Phase II & Small MS4
History
In 1972, the National Pollutant Discharge Elimination System (NPDES) program was established under the authority of the Clean Water Act. Phase II of the NPDES stormwater program was signed into law in December 1999. This regulation builds upon the existing Phase I program, developed in 1990, by requiring smaller communities, also known as small municipal separate storm sewer systems (MS4s), to be permitted.
(Phase I of the program required NPDES permit coverage for large or medium municipalities that had populations of 100,000 or more.)
In addition to expanding the NPDES Stormwater Program, the Phase II Final Rule revises the no exposure exclusion and the temporary exemption for certain industrial facilities under Phase I of the NPDES Stormwater Program and certain exemptions relating to ISTEA. The Phase II Rule also established two potential waivers for small construction activities.
No Exposure Exclusion
ISTEA Exemption: Municipally Owned & Operated Industrial Sources
Small Construction Waivers
Minimal Requirements
Small MS4 Requirements
Under Phase II, operators of regulated small municipal separate storm sewer systems (MS4s) are required to:
- Obtain a National Pollutant Discharge Elimination System (NPDES) permit
- Develop a stormwater management program which includes the six minimum control measuresImplement the stormwater management program, addressing Six Minimum Measures and using appropriate stormwater management controls, or best management practices (BMPs) Develop measurable goals for the program. Evaluate the effectiveness of the program.
More detailed overview of Phase II
State Permit Requirements
Minimum Requirement: Presume a General Urban Runoff Problem Exists (Read Below)
NPDES Phase II regulations emphasize the presumptive approach. The presumption is that each municipality has a general urban runoff problem and that this problem can be addressed through the implementation of six minimum control programs. The regulations, therefore, ask for a limited local assessment that demonstrates an awareness of the storm drain system (i.e., map of major pipes, outfalls, and topography and areas of concentrated activities likely to be sources of storm water pollution). The advantage of the presumptive approach is twofold: (1) it focuses limited program resources on program implementation without a lot of time and resources invested in up-front studies and (2) it is the most cost-effective way to implement the required elements of your program. A great deal of evidence supports the premise that polluted runoff is a problem in urban environments and you can be fairly confident that your municipality shares these general runoff problems. By accepting this premise, you can directly implement the six minimum control measures described in the regulations secure in the knowledge that the elements of your program satisfy the regulatory requirements. The disadvantage is that your municipality may have unique watershed resources or unique urban runoff problems that require custom-crafted program elements.
Lacking a detailed assessment that allows your stormwater pollution prevention plan to target specific concerns, water quality improvements may not be achieved. Furthermore, and just as importantly, without a more detailed assessment of your specific urban runoff problems, educating both the public and decision makers as to the nature of the problem — and the need for a program — may be more difficult.
Six Minimum Control Measures
Listed below are the six minimum control measures that operators of regulated small MS4s must incorporate into stormwater management programs. These measures are expected to result in significant reductions of pollutants discharged into receiving waterbodies.