1973 Rio Blanco nuclear test
By the 1970s, the Committee for Nuclear Information (CNI) had morphed to become the Committee for Environmental Information (CEI). Michael remained as Chairman of the Scientific Division of CEI. In that role, in the spring of 1973, he wrote letters to the U.S. Department of the Interior about the proposed nuclear test at Rio Blanco (Wikipedia), Colorado.
This test (which did take place, in mid-May 1973) was an effort to use underground nuclear explosions to help with natural gas production. It was in essence an early attempt akin to fracking, but with nuclear explosions.
Rio Blanco was part of the Plowshares program, (and a follow-on to Plowshares' "Gasbuggy" test), about which Michael had written in the March 1968 issue of Scientist and Citizen (CEI's newsletter).
The first PDF below is a 12 page set of documents/letters exchanged with the Department of the Interior as well as with the director of the "Potential Gas Agency" of the Mineral Resources Institute/ Colorado School of Mines Foundation. The letter from the latter individual mentions that Michael's letter to Interior had been placed in the Congressional Record by Senator Floyd Haskell (D-CT), who had only entered the Senate in January, 1973.
His letter appeared in the United States Senate's Congressional Record for May 1, 1973, pages 13706-13707, which is pages 9 and 10 of the PDF shown below. (This is the first 22 pages of the Record for that day (of a 120 page (47MB) document not included here). The pages that are shown here (well beyond the end of Michael's letter) have other discussions, letters, and testimony about Rio Blanco.
May 1, 1973: The Congressional Record
Michael's letter published on pages 9 and 10 of PDF (pp.13706-13707)