Abstract: In situ liners are impermeable compound backfilled underground rock channels which are artificially cut and laterally and vertically extensive. The backfilled channel cuts may be joined to form six-sided enclosures, five-sided basins, four-sided conduits, and three-sided (or less) diversion surfaces. The channel are backfilled by bulk materials (e.g. sand, untreated or pre-or post-placement treated), or the bulk material can be layered between spray-on liner materials on the channel hanging wall and floorwall. This in situ liner allows containment and control of solutions, liquids, gases, or solids, which may be permanently or temporarily stored, processed, or diverted.