National Laboratory (PNNL) staff in helping put this document together in its final form. Lauri Marquardt, Scott Somers, and Rick Melbihess of CHG provided invaluable technical knowledge and insights into the current operations at the Hanford tank farms and the industrial hygiene challenges involved with protection of the workers. Jim Huckaby of PNNL provided his insight into gas and vapor generation and high-probability release points associated with the single-shell tanks. Our thanks go to Charles Olaiya and Richard Grill of the ORP for their discussions on the important aspects of this work, their guidance for the prioritization of efforts, and for their support of the project. We also want to thank Mary Ann McKinney of HEHF for her excellent job of performing a high-quality and timely technical review of the document.