The risks associated with DU releases to the environment through U.S. Army activities will be specific to each application of DU and to each site where it is used. Chapter 7 provides a discussion of the mobility, fate and effect of DU in the environment. Laws, regulations, criteria and standards are constantly revised to better manage the discharge contaminants into the environment. However, the basic physical phenomena do not change when the regulatory approach changes. A risk-based management system is the only approach that provides the Army sufficient flexibility to manage DU efficiently in a fluid regulatory environment. It asserts that to develop a formal risk assessment, one must understand the transport and fate of DU and its effects on plants and animals, including man. This chapter also describes how the Army has developed a considerable understanding of DUís behavior in the environment through studies at the three firing sites used for most DU weapons development and testing.
In addition, Chapter 7 discusses remediating sites contaminated with DU and available remediation technologies. Finally, this chapter offers a number of actions the Army can take to cost-effectively protect the environment from the long-term consequences of the use of DU.
7.1 Environmental Transport and Fate
Water is the dominant mechanism of environmental transport of all metals. Metals may move in groundwater or in surface water such as rivers. For metals widely dispersed across the land, the principal concern is groundwater contamination. Runoff also can transport contamination to surface streams and ponds (Ebinger et al., 1990). In an arid environment, wind erosion can transport dust containing DU (Price, 1991). In addition to aqueous transport and airborne transport, biological transport through the food chain can move a contaminant through the environment.
As discussed in Section 2.1.3, although the radiological properties of uranium isotopes differ considerably, their chemical behavior is essentially identical. Thus, in this discussion of the physical and chemical properties of DU in the environment, DU and U are used interchangeably. In the past 50 years, a large body of knowledge regarding the transport, transformation, fate and recovery of uranium has been developed, mostly as a result of uranium mining and milling. Much of this information applies to the environmental problems associated with the use of DU in weapons. Magness (1985) provides a brief summary of the environmental transport and fate of DU. Information that DOE compiled for the Uranium Mill Tailings Remedial Action (UMTRA) Project is particularly valuable. DOE conducted this project in response to the Uranium Mill Tailings Radiation Control Act of 1978. Portillo (1992) describes the UMTRA project, giving particular attention to its history and the technology developed to mitigate impacts of uranium milling operations.
7.1.1ÝÝÝ Airborne Transport
Airborne transport of uranium involves particles. Vaporization is not a significant transport route because uranium metal has a boiling point of 3818oC. Powdered uranium metal may burn spontaneously in air, but larger pieces of metal, such as penetrators, require a heat source ranging from 700oC to 1000oC to produce ignition. A DU projectile creates very fine particles of uranium oxides (typically 75 percent U3O8 and 25 percent UO2) upon impact or burning. These particles settle according to Stokesí Law. The larger particles [> 5 micron ( m)] settle rapidly and travel only short distances through air because they are so dense (specific gravities of 8.3 and 10.96, respectively).
A number of researchers have studied the dispersal of aerosol particles of uranium after a DU penetrator hits a hard target (Mishima, 1990; Jette et al., 1990; Glissmeyer and Mishima, 1979; Fliszar et al., 1989). In addition, Pacific Battelle Northwest Laboratory published studies on this topic in 1979 and 1990. Its 1979 report (Glissmeyer and Mishima) identified several experimental problems that were subsequently resolved, so the second study (Jette et al., 1990) is believed to be more technically defensible. Jette et al. found that approximately 18 percent of a penetrator round dispersed into airborne particles when it hit a hard target. Of the aerosol particles produced by the impact, 61 percent to 91 percent were less than 10Ý m in diameter, depending on the type of round. Furthermore, they found a strong propensity for DU particles to resuspend when multiple rounds were fired, but they also found that the resuspended aerosol particles were larger on average than those from the first round fired. Lung-solubility analysis of the particles less than 10Ý m in diameter found that 24 percent to 43 percent were class ìD,î representing a 50 percent dissolution time in simulated lung fluids of less than 10 days. The rest of the particles were class ìYî materials, with a 50 percent dissolution time longer than 100 days.
Fliszar et al. (1989) reported results of firing various penetrator munitions at tanks containing DU shielding under intensively instrumented conditions in open air at the DOE Nevada Test Site. When the DU penetrator rounds hit a tank, more than 90 percent of the airborne DU remained within 50 m of the tank. During one test, a fire began inside a tank; it was allowed to burn more than 12 hours. Dense smoke from the fire plugged sampling systems disrupting measurements. However, as with the impact tests, airborne transport appeared to be minimal beyond about 50 meters (m).
7.1.2ÝÝÝÝ Aqueous Transport
As previously discussed in Chapter 2, DU fragments exposed to the atmosphere will oxidize from DU metal to U(IV) and eventually to U(VI). Uranium is thermo-dynamically stable only as U(IV) or U(VI). The oxidation rate of DU fragments depends on several factors, including fragment size, pH, humidity, soil moisture content, soil chemistry and oxygen content. Previous studies of the role of aqueous systems on the transport and fate of DU have been conducted by Hanson and Miera (1976, 1978), Ebinger et al. (1990), and Erikson et al. (1990a, 1993).
Figure 7-1 is a pe-pH (electron activity-relative alkalinity of a fluid) diagram for uranium U(IV) and U(VI) species in the environment. It summarizes the acid-base and oxidation-reduction chemistry (commonly abbreviated as redox chemistry) of uranium. The vertical scale (pe) defines the potential for oxidation-reduction reactions, while the horizontal scale (pH) defines acidic or basic conditions.
Low pH values describe acidic conditions, while high pH values represent
basic conditions. A neutral solution corresponds to a pH value of 7.0.
The diagonal dashed lines on the figure represent the stability limits
for wateróthe limits for equilibrium in environmental systems. Above the
top line, water is oxidized to oxygen gas (O2). Below the bottom
line, water is reduced to hydrogen gas (H2). Brookins (1988)
presents a formal discussion of pe-pH diagrams.
Ý
Figure 7-1.Ý pe-pH Diagram for Uranium
The pe/pH diagram in Figure 7-1 shows only two solid phases of uranium: uraninite and coffinite. More than 50 uranium-containing minerals have been identified in nature. While it is possible to construct pe-pH diagrams for these other phases, the fundamental result is the same: under oxidizing conditions, uranium is soluble; under reducing conditions, it is insoluble.
Figure 7-1 shows the two uranium oxidation states that can be stable in water. The oxidation or reduction of uranium ions occurs when the pe and pH conditions move into the region of the figure denoted as containing coffinite (uranium silicate, USiO4). Under oxidizing conditions (i.e., above the coffinite region in Figure 7-1), uranium is present as soluble uranyl species U(VI) (oxidation state of +6). In this region under acidic conditions (pH less than 5), the uranyl ion (UO22+) is dominant. At higher pH levels, these ions form weak bonds with carbonate ions to form uranyl carbonate, UO2CO3; uranyl dicarbonate UO2(CO3)22-; and, above pH 8, uranyl tricarbonate UO2(CO3)34-. Oxidizing conditions (as described above) are present in a free-flowing river or an oligotropic lake. These conditions foster maintenance of the U(VI) soluble form of uranium.
