Protecting Public Health and the Environment.

Risk Evaluation Manual

Addressing Contamination—Evaluating Risk

When contamination occurs, it is important to determine whether it presents a human health risk such as contaminated soils or ground water releasing harmful vapors into the air inside living or working spaces, contaminated ground water polluting a drinking water well, or contaminated rivers and lakes impacting drinking water systems and affecting recreationalists.

DEQ created the 2018 Risk Evaluation Manual for Petroleum Releases (Petro REM) to evaluate risks from discovering petroleum contamination through cleanup to determining whether ground water, surface water, or soil at a particular location is contaminated to the extent it poses a human health risk. The 2018 manual guides DEQ employees and others in responding when petroleum chemicals are released to the environment. It helps evaluate whether a petroleum release investigation or cleanup is needed and, if so, what its scope and nature should be, providing a consistent method for addressing contamination.

The 2012 Petro REM was developed to implement the Standards and Procedures for Application of Risk Based Corrective Action at Petroleum Release Sites (IDAPA 58.01.24), codified in May 2009 and revised in March 2012. The Petro REM is for a prescribed list of petroleum-related chemicals commonly found at petroleum release sites.

2018 Risk Evaluation Manual for Petroleum Releases

Since the 2012 adoption of the rule and guidance, many of the petroleum chemicals of concern listed in the tables in the rule and guidance have had updated toxicity information which has resulted in the screening levels found in the tables to be out of date with current toxicity criteria.

The Petro REM includes a manual reflecting revisions based on comments received during a public comment period held from June to August in 2018. The screening levels and toxicity criteria have been updated to reflect current toxicity criteria.  The manual consists of six sections describing the risk evaluation process and 12 appendices that provide supporting information and guides on implementing important parts of the process, such as evaluating the vapor intrusion pathway.

Download the manual here:

The software will be updated in the next few months to reflect the toxicity updates. Once the changes to the software are made, the updated software will be published on this webpage. In the meantime, please contact Eric Traynor at (208) 373-0565 or to discuss the risk evaluation process.

The software was originally developed as an Excel spreadsheet. DEQ has replaced the spreadsheet with a standalone Windows application that does not require additional software like Excel. Excel files will no longer be available or accepted for use.

Improvements to the new software include:

  • A user-friendly graphical interface and step-by-step process
  • A screening level evaluation step
  • Significantly smaller file sizes for individual simulations
  • Links to the petroleum risk evaluation rules, guidance, and user guide
  • Original application errors corrected

Download the software and user guide below. (Instructions)

2004 Risk Evaluation Manual and Software

The 2004 Risk Evaluation Manual (REM) and software have been removed from the DEQ website and should no longer be used by DEQ staff or others. There are several reasons for the need to discontinue the use of the 2004 REM and software, as stated below:

  1. The 2004 REM has outdated toxicity information and exposure factors, which results in the use of incorrect initial default target levels (IDTLs), incorrect risk calculations and incorrect remedial action target level calculations for certain chemicals (e.g. trichloroethylene and tetrachloroethylene).
  2. The petroleum constituent IDTLs listed in the 2004 REM are causing confusion with the residential use screening levels (RUSLs) in the “Standards and Procedures for Application of Risk Based Corrective Action at Petroleum Release Sites” (IDAPA 58.01.24). For petroleum releases, the RUSLs should be used as screening criteria.  
  3. The changes in inhalation, vapor intrusion risk, and evaluation of risk to children from chemicals with mutagenic characteristics risk assessment methodologies since development of the 2004 REM.
  4. The risk assessment methodologies in the 2004 REM are not consistent with the 2012 petroleum REM and EPA practices.

Unless identified in a previously approved corrective plan or an existing consent order, the IDTLs listed in the 2004 REM should not be used or referenced. As an alternative, the EPA Regional Screening Levels or other DEQ approved risk assessment approach can be used to determine risk-based criteria for non-petroleum chemicals of concern.

The following spreadsheets are also provided to assist in evaluating risk:

  • Mann-Kendall Calculator: A spreadsheet to conduct a Mann-Kendall analysis of trend for up to 5 chemicals and 10 sampling events.
  • UCL Calculator: A spreadsheet to calculate the 95% upper confidence limit (95% UCL) of the mean for chemical concentration data. The utility calculates the 95% UCL for normal and log-normal distributed sample data, as well as a bootstrap estimate.

Training Opportunities

DEQ periodically offers training on the Petro REM. Check DEQ’s Conferences, Trainings, and Workshops web page to learn of upcoming training opportunities.  

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Staff Contacts

Voluntary Cleanup Program Manager
Derek Young
DEQ State Office
Waste Management & Remediation Division
1410 N. Hilton
Boise, ID 83706
(208) 373-0525

More Information

U.S. EPA Regional Screening Levels

Related Pages

Environmental Covenant

Leaking Underground Storage Tanks in Idaho