EJ Screen overlays minority and low-income demographics on a map of 217,000 block groups, each having 500 to 5,000 people. (An alternative method under consideration includes additional demographic data including the percentage of people in a block group with less than a high school education, the percentage who speak English, and the number under the age of 5 and over the age of 64.)
EPA then puts that information over a map of environmental factors. Among the 12 factors EPA has selected for its first version of EJ Screen is air pollution -- including ozone levels and soot from diesel exhaust and smokestacks. The agency also includes data on a community's proximity to environmental hazards including Superfund dumps, water discharge facilities, high traffic areas and buildings built before 1960 that have a high risk for lead paint.
The result is a graphic illustration showing each block group's ranking nationwide for each environmental factor. And the maps can also be used to show how block groups compare by state or by region when it comes to each factor.
But the maps are also limited, EPA. They don't, for example, combine all the environmental factors to show cumulative impacts. For instance, how does one scientifically weigh a person's proximity to a lead paint structure against exposure to particulate matter in the air? (E&E Publishing, 7/27/2012)