This report contains information on the current state of the treatment of soil, waste, and water containing arsenic, a contaminant that can be difficult to treat and may cause a variety of adverse health effects in humans. This information can help managers at sites with arsenic-contaminated media, generators of arsenic contaminated waste and wastewater, and owners and operators of drinking water treatment plants to: ' Identify proven and effective arsenic treatment technologies ' Screen those technologies based on effectiveness, treatment goals, application-specific characteristics, and cost ' Apply experience from sites with similar treatment challenges ' Find more detailed arsenic treatment information Arsenic is in many industrial raw materials, products, and wastes, and is a contaminant of concern in soil and groundwater at many remediation sites. Because arsenic readily changes valence state and reacts to form species with varying toxicity and mobility, effective treatment of arsenic can be difficult. Treatment can result in residuals that, under some environmental conditions, become more toxic and mobile. In addition, the recent reduction in the maximum contaminant level (MCL) for arsenic in drinking water from 0.050 to 0.010 mg/L will impact technology selection and application for drinking water treatment, and could result in lower treatment goals for remediation of arsenic-contaminated sites. A lower treatment goal may affect the selection, design, and operation of arsenic treatment systems. This report identifies 13 technologies to treat arsenic in soil, waste, and water.