SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM PHYTOREMEDIATION OF ORGANICS ACTION TEAM TCE IN GROUND WATER SUBGROUP CONFERENCE CALL, DECEMBER 10, 1997

SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM
PHYTOREMEDIATION OF ORGANICS ACTION TEAM
TCE IN GROUND WATER SUBGROUP
CONFERENCE CALL

December 10, 1997
3:30 p.m. to 4:30 p.m.

On December 10, 1997, members of the Phytoremediation of Organics Action Team, TCE in Ground Water Subgroup, held their third meeting via a conference call. The following members were present:

Greg Harvey, U.S. Air Force (Subgroup Chair)
Larry Erickson, Kansas State University
Lee Newman, University of Washington School of Medicine
Milton Gordon, University of Washington School of Medicine
Rich Steimle, EPA TIO
Stuart Strand, University of Washington
Sam Taffinder, U.S. Air Force
Robert Tossell, Beak International, Inc.
Dawn Carroll, EPA TIO
Garald Horst, University of Nebraska

Also present was Ben Carlisle of Eastern Research Group, Inc. (ERG).

UPDATE ON THE CHAPPELL TCE DOCUMENT

Dawn Carroll stated that EPA is considering publishing the Chappell TCE document in a peer-reviewed journal. After that, she said, EPA will probably find a way to distribute the document for public consumption.

OVERVIEW OF TCE WORK AT KANSAS STATE UNIVERSITY

Larry Erickson discussed research that is being done at Kansas State University (KSU) concerning the role alfalfa can play in remediating both TCE and trichloroethane (TCA). Erickson and his colleagues have studied the fate of these compounds in a variety of situations.

In one experiment, Erickson said, the group sent TCE-contaminated ground water flowing horizontally through a chamber of alfalfa plants, from one end to the other; the researchers then studied the fate of the TCE under that environmental condition. When TCA was fed into the chamber, the researchers found some anaerobic biodegradation occurring within the TCE. After the researchers made some changes to the operation, the anaerobic conversion of TCE to methane seemed to slow and then cease.

Erickson said that the group is especially interested in studying the movement of TCE from its liquid phase into the atmosphere. He and his colleagues have studied the transpiration stream concentration factor in some work, and they have also looked into TCE dissipation. In many environments, Erickson said, plants will dissipate TCE at low concentrations into the atmosphere, where it will break down due to sunlight and atmospheric chemistry. Erickson described this process as a good way of dissipating TCE in those environments where plants can draw TCE up into the unsaturated zone so that it can diffuse out into the atmosphere.

Greg Harvey asked whether Erickson's group has worked mostly in the lab and whether any fieldwork has been planned. Erickson said that his group has worked in the lab thus far, though the researchers have also done some mathematical modeling of lab results; the models they have created can be used in the field. Also, within the Great Plains/Rocky Mountain Hazardous Substance Research Center, Erickson's group is working with researchers from Utah State University, and both groups are sharing their work with people at Hill Air Force Base (AFB), where some fieldwork may occur. Erickson said that personnel at Hill AFB are concerned about atmospheric concentrations associated with significant TCE plumes beneath the base. In experimental lab work undertaken at KSU, however, atmospheric concentrations tend to be fairly low.

DISCUSSION ON A DIRECTION FOR THE TCE AND GROUND WATER SUBGROUP

Harvey asked the Subgroup members for opinions on where they want to take the group and what they want to do with it.

Harvey said that, from conversations with people in the Department of Energy and the Navy, he had found a general need for information about ongoing TCE work within the phytoremediation field. Representatives of these entities want to have packaged information that they can present to state regulators. Harvey asked how the Subgroup might prepare such a package and suggested that the Subgroup could perhaps develop a Web site showing TCE/phytoremediation activity at various locations around the country.

Erickson agreed that it is valuable to share information. He said that the KSU group has posted a great deal of material on its Web site, which receives about 10,000 hits a month. Web sites are an effective way of disseminating information, Erickson said.

Harvey asked if Subgroup members would be receptive to the idea of developing a single Web site or page that would collect information on all halogenated organics and phytoremediation work. Lee Newman noted that another strategy would be to develop a site that provides links to a variety of individual Web pages, all of which present their own information about TCE/phytoremediation work.

Milton Gordon asked what type of information the Subgroup would post on such a site. Would the site include raw data and preliminary conclusions? Gordon said that sharing preliminary results can sometimes be more misleading than helpful.

Erickson replied that the KSU Web site contains proceedings from conferences (including the complete text of papers) and an annual report that includes summaries of ongoing projects (project title, objectives, approach, etc.). By updating people about ongoing projects, Erickson said, the site helps researchers contact other researchers who are doing similar work.

OVERVIEW OF TCE-REMEDIATION ACTIVITY AT THE AIR FORCE CENTER FOR ENVIRONMENTAL EXCELLENCE

Sam Taffinder described phytoremediation research being done by personnel from the Air Force Center for Environmental Excellence (AFCEE). Taffinder said that AFCEE had originally planned two mature-tree studies: one at Hill AFB and one at Cape Canaveral. AFCEE ended up moving forward only at Cape Canaveral, however, because there was almost no TCE in surface water flowing out of seeps at Hill AFB. At Cape Canaveral, the trees' root systems were either close to the ground water or within the vadose zone of the source area. All of the fieldwork at Cape Canaveral has been completed, Taffinder said, and AFCEE has sent out a draft report for Air Force review. If AFCEE does go back to Hill, it will be for an engineered tree planting at a site where ground water flows under a housing area at a depth of 10 feet.

