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Minnesota Stormwater Manual

Surface water and groundwater quality impacts from stormwater infiltration
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This page provides information on surface water and groundwater impacts associated with infiltration of stormwater runoff.

Groundwater

Although data are still limited, there has been increasing work done of assessing groundwater impacts associated with stormwater infiltration. The following discussion summarizes the current state of knowledge on the topic.

Potential risk of different chemicals to groundwater

The risk of groundwater contamination from different chemicals is summarized below. Specific information for each chemcial can be found at the links below.

Metals

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:

  • 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. 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 adsorption sites are exhausted. Breakthrough is not expected for decades in most media.

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).

Organic compounds (Pesticides; PAHs; VOCs)

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.

Nitrate

Although nitrate is poorly attenuated in most infiltration BMPs, concentrations in stormwater are generally low, resulting in low risk to groundwater.

Phosphorus

Phosphorus is strongly attracted to solid particles and the resulting risk to groundwater is low.

Chloride

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.

Pathogens

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).

Literature review

  • Weiss et al., 2008. This paper, Contamination of Soil and Groundwater Due to Stormwater Infiltration Practices - A Literature Review, provides a review of dozens of articles from peer-reviewed scientific and engineering journals.
  • Nieber et al., 2014. This paper, The Impact of Stormwater Infiltration Practices on Groundwater Quality summarizes results from monitoring studies conducted at three infiltration practices. The sites included an infiltration basin, a large rain garden (bioinfiltration), and an underground infiltration system. Lysimeters were employed beneath the practices to determine the quality of infiltrating stormwater.
  • Pitt et al. (2002). The authors discuss the potential for groundwater contamination resulting from stormwater infiltration. Groundwater risk is evaluated based on three factors: chemical mobility, abundance of the chemical in stormwater runoff, and the likelihood of the chemical being attenuated through sedimentation practices, with the most limiting of these factors determining the risk. Table 1 in the paper provides a summary of the risk to groundwater for several chemicals that may potentially impact groundwater. The paper includes additional references and work done by the same authors in the 1990's.
  • Pitt et al., 1996; 2002. These papers present an analysis of the contamination potential for a wide range of stormwater constituents. The authors evaluate groundwater risk based on three factors: chemical mobility, abundance of the chemical in stormwater runoff, and the likelihood of the chemical being attenuated through sedimentation practices, with the most limiting of these factors determining the risk. A table summarizes this information for a large number of chemicals of potential concern.
  • Clark and Pitt. This paper, Proposed Evaluation Methodology for Predicting Groundwater Contamination Potential from Stormwater Infiltration Activities, presents a 3 step process for predicting groundwater contamination potential.
  • Environmental Protection Agency. Groundwater Impacts. This webpage provides a list of 24 articles, most published in peer-review journals, with links, that address the topic of stormwater infiltration and groundwater quality.

Summary of field monitoring studies

Nieber et al. (2014) monitored leachate through three infiltration BMPs using lysimeters. The study was conducted over an 18 month period. The three BMPs included an infiltration basin, a large infiltrating rain garden ed within Como Park, and an infiltration gallery constructed in a formerly industrial area. Below is a summary of results. Note, the authors do not provide summary statistics in the report.

  • Nitrate
    • The drinking water standard was exceeded in 4 percent of samples, with exceedances occurring at the rain garden and infiltration basin sites. The infiltration basin site receives runoff from agricultural fields and animal housing units and this may account for the occasional elevated nitrate levels.
    • Median concentrations at the rain garden and underground sites were less than 1 milligram per liter (the drinking standard is 10 milligrams per liter).The median concentration at the infiltration basin site was about 3 milligrams per liter, but as stated earlier, this BMP receives runoff from agricultural fields and animal housing units.
  • Chloride
    • Chloride concentrations in leachate exceeded the drinking water standard of 250 milligrams per liter in 15 percent of samples. The rate of exceedance was similar for all three BMPs.
    • The median concentration was about 20 milligrams per liter.
  • Metals (metals sampled included cadmium, chromium, copper, lead, nickel, and zinc)
    • Concentrations of metals in leachate were well below drinking water standards for all metals except lead.
    • The standard for lead was exceeded in 8 percent of samples. The lead was considered to be associated with historical use of lead and therefore may represent a legacy contaminant.


Related pages

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