The document provides the technical background and justification for the U.S. Environmental Protection Agency's (EPA) proposed regulation (40 CFR Part 503) covering the land application and distribution and marketing of sewage sludge. The document summarizes current practices in land application and presents data supporting the risk assessment methodology used to derive human health and environmental risk-based limits for contaminants in land applied sewage sludge. The underlying assumptions of the methodology, embodied in a series of computer models, are discussed, and the risk-based contaminant limits derived by the models are presented. The three management practices associated with land application are outlined, and the twelve different pathways by which contaminants reach most-exposed individuals through land application are discussed.

Reprint. Originally published: Washington, DC : U.S. Environmental Protection Agency, Office of Water Regulations and Standards, {1986}. "PB89-136576." Includes bibliographical references (p. 7-1--7-29).