Download Chapter 3 - Lakes Environmental

Human Health Risk Assessment Protocol
Chapter 3: Air Dispersion and Deposition Modeling
September 2005
Step 4 Repeat steps 2 and 3 for each building and each stack, identifying all buildings to be
included in the BPIP. If the number of buildings exceeds the BPIP limit of eight
buildings, consider combining buildings, modifying BPIP code for more buildings, or
using third-party commercial software which implements BPIP. If two buildings are
closer than the height of the taller building, the two buildings may be combined. For
example, two buildings are 40 feet apart at their closest points. One building is 25 feet
high, and the other building is 50 feet high. The buildings could be combined into one
building for input to BPIP. For input to BPIP, the corners of the combined building are
the outer corners of the two buildings. For unusually shaped buildings with more than
the eight corners allowed by BPIP, approximate the building by using the eight corners
that best represent the extreme corners of the building. The BPIP User’s Guide contains
additional description and illustrations on combining buildings, and BPIP model
limitations (U.S. EPA 1995c).
Step 5 Mark off the facility plot plan with UTM grid lines. Extract the UTM coordinates of
each building corner and each stack center to be included in BPIP input file. Although
BPIP allows the use of “plant coordinates,” we recommend that all inputs to the air
model be prepared using UTM coordinates (meters) for consistency. UTM coordinates
are rectilinear, oriented to true north, and needed in metric units for ISCST3 modeling.
Almost all air modeling will need to use USGS topographic data (digital and maps) for
receptor elevations, terrain grid files, locating plant property, and identifying
surrounding site features. Therefore, using an absolute coordinate system will enable
you to check inputs at each step of the analysis. Also, the meteorological data are
oriented to true north. Significant errors will result from ISCST3 if incorrect stack or
building locations are used, plant north is incorrectly rotated to true north, or incorrect
base elevations are used. With computer run times requiring many hours (up to 40 hours
for one deposition run with depletion), verifying locations at each step while preparing
model inputs will prevent the need to remodel.
We recommend observing several precautions and guidelines while preparing input files for BPIP:
•
Graphically confirming the correct locations before BPIP is run. One method is to plot
the buildings and stack locations using graphics software. Several commercial programs
incorporating BPIP provide graphic displays of BPIP inputs.
•
In addition to using UTM coordinates for stack locations and building corners, also use
meters as the units for height.
•
Carefully include the stack base elevation and building base elevations according to
BPIP User’s Guide instructions.
•
Note that the BPIP User’s Guide (revised February 8, 1995) has an error on page 3-5,
Table 3-1, under the “TIER(i,j)” description, which incorrectly identifies tier height as
base elevation.
•
BPIP mixes the use of “real” and “integer” values in the input file. To prevent possible
errors in the input file, note that integers are used where a count is requested (for
example, the number of buildings, number of tiers, number of corners, or number of
stacks).
U.S. EPA Region 6
Multimedia Planning and Permitting Division
Center for Combustion Science and Engineering
U.S. EPA
Office of Solid Waste
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