Final Phase II Rule Clarification Related to Census Bureau Urban Area Designation Criteria

Final Rule

On June 7, 2023, EPA signed its final rule, NPDES Small MS4 Urbanized Area Clarification, to clarify the designation criteria for small MS4s following the Census Bureau’s recent urban area mapping revisions. EPA provided notice of the final rule’s promulgation in the Federal Register on June 12, 2023.

• Final Rule Federal Register Notice (pdf) (239.9 KB)

Background

The final rule clarifications are necessary due to the Census Bureau’s March 24, 2022 publication of final program criteria (pdf) (286.6 KB) that discontinued its practice of publishing the location of “urbanized areas” along with the 2020 Census and future censuses. The clarifications in this final rule replace the term “urbanized area” in the Phase II regulations with the phrase “urban areas with a population of at least 50,000,” which is the Census Bureau’s longstanding definition of the term urbanized areas. This change allows NPDES permitting authorities to use 2020 Census and future Census data in a manner that is consistent with existing longstanding regulatory practice.

EPA’s rule finalizes changes that were proposed on December 2, 2022 (pdf) (281.44 KB).

Rescission of Interim Guidance

In early 2022, EPA published Interim Guidance on Census Elimination of “Urbanized Area” Definition to provide interim guidance on the effect of the Census Bureau’s revised designation criteria prior to EPA revising its regulations. With the publication of the final rule, this document is no longer necessary and EPA rescinds it as of the final rule effective date on July 12, 2023. The planned rescission of the interim guidance was also announced as part of the proposed rule.

Implementation Assistance

EPA is providing technical assistance to permitting authorities as they move forward with the process of identifying newly designated small MS4s. For further information, see Urban Area Maps for NPDES MS4 Phase II Stormwater Permits.