Risk-Based Corrective Action (RBCA) At Petroleum Release Sites: Tier 1/Tier 2 Assessments & Reports Revised May 2023
This guidance document is advisory in nature but is binding on an agency until amended by such agency. A guidance document does not include internal procedural documents that only affect the internal operations of the agency and does not impose additional requirements or penalties on regulated parties or include confidential information or rules and regulations made in accordance with the Administrative Procedure Act. If you believe that this guidance document imposes additional requirements or penalties on regulated parties, you may request a review of the document.

Form #: 01-082 Guidance Documents Revised: 7/18/23

The Guidance Document above became effective July 1, 2023

Overview of changes -
This information was provided to stakeholders in June, 2023.
(See attached file: Changes to the 2023 GD.pdf)

Previous Guidance -
The guidance document below was in effect for investigation approved before July 1, 2023
(See attached file: RBCA-GD-2009.pdf)

The Guidance Document below is in effect for investigations approved before May 1, 2009
(See attached file: RBCA-GD-2-04.pdf)
Appendix A - E
(See attached file: RBCA-2-04-App.pdf)

The Petroleum Remediation Section (PRS) of the Nebraska Department of Environment and Energy (Department) has compiled this document for the purposes of conducting risk-based corrective action (RBCA) Tier 1 and Tier 2 site assessments and evaluations at petroleum release sites. It has been prepared in accordance with criteria contained in Nebraska Title 118 - Ground Water Quality Standards and Use Classification and Nebraska Title 126 - Rules and Regulations Pertaining to the Management of Wastes. Portions of this document are based on recommendations made by the Technical Advisory Committee (TAC), created by the Nebraska Legislature, and information contained in the American Society for Testing and Materials (ASTM) Standard E-1739 Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites (ASTM E-1739).

This document is intended to apply to all petroleum releases: those potentially eligible for reimbursement under Nebraska Title 200 - Rules and Regulations for Petroleum Release Remedial Action Reimbursement Fund, as well as those that are not (e.g., pipelines, transportation vessels). This guidance is not intended for investigations of petroleum wastes considered a hazardous waste in accordance with Nebraska Title 128 – Nebraska Hazardous Waste Regulations or a CERCLA-listed petroleum derivative identified in 40 CFR Part 302.



The term Risk-Based Corrective Action (RBCA) refers to a consistent decision-making process used to assess actual or likely human and/or environmental risk of exposure to a chemical release and determine appropriate remedial actions in response to such releases. Petroleum releases vary considerably in their potential risk based on a number of variables, including, but not limited to, the type of petroleum product, amount of released product, duration of the release, extent of the release, site geology/hydrogeology, number and type of exposure pathways, and location of human receptors relative to the source. Potential remedial actions may run the gamut from long-term active cleanup to no action. In recognition of this fact, the Department has developed a tiered approach to its petroleum release corrective action process to cost effectively manage impacted sites and focus the finite resources on the more critical sites.


The Department’s petroleum release RBCA process follows the general procedures outlined in the governing regulation, Title 118, Appendix B, Steps 5 – 11. Steps 1 – 4 deal with immediate threats from a release; such a site would not enter the RBCA process until the immediate threats have been mitigated. The following steps are included in the Department’s RBCA process:
  1. Pre-Investigation Site Visit *
  2. Tier 1 Site Investigation *
  3. Tier 1 Evaluation
  4. Tier 2 Site Investigation *
  5. Tier 2 Evaluation
  6. Preparation of Remedial Action Plan *
  7. Implementation of Remedial Action Plan *
  8. Review of Remedial Action Effectiveness
  9. Site Closure *

Those steps marked with an asterisk (*) require Department review and approval of workplans and cost estimates prior to work being performed for Title 200 eligible releases. Workplans and cost estimates are not required for work performed under the VRA program. Workplans and cost estimates may be required by the Department for non-Title 200 eligible releases.

The overall RBCA process is depicted in the form of a flow chart in Figure 2-1. Free product recovery is not addressed in this flow chart. Requirements for addressing free product are handled on a case-by-case basis. The presence of free product suspends the Tier 1 investigation requirements for only those exposure pathways involving ground water (see Section 4.5). A report incorporating all other Tier 1 information is still required.


During the Tier 1 investigation, sufficient site data is gathered to establish land use (present and future) in the area around the release site, the location of potential points of exposure, human receptors and pathways, chemical of concern (COC) concentration data in soils and ground water, and certain subsurface physical parameters. These data are used to generate a Site Conceptual Exposure Scenario and determine the appropriate risk-based screening levels (RBSLs) with which to compare the documented site COC concentrations. Data are collected to examine the potential risk of exposure to petroleum contaminants from the following exposure pathways:
  • Dermal contact with, ingestion of, and outdoor inhalation through air of COCs from contaminated surface soils;
  • Enclosed space inhalation of COCs from contaminated subsurface soils;
  • Leaching of COCs from contaminated surface and subsurface soils to ground water;
  • Enclosed space inhalation of COCs from contaminated, shallow ground water; and,
  • Ingestion of COCs from contaminated ground water.

The purpose of the Tier 2 investigation is to gather additional site COC concentration data and subsurface physical parameter information that is more detailed than that gathered during the Tier 1 investigation. These data are used to generate site-specific target levels (SSTLs) that are compared to representative site COC concentrations for the completed exposure pathways from Tier 1. All COCs and all complete routes of exposure will be evaluated at Tier 2.


As defined in ASTM E-1739, a Tier 1 evaluation is “a risk-based analysis to develop non-site-specific values for direct and indirect exposure pathways utilizing conservative exposure factors and fate and transport [models] for potential pathways and various property use categories ... Values established under Tier 1 will apply to all sites that fall into a particular category.” (“Direct exposure” indicates that the point of exposure is at the source of the release; “indirect exposure” indicates the existence of an intervening medium of transport between the source and a point of exposure.)

A Tier 2 evaluation is a risk-based analysis applying the same exposure factors and models used for the Tier 1 evaluation but incorporating more site-specific data to develop site-specific target levels for all COCs and all complete exposure pathways.

Based on these definitions, certain general statements can be made when comparing the individual tiers. First, when proceeding from Tier 1 to Tier 2, the amount of data collected during the investigation phase increases. Additional work at the Tier 2 phase may include more complete soil sampling, additional ground water sampling and/or subsurface physical/chemical parameter testing. Second, as more data is collected, the level of conservatism used in the evaluation of the data usually decreases. This means that the Tier 2 SSTLs will generally be greater than the Tier 1 RBSLs for the same site. However, the target risk or level of protection remains the same for both tiers.

Produced by:
Nebraska Department of Environment and Energy
Petroleum Remediation Section
P.O. Box 98922
Lincoln, NE 68509-8922

email: NDEE.PetroleumRemediation@Nebraska.gov
phone: (402) 471-2186

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SizeFile Name
681 KB Changes to the 2023 GD.pdf
2,374 KB RBCA-GD-2009.pdf
527 KB RBCA-GD-2-04.pdf
1,104 KB RBCA-2-04-App.pdf