The second uranium oxidation state presented in Figure 7-1 is U(VI) (oxidation state of +4), the insoluble form. This is present under reducing conditions either as the mineral uraninate (UO2) or as the mineral coffinite (USiO4). When reducing conditions exist, the pe is low (i.e., in or below the coffinite region in Figure 7-1). This normally corresponds to anaerobic conditions typical of deep groundwater and eutropic surface waters such as swamps, wetlands, nutrified lakes, and polluted rivers.
The most important point about this diagram is that oxidizing conditions affect the solubility and mobility of uranium. Under oxidizing conditions, most uranium is in the form of soluble uranyl ions that can move through the environment and living organisms. Under reducing conditions, most uranium is solid or insoluble. Because most soil is exposed to the atmosphere, uranium will eventually become soluble, resulting in its aqueous transport. Thomson et al. (1986) provides a more complete discussion of the redox chemistry of uranium in the environment.
Erikson et al. (1990b) found that weathered DU penetrators principally corroded into hydrated U(VI) oxides that were very soluble in water. Erikson further found that when the native soils were acidic, they could attenuate uranium species, probably through adsorption reactions. In subsequent research, Erikson studied the geochemical factors affecting the environmental fate of DU penetrators in the wet, temperate climate of APG and the extremely arid climate of YPG. This research considered several geochemical factors, including the oxidation of DU metal into more stable oxides, the solubility of the oxidation products, and the interactions of soluble DU species with site-specific soils. Measured corrosion rates were fairly small, ranging from 20 one-thousandth of an inch/year (mils/yr) to 40 mils/yr [0.05 centimeter/year (cm/yr) to 0.10 cm/yr]. Corrosion rates were higher at YPG, probably because the soil contained more carbonate minerals. The corrosion rates in both cases were large enough that they would not limit mobility or aqueous transport of DU. Studies of adsorption of uranium species onto soil found varying sorption capacities among different soils at APG and YPG. The high carbonate soils at YPG had the lowest capacity, probably due to the formation of very soluble uranyl carbonate complexes such as UO2CO3, UO2(CO3)22- and UO2(CO3)34- (Erikson et al., 1993).
Once present in the environment, soluble U(VI) species can undergo two types of reactions that will reduce their mobility: adsorption and reduction. Adsorption or ion exchange reactions involve attachment of soluble molecules to soil particle surfaces through either covalent bonds (adsorption reactions) or electrostatic bonds (ion-exchange reactions). The two types of reactions are commonly lumped together using the term ìsorption reactions.î The sorption chemistry of U(VI) species has not been well studied. Preliminary results, however, suggest strong interactions between uranyl complexes and common soil iron hydroxide minerals (Hsi and Langmuir, 1985).
Under aerobic conditions, iron can play a key role in controlling the movement of uranium through soil. Uranium will bind to many iron minerals under aerobic conditions. Iron and uranium then co-precipitate and remain bound in the soil. In addition to solubility, uranyl U(VI) complexes may be formed by adsorption on minerals or organic compounds in the soil. These adsorption reactions will attenuate uranium species and reduce their mobility, but a quantitative model of this phenomenon for uranium is not presently available. Furthermore, sorption reactions generally do not permanently remove a constituent from solution but rather temporarily bind it reversibly to the soil so it may be released to solution at a later time. Therefore, sorption reactions cannot generally be relied upon as a mitigation mechanism unless the sorbent is physically removed from the system.
The most well-characterized interactions involve adsorption of uranium and other metals onto humic and fulvic acids, large organic molecules resulting from the decay of dead plant matter. The organic content of soils at the surface ranges from less than 1 percent in desert environments to more than 30 percent in loamy soils from deciduous forests in the southeastern U.S. (Jury et al., 1991); however, in deciduous forests, the organic content at 10 cm depth is in the range of 4 percent. Uptake (complexation) by organic compounds will slow the migration of uranium through soil, often by several orders of magnitude, so that it becomes essentially immobile. High concentrations of organic material may also stimulate growth of bacteria that reduce iron and sulfate. These bacteria can reduce soluble U(VI) to insoluble U(IV) compounds, thereby limiting the mobility of uranium. This phenomenon is captured by the electron micrograph presented in Figure 7-2. Additional details on the environmental behavior of DU are available in Erikson et al. (1990a) and Langmuir (1978).
Figure 7-2.Ý Bacteria Reducing Soluble and Insoluble DU
Under anaerobic conditions, U(VI) may be biologically reduced to insoluble U(IV). This process has been the subject of considerable research for more than 10 years. Kauffman inferred microbial reduction of U(VI) by measuring uranium removal as uranium mine wastewater passed through an anaerobic wetland. This process also removed selenium and arsenic, two metals that commonly occur with uranium (Kauffman et al., 1986). In 1991, Lovley et al. first isolated an organism that unequivocally demonstrated U(VI) reduction. A more recent investigation showed that several classes of common microorganisms can reduce U(VI) to U(IV). This investigation produced transmission electron micrographs and X-ray diffraction images of uraninite crystals (UO2). These results suggest that the precipitates of U(IV) will have very low solubility and will be stable in the environment unless oxidizing conditions are reestablished (Thomson et al., 1994).
7.1.3ÝÝÝÝ Biological Transport
Magness provides a brief review of the impacts of DU munitions testing (1985). In the natural environment, uranium accumulation in plant and animal tissues is a function of uranium bioavailability, which largely depends on the solubility of the uranium species and on the soil chemistry of the area. Magness concluded that uranium is not effectively transported in the food chain, partly because U(VI) species are highly soluble and quickly excreted by organisms low in the food chain. The principal source of uranium in animals appears to be particulates deposited by air or water and eaten with vegetation or incidentally ingested during preening.
In an ongoing study, Los Alamos National Laboratory is conducting ecological risk assessments to determine the human radiological dose from DU munitions testing at JPG and APG (Ebinger, 1993a, 1993b). The study considers multiple exposure pathways, including DU accumulation in soil and plants, livestock drinking contaminated water, human consumption of contaminated water, DU doses through meat and milk consumption, soil ingestion, dust inhalation, and external exposure to DU particulates. One of the more unusual exposure pathways involves consumption of venison from deer living at the test sites. Los Alamos National laboratory (LANL) is using the residual radiation (RESRAD) computer code and supporting studies to develop recommendations to minimize human and ecological risks at both JPG and APG.
