Reserve Mining Company, a Minnesota Corporation v. Environmental Protection Agency and William D. Ruckelshaus, Individually Andas Administrator of the Environmental Protection Agency, Reserve Mining Company v. United States of America, United States of America v. Reserve Mining Company, Reserve Mining Company v. United States of America, the State of Wisconsin v. Reserve Mining Company, Minnesota Environmental Law Institute, Inc. v. United States of America, the State of Michigan v. Reserve Mining Company

The United States, the States of Michigan, Wisconsin, and Minnesota, and several environmental groups seek an injunction ordering Reserve Mining Company1 to cease discharging wastes from its iron ore processing plant in Silver Bay, Minnesota, into the ambient air of Silver Bay and the waters of Lake Superior. On April 20, 1974, the district court granted the requested relief and ordered that the discharges immediately cease, thus effectively closing the plant. United States v. Reserve Mining Co., 380 F.Supp. 11 (D.Minn.1974). Reserve Mining Company appealed that order and we stayed the injunction pending resolution of the merits of the appeal. Reserve Mining Co. v. United States, 498 F.2d 1073 (8th Cir. 1974). We affirm the injunction but direct modification of its terms. As to other issues brought before us by appeals during the course of this complex litigation, we affirm in part and reverse in part.

In this lengthy opinion, we undertake a comprehensive analysis of the relevant scientific and medical testimony and evaluate the claims of the plaintiffs that Reserve's conduct violates express provisions of federal law as well as state laws and regulations and is a public nuisance.

1) The United States and the other plaintiffs have established that Reserve's discharges into the air and water give rise to a potential threat to the public health. The risk to public health is of sufficient gravity to be legally cognizable and calls for an abatement order on reasonable terms.

2) The United States and Minnesota have shown that Reserve's discharges violate federal and state laws and state pollution control regulations, also justifying injunctive relief on equitable terms.

3) No harm to the public health has been shown to have occurred to this date and the danger to health is not imminent. The evidence calls for preventive and precautionary steps. No reason exists which requires that Reserve terminate its operations at once.

4) Reserve, with its parent companies Armco Steel and Republic Steel, is entitled to a reasonable opportunity and a reasonable time period to convert its Minnesota taconite operations to on-land disposal of taconite tailings and to restrict air emissions at its Silver Bay plant, or to close its existing Minnesota taconite-pelletizing operations. The parties are required to expedite consideration and resolution of these alternatives.

5) The evidence suggests that the threat to public health from the air emissions is more significant than that from the water discharge. Consequently, Reserve must take reasonable immediate steps to reduce its air emissions.

A. Summary of Controversy.

In 1947, Reserve Mining Company (Reserve), then contemplating a venture in which it would mine low-grade iron ore ("taconite") present in Minnesota's Mesabi Iron Range and process the ore into iron-rich pellets at facilities bordering on Lake Superior, received a permit2 from the State of Minnesota to discharge the wastes (called "tailings") from its processing operations into the lake.3

Reserve commenced the processing of taconite ore in Silver Bay, Minnesota, in 1955, and that operation continues today. Taconite mined near Babbitt, Minnesota, is shipped by rail some 47 miles to the Silver Bay "beneficiating" plant where it is concentrated into pellets containing some 65 percent iron ore. The process involves crushing the taconite into fine granules, separating out the metallic iron with huge magnets, and flushing the residual tailings into Lake Superior. The tailings enter the lake as a slurry of approximately 1.5 percent solids. The slurry acts as a heavy density current bearing the bulk of the suspended particles to the lake bottom. In this manner, approximately 67,000 tons of tailings are discharged daily.4

The states and the United States commenced efforts to procure abatement of these discharges as early as mid-1969. These efforts, however, produced only an unsuccessful series of administrative conferences and unsuccessful state court proceedings.5 The instant litigation commenced on February 2, 1972, when the United States joined eventually by the States of Minnesota, Wisconsin, and Michigan and by various environmental groups filed a complaint alleging that Reserve's discharge of tailings into Lake Superior violated § 407 of the Rivers and Harbors Act of 1899 (33 U.S.C. § 401 et seq. (1970)),6 § 1160 of the pre-1972 Federal Water Pollution Control Act (FWPCA) (33 U.S.C. § 1151 et seq. (1970))7 and the federal common law of public nuisance.

