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.
RBCA 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.
- Final Report - Evaluation of Computer Software Packages for RBCA Tier-3 Analysis
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.
RBCA Report Review Notes
The following are postings from DNR LUST staff meetings and file exchanges with the Staff Assistance Contractor (Preston Engineering). The postings discuss decision/recommendations on the administration of LUST site activities. Please consider these postings as a teaching opportunity. However, be aware the discussions in the postings generally are only applicable to specific conditions at a site and should not be considered as guidance for all sites. In addition, the comments in the file exchanges notes with the Staff Assistance Contractor should be considered as a recommendation only. DNR will make the determination on how to proceed with the site.
Please contact Elaine Douskey at 515-281-8011 or Elaine.Douskey@dnr.iowa.gov if you have questions.
- 05/25/05 Staff Assistance Contractor File Exchange Notes
- 06/01/05 Staff Assistance Contractor File Exchange Notes
- 06/22/05 Staff Assistance Contractor File Exchange Notes
- 06/29/05 Staff Assistance Contractor File Exchange Notes
- 07/06/05 Staff Assistance Contractor File Exchange Notes
- 07/13/05 Staff Assistance Contractor File Exchange Notes
- 07/20/05 Staff Assistance Contractor File Exchange Notes
- 07/27/05 Staff Assistance Contractor File Exchange Notes
- 08/03/05 Staff Assistance Contractor File Exchange Notes