Phase II of the program expands Phase I by requiring additional parties to implement programs and practices to control polluted runoff again by using NPDES permits. The Phase II Final Rule automatically covers two groups on a nationwide basis:
- Operators of small municipal separate storm sewer systems (MS4s) located in "urbanized areas." (As a practical matter, a small MS4 is any MS4 not covered in Phase I.); and
- Operators of small construction activities that disturb from one to five acres of land.
Further, small MS4s outside of urban areas, construction activity affecting less than one acre and any other storm water discharges may be covered if the NPDES permitting authority or the EPA decides they need to be regulated.
For the most part, the authority to issue permits for storm water discharges has been delegated to the states. (In a few cases, the EPA retains the authority.) In Tennessee, anyone needing an NPDES permit applies to the Tennessee Department of Environment and Conservation (TDEC) for the permit.