The various embodiments of the present invention relate generally to remediation of contaminants in the environment, and more specifically to improved chemistries, systems, and methods for in-situ immobilization of contaminants in various media. More particularly, an aspect of the present invention is directed to an in-situ method for immobilizing a contaminant in a medium, comprising: contacting a medium in-situ with a chemical reagent, the medium comprising a contaminant, wherein the contacting the medium in-situ with a chemical reagent does not involve physical mixing of the medium and the chemical reagent; and immobilizing at least a portion of the contaminant in the medium in-situ to yield an immobilized contaminant in the medium, wherein the immobilized contaminant in the medium is neither extracted from the medium nor degraded by the chemical reagent.