3:30 p.m.­ 5:00 p.m.
February 4, 1998

On Wednesday, February 4, 1998, members of the Phytoremediation of Organics Action Team, Vegetative Cap Subgroup, met in a conference call. The following members participated:

Tom Wong, Union Carbide Corporation (Subgroup Co-chair)
Steven Rock, U.S. Environmental Protection Agency (EPA) (Subgroup Co-chair)
William Albright, Desert Research Institute
Craig Benson, University of Wisconsin
Glendon Gee, Battelle
Paula Estornell, EPA
John Fletcher, University of Oklahoma
Greg Harvey, U.S. Air Force
Kelly Madalinski, EPA
Scott Potter, Geraghty & Miller, Inc.
Jeff Smith, Geraghty & Miller, Inc.

Also present was Christine Hartnett of Eastern Research Group, Inc.

ALTERNATIVE COVERS WORKSHOP--FEBRUARY 17 AND 18 IN LAS VEGAS, NEVADA

William Albright has put together a workshop that will address issues related to vegetative caps. The workshop will be held on February 17 and 18, 1998, in Las Vegas, Nevada. William Albright's main reason for organizing the workshop is to get feedback about a general proposal that he and Glendon Gee have recently put forth. Through this proposed project, William Albright and Glendon Gee hope researchers will:

• Analyze existing research sites and available data sets.

• Analyze the capabilities of existing numerical models.

• Make recommendations about additional data that need to be gathered.

• Identify modeling needs that have not yet been met and work toward identifying the most useful modeling systems.

• Establish a network of test facilities around the country. Ideally, the research team hopes to test a few side-by-side full-scale systems. William Albright envisions the test facilities being about 100 to 200 square meters in size and electronically instrumented (e.g., a data logger would collect data for daily electronic retrieval).

• Use the data collected to write a design guidance for the western part of the country.

Other researchers who have expressed interest in working on the proposed project include Glenn Wilson, Craig Benson, Mark Ankeny, Jody Waugh, and Bridgette Scanlon.

Before completing the proposal, William Albright and Glendon Gee want to get input to make sure that the proposed project would meet the needs of all interested parties rather than just soil physicists. Parties that have expressed interest in alternative final cover technologies include several government agencies (e.g., state regulators, EPA, the military, the U.S. Geological Survey, and the Bureau of Land Management--the largest single landowner in the country) and private industries (e.g., private landfill operators). Workshop invitations have been sent to representatives of these various parties, and many people have expressed interest in participating. Due to space limitations, William Albright said that he did not invite many engineering consultants, and apologized if this was misconstrued as an insult. He noted that all RTDF members are encouraged to participate. William Albright agreed to fax additional information to Greg Harvey and Scott Potter.

William Albright stressed that the meeting will not be a "conference" (i.e., there will be no formal presentation of technical papers). Instead, the workshop is designed to give different parties a forum to express their concerns about alternative final covers. William Albright and Glendon Gee will then refine their proposal to make sure that these concerns are addressed.

Steven Rock agreed to arrange for a written summary of the workshop proceedings.

MODELING

At the September 1997 Cincinnati meeting, Action Team members indicated a need to address modeling issues. Tom Wong noted that modeling will be a difficult issue to resolve and that researchers will have to decide whether the best approach is to go forth with an accepted model or to try something new. He asked people to discuss any recent experience they have had with modeling efforts.

Geraghty & Miller, Inc. Projects

Scott Potter and Jeff Smith provided an update of their recent experiences in the "world of modeling." Using a water-balance model, they have attempted to convince regulators to use their alternative cover design. Scott Potter and Jeff Smith derived the models for sites located in central Ohio and eastern Maryland.

These scientists claim that their model shows that:

• It is possible to build phytocovers that will provide the same type of long-term hydraulic performance that would be expected using conventional covers.
• Extreme climatic events will control the performance of a cover.

When Geraghty & Miller, Inc. tried to get its designs approved, however, regulators informed them that the water-balance model was too simplistic. In response, the team made their model increasingly complex, but the regulators were still not satisfied. Many regulators asked them to use the Hydrological Evaluation of Landfill Performance (HELP) model to predict the performance of phytocover design, while others asked the team to use more deterministic modeling approaches. To predict the performance of their alternative cap design, Geraghty & Miller, Inc. is now using a combination of three different models:

• Water-balance approach. The researchers are reluctant to abandon this model because they believe that it serves as a good screening tool to evaluate basic design parameters.

• Deterministic approaches

• Traditional approaches (e.g., HELP)

Recently, regulators told Geraghty & Miller, Inc. that they will consider the design if the company can show that phytocover systems can perform as well as state-mandated closure caps. The regulators told the scientists that they will need to use the same model (i.e., HELP) to evaluate both of the systems. (This recent development arose because the standard of equivalence defined for the site was recently changed. The site will now be expected to meet state regulations.) Geraghty & Miller, Inc. is reluctant to model its design solely on the HELP model because this model is not well-suited to applications involving phytocovers. For example, applying the HELP model to phytocover systems suggests that the amount of percolate peaks during the growing season rather than the dormant season. In addition, the HELP and water-balance models differ in their evapotranspiration (ET) predictions (e.g., compared to the water-balance model, the HELP model predicts that more leachate will be present). Also, Scott Potter pointed out that the HELP model does not make provisions for caps that utilize materials other than grasses.

Jeff Smith noted that Geraghty & Miller, Inc. are getting closer to gaining permission to perform a demonstration project at the Maryland site. He hopes to show the validity of their model through data collection. They are working with the Department of Energy to determine monitoring standards.

Jeff Fletcher and Glendon Gee asked about some of the details involved in formulating the Geraghty & Miller, Inc. model. Scott Potter and Jeff Smith offered the following information:

• The model formulated for the Ohio site relied heavily upon information collected in Coshocton, Ohio. A detailed study provided 37 years of daily precipitation and climatic data as well as estimates of potential ET rates for grasses.

• The researchers increased the potential ET rate by a factor of 1.3 to account for a system comprised of densely planted trees rather than grasses. (The researchers normalized consumptive use coefficient data--collected from Fort Collins--and found that consumptive use values for densely planted trees is about 1.3 to 1.6 times greater than that for grasses.) Geraghty & Miller, Inc. ramped the system up during the growing season, but scaled it back for the dormant season.

U.S. Air Force Project

Greg Harvey informed the group that a transpiration study is underway in Fort Worth, Texas. The project is using a physiologically-based transpiration model to determine when hydraulic containment is achieved. For this study, researchers are taking extensive physiological measurements (e.g., leaf area index, stomata control, predawn water potential). Greg Harvey said a final report should be complete in the fall of 1998. He noted that this study will provide valuable information for the Geraghty & Miller, Inc. team.

REGULATORY LIMITATIONS

Group members noted that regulators are skeptical about allowing researchers to install alternative covers. The following questions need to be resolved for regulators to become more comfortable with this technology:

• How should equivalence be defined? Regulators will need to decide on standards for measuring alternative cover systems.

• Does the alternative cover need to meet the standard of equivalency to be considered as a remedial option? Paula Estornell recently found some National Oil and Hazardous Substances Pollution Contingency Plan (NCP) guidance (see note at bottom of page) stating that alternative covers do not always have to meet a standard of equivalence. The guidance indicates that hybrid closures--a category into which phytocovers fall--are allowable at select Superfund sites that pose no threat to ground water. At these sites, a project manager may relax the requirements of permeability and choose to use an alternative cover to serve as a hybrid between a clean closure and a landfill closure. Paula Estornell noted that her office is currently evaluating what constitutes a threat to ground water. This issue of hybrid landfill closure is presently being discussed among policy makers, technical workers, and lawyers.

One participant asked if the guidance could be interpreted to include sites where the ground water was contaminated but was not being used. The participant wanted to know whether regulators are shifting towards risk-based decision-making. Paula Estornell did not think that sites of this nature would be included under this guidance.

