Abstract: In situ treatment of contaminated groundwater includes identifying a site contaminated with a pollutant susceptible to degradation by in situ, sulfate-reducing microorganisms. An amount of sulfate needed to support metabolization of the contaminants is estimated. The estimated amount of sulfate is applied to the site. In various alternatives of embodiments of the invention, the sulfate may be applied is a dry state or as a solution with water. The sulfate concentration in solution is in excess of 1000 ppm and may be as high as a near-saturation concentration.