Sanitary landfills were developed for municipal refuse disposal to replace open dumps (see Section 10.13). New secure landfills are used to bury non-liquid hazardous wastes in synthetically lined depressions. Secure landfills for hazardous waste disposal are now equipped with double liners, leak detection, leachate monitoring and collection, and groundwater monitoring systems. Synthetic liners are a minimum of 30 mil thickness.

Liner technology has improved greatly and continues to do so. Very large sections of liner fabric now minimize the number ofjoints. Adjacent sections are welded together to form leak-proof joints with a high degree of integrity. Liners are protected by sand bedding or finer materials free of sharp edges or points which might penetrate the inner fabric. Another layer of bedding protects the inner layer from damage by machinery working the waste. Some states allow one of the liners to be natural clay. The completed liner must demonstrate low permeability and must include a leachate collection system.

Leachate detection and collection systems are equipped with access galleys or other means of leachate removal. Double liner, leakage detection, and leachate collection systems are shown in Figure 11.12.2.

Leachate caps are detailed by the EPA. Figure 11.12.3 is a cross-section of a typical cap design. The objectives of cap design are to protect the cells from erosion, to route

Optional Soil Protective Cover

Optional Soil Protective Cover

FIG. 11.12.2 Schematic—cross section of a secure landfill double liner system. Credit: (Reprinted with permission, from W.C. Blackman, 1992.)
FIG. 11.12.3 Land disposal site cap designed for maximum resistance to infiltration (CH2M-Hill, Denver, CO). (Reprinted, with permission, from W.C. Blackman, 1992.)

potential runoff around and away from the cap, and to prevent buildup of gases generated within the landfill.

Groundwater monitoring schemes are designed to provide up-gradient (background) water quality data, and to detect down-gradient differences in critical water quality parameters. The RCRA requires a minimum of one up-gradient and three down-gradient monitoring wells to detect leakage from landfills (EPA 1981, 1987).

Landfills present two general classes of problems. The first class includes fires, explosions, production of toxic fumes, and related problems from the improper management of ignitable, reactive, or incompatible wastes. Thus, owners and operators are required to analyze wastes to provide enough information for proper management. They must control the mixing of incompatible wastes in landfill cells, and place ignitable and reactive wastes in landfills only when the waste has been rendered unignitable or nonreactive (EPA 1990).

The second class of landfill problems concerns the contamination of surface and groundwater. To deal with problems, interim status regulations require diversion of runoff away from the active face of the landfill; treatment of liquid or semisolid wastes so they do not contain free liquids; proper closure and preclosure care to control erosion and the infiltration of rainfall; and crushing or shredding landfill containers so they cannot collapse later leading to subsidence and breaching of the cover. Groundwater monitoring as described in Subpart F is required, as is collection of rainwater and other runoff from other active faces of the landfill. Segregation of waste such as acids, that would mobilize, make soluble, or dissolve other wastes or waste constituents is required (EPA 1990).

In the HSWA, Congress prohibited disposal of non-containerized liquid hazardous waste, and hazardous waste containing free liquids, in landfills.

Such landfills should be situated away from ground-water sources. These safeguards should be followed because there is no guarantee that engineering solutions will be able to contain the wastes in perpetuity. A well-built facility may allow sufficient leadtime for remedial action before environmental damage occurs.

Secure landfills meeting new RCRA standards may, under temporary variances, be able to accept a few hazardous wastes for which alternative disposal methods have not been developed. Secure landfills may also accept hazardous wastes that are treated to the best demonstrated available technology.

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