5
Protocols for Documenting Natural Attenuation

As interest in using natural attenuation to manage contaminated sites has surged, an increasing number of protocols have been developed to guide evaluations of the potential for natural attenuation to occur. This chapter reviews 14 such protocols, listed in Box 5-1.

For this review, the term “protocol” is defined very broadly to include any policy statement, state regulation, or technical document on how decision making and implementation of natural attenuation should be carried out. As defined here, a protocol is an outline of a strategy and methodology to be followed. It is an assessment and planning tool. A protocol is not necessarily a “how-to” manual, although some existing protocol documents (such as those prepared by the U.S. Air Force) have extensive appendixes that provide considerable information on field sampling techniques, analytical methods, and data interpretation. Standardizing the steps in data gathering, analysis, and decision making—using a process such as that outlined in Chapter 4—is the most important use of protocols.

Based on current activity, protocol documents for natural attenuation will continue to increase in number in the near future. Reviewing all existing protocols would be infeasible because new protocols continue to be promulgated at the rate of several per year. The protocols reviewed in this chapter represent the range of those available, from protocols prepared by federal and state agencies to those developed by private companies and industrial associations.

This chapter first defines a set of attributes that are important ele-



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Natural Attenuation for Groundwater Remediation 5 Protocols for Documenting Natural Attenuation As interest in using natural attenuation to manage contaminated sites has surged, an increasing number of protocols have been developed to guide evaluations of the potential for natural attenuation to occur. This chapter reviews 14 such protocols, listed in Box 5-1. For this review, the term “protocol” is defined very broadly to include any policy statement, state regulation, or technical document on how decision making and implementation of natural attenuation should be carried out. As defined here, a protocol is an outline of a strategy and methodology to be followed. It is an assessment and planning tool. A protocol is not necessarily a “how-to” manual, although some existing protocol documents (such as those prepared by the U.S. Air Force) have extensive appendixes that provide considerable information on field sampling techniques, analytical methods, and data interpretation. Standardizing the steps in data gathering, analysis, and decision making—using a process such as that outlined in Chapter 4—is the most important use of protocols. Based on current activity, protocol documents for natural attenuation will continue to increase in number in the near future. Reviewing all existing protocols would be infeasible because new protocols continue to be promulgated at the rate of several per year. The protocols reviewed in this chapter represent the range of those available, from protocols prepared by federal and state agencies to those developed by private companies and industrial associations. This chapter first defines a set of attributes that are important ele-

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Natural Attenuation for Groundwater Remediation ments of natural attenuation protocols. It then discusses how well the existing protocols conform to these attributes and compares the various protocols and their intended uses. The chapter also discusses decision-making tools used in the protocols. The final sections discuss several critical topics—including monitoring of sites, training of those who implement the protocols, and involvement of the public in decision making—that existing protocols generally do not address adequately. CRITERIA FOR A GOOD PROTOCOL For this review, the Committee on Intrinsic Remediation developed a list of important subject areas and subtopics that natural attenuation protocols should address. This list is the outcome of extended committee deliberations following presentations by developers of natural attenuation protocols, users of the protocols, and local community organizations and environmental advocacy groups. Box 5-2 summarizes the topics, which are discussed briefly in turn below in no implied order of precedence. Community Concerns Community Involvement As described in Chapter 2, early community involvement is especially important in order to gain public acceptance and confidence in decisions regarding natural attenuation. Without adequate community participation, natural attenuation may be viewed as a less aggressive and less costly remediation alternative that offers advantages to responsible parties without fully protecting human health and the environment. Further, natural attenuation decisions may affect community property values. For these reasons, a comprehensive natural attenuation protocol needs to identify critical decision points at which community involvement is necessary. Chapter 2 provides guidance on how community groups can be involved effectively. In some cases, no nearby community per se may exist, so flexibility on this issue is warranted. Institutional Controls Natural attenuation processes may operate for many years, during which time land reuse may have to be restricted. A comprehensive protocol has to describe the criteria for deciding whether institutional controls are necessary and how to ensure the long-term viability of these controls. Natural attenuation may differ little from other long-term remedies in

