On April 6, representatives of four federal agencies signed a memorandum of agreement to cooperatively test and document the cost and performance of three innovative technologies for treating dense, nonaqueous-phase liquids, or DNAPLs—compounds that have traditionally proven difficult to characterize and remediate. Although the MOA was signed only recently, the Interagency DNAPL Consortium’s (IDC) Core Management Team has been working together for more than a year to prepare for the side-by-side demonstration and comparison of DNAPL technologies. Early accomplishments of the team include delineating each agency’s role in the project, selecting and characterizing the demonstration site at Launch Complex 34 at the Cape Canaveral Air Station in Florida, and selecting the vendors whose technologies will be demonstrated. Members of the consortium are the U.S. Department of Energy’s Subsurface Contaminants Focus Area; the U.S. Environmental Protection Agency’s National Risk Management Research Laboratory in Cincinnati, Ohio; the U.S. Department of Defense’s Air Force Research Laboratory at Tyndall Air Force Base, Florida; the National Aeronautics and Space Administration’s Kennedy Space Center, Florida; the U.S. Air Force 45th Space Wing at Patrick Air Force Base, Florida; and the Cape Canaveral Air Station, Florida.

DNAPLs—a tough and widespread problem
Federal agencies and private industry responsible for cleanup recognize that remediating DNAPL sources is one of the most difficult environmental challenges they face. DNAPLs typically include industrial chlorinated solvents—trichloroethylene, perchloroethylene, and carbon tetrachloride. Many other volatile organic compounds and polychlorinated biphenyls are also common co-contaminants. DNAPLs are toxic, only marginally soluble in water, denser than water, and subject to becoming trapped in pore spaces between soil particles.

When DNAPLs are spilled, they tend to migrate downward through the soil and continue to sink through the groundwater until relatively impermeable material is encountered. Because gravity rather than direction of groundwater flow controls DNAPL movement, DNAPLs can flow down a sloping aquifer even when groundwater flow is in the opposite direction. As DNAPLs migrate in the subsurface, they leave behind a “trail” of droplets and ganglia in pore spaces. When low-permeability zones are encountered, DNAPLs may form pools of free product. Residual droplets, ganglia, or pools of free product may continue to contaminate groundwater for centuries.

The U.S. Air Force estimates that chlorinated solvents are, after spilled fuel, the second most common contaminant in soils and groundwater and anticipates cleaning up nearly 600 sites. Approximately 30 sites at 15 DOE facilities are confirmed or believed to have high potential for DNAPLs.

One of the largest DOE spills, at the A/M Area at the Savannah River Site, may contain up to 1,750 tons of DNAPL, which has contaminated an estimated 4 billion gallons of otherwise potable groundwater. The chemical and physical behavior of these contaminants makes them difficult to detect, characterize, and treat and raises the possibility of health-threatening contamination continuing for centuries or even millennia.

The difficulty of this challenge has been declared as unprecedented in the field of groundwater engineering. Ten years ago, the problem was described in most dire terms by Allan Freeze and John Cherry in the journal Ground Water (Volume 27, Number 3, May–June, p. 463): “There is now little doubt that at sites where DNAPLs are the problem, the local groundwater zone has terminal cancer. A cure, in the form of returning aquifer quality to drinking water standards, is unachievable at almost any cost. At DNAPL sites, costs are going up and aquifers are not much improved.” There are no established technologies available to economically address this problem—only innovative technology systems hold out hope, but comparative performance data are needed.

More progress through collaboration
Tom Early of Oak Ridge National Laboratory, who has been supporting involvement by the Subsurface Contaminants Focus Area in this collaborative effort from the beginning, says that the IDC demonstration is the first time government agencies have joined together to test DNAPL innovative technologies. “We share the problem, and we’ll share the results.” Early mentions two factors that led to federal agencies agreeing to work together on DNAPLs: a realization among DOD, EPA, and DOE that technology development programs were receiving smaller budgets each year and the shift to an emphasis on cleanup.

