BOGGS, J., delivered the opinion of the court. MOORE, J. (pp. 322-331), delivered a separate opinion concurring in the result. DOWD, D.J. (pp. 331-335), delivered a separate opinion dissenting in part and concurring in part.
OPINION
BOGGS, Circuit Judge.Brighton Township, Michigan, appeals from the determination, after a bench trial, that it is liable under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), 42 U.S.C. § 9601 et seq., for “response costs” incurred by the government in cleaning up a dumpsite used by the township and others. We vacate this finding of liability, and remand for further proceedings. The United States appeals the denial of prejudgment interest on its award. We vacate this denial, and remand for a determination of the proper amount of interest on any award that is made.
I
A
The subject of this ease is a plot of land in Brighton Township comprising roughly 15 acres. From 1960 to 1971, the property was owned by Vaughan Collett; since his death in 1971, it has been owned by his son Jack. In 1960, the township contracted with Vaughan Collett to use the site as a dump for town residents, for “waste” but not “garbage” (a distinction that was never defined). The agreement required the dump to “meet specifications of and be under the supervision of the [township’s] Board of Appeals.”1 The township agreed to pay Collett $60 a month in rent and $10 a month for maintenance. Collett was supposed to be responsible for maintaining the facility, and had full salvage rights. Township residents were admitted to the dump free of charge; non-residents could use Collett’s property as a dump as well, but they had to make their own fee arrangements with Collett.
The relationship between Brighton Township, Collett, and the dump changed over the years. In 1961, the township clarified that its agreement did not allow commercial or industrial waste, though as with waste from non-residents, Collett could make separate arrangements to accept it. In 1965, the township changed its mind, and decided to let local commercial waste into its dump along with residential waste. In early 1967, the board agreed to pay Collett a substantially higher fee, in exchange for limiting use of the dump to township residents only. Non-residents and industrial customers, who had previously been able to contract separately with Collett, were now excluded from using the facility. This arrangement remained until the township closed the dump in 1973.
The fee paid to Collett rose steadily. In 1963, it increased from $70 to $120, and two years later it grew again to $150. Early in 1967, the fee was raised to $175, and later in the year, when the dump was closed to all but township residents, it was set at $300. That same year, after two special (and unspecified) appropriations totaling $100 were made, the board decided to cease making such supplemental payments unless it had contracted to do so in advance. The monthly fee was raised to $400 in 1969, and $500 in 1970. In 1971, the allotment became $500 a month for rental, with an additional $666.66 a month for maintenance.
Over the years, the Township Board often made significant extra appropriations, for “dump repair” ($320), extra maintenance ($67.50; $552; $500), “additional expenses” ($58), bulldozing ($160; $649; $744), plowing *311for fire protection ($50), “work” ($870 to a, bulldozing company; $213; $500; $500), snow removal ($50; $150; $96 for “trenching and snow removal”; $150 for “snow removal and small dozing”), and “dozers and crane work” ($350).2 The annual appropriation made for 1968, $4200 ($300 times 12 months, plus $600), suggests that the township expected in advance that it would have to make supplemental payments. In 1969, this anticipatory excess was increased to $1400, for a total appropriation of $5000. The amount in 1969 proved to be deficient by $1561 (due in part to a hike in the monthly fee), and so a total of $12,000 was allocated for 1970. Despite the fact that less that $10,000 of this amount was spent, the board budgeted $14,-000 for 1971. The final special appropriations, made upon the dump’s closure in 1973, were for Jack Collett to cover up the dump ($3400), and for other unspecified rehabilitation work, the full amount ($4214) to be paid out only upon the satisfaction of the county health department and township officials.
B
By 1965, Collett began having trouble maintaining the dump. The township declined at first to provide funds for a clean-up, but later got an estimate on “excavating and covering” some of the “old scrap” at the “Township dump.” The next year, Collett asked the township to provide a bulldozer. The board discussed the dump’s compliance with new state regulations “regarding the operating of a dump,” and determined that after some alterations the dump would be in compliance. In August 1966, the board was still concerned with unelaborated “problems” at the dump, and delegated to a committee the job of reporting what could be done to alleviate the problems.
In May 1967, all of the board’s members agreed to visit the site. After doing so, arrangements were made (by whom is not clear) for more bulldozing, which was apparently performed the next month. The board agreed to inquire about clearing away some of the accumulated debris by having the Brighton Township Junior Fire Department burn it.
Beginning in the late 1960s, the Michigan state government began regulating dumps more carefully. For Brighton Township, part of this scrutiny included visits by the county sanitarian, who was sometimes accompanied by township officials. Conditions at the dump were so bad that the township-was told in May 1971 by the Michigan Department of Public Health to take “drastic measures” to improve the dump; if not, legal action would be faken to close it. The sanitarian’s reports noted that the ground water was not being protected; cover placed over the refuse was inadequate; there was no compaction of refuse; no responsible director of the facility was present; fires were burning in the refuse; and the salvage operation had gotten “completely out of hand.” The township supervisor was notified of most of these facts in a letter, which also noted that the site did not have the appropriate licensing under state law. 'In November, another letter from the Department of Public Health to the township supervisor noted that although there.were no fires, and the piles of appliances and automobiles had been somewhat “straightened up,” conditions were still unacceptable; the threat to close the dump was renewed. In 1972, the board discussed another stern letter from a state health officer regarding the site. The insufficiency of alternative facilities delayed the closure of the dump, but once this was remedied, the dump was shut down in 1973. The board wrote an official letter to the state health officer stating that the township had fulfilled its clean-up duties.
C
In 1989, a federal field investigation team examined the site and determined that there were hazardous materials there, particularly around a cluster of 200 deteriorating drums. In 1990, the EPA sent a technical assessment team to follow up on the earlier examination. *312The team determined that the site met the criteria under the National Contingency Plan (the set of CERCLA regulations that provides criteria for action, 40 C.F.R. Part 300) for a removal action, the cost of which it estimated at over $400,000.
Through 1995, the United States had incurred $490,948.32 in response costs, exclusive of interest. The government brought suit in March 1994, against both the township and Jack Collett. It obtained a default judgment against Collett in March 1996, and Col-lett is not participating in this appeal. After a three-day trial in March 1996, the district court, ruling from the bench, found Collett and the township jointly and severally liable for the full amount of response costs plus postjudgment interest, but did not award any prejudgment interest. Final judgment was entered in May, and both Brighton Township and the United States filed timely notices of appeal.
II
A
The township appeals the district court’s determination that it is liable for response costs. It raises four arguments. First, it argues that the Brighton Township dump comprised only three acres in the southwest corner of the fifteen-acre Collett property, and that those three acres contained no hazardous waste—therefore, the government should have defined the bounds of the site in a way that excluded the dump. Second, it contends that it did not exercise sufficient control over the site to qualify as a liable “operator” under CERCLA. Third, it claims that all of the hazardous waste at the site was contributed by non-township sources, and so the township should not be liable. Fourth, and connected to the first three arguments, it argues that the district court clearly erred when it held that the harm and costs were not divisible, and imposed joint and several liability on Brighton Township, with Collett, for the entire amount of response costs.
B
CERCLA, at 42 U.S.C. § 9607(a)(2), establishes strict liability, covering “any person who at the time of disposal of any hazardous substance owned or operated any facility at which such hazardous substances were disposed of.” The first three issues here turn on interpretations of the words “facility,” “operated,” and “disposal of any hazardous substance,” respectively.
Brighton Township’s first argument is that the “facility” in question should not have been defined to include the township dump. In other words, the Collett property should have been separated by the EPA into two parts—the township dump in the southwest corner, and the rest of the property.3 The township claims that it was only connected with the former, and points out that the government’s primary physical clean-up was confined to a “hot zone” where the main cluster of barrels was located. This area did not involve any part of the three-acre southwestern corner, which contained no significant contamination at that time.
CERCLA defines the term “facility” at 42 U.S.C. § 9601(9)(B) as “any site or area where a hazardous substance has been deposited, stored, disposed of, or placed, or otherwise come to be located....”4 Our task is to determine how broadly or narrowly the bounds of the “site” may be drawn. At one extreme, the entire Collett property (or the entire county for that matter), could be defined as a facility based on the presence of a hazardous substance in one portion of it. At the other extreme, the facility could be defined with such precision as to include only those specific cubic centimeters of Collett’s property where hazardous substances were deposited or eventually found. The first approach obviously would sweep too broadly, the second too narrowly.
*313The words of the statute suggest that the bounds of a facility should be defined at least in part by the bounds of the contamination. See Northwestern Mut. Life Ins. Co. v. Atlantic Research Corp., 847 F.Supp. 389, 395-96 (E.D.Va.1994) (“That ARC leased only a portion of the property is immaterial to defining the scope of the ‘facility.’ What matters for purposes of defining the scope of the facility is where the hazardous substances were ‘deposited, stored, disposed of, ... or [have] otherwise come to be located.’ ”) (citation and emphasis omitted; alteration in original). However, an area that cannot be reasonably or naturally divided into multiple parts or functional units should be defined as a single “facility,” even if it contains parts that are non-contaminated. See, e.g., Clear Lake Props. v. Rockwell Int’l Corp., 959 F.Supp. 763, 767-68 (S.D.Tex.1997) (rejecting argument that surface structures constitute separate “facility” from subsurface soil and groundwater); cf. Northwestern Mutual, 847 F.Supp. at 396 (counting entire area as “facility,” but only because each of its quadrants are contaminated). Were this not the case, the statute would have defined a facility as ‘those parts of a site’ with contamination. The effects of the coarseness of this definition are mitigated by the availability of divisibility (discussed in detail in Section III) and contribution.5 See 42 U.S.C. § 9613(f).
In this ease, even though township residents generally left their refuse in the southwest corner, it appears that the entire property was operated together as a dump. Nothing in the agreement between the township and Collett specified that township dumping was limited to the southwest corner (though nothing specified that it was not). Before 1967 (and perhaps illicitly after 1967 as well), Collett allowed others to dump on other parts of his property, pursuant to his agreement with the township. Most significantly, Collett often moved trash from one part of the property to another as part of his salvage operation, so that hazardous materials found in the rest of the facility might have originated in the township dump. Household appliances, the sort of object that residents discarded in the southwest corner, were moved out of the corner and across an access road, and placed in large piles. Furthermore, there was testimony that some township residents disposed of appliances in the northern part of the site, as well as testimony that barrels filled with local household trash were burned and buried with the help of a township contractor (though it is not clear if these burials were in the southwest corner, the “hot zone,” or neither).
