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LUST Site Assessment

The documents linked to this page all relate to the assessment of sites where leaking underground storage tanks (LUST) are or have been located. The process of assessment uses risk-based corrective action (RBCA). The objective of RBCA is to evaluate the risks posed by contamination to human health, safety and the environment using a progressively more site-specific, three-tiered approach. All proposed corrective actions must be submitted and supervised by a certified groundwater professional.

Corrective Action Design Report (CADR) Guidance

For updates and guidance, see also the Groundwater Professional Bulletin Board.

5 - Sampling for Bedrock Sites

All Site Monitoring Reports (SMRs) for bedrock sites should be completed using the Tier 2 Bedrock Software, version 1.20. For bedrock sites, there is no SMR module within the software program. Annual site monitoring data may be input into the version 1.20 file and software rerun to determine pathway classifications. Please indicate in a cover letter whether the report is a Tier 2 or SMR.

All data for the site, including the most recent sampling event should be entered into the analytical data sections of the bedrock model. This is different than standard Tier 2 modeling, in which data is entered into an SMR module.

Tier 2 Bedrock Report Form - When submitting a bedrock Site Monitoring Report the pages that are not printed from the software are now fillable PDF Forms.

1 - Tier 1 Assessment

The purpose of the Tier 1 assessment is to use limited site data and conservative assumptions to determine whether a site poses an unreasonable risk to public health, safety or the environment. The first form below is known as the Tier 1 report. The Tier 1 Report is followed by a guidance document.

Due to regulatory changes and compatibility issues with newer operating systems, the Tier 1 software and Tier 1 software guidance have been removed from the UST web page.  The Tier 1 software should no longer be used or submitted with the Tier 1 Report. 

The Tier 1 Guidance document has been revised to include the Pathway Evaluation Worksheet (Appendix H).  The worksheet or flowcharts can assist with completing the Tier 1 Report.

The Tier 1 Report must now be completed using current DNR Form 542-0165, which has been updated to reflect regulatory changes.  If you have questions regarding the new Tier 1 reporting procedures, please contact the DNR project manager.


2 - Tier 2 Assessment

The web-based application will be used for new and revised Tier 2 Site Cleanup Reports, and Site Monitoring Reports.  This does not apply to non-granular bedrock and granular bedrock sites. Please review the FAQ document posted on the DNR UST web page prior to using the application for RBCA purposes.

The purpose of Tier 2 assessment is to collect additional site-specific data and, with the use of Tier 2 fate and transport modeling, determine what actual and potential receptors could be impacted by chemicals of concern.

A Tier 2 Site assessment must be conducted and a Site Cleanup Report submitted for all sites when any of the following conditions occur:

  • Free phase petroleum product is present at the site.
  • The site owner or tank owner/operator has decided to bypass the Tier 1 assessment and go directly to the Tier 2 assessment phase.
  • A pathway has failed the Tier 1 assessment.
  • During drilling, bedrock was encountered before groundwater.
  • Explosive vapor levels were measured during a Tier 1 assessment or recent investigation of the site.

Tier 2 Guidance along with application will help you to fill out the assessment report. The application will perform the same functions as the former software in essentially the same ways.

Web-Based Risk Based Corrective Action (RBCA) Application

The web-based application will be used for new and revised Tier 2 Site Cleanup Reports, and Site Monitoring Reports.This does not apply to non-granular bedrock and granular bedrock sites. Please review the FAQ document posted on the DNR UST web page prior to using the application for RBCA purposes.

The Tier 2 Site Cleanup Report Guidance has been updated.  This update of the Tier 2 Guidance was undertaken in an effort to make the document more user-friendly and to better reflect current practice.  You will find most items unchanged; however, some of the updates include:

  • Tier 2 Guidance is now a searchable document in a user-friendly format with embedded links.
  • New guidance on surface water risk assessment.
  • The stabilization time for soil gas sampling (Option 2) has been changed to 24 hours.  This change will take effect 60 days after the new Tier 2 Guidance is posted to allow for projects already in progress.   This is effective September 6, 2015.
  • A section on diving plumes and free product has been added.

Tier 2 Guidance

RBCA Tier 2 and Site Monitoring Report Application User’s Manual

Site Monitoring Report (SMR) Guide (Version 2.2)

Tier 2 Report Form - The pages for the Tier 2 Report which are not printed from the application are now fillable PDF forms.

