Sunday, Jan. 24, 1999 | 9:55 a.m.
Recent news reports have alerted the public to the discovery of plutonium almost a mile from where underground nuclear weapons were exploded at the Nevada Test Site.
But scientists working to clean up the site are more concerned about another element left from the more than 900 explosions set off 65 miles northwest of Las Vegas: radioactive tritium.
Their concern is how fast and how far tritium has traveled in the ground water and whether it has escaped the site's boundaries.
Tritium is considered the most dangerous of the materials left over from the nuclear blasts because it dissolves easily in ground water and poses a threat to public health for more than 100 years.
The Department of Energy began cleaning up the Cold War's radioactive mess after 1992 when a moratorium was imposed on U.S. nuclear testing. Officials estimate it will take until 2070 to complete the task and remove the threat of widespread contamination.
Above-ground tests that spread plutonium over the land in central Nevada were cleaned up first. The emphasis was switched to ground-water contamination after DOE scientists three years ago discovered plutonium in a water well far from a nuclear-bomb cavity. If plutonium can travel a mile floating in water, then tritium, which dissolves in water, would be a greater threat, scientists say.
Congress gave the DOE's Nevada Operations Office an extra $6 million this year to drill six new wells, for a total of eight, south and west of Pahute Mesa to check for tritium in the ground water. The concern is that if tritium has flowed south and west, it will move into drinking supplies and irrigation water for crops and dairy cows.
The new wells are expected to be completed by the end of the year. Samples will be analyzed and the results made public as analysis is completed, officials involved with the project say.
The scientists also are working to determine the direction the underground water is flowing. That information may not be available until 2003, Gary Russell of the U.S. Geological Survey in Las Vegas said.
Because of the secrecy surrounding the bomb blasts, little information on the content, size or number of weapons was available to outside scientists.
By piecing together information from available public sources, physicist Anthony Hechanova, who works at the Harry Reid Center for Environmental Studies at UNLV, determined that at least 260 underground nuclear explosions took place at or under the level of the ground water at the Test Site from 1951 to 1992.
Hechanova also gleaned from 10,000 pages of recently declassified DOE documents that a total of 921 bombs were set off at different levels during the same period, and he verified the number of ground-water blasts.
He compiled his findings in a comprehensive report released last week and made available to the public at UNLV's James Dickinson Library.
"This is the first time it has been compiled into one report accessible to the public," Hechanova said.
Thus far records that give the contents of the nuclear weapons are not available, which is hindering scientists in the cleanup effort and slowing a flow of information that could offer warnings to residents if dangers exist.
Hechanova found that the 921 underground nuclear-weapons experiments were conducted in 878 shafts and tunnels at the Test Site.
"The DOE has not released source term data (information about what was left by the bombs) on the individual nuclear-test explosions at the NTS," Vernon Brechin, a former Stanford University electronics technician, said. He now is a consultant specializing in the effects of underground nuclear explosions.
"Though the DOE has this information, it is still classified, reportedly to prevent the proliferation of nuclear-weapons technology," Brechin said.
Information about the Test Site experiments has trickled out recently in DOE reports issued from the national laboratories at Los Alamos in New Mexico and Livermore in California.
Hechanova, an MIT graduate, came to the Reid Center almost four years ago to work on the project. He has used the available DOE reports as well as those issued to the public from the U.S. Geological Survey to compile the study.
The search for the nuclear elements escaping into the environment is important because the radiation could already be moving through the ground water toward communities such as Beatty and the Amargosa Valley, where crops grow and milk cows graze, Hechanova said. But he said no evidence currently exists of radiation creeping off the Test Site.
There is, however, fear that the contamination may be widespread.
In 1991, DOE Test Site Manager Nick Aquilina adopted a policy for ground-water protection while nuclear testing continued, and scientists began to try to track radioactivity moving in the ground water.
"No one is willing to jeopardize the present water supply required for NTS (Nevada Test Site) operations, which includes drinking water," said DOE scientists Gregory Nimz of Lawrence Livermore National Laboratory and Joseph Thompson of Los Alamos National Laboratory in a 1992 report.
"Clearly, ground water is capable of carrying certain dissolved nuclides (radioactive particles) appreciable distances," Nimz and Thompson reported.
In the 1960s, the Atomic Energy Commission, predecessor to the DOE, experimented with ever-larger bombs at the Test Site. To avoid leaking radiation into the atmosphere, some of the nuclear devices were detonated near or below the ground water. By "near," the DOE means within 330 feet of subsurface water.
