The Fenton-filtration process has been found to lower the arsenic (As) concentration in groundwater below the maximum contaminant level (MCL) of 10 micrograms per liter (ig/L). Oxidation of As(III) to As(V) and the addition of supplemental iron (Fe) to improve sorption were both essential for effective treatment. In the present work, Fenton-filtration was compared with chemical oxidation using conventional treatment chemicals. Both sodium hypochlorite and potassium permanganate were more effective than Fenton filtration at oxidizing As(III). Therefore, the choice of treatment method may depend on economic factors. The effect of natural organic matter (NOM) on the Fenton-filtration process was unclear. Laboratory experiments using groundwater and synthetic solutions showed that reactions involving NOM are significant, that hydrogen peroxide (H2O2) is produced in these reactions, and that there is no benefit in adding H2O2 in excess of the Fe(II) concentration. Earlier research on arsenic sorption used a double-layer model that generally under-predicted arsenic removal. A more recent triple-plane model was applied to the data from a series of Fenton-filtration tests and was found to give better predictions of soluble arsenic in treated water than the double-layer model, although it still underpredicted arsenic removal.