Compositions and methods for treating contaminated soil and/or ground water in situ. The compositions and methods comprise stabilized forms of colloidal activated carbon that are used to quickly sorb contaminants. Unlike traditional activated carbon in granular or powder form, the compounds and methods of the present invention are operative to transport particulate activated carbon through a matrix of soil and groundwater upon application by injection, gravity feed, or percolation into soil and groundwater, which in turn decontaminate groundwater in place without the cost or disruption associated with digging the contaminated soil and groundwater out of the ground for on-site purification or disposal at a hazardous waste landfill.