This issue paper identifies and summarizes experiences with proven aboveground treatment alternatives for arsenic in groundwater, and provides information on their relative effectiveness and cost. The information contained in this paper can also be found in the report “Arsenic Treatment Technologies for Soil, Waste, and Water”, EPA542-R-02-004 (Ref. 1.12), which provides cost and performance data for additional technologies that can treat arsenic in soil, waste, and water. This paper has been developed jointly by EPA’s Engineering Forum and Technology Innovation Office. EPA's Engineering Forum is a group of professionals, representing EPA Regional Offices, who are committed to identifying and resolving the engineering issues related to remediation of Superfund and hazardous waste sites. The Forum is sponsored by the Technical Support Project.