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Risk-Based Decision Making for the Remediation of Petroleum-Contaminated Sites
Introduction
The guidance document, “Risk-Based Decision Making (RBDM) for the Remediation of Petroleum-Contaminated Sites” was originally developed in September 1999 and has been updated periodically. Significant updates expanded the original RBDM guidance document in September 2003 to cover hazardous substance cleanups as well as petroleum-contaminated sites. In September 2006 and March 2007 the spreadsheets associated with the guidance document were expanded to include generic Risk-Based Concentrations (RBCs) for most of the hazardous substances of interest to DEQ. Additional updates to the spreadsheets in March 2007 included changes to some exposure factors to account for early-life exposure to certain carcinogenic hazardous substances, including some petroleum constituents.
The 2003 guidance document and the 2007 revised spreadsheets can be used for both: a) cleanup of petroleum releases from regulated underground storage tanks (USTs) under the Cleanup Rules for Leaking Petroleum UST Systems (OAR 340-122-0205 through 340-122-0260); and b) releases of hazardous substances including petroleum under the Hazardous Substance Remedial Action Rules (OAR 340-122-0100 through 340-122-0115).
The purpose of the guidance is to provide a consistent, streamlined decision-making process for evaluating risk posed to human health and the environment. Use of the guidance is optional; other models or approaches to evaluating site risk may be used by responsible parties and the Department and may be more appropriate for individual sites.
Guidance Document and Spreadsheets
In addition to the written guidance document, the Department's Environmental Cleanup and Tanks Sections revised the two spreadsheets used to calculate the generic risk-based concentrations (RBCs). These spreadsheets are provided to interested parties primarily as reference documents that contain:
- The Environmental Cleanup and Tanks Section generic RBCs; and
- The default exposure factors, chemical data, and toxicological data used to calculate the generic RBCs.
The default exposure factors, chemical data, and toxicological data in these spreadsheets can be modified to calculate site-specific risk-based cleanup levels.
For more complete information about the derivation of the RBCs, please refer to Appendix B in Risk-Based Decision Making for the Remediation of Petroleum-Contaminated Sites. Copies of the RBDM guidance document and spreadsheets can be obtained by downloading them from the links below. The spreadsheets are offered for use without warranty or support. They are designed to work with Microsoft® Excel 2002 and may not work properly with other applications or with older releases of Excel.
Spreadsheets: Your Excel's macro security setting must be set to "Medium Level" in order for the spreadsheets to open properly.
Notes on updates to spreadsheets (March 2007):
Added Chemicals
In September 2006, DEQ revised the Risk-Based Concentration (RBC) spreadsheet to include most of the hazardous chemicals of interest to the Department. The March 2007 revisions include corrections to errors and revised toxicity information to be consistent with decisions made by EPA Region 6. DEQ is now using EPA Region 6 screening values because EPA Region 9 preliminary remediation goals (PRGs) are no longer being updated by EPA The chemicals added to the RBC spreadsheet were previously included in the tables of SOCLEAN (OAR-340-122-045) values. The outdated numbers were removed by the Environmental Quality Commission from the Cleanup Program administrative rules in 2006. The prior RBC table included petroleum hydrocarbons (primarily BTEX and PAH compounds) and chlorinated volatile organic compounds (VOCs). The new spreadsheet includes additional VOCs, semi-volatile organic compounds, pesticides, and inorganic chemicals. The RBCs should be used in preference to EPA Region 6 screening values.
As before, the spreadsheet allows the user to calculate RBCs for additional chemicals, as desired. See Appendix J of the September 2003 RBDM guidance, and the introductory notes that accompany the spreadsheet for instructions on how to calculate RBCs for new chemicals.
Early-Life Exposure
The new spreadsheet incorporates early-life exposure following EPA’s cancer risk assessment guidance. In the new spreadsheet, the early-life calculations for carcinogenic polycyclic aromatic hydrocarbons (cPAHs) are activated in addition to vinyl chloride. Vinyl chloride is evaluated using the specific approach already presented by EPA in the IRIS supporting documentation. For additional information on incorporating early-life exposure into risk assessments or the calculation of RBCs, see: Memo on Incorporation of Early-Life Exposure in Human Health Risk Assessments (link listed above before "Spreadsheets").
Non-volatile Chemicals
The revised spreadsheet does not calculate RBCs for volatilization transport pathways for chemicals that are considered non-volatile. DEQ may decide to include these pathways on a site-specific basis.
Non-carcinogenic Effects of Carcinogens
RBCs for carcinogens are based on carcinogenic effects, which are generally lower than RBCs based on non-carcinogenic effects. Some chemicals, such as chromium VI, are carcinogenic by one route (inhalation), but not by other routes (such as ingestion). To calculate the appropriate RBCs for non-carcinogenic effects, you need to first change the toxicity basis in the spreadsheet from “c” to “nc”, and then re-calculate the RBCs. You should use the lower of the calculated RBCs for each exposure scenario.
TPH Calculations
Because of changes to non-cancer toxicity factors for a few chemicals, the spreadsheet for calculating RBCs for total petroleum hydrocarbons (TPH) has also been updated. However, the revisions are minor, and did not result in changes to generic RBCs for TPHgasoline, TPHdiesel, or TPHmineral-oil.
Implementation Schedule
The revised RBCs should be implemented according the following guidelines:
- For all newly initiated RBDM screening evaluations at a site, the recently revised RBCs and EPA Region 6 screening values will be used from this point forward;
- For RBDM screening evaluations currently being performed, the revised RBCs and EPA Region 6 screening values will be used on a case-by-case basis; and
- For completed RBDM screening evaluations submitted before 2 April 2007, reassessments may be performed on a case-by-case basis when a new decision is required that needs to be supported by a screening evaluation or updated risk assessment. Until that time, the current completed and approved screening evaluation will continue to be considered valid based on the guidance used when the assessment was completed.
EPA Region 6 routinely updates screening values in December of each year. DEQ will evaluate annual updates to EPA Region 6 screening values, and update RBCs in January of each year. Under special circumstances, DEQ may at any time require a revised screening value for a chemical based on new toxicity information.
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