An unsaturated fractured rock sampling technique by in situ thermoelectric condensation of water vapor

Abstract

Water vapor in the airspace of an unsaturated fractured rock may be sampled by reduction of the air temperature of the medium to its dew point and retrieval of the condensed liquid sample. The required temperature Change was generated in this research by a thermoelectric cooling module, which operates according to the Peltier cooling effect. Laboratory studies of this technique involved the development of the module’s heat sink system and calibration of the instrument for cooling temperatures and condensation rates obtained by variations in the applied current. Temperature and vapor density Changes produced in the air space surrounding the instrument when operated in a moist environment were also evaluated. Field studies performed in an unsaturated, fractured, densely-welded tuff have shown the instrument to be capable of vapor collection, although at a rate lower than that established under laboratory conditions. Applications of this technique include evaluation of oxygen and hydrogen isotopes of moisture in unsaturated media and travel time studies of flow through the unsaturated zone using isotopes as tracers.