\ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
1 WASHINGTON, D.C. 20460
Mav 11 1QQ6 OFFICE CF THE ADMINISTRATOR
Wldyoi, i^3U SCiENCc ADVISORY BOARD
^-CASAC-LTR-96-007 ^
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M. Street S.W.
Washington, DC 20460
RE: CASAC Comments on Air Quality Modeling for the Section 812
Retrospective Study
Dear Ms. Browner:
At their December 22, 1992 meeting, the Science Advisory Board's Advisory
Council on Clean Air Compliance Analysis (ACCACA, formally known as the Clean Air
Act Compliance Analysis Council, CAACAC) decided to refer review of the air quality
modeling part of the Retrospective Study of the impacts of the Clean Air Act to the
Clean Air Scientific Advisory Committee (CASAC). The request was made to CASAC in
a March 22, 1993 memo from Mr. Jim DeMocker of the Office of Policy Analysis and
Review (OPAR) in EPA's Office of Air and Radiation. Subsequently, a Panel of CASAC
members (the Air Quality Models Subcommittee, AQMS) and SAB consultants was
constituted to review the air quality modeling.
Three public conference calls on October 1, 21, and December 2, 1993 served to
brief the panel members on the charge and air quality methodology and for Panel
members to comment on the methodology. The panel members provided EPA with
numerous comments during the conference calls and subsequently in writing.
These comments were summarized for you in a June 30, 1994 letter report
(EPA-SAB-CASAC-LTR-94-009). A major concern at the time was that the
uncertainties in the air quality estimates in the "no-Clean Air Act" scenarios would be
intolerable.
The six member panel conducted a final public conference call on April 26, 1996
to review the completed air quality modeling. During the call and subsequently in
writing, the panel members provided comments to the Agency. All the panel members
expressed their satisfaction that the Agency followed the Panel's recommendations and
that the final product is sound. Our concern over the uncertainties has diminished
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U.S. Environmental Protection Agency v~cr
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Flow
Chicago, IL 60604-3590
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considerably, but nevertheless, it still exists. We have provided your staff with a number
of recommendations to explicitly articulate the uncertainties, to not overstate the
precision of the estimates, and to more carefully present the implications of the
uncertainties for the overall study results.
With the incorporation of these relatively minor changes, the Panel feels that air
quality estimates are reasonable and are appropriate to use to estimate the benefits of
the Clean Air Act. Please let me know if we can assist you any further.
Sincerely,
Dr. Ge&rge T. Wolff, Chay
Clean Air Scientific Advisory Committee
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