Element 4 – Municipal Separate Storm Sewer Systems (MS4s)

Urban stormwater management receives significantly less attention in water quality protection decisions than that given to domestic wastewater and drinking water systems. However, stormwater regulations have been evolving to require greater protection and restoration efforts of urban water bodies and their contributing watersheds.

The federal NPDES program engages a set of regulated MS4s across the nation, of which 164 are now permitted or have applied for permitting in Missouri. Regulated MS4s are required to implement stormwater management practices in the areas of new and redevelopment, illicit discharge control, municipal operations and public education and involvement. The three major MS4s must also perform stormwater quality monitoring and assessment, regulate industry and employ greater stormwater quality efforts in roadway and flood control projects. MS4 permits also require restoration where TMDLs apply.

Of particular challenge to regulated MS4s is the need to employ state-of-the practice strategies, methods and technologies in new development and redevelopment that may be contrary to conventional stormwater management. Specifically, this stormwater paradigm shifts the thinking away from large curb/gutter/basin systems and towards the application of smaller-scale, distributed on-site retention practices that aid infiltration, evapotranspiration and reuse. This shift creates a local need for significant education and outreach, changes to ordinances and codes, and the establishment of stormwater quality performance criteria and standards.

To aid their regulated MS4s, several state NPDES permitting authorities have established stormwater quality performance criteria and control specifications for development projects, such as Minnesota, Michigan and Wisconsin in the midwest, as well as Washington state and others across the nation. EPA has developed several resources dedicated to green infrastructure and low impact development to aid this endeavor. In 2013, EPA released the National Stormwater Quality Calculator to assist site developers, landscape architects, urban planners, and homeowners in selecting on-site stormwater quality control measures. Comprehensive performance data for stormwater quality control measures is also available in the international bmp database.

What Missouri is currently doing to assist MS4s in meeting the most challenging aspect of the MS4 Program:
The department is conducting MS4 Workshops to assist regulated MS4 communities to have a better understanding regarding the terms and conditions of their MS4 permit. These workshops provide technical and procedural information on how to implement a successful Stormwater Management Plan. These workshops are conducted quarterly in both the department’s regional offices and central office.

Additionally, the department published the Missouri Guide to Green Infrastructure: Integrating Water Quality into Municipal Stormwater Management, May 2012. This how-to guide for regulated MS4s was presented in several workshops across the state in 2012 and 2013, and is publicly available at the Missouri Stormwater Information Clearinghouse. The guide aids MS4s in implementing effective municipal stormwater management programs for developers while complying with NPDES requirements. In addition, the department provides administrative reviews and assessments of the MS4 programs, including feedback to the MS4s. This feedback elicits improved steps toward MS4 compliance. On a limited basis, the department has included green infrastructure requirements in consent decrees.

Surveys conducted during the MS4 workshops have identified three major challenges faced by regulated MS4 communities, which are:

  • What is the measure of compliance (i.e. what is Maximum Extent Practicable?)
  • What are adequate funding sources for their MS4 programs?
  • Are the Stormwater Management Programs for the regulated MS4 communities satisfactory?

The department is addressing each of these challenges. To start, the department first defined maximum extent practicable, which is established in each MS4 permit factsheet. Second, MS4 permits are drafted and issued with focus on maximum extent practicable. Third, the department provides technical information and assistance with respect to best management practices and measurable goals (focus on quantifiable) for all of the MS4 permit terms and conditions. The MS4 workshops focus on the more challenging minimum control measures (e.g. illicit discharge detection and elimination and post-construction stormwater management in new development and redevelopment).

The department is conducting research to determine sources of funding for MS4 programs. In addition, the MS4 Workshops are used to gather additional information regarding how regulated MS4s fund their program. The department’s focus is to assist with funding long-term, predictable funding sources. In addition, the department is drafting an MS4 funding source technical bulletin, which will be provided to all regulated MS4s.

The department is now reviewing and rating regulated MS4 stormwater management plans to ensure the MS4s are successfully implementing the terms and conditions of their MS4, which means maximum extent practicable. The department does foresee a major challenge in reviewing and rating all 164 stormwater management plans due to the fact that a stormwater management plan review can range from one to three weeks. If the review time is one week for all MS4s it will take department staff approximately three years to review. If the review time is three weeks, the review time could be up to nine years. Thus, the actual time will fall between three to nine years to review all regulated MS4 stormwater management plans.