275 F.3d 1096 (D.C. Cir. 2002)
Rogers Corporation, Petitionerv.Environmental Protection Agency, Respondent
No. 00-1542
United States Court of Appeals  FOR THE DISTRICT OF COLUMBIA CIRCUIT
Argued November 8, 2001Decided January 4, 2002

Petition for Review of an Order of the Environmental Protection Agency
Steven Ferrey argued the cause for petitioner.  With him  on the briefs was Lee D. Hoffman.
D. Judith Keith, Attorney, U.S. Department of Justice,  argued the cause for respondent.  With her on the brief was  John C. Cruden, Acting Assistant Attorney General.
Before:  Ginsburg, Chief Judge, Rogers and Garland,  Circuit Judges.
Opinion for the Court filed by Circuit Judge Rogers.
Rogers, Circuit Judge:


1
The 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.

2
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 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 concrete 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 polychlorinated 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.


3
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 violation 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 PCBcontaining 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.


4
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  (E.P.A. Aug. 2, 1990), the company argued that the phrase  "disposal site" did not refer to a narrow subcategory of places  for containing PCB-waste spilled or released prior to February 17, 1978.  The company pointed to agency regulations  proposed December 6, 1994, clarifying that PCBs disposed of prior to April 18, 1978, do not require further disposal action  unless a Regional Administrator finds that such historic waste  presents a risk to health or the environment from exposure. See Disposal of Polychlorinated Biphenyls, 59 Fed. Reg.  62,788 (proposed Dec. 6, 1994) (codified at 40 C.F.R.   761.50(b)(3)).  The company asserted that this court had  acknowledged the validity of the proposed rule as a statement  of agency policy in General Electric Co. v. EPA, 53 F.3d 1324 (D.C. Cir. 1995), and that the Environmental Appeals Board  had relied on the proposed rule as support for the respondent's position in In re CWM Chemical Services, Inc., TSCA  Appeal No. 93-1, 1995 E.P.A. App. LEXIS 20 (E.P.A. May  15, 1995).  As evidentiary support for application of the  historic waste exemption, attached to the company's motion  for accelerated decision was an affidavit of Gerry L. Langelier, an engineer at the company for 33 years, stating that the  company had ceased using PCB-based oil in 1972, and that,  since then, oil seepage from the wet seals into the bermed  containment area under the HTS 975 had never before the  1993 tests contained PCB concentrations above 50 ppm.


5
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 reflected 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 discovery of cracks in the sump area, the  company discovered PCB contaminated soil underneath the  floor.


6
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 parties 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 rejected 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 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.


7
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 evidence 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 286day 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 that 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.


8
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 that 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 Board 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.

9
On appeal, the company contends that the ALJ erred in  granting the agency's motion for accelerated decision on  liability by making, with no supporting evidence, a selfdescribed 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 company 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.

10
The Toxic Substances Control Act ("Act"), 15 U.S.C.   2601-2692 (1994), provides for regulation of the use and  disposal of toxic substances prior 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 environment.  See Envtl. Def. Fund, Inc. v.  EPA, 636 F.2d 1267, 1271 (D.C. Cir. 1980).  Section 6 sets  forth a detailed scheme to dispose of and phase out PCBs,  and directs the Administrator to promulgate rules within six  months after January 1, 1977 (the Act's effective date), prescribing methods of disposal and marking of PCBs.  15  U.S.C.  2605(e).  As relevant here,  15 identifies prohibited  acts, including failing to comply with the Administrator's  rules and orders.  Id.  2614(1).  The Act authorizes the  assessment of civil penalties not to exceed $25,000 for each  violation as well as criminal prosecution for knowing or willful  violations, and requires prior written notice of a proposed civil  penalty for violation of a prohibited act and a hearing in accordance with  554 of the Administrative Procedure Act, 5  U.S.C.  554.  15 U.S.C.  2615.


11
In 1978, the agency promulgated the first of two sets of  regulations to carry out  6(e).  See Envtl. Def. Fund, 636  F.2d at 1272.  The first regulations, the so-called "Disposal  Regulations," covered pure PCB compounds as well as materials contaminated with at least 500 ppm of PCBs.  Id. Explaining that it chose this regulatory cutoff in order to  regulate disposal of most PCBs "as soon as possible," Preamble to Final Disposal Regulations, 43 Fed. Reg. 7,151 (1978),  the agency warned that it was considering a new cutoff  "possibly in the range of 50 ppm or below" for the proposed  "Ban Regulations."  Id.  In June 1978, the agency proposed  regulations with a 50 ppm cutoff, see 43 Fed. Reg. 24,813 (1978), and this cutoff remained in the final rule.  See Polychlorinated Biphenyls (PCBs) Manufacturing, Processing,  Distribution in Commerce, and Use Prohibitions, 44 Fed.  Reg. 31,514, 31,543 (1979).


