-41- made during the build-up of the discharge level to 1,000 curies per month and a reassessment of the "safety factors" that were included in the original studies and recommendations, authoriza- tion has now been granted to discharge wastes at Windscale at the rate of 10,000 curies per month. Another area where radioactivity is being added continuously is the Pacific Ocean at the mouth of the Columbia River which receives low level liquid wastes from the Hanford plutonium production reactors. The total amount of radioactivity entering the ocean at this point is about 1000 curies per day Energy Commission, (U. S. Atomic 1960). The waters of the oceans cover 71 per cent of the earth's surface and the mean depth for all oceans is about 14,000 The ocean can be conveniently divided into three domains: the inshore area, feet. (1) including the intertidal zone, bays and harbors; (2) the shelf area, extending from the low tide line out to a depth of about 600 feet where the bottom slope increases rapidly towards the deep sea; and inshore area, (3) the deep sea. The waters of the the shelf and the uppermost part of the deep sea are thoroughly mixed by the winds and in the inshore areas by the tides. By contrast, the waters of the deep sea below the surface layer, which varies in depth but is usually about 200 that feet thick, are stratified and slow moving. both vertical and boundary between the identified by a rapid horizontal surface and decrease in -_- . This means mixing is the deeper limited. The waters is temperature with depth . a —~ ff bee. Let eh OL ee hh