OPINION OF THE COURT

GREENBERG, Circuit Judge.

This case raises a number of questions regarding the calculation of withdrawal liability under the Multiemployer Pension Plan Amendments Act of 1980 ("MPPAA"), 29 U.S.C. § 1381 et seq.:

1) How is an investment contract to be valued?

2) How is the interest rate on amortization of withdrawal liability selected when the most recent actuarial valuation of the plan uses more than one interest rate?

3) What, if any, interest is to be assessed on the withdrawal liability for the period between the calculation date and the start of payments?

4) If, after arbitration, it is ascertained that the interim liability payments exceed the employer's total withdrawal liability, may the employer be paid interest on the overpayment?

5) May lump-sum post-retirement death benefits be included in the calculation of vested benefits?

6) Can informal written amendments to a plan be effective?

7) Can a fund make a second assessment of withdrawal liability?

We conclude that assets must be valued consistently with liabilities; that if there is more than one interest rate used in the most recent actuarial valuation, that rate which was used to value vested liabilities should be used for MPPAA amortization; that one year of presumed pre-demand interest is included in the amortization schedule; that interest should be paid on overpayments of withdrawal liability; that lump-sum death benefits may not be included when calculating MPPAA unfunded vested benefits; that informal written amendments to a plan may be effective if made pursuant to the plan's amendment procedure; and that the validity of the second assessment will be determined in arbitration.

FACTS AND PRIOR PROCEEDINGS

The United Food and Commercial Workers, Local 23-Giant Eagle Pension Fund (the "Fund") is a multi-employer pension plan covered by the withdrawal liability provisions of the MPPAA. The Fund was created in 1957 in collective bargaining involving Thorofare Markets, Inc. (the "Employer"), Local 1407, Retail Clerks International Association (which later became part of Local 23 of the UFCW) and Giant Eagle Markets, Inc. The only contributing employers to the Fund have been Thorofare, Giant Eagle, and the local union on behalf of some of its own employees. Casablanca Industries, Inc. and UFCW Local 23-Giant Eagle Pension Fund, 7 EBC 2705, 2707 (1986) (Arbitrator's first opinion). On April 6, 1982, Thorofare withdrew from the Fund. Despite the requirement of 29 U.S.C. § 1399(b)(1) that a demand for withdrawal liability must be issued by a multiemployer plan "[a]s soon as practicable" after an employer's withdrawal, no demand letter was issued to the Employer until November 28, 1984 — more than two and one half years after the withdrawal. App. at 1931. This delay seems to have been due to the Fund's poor records, see 7 EBC at 2710, and its inability to obtain adequate records from the Vector Group, its outside administrators.

The Employer disputed the amount of the demand and, as it invoked arbitration under 29 U.S.C. § 1401(a), an impartial Arbitrator, Ira F. Jaffe, Esq., was selected. Arbitration hearings were held on 11 days from December 4, 1985, until April 15, 1986, and the Arbitrator issued an Opinion and Award on December 13, 1986.

That Opinion and Award directed the Fund to recompute certain figures, resulting in a substantial reduction of the Employer's liability, and provided for the Arbitrator to retain jurisdiction for review of that recomputation. In the recomputation, the Fund included calculations for liabilities based on data not provided at the initial hearing. The Employer moved to strike this new information, and the Arbitrator issued an Opinion on August 27, 1987, granting that motion. See App. at 2023-49. The Arbitrator issued a third Opinion on February 8, 1988, dealing with remaining issues, including a claim by the Employer for interest on the overpayment it had made on account of the demand initially made by the Fund. On March 21, 1988, the Arbitrator issued a Final Order setting the withdrawal liability of the Employer to the Fund, and the amount of the overpayment which must be returned by the Fund to the Employer.

This action was originated in the district court while the arbitration was still pending, as the Fund filed a complaint on January 12, 1987, challenging the portions of the first Opinion and Award of the Arbitrator unfavorable to the Fund. The action was, however, stayed pending the resolution of the remaining issues by the Arbitrator. Subsequently, an amended complaint and a supplemental complaint were filed and, in addition, the Employer counterclaimed seeking to invalidate portions of the award unfavorable to it, as well as the second assessment. The district court decided the case on cross-motions for summary judgment in an opinion dated October 30, 1989, and the appeal and cross-appeal have been taken from the accompanying order.

STANDARD OF REVIEW

It is clear that, in a MPPAA arbitration, the Arbitrator's factual findings are presumed to be correct and are "rebuttable only by a clear preponderance of the evidence." 29 U.S.C. § 1401(c); United Retail Wholesale Employees v. Yahn McDonnell, Inc., 787 F.2d 128, 135 n. 9 (3d Cir. 1986), aff'd per curiam by an equally divided court sub nom. Pension Benefit Guarantee Corp. v. Yahn McDonnell, 481 U.S. 735, 107 S.Ct. 2171, 95 L.Ed.2d 692 (1987) (" Yahn McDonnell"). The statute does not prescribe the standard of review for legal conclusions of the Arbitrator but the parties, including the amicus curiae Pension Benefit Guarantee Corporation ("PBGC"), and the district court agree that the legal conclusions of the Arbitrator must be reviewed de novo, and we concur. Of course, our review of the order of the district court is plenary.

DISCUSSION

I. There is no "Clear Preponderance of the Evidence" to Rebut the Arbitrator's Valuation of the Fund's Assets.

The Fund's calculation of the unfunded vested benefits was based on an asset valuation of $9,829,599. 7 EBC at 2711. The Arbitrator found that this did not represent the "best estimates" of the actuary, Mr. Halliwell, but "had its genesis in the Board of Trustees . . . and had as an objective the intention of inflating the withdrawal liability payments assessed against the Employer. . . ." 7 EBC at 2724. The Arbitrator concluded that the assets of the fund as of the calculation date were $14,280,901. See 7 EBC at 2726. The district court upheld this finding on the basis of the MPPAA's presumption in favor of the Arbitrator's findings of fact.

The key dispute is over the valuation of two long-term investment contracts made by the Fund with the Great West Life Assurance Company. The Trustees sought to value these at $5,677,616, their value if liquidated as of the calculation date, while the Arbitrator valued them at $10,111,474, their "guaranteed contract" or book value. As described by the Arbitrator:

The long-term investment contracts held deposits of the Fund in calendar year funds which matured over a 15 year period and which retained a fixed interest rate during that period. Each year, 6 2-3% (i.e., one-fifteenth) of the initial principal amount plus the interest earned during that year would be released into a short-term fund which the Fund could then either deposit into the next calendar year fund as part of the initial principal for that calendar year fund, maintain under the terms of short term investment contract (from which withdrawals could be made without penalty), or withdraw the sum without penalty for investment in some other asset or for use in paying benefits. Thus, absent the premature cancellation of the long-term investment contract, it would take the Fund a total of 15 years after the last deposit to recover all of the funds held on deposit under that contract by Great West.

