n many regions of the United States, users of low-level radioactive materials have nowhere to permanently dispose of their wastes. The only two major burial sites still in operation in the United States-Barnwell, SC, and the Hanford Reservation, WA-have closed their doors to all hut a handful of states. Another facility, Envirocare in Clive, UT, is limited to low-activity bulk wastes. Until new burial sites can be approved, those wastes that cannot be shipped to a permanent site are being held in “temporary” storage. Federal legislation has put much of the hurden of selecting new burial sites on state governments, which must either find a suitable low-level radioactive disposal site within their own borders or join a compact of states with access to a suitable depository (see box). The job of evaluating new sites for waste burial has fallen largely to geologists and hydrologists. Under federal law, these new disposal sites must be chosen and constructed in a manner that protects the public from harmful radiationusually described as 300 to 500 years of protection, although Nuclear Regulatory Commission (NRC) experts think that even longer periods are necessary. Many scientists are uncomfortable with certifying a disposal site as safe for hundreds of years. However, the understanding of what constitutes a good site is improving, in part because of lessons learned from past mistakes. The first of the new waste sites, in Ward Valley, CA, is currently embroiled in controversy and will probably serve as
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BY ALAN NEWMAN a test case for approving future sites. At the American Geophysical Union (AGU) meeting in Baltimore, MD, this spring geologists and hydrologists looking at the problems of evaluating disposal sites reviewed what has been learned from old sites and the state of their knowledge. Recent history “The ideal setting keeps as much water as possible away from the radioactivity,” said David F’rudic of the U.S. Geological Survey (USGS) in Carson City, NV. Although that idea seems simple, it wasn’t always fullv auureciated nor is it easilv achievid. “Back in the 1960% we disposed of wastes in low-uermeahilitv or tight formations wiere water fldw is extremely slow,” recalls Prudic. Typically, shallow trenches were dug to hold the wastes. The trenches were originally designed to safely store the wastes, hut the builders failed to fully appreciate the geology and hydrology of the site. “We ended up with trenches with a high capacity to hold water. [After heavy rains] the trenches filled with water and overflowed.” This became known as the “hathtub effect” and it led to serious contamination. For example, at a nowclosed burial site at Oak Ridge (TN) National Laboratory, an estimated 1.2-5.2 curies (Ci) of ”Sr leaked out each year between 1971 to 1975,the amount varying in direct relation to the total precipitation (I). There were other problems as well. Studies at old disposal sites
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near Sheffield, IL, and West Valley, NY, found 3H from decomposing and volatilizing wastes migrating away from the burial sites. Sections of trenches often collapsed, generally following rains. The geology at the Sheffield site was so complex that more than 100 test wells had to be drilled to define the geology and hydrology ( I ) . “Problems developed at several sites,” observed Nowell Trask of the USGS in Reston, VA. “They didn’t perform as expected.” What is buried in these waste sites differs by regions and includes trash discarded tools: solid and solidified wastes; laboratory glassware; liquid wastes (now no longer accepted); and materials packed into 55-gal drums, concrete vaults, and steel bins. Much of the current waste comes from industrial sources, more than 50% in 1992.Of the rest, most are generated by nuclear power plants, with small additional contributions from academic and medical facilities and a growing amount from biotechnology companies (2). Under the NRC’s complicated three-tier classification scheme, the majority by volume of what is disposed of in the burial sites in recent years falls into the least dangerous of the three classes. Class A, in general, contains solid, short-half-life wastes that fall below some minimum concentration. Common Class A wastes contain isotopes such as 3H 1 4 , C, and “Co. In 1992, more than 1.7 million ft3 (containing around lo6 Ci) of low-level radioactive materials were received at the Barnwell, Hanford, and the nowclosed Beatty, NV, waste sites, 96% of which was labeled Class A (2).
