Ecological Soil Screening Levels (Eco-SSLs) are concentrations of contaminants in soil that are protective of ecological receptors that commonly come into contact with soil or ingest biota that live in or on soil. Eco-SSLs are derived separately for four groups of ecological receptors: plants, soil invertebrates, birds, and mammals. These values are presumed to provide adequate protection of terrestrial ecosystems (i.e., plant and wildlife populations). The Eco-SSLs are conservative and are intended to be applied at the screening stage of an ecological risk assessment. These screening levels should be used to identify the contaminants of potential concern that require further evaluation in the site-specific baseline ecological risk assessment. The Eco-SSLs are not designed to be used as cleanup levels and U.S. EPA emphasizes that it would be inappropriate to adopt or modify these Eco-SSLs as cleanup standards. This guidance document provides the Eco-SSL values for arsenic and the documentation for their derivation. While the document is designed to communicate national policy on identifying arsenic concentrations in soil that may present an unacceptable ecological risk to terrestrial receptors, it does not substitute for EPA's statutes or regulations, nor is it a regulation itself, and hence does not impose legally-binding requirements on EPA, states, or the regulated community. Available at http://www.epa.gov/ecotox/ecossl/pdf/eco-ssl_arsenic.pdf