image turbid runoff
Suspended sediment in stormwater runoff

The U.S. EPA (1999) states: "Solids are one of the most common contaminants found in urban storm water. Solids originate from many sources including the erosion of pervious surfaces and dust, litter and other particles deposited on impervious surfaces from human activities and the atmosphere. Erosion at construction sites are also major sources of solids. Solids contribute to many water quality, habitat and aesthetic problems in urban waterways. Elevated levels of solids increase turbidity, reduce the penetration of light at depth within the water column, and limit the growth of desirable aquatic plants. Solids that settle out as bottom deposits contribute to sedimentation and can alter and eventually destroy habitat for fish and bottom-dwelling organisms ... Solids also provide a medium for the accumulation, transport and storage of other pollutants including nutrients and metals."

This article focuses on Total Suspended Solids (TSS) since this is the parameter most frequently associated with water quality impairments by solids. TSS comprises both inorganic and organic material. There is limited information on the organic fraction of TSS, but it appears the organic fraction typically accounts for about 25 to 35 percent of TSS ([1], [2]).

Source and concentrations of TSS in urban stormwater

Sources of TSS include pavement (from wear), vehicle exhaust emissions, vehicle parts, building and construction material, road salt, road paint and pedestrian debris, soil material, plant and leaf litter, and atmospheric deposition of particles. Atmospheric sources of particles may derive from outside of the river basin (Hopke et al. 1980; Taylor and Owens, 2009).

The following table summarizes a literature review we conducted on Event mean concentrations of total suspended solids in stormwater runoff.

Event mean concentrations for total phosphorus.
Link to this table

Land cover/land use Range (mg/L) Recommended value (mg/L) Notes
Commercial 0.20 - 0.34 0.200 If applicable to models being used, adjust curve numbers/runoff coefficients when calculating loads
Industrial 0.23 - 0.55 0.235
  • If applicable to models being used, adjust curve numbers/runoff coefficients when calculating loads
  • Adjust upward if specific phosphorus sources exist
Residential 0.26 - 0.38 0.325 Concentrations vary widely depending on local conditions
High-density/Multi-family residential 0.28 - 0.40 Calculate1
  • Insufficient information to recommend a specific emc
  • Concentrations vary widely depending on local conditions
Medium density residential 0.18 - 0.40 Calculate1
  • Insufficient information to recommend a specific emc
  • Concentrations vary widely depending on local conditions
Low density residential 0.24 - 0.40 Calculate1
  • Insufficient information to recommend a specific emc
  • Concentrations vary widely depending on local conditions
Freeways/transportation 0.25 - 0.45 0.280
  • Concentrations vary widely depending on inputs
  • Adjust upward for areas receiving large inputs of road salt or sediment or having very heavy traffic loads
  • Adjust downward for low traffic areas or areas with reduced inputs (e.g. little road salt application, limited truck traffic)
Mixed 0.16 - 0.84 0.290
  • Residential land use was the primary land use in most studies that cited values for mixed land use
  • If the study area can be delineated into specific land uses and impervious area for each land use is know, we recommend calculating the emc
Parks and recreation Use value for open space or calculate
  • emc will be a function of vegetative cover
  • Adjust upward if street tree canopy cover is high or pervious areas are primarily grass on compacted soils
Open space 0.12 - 0.31 0.190
Conventional roof 0.01 - 0.20 0.030
Institutional 0.14 - 0.422 See note
  • Use low values in range (0.200 mg/L or less) for facilities such as campuses, where there is considerable pervious area
  • Use high values in range (0.30 mg/L or greater) for areas with considerable impervious surface, such as sports facilities or facilities with large parking areas
Forest/shrub/grassland 0.03 - 0.45 0.090 Concentrations are likely to vary with season in areas with fall leaf drop
Open water and wetlands see Notes (next column)
  • If data exist, use the phosphorus concentration for the water body of interest
  • If data for a specific lake do not exist, use data from similar lakes in the area
  • emcs for wetlands will typically be higher than for lakes in an area. Consider using a value equal to 2 times the value for lakes in an area.
Cropland (row crops) 0.126-1.348 2 Median from our review = 0.533
Pasture 0.35-0.45 2

