DECIDING WHEN TO INTERVENE

To evaluate the potential health effects from sediment contaminated sites, the U. S. Environmental Protection Agency (EPA) Superfund program uses a Remedial Investigation and Feasibility Study (RI/FS) process to characterize the nature and extent of risks posed by uncontrolled hazardous waste sites and aid in developing and evaluating remedial options. The human health evaluation process is an integral part of the remedial response process defined by the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) of 1980, the Superfund Amendments and Reauthorization Act (SARA) of 1986, and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), the regulation that implements CERCLA. Ecological risk assessment and the role of stakeholders in the RI/FS are beyond the scope of this presentation.

Project scoping. The main objectives of project scoping are: to identify site related decisions, to determine the type (including quantity and quality) of data needed, to define data Quality Assurance/Quality Control (QA/QC) objectives, and to define the site related type and extent of investigation. The Remedial Project Manager and team members collaborate to evaluate the possible impacts of site releases on human health resulting in a site-conceptual model that qualitatively considers available information (e.g., historical, previous site investigations, etc.) to determine the source of contamination, potential pathways of exposure, and populations potentially impacted. The conceptual model is refined and updated with new information throughout the RI/FS process.

The need for developing site-specific sediment fate and transport models are also evaluated during scoping so that model data collection requirements are met. Data at sediment sites may include: hydrology, water quality and aquatic resources, waterbody physical characteristics, nature and extent of contamination, and bioaccumulation. Models may be used to evaluate the extent of contamination, the potential for migration of contaminated sediment over specified periods of time, and the uptake of sediment contaminants through the food chain.

Risk assessment. Risk assessment originally defined by the National Academy of Sciences (1983) involves: hazard identification, toxicity assessment, exposure assessment, and risk characterization. Risk assessment is used throughout the RI/FS process to develop the baseline risk assessment to evaluate risks in the absence of remediation, to refine preliminary remediation goals, and to evaluate remedial alternatives. Risk assessment provides a framework for evaluating and organizing collected information and comparing the relative risks of individual chemicals and routes of exposure.

Superfund risk assessments are designed to evaluate current and potential risks to the Reasonably Maximally Exposed Individual. Both cancer and non-cancer health effects for adults and children are evaluated. The baseline risk assessment and preliminary remediation goals are developed during the Remedial Investigation while the Feasibility Study refines the preliminary remediation goals and evaluates remedial alternatives.

Hazard identification. This involves evaluating collected data against the QA/QC objectives and selecting appropriate data for the risk assessment. The primary sediment data collected includes concentrations of chemicals in the sediment and water column, and the fate and transport of these contaminants within the aquatic environment, especially where the contaminants may bioaccumulate through the food chain. The media-specific chemicals of potential concern are characterized based on their potential to cause either cancer or non-cancer health effects, or both.

Toxicity evaluation. This involves evaluating EPA toxicity databases and sources to identify cancer and non-cancer oral and inhalation toxicity values. The databases in order of importance are: the Integrated Risk Information System (IRIS); EPA's consensus review database of over 500 chemicals; the Health Effects Assessment Summary Tables published by EPA's Office of Solid Waste and Emergency Response, including information on chemicals not available on IRIS; and EPA's National Center for Environmental Assessment provisional toxicity values.

Carcinogens are evaluated based on the Weight of Evidence and potency. The Weight of Evidence qualitatively assesses whether a chemical is known to cause cancer in humans, likely to cause cancer in humans based on animal data and limited human data, or not likely to cause cancer in humans. The chemical-specific potency is based on the cancer slope factor - a plausible upper bound estimate of the probability of a response per unit intake for a chemical over a lifetime. The slope factor combined with exposure information is used to estimate an upper bound probability of an individual developing cancer as a result of exposure to a particular level of a potential carcinogen over a lifetime.

Non-cancer health effects are evaluated using a Reference Dose (RfD) for oral and Reference Concentration (RfC) for inhalation. The RfD and RfC are defined as an estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily exposure level for the human population, including sensitive sub-populations that is likely to be without an appreciable risk of deleterious effects during a lifetime. Comparison of the exposure dose over a specific time frame to the RfD indicates a concern for potential non-cancer health effects.

Chemicals lacking toxicity are qualitatively discussed in the risk characterization. The discussion addresses the potential impacts of the missing toxicity data on the calculated risks.

Exposure assessment. This estimates the type and magnitude of chemical exposure from chemicals of concern present at or migrating from the site. The results from the exposure assessment are combined with chemical-specific toxicity information to characterize potential risks and hazards.

At sediment contaminated sites, routes of exposure may include: ingestion of contaminated river water, inhalation of chemicals volatilizing from sediment, recreational exposures (incidental ingestion of sediment and dermal contact with sediment and water), and ingestion of fish. Usually the primary risk is from ingestion of fish where chemical specific concentrations from sediment bioaccumulate.

Exposure from fish consumption involves determining the fish chemical concentration, the daily amount of fish ingested, the frequency of fish obtained from a specific source, and the duration of exposure. Fish consumption data may be obtained from site-specific creel surveys, national or regional surveys with data on the specific fish species for the site, surveys of licenses, angler fishing practices and consumption patterns, and surveys of anglers at specific fishing spots. Duration data may be obtained from census data or local mobility information.

The result of the exposure assessment is a calculated Chronic Daily Intake. The calculated dose may be adjusted for children and adults including modifications to the exposure variables that reflect the unique physiological characteristics associated with age. Dose information is combined with the cancer slope factor and the RfD, respectively, to calculate risk and hazard.

Risk characterization. This presents the calculated risks and hazards for the reasonably maximally exposed individual for each pathway and chemical, and across chemicals and pathways. A discussion of the uncertainties for all components of the risk assessment are also included in the risk characterization. The goal is to provide this information reflecting transparency in the decision-making process, clarity in the communication, consistency with other assessments, and reasonableness. The risk characterization serves as the bridge between the assessment of potential risks from the site and the risk management decision concerning the potential need for remedial actions.

Remedial actions. Risk assessment results are used by the Project Manager to determine the need for further action based on criteria in the National Contingency Plan. The Feasibility Study identifies the remedial action objectives for contaminants and media of concern, potential exposure pathways, and preliminary remediation goals including compliance with Applicable or Relevant and Appropriate Requirements (ARARs). Risk assessment is used to determine whether the goals protect public health.

Analysis of remedial actions includes assessment of the extent of contamination, ARARS, chemical-specific environmental fate and toxicity information, and engineering analysis. The remedial action alternatives and associated technologies are screened to identify those that are effective for the contaminants and media of interest at the site. The information developed in these two activities is used in assembling technologies into alternatives for the site as a whole, or for a specific portion of the site.

In determining the remedial site actions, each alternative is assessed against specific evaluation criteria and the results arrayed to allow comparisons between alternatives. The nine evaluation criteria include:

• Overall protection of human health and the environment
• Compliance with ARARs
• Long-term effectiveness and permanence
• Reduction of toxicity, mobility, or volume through the use of treatment
• Short-term effectiveness
• Implementability
• Cost
• State acceptance
• Community acceptance.

The first two criteria are threshold determinations and must be met before remedy selection. The next five criteria are balancing criteria and the last two criteria are modifying criteria. Risk information is important in the analysis of effectiveness and permanence of a remedial action by assessing residual risk after the response objectives were met. The alternatives are also evaluated with respect to the potential effects on human health during implementation of the remedial action and the length of time until protection is achieved.

Disclaimer:

The views presented in this abstract are those of the author and do not necessarily reflect the views or policies of the United States Environmental Protection Agency.

References

National Academy of Sciences. 1983. Risk Assessment in the Federal Government: Managing the Process. National Academy Press: Washington, D.C.

U. S. Environmental Protection Agency. 1989. Risk Assessment Guidance for Superfund. Volume 1. Human Health Evaluation Manual. Part A. Interim Final. U. S. Environmental Protection Agency, Office of Emergency and Remedial Response. Washington, D.C. EPA/540/1-89/002.