Document BRpqQ787qN4jYVEeXv5x8yjgw

TREATMENT -O' SOLID WASTE AND INCINERATION TECHNOLOGY CENTER SWTC-TM-85-5 628 BLDG. MIDLAND, Ml 48640 NO. June 14, 1985 0Y D. D. Fales DATE TECHNICAL MEMO: POTENTIAL FAILURE MECHANISMS OF CLAY LINERS It has been shown that much of the groundwater degradation of today originated from waste handling facilities of the past. This definite connection has given rise to a critical reevaluation of the materials and practices typically em ployed in the construction of such facilities. In general, facilities such as landfills and surface impoundments have been designed and constructed to prevent the migration of fluid outside the fa cility. Clay has been used extensively as a barrier to fluid migration. Clay's usefulness for this purpose is derived from its inherent structure. This structure is a function of the particle arrangement and resultant pore 3paces/interlayer spacing as established by the fine fraction of the soil. Soils are typically classified as clays if the fine fraction (particles less than 2 microns in size) is greater than 20 percent by weight. In general, clay soils with the greatest fine fraction can provide the lowest permeabil ities. Based on its mineral makeup, both in composition and in structure, a clay can be characterized as either a Kaolinite, an Illite or a Smectite. Kaolinites are made up of relatively large (as compared to other clays), and pure mineral particles with no internal cleavage. This lack of internal sur faces along with its natural purity, make kaolinitic clays quite invulnerable to changes in moisture content (i.e. lack shrink/swell tendencies). These same characteristics, coupled with a minimal cation exchange capacity, make kaolinite quite resistant to chemical activity as well. Illites are also relatively inactive, with a cation exchange capacity approxi mately three times that of kaolinites, but only one fourth that of smectites (montmorillonites). Also, the crystalline structure of illite promotes rigid ity and impedes water penetration, thereby limiting the swelling potential. Smectite has the smallest particle size of the three basic clay minerals. Its structure, involving areas of minimal cohesion between successive layers, al lows for a high rate of chemical activity. Smectite exhibits the greatest surface area, cation exchange capacity and shrink-swell potential of the three types of clay. In water, it can absorb on its interlayer surfaces 300% of its solid phase weight. If this water is displaced by other liquids that yield a lower interlayer spacing, the potential for shrinkage can be of definite con cern. Some of the essential properties of the three clays are tabulated in Table 1. In many cases, smectite clays such as Na-montmorillonite, have been favored for use as liners due to their relative impermeability in the dispersed, hy drated state. However, the impermeability provided by such clays is readily lost when the easily exchangeable sodium ion is replaced by some other cation, such as calcium. This causes the original dispersed structure to flocculate and become more permeable, although less reactive. Applying this principle to the other clay types, one can readily see that kaolinite and illite, being less reactive, could provide a more stable liner than smectite. However, some of the same reasons for their stability, such as larger particle size and more rigid structure, denies them the impermeability obtainable with smectites. DO 074499 CONFTDFNT TAL * SWTC-TM-85-5 Page Two Field experience and research activities have identified several failure mecha nisms in clay liners. One such mechanism, alluded to above, involves the in crease in permeability throughout the liner due to volume changes. These volume changes may occur in response to various conditions that have the po tential to alter a clay's interlayer spacing. It has been shown that inter layer spacing is a characteristic of a particular soil/liquid system depending on the clay mineralogy, the nature of the dominant adsorbed cation, and the properties of the saturating liquid. Modifications to these dependant bases can, and will, alter the spacing. For example, increasing the salt content of the saturating fluid from zero to 5.0 N NaCl was shown to reduce the original infinite spacing to less than 1.57 nanometers (Table 2) - At spacings below 1.5 nm, the clay tends to flocculate. This same effect can be correlated to the dielectric constant of the saturating liquid (see Table 3). Another mechanism for failure of a clay liner involves the dissolution of portions of the clay itself. Clay minerals typically contain both silica and aluminum in large quantities. It has been shown that these components can be solubilized in even dilute basic and acidic solutions. A dramatic example of acid solubilization was presented by Pask et. al. (1945) when 3%, 11% and greater than 33% of the original alumina content was solubilized from kaolinite, ilite, and montmorillonite, respectively, when harshly exposed to an acid. Alkaline solutions have been shown to have a similar, but less dra matic, effect on silica. Another concern regarding the effectiveness of clay liners was highlighted by Brown, Anderson, et. al. (1982), while studying the effects of organic liquids on compacted clay soils. They found that in nearly every case, the effectiv permeability of the