9 Remedial Decisions Good policy analysis recognizes that physical truth may be poorly or incompletely known. Its objective is to evaluate, order, and structure incomplete knowledge so as to allow decisions to be made with as complete an understanding as possible of the current state of knowledge, its limitations, and implications. —Granger Morgan (1978) The remedy is worse than the disease. —Francis Bacon, On Seditions Following the CERCLA remedial investigation, the feasibility study (FS) is con- ducted to analyze the benefits (i.e., risk reduction), costs, and risks associated with remedial alternatives. The use of ecological risk assessment should not end with the baseline risk assessment for the site or even with the recommendation of remedial goal options in the remedial investigation (Chapter 8). Risk assessment is integral to (1) the analysis of individual remedial alternatives; (2) the ultimate, balanced remedial decision for the site; (3) prioritization of the remediation sequence for multiple sites; and (4) the assessment of the efficacy of remediation. The baseline assessment in the RI addresses only the no-action alternative. This chapter addresses the use of ecological risk assessment in the FS and in the subsequent decision- making process. In remedial alternative analysis, the following questions should be asked: (1) How will present and future risks associated with contaminants be mitigated by each alternative? (2) What new risks may be associated with each alternative? The first question can be answered based on the baseline risk characterization, remedial goals, and the proposed remedial alternatives. No new risk assessment is necessary. The analysis required to answer the second question fully should often be a complete risk assessment: problem formulation, exposure assessment, effects assessment, risk characterization, and description of uncertainties. Stressors (most often physical) are new, and some assessment endpoints and exposure pathways are likely to be different from those in the original assessment. Some of the hazards associated with remedial actions are listed in Table 9.1. Recovery is an important part of the risk character- ization for effects of stressors associated with remedial actions. Unfortunately, reme- dial risks are rarely given due attention in the feasibility study because (1) the FS is often under a severe time constraint; (2) the FS is often performed by the engineers who design the remedial alternatives, not risk assessors; and (3) in the United States, regulators do not require or expect rigorous assessments of remedial actions. The EPA guidance for assessment of human health risks of remedial actions is much less demanding than that for baseline risk assessments, and it makes quantitative assessment optional (EPA, 1991d). The guidance for assessment of ecological risks from remedial actions is less than a page in length (Sprenger and Charters, 1997). © 2000 by CRC Press LLC Following the remedial alternative analysis, risk managers must finally decide which remedial option is best. Risks from remediation must be balanced against the baseline risks that would be mitigated. It is also advisable for the final remedy to balance human health and ecological risk—that is, for the remedial action to be as protective of ecological receptors as it is of human health. Finally, the decision, of necessity, includes the costs of each alternative. At large facilities such as the DOE Oak Ridge Reservation, multiple contami- nated sites require remediation. The process of prioritizing these sites should incor- porate principles of ecological risk assessment. For example, if all sites cannot be remediated immediately, it may be appropriate to evaluate the risk associated with a delay in remediation of each site. 9.1 REMEDIAL ALTERNATIVE ANALYSIS The best remedial option is chosen by balancing costs and benefits of the various alternatives, the latter including reduction of the ecological risks described in the remedial investigation. According to the National Contingency Plan, the detailed analysis of alternatives consists of using nine criteria to evaluate each one, and TABLE 9.1 Examples of Hazards Posed by Remedial Actions From Chemicals: Mobilization by dredging of contaminants buried in sediments Increased availability of contaminants due to use of chelating agents Exposure of consumers to high contaminant levels in hyperaccumulator plants Release of contaminants during incineration or thermal desorption Use of biocides to eliminate contaminated communities From Physical Disturbance: Destruction of benthic communities by dredging Destruction of terrestrial ecosystems by: Removal of contaminated soil Creation of roads, parking areas, laydown areas, and other support facilities Creation or expansion of waste burial grounds Creation or expansion of borrow pits for caps or fill Mowing to maintain lawns Paving to eliminate hydrological and biotic exposure to soil Rerouting, channelization, and lining of streams Destruction of soil structure by cleaning Soil erosion and compaction From Biotic Introductions: Revegetation with exotic species Invasion of ecosystems by microbes or plants introduced for bioremediation Indirect: Opening the site to human use and development Encouraging