One of the most problematic, widespread, and expensive remediation problems at both Department of Defense (DoD) and civilian sites is groundwater contaminated with chlorinated solvents. A significant portion (as much as half) of the cost is associated with the sampling and laboratory analyses required for site characterization and long-term monitoring (LTM). These costs are high because currently available analytical technology is laboratory-based, personnel intensive, and not easily adapted for use on site. Furthermore, instrumentation that can be used on site and left in place to meet LTM requirements is simply not available. As a result (and at considerable cost), a site may be either over- or under-characterized and LTM is typically limited to one to four often incomplete snapshots per year. Thus, there is a real need for a simple and cost-effective analytical tool (sensor) that can be used during site characterization and left in place to monitor chlorinated solvent compounds such as trichloroethene (TCE) and tetrachloroethene (PCE), cis- and trans- dichloroethene (DCE), and vinyl chloride (VC).
The overall objective of this project is to significantly reduce DoD site characterization, cleanup, and LTM costs through development and optimization of a novel real-time sensor technology to discriminate and quantify PCE, TCE, cis- and trans-DCE, and VC in groundwater.
Independently, Georgia Tech Research Institute (GTRI) and American Research Corporation of Virginia (ARCOVA) have developed sensors that use polymers deposited on a glass slide to reversibly select and concentrate contaminants in groundwater or air as samples pass through the sensor. Both sensors use a diode laser positioned to elicit total internal reflectance, which generates an evanescent wave perpendicular to the direction of light propagation that queries the films for the presence of contaminants. Since the evanescent wave does not propagate into the bulk solution, nonspecific interference is greatly minimized. Both sensors measure analytes that partition from the bulk solution into the polymer film. The GTRI sensor measures changes in the index of refraction of the polymer, and the ARCOVA sensor detects changes in the fluorescence of analyte-specific reporter dyes immobilized within the polymer matrix. The choice of polymers (GTRI) and polymer dye conjugates (ARCOVA) enables analytes to be differentiated, and the magnitude of the response is proportional to the concentration of the analyte. Standards are used to calibrate the response of the photodetector, and an onboard microprocessor is used to convert changes in the index of refraction (GTRI) or fluorescence (ARCOVA) to analyte concentrations.
While remedial strategies have become better understood and more efficient, site characterization and LTM have remained labor-intensive and dependent on remote laboratories for sample analyses. As a result, sites may be inadequately characterized, LTM may be infrequent or inadequate, and treatment technologies may encompass too much or too little of the site. Low-cost sensors that provide real-time measurement capabilities would significantly reduce site characterization time, increase confidence that a site is fully characterized, provide more complete data sets for modeling and monitoring programs, and reduce LTM costs. An added benefit is greater public confidence in and increased acceptance of proposed remedies. No comparable technology is currently available. (Anticipated Project Completion - 2011)