WRHSRC Research Program:
Site Assessment and Characterization

Focus Group Leader:

Jack Istok, Oregon State University

Technical Description:

Site characterization focuses on methods for determining in-situ rates of CAH transformation under intrinsic and enhanced remediation conditions. Center investigators have developed the push-pull test method for characterizing rates of in-situ transformation of BTEX compounds (Istok et al., 1997; Reinhard et al., 1997). Center projects will now extend this method to chlorinated solvents. Methods for accurately determining in-situ redox conditions will also be developed by Ingle (Lemmon et al., 1996) and used in other Center research projects.

Research is carried out at OSU's Groundwater Research Laboratory.

Project 1-OSU-03:

Development of the Push-Pull Test to Monitor Bioaugmentation of Dehalogenating Cultures

Principal Investigators:

Mark Dolan, Jennifer Field, and Jack Istok, Oregon State University

Project Initiated: 2002

 

Project Summary:

In this project the push-pull test to monitor the bioaugmentation with dehalogenating cultures is being developed. The overall goal is to modify the single-well push-pull groundwater test as a means for obtaining quantitative information on in situ dechlorinating activity before and after bioaugmentation. Two cultures characterized in Project 2 (Evanite and Pt. Mugu) that transform TCE to ethene are being used in this study. The transport of the culture(s) is being determined during injection into anaerobic physical aquifer models (PAMs). Spatial distributions of dechlorinating activity and redox are determined from a suite of assays conducted at sampling ports and at the injection/extraction well. Push-pull tests are being conducted at the injection/extraction well to assess changes in reductive dechlorination activity resulting from bioaugmentation. The investigators are currently evaluating the survivability of the cultures in groundwater/sediment microcosms and studying basic transport behavior in columns. Molecular methods, using Dehalococcoides sp. group-specific PCR primers are being used to track the dehalogenators. Serial dilutions of the Evanite culture were extracted and analyzed using Dehalococcoides group-specific PCR and dilutions down to 10-4 were detectible by this process. Future work includes expanding this testing to real-time quantifiable PCR analyses to attain better enumeration of Dehalococcoides sp.

Link to publications about the push-pull test.

Project 1-OSU-04:

Development and Evaluation of Field Sensors for Monitoring Bioaugmentation with Anaerobic Dehalogenating Cultures for In-Situ Treatment of TCE

Principal Investigator:

James Ingle, Oregon State University

Project Initated: 2002

 

Project Summary:

In this project field sensors are being developed and evaluated for determining redox conditions during in situ treatment of TCE. This study aims to refine and use redox sensors based on redox indicators as monitoring tools for assessing and optimizing redox conditions for treatment of TCE and PCE with dehalogenating cultures. Flow sensors based on redox indicators are being deployed in two primary collaborate situations for calibration and demonstration of their applicability:

1. continuous monitoring of redox conditions of cultures inside bioreactors or microcosm bottles as a tool for the optimizing conditions for effective dechlorination of PCE or TCE with enriched halorespiratory cultures, and
2. on-line monitoring of the redox status of the material in a physical aquifer model (PAM) bioaugmented with the developed dehalogenating cultures.

Research in the second year evaluated the dechlorinating culture (Project 2) in bioreactors and microcosm bottles to calibrate the response of the redox indicators to the dechlorination of PCE. The indicator data support the concept that the dechlorinating process is increasingly reduced as PCE is dechlorinated, with the most reducing step in the process being the dechlorination of vinyl chloride to ethene. Research has also focused on the development of a hydrogen sensor on membranes with platinum embedded membranes.

Project 2-OSU-06:

Development and Evaluation of Field Sensors for Monitoring Anaerobic Dehalogenation After Bioaugmenatation

Principal Investigator:

James Ingle, Oregon State University

Project Initated: 2004

 

Project Summary:

The overall objective of this study is to develop, refine and use sensors, based on redox indicators and other reagents or colored species, as on-line monitoring tools for assessing and optimizing redox and related conditions for treatment of PCE and TCE with dehalogenating cultures. These sensors will be calibrated for evaluating redox conditions and the effectiveness of dechlorination in two collaborative situations involving a bioaugmentation approach. Experimental objectives include:

