Total Suspended Solids (TSS) in stormwater

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 suspended solids.
Link to this table

Land cover/land use	Range (mg/L)	Recommended value (mg/L)	Notes
Commercial	42-164	75	If applicable to models being used, adjust curve numbers/runoff coefficients when calculating loads
Industrial	70-170	93	If applicable to models being used, adjust curve numbers/runoff coefficients when calculating loads
Residential	42-101	73
High-density/Multi-family residential		Calculate	Insufficient information to recommend a specific emc
Medium density residential		Calculate	Insufficient information to recommend a specific emc
Low density residential		Calculate	Insufficient information to recommend a specific emc
Freeways/transportation	50-90	87
Mixed	47-188	76 or calculate	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
Open space	11-70	21
Conventional roof		<20
Institutional	17-140	80
Forest/shrub/grassland	26-140	72	Sediment concentrations from forested areas vary widely with factors such as slope and forest condition. Concentrations may be very high, but the annual volume of runoff is typically much less than non-forested areas.
Open water and wetlands		see Notes (next column)	If data exist, use the TSS concentration for the water body of interest If data for a specific water body do not exist, use data from similar lakes in the area
Cropland (row crops)	50-160		Literature review was not adequate to recommend an emc
Pasture	75-150	84	Concentrations are a function of intensity of 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.

• Forms and guidance for TMDLs: includes information on completing the TMDL Annual Report form and other guidance documents.
• Information on modeling, including Available stormwater models and selecting a model and Detailed information on specific models.
• Information on pollutant removal by BMPs. Pollutant removal information is limited to structural BMPs. Each BMP included in the manual also has a section on credits, which provides useful information for determining pollutant removal for TSS for that BMP.

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.
Exposed Soil Repair	High	Use native vegetation or grass to cover and stabilize exposed soil on lawns to prevent sediment wash off.
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.
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
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.
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 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.

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
Wind Erosion Control	High	Institute a local program for wetting of open construction surfaces and other sources for windblown pollutants.
Streambank Stabilization2	High	Repair erosion occurring on a streambank of lakeshore in a timely manner; inspect bank areas for ice damage in the spring.
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.
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.
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.
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.
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 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.
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.
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.

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
Wind Erosion Control	High	Institute a local program for wetting of open construction surfaces and other sources for windblown pollutants.
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.
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.
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.
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.
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 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.

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.

• Infiltration basin, infiltration trench, underground infiltration
• Bioinfiltration (rain garden or bioretention with no underdrain)
• Permeable pavement
• Trees
• Dry swales with check dams

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 dry 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 dry 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

• Brown, S., Susfalk, R., Fellers, D., and B. Fitzgerald. 2011. Effectiveness of Street Sweeping in Incline Village, NV. Nevada Tahoe Conservation District. 78 pp.
• Hopke P.K., Lamb R.E., and F.S. Natusch. (1980) Multielemental characterization of urban roadway dust. Environ Sci Technol 14:164–172.
• Law, N.L., DiBlasi, K., and U. Ghosh 2008. Deriving Reliable Pollutant Removal Rates for Municipal Street Sweeping and Storm Drain Cleanout Programs in the Chesapeake Bay Basin. Center for Watershed Protection.
• Lin, J.P. 2004. Review of Published Export Coefficient and Event Mean Concentration (EMC) Data. WRAP Technical Notes Collection (ERDC TN-WRAP-04-3), U.S. Army Engineer Research and Development Center, Vicksburg, MS.
• Line, D.E., M. B. Shaffer, J. D. Blackwell. 2011. Sediment Export from a Highway Construction Site in Central North Carolina. Transactions of the ASABE. 54(1): 105-111.
• Line, D.E., J. Blackwell, M. Shaffer, and J. Spooner. 2009. Demonstrating and Evaluating Low Impact Development Techniques. North Carolina State University Biological and Agricultural Engineering Dept. 15 pp.
• Selbig, W.R. and R. T. Bannerman. 2007. Evaluation of Street Sweeping as a Stormwater-Quality-Management Tool in Three Residential Basins in Madison, Wisconsin. USGS Scientific Investigations Report 2007–5156.
• Sutherland, R. 2011. Street Sweeping 101. Stormwater. January-February 2011.
• Taylor, K.G., and P. N. Owens. 2009. Sediments in urban river basins: a review of sediment-contaminant dynamics in an environmental system conditioned by human activities. J Soils Sediments (2009) 9:281–303.
• United States Environmental Protection Agency. 1999. Preliminary Data Summary of Urban Storm Water Best Management Practices. EPA-821-R-99-012.
• Wolman, M. G. and Schick, A. P.. 1967. Effects of construction on fluvial sediment; urban and suburban areas of Maryland. Water Resources Res., v. 3, No. 2.