In sum, then, the facts show that (1) local household and commercial dumping was largely, but not completely, limited to the southwest corner of the property; (2) refuse was moved around on the property; and (3) Collett placed materials from non-residents and industries in other parts of the site. Collett- used the entire property as a dump, and so it is appropriately classified as a single facility. If the township was only connected to the southwest corner, the appropriate place to draw that distinction is in the divisibility analysis, not in the bounding of the facility.
C
Both parties and the district court suggest that to determine whether Brighton Township was an “operator” for CERCLA purposes, this court should use an “actual control” standard, as opposed to an “ability to control” standard. We agree, though we hold that the primary question is whether the Township’s activities satisfy the ordinary meaning of the term “operation.”
The question of what general level of operative control over a facility is necessary to make an entity an operator is one of first impression in this circuit. Fortunately, the Supreme Court has recently addressed the issue of defining “operator” status. United States v. Bestfoods, — U.S. -, 118 S.Ct. 1876, 141 L.Ed.2d 43 (1998). The statute’s *314tautological definition is not very helpful; an “operator” is “any person ... operating [a covered] facility.” 42 U.S.C. § 9601(20)(A)(ii);6 see Bestfoods, — U.S. at -, 118 S.Ct. at 1882. The Supreme Court, faced with this problem, took the sensible approach of defining “operator” according to its ordinary meaning:
[A]n operator is simply one who directs the workings of, manages, or conducts the affairs of a facility. To sharpen the definition for purposes of CERCLA’s concern with environmental contamination, an operator must manage, direct, or conduct operations specifically related to pollution, that is, operations having to do with the leakage or disposal of hazardous waste, or decisions about compliance with environmental regulations.
Id. at 1887. The Court summarized later that, “when [Congress] used the verb ‘to operate,’ we recognized that the statute obviously meant something more than mere mechanical activation of pumps and valves, and must be read to contemplate ‘operation’ as including the exercise of direction over the facility’s activities.” Id. at 1889; see also Edward Hines Lumber Co. v. Vulcan Materials Co., 861 F.2d 155, 156 (7th Cir.1988) (“The definition of ‘owner or operator’ ... must come from a source other than the text. The circularity strongly implies, however, that the statutory terms have their ordinary meanings rather than unusual or technical meanings.”).
Brighton Township suggests that several other circuits have adopted an “actual control” standard. Most of these cases, however, concern questions of liability relating to corporate form and control. See, e.g., Redwing Carriers, Inc. v. Saraland Apartments, 94 F.3d 1489 (11th Cir.1996); United States v. USX Corp., 68 F.3d 811 (3d Cir.1995); United States v. Kayser-Roth Corp., 910 F.2d 24 (1st Cir.1990), cert. denied, 498 U.S. 1084, 111 S.Ct. 957, 112 L.Ed.2d 1045 (1991). These corporate-form cases are not directly applicable to the present ease. The task of placing responsibility for an action in one or more cells of a corporate honeycomb is vastly different than evaluating (as here) the responsibility of a single entity in a vacuum, especially in the context of a strict liability statute.7
Nevertheless, these cases do highlight the importance of establishing some actual control by a putative operator. The plain meaning of the term “operator” as expounded upon in Bestfoods does, after all, require that Brighton Township have performed some affirmative acts—that they “operated” the site by “directing] the workings,” “manag[ing],” or “conducting] the affairs”—before they can be held responsible.
We hold, therefore, that an “actual control” test applies not just in the corporate context, but in the present one as well. Before one can be considered an “operator” for CERCLA purposes, one must perform affirmative acts. The failure to act, even when coupled with the ability or authority to do so, cannot make an entity into an operator.
D
Two cases from other circuits, each discussing operator liability outside of the corporate context, raise important issues for us to consider. In the first, Nurad Inc. v. William E. Hooper & Sons Co., 966 F.2d 837 (4th Cir.), cert. denied, 506 U.S. 940, 113 S.Ct. 377, 121 L.Ed.2d 288 (1992), the Fourth Circuit “decline[d] to absolve from CERCLA [§ 9607(a)(2) ] liability a hypothetical party who possessed the authority to abate the damage caused by the disposal of hazardous substances but who declined to actually exercise that authority by undertaking efforts at a cleanup.” Id. at 842. Although we decline *315to follow the Fourth Circuit and allow the imposition of operator liability based on mere “authority to control,” ibid., Nurad raises the question of the effect on liability of a failure to act.
Once affirmative acts have been found to render someone an operator, it is no defense to liability for that operator to say it was not the actor responsible for a particular hazard. To hold otherwise would allow operators to escape liability by neglecting their responsibility for proper management of then’ facilities, a result that would undo the strict liability scheme defined by § 9607(a).8 To reiterate, actual control requires affirmative acts. Omissions cannot suffice to show that. After it is established that a defendant is an operator, however, a defendant is just as responsible for hazardous conditions caused by its neglect and omissions as it is for those caused by its affirmative acts.
E
In another instructive case, FMC Corp. v. United States Dep’t of Commerce, 29 F.3d 833 (3rd Cir.1994) (en banc), the Third Circuit held that “the government [here, the federal government] can be liable when it engages in regulatory activities extensive enough to make it an operator of a facility ... even though no private party could engage in the regulatory activities at issue.” Id. at 840. Thus, a government entity, by regulating the operation of a facility actively and extensively enough, can itself become an operator. Cf. United States v. Dart Indus., 847 F.2d 144, 146 (4th Cir.1988) (declining to classify local government as operator merely for failing to regulate adequately). Our task is to distinguish (1) situations in which a governing authority uses its conventional police power to ensure that a dump does not pose a threat to public health and safety; from (2) situations in which the “regulations” are just the government’s method of macro-managing the facility.9
Asking these questions in the case at hand, we cannot conclude that Brighton Township was or was not an operator of the facility. This inquiry is properly left to the district court, utilizing the proper standard that we have set forth today. For the purpose of responding to Judge Dowd’s arguments, however, we will briefly explain why we cannot conclude as a matter of law that the Township was not an operator.
As noted by the district court, the record showed that the agreement with Collett specified that the dump “meet the specifications of and be under the supervision of the Board of Appeals.” The township was not operating at arm’s length with a contractor.10 *316Rather, it made repeated and substantial ad hoc appropriations, and it made arrangements (including with the local Junior Fire Department) for bulldozing and other maintenance when Collett himself proved unequal to the task. It also took responsibility for ameliorating the unacceptable condition of the dump, before and after scrutiny from the state government, at least as early as 1965.11 See Bestfoods, — U.S. at -, 118 S.Ct. at 1887 (defining “operator” to include entity that makes “decisions about compliance with environmental regulations”).
To summarize, mere regulation does not suffice to render a government entity liable, but actual operation (or “macromanagement”) does. We vacate the district court’s ruling that Brighton Township was an operator of the facility, and remand for further proceedings consistent with this opinion.
While we are sympathetic to the plight of the township, which could not have been happy when this dirty problem fell into its lap, there is no basis for us to conclude that the township was somehow forced to take such direct responsibility and action. Perhaps ironically, if Brighton Township had been willing to spend more money in the 1960s and 1970s, it could have made other, arm’s-length arrangements for the disposal of local refuse and the rehabilitation of Col-lett’s property, and probably avoided operator liability.
F
The district court held that “hazardous substances were released on the site during the relevant time period,” which it defined as 1960 to 1973. After defining the facility to include the township dump, and determining that Brighton Township was an operator, this determination was the final factor required for the district court to hold Brighton Township liable under § 9607(a). Although we are vacating and remanding the decision of the district court as to operator status, we pause here to affirm these findings by the district court regarding the release of hazardous substances.
*317It is undisputed that Brighton Township’s involvement with the dump ended when the dump closed in 1973; it is not disputed that the district eourt defined the relevant time period correctly. . Brighton Township claims, however, that the evidence showed that the hazardous materials found at the site were either placed there after 1973, or placed there by non-residents, beyond the scope of Brighton Township’s operator status.
On the latter claim, Brighton Township’s argument is misplaced. If an entity is an operator, it is jointly and severally liable for any hazardous material that is found, whatever its source, unless that- operator can show divisibility. This is - clear from the strict-liability language of the statute, which holds hable “any person who at the time of disposal of any hazardous substance owned. or operated any facility at which such hazardous substances were disposed of.” 42 U.S.C. § 9607(a)(2). The use of the passive voice in the second half of the clause vitiates Brighton Township’s claim.
As for the question of when the hazardous waste was deposited (a distinction for which the statutory language clearly does provide), there is sufficient evidence on which to affirm the district eourt. The district court itself cited much of this evidence. An EPA employee with relevant experience testified that the barrels excavated from the site in 1993 appeared to be twenty to thirty years old. A local resident testified that he saw rusty drums being delivered to the property in the late 1960s; that residents used to burn their trash in empty 55-gallon barrels on the site; and that residents would dispose of their old paint cans at the site. Other local residents testified that, as youths, they saw truckloads of chemical-filled drums (some of which they saw break open) being brought into the site in the early 1960s. Finally, an EPA chemist testified that pollutant chemicals found at the site were consistent with paint formulations used in the 1960s.
Brighton Township cites other evidence in the record. First, a county officer testified that he did not see the main group of 55-gallon drums when he inspected the site in 1973, and that it was his job to look for and report such things. Another state officer testified that he did not see any such group of drums during his visit, but he admitted that his search was cursory, and that he would not have seen anything that was hidden by brush or was buried. A third officer, otherwise relied on by Brighton Township, testified that he would not have seen any drums during his inspection if they were buried.
There is also the reasonable, inference to be made that it is much jnore. likely that Collett brought in the hazardous waste before 1973, when there was little or no scrutiny of the area, than after, when the dump was closed and officials monitored the area for hazardous waste more thoroughly. Altogether, there is enough evidence that hazardous materials were brought into the site before 1973 to support the district court’s determination of liability under § 9607, if the Township is held to be an operator.
Ill
The district court decided that the harm was not divisible, saying only that Brighton Township did not sustain its burden of proof, and stating the test as “whether there is a reasonable basis to conclude that the harm is divisible and whether the harm is capable of being divided.”
A
We have interpreted CERCLA “to impose joint and several liability when the environmental harm is indivisible, and to allow for apportionment when two or more persons independently are responsible for a single harm that is divisible.” United States v. R.W. Meyer, Inc., 889 F.2d 1497, 1507 (6th Cir.1989) (citation omitted) (citing United States v. Monsanto, 858 F.2d 160, 171-73 (4th Cir.1988), cert. denied, 490 U.S. 1106, 109 S.Ct. 3156, 104 L.Ed.2d 1019 (1989)), cert. denied, 494 U.S. 1057, 110 S.Ct. 1527, 108 L.Ed.2d 767 (1990).12 We affirm the *318district court’s determination of indivisibility unless it is clearly erroneous. Meyer, 889 F.2d at 1507.13 The burden of proof is Brighton Township’s. Id. at 1508.
