Environmental Risk Assessment Reports - Chapter 28

CHAPTER 28 CERCLA and RCRA Risk Assessments Carol Baker CONTENTS I. Introduction.................................................................................................515 II. Overview of Risk Assessment....................................................................516 III. Risk Assessment Process............................................................................517 A. Purpose..........................................................................................517 B. Approach.......................................................................................517 IV. CERCLA.....................................................................................................518 V. Components of a Baseline Risk Assessment.............................................520 VI. RCRA..........................................................................................................523 VII. Comparison of RCRA and CERCLA Risk Assessment............................525 VIII. Conclusion..................................................................................................526 References...................................................................................................526 I. INTRODUCTION Risk assessment is used by federal and state regulatory agencies for implementation of Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) and Resource Conservation and Recovery Act (RCRA) laws at contaminated sites. Effective use of a risk-based remediation strategy helps to focus environmental cleanup dollars on those areas of the site identified in the risk assess-ment as potentially presenting unacceptable risks. Risk assessments developed for CERCLA- and RCRA-regulated sites must be generally consistent with the various U.S. EPA guidance documents for conducting risk assessments to promote successful regulatory agency acceptance. However, strict adherence to U.S. EPA guidance is generally not conducive to developing site-specific information; deviation to address site-specific conditions and considerations is recommended and desirable. 515 © 2001 by CRC Press LLC 516 A PRACTICAL GUIDE TO ENVIRONMENTAL RISK ASSESSMENT REPORTS While there are allegations that risk assessment as it exists today is over con-servative, risk assessment is currently the best method available to predict the potential risks associated with contaminated sites. In January 1994 the Harvard Center for Risk Analysis released the results of a survey of 1000 Americans where 83% agreed “the government should use risk analysis to identify the most serious environmental problems.” Many regulatory agencies consider risk assessment an acceptable method for identifying sites that present risks to human health and the environment and prioritizing them. Risk assessment offers a site-specific alternative to the application of generic cleanup standards. This chapter will address some of the major differences between preparation of a risk assessment for a site regulated by the U.S. EPA and state regulatory agencies under CERCLA and sites that fall under the jurisdiction of RCRA. Both of these laws require that remedial actions be taken to protect human health and the environment. II. OVERVIEW OF RISK ASSESSMENT There has been a growing discontent in the 1990s in the U.S. over the approximately $115 billion spent on environmental protection. Scientists, environmental policy makers, and the public question whether the money has been spent based on the best understanding of health and environmental risks (Stone, 1994). Currently the general consensus is that remediation of many sites to background levels is inappropriate and technically infeasible. This is largely due to the limitations in remedial technologies. The traditional “cleanup to background or nondetectable levels” approach may not be necessary to protect human health but may still be required when a regulatory agency considers site remediation to be a function of regulatory standards. There is a growing movement, however, toward focusing reme-diation efforts (and funds) on a more practical goal — devising ways to minimize exposures based on the actual uses of a site, both currently and in the future. This process is called risk management. Exposures can be minimized through the use of remediation, control measures, or a combination of the two. Risk assessment can provide information that is critical in making decisions concerning the following: · The necessity of undertaking remedial action, if any, to protect human health · The implementation of risk management alternatives at the site Complete restoration and remediation to either background levels or generic stan-dards are often impossible. Site-specific risk assessment can evaluate the health impacts at a site based on the intended use of the property, identify the potential for health risks associated with exposure, and determine risk-based, medium-specific cleanup targets based on realistic and intended use of the site. These targets are critical in selecting an appropriate remedial action to protect human health and the environment to the maximum extent practicable. Risk assessment can provide the logical framework for determining which actions might reduce or eliminate risk. © 2001 by CRC Press LLC CERCLA AND RCRA RISK ASSESSMENTS 517 III. RISK ASSESSMENT PROCESS A. Purpose The risk assessment process is used to: · Identify chemical- and medium-specific preliminary remediation goals (PRGs) early in the process that can be used to focus investigatory activities · Determine the potential risks associated with site-specific exposure scenarios, assessing both the current and the hypothetical future exposures, without remedi-ation · Refine PRGs using site-specific data to generate health-protective cleanup targets for average and sensitive receptors, if potentially unacceptable risks are identified for a complete exposure pathway · Estimate current and/or future risks (or reduction in risks) potentially associated with implementation of specific remedial alternatives or institutional/engineering controls · Quantify risks potentially associated with exposure to residual chemicals following implementation of remediation and/or risk reduction measures The information generated will depend on the direction of the project, the goals of responsible parties, and the regulatory program which governs the site. The results of a risk assessment provide remediation engineers with site-specific cleanup target levels. These site- and medium-specific cleanup levels are useful in identifying appropriate cleanup alternatives. B. Approach Risk assessments developed for different sites are not always performed the same