4. Adaptive Site Management

A remediation potential assessment can be used to decide whether adaptive site management is recommended due to site challenges identified within the context of the CSM. The adaptive site management approach may be adjusted over the site’s life cycle as new site information and technologies become available. This approach is particularly useful at complex sites where remediation is difficult, the remediation potential is uncertain, and the remediation may require a long time.

4.1 Steps in the Adaptive Site Management Process

The first steps in the adaptive site management process are to identify complexity attributes within the CSM and assess whether adaptive site management is warranted. The next steps are as follows:

1. Refine the conceptual site model.
2. Set or revisit site objectives.
3. Develop interim objectives and adaptive remedial strategy.

These steps are particularly relevant at sites that are selecting an interim or final remedy or revisiting the existing remedial strategy because insufficient progress has been made towards meeting site remediation objectives. These elements can be used iteratively during the adaptive site management process (Figure 1). This process is eventually guided by the long-term management plan, which should be anticipated during remedy selection and implementation.

4.2 Refine the Conceptual Site Model

It is particularly important to revisit and refine the CSM periodically throughout the project life cycle. The CSM should be treated as a dynamic tool and updated as needed (for example, by using data generated during implementation of adaptive site management) to support remedy decisions throughout the adaptive site management process. It is a best practice to update the CSM during long-term management planning, remedy implementation, periodic evaluations of monitoring data and remedy performance data, and remedy optimization. If a remedy is not on track to meet interim objectives despite optimization, the CSM should be refined prior to revisiting the remedy (Figure 1). If additional site characterization is needed to fill data gaps and complete an effective remedy design, an integrated site characterization (ISC) process can improve site characterization and maximize the effectiveness of remediation (ITRC 2015b). Although it was developed for use at sites with DNAPL, the ISC process can be used at other sites as well. The ISC process is shown in Figure 2.

Figure 2. ISC approach (ITRC 2015b).

According to ITRC (2015b):

The ISC supports iterative refinement of the CSM over the project life cycle with information obtained during site investigation, remedy design, and remedy optimization. Similar to the USEPA’s data quality objectives (DQOs), it relies on a systematic, objectives‑based site characterization process that includes defining the uncertainties and CSM deficiencies; determining the data needs and resolution appropriate for site conditions; establishing clear, effective data collection objectives; and designing a data collection and analysis plan.

Through ISC, the most appropriate and up‑to‑date site characterization tools are selected to effectively characterize site geology (for example, stratigraphy), permeability, and contaminant distribution. Once the data are collected, the process includes evaluating and interpreting the data and updating the CSM.

Note that additional site characterization may show that some sites are more complex than initially thought. For example, fractured bedrock poses challenges for mapping groundwater flow paths. More detail on characterization in fractured rock environments is provided in recent ITRC guidance (ITRC 2017a).

When refining the CSM, using GSR approaches (ITRC 2011a) to investigate the site can result in a quantitatively greener project by consuming fewer resources and by producing lower emissions and wastes. GSR can effectively bring stakeholders into the project so that their views and needs are reflected throughout the site remediation process. Investigation phase GSR options can be identified or implemented using a tiered approach ranging from very simple (best management practices) up to very sophisticated analysis (life cycle analysis).

4.3 Set or Revisit Site Objectives

Site objectives must be determined before considering remedial strategies to achieve those site objectives. Site objectives are established based on remediation expectations and requirements for sites in CERCLA, RCRA, and other state and federal programs. Different regulatory programs may have different levels of flexibility in setting and revisiting site-specific objectives. These objectives are usually considered during remedy planning or when remedy performance is not sufficient to achieve site objectives within the expected time frame.

The process of setting objectives is addressed in Integrated DNAPL Site Strategy (IDSS), which uses the term “absolute objectives” instead of site objectives and “functional objectives” instead of interim objectives (ITRC 2011b). Chapter 3, Remediation Objectives, of the IDSS guidance describes a process for establishing absolute (site) objectives and developing functional (interim) objectives to achieve those absolute (site) objectives (ITRC 2011b). The document summarizes these terms as follows (ITRC 2011b):

In this document objectives are defined as either absolute [site] or functional [interim] (NRC 2005, ITRC 2008b). Absolute [site] objectives are based on broad social values, such as protection of public health and the environment. Functional [interim] objectives are the steps or activities that are taken to achieve absolute [site] objectives.

The IDSS guidance also provides references to examples of alternative objectives that can be used in specific instances, such as technical impracticability waivers, ACLs, and plume containment approaches.

Site and interim objectives need not be the same throughout the site. For example, off-site contamination, source areas, and plume areas may each require different objectives, remedial strategies, and remediation time frames.

One challenge at complex sites is how to identify and consistently use various regulatory approaches within their specific regulatory programs. Although some programs (particularly many state petroleum programs) permit flexibility in site objectives to achieve pragmatic results, site objectives other than MCLs are often perceived as less desirable and remain controversial to even discuss with many regulators.

At other sites, regulators have recognized that MCLs for groundwater are not an appropriate target and have approved ACLs or other site objectives for groundwater. For example, the use of non-MCL site objectives at a site with no present or future potable use has the potential benefit of reducing the remedial time frame. State programs may include nonpotable aquifer designations with non-MCL water quality standards or allow use of ICs and a designated point-of-compliance for MCLs (such as at an affected property boundary or at a point of use). CERCLA and RCRA programs have formal regulatory definitions of ACLs and other types of regulatory flexibility in setting site objectives. These regulatory approaches, if appropriate, may establish site objectives that are higher than the MCL, yet protective under the site-specific conditions. In addition, because sites with complex attributes often will not achieve objectives within a reasonable time frame, site-specific interim objectives, as discussed in Section 4.4, must be developed so that remediation management can be implemented to protect human health and the environment over the long term.

The type of remediation program (such as CERCLA, RCRA, or other state regulatory agencies overseeing site remediation) prescribes the approach to defining and meeting site objectives. Although these various programs typically share the same nominal site objectives (protection of human health and the environment, remediation of resources), programmatic differences must be considered when developing specific site objectives. The following sections present elements of the CERCLA program that define remedial action objectives (RAOs) and site objectives, followed by a discussion of differences between the CERCLA approach and approaches for RCRA sites and state remediation programs and an overview of approaches used at other Federal facilities.

Incorporating GSR considerations into the project (ITRC 2011a) provides stakeholders with the opportunity to have their perspectives considered during the process of establishing the overall project’s goals and can help maximize the environmental, social, and economic benefits.
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4.4 Develop Interim Objectives and an Adaptive Remedial Strategy

Developing interim objectives as part of an adaptive site strategy includes selecting the remedial strategy (which may be comprised of multiple phases and technologies), identifying components of each remedial approach, setting interim objectives, and documenting the selected remedial strategy. Interim objectives include short-term or technology-specific interim objectives and metrics to guide progress towards site objectives. These topics are usually considered during remedy planning or when the existing remedial strategy performance is not on track to meet interim objectives despite optimization.

The CSM should be up-to-date prior to establishing interim objectives, because inaccuracies in the CSM can affect technology implementation and performance monitoring. Original objectives may need to be revised based on new information. The concepts of applying interim objectives, optimization activities, and assessing performance relative to expectations are all aspects of adaptive site management (Figure 1) and can be incorporated into potential remedial approaches. Additional resources for decision makers in developing interim objectives as part of potential remedial approaches include USEPA guidance for optimization and phased remediation (USEPA 1990, 1992, 2004c); see also CLU-IN optimization guidance, USEPA guidance for documenting remedy changes (for example, USEPA 1990, 1999a), and the ITRC IDSS guidance (ITRC 2011b).

A comparative evaluation of potential remedial approaches can be conducted using the evaluation criteria that are appropriate for the regulatory agency overseeing site remediation (for example, CERCLA nine criteria, or analogous criteria under RCRA or other state-led programs). For complex sites, this evaluation may incorporate the following considerations:

• how each potential remedial approach addresses site complexity issues
• confidence in each potential remedial approach in terms of implementation and control of exposure during the remediation time frame
• for phased approaches, whether the first phase of the potential remedial approach could hinder use of other approaches later
• whether the potential remedial approach is particularly well suited to later modifications or synergistic with other technologies/approaches
• the type of information that could be gained by implementing the potential remedial approach and whether that information could be used to improve the CSM and better inform future remediation decision-making
• the ability to adjust and optimize the remedial approach based on performance data
• the robustness of remedial strategy design such as clear definitions of interim objectives, performance metrics, and ability to collect data that can be used to monitor performance
• whether any predictive analysis of remedy performance is needed to support the selection of the remedial approach or provide a baseline for evaluating performance after implementation (see tools in Appendix B).

