Risk assessment waste disposal

The availability of the analytes for uptake by plants, for transport through the soil, and for dissolution into water can be estimated from a well-studied speciation scheme. Risk assessment for disposal of wastes in landfills or for land disposal of dredge spoils or sewage sludges requires knowledge not only of the total metal content but also of the content in each separate fraction to begin to understand how the metals will act in the environment. Table 5.7 summarizes the methods available for speciation of metals in samples. 

The health risks from disruptive events which might constitute a significant fraction of the total health risks firom waste disposal should be assessed. 

The risk assessment has also concluded that a level of 200 mg/kg for lead in the soil will be a protective level for expected site exposures along with an excess cancer risk level for TCE-contaminated soil (56 pg/L). Based on investigations of activities at the site, the TCE-contaminated soil has not been determined to be a listed RCRA hazardous waste, as the cleaning solution records indicate the solution contained less than 10% TCE. However, the lead-contaminated soil is an RCRA hazardous waste by characteristic in this instance due to extraction procedure (EP) toxicity. None of the waste is believed to have been disposed at the site after November 19, 1980 (the effective date for most of the RCRA treatment, storage, and disposal requirements). 

On the other hand, in part II of this volume, a set of case studies are introduced. The application of the selected methodologies inside each one of the foresaid disciplines (e.g., risk assessment, life cycle assessment) to specific cases and countries is presented here. The results of such application are discussed as well as their reliability. Toxicological studies in Italy, risk assessment of electronic waste in China, or disposal of bearing lamps in India are some examples of selected scenarios. 

The German Environmental Ministry is reported to have attacked European proposals to ban substances such as specific flame retardants in forthcoming regulations for recycling electrical and electronic equipment. Initial proposals from the EU Commission on the disposal of waste electrical and electronic equipment, include a phaseout of PBDEs, despite preliminary findings under EU risk assessment that there is no need for risk reduction from the two types, decaBDE and octaBDE mainly used in such equipment. The Ministry is said to be concerned at the excessively prescriptive and restrictive system being proposed, and that substance restrictions should not be addressed in waste legislation, but should be based on life cycle risk assessments. 

The primary purpose of this Report is to present NCRP s recommendations on classification of hazardous wastes. The Report is directed at a multidisciplinary audience with different levels of technical understanding in the fields of radiation and chemical risk assessment and radioactive and chemical waste management. Anew hazardous waste classification system is proposed that differs from the existing classification systems for radioactive and hazardous chemical wastes in two fundamental respects. First, hazardous waste would be classified based on considerations of health risks to the public that arise from disposal of waste. Hazardous waste would not be classified based, for example, on its source. Second, the classification system would apply to any hazardous waste, and separate classification systems for radioactive and hazardous chemical wastes would not be retained. In the proposed system, waste would be classified based only on its properties, and the same rules would apply in classifying all hazardous wastes. 

Classification system applies to any waste that contains radionuclides or hazardous chemicals. Waste classification system does not provide a substitute for site-specific risk assessments in developing waste acceptance criteria at particular disposal facilities or in developing criteria for remediation of particular contaminated sites. 

A risk-based waste classification system must focus on the inherent characteristics of waste, representative facilities, and generic events, because the system necessarily presumes that specific disposal sites and related waste treatment and disposal technologies have not yet been identified and characterized. NCRP emphasizes that the principles, framework, and implementation details of a risk-based waste classification system do not provide a substitute for site-specific risk assessments. The two most important cases where site-specific risk must be estimated are (1) an assessment of risk for the spectrum of actual wastes at a specific disposal site for the purpose of establishing site-specific waste acceptance criteria, and (2) an assessment of risk posed by a prior waste disposal at a site for the purpose of determining whether the risk is unacceptable and, thus, whether remedial action is required at the site. 

For the purposes of this Report, a risk assessment is a written document wherein all the pertinent scientific information regarding the risk that arises from disposal of hazardous waste is assembled, critiqued, and interpreted. The goal of the assessment generally could be to calculate the likelihood of responses in humans, aquatic or terrestrial biota, or ecological systems that arise from disposal of hazardous wastes. In this Report, however, the focus is on assessment of health risks in humans (see Section 2.2.6). The magnitude of the risk depends on both the potency of hazardous substances and the amount of exposure, which is a function of the duration of exposure and the concentrations of hazardous substances. 

Estimates of risks to human health resulting from disposal of hazardous wastes will nearly always be calculated values based on models. Even if health effects were to occur in the future, they are likely to be unobservable in the background of similar effects from all causes. Therefore, mathematical predictions of risks are required. In general, risk assessment is the process by which toxicology data... 

Dose-Response Assessment. Determining the relationship between the dose of a hazardous substance and the probability of a specific response is called dose-response assessment.6 This aspect of risk assessment is needed to extrapolate from responses observed in experiments or incidents involving high doses to the much lower potential doses relevant to waste disposal and other routine exposure situations. Dose-response assessment is a major issue in establishing the foundations of a risk-based waste classification system, and it is discussed in detail in Section 3.2. 

Fig. 3.4. Depiction of probabilistic exposure and risk assessment process for hazardous waste disposal (Garrick and Kaplan, 1995).

Thus, for purposes of waste classification, it appears possible to assess the risk from the intrusion and atmospheric release pathways at a generic hazardous waste disposal site. However, a generic assessment of risk from the water release pathway normally would incorporate assumptions that would be extremely conservative for many sites (e.g., the amount of water infiltration and travel times of hazardous substances to a nearby well). 

The dominance of the risk to inadvertent intruders at near-surface waste disposal sites allows the use of this type of scenario to develop a risk-based waste classification system. However, NCRP recognizes that exposures of the public and protection of the environment also are of concern in determining acceptable disposal practices at specific sites. The potential for off-site releases of hazardous substances is the primary reason that classification of waste based on risks to hypothetical inadvertent intruders does not obviate the need for site-specific risk assessments to determine waste acceptance criteria in the form of limits on disposal of particular hazardous substances. 

Of the various ways of designating a solid waste as hazardous described above, only the toxicity characteristic is based on a quantitative assessment of potential risks resulting from waste disposal. The specifications of ignitable, corrosive, and reactive waste are based on qualitative considerations of risk, in that the presence of materials with these characteristics in a disposal facility clearly constitutes a hazard that could compromise the ability of the facility to protect public health. The specifications of listed hazardous wastes are based on risk in the sense that the listed substances have been identified as potentially hazardous to human health. However, requirements for treatment and disposal of listed waste discussed in Section 4.2.2 do not distinguish between different wastes based on considerations of risk from disposal. 

The general concern about limiting off-site releases of hazardous substances is the primary reason why classification of waste based on risks to hypothetical inadvertent intruders at waste disposal sites does not provide a substitute for site-specific risk assessments when determining acceptable disposal practices. Nonetheless, experience with risk assessments at near-surface disposal sites for low-level radioactive waste has indicated that, for most radionuclides, disposal limits that provide adequate protection of future inadvertent intruders should provide adequate protection of the public and the environment at off-site locations as well. Exceptions are expected to occur only in unusual cases of long-lived and highly mobile radionuclides. 

---