NOTE: Use of the RBCA tool kit requires:
It is recommended to 1st uninstall the RBCA Tool Kit prior to reinstallation. No other steps must be taken. However, you will be required to re-register the software. (See our FAQ regarding installation for detailed instructions.)
You will be notified via email if there are any updates to the RBCA Tool Kit. Installing updates requires uninstalling the software, downloading the new version, then installing and registering the software.
This error is caused by running the 64-bit version of Microsoft Excel. The RBCA Tool Kit makes extensive use of ActiveX controls which were compiled in 32-bit. These controls do not function in the 64-bit version of Microsoft Excel. Unfortunately, there is no work around. In order to use the RBCA Tool Kit, the user must employee the 32-bit version of Microsoft Office/Excel.
This error is due to a permissions issue in modern versions of Microsoft Windows. This error occurs when the RBCA Tool Kit is installed in a directory where the user does not have Full Control of the files, such as Program Files. If this error occurs, it is recommended to uninstall the software, then re-install to a folder such as Documents or Desktop. Then software must then be registered again.
Soil gas concentrations cannot be directly entered. However, by using the equilibrium partitioning equation, an equivalent total soil concentration can be calculated as function of soil gas concentration, which can in turn be entered into the software as the soil concentration. Assuming equilibrium partitioning among the soil, air and water phases, the bulk soil concentration can be derived from the soil gas concentration by the following:
CT (mg/kg) = Cair(mg/L) / H(dimensionless) / Ksw(kg/L)
CT (mg/kg) = bulk soil concentration
Cair (mg/L) = air phase (soil gas) concentration, (mg/L = ug/L * 10-6)
H = dimensionless Henry’s Law constant
Ksw (kg/L) = bulk soil-water partition factor, defined as follows.
Ksw = rhob / (thetaW + kd*rhob + H*thetaA)
rhob (kg/L) = soil bulk density
kd (L/kg) = soil-water partition coefficient (=foc*Koc for organics)
thetaW = volumetric water content (dimensionless)
thetaA = volumetric air content (dimensionless)
Lead is a non-cancer toxicant which is known to cause central nervous system (CNS) effects in children. The U.S. Environmental Protection Agency (USEPA) has established reference dose (RfD) values for a large number of non-cancer toxicants. Exposure to a compound at a level below the RfD is assumed to be safe. However, studies of lead toxicity have not established a “safe” exposure limit for lead. Therefore, the USEPA has not established an RfD for lead. RfD values for lead are not provided in the USEPA IRIS database or in any other toxicity database widely used to select toxicity values for the RBCA process.
The U.S. EPA has established action levels of 0.015 mg/L for drinking water, and screening levels for direct exposure to soils of 400 mg/kg and 800 mg/kg, for residential and commercial/industrial land use, respectively. However, none of these limits are actually risk-based.
When performing a RBCA assessment, comparing the results for the backward calculation (risk-based cleanup levels) to the results for the forward calculation (risk levels) does not always yield consistent results for a site. For example, concentrations detected at a site may not exceed applicable risk-based screening levels (e.g., RBSLs) for a given COC, but forward-mode calculated risks exceed target risks. When reading the following, please keep in mind that forward-mode calculations include the transient Domenico analysis worksheets, and cumulative risk calculation sheet, and backward-mode calculations include the TPH calculation worksheets.
In general, the two calculation modes use the same models and input parameters, but in certain cases, results will not always be identical because the two modes employ different assumptions. The main reasons the two methods may not always give the same results are listed below:
Backward-mode calculations sometimes include non-risk-based criteria, such as MCLs, as alternate criteria to the risk-based values.
Backward-mode calculations screen out results that exceed solubility or soil residual concentrations for indirect pathways. Target values calculated above these levels are flagged by the software as “>”, and either the aqueous solubility or soil saturation limit, depending on whether a groundwater or soil concentration is being reported. Forward-mode calculations do not screen for these values, which may result in inappropriately large risk values.
Backward-mode calculations for the surface soil pathway will combine intakes due to ingestion, dermal contact, and inhalation of volatiles and particulates. Forward mode calculations do not combine these intakes.
These inconsistencies result from standard practices within the technical community that differ between the two methods. As with any model, the user is advised to review the underlying assumptions and determine whether they are appropriate for conditions at the site being modeled.
The general equation for the upper confidence limit is as follows
UCL = mean + (standard deviation * t statistic)
Users may see certain aflags instead of numeric values in the results sheets. Many of these flags (e.g., NoMCL, Tox?, Veg?, No Z) give the user an indication of why a result cannot be calculated. The most common reason for a flag is that a required input for a selected chemical, such as a toxicity value, is not available in the chemical database. In order to remove the flag, the user must supply the missing data in the toxicity database.
Other data flags that may show in results are:
|NA||The NA value indicates that this pathway was not selected|
|NC||The NC value indicates that there is a parameter missing, and so the value was not calculated. The most common cause of this error is missing toxicity values for one of the chemicals of concern.|
|>||This flag indicates that the risk-based cleanup level exceeds the aqueous solubility or soil saturation limit for that particular chemical in the media of interest (water or soil). This suggests that the chemical will pose no risk for the corresponding exposure pathway. However, when this flag is shown, other issues such as the presence of non-aqueous phase liquids (NAPLs) or aesthetic concerns may still need to be addressed in accordance with local requirements.|
|####||The cell format is not compatible with the value, (e.g., the number is too big to fit into the window). Because the worksheets in the RBCA Tool Kit are locked, the column width or font size cannot be changed using Excel commands. However, to correct the problem, the font size for any cell may be changed as follows: select the cell, press Ctrl+Shift+F on the keyboard, and enter the desired font size. The font size may be adjusted downward until the contents of the cell can be read.|
A common misunderstanding among users is the important distinction between soil and groundwater source zones which, for purposes of RBCA calculations, do not overlap. The lower depth of affected soils should not exceed the depth to groundwater.