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Natural Attenuation for Groundwater Remediation BOX 5-1 Natural Attenuation Protocols Reviewed Federal Agencies Environmental Protection Agency “Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites,” Final OSWER Directive (OSWER Directive Number 9200. 4-17P), April 21, 1999, EPA Office of Solid Waste and Emergency Response. “Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water,” Todd H. Wiedemeier, Matthew A. Swanson, David E. Moutoux, E. Kinzie Gordon, John T. Wilson, Barbara H. Wilson, Donald H. Kampbell, Patrick E. Haas, Ross N. Miller, Jerry E. Hansen, and Francis H. Chapelle, EPA/600/R-98/128, September 1998, EPA Office of Research and Development. “Draft Region 4 Suggested Practices for Evaluation of a Site for Natural Attenuation (Biological Degradation) of Chlorinated Solvents,” Version 3.0, November 1997, EPA Region 4. Department of Energy “Site Screening and Technical Guidance for Monitored Natural Attenuation at DOE Sites,” Patrick V. Brady, Brian P. Spalding, Kenneth M. Krupka, Robert D. Waters, Pengchu Zhang, David J. Borns, and Warren D. Brady, Draft, August 30, 1998, Sandia National Laboratory. Air Force “Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination in Groundwater,” Todd Wiedemeier, John T. Wilson, Donald H. Kampbell, Ross N. Miller, and Jerry E. Hanson, Volume I and Volume II, November 11, 1995, Air Force Center for Environmental Excellence, Technology Transfer Division, Brooks AFB. “Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Groundwater,” Todd H. Wiedemeier, Matthew A. Swanson, David E. Moutoux, E. Kinzie Gordon, John T. Wilson, Barbara H. Wilson, Donald H. Kampbell, Jerry E. Hansen, Patrick Haas, and Francis H. Chapelle, Draft—Revision 2, July 1997, Air Force Center for Environmental Excellence, Technology Transfer Division, Brooks Air Force Base, San Antonio, Tex. Navy “Technical Guidelines for Evaluating Monitored Natural Attenuation at Naval and Marine Corps Facilities,” Todd H. Wiedemeier and Francis H. Chapelle, Draft—Revision 2, March 1998.

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Natural Attenuation for Groundwater Remediation State Agencies Minnesota Pollution Control Agency “Draft Guidelines—Natural Attenuation of Chlorinated Solvents in Ground Water,” Working Draft, December 12, 1997, Minnesota Pollution Control Agency, Site Response Section. New Jersey “New Jersey Administrative Code 7:26E—Technical Requirements for Site Remediation, and Classification Exception Areas: Final Guidance 4-17-1995.” Corporations Chevron “Protocol for Monitoring Intrinsic Bioremediation in Groundwater,” Tim Buscheck and Kirk O’Reilly, March 1995, Chevron Research and Technology Company, Health, Environment, and Safety Group. “Protocol for Monitoring Natural Attenuation of Chlorinated Solvents in Groundwater,” Tim Buscheck and Kirk O’Reilly, February 1997, Chevron Research and Technology Company, Health, Environment, and Safety Group,. Professional and Industry Associations American Society for Testing and Materials “Standard Guide for Remediation of Ground Water by Natural Attenuation at Petroleum Release Sites,” Draft, February 4, 1997. American Petroleum Institute “Methods for Measuring Indicators of Intrinsic Bioremediation: Guidance Manual,” American Petroleum Institute, Health and Environmental Sciences Department, Publication Number 4658, November 1997, API Publishing Services, Washington, D.C. Public/Private Consortium Remediation Technologies Development Forum “Natural Attenuation of Chlorinated Solvents in Groundwater: Principles and Practices,” Industrial Members of the Bioremediation of Chlorinated Solvents Consortium of the Remediation Technologies Development Forum, Version 3.0, August 1997.

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Natural Attenuation for Groundwater Remediation BOX 5-2 Attributes for Assessing the Adequacy of Natural Attenuation Protocols Community Concerns Community involvement: The protocol should specify points in the evaluation process where community input is especially important. Effective means to involve community groups are presented in Chapter 2. Institutional controls and long-term monitoring: The protocol should describe criteria for determining when institutional controls are needed and how the viability of these controls can be ensured. Contingency plans: The protocol should address decision making on contingency plans. Criteria for reevaluating the effectiveness of natural attenuation must be defined, along with whether contingency treatment systems should be pre-positioned. Scientific and Technical Issues Establish cause and effect: The protocol should explain the scientific underpinnings and the evidence used to assess the relationship between what is observed and what is expected. Guidelines for establishing cause and effect are provided in Chapter 4. Site condition assessment: The protocol should describe the level of data required to assess different types of sites and characterize different types of contaminant sources. Sustainability: The protocol should address methods for the long-term viability of natural attenuation. Peer review: The protocol should be peer reviewed by individuals representing various disciplines and viewpoints other than those of the organization that wrote it. Implementation Usability and user qualifications: The protocol should provide sufficiently detailed explanations so that users can follow it. The qualifications and training of implementers should be discussed. requiring institutional controls until cleanup standards are achieved. Nevertheless, ensuring the adequacy of institutional controls is especially important for natural attenuation remedies, because this approach lacks continuously operated and supervised cleanup systems. Having clear institutional controls also helps to assure the affected community that natural attenuation is more than a walk-away solution.

