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Comparison of Clay and Asphaltic Materials for use as Low Permeability Layers in Engineered Covers at the Rockv Flats Environmental Technology Site M.J. Glade arid P.A. Nixon' Parsons Engineering Science' Denver' Colorado INTRODUCTION The Rocky Flats Environmental Technology Site (RFETS) located northwest of Denver, Colorado, operated five lined Solar Evaporation Ponds (SEPs) from 1953 until 1986 for the disposal of liquid radioactive and hazardous waste. The U.S. Department of Energy (DOE) has signed an Interagency Agreement (LAG) with the Colorado Department of Public Health and the Environment (CDPHE), and the U.S. Environmental Protection Agency JOSEPH), and has agreed to close the SEPs through an Interim Measures/Inter~m Remedial Action (INDIRA) accelerated program. Through an alternatives analysis study, DOE selected an alternative to consolidate contaminated pond liners, subsurface soils, stabilized sludge, and miscellaneous contaminated debris from within the operable unit (OU) under an engineered cover. Based on the Colorado hazardous waste landfill siting regulations (6 CCR 1007-2, part 2), the DOE has designed an engineered cover closure system with an anticipated functional lifetime of 1,000 years. The engineered cover must also meet the Resource Conservation and Recovery Act (RCRA) requirements for the closure of a surface impoundment (40 CFR 265.111 and 40 CFR 265.228~. Since regulatory guidance for long-term engineered barriers does not exist, the DOE, CDPHE, and USEPA agreed that synthetic (human-made) materials that have limited long-term performance testing results should not be included as fimctional components of the engineered cover. Therefore, the engineered cover is designed with natural matenals that have expected long- te~m durability. Figure 1 presents a cross section of the proposed engineered cover. The asphaltic low-permeability layer consists of a composite of a fluid applied asphalt (FAA) over asphaltic concrete. GRAVEL MULCH FINE-GRAINED SOILS - SAND/GRAVEL LARGE RIPRAP ' ASPHALT MEMBRANE - GRAVEL BASE COURSE - FTGURE ~Engineered Cover Cross Section. f~ . ~ . . . , . , . ~ . . f ' ~-~ , ~ ~% VEGETATIVE SURFACE TOPSOIL/ORAVEL ADMIX -- SAND ~SMALL RIPRAP - SAND - ASPHALT CONCRETE CONSOLIDATED CONTAMINATED MEDIA ~ SUBSURFACE BLANKET DRAIN - EXISTING SOILS D-9O

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APPENDIX DIAPERS PRESENTED D-91 Low-permeability clay and asphaltic materials (hot-mix asphalt concrete and fluid applied asphalt) were compared for use in the engineered cover for the SEPs. Low-permeability clay layers have been used in numerous engineered covers throughout the DOE complex as well as at many other sites. Research has been conducted at the DOE Hanford Reservation, Washington, for 10 years with respect to engineered barriers in semi-arid environments. The Hanford researchers have constructed an asphalt low-permeable layer in a prototype engineered cover with a 1,000-year design life. DOE selected asphalt for the low-permeable layer In the engineered cover for the OU4 SEPs. This paper presents a comparison of {ow-permeable clay and asphaltic materials with respect to the specific environmental conditions In Colorado and the design criteria of the engineered cover. The comparison factors include hydraulic conductivity, longevity, engineering characteristics, constructability, and cost. SELECTION CRITERIA Selection criteria for the low-permeability layer were established based on the performance requirements, engineering charactenstics, constructability, and cost. The following subsections discusses each of the specific selection cntena. Hydraulic Conductivity Hydraulic conductivity (permeability) is a matenal property that is a measure of the ease with which a liquid can be transmitted through a porous material. Clay soils have been used In traditional compacted clay cover systems to meet RCRA requirements and have been shown to have permeabilities below 1 x 10~7 cm/s (USEPA, 1988). However, Day and Daniel (1985) indicated that field-measured permeability values could be 1000 times greater than laboratory- measured permeability values possibly due to the numerous hydraulic defects found in field compacted clay liners. Factors that can influence the inherent permeability of a clay material include the void ratio, composition, fabnc, and degree of saturation for the material. Field placement factors such as compacted water content, compactive energy, and desiccation can also influence the permeability of a clay material (USEPA, 19911. Large variabilities in the permeability of clays can exist due to all of these factors. The permeability of asphalt concrete is primarily controlled by the asphalt content, mineral filler content, and air void content, which are determined from the mix design. As a general rule, asphalt type, aggregate type, and batch production variables have only a minor Influence on the permeability of the asphalt concrete. However, a well-graded aggregate is preferred. A low air void content