7.2 Effects of DU on the Environment
In DU-contaminated soil, most plant injury occurs in the roots (Hanson and Miera, 1978). Some plants appear to be more tolerant than others to high concentrations of uranium in the soil. These plants may have developed a mechanism for limiting uranium intake. Hanson and Miera (1978) found that uranium concentrations may be significantly less in plants than in the surrounding soil. This observation is consistent with the findings in a study of the environmental impacts of DU munitions testing at Eglin Air Force Base, Fla. Of the 25 vegetation samples collected, yucca roots had the highest apparent uranium concentrations. However, after vigorous surface washing to remove uranium dust, uranium concentrations were too low to be detected in most samples, including yucca roots (Becker et al., 1989).
Because uranium has a low specific activity and most animals in the natural environment do not live very long, the principal hazard associated with animals ingesting uranium is toxicity, not radioactivity. Magness (1985) cites studies that found that, although insoluble uranyl-iron complexes are only slightly toxic to the kidneys, soluble uranium compounds poison the kidney long before any other organ. Burrowing animals appear to be at greater risk for uranium toxicity, particularly in arid environments where alkaline soils may increase uranium's solubility (Hanson and Miera, 1978). Ingesting DU-contaminated vegetation or water does not appear to significantly affect large grazing animals, presumably because the contaminated vegetation or water is a small fraction of their total intake.
Magness expects that continued DU testing will have no significant adverse effects on wildlife found at APG, YPG and JPG.
7.3 U.S. Test Sites
The Army has conducted most of its DU weapons development and testing at three U.S. sites: APG, JPG and YPG. It has mostly used APG to develop DU munitions and armor. JPG and YPG have primarily been used to test fire DU munitions for acceptance testing of production munitions.
Several recent studies (Ebinger et al., 1990; Ebinger, 1992a, 1992b, 1993a, 1993b) of the environmental fate and effects of DU at these sites have been conducted for the Army. These studies provide a summary of the current understanding of the behavior of DU in three distinctly different environments.
Ongoing Army activities can expose military personnel, the public, and the environment to DU. Figures 7-3, 7-4 and 7-5 illustrate potential pathways that may lead to human exposure to DU, including aquatic pathways at APG and JPG and terrestrial pathways at APG, JPG and YPG. Both APG and JPG have wet climates and dense deciduous vegetation. The aquatic pathway at JPG is strictly freshwater. The APG aquatic pathway is both freshwater and marine. Deer are harvested at both APG and JPG (1,200 and 800 animals per year, respectively). All three locations have active environmental monitoring programs.
Environmental monitoring has not detected DU migration out of impact areas at APG, JPG or YPG, but has measured limited movement within the impact areas. DU was not detected in groundwater samples at APG or JPG. Groundwater was not sampled at YPG because the water table there is approximately 700 feet below the surface.
The presence of DU at firing sites allows researchers to study transport mechanisms for heavy metals because DU can be quantitatively distinguished from natural uranium. Enrichment removes 234U and 235U from uranium, giving DU different isotopic ratios of 234U/238U and 235U/238U. These differences can be measured by inductively coupled plasma and mass spectroscopy (Ebinger et al., 1990). The isotopic ratio of 234U/238U for natural uranium, as measured by alpha activity, is 0.97; for DU it is 0.13. The 235U/238U alpha activity ratio for natural uranium is 0.047; it is 0.013 in DU.
The value of isotopic ratio data was demonstrated at JPG when groundwater monitoring detected high uranium concentrations. Isotopic measurements suggested that the source was natural uranium, not DU. Abbott et al. (1983) later showed that fertilizer used on surrounding farmland caused the elevated uranium concentrations. Further investigation revealed that Florida phosphate deposits used to produce fertilizer have a high concentration of natural uranium (Eisenbud, 1987).
Studies by LANL (Ebinger et al., 1990) and Battelle PNL found that during soft target testing at APG, DU penetrators oxidized into products that contaminated the soil directly beneath the penetrators (Price, 1991). The DU concentration decreased with depth but remained above background and retained the DU isotopic signature at a depth of 20 cm (Ebinger et al., 1990). The APG results suggest that DU migrated through the soil as soluble uranium, uranium absorbed in water-soluble organic acids, or by particulate transport as the result of erosion in the woodland environment. Unfortunately, data were not available regarding how long the penetrators were exposed to the soil.
LANL studies at YPG found much less DU in soil samples directly below a corroded penetrator. The DU concentration at 8 cm below the ground surface was below the limits of detection. However, sediment samples in an adjacent drainage channel contained DU. YPG has an arid environment, alkaline soils, and deep groundwater. The lack of deep contamination below the penetrator and the presence of DU in the channel indicate that DU transport was dominated by soil erosion. The contaminated sediment found in the arroyo (drainage channel) was from erosion during storms, not from continuous surface water flow. The sediment-transported DU moved about 50 m from the impact site. The high evaporation rate and tight soil greatly limit infiltration at YPG. Thus, DU is unlikely to contaminate YPG groundwater because vertical DU migration is very small, and the depth to groundwater is great. The differences in DU transport at APG and YPG clearly illustrate the importance of soil and climate in the transport and fate of uranium (Ebinger et al., 1990).
The variations in soil contamination observed at APG and YPG are related to the environment (soil type, moisture, temperature, etc.) and the manner in which the penetrators impacted. The studies above were not designed to define the chemical and physical mechanism of DU transport; they provide preliminary data on the migration of DU in environmental media (air, water, soil, groundwater, and ecosystem).
Figure 7-3.Ý Terrestrial Pathway at APG and JPG
Ý
Figure 7-4.Ý Aquatic Pathway at APG
Ý
Figure 7-5.Ý Terrestrial Pathway at YPG
PNL's analysis of soil and vegetation samples from YPG found DU in the soil where penetrators first hit the ground or ìskipî on or through the soil and in the areas where they ultimately came to rest. Levels of soil contamination were higher in the ìskipî areas. Small fragments and particles of DU were visible in the skip areas, indicating that abrasion caused the contamination. Preliminary evidence indicates that vegetation contamination occurred near the skip areas; however, the lack of root contamination implies that the vegetation received a surface coating from the airborne transport of DU rather than from soil uptake (Ebinger et al., 1990). Further studies of the plant contamination would be required to verify this hypothesis.
Where the penetrators landed, soil contamination levels were lower, but the total mass of DU was higher. In this region of the range, large pieces of spent penetrators account for most of the mass. This contributes to a high level of contamination under or near the spent penetrators with essentially no contamination elsewhere.
7.4 Southwest Asia Battlefields
The Army has not conducted environmental sampling and analysis for DU in Southwest Asia, but DU transport and migration should be similar to that found at YPG. However, these speculations cannot be considered definitive without field data.
