Jenny Chapman, DRI associate research hydrogeologist, the principal investigator for the Shoal project.

While an underground nuclear weapons test does not produce a mushroom cloud or level a landscape, the results are still quite dramatic--a large underground cavity, vaporized rock, and, of course, radioactive material dispersed below the surface. That's w hy, 35 years later, DOE and DRI are working together at the Shoal test site to identify where the radioactive contamination exists in the groundwater. While all of DOE's nuclear test sites are monitored carefully, Shoal is a bit different from most. The majority of Nevada's nuclear tests were conducted at DOE's Nevada Test Site in the southern part of the state--a very large and closely restricted area . The Shoal site is much more accessible. "It's a four-square-mile area, adjacent to public lands." says Chapman. "The site is remote, but nothing prevents people from accessing it. The Department of Energy and the state of Nevada recognize this differenc e and are making a special effort to protect the health and environment of the area."

And that's a complicated task. When you have a nuclear blast, some radioactive atoms or radionuclides, like tritium, are released right into the water and travel along with it. Others are actually absorbed by the surrounding rock or move slowly through it. And some, like uranium and plutonium, become sealed in nuclear melt glass. Other things to consider are recharge rates--how long it takes precipitation to reach the groundwater--and the density, chemical properties, porosity, and fractures of the ar ea's granite subsurface. Gaining a real understanding of the eventual fate of the contaminants requires a wide range of expertise; and, as it turns out, DRI is just the place to assemble such a team of researchers.

Following water through rock Brad Lyles tends multiple unreeling cables with instrumentation which will allow measurements of the movement of water through the underground rock. On the right, DRI's hydrophysical logging vehicle monitors and records data from the instruments. (Photo by Dr. Greg Pohll)

For about a year, the DRI team conducted extensive field and laboratory studies to understand the hydrologic and geologic workings of the Shoal site. But investigating what goes on under the surface of the Earth has an inherent stumbling block--you can't see it. Much of the data collection, then, relies on wells. In the early 1960s, just prior to and after the nuclear test, 10 wells were drilled and considerable hydrologic and geologic data were collected in the area. DRI researchers, including former Water Resources Center Director Dr. George Maxey, helped conduct these early studies. In 1996, four more wells were drilled under the supervision of IT Corporation. As valuable as wells are to data collection and site characterization, there's a limitin g factor to their use--cost. It's not easy to drill 1300 feet through solid granite. Add to that the regulations and monitoring required when working in a potentially radioactive site, and you come up with a price tag of about $250,000 for each of the w ells drilled in 1996. The solution, then, isn't more wells but optimum use of the ones that exist.

While much of the instrumentation used in the wells is very specialized, measuring things like water chemistry, thermal flow, or rock density--one piece of equipment is familiar to most of us, the video camera. Video well logging has been around for abo ut 50 years, according to DRI's Brad Lyles who has operated the video camera at the Shoal site. It's used for a variety of purposes--from determining why wells fail to produce water to finding sewer pipe breaks. At Shoal, the camera's job was finding un derground fractures. The Shoal site sits on nearly solid granite, meaning groundwater travels along fractures in the rock instead of seeping directly down. Thanks to a $20,000, three-inch-diameter camera, many of those fractures have been captured as d igital images. DRI's Craig Shirley handled much of the fracture analysis, helping to determine direction, size, and location, as well as incorporating the analysis into the overall picture of the groundwater system.

And that's a complicated task. When you have a nuclear blast, some radioactive atoms or radionuclides, like tritium, are released right into the water and travel along with it. Others are actually absorbed by the surrounding rock or move slowly through it. And some, like uranium and plutonium, become sealed in nuclear melt glass. Other things to consider are recharge rates--how long it takes precipitation to reach the groundwater--and the density, chemical properties, porosity, and fractures of the ar ea's granite subsurface. Gaining a real understanding of the eventual fate of the contaminants requires a wide range of expertise; and, as it turns out, DRI is just the place to assemble such a team of researchers.

