BARRIER SYSTEMS for ENVIRONMENTAL CONTAMINANT CONTAINMENT and TREATMENT - PART 3 pptx

143 3 Material Stability and Applications Prepared by* Craig H. Benson University of Wisconsin at Madison, Madison, Wisconsin Stephan F. Dwyer Sandia National Laboratories, Albuquerque, New Mexico 3.1 OVERVIEW This chapter focuses on material properties and behavior for caps, cutoff walls, and permeable reactive barriers (PRBs), with an emphasis on understanding the mechanisms and factors that affect their durability in full-scale systems. Infor- mation obtained from laboratory tests are analyzed in this context. The reader is referred to the preceding book in the containment series, Assessment of Barrier Containment Technologies (Rumer and Mitchell, 1995), as well as Daniel (1993), Gavaskar et al. (1998), LaGrega et al. (2000), Blowes et al. (2000), Naftz et al. (2002), and Reddi and Inyang (2000) for detailed information on the general characteristics of barrier materials mix design approaches and performance issues. In this chapter, the emphasis is on fundamental factors and laboratory and field observations that relate to the long-term performance of materials used in con- structing various types of containment systems. The overall performance of these systems has been analyzed holistically using the systems approach in Chapter 1. Chapter 2 dealt with models of water and contaminant fate and transport through components of containment systems. It is herein recognized that material properties * With contributions by David W. Blowes, University of Waterloo, Waterloo, Ontario, Canada; David A. Carson, U.S. Environmental Protection Agency, Nashville, Tennessee; Peter W. Deming, Mueser Rutledge Consulting Engineers, New York, New York; Jeffrey C. Evans, Bucknell University, Lewis- burg, Pennsylvania; Glendon W. Gee, Battelle Pacific Northwest National Laboratory, Richland, Washington; Hilary I. Inyang, University of North Carolina at Charlotte, Charlotte, North Carolina; Stephan A. Jefferis, University of Surrey, Surrey, United Kingdom; Mark R. Matsumoto, University of California at Riverside, California; Gustavo Borel Menezes, University of North Carolina at Charlotte, Charlotte, North Carolina; Stanley J. Morrison, Environmental Services Laboratory, Grand Junction, Colorado; Scott D. Warner, Geomatrix Consultants, Oakland, California; John A. Wilkens, DuPont, Wilmington, Delaware 4040_C003.fm Page 143 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC 144 Barrier Systems for Environmental Contaminant Containment & Treatment play a significant role in overall system performance. This chapter is divided into three primary subsections, each of which addresses materials performance for a specific type of containment structure. 3.1.1 THE ROLE OF BARRIER MATERIAL MINERALOGY AND MIX COMPOSITION ON PERFORMANCE Earthen materials or geomaterials are the most frequently used materials in containment system barrier construction. Generally, barrier mixes are composites of particles of various sizes and minerologies. For barriers that are designed to minimize flow rates and retard contaminant solute transport through physico- chemical interactions, clays are commonly used in mixes with silts; sands; and amendments such as resins, activated carbon, slags, polymers, and ash. The clays are usually alumino-silicates native to the barrier material, or they may be added to the barrier mix in cases where the natural clay content of the barrier material is insufficient to provide the required mix characteristics. In other cases, barrier materials are fabricated and used to provide specific functions. An example is a geomembrane that can be incorporated as a component into a containment structure for fluid retention, separation of clay to minimize the chance of attack by aggres- sive permeants, and diversion of gas flow to desirable control points. Table 3.1 provides a general listing of various characteristics of barriers that affect classes of phenomena that relate to the most significant barrier design objectives. Some of TABLE 3.1 Containment System Design Considerations and Material Characteristics that are Usually Evaluated in Bench-Scale Tests Physico-Chemical Design Consideration Phenomena of Concern Significant Barrier Material Properties Reduction of contaminant release and transport Advection Hydraulic conductivity Density Moisture content Gradation Porosity Crack density Diffusion Porosity Dispersion Tortuosity Leachability Crack density Chemical compatibility Inadequate retardation Density Physical durability Chemical attack Mineralogy relative to contaminant chemistry Radiation transport Density, mass attenuation coefficient 4040_C003.fm Page 144 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC Material Stability and Applications 145 the barrier parameters such as hydraulic conductivity, porosity, and crack density apply to compacted, cemented, and fabricated materials. For granular barrier materials that may be compacted or cemented into barrier layers, the component material mineralogy and specific surface area are key material factors that, in combination with the emplacement density, control the initial and long-term barrier material textures when exposed to physical stresses and chemical contact. Mineralogy controls the physico-chemical interactions (including the reactivity) of a barrier component with permeating fluids under a given environmental condition. Under the most frequently encountered temper- ature, pressure, and pH–Eh conditions in the field, clays (comprising mostly aluminosilicates) react with permeants much more aggressively than sands (com- prising mostly silica). Because of their mineralogy, the charged clay surfaces present opportunities for the chemisorption of charged contaminants such as heavy metals as summarized by Inyang (1996) in Table 3.2. For a barrier material that has favorable mineralogy (i.e., a mineralogy that favors its interaction with permeating fluids in reactions that remove solutes without degrading the barrier), the opportunity for its interaction with the per- meant is enhanced if its specific surface is high. The specific surface is the ratio of surface area to weight of a material, and it is inversely proportional to the grain size of the material. For surface reactions like cation exchange and adsorp- tion that are prevalent in barriers, their role in increasing the contaminant distri- bution coefficients (i.e., cleaning the permeating fluid in terms of its entry vs. exit chemistries) increases as the specific surface of the component material increases, as reflected in results plotted by Milne-Home and Schwartz (1989) presented in Figure 3.1. Often, even when a specific barrier component exhibits a desirable material characteristic, it may not be adequate with respect to another characteristic. For example, a clay mineral such as sodium montmorillonite may be sorptive enough for heavy metals but inadequate in terms of providing strength against desiccation. Yet still, cost considerations usually preclude the use of single-component barrier systems in waste containment. Essentially, most barrier materials are composites, the proportions of which are designed to optimize performance characteristics at minimal cost. In the case illustrated in Figure 3.2, D’Appolonia (1980) evaluated the effects of fines (% minus #200 sieve) on the permeability of soil-bentonite (SB) backfill candidate materials and found that for both plastic fines and nonplastic/low-plasticity fines, the permeability decreased as the fines content increased. Permeability values for the plastic fines were generally lower than those of the nonplastic/low-plasticity fines. Presumably, the plastic fines comprise more moisture-sensitive or expansive minerals than the nonplastic/low-plasticity fines. Figure 3.3 shows the effects of bentonite (mont- morillonite) content on the permeability of the SB backfill candidate material mixes. A bentonite content of 3% (by dry weight) was adequate to reduce the permeability values from 5 × 10 –5 to 5 × 10 –3 centimeters per second (cm/s) to about 10 –7 cm/s for well-graded coarse materials. In another investigation that illustrates the optimization of mix composition to obtain a favorable material characteristic, Ryan and Day (1986) evaluated the 4040_C003.fm Page 145 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC 146 Barrier Systems for Environmental Contaminant Containment & Treatment TABLE 3.2 Sorption Characteristics of Soil Minerals and Chemical Additives for Hazardous and Radioactive Metals Single Component Material General Properties Metals Tested Test Type Test Conditions Results Montmorillonite (Garcia- Miragaya and Page, 1976) CEC = 94.8 meql/L; particle size <2 µ m Cd 2+ Batch Initial pH range = 4.6–7.3 95%, 95%, and 90% of Cd 2+ sorbed by Na-, Ca-, and K-montmorillonite, respectively Montmorillonite from Texas (Puls and Bohn, 1988) Ca — saturated Cd 2+ , Zn 2+ , Ni 2+ Batch Initial pH = 5.5, 6.5, 7.5 50% of metals were adsorbed at pH range of 4–5.81 Vermiculite (Ziper et al., 1988) K — fixed, 500–1000 µ m particle size, SSA = 22.5 m 2 /g Cd 2+ Batch Initial pH = 5.0, 10 –9 –10 –5 M 0.9 moles of Cd 2+ adsorbed per kg Kaolinite (Puls and Bohn, 1988) Fine particles Cd 2+ , Zn 2+ , Ni 2+ Batch Initial pH = 5.5, 6.5, 7.5 Adsorption followed the order: Cd > Zn > Ni. 50% of metals were adsorbed within pH range 4.49–5.80 Kaolinite (Yong and Galvez- Cloutier, 1993) LI = 61%, SSA = 24 m 2 /g; 84% below 2 µ m Pb 2+ Batch Initial pH = 3.0. 4 g of Kaolinite in 40 mL of lead solutions Maximum Pb 2+ adsorption decreased at high pH due to precipitation Goethite (iron oxide) (Coughlin and Stone, 1995) SSA = 47.5 m 2 /g Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Pb 2+ Batch Initial pH = 3–8. NaNO 3 used to maintain selected ionic strength Coordination chemistry of oxides affects adsorption. 50% of Cu 2+ , Pb 2+ , Co 2+ , Ni 2+ removed at pH 4.5, 4.8, 6.3, 6.8, respectively Goethite (iron oxide) (Kuo, 1996) Zn 2+ , Cd 2+ , Ca 2+ Batch Initial pH = 5.3–8.3. NaNO 3 used to maintain selected ionic strength Selectivity order: Zn 2+ > Cd 2+ > Ca 2+ 4040_C003.fm Page 146 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC Material Stability and Applications 147 permeability ranges of three mix compositions for a fly ash cement-slurry wall, the results of which are presented in Figure 3.4. Test results developed (Fleming and Inyang, 1995) for fly ash amended materials, which may, in some cases, exhibit cementation if the ash mineralogy is favorable or some cementing agents are added, show that initial and longer term permeabilities of cemented barrier materials can be significantly influenced by reactions among the mix components. Figure 3.5 shows the conceptual textural patterns proposed by Fleming and Inyang (1995) in a comparative study of the effects of class F (nonreactive) fly ash and class C (reactive) fly ash amendment of barrier clay on changes in permeability under freeze-thaw action. The patterns are similar, but the reactive fly ash exhibits initial and final permeabilities that are lower than those of the nonreactive ash. 3.1.2 APPROACHES TO MATERIAL EVALUATION AND SELECTION Bench-scale tests provide the best opportunity to evaluate the fundamental char- acteristics of barrier materials. However, holistic assessments of a barrier system performance are most meaningfully performed through a combination of bench- scale testing and field quality assurance and monitoring tests. The bench-scale approach has been widely used to evaluate barrier material parameters in batch TABLE 3.2 (continued) Sorption Characteristics of Soil Minerals and Chemical Additives for Hazardous and Radioactive Metals Single Component Material General Properties Metals Tested Test Type Test Conditions Results Fly ash (Singer and Berkgaut, 1995) Hydrothermal ly treated, CEC = 2.5–3 meq/g Pb 2+ , Sr 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Cs 2+ Batch Initial pH = 5.0. Total concentration of competing ions = 0.1 N Selectivity order: Pb 2+ > Sr 2+ > Cu 2+ > Cd 2+ > Zn 2+ > Cs 2+ at 25 mg/L lead concentration, absorbed Pb = 35 µ g/g Pyrolusite (MnO 2 ) (Ajmal et al., 1995) Crushed samples Pb 2+ , Cd 2+ , Zn 2+ , Mg 2+ Batch Washed and dried at 40° C; pH range of about 2–8 At pH = 6.5, 100% of initial 22.7 mg/L of Pb 2+ was sorbed; other results show high sorption for Zn 2+ and Cd 2+ but low sorption for Mg 2+ Source: Inyang, H.I. (1996). Sorption of inorganic chemical substances by geomaterials and additives, Report CEEST/001R-96, University of Massachusetts, Lowell, MA. 4040_C003.fm Page 147 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC 148 Barrier Systems for Environmental Contaminant Containment & Treatment systems, monoliths of scaled down dimensions, or columns of media. The latter can be densely compacted, as in the case of earthen materials considered for fluid/contaminant transport barriers or loosely emplaced as in reactive columns. Most of the granular barrier material characteristics that are usually targeted are summarized in Table 3.3. Not all of these tests need to be performed for all barrier materials. Some tests, exemplified by porosimetry, are not usually performed because the influence of the pore size distribution measured is represented along with barrier material density and reactivity with specific contaminants in data obtained from column tests for contaminant retardation coefficient estimation. The tests listed in Table 3.3 have designations that vary from one country to another, although they are most standardized under the American Society for FIGURE 3.1 Specific surface vs. bulk cation exchange capacity for various sediments and minerals. (From Milne-Home, W.A. and Schwartz, F.W., 1989. Proceedings of the Conference on New Field Techniques for Quantifying the Physical and Chemical Proper- ties of Heterogeneous Aquifers, Dallas, Texas, pp. 77–98. With permission.) Specific surface (m 2 /g.) 1000 100 10 1 0.1 0.1 1 Bulk C.E.C. (meq/100 g) 10 100 Montmorillonite Illite Kaolinite Explanation American Petroleum Institute Reference clays (Patchett, 1975) Shales (Patchett, 1975) Milk River formation Mome L’Enfer, Erin formations Belly River formation (GENPAR 2) Sandstones Discrete particle clays Pore ilning clays Pore bridging clays 1 1 2 3 1 1 1 1 2 2 2 2 2 3 3 3 3 4040_C003.fm Page 148 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC Material Stability and Applications 149 rials such as geomembranes are tested under protocols that are different from those of granular barrier materials. Fundamental tests are important because they can provide data that are helpful in performing a general durability evaluation of barrier materials and understanding mechanisms that are determinants of their durability. 3.1.3 GEOSYNTHETICS AND THEIR DURABILITY IN BARRIER SYSTEMS In general, the ability of barrier materials to retard fluid transport, resist chemical and biological attack, and maintain structural integrity under externally imposed stresses depends on their composition, emplaced thickness, and the quality assur- ance practices implemented during construction. Early in the development of containment system design configurations, earthen and cementitious barrier mate- rials were used almost exclusively. A more recent development, particularly within the past two decades, is an increase in the use of geosynthetic materials to enhance containment system barrier layer performance. Both earthen and geosynthetic barrier materials have advantages and disadvantages. Earthen bar- riers are most commonly clayey soils that are either compacted into layers as in landfills and surface impoundments or emplaced as slurry backfill as in slurry cutoff walls. While they can retard contaminant transit through a variety of processes (e.g., sorption, induced precipitation of dissolved substances within inter-particle pore spaces), significant variability and uncertainty can exist in the FIGURE 3.2 Effects of fines content on the permeability of soil-bentonite backfill. (From D’Appolonia, 1982. Proceedings of the 13th Annual Geotechnical Lecture Series, Phila- delphia Section , American Society of Civil Engineers, Philadelphia, PA. With permission.) % Minus #200 sieve 80 70 60 50 40 30 20 10 0 10 −4 10 −5 10 −6 10 −7 10 −8 10 −9 Plastic fines SB Backfill permeability, cm/sec Nonplastic or low plasticity fines 4040_C003.fm Page 149 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC Testing Materials (ASTM) protocols. As evident in Section 3.2, fabricated mate- 150 Barrier Systems for Environmental Contaminant Containment & Treatment spatial distribution of barrier transport parameters such as hydraulic conductivity and diffusion coefficient. Furthermore, under aggressive chemical environments and sustained desiccation processes, earthen barriers can develop enlarged flow channels that allow contaminants in both the gaseous and liquid phases to travel through the barrier easily. Geosynthetic materials such as geomembranes have less FIGURE 3.3 Effects of bentonite content on the permeability of SB backfill. (From D’Appolonia, 1982. Proceedings of the 13th Annual Geotechnical Lecture Series, Phila- delphia Section, American Society of Civil Engineers, Philadelphia, PA. With permission.) FIGURE 3.4 The effects of cement/water ratio and fly ash/cement ratio on the perme- abilities of slurry wall mixtures. (From Ryan, C.R. and Day, S.R., 1986. Proceedings of the 7 th National Conference on Management of Uncontrolled Hazardous Waste Sites, Washington, DC. With permission.) Permeability of SB backfill, cm/sec. 10 –2 10 –3 10 –4 10 –5 10 –6 10 –7 10 –8 10 –9 0 1 2 % Bentonite by dry weight of SB backfill 3 4 5 Well-graded coarse gradations (30–70% + 20 sieve) w/10 to 25% nonplastic fines Poorly graded silty sand w/30 to 50% nonplastic fines Clayey silty sand w/30 to 50% fines Mix 3 Mix 2 Mix 1 10 –7 10 –6 K, (cm/sec.) C/W FA/C Mix 1 0.20 0.00 Mix 2 0.20 0.24 Mix 3 0.25 0.60 10 –5 Average (typ.) 4040_C003.fm Page 150 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC Material Stability and Applications 151 variability in the spatial distribution of transport parameter magnitudes because they are manufactured in tightly controlled processes. Furthermore, they are less permeable to fluids and offer the opportunity to minimize the overall design thickness of a barrier layer. On the other hand, punctures, poor joints, and internal degradation can diminish their effectiveness as barrier layers. Giroud et al. (1992, 1997) have developed quantitative methods for estimating liquid transport through geomembrane defects. Geosynthetic barrier materials have been used as barrier layers that comple- ment the functions of earthen barrier layers. Many composite cover designs such FIGURE 3.5 Effects of reactions among barrier constituents on the permeability of ash- modified clayey barrier soil subjected to freeze-thaw cycling. (From Fleming, L.N. and Inyang, H.I., 1995. ASCE Journal of Materials in Civil Engineering, 7(3), 178–182. With permission.) Before freezing After freeze - thaw cycling a. Class F fly ash-modified clay soil c. Class F fly ash-modified clay soil Permeability b. Class C fly ash-modified clay soil d. Class C fly ash-modified clay soil Longitudinal fracture Reactive ash particle Clay platelet Reacted rim Nonreactive ash particle P CA P OA P CB 0 t CB No. of freeze-thaw cycles or time t CA P OB 4040_C003.fm Page 151 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC 152 Barrier Systems for Environmental Contaminant Containment & Treatment as those consistent with the minimum design standards developed for the Resource Conservation and Recovery Act (RCRA), comprise both soil barrier layers and geosynthetic materials. Othman et al. (1997) have performed studies of the performance of such barrier configurations in the field. The results indicate that with adequate quality control, such systems can perform effectively, at least within the few decades that they have been in service. Another composite barrier system that typically produces desirably low hydraulic conductivities in barrier systems is the geosynthetic clay liner (GCL) that has been studied by many researchers (Estornell and Daniel, 1992; Rad et al., 1994; and Petrov et al., 1997). The GCL is gaining wider acceptance in the containment industry because of its cost effectiveness, relatively easy installation, and low barrier thickness. Instal- Although test protocols, design methods, and quality assurance methods have been developed [Koerner and Daniel, 1997; Haxo, 1987; United States Environ- mental Protection Agency (USEPA), 1985], concerns about the long-term dura- bility of geosynthetic materials in barrier systems remain. This concern is driven by the knowledge that all materials that are exposed to stressors degrade with time. Such degradation in the long term is not limited to geosynthetic materials, but extends to emplaced earthen barrier materials as well. For geosynthetic TABLE 3.3 General Testing Approaches and Methods for Significant Characteristics of Batch and Compacted Barrier Materials Dependent Property Test Method(s) Soil Texture Density a Direct measurement Dispersivity Indeterminate; evaluate experimentally Gradation Sieve, hydrometer tests Hydraulic conductivity a,b Permeameter tests Moisture content Drying tests Path length/tortuosity a Indeterminate; evaluate experimentally Plasticity b Atterberg limits Pore size distribution Porosimetry Porosity (effective) a Empirical methods, porosimetry Soil Composition Chemical (elemental) composition Chemical tests (e.g., x-ray fluorescence) Mineralogy (crystallinity) Mineralogy tests (e.g., x-ray diffraction) a Denotes a property dependent on compaction. b Denotes a property dependent on mineralogy. Source: Adapted from Inyang, H.I. et al. (1998). Physico-Chemical Interactions in Waste Containment Barriers, Encyclopedia of Environmental Analysis and Remediation, Vol. 2, Wiley, New York, pp. 1158–1165. 4040_C003.fm Page 152 Wednesday, September 21, 2005 12:29 PM © 2006 by Taylor & Francis Group, LLC lation methods are summarized in Section 3.4.3. [...]... Cover Type 3 3 3 3 517 156 684 847 Arid Arid Semi-arid Semi-arid and seasonal 3 3 3 3 3 30 3 3 847 905 485 485 607 722 38 1 552 Semi-arid and seasonal Semi-arid and seasonal Semi-arid and seasonal Semi-arid and seasonal Semi-arid Humid Humid and seasonal Humid and seasonal Humid and seasonal Monolithic barrier Monolithic barrier Capillary barrier Monolithic barrier 1080 mm thick Monolithic barrier 2450... 