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Consistent with CERCLA and the NCP, each remedial action selected should be cost-effective.
The NCP provides several threshold criteria that should be satisfied (40 CFR §300.430(f)(ii)(D)). Costeffectiveness is generally determined by evaluating three of the five balancing criteria: 1) long-term effectiveness and permanence; 2) reduction of toxicity, mobility, or volume of hazardous substances through treatment; and 3) short-term effectiveness. A remedy typically is considered cost effective when its cost is proportional to its overall effectiveness. As described in the preamble to the NCP, more than one alternative may be considered cost-effective (55 Federal Register (FR) 8728, March 8, 1990). The relationship between overall effectiveness and cost should be examined across all alternatives to identify which options can best afford effectiveness proportional to their cost. The evaluation of an alternative’s cost effectiveness is usually concerned with the reasonableness of the relationship between the effectiveness afforded by each alternative and its costs when compared to other available options (U.S.
For some complex sediment sites, there may be a high degree of uncertainty about the predicted effectiveness of various remedial alternatives. Where this is the case, it is especially important to identify and factor that uncertainty into site decisions. Project managers are encouraged to consider a range of probable effectiveness scenarios that includes both optimistic and non-ideal site conditions and remedy performance.
The NCP lists six “expectations” that EPA generally considers in developing appropriate remedial alternatives at Superfund sites (40 CFR §300.430(a)(1)(iii)). Highlight 7-1 discusses how the six expectations may be relevant for sites with contaminated sediment. Generally, the expectations are addressed by seeking the best balance of trade-offs among the alternatives evaluated.
7.3 CONSIDERING REMEDIES
If the baseline risk assessment determines that contaminated sediment presents an unacceptable risk to human health or the environment, remedial alternatives should be developed to reduce those risks to acceptable levels. As discussed in Chapter 3, Section 3.1, Developing Remedial Alternatives for Sediment, due to the limited number of approaches available for contaminated sediment, generally, project managers should evaluate each of the three major approaches monitored natural recovery (MNR), in-situ capping, and removal through dredging or excavation at every sediment site. Depending on sitespecific conditions, contaminant characteristics, and/or health or environmental risks at issue, certain methods or combinations of methods may prove more promising than others. Each site and the various sediment areas within it presents a unique combination of circumstances that should be considered carefully in selecting a comprehensive site-wide cleanup strategy. At large or complex sediment sites, the remedy decision frequently involves choices between areas of the site and how they are best suited to particular cleanup methods rather than a simple one-size-fits-all choice between approaches for the entire site.
Project managers should keep in mind that deeper contaminated sediment that is not currently bioavailable or bioaccessible, and that analyses have shown to be stable to a reasonable degree, do not necessarily contribute to site risks. In evaluating whether to leave buried contaminated sediment in place, project managers should include an analysis of several factors, including the depth to which significant 7-3 Chapter 7: Remedy Selection Considerations Highlight 7-1: NCP Remedy Expectations and Their Potential Application to Contaminated Sediment
EPA expects to use treatment to address the principal threats posed by a site, wherever practicable:
• In general, wastes, including contaminated sediment, may be considered a principal threat where toxicity and mobility combine to pose a potential human health risk of 10-3 or greater for carcinogens (U.S. EPA 1991d). For these areas, project managers should evaluate an alternative that includes treatment.
