The objective of this project is to fabricate and demonstrate an internal reflection sensor (IRS) prototype for the cone penetrometer. The IRS is a sensor that responds in real-time to almost any subsurface liquid contaminants. The IRS utilizes the variations of refractive index of different liquid contaminants as a sensing scheme. All the project objectives have been successfully met during the period of the program. A prototype IRS that can be easily integrated into a cone penetrometer was designed and fabricated in the first phase of the program. A controlled field evaluation of the IRS was also conducted during the first phase and results showed that the IRS was capable of locating NAPLs in soil. In the second phase of the program, the IRS was evaluated in the field and pushed into the ground using an actual cone penetrometer system. The IRS was evaluated at known contamination sites at the Savannah River Site and a commercial site in Jacksonville, Florida. Results of the field deployment of the IRS indicated that the sensor was able to sense the location of contaminants such as tetrachloroethylene in the subsurface.