Until June 8, 1973, the case was essentially a water pollution abatement case, but on that date the focus of the controversy shifted to the public health impact of the tailings discharge and Reserve's emissions into the ambient air. Arguing the health issue in the district court, plaintiffs maintained that the taconite ore mined by Reserve contained an asbestiform variety of the amphibole mineral cummingtonite-grunerite,8 and that the processing of the ore resulted in the discharge into the air and water of mineral fibers substantially identical and in some instances identical to amosite asbestos.9 This contention raised an immediate health issue, since inhalation of asbestos at occupational levels of exposure is associated with an increased incidence of various forms of cancer.

Although it is undisputed that Reserve discharges significant amounts of waste tailings into Lake Superior and dust into the Silver Bay air, the parties vigorously contest the precise physical properties of the discharges, their biological effects, and, with respect to the water discharge, the issue of whether a significant proportion of the discharge, instead of flowing to the lake bottom with the density current, disperses throughout the lake. Plaintiffs attempted to show that a substantial amount of the fibers discharged by Reserve could be classified as amosite asbestos, and that these fibers could be traced in the ambient air of Silver Bay and surrounding communities and in the drinking water of Duluth and other communities drawing water from the lake. Reserve countered that its cummingtonite-grunerite does not have a fibrous form and is otherwise distinguishable from amosite asbestos. It further maintained that the discharges do not pose any cognizable hazard to health and that, in any event, with respect to the discharge into water, the tailings largely settle to the bottom of the lake in the "great trough" area as initially planned.10

The evidence presented on these points was extensive and complex. Hearings on a motion for a preliminary injunction were consolidated with the trial on the merits and during the nine-month period of 139 days of trial, the trial court heard more than 100 witnesses and received over 1,600 exhibits. The parties introduced testimony comparing the mineralogy of Reserve's cummingtonite-grunerite with amosite asbestos, such testimony based on electron microscope analysis of morphology, x-ray and electron diffraction analysis of crystal structure, laboratory analysis of chemical composition, and other identification techniques. As for the possible dispersion of the tailings throughout Lake Superior, witnesses disputed whether Reserve's discharges provided the sole source of cummingtonite-grunerite in the lake and whether the presence of the mineral could thus be used as a "tracer" for Reserve's discharge. In an effort to assess the health hazard, the parties presented extensive expert scientific and medical testimony, and the court itself appointed certain expert witnesses, who assumed the task of assisting the court in the evaluation of scientific testimony and supervising court-sponsored studies to measure the levels of asbestos fibers in the air near Silver Bay, in Lake Superior water, and in the tissues of deceased Duluth residents.

On April 20, 1974, the district court entered an order closing Reserve's Silver Bay facility. In an abbreviated memorandum opinion,11 the court held that Reserve's water discharge violated federal water pollution laws and that its air emissions violated state air pollution regulations, and that both the air and water discharges constituted common law nuisances. The court's decision, in part, rested on these core findings:

The discharge into the air substantially endangers the health of the people of Silver Bay and surrounding communities as far away as the eastern shore in Wisconsin.

The discharge into the water substantially endangers the health of people who procure their drinking water from the western arm of Lake Superior including the communities of Beaver Bay, Two Harbors, Cloquet, Duluth (Minnesota), and Superior, Wisconsin. (380 F.Supp. at 16.)

The district court issued an extensive supplemental memorandum on May 11, 1974,12 expanding on its earlier findings of fact and conclusions of law. In proceedings detailed in the following section of this opinion, a panel of this court stayed the injunction13 and subsequently requested the district court to fully dispose of the litigation and enter final judgment. This court, sitting en banc, heard the merits of several consolidated appeals at the December 1974 session. We have also taken under consideration other appeals which have been subsequently submitted to us on briefs, but without oral argument. Our disposition follows.