will reduce the permeability of the mix. Air void contents are not only controlled by the mix design but also by the energy of compaction. Standard roadway construction equipment may be modified to produce the desired permeability. Asphalt linings 2 inches thick having 4 percent or less air voids will generally have a permeability less than 1 x 10-7 cm/s (Asphalt Institute, 19891. Freeman, Romine, and Zacher (1994) conducted detailed laboratory and field permeability tests on asphalt concrete samples for the Hanford project. Laboratory tests indicated a permeability range of 1.05 x 10~~i cm/s to 6.96 x 10~~i cm/s for an asphalt content of 6.5 percent, and 2.09 x 10-~2 cm/s to 8.25 x 10~~ cm/s for an asphalt content of 7.5-percent. The Hanford researchers also perfonned field permeability tests on a prototype barrier constructed of two 7.5 cm layers of

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D-92 BARRIER TECHNOLOGIES FOR E~IRONMENTAL MANAGEMENT compacted hot-applied asphalt concrete with an asphalt content of approximately 7.5 percent and compacted it greater than 95 percent of theoretical maximum density (151 Ib/ft31. A modified falling head permeability test was conducted at five locations of the prototype barner, and permeability results ranged from 1.91 x 10-9 cm/s to 1.08 x 10-7 calls. The Hanford researchers believe these numbers are conservative due to the fact that the samples were not confined and that the bentonite used to seal the rings of the test was still hydrating and taking up water. Permeability changes of an asphalt concrete after placement are due primarily to an increase in cracks within the asphalt concrete cover. These cracks can be generated by an improper mix design flow asphalt cement content), by freeze-thaw cycles, through the mechanism of asphalt cement stripping by water, by age hardening and embrittlement, or by stress cracks that develop due to consolidation or settlement of underlying materials. Research was conducted under the OU4 MYRA accelerated program to ensure that the proposed Deery Oil, ~c., fluid applied asphalt would perform adequately during actual field loading conditions. Confined permeability tests In accordance with ASTM D-5084 were performed with an applied normal load of 480 pounds per square foot (psf). The FAA was first applied to concrete to the desired thickness and was then covered with a layer of 1/4-~nch gravel prior to the application of the normal load. The laboratory permeability test results for both 160-mil- and 87- mil-thick FAA membranes were below 1 x 10~~ cm/s (the limits of the test apparatus) and indicate that gravel embe~nent in the FAA should not influence the results of permeability testing and field performance dramatically. Freeman et al. (1994) also conducted permeability tests on Deery Oil, Zinc., FAA that were removed from an actual placement over asphalt concrete. The results from four samples ranged between 1.18 x 10- cm/s and 2.51 x 10-~ cm/s. They concluded that no direct correlation between sample thickness and permeability was apparent. The IM/IRA accelerated program determined, based on permeability, that the variability of clay materials would make it difficult to predict the field behavior of a compacted clay cover over the 1000-year design life of the system. The local arid climate and the difficulty in locating a borrow source with the desired properties made clay an inappropriate choice based on permeability. Asphalt concrete materials and equipment are available locally. Previous laboratory and field tests confirm that asphalt concrete should meet RCRA requirements for permeability for the closure of a surface impoundment when placed at a higher asphalt content and lower air void content than typical road base designs. The asphalt concrete In combination with the FAA should provide a redundant system with added protection against the development of cracks within the low- permeability layer. Longevity The longevity of the clay and asphalt materials were compared with respect to the ability of the materials to retain the desired properties over the 1000-year design life of the cover system. The longevity of a clay soil at the RFETS is expected to be influenced primarily by the ability of the clay cover to retain low permeability characteristics. No chemical interaction with the contaminated media should be expected within the cover. The major concern with utilizing a clay soil is that desiccation cracks may develop both during construction and after placement. Should excessive differential settlement occur under the cover system, the tensile stains could farther lead to cracking of the clay laver. Since the climate is arid, the clay layer could have a relatively low water content, which could enhance the cracking of the cover. Traditional longevity arguments for the use of asphalts have centered around archeological excavation data. However, more specific data on the , ,

