An apparatus, method and insulation medium for inserting and insulating a charge medium within a borehole includes a charge tube comprised of an elongate tube having a length and diameter sufficient for containing a desired quantity of a charge medium. A charge medium in a pumpable form is provided for substantially filling the charge tube. An insulation medium in a pumpable form is provided for substantially encapsulating the charge tube and substantially filling an annular space between the charge tube and the borehole for insulating the charge tube from a downhole environment in which the charge tube is to be inserted. The apparatus, methods and insulating medium can also be used for the improvement and repair of underground liners and installations and for improved treatment of mining and hazardous waste.