We look first to § 433A of the Restatement (Second) of ToRts (1965), for the “traditional and evolving principles of common ¡aw” that we use to determine divisibility. Meyer, 889 F.2d at 1507; see also Damon v. Sun Co., 87 F.3d 1467, 1476 (1st Cir.1996); In re Bell Petroleum Servs., Inc., 3 F.3d 889, 895 (5th Cir.1993); United States v. Alcan Aluminum Corp., 990 F.2d 711, 722 (2d Cir.1993); United States v. Alcan Aluminum Corp., 964 F.2d 252, 268 (3d Cir.1992); Monsanto, 858 F.2d at 172.
The Restatement says that “[djamages for harm are to be apportioned among two or more causes where (a) there are distinct harms, or (b) there is a reasonable basis for determining the contribution of each cause to a single harm.” Restatement (Second) of Torts § 433A. Although most courts have looked to the Restatement to at least some degree, there is no consensus as to what constitutes “a reasonable basis.” The Restatement itself offers the example of factories polluting a stream, with damages apportioned based on the respective volume of pollutants that each disgorges. Id. at cmt. d.
B
As the Second Circuit has “candidly admitted],” Alcan, 990 F.2d at 722, this divisibility analysis weakens the strict liability nature of CERCLA. This is because defendants who can show that the harm is divisible, and that they are not responsible for any of the harm, have effectively fixed their own share of the damages at zero. No causation means no liability, despite § 9607(a)’s strict liability scheme.14
We agree also with the Fourth and Fifth Circuits, and reject a more expansive approach to divisibility analysis that would erode strict liability even further. See Bell, 3 F.3d at 901; Monsanto, 858 F.2d at 171 n. 22. That approach, epitomized by United States v. A & F Materials Co., 578 F.Supp. 1249 (S.D.Ill.1984), incorporates into divisibility the broad equitable bases of apportionment found in the contribution analysis of § 9613(f), notably the “Gore factors”:15
(i) the ability of the parties to demonstrate that their contribution to a discharge[,] release or disposal of a hazardous waste can be distinguished;
(ii) the amount of the hazardous waste involved;
(iii) the degree of toxicity of the hazardous waste involved;
(iv) the degree of involvement by the parties in the generation, transportation, treatment, storage, or disposal of the hazardous waste;
(v) the degree of care exercised by the parties with respect to the hazardous *319waste concerned, taking into account the characteristics of such hazardous waste; and
(vi) the degree of cooperation by the parties with Federal, State, or local officials to prevent any harm to the public health or the environment.
Id. at 1256. Although we know that we cannot define for all time what is a reasonable basis for divisibility and what is not, we do take this opportunity to reject fairness-based approaches in favor of the more precise and less normative Restatement approach, which concentrates solely on causation.16 We distinguish the divisibility defense to joint and several liability from the equitable allocation principles available to defendants under CERCLA’s contribution provision. The former is legal, the latter equitable; the respective tests used to execute them should reflect this distinction.
Finally, we note that this analysis should not be influenced by Michigan’s comparative negligence framework, which is based on notions of fault rather than causation, and which begins with the presumption that liability must be apportioned. The standard to be applied here is one of federal common law, not Michigan state law. See Monsanto, 858 F.2d at 171. Unlike comparative negligence, divisibility analysis is not an invitation to courts to attempt to ‘split the difference.’ If they are in doubt, district courts should not settle on a compromise amount that they think best approximates the relative responsibility of the parties. Rather, if they are in doubt, they should impose joint and several liability. Only if they have a reasonable basis for dividing causation should they actually apportion the damages.
To summarize, a defendant can avoid joint and several liability if it can prove divisibility in the district court, and we review the district court’s determination for clear error. The proper standards for divisibility come from the Restatement (Second) of Torts, which seeks a reasonable basis for determining the contribution of each cause to a single harm. We do not attempt an exhaustive list of bases for apportioning causation, but we do note that we accept only bases that apportion causation, not those that seek to apportion blame in a normative manner. Finally, we reiterate that divisibility is appropriate only in those cases where causation is appor-tionable on a reasonable basis.
C
Turning back to the facts in Brighton Township’s ease, we conclude that a remand is necessary on this issue. Our examination of the record provides some basis for a finding of divisibility. Even if we had affirmed with regard to liability, therefore, we would not be able to conclude that the district court’s “error” (providing no explanation for its analysis, and so presumptively applying an incorrect standard, given our extensive clarification of divisibility today) was harmless. Although we find Brighton Township’s proposed1 bases for apportionment to be only somewhat convincing, the district court,-upon reviewing its fuller record and applying the principles we assert above, may reach different conclusions.
Brighton Township offers two bases for divisible apportionment. First, it argues that it was responsible only for the wastes present in the southwest corner of the dump. Since the removal action did not include this part of the facility, the township argues, divisibility along this line would result in no liability for the township. As discussed above, however, local residents placed waste outside the southwest corner on occasion; the Colletts moved waste throughout the facility; there was nothing in the contract that limited local dumping to the southwest corner. Most importantly, Brighton Township did not show that its maintenance activities were confined to the southwest corner. Therefore, the geographic limitation alone is probably not an acceptable basis for apportionment, since it does not necessarily remove the township as a possible causal agent of the hazardous deposits. .
