Distribution of Particulate-Bound Metals for Source Area Snow in the Lake Tahoe Watershed

The porous matrix and long residence time of snow in traffic corridors can result in the accretion of particulate matter (PM) and metals. This temporary repository contributes PM-based and dissolved metals to surrounding environs during snowmelt. This study focused on distribution and settling of PM-based metals (Al, As, Cd, Cr, Cu, Fe, Pb, and Zn) in snow. Snow was sampled from six sites during four winter seasons. PM-based metals are examined herein as a function of PM granulometry, specifically particle-size distributions (PSDs) and PM surface area. Cumulative metal mass distributions across each PSD are modeled as gamma functions. Results indicate Al (15 g/kg) and Fe (4.2 g/kg) are the highest PM-based concentrations; Cd (0.18 mg/kg) and As (4.9 mg/kg) are the lowest. The PM size (d(50 m)) associated with the median metal mass ranges from 179 to 542 mu m. The constitutive gamma results are integrated with Hazen's settling algorithm to model PM-bound metal separation for a sedimentation basin at a local snow storage site. Flows are modeled in the storm water management model (SWMM) from snowmelt and historical rainfall time series. Results indicate that Type I sedimentation is capable of separating the sediment fraction (>75 mu m) and majority of metal mass. While the basin is effective at separation of coarser PM-based metals, additional practices such as pavement and drainage appurtenance cleaning, as well as adsorptive-filtration can further manage suspended PM and metals, as well as dissolved metals.