0013-936XI94/0927-48A$04.50/0 0 1994 American Chemical Society
Given the concern about l e a c h 1 of radioactivity by water, it is not surprising that arid sites should top the list of ideal new sites. At the AGU meeting several talks focused on how well the commercial waste site at Beatty had performed and how well the disposal site at nearby Ward Valley (not far from Needles, CAI is expected to perform. The Beatty site has become the test case for what may happen to a desert waste site in time. The oldest commercial site in the United States for low-level waste disposal, it accepted wastes from 1962 until 1992. Beatty still accepts hazardous wastes, but only nonradioactive materials. Environmental monitoring has been under way at the site since 1976. Radioactive wastes at Beatty were
uried in 2-15 m deep trenches, which are now covered. Below the trenches lie sand and gravel containing silt and clay. Beatty is bonedry, receiving an average rainfall of about 100 mm per year. Gronndwater is not reached until depths of 90 to 1 1 2 m, says Prudic. Groundwater collected from wells next to the waste site reveals 3H levels of less than 6 picocuries (pCi]/L, far lower than the 75 pCi/L in rainfall. At Beatty, says Prudic, water movement is up and down in the uppermost 9 m; below that depth water movement is upwards (evaporation, transpiration through plants, or atmospheric pressure changes produce upward flow.] One factor that the hydrologists have come to appreciate is the role of plants. The Beatty site is sparsely
covered with m o t e bushes, which have extensive root systems. “Native vegetation is a very good scavenger for water,” says Prudic. “If we remove the vegetation, then that increases water flow down into the mound.” I
ward Eric Lappala of Harding Lawson Associates (Denver, CO), who has evaluated the Ward Valley site, drew up a description of an ideal site based on what he describes as a consensus of federal, state, and industry guidelines: no residents or groundwater use within 10 miles; a closed topographic and groundwater basin; simple geology and hydrology: an arid climate; and a thick, effective vadose zone (the unsaturated zone between the surface
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Sta
nd Regional Compacts
The states knew it was ig. Federal legislation on low-level radioactive waste dates back to 1980 and was amended in 1985. The laws set up the regional compacts in which states could ban together lo dispose wastes al a common site in a host state (see map), established milestones for the process, and provided penalties for noncompliance and rewards for compliance. Lowlevel waste sites were expected to be in operation by 1993, in time to compensate for the closure of existing burial sites. Last year the Hanford ReSeNatiOn in Washington closed its doors to lowlevel radioactive wastes from all but the 11 states of the Northwest and Rocky Mountains compacts and, as of July 1 of this year, the last commercial facility in the United States at Barnwell, SC, accepts wastes generated in only eight nearby states of the Southeast compact. The nearest date any state is willing to predict that a new site will be opened is 1996 for Wake County, NC. That site replaces Barnwell, SC, which closes its doors lo everyone on January 1, 1996. Ward Valley’s opening, if it ever happens, has recently been pushed back to 1997. However, these expected opening dates change regularly. Meanwhile, the rest of the country will probably store wastes on site until the state or compact comes up with a permanent facility. (EPA is developing standards for temporary storage; NRC or state regulatory agencies are in charge of overseeing safety.) Given the public’s current suspicion of anything nuclear, the state’s cautious march toward identifying new sites is not surprising. “There has been a legitimate attempt to respond to controversial issues. However, efforts have been frustrated by the politics,” says Michael Weber, section leader for the LowLevel and Regulatory Issues section with NRC‘s Division of Waste Management. Then there are the unaffiliatedstates. Michigan, for example, is unaffiliated with any compact, not setting up a waste site (a suitable in-state location has been described as ”highly unlikely”), and, because it is not in compliance with federal law and thus barred from using Barnwell, has been storing low-level radioactive wastes on site since November 1990. Recently, there has been legislative action designed to look at the state’s options. New Hampshire also remains unaffiliated and, since October 1990, has been keeping wastes from its controversial Seabrook nuclear power plant on site. These states, says Weber, would affiliate with a compact if they could. But the political situation is extremely delicate in most designated host states. For example, even when Connecticut offered lo pay $100 million as quid pro quo it was unable to join a compact, and the District of Columbia has also been unable to enter a compact. Even when the states do try to progress the results are not always pretty. In le 1992, the Illinois Low-Level Radioactive Waste Disposal Siting Commison unanimously rejected the site proposed by the Illinois Department of Nuear Safety (IDNS). The Illinois legislature subsequently abolished the siting mmission, repealed the statutory siting criteria, and directed IDNS to start new. A new siting commission has been formed with a new mandate that is xused on drawing up the process for and evaluating potential sites. At about the same time, Nebraska sued the Central Compact Commission iver their choice of Boyd County, NE, for a waste site. The suit, initiated by lebraska’s governor, was filed after 90% of the voters in a straw poll of Boyd :ouniy residents said “not in my backyard.” That suit was settled in favor.of i e Commission, but other legal suits are pending. Based on the latest information from the states, the best estimate is that California, Connecticut. Illinois, Massachusetts, Nebraska, New Jersey, New York, Pennsylvania, and Texas will have operating sites by 2001. Maine and h n o n t , pending approval by the US. Congress, would join Texas in a comiact. On the other hand, the commission makes no predictions about when .ites will open in the District of Co’..-“:a, MicL:---, New Hampshire, Ohio, ’uerio Rico, or Rhode Island.