Early says that it was recognized that “funding for technology development was on the downswing and that agencies could improve the retrograde funding picture” and leverage resources by working together. “Also, the emphasis began to move toward cleanup, using innovative technologies that we had in the toolbox now.” Instead of developing more technologies, more progress could be made by focusing on the testing of technologies that could be deployed within five to ten years. “We didn’t have a good way to compare these technologies, so we were at the point to jointly sponsor a side-by-side demonstration of their performance and cost.”

Early believes the testing at Cape Canaveral is only the first step. It will be necessary to conduct other comparative demonstrations “to test the robustness of these technologies at other sites with more complex conditions than exist at Launch Complex 34.”

DOE Subsurface Contaminants Focus Area Lead Office Manager Jim Wright also stresses the importance of collaboration. “This interagency collaborative effort to clean up a DNAPL-contaminated site at the NASA Launch Pad 34 will yield many benefits. First is the demonstrated ability to put together a major remediation project with multiple agencies sharing resources and expertise to solve a common problem. Second will be the verified cost and performance data that each agency can use to advance its baseline remediation techniques. And lastly, this effort will result in a willingness to address other common problems in a cooperative and cost-effective manner.”

Technologies ready for testing
Because the traditional pump-and-treat technology is incapable of treating DNAPLs in a cost-effective manner and within a reasonable timeframe, the IDC’s Core Management Team has selected three innovative technologies to demonstrate their effectiveness and cost in removing DNAPL sources or destroying DNAPLs in situ. The Subsurface Contaminants Focus Area within DOE’s Office of Science and Technology has supported the development of all three selected technologies: Six-Phase Soil Heating, Dynamic Underground Stripping combined with Hydrous Pyrolysis/Oxidation, and In Situ Chemical Oxidation with Potassium Permanganate.

Six-Phase Soil Heating
Developed by Pacific Northwest National Laboratory, Six-Phase Soil Heating won an R&D 100 Award in 1995 and was featured in the spring 1998 issue of Initiatives. SPSH was also featured in an OST Innovative Technology Summary Report published in April 1995 (available online at http://www.em.doe.gov/plumesfa/intech/spsh). Current Environmental Solutions LLC is a new company that is working to commercialize SPSH.

SPSH relies on indigenous soil moisture to create an in situ source of steam that strips volatile and semivolatile contaminants from soils. An electrical current passes through soil, which generates heat due to the soil’s electrical resistance. The temperature within the remediation area is increased to the boiling point of water. Soil moisture becomes steam that is captured by vapor recovery wells for removal. Soil contaminants are also vaporized and are captured for ex situ treatment.

SPSH is an enhancement to soil vapor extraction, which is ineffective if contaminants cannot be easily vaporized or if the soil is tightly bound, as in silts and clays. SPSH’s electrical soil heating overcomes this obstacle by raising the temperature of the soil and contaminants, increasing the contaminants’ vapor pressure and thus their removal rate.

Dynamic Underground Stripping plus Hydrous Pyrolysis/Oxidation
In the early 1990s, researchers at Lawrence Livermore National Laboratory in collaboration with the School of Engineering at the University of California at Berkeley developed Dynamic Underground Stripping. DUS was first demonstrated in the cleanup of an underground gasoline spill at the Livermore site in 1993. OST published an Innovative Technology Summary Report on DUS in April 1995 (available online at http://www.em.doe.gov/plumesfa/intech/dus). DUS was so successful in this cleanup that contaminants were removed 50 times faster than with the pump-and-treat process. The cleanup, initially estimated to take 30 to 60 years with pump-and-treat, was completed in about one year.

In this method, the area to be cleaned is ringed with wells for injecting steam at temperatures above 100° C. Extraction wells in the central area are used to vacuum out vaporized contaminants. To ensure that thick layers of less permeable soils are heated sufficiently, electrode assemblies are sunk into the ground. The heated soil forces trapped liquids to vaporize and move to the steam zone for removal by vacuum extraction. These combined processes achieve a hot, dry, contaminant-free zone of earth surrounded by cool, damp, untreated areas. Steam injection and heating cycles are repeated as long as underground imaging, primarily Electrical Resistance Tomography, shows that cool (and therefore untreated) regions remain.

