To protect an underground aquifer from pollution due to the extraction of subsurface products from a recovery well or other subsurface mining operation, a plurality of barrier injection wells are formed around the recovery well/subsurface operation, each barrier injection well terminating in a groundwater layer to be protected. A polymer matrix material is then into the injection wells such that the material exiting each injection well expands and overlaps with material exiting from adjacent wells prior to solidification, thereby forming an isolation barrier within the groundwater layer. In the preferred embodiment, the polymer matrix material is a cellulose polymer hydrogel matrix material which is injected in gel form. Following recovery of the hydrocarbonaceous products from the recovery well(s), the injected polymer matrix material may be reheated and subsequently liquefied allowing full groundwater flow to occur.