Chief Sanitary Engineer for the State of Illinois, 1935-1970, first director of the Illinois Environmental Protection Agency and environmental consultant. Served as an expert witness at a trial, 1979-1994, regarding the dumping of toxic wastes at Love Canal in Niagara Falls, New York. Love Canal was dug in the 1890s, used as a chemical dump, and later filled in and developed for housing. The area was declared unsafe and 239 families were evacuated in 1978. The Federal Government, State of New York and other interested parties went to court in 1979 to recover the costs of tests, the purchase of homes, clean-up, and other expenses.

Includes material from the trial United States et al vs. Occidental Chemical Corporation et al, held in U.S. District Court in Buffalo, New York, 1979-1994, including memoranda, depositions, transcripts of examinations and testimony, exhibits, and reports. Klassen was an expert witness for the State of New York. Also includes a scrapbook of clippings, articles and other material on the history of the Love Canal incident, other collected articles and reports, a book on the subject, (Craig E. Colton and Peter N. Skinner, The Road to Love Canal (Austin: University of Texas Press, 1996)), and information on toxic waste dumps in Calumet City and Winnebago County, Illinois.