On 30 June 2014 10:08, James Cameron wrote: .... I'm thinking of hiring a guy with a large bulldozer to dig a long narrow trench, then buying a large shipping container. ... Can you mole plow in annealed copper tubes? May save lots of digging. How deep is deemed desirable for thermal transfer? Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .