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

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.

• Heavy metals. Heavy metals are typically present at 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 except in certain specific areas, such as vehicle operations and outdoor storage areas. Eventual breakthrough can occur in filter media due to the finite sorption capacities of the media. Periodic replacement of the upper soil layer within infiltration systems will maintain low soil concentrations and decrease the potential for contaminating groundwater.
• 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.

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., 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.

Related pages

• Overview
• Pre-treatment considerations for stormwater infiltration
• BMPs
• Pollutant fate and transport in stormwater infiltration systems
• Groundwater mounding
• Setback distances
• Karst
• Shallow soils and shallow depth to bedrock
• Shallow groundwater
• Soils with low infiltration capacity
• Potential stormwater hotspots
• Wellhead protection
• Contaminated soils and groundwater
• Decision tools
• Research needs
• References for stormwater infiltration