way, even under the same set of regulations and following the same guidelines. Either state or federal regulatory agencies may require slightly different evaluations and items in a risk assessment document. Guidelines vary from state to state, and some states have not yet developed state-specific guidance for risk assessment, but the impact of state guidance should be considered and addressed when it exists. Risk assessors must participate in all phases of site work to assure the collection of appropriate data suitable for the development of a scientifically defensible risk assessment. If involvement of a risk assessor occurs later in the process, data needed to prepare a technically defensible risk assessment may not be available. This will either result in additional field work or greater uncertainty in the results because assumptions have to be made to represent the missing data. If a risk assessor is involved early on in a project, preferably as soon as data indicate that a release has occurred, then the needs of the risk assessor can guide investigatory activities and decision making strategies. Early risk assessor involvement applies to both regulated and nonregulated sites. Data required to complete a site-specific risk assessment or to develop medium- and chemical-specific remediation goals can then be identified, and efforts can be made to collect these data while field activities are being conducted. © 2001 by CRC Press LLC 518 A PRACTICAL GUIDE TO ENVIRONMENTAL RISK ASSESSMENT REPORTS When risk assessors do not obtain adequate site-specific data for use in a risk assessment, they must rely on conservative modeling input parameters as surrogate data. Those values may or may not be appropriate to evaluate conditions and sub-sequent potential risks associated with exposure, and do not allow for a site-specific assessment of conditions at the site. Risk assessments, default exposure assumptions, and toxicity values in particular, are designed to be conservative (i.e., overprotective). Conservatism is a value judgement introduced into the risk assessment to compensate for uncertainty. The default values constitute a deliberate slant on the side of safety and protection of human health and the environment (Covello and Merkhofer, 1993). Using conservative assumptions minimizes the probability that a risk estimate will underestimate the actual risks associated with exposure under a specific scenario by producing an upper-bound risk estimate. Thus, early involvement of a risk assessor should improve the collection and incorporation of site-specific data, result in less uncertainty in the results, and help offset the ultraconservative tendency of risk assessment. IV. CERCLA Risk assessments were first required for a site regulated under the CERCLA program in 1980; the original Superfund law required action at hazardous waste sites that posed “a substantial endangerment to public health or welfare or the environment” (Section 104[a]). U.S. EPA intended to use risk assessment to assist in making decisions regarding cleanup. U.S. EPA published guidance documents dealing with risk assessment for suspected carcinogens as early as 1976 (U.S. EPA, 1976), with the first relatively comprehensive risk assessment guidelines, Superfund Public Health Evaluation Manual, available in 1986 (U.S. EPA, 1986). In 1989 the U.S. EPA released Risk Assessment Guidance for Superfund: Volume I — Human Health Evaluation Manual (Part A), Interim Final. This guidance document describes what the U.S. EPA envisioned as the baseline risk assessment (BRA) procedure, the rationale for the process, and the components of a BRA. Although this guidance was never intended as a “cookbook” for preparing risk assessments, it has often been treated that way. Deviation from the U.S. EPA’s BRA is often frowned upon by regulatory agencies. Additional and supplemental guidance has since been devel-oped, and specific mathematical expressions have been refined; however, the 1989 Guidance (U.S. EPA, 1989) is still consulted for the framework of a BRA. Once a site is listed on the National Priorities List (NPL), that site falls under CERCLA regulations and follows a prescribed process: remedial investigation (RI), BRA quantifying potential risks in the absence of remediation, feasibility study (FS), and remedial design/remedial implementation (RD/RI) (Figure 1). Immediate or interim measure actions can be implemented at any point in the process when data indicate it is necessary to take measures to protect human health and the environment. Risk assessment is a factor in each step of the CERCLA process. Following NPL identification, risk-related work occurs in at least four identified places in the CER-CLA process. © 2001 by CRC Press LLC CERCLA AND RCRA RISK ASSESSMENTS 519 Figure 1 Risk evaluation of remedial alternatives in the Superfund process. The first step in the RI process is to develop a sampling plan. At this time, risk assessors should be consulted to provide input on data needs and appropriate labo-ratory analytical techniques. For example, laboratory detection limits should not exceed health-based levels of concern. If they do, there is considerable uncertainty in the risk calculations, because even laboratory reported nondetects for certain constituents may result in unacceptable risks if exposure occurs. Due to the increas-ingly low detection limits that laboratories can routinely achieve, this has become less of a concern, but should still be considered. Second, PRGs can be developed in the RI to focus the investigation. PRGs are typically developed early in the investigation using conservative default assumptions resulting in an upper-bound, worst-case remediation target protective of a sensitive receptor. In general, if sampling data demonstrate that constituent concentrations are below the PRGs, it is likely that the area will not require remediation to protect human health and the environment. In cases where there are numerous chemicals of potential concern, the PRGs may need to be refined to consider the potential for cumulative effects of the chemicals. However, even if all chemicals are reported at concentrations below their PRGs, an agency’s interest in delineating impacts may require additional investigatory work. Third, the BRA, prepared as part of the RI, is designed to evaluate potential risks to human health and the environment posed by the site without undertaking remediation. The results of the BRA should assist in decisions to: · Identify areas of the site requiring remediation (i.e., those areas where exposure could result in potentially unacceptable health risks) · Establish the level of remediation required in each of these areas © 2001 by CRC Press LLC ... - tailieumienphi.vn