Extension of Laboratory Validated Treatment and Remediation Technologies to Field Problems in Aquifer Soil and Water Contamination by Organic Waste Chemicals

Principal Investigators
T.H. Illangasekare, University of Colorado

Abstract

Goal: The primary goal of this research is to develop and implement systematic procedures for applying, in the field, treatment and remediation technologies that have been developed in the laboratories, taking into consideration the complexities which are encountered in the field.

Rationale: The primary hypothesis is that natural heterogeneities of soil and heterogeneities due to nonaqueous phase liquid (NAPL) entrapment result in preferential flow of water and treating agents. These constraints to flow and delivery of treating agents alter effectiveness of treatment schemes in the field. This research will attempt to identify the basic processes that are affected by these complexities and determine the parameters that control the behavior at the field scale.

Approach: A systematic procedure to extend to the field the knowledge gained through experimentation at the laboratory scales of pore, cell, column, and soil flumes will be developed. Laboratory, modeling, and field investigations will focus on issues related to transport, entrapment, recovery, dissolution, fingering, and physical chemical and thermal mobilization, blob dispersion to increase dissolution, etc., that are of fundamental importance in developing remediation technologies. Laboratory experiments in cells, columns, and large tanks will be continued to identify basic parameters which need to be up-scaled to field problems. Some of the parameters that have been identified for study include hydraulic conductivity, capillary pressure versus saturation, relative permeability, entry pressure, pore size distribution, dispersivity, sorption coefficient, mass transfer coefficients, and dissolution parameters. Investigators will use chemical mixtures to look at multicomponent mass transfer and realistic field soils. Sites in Kansas, Colorado, Wyoming, and Louisiana will be selected for field studies. Once effective parameters are identified, techniques will be developed to obtain these in the field.

Status: Focus has been on the processes of entrapment, fingering, vapor flow, dissolution, and enhanced dissolution using surfactants. Preliminary test simulations conducted in large pilot scale tanks suggest the critical role played by soil heterogeneities in entrapment and dissolution behavior of NAPLs. A set of experiments were conducted in large soil tanks to understand the mechanisms of spreading and to quantify distribution of NAPLs in fields of randomly packed soil heterogeneities that are more representative of field conditions. Experiments with light NAPL in the vadose zone and a dense NAPL in the saturated zone were conducted. Experimental results show that spreading is controlled by initial water saturations, capillary barrier effects, preferential flow, and fingering. Specifically in the DNAPL experiments, fingering played a critical role in the final distribution pattern. The final entrapment distribution exhibited a random pattern. Development of a characterization methodology that will attempt to obtain statistical parameters of the random field of entrapment using multiple tracers has been initiated. This project is in its first year.

Clients/Users: The developed technologies will be of use to environmental scientists, environmental engineers, geologists, and hydrogeologists who are employed by U.S. Environmental Protection Agency and other federal and state regulatory agencies, U.S. Department of Defense, U.S. Department of Energy, environmental consulting firms, and the manufacturing industry.

Key words: aquifers, organic chemicals, nonaqueous phase liquids, remediation.

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