7.5 DU Contamination
Sites contaminated with DU may need to be cleaned up to reduce health and environmental risks. DU remediation technologies are not well developed; however, many mature technologies from the mining community and processes used for remediation of other heavy metals may be appropriate for DU remediation. In addition, catch boxes concentrate spent penetrators in one location, rather than allowing them to scatter across many thousands of acres of test range. The development and implementation of catch boxes will greatly reduce the long-term cost of remedial actions at locations where they are used.
7.5.1ÝÝÝÝ Remediation Standards
Remediation of sites contaminated with DU concerns three issues: the degree and type of contamination, the appropriate cleanup technology, and the method of waste disposal. Site remediation typically focuses on the level of DU in the soil. The current standard for soil remediation is 35 pCi/g of soil averaged over any 100 m2 area, or 100 pCi/g of soil for any 1 m2 area (58 FR 16268). These criteria are designed so that people on a site will not receive more than 1 mrad/yr of radiation to the lungs from inhalation or 3 mrad/yr to the skeletal system from all routes of exposure.
NRC closure criteria limit the levels of removable and fixed surface uranium (including naturally occurring uranium, DU and their associated decay products). Fixed surface contamination levels cannot exceed an average of 5,000 alpha disintegrations per minute per 100 cm2 (dpm alpha/100 cm2), with a maximum of 15,000 dpm alpha/10 cm2 within a 100 cm2 area. Removable contamination is limited to a maximum of 1,000 dpm alpha/100 cm2 (NRC, 1974).
Because some species of uranium are soluble, groundwater contamination is also regulated. While there is no current drinking water standard for uranium under the Safe Drinking Water Act, there is a standard of 15 picocurie/liter (pCi/L) for gross alpha radiation. This criterion is often applied to groundwater for site remediation standards. The EPA recently proposed new standards for radionuclides in drinking water, including a standard of 20Ý g/L for uranium (56 FR 33050). These standards will appear as 40 CFR 141.15. Once the standard for uranium takes affect, states will probably incorporate it in their groundwater quality regulations.
Finally, an evaluation of remediation alternatives must consider standards for disposal of material generated during remediation. Remediation of firing sites will generate soils and sludges contaminated with DU. A study of remediation options for the Naval Weapons Center (NWC) in China Lake, Calif., concluded that, based on its origin, DU is a low-level radioactive waste and, therefore, must be disposed in a licensed repository (Parkhurst et al., 1992). APG has remediated several sites in recent years. All the remediation residuals at APG have been treated as low specific activity radioactive wastes requiring disposal at a licensed low-level waste (LLW) repository.
7.5.2ÝÝÝÝ Battlefield Remediation
No international law, treaty, regulation, or custom requires the United States to remediate the Persian Gulf War battlefields. Before a decision to remediate a battlefield or range could be made, a comprehensive radiological survey and risk assessment should be conducted. A complication of such a survey is determining the location of significant DU contamination. The most significant single action to mitigate Persian Gulf War battlefield contamination is the management of DU-struck Iraqi vehicles to minimize losses of DU particles contained in those vehicles. Beyond that, if soil concentrations could be determined, environmental transport models could be developed to predict the fate and effect of DU in the environment. These data would provide the foundation for risk assessment.
Field data can verify the accuracy and sensitivity of the environmental transport and risk models. The Army can use these models to estimate the risk for various remediation alternatives, including taking no further action. Model developers need a broad data array to substantiate projections made by the transport and risk models. Therefore, it may be advisable to institute a sampling program at a highly contaminated location, such as the Tomsk, Russia, waste-tank explosion site, to provide an analog for environmental transport of DU. Environmental transport of any type of uranium is a function of its chemical, not its radiological characteristics. The high concentration of uranium oxides in the soil at sites such as Tomsk would allow modelers to gather accurate migration data at a minimum cost. These data would provide the foundation for a technically defensible environmental transport model to estimate the environmental risks of DU on the battlefield and test ranges.
These validated models would allow the Army to make more informed decisions about DU remediation alternatives.
7.5.3ÝÝÝÝ Remediation Technologies
Remediation technologies for sites contaminated with DU are likely to use one or more of the following technologies: excavation and earth moving, physical separation methods, chemical separation processes, and in-place stabilization. Because each site has a unique environment, one must assess the damage that remediation could cause before selecting a remediation technology. This assessment may indicate that it is better to stabilize the contaminant in place. Battelle PNL recently evaluated potential cleanup strategies for use at firing sites contaminated with DU in the arid environment of NWC using the TRUCleanô process (Parkhurst et al., 1992). (No one has much experience remediating DU-contaminated sites in wetter environments.)
Unless in-place stabilization is used, remediation requires excavation. This may range from complete excavation and secure disposal of all contaminated soil in a low-level waste repository, to excavation treatment to remove DU and re-emplacement of the soil. The principal hazards associated with excavating DU-contaminated soils are the mechanical hazards associated with any large earth-moving project and the toxicological hazards from uranium. If the site also is contaminated with high explosives (HE), then the risk from unexploded ordnance will dominate site remediation management.
When DU-contaminated soils are remediated, the first step is to recover spent penetrators and large fragments. Depending on soil characteristics, this may be done by size classification using a screening device, or it may require hand sorting. Simple screening has been shown to remove up to 50 percent of DU fragments from soil (Parkhurst et al., 1992). Hand sorting requires more personnel protection because it exposes workers to DU metal fragments, respirable DU and DU oxide particles.
A number of commercial processes have been proposed to remediate contaminated soil, including a process designed by TMA/Eberline to clean up Johnston Atoll, TRUCleanô, the Chemrad Process, ACT*DE*CON, B&W-NESI Soil Washing, the Mobile Soil Washing System, Frantz Magnetic Barrier Technology and NRT Soil Washing/Chemical Extraction. Some of these processes have been used for remediation; however, all of these technologies are still under development as uranium remediation systems.
Johnston Atoll Plutonium Cleanup
Nuclear weapons tests in the 1960s contaminated the soil of Johnston Atoll, a Pacific island southwest of Hawaii, with plutonium (Pu)-239 and americium(Am)-241 particles. TMA/Eberline was contracted to modify and improve a prior contractorís soil cleanup demonstration plant at the atoll. The modified Johnston Atoll Pu Cleanup Plant is an assembly of standard sand and gravel handling equipment with advanced instrumentation for monitoring radiation. This plant was designed to process 1,000 yd3 of soil each week. It uses an array of sensitive radiation detectors and software designed by Eberline Instrument Corporation. The software controls the Segmented Gate System, which diverts contaminated material from soil as it moves along conveyor belts beneath an array of 15 overlapping sodium iodide detectors. Each detector reports to a microprocessor/ computer. The computer diverts contaminated material through segmented gates and logs the radioactivity of both contaminated soil and clean soil. It automatically diverts clean soil in one direction and contaminated soil in another. A metal drum collects hot particles, and a supplemental soil-washing process removes dispersed contamination. Washed soil then passes beneath a second array of radiation detectors to verify that release criteria have been met. The system is processing approximately 100,000 yd3 of coral soil matrix containing low and intermediate levels of contamination.
