Population Data Considerations for RMP Offsite Consequence Analyses | Blog No. 120

Population data continues to come up during EPA Risk Management Program inspections and technical discussions, specifically the use of 2010 Decennial Census population data in off-site consequence analyses.

The issue is simple: that data is over a decade old.

Why this matters

Population counts directly drive the number of people potentially impacted in both worst-case and alternative release scenarios. If that input is outdated, the output is also outdated, regardless of how solid the release modeling is.

Since 2010, a lot has changed. Areas have grown, declined, been redeveloped, or completely shifted in how they’re occupied. In some cases, what used to be open land is now residential or commercial. In others, the opposite is true. Using population data from 2010 doesn’t always reflect what is actually around the facility today.

Context

For a long time, using 2010 Census data was standard. Tools like MARPLOT had the information built in, and that’s what people used. That made sense at the time.

The question now is whether that same data still holds up, given how much time has passed.

Inspection focus

In more recent inspections, population data is getting more attention. Inspectors are asking where the numbers came from, what dataset was used, and whether it reflects current conditions around the site. It’s not just a checkbox anymore; it’s something they’re digging into.

That makes the basis of your population numbers a lot more visible than it used to be.

FEMA RAPT and population data

In May 2025, FEMA updated the datasets used in its Resilience Analysis and Planning Tool. This is a mapping platform used by federal, state, and local agencies for hazard and emergency planning.

The tool is built to show how hazards interact with real populations, infrastructure, and community features, the same things that matter during an actual incident.

As part of that update, it uses U.S. Census Bureau American Community Survey five-year estimates from 2019 through 2023 for population data. That dataset is updated on a rolling basis and is intended to better represent current population conditions. FEMA documentation clearly identifies the data source and how it is maintained.

Regulatory reality

The Environmental Protection Agency does not approve specific datasets or tools for Risk Management Program analyses. Facilities are responsible for their assumptions.

That said, population data that reflects current conditions is a lot easier to explain than data tied to 2010, especially when questions start coming up during an inspection.

Summary

2010 Census data was the standard for a long time, but it is now dated. Population is one of the most visible inputs in an off-site consequence analysis, and it is getting more attention during inspections.

Relying on more current population data, like American Community Survey estimates, helps ensure the analysis reflects what is actually around the facility today and holds up better when it gets reviewed.

Previous Blog: Shall Vs. Should | Blog No. 119

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