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Summary information - total suspended solids (TSS) concentrations in stormwater runoff
Land use	Recommended emc TSS (mg/L)
Commercial	75
Industrial	93
Residential	73
Freeways/transportation	87
Mixed
Open space	21
Conventional roof	< 10
NOTE: For recommendations on adjusting these values or for land uses not included above, see the table Event mean concentrations for total suspended solids

This page provides information on event mean concentrations of total total suspended solids (TSS) in urban stormwater runoff. For a discussion of TSS in stormwater runoff, including information on sources, fate, and water quality impacts, see Total suspended solids.

Objective

Event mean concentration (EMCs) are used in several models for predicting water quality impacts from stormwater runoff and stormwater treatment practices. This page provides summary information that can be used for selecting appropriate EMCs. For a discussion of event mean concentrations, see Stormwater pollutant concentrations and event mean concentrations.

Information: Many factors affect total suspended solids concentrations in stormwater. If you are unfamiliar with the concept of event mean concentrations, We recommend you first read Stormwater pollutant concentrations and event mean concentrations

Methodology

We conducted a review of literature to develop the EMCs shown on this page. Nearly all studies provided summary information; we therefore did not analyze raw data with the exception of data from Capitol Region Watershed District (see discussion below). We compiled the summary information into a spreadsheet and conducted simple statistical analysis of the information.

Data from the following studies were used to generate emcs for total suspended solids.

• National Stormwater Quality Database. This dataset provides data from several nationwide studies. We used only data from region 1, which includes Minnesota and states with similar rainfall patterns. Data were compiled for four land uses: Commercial (n=165), industrial (n=84), residential, (n=249), and open space (n=6).
• Lin (Review of Published Export Coefficient and Event Mean Concentration (EMCs) Data. This report includes summaries of multiple studies conducted in North America. Data existed for all land uses included in the table presenting recommended emcs.
• Washington District Department of the Environment - Selection of Event Mean Concentrations (EMCs). This study summarized data from studies in the Washington D.C. area. Land uses included commercial, roadway/highway, industrial, forest/open, and residential.
• U.S. Environmental Protection Agency, 1983, Results of the Nationwide Urban Runoff Program—Executive summary. Land uses included commercial and residential.
• Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, Texas, 1992–93. Included commercial (n=42), residential (n=77), industrial (n=63) land uses.
• A review of sediment and nutrient concentration data from Australia for use in catchment water quality models . A compilation of multiple studies from Australia. Included forest (n=68) and mixed (n=36) land uses.
• Characterization of Urban Runoff Pollution between Dissolved and Particulate Phases . Study of five sites in China. Land uses included roof and transportation (roads).
• Quality Of Wisconsin Stormwater, 1989-94. Samples from mixed land use in Wisconsin (n=204).
• Analysis of Nonpoint Source Pollution Runoff from Urban Land Uses in South Korea. 23 samples in Korea from high density residential, medium desntiy residential, industrial, institutional land uses.
• Seasonal Performance Variations for Storm-Water Management Systems in Cold Climate Conditions. 15 samples from transportation land use in New Hampshire.
• Determination of event mean concentrations and first flush criteria in urban runoff. 31 samples from transportation land use in Los Angeles.
• Multiple linear regression models of urban runoff pollutant load and event mean concentration considering rainfall variables. 45 samples from commercial, industrial, and high density land uses.
• Stormwater runoff driven phosphorus transport in an urban residential catchment: Implications for protecting water quality in urban watersheds. 29 events from low density land use in Florida.
• Sources of phosphorus and street dirt from Two Urban Residential Basins in Madison, Wisconsin, 1994-95. 25 samples from medium density land use in Wisconsin.
• Nutrient Sources in Urban Areas – A Literature Review. Report summarizing multiple studies in Colorado. Land uses include residential, mixed, commercial, and open space.
• Contribution of surface runoff from forested areas to the chemistry of a through-flow lake. Forested land use in Poland.

