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Usually, governmental controls (e.g., bans on harvesting fish or shellfish) are implemented and enforced by the state or local government. Proprietary controls (often referred to as “deed restrictions”), such as easements or covenants, typically involve legal instruments placed in the chain of title of the site or property. Where enforcement tools are used to implement ICs, they may include provisions of CERCLA Unilateral Administrative Orders (UAOs), Administrative Orders on Consent (AOCs), or Consent Decrees (CD). Information devices are designed to provide information or notification to the public. The three most common types of ICs at sediment sites include fish consumption advisories and commercial fishing bans, waterway use restrictions, and land use restriction/structure maintenance agreements. Each of these ICs is discussed in more detail below.
Fish Consumption Advisories and Fishing Bans
Fish consumption advisories are informational devices that are frequently already in place and incorporated into sediment site remedies. Commercial fishing bans are government controls that ban commercial fishing for specific species or sizes of fish or shellfish. Usually, state departments of health are the governmental entities that establishes these advisories and bans. Frequently, fish consumption advisories and fishing bans are in place before a site is listed on the NPL, but if not, it could be necessary for the state to issue or revise them in conjunction with an early or interim action, or the final remedial action. An advisory usually consists of informing the public that they should not consume fish from an area, or consume no more than a specified number of fish meals over a specific period of time from a particular area. Sensitive sub-populations or subsistence fishers may be subject to more stringent advisories. Advisories can be publicized through signs at popular fishing locations, pamphlets, or other educational outreach materials and programs. Information should be provided in appropriate languages to meet the needs of the impacted communities. However, project managers should be aware that consumption advisories are not enforceable controls and their effectiveness can be extremely variable.
This is discussed further in Chapter 7, Remedy Selection Considerations.
Waterway Use Restrictions For any alternative where subsurface contamination remains in place (e.g., capping, MNR, or an in-water confined disposal site), waterway use restrictions may be necessary to ensure the integrity of the alternative. Examples include restricting boat traffic in an area to establish a no-wake zone, or prohibiting anchoring of vessels. In considering boating restrictions, it is important to determine who can enforce the restrictions, and under what authority and how effective such enforcement has been in the past. In addition, a restriction on easements for installing utilities, such as fiber optic cables, can be an important mechanism to help ensure the overall protectiveness of a remedy. It may also be necessary to evaluate remedial alternatives that involve changing the navigation status of a waterway. For a federally authorized navigation channel, deauthorization or reauthorization of the channel to a different width and/or depth configuration would be required and should be fully investigated before selecting the remedy. The state may also have additional authority to change harbor lines or the navigation status of a waterway.
Federal deauthorization can be a lengthy process that requires a formal request to the USACE, an opportunity for users of the waterway to comment, and, ultimately, deauthorization by Congress. By comparison, for those waterways or portions of waterways the USACE has placed in “caretaker” status (i.e., not actively maintained), channel reauthorization to widths and depths consistent with local requirements (e.g., to support continued recreational use) can be completed relatively quickly. Proposed channel modifications/reauthorizations are typically processed by congressional conferees and may be incorporated into the Water Resources Development Act (WRDA) or other equivalent legislative vehicles.
In designing caps to be placed within federal navigational channels, horizontal and vertical offsets, developed by the USACE based on considerations of normal dredging accuracy and overdepth allowances, can provide a factor of safety to protect the surface of the cap from potential damage during potential future maintenance dredging activities.
Land Use Restrictions and Structure Maintenance Agreements
Where contamination remains in place, it may be necessary for the project manager to work with private parties, state land management agencies, or local governments to implement use restrictions on nearshore areas and adjacent upland properties. For example, construction of boat ramps, retaining walls, or marina development can expose subsurface contamination and compromise the long-term effectiveness of a remedy. Where contaminated sediment exceeding cleanup levels is identified in proximity to utility crossings or other infrastructure and temporary or permanent relocation of utilities in support of a dredging remedy may not be feasible or practical, capping may be desirable even though temporary cap disruption may be necessary periodically.
