The MPCA, working with stakeholders, developed a checklist for conducting an inventory of bacteria sources. The checklist is not a permit requirement but may be used to meet permit requirements 22.3 and 22.4. This page provides guidance and supporting information for the checklist.
Link to the checklist: File:Checklist for bacteria source inventory.xlsx
The checklist contains four worhsheets.
These are discussed below.
This sheet provides basic general information about the checklist.
This is the sheet where users enter information. Column A contains different categories of bacteria sources and specific sources within each category. The categories include the following.
Columns B through G are where users input information.
Filling out this checklist fulfills permit requirements 22.3 and 22.4, as long as Columns B, C, D and E are completed. However, if the sources are not mapped, then an inventory (i.e. address of a dog park) needs to be documented.
This section provides some basic information about each of the potential sources included in the checklist. Where appropriate we include links where additional information can be found.
Runoff from impervious surfaces typically contains high concentrations of bacteria. The impervious surface, however, is not the source of the bacteria; it is the conveyance mechanism.
Ultimately the source of bacteria in urban stormwater is animal waste. Identifying the specific source is more challenging and likely varies with location and land use. Typical sources include domestic pets and wildlife, particularly birds. Sources of bacteria to receiving waters include urban stormwater runoff, leaking sewer lines, sewer overflows, septic systems, landfills, marinas and pumpout facilities, poorly operating packing plants, and other illicit discharges.
Some general observations from the literature are summarized below.
Land use | Median (MPN/ml) | Maximum (MPN/ml) |
---|---|---|
Commercial | 6900 | 350000 |
Industrial | 9700 | 290000 |
Residential | 20000 | 600000 |
Rooftop | 1250 | |
Open space | 4500 | |
Forested | < 100 |
Sewage typically contains fecal coliform concentrations in excess of one million most probable number per 100 milliliter (MPN/100 ml). This is about two orders of magnitude greater than urban stormwater concentrations. General indicators of bacteria sources include the following.
A complicating factor is that bacteria can survive and grow both within the storm sewer system and within receiving waters. Growth within the storm sewer systems includes both the surface and subsurface conveyances. For example, coliform bacteria have been found to survive and grow in moist soils and leaf piles. A recent study in Minneapolis indicated that catch basins are an important source, largely as a result of growth within the catch basin.
The following table provides a summary of data from the literature. Maximum concentrations are included to illustrate the tremendous variability that may occur in bacteria concentrations. The values represent a compilation of data from several sources (see references at the bottom of this page).
The following links go to tables providing management strategies for different bacteria sources.
Overview:RV dumping or leaking into the storm drains, particularly at vacation destinations, can contribute bacteria and pathogens to the storm sewer system, either by directly dumping into storm drains or by dumping onto impermeable surfaces that drain to the storm sewer system. Illicit RV dumping can be managed by providing public education on appropriate practices, publicizing RV dump locations, by proving a citizen’s reporting hotline, and by publicizing fines PATHOGENS in Urban Stormwater Systems. For an example of an RV dumping brochure, see the brochure “Think Blue San Diego”.
Where/when is this a concern: There are limited direct bacteria sources associated with illegal dumping (e.g. diapers, pet waste). However, illegal dumping of organic material (e.g. yard waste, oil) can act as a food source for microbes in the storm sewer system.
Management strategies:
Suggested references: No specific references recommended. Conduct a web search for more information.
Overview
Street litter and plant material indirectly contribute to bacteria loads by providing a food source and habitat for bacteria populations to survive and grow. A study in the Minnehaha Creek Watershed, Minnesota, indicated organic material is an important contributor to bacteria in stormwater runoff.
Where/when is this a concern
There are few studies that specifically focus on street debris as a source for bacteria. This is likely to be an important source during times of the year when organic debris is in streets and temperatures and moisture conditions are conducive to bacterial growth. Spring and early fall are therefore the most likely times for this to be an important source of bacteria.
Management strategies
Pollution prevention and source control practices, such as street sweeping, are recommended to control street litter and plant material. This table provides a summary of additional practices for residential areas, many designed to control sources of organic material to the storm sewer system.