3 - Tier 3 Assessment

Unless limited by rule, an owner or operator may choose to prepare a Tier 3 site assessment as an alternative to completion of a Tier 2 Site Cleanup Report or Corrective Action Design Report. Prior to conducting a Tier 3 site assessment, a workplan must be submitted to the department for approval. The workplan should follow an outline similar to a scientific experiment and should include an introduction, description of methods and models to be used, discussion of risk classification, summary and references.

The Tier 3 workplan may include a proposal for additional site assessment, the use of probabilistic evaluations, or more sophisticated chemical fate and transport models. Calibration of the IDNR Tier 2 model can also be considered with justification. Following approval of the workplan, a Tier 3 assessment report will be required within a reasonable time designated by the department.

The Tier 3 assessment report must include a recommendation for site classification as high risk, low risk or no action required. If a corrective action is required, the Tier 3 report must provide an outline of possible corrective actions technologies and a recommendation for implementation of a remediation technology which is consistent with the standards and policies underlying the department's risk classification and corrective action response rules.

Tier 3 Analysis

The most commonly used three-dimensional (3D) computer software packages, Groundwater Modeling System (GMS) and Visual MODFLOW, plus the two-dimensional (2D) software package, BIOPLUME III were selected to be evaluated for the purpose of the Iowa RBCA Tier 3 analysis. The 3D packages contain the well-established groundwater modeling codes, MODFLOW, MT3D, MT3DMS, and RT3D. The specific features of each of the packages are described and compared. In addition, general data requirements and modeling procedures to use these codes and packages are discussed.

A comparison of the three software packages suggests that GMS is superior to Visual MODFLOW and BIOPLUME III because (1) GMS does everything Visual MODFLOW and BIOPLUME III do and more, and (2) GMS is better documented and more users’ friendly. Other factors may have to be considered when selecting a software package. The license prices and training costs for GMS and Visual MODFLOW are similar and excellent technical support are provided. The software BIOPLUME III is free but no technical support and training course are provided by the software developer. All three software can be run on a Pentium PC with 32 MB RAM and SVGA monitor but only GMS has a UNIX version which can be run on a work station.

Guidelines for Numerical Modeling in Tier 3 Assessments and Other Corrective Actions

This document aims to provide guidance for consultants who contemplate using a numerical modeling program such as Visual MODFLOW or GMS.  The guidance stresses how one should approach a modeling project and how to report the results. The need to include in a report all details of the multi-step modeling process is treated. Three examples of numerical modeling of petroleum releases are provided from the western Iowa towns of Climbing Hill, Ida Grove, and Sioux City. The examples are not complete modeling reports of the type described in the text, but are included to show the degree of detail needed to accomplish such a project and to demonstrate validity to IDNR.

Guidelines to Determine Site-Specific Parameters for Modeling the Fate and Transport of Monoaromatic Hydrocarbons in Groundwater

The objective of the guidelines report is to provide guidelines for determining site-specific parameters to model the fate and transport of dissolved groundwater pollutants. Ground water professionals will find this report helpful in cases where tier-3 assessments need to be conducted, and when additional site characterization is required to inform a choice about corrective action or remediation system design.  This report will emphasize modeling the fate and transport of benzene. This decision is based on the facts that benzene is the most toxic of the soluble components of gasoline, is more mobile than the other aromatic hydrocarbons, and is subject to the strictest cleanup standards because of its carcinogenic properties.  Thus, benzene concentrations often determine the need for remedial action at LUST sites. Nevertheless, the fundamental principles and procedures discussed herein are applicable to other groundwater contaminants commonly associated with petroleum product releases.

BR Slug

Please note the BR SLUG Version 3 User’s Manual and files are large documents and may take some time to download from the web site.

  1. Create a new directory on your hard drive (C Drive) and label it BRSlug3.
  2. Download the files brslugver3 using WinZip® to the directory by clicking the .zip file and selecting Extract all Files.
  3. This will start the Extraction Wizard.  As a precaution, scan the files for viruses if you have antivirus software.
  4. Click Next, and then on Browse... to select the new directory created on the hard drive.
  5. Click Next and extract the files to the directory. Click on the Finish button to close the WinZip® Extraction Wizard. There will be thirteen files:
    • BRSlug1.CAB
    • BRSlug2.CAB
    • BRSlug3.CAB
    • Example 1 Class.br2
    • Example 2 Class.br2
    • Example 3 Class.br2
    • Example 4 Class.br2
    • Example 5 Class.br2
    • Example 6 Class.br2
    • Example 7 Class.br2
    • Example 8 Class.br2
    • setup.exe
  6. Double click on setup.exe. This will start the installation program for BR SLUG Version 3.  After installation, the application will be shown in Start, All Programs as BRSlug V3.0