the half life of carbon tetrachloride (CT) in a ZVI mediated reactive cell is 4.5 hra for ita degradation into methane as the end product the initial CT concentration is 1 mg/L to achieve its target concentration of 5 micrograms/L (.005 mg/L) what the required thickness of reactive cell would be? assume the groundwater flow velocity is 1 ft/day and CT has a retardation factor of 1.6