2018-03-26-minutes-public-works-study-session

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Fact Sheet 2.1 — Who's Covered? Designation and Waivers of Regulated Small MS4s Page 2 What Is a Small, Medium, or Large MS4? ❑ Urbanized Areas ❑ EPA's NPDES (National Pollutant Discharge Elimination System) stormwater permitting program labels MS4s as either "small," "medium," or "large" for the purposes of regulation. ❑ A small MS4 is any MS4 that is not already covered by the Phase I stormwater program. Small MS4s include Federally -owned systems, such as military bases. ❑ The Phase I stormwater program covers medium and large MS4s. Phase I MS4s were automatically designated nationwide as medium MS4s if they were located in an incorporated place or county with a population between 100,000 - 249,999 or as large MS4s if located in an incorporated place or county with a population of 250,000 or greater. Many MS4s in areas below 100,000 in population, however, have been individually brought into the Phase I program by NPDES permitting authorities. Such already regulated MS4s do not have to develop a Phase II program. Are All Small MS4s Covered by the Phase II Final Rule? No. The universe of small MS4s is quite large since it includes every MS4 except for the approximately 900 medium and large MS4s already regulated under the Phase I storrnwater program. Only a select sub -set of small MS4s, referred to as regulated small MS4s, is covered by the Phase II Final Rule, either through automatic nationwide designation or designation on a case-by-case basis by the NPDES permitting authority. How Is A Small MS4 Designated as a Regulated Small MS4? An urbanized area (UA) is a densely settled core of census tracts and/or census blocks that have population of at least 50,000, along with adjacent territory containing non-residential urban land uses as well as territory with low population density included to link outlying densely settled territory with the densely settled core. It is a calculation used by the Bureau of the Census to determine the geographic boundaries of the most heavily developed and dense urban areas. More information about urbanized areas maps is available at: http://www.epa.gov/npdes/storrnwater/urbanmans Additionally, information about urbanized areas is available directly from the U.S. Bureau of the Census at: http://www.census.gov/geo/www/ua/20 I Ourbanruralc lass. html O Potential Designation by the NPDES Permitting Authority — Required Evaluation An operator of small MS4 located outside of a UA have been designated as a regulated small MS4 if the NPDES permitting authority determined that its discharges cause, or have the potential to cause, an adverse impact on water quality. The Phase H Final Rule required the NPDES permitting authority to develop a set of designation criteria and apply them, at a minimum, to all small MS4s located outside of a UA serving a jurisdiction with a population of at least 10,000 and a population density of at least 1,000 people/square mile. small MS4 can be designated by the permitting authority as a regulated small MS4 in one of three ways: ❑ Designation Criteria O Automatic Nationwide Designation The Phase 11 Final Rule requires nationwide coverage of all operators of small MS4s that are located within the boundaries of a Bureau of the Census -defined "urbanized area" (UA) based on the latest decennial Census. Once a small MS4 is designated into the program based on the UA boundaries, it cannot be removed from the program on that basis that a subsequent decennial UA calculation shows that the small MS4 is no longer within the UA boundaries. However, the designated small MS4 remains eligible for a waiver if it meets the criteria. EPA recommended that the NPDES permitting authority use a balanced consideration of the following designation criteria on a watershed or other local basis: ✓ Discharge to sensitive waters; ✓ High population density; ✓ High growth or growth potential; ✓ Contiguity to a UA; ✓ Significant contributor of pollutants to waters of the United States; and ✓ Ineffective protection of water quality concerns by other programs.