The United States Environmental Protection Agency defines an illicit discharge as, “any discharge into a storm drain system that is not composed entirely of stormwater.” The Minnesota Municipal Separate Storm Sewer System (MS4) General Permit defines illicit discharge as any discharge to a municipal separate storm sewer that is not composed entirely of stormwater except discharges pursuant to a NPDES permit (other than the NPDES permit for discharges from the municipal separate storm sewer) and discharges resulting from firefighting activities.
There are many potential illicit discharges to an MS4. The concern here are sources that contribute bacteria and pathogens, or that contribute pollutants that may promote bacteria and pathogen growth (e.g. organic sources). The most important potential sources are likely to be sanitary sewer connections, including broken sanitary sewer lines where septage seeps into a storm sewer line, cross-connections, and and straight pipe discharges. These sources contribute high concentrations of bacteria and pathogens to the storm sewer system.
Many illicit discharges occur during dry weather when storm flows are not contributing, or are intermittent. This may aid in detecting illicit discharges, since storm sewer discharges during dry weather or intermittent discharges may indicate the presence of illicit discharges. There are several techniques for detecting illicit discharges, including outfall monitoring, use of tracers (e.g. smoke, dye), and use of electronic equipment (e.g. cameras). More specific information on some illicit discharges and methods for identifying them are found in the sections oncombined sewer overflows, sanitary sewer overflows, inflow and infiltration, and illicit connections to sanitary sewers.
Stormwater practitioners and managers covered under the MS4 General permit must develop and implement an illicit discharge detection and elimination (IDDE) program. Information on permit requirements is found here.
For more information, see the following documents.
Irrigation runoff is an allowed discharge to storm sewer systems, provided there are no illicit pollutants in the discharge. Irrigation runoff can contribute bacteria and pathogens to runoff and mobilize sources within the storm sewer system. In particular, irrigation runoff is a potentially important source of dry weather flows in residential and commercial areas. A study in the Minnehaha Creek Watershed, Minnesota, indicated over-irrigation and subsequent runoff from lawns was an important source of bacteria. A study in San Diego indicated a higher frequency of runoff in residential areas compared to commercial land uses. An Alabama study indicated wet-weather samples having mostly higher enterococci levels than E. coli, while dry weather source area samples (such as springs and irrigation runoff) had higher E. coli levels (Shergill and Pitt, 1984). The contribution of dry weather inflows from irrigation runoff has also been known to foster in-situ bacterial growth (Geosyntec 2010).
The primary focus on reducing inputs from irrigation should focus on reducing overirrigation. Effective methods to reduce irrigation runoff include development of educational outreach, increased inspections, fines for overwatering, tiered water rates, provide irrigation controller rebates or distribution of smart irrigation controllers and/or other financial incentive programs that decrease watering volume (Geosyntec 2012). A residential runoff study in Orange County conducted in five neighborhoods found dryweather runoff decreased by 50% in areas where weather-based irrigation controllers were installed (IRWD and OCMWD 2004). Berg et al. (2009) found dry-weather runoff reductions of 25% to 50% for a similar study of 4,100 Smart Timers installed in residential and commercial areas. Promoting better irrigation runoff management also reduces water waste and can improve water quality.
Regrowth of bacteria in the storm sewer system has been documented but is poorly understood. Regrowth is problematic because it may negate upstream efforts to control bacteria and pathogens. Regrowth typically occurs in biofilms. Biofilms are surface-attached communities of microorganisms that undergo cell attachment, growth, detachment, and sloughing. Biofilms are normally extremely diverse and include a wide variety of bacteria, including pathogenic bacteria. The pathogens E. coli O157:H7, Salmonella enterica, and Campylobacter jejuni are all known to form biofilms. Further, biofilm formation can favor the survival of all three of these organisms under both typical environmental conditions and under active disinfection. Biofilms act as a source of bacteria in stormwater runoff during periods of higher flow, which dislodges bacteria from the biofilms.
Factors that commonly limit the survival of bacterial pathogens in biofilms include low levels of available nutrients and organic material, non-favorable oxygen concentrations, and the competitive, antagonistic and predatory activities of the indigenous microbial population. High stormflow rates cause detachment and sloughing of biofilms. Biofilms can develop in urban storm sewer piping and in streets. Some researchers have questioned the utility of using indicator bacteria in conditions favorable for biofilm growth, since indicator bacteria survive and grown in biofilms while many pathogenic bacteria do not.
