United States Environmental Protection Agency
          Office of Air Quality Planning and Standards
          Research Triangle Park, North Carolina 27711





DATE:     January 13, l982

SUBJECT:  Maryland Modeling Guideline                            
                                        
                                                    
FROM:     G. T. Helms, Chief /s/
          Control Programs Operation Branch (MD-15)             


TO:       Ray Cunningham, Chief
          Air Programs Branch, Region III

     This memo is in response to your letter of December 2, l981
requesting a review of the Maryland modeling guideline.  My
comments are as follows.

     A detailed response from the modeling clearinghouse supporting
the technical aspects of the Maryland modeling guideline is
attached for your information.

     Approval of the Maryland guideline would allow EPA to
generally assume approved modeling was performed by the State when
reviewing State Implementation Plan (SIP) revisions without a
significant workload.  EPA could then use the Maryland guideline
as a basis for future auditing of Maryland's SIP activities.  
     Therefore, EPA can approve the guideline as it will help to
alleviate a significant work load when reviewing SIP submittals
containing dispersion modeling.  However, the Agency cannot
currently approve a generic SIP regulation which exempts all
revisions from submittal to EPA as formal SIP revisions where
conformance with the guideline modeling procedures is the only
test.

Attachment






          Office of Air Quality Planning and Standards
          Research Triangle Park, North Carolina 27711


Jan. 7, l982

Maryland Modeling Guideline

Joseph A. Tikvart, Chief /s/
Source Receptor Analysis Branch (MD-14)

G. T. Helms, Chief
Control Programs Operation Branch (MD-15)

THRU:  Richard G. Rhoads, Director    Jan. 7, 1982
       Monitoring and Data Analysis Division

     We have reviewed the subject guideline and find it to be, for
the most part, identical to the guidance we have provided to the
Regional Offices in the "Guideline on Air Quality Models" and in
the "Regional Workshops on Air Quality Modeling:  A Summary
Report."  Minor deviations are noted in the attachment; we do not
have a significant objection to these deviations.

     Approval of the Maryland guideline would constitute the first
instance where EPA has explicitly given a State the responsibility
and authority to select and apply models to all sources in its
jurisdiction, with no review by EPA other than an auditing role. 
In some instances, e.g., Connecticut or the proposed bubble policy,
States have the authority to apply models, but such applications
are performed without discretionary judgment, i.e., the specific
models and the manner in which they are applied are regulated.  In
the Maryland guideline, the State can operate in much the same
manner as the Regional Offices currently operate.  They can choose
models and data bases within the framework of the guideline, or
select alternative models, data bases, etc. as they deem
appropriate.  

     As a result, approval of this guideline would establish
several principles.  It would mean that EPA would accept less
responsibility for ensuring consistency among States than for
ensuring consistency among its Regional Offices under Section 301
of the Clean Air Act.  It would mean that interstate impact
disputes could be complicated by the likelihood that each State
could predict different impacts, even though both States followed
EPA approved modeling guidelines.  It would mean that the State
(instead of EPA) would bear the primary burden for technical
defense of its case-by-case modeling decisions.  And, it would mean
that EPA would no longer be involved in individual State impact
assessment, but would only review the overall State program during
routine audits.  

     In general we don't have a major objection to delegation of
modeling responsibility to Maryland because this guideline is so
similar to ours.  We could have a problem though if another State
wished to employ a guideline that was significantly different from
our own.  We are faced now with the question of how our mandates
under Section 301 and Section 165 (e)(b) of the Clean Air Act are
met with the existence of State guidelines.  Although I believe
that approval of this guideline will surface several policy and
legal issues, approval, on balance, would represent a positive step
toward transferring additional responsibility and authority to the
State. 

Attachment

cc:  D. Tyler
     C. Hopper 


     Specific Deviations of the Maryland Modeling Guideline From
EPA Guidance


     1.  The Maryland guideline provides a list of "preferred"
models identical to our list of "recommended" models.  The
difference in semantics may suggest that Maryland is less bound to
use the models.

     2.  The Maryland guideline does not discuss validation and
calibration of models as does Section 6.0 of the EPA Guideline on
Air Quality Models.

     3.  Issues I-V as identified in the November 30, l981, Region
III memo from A. Cimorelli to I. Milner.