PARENT SESSION
PM22 - Coping with Uncertainty in Fate/Exposure Models
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P406) Beneficial use of Recycled Materials in Roadways: The Effect of Hydraulic Parameters and Various Pavement Designs on Contaminant Leaching .
Apul, Defne*,1, Gardner, Kevin1, Eighmy, Taylor1, Linder, Ernst1, 1 University of New Hampshire, Durham, NH, USA
ABSTRACT- Estimates of long term leaching of contaminants are required to assess the environmantal risk posed by traditional and recycled materials used in roadways. The release and transport of contaminants is dictated in part by the hydrology of the roadway environment. A thorough understanding of hydraulic regimes coupled with corresponding advective and diffusive contaminant fluxes are two key factors for predicting long term leaching of contaminants. Towards this end, HYDRUS2D, a finite element, water movement and solute transport model was used to determine the hydraulic regimes and contaminant fluxes in the field. The data set for modeling was obtained from several different test road sections monitored and maintained by the Minnesota Department of Transportation. Water content in pavement layers, fluxes from drainage pipes, and ground water table depth data were used for calibration of the water movement model. The uncertain hydraulic parameters such as saturated hydraulic conductivity, residual water content, saturated water content, and van Genuchten fitting parameters were estimated by inverse methods. Estimated parameters and their 95% confidence intervals as well as various road scenarios (sealed versus unsealed joints) were used to evaluate the uncertainty in model predictions. The results of numerical experiments suggested that the dynamics of roadway hydraulic regimes and subsequently the extent of leaching and transport of contaminants are influenced not only by material hydraulic parameters but also by presence of cracks, joints, and unpaved shoulders. Preliminary results of contaminant leaching predictions using the linear adsorption constant were also supportive of this finding.
Key words: leaching, recycled materials, parameter uncertainty, modeling