The dissolution of a “structure breaking reagent” such as NaCl results in reduction of hydrogen bonds between water molecules and a corresponding change in the absorption of electromagnetic energy at specific absorption bands (Chap. 1). This change in energy absorption is proportional to the amount of salt dissolved in water. Sodium and Calcium Chlorides are among the strongest structure-breaking reagents, a quality which is used in deicing agents. As part of a program investigating the use of optical spectroscopy for applications to the subsurface monitoring of infrastructure materials, a study was carried out involving analysis of the Near-Infrared (NIR) spectra of EM radiation when interacting with aqueous solutions containing dissolved Sodium Chloride (NaCl). This chapter described results of sensitivity and calibration procedures for in situ intrinsic sensing of dissolved Chlorides.