TRUCleanô
Figure 7-6 presents a diagram of the TRUCleanô process under continuing development by Lockheed Environmental Systems and Technologies. The process has adapted ore milling technology from the gold and lead mining industries to recover DU from contaminated soil. It uses vibrating screens, mineral jigs and spiral classifiers to separate DU metal from soil slurries (Hall, 1993b). Gravimetric settling separates the very dense uranium metal from soil and water slurries. An oxidant and a strong acid or base are added to oxidize uranium to the U(VI) soluble oxidation state. The dissolved U(VI) is recovered by ion exchange and discarded as low-level radioactive waste. The decontaminated soil is then dewatered and assayed for residual DU.
This technology produces a slurry of decontaminated soil that has been leached with a strong oxidizing agent in a concentrated acid or base solution. This process may release other heavy metals from the soil. The concentration of other heavy metals could create problems in disposing of the decontaminated soil and/or the leachate. Furthermore, dewatering leached clays is difficult because they are hydroscopic. Leached clays are often referred to in the mining industry as ìslimesî because of their poor dewatering characteristics (Thomson, 1993).
Figure 7-6.Ý DU TRUCleanô Process
Gravimetric settling efficiently removes DU metal particulates larger than about 0.1 mm in diameter. It is not likely to remove uranium oxides. If gravimetric methods do not sufficiently decontaminate the soil, the TRUClean process can leach finely dispersed uranium from the soil with an optional chemical separation.
Pilot scale tests of TRUClean on DU-contaminated soil at NWC demonstrated reductions in radioactivity ranging from 85 percent to more than 99 percent. Pilot scale tests at Johnston Atoll reduced the Pu concentration in soil from between 65 pCi/g and 100 pCi/g or higher, to less than 10 pCi/g. The waste residuals after treatment were less than 1 percent (at NWC) and 2 percent (at Johnston Atoll) of the original contaminated soil volume (Parkhurst et al., 1992).
Chemrad Process
A process marketed by Chemrad Technologies, Inc., Louisville, Ky., is much earlier in development. (Marshall, 1993; Bagniefski, 1993). The process is proprietary, so few process details can be disclosed. However, according to Chemrad, the process prepares an acidic slurry of the contaminated soil, then leaches it with an undisclosed lixiviant to remove DU. Chemrad predicts volume reductions in excess of 95 percent based on laboratory studies, and it reports residual DU concentrations in soil of less than 10 pCi/g. After processing, all soils are decontaminated and can be returned to the site. The company has a contract to demonstrate this process on a munitions catch box at the New Mexico Institute of Technology's Energetic Material Research and Technology Center near Socorro, New Mexico. The demonstration began in early 1994, treating approximately 200,000 ft3 of contaminated soil at 125 ft3/hr. Chemrad estimated the cleanup time at 13 weeks. The projected cost is less than $35/ft3, which may be cheaper than commercial disposal of DU-contaminated soil. The Envirocare contaminated soil disposal facility in Utah charges $21/ft3 to $33/ft3 (Rice, 1993). This Envirocare cost does not include excavation, field sampling and analysis, transportation, engineering, and associated occupational and environmental safety and health costs. As of July 1994, data from the demonstration project were not available.
ACT*DE*CON
The ACT*DE*CON process (patent pending), developed by Bradtec-US Inc., has been tested at the bench scale with various soils and contaminants, including uranium, plutonium, americium and lead. This process was scheduled to be used on a pilot scale at two DOE facilities and on a full scale at one DOE facility during late 1994.
ACT*DE*CON combines dissolution with dilute selective solvents, contaminant recovery and solvent regeneration to provide a continuous recirculating treatment of soils to remove strontium, cesium, technetium, radium, actinindes (uranium and transuranics), barium and lead. The process dissolves and recovers contaminants using countercurrent extraction. The solvent typically used is composed of hydrogen peroxide, sodium carbonate, sodium bicarbonate, 8-hydroxyquinoline and ethylenediamine- tetraacetic acid. Soil is fed to the first extractor where a solvent dissolves the contaminant. The soil is then fed to the second extractor, which mixes partially treated soil and fresh solvent, resulting in further dissolution. The number of extraction stages and the contact time in the extractors is determined by the contamination level, the physical and chemical characteristics of the soil, and the level to which the soil must be treated. After the treated material leaves the final extractor, filters recover the treated soil. The filter cake is flushed with clean water before discharge. The solvent (with contaminants) is treated by either selective ion exchange or evaporation. The solvent can then be analyzed and chemically adjusted before recycling.
B&W-Nuclear Environment Services Soil Washing
B&W-NESI developed a soil-washing system for cleaning approximately 500,000 ft3 of uranium-contaminated soil from the Apollo Facility 35 miles northeast of Pittsburgh. Soil contamination ranged from zero to 2,000 pCi/g. B&W-NESI treated approximately 1,000 pounds (lbs) of contaminated soil with a bench-scale model of this technology.
Mobile Soil Washing System
The Westinghouse Scientific Ecology Group, Inc., developed the Mobile Soil Washing System technology to separate organics, polychlorinated biphenyls (PCBs), heavy metals and radioactive contaminants from soil. This system screens soil to remove large rocks and debris, then processes the soil in a rotating drum or vibrating screen to sort and prewash it. Large (>2 mm) pieces of soil are washed with leach solution, rinsed with water, monitored and returned to the site. The remaining contaminated soil is processed using equipment from the mining industry. Soils are wetted with the leach solution and the fines are separated. The washed soils are rinsed, monitored, and returned to the site. The fines and wash water go to the precipitation tank. Contaminants are chemically precipitated. The clean leachate is then further treated and sent to the leachate makeup tanks. The highly contaminated precipitate is placed in containers for disposal.
Frantz Magnetic Barrier Technology
The S.G. Frantz Magnetic Barrier Technology separates and concentrates particles according to magnetic susceptibility. It uses a magnetic energy gradient to deflect particles of selected susceptibility from the paths they would normally follow. Most soils are diamagnetic and most radioactive substances are paramagnetic. By using the concentration of diamagnetic compounds of soils, the Frantz Magnetic Barrier Technology can separate grains that are nonmagnetic by stains of inclusions of radioactive substances. It can process solids from about 2 mm to a few micrometers in size. Pretreatment by sizing, drying and reducing electrostatic charges improves separation.
NRT Soil Washing/Chemical Extraction
Nuclear Remediation Technologies developed a soil- washing/chemical-extraction technology to remove radioactive contamination. NRT performed bench-scale tests of its centrifugal-concentration/soil-washing process on DU-contaminated soils from a firing range owned by Olin Ordinance. The tested soil contained metallic DU particles (4 x 325 mesh) as well as fused silica particles containing U3O8. This process reduced the soil radioactivity by approximately 90 percent from 150 pCi/g to approximately 15 pCi/g.
