### Appendix 7 Dispersion Model Receptor Revisions and Additions

### Dispersion Model Receptor Revisions and Ad ditions for the Seven Chemical Sector Source Categories 1



### To estimate ambient concentrations for evaluating long-term exposures, the HEM-3 model uses the geographic centroids of census bl ocks (currently utiliz ing the 2010 Census) as dispersion model receptors. The census block ce ntroids are generally go od surrogates for where people live within a census bloc k. A census block generally encompasses about 40 people or 10- 15 households. However, in cases where a block ce ntroid is located on in dustrial property, or where a census block is large and the centroid le ss likely to be representative of the block’s residential locations, the block centroid may not be an appropriate surrogate.

Census block centroids that are on facility property can sometimes be identified by their proximity to emission sources. In cases where a census block centroid was within 300 meters of any emission source, we viewed aerial images of the facility to dete rmine whether the block centroid was likely located on facil ity property. The selection of th e 300-meter distance reflects a compromise between too few and too many blocks identified as being potentially on facility property. Distances smaller than 300 meters would identify only block centroids near the
emission sources and could exclude some block cen troids that are still within facility boundaries, particularly for large facilities. Distances si gnificantly larger than 300 meters would identify many block centroids that are outside facility bounda ries, particularly for small facilities. Where we confirmed a block centroid on facility prope rty, we moved the block centroid to a location that best represents the residential locations in the block.

In addition, census block centroids for blocks with large areas may not be representative
of residential locations. Risk estimates based on such centroids can be understated if there are residences nearer to a facility than the centroid, and overstated if the residences are farther from the facility than the centroid. To avoid understating the maximu m individual risk associated with a facility, in some cases we relocated bl ock centroids, or added di spersion model receptors
other than the block centroid. We examined aerial images of all large cens us blocks within one kilometer of any emission source. Experience fro m previous risks characterizations indicates that in most cases the MIR is ge nerally located within 1 km of the facility boundary. If the block centroid did not represent the residential locations, we relocated it to better represent them. If
residential locations could not be represented by a single receptor (that is, the residences were spread out over the block), we added additional r eceptors for residences nearer to the facility
than the centroid.

For these source categories, the table below contains each census block for which we changed the centroid location because it was on facility property or was otherwise not representative of the residential locations in the block. The table also cont ains blocks that were

1 Pesticide Active Ingredient Manufacturing, Polyether Polyols Production, Polymers and Resins IV ‐‐ Styrene Acrylonitrile, Polymers and Resins IV ‐‐ Polystyrene, Polymers and Resins IV ‐‐ Polyethylene Terephthalate, Polymers
and Resins IV ‐‐ Methyl Methacrylate

‐ Butadiene Styrene, and Polymers and Resins IV ‐‐ Acrylic Butadiene Styrene.

### removed because there are no apparent residences in the block and, consequently, no locations of potential human exposure. Finally, the table also contains the locations of additional receptors that were included to represent residential locations nearer to the facility than the block centroid.

Revised Census Block Centroid Locations and Additional Receptors for the Seven Chemical Sector Source Categories

