GENERATION OF HYDROGEN GAS A RESULT OF DRILLING WITHIN THE SATURATED ZONE

Hydrogen gas was discovered within the steel casing above standing wat er in a percussion-drilled borehole on the Hanford Site in south-centr al Washington state. In situ measurements of the borehole fluids indic ated anoxic, low-Eh (<-400 mV) conditions. Ground water sampled from a djacent wells in the same formation indicated that the ground water wa s oxygenated. H2 was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The gen eration of H2 within percussion-drilled boreholes that extend below th e water table may be more common than previously realized. The ambient concentration of H2 produced during drilling was limited by microbial activity within the casing-resident fluids. H2 was generated abiotica lly in the laboratory, whereby sterilized borehole slurry samples prod uced 100 times more H2 than unsterilized samples. It appears that H2 i s metabolized by microorganisms and concentrations might be significan tly greater if not for microbial metabolism.