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APPENDIX~PAPERS PRESENTED D-93 longevity of"refined" or "modified" asphalts is required. The IM/IRA accelerated program focused on reviewing the research conducted by the Hanford researchers and by the Strategic Highway Research Program(SHRP, 19941. The SHRP provided important insight into the oxidative aging of asphalts. Excessive oxidative aging can lead to asphalt hardening and embrittlement, which may ultimately contribute to cracking. It was found that the aging of asphalts is a injunction of their physical state and is highly temperature dependent. Temperature typically determines the rate of oxidation, the amount of oxidation, and the ultimate age hardening of the asphalt. The SHRP aged asphalts under pressure and at temperatures specific to, and higher than, application temperatures. This is an important factor, since the asphalt materials under the cover will not be exposed to I]V light. However, tests to determine the mechanism of age hardening were specific to pavement temperatures (140F) and higher temperatures (266F). It was found that "asphalts with different component compatibilities may exhibit similar age-hardening kinetics in the low end of the pavement temperature range but quite different kinetics in the high end." The program also determined that lon~-term changes in the _ r ~. r ~ ~ 4= physical properties of an asphalt are a function ot temperature and asphalt composition. Plots (Figure 2) of the changes in viscosity with temperature for different asphalts were constructed from samples using aging index data Tom 144 hour tests. These plots indicated that aging characteristics cannot be interpolated between two different temperatures. Another important trend of this plot is how the aging index converges between the asphalts at the lower test temperatures. It is important to note that the test temperature ranges were 140F (60C) to 180F (80C). This plot indicates that the lower the actual field temperatures are from the aging test temperatures, the less reliable the aging data. The SHRP concluded that the higher-temperature tests produced more oxidation and more stiffening of the asphalts than when the asphalts were tested at lower temperatures. The SHRP also determined that asphalts that were coated onto aggregates did not demonstrate significantly different aging characteristics from when the asphalts were aged without aggregate. The aggregate type did not appear to alter the aging of the asphalts. 30 25 20 o AS 4,, As c CR 10 5 O // - - - ///W / ///' - - 55 640 65 70 75 80 85 Aging Temperature C +MM-1 MD-1 _~MF-1 MM-1 +MK-1 -MB-1 +MC-1 ~0 MG-1 FIGURE 2 Aging Indices After Thin Oven Testing of Core Asphalts Aged by the Pressure Air Vessel Method a Different Temperatures.

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D-94 BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT Concerns were raised during the IM/IRA accelerated program that "refined" asphalts may age more quickly than "natural" asphalts. At this time, simple conclusions based on the refinement of an asphalt cannot be made. The SHRP utilized a number of asphalts that demonstrated a wide range of behavior patterns. The variability of the aging behavior of asphalts is more chemistry related than process related. The SHRP stated that the physical properties of an asphalt are best described by the effectiveness by which the polar associating materials are dispersed by a solvent moiety consisting of relatively nonpolar aliphatic particles, rather than by strict parameters such as elemental composition. The longevity of asphalt materials is specific to the type and properties of each individual asphalt. Traditional aging indexes (aged viscosity divided by unaged viscosity) may not be relevant for applications involving 1000-year criteria. The SHRP developed effective accelerated aging procedures and used direct theological measurements (penetration, softening point, viscosity, etc.) that have made aging indexes unnecessary. An accurate assessment of the longevity of asphalt materials can not be made without the benefit of further testing. Furthermore, aging mechanisms at lower temperatures (58F for buried asphalts) have not been detailed In previous investigations. Total and differential settlement of the asphaltic concrete and the FAA should be limited due to the degree of compaction of the underlying soils. The maximum estimated total settlement is 4 Inches, while the maximum estimated differential settlement is approximately 0.4 percent (about 1/2-inch for every 10 feet). The performance of the hydraulic grade asphalt concrete and FAA should not be negatively impacted (by excessive cracks) due to the estimated settlements. The selection and design of the materials was based on providing an asphalt concrete that would offer some flexibility. In order to reduce the opportunity for cracking caused by settlement' the underlying materials below the cover were specified to be compacted to 95 percent of modified Proctor density. Some other typical physical factors that may induce failures of normal asphalt concrete applications include: freeze-thaw stress changes, which can cause cracking of the asphalt concrete; traffic dynamic loading, which can cause vertical and horizontal movements in the asphalt concrete, which can lead to cracking; and shrinkage cracks, which cart occur in asphalt concrete mixes that have a high content of low-penetration asphalt (Asphalt Institute, 19891. lithe forces that produce these physical conditions on an asphalt concrete will not be present after the cover has been constructed. Engineering Characteristics The controlling factor for the design of a clay cover at the RFETS includes the 20-percent grade (11.3 slope) of the cover. Clay soils that will meet the permeability requirements may not meet slope stability requirements. RFETS slope stability analysis must include adjustments for seismic loading. The selection of a clay material must account for the large variabilities of Fiction angels and cohesion found in clays. The changes in the strength parameters due to compactive efforts should also be Investigated closely. Effective Fiction angle differences can be as great as 7 degrees, while the differences in effective cohesion can be as great as 400 psf for compactive

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APPENDIX~PAPERS PRESENTED D-9S efforts ranging between 85 and 100 percent maximum standard Proctor density (Moretto et al. 1963). The important eng~neenng characteristics to be considered for the design of the asphalt concrete cover include its stability, durability, flexibility, impermeability, and workability during placement. The mixture design may require a trial and error laboratory testing program to determine the optimal design for the RFETS site. Stability of an asphalt concrete is the ability of the asphalt concrete to resist deformation from imposed loads (Asphalt Institute, 1989) and is determined by the internal Fiction and cohesion of the mixture. internal *fiction of the mix is dependent upon the surface texture, gradation of aggregate, particle shape, density of the mix, and quantity and type of asphalt. In order to improve the stability of the mix, 70 percent of the aggregate materials retained on the No. 4 sieve were specified to have a minimum of two mechanically induced fractured faces. Stability is an important consideration, since 11 feet of cover material, which includes large nprap, was designed to be placed above the asphalt composite. Durability is a property of asphalt that is its ability to resist detrimental effects of air, water, W exposure, temperature extremes and variations, and dynamic loading. The durability of an asphalt concrete is generally improved by higher asphalt contents, well-graded aggregates and low air void content. Increased asphalt contents result in thicker film coating of the mix aggregate. Thicker fiIrns are more resistant to age hardening (Asphalt Institute, 1989~. Lower air void contents seal the mix from exposure to air and water. Mixtures involving high asphalt contents with low air void contents require care during design. Asphalt contents that are too high produce a thick film thickness that may yield a mixture that is more prone to rutting, shoving, or creep. Constructability of this mix may be difficult on a sloped surface, and stability of the asphalt mix may be reduced due to the asphalt cement acting like a lubricant rather than a binder. Flexibility of an asphalt is required to compensate for minor differential or total settlements beneath the cover system. Higher asphalt contents with smaller size aggregates will increase flexibility within the asphalt concrete. The engineering and construction properties that are important in asphalts are consistency and nur~tv. The consistency of an asphalt is described as the viscosity or degree of fluidity of the ~ ~ ~ ~1~ ~ A I ~ ~ l ~ r A An at l-=f-1 he T ~ asphalt at a given temperature. Consistency OI a paving a~r ~ any "~llU~" ~) ~ penetration or viscosity test. The asphalt cement selected for RFETS was graded by viscosity methods at 140F. The grade of the asphalt cement will effect the resistance of the asphalt cement to weather and physical changes and the stability of the asphalt cement to remain stable on significant side slopes. The purity of an asphalt can impact the longevity and performance of an asphalt concrete. Refined asphalts are composed almost entirely of bitumen, with a bitumen content of more than 99.5 percent. The impurities that may be present in the asphalt are usually inert and should not impact the performance or the grading of the asphalt concrete. Hence, asphalts that are graded the same may have dramatically different properties related to the longevity of the asphalt. Natural asphalts, such as Gilsonite or Trinidad Lake asphalts, are not refined but possess characteristics that make them difficult to use in high percentages in a asphalt concrete mix. These materials generally require the addition of a flux of! to soften the mix to produce a usable asphalt cement. The potential for the FAA to creep was a primary concern with respect to the use of asphaltic materials. Generalized creep testing of materials consists of the application of a constant uniaxial tensile load at a constant temperature sufficiently elevated to cause creep. However, field conditions at the RFETS will not be consistent with standard uniaxial tensile loading of an asphalt membrane at elevated temperatures. Furthermore, the FAA has significant adhesive properties and also will be under a significant normal load that will confine the FAA. Since asphalt materials

