A Clear Need for Guidance
One representative for a site owner summarized the difficulties with complex sites as follows:
“. . . It is a major frustration that various alternative endpoints and adaptive management strategies are permitted by regulations but are seldom practiced. The lack of detailed guidance and clear precedent leads to indecisiveness and continuing with the status quo.”
A state regulator noted the need for a cooperative approach:
“Complex sites that are transferred under Long Term Response Actions place substantial strain on states’ financial resources. States and USEPA should work together to fully understand site challenges when evaluating and selecting a remedy and creating and aligning remediation objectives that are protective and can be met in mutually agreed upon time frames that are respectful of states’ resource limitations.”
It is difficult to achieve remediation objectives at some contaminated sites because of complex, site-specific conditions. Remedial success at these complex sites may ultimately depend on integrating multiple remediation and risk management approaches and on long-term management. This section describes the need for additional guidance for remediation management of complex sites, what makes a site complex, and the significance of complex sites. Because remedial success partly depends on remediation objectives and the acceptable time frame for achieving them, this section provides a brief background on site objectives and interpretations of reasonable time frames for achieving them. Adaptive site management is a comprehensive process for managing remediation at complex sites and is presented as a framework for decision making.
Despite previous relevant guidance on aspects of remediation at complex sites, no comprehensive guidance document describes the elements, tools, and options for successful remediation at complex sites.
This guidance presents a process for managing remediation at complex sites and describes each step of the adaptive site management process. This guidance does not offer short cuts or the means to avoid site remediation, but rather describes how complex sites can be managed effectively to ensure protection of human health and the environment and progress towards site objectives. Effective management can streamline decision making, decrease remediation costs, and potentially reduce remediation time frames.
Ultimately, this guidance describes adaptive management principles that can lead to better decision making and remediation management at complex sites. ITRC guidance is intended to benefit a variety of site decision makers, including regulators, responsible parties and their consultants, and public and tribal stakeholders.
1.1 What is a Complex Site?
Terms and definitions vary among different environmental remediation programs. To avoid confusion, this guidance consistently uses a narrow set of terms defined in the Glossary. When possible, this guidance uses common terms that are not associated with a narrow, legal or policy definition. Acronyms are defined in Appendix E.
For the purposes of this guidance, ITRC defines a complex site as a “site where remedial approaches are not anticipated to bring the site to closure or facilitate transitioning to sustainable long-term management within a reasonable time frame”. Complex sites typically have multiple attributes that present remediation challenges and therefore take much longer to reach site objectives compared with typical sites. ITRC uses the term “complex site” because this guidance focuses on the technical challenges and additional nontechnical factors, similar to the focus of the National Research Council (NRC 2013).
1.2 Significance of Complex Sites
A site with substantial technical and nontechnical challenges typically has a longer remediation time frame, higher remediation cost, and larger environmental footprint (such as energy use or carbon emissions), particularly if site challenges are not adequately understood and addressed early on. Conversely, complex sites have a greater potential for cost savings, environmental footprint reductions, beneficial land reuse, and other societal benefits.
1.3 Site Objectives and Interim Objectives
Remediation at complex sites is guided by the site objectives. This guidance uses the term “site objectives” to describe the overall expectations for site remediation. Site objectives are typically established based on regulatory requirements, regardless of the technical ability to meet them. Examples include applicable or relevant and appropriate requirements (ARARs), other federal and state standards, and target risk levels that are protective of human health and the environment. Factors that are considered in establishing site objectives at Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) sites are outlined in 40 CFR 300.430(e)(2)(i). These factors include meeting identified ARARs or justifying a waiver of specific ARARs, while still reducing risks to human health and environment and returning the site to beneficial use (ITRC 2012).
Site objectives are the overall expectations for a site, which include protecting public health and the environment. If site objectives are not achievable within a time frame that is agreed upon as reasonable, then revisit the site objectives may be necessary.
Interim objectives are intermediary goals that guide progress towards achieving site objectives.
At complex sites where regulators agree it is impracticable to achieve default expectations (such as drinking water standards), regulators may require alternative site objectives, such as restoring affected media to beneficial use while protecting human health and the environment. At complex sites where it is not technically or economically practicable to restore affected media to beneficial uses, regulators may establish site objectives for source removal, containment, and exposure prevention. At these complex sites, community engagement will likely be an ongoing component of the remedy. When establishing site objectives, a thorough conceptual site model (CSM) can best represent site complexities, define remediation potential based on site complexities, and may inform the identification of ARARs or the development of site-specific target risk levels and exposure pathways of potential concern.
The term “interim objectives” is used in this guidance to describe intermediary goals that guide progress towards achieving site objectives. Interim objectives are sometimes termed “functional objectives” (ITRC 2011b). They may reflect technology-specific goals and nearer-term remediation goals. Setting interim objectives and associated performance metrics helps to keep the remedy on track to ultimately achieve site objectives. Interim objectives can be developed in parallel with remedial alternatives for each affected media or site area.
Example: Site and Interim Objectives
Scenario: Chlorinated solvents are present in a residential water supply well in a fractured bedrock aquifer.
Complexities: Fracture-controlled aqueous phase solvent distribution, propensity for solvent components to diffuse into and out of the aquifer matrix, and solvent degradation to vinyl chloride
Possible site objectives:
- Contain impaired groundwater within well head buffer area.
- Achieve drinking water criteria outside well head buffer area.
Possible interim objectives:
- Achieve hydraulic control in fractured bedrock aquifer within six months to isolate impaired groundwater from the well intake.
- Achieve hydraulic source control within one year.
