Physical and chemical characteristics of topographically affected airflow in an open borehole at Yucca Mountain, Nevada

Borehole UZ6S, on the crest of Yucca Mountain, Nevada Test Site, has exhaled approximately 106 m3 of gas annually during winter months for three successive years. The flow arises from thermal-topographic effects. The average composition of the exhausted gas is: N2 = 78%, O2 = 21%, Ar = 0.94%, CO2 = 0.125%, and CH4 = 0.2 ppMv. The CO2 has the following isotopic signature: 14C = 108.5 percent modern carbon (pmc), and δ13C = 17.1 permil. In the thirty-month observation period, there has been a net flux to the atmosphere of approximately 40 m3 of liquid water and 1150 kg of carbon. The gas flowing from UZ6S appears to originate in the soil and/or shallow unsaturated zone at Yucca Mountain crest. 25 refs., 6 figs., 4 tabs