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Natural Attenuation for Groundwater Remediation A comprehensive protocol should provide guidance on the long-term viability of institutional controls to prevent exposure to the contamination while natural attenuation takes place. SOURCE: Courtesy of Center for Health, Environment, and Justice. Contingency Plans A comprehensive protocol has to provide guidance on contingency plans in the event that natural attenuation does not perform as predicted. It describes the method for determining whether natural attenuation is adequate or is failing. It provides the decision-making tools necessary for triggering action plans and methods for deciding whether contingencies have to be pre-selected, pre-designed, or pre-positioned for deployment. Scientific and Technical Issues Cause-and-Effect Determination A comprehensive protocol has to explain clearly what scientific evidence is needed to establish that specific natural attenuation processes are responsible for observed decreases in contaminant concentrations. It should describe the class of contaminants it addresses and the general

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Natural Attenuation for Groundwater Remediation hydrogeologic setting in which natural attenuation is applicable for these contaminants. It must provide guidance on the intended use of field data to assess the relationship between what is observed and what is expected and to explain criteria for judging whether such information is adequate for evaluating critical processes. Concepts for establishing cause and effect are most advanced for fuel hydrocarbons and chlorinated solvents; thus, this issue is particularly important for natural attenuation of other classes of contaminants. The protocol’s guidelines for establishing cause and effect should follow the process recommended in Chapter 4. Site Condition Assessment A comprehensive protocol has to provide guidance on how much information is needed to understand important hydrogeologic factors affecting contaminant transport and fate at the site. It should provide criteria for delineating the sources of contamination and deciding whether they have to be removed or contained with physical or hydraulic engineered systems. Sustainability The long-term viability of natural attenuation has to be understood because a considerable period of time may be required to achieve cleanup goals. A comprehensive protocol should provide criteria for assessing the capacity of the natural attenuation processes at work at the site, whether the processes are likely to be constant, and the length of time required to reach cleanup goals. It also has to provide strategies for determining the rates of the processes, whether these are variable over space and time, and whether they are sufficient to prevent migration of contaminants to undesired locations. It must address complicating factors, such as site heterogeneity, that may influence reactions; the potential adverse effects of contaminant mixtures; the possible formation of harmful transformation by-products that may be more mobile or more toxic than the parent compound; variability with climate changes; and the potential adverse effects of other proposed remediation activities (such as source control measures) that may remove or add substances important for specific natural attenuation processes. It would provide guidance on the use of error analysis or confidence assessment for understanding the effects of important hydrogeologic factors and physicochemical and microbial phenomena.

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Natural Attenuation for Groundwater Remediation Peer Review Peer review is important for ensuring scientific credibility and completeness of natural attenuation protocols, and all protocols should be independently peer reviewed prior to publication. Because a successful natural attenuation evaluation embraces various engineering and scientific disciplines, as well as public policy and management, the peer review process likewise has to involve participation from various disciplines. Protocols should explain the peer review process, including discussion of how concerns raised during the review were addressed. As defined here, peer review is not intended to ensure conformance with all applicable regulations. However, it should be conducted by persons not directly affiliated with the organization that developed the protocol. Implementation Issues Usability and User Qualifications A comprehensive protocol has to be easily understood and implemented by individuals responsible for managing operations in the field, as well as by regulators. Detail must be sufficient to allow the protocol to serve as an effective tool for assessing natural attenuation implementation. The comprehensive protocol should describe the qualifications (such as disciplinary expertise, practical field experience, and specific training) needed to carry out the various analyses it recommends. OVERVIEW OF PROTOCOLS The protocols listed in Box 5-1 are at different stages of completeness, ranging from final published documents to drafts that may be revised in the future. Some of these protocols attempt to be comprehensive, with extensive appendixes, whereas others are much briefer, relying on previously published information. Some recent protocols are less voluminous than earlier ones, due in part to reliance on previously published information. For example, the Navy protocol, which combines discussion of hydrocarbon fuels and chlorinated solvents, is much shorter than either of the two Air Force protocols, which preceded the Navy protocol and treated these contaminants separately. In reviewing the documents listed in Box 5-1, the committee considered the following points: background and motivation, intended audience, scope,

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Natural Attenuation for Groundwater Remediation development process, organization and content, and conformance with protocol attributes listed in Box 5-2. The individual protocols are summarized briefly below; then the similarities, differences, and applicability of the different protocols are compared. Federal Agency Protocols Environmental Protection Agency Policy on Monitored Natural Attenuation The EPA document Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites is a revision of a draft published in 1997. The directive is intended to “clarify EPA’s policy regarding the use of monitored natural attenuation for the cleanup of contaminated soil and groundwater in the Superfund, RCRA Corrective Action, and Underground Storage Tank programs.” These programs are administered by the EPA’s Office of Solid Waste and Emergency Response (OSWER). The EPA’s position, as stated in the policy directive, is that monitored natural attenuation, when used as a remediation strategy, must attain remedial objectives within a time frame that is reasonable compared to other, more active methods. The EPA prefers natural attenuation processes that degrade contaminants and expects that monitored natural attenuation will be most appropriate for sites having low potential for plume generation and migration. Nonetheless, the natural attenuation processes recognized in the directive include dispersion, dilution, and volatilization, as well as sorption and chemical or biological stabilization, transformation, or destruction of contaminants. According to the directive, a remedy that includes the introduction of an enhancement of any type is no longer considered natural attenuation. The directive is intended as a policy document and, as such, provides very little technical guidance. The document comments briefly on three contaminant classes—petroleum-related contaminants, chlorinated solvents, and inorganics—but recognizes that natural attenuation processes are best understood for the benzene, toluene, ethylbenzene, and xylene (BTEX) components of petroleum fuels. The directive is intended to promote consistency in the way monitored natural attenuation remedies are proposed, evaluated, and approved, but there is no explanation of the means by which this consistency is ensured. It states several times EPA’s position that complete reliance on monitored natural attenuation is appropriate in only limited circumstances and that EPA expects source control measures almost always to be necessary. It presumes that monitored