soil increased significantly when the standard permeant (0.01N calcium sulfate) was replaced by organic fluids (see Figures 1-3). Al though this research looked only at the effects of concentrated organics (some recent studies involving dilute solutions have shown minimal effects), the data obtained and chemical explanations of the same offered, clearly demon strate an area for concern. The intent of this memo is not to bring an end to the usage of clay as a liner material, for it does indeed have some desireable qualities, including its ad sorptive capacity for various metals. However, to rely on clay liners for their "impermeable" characteristics must be done with caution and with the knowledge that permeability is usually expressed in terms of water flow through a water saturated soil. This typically is not the conditions to which clay liners are subjected in an industrial environment. Additional information relative to soil-based liners, as well as many other types, can be found in U.S. EPA's Technical Resource Document "Lining of Waste Impoundment and Disposal Facilities" (SW-870), Revised Edition (March, 1983). DO 074500 CONFIDFNTTAl SWTC-TM-85-5 Page Three TABLE 1 TYPICAL VALUES FOR PROPERTIES OF KAOLINITE, ILLITE. AMD MONTMORILLONITEa Clay Mineral Kaolinite (nonexpansive 1:1 lattice) Particle dimensions, m Largest Largest Surface Dimension Dimension Thickness Thickness Lattice Thickness nm 0.3-4.0 0.05-2.0 0.74 Charge b Deficiency Per Unit Cell 0 Surface area t m2/g Water Theoretical Vapor 12d Exchange Capacity m equiv/100 g Cation pH = 7 Anion 3-15 5-20'f Illite (nonexpansive 2:1 lattice) 0.1-0.3 >0.003 * 1.00 1.3-1.5S 52-82d 10-40 Ca-montmorillonite (limited expansion 2:1 lattice) Na-montmorilIonite (very expansive 2:1 lattice) Not easily determin able, but smaller than the figures for illite 10-100 Not easily determin able, but smaller than the figures for illite 10-100 0.96-1.80h >0.96j 0.65 0.65 ca 7501 164-206d 80-150 10-30'1 ca 7501 203-250 d 80-150 10-30e g bValues from Grim, 1968, unless otherwise stated. cUnits are multiples of electrostatic units (esu). One charge = 4.8029 x 10"' esu. dNewnham, 1956; Brindey and Robinson, 1946. Johansen and Dunning, 1959. Hoffman et. al., 1956. pH dependent. Grim et. al., 1937. .Frequently, two molecular layers of water with 1.45-1.55 nm. .Van Olphen, 1963. frequently, one molecular layer of water with 1.25 nm. DO 074501 OONFIDFNT TAl SWTC-TM-85-5 Page Four TABLE 2 EFFECT OF SALT CONCENTRATION ON INTERLAYER SPACING OF SODIUM SMECTITE Immersion Liquid Distilled Water 0.01 N NaCl 1.0 N NaCl 3.0 N NaCl 5.0 N NaCl Interlayer Spacing (nm) Infinite Infinite 1.92 1.60 < 1.57 . TABLE 3 INTERLAYER SPACING OF CALCIUM SMECTITES IN RELATION TO DIELECTRIC CONSTANTS OF VARIOUS ORGANICS Sorbed Fluid Water Methanol Butanol Benzene Dielectric Constant 78.5 32.4 17.7 2.3 Interlayer Spacing (nm) 1.92 1.71 1.45 0.99 00 074500 C0NFTDFNTIA1 SWTC-TM-85-5 Page Five FIGURE 1: Permeability of the four clay soils to standard aqueous permeant (0.01N CaSO^). PCRMEA61UTY {cm /ie cl FIGURE 2- Permeability of the four clay soils to acetone FIGURE 3: Permeability and breakthrough curves of the four clay soils treated with xylene. 0 074503 CNFTO ENTICE SWTC-TM-85-5 Page Six Distribution List SWTC-TM-85-5 Global Focal Points Groundwater Resource Team Jakob Schmerling, Franco da Rocha Dan MacDougall, Sarnia (Corp.) Steve Bolt, Sarnia Div. Bob Lutz, Fort Saskatchewan Dan Bosatra, Horgen Eberhard Dreher, Stade Harry Spaas, Terneuzen Rick Young, Coral Gables Clifton Sim, Hong Kong U.S. Area Environmental Managers W. E. Anderson, Western Div. J. B. Martin, Louisiana Div Plaquemine J. L. Mason, Consumer Products, Ind. K. W. Shewbart, Texas Operations G. R. Veurink, Michigan Div. T. M. Vinciguerra, Merrell-Dow, Cincinnati W. G. Wanamaker, Eastern Div.- Strongsville Other C. A. Royalty, 2030 B. A. Weaver, 2020 R. 0. Kagel, 2030 J. Castledine, Altona P. Canete, Coral Gables G. Bellinzona, Milan S. L. Daniels, 1702 R. E. Bailey, 1701 J. D. Wilson, 628 P. J. Sienknecht, 628 J. G. Hughes, Horgen F. A. Blanchard, 1702 J. VanAtten, EE&CS, Rotterdam J. J. Leddy, Freeport, 0CD R. R. Oubre, Freeport, OCD R. A. DeGesero, Freeport, B-2616 R. R. Swanke, PiO. Box 77, Clute, TX D. E. Waite, Midland, 433 R. L. Casteel, Midland, 834 77531 Doug Gray, Eastern Division, Strongsville Fred Teeters, Eastern Division, Strongsville Melissa Guise, Louisiana Div., Plaquemine, 3502-E Mel Heidner, Louisiana Div. Plaquemine, 3502-E Ben Baker, Michigan Division, 628 Millard Etling, Michigan Division, 1564-T Charlie Reed, Texas Operations, Freeport, B-1226 Marshal Turner, Texas Operations, Freeport, B-2621 Andree Youngson, Western Division, Pittsburg Ken Tsang, Canada, Ft. Saskatchewan, 151--A Dave Shortt,'Canada Sarnia Eberhard Dreher, Europe, Stade Harry Spaas, Europe, Terneuzen Groundwater Engineering Contacts John Tushek, Texas Operations, B-2401 Ralph Hendricks, Texas Operations, B-2401 Don Jones, Louisiana Division, 3301 Gene Wejrowski, Michigan Division, 433 Dick Davis, Michigan Division, 572 Bob Thiele, E&CS, Houston, Bin 2C7 Ray Frankson, E&CS, Houston, Bin 2A7 Randy Carson, Eastern Division, Strongsville, OH G. S. (Singh) Vij, Western Division, Pittsburg, CA Jorgen Liber, Canada, Sarnia Darryl Baron, Canada, Fort Saskatchewan Paul Cooper, Europe, EE&CS, Rotterdam Chuck Oliver, E&CS, Houston Oo 0o^?oASo"