More recently, Livermore scientists developed Hydrous Pyrolysis/Oxidation, a process that introduces oxygen into the underground to convert contaminants into benign products such as carbon dioxide, chloride ions, and water. To provide the oxygen, steam and air are injected in parallel pipes, building a heated, oxygenated zone in the subsurface. When injection is halted, the steam condenses and contaminated groundwater returns to the heated zone. The groundwater then mixes with the condensed steam and oxygen, which destroys dissolved contaminants. By destroying DNAPLs and dissolved contaminants in place, this process eliminates the need to handle, treat, and dispose of contamination at the surface.

During the summer of 1997, both DUS and Hydrous Pyrolysis/Oxidation were used at a four-acre site in Visalia, California, owned by Southern California Edison. The utility company had used the site for 80 years to treat utility poles by dipping them into creosote or a pentachlorophenol compound. By the 1970s, these highly toxic substances had seeped into the subsurface to depths of approximately 100 feet. SteamTech Environmental Services of Bakersfield, California is currently cleaning up the Visalia site. During the first six weeks of operation, between June and August 1997, the team removed or destroyed in place approximately 300,000 pounds of contaminants, a rate of about 46,000 pounds per week. As of March 1, a total of 865,000 pounds of contaminants have been removed from the site. For nearly 20 years, Southern California Edison had been removing contaminants using pump-and-treat, most recently at a rate of just 10 pounds per week.

At the IDC demonstration site at Launch Complex 34, Integrated Water Technologies of Santa Barbara, California will engineer cleanup using DUS and Hydrous Pyrolysis/Oxidation. To verify cleanup results, other Livermore-developed technologies will be used: underground imaging, noble-gas-tracer monitoring, supercomputer modeling, and accelerator mass spectrometry.

In Situ Chemical Oxidation with Potassium Permanganate
In Situ Chemical Oxidation uses oxidant solutions to flush through a contaminated aquifer by injection and extraction through multiple horizontal and vertical wells. Potassium permanganate (KMnO₄), the oxidant, chemically decomposes a wide range of organic compounds into harmless breakdown products, such as carbon dioxide, chloride ions, and manganese dioxide. KMnO₄ is typically applied at concentrations of 1–3 percent solution via injection wells. This solution, which is easily handled, mixed, and injected, is nontoxic and nonhazardous.

During a 1997 field test of this technology at the DOE Portsmouth Gaseous Diffusion Plant in Ohio, groundwater was pumped from an upgradient horizontal well and collected in a portable mix tank. Crystalline KMnO₄ was continually added to the tank to maintain an oxidant concentration of 1 percent KMnO₄. The oxidant solution was then injected into the downgradient horizontal well, while groundwater was continuously extracted from the upgradient well. The system operated in a recirculation mode for two to four weeks and successfully reduced trichloroethylene (TCE) concentrations in all sampling wells below 5 ppb (the drinking water standard). OST and the Portsmouth Office of Environmental Restoration jointly funded the demonstration. IT Corporation will be demonstrating In Situ Chemical Oxidation using Potassium Permanganate at the IDC demonstration site at Cape Canaveral.

Operational details
The three innovative DNAPL technologies will be tested in 50-ft by 75-ft cells that have been set up at the Engineering Support Building at LC-34. Testing, which will begin this summer and continue into the fall, will generate cost and performance data by which to evaluate and compare the in situ thermal and oxidation DNAPL remediation technologies. Technical reports, which are expected to be released in fall 2000, will document costs and performance and will be available for site owners, regulators, and stakeholders so that informed decisions can be made regarding the economics and performance capabilities of the DNAPL remediation technologies.

Florida State University’s Institute for International Cooperative Environmental Research will provide day-to-day field project management through a cooperative agreement with DOE. The EPA Superfund Innovative Technology Evaluation (SITE) program will conduct quality assurance, quality control monitoring, and independent technology evaluations.

More information
To learn more about the IDC demonstrations for treating DNAPLs, see the IDC homepage at http://www.getf.org/dnaplguest and the Subsurface Contaminants Focus Area DNAPL product line page at http://www.envnet.org/scfa/tech/dnapl/currdnapl.htm. To obtain a brochure on the project, contact Laymon Gray at Florida State University, (850) 644-5524, lgray@ispa.fsu.edu.