In the
 United States Court of Appeals
               For the Seventh Circuit
                          ____________

No. 02-8018
THERESA MEJDRECH, et al.,
                                                  Plaintiffs-Appellees,
                                  v.

MET-COIL SYSTEMS CORP.,
                                                Defendant-Appellant.
                          ____________
             Appeal from the United States District Court
        for the Northern District of Illinois, Eastern Division.
              No. 01 C 6107—William J. Hibbler, Judge.
                          ____________
  SUBMITTED OCTOBER 10, 2002—DECIDED FEBRUARY 11, 2003
                          ____________


  Before POSNER, COFFEY, and DIANE P. WOOD, Circuit
Judges.
  POSNER, Circuit Judge. The defendant seeks permission
to appeal under Fed. R. Civ. P. 23(f) from the grant of
class certification. We grant permission in order to deter-
mine the appropriateness of class action treatment in
pollution cases, a matter on which the case law is sparse
and divided, compare Sterling v. Velsicol Chemical Corp., 

, 1197 (6th Cir. 1988); Cook v. Rockwell Int’l Corp.,

, 480-82 (D. Colo. 1998), and Yslava v. Hughes
Aircraft Co., 

, 713 (D. Ariz. 1993), with
Church v. General Electric Co., 

, 181-82
2                                              No. 02-8018

(D. Mass. 2001), and Thomas v. FAG Bearings Corp., Inc., 

, 1403-05 (W.D. Mo. 1994), although the only
appellate case (Sterling) permits such treatment and the
district court cases that reject it (Church and Thomas) do
so without extended discussion. This court has not spoken
to the issue.
   The defendant, Met-Coil, owns a factory in Lisle, a town
outside Chicago. The homes of the approximately 1,000
members of the plaintiff class are within a mile or two of
the factory. The complaint alleges that a storage tank on
Met-Coil’s property has leaked a noxious solvent, TCE,
that has seeped into the soil and groundwater beneath
the class members’ homes, impairing the value of their
property. The suit seeks injunctive and monetary relief
under federal and Illinois environmental law. Mindful
that not only the amount but the fact of damage might
vary from class member to class member, the district
judge limited class treatment to what he described as “the
core questions, i.e., whether or not and to what extent
[Met-Coil] caused contamination of the area in question.”
Whether a particular class member suffered any legally
compensable harm and if so in what dollar amount are
questions that the judge reserved for individual hearings
if and when Met-Coil is determined to have contaminated
the soil and water under the class members’ homes in
violation of federal or state law.
  We think the district judge’s determination was reason-
able, indeed right. Rather than parse the subdivisions of
Rule 23 as the district judge (appropriately) did, we mere-
ly point out that class action treatment is appropriate and
is permitted by Rule 23 when the judicial economy from
consolidation of separate claims outweighs any concern
with possible inaccuracies from their being lumped to-
gether in a single proceeding for decision by a single judge
No. 02-8018                                                3

or jury. Often, and as it seems to us here, these competing
considerations can be reconciled in a “mass tort” case by
carving at the joints of the parties’ dispute. If there are
genuinely common issues, issues identical across all the
claimants, issues moreover the accuracy of the resolution
of which is unlikely to be enhanced by repeated proceed-
ings, then it makes good sense, especially when the class
is large, to resolve those issues in one fell swoop while
leaving the remaining, claimant-specific issues to indi-
vidual follow-on proceedings. Hardy v. City Optical Inc.,

, 771 (7th Cir. 1994); In re Hanford Nuclear Res-
ervation Litigation, 

, 1133-35 (9th Cir. 2002);
Sterling v. Velsicol Chemical 

, 855 F.2d at 1200;
Weiss v. York Hospital, 

, 809 (3d Cir. 1984);
3 Herbert B. Newberg & Albert Conte, Newberg on Class
Actions § 17.10 (3d ed. 1992). The questions whether Met-
Coil leaked TCE in violation of law and whether the TCE
reached the soil and groundwater beneath the homes of
the class members are common to all the class members.
The first question is particularly straightforward, but the
second only slightly less so. The class members’ homes
occupy a contiguous area the boundaries of which are
known precisely. The question is whether this area or
some part of it overlaps the area of contamination. Sup-
posing all or part of it does, the next question is the par-
ticular harm suffered by particular class members whose
homes are in the area of contamination. The answer to
this question would depend on such things as whether
the class member gets his water from Lake Michigan
or from a well—in the former case his water supply, at
least, is unlikely to have been contaminated. This has
to be decided class member by class member rather than
in a consolidated proceeding.
  When enormous consequences turn on the correct res-
olution of a complex factual question, the risk of error in
4                                                  No. 02-8018

having it decided once and for all by one trier of fact
rather than letting a consensus emerge from several trials
may be undue. In re Bridgestone/Firestone, Inc., Tires Prod-
ucts Liability Litigation, 

, 1020 (7th Cir. 2002);
In re Rhone-Poulenc Rorer, Inc., 

, 1298-99 (7th
Cir. 1995). This is not such a case. First, the two questions
that the judge has set for class treatment—whether there
was unlawful contamination and what the geographical
scope of the contamination was—are not especially com-
plex. Second, even if these questions are answered against
Met-Coil, the consequences for it will not be catastrophic.
The individual class members will still have to prove the
fact and extent of their individual injuries. The need for
such proof will act as a backstop to the class-wide deter-
minations. If the judge erroneously finds that the class
members’ homes were in the area of contamination, none
of the class members will be able to prove any damages
and as a result the cost of this lawsuit to Met-Coil, though
not trivial, will be limited to the cost of defending the suit.
  This is also not a case in which, because class members
are scattered around the country and proceeding under
the laws of different states, determination of class-wide
issues would require the judge to create a composite legal
standard that is the positive law of no jurisdiction. In re
Bridgestone/Firestone, Inc., Tire Products Liability 

, 288 F.3d at 1020; In re Rhone-Poulenc Rorer, 

,
51 F.3d at 1300. All the class members are residents of
the same state and are proceeding under the same fed-
eral and state laws.
  We can see, in short, no objection to the certification
other than one based on a general distaste for the class-
action device.
                                                    AFFIRMED.
No. 02-8018                                             5

A true Copy:
       Teste:

                       _____________________________
                       Clerk of the United States Court of
                         Appeals for the Seventh Circuit




                USCA-02-C-0072—2-11-03