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RADIOACTIVE WASTE DISPOSAL INTO ATLANTIC AND GULF COASTAL WATERS SUMMARY A study has been made of the feasibility of using selected areas in the Atlantic and Gulf of Mexico coastal waters of the United States as receiving grounds for the disposal of packaged, low level radioactive wastes. The primary objective of the study has been to provide an esti- mate of the rate of return of radioactive substances to man, arising from stated rates of disposal into the coastal areas. The limiting rate of disposal has been taken as that which through a combination of physi- cal and biological processes will return the radioactivity to man at a rate equal to the maximum permissible rate of ingestion of a given ra- dionuclide in drinking water. These rates were based on the occupational MFC's (maximum permissible concentration) given in Handbook 52 (3). The MFC's for the general population according to recent information should be low- ered by a factor of 10. The revised MFC's of some isotopes may be reduced even further. It is believed, however, that the conservative assumptions contained in this report offset the effects of these reduc- tions in MFC values. The present practice of using 55 gallon steel drums as disposal canisters containing the waste mixed with concrete is estimated to pro- vide containment of approximately 10 years, during which time radio- active decay will have destroyed all radioisotopes (based upon Oak Ridge National Laboratories current rate of production and shipment) to below hazardous levels, with the exception of Sr 90, Cs 137, and pos- sibly Co 60. Coastal circulation is not known in sufficient detail to provide quantitative estimates of the rate of transport of a contaminant out of any of the areas selected as possible disposal sites. These estimates can be made only after detailed circulation studies have been completed. Especially lacking is knowledge of the circulation of bottom waters. Nevertheless, several areas stand out as being probably unsuited as disposal sites. They are the coastal estuaries and bays, and the regions immediately seaward of these areas. Shoreward transport along the bottom in these regions would tend to intensify the rate of return of a contaminant to man. Also, a region southeast of Long Island, extending out to approximately 50 fathoms, appears to have restricted bottom
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circulation during the summer months and therefore might accumulate larger quantities of contaminant than other coastal areas. A theoretical study of the dilution of contaminant by turbulent mixing processes has been made. The results of the study provide the means of evaluating the effects of changing environmental parameters and of various disposal methods on the dilution of a contaminant. Be- cause of the assumptions made all estimates of concentration at a given distance and time are probably higher by at least a factor of ten than would actually exist in practice. Even with these conservative assump- tions calculations show that given a rate of disposal of 100 curies per year of uncontained waste into water 30 meters deep with a current of 5 miles per day, the maximum concentration of waste which will appear one kilometer (approximately 5/8 miles) from the disposal site will be 2 x 10"7 Lie/ml, a concentration that is lower than the maximum permis- sible concentration of Sr 90 in drinking water. Sr 90 has the lowest MPC value of all radioisotopes listed. In addition, the relationships between both relative concentration and time after release and distance from the disposal site, under the unlikely condition that no current will aid in diffusive mixing, have been developed. In arriving at recommended disposal rates the interaction of a contaminant with suspended solids and bottom sediments has been neg- lected. It was found impossible to make a quantitative estimate of the magnitude of this reaction. Neglecting this factor puts a certain factor of safety in the recommendations, as sorption onto bottom sediments within the disposal area will provide additional containment, thus allow- ing for further destruction of the contaminant by radioactive decay. In the case of disposal into areas productive in commercially important shellfish (oysters, clams, etc.) the sorption onto bottom deposits may become a potential hazard rather than a safety factor. This situation has been eliminated by selecting areas in which no shell fisheries occur. The return of radioactive wastes to man by ingestion of contam- inated marine food products is considered to be the most likely poten- tial source of hazard that could result from disposal into coastal waters. An estimate has been made of the maximum permissible concentration of each of several radioisotopes in sea water, below which contamina- tion of marine food products will not lead to greater than allowable in- take by humans whose sole source of protein is fish. This estimate was derived from the maximum permissible concentration of the iso- topes in drinking water, from which was computed the maximum weekly intake of each of the isotopes; the weekly ingestion rate of fish, taken as 1.5 kg, a value that is high compared with the per capita value for this country but has been taken on the assumption that some indi- viduals obtain all of their protein from fish; and the extent to which marine organisms can concentrate the various isotopes within them- selves above the level in their environment. The most hazardous iso- tope in the list is Sr 90, for which the maximum permissible concen- tration in sea water is 8 x 10-? jj.c/ml, which by coincidence is identical with the MPC value for drinking water.