1The link takes you to information on calculating event mean concentrations for areas with multiple land uses.
2Our literature review was not extensive enough to warrant a specific recommend emc for this land use


Sediment export varies with the amount of runoff and is calculated by multiplying the TSS concentration by the volume of runoff. The Simple Method can be used to estimate TSS loading as a function of different land uses. Export coefficients are presented in the literature for different land uses. The data are highly variable as a result of the differences in impervious surface, even within specific land uses. Typical annual TSS export are shown below (data adapted from the National Stormwater Quality Database).

  • Residential: 76 pounds per acre (n=1042, covar=3.7)
  • Mixed residential: 111 pounds per acre (n=611, covar=2.1)
  • Commercial: 221 pounds per acre (n=527, covar=1.2)
  • Industrial: 193 pounds per acre (n=566, covar=1.1)
  • Freeway: 560 pounds per acre (n=185, covar=1.4)
  • Open space: 35 pounds per acre (n=49, covar=1.5)

Meeting TSS water quality targets

Information on this page can be used to help meet water quality targets. Water quality targets are established for various purposes including meeting Clean Water Act (CWA) requirements, meeting local water quality goals or requirements, and meeting non-regulatory targets. CWA requirements include antidegradation, total maximum daily load (TMDL) limits, and NPDES permit requirements. Each of these are described below.

Information: Note that information presented in the Stormwater Manual can be used to meet NPDES permit requirements. This includes information on all BMPs discussed in the Manual unless otherwise noted. Check with MPCA's Stormwater Program for applicability of information not contained in the Manual, including BMPs and BMP credits.

Antidegradation

Water quality standards include an antidegradation policy and implementation method. The water quality standards regulation requires States and Tribes to establish a three-tiered antidegradation program to protect existing water quality and water uses in receiving waters (see [3]).

Compliance with Minimum Control Measure (MCM) 5 of the MS4 permit constitutes compliance with antidegradation requirements. The permit requires no net increase in discharges of volume, total phosphorus and total suspended solids (TSS) for new development, while a reduction in these are required for redevelopment projects covered under the permit. Practices that infiltrate or capture and reuse stormwater runoff are typically used to meet these permit requirements.

Total Maximum Daily Loads (TMDLs)

There are several rivers and streams that have approved TMDLs or are listed as impaired for turbidity and TSS. TSS was used as the surrogate pollutant for most turbidity TMDLs. In addition, many streams and rivers listed as impaired for aquatic life have or will have TMDLs written with TSS as the surrogate pollutant. Click here to link to MPCA's impaired waters website.

The MS4 permit requires permittees to demonstrate progress toward meeting applicable Wasteload Allocations in U.S. EPA-approved TMDLs. General information on meeting TMDL requirements in NPDES permits is found here, while reporting requirements are found here. Below is additional information that may be useful.

Permittees with required reductions in TSS loading should implement a treatment train approach, which is discussed in greater detail below.

Stormwater management for total suspended solids

Management of urban stormwater to control or reduce TSS concentrations and loading should focus on identifying the most important sources and then employing either specific practices to address those sources or utilize a treatment train approach.

TSS concentrations in runoff from construction sites typically greatly exceed concentrations from other urban land uses and generally exceed 1000 mg/L. Sediment export from construction sites typically ranges from 2000 to 16000 pounds per acre per year (Line et al., 2009; Line et al., 2011; Wolman and Schick, 1967). Methods for managing runoff and erosion from construction sites are found in Chapter 6 of MPCA's Stormwater Best Management Practices Manual.

A treatment train approach should be utilized when controlling or reducing TSS concentrations in urban stormwater runoff. The treatment train approach for TSS focuses on implementing the following hierarchy of practices.

