SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM
PHYTOREMEDIATION OF ORGANICS ACTION TEAM
ALTERNATIVE COVER SUBGROUP
CONFERENCE CALL

3:00 p.m. ­ 5:00 p.m.
May 4, 1998

On Monday, May 4, 1998, the following members of the Phytoremediation of Organics Action Team, Alternative Cover Subgroup, met in a conference call:

Tom Wong, Union Carbide Corporation (Subgroup Co-chair)
Steven Rock, U.S. Environmental Protection Agency (EPA) (Subgroup Co-chair)
William Albright, Desert Research Institute (DRI)
Mary Beck, EPA Region III
Craig Benson, University of Wisconsin
Dave Carson, EPA
John Fletcher, University of Oklahoma
Kelly Madalinski, EPA
Scott Potter, Geraghty & Miller, Inc.
Tina Stacks, Arcadis Geraghty & Miller, Inc.
Jeff Smith, Geraghty & Miller, Inc.
Steve Wall, EPA Region IX
Glenn Wilson, DRI

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

PHASE I OF THE ALTERNATIVE COVERS ASSESSMENT PROGRAM (ACAP)

Steve Rock explained that the ACAP is being executed in two phases. EPA has contracted with Science Applications International Corporation and DRI to perform the tasks of Phase I and prepare the way for Phase II, and the RTDF Subgroup will lead Phase III. Phase I involves identifying sites, reviewing computer codes, and establishing a monitoring scheme.

Site Identification Activities

William Albright is leading the effort to identify candidate sites for the ACAP program. Conference call participants agreed that candidate sites can be divided into two categories: (1) sites that have not been capped and (2) sites that have been capped but not closed completely. For the latter sites, the ACAP team plans to examine each site's existing instrumentation and cap to determine whether the site can be retrofitted to generate the data ACAP requires.

Albright plans to collect detailed site information by distributing surveys to regulators and site owners. He has completed a first draft of the survey. Albright noted that it is challenging to write a good survey that contains enough information but is not too lengthy. He said respondents are less likely to complete a lengthy survey.

Rock recommended that Albright distribute the draft survey to the conference call participants, Felix Flechas, and some state regulators. Rock noted that distributing it to these people will allow Albright to get feedback from regulators (e.g., Mary Beck, Felix Flechas, and Steve Wall [regional regulators]) and site representatives (e.g., Tom Wong). To determine whether the survey is too lengthy, Rock recommended that reviewers time themselves while completing the survey.

Participants talked briefly about which types of sites to choose for the ACAP. Originally, Rock said that the type of site is inconsequential. Craig Benson and John Flethcer disagreed, noting that a site's waste type influences which plants can be used. (Certain wastes are toxic to plants.) Conference call participants agreed it would probably be best to pick a mixture of municipal solid waste and hazardous waste sites. John Fletcher asked the ACAP team to consider sites with chemical waste, oil-refinery-type waste, and sludge lagoons. Fletcher said he has specific site owners in mind but is unsure whether they will be interested in participating in the ACAP.

Participants talked about some of the potential test sites that had been identified at the time of the conference call. Rock was confident that the City of Cincinnati, the City of Glendale, and Sacramento County would provide sites. Participants recommended contacting Mark Ankeny and representatives from Hill Air Force Base (AFB).

Computer Code Review

Glenn Wilson said he is gathering literature on some of the available computer codes.

Monitoring Plan

Rock noted that it is important to establish a monitoring scheme so that consistent data is collected across ACAP sites. Rock compiled a draft monitoring scheme and attached it to the March 30, 1998, conference call summary notes. Rock said the team should take a tiered approach to monitoring. That is, he said the monitoring plan should separate monitoring tasks into three categories: (1) tasks that are essential, (2) tasks that are informative but not essential, and (3) tasks that a site owner or regulator might request.

Assessing Containment

Rock said that the primary goal of the ACAP is to determine whether alternative covers can achieve containment. To assess containment, he noted, investigators will need to measure the amount of leachate that is generated as well as the amount of water infiltration through the system.

Rock said that the ACAP's primary goal should be to measure leachate directly. He said there are a couple of ways to do this. Rock knows of a site in Cincinnati that has a leachate trench, and he plans to use this trench to monitor leachate collection. At sites with fairly accessible ground-water tables, Rock said leachate could be tracked by collecting samples from up- and down-gradient wells. Albright liked the idea of using up- and down-gradient wells, but Benson was skeptical because he was unsure whether ground-water monitoring could yield enough useful information within 5 years.