7.5.4ÝÝÝÝ Army Evaluation of Remediation Technologies
The Army needs to evaluate the effectiveness and cost of remediation technologies. It should also identify research and development requirements for new and improved technologies. The Army needs a strategy to address its long-term liabilities from DU contamination of test ranges and perhaps battlefields. This may require examining historical information on the early research and testing of DU-containing weapons. Finally, the Army needs to adequately fund site investigations, and research into remediation technologies and activities.
7.6 Protecting the Environment from Long-Term Consequences of the Use of DU
This report documents several potential environmental hazards created by using DU. These hazards are potential because, as noted throughout this report, gaps exist in the data needed to develop environmental transport and risk models. To achieve long-term, comprehensive, environmentally astute DU management, the Army needs well-funded, thorough investigations to develop and validate models using diverse field data.
This section outlines candidate Army actions that may be used to improve Army management of DU.
7.6.1ÝÝÝÝ Regulatory Cross Links
The review of DoD and Army documents in Chapter 3 indicates that adequate environmental, system safety, and health hazard assessment policies regulate the acquisition of weapon systems. These policies require that the PM conduct environmental, system safety and health hazards analyses of the impacts of a weapon system from its initial developmental concept until DoD accepts the weapon system as an operational inventory item. The acquisition staff concentrates on the life cycle of a system through its operational use in the field. Acquisition policies, however, do not adequately consider the environmental consequences of system disposal. The regulations do not explicitly require the PM to consider the environmental costs from development through acquisition, use, demilitarization, and disposal.
Chapter 3 also indicates that when a system is obsolete, demilitarization and disposal policies require the Army to consider the environment when determining final disposition. These policies also regulate the transfer of obsolete systems from operational forces to demilitarization and disposal personnel. In addition, the PM must develop a demilitarization and disposal plan before producing ammunition and releasing it to operational forces. This study found several such plans for demilitarization or disposal of DU ammunition. However, acquisition regulations do not explicitly require a disposal plan and R&D and Demilitarization and Disposal regulations do not explicitly refer to environmental regulations. Thus, the regulatory requirements do not appear to be cross-referenced.
If the regulations were cross-referenced, the relationship between acquisition and disposal of weapon systems regarding environmental requirements would be much clearer. Furthermore, demilitarization and disposal staff members would know what to expect when they receive an obsolete system.
The existence of environmental and safety policies and procedures does not guarantee that the Army adequately analyzes environmental, system safety and health hazards when acquiring and disposing of weapon systems. Acquisition and disposal PMs must also receive adequate environmental training. The Army needs to audit its environmental training programs for these managers.
Besides the environmental, safety and health hazard policies that exist in acquisition, demilitarization and disposal regulations, AR 200-2, Environmental Effects of Army Actions, provides detailed environmental policies. AR 200-2 describes each step of the environmental analysis [specified by the National Environmental Policy Act (NEPA)] that a PM must consider for every new system. It also provides a way for the Army to examine any new environmental issuesóthe Life-Cycle Environmental Document (LCED). Given that some DU work began before NEPA, LCED offers the best available means to reexamine the environmental consequences of DU systems. In view of the current concerns relating to DU, an Army review of all of these documents to develop a baseline of knowledge on the environmental documentation for all DU systems could prove useful. This overview might lead to an Army decision to prepare a new programmatic LCED, or it might provide sufficient data to avoid this costly and time-consuming exercise.
The DoD 5000 series regulates all weapons development. It stipulates that a PM must consider the total cost of a system, including development, acquisition, support and disposal. This total cost is called the Life-Cycle Cost (LCC). LCC is an integral part of decisions in several areas, such as the Program Office Life-Cycle Estimate, Independent Cost Estimates, and selection of materials (including hazardous and radioactive materials). However, the 5000 series often uses the term LCC to refer only to the cost of development, testing, production and support. For example, DODI 5000.2, Part 4, Section E, states that LCC ìreflects the cumulative costs of developing, procuring, operating, and supporting a system.î Disposal is not considered. In addition, formats in DODM 5000.2-M, such as in Part 4, Section C, do not include disposal in the Program Life-Cycle Cost Estimate Summary. The 5000 series does not need major changes; however, some minor changes could significantly affect how the Army accounts for disposal costs. These changes would also help the services focus on the ultimate financial impact over the life cycle of each system.
7.6.2ÝÝÝÝ Federal Acquisition Regulation
The Federal Acquisition Regulation (FAR) does not require contractor proposals for DU weapon system production to include costs for equipment and facility decontamination once manufacturing has concluded. Because a facility can operate for many years, the Army has treated these costs as contingent liabilities and not as allowable costs under FAR. However, because defense funding is shrinking, more facilities are closing, making facility decontamination issues more important. By precluding cleanup costs in weapon systems proposals, FAR creates a subtle disincentive for contractors to maintain clean facilities. This may subsequently lead to disputes between contractors and the Army over cleanup liability. Therefore, FAR should mandate that all contract bids include cleanup costs.
7.6.3ÝÝÝÝ NEPA Documentation
AR 200-2 requires that the Army follow the NEPA process, which includes preparing appropriate environmental documentation while fielding and deploying weapon systems. As of July 1994, all the environmental assessments that the Army prepared for DU weapon systems have had a Finding of No Significant Impact (FNSI).
10 CFR 51.22 (c)(14)(xv) categorically excludes the NRC action of issuing, amending or renewing materialsí licenses issued for possessing, manufacturing, shipping, testing, or other use of DU in military munitions from NEPA. It does not relieve licensees of the responsibility for assessing the impact of a DU license on the environment. The regulation states, however, that NRC is not required to comply with NEPA when granting the license.
The NCR's categorical exclusion and the Armyís environmental assessments consider only peacetime manufacture, storage, transportation, testing, and disposal. Environmental impacts under likely battlefield uses have not been formally assessed. In light of concerns about the long-term environmental effect of using DU, it may be appropriate for the Army to explore the possibility of preparing a comprehensive Programmatic Environmental Impact Statement (PEIS) for DU weapon systems.
7.6.4ÝÝÝÝ Environmental Assessments
According to AR 200-2 and NEPA, the Army has prepared environmental documentation for all its systems containing DU except those developed before NEPA. Section 3.3 identifies 16 such environmental documents. The environmental documentation reviewed during this study showed a steady improvement in the amount of detail and research in each successive system document. In applications outside the Army, such as construction projects, an EA is site-specific. Within the Army, however, an EA is usually an item-specific document that attempts to cover sites where the item will probably be manufactured, tested, stored, or demilitarized. When the Army prepares a site-specific EA, the document assesses the cumulative impact of many systems. Use of the same term for two entirely different applications may be confusing and could lead to the erroneous conclusion that the appropriate environmental documentation has been prepared.