However, the practicability of treatment, and whether a treatment alternative should be selected, should be evaluated against the NCP’s nine remedy selection criteria. Based on available technology, treatment is not considered practicable at most sediment sites • Containment options for sediment generally focus on in-situ capping. A project manager should evaluate in-situ capping for every sediment site that includes low-level threat waste. Where a containment alternative is clearly not appropriate for a detailed evaluation, project managers should evaluate ex-situ containment (i.e., disposal without treatment). It should be recognized that in-situ containment can also be effective for principal threat wastes, where that approach represents the best balance of the NCP nine remedy selection criteria • Large or complex contaminated sediment sites or operable units frequently require development of alternatives that combine various approaches for different parts of the site. For a broader discussion on this topic, refer to Chapter 3, Section 3.1.1, Alternatives that Combine Approaches • Institutional controls such as fish consumption advisories, fishing bans, ship draft/anchoring/wake controls, or structural maintenance requirements (e.g., dam or breakwater maintenance) are frequently a part of sediment alternatives, especially where contaminated sediment is left in place, or where remedial goals in fish tissue cannot be met for some time. See Chapter 3, Section 3.6, Institutional Controls, for additional discussion EPA expects to consider using innovative technology when such technology offers the potential for comparable or superior treatment performance or implementability, fewer or lesser adverse impacts than other available
approaches, or lower costs for similar levels of performance than demonstrated technologies:
• Innovative technologies are technologies whose limited number of applications may result in less cost and performance data, frequently due to limited field application. Additional cost and performance data may be needed for many sediment remedies, and field demonstrations of new techniques and approaches may be especially needed, including both innovative in-situ and ex-situ technologies. Although most innovations for sediment remedies are currently in the research phase, as they become available, project managers should consider using them EPA expects to return reusable ground waters to their beneficial uses wherever practicable, within a time frame that is reasonable given the circumstances for the site. When restoration of ground water to beneficial uses is not practicable, EPA expects to prevent further migration of the plume, prevent exposure to the contaminated ground
water, and evaluate further risk reduction:
• Ground water may be a continuing source of sediment and surface water contamination. Where this is the case, ground water migration prevention may be very important to a successful sediment cleanup and to protect benthic biota. Ground water restoration may also be needed to return the ground water to a beneficial use 7-4 Chapter 7: Remedy Selection Considerations populations of organisms burrow, the potential for erosion due to natural or anthropogenic (man-made) forces, the potential for contaminant movement via ground water, and the effectiveness of any institutional controls (ICs) to limit sediment disturbance. In some cases, the most appropriate approach may be long-term monitoring, with contingency actions, if necessary.
To assist project managers in evaluating cleanup options, two summary highlights are presented below. Highlight 7-2 provides general site, sediment, and contaminant characteristics or conditions especially conducive to each of the three common sediment approaches. This highlight is intended as a general tool for project managers as they look more closely at particular approaches when most of these characteristics are present. Project managers should note that these characteristics are not requirements.
It is important to remain flexible when evaluating sediment alternatives and when considering approaches that at first may not appear the most appropriate for a given environment. When an approach is selected for a site that has one or more site characteristics or conditions appearing problematic, additional engineering or ICs may be available to enhance the remedy. Some of these situations are discussed in the remedy-specific chapters (Chapters 4, 5, and 6).
Highlight 7-3 may assist project managers in evaluating cleanup options. For convenience, these comparisons are organized around the NCP’s nine remedy selection criteria. This highlight is intended only to identify some of the general differences between these three remedy types, not as an example of an actual comparative alternatives analysis for a site. An actual site alternatives analysis would typically include more complex alternatives and many site-specific details, as described in the ROD Guidance (U.S. EPA 1999a) and EPA’s Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (U.S. EPA 1988a, commonly referred to as the “RI/FS Guidance”). The example criterion components column used in Highlight 7-3 below are adapted from the RI/FS Guidance and are 7-6 Chapter 7: Remedy Selection Considerations intended only as examples of some of the components that may be considered when evaluating each remedy selection criterion.
7.4 COMPARING NET RISK REDUCTIONEach approach to managing contaminated sediment has its own uncertainties and potential relative risks. The concept of comparative net risk reduction was discussed by the NRC as a method to ensure that all positive and negative aspects of each sediment management approach were appropriately considered at contaminated sediment sites. The Committee on Remediation of PCB-Contaminated
Sediments states that (NRC 2001):
All remediation technologies have advantages and disadvantages when applied at a particular site, and it is critical to the risk management that these be identified individually and as completely as possible for each site. For example, managing risks from contaminated sediment in the aqueous environment might result in the creation of additional risks in both aquatic and terrestrial environments... Removal of contaminated materials can adversely impact existing ecosystems and can remobilize contaminants, resulting in additional risks to humans and the environment. Thus, management decisions at a contaminated sediment site should be based on the relative risks of each alternative management action... For a site, it is important to consider “overall” or “net” risk in addition to specific risks.
