No slip, no sliding away with SEAR-NB

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A new technology for preventing dense, nonaqueous-phase liquids (DNAPLs) from being swept away during surfactant flooding is the subject of a multiagency demonstration underway at a former industrial site in New Hampshire. The Subsurface Contaminants Focus Area (SCFA) is one of several organizations that are sponsoring a demonstration of Surfactant-Enhanced Aquifer Remediation at Neutral Buoyancy (SEAR-NB) at the OK Tool Site in Milford, New Hampshire. SEAR-NB is an extension of recent SEAR technology and is designed to help remediate DNAPLs in aquifers that do not have confining layers or cannot be characterized enough to know the extent of their confining layers.

DNAPLs present unique problems in remediation because they are denser than groundwater and tend to migrate downward until they encounter and pool on less permeable zones, where they act as a source of continuous contamination for many years. SEAR technology has been successful in remediating DNAPLs from groundwater, but it can cause them to migrate downward. Therefore, SEAR can be used only in wells that have relatively impermeable confining layers. Because it is often difficult to know the extent of confining layers or even whether they exist, a new technology was needed that could remediate DNAPLs without the need for confining layers. SEAR-NB fills this niche because it prevents the vertical migration of DNAPLs, thus removing the fear that DNAPLs will sink, pool, and continue to contaminate groundwater.

Both SEAR and SEAR-NB work by injecting surfactants into aquifers. However, where SEAR technology may also mobilize DNAPLs, SEAR-NB relies only on solubilization. When sufficient light alcohol is injected along with the surfactant into the well, a microemulsion with a density very near to that of groundwater forms, thus preventing the vertical migration of DNAPLs. The solvents used during SEAR-NB do not contribute to aquifer contamination or create additional waste streams.

Migration of solubilized DNAPL can be predicted and minimized to avoid uncontrolled vertical migration. Variables in the figure are L - well spacing, H - overall aquifer thickness; and h - actual vertical movement of solubilized DNAPL.

The SEAR-NB process begins with partitioning interwell tracer tests that verify the existence of DNAPL and help determine the amount. Tests to determine aquifer properties are also performed. The test results are analyzed to determine the amount of surfactants and light alcohol needed to remediate the aquifer. Then, the proper amount of solvents is injected into a series of wells while water is pumped from extraction wells. This injecting/pumping process pushes DNAPLs through the aquifer and extraction wells. After the correct amount of solvent is injected, plain water can be used to help push contaminants through the aquifer.

Based on research and results from previous SEAR demonstrations, SEAR-NB is predicted to significantly reduce cost and cleanup time. For example, a demonstration of SEAR at Hill Air Force Base in 1997 successfully removed over 99 percent of DNAPL in 30 days instead of the estimated 30 years for pump and treat.

Showing what SEAR-NB can do at the OK Tool Site

The primary contaminant at the site is perchloroethylene (PCE), which was used as a degreaser by the OK Tool Company. Participating with SCFA in demonstrating SEAR-NB are EPA Region 1, EPA–Las Vegas, EPA’s Superfund Innovative Technology Evaluation (SITE) Program, the Superfund Technology Center, Lockheed-Martin Idaho Technologies, the state of New Hampshire, the U.S. Geological Survey, Duke Engineering, and several subcontractors.

Tracer tests have been performed for the site and are being analyzed. Michael Shook, SEAR-NB principal investigator at the Idaho National Engineering and Environmental Laboratory, says that no additional SEAR-NB demonstrations are planned right now, but several DOE sites have shown an interest in the technology and are awaiting results from the OK Tool Site.

EPA and DOE are sponsoring a visitors’ day next spring as part of the SEAR-NB demonstration at the OK Tool Site. It will include a welcome/introduction, site history, technology overview, site tour, update on status and performance, and a question/answer session. For more information, contact either Emily Charoglu at EnviroIssues, (206) 269-5041, echaroglu@enviroissues.com, or Cindy Loney at Tetra Tech EM, Inc. at (513) 564-8348, loneyc@ttemi.com.

Shook, working with researchers from the University of Texas at Austin, discovered how SEAR-NB could be applied to environmental remediation in 1996–97. The patent on the technology’s environmental use is pending. Shook says that SEAR is not a new technology. “This technology has been in the oil field since the late 1960s but has been changed significantly as applied to the environment. In particular, the neutral buoyancy approach is novel. The technology is well established, with many millions of dollars in R&D in the oil field. It is a tried and true technology. I feel comfortable with the technology and see no reason why it should not work in the environmental field.”

For more information on SEAR-NB, contact Michael Shook at (208) 526-6945.