Risk-Based Waste Classification in California (1999)

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Model Selection:

Is it appropriate to use a multimedia, multipathway risk assessment model to establish concentration limits on organic chemical constituents in various classes of waste? Reference Tab 3 Appendix 3(pg 50) and Tab 4a (pg 76)

Chapter 2- Multimedia & Multipathway Risk Assessment

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Is it appropriate to use a simple exposure model to establish concentration limits on inorganic chemical constituents in various classes of waste? Reference Tab 3 Appendix 3 (pg 50) and Tab 4c (pg 784)

Chapter 3- Analysis of Scenarios and Modeling; Chapter 4- Preliminary Endangerment Assessment

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Is it appropriate to use a lead uptake/blood lead model to establish concentration limits on lead in various classes of waste? Reference Tab 3, Appendix 3 (pg 50) and Tab 4b (pg 775)

Chapter 4- LeadSpread

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Scenario Selection:

Are the waste management worker and the nearby resident scenarios appropriate to represent populations potentially exposed to lower-tier hazardous wastes? The exposures of these populations would be used to establish a ''bright line'' to separate wastes which are subject to pre-disposal requirements and must be disposed of in RCRA subtitle C (hazardous waste) landfills from those which are subject to reduced pre-disposal and can be safely disposed of in RCRA subtitle D (MSW) facilities? Reference Tab 3, Appendix 3 (pg 50) The Department recognizes that some wastes may be disposed of in ways that have less potential exposure. Soil is an example of a waste that has a high probability of being disposed of in a way the results in less dilution and therefore potentially greater exposure.

Chapter 3- Scenarios: Connection to Policy

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All assessments of carcinogenic risk are based on estimated exposure to a composite person, having characteristics between those of a child and those of an adult. CalTOX also uses this approach for non-carcinogenic effects, while the PEA-based model and the Lead Risk Assessment Spreadsheet assesses exposure to children and adults separately for non-carcinogenic effects. Which approach is appropriate for carcinogens? For non-carcinogens?

Chapter 4

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Pathways and Parameters:

Do the exposure pathways evaluated for workers and residents reasonably represent the exposure potential for these groups of people? Reference Tabs 4a (pg 76), 4b (pg 775), and 4c (pg 784)

Chapter 3- Scenarios: Connection to Policy

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In the original submission it was assumed that 30% of a worker's skin is exposed. The 30% figure used in the assessment falls between worst case and typical case. The latter would involve about 13% exposure. The Department was able to obtain only anecdotal information about landfill workers' attire. Is 30% a reasonable mean value for fraction of skin exposed?

Beyond the scope of the committee's task; however, see Chapter 4- Parameter Selection within Specific Models for discussion of landfill worker scenario and model parameters

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Although daily cover of active disposal areas is required and only a limited area of a landfill may be active at any given time, no cover was assumed in modeling the landfill. This may be less important for vapors which are expected to escape through gas collection systems regardless of daily cover or capping. With adequate data, a distribution of uncovered areas for California landfills and waste piles could theoretically be developed. However, DTSG used conservative modeling parameters partly because of data limitations and also because workers and residents may be exposed to vapors and particles from waste piles, which may not have daily cover.

Chapter 3- Scenarios: Completeness and Coverage

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The degree of overestimation of exposure from a landfill source may be considerable for particulate pollutants because their release should be significantly reduced by daffy cover or a cap. The degree of overestimation of exposure from a landfill source would likely be much less for vapors, because advective transport is likely to result in vapor emissions, usually through a gas collection system, regardless of daffy cover or permanent cap. However, only a fraction of the landfill would be producing gases at any given time.

Chapter 3- Mathematical Models and Their Implementation; Chapter 4- Preliminary Endangerment Assessment, CalTOX

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No dust dilution was assumed for PEA and Lead spreadsheet modeling, i.e., all respirable particulates are assumed to come from the waste. Monitoring data for California land-

Chapter 4- Preliminary Endangerment Assessment

fills and waste piles were sought, but most existing data are based on complaint follow-ups, and would be highly biased.

