Contaminants in the Subsurface Source Zone Assessment and Remediation (2005) / Chapter Skim
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6 Elements of a Decision Protocol for Source Remediation
6 Elements of a Decision Protocol for Source Remediation
Pages 306-334
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From page 306... ...
Although part of this challenge arises from the fact that historical releases of DNAPLs and explosives are technically difficult to clean up, the problem is also attributable to how source zones are managed. The design and implementation of a successful source remediation project involves the iterative characterization of the source zone, development of remediation objectives, and evaluation of technologies, each of which is emphasized in previous chapters of this report.
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From page 307... ...
. Rather, this chapter is intended to help standardize the conceptual process for evaluating source remediation, including data gathering and analysis, setting objectives, and selecting remedial actions.
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From page 308... ...
yes yes 2. Identify Absolute Collect Data and Refine SCM Objectives no Are there enough data to determine functional objectives?
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From page 309... ...
Although one could potentially limit use of Figure 6-1 to only the most complex DNAPL sites, it was designed to encompass all sites with source zones, regardless of their complexity. The potential technologies considered in Step 4 can include all those discussed in Chapter 5, including presumptive remedies like excavation and physical or hydraulic containment.
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From page 310... ...
Furthermore, remedial actions may be viewed as being less aggressive and less costly alternatives that offer advantages to responsible parties without fully protecting human health and the environment. Another concern is that the presence of a source area may affect community property values.
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From page 311... ...
This could include, for example, guidance on how much information is needed to understand the hydrogeology controlling contaminant transport and fate at the site, criteria for delineating the source zone, tabulations of common data sources, suggestions for the development of preliminary site conceptual models, lists of common exposure scenarios to consider, and descriptions of risk assessment methodologies. IDENTIFY ABSOLUTE OBJECTIVES Identifying absolute objectives is specifically denoted in Figure 6-1 because in many cases examined by the committee, it was not clear that this was done properly or that it was done at all.
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From page 312... ...
IDENTIFY FUNCTIONAL OBJECTIVES AND PERFORMANCE METRICS As discussed in Chapter 4, the relationship between absolute and functional objectives is not always simple. One functional objective may serve multiple absolute objectives.
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From page 313... ...
Downgradient from the site is a residential neighborhood, Duke Estates, home primarily to persons formerly employed at Fort Alpha and their families. After passing beneath the residential neighborhood, the plume discharges to Halftrack Memorial State Wetlands Reserve 500 m from the source.
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From page 314... ...
. For the protection of public health, there can be no complete exposure pathways to the population at unacceptable concentrations.
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From page 315... ...
Similarly, it is one of many ways to pre vent adverse effects on health and is agreed to be deferred to the consideration of functional objectives. Stakeholder discussions led to the following list of noneconomic absolute ob jectives, with the understanding that not every objective is absolute for each stake holder, that there remains considerable overlap, and that not every stakeholder's objectives are viewed as attainable by the others: · Restoration to background conditions by achieving MCLs throughout the aquifer (at least at some point in the future)
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From page 316... ...
For example, prevention of human exposure to site contaminants can be achieved by removing the contaminants or by removing the people from a given area. The difficult part of setting functional objectives, and identifying alternative functional objectives, is generally the integration of multiple absolute objectives.
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From page 317... ...
BOX 6-2 Translating Absolute Objectives into Functional Objectives at Fort Alpha Functional Objectives to Achieve Interruption of the Human and Environmental Exposure Pathways Most or all of the noneconomic absolute objectives for many of the stakeholders in Box 6-1 can be obtained by any functional objective that interrupts the pathway between the source and various receptors. For example, the absolute objective specified by some of the stakeholders was to protect the public from excessive concentrations of site contaminants by disrupting human exposure pathways (at present, this is only relevant to residents of Duke Estates)
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From page 318... ...
Functional Objectives to Achieve Source Elimination As can be seen from Box 6-1, only complete elimination of the source area will meet the absolute objectives of Mr. Jones, of the Natural Resources Trustee, and of the state site manager.
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From page 319... ...
Unknown FIGURE 6-2 Multidimensional screening cube for identifying candidate technologies based on their potential for success (high, medium, low, unknown) relative to specific functional objectives and in different hydrogeologic settings.
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From page 320... ...
are not applicable to lowpermeability media due to slow rates of fluid delivery and recovery. The output envisioned in Figure 6-4 describes the potential of those technologies appropriate for a given contaminant and in a given setting to achieve different functional objectives.
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From page 321... ...