development in the surrounding area by removing the stigma of contamination © 2000 by CRC Press LLC then identifying relative advantages and disadvantages of each (EPA, 1990a). The criteria are 1. Protection of health and the environment 2. Compliance with federal applicable or relevant and appropriate require- ments (ARARs) 3. Long-term effectiveness and permanence 4. Reduction of toxicity, mobility, or volume through treatment 5. Short-term effectiveness 6. Implementability 7. Cost 8. State acceptance 9. Community acceptance Additional criteria that risk managers consider prior to making a decision about remediation are existing background levels of chemicals, present and future land uses, present and future resource uses, and ecological significance of the site, both locally and nationally (Sprenger and Charters, 1997). The first two criteria are threshold criteria and should be weighed more heavily than others (Sprenger and Charters, 1997). Clearly, the first criterion should include effects of the remedial action. Few references to risks from remediation are made in the National Contingency Plan, although potential negative impacts of remediation are alluded to in a discussion regarding the EPA expectation that the preferred alter- native will often be treatment of contaminated media. Treatment will be limited when “implementation of a treatment-based remedy would result in greater overall risk to human health and the environment due to risks posed to workers and the surrounding community during implementation” and “severe effects across environmental media resulting from implementation would occur” (EPA, 1990a). The third criterion addresses “any residual risk remaining at the site after completion of the remedial action” (discussed in Chapter 10). Short-term effectiveness, the fifth criterion, refers to adverse and beneficial effects of the action during implementation and construction. State acceptance and community acceptance criteria relate to ecological risk assessment to the extent that the state regulatory agency and community value ecological receptors. Indeed, for three units on the Oak Ridge Reservation, Lower East Fork Poplar Creek and two ponds at the K-25 site, members of the public insisted that the DOE balance risks from the proposed remedial action against risks identified in the remedial investigation to choose the appropriate alternative. These representatives of the community were in favor of maximum ecological protection at reasonable cost. It is also notable that state and local communities may accept the risks associated with minimal clean-up if the site is designated a “brownfield” (i.e., an industrial land-use site), particularly if the alternative is to construct a facility on cleaner land. Finally, the risk manager chooses the most appropriate remedy for the site. The balancing of factors involved in this decision is discussed in Section 9.2. Although final remedial actions always require the consideration of the factors above, interim actions do not. At any time during the remedial investigation and feasibility study © 2000 by CRC Press LLC process, the risk manager may decide that a chemical release or the threat of a release of pollutants necessitates an interim action. This time-critical response, termed a removal action , is not a comprehensive or final remedy for the site. Thus the nine criteria do not apply (EPA, 1990a). For example, a decision was made to treat a TCE plume beneath the K-25 site on the Oak Ridge Reservation, based on human health concerns and the potential for the plume to migrate off-site. Ecological concerns, such as the impacts of the reduced flow to a stream, were not required to be considered prior to the removal action decision. 9.1.1 R ISKS A SSOCIATED WITH R EMEDIAL A LTERNATIVES The conventions of ecological risk assessment are rarely followed to identify and characterize ecological risks that may be associated with remedial alternatives. Thus, risk assessment associated with remediation is discussed at length here. During nego- tiations among stakeholders concerning remediation, it is often expected that health and safety issues will arise, including risks to construction workers, risks to the public from incinerator emissions, and risks to the public from dump truck traffic. However, the prospect of new ecological risks is rarely a concern. It is probably assumed that any ecological risks from remediation are short-lived. EPA and state regulatory agen- cies do not typically require well-structured, prospective ecological risk assessments as part of Superfund remedial feasibility studies. Although the EPA definition of stressor in its “Guidelines for Ecological Risk Assessment” is broad and includes physical stressors, risks associated with CERCLA remediation are not a focus of the document (EPA, 1998). Nonetheless, the “Ecological Risk Assessment Guidance for Superfund” (Sprenger and Charters, 1997) states that the ecological impacts of reme- dial options are an important aspect of protecting the environment. Given the often haphazard ecological analyses in feasibility studies, decision makers are at risk of unknowingly substituting ecological risks from remedial alternatives for human health and ecological risks that have been identified in the