Irrigation runoff can contribute to formation of biofilms in storm sewers that can be an on-going source of bacteria discharged from the storm sewer system Green Infrastructure Implementation Strategy (2018). Other factors that may favor biofilm development include organic debris in streets, favorable surfaces for attachment within the storm sewer system (e.g. submerged aprons, particularly those constructed of concrete), and increased loading with natural sediments containing naturally occurring biofilms, stormwater enriched in bacteria. During prolonged periods between runoff events, environmental biofilms (i.e. naturally-occurring) appear to outcompete and replace biofilms consisting of bacteria originating from stormwater flows. Enhancing the storm sewer environment to favor environmental bacteria may be one approach to reducing loading of bacteria from stormwater flows.
For more information, see Urban Water Resources Research Council (2014), Roberts (2012), and Burkhart (2013).
Leaky sewer pipes potentially can contribute very high concentrations of bacteria to storm sewer systems. Leaking sewer systems are more common in areas with aging infrastructure, where contributions from leaking systems can be as high as 20 percent of annual flow in the sanitary sewer system. For a detailed discussion of contributions from leaking sewer systems, see Sercu et al. (2011), Vasquez-Sune et al. (2011), Yang et al. (1999), Rutsch (2006), and Prigiobbe and Giulianelli (2011)
For more information on potential effects of leaking sewer infrastructure, methods of detecting leaks, and management strategies, see the section on illicit discharges and the section on sanitary sewer inflow and infiltration.
Urban lawns and other grass areas can be a source of bacteria and pathogens to stormwater runoff. Concentrations of indicator bacteria in runoff typically exceed water quality standards in all land uses, often by more than an order of magnitude, with concentrations tending to be higher from residential areas compared to commercial, industrial, and open space land uses (Minnesota Stormwater Manual). Grass swales and grass strips typically have higher concentrations of bacteria and enterococci in outflow water compared to inflow, although if these practices infiltrate water the total loading may be decreased by the practices (International BMP Database). Contributions of bacteria to runoff from grass areas is not well understood. Hathaway and Hunt (2010) conducted a study of bacteria in runoff from residential areas in North Carolina and concluded the following.
Practices or factors that potentially contribute to bacteria loading from grass areas include the following.
Practices to reduce bacteria inputs from grass areas include the following.
Combined sewer systems (CSS) are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. During wet weather conditions, the volume of stormwater runoff can exceed the capacity of the CSS infrastructure, including both the piping system and/or the treatment plant. This is common where where older CSS infrastructure is in place, combining sanitary and storm drain flows. When the capacity of the CSS is exceeded, excess water can bypass treatment and bypassed flow will be mixed with the treated water prior to disinfection and just prior to discharge to the receiving water. While both stormwater runoff and sanitary sewer discharges contain bacteria, concentrations are much higher in untreated sewage. Thus, CSOs can lead to very high concentrations of bacteria in water delivered to receiving waters. For more information, see [3], [4], [5], [6], [7].
Sanitary sewer systems collect and transport domestic, commercial, and industrial wastewater. Some sanitary sewer systems may contain limited amounts of stormwater and infiltrated ground water to treatment facilities, but they are designed to carry just sewage and industrial wastewater. Occasionally, sanitary sewers will release raw sewage. These types of releases are called sanitary sewer overflows (SSOs). Possible causes of SSOs include blockages, line breaks, sewer defects that allow stormwater and groundwater to overload the system, power failures, improper sewer design, and vandalism. The adjacent image indicates line blockages appear to be an important cause of SSOs. An EPA survey indicated SSOs are most common during wet weather flows.
SSOs that discharge to surface waters are considered point source discharges and are thus prohibited unless authorized by a NPDES permit. SSOs may be indicative of improper operation and maintenance of the sewer systems, and may violate NPDES permit conditions. Effective illicit discharge and elimination practices and programs minimize the occurrence and impacts from SSOs. Other management strategies include the following.