and groundwater). Based on these guidelines and state l a w requirements, “We essentially screened the state of California for one square mile,” says Lappala. The r e s u l t was W a r d Valley, which seems to fulfill many of Lappala’s stated ideals. The valley nor490 A
mally receives < 125 mm per year of rainfall, and i t s vadose zone i s 200 m thick, says Lappala. Moreover, i t l i e s in a sparsely populated region of the Mohave Desert. Field measurements indicate that below a few meters, the hydraulic gradient i s upwards.
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Federal law requires that potent i a l low-level radioactive waste sites be carefully monitored prior to l i c e n s i n g for at least one year (through seasonal changes) and that this record, which includes rainfall, must be measured against the historical record. Even then, additional tests were conducted to evaluate the site under extreme conditions. The most dramatic example was t h e large-scale infiltration test, which rapidly dumped 5900 gal of water into a 6 ft deep by 15 ft square pit dug at the site, simulating a very rare major rainfall and flood: According to Lappala, the water disappeared into the ground in less than 24 h, and after 139 days had not penetrated deeper than 19 ft, which i s less than t h e thickness of t h e trench caps. “The p r i n c i p a l component [of picking a good location] i s site characterization,” says Lappala. “The rest--design, monitoring, and land ownership [by t h e statel-only make i t safer.” Even w i t h what appears to be favorable geology and hydrology, the Ward Valley site has run into a major challenge. “Ward Valley i s a good place to look, but we don’t have complete data,” warns Howard Wilshire, a USGS geologist at Menlo Park, CA. Wilshire and two other geologists, initially working on their own time, have charged that there are potentially serious problems with the Ward Valley site. Arguing that one year i s not sufficient time to truly characterize a site, Wilshire says, “You have to be just as thorough as the current work at the Beatty site. Investigators start with l i t t l e information and study the site out to a one-mile radius. But they need to know the regional hydrology and which way and how fast groundwater i s actually moving. Geographic information indicates several possible connecting routes for groundwater movement between the valley site and the Colorado River.” What has become known as t h e Wilshire Report raises several technical flags ahout the site. According to Wilshire, 3H was detected to depths of 100 ft, which h e says corresponds to a downward rate of water movement of 0.8 miyear, rapid enough for radionuclides to reach the water table in fewer than 300 years. Moreover, there i s the potential of lateral subsurface movement of water through the site because of relatively impermeable buried soils. This water c o u l d i n f i l t r a t e t h e burial trenches and eventually mi-
grate to the water table. Wilshire points to areas near the proposed trench site that may have higher water content (as measured by the electrical resistance of the soil) and could represent a current recharge zone that could eventually feed the Colorado River. “We find the data on the site very flawed,” says Wilshire, “Certain data weren’t followed up on that could give a different picture of Ward Valley.” Lappala disputes Wilshire’s criticisms, saying that the 3H is from the gas rather than liquid phase (gases can have a downward concentration-driven gradient even when the liquid gradient is upwards), that the buried impermeable soils (clay-carbonate) are not continuous, and that the nearby wet areas are wet only by comparison to the general aridity and not really very wet at all. Moreover, during the large-scale infiltration test the water flooding the pit moved laterally less than 25 ft. The scientific arguments have made their way into the legal battles over the site. Although Ward Valley did receive licensing approval (in 1993), a state court recently set aside the approval w h i l e the Wilshire Report is considered further. The report has some powerful allies, including U.S. Senator Barbara Boxer (D-CA), who originally asked Wilshire to write the report. The entire issue has been turned over to the National Academy of Sciences, which is now evaluating the scientific and technical questions raised by the Wilshire Report. The Academy is expected to issue its own report this year. The Ward Valley site is owned by the federal government, and if it is finally licensed then the Interior Department could transfer ownership of the land to the state.
