Storm Water Runoff From Municipal Separate Storm Sewer Systems (MS4)

As defined in 401 KAR 5:002, Section 1(184), a municipal separate storm sewer system (MS4) is a conveyance, or system of conveyances, including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, manmade channels or storm drains that are (1) owned or operated by a state, city, town, county, district, association or other public body having jurisdiction over disposal of storm water that discharges to waters of the commonwealth, (2) is designed or used for collecting or conveying storm water, (3) is not a combined sewer and (4) is not a part of a publicly owned treatment works. 

The U.S. Environmental Protection Agency has categorized MS4s into the three categories of small, medium and large based on population served.

The medium and large categories are regulated under the Phase I storm water program.

• Final Rule Phase I, Nov. 16, 1990, Federal Register.
• Large Systems 250,000 or greater population (e.g., Louisville).
• Medium Systems 100,000 to less than 250,000 (e.g., Lexington).
• Both systems are in the second five-year permitting cycle.
• Annual update reports required.

The small MS4 (SMS4) category is regulated under the Phase II storm water program.

This category covers all MS4s not covered under Phase I. Since this is a very large number of systems, only a select group are regulated under the Phase II rule as automatically designated or on a case-by-case basis due to potential to cause adverse impact to the receiving stream (Download Acrobat free to view these PDF documents). This link to an Excel document provides three information tab spread sheets with a complete list of target MS4 communities in Kentucky. This Excel document contains a list of contacts for MS4 communities. 

• Dec. 8, 1999 - Final Rule, Federal Register.
• June 15, 2001 - Draft General Permit for SMS4 to Public Notice (PDF document). December 2002 - General Permit Issuance Deadline (PDF document).
• December 2002 General Permit Issuance Deadline. (PDF document) 
• March 2003 - Deadline for Application (PDF document) (Word document) for Coverage.
• All Small MS4 Programs Fully Developed and Implemented no later than the end of First Permit Term (five years).
• Annual Summary Reports for First Permit Term. Years 2 and 4 for Subsequent Permit Terms.

Permittee shall choose best management practices (BMPs) and measurable goals to comply with the six minimum control measures to the maximum extent practicable. In accordance with 40 CFR Section 122.34(d)(2), the Kentucky Division of Water provides the EPA menu of BMPs to consider when developing a storm water management program. The menu includes examples of BMPs and associated measurable goals, although other BMPs and measurable goals may be used. Additional Storm Water Phase II information is provided below.

Frequently asked questions about Kentucky's MS4 program in Word and in PDF.

Power Point presentation on MS4 program requirements.

EPA Web sites:

• Storm Water Discharges From Municipal Separate Storm Sewer Systems (MS4s)   
• Frequently asked questions     
• NPDES Storm Water Program for Medium and Large MS4s    
• NPDES Storm Water Program for Regulated Small MS4s  
• Storm Water Publications

 

Direct questions concerning MS4 to Abigail Rains, Division of Water, 502-564-3410.