The document summarizes an assessment of a zero-valent iron permeable reactive barrier (PRB) installed in 2002 to treat trichloroethene (TCE) contamination at a former air force base in Texas. Monitoring showed the PRB effectively treated TCE for the first 5 years by promoting abiotic dechlorination. However, starting in 2008, concentrations of vinyl chloride and other daughter products increased downgradient. The assessment found the PRB performance was mixed - sections effectively treated TCE through abiotic and biotic processes, while other sections were bypassing treatment, causing increased downstream contamination. Geochemical data from different sections of the PRB supported varying levels of reactivity and treatment effectiveness over time.