Stochastic Method for Evaluating Removal, Fate and Associated Uncertainties of Micropollutants in a Stormwater Biofilter at an Annual Scale

Abstract

A stochastic method for evaluating the in situ mass balance of micropollutants in a stormwater biofilter, accounting for inlet and outlet loads and the evolution of pollutant mass in the filter media (ΔMsoil) at an annual scale, is proposed. In the field context, this type of calculation presents a number of methodological challenges, associated with estimating water quality for unsampled rain events, reconstituting missing or invalidated flow data and accounting for significant uncertainties associated with these estimations and experimental measurements. The method is applied to a biofiltration swale treating road runoff for two trace metals, Cu and Zn and six organic micropollutants: pyrene (Pyr), phenanthrene (Phen), bisphenol-A (BPA), octylphenol (OP), nonylphenol (NP) and bis(2-ethylhexyl) phthalate (DEHP). Pollutant loads were reduced by 27–72%. While organic micropollutants are likely to be lost to degradation or volatilization processes in such systems, dissipation could not be demonstrated for any of the organic micropollutants studied due to emissions from construction materials (case of BPA, OP, NP and DEHP) or high uncertainties in ΔMsoil (case of Pyr and Phen). The necessary conditions for establishing an in situ mass balance demonstrating dissipation, which include acquisition of data associated with all terms over a period long enough that uncertainty propagation is limited and the absence of additional sources of pollutants in the field, are discussed.

Contamination of Urban Stormwater Pond Sediments: A Study of 259 Legacy and Contemporary Organic Substances

“…Most previous studies analyzing phthalates in stormwater sediments and particles have detected them, 16 , 44 , 62 , 63 with the exception of a study of stormwater pond sediments in Florida in which DBP was never detected due to a very high LOQ (a 100-fold higher than in the present study). 35 DEHP concentrations measured in sediments from 15 stormwater ponds in Minnesota 44 and a sedimentation tank treating highway runoff in Gothenburg, Sweden 62 were of the same order as those in the present study, with the Gothenburg samples corresponding to the most contaminated samples in this study.…”

“…NP concentrations previously observed in sediments from a detention basin in an industrial area of Lyon, France 42 and a stormwater tank in Gothenburg, Sweden, 43 as well as in the particulate phase of stormwater from a dense urban catchment 16 and a heavily trafficked road 63 in the Paris region of France all fit within the range observed in this study. These same studies observed OP either in the same range as the present study 16 , 42 or at higher concentrations.…”

“… 35 DEHP concentrations measured in sediments from 15 stormwater ponds in Minnesota 44 and a sedimentation tank treating highway runoff in Gothenburg, Sweden 62 were of the same order as those in the present study, with the Gothenburg samples corresponding to the most contaminated samples in this study. However, phthalate concentrations measured in the particulate phase of stormwater in the Paris region (DEHP from a dense urban catchment 16 and DEHP, DBP, and DiBP concentrations from a heavily trafficked road 63 ) were distinctly higher than those in this study.…”

“…A high intersite variability was observed, and concentrations of NP (<0.1 to 30.5 mg/kg) were typically higher than those of OP (<0.02 to 0.53 mg/kg), as would be expected due to the fact that NPs account for a higher proportion of industrial applications of alkylphenols than OPs. 65 NP concentrations previously observed in sediments from a detention basin in an industrial area of Lyon, France 42 and a stormwater tank in Gothenburg, Sweden, 43 as well as in the particulate phase of stormwater from a dense urban catchment 16 and a heavily trafficked road 63 in the Paris region of France all fit within the range observed in this study. These same studies observed OP either in the same range as the present study 16,42 or at higher concentrations.…”

“…These same studies observed OP either in the same range as the present study 16 , 42 or at higher concentrations. 49 , 63 Interestingly, high concentrations of OP appear to be associated with catchments containing heavily trafficked roads, both in the scientific literature 49 , 63 and this study; this may be due to the presence of OP in tires, 66 at least in the European market. By contrast, a study of sediments from 15 stormwater ponds in Minnesota observed NP more frequently (100% of samples) and at higher concentrations than the present study but never detected OP, despite lower LOQs than the present study.…”