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Census Bureau Proposes New Criteria for Urbanized Areas; Impact to MS4s Unclear

Apr 14, 2021

The U.S. Census Bureau has recently proposed changing the criteria for defining urban areas – a common step after each decennial census. The proposed changes could potentially impact the Clean Water Act’s municipal separate storm sewer system (MS4) program and how EPA determines communities that must be permitted. Currently, small MS4 Phase II communities are identified by the Census Bureau’s definition of urbanized areas.

Specifically, the Census Bureau is proposing to adopt a housing unity density threshold of 385 housing units per square mile as the primary criterion for determining whether a census block qualifies for inclusion in an urban area. This proposed change would replace the use of population density and could provide a “more direct measure” and allow for a more accurate account for urban landscape. This would also allow the Census Bureau to account for smaller than average person households or seasonal populations.

The Census Bureau is also proposing to qualify urban areas as those with at least 4,000 housing units or has a population of at least 10,000 people – a move that could expand the footprint and envelope new communities as well as enlarge the requirements of existing small MS4s. Currently, the Census Bureau defines – and EPA uses – an urbanized area of 50,000 or more people.

While the Census Bureau’s has its own goals with this proposal which are likely detached from the potential impact to communities required to comply with Clean Water Act permitting schemes, it remains unclear on how EPA may respond to the proposed changes to urban area. NACWA has shared its concerns with EPA and will keep members apprised of any developments.

Please contact Emily Remmel, NACWA’s Director of Regulatory Affairs.

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