Microbial pathogens and contaminants of emerging concern in groundwater at an urban subsurface stormwater infiltration site

Authors: DE DAMBERT, JANE - MINNESOTA DEPARTMENT OF HEALTH; WALSH, JAMES - MINNESOTA DEPARTMENT OF HEALTH; SCHER, DEANNA - MINNESOTA DEPARTMENT OF HEALTH; FIRNSTAHL, AARON - U.S. GEOLOGICAL SURVEY (USGS); BORCHARDT, MARK

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2021
Publication Date: 2/10/2021
Citation: De Dambert, J.R., Walsh, J.F., Scher, D.P., Firnstahl, A.D., Borchardt, M.A. 2021. Microbial pathogens and contaminants of emerging concern in groundwater at an urban subsurface stormwater infiltration site. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2021.145738.
DOI: https://doi.org/10.1016/j.scitotenv.2021.145738

Interpretive Summary: Stormwater runoff in urban areas can pollute nearby surface water (lakes and rivers) with microorganisms and household products such as cleaners and artificial sweeteners. To prevent runoff from reaching surface water one idea is to capture it and place it underground to be filtered by soil. We studied a stormwater capture system in Minneapolis, Minnesota and measured the pollutants as they moved downward through the soil and into groundwater. Pollutant concentrations in the soil and groundwater beneath the capture system were less than the original concentrations in the stormwater. Concentrations decreased as the pollutants moved downward. However, when it rained the concentrations of microorganisms were not as effectively diminished. The capture system was located at a site with fine-grained soils, which improved pollutant reduction. Other stormwater capture systems located at sites with more vulnerable groundwater may not be as effective. Drinking water for urban residents is often supplied by groundwater pumped from wells located in the city. The information gained from this study will help with locating urban stormwater capture systems in ways that avoid contaminating nearby drinking water wells.

Technical Abstract: Urban stormwater may contain a variety of pollutants, including viruses and other pathogens, and contaminants of emerging concern (pharmaceuticals, artificial sweeteners, and personal care products). In vulnerable geologic settings, the potential exists for these contaminants to reach underlying aquifers and contaminate drinking water wells. Viruses and other pathogens, as well as other contaminants of emerging concern were measured in stormwater and groundwater at an urban site containing a stormwater cistern and related subsurface infiltration gallery, three shallow lysimeter wells, and a monitoring well. Five of 12 microbial targets were detected more than once across the eight rounds of sampling and at multiple sampling points, with human-specific Bacteroides detected most frequently. The microbial and chemical contaminants present in urban stormwater were much lower in the water table monitoring well than the vadose zone lysimeters. There may be numerous causes for these reductions, but it is likely they are related to transit across fine-grained sediments that separate the water table from the vadose zone at this location. Precipitation amount prior to sample collection was significantly associated with microbial load. The reduction in number and concentrations of contaminants found in the monitoring well suggests that while geologically sensitive aquifers receiving urban stormwater effluent in the subsurface may be prone to contamination, those with a protective cap of fine-grained sediments are less vulnerable. These results can inform stormwater infiltration guidance relative to drinking water wells, with an emphasis on restricting infiltration near water supply wells finished in geologically sensitive aquifers to reduce public health risks.