The Army publishes each EA and a description of its findings in local newspapers serving the installation that prepared it. After publication, the Army establishes a comment period. Picatinny Arsenal, in N.J., prepares EAs for ammunition, while TACOM, in Warren, Mich., prepares EAs for tank armor. However, as discussed in Chapter 3, DU components for Army systems are manufactured, assembled, tested, stored, and disposed at many U.S. sites. The Army does not publish EAs in newspapers serving each site, so communities do not always know they can comment on the documented findings. The Army could resolve this issue by publishing EAs and FNSIs in a national medium and local media in all affected areas.
7.6.5ÝÝÝÝ Programmatic Environmental Impact Statement
Because of controversy about the use of DU in Desert Storm and at DoD test ranges, the Army should consider preparing a DU LCED at a programmatic level. This document could be an umbrella environmental assessment or impact statement covering all aspects of DU use, testing, and disposal in the Army. Future use of DU that might require an EA could be appended to the LCED, reducing the cost of site-specific EAs. Finally, a generic DU LCED could be used to educate the public concerning Army environmental programs to manage DU.
7.6.6ÝÝÝÝ NRC License Management
Various AMC subordinate commands hold 14 NRC licenses for managing DU ammunition and armor. The licenses are site- or mission-specific. This arrangement should accommodate the licensee missions, but the lack of coordination between the license holders has resulted in management problems. These problems have surfaced in instances where DU ammunition has been shipped to locations not authorized to store DU and also in situations where excess DU has not been properly removed from inventory.
A licensee that ships DU is liable for the shipment of radioactive material and must ensure that the recipient is licensed to receive the shipment. AMCCOM and ARDEC hold NRC licenses. AMCCOM's license is restricted to specific, type-classified ammunition, while ARDEC's is limited to use and storage of DU for R&D at Picatinny Arsenal. Item managers at AMCCOM, ARDEC, PM Tank Main Armament Systems (TMAS) and PM Bradley can ship DU ammunition. Unfortunately, ammunition item managers have violated license restrictions by directing ARDEC to ship R&D ammunition to locations not licensed to store or use it.
Ammunition item managers could avoid these violations if AMCCOM's license authorized all DU ammunition, including R&D ammunition. Because licensees can be cited and/or fined for license violations, licensees have established several restrictions to ensure that they can accomplish their missions without being held responsible for personnel actions beyond their control. AMCCOM and ARDEC are apparently reluctant to expand their responsibilities because they do not think their missions require such changes; they think the changes could increase their liability.
NRC limits the amount of DU that Army test centers can possess. Test centers have DU in ammunition awaiting testing and in unrecovered penetrators in impact areas and catch boxes. They also may have radioactive wastes from enclosed firing ranges and armor targets. In addition, because licensed developers do not provide disposition instructions for R&D ammunition that has completed testing, test centers must store this ammunition, which NRC includes in their DU inventories. This storage may prevent test centers from receiving new test material if they are approaching their possession limits. The test centers cannot dispose of the material as radioactive waste because it must first be demilitarized. They cannot ship it to a depot for storage without the item manager's direction. On the surface, this appears to be an AMC management problem, but it actually extends to the Secretariat level because PM Bradley and PM TMAS report to the Assistant Secretary of the Army for Research, Development and Acquisition.
The Army could improve its management of DU by consolidating the 14
current licenses into a single NRC license managed by AMC Headquarters
(HQ), the DA, or a centralized DU management and research authority. AMC
management would require cooperation by the various PMs. DA management
could follow the policies now practiced by the Air Force and Navy; each
have consolidated their licenses into a master materials license managed
at the department level. A central DU management and research organization
could also ensure compliance with Army policies and NRC license requirements.
AMC is currently the principal Army DU management and research authority.
Regardless of the licensing structure, systemic issues concerning DU will
require substantive AMC involvement.
7.6.7ÝÝÝÝ Catch Boxes
The Army has shown that catch boxes can limit the amount of DU dispersed in the environment. Concentrating DU within catch boxes reduces the DU available to contaminate ecosystems in impact areas. The expense of periodically remediating and recovering contaminated sand and DU in catch boxes will increase the cost of testing DU penetrators. However, remediating a catch box is more cost-effective than remediating thousands of acres of a range. DU range remediation is an RDT&E cost that is deferred until the range is taken out of service. There is no current plan to escrow these costs or attribute them to development of the weapon systems that generate the contamination. Therefore, because the Army cannot place RDT&E funding in escrow, developers and PMs must address planning and funding for remediation independently of the systems that created the contamination. This discontinuity does not meet the spirit of AR 200-2.
7.6.8ÝÝÝÝ Demilitarization and Recycling
The Army, as reported in Chapter 3, is developing a DU weapon system demilitarization process. This process will develop standard processes for weapons demilitarization that comply with applicable environmental laws and regulations, including waste treatment and disposal criteria. Once complete, the Depot Maintenance Work Requirements (DMWRs) will be revised to reflect the protocols for DU weapons demilitarization.
In addition to programmatic demilitarization planning, the Army has undertaken efforts to recycle DU materials. Recovering and reusing DU may reduce the potential long-term liabilities of disposal. The Army should continue to support these programs.
7.6.9ÝÝÝÝ Disposal
Managers of Army firing sites face many challenges and substantial uncertainties when disposing of DU waste. Table 7-1 summarizes DU waste management actions for APG during 1992.
Because USACSTA and ARL-Aberdeen test fire DU penetrators against conventional and DU armor plate, APG is the biggest generator of non-medical low-level radioactive waste in the Army. These tests have generated waste faster than funds or landfill space have become available, forcing APG to maintain a backlog of DU waste. While these problems do not now prevent firing sites from testing DU projectiles, these problems could in the future if the Army does not resolve three problems:
The lack of funding for current and projected waste disposal requirements is manifested in two ways. First, AMC delays sending funding to waste management programs. For example, AMCCOM, the Army unit that manages radioactive waste, did not receive funds budgeted for programs at APG during FY92 until September 1992. As of July 1, 1993, AMCCOM had not received funds for APG to initiate FY93 programs. Budgets were revised several times during each fiscal year (FY) before the money was finally received. It is difficult to manage a system when neither the amount of money nor its arrival within the FY are known in advance.
Second, budgeted funds are not adequate for current waste disposal and recycling mandates. For example, in FY92, YPG requested funds for disposal of 40,000 ft3 of DU- contaminated soil, but AMC denied the request because of a lack of funds. APG has approximately 12,000 ft3 of contaminated soil in storage that is ready for disposal. Moreover, it is estimated that another 20,000 ft3 of contaminated soil must be cleaned up at APG in the future. The Appalachian Low-Level Waste Compact, which includes Maryland, has approved disposal of this material as a low-specific activity waste at Envirocare of Utah, but APG has no funds budgeted for this disposal. The current estimate for disposal of the existing stored soils at APG is $3 million. Costs for loading, packaging and transporting this material to the Utah facility are estimated at $120,000.