48.4 3. 1 0.2 0.0 0.0 0.0 0.0 91 .3 1 43. 1 3. 7 (0 .3% ) (0.0%) ( 13. 3%) (11.1%) (0.7%) (0.1%) (0.0%) (0.0%) (0.0%) (0.0%) (7.2%) (15.6%) (0.5%) 3. 7 (0.5%) 4040_C0 03. fm Page 164 Wednesday, September 21, 2005 12:29 PM Altamont, CA Apple Valley, CA Marina, CA Sacramento, CA Duration (Days) 552 Site Design Criterion (mm/year) 164 Barrier Systems for Environmental Contaminant Containment & Treatment TABLE 3. 5... loam 30 0 200 100 0 9 /30 /1994 9/29/1996 9 /30 /1998 Date 9/29/2000 9 /30 /2002 FIGURE 3. 11 Temporal variation in mean soil water storage in the silt-loam in the Hanford cap Monitoring was interrupted 1998–2000 Horizontal dashed lines represent estimated storage limits for caps with silt-loam layers 2 m, 1.5 m, and 1.0 m thick (From USDOE, 1999 200-BP-1 Prototype Barrier Treatability Test Report DOE/RL-9 9-1 1,... PM Material Stability and Applications 167 200 1080-mm monolithic cover Precipitation 1200 150 Evapo-transpiration 1000 800 100 Percolation 600 Surface runoff 400 50 Soil-water storage 200 0 7/1/99 Percolation and surface runoff (mm) Cumulative precipitation, evapo-transpiration, and soil-water storage (mm) 1400 0 3/ 31/00 12 /30 /00 9 /30 /01 7/1/02 FIGURE 3. 13 Water balance quantities for thin cover (1080... existed in place for thousands of years were selected The top-to-bottom profile consists of a 2-m-thick layer of vegetated siltloam overlying layers of sand, gravel, basalt rock (riprap), and asphalt (Figure 3. 10) Each layer serves a distinct purpose The silt-loam is for storing infiltration (600 mm of water can be stored in the silt loam before it will drain) and provides the medium for establishing... Group, LLC 4040_C0 03. fm Page 170 Wednesday, September 21, 2005 12:29 PM 170 Barrier Systems for Environmental Contaminant Containment & Treatment pH–Eh diagrams to assess the potential for contaminant removal If contaminant removal is possible, then laboratory treatability testing is considered Laboratory treatability tests can be used to assess the potential for contaminant removal and develop reaction... used to provide preliminary estimates of barrier performance and longevity and to design parameters for pilot- or full-scale installations 3. 3.2 EVALUATION OF FIELD PERFORMANCE USING PILOT TESTING The decision whether to conduct a pilot-scale test or move directly to full-scale implementation depends on the history of the technology and the confidence of the client and regulators Many PRB technologies have... (2002) Field Hydrology and Model Predictions for Final Covers in the Alternative Cover Assessment Program — 2002, Geo-Engineering Report No 0 2-0 8, University of Wisconsin, Madison, WI © 2006 by Taylor & Francis Group, LLC 4040_C0 03. fm Page 160 Wednesday, September 21, 2005 12:29 PM 160 Barrier Systems for Environmental Contaminant Containment & Treatment demolition projects and contained a variety... treating each of these contaminants Concentrations of all contaminants decreased to low levels in the PRB during 2.7 years of its operation (Morrison et al., 2001) © 2006 by Taylor & Francis Group, LLC 4040_C0 03. fm Page 178 Wednesday, September 21, 2005 12:29 PM 178 Barrier Systems for Environmental Contaminant Containment & Treatment Solid phases in the gravel-iron panel and the iron-only panel were sampled... tests or full-scale applications have used © 2006 by Taylor & Francis Group, LLC 4040_C0 03. fm Page 168 Wednesday, September 21, 2005 12:29 PM 168 Barrier Systems for Environmental Contaminant Containment & Treatment (a) Waste area ARTZ Groundwater Flow direction Aquifer Plume Remediated water FIGURE 3. 14 Schematic of a PRB used to intercept and treat a plume of contaminated groundwater TABLE 3. 7 List of . Section 3. 2, fabricated mate- 150 Barrier Systems for Environmental Contaminant Containment & Treatment spatial distribution of barrier transport parameters such as hydraulic conductivity and. Francis Group, LLC 160 Barrier Systems for Environmental Contaminant Containment & Treatment demolition projects and contained a variety of debris, including reinforcing bars and angular chunks. limits for caps with silt-loam layers 2 m, 1.5 m, and 1.0 m thick. (From USDOE, 1999. 200-BP-1 Prototype Barrier Treatability Test Report. DOE/RL-9 9-1 1, U.S. Department of Energy, Richland, WA;