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Uk 11, VN(;1NFFR1M;/kAA0M.k 1994 For those infrequent occasions Aft the moisture retention capabilities of the fine -soil layer aiceeded, the low -perme- ability asphalt layers located lower in the barrier profile will provide another barrier to water infiltration. ASPHALT: THE FINAL STOP One promising asphalt formulation currently being tested con- sists of a composite layer of asphaltic concrete (with 8% asphalt and low voids) overlain by a 5 mm thick layer of polymer modi- fied asphalt. Such composite layers provide much lower perme- abilities than single layers. The asphalt layer in the cover de- sign provides features not present in the standard RcRA design, which uses compacted clay layers. The low permeability and longevity of asphalt, coupled with low water content, mean that asphalt is ideally suited in preventing not only water intrusion but biotic intrusion as well. Over the next three years, we will conduct additional re- search and testing on the low -permeability asphalt layers. We will determine the physical properties of the various types of asphalt under consideration including large-scale permeability and the stress -strain relationships associated with three-di- mensional deformation. We will also continue to study the longevity of asphalt as a low -permeability component. The as- phaltic layers must be durable enough to provide the level of impermeability needed over the design life of the permanent isolation barriers. As part of the asphalt longevity studies, we are analyzing as- phalt artifacts that have existed for hundreds to thousands of years. These 500 -3,000 -year-old asphalt specimens were inten- tionally buried after they were made, and were discovered in the vicinity of natural asphalt seeps, believed to have been the source for the artifacts. By comparing the physical and chemi- cal of the artifacts with the fresh, naturally occurring asphalts located nearby, scientists are able to characterize the long-term aging process of asphalt in buried environments. From this re- search, team members are preparing artificially aged asphalt samples to use in experiments that will determine the effects of aging on asphalt's p1 and hydrological properties. The low-permeabiM layers, in concert with a sloped barrier surface (engineered to maximize runoff and minimize erosion) as well as the capillary barrier (which blocks the downward movement of percolating water), are expected to perform in such a way that we can achieve near -zero drainage rates through the barrier. The results of other development tasks also have con- tributed to the current design and performance assessment of the barrier. We have attempted to predict future climatic condi- tions based on the reconstruction of past climatic changes. Erosion resistance is being studied through wind -tunnel stud- ies and field tests. Through studies on small and large mam- mals, we've found that animal burrowing does not adversely af- fect the moisture retention capabilities of a protective barrier and may actually enhance evaporative losses. Near -surface wa- ter -balance modeling capabilities are being developed to simu- late barrier performance for extremely long periods of time. Surface and subsurface marker concepts have been developed to warn future generations of the dangers of the wastes buried beneath a protective barrier. The Hanford prototype cost about $350,000—$390,000 per'. acre. Typical RcRA barriers cost between $50,000 and $300,000 per acre. Comparing long-term barrier costs with RcRA cover costs, however, is like comparing apples and oranges. When comparing the two types of covers, life -cycle costs should be considered, as well as costs associated with surveillance, main- tenance, repairs and the required institutional control of RcRA covers. When those aspects are considered, long-term barriers are not significantly more expensive than RcRA covers. The recently completed full-scale prototype barrier will en- able engineers and scientists to gain insights and experience on barrier design, construction and performance that have not been possible with the individual tests and experiments con- ducted so far. Over the next three years, several tests and ex- periments xperiments will be conducted to acquire performance data on water redistribution, drainage, erosion, physical stability, and intrusion by plants and animals. Because only a finite amount of time exists to test a prototype barrier in- tended to function for a minimum of 1,000 years, we have designed the testing program to stress the pro- totype. Water and snow will be added, in amounts that will equal or exceed 100 -year storm events and at least three times the annual average precipitation. The development, testing and evaluation of perma- nent isolation surface barriers is critical to support the Hanford site's mission of environmental restoration. Because no proven long-term barrier is available, the development of permanent isolation surface barriers is necessary to meet key cleanup objectives. Also, a bar- rier probably will be needed to support future Super - fund and RcRA actions. Finally, the barrier may protect', human health and the environment at the Hanford facility and other waste sites throughout the U.S. Q FOR SEVERAL YEARS, ENGINEERS TESTED THEIR THEORIES ABOUT THE CAPILLARY BARRI- ER AT A FIELD LYSIMETER TEST FACILITY, LOCATED AT DOE'S HANFORD SITE. 41 N Richard Wing, P.E., is a senior engineer at West- inghouse Hanford Co., Richland, Wash. Glendon W. Gee is a senior staff scientist at the Pacific Northwest Laboratorv. Richland.