Groundwater Circulation Well (GCW)
A groundwater circulation well (GCW) treats groundwater and soil contaminated with hydrocarbons. In this process, groundwater is pumped to the surface and aerated, removing most of the volatile vapors. The aerated groundwater is distributed over an area of contaminated soil. The aerated water carries oxygen to the subsurface soil, promoting biodegradation. The combined process of biological treatment and physical extraction reduces the time required to achieve remediation goals and lowers contaminant concentrations.
Limitations and Concerns
To be effective, circulating groundwater wells require a well-defined contaminant plume to prevent the spreading or smearing of the contamination. Contaminant mobility can be increased as a result of increased water in the soil. Additional monitoring wells may be necessary.
Vapors that are stripped off should be evaluated and treated if necessary before being discharged to the atmosphere. Subsurface heterogeneity can interfere with uniform flow in the aquifer around the well.
Circulation well systems should not be applied to sites containing nonaqueous-phase liquids (NAPLs) to prevent the possibility of smearing the contaminants.
Technology Development Status
GCW treatment has been fully demonstrated in the field and is considered commercial for fuel and VOCs. It is in the field test stage for explosive compounds such as RDX.
Other Resources and Demonstrations
See A Field-Scale Test of In Situ Chemical Oxidation through Recirculation, 1998. O.R. West; S.R. Cline, W.L. Holden, F.G. Gardner, B.M. Schlosser, R.L. Siegrist, T.C. Houk. ORNL/CP-98459, NTIS: DE98003584, 9 pp. Successful implementation of in situ chemical oxidation requires an effective means for dispersing the oxidant to contaminated regions in the subsurface. A technique has been developed in which an oxidant is added to extracted ground water, and the oxidant-laden ground water is then injected and re-circulated into a contaminated aquifer through multiple horizontal and/or vertical wells. This technique is referred to as in situ chemical oxidation through recirculation (ISCOR). A field-scale test of ISCOR using a pair of parallel horizontal wells with 200-ft screened sections was conducted at Portsmouth Gaseous Diffusion Plant where ground water is contaminated with trichloroethylene (TCE).
See Development of a Vertical Recirculation Well System for the A/M Area of the Savannah River Site, 1996. D.G. Jackson Jr., B.B. Looney, Westinghouse Savannah River Company, NTIS Order Number DE98052107, 150 pp. This report describes the development and siting of a recirculation well system to contain the 500 ppb trichloroethylene plume at the Savannah River Site.
See http://costperformance.org/pdf/itsr1742.pdf for implementation of circulating wells at DOE’s Hanford Site.
See http://www.serdp-estcp.org/content/download/8182/100294/file/CU-9602-FR-01.pdf Groundwater Circulating Well Technology Assessment, 1999. This report documents the successes and shortcomings of GCW system performance based on a survey of demonstrations at various Federal and public sites.
See http://www.clu-in.org/products/newsltrs/gwc/gwc1001.htm#gcws for a description of pilot studies on a dual system using ground-water circulation wells equipped with an in-well air stripper system to treat trichloroethylene (TCE) and an ultra-violet (UV) light treatment unit to destroy RDX. After nine months of operation at the former Nebraska Ordnance Plant site, the systems demonstrated mass removal rates greater than 96 percent.