Floyd Lee Galpin, 64, a retired senior engineer and Public Health Service captain who was an expert at the Environmental Protection Agency on the disposal of radioactive waste, died of cancer Dec. 5 at his Derwood home.

Mr. Galpin, who retired in 1993, directed EPA's national program for radiation monitoring and assessment and issued the first EPA reports on the radioactive state of the environment.

He was born in Iowa and raised in Brainerd, Minn. He was a graduate of the University of Oklahoma, where he also received a master's degree in civil engineering. He did graduate work in public health at the University of Michigan.

He served as a chemical corps officer in the Army.

Mr. Galpin began his career with the Oklahoma health department and joined the Public Health Service in 1963. He was assigned to the National Center for Radiological Health, in what was then the Department of Health, Education and Welfare.

He switched to EPA when it was created in 1970. After he retired, he managed the Washington office of Rodgers and Associates Engineering Corp.

His honors included the Outstanding Service and Commendation medals of the PHS.

Mr. Galpin was a director of the regional chapter of the Health Physics Society and a member of the American Nuclear Society, the American Conference of Governmental Industrial Hygienists and the Commissioned Officers Association of the PHS.

His marriage to Daryl Galpin ended in divorce.

Survivors include his wife of 22 years, Patricia T. Galpin of Derwood; two daughters from his first marriage, Mona Galpin of Rockville and Brenda L. Fookes of Silver Spring; two stepchildren, Pam Rubin of Poolesville and Daniel Herbert of New Market, Md.; and a grandson.

A son from his first marriage, Steven J. Galpin, died in 1989.