Pollutant fate and transport in stormwater infiltration systems
As stormwater travels across the land surface into infiltration BMPs, it can pick up various pollutants and deliver them to the subsurface. The fate and transport of these pollutants into soil, the vadose zone and ultimately groundwater depends on the type and amount of pollutant present, the volume of infiltration, the type of infiltration BMP, and subsurface conditions.
Typical stormwater pollutants
Common stormwater pollutants and their most important sources are described in the first table below. The second table provides typical pollutant concentrations in stormwater runoff. The concentrations are based on data from the International Stormwater Database.
Common pollutants of concern and sources in stormwater runoff. Adapted from USGS, 2014.
Link to this table.
| Contaminant | Contaminant source1 |
|---|---|
| Nitrogen | Naturally occurring from vegetation decomposition. Anthropogenic sources include fertilizers, farm-animal waste, faulty septic systems |
| Chloride | Salts applied to roads and parking lots during the winter. Natural sources include mineral dissolution |
| Copper | Industrial and domestic waste, mining, mineral leaching, automobile parts and fluids |
| Zinc | Industrial waste; automobile parts and fluids |
| Manganese | Found naturally in sediment and rocks. Anthropogenic sources include mining waste, industrial waste, automobile parts and fluids |
| Nickel | Naturally occurring. Anthropogenic sources include stainless steel and alloy products, mining, refining, automobile parts and fluids |
| Cadmium | Small amounts are naturally occurring. Anthropogenic sources include industrial discharge, mining waste, automobile parts and fluids |
| Chromium | Old mining operations; fossil-fuel combustion; mineral leaching; automobile parts and fluids |
| Pesticides | Residential use of lawn care products; commercial landscaping; animal wastes; municipal right-of-ways; agriculture; feedlots |
| Cyanide | Road salt; fertilizer production |
| PAHs2 | Auto emissions; elicit discharges; asphalt pavement (driveways, roadways and parking lots) with coal tar sealants3 |
| VOCs2 | Crude oil; insecticides; varnishes; paints; gasoline products; degreasers; municipal maintenance activities |
| Oil and grease | Gasoline products; plastics; dyes; rubbers; polishes; solvents; crude oil; insecticides; inks; varnishes; paints; disinfectants; paint removers; degreasers; automobile fluids |
| Microbes (including fecal coliform, E. coli, and pathogens) | Domestic sewage; animal waste; plant or soil material |
1The list of sources is for stormwater runoff only
2PAHs=polyaromatic hydrocarbons; VOCs=volatile organic compounds
3MPCA, 2014
Source: USGS, 2014, with permission
Concentrations of contaminants found in stormwater. Source: International Stormwater Database7. Because the data below are from a single source, values may differ from those contained on this page. We recommend if you are using emcs to quantify pollutant loading, you use this data instead of data from this table. Note that the table does not include information for chloride, a common pollutant in stormwater. Chloride concentrations vary seasonally and would be misrepresented in a single table. For more information on chloride concentrations in stormwater, see here.
Link to this table.
| Land use | TSS 1 | NO2 + NO3 1 | TN 1 | TP 1 | Cu 2 | Zn 2 | Ni 2 | Cd 2 | Cr 2 | CN 2,5 | Oil and grease 2 | VOCs 2,5 | Pesticides 2,4,5 | FC 3,5 | EC 3,5 | FS 3,5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Commercial | ||||||||||||||||
| Number of sites | 56 | 50 | 13 | 56 | 60 | 62 | 40 | 51 | 38 | 2 | 44 | 4 | 1 | 4 | -- | 3 |
| Number of observations | 857 | 786 | 77 | 948 | 785 | 867 | 291 | 543 | 294 | 6 | 394 | 160 | 6 | 19 | -- | 7 |
| % of samples above detection | 98.7 | 98.9 | 97.4 | 94.5 | 85 | 99.2 | 51.5 | 38.1 | 52.0 | 0 | 65.5 | 65.5 | 0 | 73.7 | -- | 100 |
| Minimum | <0.5 | <0.1 | <1.5 | <0.01 | <0.2 | <0.3 | <1 | <0.03 | <0.7 | n/a | <0.5 | <0.05 | n/a | <200 | -- | 310 |
| Maximum | 2385 | 8.2 | 18.1 | 4.27 | 569.1 | 3050.5 | 110 | 80 | 100 | n/a | 359 | n/a | 28000 | -- | 24000 | |
| Median | 52 | 0.6 | 1.75 | 0.2 | 17 | 110 | 8 | BDL6 | 4 | BDL | 5 | 0.7 | n/a | 450 | -- | 3100 |
| Industrial | ||||||||||||||||
| Number of sites | 58 | 51 | 13 | 57 | 65 | 67 | 43 | 60 | 42 | 2 | 48 | 3 | -- | 6 | -- | 4 |
| Number of observations | 619 | 536 | 85 | 638 | 569 | 627 | 300 | 525 | 312 | 9 | 370 | 144 | -- | 32 | -- | 12 |
| % samples above detection | 99.5 | 97.0 | 95.3 | 95.1 | 85.1 | 98.9 | 58.0 | 48.6 | 72.4 | 0 | 59.7 | 10.4 | -- | 90.6 | -- | 91.7 |
| Minimum | <1 | <0.02 | <1.5 | <0.02 | <0.2 | <0.5 | <2 | <0.03 | <0.7 | n/a | <0.5 | <0.05 | -- | <1 | -- | <1 |
| Maximum | 2490 | 8.4 | 15.2 | 7.9 | 1360 | 8100 | 120 | 334 | 150 | n/a | 408 | -- | 3600000 | -- | 48000 | |
| Median | 75 | 0.68 | 1.7 | 0.23 | 19 | 155 | 10 | BDL | 10 | BDL | 5 | BDL | -- | 3950 | -- | 24000 |
| Residential | ||||||||||||||||
| Number of sites | 146 | 127 | 20 | 148 | 147 | 151 | 77 | 114 | 72 | -- | 95 | 7 | 1 | 10 | 3 | 4 |
| Number of observations | 2257 | 1772 | 131 | 2380 | 1743 | 2013 | 418 | 1123 | 408 | -- | 694 | 210 | 6 | 94 | 19 | 23 |
| % of sample above detection | 99.9 | 99.0 | 98.5 | 98.2 | 86.5 | 97.0 | 42.2 | 40.4 | 48.8 | -- | 56.8 | 20.1 | 0 | 85.9 | 100 | 95.7 |
| Minimum | <0.5 | <0.03 | <1.5 | <0.01 | <0.2 | <0.5 | <0.5 | <0.03 | <0.7 | -- | <0.5 | <0.05 | n/a | <1 | 10 | <1 |
| Maximum | 4168 | 66.4 | 18.3 | 19.90 | 590 | 14700 | 100 | 70 | 70 | -- | 419 | 3.42 | n/a | 5230000 | 35000 | 200000 |
| Median | 58 | 0.60 | 2.24 | 0.26 | 11 | 69.9 | 5 | BDL | 3 | -- | 4 | BDL | BDL | 9400 | 1000 | 23500 |
| Open space | ||||||||||||||||
| Number of sites | 15 | 13 | 4 | 15 | 12 | 12 | 9 | 8 | 7 | 3 | 9 | 1 | -- | 2 | 1 | -- |
| Number of observations | 105 | 109 | 13 | 111 | 44 | 49 | 38 | 41 | 36 | 13 | 26 | 5 | -- | 6 | 5 | -- |
| % of samples above detection | 97.1 | 92.7 | 92.3 | 93.7 | 64.4 | 65.3 | 23.1 | 39.0 | 36.1 | 15.4 | 34.6 | 60.0 | -- | 100 | 100 | -- |
| Minimum | <1 | <0.1 | <0.5 | <0.01 | <0.8 | <5 | <2 | <0.04 | <0.7 | <0.01 | <1 | <0.2 | -- | 1900 | 100 | -- |
| Maximum | 4168 | 3.4 | 3.3 | 0.76 | 210 | 390 | 100 | 8 | 120 | 0.08 | 11 | 0.84 | -- | 63000 | 4700 | -- |
| Median | 58 | 0.5 | 1.1 | 0.129 | 6 | 25 | BDL | BDL | BDL | BDL | BDL | 0.77 | -- | 2150 | 1100 | -- |
| Rooftop | Water quality from rooftops varies with the type of roof. For more information see the section on Water quality considerations for stormwater and rainwater harvest and use/reuse | |||||||||||||||
TSS=total suspended solids, NO2=nitrite, NO3=nitrate, TN=total nitrogen, Cl=chloride, Cu=copper, Zn=zinc, Ni=nickel, Cd=cadmium, Cr=chromium, CN=cyanide, VOC=volatile organic compound, FC=fecal coliform, EC=E. coli, FS=fecal streptococci
1 Concentrations are in milligrams per liter
2 Concentrations are in micrograms per liter
3 Concentrations are in Number per 100 milliliters
4Data is for trans-1,3-Dichloropropene and bromomethane
5 Data was selected from states with a similar climate to MN. The appropriate states were determined using Figure 1.3 from the Stormwater BMP Design Supplement for Cold Climates document.
6BDL = below detection level
7The following censoring techniques were used for this data:
- If detection rates were 90% or greater, a value of "0" was substituted for non-detects.
- If detection rates were greater than 50% but 90% or less, a value of 1/2 the detection limit was substituted for non-detects.
- If detection rates were 50% or less, the median was assumed to be below the method detection level.
Nitrogen
| Summary of characteristics of nitrate-nitrogen. Sources:Pitt et al., 1994, 1999; Weiss et al., 2008; ATSDR, 2011. | |
| Mobility | Mobile |
| Solubility | High |
| Abundance in stormwater | Low/moderate |
| Toxicity | Low. Primary concern is for infants less than 3 months in age. |
| Degradation potential | High in anaerobic environments; low in aerobic environments |
| Adsorption/absorption | Low |
| Plant uptake | High |
| Potential risk to groundwater | Low/moderate based on high mobility but relatively low concentrations in urban stormwater. |
Nitrogen can be found in many forms in the stormwater runoff/infiltrating water, with the most common forms being ammonia, nitrate, and nitrite. Nitrate is estimated to be the most common nonpoint-source groundwater contaminant in the world (Gurdak & Qi, 2012). Despite its high solubility, nitrite is detected with much less frequency than nitrate because nitrite oxidizes rapidly to form nitrate. Nitrogen, expressed as total nitrogen (TN), was detected in approximately 97 percent of the 4,077 samples submitted to the International Stormwater Database. nitrate was detected in 100 percent of 12 samples, and nitrite was detected in 83 percent of 6 samples.
In regards to the toxicity of nitrogen, ammonia and nitrate are two forms of particular concern. As ammonia undergoes nitrification, it uses large amounts of oxygen. This in turn can kill fish and other aquatic wildlife. When nitrate contaminates drinking water at high levels, it can lead to the phenomenon known as “blue baby syndrome” which affects babies less than 6 months old (Prey et al., 2000). Nitrates and nitrites have not been classified as carcinogenic, however a metabolic pathway exists that lead to formation of N-nitroso compounds, some of which are carcinogenic. (ATSDR, 2011). Areas at risk for contamination of shallow groundwater due to nitrogen are shown in Figure 1.4.