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Risk Based Decision Making: Frequently Asked Questions



​You should download the Excel spreadsheets onto your computer before trying to run them. To download a file you should right-click on the link. This will bring up a menu. Then left-click on "Save Target As..." (in Internet Explorer). Other browsers should have a similar option. The computer's standard "Save As" box will then open and allow you to select the folder in which you want to save the file. (Be sure to remember the folder.) After you click on "Save," the file will be downloaded onto your computer. You should then close your browser and open the spreadsheet as you would any other file on your computer.
​This may happen if Excel is set to "disable macros." You should change the Excel setting to "allow macros." To do this, open Excel, select the "Developer" tab on the ribbon bar and select the "enable all macros" radio button before opening the spreadsheet.
​You should not have both spreadsheets open at the same time. Because the two spreadsheets have similar codes in them, having both open at the same time can cause them to function improperly. Never open one spreadsheet until the other has been closed.
​When you add a new chemical to the spreadsheet you don't have to enter data into all the empty cells. Some of the cells are protected because they're cells the spreadsheet will calculate for you. Protected cells are usually shown in gray and unprotected cells in white. Note that all of the cells on the risk-based concentration page are protected. You only need to add data to the white cells on the ChemData page and the ToxData page in order to add a new chemical. For example, you start by adding the chemical name, molecular weight, solubility, etc. on the ChemData page. You cannot, however, enter the volatility, vapor pressure, Csat, etc. They are calculated by the spreadsheet. Likewise, you cannot enter a chemical name on the ToxData page. The chemical name from the ChemData page is automatically copied onto the ToxData page.

No, you can not use VPH or EPH data from groundwater samples in the DEQ spreadsheet to calculate site-specific risk-based concentrations. You can only use data that represent the composition of the product as it exists today. The best data for that purpose come from soil samples. Water samples will be enriched in the constituents that dissolve the most and depleted in the ones that dissolve the least. Even when using soil samples you should use relatively heavily contaminated samples.

The reason you must use data that represent the product is that models used in DEQ's TPH risk-based concentration spreadsheet are based on the assumption that you're starting out with product. The models calculate concentrations that are likely to end up in the air and water, and uses those concentrations to estimate risk-based concentrations.

VPH data from a groundwater sample would allow you to calculate risk from direct exposure to the water, such as from ingestion and/or dermal exposure. However, you'd have to do that manually by determining the risk (hazard quotient) for each component and then summing them to get the total risk (hazard index) from the entire product.

​No. Generic TPH risk-based concentrations only take into account the risk from exposure to a product having a composition like that of a typical diesel (see Appendix F for that composition). Therefore, the diesel risk-based concentrations do not address the risk from exposure to the heavier compounds in products such as a lube oil or No. 6 fuel oil.
​Generic risk-based concentrations are typically used for screening. However, the only generic TPH risk-based concentrations are for gasoline, diesel or heating oil, and transformer mineral insulating oil. For other petroleum products, either individually or as a mixture, you're limited to using either the soil matrix cleanup level or site-specific risk-based concentrations. If TPH concentrations at your site exceed the soil matrix cleanup level and remediation to that level is not feasible, you have the option of following the instructions for Method 2, Option 2 on the TPH spreadsheet to calculate site-specific values. For example, for a generic lube oil, or oil that may be used in a wind turbine, compositional information is necessary in order to derive risk-based concentrations specific to that, or any other product.
​In some instances risk-based concentrations calculated using the currently accepted toxicity values and computational approaches may result in concentrations that are below readily achievable detection or reporting limits. This may result in less precise concentration estimates or the inability to determine if a compound is present above risk based levels in the media analyzed.

In these instances, DEQ will usually accept non-detection based on the best commercially available technology as sufficient evidence that the compound is not present. Moreover, levels below the quantitation limit (e.g., practical quantitation limit or method reporting limit) are understood to be less precise and therefore have greater uncertainty. DEQ may not always accept non-detection as adequate evidence that a compound is not present, where there is a reason to believe based on site history or other knowledge that a compound could be present. For example, non-detections of polychlorinated biphenyls as aroclors by EPA method 8082 may not be sufficient evidence of the absence of PCBs. PCBs are often found to be present in samples by method 1668 at levels below what can be detected by method 8082 and are known to be widely present in soils and sediment.
​You must show that both the carcinogenic risk from constituents and the noncarcinogenic risk from TPH are acceptable. You've already met the requirement for the constituents, but you still must show that the TPH risk is acceptable. Since there are no generic TPH risk-based concentrations for waste oil, you can either use the soil matrix cleanup levels or calculate a site-specific cleanup level by testing the waste oil with the new extractable petroleum hydrocarbon test and using the data with the TPH spreadsheet.
​The symbol means that the lowest risk-based concentrations vary depending on the endpoint and scenario, and the spreadsheet cannot show all the lowest RBCs simultaneously. The spreadsheets are designed to calculate RBCs for either non-cancer or cancer-based endpoints, based on user selection of the desired endpoint. Generally, RBCs based on cancer endpoints are lower because of mathematical models and assumptions associated with this endpoint. For some chemicals, the lowest RBCs vary by both scenario and endpoint. That is, non-cancer RBCs are lower in some columns and cancer RBCs are the lowest for others. Therefore, the spreadsheet must be run in both cancer and non-cancer modes to derive all the lowest RBCs. Alternatively, all the lowest RBCs are presented in the Adobe PDF® tables.
​DEQ and EPA use equivalent methods to calculate risk-based concentrations. However, for some substances the parameters used may vary slightly due to selection of different estimates of chemical properties or different values for some exposure parameters. Both the EPA and DEQ parameter choices are valid, and represent slightly different choices. In some of these instances, the resulting absolute value of the RBCs can be quite different. As one example, the RBC for anthracene in the May/June 2011, EPA table for residential soil is 17,000 mg/kg. In the November 2011 DEQ table, the corresponding value is 23,000 mg/kg- a difference of 6,000 mg/kg. In absolute terms the difference seems large. However, the difference is only 26 percent. Therefore, in relative terms, the values are not substantially different. The difference illustrates the range of similar RBCs that could be derived. For Oregon sites, the DEQ RBCs should be used. If a chemical does not have a DEQ RBC, then the EPA regional screening level should be used.
​​The value of RBCsi (vapor intrusion into indoor air) for generic gasoline goes from 94 parts per million for the residential scenario to >MAX for the occupational scenario. Why does this risk-based concentration increase so much when the occupational exposure is not that much less than the residential scenario?

Answer



Contact

Michael Greenburg
Emergency Response Coordinator
503-229-5153



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