For more information, see [8], [9], [10], [11]
Groundwater infiltration and rainfall derived inflow and infiltration, commonly referred to as inflow, are components of most sanitary sewer systems. These inputs, called I&I, should be a minor component of the sanitary sewer flow. However, infiltration and inflow may be considered excessive when it is the cause of overflows (SSO) or bypasses in the sanitary sewer system. In addition, I&I is treated at wastewater treatment plants even though it is relatively clean water, resulting in extra cost.
EPA provides guidance for estimating the input and importance of I&I in a sanitary sewer system. To assess extraneous water entering your system at least a year of influent flow data to the treatment facility should be examined. For infiltration analysis, flow data collected during the high groundwater periods is used. For inflow analysis, the Average Wet Weather (AWW) flow can be estimated from flow data for a one week period when there has been significant rain. If a single storm event is used to analyze wet weather inflow, it should be an event large enough to cause surface ponding and runoff. Other techniques can be used to determine the presence of I&I, including manhole testing and maintenance, dye tracing, smoke testing, use of cameras, and private property inspection for improper connections. Examples of improper connections include downspouts, groundwater sump pumps, foundation drains, drains from window wells and outdoor basement stairwells and drains from driveways.
Proper evaluation of I&I sources is necessary to manage them. Once detected, they can be eliminated or minimized. Several cities, for example, have programs and ordinances prohibiting illicit connections on private property.
For more information, see [12], [13], [14], [15]
The Municipal Separate Storm Sewer System (MS4) General Permit defines illicit discharge as "any discharge to a municipal separate storm sewer that is not composed entirely of stormwater except discharges pursuant to a NPDES permit (other than the NPDES permit for discharges from the municipal separate storm sewer) and discharges resulting from firefighting activities". Not all illicit discharges contain bacteria and pathogens, but examples of illicit discharge sources containing bacteria and pathogens include sewage and septage, washwater, irrigation water, some commercial and industrial water,
Illicit discharges to the storm sewer system can be classified as direct or indirect. Direct discharges are directly connected to the storm drain pipe through a sewage pipe, shop drain, or other kind of pipe. Direct discharges are typically continuous or intermittent and occur when two different kinds of “plumbing” are improperly connected. The three main situations where this occurs are sewage cross-connections, straight pipes, and industrial and commercial cross-connections. Indirect discharges are generated outside the storm drain system and enter through storm drain inlets or by infiltrating through the joints of the pipe. Generally, indirect discharges are intermittent or transitory, with the exception of groundwater seepage. Indirect discharges include groundwater seepage, spills, dumping, outdoor washing, and irrigation.
Certain types of illicit discharges can be associated with specific land uses. For example, failing septic systems and irrigation sources are more common in residential areas, while in commercial areas important sources include washing, dumping, and spills. This EPA document provides a table and discussion of likely sources for different land uses.
For entities covered under municipal NPDES stormwater permits, Minimum Control Measure 3 requires establishment and maintenance of an illicit discharge detection and elimination (IDDE) program. The permit contains specific items that are required as part of an IDDE program.
Techniques for detecting illicit discharges include techniques for detecting infiltration and inflow. These include monitoring, dye tracing, smoke detection, use of camera, and focused inspections.
For more information see [16], [17], [18].
If properly placed and maintained, porta potties should not be a source of bacteria to the stormwater system. However, they have the potential to contribute high concentrations of bacteria and pathogens. In addition, cleaning of portable toilets may contribute other pollutants, such as disinfectants, to runoff.
There are numerous fact sheets and guidance documents concerning porta potties. Some useful links are provided below. Common practices for properly managing porta potties include the following.
For more information, see [19], [20], [21], and [22].
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Dumpsters may contain materials that are direct sources of bacteria and pathogens (e.g. diapers, pet waste bags) and may attract wildlife that contribute bacteria and pathogens. Leaking dumpsters can therefore be a source of bacteria to the stormwater system. Concentrations of bacteria are typically very high from dumpsters, particularly from dumpster washdowns, which can constitute an important dry weather source of bacteria.
Practices to reduce bacteria from dumpsters include the following.
For more information see [23], [24], [25], and [26].
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Dog parks represent an obvious potential source of bacteria and pathogens. Recommended practices for minimizing bacteria loading from dog parks include the following.
For more information, see [27], [28], [29], and [30].
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