B. Discussion of Rulings by the District Court and Previous Proceedings in this Court.

In its memorandum opinions of April 20, and May 11, ordering Reserve to cease immediately its discharges into the air and water, the district court predicated its determinations on several counts. On the discharge into water, the court found a violation of several sections of the Minnesota water quality standards. These standards, promulgated pursuant to § 1160(c)(5) of the FWPCA and subsequently approved by the federal government, are denominated as Minnesota Water Pollution Control Regulation 15 (WPC 15). The district court found the following parts of WPC 15 violated: WPC 15(a)(4), providing that waters of naturally high quality shall not be degraded; WPC 15(c)(2), a broad provision prohibiting the discharge of wastes which create nuisance conditions or cause "offensive or harmful effects;" WPC 15(c)(6), limiting the allowable suspended solid content of effluent discharges to 30 milligrams per liter; WPC 15(d)(1), controlling the discharge of substances that make certain waters unfit to drink even after chemical treatment; and WPC 26, a general effluent standard for Lake Superior incorporating the standards of WPC 15. Further, the court found that the discharge into Lake Superior endangered the health and welfare of persons in Minnesota, Wisconsin, and Michigan and therefore was subject to abatement pursuant to §§ 1160(c)(5) and (g)(1) of the FWPCA. Finally, the court found that the endangerment to health also constituted both a federal common law nuisance and a nuisance under the applicable laws of Minnesota, Wisconsin, and Michigan. 380 F.Supp. at 55.

As for the air emissions, the court also found liability under both federal and state common law nuisance. Additionally, the court cited Reserve for the violation of several Minnesota air pollution control regulations: APC 1, setting primary and secondary air standards; APC 5 and 6, controlling particulate emissions; and APC 17, setting an emission standard for asbestos. 380 F.Supp. at 55-56.

The trial court based its closure decision on two independent determinations. First, as noted above, the court had concluded that the discharges "substantially endanger" the exposed populations. Second, the court had concluded that, although a method of abatement providing for an alternate means of disposal of wastes with some turn-around time represented a desirable middle course in this litigation,14 Reserve had demonstrated such intransigence on the issue of abating its water discharge as to render any such middle course impossible. The court thus believed it had no alternative but to immediately enjoin the discharges:

Defendants have the economic and engineering capability to carry out an on land disposal system that satisfies the health and environmental considerations raised. For reasons unknown to this Court they have chosen not to implement such a plan. In essence they have decided to continue exposing thousands daily to a substantial health risk in order to maintain the current profitability of the present operation and delay the capital outlay (with its concomitant profit) needed to institute modifications. The Court has no other alternative but to order an immediate halt to the discharge which threatens the lives of thousands. In that defendants have no plan to make the necessary modifications, there is no reason to delay any further the issuance of the injunction. (380 F.Supp. at 20.)

Reserve promptly appealed the injunction order of the district court and we issued a temporary stay of that order on April 22, 1974, and scheduled a hearing on Reserve's application for a stay of injunction pending its appeal. That hearing was held on May 15, 1974, before a panel of this court consisting of Judges Bright, Ross, and Webster, and on June 4, 1974, the court issued an opinion granting Reserve a 70-day stay of the injunction. Reserve Mining Co. v. United States, 498 F.2d 1073 (8th Cir. 1974). The court conditioned the stay upon Reserve taking prompt steps to abate its air and water discharges, and provided for further proceedings to review whether Reserve had proceeded with the good faith preparation and implementation of an acceptable plan.15

The State of Minnesota applied to the Supreme Court to vacate this stay. The Court denied Minnesota this relief in an order entered July 9, 1974. Minnesota v. Reserve Mining Co., 418 U.S. 911, 94 S.Ct. 3203, 41 L.Ed.2d 1156 (1974). Meanwhile, in accordance with the stay order, the district court evaluated compliance with our order that Reserve proceed in good faith to present a plan of abatement. In a memorandum opinion filed August 3, 1974,16 the district court, taking cognizance of the opposition of the State of Minnesota to Reserve's proffered plan (the so-called Palisades Plan), rejected Reserve's proposal as unreasonable and recommended against any further stay during the pendency of this litigation. Also, pursuant to our earlier request for advice on the status of unresolved claims, the district court indicated that it had "severed for later resolution the issue of the biological effect of Reserve's discharge on the Lake itself" and that several other issues remained under advisement. 380 F.Supp. at 91 n. 6.