The inability to dispose of accumulated DU and contaminated soil could limit activities at existing firing sites. As previously explained, each site operates under a license, issued by NRC or an ìagreement state,î that specifies the total amount of radioactive material the facility may have in its inventory. Accumulated waste material and stored R&D ammunition are subject to the provisions of these licenses, such that a large inventory of waste may limit the ability of a facility to receive additional DU material for testing. At the end of FY91, the total amount of DU waste material generated at USACSTA was estimated to be 100,000 kilogram (kg), most as metal from recovered and unrecovered penetrators and DU armor. This material counts against the maximum permitted mass of DU under provisions of USACSTA's license. Any interruption in recycling and disposal activities resulting in the accumulation of additional DU could force USACSTA to stop testing unless NRC approves an increase in the maximum permitted mass.
In addition to the problem of funding inadequacies for waste disposal, there is legitimate concern that LLW disposal sites will not be available. The Low-Level Radioactive Waste Policy Act required all states to take responsibility for disposal of their LLW. To motivate states to take this responsibility, the act allowed commercial repositories to refuse waste shipments from states that do not have their disposal facilities or did not enter compacts by December 31, 1992, with states that have disposal facilities. Only two commercial sites now receive low-level waste: Hanford, Wash., and Envirocare of Utah. Barnwell, S.C., stopped accepting Army LLW in July 1994. Until their compact sites are operating, Army facilities outside compact states served by the commercial LLW disposal facilities (YPG, APG, and JPG) may encounter difficulties disposing of DU wastes. For example, the Appalachian Compact, which includes Maryland, is not scheduled to open until 1999 (Cardenuto, 1993b). This aspect of the act may seriously affect Army management of waste materials containing DU because the Army has installations across the country and no reasonable way to facilitate formation and management of regional LLW compacts.
Under the Appalachian Compact, no member state will be allowed to dispose of more than 25 percent (averaged over 3 consecutive years) of the amount of waste generated by Pennsylvania, the state that will host the final repository. APG was the major generator of LLW in Maryland from 1987 to 1989, disposing of 41,644 ft3, which represented 21.2 percent, 61.9 percent and 46.3 percent of the total waste the state disposed in each of those years, respectively. Under compact provisions, the waste disposed by Maryland from 1987-1989 had a 3-year average of 22.7 percent of the total waste disposed by Pennsylvania, thereby approaching the 25 percent allowed. If Maryland were to exceed its allowance in the compact, it is not clear how APG would be treated in terms of its waste allocation.
This combination of factors may constrain APG's ability to dispose of waste, thereby, increasing its DU inventory. This could, in turn, limit its testing. If the diversity of DU-related activities across the Army is viewed in the national context, the current state-compact approach to managing LLW may adversely affect the national interest. The Army should encourage Congress to consider a system that evaluates the relative value added in each phase of development, testing and fielding a DU weapon system and allocates a proportional share of the waste generated to all states that benefit from the process.
To preclude future disposal and cross-contamination problems, the Army needs to provide a means to ensure the timely disposal of waste residuals from DU firing ranges. Improved recovery and recycling programs are part of the answer to this problem. The Army should continue to investigate ways to improve the technology for containing and recovering DU from firing ranges, as well as ways to encourage development of markets for recycled DU. The Army should also recognize that DU testing will always produce waste. The Army should continue to actively participate in developing disposal options for LLW, including volume reduction, waste minimization, waste-form modification and new disposal facilities.
7.7 Summary
Uranium, regardless of the isotopic mix (DU, enriched, naturally occurring, etc.), is identical in matters of chemical toxicity and environmental mobility. DU can be moved through the environment by water, wind and biological transport. Army studies of the dispersal of DU particles after a penetrator hits a hard target show that the extreme density of the particles limits most airborne transport. DUís mobility during aqueous transport is determined almost exclusively by its solubility, which in turn is determined by its oxidation state. Minerals in the soil where a DU penetrator lands affect how fast the penetrator will corrode and become soluble. Research has shown that DU is not effectively transported in the food chain, partly because organisms low in the food chain quickly excrete most soluble uranium species.
Plants growing in soil contaminated with DU typically concentrate DU in their root systems. Some plants appear to have a mechanism to limit their DU intake. Because DU has a low specific activity and most animals in the natural environment do not live very long, the principle hazard associated with animals ingesting uranium is toxicity, not radioactivity.
Studies at YPG found DU in two locations on firing ranges: in the skip areas, where penetrators passed through the soil, and in the areas where they landed. Contamination was higher in the skip areas but a greater mass of DU was found where the penetrators landed. Studies at APG, JPG and YPG have shown that although DU has not migrated out of firing areas, it has moved some within these areas. DU was not detectable in groundwater samples at APG or JPG. Groundwater was not tested at YPG because the water table there is about 700 feet below ground. DU contaminated more soil directly beneath corroded penetrators in the wet, deciduous climate of APG than in the arid climate of YPG. However, DU contaminated an arroyo near an impact area at YPG. The DU moved less than 50 m from the impact area and is unlikely to contaminate the very deep water table at YPG.
Although studies have not been done in Southwest Asia, DU transport
and migration there would probably be similar to that found at YPG.
Site remediation typically focuses on the level of DU in the soil.
Although water quality standards currently do not regulate uranium in drinking
water, revised drinking water regulations will probably specify a limit
for uranium of 20Ý g/L. Evaluation of remediation alternatives must also
consider standards for disposal of material generated during remediation.
No international law, treaty, regulation, or custom requires the U.S. to remediate Operation Desert Shield/Desert Storm battlefields. Before remediation could occur, a comprehensive radiological survey and risk assessment should be conducted, but this would not be possible until scientists have developed an environmental transport model that predicts the movement and transformations of DU in the environment.
To develop an environmental transport model, researchers need to study a site with a high concentration of radioactive contamination, such as the Russian waste-tank explosion site at Tomsk. The high concentration of actinides in the soil there should provide the broad data array necessary for developing an accurate model. Once a model is developed, it can be used in surveying any DU contamination site, including those in the U.S.
The Army needs to develop a strategy to address the long-term liabilities of DU contamination at test sites and perhaps at battlefields.
Numerous commercial remediation processes are available for contaminated sites. Almost all of these processes use one or more of the following technologies: excavation and earth moving, physical separation methods, chemical separation processes, and in-place stabilization. The Army needs to evaluate the effectiveness and cost of existing remediation technologies and to continue to seek new and improved technologies.
The Army should consider the following candidate actions that may be used to improve Army management of DU. It should consider: