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TSS in Stormwater: Analysis and Impact (Part 1 of 3)

Total Suspended Solids (TSS) problems? Unfortunately, it’s everywhere. However, if you are dealing with TSS issues on your industrial site there are some things you should know about where it might be coming from and what you can do about it through Best Management Practices (BMPs). Don’t worry, all is not lost when it comes to dealing with TSS. Our three-part series is going to dive into the details of TSS from its’ the analysis in the laboratory and what TSS can do to the environment (Part 1) to potential sources of TSS on your industrial site (Part 2) to finally, some solutions or BMPs for your industrial facility (Part 3).


First off, a little background on TSS. TSS is defined as the suspended particulates in stormwater with a diameter greater than 1.5 microns that do not pass through a glass fiber filter. The suspended particulates that are used to determine a TSS concentration include both inorganic and organic constituents. That means those little pieces of mulch or silica sand both count towards a TSS concentration in a water quality sample. Samples for TSS analysis are collected using a clean, plastic bottle with no preservative (e.g. HCl or HNO3) and sent to an analytical laboratory.


Filter from TSS sample

In the laboratory, the industrial stormwater sample’s volume is measured and then filtered through a glass fiber filter. The filter(s) and suspended materials that are captured are dried in an oven and the mass recorded after drying. The end TSS result is mass (milligrams [mg]) of solids over the volume of the stormwater sample (liters [L]) and is reported in milligrams per liter (mg/L) for an industrial stormwater general permit (IGP and ISGP) and multi-sector general permit (MSGP) purposes.


Stormwater Benchmarks

For IGP and MSGP, there is typically a stormwater benchmark of 100 mg/L for TSS. For example, the United States Environmental Protection Agency (USEPA)’s MSGP, which is used by Massachusetts, New Hampshire, New Mexico, Idaho, and Washington DC, has a TSS benchmark of 100 mg/L. Likewise, Washington and Oregon also use a TSS benchmark in their industrial stormwater permits of 100 mg/L and California’s IGP has an annual Numeric Action Level (NAL), basically a benchmark, of 100 mg/L. However, for 303d or impaired waterbodies in Washington, a benchmark of 30 mg/L is used and in California, the instantaneous NAL is 400 mg/L, meaning two samples with TSS concentrations over 400 mg/L is an exceedance (uh oh!). Without getting too much in the weeds on an individual state’s permit specifics on TSS concentrations, it is useful to know that 100 mg/L is generally the benchmark in the United States.

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