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® Comprehensive Environmental Response, Compensation, and Liability Act ® Resource Conservation and Recovery Act Clean Air Act ® Occupational Safety and Health Act ® Department of Transportation Rules 4.1.2 Soil and Groundwater Cleanup Goals for Arsenic, Cadmium, Chromium, Lead, and Mercury at Selected Superfund Sites Cleanup goals are one of the most important of the regulatory requirements that will determine whether a treatment option is potentially acceptable. Table 4-1 summarizes the cleanup goals determined for a variety of metal-contaminated sites. Cleanup goals are developed based on a site-specific risk assessment. Cleanup goals may be stated either as total metal content or leachable metal content depending on the risk assessment and the technology selected. Treatability standards must be expressed in temps consistent with the type of treatment option. For technologies designed to reduce contaminant mobility(for example solidification/stabilization or vitrification),performance goals for the treated waste are stated as leachable metal content. Toxicity Characteristic Leaching Procedure (TCLP) (see Table 4-2) or other leaching data generally will be required to demonstrate that the treatment option immobilizes the contaminants. Particularly when the treated waste is discarded on-site, the immobilization technologies (containment,solidification/stabilization,and vitrification)addressed in this document pose a degree of risk to human health and the environment not shared by processes that remove the toxic metals from the waste. The performance standards and monitoring requirements applied to immobilized wastes should be selected to ensure low leaching potential in the disposal environment, physical durability, and chemical stability of the treated waste system. For an in-depth discussion on performance measures, see Technical Resource Document.• Solidification/Stabilization and its Application to Waste Materials (EPA/530/R-93/012), June 1993.The performance standards for technologies to remove metals(for example metal extraction)generally will be stated as total metal concentration remaining in the treated residual. 4.2 IMMOBILIZATION TREATMENT This subsection discusses technologies that reduce the mobility of contaminants in a solid matrix or the transport of contaminated groundwater by one or more of the following three mechanisms: 1. Reducing infiltration of fluids into the contaminated media by using barriers. 2. Reducing infiltration of fluids by modifying the permeability of the contaminated matrix. 3. Reducing the solubility and hence mobility of the contaminant in groundwater or other fluids with which it is in contact. 4.2.1 Containment Technologies Containment technologies for application at Superfund sites include capping,vertical barriers, and horizontal barriers. Since the selection of these containment technologies is not significantly influenced by the type of metal contaminant, and these technologies are already adequately addressed in the Handbook for Stabilization Technologies for RCRA Corrective Actions(EPA/625/6-91/026,August 1991);they are not discussed here. The Hydrologic Evaluation of Landfill Performance (HELP) computer program is available for computer analysis of landfill performance. The HELP program is an easy-to-use model that was developed to assist landfill designers and regulators by providing a tool to allow rapid,economical screening of alternative designs. HELP is a quasi-two-dimensional model that computes a daily water budget for a landfill represented as a series of horizontal layers. Each layer corresponds to a given element of a landfill design (e.g., cap, waste cell, leachate collection system, and liner). HELP considers a broad range of hydrologic processes including surface storage, runoff, infiltration, percolation, evapotranspiration, lateral drainage, and soil moisture storage (EPA/625/6-91/026, 1991). 4-2