Total Suspended Solids (TSS) in stormwater
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 accounts for about 25 to 35 percent of TSS (, ).
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).
Concentrations of TSS in urban stormwater runoff are highly variable. Concentrations are similar across different land uses. Data below are from the International Stormwater Database, Version 3 (2008). For additional information, Lin (2004) provides a good review of published event mean concentration data.
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 export coefficients are shown below (data adapted from studies cited in Lin (2004)).
Residential: 76 pounds per acre
Mixed residential: 111 pounds per acre
Commercial: 221 pounds per acre
Industrial: 193 pounds per acre
Freeway: 560 pounds per acre
Open space: 35 pounds per acre
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 CWA requirements, meeting local water quality goals or requirements, and meeting non-regulatory targets. CWA requirements include antidegradation, TMDL limits, and NPDES permit requirements. Each of these are described below.