Summary of the RTDF Phytoremediation of Organics Action Team TCE in Ground Water Subgroup Conference Call

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

October 2, 1997
2:00 p.m. to 3:00 p.m.

On October 2, 1997, members of the Phytoremediation of Organics Action Team, TCE in Ground Water Subgroup, held their second meeting via a conference call. The following members were present:

Greg Harvey, U.S. Air Force (Subgroup Co-Chair)
Dawn Carroll, EPA/TIO
Cliff Casey, U.S. Navy
Harry Compton, EPA
Larry Erickson, Kansas State University
Charles Giammona, Texas A&M University
Cristina Negri, Argonne National Laboratory
Elaine Richardson, Applied Natural Sciences, Inc.
Stuart Strand, University of Washington
Bob Tossell, Beak International, Inc.
Sankar Venkatraman, McLaren Hart Environmental Engineering Corporation

Also present were Ray Hinchman of Argonne National Laboratory, George Prince (associate of Harry Compton), Sandra Eberts (associate of Greg Harvey), and Ben Carlisle of Eastern Research Group, Inc. (ERG).

FINDING A NICHE FOR PHYTOREMEDIATION

Subgroup Co-Chair Greg Harvey said that it is important to find an appropriate niche for phytoremediation. Those who are developing the technology should not oversell it, nor should they make claims that the technology can't fulfill. Harvey believes that somewhere between natural attenuation and engineered bioremediation exists a niche which phytoremediation can fill very nicely. One of the missions of the Action Team is to find that niche.

Bob Tossell agreed with Harvey's statement. Tossell said that his greatest concern about the phytoremediation initiative is that people will over-promote the technology--people who are interested in the technology simply because it's "hot" or who are just looking at the bottom-line dollar value.

Harvey said that, while mechanical pump-and-treat systems are known to be problematic, it is important not to give the impression that plants are strictly solar-powered pumps. Instead, he said, scientists must show that plants are capable of degrading contaminants, altering the geochemistry within their soil zone, and increasing zones of microbial activity. The literature contains encouraging results from laboratories (including work done by Stuart Strand and others at the University of Washington), but scientists need to prove that what's going on in the lab is also going on in the field.

Strand replied that field work in phytoremediation takes a little extra time because the plants grow slowly. As time goes on, Strand said, results will come out, and we'll be able to find that niche we're looking for. However, some people are promoting the technology without waiting for the results.

Harvey said it appears that the Subgroup's goals should be: 1) to get a better handle on phytoremediation's niche, and 2) to address the equivalency issues. He said that the group should try to anticipate major issues that will arise to confront the technology.

Charles Giammona said that phytoremediation should prove to be a useful tool within the military. Both remedial project managers doing the work at the bases and managers at higher levels within DOD should be interested. He added that groups such as this Action Team will have to communicate effectively with people at both levels and with the academic, regulatory, and user communities as well.

Harvey then pointed out that while this Subgroup contains a variety of people--researchers, vendors of technology, owners of sites--it does not include many architecture and engineering firms, which are traditionally the middlemen in remediation projects. He asked if more representatives from these firms should be included.

Strand replied that some such firms are interested in phytoremediation; however, they often seem to view the technology as a dehydration or immobilization method, or as a strategy for beautifying sites cleaned up by other vendors.

Sankar Venkatraman said that there is currently a communication gap between clients and vendors. Clients are hesitating to implement the technology and are looking for guarantees that it will work and prove cost-effective. Phytoremediation hasn't progressed to a point where we can answer these engineering-type questions, Venkatraman said.

Larry Erickson then named two architecture and engineering firms that are interested in phytoremediation. Erickson gave their phone numbers to Harvey, who will invite them to participate in Subgroup conference calls.

HYDRAULIC CONTROL

Harvey raised a new question for discussion: Can plants achieve hydraulic control? He then introduced his colleague, Sandra Eberts, who told the Subgroup about some research she and her colleagues are doing at their site in Fort Worth, Texas. Eberts said that Forest Service personnel are measuring transpiration rates, then entering the data into a model that will predict future transpiration rates. Simultaneously, they are building a ground-water flow model to determine how much pumpage will be required to achieve hydraulic control. When the two models are done, Eberts said, the researchers are going to merge the data sets to predict the time it will take for trees to achieve hydraulic control.

Ray Hinchman stated that Ed Gatliff's company, Applied Natural Sciences, Inc., has used trees (including hybrid poplars and willows) to remediate inorganics and heavy metals at a site in New Jersey. Gatliff's data have shown evidence of hydraulic control. Hinchman characterized Applied Natural Sciences as something between a research firm and an architecture and engineering firm.

Hinchman then asked Strand whether he is close to getting similar data at another site. Strand replied that his site is a shallow, lined bed, somewhat different from a classic field aquifer, and that it wouldn't provide much data related to hydraulic control. The site has exhibited hydraulic control since the end of the first study season and emits little effluent, except on wet weeks.

Hinchman said that Lou Licht, whose company, Ecolotree, is somewhat similar to Applied Natural Sciences, could provide additional information on hydraulic control. Hinchman also referred to a paper by Gatliff and Evan Nyer, published in Groundwater Monitoring and Remediation (16:58-62), which contains some of the data on hydraulic control from the New Jersey site.

Elaine Richardson, who works with Gatliff at Applied Natural Sciences, said that they had recently received data collected at the New Jersey site over the past 2 years. They now have 5 years of data showing hydraulic control and the contraction of two plumes.

Eberts asked about the hydrogeology of the site and the depth to ground water. Hinchman stated that the depth to ground water was 16 feet. Richardson said that she didn't currently have specific information on the hydrogeology, but her company is putting together a data sheet that will show information from all 5 years, including data on contaminant reduction. The data sheet will become available within the next few weeks, she said.

Harvey asked Richardson whether her company had experienced any seasonal fluctuations in the hydraulic control at the New Jersey site. Richardson said it had not.

Tossell said that his company, Beak International, is looking at hydraulic control at two sites, including one in Palo Alto, California, beside San Francisco Bay. Because of the brackish conditions of the ground water at the Palo Alto site, company personnel are planning to plant a variety of species. They are also dealing with the monitoring question--that is, how can you demonstrate to regulators that you have achieved hydraulic control in the field? Tossell said he believes that, by pooling classic monitoring data with data from sites where other methods have been employed (e.g., modeling), you can begin to determine the steps you need to take to demonstrate hydraulic control. He said that the company's other site is located in a northern climate, where seasonality becomes a concern. The company is looking at a variety of species for that site--probably a mix of deciduous and coniferous, although coniferous trees would have a reduced transpiration capacity.

Erickson remarked that he had always observed hydraulic control through the use of monitoring wells. Eberts said that Erickson's method was a reasonable one, although hydraulic control might not occur within the time frame of some demonstrations. Modeling helps project future results, Eberts said.

Tossell stated that, at the Palo Alto site, Beak International used modeling at the start of the project to decide whether phytoremediation was a practical choice of technology. After deciding that phytoremediation might work, the company proceeded with Phase I of the project last year and may soon plant up to 200 trees as part of Phase II.

BIODIVERSITY

Harvey asked whether the Subgroup should discuss biodiversity issues. He raised the following issue for discussion: Do monocultures present future problems?

Tossell said that his company had talked about biodiversity with the California Water Control Board. Rather than plant a monoculture, Beak International was considering two species--tamarisk and eucalyptus--that it thought would be appropriate for the Palo Alto site, along with a variety of vegetation.

Harvey stated that eucalyptus and salt cedar (a tamarisk) are great for "going after water," though many people currently seem to be pushing for the use of native trees. He asked Tossell whether California regulators had voiced any objections to the use of eucalyptus and salt cedar.

Tossell said that Californians view salt cedar as a weed and feel similarly about eucalyptus. Beak International encountered some opposition to the selection of these species, he said, but the company continues to feel that the species are appropriate for the purposes of the site. Both species exist in California, though they may not be native. So far, Tossell said, the Water Control Board seems to be going along with the company's plan.

Hinchman said that he, Gatliff, and Christina Negri had discussed the qualities of tamarisk--particularly the fact that it is deep rooting and salt tolerant--and would be interested in seeing Tossell's results. Hinchman said that, by pruning tamarisks before they develop seeds, it is possible to keep the trees from spreading.

Harvey repeated something that he had read: that salt cedars can out-compete cottonwoods and willows in riparian environments. Though salt cedars excel at certain things (e.g., living in areas of high salinity), their prolific nature is a concern. Harvey asked whether there is a sterile salt cedar that could be used in phytoremediation. He also asked whether salt cedars are a monecious species (meaning one that has unisexual reproductive flowers).

Tossell said that salt cedars are indeed monecious, though he didn't know whether a sterile strain exists. (He suggested that plant breeders could probably create one.) He agreed that, under the right conditions, salt cedars could out-compete virtually any tree, though there are mechanical means for dealing with salt cedars' tendency to spread (such as the pruning method described by Hinchman).

Harvey said that there are some areas (e.g., rights of way for flight paths) where large trees aren't appropriate for phytoremediation. In such circumstances, he has considered using alfalfa or deep-rooted grasses. He asked for feedback from the group.

Erickson said that he uses alfalfa for a couple of reasons: it's a great water user, and it also fixes nitrogen, which is useful if the goal is to encourage biodegradation. Alfalfa lives 4 to 5 years and, in some cases, can be harvested as a cash crop.

Harvey mentioned enzymes such as mixed-function oxidases and dehalogenases. He asked whether anyone had used these enzymes with grasses.

Hinchman said that he was not aware of any data on enzyme systems. He noted that Argonne National Laboratory did use greenhouse studies to look into several grasses, including two with extensive, fibrous root systems that could be useful for remediation in the top few feet of soil: eastern gamma grass (a robust, native plant with high transpiration rates) and veniver grass (a nonnative plant with deep roots and a high pumping rate). Both could be considered as potential herbaceous phytoremediation species.

TCE DIFFUSION

Harvey reminded the Subgroup members that they had discussed food chain effects during their previous conference call (July 30, 1997). The consensus at that time was that such effects aren't a problem. He asked whether the group wants to pursue this topic further, or whether the members are comfortable telling regulators that food chain effects don't present a concern, even when animals forage on crops grown in TCE-contaminated soil.

Erickson replied that he had studied the degree to which TCE diffuses into the atmosphere as it is brought up into unsaturated zones and then transported out of the root and into the soil. In his experimental work, he had not found TCE in the upper parts of plants in an open chamber, and he believes that little TCE reaches the top parts of plants. Instead, most TCE diffuses out of the root and into the unsaturated zone soil (where there is good gas-phase diffusion), and then simply dissipates into the atmosphere.

Tossell said that Beak International deals with regulators at a number of TCE-contaminated sites and has encountered regulators who are concerned about the food chain effects of both bioremediation and phytoremediation. He thinks these concerns will have to be addressed, and he recommended dealing with the issue through a risk framework.

Strand said that he is involved in ongoing studies of the transfer of chlorinated byproducts to detritus consumers (mostly pill bugs, at his site) and of possible kinetic effects in the detritus consumers. So far the researchers have found no problems in the poplar system being studied, though Strand cautioned that variation probably occurs from plant to plant. Strand believes that the issue should be a concern in any application and that researchers need to analyze whether there is an accumulation of transferable materials in the plant tissue.

Harvey then asked about situations in which cattle forage contaminated crops, taking TCE directly into the food chain, or in which particle board is fabricated out of wood used in phytoremediation. Should we be concerned about such cases?

Strand said that he had been concerned about the accumulation of chlorinated materials in the poplars at his site. He envisioned a scenario in which chlorinated organics could accumulate to the point where the wood itself becomes hazardous waste. So far, he said, this doesn't seem to be happening in his poplar system, though it's something that should be kept in mind. Using a plant that could be consumed by cattle, he noted, is especially a cause for concern.

George Prince then described an unusual situation at one of his sites. The site is a small piece of land (two-thirds of an acre) planted with hybrid poplars and overlying a shallow ground-water system. The contaminants of concern are primarily PCE and methylene chloride. Prince said that he had detected low levels of chloromethane gas in transpirational gases at the site. He said that chloromethane had not been identified in the ground water, and he was wondering if the gas could be a breakdown product produced by the trees' metabolism.

Harvey said that, a couple of years ago, he had detected chloromethane near streams and water at a site in Texas. He said that he had consulted a toxicological profile distributed by the Agency for Toxic Substances and Disease Registry and had discovered that chloromethane is a compound that occurs naturally near bodies of water.

RESEARCH NEEDS

Harry Compton stated that everyone in the Subgroup seems to be doing different types of work. He asked if someone could suggest a minimal number of monitoring efforts that could be performed at every site so that group members could consistently compare data.

Harvey said that he and his colleagues are investigating some conditions of their site's geochemistry, such as dissolved oxygen, carbon levels, TOC, iron, and other conditions that promote reductive dechlorination. He said that their initial results have shown lower levels of dissolved oxygen and higher levels of iron, carbon, bicarbon, and "other things" that would be conducive to reductive dechlorination and altering the geochemistry.

Compton said that he was thinking more in terms of "big picture stuff," such as soil community structure, transpiration gas, and the condensate water that develops in bags when you collect transpiration gas--in other words, conditions that show that something is working.

Tossell stated that researchers need to study not only what is happening in the plant, but also what is happening in the rhizosphere. (Chloromethane, he said, is an anaerobic byproduct that occurs within the rhizosphere.) Tossell referred to a researcher with the U.S. Department of Agriculture who has spent a lot of time studying the activities of microbial enzymes in the rhizosphere--an area of phytoremediation that is not well understood and that has received little attention in the Subgroup's discussions.

WRAP UP

Members of the Subgroup agreed that they would schedule the next conference call for early December. Venkatraman asked Harvey about the availability of the Chapelle TCE document. Harvey said that he was still looking into the status of the document, which was originally released as an internal EPA document. Several Subgroup members said that they would speak with Walter Kovalick about releasing the document for the general public.