Second, Brighton Township argues for a volumetric basis of apportionment, because the hazardous waste in 55-gallon drums in *320the hot zone was from industrial and non-local sources. Although some of the hazardous waste apparently came from paint and batteries, which could have been from local sources, the record supports a conclusion that much or most of the hazardous waste was industrial. As such, it probably came from side deals between Collett and industrial and non-local sources before 1967. Because there is reason to conclude that the township took an active role in maintaining the site at least as early as 1965, however, this volumetric apportionment may nevertheless be inappropriate as well. However, we leave this determination for the district court.
■ Judge Moore’s opinion contends that, because operator liability has two components — (1) being an operator (2) when there is a release of hazardous material — that the only possible basis for divisibility is temporal. Op. at 330-31. That is, if Brighton Township can show that it was only an operator after a particular year, and that only a eei'tain percentage of the hazardous material was introduced into the property after that year, it can show divisibility and be held liable only for the releases occurring after it became an operator. Judge Moore is correct’that the distinction between operator liability and other forms. of liability is very important to consider when determining divisibility. Furthermore, time seems the most obvious and probable way that an operator can show divisibility. However, it is not the only one.
As an example, if Brighton Township could show (as it tried to do here) that its “operating” activities were completely limited to a discrete and measurable section of the property, and that the releases onto or from that section represented a discrete and measurable harm, this would provide a reasonable basis for apportionment.
That Judge Moore’s limitation of divisibility to the “root” of 'the liability is misplaced can be seen from a single example: the suggested use by the Third Circuit of bases like “relative toxicity, migratory potential, degree of migration, and synergistic capacities of the hazardous substances” for arrangers’ liability. United States v. Alcan Aluminum Corp., 990 F.2d 711, 722 (2d Cir.1993). These can be reasonable bases for dividing harm (even between two contemporaneous operators, if their operating responsibilities are sufficiently distinguishable), even though the statute says nothing about “relative toxicity” in announcing that arrangers are generally liable. See 42 U.S.C. § 9607(a)(3). Divisibility seeks to apportion liability based on relative contribution to harm, if such is reasonably ascertainable. That this may import additional considerations that are not present at the initial stage, when liability is imposed jointly and severally, should come as no surprise. See Alcan, 990 F.2d at 722 (“[W]e candidly admit that causation is being brought back into the case[.]”). Of course, as a practical matter, such complicated multi-factor analyses will provide reasonable bases for divisibility primarily when they are used to show that a defendant is not responsible for any harm at all. See ibid.
We therefore remand to the district court for an examination of possible bases of divisibility, consistent with the guidelines we have set forth. The district court should be receptive to any argument for divisibility that provides a reasonable basis — sounding in causation, not equity or normative fault — -for distinguishing between that harm caused by Brighton Township and that harm caused by others.
IY
The United States cross-appealed against Brighton Township and Collett on the failure of the district court to award prejudgment interest, which the United States argues is mandatory. Ruling from the bench, the district court said that it would not grant any prejudgment interest, but gave no explanation for that holding.
As a preliminary matter, we must determine the standard of review. We have generally used the abuse of discretion standard in those instances where an award of prejudgment interest is discretionary, see, e.g., Anderson v. Whittaker Corp., 894 F.2d 804, 809 (6th Cir.1990). If such an award is mandatory under CERCLA, however, an unexplained failure to make such an award is an *321abuse of discretion per se. Furthermore, the determination of whether CERCLA mandates, or merely allows, prejudgment interest is a question of law, which we review de novo. United States v. Baro, 15 F.3d 563, 566 (6th Cir.), cert. denied, 513 U.S. 912, 115 S.Ct. 285, 130 L.Ed.2d 201 (1994).
Awards of prejudgment interest are provided for by 42 U.S.C. § 9607(a), which states: “The amounts recoverable in an action under this section [which states that certain persons “shall be liable for” certain costs] shall include interest_ Such interest shall accrue from the later of (i) the date payment of a specified amount is demanded in writing, or (ii) the date of the expenditure concerned.” (emphasis added). Based on this language, we conclude that prejudgment interest is mandatory when § 9607 damages are awarded. See Bancamerica Commercial Corp. v. Mosher Steel, 100 F.3d 792, 802 (10th Cir.1996) (mandating prejudgment interest awards under § 9607), amended by 103 F.3d 80 (10th Cir.1996); Meyer, 889 F.2d 1497, 1505-06 (6th Cir.1989) (quoting mandatory language in Superfund Amendments and Reauthorization Act (SARA) legislative history at 1986 U.S.C.C.A.N. 2835, 2855 (“The section gives the Administrator authority to obtain prejudgment interest in all cost recovery actions.”)).
Brighton Township suggests that it was proper for the court to refuse to award prejudgment interest in this case, because the United States did not provide the district court with any data with regard to interest rates or methods of calculation. It cites the Tenth Circuit’s decision in Bancamerica for the proposition that this constitutes fatal neglect by the United States:
[I]t is appropriate to require those requesting prejudgment interest to provide the court with proper calculations setting forth the interest they seek. However, we also agree with Bancamerica and ASARCO that, because interest determinations are compounded calculations, it may be impossible for parties to provide accurate calculations prior to the court’s allocation of response cost liability. In such instances, parties may submit their interest calculations to the court subsequent to that finding.
