Impacts of salinity on the dynamics of fine particles and their associated metals in infiltration-based stormwater management practices (SMPs)

Abstract:

Elevated salinity in stormwater runoff may negatively impact the efficacy of stormwater management practices (SMPs) in intercepting metals. Field soil samples were employed to characterize the impacts of salinity on suspended solids and metal desorption. Varying concentrations (0.01 M to 1M) of chloride salts (NaCl, MgCl₂, KCl, and CaCl₂) were applied to suspended particle samples to assess the changes in particle size distribution (PSD) and metal desorption from particles. The concentration of fine particles (d<10um) was higher in synthesized samples treated with monovalent cations (i.e., Na⁺ and K⁺) up to 0.1 M. This was attributed to the ion attraction to the particle’s surface resulting in induced repulsive forces which prevented coagulation. In the presence of divalent cations (i.e., Mg²⁺ and Ca²⁺), particle stability (i.e., no coagulation) was observed in samples treated up to 0.05 M. Particle aggregation could be observed in higher salt concentrations, associated with ionic strength larger than ~ 0.1 M, because of compressed double-layer that restrained the repulsive force. Generally, elevated salinities resulted in increased desorption of exchangeable Cr, Fe, Cu, Zn, and Pb, which is likely a combination of cation exchange and formation of aqueous metal-chloride complexations. Increased fine particle fractions and dissolved metals would negatively impact the functionality of the SMP, potentially leading to increased media clogging and increased transport of metals to underlying groundwater and downstream water bodies. This study highlighted the importance of limiting the introduction of salts and proper maintenance of SMPs, particularly in locations where applying deicing salts (e.g., NaCl) is a necessary safety measure.