadings, the parties’ joint stipulation of July 3, 1997 and attachments, and two affidavits of the company’s engineer, Mr. Langelier. In addition, the company proffered the expert testimony of Mr. Potterton to the effect that there was a physical and chemical basis for the unexpected appearance in 1993 of PCB concentrations in excess of 50 ppm, and, thus, no new spill or uncontrolled discharge in 1993. The undisputed evidence shows that PCB concentrations found in samples taken from the berm under the HTS 975 between April and December 1993 exceeded 50 рpm. The undisputed evidence also shows that the company had ceased using oils containing PCBs in 1972, and thereafter it had properly flushed its system in 1977 and 1988, and that the samples taken through 1992 had shown PCB concentrations of less than 50 ppm. Further, there was evidence from the company’s manager *1104 of environmental engineering that the company had “dramatically” increased its production in 1992, running the HTS 975 for 24 hours a day, 7 days a week, through 1993 and into 1994.
The ALJ granted the agency’s motion for partial accelerated decision, relying on
Standard Scrap,
1990 E.P.A.App. LEXIS 8, at *6 n. 6, in which the Board stated that the agency presents a prima facie ease of a violation by showing that the samples contain PCBs in excess of 50 ppm and that the PCBs were not disposed of in a proper site, a conclusion that may be inferred from where the PCBs were found. The Board, on
de novo
review, approved of the ALJ’s reliance on the inference that because there was an unexplained presence of PCBs on the concrete floor, one or more uncontrolled discharges of PCBs took place. Ruling that the timing of an improper disposal is an element of the historic waste affirmative defense, not a part of the agency’s prima facie case, the Board agreed that the company had failed to meet its burden of showing entitlement to the historic waste exemption. Pretermitting the correctness of the Board’s position on the parties’ burdens, we hold that the Board’s conclusion that the administrative record during the liability phase of the proceedings did not present a genuine dispute of material fact was erroneous, and thus its grant of the agency’s motion for accelerated decision was arbitrary and capricious.
See Envtl. Def. Fund,
Inc.
v. Costle,
The company presented undisputed evidence that it had not introduced any PCB-containing heat transfer fluids since 1972 and that the results of its flushing, refilling, and testing of the HTS 975 through at least 1992 had shown PCB conсentrations of less than 50 ppm. In addition, the company presented evidence that it had discovered cracks in the concrete berm and that PCB concentrations in the soil below were very high. In light of this evidence, the company’s inference that the increase in PCBs was caused by PCBs leaching up from the PCB-rich concrete and soil into the berm, rather than leaking down from the HTS 975, would appear to raise a disputed issue of material fact. Any doubt is, in any event, dispelled by the company’s proffered expert testimony in its pleadings that itself raised a material question as to whether an uncontrolled discharge had occurred in 1993. Neither the Board nor the ALJ nor the agency on appeal challenge the sufficiency of the proffers, but rather the agency defends the Board’s decision on the ground that the company “failed to proffer ... alleged evidence in support [of its causation theory].” Resp’t’s Br. at 46. Contrary to the agency’s argument, and the ALJ’s finding, the company both proffered evidence and a theory about how the samples contained excessive concentrations of PCB in the absence of a spill in 1993. By affidavits, the company, in addition, introduced evidence to support its theory.
The company’s evidence that it had not introduced PCB-containing fluid into its system since 1972 and that it had discovered PCB-rich soil below the berm and cracks in the berm could not be dismissed as “a scintilla of evidence.” BWX, 2000 E.P.A.App. LEXIS 13, at *40. The evidence showed that, prior to 1993, samples from the berm contained only PCB concentrations below 50 ppm. The ALJ concluded, and the agency maintains on appeal, that the presence of PCBs in unregulated quantities contradicted the company’s “assertion” that it had not used PCB-containing fluids since 1972. Not so. Unlike Standard Scrap, in which there was evidence that PCB-containing fluid had been contemporaneously intro *1105 duced into the system, Standard Scrap, 1990 E.P.A.App. LEXIS 8, at *13-*14, here there was undisputed evidence, which the ALJ must credit, that no such fluids had been introduced. That PCBs were detected at below 50 ppm for twenty years — viewing the evidence in the light most favorable to the company— does not contradict the inference from the company’s evidence that the presence of PCBs in 1993 was linked to excessive PCBs in the soil or concrete resulting from pre-1978 PCB usage. In view of the company’s evidence and its proffered expert testimony, the agency could not dismiss the company’s theory that the PCBs leached up from the berm as speculative. Put otherwise, once the company presented evidence that there was no new source of PCBs in excess of 50 ppm because it stopped using PCB-containing oil in 1972, and proffered that there was a “physical/chemical” explanation for the presence of PCBs in excess of 50 ppm in 1993, the agency was not entitled to an accelerated decision on liability in the absence of either evidence that a spill had occurred in 1993 or other evidence sufficient to show that no reasonable factfin-der could conclude by a preponderance of the evidence that any spill was historic.
