Appendix 7 Dispersion Model Receptor Revisions and AdditionsDispersion Model Receptor Revi sions and Additions for the Off-Site Waste and Recovery Operations 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 th an 300 meters woul d 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 from previous risks characteri zations show that in most cases the MIR is generally 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 contains the locations of additional receptors that were incl uded to represent residential locations nearer to the facility than the block centroid.Revised Census Block Centroid Locations and A dditional Receptors for Off-Site Waste and Recovery Operations

Recommended Corr.

Facility ID Latitude Longitude Note NEIKS325 37.081590 -95.587250 Add User Defined Receptor

NEIKY103236 38.437410 -85.2367 70 Add User Defined Receptor

NEIKY103236 38.43216 -85.238493

NEI32966 38.210103 -85.841025 Add User Defined Receptor

NEIMIN0731 42.35858 -82.9621 59 Add User Defined Receptor

NEIOHT$5677 39.984220 -82.4667 50 Add User Defined Receptor

NEI40462 41.322633 -82.037665 Add User Defined Receptor

NEI40462 41.322409 -82.039941 Add User Defined Receptor

NEI42539 43.078957 -89.194301 Add User Defined Receptor

NEI18116 44.754340 -91.452468 Add User Defined Receptor

NEI18116 44.757789 -91.453563 Add User Defined Receptor