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Natural Attenuation for Groundwater Remediation natural attenuation will require more substantiation than other remedies, including more detailed site characterization data and performance monitoring than needed to support active remediation. The EPA directive indicates that three types of characterization data provide evidence of natural attenuation: (1) historical data demonstrating decreasing contaminant mass or concentration, (2) hydrogeologic or geochemical data demonstrating indirectly the attenuation process, and (3) data from field or microcosm studies (conducted in or with actual contaminated media) that show the occurrence of a particular attenuation process. It indicates that the first line of evidence may be adequate if the overseeing regulatory authority determines that these data are of sufficient quality and duration to support a decision to select monitored natural attenuation as the remedy. Otherwise, the second line of evidence should be provided. Where both the first and second lines of evidence are inadequate or inconclusive, the third line of evidence also may be necessary. According to the directive, criteria triggers that signal unacceptable performance include unpredicted increases in contaminant concentrations, indications of new or renewed release, sentry or sentinel wells showing contaminants not decreasing at a sufficiently rapid rate to meet remediation objectives, and changes in land or groundwater use. The directive says that contingency remedies generally should be included as part of a monitored natural attenuation remedy for selections that are based primarily on predictive analyses rather than on documented trends of decreasing contaminant concentrations. The EPA defines contingency as a backup technology or modification of the selected technology to be used if needed. The directive cautions strongly against reliance on non-EPA documents that may provide technical information, despite the fact that it recognizes that little EPA guidance exists “concerning appropriate implementation of monitored natural attenuation remedies.” Non-EPA guidances are not “officially endorsed by EPA, the EPA does not necessarily agree with all their conclusions, and all parties involved should clearly understand that such guidances do not in any way replace current EPA … guidances or policies addressing the remedy selection process,” according to the directive. EPA may change this position with experience, as the agency acknowledges that non-EPA documents may provide useful technical information to site managers. EPA Technical Protocol In September 1998, the EPA Office of Research and Development released a protocol entitled Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water. The intended audience for

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Natural Attenuation for Groundwater Remediation the protocol includes project managers, contractors, consultants, scientists, and regulatory personnel. The document focuses on biological processes occurring in groundwater contaminated with mixtures of fuels and chlorinated aliphatic hydrocarbons. It relies on methods developed by the Air Force Center of Environmental Excellence for assessing natural attenuation at sites contaminated with fuel hydrocarbons and chlorinated solvents. In fact, all of the authors of the EPA protocol were coauthors of one or both of the Air Force documents. The protocol was a joint effort involving the Bioremediation Research Team at the EPA’s laboratory in Ada, Oklahoma; the Air Force Center for Environmental Excellence; the U.S. Geological Survey (USGS); and Parsons Engineering Science, Inc. For these reason, the EPA protocol is similar to the Air Force chlorinated solvent protocols (discussed later in this chapter). The protocol includes a screening process for assessing contaminant biodegradation potential that employs a scoring system based on analytical parameters adopted from the Air Force protocol. The scoring system is designed to recognize geochemical environments where reductive dechlorination (see Chapter 3) is plausible. The protocol states that the scoring system is applicable to various chlorinated compounds and is weighted toward chemical indicators of a reducing environment and the production of associated daughter products. The scoring system compares data from the contaminant source area, within the plume, downgradient from the plume, and upgradient and lateral locations not affected by the plume. If the score is sufficiently high (15 or more points) in the zones of contamination, then the investigation continues with determination of groundwater flow and solute transport parameters. The protocol recommends using the analytical model BIOSCREEN to assess whether natural attenuation processes will be capable of meeting site-specific remediation objectives downgradient from the source. It suggests using the numerical model BIOPLUME III to estimate whether site contaminants are attenuating at a rate fast enough to restore the plume to appropriate cleanup levels. The protocol provides case study examples illustrating the use of total chloride or chlorine as a tracer and mass-balance concepts to estimate the biodegradation rate. It does not provide guidance on long-term monitoring. The protocol underwent external and internal peer and administrative review by the EPA and the Air Force. EPA Region 4 Protocol EPA Region 4 in 1997 developed a document entitled Draft Region 4 Suggested Practices for Evaluation of a Site for Natural Attenuation (Biological Degradation) of Chlorinated Solvents that describes suggested practices for

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Natural Attenuation for Groundwater Remediation The scoring system includes items that are of current research interest (for example, hydrogen concentration), but that may have limited practical impact on making remediation decisions. The system identifies interactions between contaminants only for electron donors. Nyer et al. (1998) discuss the use of the Air Force scoring system for a case study at a former aerospace manufacturing facility in Irving, Texas, that is contaminated with TCE and trichloroethane. They found that site screening using the Air Force scoring method indicated limited potential for biodegradation. However, further analysis suggested that the groundwater sampling data were indicative of geochemical characteristics within the larger pore spaces of the sand and gravel alluvium and not of clayey soils where groundwater flow was much slower and reductive dehalogenation was believed to be occurring. The authors caution against using the scoring system as a primary method of substantiating natural attenuation and suggest that many sites will require assessments beyond those specified in the Air Force protocol. As discussed previously, the DOE technical guidance for monitored natural attenuation proposes using a score known as the NAF that is estimated from the sum of four factors representing different processes that affect the contaminants. The NAF is expressed on a scale of 1 to 100, with a score of 50 or more indicative of natural attenuation. The calculation is facilitated by use of interactive software that can be accessed remotely through the Internet. The methodology, the engineering and scientific underpinnings, and validation have not been subjected to comprehensive, independent peer review. To date, the NAF has not been widely used, and the committee is concerned about whether the NAF is meaningful. Because scoring systems are susceptible to misuse and because approaches to natural attenuation have been advanced in recent years, the committee recommends the abandonment of scoring systems in screening sites for natural attenuation. Instead, the committee recommends site-specific conceptual models and footprints as described in Chapter 4. ADEQUACY OF TRAINING Decisions regarding natural attenuation require a considerable amount of expert judgment. Thus, adequate training of protocol users is essential to ensure that the protocols are implemented properly. The training needed to implement natural attenuation protocols differs depending on an individual’s role. Regulators, responsible parties, remediation consultants, and community-based organizations that participate in decision making have different training needs.

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Natural Attenuation for Groundwater Remediation Responsible Parties Responsible parties need to be able to evaluate the work of remediation consultants and make remediation decisions based on consultants’ work. Thus, such individuals should have sufficient technical background and experience to actively manage their consultants and negotiate responsibly with environmental regulators. Responsible parties who rely solely on attorneys or external project managers to handle their remediation programs do so at the risk of receiving poor-quality work. Responsible party representatives should always have a technical degree and understand quality evaluation of field data and consultant reports, fundamentals of risk evaluation, and the necessity for community involvement. In some organizations, especially the military, environmental managers may be “short-timers” with little environmental background. A number of good short courses on natural attenuation are available from the EPA, the Interstate Technology Regulatory Cooperation (ITRC) Work Group, and the National Ground Water Association. Responsible party representatives without experience with natural attenuation (but who do have other qualifications) should take at least one such course. Consultants Remediation consulting firms employ two tiers of personnel on most projects: senior technical leaders and field personnel. Senior technical leaders: A consulting firm should have a lead natural attenuation expert with considerable understanding of natural attenuation science. These experts should specialize in natural attenuation to the degree possible, know the methods applied to natural attenuation studies, recognize the typical pitfalls of these studies, and be able to identify which natural attenuation protocols to use and apply. Consulting leaders develop professional judgment about natural attenuation based on fundamental understanding of the scientific principles combined with experience from a number of sites. These leaders need the technical skills to understand unique contaminants and situations outside the scope of protocols and communications skills to effectively transmit their conclusions. Experience suggests that broad training with grounding in environmental science and engineering fundamentals is considerably more useful than more focused training, such as a specific bioremediation curriculum. Field sampling personnel: High-quality field data are essential for understanding the geochemical and biochemical environment in the subsurface to determine which natural attenuation processes are possible at