Taffinder said that AFCEE has really just gotten started on the phytoremediation demonstrations it had planned last year. AFCEE did write a phytoremediation feasibility study for Travis AFB, near Sacramento, California; comments on the draft feasibility study have just been completed. Another tree planting may take place at Beale AFB, northeast of Sacramento. AFCEE personnel might participate at Beale AFB as consultants, Taffinder said, helping to plant trees and working with the water balance model. In all, AFCEE may be involved in as many as three or four sites. If AFCEE personnel continue with work at Cape Canaveral, they would have to plant a dense stand of trees, because the trees in that environment can only uptake about 50 percent of the moisture they receive each year. Precipitation at the site exceeds transpiration, and the trees' roots don't have to chase ground water. AFCEE considered three different species at the site, of which two (native live oak and native saw palmetto) are transpiring TCE at very low levels. AFCEE believes that it is soil gas partitioning through the roots and being transpired, not ground water.

Gordon asked Taffinder whether AFCEE is equating the transpiration of TCE with phytoremediation. Taffinder said yes. Gordon asked whether AFCEE considered the decomposition within the plant itself. Taffinder said that the researchers found some breakdown products, but not in large concentrations. He said that they looked for metabolic breakdown products and measured the amount of TCE and moisture being transpired.

Gordon said that, in studies of poplars, researchers at the University of Washington had found about 95 percent of contaminants stored within the tree. Taffinder said that AFCEE believes that the amount of TCE transpired by trees at the Cape Canaveral site is more than the amount metabolized.

Harvey asked whether any Subgroup members have found that trees cause changes in ground-water chemistry. At a site in Fort Worth, Texas, Harvey and his colleagues have noted that the geochemistry under mature trees has shown depressed dissolved oxygen, elevated iron, increased bicarbonate, and an altered VOC signature.

Erickson said that it's typical to see some interaction between the roots and the ground water; oxygen is often needed for metabolic processes, so it's not unusual to see a reduction of dissolved oxygen compared to atmospheric conditions. Taffinder said that AFCEE is still waiting for geochemistry data from the Cape Canaveral site.

Harvey asked Taffinder whether members of the RTDF would be able to look at the Cape Canaveral report after the Air Force is finished reviewing it. Taffinder replied that the Air Force would figure out a way to make the report---or some part of it---available. He stressed that AFCEE is just beginning to learn about the science of phytoremediation.

Erickson alerted Taffinder to KSU's upcoming vegetation workshop (January 7 to 9). Information about the workshop is available on the KSU Web site (www.engg.ksu.edu/HSRC).

UPDATE ON WORK AT THE UNIVERSITY OF WASHINGTON

Harvey asked Subgroup members from the University of Washington to update the group about their work using poplars to phytoremediate TCE at a site in Oregon. (Harvey had read an article about their work in the December issue of Scientific American; that article is available over the Internet at http://www.sciam.com/1297issue/1297techbus4.html.)

Newman said that the University of Washington team planted the poplars in May of this year; at this point, they are about 10- to 12-feet tall. She said that the contaminated aquifer is moderately deep---20 to 25 feet---so the team doesn't expect to see any results until sometime next year. The regulators who funded the study understand that it will take time to achieve results and are waiting patiently.

Harvey asked whether the poplar plantation is a monoculture. Newman replied that the team planted two different clonal lines of populus tricarpa. In the lab, a single line was used, and it flourished; however, the soil at the site contains heavy clay and a lot of rocks. The second variety selected by the team is a heartier clone that should thrive under these conditions. The team plans to monitor the success of the two lines in the field, then remove the less successful line during thinning.

Erickson asked whether the team has collected any data on what fraction of the TCE comes to the soil surface in the vegetation instead of leaving directly through the soil. Newman replied that the team has frozen soil samples from the site in liquid nitrogen, then analyzed them for TCE and any anaerobic degradation products. Newman said that the team hasn't found TCE or any of these products at the soil surface---or has found only very low hits. The highest levels occur down close to the aquifer, and the levels decrease as you approach the surface.

Erickson said that his group has found similar results. He added, however, that as you get into the unsaturated zone you get very rapid gas-phase diffusion, and a good deal of TCE probably leaves the soil through this diffusion.

Stuart Strand asked Erickson if he had ever actually measured the flux off the soil surface. Erickson said he had, using each of two methods. In one method, he inverts containers on the soil surface and allows the diffusing gas to flow into them; then he samples from the containers. The second method involves enclosing the entire chamber, then studying the gas phase using infrared instrumentation.

Newman asked Erickson how much soil covers the TCE in his test chambers. Erickson said that he has about 30 centimeters of soil in one chamber and slightly more in the other. Gordon asked whether the soil is relatively loose and porous. Erickson said that the soil is sandy, with a little bit of silt---fairly porous, in general. The movement of TCE through clay would probably be quite different, Erickson said. Several Subgroup members then stated that every site is different, and that researchers must take these differences into account.

WRAP UP

Harvey asked whether the Subgroup should work with EPA's Technology Innovation Office (TIO) to set up a Web site that would refer users to other Web pages for information on happenings in the TCE/phytoremediation field. Carroll, the Subgroup's TIO liaison, said that she thought a Web page was a great idea and that she could begin developing a site. Harvey said that Subgroup members might want to submit photographs of phytoremediation sites to make the Web site visually appealing. Carroll said that all materials should be sent to her (carroll.dawn@epamail.epa.gov).

Newman said that the Chappell document contains references to fieldwork being done by a variety of researchers. In some cases, she said, researchers may want to clear up the document's description of their own work, and she asked how researchers should go about doing this. To whom should they provide comments? Carroll suggested contacting either Steve Rock, Phil Sayre, or herself.

The Subgroup tentatively agreed to hold its next conference call on Friday, February 13, from 1:30 p.m. to 2:30 p.m. (Eastern Standard Time).