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<br /> Clay soils treated by them, using sev- structure, that it no longer contains bentonite and other montmorillonitic
<br /> oral different chemical compounds, the clay mineral,montmorillonite,and clay soils,and that significant unfore-
<br /> t not only are permanently changed that its structure is permeable. Al- seen leakage from clay-lined pits may -
<br /> mineralogically but also exhibit signif- though this illustration is essentially range in probability between possible
<br /> icantly increased permeability. for pure bentonite,all montmorillonit- and probable. Such leakage may be
<br /> As an example of such changes, is clays exhibit similar behavior. environmentally adverse and have ad-
<br /> consider what occurs when two col- . From the standpoint of hazardous verse legal consequences.
<br /> umns of compacted bentonite,about 8 waste disposal, these changes in per- The professions should be aware
<br /> in.(203 mm)high,are exposed to two meability of a clay upon exposure to that (1) the impermeability of clay
<br /> differentfluids. If either tap water or certain chemicals must be a matter for barriers to azar ous wastes cannot be
<br /> distilled water is poured onto the top serious concern. uaranteed;and(2)the impermcabih- .
<br /> of one column, the compacted clay Pits excavated for disposal of chem- ty o ca rriers can under some -
<br /> surface absorbs water upon contact ical wastes are commonly lined with ditions be permanentlyestt9yed_
<br /> and swells, sealing the clay below several feet of compacted clay to pro thus destroying their function.There-
<br /> against further water penetration; if vide a supposedly impermeable Barri- fore, all chemical materials pro s
<br /> water is maintained at the top of the er, to'assure`that chemical wastes for disposal into clay-sealed,waste dis
<br /> column for two.years, its penetration placed into the pits will not penetrate' 1 its should be identified; and
<br /> into the clay column may be no deeper through the clay barrier and contami- those o a caustic nature.should be
<br /> than about 14 in. (6 mm� If an aque- nate undgrlying ground water. This neutralized by proper mixing with.
<br /> ous solution of certain caustics, con- reliance upon the typical very low per- those of an acid nature before either is
<br /> taining 80%or more water, is instead meability of compact-__ montmoril- introduced into clay-lined waste dis-
<br /> poured on the top of the second col- 1 jonitic clay is justified onwhe_n pure posal pits.
<br /> umn of compacted bentonite, it will water is likely to reach and affect it. To the best of the writer's knowl-
<br /> penetrate completely through the clay Discussions with a number of waste edge, this precaution has not hereto-
<br /> sample and begin draining from its fill operators indicate that disposal of fore been emphasized. Considering
<br /> bottom in about two minutes; signifi- chemical wastes into such pits often the thousands of hazardous waste dis-
<br /> cantly,•pure water subsequently occurs directly, without special effort posal sites operating in the U.S., it is
<br /> poured on the sample will similarly to assure that the wastes will not probable that a number of them are
<br /> drain through it just as quickly.Exam- adversely affect clay pit linings. It is experiencing leakage due to the cause
<br /> ination of the bentonite sample follow- probable that a large number of chem- cited. It is Important chat t e pro cl-
<br /> ing its exposure to the caustic will ical compounds will affect clay perme- sions and landfill operators be aware
<br /> reveal that it has an entirely different ability, in the manner described for of the possibilities.
<br /> actual waste mixtures are unknown. approach" be adopted. He and Dr. R. eration and stabilization in synthetic rock
<br /> "One problem with RCRA," he says, Anne Jones of CSU have developed such through the Stablex process.(mainly for .
<br /> "is that it still doesn't require that the an approach, a methodology for deter- inorganic wastes such as heavy metals)
<br /> waste mixtures which could affect the mining the potential hazards of disposing have been described in previous CE arti-
<br /> liners be evaluated as to their impact on of a particular material in a particular cles (see CE April 1981, pp. 53-56; Sep-
<br /> liner integrity.The kev message is this:as region."Any group applying for a dispos- tember 1979, pp. 81-86; and December
<br /> part of ermittin a site, the ermittin al permit should be required to do such a 1978, pp. 39-45). New York State is
<br /> agency s ould require that representative hazard assessment for the chemicals they working on a state hazardous waste man-
<br /> / natena TsFe test a ainst the clays plan to dispose of," he says. agement program which will emphasize
<br /> wt used there.The current way's notincineration and stabilization, according
<br /> What about the alternatives? to Peter Skinner.The state is planning to
<br /> protecting.t e ublic." P 8
<br /> e says e s not surprised to hear that Some have proposed cement-bentonite provide land for a state-of-the-art, high-
<br /> strong caustics, as well as solvents, may and other slurry trench liners for contain- tech facility for treatmern and-disposal of
<br /> have drastic effects on clay structures. ment of toxics;others are enthused about high-hazard toxic---wastes.--"In--New-
<br /> "We
<br /> New"We wouldn't be surprised to find that the chemical resistance of plastic liners. York," Skinner says, "the goal is that
<br /> strong acids`or other organics do too,"he But the engineers interviewed for this anything eventually landfilled will be pre
<br /> adds. Nor would he single out expansive article say there are serious questions treated by either incineration, stabiliza-
<br /> clays as being more prone to problems about the reliability of these methods. tion, or neutralization, and pre-com-
<br /> than the other types. Bentonite-based slurries, according to parted with little or no liquid."
<br /> In addition to site-specific drum-by- Earl Jones,would in all likelihood be vul- Some chemical waste will probably
<br /> drum waste evaluation,Lee sees pretreat- nerable to the same compounds that mod- always need to be securely buried. Pre-
<br /> ment of wastes before burial as a necessi- ify other clays. When properly placed, treatment and testing could solve many
<br /> ty.Acids and caustics can be neutralized, liners of polyethylene and other materials landfill problems, but first, says Fred
<br /> wastes can be consolidated, and liquids may be resistant to certain chemicals,but Lee, much more will have to be known
<br /> can be reduced or eliminated. A require- placing them properly and maintaining about the technology and chemistry of
<br /> ment to pretreat wastes at these sites is on them once placed is difficult indeed. secure disposal of hazardous wastes.Then
<br /> the horizon due to a combination of pend- "There hasn't been a plastic liner yet that the new methods will have to be followed
<br /> ing RCRA and,in some states,state reg- won't get holes in it," remarks Fred Lee. up with strict enforcement, continuous
<br /> ulations. But at this point, with many "I don't think we have the technology yet monitoring, and perpetual care to pre-
<br /> RCRA reqs still pending from EPA,and to use plastic liners alone to construct and serve the integrity of the landfill. It's no
<br /> with Rcagan Administration policy on maintain a secure chemical landfill." wonder that some environmental engi-
<br /> RCRA still uncertain,it's hard to predict Others feel that the best alternatives neers find their enthusiasm for landfilling
<br /> what will or will not be required. are in treatment,not burial of hazardous of toxics waning,especially in light of the
<br /> Lee urges that a "hazard assessment wastes.-Such treatment methods as incin- promising alternatives.
<br /> July 1981 Civil Engineering-ASCE 63
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