Tritium in Unsaturated Zone Gases and Air at the Amargosa Desert Research Site, and in Spring and River Water, near Beatty, Nevada, May 1997

By Robert G. Striegl, Richard W. Healy, Robert L. Michel, and David E. Prudic

ABSTRACT

Elevated tritium concentrations in the unsaturated zone at the Amargosa Desert Research Site (ADRS), immediately south and west of the low-level radioactive-waste burial site south of Beatty, Nevada, have stimulated research of processes that control the transport of tritium in arid unsaturated zones. In May 1997, 58 samples were collected from 1.5 m (meters) depth within a 250 m by 250 m grid at the ADRS. Measured concentrations ranged from 16 ± 9 to 36,900 ± 300 tritium units (TU), decreasing from northeast to southwest, possibly along an ancestral Amargosa River channel.

The 10 air ports at test hole UZB-2 also were sampled, including ports at 57.6, 106.4, and 108.8 m depths that had not been sampled since 1994. Of the remaining seven ports, five were sampled in 1994, 1995, and 1996, and two were sampled in 1994 and 1996. Tritium concentrations at the four ports deeper than 50 m ranged from 791 ± 15 to 1765 ± 29 TU, having increased since they were last sampled. Tritium concentrations at the six ports shallower than 50 m ranged from 367 ± 11 to 1283 ± 20 TU, and appear to have stabilized since 1996.

Tritium concentration in water vapor collected from air within the creosote bush canopy was 75 ± 9 TU near test hole UZB-2 and 9 ± 6 TU near the uncontaminated Fischer test hole, 3.2 km to the south. Elevated tritium concentration in air near test hole UZB-2 was attributed to plant transpiration removing water from the unsaturated zone. Nearby surface water tritium concentrations were 6.3 ± 0.4 TU at Specie Spring, 0.0 ± 0.3 TU at Lower Indian Springs and at Upper Indian Springs, and 0.8 ± 0.6 TU in Amargosa River water.

This abstract was published in USGS Open-File Report 97-778.