Rock claimed that the team's primary goal should be to monitor leachate generation, but Benson questioned whether the team would be able to assess cover performance using this approach. Benson agreed that useful qualitative information can be obtained by monitoring leachate but was unsure about quantitative information. He emphasized that it takes a while for leachate to migrate to the bottom of a system, partially because waste usually has a tremendous storage capacity. Benson thought efforts might be better spent if the team focused on examining the upper portions of test sites.

Rock said the team will install monitoring devices beneath the cap's root zone to determine how effectively alternative covers prevent water infiltration. Rock recommended using a time domain reflectometry (TDR) device to obtain a soil moisture measurement and asked participants whether they are familiar with a system made by MoisturePoint. Benson has used this company's TDR device on two different projects. He said that MoisturePoint's TDR system uses a proprietary multisegment wave guide software package. Benson listed three things he does not like about the MoisturePoint system. First, Benson does not like to use proprietary materials. Second, he said that using a vertically inserted profiling wave guide provides spatial averages rather than point measurements. Third, he had trouble sealing the wave guide in place (i.e., Benson said it was difficult to prevent air gaps from forming between the soil and the wave guide). Wilson agreed with Benson's points, stressing that experience has taught him that horizontal wave guides are more accurate than vertical ones.

Albright, Benson, and Wilson said that while TDR systems provide excellent data on soil moisture, they cannot provide a direct flux measurement. They said that indirect flux estimates can be obtained when TDR data is combined with matric potential data but that the estimates are not maximally accurate. Inaccuracy results because it is difficult to obtain good matric potential data, particularly in semiarid and arid environments.As Albright explained, the matric potential is a measure of the capillarity—attractive forces due to adhesion and cohesion between the liquid and solid phases—of a soil. The hydraulic gradient is calculated based on the pressure, matric, and gravity potential readings. Because the system is subatmospheric, obtaining matric potential readings is difficult and requires complicated instrumentation. (Wilson noted that the matric potential cannot be measured using a well with a pressure transducer.)

Albright, Benson, and Wilson advised using lysimeters rather than TDR systems because the former can measure flux directly. Rock said he was initially excited about using lysimeters but recently became concerned with the capillary break issue. Benson and Wilson acknowledged that this issue can impact data but contended that the lysimeter still offers the most accurate flux measurements.

After hearing the conference call participants' arguments, Rock agreed that lysimeters should be recommended as a first option. He noted, however, that site owners who have caps in place may resist the idea of digging up their caps so that lysimeters can be installed. Rock asked the group whether it would be a good idea to recommend using TDR systems at sites that are already capped. Albright, Benson, and Wilson objected to this idea, noting that:

• It may be fairly easy to convince site owners to dig up their caps. According to Benson, site owners are typically willing to dig up their caps to install monitoring equipment. Wong asked whether digging up a cap is a good idea, because it will be impossible to re-create the cap's original conditions. Benson acknowledged that the conditions cannot be replicated but that very similar conditions can be. In Benson's opinion, a lysimeter is worth installing if the owner will allow it. Rock asked Beck and Wall whether regulators would object to the idea of digging up caps. Beck said they should not as long as the sites had permission to experiment with an alternative cover.
• The ACAP is likely to generate wide enough interest so that the ACAP team can reject sites that will not install appropriate instrumentation. Albright said that numerous site owners and consulting firms have called him to express interest in the ACAP. He thinks the team may be inundated with requests. Because the ACAP aims to study only 10 to 25 sites, the team will likely be able to choose sites based on their instrumentation capabilities.
• It would be better to use a less precise lysimeter system than to use TDR systems to measure flux. Ideally, the ACAP team wants to have large-pan lysimeters installed at test sites. Wilson noted that small-pan lysimeters might be a better option at sites that already have caps.

Assessing Plant Uptake

Wong remarked that it may be difficult to get permitting approval if the group does not address the issue of vegetative uptake. Assuming that some roots will be able to penetrate underlying wastes, the Subgroup must be able to give regulators an idea of how plants will be impacted. Benson thought Wong's concern was valid, noting that the plants could be considered another waste transport pathway. Benson asked whether the plants would be considered solid waste or hazardous waste. No call participant could answer this question. Albright suggested addressing this issue later, but Wong was concerned that this issue could delay the approval process. The team discussed the matter and decided to add annual plant sampling to the first tier of the monitoring protocol. Wong noted that investigators will need to study the wastes at each site so they know what to look for in the plant matter. Benson said that the plant sampling might have to extend over 5 years because it takes a while for roots to extend deeply. To minimize the years for which sampling must be performed, Wong suggested setting up areas next to the test covers that are designed to encourage more rapid root growth.

