ACWA supports the Environmental Protection Agency’s (EPA) decision to publish a direct to rule clarification that the urbanized area designation criteria for small phase II municipal separate storm sewer systems (MS4s) will remain at a population of 50,000 people. This regulatory clarification became necessary when the Census Bureau’s decided to modify how urban population data was analyzed. This change will allow NPDES permitting authorities to use 2020 and future Census data in a manner that is consistent with existing and longstanding regulatory practice. ACWA does not view this change as intending to preclude a state’s authority to regulate municipalities smaller than this threshold.
Final Stormwater Letter Small Ms4 Urbanized Areas 1-18-2023