remedial investigation. Ecological risks from remediation may be classified into two categories: (1) the exacerbation of existing contaminant risks or (2) the physical destruction or trans- formation of ecological habitats and associated ecological communities. In the first instance, a removal action may cause further contamination of groundwater and surface water, or remedial technologies may increase the bioavailability of contam- inants. An addendum to the baseline exposure assessment may be necessary to characterize these risks from chemicals. In contrast, it is primarily the problem formulation phase of the risk assessment that must be improved if ecological risk assessment is to contribute to the assessment of nonchemical remedial alternatives, such as excavation and dredging. Components of the problem formulation that merit discussion are the identification of stressors and assessment endpoints and the development of conceptual models. Exposure and exposure–effects relationships may be obvious if ecosystems or portions of them are eliminated by physical disturbance. In addition, the risk characterization for physical stressors associated with remediation should evaluate the recovery of the affected ecological receptors. If a large number of activities are associated with a single remedial action, or if multiple remedial actions are undertaken concurrently and in close proximity, it © 2000 by CRC Press LLC may be necessary to use an ecological risk assessment framework that has been developed for multiple activities. The standard ecological risk assessment framework was developed for assessments of individual chemicals and other individual agents and does not incorporate a logical structure for assessing multiple agents and inte- grating their risks (EPA, 1998). Similarly, indirect or secondary effects are not addressed. Suter (1999b) developed a framework for the assessment of military testing and training programs that would be applicable to complex remedial actions. Suter recommends that impacts of each activity be assessed separately and integrated in the risk characterization, and provides a conceptual approach for addressing combined effects. The sections below are organized according to the EPA ecological risk assess- ment framework. Although environmental impacts of remedial actions are required to be assessed in the feasibility study, the EPA framework is not required to be used. Nonetheless, the authors believe that the framework is helpful in organizing the process of analyzing and characterizing risks from remediation. 9.1.2 P ROBLEM F ORMULATION 9.1.2.1 The Nature of Stressors Physical, chemical, and biological stressors may be introduced as a result of par- ticular remedial actions. Technologies that may introduce new chemical stressors include microbial bioremediation, phytoremediation, solvent extraction, chemical oxidation, and poisoning of contaminated fish prior to removing them. Chemical stressors associated with bioremediation could include toxic metabolites of the process (e.g., vinyl chloride from TCE), nutrients added to enhance the process, surfactants added to enhance the process, and peroxide added to provide a source of oxygen to bacteria. The microorganisms themselves could be biological stressors, if their multiplication and dispersal would constitute a hazard. Similarly, some plants introduced for phytoremediation or revegetation could become weeds. A summary of chemical emissions from conventional remedial technologies is pre- sented in EPA (1991d). Physical stressors associated with remediation might be the most harmful, at least in the short term. Examples include removal of vegetation and topsoil and soil compaction by heavy equipment and human activity. Similarly, the maintenance of lawn would be a stressor to the plant community and wildlife populations. In aquatic systems, changes in water flow, erosion of stream banks, dredging of sediments, and decreased riparian vegetation would be potential stressors. In all environments, the removal of habitat is a stressor that would be expected to result from a physical removal action. 9.1.2.2 Conceptual Models for Alternatives Assessment The presentation of conceptual models could potentially increase the clarity and rigor of the alternatives assessments. For no-action alternatives or alternatives that are intended as human health rather than as ecological remedies (e.g., fences, fishing advisories, land-use controls), conceptual models for the baseline risk assessments © 2000 by CRC Press LLC are applicable. In addition, these conceptual models may be used if the remedial action may mobilize chemical contaminants. However, the remedial alternatives that involve removal, isolation, or treatment of soil or sediment require disturbance not only of the contaminated areas but also of uncontaminated areas used for roads, structures, laydown areas, borrow pits, landfills, or treatment facilities. Hamby (1996) reviews common remedial technologies for soils, surface water, and ground- water. The Federal Remedial Technologies Roundtable provides a Web site listing in situ and ex situ technologies that have been used in over 100 case-study remedi- ations (http://www.frr.gov). Generic conceptual models for potential impacts of these