Quantitative information about in situ natural degradation mechanisms and rates for carbon tetrachloride (CT) is needed to support remedy implementation with respect to the operational lifetime of the 200 West Groundwater Treatment Facility (200W P&T system) and transition to monitored natural attenuation. Laboratory studies estimated the hydrolysis half-lives of CT and chloroform (CF) under Hanford groundwater conditions (pH 7.8, 16 °C) to be 630 and 3,400 years, respectively. This rate of CT hydrolytic degradation is too slow and will not have a consequential impact on groundwater CT remediation. Biotic and coupled biotic-abiotic mechanisms of natural CT degradation have not been evaluated or measured with respect to a natural attenuation remedy for 200 West Area aquifer (200W aquifer) conditions. Summarized in this report are biotic and abiotic reductive degradation mechanisms for CT, as well as chlorinated byproducts, along with normalized reaction rates for each mechanism based on published values from controlled laboratory studies and field trials. CT degradation mechanisms were used to identify indicators of degradation activity. 200 West Area groundwater data and the relative significance of measured trends in groundwater chemistry were evaluated, taking into account the effect of 200W P&T activities on monitoring well data.