12
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 constitute the disposal of PCBs."  Id.  761.60(d)(1).  A  prefatory note to Subpart 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 "removal 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).


13
The Board interpreted the prefatory note in Subpart D of  the disposal regulations in Standard Scrap, 1990 E.P.A. App.  LEXIS 8.  The case involved a civil enforcement proceeding  under  16(a) of the Act charging violations of 40 C.F.R.  761.60 and 15 U.S.C.  2614.  Id. at *1-*2.  The Board  stated that "[f]rom the unexplained presence of PCBs in the  soil, it can be inferred that one or more 'uncontrolled discharges' of PCBs took place."  Id. at *6.  Under  761.60(d)  of the regulations, the Board ruled, such a discharge amounts  to an improper disposal.  Id.  Standard Scrap argued that  the PCBs at issue fell within the historic waste exemption  provided in the prefatory note to Subpart D.  Id. at *8.  The  Board disagreed.  The Board stated that the historic waste  exemption is available only as an affirmative defense, and that  the respondent bears the initial burden of production and the  ultimate burden of persuasion on the applicability of the  exemption.  See id. at *10.  Because Standard Scrap had  failed to show by a preponderance of the evidence that the  PCBs in the soil samples were "placed in a disposal site"  prior to February 17, 1978, the Board ruled that it could not  avail itself of the exemption.  Id. at *13.  In the alternative,  the Board held that "a 'disposal site' is something more than  a place where PCBs have been accidentally discharged."  Id.  at *21.


14
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 prior 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 case-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 land disposal facility,  spilled, or otherwise released into the environment[.]"  Id.   761.50(b)(3)(iii).

B.

15
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., 477 U.S.  242 (1986), and Celotex Corp. v. Catrett, 477 U.S. 317 (1986),  construing Federal Rule of Civil Procedure 56.  See In re  BWX Tech., Inc., RCRA (3008) Appeal No. 97-5, 2000 E.P.A.  App. LEXIS 13, at *34-*41 (E.P.A. Apr. 5, 2000).  Thus, the  movant is entitled to an accelerated decision only if it presents "evidence that is so strong and persuasive that no  reasonable [factfinder] is free to disregard it."  Id. at *38*39.  Evidence not too lacking in probative value must be  viewed in the light most favorable to the party opposing the  motion.  See Anderson, 477 U.S. at 251, 255.  Although the  finder of fact may draw inferences from the evidence, they  must be "reasonably probable," BWX, 2000 E.P.A. App.  LEXIS 13, at *45 n.22, and based on more than speculation. See, e.g., Matsushita Elec. Indus. Co. v. Zenith Radio Corp.,  475 U.S. 574, 587-88 (1986);  BWX, 2000 E.P.A. App. LEXIS  13, at *45 n.22;  In re Clarksburg Casket Co., EPCRA Appeal  No. 98-8, 1999 E.P.A. App. LEXIS 23, at *28 (E.P.A. July 16,  1999).  Summary judgment is inappropriate when contradictory inferences may be drawn from the evidence.  See, e.g.,  Londrigan v. FBI, 670 F.2d 1164, 1171 n.37 (D.C. Cir. 1981).


16
To prevail, then, on a motion for accelerated decision on  liability, the agency "must show that it has established 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, 477 U.S. at 323-24).  "If the satisfies this burden, [the respondent], as the non-movant  bearing the ultimate burden of persuasion on its affirmative  defense, must meet its countervailing burden of production by  identifying 'specific facts' from which a reasonable factfinder  could find in its favor by a preponderance of the evidence." Id.


17
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 ppm.  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 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.


18
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 case 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, 657 F.2d 275, 282-83 (D.C. Cir.  1981);  5 U.S.C.  706(2)(A).


19
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 concentrations 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.


20
The company's evidence that it had not introduced PCBcontaining 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 introduced 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 factfinder could conclude  by a preponderance of the evidence that any spill was historic.


21
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.P.A. App. LEXIS  13, at *38-*39.


22
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 the 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 came 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 among reasonable inferences where the evidence is fully 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  fact 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 company  proffered additional evidence regarding the chemical and  physical basis for the 1993 PCB concentrations.


23
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 "law 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.


24
Accordingly, we grant the petition and remand the case to  the Board for further proceedings.