Judges Bright and Ross convened a prehearing conference under Fed.R.App.P. 33 to inquire into consolidation, clarification, and simplification of issues pending an appeal and to advise this court of the time necessary to submit unresolved issues pending before the district court. The cause was then remanded with a request that the district court expedite disposition of the unresolved issues, with this court retaining jurisdiction over the pending appeal of the district court injunction.

Additionally, this court, on its own motion, scheduled a hearing before a panel consisting of Judges Bright, Ross, and Webster to consider the recommendations of the district court against continuing the stay order pending appeal. Following hearings, this court entered an order continuing the stay, concluding that:

1) The representations of counsel at the hearing on August 27, 1974, satisfy us that significant progress has been achieved by the parties in seeking agreement for an on-land disposal site and method for abatement of Reserve's discharge into Lake Superior. These negotiations are continuing and will not impede the processing of the pending appeal upon the merits, (and)

2) No substantial reason has been advanced why the stay order should not be continued pending such appeal other than the argument of imminent health hazard, which this court, for purposes of the stay pending appeal, has already determined adversely to appellees. (Reserve Mining Co. v. United States, No. 74-1291 (8th Cir., Aug. 28, 1974).)

Minnesota and the United States applied to the Supreme Court for relief from this further stay order. The Court denied the applications, with Mr. Justice Douglas dissenting. Minnesota v. Reserve Mining Co., 419 U.S. 802, 95 S.Ct. 287, 42 L.Ed.2d 33 (1974).

On October 18, 1974, the district court issued an unpublished memorandum resolving certain other issues in the case and, noting that there was no just reason for delay, directing the entry of final judgment on all claims decided to date. See Fed.R.Civ.P. 54(b).

The district court made the following additional rulings: 1) that Reserve's discharge into the water constitutes a violation of the Refuse Act, 33 U.S.C. § 407; 2) that Reserve's counterclaims, alleging that interference with its present modes of discharge as sanctioned by permits amounts to a deprivation of property and an impairment of contractual rights, should be dismissed; 3) that Reserve's air emissions violate Minnesota air pollution control regulation (APC) 3 and Minn.Stat.Ann. § 116.081(1), which require that permits be obtained for the operation of certain emission facilities; 4) that Reserve's discharge of wastes into the Dunka and Partridge Rivers of Minnesota violates Minn.Stat.Ann. § 115.07(1), which requires a permit for the operation of a disposal system; 5) that Minn.Stat.Ann. § 115.07(1) is also violated by Reserve's discharge of wastes from its pilot plant into Lake Superior without a permit; 6) that the evidence is insufficient to justify liability under Minn.Stat.Ann. § 105.41, which makes unlawful the appropriation of state water without a permit; and 7) that the State of Wisconsin could not assert the state's "public trust doctrine" as an affirmative cause of action against Reserve's discharge into Lake Superior. Finally, the court left certain matters undecided, stating:

The question of fines and penalties, the question of sanctions for failure to make discovery, and the question of liability of defendants for the water filtration systems that may be installed in Duluth, Minnesota, and Superior, Wisconsin, cannot be decided at this time. (Order of Oct. 18, 1974, at 19.)

This final order has produced several additional appeals. We now have under submission the following:

No. 73-1239: Reserve Mining Co. v. Environmental Protection Agency, in which Reserve urges that WPC 15 is arbitrary and unreasonable and challenges the failure of the Administrator of the EPA to require its revision.