Entering values indicating that affected soils extend below the depth to groundwater can lead to miscalculations in the soil leaching to groundwater pathway. The base of the affected soil should be above the top of the water bearing unit.
Some users outside of the United States have reported problems loading and saving RBCA Tool Kit data files. Specifically, when Windows is configured to use the “,” (comma) for the decimal and the “.” (period) for the digit grouping symbol, then values for some input parameters may be corrupted when data is saved or loaded into the RBCA Tool Kit, depending on the particular language/version combination of Windows and Excel (e.g. English Windows with Portuguese Excel).
This problem does not occur when the Regional Settings feature in Windows is set to “English (United States)”. Alternatively, the Regional Settings language/country setting may be left as is, and under the “Number” tab choose “.” (period) for the decimal symbol and “,” (comma) for the digit grouping symbol.
In the RBCA Tool Kit for Chemical Releases, the air inhalation pathway calculations are based on reference concentrations, as opposed to reference doses for non-carcinogens, and unit risk factors, as opposed to slope factors for carcinogens (please see the air pathway equations on page A-12 of the software manual). These are the inhalation toxicity parameters actually measured for each COC in toxicological studies and reported by EPA in IRIS, HEAST, etc. These values are independent of inhalation rates and body weight. Converting reference concentrations to reference doses or unit risk factors to slope factors requires assumptions regarding inhalation rates and body weight (typically the RME values). Thus, whenever you see an inhalation reference dose or slope factor, implicit assumptions regarding inhalation rates and body weight have already been made in order to calculate that value.
Although the calculations in the RBCA Tool Kit make no assumption with regard to inhalation rates, in essence you can account for varying assumed rates by scaling the exposure duration or exposure frequency parameters by the corresponding factors. For example, if you wanted to assume an inhalation rate of 15 m3/day, as opposed to a 20 m3day RME value, you could scale the default exposure frequency of 350 days/yr to (350*15/20)=262.5 days/yr to account for an equivalent reduction in inhalation exposure, based on the measured reference concentration or unit risk factor.
The RBCA Tool Kit does not explicitly account for exposure time (ET, hours per day) in the calculation of inhalation risks; therefore, all inhalation exposures are implicitly assumed to occur on a 24-hr/day basis. If needed, one can effectively account for shorter inhalation exposure times (e.g., 8 hr/day for a commercial worker) by scaling either the exposure duration (ED) or exposure frequency (EF) parameter by the corresponding fraction of a day (i.e., the applicable ET value divided by 24 h/day). For example, an effective exposure frequency of 83 d/year (250 d/year*8/24) could be used to represent to 8 hr/day of exposure for 250 days per year.
To develop performance standards for a groundwater barrier wall, the RBCA Tool Kit can be run in “backward mode” to determine the applicable groundwater SSTLs based on the site-specific source location, groundwater parameters, and applicable point of exposure. These calculated SSTL values for each COC can then be entered into the software as the Representative Source Concentrations and the software rerun in “forward mode” using the Transient Domenico worksheet to determine the predicted steady-state plume concentrations at each point downstream of the source location. As long as an engineered barrier serves to prevent the downstream concentrations from exceeding these allowable levels, the risk limits at the point of exposure will not be exceeded. In other words, the steady-state Domenico plot shows how much the groundwater barrier can leak before it becomes a problem. If a barrier wall is installed, the concentration limits determined in this manner can be used to monitor the performance of the wall.
A similar analysis can be run for the soil leaching pathway by i) entering the actual measured soil COC concentrations and other site-specific soil and groundwater data and ii) running the software in the forward mode, and iii) adjusting the net rainfall infiltration level until you find the maximum level allowable such that none of the COCs cause a risk limit exceedance at the point of exposure. This final rainfall infiltration rate is the maximum seepage that can be allowed by a site cover. This level represents the rate up to which the site cover can leak before it poses a problem.
Users of the RBCA Tool Kit may wish to note that it is possible to keep multiple customized chemical databases, which is useful for those who perform risk assessments in locations with different regulatory standards.
The customized chemical database is stored in a file called “UserChemTox.xls”. Users who wish to keep multiple databases can rename this file with a meaningful name after use. The RBCA Tool Kit only accesses the file UserChemTox.xls for all of its custom information, so the storage files must be renamed whenever you switch custom databases.
There are no plans to implement the simultaneous support of multiple custom databases in the RBCA Tool Kit.
For users who have to reinstall the RBCA Tool Kit, it is also worth noting that you can move the UserChemTox.xls file to another location in order to preserve your custom database when reinstalling. After installation is complete, simply move the UserChemTox.xls file back into the RBCA Tool Kit folder.
For various reasons, we do not typically grant user requests for chemical information. However, the following links may be of help:
This may occur in some versions of the RBCA Tool Kit for Chemical Releases v.2.6.
Please follow these instructions and to resolve this issue. (This requires that you change the database and re-enter any changes you may have made to the database.)
To change to the new database, do this:
After this, if you go into Change the database, you will be able to edit all rows (after selecting Lock/Unlock).
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