Bancamerica, 100 F.3d at 802. The Banc-america court noted, however, that a district court abuses its discretion when it refuses to grant prejudgment interest merely because of the plaintiffs failure to provide an interest rate or a method of calculation. The appeals court noted that the interest rate is prescribed by the statute, see 42 U.S.C. § 9607(a), and that generally acceptable accounting principles should be used to calculate the total. Bancamerica, 100 F.3d at 802. We agree.
In this ease, the United States did not submit any calculations to the district court to accompany its request for prejudgment interest, nor did it do so “subsequent to [the] finding” of liability in the form of a motion for reconsideration. Neither, however, did the district court request any assistance in calculating the interest, and, as the Tenth Circuit noted in Bancamerica, the interest rate is mandated in the statute. The only information that the district court needed from the parties was the starting date for calculation, “the later of (i) the date payment of a specified amount is demanded in writing, or (ii) the date of the expenditure concerned.” 42 U.S.C. § 9607(a).
The United States claims, without refutation, that it issued a demand letter in July 1993 (Cross-Appellant’s Reply Brief at 2). Brighton Township notes that the removal action ended in November 1990 (Appellant’s Brief at 8). The court awarded damages, thus recognizing the precise amount spent by the government. There was, therefore, an adequate basis for the district court to calculate prejudgment interest. To the extent that the United States did not provide sufficient data for a precise calculation, the district court simply should have erred on the side of a lower amount. It should not have responded by settling on the very precise (but wholly inaccurate) figure of zero. Therefore, we remand to the district court for a calculation and award of prejudgment interest to the United States, if the district court imposes liability on Brighton Township.
*322V
For the foregoing reasons, we VACATE the district court’s decision, and REMAND for further proceedings consistent with this opinion, to determine if Brighton Township is an “operator,” and, if it is held to be, to determine whether the liability is divisible, and to calculate and award appropriate prejudgment interest.
CONCURRENCE IN RESULT
. This information is taken from the minutes of the Brighton Township Board. It is nowhere explained who or what the Township’s Board of Appeals is, although Brighton Township explains that the two boards are separate official entities.
. In 1969, the board approved two appropriations (crane work for $500 and ‘‘digging and coverage” for $800), with payment contingent upon Collett’s determination that the work had been done to his satisfaction. There is record only of the second appropriation actually being spent.
. For its part, the district court recognized that it was denominating the entire Collett property as the "facility,” including the Brighton Township dump, but it referred to the entire site as "the Brighton township dump site.”
. There is another set of definitions of a facility in 42 U.S.C. § 9601(9)(A), which Judge Moore ably considers in her separate opinion.
. Contribution is not as important a consideration in this case as it is in many CERCLA cases, because there are only two defendants, Brighton Township and Jack Collett. Mr. Collett is probably judgment proof, and so divisibility may be Brighton Township’s only opportunity to reduce its damages. However, there is nothing preventing Brighton Township from attempting to identify further responsible parties and seeking contribution from them.
. Governmental entities are not exempt from this designation. 42 U.S.C. § 9601(20)(D).
. Our opinion should not be read to suggest, as Judge Dowd characterizes it, that "a governmental entity should be held to a lower threshold level of control.” Op. at 333. Contrary to Judge Dowd's characterization, ibid., we apply the same plain-meaning standard articulated in Best-foods to any context, whether the defendant is acting in a corporate, governmental, or any other capacity. To be sure, part of the application of the law to the facts in Bestfoods (quoted and relied upon by Judge Dowd, id. at 333.) rests on nuances of corporate structure, but that fact-specific application is not applicable to this case.
. Indeed, it is a defense to liability to establish that the act or omission of a third party caused the harm. 42 U.S.C. § 9607(b)(3). Brighton Township does not raise this defense, because the defense excludes from consideration those third parties to whom the putative operator is bound contractually. Ibid.
. Judge Moore offers some factors in her concurrence that should provide some assistance to the district court in determining whether a government entity is an operator or is merely a regulator. As the concurrence points out, however, ours is a fact-intensive inquiry. Precisely because this is a fact-intensive inquiry, district courts should not feel bound to weigh any factors that do not apply to the facts of their particular case.
All too often, lower courts transform our suggestions into requirements. No court should feel bound by the list of factors the concurrence has provided, helpful though it is. Rather, courts should see if the plain language of the statute applies—that is, whether the defendant is an "operator''—and should look to the results we and others have reached, and to the facts we have found most dispositive in reaching them. What courts should not do (and what the Supreme Court refused to do in Bestfoods, - U.S. at -, 118 S.Ct. at 1889), however, is take a list of reasons why the facts in one case led the court to a particular result, and transform it into a mechanical checklist of narrow and rigid factors.
For instance, Judge Moore suggests that our district courts should consider, among other things, six factors out of the eleven factors decreed in United States v. Stringfellow, 1990 WL 488730, 20 Envtl. L. Rep. 20,656, 20,658 (C.D.Cal. Jan.9, 1990) ("There are eleven factors to look at.”). There is no explanation why she leaves out several of the Stringfellow factors, or of why Stringfellow, an unpublished district court case, deserves to be written into Sixth Circuit law.
