Strategies for the Successful Use of Risk-Based Target Levels
at Petroleum-Impacted Sites in Pennsylvania
By
David W. Parsonage, American Geosciences Inc.
Troy E. Scott, P.E., American Geosciences Inc.
Bruce A. Shaw, P.G., American Geosciences Inc.
With the accumulation of decades of site investigation and remediation experience, regulators, environmental professionals, and responsible parties are increasingly recognizing that impacted sites are frequently faced with limitations on the feasibility of remediating to predefined cleanup standards that don’t always consider the unique characteristics of the site and its potential receptors. This, coupled with the vast number of petroleum-impacted sites across the country, has created the need for acceptable methods for determining an appropriate level of site treatment. The application of Risk-Based Target Levels (RBTLs) as an approach for addressing site-specific impacts to petroleum-impacted sites is gaining greater acceptance in the regulatory community and many states are implementing programs that provide clearer guidance for developing and implementing RBTLs at these sites.
This paper presents some general strategies for the successful use of RBTLs at petroleum-impacted sites and provides a case study of a petroleum-impacted site in northwestern Pennsylvania where RBTLs were applied to achieve closure. Specifically, the topics presented in this paper include:
Overview of Pennsylvania’s Regulatory Setting for UST Release Sites
In Pennsylvania, the primary framework for regulating underground storage tank (UST) releases, their assessment, and cleanup is the Storage Tank and Spill Prevention Act (Act 32) and its associated regulations (25 PA Code, Chapter 245, Subchapter D, Storage Tanks; Corrective Action). In 1995, Pennsylvania passed the Land Recycling and Environmental Remediation Standards Act (Act 2) that provides the basis for developing RBTLs under the “site-specific cleanup standard,” (25 PA Code, Chapter 250). In 2001, the corrective action and Act 2 regulations were revised to better integrate their requirements, more clearly defining the opportunities for achieving closure of storage tank release sites through the development of site-specific cleanup standards. A brief overview of Pennsylvania’s regulatory framework regarding petroleum-impacted UST sites is provided.
Site Characterization Strategies and Assessment Tools for developing RBTLs
For RBTLs to be successfully implemented, careful consideration must be given to properly identifying the potential exposure pathways. Through diligent site characterization and the use of reliable modeling techniques, many tools are available for effectively determining the fate and transport of site-related impacts and for developing appropriate risk based standards. Several site characterization strategies and assessment tools for developing RBTLs are discussed in this paper.
Combining RBTLs with Other Corrective Action Strategies to Achieve Site Closure
While it is not always feasible to restore impacted sites to stringent generic cleanup standards such as drinking water maximum contaminant levels (MCLs) using active remediation technologies, constituent concentrations can frequently be reduced and potential exposure pathways can be effectively eliminated. By using active remediation technologies in source areas and implementing appropriate engineering controls, RBTLs can be established to attain site closure. A summary of active remediation approaches that may be advantageous at sites where RBTLs may be applied is presented.
Case Study of Successful Application of RBTLs to a Petroleum-Impacted site in Pennsylvania
This case study will present the key aspects of a project in which a combination of thorough site characterization, targeted active remediation in the source area, modeling, and risk evaluation were used to obtain site closure. The setting of this gasoline spill site provided several challenges including an onsite drinking water well, nearby reservoir, and difficult lithology. These challenges were overcome through the application of the strategies presented in this paper.