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Natural Attenuation for Groundwater Remediation sites. Field personnel who are trained to recognize and correct problems as they occur and adapt to changeable conditions in the field are a major asset. The necessary skills may be obtained via experience, although some schools offer associate’s degrees in environmental science that can be helpful. Specific key skills include the Occupational Health and Safety Administration 1910.120 hazardous materials training, well purging, and groundwater collection techniques; basics of chemical analysis; field instrument calibration and field lab techniques; sample shipping requirements; and first aid. State and Federal Regulators State and federal regulators are charged with evaluating the merits of the various remediation proposals they receive and making responsible judgments on whether natural attenuation proposals have sufficient technical justification. Regulators must be able to understand a wide variety of technical and policy information. Groundwater regulators should have technical degrees; a graduate degree is preferred to ensure an appropriate level of understanding. Desirable disciplinary skills include environmental engineering, geology, chemistry, and biology. Natural attenuation training for regulators should include the fundamentals of relevant environmental regulations, development and use of conceptual models, use of mathematical tools and models to estimate contaminant movement and degradation, fundamentals of risk evaluation, and methods for working with stakeholders. Training also should include education in natural attenuation protocols and how natural attenuation remedies compare to other potential remedies with respect to risk and cost. Training of regulators can be aided by short courses and mentoring under more experienced personnel. For example, ITRC offers a short course for state regulators (see Box 5-3). Some regulatory agencies (for example, in Oregon) employ technology specialists who are available to help regulators with complex situations. Community-Based Organizations As explained in Chapter 2, members of communities affected by contaminated sites where natural attenuation is proposed as a remedy should be included in the decision-making process as early as possible and have the resources necessary to participate in this process. Community members may desire technical training to help them understand the natural attenuation proposal, and they should have the opportunity to receive this training.

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Natural Attenuation for Groundwater Remediation BOX 5-3 ITRC Natural Attenuation Training for State Regulators The Interstate Technology Regulatory Cooperation Work Group, which consists of about 26 state agencies working on guidance documents on various remediation techniques, offers a two-day training course aimed specifically at the needs of state groundwater regulators. The goals of the course are to provide current scientific information concerning natural attenuation of chlorinated solvents and to provide participants with tools for evaluating proposals for natural attenuation. The first day covers basics of environmental biodegradation and provides detailed examples showing how real-world sites are evaluated. Day 2 emphasizes how to interpret information from real sites. The class divides into small groups and evaluates the technical suitability of natural attenuation on two computer-simulated sites. State regulators lead two free-form discussions on regulatory concerns about natural attenuation, before and after the practical exercises. An EPA representative explains the agency’s recent natural attenuation directive. Although the course was developed for regulators, it is also open to consultants and industry. Preference in registration is given to regulators. Consultants and industry employees pay a modest registration fee. These fees are used to pay the travel and living expenses of state and federal regulators, public stakeholder representatives, and course instructors. The ITRC operates the course on a nonprofit basis. There are several ways to provide training opportunities for community members. Possibilities include making information readily and frequently available; providing funds directly to a community organization to hire an expert; providing opportunities for community leaders to enroll in a training course offered by a neutral, nonprofit organization; holding workshops or seminars in the community to explain technical issues; and holding a regional conference that brings together scientists and community representatives. Information and training should be provided by individuals who are independent of the responsible party and the regulating agency. For training directed specifically at a local community, training topics should be selected in collaboration with community leaders, and training should be held at times that are convenient for the community. The goal of training community leaders and members is to help them understand the technical complexities of natural attenuation, including its strengths and weaknesses, its effectiveness in addressing the specific contaminants, its suitability at a particular site, and the short- and long-term risks. Training topics might include a basic introduction to contami-

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Natural Attenuation for Groundwater Remediation nant behavior in the environment, including chemical, physical, and microbial processes; a review of strengths and weaknesses of natural attenuation; a description of methods for measuring natural attenuation at a site; a review of how site conditions and contaminants affect natural attenuation; and a discussion of ways to verify the effectiveness of natural attenuation. ADEQUACY OF POLICIES CONCERNING USE OF PROTOCOLS Despite the limited EPA guidance on implementation of monitored natural attenuation remedies, EPA cautions strongly against reliance on non-EPA documents. Although it acknowledges that such documents may provide useful technical information, EPA does not officially endorse non-EPA protocols. Nonetheless, for very good reasons, users and agencies have proceeded with the development of various protocols. Some of these protocols have been prepared with the direct involvement of EPA research personnel. Yet, how these non-EPA protocols can be used in satisfying the regulatory requirements of groundwater and soil cleanup programs administered by EPA is unclear. Adding to the confusion, each state also administers its own groundwater cleanup programs for sites not regulated by EPA, and state requirements can vary widely. In some cases multiple agencies may have jurisdiction over a site, and the goals, criteria, constraints, and process of selecting remedies can be a mixture of federal, state, and local laws and policies. Natural attenuation remedies, like engineered remedies, must be approved by the site regulator, but regulatory acceptance of existing protocols to document natural attenuation varies highly from site to site. No standard regulatory approval process is available. Legal requirements for cleanup using natural attenuation (or any other process) vary significantly depending on the regulatory program under which the site is being restored. Therefore, the application of natural attenuation protocols varies, as well. Site owners wishing to use natural attenuation must demonstrate to regulators, through use of an appropriate protocol or other means, that natural attenuation will achieve whichever remediation requirements apply to the site. Although drinking water standards historically have been chosen as groundwater remediation goals at Superfund and Resource Conservation and Recovery Act (RCRA) corrective action sites, goals can vary depending on what decisions regulators make about future land use (NRC, 1997). If an aquifer is not used as a domestic water supply, there can be a substantial (e.g., hundredfold or more) difference between a federal drinking water standard and a risk-based concentration limit. Because this difference can be large, the applicability of natural attenuation at a site may