7 EBC at 2712-13.

The process of withdrawing the funds in the long-term contracts without reinvestment is referred to as "rolling out." As one alternative to "rolling out" the contracts, the Trustees could immediately cash out the contracts before their scheduled maturity, but if they did so would only receive the "current capital value." The current capital value took account of the difference between the contract interest rates — which ranged from 8.7% to 12.25%, see 7 EBC at 2713 — and the current, or "new money" interest rate, which, as of the calculation date, September 30, 1981, was 15.25%. See 7 EBC at 2714. The contractual formula used to determine the current capital value magnified the economic loss resulting from the difference in rates, in the sense that there was a penalty provided for cashing out which reduced the recovery on the contracts to an amount below that which would have been produced by computations predicated solely on interest rate differentials. As we conceive it, the situation seems to be similar to that occasioned by the premature cashing of a certificate of deposit with a penalty for early withdrawal. The Arbitrator found that in order to have cashing out make economic sense, the Fund would need to find an investment with a guaranteed long-term return of 20%, an impossible task. See 7 EBC at 2714. Valuing the approximately $10.1 million in fund assets subject to the penalty at the "Current Capital Value" would represent a paper loss of over $4.4 million, a "distress" valuation. Id.

The Arbitrator found that the Fund had no need to sell assets at distress, see 7 EBC at 2714, a finding supported by the testimony of trustee Raymond Huber, see App. at 714. In addition to the cash flow from Giant Eagle's normal contributions, there were more than $3.5 million in investments that could be liquidated without penalty. See 7 EBC at 2713. The Arbitrator concluded that "the Fund is seeking [to] collect a windfall from the Employer based upon an unreasonable discounting of those investment contracts. . . ." 7 EBC at 2719.

The Arbitrator found that if the stream of payments from the funds were discounted at 8%, the rate used to discount the liabilities of the Fund, the present value would be 107% of the book value. If the stream of payments were discounted at 10.75%, one-half percentage point above the PBGC immediate annuity rate of 10.25% in effect on September 30, 1981, the present value would be 97% of the book value. He therefore concluded that the "guaranteed contract" or book value was a reasonable measure of the value of the contracts. 7 EBC at 2718, 2724-25.

The Fund argues that the Arbitrator's use of a stream-of-payments valuation was unreasonable because the Trustees might have been able to invest the proceeds of a cash-out of the contract funds at higher rates of return than the funds were paying. In support of this argument, it points to the high appreciation of the Dow Jones Industrial Average. See Fund's Brief at 16. It suggests that the Arbitrator's approach "ignore[s] [the trustees'] fiduciary obligation to make an annual decision with respect to each rollout; namely, whether it was best to take the rollout and invest it elsewhere, or to reinvest it under the contract. . . ." See id. at 17-18. This argument is supported by the recent decision of the Court of Appeals for the Fourth Circuit in Masters, Mates Pilots Pension Plan v. USX Corp., 900 F.2d 727, 734 (4th Cir. 1990) ("The current level of the risk-free rate might be relevant in determining what range of interest rates will likely be earned within a certain time frame; but its existence cannot be considered a floor for valuing benefits, or else, pension plans would be forced to invest in only government securities since they could not chance holding a riskier portfolio and producing less than the riskless rate of return.")

That analysis confuses the question of what the Fund may invest in with the prediction of the Fund's rate of return. The Trustees may well consider other investments, either as payments are rolled out, or indeed through the "distress" cashing out. It is also possible that riskier investments may in retrospect result in a lower rate of return. However, it must be assumed that the Trustees will only make investments for which, at the time of the investment, the expected rate of return, after accounting for transaction costs, is equal to or better than the contract. To do otherwise would be to ignore their fiduciary duty. See RESTATEMENT (2D) of TRUSTS § 227(a) (1959) (trustee must "make such investments and only such investments as a prudent man would make of his own property"), id. at comment e ("No man of intelligence would make a disposition of property where in view of the price the risk of loss is out of proportion to the opportunity for gain.")

We agree with the analysis of the district court in Jerome Mirza Assoc., Ltd. v. United States, 692 F. Supp. 918 (C.D.Ill. 1988), aff'd, 882 F.2d 229 (7th Cir. 1989), cert. denied, ___ U.S. ___, 110 S.Ct. 2166, 109 L.Ed.2d 496 (1990). In that case, the court rejected as unreasonable a 5% assumption of the rate of return for a pension plan. The court noted that the plan could obtain a guaranteed return of over 12% by investing in U.S. Treasury Bonds, and concluded that "the only reason a prudent investor would not buy them would be due to a belief that they could get a higher yield with other investments." Id. at 923. The fact is that there was simply no reason to cash out here and thus cause the Fund a substantial loss. The investments with Great West were not transferable and cannot reasonably be considered the equivalent of investments with a recognized market value subject to liquidation at a value established in an open market. Rather, the current capital value received upon their liquidation was governed by the contracts themselves, which, though taking into account current interest rates, magnified the loss upon liquidation. Accordingly, we cannot conclude that the Arbitrator was unreasonable in his conclusion.

The Fund also contends that "the arbitrator's mandated asset valuation is unreasonable and clearly erroneous when used in combination with an 8% assumption to discount liabilities." Fund's Brief at 20. The Fund suggests that the use of an 8% discount rate for liabilities is very generous because "many multiemployer funds have used discounting factors well below 8%," Fund's Brief at 21. The Fund suggests that by increasing the valuation of the assets, the Arbitrator destroyed a balance established by the actuary.

The statute requires that "withdrawal liability . . . be determined . . . on the basis of actuarial assumptions . . . which, in the aggregate, are reasonable . . . and which in combination, offer the actuary's best estimate of anticipated experience under the plan." 29 U.S.C. § 1393(a)(1). This language means, inter alia, that assumptions used to discount assets must be consistent with those used to discount liabilities. Aside from reasonable adjustments for risk, a dollar of projected income has the same value as a dollar of pension payment to be made at the same point in time. Accordingly, the relevant comparison is not between the discount rate used in this valuation and that used in other reported cases, but between this plan's discount rate for liabilities and this plan's discount rate for assets. Since the assets for this plan were earning interest at rates ranging from a minimum of 8.7% to 17%, the use of an 8% discount rate for the liabilities does not seem unreasonably generous to the Employer.

The Fund also contends that the Arbitrator should have presumed that the demand figures represented the actuary's "best estimate," pursuant to section 1401(a)(3)(B). They point out that Yahn McDonnell involved the bias of a plan's sponsor, not the plan's actuary. See Fund's Brief at 11 n. 2.

However, the rationale of Yahn McDonnell — trustee bias in favor of the fund — carries over to an actuary selected and paid by the trustees. As Alexander Hamilton noted in explaining the Compensation Clause of Article III in The Federalist No. 79, "a power over a man's subsistence amounts to a power over his will." See also United States v. Will, 449 U.S. 200, 217-19, 101 S.Ct. 471, 482, 66 L.Ed.2d 392 (1980).

The principle was magnificently demonstrated in this case. On July 31, 1984, the actuary, Halliwell, submitted a report to the trustees valuing the assets of the Fund at the guaranteed contract value of $14 million. See App. at 1830-31. On August 8, 1984, the minutes of a Board of Trustees meeting reveal that:

The Board expressed its concern over Mr. Halliwell's method of calculating withdrawal liability . . . The Board expressed lack of confidence in the calculations and Mr. Halliwell's advice. The Board agreed that it should consider other actuaries at the next Board of Trustees meeting, to provide services to the Fund including a final calculation of withdrawal liability in accordance with the statute.

App. at 1834.

