A Critical Analysis of Leaching and Environmental Risk Assessment for Reclaimed Asphalt Pavement Management

Abstract In the last couple of decades, studies have examined the potential environmental risks associated with reclaimed asphalt pavement (RAP) management through a range of approaches. Variable risk assessment methodologies and uncertainty on RAP behavior in a stockpile or during reuse have led to inconsistent regulatory oversight in many jurisdictions. The objective of this literature review is to provide clarity on the findings pertaining to RAP leaching and assess the potential human and environmental health risks associated with reported constituent mobility from RAP. The reviewed literature focuses on the leaching of metals and organic compounds; direct exposure risk was briefly reviewed and found not to exceed natural soils or aggregates. On occasion, the literature reports elevated leached concentrations of certain metals (e.g., lead) and some polycyclic aromatic hydrocarbons (PAHs) from a few RAP samples. These elevated RAP leachate concentrations are assessed via fate and transport model (US EPA IWEM) to estimate dilution and attenuation of select metals and PAHs under typical environmental conditions and reuse or storage scenarios (e.g., stockpiling). This analysis suggests that most reported leachate concentrations of potential concern would be effectively attenuated at the most conservative conditions simulated (10 m, 100% infiltration); limitations with modeling are acknowledged. Pavement materials and external sources, along with chosen testing protocols, influence RAP leachate concentrations, affecting conclusions for potential environmental impacts of RAP in the literature. Understanding how these variables impact leaching and risk assessment is necessary to maximize and continue beneficial reuse of RAP while safeguarding human and environmental health.