activities on compo- nents of terrestrial ecosystems, aquatic ecosystems, and wetlands are presented in Figures 9.1, 9.2, and 9.3, respectively. These conceptual models for physical distur- bance differ from typical models for chemicals in that the arrows represent chains of causal processes rather than flows of chemicals. Additionally, the receptors are defined broadly because the consequences of physical disturbances tend to be less discriminatory than those of chemicals. Because of the great diversity of physical disturbances that could occur during remediation, these generic models require substantial adaptation to specific cases. The generic models should be modified as remediated sites are monitored and unexpected links emerge. For example, on the Oak Ridge Reservation a TCE-contaminated aquifer is being remediated through a pump-and-treat technology. To prevent Mitchell Branch, a neighboring stream, from being drained by the remedial measure, a length of the stream has been altered to a culvert. Damage to the stream, soil compaction, and the trampling of the riparian community along the stream should be included in the conceptual model or models for the remedial action. Large-scale physical or chemical remedial measures may impact neighboring sites. Thus, remedial decisions should be considered in the context of the manage- ment of neighboring sites. For example, on the Oak Ridge Reservation land managers have proposed draining a contaminated pond to mitigate risks to trespassing fisher- men and avian piscivores. Hydrologically connected to this pond is a waste burial ground, contaminated groundwater, and an associated spring. All of these elements should be components of the conceptual model for the remedial action. For example, rotenone added to the pond to kill PCB-contaminated fish may escape from the pond to hydrologically connected water bodies. Similarly, Garten (1999) has found that forest vegetation mitigates leaching of strontium-90 from soils at locations where transport is controlled mainly by subsurface flow. Thus, a conceptual model for the removal of trees from a similar strontium-90-contaminated site should include a pathway to groundwater and possibly to surface water and aquatic organisms. More indirect effects of remediation may interfere with goals for protection of ecological receptors. For example, chelation agents added to soil to aid in phytore- mediation may strip the soil of particular nutrients (Entry et al., 1996), thus causing adverse effects on the plant community. These agents could also increase the uptake of contaminants by soil invertebrates and increase food web transfer. Thermal clean- ing of soil destroys its structure and organic matter, raises its pH, and has a sterilizing effect (Tamis and Udo de Haes, 1995). Not only are the native soil flora and fauna affected, but plants seeded on the cleaned soil are likely to be adversely impacted. © 2000 by CRC Press LLC A more complex example involves the remediation of the Rocky Mountain Arsenal, including the demolition of chemical factories at the site. This reduction in the stigma of contamination and the improvement in aesthetics are leading to increased devel- opment on nearby lands. The development threatens the wildlife habitat that exists in the vicinity of the site and provides a habitat corridor between the site and the Front Range (Baron, 1997). Risk assessors and managers must decide which stres- sors have been created indirectly by the remedial action and pose likely or potentially high-magnitude risks. If conceptual models are consistent with remedial alternatives, the models may include the ultimate environmental fate of the contaminated medium. Where will dredged sediments be deposited? Is treated soil proposed to be returned to its site of origin? Tamis and Udo de Haes (1995) note that in the Netherlands cleaned soil has a stigma associated with it. Soil that has been cleaned through thermal processes is generally used as fill in construction because of the loss of structure and organic matter (Tamis and Udo de Haes, 1995). Soil cleaned through the use of chemical extraction is used in the concrete and asphalt industries. Biologically remediated soil is often used to cover waste dumps (Tamis and Udo de Haes, 1995). Suter (1999a) notes that conceptual models that represent multiple activities, multiple agents, nonchemical agents, and indirect effects, all of which may be associated with remedial actions, can be difficult to develop. Because these concep- tual models do not simply represent flows of contaminants, it is advisable to define the processes that link the physical components of the models. Because these models may become quite complex, it is often desirable to structure them hierarchically in FIGURE 9.1 Generic conceptual model of the effects of physical disturbance on terres- trial ecosystems. © 2000 by CRC Press LLC both detailed and aggregated form. Suter (1999a) also recommends that risk asses- sors create modular component models that can be reused in different combinations for different assessments. 