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.