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D-96 BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT generally demonstrate classic creep behavior, a creep-testing program was initiated during the MYRA accelerated program to determine the influence of the f~eld-applied dead load on the creep characteristics of the FAA. The asphalt concrete is not expected to creep significantly under the 11.3 slope and a constant temperature of approximately 58 F. Research conducted by Hills and McAughtry (1986) indicate that creep deformation should be minimal for the RFETS conditions. However, creep deformation may occur during construction operations during the hot application of the asphalt concrete. The testing program to study the creep behavior of the FAA over the asphalt concrete was initiated to determine if it could affect the integrity of the overlying cover materials (biotic barrier and topsoil). The testing program was developed to incorporate buttressing effects, cover specific materials, and determine the maximum allowable slope of the cover. The test consisted of three large-scale consolidation/creep test frames configured to evaluate downslope creep under an applied dead load on an infinite slope. All tests were performed in an environmentally controlled chamber that was held at a constant 58F. Each test station incorporated devices to measure vertical and horizontal deflections. The lower slope frame (sloped at 11.3) was constructed of roughened concrete with the designated thickness of FAA applied to the upper surface of the concrete. The upper loading platen was a custom angled solid aluminum block with a test surface area incorporating a 1/4-~nch sand representative of the site cushion sand firmly embedded into the surface. The sustained applied dead load for each test was 480 psf, with a minimum testing duration of 40 days. The FAA was placed over roughened concrete samples to simulate the asphalt concrete. Due to the accelerated schedule of the MYRA program, not enough time was available to cure asphalt concrete properly prior to the creep tests. Three tests were initiated under the stated testing conditions. FAA nominal thicknesses of 87, 1 1 S. and 160 mil were tested. The 87-mil sample saw an initial embedment of the upper surface platen into the membrane within a period of 16 hours after which a time the platen did not creep. The sample did not demonstrate any creep characteristics over the 40-day test duration. The 1 18- mi! sample appears to have taken longer to become embedded into the FAA. It took approximately 22 days for the sample to become embedded into the FAA prior to the cessation of creep behavior. The 160-mi] sample continued to creep at an unacceptable rate for a duration of over 75 days of testing. The rate of creep was estimated to be at 0.07 inches per year. It was determined that over the 1,000-year design life of the cover, this rate would be excessive. The results of the creep testing indicate that a relationship exists between the thickness of the FAA and possibly the angularity and size of the surface aggregate. Surface roughness of the underlying material (roughened concrete) likely influences the creep behavior of the system. Following the results of the creep tests, it was determined that no creep behavior characteristics would be allowed for the FAA materials. Hence, the maximum allowable thickness for the FAA was established at 1 18 milt Constructability Clay Soils The difficulty in constructing a clay cover at the RFETS would not be in the construction equipment's ability to perform, but rather in the contractor's ability to control the conditions to which the clay soil is placed and compacted. As discussed in earlier sections, a clay soil requires the application of significant quantities of water to ensure that permeability requirements are met and

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APPENDIX DIAPERS PRESENTED D-97 that desiccation cracking be kept to a minimum. Furthermore, dust suppression is an important issue at the RFETS. The application of water to clay layers during construction by water trucks is generally a "less than scientific" operation. One of the important factors in modeling the leaching of contaminants from under the cover at RFETS was the insurance that excessive water would not exist in the contaminated zone. The introduction of free water that could infiltrate the waste zone is against the design basis for the construction of the cover at the RFETS. Quality Assurance/Quality Control (QA/QC) operations for the construction of a clay cover must be enforced strictly. Areas of the cover that are out of compliance would require significant