![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Passive Remediation of Sulfide Wastes: A Study of Oxygen Diffusion Through Composite Barrier Covers
Primary Issue Addressed: Source Control
Secondary Issue Addressed: None
Project Site: Montana Tech of the University of Montana
Collaborating Entities: Montana Tech
Cost Share: None
Project Description
The main objective of this project is to determine oxygen flux through one component of a typical barrier cap at a variety of moisture conditions. Oxygen flux will be determined through a combination of percent oxygen measurements and the use of theoretical equations. The goal is to develop a best fit curve to describe oxygen diffusion under differing moisture conditions.
The theory behind oxygen movement is that oxygen will move through material such as waste rock by processes called diffusion and/or convection. Based on this process, several researchers have presented methods of modeling to represent this movement. A recent method for determining oxygen movement through a geosynthetic clay liner (GCL) system was developed in 1999 by a group of Canadian researchers. In a 1999 paper entitled “Evaluation of diffusive gas flux through covers with a GCL” (Aubertin), the researchers specifically set out to determine the rate of oxygen movement through GCLs. Earlier methods of modeling were only able to estimate the influence of a GCL on oxygen diffusion. In this study, the GCL was specifically examined to estimate the diffusion. This method does not produce a depth of oxygen diffusion; rather, it produces a rate at which oxygen diffuses per year and an acceptable range for the prevention of acid rock drainage (ARD) production. A critical parameter in determining acid generation is the flux of oxygen, which determines the rate of acid production through the oxidation of sulfide materials contained in the waste materials. Controlling this rate over time will control the rate of acid production. Determination of the diffusion coefficient is a key parameter in determining oxygen flux. Materials at or near saturation exhibit reduced oxygen fluxes owing to the relatively low solubility of oxygen in water and the low diffusion coefficient for oxygen in water relative to that in air.
Status
Researchers have been conducting a literature search, as well as formulating
a design for the diffusion cells. Currently, optimization experiments
have been performed to refine the experimental design. It is anticipated
that critical data collection will begin as soon as the quality assurance
project plan is finalized with the project final report being completed
in FY05.