9.1.2.3 Assessment Endpoints As stated in Section 2.5, ecological assessment endpoints are statements of environ- mental values, i.e., entities and associated properties that are to be protected. Can- didate assessment endpoints in the remedial feasibility study should include both those that were selected as endpoints for the baseline ecological risk assessment and those that were excluded because they were not deemed to be exposed to contami- nants at the site. Some of these receptors could be at risk from the physical distur- bances associated with remediation. In addition, assessment endpoints should include receptors at neighboring sites, such as terrestrial or aquatic communities FIGURE 9.2 Generic conceptual model of the effects of physical disturbance on aquatic ecosystems. © 2000 by CRC Press LLC affected by off-site activities such as road construction and creation of borrow pits and waste disposal sites. As in the baseline ecological risk assessment, ecosystems and organisms with special regulatory status, such as wetlands and threatened and endangered species, should be assessment endpoints if an exposure pathway exists. Some physical remedial actions are likely to severely disrupt habitat for endpoint populations or communities by virtue of their severity or large spatial scales. Although hazardous waste sites that are entirely denuded of vegetation because of contamination are rare, the removal of soil and the associated plant community as a remedial measure is common. Thus, the physical disruption of habitat, which could put associated populations of organisms at risk, should dictate that these populations be selected as assessment endpoints. Appropriate assessment endpoints in the context of physical disturbance might include diversity of the plant community and popu- lations of wildlife that might be affected by the new arrangement of patches of habitat and forage vegetation (see Figure 9.1). The boundary of a proposed action may determine whether a rare or highly valued plant community would be entirely removed. It is notable that some of the more subtle properties of assessment end- points for contaminated sites, such as reproductive potential, would not be appro- priate for locations where the removal of an entire community is planned. 9.1.2.4 Reference The assessment of risks from remediation must be performed with respect to a reference condition, which should be chosen in the problem formulation (or FIGURE 9.3 Generic conceptual model of the effects of physical disturbance on wetlands. © 2000 by CRC Press LLC equivalent) for the feasibility study. Two alternatives are possible: (1) an uncontam- inated and relatively undisturbed reference site or (2) the contaminated site prior to remediation. If baseline risks from the contaminants are balanced against remedial risks, as is suggested in Section 9.2 below, then the conditions resulting from both types of risks should be compared with the reference conditions (e.g., background soils) that are used in the baseline risk assessment (Section 2.7.3). 9.1.3 E XPOSURE A SSESSMENT The feasibility study should include an estimate of exposure of all assessment endpoints to all significant stressors for each remedial alternative. If any new expo- sure pathways are identified in the conceptual model for the remedial action, a new exposure assessment may be required. An example is the introduction of new chem- icals into soil or water, either as reactants in the remedial technology or as degra- dation products of the initial toxicant. The volatilization of organic contaminants during water evaporation from dredged sediments is another example (Chiarenzelli et al., 1998). If contaminated media are moved (e.g., dredge spoil transported upland for disposal), new assessment endpoints may be appropriate. In the case of dredge spoil, the models used to estimate uptake of contaminants by wildlife foods in soil (Section 3.5.2) may not be appropriate for estimating accumulation of chemicals from disposed sediment (Edwards et al., 1998). If the remedial technology has the potential to increase the bioavailability of the remaining contaminants, an amendment to the baseline exposure assessment is required. For example, the hyperaccumulation of contaminants by plants in phy- toremediation could increase the availability of the contaminants to herbivores. Solvent extraction, if performed in situ , could increase the bioavailability of aged organic chemicals or reduce the ability of the soil to support a community of microorganisms that could otherwise degrade the chemical. For example, Inoue and Horikoshi (1991) found that in liquid culture, none of 61 bacteria tested could grow in the presence of organic solvents with values for the log octanol–water partition coefficient (log K ow ) less than 3.1, and most could not grow in the presence of a solvent of log K ow less than 4.0. Also, dredging suspends contaminated and anoxic sediments in the water column, increasing exposure of aquatic organisms in the water column to contamination. Information concerning the release of contaminants or changes in their form due to remediation may be obtained from the results of treatability studies. These are bench-scale or small field trials of proposed technologies using the actual contam- inated medium from the site. Another source of information is monitoring conducted at sites where the remedial technology has been previously applied. The estimated exposure of assessment endpoint receptors to physical stressors (such as soil removal or trampling) may consist of only a description of spatial extent, intensity, frequency, and duration, if known. Exposures to any indirect stres- sors, such as impacts on habitat, should be considered, even if only qualitative assessment is possible. Only quantities that can be related to effects are used to estimate risks; other exposures are noted as having uncertain impacts in the risk characterization. Because an exposure assessment for a remedial action would be a © 2000 by CRC Press LLC [...]