  • pollution prevention and source control
  • pre-treatment for structural BMPs
  • infiltration
  • settling
  • filtration

Pollution prevention and source control

These practices reduce the amount of TSS generated or remove TSS prior to it being entrained in runoff. These are summarized below for residential, municipal, and industrial sources.

Prevention practices for residential areas

The following table summarizes prevention practices that are effective at reducing TSS concentrations. The table indicates the relative effectiveness of each practice and provides a short description of the practice. TSS removal efficiencies are not established for these BMPs.


Residential pollution prevention methods effective for controlling or reducing total suspended solids (TSS).
Link to this table

Practice Relative effectiveness Method Image1
Better Sidewalk and Driveway Cleaning High Sweep sidewalks and driveways and dispose of sweepings in the trash instead of using hoses or leaf blowers to clean surfaces.
Better sidewalk driveway cleaning.jpg
Exposed Soil Repair High Use native vegetation or grass to cover and stabilize exposed soil on lawns to prevent sediment wash off.
Exposed soil repair.jpg
Native Landscaping High Reduce turf areas by planting native species to reduce and filter pollutant-laden runoff and prevent the spread of invasive, non-native plant species into the storm sewer system.
Native landscaping.jpg
Healthy Lawns High Maintain thick grass planted in organic-rich soil to a height of at least 3 inches to prevent soil erosion, filter stormwater contaminants, and absorb airborne pollutants; limit or eliminate chemical use and water and repair lawn as needed
Healthy lawns.JPG
Yard Waste Management Moderate Prevent yard waste from entering storm sewer systems and water bodies by either composting or using curbside pickup services and avoiding accumulation of yard waste on impervious surfaces; keep grass clippings and leaves out of the street.
Yard waste management.jpg
Better Car and Equipment Washing Moderate Wash cars less often and on grassy areas using phosphorus free detergents and non-toxic cleaning products or use commercial car washes to prevent dirty wash water from flowing to storm sewer systems and water bodies.
Better car washing.jpg
Better Sidewalk and Driveway Deicing Moderate Reduce or eliminate the need for deicing products by manually clearing sidewalks and driveways prior to deicer use; use environmentally-friendly deicing products when possible, apply sparingly and store properly if used.
Better sidewalk driveway deicing.jpg

1 Photo credits


Prevention practices for municipalities

The following table summarizes prevention practices that are effective at reducing TSS concentrations. The table indicates the relative effectiveness of each practice and provides a short description of the practice. TSS removal efficiencies are not established for these BMPs.

Municipal prevention practices for TSS.
Link to this table

Practice Relative effectiveness Method Image1
Temporary Construction Sediment Control High Implement and encourage practices to retain sediment within construction project area; see Temporary Construction Erosion and Sediment Control Factsheets for additional information
Temporary construction sediment control.jpg
Wind Erosion Control High Institute a local program for wetting of open construction surfaces and other sources for windblown pollutants.
Wind erosion control.jpg
Streambank Stabilization2 High Repair erosion occurring on a streambank of lakeshore in a timely manner; inspect bank areas for ice damage in the spring.
Streambank stabilization.jpg
Material Storage Control High Reduce or eliminate spill and leakage loss by properly inspecting, containing, and storing hazardous materials and having a cleanup plan that can be quickly and efficiently implemented.
Material storage control.jpg
Better Street and Parking Lot Cleaning High Maintain streets and parking lots frequently and especially in the spring by sweeping, picking up litter, and repairing deterioration; pressure wash pavement only as needed and avoid using cleaning agents.
Better street parking lot cleaning.jpg
Proper Vehicle Management High Ensure that vehicles are fueled, maintained, washed and stored in a manner that prevents the release of harmful fluids, including oil, antifreeze, gasoline, battery acid, hydraulic and transmission fluids, and cleaning solutions.
Proper vehicle management.jpg
Storm Sewer System Maintenance High Regularly clean debris from storm sewer inlets, remove sediment from catch basin sumps, and remove any illicit connections to storm sewer systems.
Storm sewer system maintenance.jpg
Better Street and Parking Lot Deicing Moderate Properly store and conservatively apply salt, sand, or other deicing substances in order to prevent excessive and/or unnecessary contamination; implement anti-icing and prewet salt techniques for increased deicing efficiency.
Better street parking lot deicing.jpg
Better Turf Management Moderate Ensure that mowing, fertilization, pesticide application, and irrigation are completed in ways that will prevent or reduce grass clippings, sediment, and chemicals from entering storm sewer systems; use native vegetation where possible.
Better turf management.jpg
Public Education Moderate Label storm drains to indicate that no dumping is allowed and institute pollution prevention programs to educate and implement needed community practices.
Public education.jpg
Staff, Employee, and Volunteer Education Moderate Provide internal training for staff and provide direction to hired employees or volunteers regarding pollution prevention techniques to be used during work activites.
Staff employee volunteer education.jpg