Ownership of aquatic lands varies by state and locality. In many cases, nearshore areas can be privately owned out to the end of piers. For private property owners, more traditional ICs, such as proprietary controls or enforcement tools with IC components, can be considered. Potentially, some of these restrictions can be implemented through agencies who permit construction activities in the aquatic environment. Several federal, state, and local laws place restrictions on and may require permits or substantive requirements documents to be obtained for dredging, filling, or other construction activities in the aquatic environment. These include Section 404 of the Clean Water Act, Title 33 United States Code 3-24 Chapter 3: Feasibility Study Considerations (U.S.C.) Section 1344, and Sections 9 and 10 of the Rivers and Harbors Act of 1899, 33 U.S.C. 401 and
403. It may also be possible to implement some ICs through coordination with existing permitting processes. Harbor Master Plans, state-designated port areas, and local authorities may also function to restrict certain uses. In addition, long-term maintenance of structures such as dams or breakwaters may be a necessary component of some sediment remedies. Where this is the case, it is important that project managers clarify how this maintenance is part of the remedy and who is responsible for the remedy.
Where maintenance decisions may change through time, contingencies may be needed for additional actions.
Highlight 3-4 summarizes some important points to remember about feasibility studies at sediment sites.
Highlight 3-4: Some Key Points to Remember about Feasibility Studies for Sediment C Generally, project managers should implement and then evaluate the effectiveness of major source control actions before finalizing the evaluation of alternatives for sediment C Generally, project managers should evaluate each of the three major approaches: MNR, in-situ capping, and removal through dredging or excavation, at every sediment site C At sites with multiple water bodies or sections of water bodies with different characteristics or uses, alternatives that combine a variety of remedial approaches are frequently the most promising C MNR, in-situ capping, and sediment removal may each be capable of achieving acceptable levels of longterm effectiveness and permanence; site-specific site characteristics should be reviewed to ensure that the selected alternative will be effective at a particular site C Accurate cost estimates, including long-term O&M costs and, where appropriate, materials handling, transport, and disposal costs, are very important to a good comparison of alternatives; a Actual costs from pilot projects at a site and at similar, completed sediment sites are among the best cost resources C Institutional controls can be used at all stages of the remedial process to reduce exposure to contamination; project managers should consider the effectiveness and enforce ability of controls used at the site and evaluate their role in risk reduction
Monitored natural recovery (MNR) is a remedy for contaminated sediment that typically uses ongoing, naturally occurring processes to contain, destroy, or reduce the bioavailability or toxicity of contaminants in sediment. Not all natural processes result in risk reduction; some may increase or shift risk to other locations or receptors. Therefore, to implement MNR successfully as a remedial option, project managers should identify and evaluate those processes that contribute to risk reduction. MNR usually involves acquisition of information over time to confirm that these risk-reduction processes are occurring. Project managers should also be aware of the potential for combining natural recovery with engineering approaches, for example by installing flow control structures to encourage deposition or by the placement of a thin layer of additional clean sediment or additives to enhance sorption or chemical transformation. These combined approaches are discussed further in Section 4.5, Enhanced Natural Recovery.
MNR may rely on a wide range of naturally occurring processes to reduce risk to human and/or ecological receptors. These processes may include physical, biological, and chemical mechanisms that act together to reduce the risk posed by the contaminants. Depending on the contaminants and the environment, this risk reduction may occur in a number of different ways. Highlight 4-1 lists the most common risk reduction processes. Natural processes that reduce toxicity through transformation or reduce bioavailability through increased sorption are usually preferable as a basis for remedy selection to mechanisms that reduce exposure through natural burial or mixing-in-place because the destructive/sorptive mechanisms generally have a higher degree of permanence. However, many contaminants that remain in sediment are not easily transformed or destroyed. For this reason, risk reduction due to natural burial through sedimentation is more common and can be an acceptable sediment management option. Dispersion is the least preferable basis for remedy selection based on MNR. While dispersion may reduce risk in the source area, it generally increases exposure to contaminants and may result in unacceptable risks to downstream areas or other receiving water bodies. As reiterated in Chapter 7, Remedy Selection Considerations, project managers should carefully evaluate the effects of this increased exposure and risk to receiving water bodies before selecting MNR where dispersion is one of the risk reduction mechanisms, to ensure that it is not simply transferring risk to a new area. Project managers should be aware that at most sites, a variety of natural processes are occurring that may reduce risk.
