43. 



DR. M. HA/VKINS: Do materials forming the terraced plain 

 rest on basalt ? 



MR. PIPER: The basalt passes underneath, and there are 

 some irregularities in its upper surface. We haven't the data to plot 

 the rock profile. The overburden is outwash and some material that 

 may be non-glacial. 



DR. HAWKINS: What would be the normal rate of water move- 

 ment toward the river if the mounds were not present? 



MR. PIPER: That is the sort of question a ground-water man 

 never answers. (Laughter) Regardless of the average rate of move- 

 ment, we know that in other areas contaminating (but non-radio- 

 active) fluid moves largely by displacement, as though floating. The 

 great uncertainty is that there is no indication of impending trouble 

 until the contaminant suddenly appears. The average rate of move- 

 ment is no measure of the movement in the most permeable threads. 



DR. GILLULY: In a laboratory test of the soil column, solu- 

 tions can be passed through samples in a beaker or diffusion column 

 without duplicating the conditions in nature; in nature there are going 

 to be high permeable channels through which the flow will be concen- 

 trated. The natural conditions are far from homogeneous and very 

 different from the conditions and results one is apt to get in a test in 

 a laboratory. 



MR. PIPER: That is very true. Any test in a cylinder of re- 

 stricted size is difficult to extrapolate to natural conditions. For one 

 reason there is a boundary effect in any cylinder of laboratory size 

 that may greatly distort the results. The lack of homogeneity is shown 

 by the tests made around some of the cribs: I sketched a smoothly 

 bounded zone /of fission-product adsorption/ but they are not all that 

 way by any means. In the ideal case the solutions moved down through 

 uniformly permeable material; where the permeability is discontinuous 

 there is considerable irregular lateral spreading. You can get all 

 sorts of queer details reflecting local inhomogeneity . Yet, on the 

 whole, the material is permeable throughout. 



MR. S. G. LASKY: Why do you say that the test holes at the 

 ground water table may not pick up any radioactive material? 



MR. PIPER: A well is drilled to the water table for the purpose 

 of detecting the passage of a contaminated fluid. There is water in 