No. 74-1291: Reserve Mining Co. v. United States, in which Reserve seeks to vacate the April 20, 1974, order enjoining its discharges into the air and water.

No. 74-1466: United States v. Reserve Mining Co., in which the United States appeals from the district court's order (April 19, 1974) directing that the Corps of Engineers of the United States provide filtered water at government expense to certain Minnesota communities located on the North Shore of Lake Superior.

No. 74-1816: Reserve Mining Co. v. United States, in which Reserve appeals from the most recent judgment entered October 18, 1974.

No. 74-1977: State of Wisconsin v. Reserve Mining Co., in which appellant-Wisconsin contests the district court's determination that the Wisconsin public trust doctrine does not provide an affirmative cause of action against Reserve's discharge into Lake Superior.17

No. 75-1003: Minnesota Environmental Law Institute v. United States, in which various environmental plaintiffs contest the district court's decision to "sever" the issue of whether Reserve's discharge constitutes biological pollution of Lake Superior.

No. 75-1005: State of Michigan v. Reserve Mining Co., in which appellant-Michigan contests the district court's decision to "sever" the issue of whether Reserve's discharge constitutes biological pollution of Lake Superior.

During oral arguments and by written submissions, Reserve has advised us that it no longer asks Minnesota to accept its plan to dispose taconite tailings at the Palisades location, see discussion at p. 504 supra. Reserve has now submitted a second proposal to Minnesota for an on-land disposal site in which it proposes to spend approximately $243,000,000 in order to end its discharge of tailings into Lake Superior and curtail its emission of contaminants into the air. This proposed site, which Minnesota has under consideration, is located approximately seven miles inland from the Silver Bay facility, and is referred to as Milepost 7, or Lax Lake site.

The initial, crucial question for our evaluation and resolution focuses upon the alleged hazard to public health attributable to Reserve's discharges into the air and water.

We first considered this issue on Reserve's application for a stay of the district court's injunction pending a determination of the merits of its appeal. We noted the usual formulation of the applicable standards to be met by the party seeking a stay. One of those standards addresses the likelihood of success by the moving party on the merits of the appeal. In applying this standard we made a preliminary assessment of the merits of Reserve's appeal from the trial court's injunction order. We noted that the "rather drastic remedy ordered by the district court * * * was a response to the finding of a substantial danger to the public health," and that our preliminary assessment of whether such a substantial danger was presented "should control our action as to whether to grant or deny a stay." 498 F.2d at 1076-1077.

In this preliminary review, we did not view the evidence as supporting a finding of substantial danger. We noted numerous uncertainties in plaintiffs' theory of harm which controlled our assessment, particularly the uncertainty as to present levels of exposure and the difficulty in attempting to quantify those uncertain levels in terms of a demonstrable health hazard. As we stated then, " * * * it is not known what the level of fiber exposure is, other than that it is relatively low, and it is not known what level of exposure is safe or unsafe." 498 F.2d at 1082. In confirmation of our view, we noted the opinion of Dr. Arnold Brown,18 the principal court-appointed expert, that no adverse health consequences could be scientifically predicted on the basis of existing medical knowledge. Additionally, we noted the district court's conclusion that there is " ' * * * insufficient knowledge upon which to base an opinion as to the magnitude of the risks associated with this exposure.' " 498 F.2d at 1083. We thought one proposition evident:

(A)lthough Reserve's discharges represent a possible medical danger, they have not in this case been proven to amount to a health hazard. The discharges may or may not result in detrimental health effects, but, for the present, that is simply unknown. (Id.)

On the basis of the foregoing we forecast that Reserve would likely prevail on the merits of the health issue.19 We limited this forecast to the single issue before us whether Reserve's plant should be closed immediately because of a "substantial danger" to health:

While not called upon at this stage to reach any final conclusion, our review suggests that this evidence does not support a finding of substantial danger and that, indeed, the testimony indicates that such a finding should not be made. In this regard, we conclude that Reserve appears likely to succeed on the merits of its appeal on the health issue. 498 F.2d at 1077-1078. (Emphasis added).

