Department of
Environmental Quality

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 has created two guidance documents, Risk Evaluation Manuals, as roadmaps for evaluating these risks, from discovery of contamination through cleanup, to determine whether ground water, surface water, or soil at a particular location is contaminated to the extent it poses a human health risk. The manuals guide DEQ employees and others in responding when chemicals are released to the environment. They help evaluate whether an investigation or cleanup is needed and, if so, what its scope and nature should be and thereby provide a consistent method for addressing contamination.

The original Risk Evaluation Manual, or REM, released in 2004, addresses a wide range of chemicals, such as metals, herbicides, chlorinated solvents, and petroleum hydrocarbons. The Risk Evaluation Manual for Petroleum Releases (Petro REM), released in July 2012, 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 replaces the procedures previously described in the REM for a prescribed list of petroleum-related chemicals commonly found at petroleum release sites. The original REM can still be used for other classes of chemicals.

2012 Risk Evaluation Manual for Petroleum Releases

The Petro REM includes a manual and software reflecting revisions based on comments received during a public comment period held August 3-31, 2011. The manual consists of 6 sections describing the risk evaluation process and 12 appendices that provide supporting information and guides on implementing important parts of the process, such as evaluation of the vapor intrusion pathway.

Download the manual here:

• Risk Evaluation Manual for Petroleum Releases

The software includes only the petroleum chemicals of interest specified in the rule. It also incorporates toxicity factor values from the revised rule and EPA recommendations on chemical-specific fate and transport property values. Finally, calculations involving inhalation risk and early childhood risk to mutagenic chemicals, incorporating recent EPA guidance on these topics.

The software was developed as an Excel spreadsheet. As a result of the release of new versions of Excel and changes in the Excel programming language, Visual Basic for Applications, over time, users may experience difficulties when using the software. A troubleshooting guide has been developed to assist users in minimizing these difficulties.

Download the software and troubleshooting guide here:

• Petroleum Risk Evaluation Software
• Petro REM Software Troubleshooting Guide

2004 Risk Evaluation Manual and Software

The REM consists of 12 sections describing the risk evaluation process and 14 appendices. The appendices contain supporting information to assist in implementation of the evaluation process.

Download the manual here:

• Risk Evaluation Manual (Main Document)
• Appendix A (IDTL Values)
• Appendix less Appendix M
• Appendix M (Software User's Guide)

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

• Risk Evaluation Software: A computational spreadsheet to calculate risks and target levels
• Mann-Kendall Calculator: A spreadsheet to conduct a Mann-Kendall analysis of trend for up to five chemicals and ten 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 webpage to learn of upcoming training opportunities.