ton nuclear tests except those which were fired for cratering purposes. These tests which were examined in cepth were fired in vertical drilled holes, some in drilled hole at a later. horizontal tunnels - which we'll take a leok By far the greatest nuaber of tests have been fired in these vertical holes without pipes or other direct communications with the surface and stemmed with sand, gravel,and cement just above the test device to the ground surface. Considering all the tests in this general category and size, since the resumption of nuclear testing in 1961, only ten released radioactivity of any consequence. Of these only three re- leased radioactivity that could be detected outside the controlled area of the Test Site. Of these ten, (300 ground fissures) commencing within a few minutes of the explosion, the other seven seeped radioactivity after cavity collapsed. Of the ten, seven were tests with yields of less than 5 ket. We have never experienced a venting in the upper or higher yield ranze. To give you some comparison, we also support the Department of Defense, particularly DASA, in its effects experiments. This illustrates a tunnel configuration involving a line of sight canister for the Minute Gun Sertes. I think it is very clear the extreme complexity of this type of event. During the fll and winter of 1965, a great deal of thought was being ziven to site locations where higher yields would be acceptable. During the winter of 1966, several possible supplemental test areas were examined and evaluated, We looked very carefully at the geology and logistical character- istics and safety problems upon the proximity of the human population centers. AS 4a result of this investigation, three sites were selected for further