We reached no preliminary decision on whether the facts justified a less stringent abatement order.

As will be evident from the discussion that follows, we adhere to our preliminary assessment that the evidence is insufficient to support the kind of demonstrable danger to the public health that would justify the immediate closing of Reserve's operations. We now address the basic question of whether the discharges pose any risk to public health and, if so, whether the risk is one which is legally cognizable. This inquiry demands separate attention to the discharge into the air of Silver Bay and the discharge into Lake Superior.20

A. The Discharge Into Air.

As we noted in our stay opinion, much of the scientific knowledge regarding asbestos disease pathology derives from epidemiological studies of asbestos workers occupationally exposed to and inhaling high levels of asbestos dust. Studies of workers naturally exposed to asbestos dust have shown "excess" cancer deaths21 and a significant incidence of asbestosis.22 The principal excess cancers are cancer of the lung, the pleura (mesothelioma) and gastrointestinal tract ("gi" cancer).

Studies conducted by Dr. Irving Selikoff,23 plaintiffs' principal medical witness, illustrated these disease effects. Dr. Selikoff investigated the disease experience of asbestos insulation workers in the New York-New Jersey area, asbestos insulation workers nationwide, and workers in a New Jersey plant manufacturing amosite asbestos. Generally, all three groups showed excess cancer deaths among the exposed populations, as well as a significant incidence of asbestosis. With respect to cancer generally, three to four times the expected number of deaths occurred; with respect to lung cancer in particular, five to eight times the expected number; and with respect to gastrointestinal cancer, two to three times that expected. Dr. Selikoff described the increase of gastrointestinal cancer as "modest." (A.10:286-287.)

Several principles of asbestos-related disease pathology emerge from these occupational studies. One principle relates to the so-called 20-year rule, meaning that there is a latent period of cancer development of at least 20 years. (A.10:284-285.) Another basic principle is the importance of initial exposure, demonstrated by significant increases in the incidence of cancer even among asbestos manufacturing workers employed for less than three months (although the incidence of disease does increase upon longer exposure). (A.10:279-280.) Finally, these studies indicate that threshold values and dose response relationships,24 although probably operative with respect to asbestos-induced cancer, are not quantifiable on the basis of existing data.25 (A.10:280, 317-19.)

Additionally, some studies implicate asbestos as a possible pathogenic agent in circumstances of exposure less severe than occupational levels. For example, several studies indicate that mesothelioma, a rare but particularly lethal cancer frequently associated with asbestos exposure, has been found in persons experiencing a low level of asbestos exposure.26 Although Dr. Selikoff acknowledged that these studies of lower-level exposure involve certain methodological difficulties and rest "on much less firm ground" than the occupational studies,27 he expressed the opinion that they should be considered in the assessment of risks posed by an asbestos discharge.

At issue in the present case is the similarity of the circumstances of Reserve's discharge into the air to those circumstances known to result in asbestos-related disease. This inquiry may be divided into two stages: first, circumstances relating to the nature of the discharge and, second, circumstances relating to the level of the discharge (and resulting level of exposure).

1. The Nature of the Discharge.

The comparability of the nature of Reserve's discharge to the nature of the discharge in known disease situations raises two principal questions. The first is whether the discharged fibers are identical or substantially identical to fibers known to cause disease; the second is whether the length of the fibers discharged is a relevant factor in assessing pathogenic effect. The district court found that Reserve's discharge includes known pathogenic fibers and that a lower risk to health could not be assigned to this discharge for reasons of fiber length.

On the first question the issue of the identity of the fibers the argument focuses on whether the ore mined by Reserve contains (and yields wastes during processing consistent with) amosite asbestos. The inquiry is critical because studies demonstrate that amosite, at least in occupational settings, may serve as a carcinogenic (cancer-producing) agent. A principal dispute concerns the precise composition of the mineral cummingtonite-grunerite found in Reserve's taconite ore: Reserve maintains that the cummingtonite-grunerite present in its Peter Mitchell Mine at Babbitt is not asbestiform and is not chemically consistent with amosite asbestos; plaintiffs argue that much of the cummingtonite-grunerite mined by Reserve is substantially identical to amosite asbestos.

