TECHNOLOGY UPDATE ride solution. The refined Tris-buffer method replaces both peroxide botties with two botties of tris(hydroxymethyl) aminomethane solution. Both refined methods use the same amount of permanganate as did Method 29. "These methods provide better collection efficiency of the oxidized form of the mercury compared to Method 29," explained Laudal. EERC is actively working with the American Society for Testing Methods, the International Standards Organization, and EPA to standardize the new manual impinger-based methods, a first step in the development of new testing hardware. The researchers expect to complete the necessary tests for standardization by this fall.
New testing methods detect gaseous mercury species Two new testing methods being refined at the University of North Dakota's Energy & Environmental Research Center (EERC) can be used to differentiate between elemental and oxidized forms of mercury. The current EPA standard method for measuring gaseous mercury emissions, known as Method 29 or the Multi Metals Train, cannot consistendy distinguish between mercury species. EERC's mercury detection methods have recently been verified by bench studies and simulations as well as performance in the organization's pilot coal-burning facility. The main impetus for the project, which was funded by the Electric Power Research Institute (EPRI) and the Department of Energy (DOE), is to prepare for the possibility of increased scrutiny of mercury emissions. In response to a congressional request, EPA is currendy determining whether airborne mercury, especially that emanating from coal-fired power plants requires regulation under the 1990 Clean Air Act Amendments Mediod 29 has difficulty distinguishing between different forms of mercury in the presence of sulfur dioxide a major bvoroduct of buming'coal Accurate tracking of mercury emissions is important because of the potential health risks associated with the two forms of gaseous mercury. The oxidized and elemental species present in flue gases differ both in their range of transport in the atmosphere and tiieir fate once deposited. Oxidized mercury is soluble in water, and its transport is limited. Many current pollution control systems can remove it from the atmosphere. Airborne elemental mercury does not dissolve in water and can remain suspended in the atmosphere for up to two years, traveling hundreds or thousands of miles from its source. When elemental mercury lands in bodies of water, it
Mercury speciation methods are tested at the University of North Dakota. Eight sample trains (four on each level) measure elemental and oxidized forms of mercury in flue gas. (Courtesy Dennis Laudal, EERC)
can be transformed by algae and bacteria into various organomercuries that tend to bioaccumulate as they move up the aquatic food chain. The end result in places such as the Great Lakes can be contaminated fish populations. "We have to have good measurement methods before we can even think about putting regulations on the utilities," explained Dennis Laudal, the EERC research manager heading the project. EERC's improved approaches, known in the field as the Ontario Hydro and Trisbuffer methods, rely on new chemical solutions that can accurately characterize trace amounts of mercury. "No [other] methods we've tested have been shown to speciate mercury properly in flue gas streams " said Laudal. EPA's Method 29 uses two botties of acidified hydrogen peroxide and two bottles of acidified potassium permanganate. EERC's refined version of the Ontario Hydro method replaces die first peroxide botde with three botties of potassium chlo-
1 7 0 A • VOL. 3 1 , NO. 4, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
DNAPL cleanup strategy achieves 99% removal A pair of technologies that facilitate the arduous undertaking of identifying and remediating dense nonaqueous phase liquids (DNAPLs) have completed successful field demonstrations at Utah's Hill Air Force Base. The technologies—a tracer test and surfactant-enhanced aquifer remediation were developed by researchers from INTERA, Inc., an international environmental and petroleum consulting firm, and the University of Texas, Center for Petroleum and Geosystems Engineering. Previous remediation strategies using the surfactant technology alone removed less than 90% of the DNAPLs, according to the center's Gary Pope, who reported that the dual methods achieved 99% removal. "This is a breakthrough in the sense that we've shown that surfactant remediation can be used in a highly effective way in a field environment," added Pope. The two technologies showcased in the Utah demonstration benefited from advance planning using the university's UTCHEM computer model, a "chemical flooding simulator," according to Pope. Partitioning interwell tracer tests were used to
0013-936X/97/0931-170A$14.00/0 © 1997 American Chemical Society
verify the existence of and quantify subsurface DNAPLs. This technique relies on the simultaneous injection and tracking of several tracers with differing partition coefficients. Gas chromatography is used to identify the substances. Once characterized, the DNAPLs were remediated in record time using a surfactant-enhanced aquifer remediation method INTERA refers to as chemically enhanced solubilization for aquifer remediation. First, a dilute solution of surfactant is injected into the subsurface in the DNAPL zone. The surfactant increases DNAPL solubility by several orders of magnitude, substantially enhancing the amount of DNAPL that can dissolve and the rate at which it dissolves. Extraction wells men pump out the resulting DNAPL/surfactant mixture The combined technologies removed more than 99% of the residual DNAPL contamination in the Utah test area in less man three months. Pope estimated that it would have taken at least 30 years and $15 million to remove and treat the same volume of DNAPLs with the conventional pump-and-treat technology currendy being used at the Air Force base. Because a clay layer at the site formed an effective capillary barrier, the increased contaminant mobility was not a concern. Engineers at the University of Texas and INTERA are researching ways to render the DNAPL/surfactant solutions neutrally buoyant for other soil structures. They plan to demonstrate these enhanced approaches in the near future.
