Risk Based Corrective Actions
Over the past several years environmental consulting has undergone a tremendous change as regulatory agencies around the world switched to risk based corrective actions (RBCA). The reasons for this shift are varied and includes the increasing discouragement for the disposal of contaminated soil in the limited landfill space, the limited effectiveness and high cost of current remedial methods, and the realization that soil types and other site-specific conditions may provide for a natural protection of human health and the environment.
Basically, application of the RBCA approach means that if you can demonstrate that the contamination poses a limited risk to human health and the environment, that portion of the contamination can be left in place. This often results in a significant cost savings.
RBCA methods include provisions for the development of site-specific cleanup concentrations. Although there can be significant differences depending on specific regulatory requirements, the RBCA method typically involves the use of a three tiered process outlined below.
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Tier 1
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Contaminant concentration lookup tables.
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Tier 2
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Simple equations that incorporate some site-specific properties.
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Tier 3
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Transport and fate modeling based on site-specific properties.
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Tier 1
Tier 1 concentrations are typically developed based on transport and fate modeling. Modeling scenarios are established based on a likely range of conditions under regulatory control. Tier 1 values are then set using the worst-case scenario. By selecting the worst-case the Tier 1 concentrations can safely be applied to any site. This means that unless your site happens to represent the worst-case scenario, cleaning up to the Tier 1 values would likely waste a significant amount of money. In addition, as remediation may be performed on relatively low level contamination, this may result in only a minimal reduction of overall risk.
Tier 2
Tier 2 methods were developed based on the realization that most sites do not represent the worst-case scenario. Unlike Tier 1 and Tier 3, which are typically based on modeling, Tier 2 methods often utilize simple equations. These equations incorporate some site-specific properties. Obviously, these simple equations cannot compete with the sophistication of a transport and fate model (If they did, Tier 1 values would be established based on them).
Although some site-specific properties are included, as with all aspects of the RBCA process Tier 2 results are designed to be very conservative. As such, Tier 2 values often provide little to no improvement over Tier 1 values. As with Tier 1 cleaning up to Tier 2 values may waste a significant amount of money, while providing for a minimal reduction of overall risk. It should be pointed out that in some instances with specific chemical and site properties application of Tier 2 methods can result in significantly higher clean up objectives.
Tier 3
Tier 3 typically consists of using the same transport and fate models that were used to develop the Tier 1 concentrations. It is a common misconception that since the Tier 1 values are based on modeling, site-specific modeling would only produce similar values.
This does not occur as modeling is performed using site-specific properties.
This often results in cleanup concentrations that are orders of magnitude higher than the Tier 1 and Tier 2 values. Believe it or not, Tier 3 values are also designed to be conservative. The higher concentrations are the result of a combination of the model capabilities and site properties. Not only can this save money, it provides for a better understanding of the risks posed by the contaminants. An additional benefit is a reduction in the disruption of normal site activities.
The problem with Tier 3 is not the limited effectiveness of the method, but the difficulty and time involved in using the models. You can see that application of Tier 1 or Tier 2 values to all sites would be prohibitively expensive. In addition, if remediation objectives continue to be based upon Tier 1 or Tier 2 values, RBCA methods will fail to provide a solution as promised.
SEVIEW
That is where SEVIEW comes in. SEVIEW was designed to simplify the development of Tier 3 contaminant concentrations to the point where almost any environmental professional can do it. This advanced software package sets a new standard in modeling ease of use and versatility. It allows users to focus on modeling the site, not running the models. The graphical reports allow users to accomplish more in one afternoon than can be accomplished in a month using any other package. Not only does SEVIEW out perform the competition, it cost hundreds of dollars less.
SEVIEW includes the SESOIL, and AT123D models, both chemical property and climatic databases, and a 344-page user's guide. Most regulatory agencies either require or accept SESOIL and AT123D results for the development of site-specific contaminant cleanup concentrations. These models have been used by state and federal agencies to establish Tier 1 values and to review Tier 3 submittals. To learn more about SEVIEW check out web site at
www.seview.com.
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