Event mean concentrations for total suspended solids

Pollutant loads in stormwater runoff equal the pollutant concentration times the runoff volume. Thus, when calculating pollutant loading, it is necessary to consider not only the event mean concentration but factors affecting the volume of runoff. For most models and calculations, this requires adjusting curve numbers or runoff coefficients to account for differences in directly connected impervious surface between different land uses. There may be other adjustments to volume, such as accounting for interception by trees. See the discussion [Accounting for differences in pollutant loading].

The following table summarizes results from our literature review. The table includes a range of values observed in the literature. Note this range does not represent a statistically-derived range but instead is based on a combination of data analysis and best professional judgement. For example, we did analyze the data for outliers, but also omitted entire studies if we felt the data were not representative of conditions likely to be encountered in Minnesota. To see the full range of values compiled from the literature, open the Excel spreadsheet containing the data.

Residential land use

Studies from the literature frequently provide concentrations for residential land use or occasionally for different types of land use, typically low-, medium-, or high-density residential. Most studies do not define criteria for dividing residential land use into these subcategories. Various definitions can be found in the literature. We use the following definitions.

• Residential: land use where the current or intended use includes, but is not limited to, housing (single and multiple dwellings), educational facilities, day care, agricultural land, correctional facilities, custodial care or long term health care.
• High-density residential: More than 10 units per acre; can include multiple-occupant dwellings
• Medium-density residential: 1-10 dwellings per acre; can include multiple-occupant dwellings
• Low-density residential: one dwelling per 1-5 acres; can include multiple-occupant dwellings

Note that residential land uses can include other land uses, such as commercial and industrial. Many studies therefore classify land uses as mixed or urban, even though a specific land use may dominate a particular area.

Because of the variable and arbitrary manner in which residential land use is classified, we provide a single recommended value for event mean concentrations in residential land uses. We provide additional discussion below so that users can adjust this recommended value depending on local conditions. We used the following references for generating a recommended value for residential land use.

• Wisconsin; 10 sites; n=25; median=46
• Korea; 6 sites; n=23; median=63.3
• LA; 2 sites; 4 samples; median = 91.2
• NURP median = 101
• Dallas median = 78
• China median = 68
• NSQD 250 sites; median = 92 (region 1)
• Line 42

We chose these studies because they contained large amounts of data and they were located in humid and sub-humid areas of the U.S. The median of the above 7 values is 73 mg/L.

Information: The recommended event mean concentration for total suspended solids in residential areas is 77 mg/L

Commercial land use

"Commercial land use is the use of land for commercial purposes including building offices, shops, resorts and restaurants as opposed to construction of a residential house" (Reference, accessed December 24, 2019). Commercial areas considered in this analysis do not include areas used for commercial crop production.

We used the following studies in our analysis. Commercial

• NSQD; n=164; median = 97.15
• NURP median = 69
• Dallas median = 42
• L.A.; n=5; mean = 49.6
• China Median = 81
• Harper87.7

The median concentration from these studies is 75 mg/L.

Information: The recommended event mean concentration for total suspended solids in commercial areas is 75 mg/L

Industrial land use

We used the following studies in our analysis.

• NSWD; n=84; median=70
• Dallas median = 104
• Korea median = 78.8; 6 sites
• LA median = 92.2; 6 sites
• Harper93.3
• Line 170

The median TSS concentration from these studies is 93 mg/L. TSS concentrations do not appear to vary much across different industrial land uses, with the primary sources likely being road salt and atmospheric deposition. However, the following may contribute to higher TSS loads in industrial areas.