1 Photo credits
2Reductions in pollutant loading associated with this BMP are not eligible for credit toward NPDES permit requirements unless the stabilization is above the ordinary high water mark (i.e. the work is not completed within a Water of the State), prior to a permittee's discharge, and the load reduced from this action is included in a Wasteload Allocation in a U.S. EPA-approved TMDL.


Prevention practices for industrial sources

The following table summarizes prevention practices that are effective at reducing TSS concentrations. The table indicates the relative effectiveness of each practice and provides a short description of the practice. TSS removal efficiencies are not established for these BMPs.

Industrial prevention practices for TSS.
Link to this table

Practice Relative effectiveness Method Image1
Temporary Construction Sediment Control High Implement and encourage practices to retain sediment within construction project area; see Temporary Construction Erosion and Sediment Control Factsheets for additional information
Temporary construction sediment control.jpg
Wind Erosion Control High Institute a local program for wetting of open construction surfaces and other sources for windblown pollutants.
Wind erosion control.jpg
Material Storage Control High Reduce or eliminate spill and leakage loss by properly inspecting, containing, and storing hazardous materials and having a cleanup plan that can be quickly and efficiently implemented.
Material storage control.jpg
Better Parking Lot Cleaning High Maintain streets and parking lots frequently and especially in the spring by sweeping, picking up litter, and repairing deterioration; pressure wash pavement only as needed and avoid using cleaning agents.
Better street parking lot cleaning.jpg
Proper Vehicle Management High Ensure that vehicles are fueled, maintained, washed and stored in a manner that prevents the release of harmful fluids, including oil, antifreeze, gasoline, battery acid, hydraulic and transmission fluids, and cleaning solutions.
Proper vehicle management.jpg
Storm Sewer System Maintenance High Regularly clean debris from storm sewer inlets, remove sediment from catch basin sumps, and remove any illicit connections to storm sewer systems.
Storm sewer system maintenance.jpg
Better Impervious Surface Deicing Moderate Properly store and conservatively apply salt, sand, or other deicing substances in order to prevent excessive and/or unnecessary contamination; implement anti-icing and prewet salt techniques for increased deicing efficiency.
Better street parking lot deicing.jpg
Better Turf Management Moderate Ensure that mowing, fertilization, pesticide application, and irrigation are completed in ways that will prevent or reduce grass clippings, sediment, and chemicals from entering storm sewer systems; use native vegetation where possible.
Better turf management.jpg

1 Photo credits


Street sweeping

The primary source control practice for TSS is street sweeping. This Manual currently has a short page describing street sweeping practices as they relate to phosphorus management. However, many of the practices described on that page are relevant for TSS. The page includes a link to a calculator developed at the University of Minnesota. The calculator estimates reductions in wet and dry solids as a function of different management practices.

Several articles in the literature present results from street sweeping studies. Examples include the following.