If a technology that is not well documented in the scientific and engineering literature is chosen, then the primary functional objective may need to shift to demonstrating an innovative technology as opposed to achieving specific objectives for the site itself. Ideally, only technologies that are rated "high" should be carried further through the evaluation process.
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From page 322... ...
Due to the adjacency of the shale to the alluvium, not treating the shale will diminish the likelihood of achieving the noted local aqueous concentration reduction and/or mass flux reduction in overlying adjacent alluvium. One notable exception to this is the soil mixing/chemical reduction technology.
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From page 323... ...
The objective of interrupting human expo sure pathways was discussed in Box 6-2 as being achievable in several ways: moving the humans, decreasing the concentrations to which they might be exposed, interspersing barriers to contaminant transport, or preventing release of contaminants from a confined area. While none of the objectives used in the cube and Table 5-7 precisely match the two absolute objectives at Fort Alpha, mass removal and mass flux reduction were interpreted to be closest to source elimina tion and elimination of the human exposure pathway, respectively.
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From page 324... ...
A potential pitfall at this point is for the "best available technology" to be chosen without rigorously determining whether it will work at the site or questioning whether the absolute objectives will be addressed. Decisions of this nature typically reflect a desire to do the "best thing." Unfortunately, actions that are not tied closely to functional objectives often fall short of expectation and/or needs.
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From page 325... ...
One possible outcome of Step 6 is that none of the specific technologies will remain viable, given the objectives of Table 6-1 and site-specific conditions. In this case, it is necessary to revisit the absolute and functional objectives (Steps 2 and 3)
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From page 326... ...
In addition to the functional objectives of mass removal and mass flux reduction chosen for the site, the Army also desires to have a safe working environment, to be in compliance with all regulations, to have the community accept the remedial action, and to minimize the life cycle cost of the remedy. All of these objectives appear in the matrix below, which is filled in Objectives Technical Mass Flux Life Cycle Alternatives Mass Removal Reduction Cost Minimization Excavation High High Medium All mass should be Flux out of source zone removed if excavation should be 0.
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From page 327... ...
Regulatory Worker Safety Community Acceptance Compliance Medium High High Potential exposure Highly visible, may Reduces mobility, during excavation and be concerns about toxicity, volume transportation transportation, perceived as final High Medium High-Medium Little contact with media, Community may not Reduces mass, separation step might expose understand the technology volume; low impact on toxicity Medium High High Standard risks of large Highly visible, perceived Rapidly reduces mass, construction equipment as final treatment toxicity, volume Medium Medium Medium High current flows, collection Community may not Reduces volume, and treatment of vapor pose understand the technology possibly mobility; does an exposure hazard not change toxicity High Medium Low Some exposure during Highly visible, results are Controls mobility, little installation and operation long-term impact on volume, none on toxicity
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From page 328... ...
Because these regulators must be able to understand a wide variety of technical information, desirable skills include knowledge of environmental engineering, geology, chemistry, and biology principles, as well as how to use conceptual models, mathematical tools and models to estimate contaminant movement and degradation, and funda mentals of risk evaluation. Community-Based Organizations The members of communities affected by contaminated sites where source remediation is being considered should be included in the decision-making process as early as possible and should have the resources necessary to participate in this process.
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From page 329... ...
. However, in order to be granted a TI waiver, the responsible party must provide their best estimation of a technically practicable alternative remedial strategy that will prevent migration of contamination beyond the source zone (see EPA, 1993, and NRC, 2003 for greater explanation of technical impracticability)
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From page 330... ...
identification of functional objectives and metrics, (4) elucidation of potential technologies given
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From page 331... ...
Stakeholder participation is needed to better understand the range of absolute objectives at a given site, to develop functional objectives, and to gain consensus on appropriate actions. Without adequate public participation, critical elements of solutions may be missed, a subset of the involved parties may feel that their needs have been ignored, and/or false expectations may develop as to what can be achieved.
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From page 332... ...
It is evident from the review of source zone remediation projects at Army facilities and elsewhere that the steps presented in Figure 6-1 -- determining whether a source exists; developing clear absolute and functional objectives and their metrics; selecting, designing, and implementing a technology; and collecting data to support all these decisions -- have seldom been conducted in the manner described in this report. The efforts of potentially responsible parties to date suggest that in some cases, source remediation technologies are being prematurely scaled up at poorly characterized sites, at sites where there is known complex hydrogeology, and at sites where there is no clear reason for proceeding with the project.
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From page 333... ...
1996. Technical protocol for evaluating natural attenuation of chlorinated solvents in groundwater.
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