Project managers are encouraged to use the concept of comparing net risk reduction between alternatives as part of their decision-making process for contaminated sediment sites, within the overall framework of the NCP remedy selection criteria. Consideration should be given not only to risk reduction associated with reduced human and ecological exposure to contaminants, but also to risks 7-13 Chapter 7: Remedy Selection Considerations introduced by implementing the alternatives. The magnitude of implementation risks associated with each alternative generally is extremely site-specific, as is the time frame over which these risks may apply to the site. Evaluation of both implementation risk and residual risk are existing important parts of the NCP remedy selection process. By evaluating these two concepts in tandem, additional information may be gained to help in the remedy selection process. Highlight 7-4 provides examples of elements that could be evaluated by project managers in this comparative evaluation.
Highlight 7-4: Sample Elements for Comparative Evaluation of Net Risk Reduction Elements Potentially Reducing Risk • Reduced exposure to bioavailable/bioaccessible contaminants • Removal of bioavailable/bioaccessible contaminants • Removal or containment of buried contaminants that are likely to become bioaccessible
• Continued exposure to contaminants already at sediment surface and in food chain • Potential for undesirable changes in the site’s natural processes (e.g., lower sedimentation rate) • Potential for contaminant exposure due to erosion or human disturbance
For In-Situ Capping:
• Contaminant releases during capping • Continued exposure to contaminants currently in the food chain • Other community impacts (e.g., accidents, noise, residential or commercial disruption) • Worker risk during transport of cap materials and cap placement • Releases from contaminants remaining outside of capped area • Potential contaminant movement through cap • Disruption of benthic community
For Dredging or Excavation:
• Contaminant releases during sediment removal, transport, or disposal • Continued exposure to contaminants currently in the food chain • Other community impacts (e.g., accidents, noise, residential or commercial disruption) • Worker risk during sediment removal and handling • Residual contamination following sediment removal • Releases from contaminants remaining outside dredged/excavated area • Disruption of benthic community
7.5 CONSIDERING INSTITUTIONAL CONTROLS (ICs)
Institutional controls (ICs) such as fish consumption advisories, fishing bans, or ship draft/anchoring/wake controls are common parts of sediment remedies (see Chapter 3, Section 3.6, Institutional Controls). Structural maintenance agreements are another legal mechanism that may be important for protecting some remedies. 40 CFR §300.430(a)(1)(iii)(D) contains the following general EPA expectations with respect to ICs. These expectations generally apply to all Superfund sites,
including sediment sites:
7-14 Chapter 7: Remedy Selection Considerations
• The use of institutional controls shall not be substituted for active response measures (e.g., treatment and/or containment of source material, restoration of ground waters to their beneficial uses) as the sole remedy unless such active measures are determined not to be practicable, based on the balancing of tradeoffs among alternatives that is conducted during the selection of remedy.
EPA policies concerning ICs are explained in Institutional Controls: A Site Manager’s Guide to Identifying, Evaluating, and Selecting Institutional Controls at Superfund and RCRA Corrective Action Cleanups (U.S. EPA 2000f). In addition to considering the NCP expectations concerning ICs, the project manager should determine what entities possess the legal authority, capability and willingness to implement, and where applicable, monitor, enforce, and report on the status of the IC. An evaluation should also be made of the durability and effectiveness of any proposed IC. The objectives of any ICs contained in the selected alternative should be clearly stated in the ROD or other decision document together with any relevant performance standards. While the specific IC mechanism need not be identified, the types of ICs envisioned should be discussed in sufficient detail to support a conclusion that effective implementation of the ICs can be reasonably expected. For some federal facilities in the CERCLA program, the IC implementation details (i.e., the specific IC mechanism) should be placed in the ROD. The program manager should refer to EPA’s Guidance on the Resolution of the Post-ROD Dispute (U.S. EPA 2003d) for guidelines describing and documenting ICs in Federal Facility RODs, Remedial Designs, Remedial Action Workplans, and Federal Facility Agreements/Interagency Agreements.