... acceptable for the former Second, studies of risk perception indicate that familiar risks are more acceptable than unfamiliar risks (Slovic, 19 87) Indeed, McDaniels et al (19 97) used a principal components analysis to identify four factors that characterize perceived ecological risk: ecological and human impact, human benefit, controllability, and knowledge Therefore, the familiar clearing of 20% of a forest... authorities However, it is for illustrative purposes only, and may not be acceptable at other sites De manifestis ecological risk • Risk to an ecological entity (e.g., threatened and endangered species or wetlands) that has a high level of specific legal protection • Risk to an ecological component of a site that has extraordinary local value Intermediate ecological risk • Ecological risk of magnitude between... are acceptable to the risk managers and the public For other examples of combinations, it is advisable for decision makers to balance health and ecological risks with cost and other considerations For example, if the health risk is de minimis, but the baseline ecological risks due to contaminants are de manifestis and the remedial ecological risks are de manifestis, then the risk managers must balance... minimis risks), and some possibly require remediation, depending on considerations such as costs and competing risks (intermediate risks) This categorical scale has been applied to health risks (Travis et al., 19 87; Whipple, 19 87; Kocher and Hoffman, 1991), and recently to ecological risks (Suter et al., 1995) The categorization has been used to create a common scale for balancing health and ecological risks... of risk to most population- or community-level assessment endpoints Thus, toxicity tests may be thought of as measures of the effectiveness of a remedial technology as well as evidence for new risks (The assessment of efficacy following the implementation of remedial actions is described in Section 10.2.4.) Surveys of biota cannot be performed at the site of concern in a prospective risk assessment for. .. resulted in nine possible ecological risk categories in the case of East Fork Poplar Creek (Table 9.4) Only two health risk categories were possible; risks to human health from remediation were deemed to be negligible, and no intermediate health risk category was © 2000 by CRC Press LLC TABLE 9.4 Human Health and Ecological Risk Integration Ecological Risk Baseline Contaminant Risk de minimis Intermediate... populations that is equivalent to the loss of 5 ha of bottomland hardwood forest, much less to determine the level of either ecological risk that is equivalent to a 1 0-6 human cancer risk Moreover, the greater conservatism in health risk assessments compared with typical ecological risk assessments makes the comparison difficult 9.2.2 LAND-USE CONFLICTS Issues of current and future land use are also relevant... estimated As discussed in Chapter 2, these units should be defined on the basis of physical, ecological, or land-use discontinuities 9.2.3.4 Risk Balancing Based on a Common Scale Three categories of risks ecological risks from exposure to contaminants, ecological damage from remediation, and human health risks—must be factors in the final remedial decision The combinations of these sets of risk categories resulted... BALANCING RISKS In the following sections, an approach for creating a common scale of health and ecological risks and a method for applying the approach to make remedial decisions © 2000 by CRC Press LLC TABLE 9.3 Relationship of Human to Ecological Dominance of Land Uses and Ecological Habitats Relationship of Human to Ecological Dominance Human-dominated land use Intermediate dominance Ecologically... ecological, and remedial ecological risks, the full matrix would be 9 × 9 = 81 combinations Once the matrix of risk categories is defined, the decision about whether or not to choose the remedial action is obvious for most combinations of categories (Table 9.4) For example, if both human health and ecological risks are de minimis, remediation is not necessary if the methods and results of the risk assessment . multiple contami- nated sites require remediation. The process of prioritizing these sites should incor- porate principles of ecological risk assessment. For example, if all sites cannot be remediated. necessary to use an ecological risk assessment framework that has been developed for multiple activities. The standard ecological risk assessment framework was developed for assessments of individual. “Guidelines for Ecological Risk Assessment is broad and includes physical stressors, risks associated with CERCLA remediation are not a focus of the document (EPA, 1998). Nonetheless, the Ecological Risk