The comparative evaluation of potential remediation strategies typically uses some form of weighting that creates a combined evaluation for each potential remedial approach based on how well the potential remedial approach meets the individual evaluation criteria. Following this comparative evaluation and discussion of considerations outlined in pertinent regulatory guidance, one of the potential remedial approaches is typically recommended and selected for implementation. Recommended strategies are subject to modifications based on input from the public and regulators following the remedy selection process mandated by the regulatory remediation program.

To determine the most appropriate remediation strategy, the components needed to achieve the strategy must be identified. The term “components” refers to remediation technologies, containment methods, institutional controls, and any other technical or management approaches that can be used in combination at a site in order to address the site objectives.

Potential remedy components are listed in Table 10. Key resources for information about these components include the USEPA CLU-IN website (USEPA 2017b), the Federal Remediation Technology Roundtable (FRTR 2016), the Naval Facilities Engineering Command website (NAVFAC), and the Center for Public Environmental Oversight website (CPEO 2010).

Table 10. Examples of potential remedy components

A complex site may be divided into multiple segments (for instance, source and plume, sands and clays, on-site and off-site contamination) and components of the remedial approach can be identified for each segment. Table 11 provides an example of how options can be identified for each component of the remedial approach and site segment. Table 11 also identifies the potential remedy components for a hypothetical site and illustrates how a similar site-specific table could be used.

Table 11. Potential remedy components identified at a hypothetical site

When compiling candidate remediation approaches, it may be useful to develop a conceptual design for each option to describe how it could be configured and to evaluate the predicted performance and viability as part of an adaptive remedial strategy (see tools in Appendix B). Candidate remedial approaches can be developed using remedy components identified for specific site segment. When assembling remedy components into viable candidate remedial approaches, it may be useful to vet each remedial approach by considering its value in advancing the site towards achieving its objectives and managing contamination during that time.

Viable remedial approaches should include provisions to be managed and adapted over time to meet the remediation challenges posed by site complexities. Interim objectives can then be established associated with remedy management and adaptation. Interim objectives should be selected to guide the specific actions taken to achieve short-term and long-term progress towards the site objectives. Interim objectives are specific, measurable, attainable, relevant, and time-bound (SMART) objectives and are further described in the IDSS guidance (ITRC 2011b). According to ITRC (2011b), “functional objectives (interim objectives) should have relatively short time frames–years to less than one generation– to encourage accountability for specific actions and to make it easier to measure progress towards the objectives.”

As shown in Figure 1, this process of remedy evaluation may be repeated as appropriate as the remedy progresses, until long-term site objectives are reached. Note that optimization is not typically the focus of adaptive site management, but is often appropriate as part of the adaptive site management process.

4.5 Document Interim Objectives and the Remedial Approach

The selected remedial approach is documented by describing each component of the remedial approach, articulating how the components of the remedial approach work together, setting interim objectives associated with each component of the remedial approach, and listing performance metrics that can guide evaluations of remediation progress. Documentation should clearly state how the performance of each component will be evaluated to meet interim objectives (see tools in Appendix B). This type of documentation describing how the remedial approach will be implemented can facilitate the transition to remedy design, implementation, and long-term management. Documentation is subject to the requirements of the site’s regulatory program.

When documenting the interim objectives and remedial approach, consider ways to incorporate flexibility into the remedial system design to provide opportunities to optimize or enhance the system performance without special approval for significant system modifications. For example, flexibility to redirect or adjust extraction and injection rates at various monitoring wells can maintain an effective dynamic groundwater recirculation program.

The remedial approach may include adaptive design elements. For example, a remedial strategy may plan to use multiple technologies in combination or sequentially, guided by technology performance. If the remedial strategy incorporates multiple technologies, documentation can also include a site-specific process and metrics to evaluate when and how to transition from one technology to the next. For example, CERCLA decision documents can specify a contingency remedy as part of the final remedy with guidelines or criteria on when the contingency remedy would be considered for implementation. More detail on establishing performance metrics and evaluating performance is provided in this guidance, along with details on strategy adaptation guided by performance.

4.5.1 Transition Assessment

When remediation strategies include a transition from one technology to another, NRC guidance NRC (2013) may offer potentially useful concepts regarding remedy transition and documentation of decisions. The NRC document describes the concept of a transition assessment, which NRC developed after it concluded that the decision-making process of existing remediation programs should more fully reflect the fact that drinking water standards will not be attained for decades at most complex sites. NRC’s alternative decision-making approach includes the explicit charting of risk reduction over time. A transition assessment would be considered at sites where the effectiveness of remediation reaches a point of diminishing returns (evaluated on a basis of future risk reduction) prior to reaching site objectives, and optimization has been exhausted. In particular, NRC proposed that a key trigger for a transition assessment would be asymptotic behavior of plume conditions or remedy performance. USEPA guidance on optimization and phased remediation (USEPA 1990, 1992, 2004c); see also CLU-IN optimization guidance) and documenting remedy changes (for example, USEPA 1990, 1999a) should also be considered, although USEPA does not use the term “transition assessment.”

