Investigating Stormwater Hydrocarbon Fate and Biodegradation in Bioretention Areas

April 2012

“Conventional” stormwater mitigation practices, i.e., retention ponds, appear ineffective at controlling some pollutants (Kamalakkannan et al. 2004; Weinstein et al. 2010). For example, polycyclic aromatic hydrocarbons (PAHs) tend to accumulate in retention pond sediments suggesting that ponds are unable to attenuate this important class of pollutants (Kamalakkannan et al. 2004; Weinstein et al. 2010). Low impact development (LID) is an alternative stormwater management approach that reduces negative impacts of stormwater on the watershed by using infiltration to mimic the native hydrology (National Research Council 2008). One common LID best management practice (BMP) in use is bioretention. Bioretention cells, also called raingardens or bioinfiltration practices, are shallow vegetated depressions containing an engineered soil or media (e.g., compost-amended sand) into which stormwater from impervious surfaces is directed for infiltration. Current research indicates that properly designed and installed raingardens are effective at infiltrating the majority of small rainfall events (Davis et al. 2009; LeFevre et al. 2010). Nevertheless, concerns have been expressed about the potential for contaminating groundwater resources due to intentional infiltration of pollutant-containing stormwater (Pitt et al. 1999; Weiss et al. 2008).