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U.S. EPA has withdrawn the oral cancer potency factor for beryllium. Treating beryllium as a carcinogen only by the inhalation route would result in about a six-fold increase in the beryllium TTLC. Should beryllium be treated as an oral carcinogen?

(Not discussed)

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Other Issues:

Is the proposed stepwise approach to ensuring that TTLCs based on human toxicity will protect non-human biota reasonable? Reference Tab 3, Appendix 3 (pg 50) and Tab 4d (pg 844)

Chapter 3- Ecological Scenario

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Is the proposed use of two times the estimated quantitation level (EQL) in lieu of a TTLC when the calculated concentration is less than the EQL reasonable? Reference Tab 5b (pg 864)

Chapter 4- Analytical Methods

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Is the proposed approach to considering ambient levels of elements and compounds in setting TTLCs appropriate? Reference Tab 5a (pg 859)

Chapter 4- Analytical Methods

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SERTs are based on the lowest of (1) health-based concentrations calculated by DTSC, (2) California Maximum Contaminant Levels established by the Department of Health, or (3) U.S. EPA Ambient Water Criteria for the protection of aquatic life. Is this paradigm appropriate? Reference Tab 3, Appendix 2 (pg 43)

Chapter 4- Soluble or Extractable Regulatory Thresholds

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Is the dilution/attenuation factor of 100 for the SERTs appropriate? Reference Tab 3, Appendix 2 (pg 43)

Chapter 4- Soluble or Extractable Regulatory Thresholds

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Is the use of a factor to account for the retardation of leakage from the landfill due to the

Chapter 4- Soluble or Extractable

presence of a synthetic liner appropriate? Reference Tab 3 Appendix 2 (pg 43) Was the liner protection factor calculated appropriately? Reference Tab (12) (pg 1485)

Regulatory Thresholds

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The current STLCs and proposed SERTs are based on an assessment of the environmental effects of leachates from solid wastes in a landfill, but apply also to liquid wastes that are not disposed of in a landfill. Should the effects of released liquids be assessed separately? Reference Tab 2, Appendices 2 (pg 43) and Tab 6 (pg 869)

Chapter 2- Implementation Practicality and Evaluation

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Is laboratory extraction of toxic constituents from solid wastes with municipal solid waste leachates a reasonable standard against which to compare the performance of laboratory extraction protocols such as the WET, the TCLP, and the SPLP? Is the Department's conclusion that the WET is not a better estimator of leaching potential than the TCLP justified? Reference Tab 6 (pg 869), Tab (9) (pg 1046), Tab (10) (pg 0178) and Tab (11) (pg 1255)

Chapter 4- Analytical Issues

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We concluded that the extraction by municipal solid waste leachates of elements capable of forming oxyanions was not simulated by the WET or by the TCLP. Is this a reasonable conclusion? Reference Tab 3 Appendix 2 (pg 43) and Tab 6 (pg 869), Tab (9) (pg 1046), Tab (10) (pg 0178) and Tab (11) (pg 1255)

Chapter 4- Analytical Issues

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In the current proposal, ingestion of ground water is the only human exposure pathway evaluated. Does this approach seriously underestimate risk? Reference Tab 3 Appendix 2 (pg 43)

Chapter 3- Scenarios: Connection to Policy

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Is the use of the 90^th percentile concentration of arsenic in monitored Calif. drinking-water supplies appropriate as a basis for the arsenic SERT? Reference Tab 3 Appendix 2 (pg 43)

Chapter 4- Soluble or Extractable Regulatory Thresholds

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Is the proposed use of two times the estimated Quantitation level (EQL) in lieu of a SERT when the calculated concentration in less than the EQL reasonable? Reference Tab 5b (pg 864)

Chapter 4- Analytical Issues

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Can the STLC values for arsenic, antimony, molybdenum, selenium, and vanadium be adjusted in a scientifically sound manner to compensate for the extent of inaccuracy of the testing procedure (TCLP) for those constituents?

Chapter 4- Analytical Issues

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Is the Department's proposed approach to setting acute oral, dermal, and inhalation toxicity thresholds reasonable? Reference Tab 3 Appendix 4 (pg 72)

Chapter 4- Toxicity Tests