Protecting Public Health and the Environment.

Risk Evaluation Manual

Addressing Contamination - Evaluating Risk

DEQ's "Risk Evaluation Manual" - or REM - presents a roadmap for evaluating risk, from discovery 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 manual guides DEQ employees and others in responding when chemicals are released to the environment. It helps evaluate whether an investigation or cleanup is needed and, if so, what its scope and nature should be and thereby provides a consistent method for addressing contamination.

When contamination does occur, it is important to determine whether it presents a health risk. Contamination in ground water can pollute drinking water. Contaminated rivers and lakes can poison fish or waterfowl. Contaminated soils can release harmful vapors into the air.

Overview of Risk Evaluation Manual and Software

The manual consists of 12 sections and 14 appendices. Section 2.0 presents a brief description of the steps in the risk evaluation process. Sections 3.0 and 4.0 present general information related to data requirements and implementation of the risk evaluation process. The next seven sections present details of each of the steps in the process. The final section provides a list of references cited and additional useful references.

The appendices contain a large amount of information to assist in implementation of the evaluation process. This information includes:

  • tables of the Initial Default Target Levels (IDTLs) for the chemicals selected
  • physical, chemical, and toxicological values for these chemicals
  • rationale for the selection of screening default fate and transport
  • and exposure factor parameter values
  • equations implemented in the calculations, guidance on natural attenuation and
  • evaluation of the vapor intrusion pathway
  • software user's guide
  • examples of reporting formats and deed restriction language

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

  • A computational application to calculate risks and targets levels
  • A utility to conduct a Mann-Kendall analysis of trend for up to five chemicals and ten sampling events
  • A utility 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-t estimate.

Manual Availability

The manual and software may be downloaded after registering (name, agency, and email address). Registration enables DEQ to notify all users when updates or additions become available, thereby ensuring all users have access to the most current information at all times. Copies of the manual and accompanying software are also available electronically.

Registration / Login

Training Opportunities

Training on the manual is offered periodically throughout the year. Registering for the download of the manual and software automatically includes you on DEQ's Risk Evaluation Training Notification List. Once training is available, you will be notified by email. If you already have the manual and software and wish to be included on the training list, call or e-mail Teri Gregory, DEQ State Office, at (208) 373-0502 or teri.gregory@deq.idaho.gov.

Note: Suspended Use of Three Chemicals of Concern

EPA has discontinued discussions regarding the toxicity of the chemicals 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and 2-methylnaphthalene. Until there is more clarity about these chemicals of concern, DEQ will no longer consider 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and 2-methylnaphthalene when applying REM to assess health risks at contaminated sites.

Draft Risk Evaluation Manual for Petroleum Releases

A public comment period was held August 3-31, 2011, on a separate draft Risk Evaluation Manual for Petroleum Releases to implement the Standards and Procedures for Application of Risk Based Corrective Action at Petroleum Release Sites (IDAPA 58.01.24), which were codified in May 2009, and the rule revisions proposed under Docket No. 58-0124-1101.

The document includes a draft manual and software. The draft manual provides guidance on evaluating potential risks to human health and the environment resulting from petroleum releases and implementing corrective action measures to mitigate those effects, if needed. The draft software limits the chemicals evaluated to only those specified in the rule, modifies calculations that involve inhalation risk, and adds appropriate toxicity factor values. In addition, it incorporates EPA recommendations on calculation of risk and chemical-specific fate and transport property values.

Public Comments Received

Comment on Date Received Submitted by
Draft Manual 08/31/11 Olympus Technical Services, Inc.
Draft Manual Appendices 08/31/11 Olympus Technical Services, Inc.

Staff Contact

Voluntary Cleanup Program Manager
Bruce Wicherski
DEQ State Office
Waste Management & Remediation Division
1410 N. Hilton
Boise, ID 83706
(208) 373-0246
bruce.wicherski@deq.idaho.gov

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