Objective:

Groundwater circulating wells (GCWs), alternatively known as in-well vapor-stripping, are an in-situ remediation technology that integrates the principles of groundwater recirculation with air stripping of volatile organic compounds. The objective of this effort was to complete a survey of GCW technology based on demonstrations at a number of federal and public sites documenting the successes and shortcomings of system performance. An additional objective was to document and develop guidelines for the use of the technology and make recommendations for additional data requirements to either support or argue against the use of this technology for particular contaminant and hydrogeologic applications.

Results:

Demonstration results showed various degrees of operational success. Although contamination reduction was achieved, deficiencies in hydraulic performance were experienced, resulting in lower than anticipated groundwater capture and throughput through the treatment wells. To ensure the appropriate use of GCW technology by the Department of Defense (DoD), a Groundwater Circulating Well Technology Assessment document was produced. This document provides: (1) an overview of the GCW technology; (2) a description of the GCW products offered by different vendors; (3) nine detailed DoD case histories; (4) a discussion of GCW limitations; and (5) an overall assessment of the technology.

Benefits:

GCW is an innovative in-situ technology that could reduce the time and cost required to achieve remediation goals compared to conventional technologies such as soil vapor extraction and pump-and-treat (P&T) systems. However, meaningful performance comparisons with conventional P&T systems have not been made, although capital costs up to $180k and annual operating and maintenance (O&M) costs of $42-72k were documented.

Implications:

Even though GCW systems have been installed at more than 100 sites in the U.S. and Europe, the technology at its current level of maturity is more suited to sites with relatively uniform hydrogeology, and for contaminant degradation in source areas rather than for plume containment. Detailed hydrogeological characterization, particularly to determine vertical hydraulic conductivity through the aquifer would be necessary for more complex sites (with associated, additional cost). However, implementation of GCW technology at DoD remediation sites, if appropriate, could potentially reduce both capital and annual operating costs compared to conventional P&T technology by avoiding high energy costs and ex-situ treatment of secondary waste streams. (Project Completed - 1999)

References:

1. Armstrong Laboratory Report, AL/EQ-TR 1995-0039.
2. Radian Corporation. Technology Performance and Application Analysis of UVB Groundwater Circulating Well Technology, Operable Unit 6, Hill AFB. 1996
3. Spargo, Barry, Naval Research Laboratory (NRL), Washington, D.C. Groundwater Circulating Well Technology Assessment. NRL/PU/6115-99-384. May 1999.
4. Spargo B. J., Naval Research Laboratory, Washington, D.C. In Situ Bioremediation and Efficacy Monitoring. NRL/PU/6115-96-317. October 1996.