- Reduce mass flux off site by 50% within five years so that hydraulic control at the well is no longer needed.
- Begin groundwater restoration at the source area within three years, and continue O&M until asymptotic performance is reached
- Execute on site groundwater use prohibition within one year, and continue long-term management until off site groundwater meets drinking water criteria under natural flow conditions.
1.4 Remediation and a Reasonable Remediation Time Frame
State and federal regulations often require remediation within a reasonable time frame. For example, USEPA expects to return usable ground waters “…to their beneficial uses wherever practicable, within a time frame that is reasonable given the particular circumstances of the site”; see 40 CFR 300.430(1)(a)(iii)(F). USEPA does not, however, offer a specific numerical criterion for a reasonable time frame for remediation within its guidance or regulations.
Determining a reasonable time frame for achieving and maintaining site objectives is a complex and site-specific decision. A generic period applied to all sites and facilities is not appropriate (ITRC 2010a). There are typically multiple remedy components at complex groundwater sites (see Table 10); each component may require many years to achieve interim objectives. For example, when monitored natural attenuation (MNA) is a remedy component, its implementation will run “for some time agreed upon by site owners, regulators, and stakeholders” (ITRC 2010a).
1.5 What is Adaptive Site Management?
The term “adaptive site management” refers to a comprehensive, flexible, and iterative process that can be used to manage the remediation process. NRC (2003) coined the term “adaptive site management” referring to “a comprehensive and flexible approach… for dealing with difficult-to-remediate hazardous waste sites over the long term” or where “…current technologies have proved to be ineffective in reaching site objectives for many types of contamination.” Adaptive site management can be used to make decisions in response to remedy performance, while considering changes in site conditions, the CSM, technology performance, and technological advances over time.
Figure 1 shows how adaptive site management can be applied to the remediation of complex sites. ITRC’s definition of “adaptive site management” consists of the following steps, repeated as needed:
- Identify site challenges within the context of the CSM.
- Conduct a remediation potential assessment to decide if adaptive site management is warranted due to site challenges.
- Refine CSM.
- Set or revisit site objectives.
- Develop interim objectives and adaptive remedial strategy.
- Develop a long-term management plan.
- Design and implement remedy.
- Monitor and evaluate performance.
- Apply decision criteria to adjust, optimize, or reevaluate the remedy.
Figure 1. Framework for remediation of complex sites.
1.6 Notable Previous Guidance for Complex Sites
Although comprehensive guidance for complex sites is lacking, USEPA, DOD, and ITRC have published some prior guidance for these sites. Specifically, USEPA has published two documents to address management of sites that have contaminated groundwater, which often is present at challenging sites:
- Groundwater Road Map – Recommended Process for Restoring Contaminated Groundwater at Superfund Sites (USEPA 2011c). This guidance “summarizes the steps and decisions related to selecting a groundwater remedy; designing, constructing, and initiating the remedy; operating, monitoring, evolution, and optimizing the remedy; modifying the remedy, as appropriate; and documenting completion of the site response action.”
- Groundwater Remedy Completion Strategy: Moving Forward with the End in Mind (USEPA 2014b). The purpose of this guidance is to “… help focus resources on the information and decisions needed to effectively complete groundwater remedies and to ensure that these remedies protect human health and the environment.” This guidance also provides a technical and scientific process for evaluating whether sufficient data have been obtained to assess the likelihood that a groundwater remedy has or will achieve the site objectives in a reasonable time frame.
Additionally, DOD recognized the problem of complex sites many years ago and issued relevant guidance (United States Army 2002). In a more recent publication, the NRC described “transition assessments” as an approach to manage remediation decision making at complex sites that already have a remedy in place, but have reached asymptotic performance (NRC 2013).
The following ITRC guidance describes topics and tools that are relevant to site complexities, technologies for adaptive site management, and streamlining remediation management:
- A Decision Framework for Applying Monitored Natural Attenuation Processes to Metals and Radionuclides in Groundwater (ITRC 2010a)
- Characterization and Remediation of Fractured Bedrock Guidance (ITRC 2017a)
- EMD – New Site Characterization and Remediation Enhancement Tools (ITRC 2013b)
- Enhanced Attenuation: Chlorinated Organics (ITRC 2008a)
- Evaluating LNAPL Remedial Technologies for Achieving Project Goals (ITRC 2009a)
- Evaluating Natural Source Zone Depletion at Sites with LNAPL (ITRC 2009b)
- Geospatial Analysis for Optimization at Environmental Sites (ITRC 2016a)
- Green and Sustainable Remediation: A Practical Framework (ITRC 2011a)
- Groundwater Statistics and Monitoring Compliance (ITRC 2013c)
- Improving Environmental Site Remediation Through Performance-Based Environmental Management (ITRC 2007a)
- In Situ Bioremediation of Chlorinated Ethene: DNAPL Source Zones (ITRC 2008b)
- Integrated DNAPL Site Characterization and Tools Selection (ITRC 2015b)
- Integrated DNAPL Site Strategy (ITRC 2011b)
- Long Term Contaminant Management Using Institutional Controls (ITRC 2016b)
- Permeable Reactive Barrier: Technology Update (ITRC 2011c)
- Planning and Promoting Ecological Land Reuse of Remediated Sites (ITRC 2006b)
- Property Revitalization – Lessons Learned from BRAC and Brownfields (ITRC 2006c)
- Use and Measurement of Mass Flux and Mass Discharge (ITRC 2010b)
- Using Remediation Risk Management to Address Groundwater Cleanup Challenges at Complex Sites (ITRC 2012)