As a general scientific proposition, it is clear that cummingtonite-grunerite embraces a range of chemistries, including the chemistry of amosite asbestos. The mineral also embraces a range of morphologies, from asbestiform, needle-like fibers to block-shaped, crystal aggregates. The crucial factual determination is, thus, whether the particular cummingtonite-grunerite mined by Reserve contains asbestiform fibers consistent with the properties of amosite asbestos.

The trial court heard extensive evidence as to the chemistry, crystallography and morphology of the cummingtonite-grunerite present in the mined ore. This evidence demonstrated that, at the level of the individual fiber, a portion of Reserve's cummingtonite-grunerite cannot be meaningfully distinguished from amosite asbestos. Reserve attempted to rebut this testimony by showing that the gross morphology of the two minerals differed and that characteristics of the two minerals varied when considered in crystal aggregations. Since, according to the opinions of some experts, the individual fiber probably serves as a carcinogenic agent, the district court viewed the variations in mineralogy as irrelevant and determined that Reserve discharges fibers substantially identical and in some instances identical to fibers of amosite asbestos.

The second question, that of fiber length, reflects a current dispute among scientists as to whether "short" fibers (i.e., fibers less than five microns in length) have any pathogenic effect. Most of the fibers detected in Reserve's discharges may be termed "short."28 The evidence adduced at trial included conflicting scientific studies and diverse opinions on this question. Several Reserve witnesses testified concerning animal studies which seem to demonstrate that short fibers are nontumorigenic.29 Plaintiffs offered opposing evidence based on contrary studies.30 Dr. Brown noted his general criticism of the studies on fiber size, stating that the researchers typically did not use electron microscopy to properly "size" the fibers, and thus it cannot be said that the animals are in fact being exposed to only short or only long fibers. (A.23:338-40.)

Presented with this conflicting and uncertain evidence from animal experimentation, and the fact that there are no human epidemiological studies bearing on the issue, the district court concluded that short fibers could not be assigned a lower relative risk than long fibers.31 This conclusion comports with the uncertain state of scientific knowledge. Furthermore, Dr. Brown and the National Academy of Sciences reached the same conclusion.32

2. The Level of Exposure.

The second major step in the inquiry of the health aspects of Reserve's air emissions is an assessment of the amount of the discharge and the resulting level of exposure. Two principal issues are raised: first, what in fact is the level of exposure; second, does that level present a cognizable risk to health? The district court found the level "significant" and comparable to the levels associated with disease in nonoccupational contexts. 380 F.Supp. at 48.

The first issue was addressed at length in our stay opinion. We noted there the great difficulties in attempted fiber counts and the uncertainties in measurement which necessarily resulted. 498 F.2d at 1079-1080. Commenting on these difficulties, Dr. Brown stated that the fiber counts of the air and water samples could establish only the presence of fibers and not any particular amount, i. e., such a count establishes only a qualitative, and not a quantitative, proposition. The district court recognized these difficulties in counting fibers and observed that "(t)he most that can be gained from the Court (ordered) air study is the very roughest approximation of fiber levels." 380 F.Supp. at 49.

A court-appointed witness, Dr. William F. Taylor,33 made the most sophisticated attempt to use the fiber counts in a quantitative manner. By taking the average fiber count of five testing sites in Silver Bay, Dr. Taylor concluded that the burden of fibers in the air of Silver Bay exceeded that present in St. Paul, Minnesota, (used as a control) by a margin which could not be attributed to chance.34 (A.23:117.)

The experts indicated that the counting of fibers represents a scientifically perilous undertaking, and that any particular count can only suggest the actual fiber concentration which may be present. Nevertheless, Dr. Taylor's computation indicating some excess of asbestiform fibers in the air of Silver Bay over that of the control city of St. Paul appears statistically significant and cannot be disregarded. Thus, as we indicated in the stay opinion and as the dist