Groundwater contamination potential from infiltration of urban stormwater runoff

Infiltration of urban stormwater runoff is becoming more common in many areas of the United States and throughout the world. For infiltration to be successful as a stormwater management strategy, however, it is imperative that suitable sites be identified and their lifespan and maintenance requirements be predicted. Infiltrating in unsuitable areas can result in groundwater contamination and associated impairment of beneficial uses. This paper reviews several categories of urban stormwater pollutants and their groundwater contamination potential. Case studies, both from the field and the laboratory, then are presented to summarize information regarding the potential factors affecting pollutant transport through the vadose zone. Finally, two levels of prediction models to assess the susceptibility of groundwater contamination from urban stormwater infiltration are presented. However, the current use of these models is limited by the lack of supporting data, especially the lack of fundamental research into the processes controlling stormwater treatment in the vadose zone. Preliminary methods to address these deficiencies are presented, but, similar to the models, these are screening tools only. Until these deficiencies are addressed (for example, as outlined at the end of the chapter), the models should be seen as providing guidance and as preliminary screening tools, not as providing absolute answers.