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Title:
Introduction
Text: The goal of the Department of the Navy (DON) Environmental Restoration Program is to "achieve environmentally protective site closeouts at least cost." To achieve this goal, DON has put great emphasis on the development of optimization procedures and guidance to educate Remedial Project Managers (RPMs) and enable them to implement measures to maximize the effectiveness of remedial strategies.
Remedial technologies all have limitations; therefore most remedial strategies will require the implementation of more than one technology. Awareness of technology limitations and the appropriate point to discontinue a technology are key to remedial optimization.
This Web tool will describe technology performance objectives and how they should be developed and implemented as triggers for technology transition and/or discontinuation over the life cycle of a remediation project.
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Title:
What are Remedial Performance Objectives?
Text: Remedial performance objectives are criteria that measure the operational efficiency and suitability of a particular remedial technology.
They trigger a response to:
1) Modify or optimize the current system,
2) Transition to an alternate (less active and more cost effective) technology, or
3) Discontinue a unit process or remediation altogether (an exit strategy).
Performance objectives help to define what the expected effective operational range of a given remedial approach may be and can allow for flexibility within the remedial decision process to discontinue use of a specific technology once it is no longer operating within its pre-determined, cost-effective range.
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Title:
Remedial Performance vs. Remedial Action Objective
Text: Performance objectives are typically distinct from remedial action objectives and final cleanup goals because they take into account typical engineering performance and the limitations of the individual technology.
Remedial Action (RA) Objectives are site-specific cleanup goals that are based on the chemicals of concern (COCs), the impacted media, fate and transport of the COCs, the exposure routes and the potential receptors as identified in the conceptual site model (CSM). They should provide a clear and concise description of what the remedial action should accomplish to protect human health and the environment.
Remedial Performance Objectives are developed for each specific technology implemented and consider the limitations/constraints of that technology.
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Title:
Treatment Train Concept
Text: The optimal remedial action at a given site often requires the use of multiple technologies. A group of technologies working together is referred to as a "treatment train." These technologies may be used either sequentially or concurrently.
A single remedial technology is rarely the most cost-effective approach throughout the life cycle of a cleanup project. The treatment train concept emphasizes that multiple remedial technologies often are needed to achieve cost-effective remediation at a given site.
Sequential technology implementation over time allows specific technologies to be used for particular phases of the cleanup that cannot technically or cost-effectively meet remedial action objectives. Performance objectives trigger the transition to the next phase of the treatment train and can be used to make that transition occur at the optimum time to prevent a technology from operating beyond the point of diminishing returns.
Simultaneous technology implementation of multiple unit processes in a single treatment system allows specific technologies to be used for particular COCs that would otherwise not be appropriate or cost-effective for all contaminants. As site conditions change, it may not be necessary or cost-effective to continue using all unit processes of the treatment train. Performance objectives can be used to trigger the modification of the treatment train at the optimal time to prevent a unit process from being used beyond the point that it is necessary or cost-effective.
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Title:
Importance of Performance Objectives (1 of 2)
Text: During Remedial Action Operation, COC concentrations should decrease with time and ideally achieve the RA Objective. However, the RA Objective is rarely reached with a single treatment technology. Instead, COC concentrations normally level off above the RA Objective.
At this time, or even sooner, it becomes more efficient and cost effective to transition to another (possibly less active) technology or to exit altogether, than to continue with the initial remediation technology.
Predetermined performance objectives trigger the transition to a less active or passive technology at the optimal time. This optimal time may occur immediately after an initial reduction in COC concentration, rather than after a prolonged period of operating at the reduced concentration.
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Title:
Importance of Performance Objectives (2 of 2)
Text: The use of well-defined performance objectives triggers the transition to a more suitable technology at the optimal time, thus avoiding the use of non-optimal technologies beyond the point of diminishing returns. This reduces the life-cycle project cost. This figure illustrates the cost savings that result from treatment train application with well-defined performance objectives.
The magenta line illustrates the cost over time using a single treatment technology. As concentrations decrease, the same aggressive technology that was suitable during initial conditions is used throughout the entire project resulting in high total project costs.