1. Evaluate redox conditions and dechlorination activity in packed columns and physical aquifer models (PAMs) packed with aquifer sediment after bioaugmentation with the developed redox monitoring system based on immobilized redox indicators. Key elements are spatial resolution along the flow axis in columns and PAMs and the correlation of the reduction of different redox indicators to specific dechlorination steps during the sequential transformation of PCE to ethene
2. Modify, develop, and test new sensing media, strategies, instrumental components and sensor designs for on-line monitoring of the status of dechlorinating systems in packed columns, laboratory vessels, PAMs, and sub-surface systems.
   • Develop and test improved sensing membranes including redox membranes with embedded catalysts such as Pt to monitor H2 , an electron donor which is essential for effective reductive dechlorination.
   • Investigate alternative sampling/reagent systems including push-pull sensors, measurement of redox capacity, and fiber optic sensors. Other probe species such as quinones may provide unique information about dechlorination activity.
   • Improve portable spectrometers for monitoring changes in the absorbance or fluorescence of sensing species. Convenient, portable, and affordable instrumentation is critical for routine use of the developed techniques and sensors.
3. Continue to investigate the characteristics of dechlorinating cultures in bioreactors and microcosm bottles to improve on-line sensors based on redox indicators and to develop new types of sensors. The goal is to develop the best sensors that indicate when conditions are appropriate for specific dechlorination steps and for optimizing and maintaining effective dechlorination of PCE.

The expected results of this research include the development of new techniques and devices for monitoring redox status and dechlorination activity in the laboratory and at contaminated ground water sites that complement existing techniques and provide unique advantages such as on-line monitoring of oxygen-sensitive information with minimally-evasive sampling/analysis steps, and inexpensive, miniaturized, and portable instrumentation. These on-line monitoring techniques will be beneficial 1) for the initial assessment of laboratory samples and subsurface conditions at a site, 2) for continued assessment of the progress of remediation, and 3) for control of injections of amendments (e.g., substrates, nutrients) during remediation.

Project Update Slide (November 2004):

To download a copy of this slide, click here.

Project 2-SU-04:

Novel Methods for Laboratory Measurement of Transverse Dispersion in Porous Media

Principal Investigator:

Peter Kitanidis and Craig Criddle, Stanford University

Project Initated: 2004

 

Project Summary:

Transverse dispersion in porous media measures the rate of spreading of a solute in the direction perpendicular to flow. Pore-scale transverse dispersion is widely accepted as playing a dominant role in determining the actual rate of dilution of solutes and mixing of reactants in porous media. For example, consider a long plume of contaminants emanating from a constant source. The rate of intrinsic remediation is determined by the rate of transverse mixing of contaminants in the plume with reactants from the surrounding groundwater. In many cases, biogeochemical reactions are relatively fast and so-called “mass transfer” or “diffusion” processes limit the realized reaction rates.

These limiting processes are primarily transverse dispersion. Better understanding of transverse dispersion would ultimately improve our understanding of diffusion-limited processes, such as intrinsic remediation dissolution from sources. Despite its importance, transverse dispersion remains insufficiently understood. Part of the difficulty is the lack of accurate and efficient methods for laboratory measurements.

In most existing methods for the determination of transverse dispersion, the measured quantity is proportional to the dispersion coefficient, and thus small and swamped by experimental error. However, we have recently developed new methods for the measurement of local transverse dispersion in isotropic porous media based on a helical and a cochlea-like device. The basic idea is to perform an experiment similar to the tracer test through a laboratory column packed with a porous medium and to measure the breakthrough curve; however, the objective is not to determine the longitudinal dispersion but the elusive transverse dispersion! The way the method works is that there is shear flow inside the device that creates strong longitudinal dispersion in the observed breakthrough curve; transverse mixing tends to negate the effects of shear flow and thus reduce the observed dispersion. The relation between the observed quantity, the spreading in the breakthrough curve, and the unknown, the pore-scale transverse dispersion, is exact. These methods combine the simplicity of operation of classic column experiments with high accuracy. In fact, the smaller the transverse dispersion, the more accurately it can be determined, which is in sharp contrast with previous methods. We have already developed these methods and built working prototypes of the devices.

In this project we will continue work on these novel experimental techniques in order to: (a) refine them in terms of experimental protocols and methods of data analysis; (b) independently verify their accuracy; (c) perform extensive experiments to determine relations of transverse dispersivity with conductivity, longitudinal dispersivity, mean grain size, degree of non-uniformity, etc.

Project Update Slide (November 2004):

To download a copy of this slide, click here.