operations to recompact or replace the clay materials. The use of large rototillers to blend the clay soil could disturb underlying layers of the cover. Lifts of the clay soils that are not correctly bonded, through scarifying or other methods, may provide channels for water migration. Asphalt Concrete The construction of the asphalt concrete cover would not require any construction methods that would introduce excessive moisture into the waste zone. Dust suppression would not be an issue during the placement of the asphalt concrete. The difficulty in constructing the asphalt cover would be in the placement of the high asphalt content hot mixture on the sloping surface (11.3 slope). Shoving and inadequate compaction could result if the operations are not performed properly. Excess shoving could lead to the development of transverse hairline cracks. A test pad is recommended for the asphalt concrete and FAA application to confirm the placement methods and any unique behavior properties that may occur during placement. Cost The costs for the construction of a clay or asphalt cover will be dependent upon many variables. The estimated in-place cost for the asphalt and base course materials for the currently designed cover ot the ~1xA Is ~:z per square yard. The total cost of the asphalt for the 12-acre engineered cover would be $1.8 million. Estimates for the in-place cost of a 2-foot-thick clay cover (only the clay portion) are approximately $8 per square yard depending on the borrow location. The total cost of the clay layer for the 12-acre engineered cover would be $465,000. DESIGN OF SELECTED MATERIAL The following section discusses the detailed design of the asphaltic low-permeability layer in the engineered cover. The objectives of the total design for the asphalt concrete and FAA were to design a cover that meets RCRA requirements for the closure of a surface impoundment, has the longevity and durability to last the 1,000-year design life of the cover, and be constructable using common construction equipment and techniques.

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D-98 BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT Asphalt Composite Design The composite design of the FAA installed above asphaltic concrete was selected as a fail- safe measure. It is believed that the FAA will span the cracks in the asphalt concrete that may occur due to settlement. The FAA also appears to have "self-healing" properties, as demonstrated during the performance of the creep tests with sand embedment. The design specifications called for an asphalt concrete that would meet the following requirements as determined by American Society for Testing and Materials (ASTM) D 1559: Air Voids: 4 percent maximum Asphalt Content: 6-9 percent Marshall Stability: 750 pound minimum Design compaction by the Marshall Method is limited to 35 blows on each end of the specimen . Voids in Mineral Aggregate: 15 percent minimum The asphalt cement was specified as an AC-10 grade. The aggregate material was specified with 100 percent passing the 5/8-inch sieve. These design specifications are subject to change following the performance of more detailed laboratory tests. The FAA was specified as Deery Oil Co. Membrane 6 or approved substitute. The tests for the MYRA project were performed utilizing this matenal. Specific required tests for the FAA ;~1.~A^. mixer Saint {~Tl\/r n ~ ~ne~it1~ ~v1tV (AN l M ~ /~: penetration (ASTM 3407); lll~lU~I~. vVlL~ll~l~ ~V~1~ ~ *~ ~ ~ ~^ ~ JO 7 vim ~ _ viscosity (ASTM D4402)7 and elongation (ASTIR D4885). Long-Term Testing Current tests that simulate the chemical and physical property changes in asphalts during hot mix plant operations traditionally have been used as indicators for the longevity of an asphalt. However, the SHRP determined that the extended fumes and high temperatures of traditional tests cause excessive loss of volatiles and the tests are not a reliable source for predicting the behavior of asphalt aging at lower temperatures. The behavior of asphalt materials over the life of the cover is one of the few factors that is not predictable. Available data on the performance of asphalts does not provide enough detail to confirm that the properties will remain acceptable. It is suggested that accelerated age-testing followed by physical performance tests be conducted on the asphalt samples under "aged" conditions. Freeman and Romine (1994) provide details of a testing program to provide valuable information on the performance of aged asphalts. The Hanford researchers recommended the following activities be conducted to provide data to support the longevity of an asphalt cover system for a 1,000-year design life cycle: 1. Develop a defensible, accelerated aging test procedure to allow for measurements of asphalt baIlier properties as a fimction of age for a minimum of 1,000 years. Accelerated test procedures would be based on the procedures developed by the SIP. The procedures would be modified to account for the conditions expected in the subsurface conditions versus highway exposures.