Jeff Smith asked Paula Estornell how state regulators were reacting to this federal regulation. He said he fears that the states will force people to meet more stringent state regulations rather than the federal regulations. Paula Estornell acknowledged that this will happen, but pointed out that at least one state has already chosen to defer to the federal government for guidance on this topic.

Tom Wong asked Paula Estornell whether regulators think alternative caps are a suitable option for sites where ground-water recovery systems are already in place. Paula Estornell responded that this is unclear and noted that the NCP language is nebulous and open to interpretation.

• If a team does have to prove equivalence, which models are needed to show that the cover meets the standard? The majority of regulators do not feel that the available models suitably evaluate alternative covers. Tom Wong suggested that at the workshop in February, the group should try to get a better idea of how existing models can be modified to better reflect field conditions (e.g., by incorporating a larger leaf area index or accounting for a higher ET rate). William Albright recommended holding a panel discussion at the workshop, led by people who have developed models.

• How can researchers best communicate their models? Jeff Smith said he thinks regulators turned down the Geraghty & Miller, Inc. model because the team was unable to effectively communicate their ideas to the regulators.

Tom Wong asked the group whether they thought the RTDF group should focus on eliminating regulatory limitations. Jeff Smith said that the group will naturally accomplish this by concentrating its efforts on gathering data. He said the regulators need to see data sets from actual case studies before they will accept alternative cover technology. Paula Estornell agreed. Tom Wong noted that the group faces a "chicken and egg" dilemma because it needs to hurry up and collect data, yet it is hindered from doing so because it is hard to get regulatory permission to set up field sites. The difficulty of gaining approval varies dramatically from state to state. In some cases, teams have gotten approval from regulators by agreeing to construct a conventional cap if the alternative cover were to fail to perform adequately.

SITE UPDATES/FIELD PROJECTS

Sites Being Investigated by the University of Oklahoma and Union Carbide

Tom Wong and John Fletcher provided an update on some of the phytocovers that they are testing. They are currently working with a 1-acre system and two 17-acre full-scale systems. These researchers have proceeded with the full-scale systems without regulatory approval, with the hope that data yielded from the 1-acre demonstration project will provide enough evidence for regulators to approve the 17-acre system in the future. They have offered the regulators a contingency clause and have agreed to build a conventional impermeable cap if the phytocover does not work well. Ground-water recovery systems are already in place at these experimental sites.

John Fletcher and Tom Wong reported an interesting finding. At the 1-acre site, the trees are growing differently than they do in native soil. John Fletcher said that although polycyclic aromatic hydrocarbon (PAH) contaminants are present in the soil, volatile constituents in the sludge are responsible for this unnatural behavior. Volatiles can move up to higher parts of the root zone. (These compounds degrade more readily in the higher zone.) The upward movement of volatiles clears a zone for roots to grow deeper into the soil. In this way, the plants are achieving continued advancement of downward root growth. The presence of PAHs in the soil does not seem to inhibit root growth. A final report on on this finding at the 1-acre site is scheduled for release within the next 3 to 4 months.

Site in New York

Members of the subgroup reported that regulators are on the verge of granting approval for a project in New York. Researchers hope to install both a conventional cap and a phytocover at this site. Such a setup would allow for an interesting side-by-side analysis.

FUTURE RTDF NEEDS AND ACTION ITEMS

Goals and Direction For the RTDF Alternative Cover Subgroup

Steve Rock explained that there are a range of directions that the Subgroup can take in the future. He described the activities of the two other Phytoremediation Action Team subgroups to provide an example of how different subgroups are operating:

• Trichloroethylene (TCE) and Ground Water Subgroup. This group is a discussion group only and is not moving towards field work. Members meet on the phone every 2 months to keep each other abreast of the latest developments at different sites.

• Total Petroleum Hydrocarbon (TPH) Subgroup. This group is performing field research at one or two sites.

