This exploratory project will investigate the development of fiber optic sensors to measure groundwater contaminant mass fluxes and cumulative contaminant-specific microbial activity in-situ and real time. A novel, integrative mass-flux based assessment approach is proposed in preference to traditional concentration-based approaches. Mass flux quantification is necessary to evaluate the effectiveness of remediation, through either intrinsic (i.e., natural attenuation) or active (e.g., pump and treat of in situ flushing) means. The contaminants of interest are chlorinated hydrocarbons, specifically TCE and PCE and their degradation products. Quantification of contaminant mass flux will be especially useful in characterizing risks to humans and the environment from groundwater contamination.