An in situ reactor for use in a geological strata includes a liner defining a centrally disposed passageway and a sampling conduit received within the passageway. The sampling conduit may be used to receive a geological specimen derived from geological strata therein and a lysimeter is disposed within the sampling conduit in communication with the geological specimen. Fluid may be added to the geological specimen through the passageway defined by the liner, between an inside surface of the liner and an outside surface of the sampling conduit. A distal portion of the sampling conduit may be in fluid communication with the passageway.