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Natural Attenuation for Groundwater Remediation depend on whether a risk-based concentration limit or a drinking water standard has to be achieved. Remediation requirements at sites regulated under state programs differ markedly, as well. Some state Superfund programs require restoration to background levels of contaminants, while others set higher concentration goals (NRC, 1994). Nondegradation policies for groundwater can be interpreted as discouraging, if not precluding, the selection of natural attenuation. If, however, the policy is interpreted as allowing a reasonable time to restore the aquifer, natural attenuation may be acceptable, depending on the local determination of what constitutes a reasonable time frame and the strength of the expectation that natural attenuation can restore the aquifer to local standards within the allowed time frame. For the cleanup of underground storage tanks, most of which are delegated to the states, remediation goals also vary considerably. Many states have adopted a risk-based approach to setting site-specific cleanup levels for leaking underground storage tanks; other states use state-specific groundwater standards to define remediation goals. Like remediation requirements, the level of detail of data required to demonstrate that natural attenuation can achieve remediation goals—and whether natural attenuation can be accepted at all—varies with the regulatory program and with the individual regulator. For example, at Superfund and RCRA sites, EPA’s monitored natural attenuation policy generally requires applications for use of natural attenuation to demonstrate that (1) contaminant concentrations are decreasing and (2) hydrogeologic and geochemical conditions are sufficient to support natural attenuation at rates that will achieve cleanup goals in a reasonable time (EPA, 1999). In some cases, EPA, at the discretion of individual site regulators, also may require microcosm or field studies showing that natural attenuation potential is realized under actual site conditions. In contrast, at gas stations with leaking underground storage tanks, some state regulators require only proof that contaminant concentrations are decreasing over time (Arulanantham, 1998). Further complicating matters, the framework and structure of regulatory management of natural attenuation sites are in a rapid state of flux. In the case of sites contaminated with petroleum hydrocarbons, there has been a radical shift in some states over the past two years from a position of requiring a demonstration that natural attenuation is appropriate to expecting site owners to demonstrate why it is not adequate. The State of Wisconsin, for example, will no longer provide funds to reimburse owners of leaking underground storage tanks for cleanups that involve engineered remedies. In sum, the goals that natural attenuation must achieve and the regulatory requirements for documenting natural attenuation are highly vari-

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Natural Attenuation for Groundwater Remediation able from site to site. How natural attenuation protocols are to be used in the context of existing regulatory programs requires further clarification. CONCLUSIONS More than a dozen documents providing guidance on whether natural attenuation is an appropriate remedy for managing contaminated sites have been issued within the past few years. As proposals to use natural attenuation continue to multiply in number, more protocols likely will be developed. With the exception of the DOE protocol, the available natural attenuation protocols address only organic contaminants and only two classes of such: fuel hydrocarbons and chlorinated solvents. A large body of empirical evidence and scientific and engineering studies in recent years has been developed to support understanding of natural attenuation of these classes of organic contaminants under certain conditions. However, natural attenuation of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, explosives, and other classes of persistent organic contaminants is not addressed in any protocol. Further, while the DOE protocol proposes a method for assessing natural attenuation processes for inorganics, such processes are not well understood, posing concerns about whether results generated with the DOE protocol are accurate enough to be meaningful. The Committee on Intrinsic Remediation reviewed 14 of the available natural attenuation protocols in detail. These protocols were developed by a range of organizations, from federal and state agencies, to private companies, to industry associations. At the time of preparation of this report, they represented most of the available documents providing guidance on decisions related to natural attenuation. The committee compared these protocols against a list describing the characteristics of a comprehensive protocol, which would cover three broad subject areas: Community concerns: A comprehensive protocol would indicate key points for receiving community input. It would also include plans for maintaining institutional controls to restrict use of the site until cleanup goals are achieved, monitoring the site, and implementing contingency measures when natural attenuation fails to perform as expected. Scientific and technical issues: A comprehensive protocol would describe how to document which natural attenuation processes are responsible for observed decreases in contaminant concentration; how to assess the site for contaminant source, hydrogeologic, and geochemical characteristics that affect natural attenuation; and how to assess the sustainability

