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Risk-Screening Environmental Indicators (RSEI) Model

RSEI Grid and Locational Information

This page describes how EPA's Risk-Screening Environmental Indicators (RSEI) model locates facilities, people and other modeling inputs on a geographic grid composed of 810 meter by 810 meter grid cells.

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RSEI grid system

In order to calculate location-specific impacts, RSEI must determine the location of each facility and the characteristics of the environment around the facility, like meteorology and water body characteristics.

To make geographically based calculations faster, RSEI describes the United States and its territories as a system of 810 meter by 810 meter grid cells. Each cell in the grid system, and any facility or geographic feature, can be assigned an (x,y) “address.”

RSEI uses a standard Albers Equal-Area projection to create each of the grids used in the model. The grid system is split into six individual grids which cover the continental United States, Alaska, Hawaii, and the territories. Each unique cell address is composed of (1) the grid number, and (2) the (x,y) address of the cell in that grid. Section 5.1 of the RSEI methodology document has the technical specifications for the grid, as well as the equations for translating latitude and longitude into an (x,y) address.

RSEI Geographic Microdata provides results at the grid cell level. Crosswalks to translate data from the RSEI grid cell system to U.S. census block geographies are provided so that users can combine RSEI results with other data and aggregate the results to any census geography, like block, block group, or tract.

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RSEI locational information

Because the location of a facility is key to the subsequent exposure modeling, it is important that the facility coordinates be as accurate as possible. For reporting facilities, RSEI uses coordinates from EPA’s Facility Registry System (FRS), which collects coordinates and related documentation on location from programs across EPA. For off-site facilities, RSEI maintains a master database of names, address, and locations based on EPA locational data and manual verifications from previous versions of RSEI.

The facility latitude/longitude coordinates are projected onto the relevant grid, and the (x,y) coordinates of the grid cell to which the facility maps are assigned. The facility is then modeled as being located at the center of its assigned cell.

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Population estimates

The model uses decennial U.S. census data for 1990, 2000 and 2010 at the block level. Census blocks are the smallest geographic area for which decennial census data are collected, with more than 11 million blocks in 2010. For some of the territories and island areas (Puerto Rico, the U.S. Virgin Islands, American Samoa, Guam, and the Northern Mariana Islands), block-level data were not always available. In these cases, data at the most detailed level available were used. Section 5.1 of the RSEI methodology document has details on the data used in each case.

The block-level data are used to create detailed age-sex population groups for each of the census blocks in the United States for 1990, 2000 and 2010, and then the block-level data are transposed onto the RSEI grid using block shapefiles and the grid geometries.

To create annual estimates for 1991 through 1999, a straight-line interpolation at the grid cell-level is performed within the model between the 1990 and 2000 datasets; annual datasets for 2001 through 2009 are created using a straight-line interpolation between the 2000 and 2010 datasets. The 1990-2000 line is extrapolated backward to create annual datasets for 1988 and 1989 and the 2000-2010 line is extrapolated forward to the current year.

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