The article below is excerpted from SERDP and ESTCP’s Partners in Environmental Technology Information Bulletin, Late Fall 2008 Issue. A seminar discussing this material also is available.
Chlorinated solvents are the most prevalent groundwater contaminants, with an estimated 15,000 to 25,000 contaminated sites in the United States. They are also particularly difficult and costly to remediate, so the selection of appropriate management strategies for chlorinated solvents and other dense nonqueous phase liquids (DNAPL) can be controversial. To help state regulators, federal regulators, consultants, DoD staff, and community members make site management decisions based on the best available science, an ESTCP team including Dr. Tom Sale (Colorado State University), Dr. Chuck Newell (GSI Environmental), Dr. Rob Hinchee (IST), Dr. Paul Johnson (Arizona State University), and Dr. Hans Stroo (HydroGeoLogic, Inc.) has compiled a Frequently Asked Questions (FAQ) document on chlorinated solvent site management.
The document entitled Frequently Asked Questions Regarding Management of Chlorinated Solvents in Soils and Groundwater addresses 25 key questions, providing a concise overview of current knowledge regarding the management of subsurface chlorinated solvent releases. It begins with an overview of the technical challenges posed by chlorinated solvent sites, including the properties of chlorinated solvents and their behavior and fate after being released to the subsurface. Source zone areas are defined and discussed, with summaries of the benefits and limitations of various source characterization and remediation technologies. The document presents a “new” way of thinking about chlorinated solvent sites that recognizes current technical and practical limitations, as well as the changes that have occurred over time at most chlorinated solvent sites. Key findings that have affected the approach to managing these sites include the significant mass of persistent contamination that can be present in lower permeability zones and the experiences from recent attempts to remediate chlorinated solvent source zones. These findings can help site managers set realistic goals for subsurface chlorinated solvent remediation.
Although the document is not meant to foster or discourage source zone treatment, it takes a hard look at the costs and performance of the most commonly used source zone treatment technologies and compares source treatment to alternative containment approaches. Results of realworld remediation projects are summarized to evaluate the impacts of treatment, including both the remaining mass and groundwater concentrations within treated source zones and the risks and longevity of the associated plumes. Most importantly, the document examines how decisions are made at sites impacted by chlorinated solvents and suggests an approach to develop cleanup objectives that are attainable, cost effective, and protective of human health and the environment. The final questions address the conditions and reasoning that can lead to improved success in solvent remediation efforts.
Developed under ESTCP project Protocol for Selecting Remedies for Chlorinated Solvent Releases (ER-200530), the FAQ document is intended to be a concise overview, while the more extensive companion document, Guide for Selecting Remedies for Subsurface Releases of Chlorinated Solvents, is planned for release in 2009. Both documents are expected to contribute to better use of resources, more effective remediation and risk management, and more productive cooperation between the parties involved in site cleanups.