100. 



site is satisfactory this would be ■worth looking into for 

 liquid wastes . 



Mines are also very promising for solid storage. 



C. Special Excavations, including solution cavities in salt. 



(1) General statement. Special excavations have all the ad- 

 vantages of mines except for their higher cost. In addi- 

 tion, we can choose the location, geologic horizon, 

 geometry, etc. The cost of special shafts would be about 

 $200 a foot for the main shaft with a 6 to 8-foot diameter, 

 $100/ft. for cross cuts, and $100/ft. for ventilation shafts. 

 As in mines, heat dissipation would be a problem, but the 

 excavation could be designed to aid this dissipation. 



(2) Excavation of solid rock. Deep shafts in crystalline rocks 

 might be practical -- they would have the same character- 

 istics as deep abandoned mines. Also, it seems worth 

 while investigating artificial excavations in shale. Al- 

 though surface pits in the shale are probably not leak- 

 proof, excavations in thick shale beds in Illinois have re- 

 mained bone-dry since they were made (Loofbourow) . It 

 was the opinion of several engineering geologists that dry 

 chambers can be excavated at relatively shallow depths 



in thick shale formations. A great deal of testing would 

 be necessary, however, before one of these cavities 

 could be endorsed for the disposal of liquid wastes. Type 

 of research needed is: mechanical strength tests of the 

 particular formation involved, stability of the shale in the 

 presence of the particular solutions, etc. The cost of 

 propane storage in this type of cavity runs from 7 to 14 

 dollars a barrel. 



(3) Dissolved cavities in salt. Solution cavities in salt are 

 probably the most promising sites for relatively shallow 

 disposal of liquid wastes. Both bedded salt and salt domes 

 are possible, although bedded salt would have more prob- 

 lems, such as the greater difficulty of controlling the size 

 and shape of the cavity and the additional testing of the 

 roof and floor rocks . 



a. Advantages of salt cavities. 



