Effects of Redox Zones on the Fate and Transport of Contaminants in the Saturated Subsurface: Characterization and SimulationEPA Grant Number: GF9500260
Title: Effects of Redox Zones on the Fate and Transport of Contaminants in the Saturated Subsurface: Characterization and Simulation
Investigators: Abrams, Robert H.
Institution: Stanford University
EPA Project Officer: Broadway, Virginia
Project Period: September 1, 1995 through January 1, 2000
Project Amount: $34,000
RFA: STAR Graduate Fellowships (1995) Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Earth
The purpose of this project is to investigate the impact that redox zones have on the fate and transport of miscible substances in groundwater. Specifically, this project will focus on the interrelationship between dissolved iron and redox zones at the USGS Toxic Substances Hydrology Research Program field site located in Cape Cod, MA, by analyzing and interpreting field data and conducting concept- development solute transport and geochemical simulations with a physics and chemistry based numerical model. The specific approach includes: 1) developing saturated subsurface fluid flow, geochemical, solute transport, and coupled flow and solute transport/geochemical models based on extensive field data; 2) performing sensitivity studies to determine which chemical components and reactions and which hydrologic variables are essential to developing a robust model of field-scale phenomena; and 3) quantitatively evaluating model performance using statistical and graphical methods. In the first phase of study, a model based solely on thermodynamics will be constructed to determine what set of reactions are controlling/producing dissolved Fe(II) in the iron zone. Using the maximum reaction set initially derived from the literature, a preliminary list of components will be made from the reactions, with Mn(II), dissolved oxygen, nitrogen species, and Fe(II) chosen as target constituents upon which changes in their concentration will be the basis for eliminating reactions and components. Components and reactions that contain them will be eliminated if they do not significantly influence Fe(II) concentrations using a batch chemical equilibrium computer code. The second phase of study will investigate processes that affect Fe(II) during transport at the Cape Cod site. Components studied will include physical properties, chemical properties, and variations in the amount and composition of the treated sewage that was input to the system. A one-dimensional model will be developed and applied to simulate the development of the sewage plume and the iron zone, oriented longitudinally along the flow line, and the local equilibrium assumption will be examined. The third phase of study will apply a coupled chemical speciation/solute transport model to the field site by developing a two dimensional vertical cross- section flow model that extends along a flow line from the disposal beds to a distance well downgradient from the leading edge of the iron zone; simulating transport in two dimensions; and coupling the transport problem to the flow system. Once the coupled simulation approach has been assessed and found to be acceptable within a calibrated range it will be used to predict the future fate of the iron zone, which can subsequently be used in the ongoing evaluation of model performance.