Calculating Preliminary Remediation Goals (PRGs)
Often a risk assessor is called upon to help plan a remedial action at a site. The goal of all such actions is to ensure that the residual risks that remain at the site after cleanup will be within some specified limit of acceptability. Thus, the first step in the process is for the risk manager to specify the maximum level of residual risk that will be considered acceptable. Based on this, the risk assessor can then solve the basic risk equations to find the concentration of a chemical that corresponds to the specified "target risk." Concentration values derived in this way are thus referred to as preliminary remediation goal (PRGs).
The PRG is the average concentration of a chemical in an exposure area that will yield the specified target risk in an individual who is exposed at random within the exposure area.
A key concept is that a PRG is the average concentration of a chemical in an exposure area that will yield the specified target risk in an individual who is exposed at random within the exposure area. Thus, if an exposure area has an average concentration above the PRG, some level of remediation is needed. However, it is not necessary that all concentration values above the PRG be remediated. Rather, all that is required is that the average concentration be reduced to the PRG or below. Thus, some concentration values may remain that are above the PRG. The concentration value that is to be removed in order to reduce the mean to the PRG or below is often referred to as the remedial action level (RAL). It is important not to confuse the nature and purpose of PRG and RAL values.
Below are key EPA documents and links that provide direction on how to calculate PRGs and RALs for various media, and how to tell when a remedial action has been successful.
Resources
RAGS I Part B: Development of Risk-based Preliminary Remediation Goals (OSWER 9285.7-01B, December 1991)
RAGS III Part A: Process for Conducting Probabilistic Risk Assessment (OSWER 9285.7-45, December 2001) *See Chapter 7, Using PRA to Calculate Preliminary Remediation Goals
Guidance on Surface Soil Cleanup at Hazardous Waste Sites: Implementing Cleanup Levels - Peer Review Draft (PDF) (EPA 9355.0-91, April 2005 Peer Review Draft)
Soil Screening Guidance (1996)
- Soil Screening Guidance Calculation Tool
- Soil Screening Guidance for Radionuclides (2000)
- Soil Screening Guidance for Radionuclides Calculation Tool
Bowers, T. S., N. S. Shifrin, and B. L. Murphy. 1996. Statistical approach to meeting soil cleanup goals. Environ. Sci.Technol. 30:1437-1444. Exit
Schulz, T. W., and S. Griffin. 2001. Practical methods for meeting remediation goals at hazardous waste sites. Risk Analysis 21(1):43-52.
Statistical Methods for Assessing Attainment of Goals
Methods for Evaluating the Attainment of Cleanup Standards, Volume 1: Soils and Solid Media (PDF) (EPA 230/02-89-042, February 1989) (262 pp, 4 MB, About PDF) Exit
Methods for Evaluating the Attainment of Cleanup Standards, Volume 2: Ground Water (PDF) (EPA 230-R-92-14, July 1992) (363 pp, 6.5 MB, About PDF) Exit
Statistical Methods for Evaluating the Attainment of Cleanup Standards, Volume 3: Reference-Based Standards for Soils and Solid Media (PDF) (EPA 230-R-94-004, December 1992) (140 pp, 4 MB, About PDF) Exit