Defne Apul

The goal of this research was to provide a tool for regulators to evaluate the groundwater contamination from the use of virgin and secondary materials in road construction. A finite element model, HYDRUS2D, was used to evaluate generic scenarios for secondary material use in base layers. Use of generic model results for particular applications was demonstrated through a steel slag example. The hydrology and reactive transport of contaminants were modeled in a two-dimensional cross section of a road. Model simulations showed that in an intact pavement, lateral velocities from the edge towards the centerline may transport contaminants in the base layer. The dominant transport mechanisms are advection closer to the edge and diffusion closer to the centerline. A shoulder joint in the pavement allows 0.03 to 0.45 m 3 /day of infiltration per meter of joint length as a function of the base and subgrade hydrology and the rain intensity. Scenario simulations showed that salts in the base layer of pavements are depleted by 99% in the first 20 years, whereas the metals may not reach the groundwater in 20 years at any significant concentrations if the pavement is built on adsorbing soils.

Predictive methods for contaminant release from virgin and secondary road construction materials are important for evaluating potential long-term soil and groundwater contamination from highways. The objective of this research was to describe the field hydrology in a highway embankment and to investigate leaching under unsaturated conditions by use of a contaminant fate and transport model. The HYDRUS2D code was used to solve the Richards equation and the advection–dispersion equation with retardation. Water flow in a Minnesota highway embankment was successfully modeled in one dimension for several rain events after Bayesian calibration of the hydraulic parameters against water content data at a point 0.32 m from the surface of the embankment. The hypothetical leaching of Cadmium from coal fly ash was prob-abilistically simulated in a scenario where the top 0.50 m of the embankment was replaced by coal fly ash. Simulation results were compared to the percolation equation method where the solubility is multiplied by the liquid-to-solid ratio to estimate total release. If a low solubility value is used for Cadmium, the release estimates obtained using the percolation/equilibrium model are close to those predicted from HYDRUS2D simulations (10 4 –10 2 mg Cd/kg ash). If high solubility is used, the percolation equa-156

Predictive methods for contaminant release from virgin and secondary road construction materials are important for evaluating potential long-term soil and groundwater contamination from highways. The objective of this research was to describe the field ...

Significant amounts of recycled materials are being used in structural components of highways such as base, subbase, Portland cement and asphalt concrete, and embankments. Past experience with recycled materials in highways has not shown a risk ...

... Defne S. Apul1 · Kevin H. Gardner2 · Taylor T. Eighmy2 1 Environmental Research Group, Department of Civil Engineering, University of New Hampshire, Durham, NH 03824, USA dapul@cisunix.unh.edu 2 Recycled Materials Resource Center, Department of Civil Engineering ...

Recovered materials from the transportation sector or secondary or by-product materials from the industrial, municipal, or mining sector can be used as substitutes for natural materials in the construction of highway infrastructure. The environmental impact of traditional and newer secondary materials needs to be determined for the conditions of their expected use. The purpose of this paper is to introduce

ABSTRACT Computer modeling can be an instructive tool to evaluate potential environmental impacts of coal combustion byproducts and other secondary materials used in road and embankment construction. Results from the HYDRUS2D model coupled with an uncertainty analysis suggest that the cadmium fluxes will be significantly less than the output from simpler models with worst case scenarios. Two dimensional analysis of the leaching from the base layer also suggest that concentrations leaching ground water will not be significant for metals unless the pavement is completely damaged and built on sandy soils. Development and verification of these types of tools may lead the way to more informed decision with respect to beneficial use of coal combustion byproducts and other secondary materials. 5 figs., 1 tab.

ABSTRACT Recycled materials, such as recovered materials from the transportation sector or secondary or by-product materials from the industrial, municipal, or mining sectors can be used as substitutes for natural materials in the construction of highway infrastructure. Trace metals in these recycled materials may leach out and contaminate the groundwater and soil posing a long-term environmental problem. Environmental risk assessments are necessary to evaluate which recycled material applications are acceptable. The first step for determining the environmental risk of using recycled materials is to characterize the source term. Estimates of contaminant release fluxes can then be used in a comparative risk assessment. This paper will give an example of a comparative, probabilistic approach for exposure assessment. Existing deterministic models for estimating contaminant release will be presented and incorporation of variability in these models will be discussed.

... A Geographic Information System (GIS), with its advanced data integration, query, analysis ... Because GIS products can be produced quickly, multiple scenarios can be evaluated ... from local or regional impacts on the ambient atmosphere, streams, groundwater aquifers, vegetation ...

Abstract Significant amounts of recycled materials are being used in structural components of highways such as base, subbase, Portland cement and asphalt concrete, and embankments. Past experience with recycled materials in highways has not shown a risk ...

... Defne S. Apul1 · Kevin H. Gardner2 · Taylor T. Eighmy2 1 Environmental Research Group, Department of Civil Engineering, University of New Hampshire, Durham, NH 03824, USA dapul@cisunix.unh.edu 2 Recycled Materials Resource Center, Department of Civil Engineering ...