The impact of polycyclic aromatic hydrocarbons (PAHs) on beneficial use of waste materials

Wastes generated from municipal cleaning activities such as street sweeping, ditch cleaning, stormwater pond maintenance and catch basin sediment removal need to be managed appropriately. Also requiring management are reclaimed asphalt pavement (RAP) and milled asphalt shingles. The common management practices for these waste streams are direct landfilling and stockpiling for future use or disposal. Beneficial use of these types of waste is a good alterative to landfilling. However, there are genuine concerns about possible soil and groundwater contamination by pollutants such as polycyclic aromatic hydrocarbons (PAHs), which are known to occur in low concentrations in several of these waste streams. The absence of sufficient scientific data on these PAHs has limited scientists, engineers, and policy-makers when making decisions concerning reuse of these wastes. In addition, inflow of new scientific information on PAHs has lead to downward revision of regulatory thresholds for some of these organic pollutants over the years, rendering previous research work inconclusive. Regulatory threshold values for solid waste are based on risk assessments. These assessments using animals usually assume a one hundred percent bioavailability. This could lead to over-conservative limitation of beneficial use of solid waste.;The purpose of this research was to investigate the impact of PAHs on beneficial use of roadway and storm system residuals and asphalt waste materials. Total and leachable concentrations of PAHs in roadway and storm system residuals were investigated using United States Environmental Protection Agency (US EPA) methods 3550 and 1312. Column leaching studies and batch leaching tests using the synthetic precipitation leaching procedure (USEPA method 1312) were conducted on reclaimed asphalt pavement (RAP) and milled shingles to determine potential leaching of PAHs from these wastes. Size fractionation was performed on the roadway and storm system residuals and the PAHs associated with each fraction determined. An in vitro study was conducted using a gastrointestinal leaching test to ascertain bioaccessibility of PAHs in these waste streams. Analyses of the samples were achieved by employing high-performance liquid chromatography (HPLC) equipped with ultraviolet (UV) and fluorescence detectors.;Results in this study showed the presence of all the 16 US EPA priority PAHs in measurable quantities. The measured total and leachable PAH concentrations were lower than the regulatory Soil Cleanup Target levels (SCTLs) and Ground Water Cleanup Target Levels (GWCLs) except for benzo(a)pyrene. The mean benzo(a)pyrene concentration in the sampled street sweepings was above the residential SCTL, but lower than the industrial SCTL. PAHs were found mobilized in the lower fine and medium coarse fractions of the waste. Abraded asphalt particles from roadways were believed to be the source of PAHs in the coarse fractions. Microscopic studies of the fractionated samples revealed the presence of asphalt particles in these fractions. In vitro study results found PAH bioaccessibility to range from 1.7% to 49% in six samples studied.