Following the water Following the water flow through the ground under these arid conditions is far from easy. “We don’t have standard techniques to determine water flow in sediments with extremely low water contents,” says Prudic. One indicator that has been used with success in arid regions is C1- concentration in the pore water. “It is the most soluble of the various ions,” explains Prudic. Other methods include 3H age dating of subsurface water and tracking ”Cl-, a byproduct from the age of aboveground nuclear bomb testing, Furthermore, as demonstrated by David Stonestrom of the USGS at Menlo Park, CA, the theoretical un-
derpinnings of water flow under arid conditions may also be inadequate. His group’s laboratory modeling of water flow under these cond i t i o n s demonstrated serious deviations from theory (in this case, from predictions based on the Richards equation). Thus, without some better models, waste site builders will need to “over-engineer” facilities. “Engineers are used to working in theoretical ‘incorrectedness’,” observes Stonestrom. Other factors must be taken into account at these sites, for instance, vertical fractures that can be conduits for water. This problem was particularly severe at the shallow burial site near Maxey Flats, KY. Among the wastes that were buried at the site were glass containers of tritiated water inside 55-gal drums. Some of the glass containers broke as new wastes were dumped on top and the radioactive water migrated into the fractures. Maxey Flats was closed in 1977 and declared a priority EPA cleanup site ( 2 , 3 ) .
Disposal in humid climates If arid sites represent the ideal, then where can wastes be stored in humid regions? NRC’s 1982 directives on the issue (Subparts C and D, 10 CFR part 61) offer primarily a health risk guideline. Any radioactivity that escapes into the air, water, and soil or is taken up into plants or animals must not result in an annual dose exceeding an equivalent of 25 millirems to the whole body, 75 millirems to the thyroid, and 25 millirems to any other organ of any member of the public. (All millirem units are in radiation dose equivalent.) In terms of geology and hydrology, most of the NRC’s directives reflect what has become the common wisdom described above of isolating wastes from water and population ( 3 ) . Unfortunately, in humid regions the water table is often close to the surface. As a result, how the site is constructed will be just as essential as location. Learning from past history, shallow trench burial, like that used at Beatty and Maxey Flats, is banned in most states east of the Mississippi River. A proposed alternative is to construct sites below the water table. However, that is a costly solution that isn’t now being pursued in the United States. Another approach is to mimic, to some degree, the commercial burial site at Barnwell, SC. Although rainfall can be as much as 24 cm/month at this site, the bathtub effect is not
observed here because of the surface soil’s permeability to water. In addition, humid sites will need what Trask calls “a lot of engineering enhancement.” One approach is to store wastes under a carefully constructed mound, which could include drains for surface water, a protective cover or native vegetation on top, as well as barriers below the waste. Another method is to seal the wastes in concrete and place them underground. Here, too, the site could also include drains and low-permeability barriers. Engineered sites would have to control their integrity and if they do break down, degrade slowly. NRC stipulates careful monitoring and control of the site by the state for the first five years and continued monitoring by the site’s custodian for up to 100 years. In effect, NRC seems to recognize that nothing is forever and is willing to accept some degradation as the health risks of shortlived isotopes diminish ( 3 ) . Yet, given all the factors that need to be juggled, can geologists and hydrologists certify the safety of a lowlevel waste site for at least 500 years? “I think that we are deluding ourselves if we say we can,” admits Prudic. “We can, however, find suitable locations where the likelihood for off-site migration is minimized.” Moreover, Lappala argues that increasingly sophisticated monitoring techniques will allow regulators to carefully observe facilities for problems. Without such sites, the researchers warn, radioactive wastes will just accumulate in “temporary storage” at the power plants, hospitals, and other locations where they are generated.
References (1) U.S. Geological Survey. “Safe Dis-
posal of Radionuclides in Low-Level Radioactive Waste Repository Sites: Low-Level Radioactive-Waste Disposal Workshop”; USGS Circular 1036; U.S. Government Printing Office: Washington, DC, 1990. (2) Information Digest. U.S. Nuclear Regulatory Commission: Washington, DC, March 1994; NUREG-1350, Vol. 6.
(3) Bedinger, M. S. “Geohydrologic Aspects for Siting and Design of LowLevel Radioactive-Waste Disposal”; U.S. Geological Survey Circular 1034; U.S. Government Printing Office: Washington, DC, 1989.
Alan Newman is an associate editor on the Washington staff of ES&T.
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