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====[http://stormwater.pca.state.mn.us/index.php/Pollutant_fate_and_transport_in_stormwater_infiltration_systems#Metals_in_stormwater '''Metals''']==== | ====[http://stormwater.pca.state.mn.us/index.php/Pollutant_fate_and_transport_in_stormwater_infiltration_systems#Metals_in_stormwater '''Metals''']==== | ||
− | Metals are typically present at [http://stormwater.pca.state.mn.us/index.php/Pollutant_fate_and_transport_in_stormwater_infiltration_systems low levels] in urban stormwater and are generally retained in the upper soil layers via adsorption to solid particles. They therefore represent a low risk to groundwater. Exceptions may occur under the following conditions: | + | Metals are typically present at [http://stormwater.pca.state.mn.us/index.php/Pollutant_fate_and_transport_in_stormwater_infiltration_systems low levels] in urban stormwater and are generally retained in the upper soil layers via adsorption to solid particles ([http://www.scielo.cl/pdf/jsspn/v10n3/art05.pdf Violante et al.], 2010). They therefore represent a low risk to groundwater. Exceptions may occur under the following conditions: |
*in certain land use settings where concentrations are very high, such as vehicle operations and outdoor storage areas | *in certain land use settings where concentrations are very high, such as vehicle operations and outdoor storage areas | ||
*if soil or media conditions are conducive to metal transport, such as low pH soil or media. [[Glossary#K|Kakuturu and Clark]] (2015) observed displacement and downward migration of metals from bioretention media by sodium at salt concentrations of 150 and 1200 milligrams per liter. | *if soil or media conditions are conducive to metal transport, such as low pH soil or media. [[Glossary#K|Kakuturu and Clark]] (2015) observed displacement and downward migration of metals from bioretention media by sodium at salt concentrations of 150 and 1200 milligrams per liter. |
This page provides information on surface water and groundwater impacts associated with infiltration of stormwater runoff.
The risk of groundwater contamination from different chemicals is summarized below. Specific information for each chemcial can be found at the links below.
Metals are typically present at low levels in urban stormwater and are generally retained in the upper soil layers via adsorption to solid particles (Violante et al., 2010). They therefore represent a low risk to groundwater. Exceptions may occur under the following conditions:
Management strategies to reduce the risk of metals leaching to groundwater include periodic replacement of the upper soil layer within infiltration systems, preventing runoff water containing high concentrations of sodium from entering infiltration BMPs, and maintaining soil conditions favorable to metal attenuation (e.g. near neutral pH).
Because of the diversity of organic compounds, it is difficult to generalize, but typically these are at low concentration in stormwater runoff. Many compounds are attenuated within the infiltration media, where they may be degraded or immobilized. Risk to groundwater from organic chemicals is typically low. BMPs with little or no organic material, particularly underground practices, may present some risk if concentrations of organic chemicals are elevated in stormwater runoff.
Although nitrate is poorly attenuated in most infiltration BMPs, concentrations in stormwater are generally low, resulting in low risk to groundwater.
Phosphorus is strongly attracted to solid particles and the resulting risk to groundwater is low.
Chloride is not attenuated within infiltration systems. Chloride presents a concern for groundwater where concentrations are high in stormwater runoff. This occurs in areas where application of choride-based deicers is high, such as major transportation and high density commercial areas.
Concentrations of pathogens in stormwater runoff are often high. There is limited information on fate and transport of pathogens through infiltration systems. Infiltration practices that utilize media with organic matter are likely to be most effective in attenuating pathogens, while systems with little or no organic matter, particularly underground systems, are less effective. More information is needed on the fate of pathogens in stormwater infiltration systems. Once in groundwater, survival of microorganisms depends on factors such as temperature, pH, and presence of organic matter. Die-off of most microorganisms is fairly rapid, with a three order magnitude decrease in population within 100 days or less. Some organisms, viruses in particular, may survive for one year or more, however (Krauss and Griebler, 2011; Bitton et al., 1983: Toze, 2003).