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The Influence of Stormwater Management Practices and Wastewater Infiltration on Groundwater Quality: Case Studies
Beak, D., M. Borst, Steve Acree, R. Ross, Ken Forshay, R. Ford, J. Huang, C. Su, J. Brumley, A. Chau, AND C. Richardson. The Influence of Stormwater Management Practices and Wastewater Infiltration on Groundwater Quality: Case Studies. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-20/143, 2020.
The use of green infrastructure (GI) in many areas could potentially mitigate local problems such as flooding, water shortages, etc. The data collected can be used by state and local agencies to understand under what conditions groundwater quality may or may not be adversely impacted by the use of GI.
In 2015, U.S. EPA initiated a study to examine the potential impacts to groundwater quality from the use of GI and the results will be presented in this report. This study was conducted under the Safe and Sustainable Water Resources program (SSWR). An overarching objective of the SSWR program is to support increased adoption of green infrastructure into community stormwater management plans and watershed/sewershed sustainability goals by providing information and guidance. As part of this SSWR project, three diverse locations were selected to study based on climate, geology, type of infrastructure used, and geographic location. The three sites are Louisville, Kentucky, Fort Riley, Kansas, and Yakima, Washington. The Louisville site is located in the CSO-190 sewershed and primarily uses underground storage galleries as the GI to capture the stormwater runoff. The Louisville study site has a humid sub-tropical climate. The Yakima site has an arid climate and the study is unique because wastewater is being infiltrated on the flood plain of the Yakima River. The Fort Riley site has a permeable pavement system that infiltrates stormwater runoff and is located at Seitz Elementary School on U.S. Army Fort Riley post. Fort Riley is in north eastern Kansas which has a humid sub-tropical climate. The purpose of this report is to draw conclusions from these studies to provide an initial assessment on the influence of GI on groundwater quality. This assessment will look at the individual site monitoring data through the autumn of 2018. In general, all three studies measured a common set of geochemical and groundwater parameters and fall into the following general categories: field parameters, carbon species, nutrients, anions, dissolved metals, and stable isotopes of water. With a few exceptions within any category the measured parameters were identical. The Fort Riley study had additional organic parameters measured that were not measured in the other two studies. For the two studies that used engineered GI systems, Louisville and Fort Riley, the hydrology of the system was investigated. The hydrology investigations of the system used sensors, hydrogeological methods, and geophysical tools to understand the movement of water in the system. Key observations and findings were as follow. All three studies showed changes in groundwater quality. Mixing infiltrate water with groundwater can cause groundwater changes downgradient of the GI infrastructure. One of the greatest risks to groundwater quality is the dilution effect caused by the infiltration of stormwater into the groundwater. Dilution of the groundwater by the infiltrated water could change the drinking water source chemistry and impact water treatment. Dilution can be problematic if the groundwater is used as a source of drinking water. Reverse ion exchange is potentially occurring at the Louisville and Fort Riley study sites. Increased sodium loading on the fine-grained particles in the vadose zone could lead to clogging of the pore spaces and diminish infiltration and water movement. The concentration of traditional stormwater contaminants did not pose a concern with the potential exception of chromium in the groundwater in Louisville. Phosphate concentrations increased once infiltration of water began although the phosphate concentration increases in the Fort Riley study may not be related to GI. The solubility and mobility of barium was affected by the concentrations of chloride. When chloride concentrations increase the barium concentrations also increased. The converse was also true. This relationship between chloride and barium can also happen with other metals such as cadmium. The enhanced mobility of some metals could be potentially problematic when chloride salts are applied as de-icing agents and the stormwater is infiltrated.
URLs/Downloads:EPA600R20143_APPENDICES2OF2.PDF (PDF, NA pp, 10821 KB, about PDF)
EPA600R20143_APPENDICES1OF2.PDF (PDF, NA pp, 9984 KB, about PDF)
THE INFLUENCE OF STORMWATER MANAGEMENT PRACTICES AND WASTEWATER INFILTRATION ON GROUNDWATER QUALITY-CASE STUDIES.PDF (PDF, NA pp, 12060 KB, about PDF)