Definitions related to MS4 and NR 216 Phase II Rules

Best Management Practices (BMP)
Schedules of activities, prohibitions of practices, maintenance procedures, structural controls, source area controls, treatment requirements, operating procedures, outdoor storage containment and other management practices to prevent or reduce pollutants in runoff entering waters of the state.

Illicit Discharge
Any discharge to a municipal separate storm sewer that is not composed entirely of runoff, except discharges authorized by a WPDES permit or any other discharge not requiring a WPDES permit such as water line flushing, landscape irrigation, individual residential car washing, fire fighting and similar discharges.  

Maximum Extent Practicable (MEP)
A level of implementing best management practices in order to achieve a performance standard specified in Wisconsin Administrative Code NR 151 which takes into account the best available technology, cost effectiveness and other competing issues such as human safety and welfare, endangered and threatened resources, historic properties and geographic features. MEP allows flexibility in the way to meet the performance standards and may vary based on the performance standard and site conditions.

MS4 (Municipal Separate Storm Sewer System)
MS4s include (or can include) systems owned by ctiies, villages, towns, and counties as well as state, federal and other governmental systems. An MS4 also is not always just a system of underground pipes - it can include roads with drainage systems, gutters, and ditches. The complete definition of MS4 is contained in s. NR 216.002(17).

Notice of Intent (NOI)  
An NOI constitutes notice that the landowner intends to be authorized by a general WPDES permit issued for storm water discharges associated with land disturbing construction activities in the State of Wisconsin. Becoming a permittee obligates the landowner to comply with the terms and conditions of the general permit.

Performance Standard
A narrative or measurable number specifying the minimum acceptable outcome for a facility or practice.

Physically Interconnected
Physically interconnected means that one MS4 is connected to a second MS4 in such a way that it allows for direct discharges into the second system.

Urbanized Area (UA)
An urbanized area (UA) is a land area comprising one or more places - central place(s) - and the adjacent densely settled surrounding area - urban fringe - that together have a residential population of at least 50,000 and an overall population density of at least 500 people per square mile. 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.