The green line illustrates the reduced cost that resulted from switching to less aggressive technologies, though the transitions were made later than the optimal time.
The blue line illustrates the further cost savings when well-defined performance objectives allow the Project Manager to know the optimal time to switch to a less active technology and when to exit altogether.
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Title:
Importance of Documentation
Text: Throughout the entire project, it is imperative that performance objectives be documented so that an exit or transition can take place at the optimal time. Agreements for such exit or transition points should be established in advance and in written form to avoid negotiations or discussions which extend the time of unsuitable application of that technology.
Remedial performance objectives should be developed throughout the remedy development process, beginning with the Feasibility Study and continuing through the Record of Decision (ROD) and Remedial Design documents. These should include the criteria for a transition based on observed site conditions, performance data, and cost effectiveness.
During remedial action operation, performance can then be compared against the objectives. Monetary costs can serve as a trigger for transition to an alternative, based on the cost per unit mass or volume of contaminant removed or destroyed. As more mass or volume of the contaminant is removed and the efficiency decreases, the cost per unit mass or volume increases tremendously. The cost can then be compared to the alternate (less active) technology with a lower cost per pound to determine if a transition is needed.
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Title:
Ex Situ Performance Objectives and Examples
Text: Ex situ processes include such technologies as groundwater treatment (e.g., air stripping, liquid-phase granular activated carbon [GAC], UV oxidation, metals precipitation) and air emission controls (e.g., oxidation, vapor-phase GAC).
Developing performance objectives for ex situ processes requires consideration of such aspects as influent concentrations, contaminant removal efficiency, discharge limits, and cost. These objectives define when an exit or transition should occur; therefore, they must be clear and well-written. In a multiple unit operation system, each unit operation can have an individual performance objective. The attached table lists three ex situ treatment technologies, along with example performance objectives, criteria, exit criteria, and data needs. This table may be printed to view in full.
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Title:
Evaluating the Need for a Process Unit
Text: An Exceedance Probability Interactive Tool has been developed to evaluate the need for a unit process. This need is based on a statistical evaluation of the COC concentration prior to treatment by the unit process compared to the discharge limit.
Click on the interactive tool at the left to calculate the probability/confidence interval that the discharge limit will continue to be met even if the particular unit operation is eliminated. This tool will calculate the probability of compliance as a function of the number of future sampling events.
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Title:
Air Stripping vs. GAC Treatment
Text: Comparing the cost to remove the contaminant as a function of the contaminant concentration for different technologies can allow one to determine which technology is the most efficient, when to use it, and when to transition to a different technology.
For example, when extracted groundwater concentrations are high, air stripping is the most economical, and additional polishing with GAC may be needed to meet the effluent limits. As extracted concentrations decrease, polishing with liquid-phase GAC will no longer be needed. As extracted concentrations continue to decrease, switching to liquid-phase GAC alone will be most economical.
Note that the choice of technology is based on the cost of contaminant removal at different contaminant concentrations, with the condition that the effluent limits be met with each implemented technology.
Developing figures like the one shown here can serve as the basis for the performance objective. This type of figure can be developed during the design phase of a project and then the Project Manager can refer to this during system operation. When the contaminant concentration decreases to the point where the figure indicates that a transition may be warranted, an evaluation of the treatment train should be performed.
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Title:
Cost Curves for Emission Control Options
Text: Before system operation begins, performance objectives may be developed based on cost curves showing operating cost vs. contaminant concentration for multiple technologies. This type of figure should be developed to indicate when transitions should be made between these technologies.
As the example provided in the linked PDF file shows, the operating cost is less for oxidation at high concentrations, but as concentrations decrease over time, a point will be reached when GAC has a lower operating cost. For this example, the initial treatment technology should be transitioned to the secondary technology based on the influent concentrations.
Well-defined performance objectives help to trigger these transitions by indicating where the technology cost curves intersect.
