Risk-Based Waste Classification in California (1999) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-13
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As part of its regulatory structure update process, the California Environmental Protection Agency's Department of Toxic Substances Control (DISC) has reviewed those characteristics and has undertaken to propose a new waste-cIassification system for hazardous wastes.)
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Before the proposed classification system and subsequent regulations can go into effect, DTSC is required by California statute to "conduct an external scientific peer review of the scientific basis of any new rule" (California Health and Safety Code § 570043. Consequently, DTSC requested that the National Research Council (NRC)
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The proposed classification system reviewed in this report is unchanged from the descriptions in the original documentation received by the NRC, albeit with some clarification on specific issues from DTSC and other individuals and organizations. DTSC'S CURRENT CIASSIFICATION SYSTEM As presented in its report, DTSC currently uses a one-threshold system to classify wastes either as hazardous or nonhazardous based on the toxicity of the whole waste or the waste components.3 Under the current system, DTSC has established eight toxicity criteria by which a waste might be considered hazardous: · Federal definition of a hazardous waste according to its toxicity characteristic.
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. For wastes that are not considered hazardous under RCRA, DTSC currently determines whether the waste contains any specific chemicals that exceed thresholds established for soluble threshold limit concentrations, or whether the total amounts of any specific chemicals exceed established total threshold limit concentrations.
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Environmental Protection Agency's proposed Hazardous Waste Identification Rule. The proposed upper and tower soluble or extractable regulatory thresholds were derived by a different method from that used to calculate the total threshold limit concentrations.
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For acute toxicity thresholds, acute exposure scenarios were used. The upper acute oral and dermal toxicity thresholds were based on exposure of adults, and the lower toxicity thresholds on exposure of children.
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Exposure Pathway Integration The committee recommends that DTSC adopt a comprehensive approach to its proposed multimedia implementation by integrating risks from all
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The DTSC documentation should describe how all exposure scenarios were developed for residents, workers, and nonhuman organisms, and screened for acceptability and completeness. The rationale for choosing the ~ong-term exposure scenarios for the total threshold limit concentrations and for the soluble or extractable regulatory thresholds should be clearly explained, as should the short-term exposure scenarios used to develop the acute toxicity thresholds.
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With a more complete statement of policy goals, including the desired levels of protection and the populations to be protected, the correct treatment of uncertainty and variability should become apparent and should be explicitly discussed in the context of the policy goals. The committee recommends that DTSC conduct a thorough sensitivity analysis to identify critical parameters and dominant pathways in the exposure models.
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The committee recommends that DTSC establish the protectiveness of this default value. DTSC proposes to use the federal RCRA toxicity characteristic leaching procedure to extract wastes rather than the current California waste extraction test to detect soluble chemicals in landfill leachate.
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If only acute toxicity data are available for the risk assessment, the committee recommends that DTSC follow standard practice and use an uncertainty factor to account for the lack of chronic toxicity data. Failure to consider chronic effects could seriously underestimate the risks posed to human health and the environment from long-term exposure to wastes.
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The committee believes that DTSC's basic approach of considering the likely risks associated with waste disposal rather than just the toxicity of the waste, and using multimedia, multipathway exposure models for assessing these risks, represents a significant improvement in developing waste management regulations. The committee appreciates the difficulty faced by DTSC, or any organization, when
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Environmental Protection Agency in addressing similar waste classification issues. The committee, therefore, urges DISC to address the concerns presented in this report, and submit the revised report to a detailed and comprehensive scientific (and editorial)
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