410395 January 11, 1357 Dr, Allyn H, Ssymour Marine Blologist, Biclogy Department Division of Biology anc Medleinc U.S. Atomic Enerzy Commission 1901 Constitucion Avenue Now. Washington 25, D.C. , BEST COPY AVAILABLE Dear Al: uring a conversation while Sc and I were in Washington last month, you mentioned that the activity levels in the water at Rongelap were higher in July 1956 than the levels reported in UWEL-43 obtained at earlier visits. looked up the data anc summarized it. Ed has The best evidence seems to indicate that the ineress noted in the July 1956 samples 1s Jue to the recontamination of Rongelap from the 1956 series of weapons tests. c Jfeny of the newly acded recdloactivity is such that it will soon be insignificant when compares with that from the 1954 serics, The cecay of activity of the particulate matter anc tne iltrate of &@ cistern water and a lagoon water sample col- cated at Rongelap Islan! in July 1956 was followed. Although he eounting error is too large to permit a precise evaluation ’ the decay rate, it Ls clear that the half life immetiately .fter August 22 (first counting date) was between 20 aad 40 says, indicating the presence of short half-life radionuclivies. The count of January 1957 resulted in values which compare to those found in Oetober 1956 and reported in UWFL-43, Table 13, as follows (values in d/mAliter): Collection Date Counting Date det. '55 Oct. '55 Cistern water particulate matter 75°17 Cistern water filtrate . + 310-199 Lagoon water a yarticulate matter Lagoon water riltrate + GO=120 July ‘56 Aug. '56 — 390t17 July '5¢ Jan. '57 + 91=10 a 110-73 910f100 + 1410-12 ' 2ho0te210 2000#200 Sincerely, | 64480 + 24-5 ro auot1cs