Source Category Block ID NEI ID New
Latitude New Longitude Comment

PAI 010970057003073 30.934591

‐ 88.004772 Centroid doesn't represent population

PAI 220479532003021 30.232813

‐ 91.106034 On plant property

PAI 220479532003028 Remove ‐ no apparent population

PAI 260639512004004 43.850451

‐ 82.652354 On plant property

PAI 291279601002004 39.826082

‐ 91.411017 Centroid doesn't represent population

PAI 480396645012046 28.972839

‐ 95.398462 Centroid doesn't represent population

PAI 540390114021035 38.24671

‐ 81.543117 Centroid doesn't represent population

PP 220050303001069 30.161006

‐ 90.989435 Centroid doesn't represent population

PP 220890627001013 Remove ‐ no apparent population

PP 220890627001028 29.988181

‐ 90.424947 Centroid doesn't represent population

PP 220890627001059 29.987055

‐ 90.421922 Centroid doesn't represent population

PP 261635801001003 42.230185

‐ 83.148653 On plant property

PP 420350302004066 41.112823

‐ 77.469265 Centroid doesn't represent population

PP 450830229003131 35.027623

‐ 82.073821 On plant property

PP 480570005001030 28.509267

‐ 96.736011 Centroid doesn't represent population

PP 481830105004003 32.40865

‐ 94.688783 Centroid doesn't represent population

PP 482012526003180 29.828717

‐ 95.087191 Centroid doesn't represent population

PP 482030206042068 32.4262

‐ 94.646719 Centroid doesn't represent population

PR4

‐ ABS 090117012002027 41.433666

‐ 72.086528 Centroid doesn't represent population

PR4

‐ MBS 211110127011012 38.225737

‐ 85.825854 On plant property

PR4

‐ PE T 011030051012033 34.62329

‐ 87.060798 Centroid doesn't represent population

PR4

‐ PE T 370370207022034 35.624683

‐ 79.050146 Centroid doesn't represent population

PR4

‐ PE T 371590519011005 35.713365

‐ 80.620958 On plant propertySource Category Block ID NEI ID New
Latitude New Longitude Comment

PR4

‐ PE T 450179501001002 33.854628

‐ 81.003794 Centroid doesn't represent population

PR4

‐ PE T 510411004031004 37.359812

‐ 77.31268 Centroid doesn't represent population

PR4

‐ PS 220479532003048 30.218114

‐ 91.083684 Centroid doesn't represent population

PR4

‐ PS 360010143024020 42.586073

‐ 73.854949 Centroid doesn't represent population

PR4

‐ PS 391670203001019 39.383083

‐ 81.505112 Centroid doesn't represent population

PAI 22047NEI5992 30.234536

‐ 91.11074 Additional receptor

PP 22089NEILA13809 29.989074

‐ 90.433287 Additional receptor

PP 42035NEIPA13

‐ 5603 41.114421

‐ 77.472729 Additional receptor

PP 48201NEI11319 29.809934

‐ 95.109341 Additional receptor

PP 48201NEI11319 29.810593

‐ 95.103182 Additional receptor

PP 48291NEI8432 30.000748

‐ 94.958395 Additional receptor

PP 48291NEI8432 30.006498

‐ 94.953137 Additional receptor

PP 48291NEI8432 29.997325

‐ 94.95161 Additional receptor

PR4

‐ ABS 09011NEI43289 41.440671

‐ 72.079033 Additional receptor

PR4

‐ ABS 09011NEI43289 41.437822

‐ 72.079675 Additional receptor

PR4

‐ ABS 17099NEI51461 41.323494

‐ 88.766613 Additional receptor

PR4

‐ ABS 39061NEI43304 39.126067

‐ 84.724342 Additional receptor

PR4

‐ MBS 21111NEI32966 38.21207

‐ 85.838867 Additional receptor

PR4

‐ MBS 21111NEI32966 38.2068

‐ 85.854378 Additional receptor

PR4

‐ PE T 37037NEI44658 35.619895

‐ 79.031026 Additional receptor

PR4

‐ PE T 37037NEI44658 35.620662

‐ 79.051028 Additional receptor

PR4

‐ PE T 45063NEI41393 33.851709

‐ 81.010661 Additional receptor

PR4

‐ PS 09011NEI43289 41.440671

‐ 72.079033 Additional receptor

PR4

‐ PS 09011NEI43289 41.437822

‐ 72.079675 Additional receptor

PR4

‐ PS 21059NEI32867 37.789791

‐ 87.157104 Additional receptor

PR4

‐ PS 21059NEI32867 37.799681

‐ 87.152048 Additional receptor

PR4

‐ PS 39167NEI40518 39.374087

‐ 81.531627 Additional receptor