As used in this guidance, MNR is similar in some ways to the Monitored Natural Attenuation (MNA) remedy used for ground water and soils [U.S. Environmental Protection Agency (U.S. EPA 1999d)]. The key difference between MNA for ground water and MNR for sediment is in the type of processes most often being relied upon to reduce risk. Transformation of contaminants is usually the major attenuating process for contaminated ground water, these processes are frequently too slow for the persistent contaminants of concern (COCs) in sediment to provide for remediation in a reasonable time frame. Therefore, isolation and mixing of contaminants through natural sedimentation is the process most frequently relied upon for contaminated sediment.
4-1 Chapter 4: Monitored Natural Recovery Highlight 4-1: General Hierarchy of Natural Recovery Processes for Sediment Sites Many different natural processes may reduce risk from contaminated sediment, including the following, listed from
generally most to least preferable, though all potentially acceptable, as a basis for selecting MNR:
C Exposure levels are reduced by a decrease in contaminant concentration levels in the nearsurface sediment zone through burial or mixing-in-place with cleaner sediment
• A predictive tool (generally based either on computer modeling or extrapolation of empirical data) to predict future effects of those processes;
• A means to control any significant ongoing contaminant sources;
• The ability to monitor the natural processes and/or concentrations of contaminants in sediment or biota to see if recovery is occurring at the expected rate.
Some consider that all sediment site remedies are using natural recovery to some extent because natural processes are ongoing whether or not an active cleanup is underway [e.g., National Research Council (NRC) 2001]. It is true that natural processes in most cases will continue whether or not an active cleanup is underway, but these processes may either reduce, transfer, or increase risk. Natural processes may reduce residual risk following dredging or in-situ capping at many sites, and it can be very valuable to monitor further risk reduction. However, it is also important for project managers to distinguish whether they are relying upon natural processes to reduce risk to an acceptable level (i.e., using MNR as a remedy), or simply noting the fact that natural processes are ongoing at a site and are expected to continue to reduce residual risks. Therefore, the key factors that normally distinguish MNR as a remedy are the presence of unacceptable risk, the ongoing burial or degradation/transformation, or dispersion of the contaminant, and the establishment of a cleanup level that MNR is expected to meet within a particular time frame.
4-2 Chapter 4: Monitored Natural Recovery MNR has been selected as a component of the remedy for contaminated sediment at approximately one dozen Superfund sites so far. Historically, at many sites MNR has been combined with dredging or in-situ capping of other areas of a site. Although natural recovery following effective source control has been observed (e.g., decreases in sediment contaminant levels, sediment toxicity, and shellfish tissue contaminant levels), long-term monitoring data on fish tissue are not yet available at most sites to document continued risk reduction (see e.g., Magar et al. 2003). However, monitoring results documented at some sites are promising (e.g., Patmont et al. 2003, U.S. EPA 2001g, U.S. EPA 2001h, Swindoll et al. 2000). When hazardous substances left in place are above levels that allow for unlimited use and unrestricted exposure, a five-year review pursuant to Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) §121(c) may be required (U.S. EPA 2001i).
Although each of the three potential remedy approaches (MNR, in-situ capping, and removal) should be considered at every site at which they might be appropriate, MNR should receive detailed consideration where the site conditions listed in Highlight 4-2 are present.
Highlight 4-2: Some Site Conditions Especially Conducive to Monitored Natural Recovery • Anticipated land uses or new structures are not incompatible with natural recovery • Natural recovery processes have a reasonable degree of certainty to continue at rates that will contain, destroy, or reduce the bioavailability or toxicity of contaminants within an acceptable time frame • Expected human exposure is low and/or can be reasonably controlled by institutional controls • Sediment bed is reasonably stable and likely to remain so • Sediment is resistant to resuspension (e.g., cohesive or well-armored sediment) • Contaminant concentrations in biota and in the biologically active zone of sediment are moving towards risk-based goals on their own • Contaminants already readily biodegrade or transform to lower toxicity forms • Contaminant concentrations are low and cover diffuse areas • Contaminants have low ability to bioaccumulate