For about a year, the DRI team conducted extensive field and laboratory studies to understand the hydrologic and geologic workings of the Shoal site. But investigating what goes on under the surface of the Earth has an inherent stumbling block--you can't see it. Much of the data collection, then, relies on wells. In the early 1960s, just prior to and after the nuclear test, 10 wells were drilled and considerable hydrologic and geologic data were collected in the area. DRI researchers, including former Water Resources Center Director Dr. George Maxey, helped conduct these early studies. In 1996, four more wells were drilled under the supervision of IT Corporation. As valuable as wells are to data collection and site characterization, there's a limitin g factor to their use--cost. It's not easy to drill 1300 feet through solid granite. Add to that the regulations and monitoring required when working in a potentially radioactive site, and you come up with a price tag of about $250,000 for each of the w ells drilled in 1996. The solution, then, isn't more wells but optimum use of the ones that exist.

While much of the instrumentation used in the wells is very specialized, measuring things like water chemistry, thermal flow, or rock density--one piece of equipment is familiar to most of us, the video camera. Video well logging has been around for abo ut 50 years, according to DRI's Brad Lyles who has operated the video camera at the Shoal site. It's used for a variety of purposes--from determining why wells fail to produce water to finding sewer pipe breaks. At Shoal, the camera's job was finding un derground fractures. The Shoal site sits on nearly solid granite, meaning groundwater travels along fractures in the rock instead of seeping directly down. Thanks to a $20,000, three-inch-diameter camera, many of those fractures have been captured as d igital images. DRI's Craig Shirley handled much of the fracture analysis, helping to determine direction, size, and location, as well as incorporating the analysis into the overall picture of the groundwater system.

Besides determining how groundwater moves, the composition of the granite beneath the Shoal site also affects the behavior of the radionuclides released during the test. Some of these radionuclides actually cling to the rock; they have an affinity for so lids and therefore don't move through the rock at the same rate as the groundwater itself. Using pieces of granite collected from the site, DRI's Dr. Charalambos Papelis conducted laboratory experiments to estimate the retardation of many of these radion uclides. That is, how long do the radionuclides remain tied up in the rock and out of the groundwater? Other radionuclides achieved a solid state in a more dramatic way. "The nuclear blast vaporized the surrounding rock," explains Chapman, "which then dripped down the sides of the cavity, puddled, and hardened. This puddle glass contains many of the long-l ived radionuclides." Part of Chapman's job was to look at how those radionuclides will be eventually dissolved from the glass and released into the groundwater.

Melt glass, retardation rates, and fracture analysis are just a few of the factors that were rigorously studied during the field portion of the project. Several other DRI researchers, including Todd Mihevc, Sam Earman, and Dave Gillespie--lent their own expertise covering areas such as the chemical properties of groundwater and recharge rates of the aquifer. And, while all that field work was a massive effort, it was only the first part of the job. Next came the task of turning the vast quantity of col lected information into a comprehensive picture of the fate and transport of the contaminants beneath the Shoal test site. Integrating the field data into a computer model was the job of DRI's Dr. Greg Pohll and Dr. Roko Andricevic with assistance from D r. Ahmed Hassan, a postdoctoral fellow from Egypt. The result is an extremely complex model run by 11 different computer programs. Using the information collected in the field, the model creates a three-dimensional picture of how water and contaminants m ove through the area. All the various factors that affect the flow system can be adjusted to give a very site-specific picture of what's going on below the surface. And, while not perfected, the model is the key to helping the researchers decide what a dditional field work will be necessary. "There's still too much uncertainty in the flow system," explains Pohll. "But, we're using the computer model to go back and determine what parameters are most critical and what we need to look at again." Rather t han repeating all the field studies, Pohll says they can use the computer model to determine "which field activities will give us the most information for the least cost."

The model shows that some parameters, like porosity, are crucial to producing a reliable result. Very small changes in porosity translate into very large differences in how the model predicts the contaminants will move. Therefore, the researchers know t hat pinning down more certain values for porosity is crucial; and they can concentrate field efforts in that area. Once additional field tests have been conducted, the computer model will be reworked and, hopefully, the level of uncertainty reduced enough to accurately predict movement of the contaminants. Once that happens, the DRI team will have accomplished its ta sk--giving DOE and the state of Nevada the reliable information it needs to decide the fate of the site. It's quite possible that this little island will be released from DOE control and become another closed chapter in our nuclear history.

Jackie Allen