Traffic-derived contaminant loading in snow storage facilities during spring melt

Stormwater results from precipitation events and melting snow running off urban landscapes and typically being released into receiving water bodies with little to no treatment. Despite evidence of its deleterious impacts, snowmelt (SM) management and treatment are limited, partly due to a lack of quality and loading data. This study examines snowmelt quality during the spring for a cold climate, semi-arid Canadian city (Saskatoon, Saskatchewan). Four snow storage facilities receiving urban snow plowed from roads in mixed land use urban catchments (228 km²) were sampled including snow piles (five events) and SM (twelve events) runoff in 2019 and 2020. Samples were analyzed for pH, EC, TDS, TSS, COD, DOC, metals, chloride, PAHs, and Raphidocelis subcapitata and Vibrio fischeri toxicity. Notable event-specific TSS spikes occurred on April 13, 2019 (3,513 mg/L), and April 24, 2019 (3,838 mg/L), and TDS, chloride, and manganese on March 26, 2020 (15,000 mg/L, 5,800 mg/L, 574 mg/L), April 17, 2020 (5,200 mg/L, 2,600 mg/L, 882 mg/L), and April 23, 2020 (5,110 mg/L, 2,900 mg/L, 919 mg/L), though chloride remained elevated through May 1, 2020, samples (1,000 mg/L). Additionally, at two sites sampled April 13, 2019, pulses of aluminum (401 mg/L) and PAHs (pyrene, phenanthrene, anthracene; 71 µg/L, 317 µg/L, 182 µg/L) were detected. Concentrations of fluorene, benzo[a]pyrene, pyrene, phenanthrene, and anthracene in almost all SP samples exceeded national aquatic toxicity guideline thresholds, while 50% of SM samples exceeded guideline thresholds for benzo[a]pyrene and pyrene, and almost all exceeded the threshold for anthracene. Nevertheless, the EC₅₀ for R. subcapitata and V. fischeri was observed, if at all, above expected toxicity thresholds.