Natural Attenuation for Groundwater Remediation (2000) / Chapter Skim
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5 Protocols for Documenting Natural Attenuation
5 Protocols for Documenting Natural Attenuation
Pages 212-254
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From page 212... ...
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.
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From page 213... ...
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.
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From page 216... ...
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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From page 217... ...
Scientific arc! Technical Issues Cause-a ncl- 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.
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From page 218... ...
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.
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From page 219... ...
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.
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From page 220... ...
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.
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From page 221... ...
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 Protocolfor Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water.
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From page 222... ...
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.
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From page 223... ...
At this time a date for this guidance is not known." Presumably, the 1998 EPA technical protocol for natural attenuation of chlorinated solvents is a step toward that eventuality. Department of Energy (DOE)
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From page 224... ...
] , where a score greater than 50 is proposed to favor monitored natural attenuation.
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From page 225... ...
Solvents The Air Force Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Groundwater is intended for use where ground
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From page 226... ...
This scoring system has been adopted by others, including the EPA and the State of Minnesota. Navy Technical GuicleIines The Navy document entitled Technical Guidelines for Evaluating Monitored Natural Attenuation addresses petroleum hydrocarbons and chlorinated solvents, whether singly or mixed.
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From page 227... ...
The protocol draws on the preliminary screening model put forward in the Air Force protocol for chlorinated solvents. It outlines procedures for comparing the estimated rate of biodegradation with the estimated rate of contaminant migration using the nonproprietary BIOSCREEN model to rapidly assess the potential for natural attenuation as a promising remedy.
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From page 228... ...
and one for chlorinated solvents (entitled Protocolfor Monitoring Natural Attenuation of Chlorinated Solvents in Groundwater)
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From page 229... ...
Key areas of difference include the following: · the range of contaminants addressed (ASTM's document covers only petroleum hydrocarbons, while EPA's guidance is intended to apply to all contaminants) ; · whether or not site characterization data have to be more detailed than those for active remediation, as stated by the EPA; · whether or not natural attenuation is more likely appropriate if the plume is not expanding, as described by the EPA; and · whether or not source removal or control is mandatory, as emphasized by the EPA.
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From page 230... ...
The document is organized into sections, including one on technical challenges associated with sites contaminated with chlorinated solvents and the types of chlorinated solvent attenuation processes known to occur, one on how natural attenuation studies are generally conducted, and one on how a stepwise process and flow chart generally are used to implement natural attenuation at chlorinated solvent sites. The document discusses the three lines of evidence that form the basis for current protocol and guidance documents: (1)
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From page 231... ...
ASTM standard guide for natural attenuation at petroleum release sites, 6. EPA technical protocol for natural attenuation of chlorinated solvents, and 7.
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From page 232... ...
sol. = chlorinated solvents are primary focus of the document; 0RD = Office of Research and Development; RTDF = Remediation Technologies Development Forum.
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From page 233... ...
PROTOCOLS FOR DOCUMENTING NATURAL ATTENUATION and 233 Scientific and Technical Issues Implementation Issues Cause and Effect Site Condition Assessment Sustainability o .= .'4 a, u ~ < L)
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From page 234... ...
The following discussion assesses the adequacy of existing protocols with respect to the attributes listed in Box 5-2 and Table 5-1. Community Concerns Community Involvement None of the protocol documents provides guidance on steps in the evaluation process where public input is important, although the EPA directive and the New lersey and RTDF documents mention community participation in passing.
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From page 235... ...
Several sections of the EPA guidance document mention institutional controls, but the guidance does not discuss this topic in detail. Institutional controls are important for natural attenuation remedies, because many years may be required to achieve remedial objectives.
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From page 236... ...
Some protocols (e.g., Air Force, EPA chlorinated solvents, Navy) recommend placing sentinel wells within the plume and at its fringe to provide an ongoing indication of whether the plume is expanding or the geochemical processes are changing.
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From page 237... ...
In part, this variability occurs because the individual protocols address different types of contaminants. For example, a more thorough investigation is generally outlined in protocols for chlorinated solvents than for petroleum fuels, because the degradation pathways for solvents are more complex than those for fuels.
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From page 238... ...
However, except for the Air Force protocols (and the related EPA protocol for solvents) , the protocols give surprisingly little attention to characterizing contaminant sources and using source characterization data to determine whether source removal or control is necessary.
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From page 239... ...
The EPA chlorinated solvents protocol encourages the use of BIOSCREEN and BIOPLUME III to determine whether natural attenuation processes may meet site-specific remediation objectives and whether site contaminants are attenuating fast enough to restore the plume to appropriate cleanup levels. Several of the protocols mention complicating factors, but only the Navy guidelines address this topic in detail.
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From page 240... ...
Although the reviews are not specifically documented, the Air Force and Navy protocols and the EPA's guidance document underwent wide in-house review, and the Air Force chlorinated solvents protocol underwent some external review. Preparation of the Air Force and Navy protocols, as well as the EPA guidance, drew extensively on peer-reviewed literature and involved groups from both the public and the private sectors, including some of the most knowledgeable natural attenuation experts in the country.
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From page 241... ...
Most of the tools were created by a small group of authors who work together. Thus, the decision tools for fuels and chlorinated solvents take quite similar approaches.
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From page 242... ...
For example, both the EPA Office of Research and Development and the EPA Region 4 protocols present flow charts showing the steps involved in a natural attenuation demonstration and the important regulatory decision points. The available flow charts deal with deciding whether to employ natural attenuation, to use natural attenuation in combination with another technology, or to use another technology without any contribution from natural attenuation.
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From page 243... ...
Unfortunately, this scoring system is being widely adopted for uses that the authors never intended. For example, many states are using it to evaluate natural attenuation for all types of chlorinated solvents.
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From page 244... ...
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.
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From page 245... ...
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.
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From page 246... ...
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.
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From page 247... ...
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.
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From page 248... ...
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.
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From page 249... ...
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.
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From page 250... ...
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.
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From page 251... ...
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.
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From page 252... ...
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)
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From page 253... ...
1999. Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites.
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