Participants said the Vegetative Cap Subgroup should try to do the following:

• Focus on what kind of data need to be collected at sites and what kind of models should be used. As noted by Steve Rock, the RTDF should try to set up some data collection standards so that data collected by different groups is uniform. This issue will be a major area of discussion at the February 1998 workshop. Craig Benson said he is excited about the proposal that William Albright's team is planning to produce, but is concerned that the proposed project will require a long time to complete. Craig Benson thinks that while this project will offer a good long-term solution, regulators need guidance now. He is concerned that certain states are already setting precedence about how to evaluate alternative covers (e.g., in New Mexico regulators allow alternative covers to be designed via HELP models) and that it will be impossible to get these states to abandon HELP in the future. Craig Benson encouraged the Subgroup to compile some sort of guidance (or at least a list of issues) and distribute it to regulators quickly. He reminded the group that solid waste guidelines were created before people had all of the answers. Paula Estornell noted that EPA's Ken Skahn is currently writing an update to the RCRA/CERCLA landfill cover guidance and is planning to include a brief section on alternative covers. Paula Estornell recommended that Craig Benson talk to Ken Skahn about enhancing this section. The updated guidance is scheduled for release within the next year and a half.

• Identify ways to share data.

Subgroup Meetings

Members of the subgroup agreed that they should meet in person once a year and over the phone every 2 months. There was discussion about whether the group would be best served by:

• "Piggybacking" with another conference. Some participants suggested meeting informally at a non-RTDF sponsored conference that they would all probably go to anyway. Some participants suggested meeting at the Jackson Hole conference. (This conference was held last year and some participants think it may be held again this year, although none were able to confirm this.)

• Holding a more structured conference or workshop. Some group members thought it would be best to have a more "directed" conference. One participant noted that a lot of projects in the midwest are on the brink of getting regulatory approval. The group could help to accelerate the approval process by holding a conference/workshop that included both project proponents and regulators. Members felt that such a conference would allow groups to present their cases to regulators and would provide an opportunity to respond to regulatory concerns.

Splitting the Subgroup Into Spin-off Groups

Tom Wong said he liked the idea of forming spin-off groups within the Subgroup. He suggested that the group talk more about this possibility when it meets at the Las Vegas conference. Participants did not identify specific spin-off groups, but they did note that alternative cover projects could be separated into projects in arid and wet climates. (Phytocovers in wet environments can accomplish water control and biological treatment, while systems operating in arid climates are less focused on treatment.) One participant said that systems with treatment components should be evaluated separately from those without such components. (Several participants felt that systems that offer both water control and treatment will be less readily accepted by regulators than those aimed just at water control.)

Members said that if the Subgroup does separate into spin-off groups, the spin-off groups could communicate on a regular basis, and meet with the entire Subgroup less frequently (i.e., once a year in person and once every 2 months on the phone).

Changing the RTDF Action Team's Name

Several group members thought that the RTDF group name--Phytoremediation of Organics Action Team--should be changed because the phrase "of organics" is too restrictive. Participants noted that alternative covers can be used to treat sites with non-organic contamination, such as municipal solid waste landfills and mining waste dumps. Steve Rock plans to address this issue with EPA's Walter Kovalick.

Members also pointed out that the name of the Subgroup should be officially changed from "Vegetative Cap" to "Alternative Cover."

RTDF COMMITMENTS

Steve Rock said that he will bring his "basket" of commitments to the February 1998 Las Vegas conference. He will have a list of activities that people will be required to sign up for. He said this approach will help establish some minimum criteria for monitoring and getting networks set up.

Tom Wong asked if the group thought it was better to ask for commitments from members or to allow members to come and go from meetings and conference calls as their schedules permit. The group did not reach a decision on this question.

DATE FOR NEXT CALL

The next conference call will be scheduled for April 1998.

Note: For copies of relevant documents, contact Kelly Madalinski, U.S. EPA Technology Innovation Office, at 703-603-9901 or madalinski.kelly@epa.gov.