Year-round monitoring of chloride releases from three zero-exfiltration permeable pavements and an asphalt parking lot.

Winter deicers, though essential for maintaining safe pavement conditions in winter, increase chloride (Cl) concentrations in receiving water bodies above recommended environmental guidelines. Zero-exfiltration or lined permeable pavement is an important technological innovation for controlling particulate-bound pollutants at the source. As stormwater does not infiltrate into the ground, soluble pollutants like Cl are ultimately discharged into receiving water bodies. Our aim was to examine Cl concentrations in effluents from three zero-exfiltration permeable pavement cells (Permeable Interlocking Concrete Pavement (PICP), Pervious Concrete (PC), Porous Asphalt (PA)) and compare them with runoff from a Conventional Asphalt (ASH) cell. The study conducted at a parking lot in St. Catharines, Ontario, Canada, from January 2016 to May 2017 observed that the permeable pavements provided only temporary attenuation of Cl during winter but exhibited a quick release during spring melt. Cl concentrations and loadings were different for each permeable pavement system in terms of timing and magnitude. Cl concentration in ASH runoff frequently had very high spikes (21,780 mg/L); however, the median winter Cl concentration in ASH runoff was lower than Cl levels in the permeable pavements' effluents and later declined drastically after spring melt, but in few instances, was above the chronic water quality guideline (120 mg/L). The average event mean concentration (EMC) of Cl was 1600 and 120 mg/L in the permeable pavements' effluents during salting and non-salting season, respectively. In one year, each permeable pavement system released approximately 67-81 kg of Cl with significant differences being observed in Cl loads between the 2016 and 2017 seasons. Therefore, a multi-year data collection and monitoring plan captured the variability in winter conditions. The study provided insights into the behaviour, retention and release of Cl from traditional and permeable hardscape surfaces and possible avenues for Cl attenuation, source control and aquatic habitat conservation.