. Brighton Township argues that, if the township’s use of the facility, contributed no hazardous waste to the site, and all of the hazardous waste on the site resulted from the Colletts' operations beyond the scope of Brighton Township's control over them (i.e., it came from non-resi*316dents), then Brighton Township cannot be considered an operator. In other words, Brighton Township's control over one part of the site should not make it liable by association for the disposal, over which it had no control, of hazardous materials on another part of the site.
This argument founders on the passive and expansive language of the statute, which malees liable “any person who at the time of disposal of any hazardous substance owned or operated any facility at which such hazardous substances were disposed of." 42 U.S.C. § 9607(a)(2). Since, as discussed in the last section, the entire site is defined as a single facility, if Brighton Township exercised authority over the facility, it is liable. The question that Brighton Township would have this court answer is whether the definition of an entity as an operator should take into account the extent of its control; that is, did Brighton Township's lack of control over Collett and the rest of the facility suffice to prevent its classification as an operator overall? But this is a question best answered in the divisibility analysis. See United States v. R.W. Meyer, Inc., 932 F.2d 568, 570-71 n. 2 (6th Cir.1991) ("Joint and several liability may be imposed on a responsible party, even though its role in creating the hazardous site was small, if the harm is indivisible.”); United States v. R.W. Meyer, Inc., 889 F.2d 1497, 1507 (6th Cir.1989) ("CERCLA has been interpreted to impose joint and several liability when the environmental harm is indivisible, and to allow for apportionment when two or more persons independently are responsible for a single harm that is divisible.”) (citation omitted), cert. denied, 494 U.S. 1057, 110 S.Ct. 1527, 108 L.Ed.2d 767 (1990).
. Judge Dowd's dissent notes two cases from other jurisdictions in which government entities were found not to be operators, and implies that there is an implicit requirement of control over "day-to-day operations” for government “operators.” See Dart, supra; United States v. New Castle County, 727 F.Supp. 854 (D.Del.1989). In Dart, the Fourth Circuit found that the government’s activities were not sufficiently "hands-on” to warrant a finding that the government entity was an operator as opposed to a mere regulator. Dart, 847 F.2d at 146. In New Castle, the court found that a government entity that merely regulated a disposal site, and only performed hands-on activities that the regulation required (such as dictating soil compaction standards), was not an operator. New Castle, 727 F.Supp. at 869.
In both of these cases, then, the dispositive question, as here, was whether the government entity was running the facility or merely regulating it. In the present case, Brighton Township took hands-on, non-regulatory action distinct from that of the entities in Dart and New Castle. Obviously the facts of this case are closer to Dart than they are to FMC, but our task is not to split the difference between two cases from other circuits and with distinguishable facts. Rather, our task is to say what the law is, and to apply that law to this set of facts.
. Later in Meyer, we wrote that "CERCLA contemplates strict liability for landowners, who, absent a defense recognized under section 9607(b) [acts of God, acts of war, and acts of *318certain third parties], are deemed responsible for some of the harm.” Meyer, 889 F.2d at 1507. Taken literally, this is clearly incompatible with the principle of divisibility Meyer establishes just above. We take this opportunity to clarify that defendants are limited to the defenses in § 9607(b) only when the harm is indivisible. See United States v. Alcan Aluminum Corp., 990 F.2d 711, 721-22 (2nd Cir.1993).
. Brighton Township asks this court to reverse Meyer and apply a de novo standard. See In re Bell Petroleum Services, Inc., 3 F.3d 889, 902 (5th Cir.1993) (holding that the divisibility determination is a question of law). We see no reason to do so. As we conclude below, divisibility is a question of causation. In this circuit, questions of causation are subject to "clearly erroneous” review. Bell v. United States, 854 F.2d 881, 886 (6th Cir.1988).
. This possible anomaly in CERCLA corresponds to one in the Restatement. Under the standard Restatement scheme'—non-strict liability—the burden is initially on the plaintiff to prove that the defendant is responsible for the harm. Any defendant who can winnow his share of the blame down to zero presumably will do so at this initial causation stage, and avoid the divisibility exercise altogether. See Bell, 3 F.3d at 901. This anomaly is not a result of our analysis, however. Rather, it can be attributed to Congress’s intent to incorporate the Restatement into CERCLA via the analysis of United States v. Chem-Dyne Corp., 572 F.Supp. 802 (S.D.Ohio 1983). See H.R.Rep. No. 99-253(I), 99th Cong., 1st Sess. 74, reprinted in 1986 U.S.C.C.A.N. 2835, 2856 ("fully subscribing]” to Chem-Dyne rule).
. The factors are so called because they were part of an unsuccessful amendment'to CERCLA proposed by then-Representative Gore of Tennessee.
. Some of the Gore factors (1, 2, and 3) are compatible with causation analysis; others (5 and 6) reflect fairness.concerns; at least one (4) does both.
. The dissent argues that in holding that the entire Collett property operated as a single facility, Judge Boggs and I improperly draw factual inferences from the record that were never made by the district court. Although the dissent correctly points out that the district judge failed to address whether the Collett property operated as a single facility, the facts I rely upon are not in dispute. Brighton Township concedes that "there was indeed, ultimately, 'refuse' throughout [the Collett] property.” Def.-Appellant/Cross-Appellee's Reply/Response Br. at 22. Nor does the Township challenge Roten’s testimony that Vaughn Collett moved waste from one part of the property to another, or point to any testimony or evidence contradicting Roten’s testimony. Because these material facts do not appear to be in dispute, I see no reason to remand to the district court for further fact-finding on this matter.