First, today's scientists need to know the nuclear contents at the heart of those deep holes where the atomic explosions occurred, Hechanova said. Then researchers can begin piecing together information on radiation migration from the caverns through surrounding ground water and rock.
Hechanova is trying to find out how much radioactivity is trapped in the caverns created by the original bomb blasts. "Then we can work our way out," he said.
While DOE scientists at both Livermore and Los Alamos have reported plutonium riding tiny particles in the ground water, called colloids, a mile away from an underground nuclear test, the real health threat to people from ground-water contamination comes from tritium, Hechanova said.
Hechanova and UNLV radiochemistry professor Vernon Hodge examined 78 possible radioactive contaminants in the Test Site's ground water.
"We are trying to define the radioactivity posing the most risk to people," Hechanova said.
The risk from plutonium in the ground water is small because the particles that get into the water don't move very far. It's unlikely they would reach a populated area.
"Part of the problem is the perception that plutonium is very deadly, often called the most dangerous substance known to man," Hechanova said. Risks from plutonium exposure are much less than that of other radioactive materials left from bombs such as tritium, neptunium, americium, thorium and uranium, he said.
The danger from plutonium comes if a speck of it is inhaled or ingested.
Tritium appears to be the leading contender as the contaminant with the best chance of posing a threat to the public. Scientists must find out whether it's in the ground water and which way the water is heading.
However, the Test Site is larger than Rhode Island. Scientists must play a guessing game on where to look.
"The real problem, the real huge question is, where is the tritium plume?" Hechanova asks.
Hechanova estimates that 100 million curies of the total blast residues came from tritium. The Environmental Protection Agency considers drinking a daily dose of more than 20,000 picocuries (one-trillionth of a curie) of tritium dissolved in two quarts of water to be dangerous.
The rest of the radiation in the Test Site's ground water could come from cesium, strontium, iodine, plutonium, carbon, uranium or other remains of a nuclear blast.
The DOE cleanup effort is focusing on water flowing south and west of Pahute Mesa in the northwest corner of the Test Site. The extra wells will be drilled in the potential path of the ground water. Pahute Mesa was loaned to the DOE by the Air Force for nuclear experiments so, technically, contaminated water on the mesa could be considered off-site.
If radiation is found in the new wells, it would show that contaminated water had migrated off the Test Site property and could be heading for residents in Beatty and the Amargosa Valley.
The DOE's own program for monitoring ground water chose to look at lead, carbon-14, tritium, iodine-129, uranium, cesium and plutonium because they were found in measurable quantities in water taken from the bomb cavities or nearby monitoring wells on the site. Scientists also are looking at how the radiation affects human health.
The DOE is not only worried about people living around the Test Site, it also must examine the ground water to prevent workers drilling sampling wells from coming in contact with radioactive water, DOE Project Manager Bob Bangerter said.
Tritium, iodine and carbon-14 dissolve and flow along with the ground water. Cesium, lead and plutonium normally cling to soil particles and move at a slower rate. Uranium can migrate somewhere between the other two groups.
For Hechanova, who was blocked by secrecy, it took three years to find enough information to allow him to report on how much tritium was contained in five blast cavities.
The size of some nuclear blasts and ground-water samples taken from nearby water wells years after the explosions existed in open government files. They gave Hechanova a good estimate of the tritium inside the cavities left by five nuclear experiments: Bilby, Dalhart, Baseball, Cambric and Cheshire.
Bilby, a 249-kiloton blast triggered under the surface of the Test Site's northeast section in 1963, was the first underground nuclear experiment that rocked Las Vegas, about 75 miles southeast of the explosion.
Hechanova and former Test Site scientist James O'Donnell combed U.S. Geological Survey and national earthquake records for Bilby's impact. It registered a 5.8 on the Richter scale at the International Data Center in Virginia. "That was a good-sized bomb," Hechanova said.
In 1965, Cambric exploded with a force less than a kiloton -- or less than 1,000 tons of TNT -- but produced extremely high tritium, nine times larger per kiloton than what was expected from such shots in or near the ground water. Hechanova has a number of theories: the nuclear device fizzled, the scientists wanted to create tritium or the results were unexpected.
Once Hechanova figures out the source amounts of tritium in the bomb caverns, he plans to develop a simple monitor available to anyone living near the Test Site's boundary. "Nothing like it exists now for the average person to sample well water," he said.
If he receives a $100,000 grant request, Hechanova hopes to develop a tritium monitor at the Harry Reid Center with assistance from UNLV professors. "It's an early warning system that any farmer could put down his well," he said.
archive