Assessing Other Parameters

Albright, Benson, and Wilson talked about other parameters that must be monitored, including:

• Surface runoff. Benson noted that investigators need information on surface water runoff to be able to assess the predictive quality of models.
• Root density and root growth. Wilson said that the group is considering using minirhizotrons to monitor root growth. With these devices, the group should be able to lower a small videocamera into the root zone.
• Plant canopy. Albright and Benson said that investigators will need to analyze the plant canopy to see how much of the test site is covered, which species are involved, and to make leaf area index calculations.

PLANT SELECTION

Rock said that plant selection should be based on climatic suitability and the types of waste at the site. Fletcher noted that the latter must be considered, because certain plants cannot withstand the toxicity of certain contaminants. Benson questioned whether it is important to consider waste type. He argued that caps will likely be at least 1.5 meters deep and doubted that many roots will extend deeper. Benson's comment sparked a debate about root depth. Wong said that root systems often penetrate below 1.5 meters in the arid western portions of the United States; the roots of many grass species extend downward 2 to 3 meters. Fletcher pointed out that, to some extent, investigators can control how deeply roots penetrate by selecting species that are genetically designed to have short roots. (Fletcher did not list species that have short roots but did name several species that have long roots [i.e., 2 to 3 meters], including big blue grass, little blue grass, switch grass, and Indian grass.)

Wilson agreed that selecting plants that are genetically designed to have short roots minimizes the amount of root penetration, but he stressed that these plants can still, occasionally, send roots into the waste layer. He said the literature offers scant information about the distribution of deep roots in many of these species. Fletcher said that some useful information can be gleaned from old ecological studies.

Fletcher noted that deep roots would be preferable if the team decided to remediate rather than just contain waste. Wilson agreed that remediation and containment are complementary projects but said that the ACAP will only address the latter. He also said that testing both components simultaneously would be problematic because introducing deep root channels could compromise the integrity of the cover. Also, as Benson noted it would be difficult to use lysimeters if the roots are allowed to penetrate the waste zone. (The lysimeters must be installed below the root zone.)

Fletcher advised the team to consider transpiration rates when trying to select plant species. He noted that few efforts have been initiated to create vegetative systems that maximize transpiration. He suggested using data on growing season and transpiration rates to estimate how much evaportanspiration (ET) will result with a certain plant system. Wilson said that he plans to work with Fletcher, Albright, Glendon Gee, and Jody Waugh to estimate ET rates.

COOPERATIVE RESEARCH AND DEVELOPMENT AGREEMENT (CRADA)

Wall asked for an update on Rock's efforts to form a CRADA. Rock said forming a CRADA is a bit of a "chicken and egg" process. Before he is able to provide a draft CRADA, he must estimate the amount of money the group will need. Rock said drafting a CRADA is not time consuming but that lawyers need time to review it. He said he hoped to have a CRADA drafted by the next conference call. One participant asked Rock how many hosts/contributors have to be identified before a CRADA can be drafted. Rock said only three or four are needed to get started.

ACTION ITEMS

• Develop a design plan. Wilson said that he, Albright, Benson, and Gee will work together to compile a design plan. Benson will take the lead on the project. Benson, Albright, and Wilson agreed to meet in a conference call late on May 4, 1998. Albright said he will fax Benson a working draft of some conceptual drawings. Rock said he would try to send Benson the design that was generated for Warren. Ideally, Wilson said that the design plan should be completed within a week, sent to Rock for comments, and then released to the rest of the conference call participants.

  The design plan will incorporate Rock's monitoring plan and will provide design suggestions for two types of facilities: (1) a stand-alone facility and (2) a facility that must be integrated into an existing cap. For both designs, the investigators will try to address the following questions:

  —     How sensitive is the analysis to the barrier effect at the drain interface?

  —     How do you build the sump?

  —     Should you use sand or geonet?

  —     How should you build the surface run-on and run-off system?

  —     How should you cut off the capillary break?

  —     What kind of plastics should you use?

  —     What kind of geotextiles should you use?

Wilson asked Rock whether the ACAP's design plan will be proprietary. Rock said it will not.

• Albright agreed to send a draft survey to the conference call participants, Felix Flechas, and a few state regulators. Albright said he would identify some state regulators.
• Albright agreed to talk to people within DRI to gather additional information on Hill AFB.
• Albright and Wilson agreed to coordinate with other members of the ACAP team (e.g., Benson and Gee) and to send Rock a detailed timeline of Phase I activities. (Rock said it would be fine to include only activities through the end of the year.) Wilson noted that the timeline will be impacted by whether Pacific Northwest National Laboratory can resolve contract issues. Rock said that the work assignment recently arrived at EPA and that he would look at it to see why contracts are being delayed.
• Albright agreed to send a list of site contacts to Rock.

NEXT CONFERENCE CALL

The next conference call is scheduled for June 3, 1998, between 3:00 p.m. and 5:00 p.m. (EST).