Upon reaching asymptotic performance, NRC (2013) suggests that transition to MNA or some other management approach be considered using this transition assessment. The transition assessment is similar to a focused feasibility study (FFS) and considers alternatives for site management—choosing a new remedy or transitioning to long-term management or other alternative site objectives (Deeb et al. 2011). The transition assessment concept is consistent with the adaptive site management concept developed in “Environmental Cleanup at Navy Facilities: Adaptive Site Management” (NRC 2003), but focuses specifically on complex sites where long-term management will be a likely component of any remedy completion strategy.

The NRC 2013 report did not present a specific process for conducting a transition assessment. Based on the supporting discussion in the NRC report, a transition assessment should include an assessment of site complexities and the limitations they impose on remediation, such as asymptotic plume behavior. Then, the transition assessment would identify and evaluate options for remediation strategies to make progress toward site objectives, recognizing that a long remediation time frame will be required. Strategies would be expected to include the following:

• control of contaminant exposure pathways during the remediation process
• mitigation of plume or source expansion, especially to maintain contamination within an area where institutional or engineering controls to limit exposure can be applied during remediation
• an appropriate approach to contaminant reduction, realizing that contaminant reduction may be difficult or require a long time
• an implementation approach using adaptive site management to address the uncertainties inherent in the site complexities that lead to remediation difficulties

NRC’s transition assessment is relevant to complex sites because these sites may not achieve site objectives in a reasonable time frame, and remedial efforts may eventually reach the asymptotic performance considered by the NRC as indicating a need for a transition assessment. While not specifically mentioned by NRC, monitoring after a remedy is turned off can detect aquifer rebound dynamics and clarify fate and transport mechanisms that can improve the CSM and subsequent remedies.

4.5.2 Maintaining Protectiveness and Preventing Exposure over Long Time Frames (ICs and LUCs)

Documentation of interim objectives and the remedial approach should describe how protectiveness of human health and environment will be maintained. This element of a remedy is common to CERCLA, RCRA, and other state and federal regulatory remediation programs. This protection is especially important at complex sites, where long time frames are required for remediation. Including protective elements such as ICs and LUCs as part of the remedy approach and these elements should be integrated into a long-term management approach.

State survey results highlighted that ICs and LUCs are commonly accepted components of remedial strategies to prevent exposure until groundwater standards are met. Examples of ICs and LUCs include deed restrictions (with landowner concurrence), fish advisories, and fencing. However, ICs and LUCs are rarely approved as stand-alone remediation strategies and are not a driver for changing site objectives or a substitute for remediation. Maintaining and monitoring ICs and LUCs over long time frames are addressed when planning for long-term management of a complex site.

In Long Term Contaminant Management Using Institutional Controls (ITRC 2016b), ITRC has identified critical elements of an effective ICs management program based on successes from established state and federal agency programs, along with other available innovative tools. In developing this guidance, ITRC surveyed state programs and determined what kinds of IC programs are in place across the country, what makes these programs effective, and what common issues affect the durability of ICs. This information can assist decision makers with developing, improving, and stewarding ICs over long time frames. In order to best apply ICs, ITRC also developed a tool to help create a long-term ICs stewardship plan tailored to a specific site (ITRC 2016b). This guidance is relevant to state, federal, and tribal agencies, municipal and local government, private and public/governmental responsible or obligated parties (OPs), current site owners and operator, environmental consultants, and prospective purchasers of property and real estate agents. Additionally, stakeholders who have an interest in a property will find this guidance helpful in understanding the elements required to manage ICs throughout the life cycle (ITRC 2016b).

Because the IC guidance focuses on long-term management of ICs that are already in place, it does not address the details of selecting ICs. Properly selecting and implementing ICs, however, is essential for the long-term durability and effectiveness of a remedy. The guidance summarizes some of the key components that should be considered when choosing ICs, including decision-making aspects of IC implementation and planning that can affect the long-term durability of an IC, with links to additional guidance on IC selection.

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