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This action updates the Stormwater Phase II Rule, which automatically covers, on a nationwide basis, all small Municipal Separate Storm Sewer Systems (MS4s) located in urbanized areas” as determined by the latest U.S. Decennial Census. In March 2022, the Census Bureau finalized its latest regulatory revisions based on the 2020 Decennial Census and no longer uses the term urbanized areas.” This action updates the regulatory definition of small MS4 by replacing the retired term urbanized area” with language consistent with the long-standing definition of urbanized area.” This eliminates potential uncertainty that would have been caused by continuing to use a term that cannot be found in the latest Decennial Census. This action clarifies that permittees will continue to be automatically designated, based on the most recent census data, as Phase II MS4s in the same manner that they have been since the promulgation of the Phase II stormwater regulations. This action establishes a clear, lasting, and nationally consistent way to ensure that discharges from MS4s are adequately controlled as needed to protect water quality,” consistent with CWA 402(p)(6).