Guidance for meeting bacteria TMDL MS4 permit requirements

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Bacteria Total Maximum Daily Loads (TMDLs)

Escherichia (E). coli is an indicator bacteria, meaning that it indicates the potential presence of disease causing pathogens that can be harmful to human health. Currently there are X TMDLs that include MS4 WLAs for bacteria. Click here to link to MPCA's impaired waters website. A map illustrating U.S. EPA-approved listings for E. coli and fecal coliform is shown on the right (insert map).

The MS4 permit requires permittees that have an applicable wasteload allocation (WLA) for bacteria to:

1. Maintain a written or mapped inventory of potential areas and sources of bacteria (e.g., dense populations of waterfowl or other birds, dog parks) (Permit requirement 18.14).
2. Maintain a written plan to prioritize reduction activities to address the areas (Permit requirement 18.15).

Maintain a written or mapped inventory of potential areas and sources of bacteria (Permit requirement 18.14)

The written or mapped inventory should identify potential areas and sources of bacteria. Some common sources that will likely be identified include sanitary sewer overflow locations, areas that attract nuisance birds and/or wildlife (parks, golf courses, etc.), dog parks, known septic systems, etc. (see Table 1 for additional potential sources).

Potential sources of bacteria and actions to address
Link to this table

General Category	Source	Action
Municipal Sanitary Infrastructure	Combined Sewer Overflows1	Replace infrastructure, if possible
	Sanitary Sewer Bypasses/Overflows	Line sanitary sewer pipes
	Inflow and Infiltration	Minimize and eliminate through repairing damaged sewers
	Illicit discharges from unsewered communities	Detect and eliminate illicit discharges
Human Sanitary Sources	Leaky/failing septic systems	Update and enforce subsurface sewage treatment system (SSTS) ordinances
		Educate homeowners on septic system maintenance and opportunities for replacement
		Implement higher standards for setbacks for installing septic systems near receiving water bodies
	Porta-potties	Ensure construction site temporary toilets have appropriate pollution prevention BMPs
Domestic pets	Dogs, cats, dog parks, walking trails, residential yard and sidewalk runoff (spring runoff after winter accumulation)	Establish pet waste disposal stations along trails, in dog parks, etc.
		Pass and enforce pet waste ordinances and educate pet owners about them
		Add infiltration BMPs downstream of parks/residential areas and upstream of stormwater pipes (i.e., somewhere between the park/residential area and the stormwater outfall so as to intercept and infiltrate some or all of the flow from these areas)
		Reduce transport from parks, residential, and other areas by the use of buffer zones and other disconnection of flow pathways (e.g. impervious surface, disconnection, downspout disconnection)
Urban wildlife	Rodents (raccoons, squirrels, etc.), deer, etc., birds (geese, ducks, swallows, etc.), areas where wildlife congregate such as fields, parks, and golf courses	Wildlife feeding bans and control of nuisance populations, including ducks and geese and other wildlife
		Remove community facilities such as vending machines for feeding ducks and geese
		Add buffers in riparian zones near waterbodies to deter waterfowl congregation
		Consider wildlife barriers if wildlife (e.g. raccoons) are found to be living in storm sewers
		When possible, use infiltration BMPs instead of detention ponds in residential developments and other areas where wildlife may congregate
Other Urban Sources (non-stormwater)	Excessive irrigation/overspray	Assess the extent to which irrigation over-spray occurs at city-owned facilities and eliminate overspray as appropriate
		Education on water conservation
MS4 Infrastructure	Illicit sanitary connections to MS4	Detect and eliminate illicit discharges
	Leaky sewer pipes	Line sewer pipes
	Biofilms/regrowth	Reduce dry weather flows, which provide conditions that promote bacteria growth. Dry weather flows could be from night time irrigation of lawns/parks or leaky stormsewer pipes.
	Decaying plant matter, litter, and sediment in the storm drain system	Enhance street sweeping program.
		Prevent the discharge of grit chamber clean out effluent
		Remove leaf litter and soil in street and gutters: implement an Adopt-a-storm drain program
Other Natural Sources	Stream Bank Erosion	Streambank restoration

¹Note only a few combined sewers remain in Minneapolis
*This table was created using information from the Upper Mississippi River Bacteria TMDL Study (2014) and Protection Plan and the Upper Mississippi River Bacteria TMDL Implementation Plan (2016), Pathogens in Urban Stormwater Systems (2014), and the Minnehaha Creek Bacterial Source Identification Study (2017).

Information that can be used to identify potential sources of bacteria in the impaired watershed may already be available in:

• TMDL Reports
• TMDL Implementation Plans
• Watershed Restoration and Protection Strategies Reports
• Local water plans (e.g., Watershed Management Organizations, Watershed Districts, Soil and Watershed Districts, Conservation Districts, County, City, and One Watershed One Plans)
• Source Water Protection Plans

Many TMDL reports contain information on potential sources and relative contributions of sources in the TMDL impaired subwatershed. For example, the Vermillion River Watershed TMDL Report (2015) includes the table to the right which shows potential sources of bacteria in each impaired reach.

You may also choose to create a mapped, rather than written, inventory of potential sources of bacteria. This could be done using GIS to show areas where there may be potentially high levels of bacteria. A hypothetical example is shown below. Note that the map shows the subwatershed area of the impaired reach outlined in blue and the jurisdictional boundary outlined in black. The sources indicated on the map include SSTS, sanitary sewers, and dog parks (note that the features are not based on real data). In this hypothetical example the MS4 may choose to focus their initial implementation efforts on working with residents to update any non-compliant septic systems, detecting and eliminating any illicit discharges from sanitary sewers, and implementing an education campaign focused on dog park users.

Your MS4 may also want to consider further activities to determine potential sources of bacteria. Some voluntary activities could include:

1. Conduct an E. coli monitoring study along the stream to help identify hot spots of higher bacteria concentrations. Monitor the tributaries flowing into the stream and consider monitoring stormwater outfalls. Sampling at the correct times is critical if this approach is utilized. See bacteria monitoring guidance for more information (include link).
2. Identify subwatersheds for each stormwater outfall or tributary to the stream, making note of potential high-loading features within these such as wildlife congregation areas, parks (especially dog parks), sanitary systems that are potentially located above stormwater systems. Stormwater outfall monitoring could be targeted based on the results from the written and/or mapped inventory.
3. Walk to stream and visually inspect stormwater outfalls during dry weather for flows, odor, color, condition, etc. that would be indicative of an illicit discharge. Take the appropriate actions to eliminate the illicit discharge.

Maintain a written plan to prioritize reduction activities to address the areas identified under requirement 18.14 (Permit requirement 18.15)

MS4s with a bacteria WLA are required to create and maintain a written plan to prioritize reduction activities to address bacteria. Sources of bacteria and potential actions. Potential sources of bacteria and potential activities to address each source are included in the table above.

Prioritize any human sources of bacteria first

It is recommended that human sources of bacteria are addressed first since they are associated with more of a human public health risk (e.g. failing septic systems, illicit discharges, etc.). Streams that exceed the State water quality standards for E. coli may have increased levels of waterborne pathogens that can be harmful to human health when the streams are used as drinking waters sources and for recreation activities. So, it is also important for your MS4 to also prioritize implementation activities that reduce bacteria to bacteria impaired waters that people use for drinking and/or recreating (fishing, swimming, boating, etc.).