Purpose:

Improved groundwater contaminant monitoring requires a cost-effective method that allows for low-level detection of individual compounds in real time. Colorado State University (CSU) has developed fiber optic biosensors that are ideally suited for field monitoring of groundwater contaminants. The primary performance issues to be validated in this field demonstration are the ability of this biosensor technology to function accurately as a field analytical device (to replace or supplement traditional field sampling and offsite lab analysis), provide in situ discrete-depth measurements in monitoring wells instead of the averaged values obtained with traditional methods, and function in a monitoring mode over a period of approximately one week.

Description:

Generally, a biosensor is a device that utilizes a biological recognition element (typically enzymes or antibodies) to sense the presence of an analyte and create a response that is converted by a transducer to an electrical or optical signal. The CSU biosensor concept is a two-layer detection element immobilized on the tip of an optical fiber. The outer layer of the detection element contains bacteria with a hydrolytic dehalogenase. The inner detection layer is a pH-sensitive fluorescent dye. Thus, the presence of the contaminant leads to a pH change on the fiber tip, which can be measured as a fluorescence change. Since the change in fluorescence depends on the contaminant concentration, these sensors provide quantitative output. The biosensors will be demonstrated at three Department of Defense (DoD) sites. The analyte for the first site will likely be either ethylene dibromide or 1,2-dichloroethane, since sensors that detect these compounds have already been tested in the laboratory. Demonstrations at the other two sites will use bundled fiber optic sensors to measure multiple analytes, potentially vinyl chloride and 1,2-dichloroethene.

Benefits:

Relative to traditional, discrete sampling approaches, these fiber optic biosensors have the following advantages: the capability of providing low cost, simultaneous measurements at different depths in a well; the capability of providing low cost, continuous monitoring; and the capability of bundling biosensors for different contaminants (as well as similar optical sensors for dissolved oxygen, pH, and temperature) into an optical cable that would provide simultaneous, continuous multiparameter measurements with one small device that can be lowered through a small well for measurement. In situ measurements by these fiber optic biosensors can be used to reduce costs at DoD sites through the monitor of groundwater contaminant concentrations in existing plumes, either by permanent installation for monitoring over time or by analysis of wells at discrete time points; installation in sentry wells between a plume and a receptor (or downgradient from a treatment barrier) to detect contaminant migration; and site characterization in that following well installation, biosensor results can be used to direct the placement of the next characterization probe. (Project Completed - 2006)

Contacts:

Technical Contact:
Roger L. Olsen
Camp Dresser & McKee Inc.
1331 17th Street, Suite 1200
Denver, CO 80202
Telephone: (303) 298-1311
Fax: (303) 293-2836
E-mail: olsenrl@cdm.com

DoD Liaison Officer:
Herbert L. Fredrickson
U.S. Army Engineer Research and Development Center
Environmental Laboratory, CEERD-EP
3909 Halls Ferry Road
Vicksburg, MS 39180
Telephone: (601) 634-3716
Fax: (601) 634-3410
E-mail: fredrih@wes.army.mil