Within a few days, both Halliwell's advice and the Board's opinion of him had changed. On August 29, 1984, the Board's minutes reveal that

Ray Huber asked whether a demand for withdrawal liability could be sent at this time. Mr. Halliwell responded by stating he could complete a final calculation of withdrawal liability within five days upon receiving guidance from the Board on outstanding issues. . . . Ray Huber made a motion, which was seconded by Mr. Rees, that the Board of Trustees continued to retain Halliwell Co. and that Mr. Halliwell be requested to calculate Thorofare's withdrawal liability based on assumptions which he could support that were in the best interests of the Fund.

App. at 1835-36 (emphasis added).

Accordingly, even if we were inclined to distinguish the holding of Yahn McDonnell as a case involving bias of a board of trustees rather than an actuary, this would not be an appropriate case in which to do so. We thus will affirm the district court on the valuation issue.

II. Interest Rate to be used for Amortization of Withdrawal Liability Payments.

Once the Employer's share of the unfunded vested benefits has been ascertained, the amortization schedule must be determined. The factors to be determined are:

1) the amount of each payment

2) the frequency of the payments

3) the interest rate to be applied.

Based upon these factors, the number of payments is mechanically calculated.

Item (1), the amount of each payment, is based on the Employer's contribution history over the past 10 years and is not in dispute here. See generally, 29 U.S.C. § 1399(c)(1)(C). The statute requires that the schedule be calculated as if the payments were annual. 29 U.S.C. § 1399(c)(1)(A)(i). However, the parties disagree over item (3), the interest rate to be used for this amortization schedule.

The statute requires that the determination of the amortization period for the Employer's withdrawal liability payments "shall be based on the assumptions used for the most recent actuarial valuation for the plan." 29 U.S.C. § 1399(c)(1)(A)(ii). An actuarial valuation is required every three years, and must contain "a description of the funding method and actuarial assumptions used to determine costs under the plan," 26 U.S.C. § 6059(b)(1) and "a certification of the contribution necessary to reduce the accumulated funding deficiency to zero," 26 U.S.C. § 6059(b). At the time of the demand in this case, the most recent actuarial valuation had been performed as of October 1, 1980. If that valuation had used only one interest rate, then that would have been the appropriate interest rate. However, the Fund's actuarial valuation used two interest rates: 6.25% for the payments required to fund fully the plan as defined under 26 U.S.C. § 412, and 8.0% to value vested benefits. See App. at 1462.

The Fund determined that the 8% vested benefit valuation rate was appropriate for the amortization of the withdrawal liability. The Employer contended that the section 412 rate of 6.25% should have been used. The Arbitrator agreed with the Employer, reasoning that since withdrawal liability payments were meant to substitute for the lost stream of contributions which the employer would have otherwise provided, and since the normal contributions made by the employer prior to withdrawal are based on the section 412 rate,

[i]t is logical to infer, therefore, that Congress, which desired specificity in the interest used by the Fund to calculate the duration of the withdrawal liability payment schedule, would have required that the interest rate used to value future contributions to the Fund be applied to the future stream of withdrawal liability payments which the fund was to receive.

7 EBC at 2729-30.

Thus, the Arbitrator did not find that the 6.25% rate was more appropriate based on the characteristics of this plan, a finding that would have been entitled to deference. Rather, the Arbitrator's decision on this issue was based on statutory interpretation, an area in which deference is not due.

The district court reversed the Arbitrator, since it "[found] nothing in the statute which requires the Fund to use the § 412 assumptions." App. at 2093. The PBGC agrees with the district court because "nothing in 29 U.S.C. § 1399(c)(1)(A)(ii) requires a plan to use the IRC § 412 rate." Brief of amicus PBGC at 38. The PBGC noted that "if Congress had intended to require a plan to use the [§ 412] funded rate, it knew how to say so," citing section 1393(b)(1) which refers to "the most recent complete actuarial valuation used for purposes of section 412 of Title 26. . . ." We are persuaded by this reasoning.

The PBGC also notes that

[s]ome plans use one rate, the so-called Section 412 rate, to calculate their statutory minimum funding requirements, and another rate to value unfunded vested benefits. This practice can be explained because vested benefit liabilities are payable over a shorter time horizon than total accrued liabilities. Therefore, the actuary need not be as conservative in his choice of an interest rate assumption for vested benefits. See generally Feuer, The Selection and Arbitration of Withdrawal Liability Interest Rates, 10 EMPLOYEE BENEFITS JOURNAL 23 (1985).

Brief of amicus PBGC at 37-38.

Since the withdrawal liability payments are meant to fund the accrued vested liabilities, as opposed to the accrued total liabilities, we are persuaded that it was appropriate for the Fund to select the rate used to value the vested liabilities. We therefore will affirm the district court's holding that the appropriate amortization interest rate was 8%.

III. The Language of the Statute clearly compels the imposition of First Year Interest, but not Pre-Demand Interest.

The unfunded vested benefits of the plan (i.e., the present value of the vested benefits less that of the assets of the plan) are calculated as of the last day of the plan year preceding that in which the employer withdraws. See 29 U.S.C. § 1391. They represent the amount which, if contributed on that day, would fully fund the plan.

The Fund assessed interest on the amount demanded for the period between October 1, 1981 (the day after the calculation date for the withdrawal liability), and December 1, 1984 (the date the first payment was due). For purposes of analysis, this interval will be separated into two periods: The period between October 1, 1981, and September 30, 1982 ("first year interest"), and the period between October 1, 1982, and December 1, 1984 ("pre-demand interest").

The section of the statute that governs this interest question is 29 U.S.C. § 1399(c)(1), which provides:

Except as provided in subparagraphs (B) and (D) of this paragraph and in paragraphs (4) and (5), an employer shall pay the amount determined under section 1391 of this title, adjusted if appropriate first under section 1389 of this title and then under section 1386 of this title over the number of years necessary to amortize the amount in level annual payments determined under subparagraph (C), calculated as if the first payment were made on the first day of the plan year following the plan year in which the withdrawal occurs and as if each subsequent payment were made on the first day of each subsequent plan year. Actual payment shall commence in accordance with paragraph (2). (emphasis supplied).

The Arbitrator concluded that neither first year nor pre-demand interest was payable. He reasoned that the Act contained no provision requiring first year interest, and that assessment of first year interest could result in a double assessment of interest in a case where an employer withdraws early in the plan year and a fund quickly calculates and demands the withdrawal liability. See 7 EBC at 2728-29. The Arbitrator concluded that while equity might counsel that the Fund was entitled to pre-demand interest to compensate it for the loss of the use of the money during the period in question, the statute would not allow it. He was persuaded that the "clear Congressional statement in Section 4219(c)(3) [ 29 U.S.C. § 1399(c)(3)] allowing the imposition of interest in cases where payments are not made when due . . . impliedly precludes the assessment of pre-demand interest . . . for times when the Employer was not in breach of any payment obligation." App. at 1973.

The district court concluded that interest should accrue starting from the date of the Employer's withdrawal, reasoning on the one hand that

[t]he employer's debt to the Fund is not incurred until an actual withdrawal occurs, International Harvester, 681 F. Supp. at 516, even if the statute provides for computation of liability on the basis of an arbitrary date . . .

and on the other hand that

Congress intended for plan participants to be protected from the loss of resources due to the passage of time; consequently we find that interest may be included as part of the employer's withdrawal liability obligation in order to counteract any erosion of the plan's resources caused by delayed funding of the plan.

App. at 2091.

