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EJSCREEN: Environmental Justice Screening and Mapping Tool

Limitations and Caveats in Using EJSCREEN

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Appropriate Uses of EJSCREEN

EJSCREEN was developed by EPA to highlight places that may be candidates for further review, analysis or outreach to support the agency's environmental justice work. EPA is releasing EJSCREEN to the public in part to be more transparent about how the agency considers environmental justice in its work. There is no mandate or guidance expressed or implied that state governments or other entities should use the tool or its underlying data.

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Issues not Covered by EJSCREEN

Additionally, it is important to understand that EJSCREEN is not a detailed risk analysis. It is a screening tool that examines some of the relevant issues related to environmental justice, and there is uncertainty in the data included. It is important to understand both of these limitations.

The first limitation arises because a screening tool cannot capture all the relevant issues that should be considered (e.g., other environmental concerns). Any national screening tool must balance a desire for data quality and national coverage against the goal of including as many important environmental factors as feasible given resource constraints.

Many environmental concerns are not yet included in comprehensive, nationwide databases. For example, data on environmental factors such as drinking water quality and indoor air quality are not available with adequate quality, coverage and/or resolution to be included in this national screening tool. EJSCREEN cannot provide data on every environmental impact and demographic factor that may be important to any location. Therefore, its initial results should be supplemented with additional information and local knowledge whenever appropriate, for a more complete picture of a location.

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Uncertainty in Estimates for Small Areas

The second important limitation is that EJSCREEN relies on demographic and environmental estimates that involve substantial uncertainty. This is especially true when looking at a small geographic area, such as a single Census block group. A single block group is often small and has uncertain estimates. Therefore, it is typically very useful and advisable to summarize EJSCREEN data within a larger area that may cover several block groups, in what is called a "buffer" report.

The demographic estimates, such as percent low-income, come from surveys, not a full census of all households. This means the Census Bureau may estimate that a block group is 30% low-income, for example, but it might actually be 20% or 40% in some cases.

All indicators are calculated for each block group. The only exception is certain environmental indicators for air quality (PM, ozone, and NATA indicators). Those air data were obtained for each Census tract, so each block group in a tract was assigned the same environmental indicator value, as described in the Technical Documentation.

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Screening-Level Indicators

Related to the issue of uncertainty is that fact that the environmental indicators are only screening-level proxies for actual health impacts. This is particularly true for the proximity indicators. Even for indicators that directly estimate risks or hazards, as with the air toxics cancer risk indicator, estimates have substantial uncertainty because the following indicators are uncertain:

  • emissions
  • ambient levels in the air
  • exposure of individuals
  • toxicity

View technical details on Environmental Indicators in the EJSCREEN Technical Documentation.

In summary, as with any screening tool, EJSCREEN cannot address all the considerations that may be relevant to a given situation because of the factors described above. Therefore, it is generally not appropriate to rely on any screening tool as the basis for a key decision. It is often very useful to obtain information on other issues not included in EJSCREEN, updated information when available, as well as local knowledge, data and concerns.

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