Another controversy over nuclear waste site.

Another controversy over nuclear waste site

Geoscientists working for the State of Nevada are questioning the accuracy of federal studies looking at the geologic stability of Yucca Mountain, Nev. -- the proposed site for the nation's first high-level nuclear waste dump [SN: 2/27/88, p.139].

Plans for the repository call for placing radioactive waste into sealed rooms 1,000 feet below the surface of the mountain, a remote ridge of volcanic rock expected to keep the waste from leaking into the environment for thousands of years. the Department of Energy is collecting information to assess whether this site, 100 miles northwest of Las Vegas, is suitable for the repository. In order to make this decision, federal officials will require assurance that future earthquakes, volcanic eruptions or climate changes will not threaten the repository.

At the meeting of the Geological Society of America in Denver this week, Ronald Dorn of Arizona State University in Tempe and colleagues from the Univeristy of Nevada in Reno said their work, conducted separately from the Energy Department research, shows the federal scientists may be analyzing their data in a way that could underestimate hazards in the Yucca Mountain area.

The controversy between the two investigations centers on a relatively new technique called varnish dating. When a geologic event such as a landslide or an earthquake exposes rocks to air, it can cause dust and bacterial residue to collect on the newly uncovered surfaces, creating a thin black varnish. Over time, air and water leach elements from this coating. By analyzing the ratio of the remaining elements and then matching these ratios against a standard, researchers can date the varnish and thus the geologic event.

Dorn, who helped develop this technique in the early 1980s, says the problem with the federal studies lies in the way they calibrate the elemental ratios against a standard. "The ages they are getting for the varnish have a reasonably strong possibility of being too old and hence of minimizing the hazard," he says.

Researchers studying a certian fault may use a varnish date to determine when the fault began to move. If the varnish date is too old, investigators would underestimate the recent activity of the fault, possibly leading to false calculations of the stability of Yucca Mountain, says Dorn, who advocates a different calibration technique.

Charles D. Harrington from the Los Alamos [N.M.] National Laboratory, one of the researchers performing rock varnish work for the Energy Department studies, acknowledges that "calibration techniques are a problem." Yet, he says, it will take much more research to tell whether either of the controversial calibration methods yields inaccurate results.