In September 2016, the Montana Department of Environmental Quality (DEQ) updated its Risk-Based Corrective Action Guidance for Petroleum Releases (RBCA). The primary reasons for the update were the release of updated United States Environmental Protection Agency (EPA) inhalation Provisional Peer Reviewed Toxicity Values (PPRTVs, September 2009) and February 2014 Human Health Evaluation Manual, Supplemental Guidance: Update of Standard Default Exposure Factors. In addition, DEQ updated leaching to groundwater parameters to match those currently used in the May 2016 EPA Regional Screening Levels tables. RBSLs for 1-methylnaphthalene and 2-methylnaphthalene were also added since these polycyclic aromatic hydrocarbons (PAHs) are often found along with other PAHs.
DEQ also took this opportunity to expand the RBCA Guidance with a description of a RBCA Tier 2 process involving adjustment of RBSLs based upon site-specific conditions. The guidance now includes information regarding the Air-Phase Hydrocarbon Calculator and an updated Calculator to account for concentrations of compounds found in DEQ’s August 2012 Typical Indoor Air Concentrations of Volatile Organic Compounds in Non-Smoking Montana Residences Not Impacted by Vapor Intrusion that are higher than their screening levels.
In general, the RBCA text has also been updated and clarified as necessary. The RBSLs are still based upon the same fractions originally included in Massachusetts guidance, so DEQ added text regarding conversion of old total petroleum hydrocarbon, diesel range organics and gasoline range organics data to estimated petroleum fraction data.
The RBCA Guidance now includes language regarding conceptual site models that will assist with site characterization and evaluation. DEQ evaluated and clarified language regarding metals analyses and proper analytical methods. In addition, DEQ changed the number of significant figures of each RBSL from one to two based upon EPA risk assessment guidance.
The result of all the changes is that some of the RBSLs are higher than those in the 2009 RBCA Guidance and some are lower. Whether an RBSL went up or down was dependent upon whether it is based upon leaching or direct contact. The fractions with inhalation toxicity changed substantially due to the change in toxicity criteria. Some more minor changes resulted from the changes in exposure factors. Minor RBSL concentration changes may be the result of different rounding.
Changes to various DEQ rules will be proposed to incorporate the new 2016 RBCA Guidance. In the future, DEQ intends to review the RBCA Guidance annually to determine if revisions are necessary. It is anticipated that the RBCA Guidance will only be updated if substantive changes have occurred.
If you have questions on the updated RBCA Guidance, contact Aimee Reynolds at 406-444-6435 or firstname.lastname@example.org, or Katie Shepard at 406-444-5595 or email@example.com.