ABSTRACT
Groundwater contaminants can be detected in situ by making spectroscopic measurements through fiber optics. In addition to direct measurements, it is possible to couple fiber optics with chemical indicators that interact with the contaminants to enhance their detectability. Direct fluorescence measurements have been used to sensitively detect aromatic hydrocarbons in fossil fuels. Direct Raman measurements are also possible but can only detect relatively high concentrations (>0.1%). Parts per billion levels of nitroaromatics and halogenated hydrocarbons can be detected using indicators that react to form colored products. The rate at which the absorbance of the colored product increases is proportional to concentration. Refractive index measurements offer a rugged, reversible approach to detecting classes of organic contaminants in the low parts per million range. Other spectroscopic techniques are considered in this chapter but are not practical for in situ groundwater monitoring at this time. A few of the more promising methods are ready for commercial development while many others require considerable further development before they can be reliably used on a routine basis.