In finding liability, the ALJ did not rely on contrary evidence from the agency. The ALJ instead inferred from the company’s evidence, and the Board agreed, that the increased production resulted in a spill in 1993. Yet the ALJ’s inference was based on nothing more than speculation. The agency offered no technological or other evidence to show either that the increased use of the HTS 975 was related to the increased PCBs in the berm, or that the wet seals harbored PCBs until dislodged by the increased production. As the Board observed, the evidence was “very limited,” and clearly there was none to support the inference that the PCBs had been stuck inside the HTS 975 for twenty-one years and had suddenly come loose other than the samples themselves. Given the company’s undisputed evidence of its discontinuance of PCB-based oil in 1972, the agency was not entitled to an accelerated decision on liability based on the speculative notion that PCBs in the HTS 975 could affect the samples more than twenty years after termination of the use of PCB-containing oil. See BWX, 2000 E.PAApp. LEXIS 13, at *38-*39.
The company’s evidence, when viewed in the light most favorable to the company, as the ALJ and Board were required to do on accelerated decision, created a genuine issue of material fact whether the company had met its burden of proving its affirmative defense that the spill was historic. Because thе company’s evidence presented a disputed issue of material fact regarding the timing of the spill that led to the presence of PCBs in excess of 50 ppm in 1993, and thus, a disputed issue whether a spill had occurred in 1993, neither the Board nor the ALJ could find that “no genuine issue of material fact exists.” 40 C.F.R. § 22.20(a). An accelerated decision, like the grant of summary judgment, is inappropriate when there is a disputed issue of material fact giving rise to conflicting inferences and a choice among them would amount to fact finding. BWX, 2000 E.P.A.App.LEXIS 13, at *44. The Board’s affirmance of the finding of liability, resting on both the ALJ’s inference that “the increased PCB levels likely cаme about as a result of the residual PCBs in the HTS 975 being dislodged by increased production” and the ALJ’s rejection of the company’s proffered inference, was exactly that — an improper choice between two competing theories as to the source of the PCBs. Although a factfinder may be entitled, on cross motions for accelerated decision, to decide *1106 among reasonable inferences where the evidence is folly developed, the case did not come before the ALJ in this posture. See BWX, 2000 E.P.A.App. LEXIS 13, at *20 n. 10. Both the ALJ and Board relied on the company’s assertions that no genuine issues of material faсt existed and that “[w]hy the PCBs suddenly showed up in 1993 berm samples is a matter of speculation and in any case is irrelevant to this case.” Board’s Order (Nov. 28, 2000) (quoting Resp. to Partial Accelerated Decision Mot. at 3 n.2). These statements were made in the context of the company’s legal argument that the agency bore the burden of proving that a spill took place in 1993. Once the company lost that legal argument, there was no basis for the ALJ or Board to conclude that the company had conceded that there was no dispute as to the source of PCBs, particularly in view of the fact that prior to the 1997 Order on liability the cоmpany proffered additional evidence regarding the chemical and physical basis for the 1993 PCB concentrations.
Although the ALJ ruled alternatively that the company was not entitled to the historic waste exemption because the berm was not a proper disposal site, the Board on de novo review did not adopt this alternative holding. Whether the company can, on remand, meet its burden of showing that it is entitled to the historic waste exemption remains to be seen. At this stage, we need hold only that the Board erred in affirming the accelerated decision on liability. Because we hold that the decision the Board invoked as “lаw of the case” must be revisited because it was improper for the ALJ to grant the agency’s motion for accelerated decision based on the evidence presented, on remand there will be no occasion to revisit the question whether the ALJ properly could exclude new liability evidence at the penalty phase, and hence we need not address whether the Board and ALJ erred in considering the law of the case argument. Further, because the 1998 regulations are now final, we need not address whether the ALJ and the Board should have considered the company’s reliance on the proposed regulations as reflecting agency policy.
Accordingly, we grant the petition and remand the case to the Board for further proceedings.