AbstractThe degradation of 2,4,6‐trinitrotoluene (TNT) and other explosives by zero‐valent iron (ZVI) is rapid and, as a result, potentially useful for both ex situ ground water “pump‐and‐treat” systems and in situ permeable reactive barriers. However, the usefulness of ZVI in either configuration may be limited by reaction‐induced reduction in both hydraulic conductivity (K) and reactivity (as represented by the surface area–normalized rate constant, ksa). The impacts of dissolved oxygen and TNT on K and ksa are examined here using field and laboratory columns. The data suggest that K reduction in ZVI columns can be significant when dissolved oxygen is present. However, when TNT is present at approximately the same concentration (10 mg/L), it does not cause significant reduction in K. In contrast, TNT causes a significant reduction in ksa, while dissolved oxygen appears to have relatively little impact on the reactivity of the columns toward TNT.