Managing Groundwater as Cities Grow: Stormwater Quality Issues and Solutions in the United States
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Urban stormwater can affect groundwater through both natural and modified means. This book examines the potential of urban stormwater to contaminate groundwater. In general, groundwater contamination potential from stormwater is decreased when runoff is infiltrated from a drainage area having little contamination potential. For areas having a high contamination potential, treatment before infiltration is necessary. Depth to groundwater and the character of the underlying soil material also affects contaminant transport to the water table. Increased groundwater infiltration may also increase groundwater seepage to adjacent urban streams.
This book highlights the necessity of understanding the characteristics of the critical pollutants (particulate-bound or filterable), the chemical characteristics of the filterable pollutants, the subsoil characteristics (texture, and clay and organic matter content), and depth (and use) of groundwater. These all affect the best approach to protect local groundwater resources from stormwater contamination. The field projects summarized in the book also highlight a general lack of knowledge of local groundwater conditions (mainly depth to the water table and subsurface soil characteristics) in urban areas. This basic information is needed to better understand the threat to groundwater from recharge with urban stormwater.
Runoff from residential areas (the largest component of urban stormwater for most cities) is generally the least contaminated stormwater flow source and should be considered for infiltration. Very little pretreatment of residential area stormwater runoff would likely be needed before infiltration if surface infiltration is used, such as through grass swales or bioretention systems. If subsurface infiltration devices (French drains, infiltration trenches, dry wells, etc.), which are deeper than surface soils, are used, then additional pretreatment may be needed, such as by using grass filter strips, biofilters, media filters, or other surface filtration devices.