Field test compares NAPL cleanup methods Early results from a four-year field demonstration of nine nonaqueous phase liquids (NAPLs) removal technologies at the Hill Air Force base in Utah show that at least five of the technologies are quicker and less expensive than current removal methods, according to Carl Enfield, who is heading the demonstration for EPA. NAPL removal has been a pressing problem at Superfund sites, where EPA is getting poor results from traditional pump-and-treat technology. "We have just finished the field activity and are in the process of analyzing the data from all the tests,"
Enfield said in January. The methods demonstrated used solubilization or mobilization in groundwater and transfer to the vapor phase with sparging or venting. Each of the nine technologies was tested in a separate 3 m x 5 m cell that was sealed with sheet pile and equipped wim four injection wells. The technologies showing promise include surfactant solubilization, middle-phase mobilization, singlephase microemulsion, cosolvent solubilization, and cosolvent mobilization. According to Enfield, these five methods reduced the cost and time needed to remove NAPLs from contaminated soils. The demonstrations were conducted by research groups from the University of Oklahoma, Clemson University, and the University of Florida Although surfactants have previously been tested on cleanup sites, they have not been tested alongside other technologies in a comparative study, said Lynn Wood, an EPA researcher working on the project. This was the first field test of cosolvent solubilization and mobilization at a contaminated site or the use of microemulsions. Researchers have found that surfactants must be injected into the soil in high concentrations to be effective, said Enfield. Surfactant solutions can also be designed to mobilize NAPLs as a separate organic phase, essentially pushing the NAPLs to the extraction well. Single-phase microemulsion reduced the NAPL into a single-phase, low-viscosity fluid. Cosolvent mobilization causes NAPLs to swell and reduces surface tension between NAPLs and soil. Enfield said that traditional pump-and-treat methods cost between $30,000 and $40,000 per gallon of contaminant removed, whereas promising demonstration methods would cost only one-tenth of that amount. They would also be much quicker, he said, explaining that traditional pump-and-treat methods require about 5000 pore volumes to rid soil of a contaminant but demonstration methods required only 5 to 10 pore volumes. The demonstration was conducted as part of the Strategic Environmental Research Development Program, a joint research program of EPA, DOE, and the Department of Defense. Several universities and CSIRO, the Australian research organization, are also participating.
ENVIRONMENTAL SCIENCE & TECHNOLOGY "HOT ARTICLES"
on the web Selected ES&T feature articles, hews stories, and research papers are accessible free of charge on the World Wide Web. Visit the American Chemical Society's Publications Division home page (http://pubs.acs.org) and click on "Hot Articles." Articles currently available include:
FEATURES U.S. Nuclear Cleanup Progresses (March 1997) Research Priorities for the 21st Century (Jan. 1997) Environmental Biosensors: A Status Report (Nov. 1996) NEWS Sound science, regulatory review top Congress' agenda (Feb. 1997) Critics doubt Clinton's second term will advance regulatory reforms (Dec. 1996) RESEARCH Measuring Transport of Lawn-Applied Herbicide Acids from Turf to Home (Nov. 1996)
http://pubs.acs.org Questions, comments? Write to ES&T at
[email protected] VOL. 31, NO. 4, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 1 7 1 A