  • Selbig and Bannerman (2007) found street-dirt yield was reduced by an average of 76, 63, and 20 percent in regenerative-air, vacuum-assist, and high-frequency broom basins, respectively, while low-frequency broom basin showed no significant reductions in street-dirt yield.
  • Brown et al. (2010) showed street sweeping reduced fine sediment mass per unit area in stormwater approximately 50 percent but the minimum practical fine sediment mass per unit area that the street sweeper could achieve was 3.3 grams per square meter.
  • Law et al. (2008) found for a given set of assumptions and sweeping frequencies, it is expected that the range in pollutant removal rates from street sweeping for total solids was 9 to 31 percent, with the lower end representing monthly street sweeping by a mechanical street sweeper and the upper end the pollutant removal efficiencies using regenerative air/vacuum street sweeper at weekly frequencies.
  • Sutherland (2011) provides a comprehensive summary of street sweeping, including information on effectiveness of different sweepers and factors affecting the performance of street sweeping.

Pretreatment

Pre-treatment is needed to protect infiltration and filtration BMPs from the build-up of trash, gross solids, and particulate matter. When the velocity of stormwater decreases, sediment and solids drop out. If pre-treatment is not provided, this process will occur in the infiltration or filtration cell, resulting in long-term clogging and poor aesthetics. Therefore, pre-treatment is a required part of the design for infiltration and filtration BMPs. There are three typical methods for pre-treatment: vegetated filter strips (VFS), forebays, and vegetated swales. These are discussed in the section on pretreatment.

Infiltration

Infiltration practices are structural Best Management Practices (BMPs) designed to capture stormwater runoff and allow the captured water to infiltrate into soils underlying the BMP. Infiltration BMPs are designed to capture a particular amount of runoff. For example, the construction stormwater permit requires that post-construction BMPs capture the first inch of runoff from new impervious surfaces, assuming there are no constraints to infiltration. BMPs designed to meet the construction stormwater permit are required to infiltrate captured water within 48 hours, with 24 hours recommended when discharges are to a trout stream.

TSS removal is assumed to be 100 percent for all water that infiltrates. Any water bypassing the BMP does not receive treatment. Examples of infiltration BMPs, with links to appropriate sections in the Manual, include the following.

The links above take you to the main page for each BMP. Each BMP section has a page on pollutant credits. These credit pages provide information on runoff volume and pollutant removal for the BMP, including credits that can be applied to meet a performance goal such as a Total Maximum Daily Load (TMDL).

In soils where there are constraints on infiltration, BMPs may be designed with underdrains. Unless the BMP is lined, some water will infiltrate through the bottom and sides of the BMP. TSS removal for the portion of captured runoff that infiltrates is 100 percent. Water draining to the underdrain undergoes some treatment. These BMPs are discussed in more detail in the filtration section below.

Settling practices

Information: Note that we refer to constructed ponds and constructed wetlands in this section. Natural ponds and wetlands are not stormwater treatment practices and are therefore not included in this discussion.

If prevention, source control and infiltration practices cannot fully meet protection or restoration targets for stormwater, settling and filtration practices may be used. Settling practices include constructed stormwater ponds, including variants, and constructed stormwater wetlands, including variants. Manufactured devices and forebays are both settling practices but are primarily used for pretreatment.

Constructed ponds are very effective at removing TSS, with removal rates ranging from 60 to 90 percent depending on the design. Constructed wetlands are also very effective at removing TSS, with removal rates ranging from 39 to 81 percent depending on the design.

Information on design, construction, operation and maintenance, credits, and other characteristics of these BMPs can be found on the main pages for constructed stormwater ponds and constructed stormwater wetlands.

Filtration practices

If prevention, source control and infiltration practices cannot fully meet protection or restoration targets for stormwater, filtration practices may be used. Filtration practices include green roofs, media filters, and swales. Vegetated filter strips are often used as a pretreatment practice.

Media filters are very effective at removing TSS, with removal rates ranging from 77 to 90 percent depending on the design. Vegetated filter, including swales, are also effective, with removal rates ranging from 39 to 78 percent depending on the design.

Information on design, construction, operation and maintenance, credits, and other characteristics of these BMPs can be found on the main pages for media filters and swales.

References

This page was last edited on 16 March 2020, at 15:54.

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