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APPENDIX~PAPERS PRESENTED D-99 2. Age potential the asphalt materials over the conditions expected in the actual subsurface environment. 3. Measure the changes of the asphalt chemical and physical properties using standard and modified testing procedures. 4. Supplement and validate the laboratory aging data by comparing the chemical properties with several-hundred- to several-thousand-year-old asphalt artifacts. 5. Estimate the response and performance of aged asphalt materials to a range of performance tests including settlement and permeability tests. CONCLUSIONS AND RECOMMENDATIONS Asphalt matenals were chosen over clay soils for use as a Tow-permeability layer to meet RCRA requirements for the closure of a surface impoundment that will have a 1,000-year design life. It is believed that the asphalt materials will outperform clay soils based on permeability, longevity, and constructability considerations. However, the asphalt materials could cost as much as 3-4 times more than clay. Creep testing should be conducted for the design of an engineered cover utilizing asphaltic materials. Creep testing should be performed on the selected asphalt materials and should be a combination of the asphalt concrete and FAA. The FAA will have to be applied at a range of 60-118 mil at the OU4 SEPs, based on the specific side slope and loading conditions. The 60-mil lower-thickness limit was developed from the acceptable permeability test (below ~ x 10- calls), while loaded at 480 psf. The upper-thickness limit of 118 mil was developed Tom the performance of the creep tests. Age testing is necessary in order for asphalt materials to become widely accepted throughout the engineering industry for use as long-term low-permeability layers in engineered covers. The SHRP found that aging kinetics are highly dependent on how temperature will effect the molecular structure of an asphalt. Aging tests need to be specific to the materials and environmental conditions expected within engineered covers. It is important to determine the mechanisms for the aging of asphalts and the subsequent physical and chemical changes in the materials. Realistic tests could determine if premature age hardening may lead to a breakdown in the performance of asphaltic materials. BIBLIOGRAPHY American Society for Testing and Materials (ASTM). 1990. Annual Book of ASTM Standards, Part 3 1. Asphalt Institute. 1989. The Asphalt Handbook, Manual Series No. 4 (DISC. Lexington, Ky. Beckwith, G. H., G. D. Allen, and A. C. Ruckrnan. 1988. Asphaltic Concrete Leach Pads. Second International Conference on Gold Mining. Gold Mining 88. Society of Mining Engineers. Boynton, S. S., and D. E. Daniel. l9SS. Hydraulic Conductivity Tests on Compacted Clay. Journal of Geotechnical Engineenng. 111~41: 465-478. Day, S. R., and D. E. Daniel. 1985. Hydraulic Conductivity of Two Prototype Clay Liners. Journal of Geotechnical Engineering. 111~: 957-970.

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D-100 BARRIER TECHNOLOGIES FOR ENVIRONMENTAL MANAGEMENT Freeman, H. D., and R. A. Romine. 1994. Hanford permanent isolation barrier program: Asphalt technology development. Pp. 491 -505 In Proceedings of the Thirty-Third Hanford Symposium on Health and The Environment. In-Situ Remediation: Scientific Basis for Current and Future Technologies. Freeman, H. D., R. A. Romine, and A. H. Zacher. 1994. Hanford Permanent Isolation Barrier Program: Asphalt Technology Data and Status Report - FY 1994. PNL-10194, UC-702, Pacific Northwest Laboratory, Richiand, Wash. Hills, I. F., and D. McAughtry. 1986. Deformation of Asphalt Concrete Linings on Slopes. Journal of Engineenng Mechanics. 112~10~: 1076-1089. Lambe, T. W., and R. V. Whitman. 1969. Soil Mechanics. New York: John Wiley and Sons, Inc. Moretto, O., A. I. L. Bolognesi, A. O. Lopez, and E. Nunez. 1963. Propiedades Y Comportamiento De Un Suelo L~moso De Baja Plasticidad. Proceedings of the Second Panamerican Conference on SM and FE. Vol. II, p. 131. Brazil. Strategic Highway Research Program (SHRP). 1994. Binder Characterization and Evaluation, Vol. 1. (SHRP-A-367), Vol. 2. (SHRP-A-368), Vol. 3. (SHRP-A-3694. Washington, DC.: National Research Council. U.S. Environmental Protection Agency (USEPA). 1988. Design, Construction, and Evaluation of Clay Liners for Waste Management Facilities. EPA/530/SW-86/007F. U.S. Environmental Protection Agency (USEPA). 1991. Design and Construction of RCRA/CERCLA Final Covers. EPA/625/4-91/025