However, while the liability for unfunded vested benefits became accelerated on the date the employer withdrew, it did not magically appear on that date. Unfunded vested benefits are benefits which are "promised and earned but not yet funded" as of the calculation day. "[T]he liability for UVBs represents a pre-existing obligation on the employer's part, and is not simply `incurred' as of the date of withdrawal." Du Art Technicolor v. Motion Picture Local 702 Pension Fund, 10 EBC 1326, 1328 (S.D.N.Y. 1988). In other words, the unfunded vested benefit calculation represents an employer's share of the amount needed for a fund to break even as of the calculation date. Due to the time value of money, that amount will grow between the calculation date and the withdrawal date.

The PBGC takes the position that MPPAA does not authorize any pre-demand interest, reasoning that MPPAA is minutely clear about issues such as the date and amount of the first payment, but indicates nothing about pre-demand interest. It contends, moreover, that

Congress knew how to provide for interest. It clearly provided for interest in other sections of MPPAA. . . . In this context, the fact that Congress did not enact an equally explicit provision for the inclusion of interest accruing for any period preceding the demand as part of the withdrawal liability amount can only mean that it did not intend for the inclusion of such interest.

Brief of amicus PBGC at 34.

Of course, "considerable weight should be accorded" to the PBGC's "construction of a statutory scheme it is entrusted to administer." See Chevron, U.S.A., Inc. v. Natural Resources Defense Council, 467 U.S. 837, 844, 104 S.Ct. 2778, 2782, 81 L.Ed.2d 694 (1984). But the PBGC interpretation does not give effect to the provision of 29 U.S.C. § 1399(c)(1) that the withdrawal liability must be calculated "in level annual payments . . . as if the first payment were made on the first day of the plan year following the plan year in which the withdrawal occurs and as if each subsequent payment were made on the first day of each subsequent plan year." By denying all interest, the PBGC would calculate the liability as if the first payment were made on the first day of the plan year of withdrawal.

"In construing a statute we are obliged to give effect, if possible, to every word Congress used." United States v. DiSantillo, 615 F.2d 128, 135 (3d Cir. 1980). See also Mountain States Tel. Tel. v. Pueblo of Santa Ana, 472 U.S. 237, 105 S.Ct. 2587, 2594, 86 L.Ed.2d 168 (1985) ("`elementary canon of statutory construction that a statute should be interpreted so as not to render one part inoperative'"); 2A Sutherland, Statutory Construction § 46.06 (4th ed. 1984).

The PBGC responds that

[d]espite considerable examination of this provision by those who are expert in MPPAA, there is no clear answer as to what Congress intended by this language. The most likely meaning is that additional interest does not accrue on an annual payment simply because each annual payment is divided into quarterly payments.

Brief of amicus PBGC at 36 n. 13.

The problem with this "most likely meaning" is that it renders superfluous the "first day of the plan year following" language. The meaning which the PBGC ascribes could have easily been stated "as if the payments were made annually."

We acknowledge that when interpreting ERISA, "the Court of Appeals should consider the views of the PBGC and the IRS. For a court to attempt to answer these questions without the views of the agencies responsible for enforcing ERISA, would be to `embar[k] on a voyage without a compass.'" Mead Corp. v. Tilley, 490 U.S. 714, 109 S.Ct. 2156, 2164, 104 L.Ed.2d 796 (1989). The PBGC has submitted an extraordinarily clear and helpful amicus brief in this case, "a sextant, enabling us to navigate our journey into uncharted, treacherous seas," Masters, Mates Pilots, 900 F.2d at 732 n. 4, but has confessed that "despite considerable examination" of the statutory language in question, it has been unable to ascertain what Congress intended. When one is caught on the high seas with a broken compass, one must navigate by the stars, in this case canons of statutory construction.

The calculation mandated by 29 U.S.C. § 1399(c)(1)(A) seems certain, even if understanding it requires some effort:

1) The date of the first payment is the first day of the plan year after withdrawal.

2) The payments are presumed to be annual.

3) The annual payment is determined by section 1399(c)(1)(C).

4) The interest rate is "based on the assumptions used for the most recent actuarial valuation for the plan," see 29 U.S.C. § 1399(c)(1)(A)(ii).

5) The principal amount is the Employer's share of the unfunded vested benefits as of the last day of the plan year preceding the year of withdrawal.

In rejecting the Fund's claim for first year interest, the Arbitrator suggests that "the `calculated as if' language . . . appears directed to the issue of whether the payment schedule should be constructed on the basis of an immediate annuity concept or a deferred annuity concept (also known as an annuity-due)." 7 EBC at 2728. He did not, however, take this analysis to its logical conclusion.

All other factors being equal, the amortization period for an annuity-due will be shorter than that of an immediate annuity because the first payment of an annuity-due is made at the beginning of the interval, and is therefore applied entirely to principal — no interest has yet accrued. On the other hand, a significant portion of the first payment of an immediate annuity is applied to interest — the interest on the principal for the first interval.

It is clear that in the MPPAA context we are dealing with an immediate annuity. The interval is one year, and the first payment is presumed to be due at the end of the first year. If Congress meant to have an annuity due, there did not have to be any presumed first payment date. The only way to construe a calculation date at the beginning of one year, and a first payment date at the beginning of the next, is as an immediate annuity.

Much is made over 29 U.S.C. § 1399(c)(4) which provides:

The employer shall be entitled to prepay the outstanding amount of the unpaid annual withdrawal liability payments determined under paragraph (1)(c), plus accrued interest, if any, in full or in part, without penalty. (emphasis supplied).

The PBGC suggests that

[i]f pre-demand interest were permitted, the words `if any' would be meaningless, as a withdrawn employer that chose to prepay its withdrawal liability under this section would invariably owe accrued interest.

Brief of amicus PBGC at 34 n. 11.

This argument assumes that the only type of prepayment to which the cited paragraph refers is a prepayment made immediately upon receipt of the demand letter. But the paragraph does not refer to "the withdrawal liability" but rather "the outstanding amount of the unpaid annual withdrawal liability payments." The employer may pre-pay the outstanding principal amount of the withdrawal liability at any time during the amortization period, including at a point immediately after a scheduled payment, at which point all accrued interest has been paid. After all, the amortization period can extend as long as 20 years after payments begin. See section 1399(c)(1)(B). It is possible that, during that time, long term interest rates could drop below the interest rate assumed in the amortization of the withdrawal liability payments. At that point, an economically rational employer might want to borrow the outstanding amount from a lender at the lower rate, so as to avoid paying interest to the plan at the higher rate. Because interest rates may change, many long term, fixed rate loans provide for a prepayment penalty. Otherwise, during times of low prevailing interest rates, a borrower could pay off a high rate loan, while the lender does not have the equivalent power to call the loan. The statute explicitly rejects any pre-payment penalty.

This also answers the argument raised by the Arbitrator and the Employer that the statute calls for payment "without penalty," and the suggestion by the Arbitrator that

[i]n certain cases, the employer might elect to tender [prepayment of the withdrawal liability] (assuming a promptly issued demand letter) before the end of the plan year in which withdrawal took place. To impose upon an employer in that situation an interest penalty [by charging a full year's interest] would appear contrary to the language of the Act and Congressional intent.

7 EBC at 2728.

The penalty to which the Arbitrator referred is not the penalty to which Congress was referring.

But what of the inequity of possible double interest? As we note below, the statute does not provide for pre-demand interest after the first year. In other words, interest will be assessed assuming that payment begins on the first day of the plan year after the withdrawal, whether payments begin before that date, as in the example posited by the Arbitrator, or long after that date, as actually happened in this case. If the employer pays some quantum of interest not really earned, that is fortuity, not penalty. As the PBGC notes in discussing this very point, "Congress was interested in rough equity, not precision." Brief of amicus PBGC at 36. An assumption that payments will begin on the first day of the plan year after withdrawal — not before and not after — is just that sort of rough equity. In any event, an employer could avoid this possibility by withdrawing near the end of the plan year.

This same reasoning precludes any assessment of interest for the period between September 30, 1982, and December 1, 1984. Congress clearly distinguished between the presumed first payment date and the actual first payment date. See section 1399(c)(1)(A)(i) ("an employer shall pay . . . calculated as if the first payment were made on. . . . Actual payment shall commence in accordance with paragraph (2).") (emphasis supplied). The actual payment start date is irrelevant here — this calculation is made on an "as if" basis. Accordingly, no interest may be charged for the period between September 30, 1982, and December 1, 1984. There is no inequity in this result, as the delay in making the demand was attributable to the Fund, apparently because of the state of its records. A prompt demand would have obviated its problem. Therefore, we will modify the district court's order with respect to interest to provide only for first year interest.

IV. Payment of Interest to the Employer on the Return of Overpayments

As we have indicated, inasmuch as the withdrawal liability payments made by the Employer on the Fund's demand exceeded the withdrawal liability found by the Arbitrator, a refund was required. The Arbitrator ruled that, consistent with PBGC regulations (29 C.F.R. § 2644.3), interest on those overpayments must be paid. He felt that "[i]t would be inequitable and would raise serious constitutional questions to compel the payment of disputed interim payments and then deny to employers who have made such payments under protest the right to recover the true value of any such payments determined to have been improperly collected by the plan." App. at 2056. He also noted that "adoption of a contrary approach could encourage plans to demand excessive withdrawal liability frivolously (or even in bad faith) so as to benefit from the permanent retention of the investment income produced by the interim payments. . . ." Id. at 2056-57.

The district court disagreed as it found that interest on overpayments of withdrawal liability is not allowed by ERISA. The court therefore concluded that 29 C.F.R. § 2644(2)(d), requiring the payment of such interest, violated the anti-inurement provisions of the statute. App. at 21-22.

The Employer and amicus PBGC urge that the regulation is a valid interpretation by the PBGC of the statute it is charged with administering, and that failure to allow interest on overpayments would render the statute subject to serious constitutional challenge. Though we disagree with the first contention, we agree with the second and thus conclude that the district court must be reversed on this point.

In striking down the regulation, the district court relied on Airco Industrial Gases, Inc. v. Teamsters Health and Welfare Pension Fund, 850 F.2d 1028 (3d Cir. 1988), a case involving an employer's mistaken overpayment of contributions to a plan. We found that the overpayment could be returned in part, but that interest could not be paid, a result we predicated on the anti-inurement provision of ERISA, which states that

[e]xcept as provided in paragraph (2), (3), or (4) or [other exceptions not relevant here] the assets of a plan shall never inure to the benefit of any employer and shall be held for the exclusive purposes of providing benefits to participants in the plan and their beneficiaries and to frame reasonable expenses of administering the plan.

29 U.S.C. § 1103(c)(1).

An exception is provided for payments or contributions made by mistake:

In the case of contribution, or a payment of withdrawal liability under part 1 of subtitle E of subchapter III of this chapter made by an employer to a multi-employer plan by mistake of fact or law . . . paragraph (1) shall not prohibit the return of such contribution or payment to the employer within six months after the plan administrator determines that the contribution was made by such a mistake.

29 U.S.C. § 1103(c)(2)(A)(ii).

We ruled in Airco that "`[i]nterest, which is the accrued value of money over time, is not a part of the overpayment but an incident of it. The amount of interest a court might award comes directly from the plan's assets and will deprive participants and beneficiaries of its use.'" Airco, 850 F.2d at 1037. Thus, we concluded that "the anti-inurement policy of ERISA bars an award of interest on any refund, regardless of the Fund's financial stability." Id.

The PBGC notes that, unlike the mistaken over-contribution situation in Airco, the agency has promulgated regulations providing for interest to be paid on overpayments. See 29 C.F.R. § 2644.2(d). The PBGC asserts that Congress was silent with regard to whether interest could be paid, and that, therefore, under Chevron, U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467 U.S. at 837, 104 S.Ct. at 2778, it is entitled to construe the statute.

The problem with this analysis, however, is that Congress was not silent on this issue. As noted by the Supreme Court in Chevron, in considering this issue we must first determine "whether Congress has directly spoken to the precise question at issue. If the intent of Congress is clear, that is the end of the matter. . . ." Id. at 842, 104 S.Ct. at 2781.

Section 1103(c)(1) clearly provides that "the assets of a plan shall never inure to the benefit of any employer." If the statute had stopped at that point, one might well argue that overpayments on withdrawal liability were simply never assets of the plan, perhaps under an implicit trust theory. However, the statute goes on to provide exceptions, among them the provision that "[i]n the case of a withdrawal liability payment which has been determined to be an overpayment, paragraph (1) shall not prohibit the return of such payment to the employer within six months after the date of such determination." 29 U.S.C. § 1103(c)(4) (emphasis supplied). Accordingly, it is clear that Congress treated even the overpayment as an asset of the plan. But when Congress allowed the return of "such payment," it did not provide for the payment of interest.

It is true that Congress did not explicitly prohibit the payment of interest on overpayments. However, the absence of an explicit prohibition does not necessarily create an implicit statutory gap. Rather, we must determine whether "Congress had an intention on the precise question at issue" using "traditional tools of statutory construction." Chevron, 467 U.S. at 843 n. 9, 104 S.Ct. at 2781-82 n. 9. See also Pension Benefit Guarantee Corporation v. LTV Corp., ___ U.S. ___, 110 S.Ct. 2668, 2676-77, 110 L.Ed.2d 579 (1990).

One traditional maxim of statutory construction is "expressio unius est exclusio alterius." See 2A SUTHERLAND, STATUTORY CONSTRUCTION § 47.23 (4th ed. 1984). As expressed by the Supreme Court in I.N.S. v. Cardoza-Fonseca, 480 U.S. 421, 432, 107 S.Ct. 1207, 1213, 94 L.Ed.2d 434 (1987), "`[w]here Congress includes particular language in one section of the statute, but omits it in another section of the same Act, it is generally presumed that Congress acts intentionally and purposely in the disparate inclusion or exclusion.'" Congress explicitly provided for interest in some sections of the MPPAA. See, e.g., 29 U.S.C. § 1399(c)(3) (interest in the event of default). To quote another portion of the PBGC's brief, "Congress's silence . . . is telling in a statute otherwise so explicit. . . . Obviously, Congress knew how to provide for interest. It clearly provided for the accrual of interest in other sections of MPPAA." Brief of amicus PBGC at 34. Furthermore, though Airco arose in a completely different context, we are bound, at least in the absence of specific provisions elsewhere in law, by its conclusion that the anti-inurement policy of ERISA bars interest on refunds, as there is nothing in 29 U.S.C. § 1103(c)(1) which distinguishes among the situations in which a claim for interest on refunds might arise.

Based solely on the statute, then, the regulation could not stand. However, the Employer and the PBGC suggest that "requiring refunds with interest on employer overpayments is necessary to save the [MPPAA]'s draconian interim payment procedure from serious constitutional defects." Employer's Brief at 45; see Reply Brief of Amicus PBGC at 6.

The interim payment procedure is indeed severe. The employer must begin payments no later than 60 days after notification by the trustees of the schedule of liability payments, "notwithstanding any request for review or appeal of determinations of the amount or of the schedule." 29 U.S.C. § 1399(c)(2). Any dispute regarding either of these issues must be resolved through arbitration. See 29 U.S.C. § 1401(a)(1); Carl Colteryahn Dairy, Inc. v. Western Pennsylvania Teamsters and Employers Pension Fund, 847 F.2d 113, 122-23 (3d Cir. 1988), cert. denied, 488 U.S. 1041, 109 S.Ct. 865, 102 L.Ed.2d 989 (1989); Flying Tiger Line v. Teamsters Pension Trust Fund, 830 F.2d 1241 (3d Cir. 1987). Payments must continue in accordance with the schedule "until the arbitrator issues a final decision with respect to the determination submitted for arbitration." 29 U.S.C. § 1401(d). Depending on the amount of the interim payments determined by the trustees, the amount of the withdrawal liability determined by the arbitrator, and the length of the arbitration proceedings, the employer may deprived of (and the trustees allowed) the use of a considerable sum for a substantial period of time.

In Yahn McDonnell, we ruled that the requirement in section 1401(a)(3)(A) that the trustees' determination be accorded a presumption of correctness was a violation of due process, given the trustees' bias stemming from their "fiduciary duty to the plan, and their consequent personal liability if the plan is not adequately funded." 787 F.2d at 140. However, we were "satisfied that if the arbitrator does not accord the trustees' determination a presumption of correctness, MPPAA will meet the constitutional requirement of providing an impartial decisionmaker." Id. at 143. In this administrative context, any harm suffered by an employer from having the initial determination made by a biased decisionmaker was relieved by a de novo determination by a neutral arbitrator.

This solution is complete so long as an employer has not been forced to overpay. The arbitrator simply reduces the number or amount of payments the employer is required to make in the future. In Yahn McDonnell, arbitration had not begun, and payments had not been made, so the possibility of overpayment by the employer was not presented. In this case, the problem is manifest. The Employer has been forced by a biased decisionmaker to make what was in effect an interest free loan of excess interim liability payments. A refund would only in part cure the defect, as the difference between permanent and temporary loss of the use of property is a matter of degree, not of kind. See First English Evangelical Lutheran Church v. County of Los Angeles, 482 U.S. 304, 318-19, 107 S.Ct. 2378, 2388, 96 L.Ed.2d 250 (1987).

Just as in Yahn McDonnell, see 787 F.2d at 142-43, the constitutional problem can be solved by severing the unconstitutional aspect of the statute. In this case, the least intrusive means of adjusting the statute to preserve its constitutionality is to strike down the application of the anti-inurement clause of section 1103(c) to interest on overpayments of interim withdrawal liability payments. If the Employer can be awarded interest on the overpayment, the harm caused by the biased decisionmaker is alleviated. The Employer is compensated for the loss of the use of the funds, and the incentive for the trustees to seek an interest-free loan is removed.

In the statutory scheme as adjusted, there is a gap, specifically the calculation of the amount of the interest on overpayments. The PBGC regulation, 26 C.F.R. Part 2644, reasonably fills that gap, and is therefore valid. We will therefore reverse the decision of the district court insofar as it invalidates the PBGC regulations providing for interest on refunds of overpayments.

V. Post-retirement death benefits may not be included in the unfunded vested benefit calculation.

The MPPAA provides that only "nonforfeitable" benefits are considered in the calculation of "unfunded vested benefits." 29 U.S.C. § 1393(c). The Fund's actuary included as vested a $2,500 lump sum post-retirement death benefit provided by the plan. See 7 EBC at 2735. The Arbitrator found these benefits were not "nonforfeitable" under the statutory definition. The district court reversed the Arbitrator on this point, reasoning that "death is not a condition for entitlement to benefits under the plan, but simply the time at which the vested benefits are paid out to plan participants," and that every participant who is vested in the benefit will die eventually. See App. at 2097-98.

The PBGC suggests that the important question is whether, as of the valuation date, "a participant has satisfied the stated conditions of entitlement to a particular benefit." Reply Brief of amicus PBGC at 9. For lump sum death benefits, death is a condition, and it must be met by the valuation date.

The PBGC has taken the position since 1975 that lump sum death benefits are not non-forfeitable. In final rules promulgated at 40 Fed.Reg. 43,509 (1975), the PBGC stated that

a benefit payable with respect to a participant is considered to be nonforfeitable, if on the date of termination of the plan the participant has satisfied all of the conditions required of him under the provisions of the plan to establish entitlement to the benefit, except the submission of a formal application, retirement, or the completion of a required waiting period.

40 Fed.Reg. at 43,511 [codified at 29 C.F.R. § 2605.6(a)] [since amended and redesignated 29 C.F.R. 2613.6(a)]. Moreover, the PBGC stated that it would

not guarantee a benefit payable in a single installment (or substantially so) upon the death of a participant or his surviving beneficiary unless that benefit was substantially derived from a reduction in the pension benefit payable to the participant or surviving beneficiary.

40 Fed.Reg. at 43,511 [codified at 29 C.F.R. § 2605.4(c)] [now redesignated 29 C.F.R. 2613.4(c)].

In 1980, Congress codified the PBGC's regulation, which the committee report described as "correctly stat[ing] the definition of `nonforfeitable.'" That definition is:

`Non-forfeitable benefit' means, with respect to a plan, a benefit for which a participant has satisfied the conditions or requirements under the plan or the requirements of this chapter (other than submission of a formal application, retirement, completion of a required waiting period, or death in the case of a benefit which returns all or a portion of a participant's accumulated mandatory employee contributions upon the participant's death), whether or not the benefit may subsequently be reduced or suspended by a plan amendment, and occurrence of any condition, or operation of this chapter or Title 26.

29 U.S.C. § 1301(a)(8) (emphasis supplied).

The PBGC notes that "[i]f Congress had intended all death benefits to be non-forfeitable, it could easily have drafted the language of [§ 1301(a)(8)] to accomplish that purpose." Brief of amicus PBGC at 291. The Fund fails to explain why Congress chose to qualify "death" if all death benefits were to be considered vested.

By referring to "death" in a list of exceptions to "conditions or requirements" of the plan that must be satisfied, Congress clearly contemplates that death can be a "condition or requirement" for entitlement to a death benefit. By limiting this exception to the case of a certain type of benefits, Congress implicitly denies the exception to the case of other types of benefits. Since the lump-sum death benefit in this case had nothing to do with the return of mandatory employee contributions, the exception has no application to this case. We will therefore reverse the district court and hold that lump-sum benefits are not to be included in the calculation of unfunded vested benefits.

VI. Informal written adoption of plan changes by the Trustees was effective.

The Employer challenges two categories of amendments to the plan: first, a number of increases in benefits, and second, a change in the method for allocating liabilities among employers. ERISA requires that "[e]very employee benefit plan shall be established and maintained pursuant to a written instrument." 29 U.S.C. § 1102(a)(1). "A written plan is required in order that every employee may, on examining the plan documents, determine exactly what his rights and obligations are under the plan." H.R.Conf.Rep. No. 1280, 93d Cong., 2nd Sess., reprinted in 1974 U.S. CODE CONG. ADMIN. NEWS 4639, 5038, 5077-78.

A. Benefit increases

The Arbitrator found as a fact that the benefit increases were not embodied in an executed plan document. See 7 EBC at 2738. However, he also found that these changes had all been adopted pursuant to resolutions of the Board of Trustees, and written in the minutes of the meetings. See 7 EBC at 2739. He noted that "[t]he plan amendment provisions of the executed, 1976 Plan document, granted the Trustees broad powers to amend the plan, without limitations on the particular format of such actions." Id. Moreover, he found that

there was no dispute that the Employer was aware of the benefit increases as they were implemented. Further, despite its representation on the Board of Trustees, no objection was raised by the Employer prior to its withdrawal regarding either the increases in benefits or the lack of any contemporaneous written, signed amendment to the Plan with regard to those increases.

Id. at 2740. He concluded that the amendments were effective because of the actions of the Trustees in

a) considering improvements in benefit levels,

b) seeking actuarial advice concerning the proposed benefit improvement,

c) determining by resolution and unanimous vote of the Fund Trustees that the improvement in benefits is warranted,

d) confirming those resolutions by written minutes signed and dated by the Plan Administrator, and

e) implementing those benefit improvements.

Id. at 2738-39. The district court upheld the Arbitrator on this point.

The Employer relies on Nachwalter v. Christie, 805 F.2d 956, 960 (11th Cir. 1986), for the proposition that "`Congress expressly prohibited informal . . . amendments of ERISA plans.'" See Employer's Brief at 20. However, Nachwalter does not help the Employer. The issue in Nachwalter was whether an oral modification to a plan would be recognized. The court, in interpreting ERISA to prohibit "informal written modifications," noted that:

ERISA requires that each plan shall `provide a procedure for amending such plan, and for identifying the persons who have authority to amend the plan.' 29 U.S.C. § 1102(b)(3). By explicitly requiring that each plan specify the amendment procedures, Congress rejected the use of informal written amendments.

Id.

We read Nachwalter to prohibit amendment of a plan by such informal means as an oral communication or a letter to a participant. We recently held, relying in part on Nachwalter, that "ERISA precludes oral amendments to employee benefit plans." Hozier v. Midwest Fasteners, Inc., 908 F.2d 1155, 1163 (3d Cir. 1990). However, we have also recently recognized that

in order not to frustrate the legitimate expectation of employees courts have upheld plans that do not meet the reporting, disclosure, and other formality requirements of ERISA. . . . Where a plan has complied with ERISA by setting forth a method for accomplishing amendment, of course each putative amendment will be evaluated by reference to that method.

Frank v. Colt Industries, Inc., 910 F.2d 90, 97-98 (3d Cir. 1990).

Here the plan had a procedure for amendment — modification by "the Trustees" — and the Arbitrator found that this procedure was followed at a regularly constituted Board meeting, and recorded in writing in the minutes of the meeting. We therefore accept the Arbitrator's conclusion that the benefit increases were duly adopted amendments to the plan.

The Employer also notes that on the annual reports filed with the United States Department of Labor (Form 5500), the trustees indicated under penalty of perjury that no amendments to the plan had been adopted. We agree with the Arbitrator that "[w]hatever the consequences that may flow in other forums from the Trustees' failure to have reported those amendments, that failure cannot be found to invalidate the plan amendments." App. at 2004. Thus, we will affirm the order of the district court on this issue.

B. Changes in attribution method

The MPPAA provides that the withdrawing employer's share of the plan's unfunded vested benefits shall be calculated by one of four methods, any of which is freely adoptable by the plan, or by another method if approved by the PBGC. See 29 U.S.C. § 1391(c); see generally Feuer, The Selection and Arbitration of Withdrawal Liability Interest Rates, EMPLOYEE BENEFITS JOURNAL, March 1985, at 23, 24-25.

If a plan does not elect otherwise, the "presumptive method" is used. That method allocates the unfunded vested benefits based on the contributions of the various employers over the past years. See 29 U.S.C. § 1391(b)(1). The Fund purportedly adopted one of the statutory alternatives, commonly known as the "direct attribution method," in which the unfunded vested benefits are allocated based on each participant's service with each employer. This method requires extremely complete and accurate records, see Feuer, supra, at 24, which the Fund lacked. See 7 EBC at 2732.

The Fund allocated the unfunded vested benefits using the direct attribution method, but used a "last employer" assumption, which presumed that all of the benefits earned by each employee were earned with his or her last employer, as of the calculation date. The Arbitrator found, based on the minutes of a Board of Trustees meeting on January 28, 1981, that the Fund had adopted the direct attribution method of allocating unfunded vested benefits. See 7 EBC at 2732. However, the minutes said nothing about the "last employer" rule. The Arbitrator concluded that the Fund's adoption of the direct attribution method was effective. 7 EBC at 2733. We accept this conclusion for the reasons expressed in our discussion of the benefit increases. Thus, we will reverse the district court's order which required recomputation of the Employer's liability by use of the presumptive method.

The Employer questions whether the "last employer" assumption was duly adopted by the Trustees, and, if it was, whether the addition of the assumption transformed the attribution method from one acceptable under section 1391(c)(4) without PBGC approval to an alternative method that required PBGC approval under section 1391(c)(5). We need not reach this issue, as we accept the Arbitrator's finding that, given the unrebutted testimony of extremely low employee interchange between the two employers, one may view the last employer assumption as a reasonable simplifying assumption by the Fund actuary. See 29 U.S.C. § 1393(a)(1); 7 EBC at 2735.

VII. The Second Assessment of Withdrawal Liability.

At the conclusion of his first Opinion and Award, on December 13, 1986, the Arbitrator directed the Fund to recalculate the Employer's withdrawal liability and retained jurisdiction to review that reassessment. On February 19, 1987, the Fund issued its redetermination of withdrawal liability, but included in this redetermination liabilities for a total of 120 employees (84 of them attributable to the Employer) allegedly erroneously excluded from the Fund's first calculation. The Employer moved to strike the addition of this new information, and the Arbitrator granted this motion. The Fund challenged this decision in the proceedings before the district court. The district court dismissed this challenge, finding the issue moot because of the Fund's issuance of a second withdrawal liability assessment.

We consider questions of mootness under a plenary standard of review. See International Brotherhood of Boilermakers v. Kelly, 815 F.2d 912, 914 (3d Cir. 1987). We have found that the "central question" in mootness inquiries is "`whether changes in circumstances that prevailed at the beginning of the litigation have forestalled any occasion for meaningful relief.'" Id. at 915. We find that there is a possibility for meaningful relief here, since, if the Arbitrator erred in striking the new material, the case may be remanded to him with instructions to admit the additional evidence and substantive consequences could follow. Furthermore, it is conceivable that the results of a new arbitration might be different than those obtained at a reopening of the original proceedings. Overall, therefore, we find that the rendering of the second assessment does not make the challenge to the Arbitrator's order striking the new information moot and we consider the order on the merits.

