Dear Rosalina,

I have one addendum to my comments on the VISTAS BART modeling protocol;
this is a comment that addresses the assessment of alternative emissions
scenarios to the BART determination with CALPUFF, so it does not affect
near-term modeling for BART exemptions.  I'm sorry for the late
submittal of this comment.

Basically, the comment #19 that I provided last week on the draft VISTAS
BART modeling protocol discussed CALPUFF modeling to address
interpollutant and/or intra-plant alternative emissions scenarios, in
which enhancing controls of one pollutant can accommodate lesser
controls on another pollutant at a given facility, either on a single
unit or among multiple BART units.  In the more general case of
emissions trading for facilities at different locations, it is likely
that the changes to visibility impacts at Class I areas from the
shifting controls to a different facility will not necessarily be
coincident in time and space with the predicted changes in visibility
from the original BART facility.  Therefore, the test for whether an
alternative approach is at least as good as the BART approach must be
done unpaired in time and space.  For this test, I recommend that the
total number of receptor-days with impacts over 0.5 and 1.0 deciviews be
tallied for the BART scenario and for each alternative emissions
scenario in a given Class I area.  The alternative that results in the
lowest total number of such receptor-days over the entire modeling
period should be determined to be the best choice.

Regards,

Bob Paine, CCM, QEP
ENSR Corporation
2 Technology Park Drive
Westford, MA  01886
phone:  978-589-3164
fax:      978-589-3374
e-mail: bpaine@ensr.com