Oregon
Each issue of the SEVIEW REVIEW will focus on the risk-based corrective action (RBCA) process for a state. This month we look at the Oregon Department of Environmental Quality (ODEQ). This is a great place to start, as the ODEQ was one of the first agencies to develop risk-based soil cleanup objectives back in 1991.
In Oregon, soil cleanup objectives protective of groundwater quality are established based on a two-step process. Step one consists of regulatory lookup tables. Step two consists of the development of site-specific values. Site-specific values can be developed using numerous methods. This can range from simple calculations to complex transport and fate modeling. For the purposes of this article, I have separated the second step into four substeps as outlined below.
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Step
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Method
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Number of
Sites
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1
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Lookup Tables
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All
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2
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Simple Equations
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Nearly All
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Simple Modeling
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Most
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Detailed Modeling
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Some
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Complex Modeling
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Almost None
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Lookup Tables
Baseline soil contaminant cleanup concentrations for 76 contaminants were developed in 1991. The cleanup objectives for the protection of groundwater quality were developed using SESOIL and AT123D. In 1998, 25 additional baseline concentrations were developed using soil:water partitioning and groundwater dilution-attenuation factor (DAF) equations. Soil:water partitioning is used to estimate soil pore water concentrations. The DAF is then used to estimate the resulting groundwater concentration.
Baseline values were established based on predicted groundwater concentrations directly below the soil contamination. In general, baseline values should only be applied to sites with similar characteristics to the baseline scenarios. As use of this method simply involves looking up values, a detailed knowledge of the site characteristics is not required.
Simple Equations
This process utilizes the same soil:water partitioning and DAF equations used to develop the 1998 baseline values. All a user has to do is replace the default information with site-specific values. Use of this method requires collection of additional site-specific characteristics used in the equations.
Reporting is typically limited to several paragraphs in the site investigation report. The report should provide support for the selection of site-specific values over the default values. Depending on the number of contaminants this process can typically be completed in about 1 to 4 hours.
Simple Modeling
Like the simple equations option, this method depends heavily on baseline input parameters. Modeling is performed by replacing select default input parameters with site-specific values. Application of this process requires collection of additional site-specific properties.
Basically, a few site-specific parameters are entered into the models for each contaminant. As modeling is based on default values typically only one model scenario is run for each contaminant. Since the conservative input values are used there may be no need to perform sensitivity analysis or to develop a detailed CSM.
Modeling is typically performed using the same models that were used to develop the baseline values. This should be done for several reasons. First, although different models may include the same input parameters it does not mean they are used in the same way. Second, some model specific parameters cannot be easily transferred from one model to the next.
This process typically includes both unsaturated soil (vadose zone) and groundwater modeling. Groundwater modeling is done even when the point of compliance is directly below the soil contamination to evaluate the influence of groundwater dilution. Application of a DAF may suffice in some cases, however limitations in the method may severely restrict the effectiveness.
Documentation typically consists of a separate modeling section in the site investigation report. The report should include selection rationale for all site-specific input parameters and printouts of the model results. Like the simple equations method, most environmental professionals should be capable of performing this evaluation. Using the SEVIEW package simple modeling can typically be completed in an afternoon.
Detailed Modeling
This is what most people intuitively think of when someone mentions modeling. Proper application of this method requires a detailed site investigation. A CSM should be developed to evaluate the influence of site-specific conditions on the fate of contaminants.
As with simple modeling methods, modeling is typically performed using the same models used to develop the baseline values. However, an evaluation as to applicability of the model capabilities to site conditions may be required. Sensitivity analysis which consists of varying select input parameters over a likely range should be performed. This process usually includes both vadose zone and groundwater modeling.
In some cases, if it can be demonstrated that groundwater will not be developed based on current and potential future uses of the property, the point of compliance can be moved to the property boundary. However, use of an alternative point of compliance would likely require a deed notification.
Projects of this level are typically documented in a separate report. The report should include a description of the CSM. The report should provide an explanation as to why each input values were used. Development of the CSM, modeling, and report preparation usually takes between about 3 to 10 days to perform. This is assuming modeling is performed using the SEVIEW package.
Complex Modeling
Most people intuitively lump this process in with detailed modeling, but it is very different. This method involves evaluation of additional influences on transport and fate. For instance, this could include complex geological conditions or the influence of a pumping well on groundwater flow. This process usually includes both vadose zone and groundwater modeling. Proper application of this method requires a very detailed and expensive site investigation. A detailed CSM should be developed.
An evaluation of model capabilities and applicability to your site should be performed. In some cases, this may even include making modifications to the models themselves. Sensitivity analysis must be performed. This is because only site-specific parameters are used and different models may have been selected.
Modeling projects of this level are typically documented in a separate report. The report should provide an explanation as to why each input value was used. Development of the CSM, modeling, and report preparation usually takes at least two weeks to perform. However, in some cases, modeling projects of this type may take several months to complete.
Diminishing Returns
Although the steps are laid out, one of the main problems with the development of site-specific cleanup values is knowing when to stop. Stop too soon, and you needlessly waste money remediating the site to the lower levels. Keep moving through the process and you'll waste money attempting to achieve ever higher cleanup values.
The ODEQ calls these "off ramps". An off ramp provides an opportunity to evaluate the status of the process. A decision to continue or exit is dependent upon several factors. Most of the time cost is the most important factor. For instance if site remediation would cost about the same or less than moving to the next level, then exit. An additional advantage of this approach is that consultants can move through the process according to their comfort level.
Also important is achievement of specific project goals. These goals can be established based upon numerous factors including current and future land use, acceptability of deed restrictions, and even public consent. As such, these goals can have a significant influence on when to exit.
Click on the links below, to learn more about RBCA process in Oregon.
www.deq.state.or.us/wmc/tank/rbdm.htm
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RBCA Process
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