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Title:
In Situ Objectives and Examples
Text: In situ technologies include groundwater containment, passive treatment walls, product recovery, in situ air sparging (IAS) with soil vapor extraction (SVE), in situ chemical oxidation (ISCO), thermal remediation, and biological degradation. The attached table lists some example in situ treatment technologies, performance objectives, criteria, exit criteria, and data needs. Print the table at the left to view in full.
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Title:
In Situ Example: Sequential Operations
Text: This example from a petroleum-contaminated site illustrates how performance objectives were used to sequentially transition from more- to less-active treatment technologies.
Established Treatment Train:
-Phase I: Multiphase Extraction (MPE)
-Phase II: Pulsed IAS/SVE
-Phase III: Biosparge with no SVE
-Phase IV: MNA
To prevent any technologies from operating beyond the point of diminishing returns and to establish clear transitions to the next technology, performance objectives were established as follows:
1) Operate MPE until the product recovery rate is reduced to a specified level and the VOC concentration in the off-gas can no longer sustain the oxidizer without supplemental fuel. This triggered a transition to IAS/SVE, which increased the concentration in the off-gas, therefore increasing mass removal and decreasing supplemental fuel for the oxidizer.
2) Operate IAS/SVE until the VOC concentration in the off-gas can no longer sustain the oxidizer without supplemental fuel and the benzene concentrations in the off-gas and shallow soil no longer present a health risk. This triggered a transition to biosparging, which eliminated the need to operate the SVE system and the oxidizer and therefore reduced operating cost and resource consumption.
3) Operate in the biosparging mode until the concentrations in soil meet risk-based criteria that are protective of human health based on groundwater solute transport modeling. This triggered a transition to MNA, therefore reducing operating cost and resource consumption.
Affects on the remedy: Allowed the use of the optimal technology for each phase of the remediation.
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Title:
Exit Strategy Considerations
Text: An exit or transition in technologies should be considered if you are experiencing decreasing concentrations, declining effectiveness/removal rate, or if the current technology is less cost-effective than an alternate (less active) technology.
The following slides discuss two additional factors that should be considered when developing and evaluating performance objectives regarding when to exit: non-monetary factors and rebounding.
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Title:
Operational Risk Factors
Text: To further evaluate transition and exit strategy options, operational risk factors may be considered.
Many times, a remediation technology may actually cause more risk or environmental damage than if passive strategies were used. Some technologies may simply transfer COCs to another medium, such as air stripping. Emissions from diesel, gasoline, coal, and other fuels, as well as pollution from production of raw materials, may be considered.
One way to evaluate the effect of these factors is to graph the pollution generated or energy expended versus the pounds or volume of COC removed. As seen in the graph on the left, as the concentration of the VOC decreases, the ratio of greenhouse carbon dioxide gas produced from the remediation technology increases exponentially.
In some cases, this should be considered along with other factors in determining the appropriate time to transition to a less active or passive technology.
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Title:
Performance Objectives for Contaminant Rebounding
Text: The issue of contaminant rebounding is an important consideration when discontinuing an active groundwater treatment system. Rebounding refers to an increase in contaminant concentration following the shutdown of an active treatment system. In most cases, rebound is minimal and/or temporary. Performance Objectives should be developed to address rebounding so that potential actions, such as restarting the remediation system, will have specific triggers.
Key points about rebounding are as follows:
The rebounding evaluation should not be based on a single round of sampling. Trends should be evaluated after SEVERAL rounds of sampling.
Use statistical approaches to evaluate rebounding.
Take care not to overreact to early indications of rebounding.
Reevaluate risk caused by rebound levels.
Consider the demonstrated limitations of the applied technology.
Don't get caught in a loop of restarting the system over and over.
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Title:
Rebound Equation and Example
Text: A common equation used to quantify rebound is shown here. Performance objectives may propose a range of rebound that is acceptable. For example, the following are typical rebound rates at air sparging sites (Bass et al., 2000):
Rebound less than 0.2 = permanent reduction
Rebound greater than 0.5 = substantial rebound
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Title:
Contact Information
Text: For more information about establishing Remediation Performance Objectives, please contact:
NFESC POC
(805) 982-1656
PRTH_NFESCT2@navy.mil
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