We will review the selection of factors the Arbitrator considered in deciding whether to strike the additional information under a plenary standard of review, but will review the application of those standards to the facts of this case under the deferential standard mandated by the statute. The new data was discovered by the Fund during a recomputation process in progress during the arbitration hearing. The Arbitrator found as fact that "the Fund did not deliberately conceal the corrected, updated data." App. at 2024. In considering the Employer's motion to strike the introduction of this new material, and the Fund's opposition thereto, the Arbitrator found that four issues were raised:

1) Did the first award specifically sanction the Fund's inclusion of liabilities associated with participant data different from that employed in the initial withdrawal liability determination?

2) If not, do adequate grounds exist for reopening the record to include this new, more accurate data?

3) If not, do adequate grounds exist for an arbitral grant of relief from the first award?

4) If not, do section 1399 and/or 1401 preclude or permit the issuance of the supplemental determination at this time by the Fund based upon the new data and would any such supplemental determination be within the jurisdiction of the arbitrator in this case?

App. at 2028 (Arbitrator's decision on motion to strike).

The Arbitrator answered the first question, whether his initial award permitted the introduction of new data, with a resounding "no." See App. at 2031. With regards to the second question, whether adequate grounds existed for reopening the record, the Arbitrator determined that, based upon any regulations applicable, reopening would depend upon the satisfaction of three conditions:

1) The reopening is likely to result in new information that will have a material effect on the outcome of the arbitration;

2) Good cause exists for the failure of the party that requested reopening to present such information at the [initial] hearing;

3) The delay caused by the reopening will not be unfairly injurious to any party.

App. at 2034.

The Arbitrator found that the first of these requirements had been met, since the relevance and materiality of the new participant data was not disputed by the parties, and since the inclusion of that data would significantly increase the employer's liability. He also concluded that the delay did not cause any injury to the Employer, since the Employer would still retain the opportunity to challenge the validity of the revised data as well as the calculations made on the data. The Arbitrator found that the Employer's claim that it would be subjected to endless litigation was "unpersuasive when balanced against the Fund's strong interest in being fairly compensated for withdrawal liability properly due and owing in this case." App. at 2034-35.

However, the Arbitrator found that the Fund did not meet the second, "good cause" prong of the test:

The question of the accuracy and completeness of the Fund's data was raised repeatedly by the Employer during the trial of the arbitration case. The Fund and its actuary consistently and repeatedly replied that the state of the Fund's records was excellent and more than adequate for purposes of the computation of the amount of withdrawal liability due by the Employer. No persuasive reason was proffered by the Fund as to why it neither completed the recomputation prior to the close of the hearings nor moved prior to the close of the hearings and the issuance of the Interim Opinion and Award to reopen the record for the receipt of the results of that reposting of the underlying data.

App. at 2035-36.

The Fund objects to the Arbitrator's application of the "good cause" standard. The Fund suggests, without support, that "this standard simply means that the reason must be other than tactical." Fund's Brief at 42. We reject this interpretation, which ignores the word "good" in "good cause."

The Arbitrator also found that no adequate grounds existed for an arbitral grant of relief from the interim award. The Arbitrator expressed doubt as to whether he had the power to set aside a final order as is enjoyed by the federal judiciary pursuant to Fed.R.Civ.P. 60, and found that even if he had such power, he was not persuaded that this is a case in which the requirements of Rule 60(b) had been met. See App. at 2041. The Fund suggests that, even under the due diligence standard of the federal rules, "a new trial may be granted after trial is concluded to prevent a manifest injustice." Fund's Brief at 42. However, in Moolenaar v. Gov't of the Virgin Islands, 822 F.2d 1342 (3d Cir. 1987), this court held that the fact that a "manifest injustice" might occur is not sufficient to justify a new trial. Rather, "the exercise of a district court's discretionary power [to grant a new trial] requires an extraordinary circumstance." Id. at 1346-47. The only extraordinary circumstances in this case are that the Fund, despite the statutory command that it notify the Employer of the amount of the withdrawal liability "as soon as practicable" after withdrawal, issued its initial demand more than two and one half years after withdrawal, and that this newly discovered evidence was first presented almost five years after the withdrawal. These circumstances did not demonstrate manifest injustice to the Fund.

The Arbitrator then considered the question of whether section 1399 or section 1401 of 29 U.S.C. precluded or permitted the issuance of a supplemental withdrawal liability determination. He ultimately declined to rule on this question, as he concluded that he lacked jurisdiction to do so. App. at 2047. We express no views as to the correctness of this conclusion, as it is not challenged by either of the parties.

We have carefully reviewed the Arbitrator's reasons for striking the new information and conclude he was clearly correct. In the circumstances we have determined that it is not necessary to expand on his reasoning.

Of course, the district court's conclusion that the review of the order striking the additional information was moot did not resolve the direct challenge to the assessment. The district court concluded that any questions as to whether the second assessment was precluded by the doctrine of res judicata, or whether the employer had properly and timely initiated arbitration on the second demand should, in the first instance, be decided by an Arbitrator. The court noted that the statute provides that "[a]ny dispute between an employer and the plan sponsor of a multiemployer plan concerning the determination under sections 1381 to 1399 of this title shall be resolved through arbitration." 29 U.S.C. § 1401(a)(1). "[H]ere, Casablanca is questioning the Fund's legal power under 29 U.S.C. § 1399 to issue a second assessment of withdrawal liability." App. at 2108-09.

This result is fully supported by our decisions in Flying Tiger Line v. Teamsters Pension Trust Fund, 830 F.2d at 1241, and Carl Colteryahn Dairy, Inc. v. Western Pennsylvania Teamsters and Employers Pension Fund, 847 F.2d at 113 and we will affirm it. In Flying Tiger, we "emphasize[d] the importance of `the legislature's decision that arbitration, and not the courts, is the proper forum for the initial resolution of disputes [under MPPAA.]'" 830 F.2d at 1249. Colteryahn involved an employer's withdrawal from a multiemployer fund which had recently absorbed the smaller fund of which the employer had been a member. There we distinguished between two claims: whether certain payments made at the time of the merger should be considered contributions for the purpose of calculating withdrawal liability, a claim we found subject to arbitration, and a claim that the employer had been fraudulently induced to assent to the merger, a claim we found not subject to arbitration because it "concern[ed] events external to the actual calculation" of the withdrawal liability. See 847 F.2d at 123. See also Crown Cork Seal Co. v. Central States etc. Pension Fund, 881 F.2d 11, 19 (3d Cir. 1989).

The claims raised by both parties regarding the second assessment all concern the validity of the assessment, and arbitral procedure. These issues are central to the calculation of the withdrawal liability, and are reserved for arbitration.

CONCLUSION

We will affirm the order of the district court of October 30, 1989, insofar as it accepted the Arbitrator's calculation of assets, ordered the use of an 8% amortization rate for withdrawal liability payments, accepted the inclusion of the benefit increases, and directed arbitration of the second assessment. We will reverse the order of October 30, 1989, insofar as it struck down the PBGC regulations on interest for overpayments, mandated inclusion of post-retirement death benefits in the liability calculations, refused to accept the change in attribution method, and directed payment of interim payments on the second assessment. We will modify the district court's calculation of pre-demand interest to provide only first-year interest. We will further modify the order of the district court so that the order of the Arbitrator striking the Employer's motion to add the new information is upheld. The case will be remanded to the district court for further proceedings consistent with this opinion.