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Natural Attenuation for Groundwater Remediation of natural attenuation over the long term. It should be independently peer reviewed. Implementation issues: A comprehensive protocol is easy to follow and would describe qualifications necessary to implement the protocol. None of the protocols meets all of the characteristics defined by the committee. To some extent, this gap reflects the purposes for which these protocols were developed. Some are detailed technical guides; others are intended to help ensure consistency in site evaluation within a particular organization (such as a private corporation or a branch of the military); others are intended to guide policy. Nonetheless, key limitations in the existing body of protocols must be addressed. In general, the existing protocols are silent on when and how to involve the public in site decisions and when and how to implement institutional controls. In the few instances where these matters are mentioned, the discussion is typically brief, almost in passing. Discussion of when and how to implement contingency plans in case natural attenuation does not work is inadequate in many of the protocols. The protocols also provide insufficient guidance on when engineered methods to remove or contain sources of contamination benefit natural attenuation and when they interfere with it. Guidance on how to conduct long-term monitoring to ensure that natural attenuation is continuing at an adequate rate is also inadequate. All of the protocols are silent, as well, on the issue of type and level of training or experience needed to implement the protocol. For the most part, the existing protocols have not been subjected to independent peer review. An additional limitation of some of the protocols relates to uncertainties in “scoring systems” used to reach conclusions about whether a site is a candidate for treatment by natural attenuation. Protocols with such scoring systems yield numeric values for the site in question, and if this value is above a certain level, the site is judged an eligible candidate for natural attenuation. Typically, such scores imply more confidence in the decision than is justified by field experience and literature to date. A final problem with the existing body of protocols is the lack of sufficient guidance on which protocols are appropriate for use in various regulatory programs. None of the existing protocols developed by organizations other than the EPA is officially recognized by the agency, yet even EPA recognizes that a number of these might prove very useful in assessing sites that it regulates. Although EPA does not officially recognize any protocols other than those developed by the agency, a number of regulators at the state level advocate that for some sites, no protocol is needed to judge whether natural attenuation is occurring and that such determinations can be based on trends in contaminant concentration

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Natural Attenuation for Groundwater Remediation alone. A process is needed to ensure consistent, logical application of professional judgment at all sites where natural attenuation is being considered. As the federal agency with responsibility for addressing environmental contamination, the EPA has to take charge of developing a consistent evaluation process. In sum, the existing body of natural attenuation protocols is limited in several important areas. Where and how the existing protocols can be used to meet regulatory requirements for documenting site cleanup—and whether such protocols are required at all—is also unclear. RECOMMENDATIONS The EPA should lead an effort to develop national consensus guidelines for protocols on natural attenuation. As soon as possible, EPA should undertake an effort to work with other federal agencies, professional organizations, industry groups, and community environmental organizations to assess natural attenuation protocols and how they can be used in existing regulatory programs (including Superfund, the RCRA corrective action program, and the leaking underground storage tank program). Ideally, these guidelines should address in detail the attributes listed across the top of Table 5-1. The guidelines should be updated regularly to include new knowledge and should allow flexibility for regional geologic differences and variations in policies by state or region. The guidelines should give special attention to community involvement, source removal, long-term monitoring, contingency plans, sustainability of natural attenuation, and training for protocol users. The national consensus guidelines and all future natural attenuation protocols should be peer reviewed. The peer review should be conducted by independent experts who are not affiliated with the authoring organization. The national consensus guidelines and future protocols should eliminate the use of “scoring systems” for making decisions on natural attenuation. The evaluation methods outlined in Chapter 4 of this report, using conceptual models and footprints of natural attenuation, should replace scoring systems. Scoring systems are generally too simple to represent the complex processes involved and often are used erroneously in judging the suitability of a site for natural attenuation. For this reason, scoring systems, including DOE’s monitored natural attenuation toolbox and scorecard, should not be used. Developers of natural attenuation protocols should write easy-to-understand documents to explain the protocol to nontechnical audiences. Such documents should be made available to interested members of communities near contaminated sites.

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Natural Attenuation for Groundwater Remediation The EPA, other federal and state agencies, and organizations responsible for contaminated sites should provide additional training on natural attenuation concepts for interested regulators, site owners, remediation consultants, and community and environmental groups. The training should be provided by neutral organizations. The cost of attendance should be subsidized for regulators and community group members. REFERENCES Arulanantham, R. 1998. Presentation to the Committee on Intrinsic Remediation, Third Meeting, Woods Hole, Mass., June 1-2. EPA (Environmental Protection Agency). 1999. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites. Directive No. 9200.U-17P. Washington, D.C.: EPA, Office of Solid Waste and Emergency Response. Kelly, M. 1998. Presentation to the Committee on Intrinsic Remediation, Second Meeting, Irvine, Calif., March 12-13. NRC (National Research Council). 1994. Alternatives for Ground Water Cleanup. Washington, D.C.: National Academy Press. NRC. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, D.C.: National Academy Press. Nyer, E., P. Mayfield, and J. Hughes. 1998. Beyond the AFCEE Protocol for Natural Attenuation. Ground Water Monitoring Review Summer (1998):70-77. Ruhl, S. 1998. Presentation to the Committee on Intrinsic Remediation, Second Meeting, Irvine, Calif., March 12-13.

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