• Cleaning and washing operations
• Heavy vehicle traffic
• Specific industries such as food processing plants, meat packing plants and lockers, metal finishing facilities, and industries that generate or handle animal waste (including human sources)

Information: The recommended event mean concentration for total suspended solids in industrial areas is 93 mg/L

Open space

Open space consists of land that is undeveloped. Typically it will not contain buildings or other built structures. Many open spaces are accessible to the public. Open space generally consists of green space (land that is partly or completely covered with grass, trees, shrubs, or other vegetation). Abandoned parcels lacking structures may be considered open space, but it is generally more accurate to include these areas in the land use that existed prior to the parcel being vacant, or including it in adjacent land use categories. The following references were used to generate a recommended value a TSS emc for open space.

• NSQD; n=6; median = 20.5
• NURP median = 70
• Harper11.1

Parks and recreation areas are generally included in open space.

Information: The recommended event mean concentration for total suspended solids in open space, urban parks, and urban recreations areas is 21 mg/L

Transportation corridors, highways, and freeways

This land use includes major transportation corridors where the land use is exclusively transportation. These areas are typically highly impervious and may include only small vegetated areas consisting of swales or medians, and relatively small right-of-way areas. This land use does not include arterial streets in residential, commercial, and industrial areas. The following references were used to generate a recommended value a TSS emc for open space.

• China median=86.72
• Fort Worth median =90; n=27
• New Hampshite median = 55.54; n=27
• LA median = 87.54; n=39
• Harper50.3

The median value from these studies is 87 mg/L.

Information: The recommended event mean concentration for total suspended solids in transportation areas is 87 mg/L

TSS concentrations from transportation corridors are highly variable depending on inputs. The primary inputs include road salt, sediment, and vehicle-related wastes, including oil. The recommended value should be adjusted based on vehicle traffic and likely suspended solids sources and inputs.

Roofs

Information: The recommended event mean concentration for total suspended solids in runoff from conventional (non-green) roofs is less than 10 mg/L

Mixed land use

• DC median = 47.25; 4 sites
• Australia; n=49; median=105
• Korea median = 153.3
• Korea median =76; n=45
• WI median = 188; 2 sites
• NURP median=67

An emc can be calculated if the total area of interest (A_total), the area of each land use in the area of interest, and the emc for each land use in the area of interest are known.

Site emc = Σ₁ⁿ ((A_{Area 1} * emc_{Area 1})/ (A_total) + ... ((A_{Area n} * emc_{Area n}) / (A_total)

where A = area in acres.

Example calculation

• 10 acres of residential; emc = 0.325 mg/L
• 10 acres of commercial; emc = 0.200 mg/L
• 10 acres of industrial' emc = 0.235 mg/L
• 1 acre of transportation; emc = 0.28 mg/L

Overall emc = ((0.325 * 10)/31) + ((10 * 0.200)/31) + ((10 * 0.235)/31) + ((1 * 0.28)/31) = 0.254 mg/L

NOTE: To calculate loads for a mixed land use, a curve number or runoff coefficient must be calculated based on the impervious surface for each of the land uses.

Event mean concentrations for total suspended solids

References

• Schiff, Kenneth C., and Liesl L. Tiefenthaler. 2011. Seasonal flushing of pollutant concentrations and loads in urban stormwater. Jour. Amer. Water Works Assoc. 47:1:136-143
• Yang, Yun-Ya, and Gurpal S. Toor. 2018. runoff driven phosphorus transport in an urban residential catchment: Implications for protecting water quality in urban watersheds. Scientific Reports. 8:1-10
• University of Wisconsin at Milwaukee. Phosphorus Speciation and Loads in Stormwater and CSOs of the MMSD Service Area (2000 – 2008) Final Report: February, 2011
• Lee-Hyung Kim. 2003. Determination of event mean concentrations and first flush criteria in urban runoff. Environ. Eng. Res. 8:4:163-176.
• Jae-Woon Jung, Ha-Na Park, Kwang-Sik Yoon, Dong-Ho Choi, Byung-Jin Lim. 2013. Event mean concentrations (EMCs) and first flush characteristics of runoff from a public park in Korea. Journal of the Korean Society for Applied Biological Chemistry. October 2013, Volume 56, Issue 5, pp 597–604.